Instrument Flying Handbook.indb FAA_Instrument Handbook_2007 FAA Handbook 2007

User Manual: FAA_InstrumentFlyingHandbook_2007

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FAA-H-8083-15A

Instrument
Flying Handbook

U.S. Department
of Transportation
FEDERAL AVIATION
ADMINISTRATION

Instrument Flying
Handbook

2007

U.S. Department of Transportation
FEDERAL AVIATION ADMINISTRATION
Flight Standards Service

ii

Preface
This Instrument Flying Handbook is designed for use by instrument flight instructors and pilots preparing for instrument
rating tests. Instructors may find this handbook a valuable training aid as it includes basic reference material for knowledge
testing and instrument flight training. Other Federal Aviation Administration (FAA) publications should be consulted for
more detailed information on related topics.
This handbook conforms to pilot training and certification concepts established by the FAA. There are different ways of
teaching, as well as performing, flight procedures and maneuvers and many variations in the explanations of aerodynamic
theories and principles. This handbook adopts selected methods and concepts for instrument flying. The discussion and
explanations reflect the most commonly used practices and principles. Occasionally the word “must” or similar language
is used where the desired action is deemed critical. The use of such language is not intended to add to, interpret, or relieve
a duty imposed by Title 14 of the Code of Federal Regulations (14 CFR).
All of the aeronautical knowledge and skills required to operate in instrument meteorological conditions (IMC) are detailed.
Chapters are dedicated to human and aerodynamic factors affecting instrument flight, the flight instruments, attitude instrument
flying for airplanes, basic flight maneuvers used in IMC, attitude instrument flying for helicopters, navigation systems, the
National Airspace System (NAS), the air traffic control (ATC) system, instrument flight rules (IFR) flight procedures, and
IFR emergencies. Clearance shorthand and an integrated instrument lesson guide are also included.
This handbook supersedes FAA-H-8081-15, Instrument Flying Handbook, dated 2001.
This handbook may be purchased from the Superintendent of Documents, United States Government Printing Office (GPO),
Washington, DC 20402-9325, or from GPO's web site.
http://bookstore.gpo.gov
This handbook is also available for download, in PDF format, from the Regulatory Support Division's (AFS-600) web
site.
http://www.faa.gov/about/office_org/headquarters_offices/avs/offices/afs/afs600
This handbook is published by the United States Department of Transportation, Federal Aviation Administration, Airman
Testing Standards Branch, AFS-630, P.O. Box 25082, Oklahoma City, OK 73125.
Comments regarding this publication should be sent, in email form, to the following address.
AFS630comments@faa.gov

iii

iv

Acknowledgements
This handbook was produced as a combined Federal Aviation Administration (FAA) and industry effort. The FAA wishes
to acknowledge the following contributors:
The laboratory of Dale Purves, M.D. and Mr. Al Seckel in providing imagery (found in Chapter 1) for visual illusions
from the book, The Great Book of Optical Illusions, Firefly Books, 2004
Sikorsky Aircraft Corporation and Robinson Helicopter Company for imagery provided in Chapter 9
Garmin Ltd. for providing flight system information and multiple display systems to include integrated flight, GPS and
communication systems; information and hardware used with WAAS, LAAS; and information concerning encountering
emergencies with high-technology systems
Universal Avionics System Corporation for providing background information of the Flight Management System and
an overview on Vision–1 and Traffic Alert and Collision Avoidance systems (TCAS)
Meggitt/S-Tec for providing detailed autopilot information regarding installation and use
Cessna Aircraft Company in providing instrument panel layout support and information on the use of onboard systems
Kearfott Guidance and Navigation Corporation in providing background information on the Ring-LASAR gyroscope
and its history
Honeywell International Inc., for Terrain Awareness Systems (TAWS) and various communication and radio systems
sold under the Bendix-King name
Chelton Flight Systems and Century Flight Systems, Inc., for providing autopilot information relating to Highway in
the Sky (Chelton) and HSI displays (Century)
Avidyne Corporation for providing displays with alert systems developed and sold by Ryan International, L3
Communications, and Tectronics.
Additional appreciation is extended to the Aircraft Owners and Pilots Association (AOPA), the AOPA Air Safety Foundation,
and the National Business Aviation Association (NBAA) for their technical support and input.

v

vi

Introduction
Is an Instrument Rating Necessary?
The answer to this question depends entirely upon individual
needs. Pilots may not need an instrument rating if they fly in
familiar uncongested areas, stay continually alert to weather
developments, and accept an alternative to their original plan.
However, some cross-country destinations may take a pilot
to unfamiliar airports and/or through high activity areas in
marginal visual or instrument meteorological conditions
(IMC). Under these conditions, an instrument rating may
be an alternative to rerouting, rescheduling, or canceling
a flight. Many accidents are the result of pilots who lack
the necessary skills or equipment to fly in marginal visual
meteorological conditions (VMC) or IMC and attempt flight
without outside references.
Pilots originally flew aircraft strictly by sight, sound, and
feel while comparing the aircraft’s attitude to the natural
horizon. As aircraft performance increased, pilots required
more inflight information to enhance the safe operation of
their aircraft. This information has ranged from a string tied
to a wing strut, to development of sophisticated electronic
flight information systems (EFIS) and flight management
systems (FMS). Interpretation of the instruments and aircraft
control have advanced from the “one, two, three” or “needle,
ball, and airspeed” system to the use of “attitude instrument
flying” techniques.
Navigation began by using ground references with dead
reckoning and has led to the development of electronic
navigation systems. These include the automatic direction
finder (ADF), very-high frequency omnidirectional range
(VOR), distance measuring equipment (DME), tactical air
navigation (TACAN), long range navigation (LORAN),
global positioning system (GPS), instrument landing system
(ILS), microwave landing system (MLS), and inertial
navigation system (INS).
Perhaps you want an instrument rating for the same basic
reason you learned to fly in the first place—because you like
flying. Maintaining and extending your proficiency, once you
have the rating, means less reliance on chance and more on
skill and knowledge. Earn the rating—not because you might

need it sometime, but because it represents achievement and
provides training you will use continually and build upon
as long as you fly. But most importantly it means greater
safety in flying.
Instrument Rating Requirements
A private or commercial pilot must have an instrument
rating and meet the appropriate currency requirements if
that pilot operates an aircraft using an instrument flight
rules (IFR) flight plan in conditions less than the minimums
prescribed for visual flight rules (VFR), or in any flight in
Class A airspace.
You will need to carefully review the aeronautical knowledge
and experience requirements for the instrument rating as
outlined in Title 14 of the Code of Federal Regulations
(14 CFR) part 61. After completing the Federal Aviation
Administration (FAA) Knowledge Test issued for the
instrument rating, and all the experience requirements have
been satisfied, you are eligible to take the practical test. The
regulations specify minimum total and pilot-in-command
time requirements. This minimum applies to all applicants
regardless of ability or previous aviation experience.
Training for the Instrument Rating
A person who wishes to add the instrument rating to his or
her pilot certificate must first make commitments of time,
money, and quality of training. There are many combinations
of training methods available. Independent studies may be
adequate preparation to pass the required FAA Knowledge
Test for the instrument rating. Occasional periods of ground
and flight instruction may provide the skills necessary to
pass the required test. Or, individuals may choose a training
facility that provides comprehensive aviation education and
the training necessary to ensure the pilot will pass all the
required tests and operate safely in the National Airspace
System (NAS). The aeronautical knowledge may be
administered by educational institutions, aviation-oriented
schools, correspondence courses, and appropriately rated
instructors. Each person must decide for themselves which
training program best meets his or her needs and at the same
time maintain a high quality of training. Interested persons

vii

should make inquiries regarding the available training at
nearby airports, training facilities, in aviation publications,
and through the FAA Flight Standards District Office
(FSDO).
Although the regulations specify minimum requirements,
the amount of instructional time needed is determined not
by the regulation, but by the individual’s ability to achieve
a satisfactory level of proficiency. A professional pilot with
diversified flying experience may easily attain a satisfactory
level of proficiency in the minimum time required by
regulation. Your own time requirements will depend upon a
variety of factors, including previous flying experience, rate
of learning, basic ability, frequency of flight training, type of
aircraft flown, quality of ground school training, and quality
of flight instruction, to name a few. The total instructional
time you will need, the scheduling of such time, is up to the
individual most qualified to judge your proficiency—the
instructor who supervises your progress and endorses your
record of flight training.
You can accelerate and enrich much of your training by
informal study. An increasing number of visual aids and
programmed instrument courses is available. The best course
is one that includes a well-integrated flight and ground school
curriculum. The sequential nature of the learning process
requires that each element of knowledge and skill be learned
and applied in the right manner at the right time.
Part of your instrument training may utilize a flight simulator,
flight training device, or a personal computer-based aviation
training device (PCATD). This ground-based flight training
equipment is a valuable tool for developing your instrument
cross-check and learning procedures, such as intercepting and
tracking, holding patterns, and instrument approaches. Once
these concepts are fully understood, you can then continue
with inflight training and refine these techniques for full
transference of your new knowledge and skills.
Holding the instrument rating does not necessarily make you a
competent all-weather pilot. The rating certifies only that you
have complied with the minimum experience requirements,
that you can plan and execute a flight under IFR, that you
can execute basic instrument maneuvers, and that you have
shown acceptable skill and judgment in performing these
activities. Your instrument rating permits you to fly into

viii

instrument weather conditions with no previous instrument
weather experience. Your instrument rating is issued on
the assumption that you have the good judgment to avoid
situations beyond your capabilities. The instrument training
program you undertake should help you to develop not only
essential flying skills but also the judgment necessary to use
the skills within your own limits.
Regardless of the method of training selected, the curriculum
in Appendix B, Instrument Training Lesson Guide, provides
guidance as to the minimum training required for the addition
of an instrument rating to a private or commercial pilot
certificate.
Maintaining the Instrument Rating
Once you hold the instrument rating, you may not act as pilotin-command under IFR or in weather conditions less than the
minimums prescribed for VFR, unless you meet the recent
flight experience requirements outlined in 14 CFR part 61.
These procedures must be accomplished within the preceding
6 months and include six instrument approaches, holding
procedures, and intercepting and tracking courses through the
use of navigation systems. If you do not meet the experience
requirements during these 6 months, you have another 6
months to meet these minimums. If the requirements are
still not met, you must pass an instrument proficiency check,
which is an inflight evaluation by a qualified instrument
flight instructor using tasks outlined in the instrument rating
practical test standards (PTS).
The instrument currency requirements must be accomplished
under actual or simulated instrument conditions. You may log
instrument flight time during the time for which you control
the aircraft solely by reference to the instruments. This can
be accomplished by wearing a view-limiting device, such as
a hood, flying an approved flight-training device, or flying
in actual IMC.
It takes only one harrowing experience to clarify the
distinction between minimum practical knowledge and a
thorough understanding of how to apply the procedures and
techniques used in instrument flight. Your instrument training
is never complete; it is adequate when you have absorbed
every foreseeable detail of knowledge and skill to ensure a
solution will be available if and when you need it.

Table of Contents
Preface ...................................................................iii
Acknowledgements ................................................v
Introduction...........................................................vii
Is an Instrument Rating Necessary? ............................vii
Instrument Rating Requirements .................................vii
Training for the Instrument Rating..............................vii
Maintaining the Instrument Rating ............................viii
Table of Contents ..................................................ix
Chapter 1
Human Factors ....................................................1-1
Introduction ....................................................................1-1
Sensory Systems for Orientation ...................................1-2
Eyes ............................................................................1-2
Vision Under Dim and Bright Illumination ............1-3
Ears .............................................................................1-4
Nerves.........................................................................1-5
Illusions Leading to Spatial Disorientation....................1-5
Vestibular Illusions ....................................................1-5
The Leans................................................................1-5
Coriolis Illusion ......................................................1-6
Graveyard Spiral .....................................................1-6
Somatogravic Illusion .............................................1-6
Inversion Illusion ....................................................1-6
Elevator Illusion......................................................1-6
Visual Illusions ...........................................................1-7
False Horizon ..........................................................1-7
Autokinesis .............................................................1-7
Postural Considerations .................................................1-7
Demonstration of Spatial Disorientation .......................1-7
Climbing While Accelerating.....................................1-8
Climbing While Turning ............................................1-8
Diving While Turning ................................................1-8
Tilting to Right or Left ...............................................1-8
Reversal of Motion .....................................................1-8
Diving or Rolling Beyond the Vertical Plane ............1-8
Coping with Spatial Disorientation................................1-8
Optical Illusions .............................................................1-9
Runway Width Illusion ..............................................1-9

Runway and Terrain Slopes Illusion ..........................1-9
Featureless Terrain Illusion ........................................1-9
Water Refraction ........................................................1-9
Haze ............................................................................1-9
Fog ..............................................................................1-9
Ground Lighting Illusions ..........................................1-9
How To Prevent Landing Errors Due To Optical
Illusions ..........................................................................1-9
Physiological and Psychological Factors .....................1-11
Stress ........................................................................1-11
Medical Factors............................................................1-12
Alcohol .....................................................................1-12
Fatigue ......................................................................1-12
Acute Fatigue ........................................................1-12
Chronic Fatigue ....................................................1-13
IMSAFE Checklist ...................................................1-13
Hazard Identification ....................................................1-13
Situation 1 ................................................................1-13
Situation 2 ................................................................1-13
Risk Analysis............................................................1-13
Crew Resource Management (CRM) and Single-Pilot
Resource Management (SRM) .....................................1-14
Situational Awareness..................................................1-14
Flight Deck Resource Management .............................1-14
Human Resources .....................................................1-14
Equipment ................................................................1-14
Information Workload ..............................................1-14
Task Management ........................................................1-15
Aeronautical Decision-Making (ADM) .......................1-15
The Decision-Making Process .................................1-16
Defining the Problem ...............................................1-16
Choosing a Course of Action ...................................1-16
Implementing the Decision and Evaluating
the Outcome .............................................................1-16
Improper Decision-Making Outcomes ....................1-16
Models for Practicing ADM ........................................1-17
Perceive, Process, Perform .......................................1-17
The DECIDE Model.................................................1-17
Hazardous Attitudes and Antidotes .............................1-18

ix

Chapter 2
Aerodynamic Factors ..........................................2-1
Introduction ....................................................................2-1
The Wing ....................................................................2-2
Review of Basic Aerodynamics .....................................2-2
The Four Forces .........................................................2-2
Lift ..........................................................................2-2
Weight.....................................................................2-3
Thrust ......................................................................2-3
Drag ........................................................................2-3
Newton’s First Law, the Law of Inertia .....................2-4
Newton’s Second Law, the Law of Momentum ........2-4
Newton’s Third Law, the Law of Reaction ................2-4
Atmosphere ....................................................................2-4
Layers of the Atmosphere ..........................................2-5
International Standard Atmosphere (ISA)..................2-5
Pressure Altitude .....................................................2-5
Density Altitude ......................................................2-5
Lift..................................................................................2-6
Pitch/Power Relationship ...........................................2-6
Drag Curves ...................................................................2-6
Regions of Command .................................................2-7
Control Characteristics ...........................................2-7
Speed Stability............................................................2-7
Normal Command ..................................................2-7
Reversed Command ................................................2-8
Trim................................................................................2-8
Slow-Speed Flight..........................................................2-8
Small Airplanes ..........................................................2-9
Large Airplanes ..........................................................2-9
Climbs ..........................................................................2-10
Acceleration in Cruise Flight ...................................2-10
Turns ............................................................................2-10
Rate of Turn .............................................................2-10
Radius of Turn ..........................................................2-11
Coordination of Rudder and Aileron Controls .........2-11
Load Factor ..................................................................2-11
Icing .............................................................................2-12
Types of Icing ..............................................................2-13
Structural Icing .........................................................2-13
Induction Icing .........................................................2-13
Clear Ice ...................................................................2-13
Rime Ice ...................................................................2-13
Mixed Ice..................................................................2-14
General Effects of Icing on Airfoils .........................2-14
Piper PA-34-200T (Des Moines, Iowa) ................2-15
Tailplane Stall Symptoms ........................................2-16
Propeller Icing ..........................................................2-16
Effects of Icing on Critical Aircraft Systems ...........2-16
Flight Instruments .................................................2-16
Stall Warning Systems ..........................................2-16
x

Windshields ..........................................................2-16
Antenna Icing ...........................................................2-17
Summary ......................................................................2-17
Chapter 3
Flight Instruments ...............................................3-1
Introduction ....................................................................3-1
Pitot/Static Systems .......................................................3-2
Static Pressure ............................................................3-2
Blockage Considerations ............................................3-2
Indications of Pitot Tube Blockage ........................3-3
Indications from Static Port Blockage ....................3-3
Effects of Flight Conditions....................................3-3
Pitot/Static Instruments ..................................................3-3
Sensitive Altimeter .....................................................3-3
Principle of Operation.............................................3-3
Altimeter Errors ......................................................3-4
Cold Weather Altimeter Errors ...............................3-5
ICAO Cold Temperature Error Table ........................3-5
Nonstandard Pressure on an Altimeter ...................3-6
Altimeter Enhancements (Encoding) .....................3-7
Reduced Vertical Separation Minimum (RVSM) ..3-7
Vertical Speed Indicator (VSI) ...................................3-8
Dynamic Pressure Type Instruments .............................3-8
Airspeed Indicator (ASI) ............................................3-8
Types of Airspeed ...................................................3-9
Airspeed Color Codes ...........................................3-10
Magnetism....................................................................3-10
The Basic Aviation Magnetic Compass ..................3-11
Magnetic Compass Overview ...............................3-11
Magnetic Compass Induced Errors .......................3-12
The Vertical Card Magnetic Compass .....................3-14
The Flux Gate Compass System ..............................3-14
Remote Indicating Compass.....................................3-15
Gyroscopic Systems .....................................................3-16
Power Sources .........................................................3-16
Pneumatic Systems ..............................................3-16
Vacuum Pump Systems ........................................3-17
Electrical Systems .................................................3-18
Gyroscopic Instruments ...............................................3-18
Attitude Indicators ....................................................3-18
Heading Indicators ...................................................3-19
Turn Indicators .........................................................3-20
Turn-and-Slip Indicator ........................................3-20
Turn Coordinator ..................................................3-21
Flight Support Systems ................................................3-22
Attitude and Heading Reference System (AHRS) ...3-22
Air Data Computer (ADC) .......................................3-22
Analog Pictorial Displays ............................................3-22
Horizontal Situation Indicator (HSI) .......................3-22

Attitude Direction Indicator (ADI) .........................3-23
Flight Director System (FDS) ..................................3-23
Integrated Flight Control System ............................3-24
Autopilot Systems .................................................3-24
Flight Management Systems (FMS) ............................3-25
Electronic Flight Instrument Systems ......................3-27
Primary Flight Display (PFD)......................................3-27
Synthetic Vision .......................................................3-27
Multi-Function Display (MFD) ................................3-28
Advanced Technology Systems ...................................3-28
Automatic Dependent Surveillance—
Broadcast (ADS-B) ..................................................3-28
Safety Systems .............................................................3-30
Radio Altimeters ......................................................3-30
Traffic Advisory Systems ........................................3-31
Traffic Information System ..................................3-31
Traffic Alert Systems ...........................................3-31
Traffic Avoidance Systems ...................................3-31
Terrain Alerting Systems .....................................3-34
Required Navigation Instrument System Inspection ...3-34
Systems Preflight Procedures ...................................3-34
Before Engine Start ..................................................3-36
After Engine Start.....................................................3-37
Taxiing and Takeoff .................................................3-37
Engine Shut Down ...................................................3-37
Chapter 4, Section I
Airplane Attitude Instrument Flying
Using Analog Instrumentation ...........................4-1
Introduction ....................................................................4-1
Learning Methods ..........................................................4-2
Attitude Instrument Flying Using the Control and
Performance Method .................................................4-2
Control Instruments ...............................................4-2
Performance Instruments .......................................4-2
Navigation Instruments ..........................................4-2
Procedural Steps in Using Control and
Performance ............................................................4-2
Aircraft Control During Instrument Flight .............4-3
Attitude Instrument Flying Using the Primary and
Supporting Method .....................................................4-4
Pitch Control ...........................................................4-4
Bank Control ...........................................................4-7
Power Control .........................................................4-8
Trim Control ...........................................................4-8
Airplane Trim .........................................................4-8
Helicopter Trim ....................................................4-10
Example of Primary and Support Instruments .........4-10
Fundamental Skills.......................................................4-10
Instrument Cross-Check ...........................................4-10

Common Cross-Check Errors ...............................4-11
Instrument Interpretation ..........................................4-13
Chapter 4, Section II
Airplane Attitude Instrument Flying
Using an Electronic Flight Display ..................4-15
Introduction ..................................................................4-15
Learning Methods ........................................................4-16
Control and Performance Method ............................4-18
Control Instruments ..............................................4-18
Performance Instruments ......................................4-19
Navigation Instruments .........................................4-19
The Four-Step Process Used to Change Attitude .....4-20
Establish ................................................................4-20
Trim ......................................................................4-20
Cross-Check ..........................................................4-20
Adjust ....................................................................4-20
Applying the Four-Step Process ...............................4-20
Pitch Control .........................................................4-20
Bank Control .........................................................4-20
Power Control .......................................................4-21
Attitude Instrument Flying—Primary and
Supporting Method ...................................................4-21
Pitch Control .........................................................4-21
Straight-and-Level Flight......................................4-22
Primary Pitch ........................................................4-22
Primary Bank ........................................................4-23
Primary Yaw .........................................................4-23
Primary Power ......................................................4-23
Fundamental Skills of Attitude Instrument Flying ......4-23
Instrument Cross-Check ...........................................4-24
Scanning Techniques ...................................................4-24
Selected Radial Cross-Check ...................................4-24
Starting the Scan ...................................................4-24
Trend Indicators ....................................................4-26
Common Errors............................................................4-28
Fixation.....................................................................4-28
Omission...................................................................4-28
Emphasis ..................................................................4-28
Chapter 5, Section I
Airplane Basic Flight Maneuvers
Using Analog Instrumentation ...........................5-1
Introduction ....................................................................5-1
Straight-and-Level Flight ...............................................5-2
Pitch Control ..............................................................5-2
Attitude Indicator ....................................................5-2
Altimeter .................................................................5-3
Vertical Speed Indicator (VSI) ...............................5-4

xi

Airspeed Indicator (ASI) ........................................5-6
Bank Control ..............................................................5-6
Attitude Indicator ....................................................5-6
Heading Indicator ...................................................5-7
Turn Coordinator ....................................................5-7
Turn-and-Slip Indicator (Needle and Ball) .............5-8
Power Control ............................................................5-8
Power Settings ........................................................5-9
Airspeed Changes in Straight-and-Level Flight ...5-11
Trim Technique ........................................................5-12
Common Errors in Straight-and-Level Flight .........5-12
Pitch ......................................................................5-12
Heading .................................................................5-13
Power ....................................................................5-13
Trim ......................................................................5-13
Straight Climbs and Descents ......................................5-14
Climbs ......................................................................5-14
Entry .....................................................................5-14
Leveling Off..........................................................5-16
Descents ...................................................................5-16
Entry .....................................................................5-17
Leveling Off..........................................................5-17
Common Errors in Straight Climbs and Descents ...5-17
Turns ............................................................................5-19
Standard Rate Turns .................................................5-19
Turns to Predetermined Headings ............................5-20
Timed Turns .............................................................5-21
Compass Turns .........................................................5-21
Steep Turns ...............................................................5-22
Climbing and Descending Turns ..............................5-24
Change of Airspeed During Turns ...........................5-24
Common Errors in Turns..........................................5-25
Pitch ......................................................................5-25
Bank ......................................................................5-25
Power ....................................................................5-26
Trim ......................................................................5-26
Errors During Compass Turns ..............................5-26
Approach to Stall .........................................................5-26
Unusual Attitudes and Recoveries ...............................5-26
Recognizing Unusual Attitudes ................................5-27
Recovery from Unusual Attitudes ............................5-27
Nose-High Attitudes .................................................5-27
Nose-Low Attitudes .................................................5-28
Common Errors in Unusual Attitudes ......................5-28
Instrument Takeoff.......................................................5-29
Common Errors in Instrument Takeoffs ..................5-29
Basic Instrument Flight Patterns ..................................5-30
Racetrack Pattern......................................................5-30
Procedure Turn .........................................................5-30
Standard 45° Procedure Turn ...................................5-30
xii

80/260 Procedure Turn .............................................5-31
Teardrop Patterns .....................................................5-31
Circling Approach Patterns ......................................5-32
Pattern I .................................................................5-32
Pattern II ...............................................................5-32
Chapter 5, Section II
Airplane Basic Flight Maneuvers
Using an Electronic Flight Display ..................5-33
Introduction ..................................................................5-33
Straight-and-Level Flight .............................................5-34
Pitch Control ............................................................5-34
Attitude Indicator ..................................................5-34
Altimeter ...............................................................5-36
Partial Panel Flight ...............................................5-36
VSI Tape ...............................................................5-36
Airspeed Indicator (ASI) ......................................5-37
Bank Control ............................................................5-37
Attitude Indicator ..................................................5-37
Horizontal Situation Indicator (HSI) ....................5-38
Heading Indicator .................................................5-38
Turn Rate Indicator ...............................................5-38
Slip/Skid Indicator ................................................5-39
Power Control ..........................................................5-39
Power Settings ......................................................5-39
Airspeed Changes in Straight-and-Level Flight ...5-40
Trim Technique ........................................................5-43
Common Errors in Straight-and-Level Flight ..........5-43
Pitch ......................................................................5-43
Heading .................................................................5-44
Power ....................................................................5-45
Trim ......................................................................5-45
Straight Climbs and Descents ......................................5-46
Entry .........................................................................5-46
Constant Airspeed Climb From Cruise
Airspeed ................................................................5-46
Constant Airspeed Climb from Established
Airspeed ................................................................5-47
Constant Rate Climbs ...........................................5-47
Leveling Off..........................................................5-48
Descents ...................................................................5-49
Entry .........................................................................5-49
Leveling Off..........................................................5-50
Common Errors in Straight Climbs and Descents ...5-50
Turns ............................................................................5-51
Standard Rate Turns .................................................5-51
Establishing A Standard Rate Turn ......................5-51
Common Errors ....................................................5-51
Turns to Predetermined Headings ............................5-52

Timed Turns .............................................................5-53
Compass Turns .........................................................5-53
Steep Turns ...............................................................5-53
Unusual Attitude Recovery Protection .................5-55
Common Errors Leading to Unusual Attitudes ....5-58
Instrument Takeoff.......................................................5-60
Common Errors in Instrument Takeoffs ..................5-61
Basic Instrument Flight Patterns ..................................5-61
Chapter 6
Helicopter Attitude Instrument Flying ...............6-1
Introduction ....................................................................6-1
Flight Instruments ..........................................................6-2
Instrument Flight............................................................6-2
Instrument Cross-Check .............................................6-2
Instrument Interpretation ............................................6-3
Aircraft Control ..........................................................6-3
Straight-and-Level Flight ...............................................6-3
Pitch Control ..............................................................6-3
Attitude Indicator ....................................................6-3
Altimeter .................................................................6-4
Vertical Speed Indicator (VSI) ...............................6-5
Airspeed Indicator ..................................................6-5
Bank Control ..............................................................6-5
Attitude Indicator ....................................................6-5
Heading Indicator ...................................................6-6
Turn Indicator .........................................................6-7
Common Errors During Straight-and-Level Flight ....6-7
Power Control During Straight-and-Level Flight ......6-7
Common Errors During Airspeed Changes .............6-10
Straight Climbs (Constant Airspeed and
Constant Rate)..............................................................6-10
Entry .........................................................................6-10
Level Off ..................................................................6-12
Straight Descents (Constant Airspeed and
Constant Rate)..............................................................6-12
Entry .........................................................................6-12
Level Off ..................................................................6-13
Common Errors During Straight Climbs and
Descents ...................................................................6-13
Turns ............................................................................6-13
Turn to a Predetermined Heading ............................6-13
Timed Turns .............................................................6-13
Change of Airspeed in Turns ...................................6-14
Compass Turns .........................................................6-15
30° Bank Turn ......................................................6-15
Climbing and Descending Turns ..............................6-15
Common Errors During Turns .................................6-15
Unusual Attitudes.........................................................6-16
Common Errors During Unusual Attitude
Recoveries ................................................................6-16

Emergencies .................................................................6-16
Autorotations ............................................................6-17
Common Errors During Autorotations .................6-17
Servo Failure ............................................................6-17
Instrument Takeoff.......................................................6-17
Common Errors During Instrument Takeoffs ..........6-18
Changing Technology ..................................................6-18
Chapter 7
Navigation Systems ............................................7-1
Introduction ....................................................................7-1
Basic Radio Principles ...................................................7-2
How Radio Waves Propagate .....................................7-2
Ground Wave ..........................................................7-2
Sky Wave ................................................................7-2
Space Wave ............................................................7-2
Disturbances to Radio Wave Reception .....................7-3
Traditional Navigation Systems.....................................7-3
Nondirectional Radio Beacon (NDB) ........................7-3
NDB Components ...................................................7-3
ADF Components ...................................................7-3
Function of ADF .....................................................7-4
Operational Errors of ADF .....................................7-8
Very High Frequency Omnidirectional
Range (VOR)..............................................................7-8
VOR Components .................................................7-10
Function of VOR ..................................................7-12
VOR Operational Errors .......................................7-14
VOR Accuracy......................................................7-16
VOR Receiver Accuracy Check ...........................7-16
VOR Test Facility (VOT) .....................................7-16
Certified Checkpoints ...........................................7-16
Distance Measuring Equipment (DME) ...................7-16
DME Components ................................................7-17
Function of DME ..................................................7-17
DME Arc ..............................................................7-17
Intercepting Lead Radials .....................................7-19
DME Errors ..........................................................7-19
Area Navigation (RNAV) ........................................7-19
VOR/DME RNAV................................................7-23
VOR/DME RNAV Components ..........................7-23
Function of VOR/DME RNAV ............................7-23
VOR/DME RNAV Errors.....................................7-24
Long Range Navigation (LORAN) ..........................7-24
LORAN Components ...........................................7-25
Function of LORAN .............................................7-26
LORAN Errors......................................................7-26
Advanced Technologies ...............................................7-26
Global Navigation Satellite System (GNSS) ...........7-26

xiii

Global Positioning System (GPS) ............................7-27
GPS Components ..................................................7-27
Function of GPS ...................................................7-28
GPS Substitution ...................................................7-28
GPS Substitution for ADF or DME .....................7-29
To Determine Aircraft Position Over a DME
Fix: ........................................................................7-29
To Fly a DME Arc: ...............................................7-29
To Navigate TO or FROM an NDB/Compass
Locator: .................................................................7-29
To Determine Aircraft Position Over an NDB/
Compass Locator: .................................................7-29
To Determine Aircraft Position Over a Fix Made
up of an NDB/Compass Locator Bearing
Crossing a VOR/LOC Course: .............................7-30
To Hold Over an NDB/Compass Locator: ...........7-30
IFR Flight Using GPS ...........................................7-30
GPS Instrument Approaches.................................7-31
Departures and Instrument Departure
Procedures (DPs) ..................................................7-33
GPS Errors ............................................................7-33
System Status ........................................................7-33
GPS Familiarization..............................................7-34
Differential Global Positioning Systems (DGPS) ....7-34
Wide Area Augmentation System (WAAS) ............7-34
General Requirements ..........................................7-34
Instrument Approach Capabilities ........................7-36
Local Area Augmentation System (LAAS) .............7-36
Inertial Navigation System (INS) .............................7-36
INS Components ...................................................7-37
INS Errors .............................................................7-37
Instrument Approach Systems .....................................7-37
Instrument Landing Systems (ILS) ..........................7-37
ILS Components ...................................................7-39
Approach Lighting Systems (ALS) ..........................7-40
ILS Airborne Components ....................................7-42
ILS Function .............................................................7-42
ILS Errors .................................................................7-44
Marker Beacons ....................................................7-44
Operational Errors ................................................7-45
Simplified Directional Facility (SDF) ......................7-45
Localizer Type Directional Aid (LDA) ....................7-45
Microwave Landing System (MLS) .........................7-45
Approach Azimuth Guidance ...............................7-45
Required Navigation Performance ...............................7-46
Flight Management Systems (FMS) ............................7-48
Function of FMS ......................................................7-48
Head-Up Display (HUD) .............................................7-49
Radar Navigation (Ground Based)...............................7-49
xiv

Functions of Radar Navigation ................................7-49
Airport Surface Detection Equipment ..................7-50
Radar Limitations .....................................................7-50
Chapter 8
The National Airspace System ...........................8-1
Introduction ....................................................................8-1
Airspace Classification ...............................................8-2
Special Use Airspace ..................................................8-2
Federal Airways .........................................................8-4
Other Routing .............................................................8-5
IFR En Route Charts ......................................................8-6
Airport Information ....................................................8-6
Charted IFR Altitudes ................................................8-6
Navigation Features....................................................8-7
Types of NAVAIDs ................................................8-7
Identifying Intersections .........................................8-7
Other Route Information.......................................8-10
Weather Information and Communication
Features .................................................................8-10
New Technologies .......................................................8-10
Terminal Procedures Publications ...............................8-12
Departure Procedures (DPs) .....................................8-12
Standard Terminal Arrival Routes (STARs) ............8-12
Instrument Approach Procedure (IAP) Charts ............8-12
Margin Identification ................................................8-12
The Pilot Briefing .....................................................8-16
The Plan View ..........................................................8-16
Terminal Arrival Area (TAA) ......................................8-18
Course Reversal Elements in Plan View and
Profile View..............................................................8-20
Procedure Turns ....................................................8-20
Holding in Lieu of Procedure Turn ......................8-20
Teardrop Procedure ..............................................8-21
The Profile View ...................................................8-21
Landing Minimums ..................................................8-23
Airport Sketch /Airport Diagram .............................8-27
Inoperative Components ..........................................8-27
RNAV Instrument Approach Charts ........................8-32
Chapter 9
The Air Traffic Control System...........................9-1
Introduction ....................................................................9-1
Communication Equipment ...........................................9-2
Navigation/Communication (NAV/COM)
Equipment ..................................................................9-2
Radar and Transponders .............................................9-3
Mode C (Altitude Reporting)..................................9-3
Communication Procedures ...........................................9-4
Communication Facilities ..............................................9-4

Automated Flight Service Stations (AFSS) ...............9-4
ATC Towers ...............................................................9-5
Terminal Radar Approach Control (TRACON).........9-6
Tower En Route Control (TEC) .................................9-7
Air Route Traffic Control Center (ARTCC) ..............9-7
Center Approach/Departure Control ..........................9-7
ATC Inflight Weather Avoidance Assistance ..............9-11
ATC Radar Weather Displays ..................................9-11
Weather Avoidance Assistance ................................9-11
Approach Control Facility ...........................................9-12
Approach Control Advances ........................................9-12
Precision Runway Monitor (PRM) ..........................9-12
Precision Runway Monitor (PRM) Radar ............9-12
PRM Benefits ........................................................9-13
Control Sequence .........................................................9-13
Letters of Agreement (LOA) ....................................9-14
Chapter 10
IFR Flight ............................................................10-1
Introduction ..................................................................10-1
Sources of Flight Planning Information.......................10-2
Aeronautical Information Manual (AIM) ................10-2
Airport/Facility Directory (A/FD) ............................10-2
Notices to Airmen Publication (NTAP) ...................10-2
POH/AFM ................................................................10-2
IFR Flight Plan.............................................................10-2
Filing in Flight ..........................................................10-2
Cancelling IFR Flight Plans .....................................10-3
Clearances ....................................................................10-3
Examples ..................................................................10-3
Clearance Separations ..............................................10-4
Departure Procedures (DPs) ........................................10-5
Obstacle Departure Procedures (ODP) ....................10-5
Standard Instrument Departures ...............................10-5
Radar Controlled Departures ....................................10-5
Departures From Airports Without an
Operating Control Tower .........................................10-7
En Route Procedures ....................................................10-7
ATC Reports ............................................................10-7
Position Reports .......................................................10-7
Additional Reports ...................................................10-7
Planning the Descent and Approach ........................10-8
Standard Terminal Arrival Routes (STARs) ............10-9
Substitutes for Inoperative or Unusable
Components ..............................................................10-9
Holding Procedures......................................................10-9
Standard Holding Pattern (No Wind) .......................10-9
Standard Holding Pattern (With Wind) ....................10-9
Holding Instructions .................................................10-9
Standard Entry Procedures .....................................10-11
Time Factors ...........................................................10-12

DME Holding .........................................................10-12
Approaches ................................................................10-12
Compliance With Published Standard Instrument
Approach Procedures .............................................10-12
Instrument Approaches to Civil Airports ...............10-13
Approach to Airport Without an Operating
Control Tower .....................................................10-14
Approach to Airport With an Operating
Tower, With No Approach Control ....................10-14
Approach to an Airport With an Operating
Tower, With an Approach Control .....................10-14
Radar Approaches ..................................................10-17
Radar Monitoring of Instrument Approaches ........10-18
Timed Approaches From a Holding Fix ................10-18
Approaches to Parallel Runways............................10-20
Side-Step Maneuver ...............................................10-20
Circling Approaches ...............................................10-20
IAP Minimums .......................................................10-21
Missed Approaches ................................................10-21
Landing...................................................................10-22
Instrument Weather Flying ........................................10-22
Flying Experience ..................................................10-22
Recency of Experience .......................................10-22
Airborne Equipment and Ground Facilities ........10-22
Weather Conditions ................................................10-22
Turbulence ..........................................................10-23
Structural Icing ...................................................10-24
Fog ......................................................................10-24
Volcanic Ash ......................................................10-24
Thunderstorms ....................................................10-25
Wind Shear .........................................................10-25
VFR-On-Top ..........................................................10-26
VFR Over-The-Top ................................................10-27
Conducting an IFR Flight ..........................................10-27
Preflight ..................................................................10-27
Departure ................................................................10-31
En Route .................................................................10-32
Arrival ....................................................................10-33
Chapter 11
Emergency Operations .....................................11-1
Introduction ..................................................................11-1
Unforecast Adverse Weather .......................................11-2
Inadvertent Thunderstorm Encounter.......................11-2
Inadvertent Icing Encounter .....................................11-2
Precipitation Static ...................................................11-3
Aircraft System Malfunctions ......................................11-3
Electronic Flight Display Malfunction .....................11-4
Alternator/Generator Failure ....................................11-4
Techniques for Electrical Usage ..............................11-5

xv

Master Battery Switch ..........................................11-5
Operating on the Main Battery .............................11-5
Loss of Alternator/Generator for Electronic Flight
Instrumentation.........................................................11-5
Techniques for Electrical Usage ..............................11-6
Standby Battery ....................................................11-6
Operating on the Main Battery .............................11-6
Analog Instrument Failure ...........................................11-6
Pneumatic System Failure............................................11-7
Pitot/Static System Failure...........................................11-7
Communication/Navigation System Malfunction .......11-8
GPS Nearest Airport Function .....................................11-9
Nearest Airports Using the PFD...............................11-9
Additional Information for a Specific Airport ......11-9
Nearest Airports Using the MFD ...........................11-10
Navigating the MFD Page Groups .....................11-10

xvi

Nearest Airport Page Group ...............................11-10
Nearest Airports Page Soft Keys ........................11-10
Situational Awareness................................................11-11
Summary .............................................................11-12
Traffic Avoidance ...................................................11-14
Appendix A
Clearance Shorthand ......................................... A-1
Appendix B
Instrument Training Lesson Guide ................... B-1
Glossary ..............................................................G-1
Index ......................................................................I-1

Chapter 1

Human
Factors
Introduction
Human factors is a broad field that examines the interaction
between people, machines, and the environment for the
purpose of improving performance and reducing errors. As
aircraft became more reliable and less prone to mechanical
failure, the percentage of accidents related to human factors
increased. Some aspect of human factors now accounts for
over 80 percent of all accidents. Pilots who have a good
understanding of human factors are better equipped to plan
and execute a safe and uneventful flight.
Flying in instrument meteorological conditions (IMC) can
result in sensations that are misleading to the body’s sensory
system. A safe pilot needs to understand these sensations and
effectively counteract them. Instrument flying requires a pilot
to make decisions using all available resources.
The elements of human factors covered in this chapter
include sensory systems used for orientation, illusions in
flight, physiological and psychological factors, medical
factors, aeronautical decision-making, and crew resource
management (CRM).

1-1

Sensory Systems for Orientation
Orientation is the awareness of the position of the aircraft
and of oneself in relation to a specific reference point.
Disorientation is the lack of orientation, and spatial
disorientation specifically refers to the lack of orientation
with regard to position in space and to other objects.
Orientation is maintained through the body’s sensory organs
in three areas: visual, vestibular, and postural. The eyes
maintain visual orientation. The motion sensing system in
the inner ear maintains vestibular orientation. The nerves in
the skin, joints, and muscles of the body maintain postural
orientation. When healthy human beings are in their natural
environment, these three systems work well. When the
human body is subjected to the forces of flight, these senses
can provide misleading information. It is this misleading
information that causes pilots to become disoriented.
Eyes
Of all the senses, vision is most important in providing
information to maintain safe flight. Even though the
human eye is optimized for day vision, it is also capable
of vision in very low light environments. During the day,
the eye uses receptors called cones, while at night, vision is
facilitated by the use of rods.
Both of these provide a level
of vision optimized for the
lighting conditions that they
were intended. That is, cones
are ineffective at night and
rods are ineffective during
the day.
Rods, which contain rhodopsin
(called visual purple), are
especially sensitive to light
and increased light washes out
the rhodopsin compromising
the night vision. Hence, when
strong light is momentarily
introduced at night, vision
may be totally ineffective as
the rods take time to become
effective again in darkness.
Smoking, alcohol, oxygen
deprivation, and age affect
vision, especially at night. It
should be noted that at night,
oxygen deprivation such as one
caused from a climb to a high
altitude causes a significant
reduction in vision. A return
back to the lower altitude will
1-2

not restore a pilot’s vision in the same transitory period used
at the climb altitude.
The eye also has two blind spots. The day blind spot is the
location on the light sensitive retina where the optic nerve
fiber bundle (which carries messages from the eye to the
brain) passes through. This location has no light receptors,
and a message cannot be created there to be sent to the brain.
The night blind spot is due to a concentration of cones in an
area surrounding the fovea on the retina. Because there are
no rods in this area, direct vision on an object at night will
disappear. As a result, off-center viewing and scanning at
night is best for both obstacle avoidance and to maximize
situational awareness. [See the Pilot’s Handbook of
Aeronautical Knowledge and the Aeronautical Information
Manual (AIM) for detailed reading.]
The brain also processes visual information based upon color,
relationship of colors, and vision from objects around us.
Figure 1-1 demonstrates the visual processing of information.
The brain assigns color based on many items to include an
object’s surroundings. In the figure below, the orange square
on the shaded side of the cube is actually the same color
as the brown square in the center of the cube’s top face.

Figure 1-1. Rubic’s Cube Graphic.

Isolating the orange square from surrounding influences
will reveal that it is actually brown. The application to a real
environment is evident when processing visual information
that is influenced by surroundings. The ability to pick out an
airport in varied terrain or another aircraft in a light haze are
examples of problems with interpretation that make vigilance
all the more necessary.
Figure 1-2 illustrates problems with perception. Both tables
are the same lengths. Objects are easily misinterpreted in
size to include both length and width. Being accustomed to
a 75-foot-wide runway on flat terrain is most likely going
to influence a pilot’s perception of a wider runway on
uneven terrain simply because of the inherent processing
experience.

Vision Under Dim and Bright Illumination
Under conditions of dim illumination, aeronautical charts and
aircraft instruments can become unreadable unless adequate
flight deck lighting is available. In darkness, vision becomes
more sensitive to light. This process is called dark adaptation.
Although exposure to total darkness for at least 30 minutes is
required for complete dark adaptation, a pilot can achieve a
moderate degree of dark adaptation within 20 minutes under
dim red flight deck lighting.
Red light distorts colors (filters the red spectrum), especially
on aeronautical charts, and makes it very difficult for the
eyes to focus on objects inside the aircraft. Pilots should

use it only where optimum outside night vision capability is
necessary. White flight deck lighting (dim lighting) should
be available when needed for map and instrument reading,
especially under IMC conditions.
Since any degree of dark adaptation is lost within a few
seconds of viewing a bright light, pilots should close one eye
when using a light to preserve some degree of night vision.
During night flights in the vicinity of lightning, flight deck
lights should be turned up to help prevent loss of night vision
due to the bright flashes. Dark adaptation is also impaired by
exposure to cabin pressure altitudes above 5,000 feet, carbon
monoxide inhaled through smoking, deficiency of Vitamin A
in the diet, and by prolonged exposure to bright sunlight.
During flight in visual meteorological conditions (VMC),
the eyes are the major orientation source and usually provide
accurate and reliable information. Visual cues usually
prevail over false sensations from other sensory systems.
When these visual cues are taken away, as they are in IMC,
false sensations can cause the pilot to quickly become
disoriented.
An effective way to counter these false sensations is to
recognize the problem, disregard the false sensations, rely
on the flight instruments, and use the eyes to determine the
aircraft attitude. The pilot must have an understanding of
the problem and the skill to control the aircraft using only
instrument indications.

Figure 1-2. Shepard’s Tables.

1-3

Figure 1-3. Inner Ear Orientation.

Ears
The inner ear has two major parts concerned with orientation,
the semicircular canals and the otolith organs. [Figure 1-3] The
semicircular canals detect angular acceleration of the body
while the otolith organs detect linear acceleration and gravity.
The semicircular canals consist of three tubes at right angles
to each other, each located on one of three axes: pitch, roll,
or yaw as illustrated in Figure 1-4. Each canal is filled with
a fluid called endolymph fluid. In the center of the canal is
the cupola, a gelatinous structure that rests upon sensory
hairs located at the end of the vestibular nerves. It is the
movement of these hairs within the fluid which causes
sensations of motion.
Because of the friction between the fluid and the canal, it
may take about 15–20 seconds for the fluid in the ear canal
to reach the same speed as the canal’s motion.

Figure 1-4. Angular Acceleration and the Semicircular Tubes.

1-4

To illustrate what happens during a turn, visualize the aircraft
in straight and level flight. With no acceleration of the aircraft,
the hair cells are upright and the body senses that no turn
has occurred. Therefore, the position of the hair cells and the
actual sensation correspond.
Placing the aircraft into a turn puts the semicircular canal and
its fluid into motion, with the fluid within the semicircular
canal lagging behind the accelerated canal walls.[Figure 1-5]
This lag creates a relative movement of the fluid within the
canal. The canal wall and the cupula move in the opposite
direction from the motion of the fluid.
The brain interprets the movement of the hairs to be a turn in
the same direction as the canal wall. The body correctly senses
that a turn is being made. If the turn continues at a constant
rate for several seconds or longer, the motion of the fluid in

Figure 1-5. Angular Acceleration.

the canals catches up with the canal walls. The hairs are no
longer bent, and the brain receives the false impression that
turning has stopped. Thus, the position of the hair cells and the
resulting sensation during a prolonged, constant turn in either
direction will result in the false sensation of no turn.

Illusions Leading to Spatial
Disorientation

When the aircraft returns to straight-and-level flight, the fluid
in the canal moves briefly in the opposite direction. This sends
a signal to the brain that is falsely interpreted as movement
in the opposite direction. In an attempt to correct the falsely
perceived turn, the pilot may reenter the turn placing the
aircraft in an out of control situation.

Vestibular Illusions

The otolith organs detect linear acceleration and gravity in a
similar way. Instead of being filled with a fluid, a gelatinous
membrane containing chalk-like crystals covers the sensory
hairs. When the pilot tilts his or her head, the weight of these
crystals causes this membrane to shift due to gravity and
the sensory hairs detect this shift. The brain orients this new
position to what it perceives as vertical. Acceleration and
deceleration also cause the membrane to shift in a similar
manner. Forward acceleration gives the illusion of the head
tilting backward. [Figure 1-6] As a result, during takeoff and
while accelerating, the pilot may sense a steeper than normal
climb resulting in a tendency to nose-down.

The sensory system responsible for most of the illusions
leading to spatial disorientation is the vestibular system.
Visual illusions can also cause spatial disorientation.

The Leans
A condition called the leans can result when a banked attitude,
to the left for example, may be entered too slowly to set in
motion the fluid in the “roll” semicircular tubes. [Figure 1-5]
An abrupt correction of this attitude sets the fluid in motion,
creating the illusion of a banked attitude to the right. The
disoriented pilot may make the error of rolling the aircraft
into the original left banked attitude, or if level flight is
maintained, will feel compelled to lean in the perceived
vertical plane until this illusion subsides.

Nerves
Nerves in the body’s skin, muscles, and joints constantly
send signals to the brain, which signals the body’s relation to
gravity. These signals tell the pilot his or her current position.
Acceleration will be felt as the pilot is pushed back into the
seat. Forces created in turns can lead to false sensations of
the true direction of gravity, and may give the pilot a false
sense of which way is up.
Uncoordinated turns, especially climbing turns, can cause
misleading signals to be sent to the brain. Skids and slips
give the sensation of banking or tilting. Turbulence can create
motions that confuse the brain as well. Pilots need to be aware
that fatigue or illness can exacerbate these sensations and
ultimately lead to subtle incapacitation.

Figure 1-6. Linear Acceleration.

1-5

Coriolis Illusion
The coriolis illusion occurs when a pilot has been in a turn
long enough for the fluid in the ear canal to move at the same
speed as the canal. A movement of the head in a different
plane, such as looking at something in a different part of the
flight deck, may set the fluid moving and create the illusion
of turning or accelerating on an entirely different axis.
This action causes the pilot to think the aircraft is doing a
maneuver that it is not. The disoriented pilot may maneuver
the aircraft into a dangerous attitude in an attempt to correct
the aircraft’s perceived attitude.
For this reason, it is important that pilots develop an instrument
cross-check or scan that involves minimal head movement.
Take care when retrieving charts and other objects in the flight
deck—if something is dropped, retrieve it with minimal head
movement and be alert for the coriolis illusion.

Graveyard Spiral
As in other illusions, a pilot in a prolonged coordinated,
constant rate turn, will have the illusion of not turning.
During the recovery to level flight, the pilot will experience
the sensation of turning in the opposite direction. The
disoriented pilot may return the aircraft to its original turn.
Because an aircraft tends to lose altitude in turns unless the
pilot compensates for the loss in lift, the pilot may notice
a loss of altitude. The absence of any sensation of turning
creates the illusion of being in a level descent. The pilot may
pull back on the controls in an attempt to climb or stop the

Figure 1-7. Graveyard Spiral.

1-6

descent. This action tightens the spiral and increases the loss
of altitude; hence, this illusion is referred to as a graveyard
spiral. [Figure 1-7] At some point, this could lead to a loss
of control by the pilot.

Somatogravic Illusion
A rapid acceleration, such as experienced during takeoff,
stimulates the otolith organs in the same way as tilting the
head backwards. This action creates the somatogravic illusion
of being in a nose-up attitude, especially in situations without
good visual references. The disoriented pilot may push the
aircraft into a nose-low or dive attitude. A rapid deceleration
by quick reduction of the throttle(s) can have the opposite
effect, with the disoriented pilot pulling the aircraft into a
nose-up or stall attitude.

Inversion Illusion
An abrupt change from climb to straight-and-level flight can
stimulate the otolith organs enough to create the illusion of
tumbling backwards, or inversion illusion. The disoriented
pilot may push the aircraft abruptly into a nose-low attitude,
possibly intensifying this illusion.

Elevator Illusion
An abrupt upward vertical acceleration, as can occur in
an updraft, can stimulate the otolith organs to create the
illusion of being in a climb. This is called elevator illusion.
The disoriented pilot may push the aircraft into a nose-low
attitude. An abrupt downward vertical acceleration, usually

in a downdraft, has the opposite effect, with the disoriented
pilot pulling the aircraft into a nose-up attitude.
Visual Illusions
Visual illusions are especially hazardous because pilots rely
on their eyes for correct information. Two illusions that lead
to spatial disorientation, false horizon and autokinesis, are
concerned with only the visual system.

largely dependent upon these signals. Used in conjunction
with visual and vestibular clues, these sensations can be
fairly reliable. However, because of the forces acting upon
the body in certain flight situations, many false sensations
can occur due to acceleration forces overpowering gravity.
[Figure 1-8] These situations include uncoordinated turns,
climbing turns, and turbulence.

Demonstration of Spatial Disorientation
False Horizon
A sloping cloud formation, an obscured horizon, an aurora
borealis, a dark scene spread with ground lights and stars,
and certain geometric patterns of ground lights can provide
inaccurate visual information, or false horizon, for aligning
the aircraft correctly with the actual horizon. The disoriented
pilot may place the aircraft in a dangerous attitude.

Autokinesis

There are a number of controlled aircraft maneuvers a pilot
can perform to experiment with spatial disorientation. While
each maneuver will normally create a specific illusion, any
false sensation is an effective demonstration of disorientation.
Thus, even if there is no sensation during any of these
maneuvers, the absence of sensation is still an effective
demonstration in that it shows the inability to detect bank
or roll. There are several objectives in demonstrating these
various maneuvers.

In the dark, a stationary light will appear to move about when
stared at for many seconds. The disoriented pilot could lose
control of the aircraft in attempting to align it with the false
movements of this light, called autokinesis.

1.

They teach pilots to understand the susceptibility of
the human system to spatial disorientation.

2.

They demonstrate that judgments of aircraft attitude
based on bodily sensations are frequently false.

Postural Considerations

3.

They help lessen the occurrence and degree of
disorientation through a better understanding of the
relationship between aircraft motion, head movements,
and resulting disorientation.

4.

They help instill a greater confidence in relying on
flight instruments for assessing true aircraft attitude.

The postural system sends signals from the skin, joints, and
muscles to the brain that are interpreted in relation to the
Earth’s gravitational pull. These signals determine posture.
Inputs from each movement update the body’s position to
the brain on a constant basis. “Seat of the pants” flying is

Figure 1-8. Sensations From Centrifugal Force.

1-7

A pilot should not attempt any of these maneuvers at low
altitudes, or in the absence of an instructor pilot or an
appropriate safety pilot.
Climbing While Accelerating
With the pilot’s eyes closed, the instructor pilot maintains
approach airspeed in a straight-and-level attitude for several
seconds, and then accelerates while maintaining straight-andlevel attitude. The usual illusion during this maneuver, without
visual references, will be that the aircraft is climbing.
Climbing While Turning
With the pilot’s eyes still closed and the aircraft in a straightand-level attitude, the instructor pilot now executes, with a
relatively slow entry, a well-coordinated turn of about 1.5
positive G (approximately 50° bank) for 90°. While in the
turn, without outside visual references and under the effect of
the slight positive G, the usual illusion produced is that of a
climb. Upon sensing the climb, the pilot should immediately
open the eyes and see that a slowly established, coordinated
turn produces the same feeling as a climb.
Diving While Turning
Repeating the previous procedure, with the exception that
the pilot’s eyes should be kept closed until recovery from
the turn is approximately one-half completed can create this
sensation. With the eyes closed, the usual illusion will be
that the aircraft is diving.
Tilting to Right or Left
While in a straight-and-level attitude, with the pilot’s eyes
closed, the instructor pilot executes a moderate or slight skid
to the left with wings level. This creates the illusion of the
body being tilted to the right.
Reversal of Motion
This illusion can be demonstrated in any of the three planes of
motion. While straight and level, with the pilot’s eyes closed,
the instructor pilot smoothly and positively rolls the aircraft to
approximately a 45° bank attitude while maintaining heading
and pitch attitude. This creates the illusion of a strong sense
of rotation in the opposite direction. After this illusion is
noted, the pilot should open his or her eyes and observe that
the aircraft is in a banked attitude.
Diving or Rolling Beyond the Vertical Plane
This maneuver may produce extreme disorientation. While
in straight-and-level flight, the pilot should sit normally,
either with eyes closed or gaze lowered to the floor. The
instructor pilot starts a positive, coordinated roll toward a
30° or 40° angle of bank. As this is in progress, the pilot
tilts his or her head forward, looks to the right or left, then
immediately returns his or her head to an upright position.
1-8

The instructor pilot should time the maneuver so the roll is
stopped as the pilot returns his or her head upright. An intense
disorientation is usually produced by this maneuver, and the
pilot experiences the sensation of falling downward into the
direction of the roll.
In the descriptions of these maneuvers, the instructor pilot is
doing the flying, but having the pilot do the flying can also
be a very effective demonstration. The pilot should close his
or her eyes and tilt the head to one side. The instructor pilot
tells the pilot what control inputs to perform. The pilot then
attempts to establish the correct attitude or control input with
eyes closed and head tilted. While it is clear the pilot has no
idea of the actual attitude, he or she will react to what the
senses are saying. After a short time, the pilot will become
disoriented and the instructor pilot then tells the pilot to
look up and recover. The benefit of this exercise is the pilot
experiences the disorientation while flying the aircraft.

Coping with Spatial Disorientation
To prevent illusions and their potentially disastrous
consequences, pilots can:
1.

Understand the causes of these illusions and remain
constantly alert for them. Take the opportunity to
understand and then experience spatial disorientation
illusions in a device such as a Barany chair, a
Vertigon, or a Virtual Reality Spatial Disorientation
Demonstrator.

2.

Always obtain and understand preflight weather
briefings.

3.

Before flying in marginal visibility (less than 3 miles)
or where a visible horizon is not evident such as flight
over open water during the night, obtain training and
maintain proficiency in airplane control by reference
to instruments.

4.

Do not continue flight into adverse weather conditions
or into dusk or darkness unless proficient in the use of
flight instruments. If intending to fly at night, maintain
night-flight currency and proficiency. Include crosscountry and local operations at various airfields.

5.

Ensure that when outside visual references are used,
they are reliable, fixed points on the Earth’s surface.

6.

Avoid sudden head movement, particularly during
takeoffs, turns, and approaches to landing.

7.

Be physically tuned for flight into reduced visibility.
That is, ensure proper rest, adequate diet, and, if flying
at night, allow for night adaptation. Remember that
illness, medication, alcohol, fatigue, sleep loss, and
mild hypoxia are likely to increase susceptibility to
spatial disorientation.

8.

Most importantly, become proficient in the use of
flight instruments and rely upon them. Trust the
instruments and disregard your sensory perceptions.

The sensations that lead to illusions during instrument
flight conditions are normal perceptions experienced by
pilots. These undesirable sensations cannot be completely
prevented, but through training and awareness, pilots can
ignore or suppress them by developing absolute reliance
on the flight instruments. As pilots gain proficiency in
instrument flying, they become less susceptible to these
illusions and their effects.

Optical Illusions
Of the senses, vision is the most important for safe flight.
However, various terrain features and atmospheric conditions
can create optical illusions. These illusions are primarily
associated with landing. Since pilots must transition from
reliance on instruments to visual cues outside the flight
deck for landing at the end of an instrument approach, it is
imperative they be aware of the potential problems associated
with these illusions, and take appropriate corrective action.
The major illusions leading to landing errors are described
below.
Runway Width Illusion
A narrower-than-usual runway can create an illusion the
aircraft is at a higher altitude than it actually is, especially
when runway length-to-width relationships are comparable.
[Figure 1-9A] The pilot who does not recognize this illusion
will fly a lower approach, with the risk of striking objects
along the approach path or landing short. A wider-than-usual
runway can have the opposite effect, with the risk of leveling
out high and landing hard, or overshooting the runway.
Runway and Terrain Slopes Illusion
An upsloping runway, upsloping terrain, or both, can create
an illusion the aircraft is at a higher altitude than it actually
is. [Figure 1-9B] The pilot who does not recognize this
illusion will fly a lower approach. Downsloping runways and
downsloping approach terrain can have the opposite effect.
Featureless Terrain Illusion
An absence of surrounding ground features, as in an
overwater approach, over darkened areas, or terrain made
featureless by snow, can create an illusion the aircraft is at
a higher altitude than it actually is. This illusion, sometimes
referred to as the “black hole approach,” causes pilots to fly
a lower approach than is desired.

Water Refraction
Rain on the windscreen can create an illusion of being at a
higher altitude due to the horizon appearing lower than it is.
This can result in the pilot flying a lower approach.
Haze
Atmospheric haze can create an illusion of being at a greater
distance and height from the runway. As a result, the pilot
will have a tendency to be low on the approach. Conversely,
extremely clear air (clear bright conditions of a high attitude
airport) can give the pilot the illusion of being closer than he
or she actually is, resulting in a high approach, which may
result in an overshoot or go around. The diffusion of light
due to water particles on the windshield can adversely affect
depth perception. The lights and terrain features normally
used to gauge height during landing become less effective
for the pilot.
Fog
Flying into fog can create an illusion of pitching up. Pilots
who do not recognize this illusion will often steepen the
approach quite abruptly.
Ground Lighting Illusions
Lights along a straight path, such as a road or lights on moving
trains, can be mistaken for runway and approach lights. Bright
runway and approach lighting systems, especially where
few lights illuminate the surrounding terrain, may create the
illusion of less distance to the runway. The pilot who does not
recognize this illusion will often fly a higher approach.

How To Prevent Landing Errors Due to
Optical Illusions
To prevent these illusions and their potentially hazardous
consequences, pilots can:
1.

Anticipate the possibility of visual illusions during
approaches to unfamiliar airports, particularly at
night or in adverse weather conditions. Consult
airport diagrams and the Airport/Facility Directory
(A/FD) for information on runway slope, terrain, and
lighting.

2.

Make frequent reference to the altimeter, especially
during all approaches, day and night.

3.

If possible, conduct aerial visual inspection of
unfamiliar airports before landing.

1-9

Figure 1-9. Runway Width and Slope Illusions.

4.

Use Visual Approach Slope Indicator (VASI) or
Precision Approach Path Indicator (PAPI) systems
for a visual reference, or an electronic glide slope,
whenever they are available.

5.

Utilize the visual descent point (VDP) found on many
nonprecision instrument approach procedure charts.

1-10

6.

Recognize that the chances of being involved in an
approach accident increase when some emergency or
other activity distracts from usual procedures.

7.

Maintain optimum proficiency in landing procedures.

Physiological and Psychological Factors
Physiological or psychological factors can affect a pilot
and compromise the safety of a flight. These factors are
stress, medical, alcohol, and fatigue. Any of these factors,
individually or in combination, significantly degrade the
pilot’s decision-making or flying abilities.
Stress
Stress is the body’s response to demands placed upon it. These
demands can be either pleasant or unpleasant in nature. The
causes of stress for a pilot can range from unexpected weather
or mechanical problems while in flight, to personal issues
unrelated to flying. Stress is an inevitable and necessary part
of life; it adds motivation to life and heightens an individual’s
response to meet any challenge. The effects of stress are
cumulative and there is a limit to a person’s adaptive nature.
This limit, called the stress tolerance level (or channel
capacity), is based on the ability to cope with the situation.
At first, some amount of stress can be desirable and can
actually improve performance. However, higher stress levels,
particularly over long periods of time, can adversely affect
performance. Performance will generally increase with the
onset of stress, but will peak and then begin to fall off rapidly
as stress levels exceed the ability to cope. [Figure 1-10]

4.

Develop a lifestyle that will buffer against the effects
of stress.

5.

Practice behavior management techniques.

6.

Establish and maintain a strong support network.

Good flight deck stress management begins with good life
stress management. Many of the stress coping techniques
practiced for life stress management are not usually practical
in flight. Rather, pilots must condition themselves to relax and
think rationally when stress appears. The following checklist
outlines some methods of flight deck stress management.
1.

Avoid situations that distract from flying the aircraft.

2.

Reduce flight deck workload to reduce stress levels.
This will create a proper environment in which to make
good decisions. Typically, flying involves higher stress
levels during takeoff and landing phases. Between the
two generally lies a period of low activity resulting
in a lower stress level. Transitioning from the cruise
phase to the landing phase is generally accompanied
by a significant workload that, if not properly
accommodated, will increase stress significantly.
Proper planning and prioritization of flight deck
duties are key to avoiding events that affect the pilot's
capacity to maintain situational awareness.

At this point, a pilot’s performance begins to decline and
judgment deteriorates. Complex or unfamiliar tasks require
higher levels of performance than simple or overlearned
tasks. Complex or unfamiliar tasks are also more subject to
the adverse effects of increasing stress than simple or familiar
tasks. [Figure 1-10]
The indicators of excessive stress often show as three types
of symptoms: (1) emotional, (2) physical, and (3) behavioral.
Emotional symptoms may surface as over-compensation,
denial, suspicion, paranoia, agitation, restlessness, or
defensiveness. Physical stress can result in acute fatigue
while behavioral degradation will be manifested as sensitivity
to criticism, tendency to be argumentative, arrogance, and
hostility. Pilots need to learn to recognize the symptoms of
stress as they begin to occur.
There are many techniques available that can help reduce
stress in life or help people cope with it better. Not all of the
following ideas may be a solution, but some of them should
be effective.
1.

Become knowledgeable about stress.

2.

Take a realistic self-assessment. (See the Pilot’s
Handbook of Aeronautical Knowledge).

3.

Take a systematic approach to problem solving.

Figure 1-10. Stress and Performance.

1-11

3.

If a problem occurs, remain calm. If time is not a
pressing factor, follow the analytical approach to
decision-making: think for a moment, weigh the
alternatives, select and take an appropriate course of
action, and then evaluate its effects.
If an emergency situation occurs, remain calm and
use the aeronautical decision-making (ADM) process
to resolve the emergency. This process relies on the
pilot’s training and experience to accurately and
automatically respond to an emergency situation.
Constant training in handling emergency procedures
will help reduce pilot stress when an emergency
occurs.

4.

Become thoroughly familiar with the aircraft, its
operation, and emergency procedures. Also, maintain
flight proficiency to build confidence.

5.

Know and respect personal limits. Studies have
suggested that highly experienced pilots have taken
more chances when flying into potential icing
conditions than low time or inexperienced pilots.
Very low time pilots without experience may analyze
and interpret the likelihood for “potential” flight into
icing without the benefit of life experience, thereby
making decisions closely aligned with the compilation
of their training and recent academic knowledge.
Highly experienced pilots may evaluate the current
situation based upon the empirical information
(sometimes diluted with time) coupled with their
vast experience. This may lead to a level of greater
acceptability of the situation because their experience
has illustrated successful navigation of this problem
before. Therefore, the automatic decision may be in
error because not all salient facts are evaluated.

6.

Do not allow small mistakes to be distractions during
flight; rather, review and analyze them after landing.

7.

If flying adds stress, either stop flying or seek
professional help to manage stress within acceptable
limits.

Medical Factors
A “go/no-go” decision based on a pilot’s medical factors is
made before each flight. The pilot should not only preflight
check the aircraft, but also himself or herself before
every flight. A pilot should ask, “Can I pass my medical
examination right now?” If the answer is not an absolute
“yes,” do not fly. This is especially true for pilots embarking
on flights in IMC. Instrument flying is much more demanding
than flying in VMC, and peak performance is critical for the
safety of flight.

1-12

Pilot performance can be seriously degraded by both
prescribed and over-the-counter medications, as well as
by the medical conditions for which they are taken. Many
medications, such as tranquilizers, sedatives, strong pain
relievers, and cough suppressants, have primary effects
that impair judgment, memory, alertness, coordination,
vision, and the ability to make calculations. Others, such
as antihistamines, blood pressure drugs, muscle relaxants,
and agents to control diarrhea and motion sickness, have
side effects that impair the same critical functions. Any
medication that depresses the nervous system, such as a
sedative, tranquilizer, or antihistamine, makes a pilot much
more susceptible to hypoxia.
Title 14 of the Code of Federal Regulations (14 CFR) prohibits
pilots from performing crewmember duties while using any
medication that affects the faculties in any way contrary to
safety. The safest rule is not to fly as a crewmember while
taking any medication, unless approved to do so by the
Federal Aviation Administration (FAA). If there is any doubt
regarding the effects of any medication, consult an Aviation
Medical Examiner (AME) before flying.
Alcohol
14 CFR part 91 prohibits pilots from performing crewmember
duties within 8 hours after drinking any alcoholic beverage or
while under the influence. Extensive research has provided a
number of facts about the hazards of alcohol consumption and
flying. As little as one ounce of liquor, one bottle of beer, or
four ounces of wine can impair flying skills and render a pilot
much more susceptible to disorientation and hypoxia. Even
after the body completely metabolizes a moderate amount of
alcohol, a pilot can still be impaired for many hours. There
is simply no way of increasing the metabolism of alcohol or
alleviating a hangover.
Fatigue
Fatigue is one of the most treacherous hazards to flight safety,
as it may not be apparent to a pilot until serious errors are
made. Fatigue can be either acute (short-term) or chronic
(long-term).

Acute Fatigue
A normal occurrence of everyday living, acute fatigue is
the tiredness felt after long periods of physical and mental
strain, including strenuous muscular effort, immobility, heavy
mental workload, strong emotional pressure, monotony, and
lack of sleep. Adequate rest, regular exercise, and proper
nutrition prevent acute fatigue.

Indications of fatigue are generally subtle and hard to
recognize because the individual being assessed is generally
the person making the assessment, as in single pilot
operations. Therefore, the pilot must look at small errors
that occur to provide an indication of becoming fatigued.
These include:
•

Misplacing items during the preflight;

•

Leaving material (pencils, charts) in the planning
area;

•

Missing radio calls;

•

Answering calls improperly (read-backs); and

•

Improper tuning of frequencies.

Chronic Fatigue
Chronic fatigue occurs when there is not enough time for a
full recovery from repeated episodes of acute fatigue. Chronic
fatigue’s underlying cause is generally not “rest-related” and
may have deeper points of origin. Therefore, rest alone may
not resolve chronic fatigue.
Chronic fatigue is a combination of both physiological
problems and psychological issues. Psychological problems
such as financial, home life, or job related stresses cause a
lack of qualified rest that is only resolved by mitigating the
underpinning problems. Without resolution, performance
continues to fall off, judgment becomes impaired, and
unwarranted risks are taken. Recovery from chronic fatigue
requires a prolonged and deliberate solution. In either case,
unless adequate precautions are taken, personal performance
could be impaired and adversely affect pilot judgment and
decision-making.
IMSAFE Checklist
The following checklist, IMSAFE, is intended for a pilot’s
personal preflight use. A quick check of the items on this
list will help a pilot make a good self-evaluation prior to any
flight. If the answer to any of the checklist questions is yes,
then the pilot should consider not flying.
Illness
Do I have any symptoms?
Medication
Have I been taking prescription or over-the-counter drugs?
Stress
Am I under psychological pressure from the job? Do I have
money, health, or family problems?

Fatigue
Am I tired and not adequately rested?
Eating
Have I eaten enough of the proper foods to keep adequately
nourished during the entire flight?

Hazard Identification
In order to identify a hazard, it would be useful to define what
a hazard is. The FAA System Safety course defines a hazard
as: “a present condition, event, object, or circumstance that
could lead or contribute to an unplanned or undesired event.”
Put simply, a hazard is a source of danger. Potential hazards
may be identified from a number of internal and external
sources. These may be based upon several concurrent factors
that provide an indication and ultimate identification of a
hazard. Consider the following situations:
Situation 1
The pilot has just taken off and is entering the clouds. Suddenly,
there is an explosive sound. The sudden noise is disturbing and
occurs as the pilot is given a new heading, a climb restriction,
and the frequency for the departure control.
Situation 2
The pilot took off late in a rented aircraft (first time flying
this model), and is now in night conditions due to the delay,
and flying on an instrument flight rules (IFR) flight plan in
IMC conditions. The radios do not seem to work well and
develop static. They seem to be getting weaker. As the pilot
proceeds, the rotating beacon stops flashing/rotating, and the
lights become dimmer. As the situation progresses, the pilot
is unaware of the problem because the generator warning
light, (on the lower left of the panel) is obscured by the chart
on the pilot’s lap.
Both situations above represent hazards that must be dealt
with differently and a level of risk must be associated with
each depending on various factors affecting the flight.
Risk Analysis
Risk is defined as the future impact of a hazard that is not
eliminated or controlled. It is the possibility of loss or injury.
Risk analysis is the process whereby hazards are characterized
by their likelihood and severity. Risk analysis evaluates
the hazards to determine the outcomes and how abrupt that
outcome will occur. The analysis applied will be qualitative
to the degree that time allows resulting in either an analytical
or automatic approach in the decision-making process.

Alcohol
Have I been drinking within 8 hours? Within 24 hours?
1-13

In the first situation, the decision may be automatic: fly the
airplane to a safe landing. Since automatic decision-making
is based upon education and experience, an inexperienced
pilot may react improperly to the situation which results in
an inadequate action. To mitigate improper decision-making,
immediate action items from emergency procedures should
be learned. Training, education, and mentorship are all key
factors in honing automatic decision-making skills.
In the second situation, if the pilot has a flashlight onboard, it
can be used for illumination, although its light may degrade
night vision. After changing the appropriate transponder
code, and making calls in the blind, awareness of present
location becomes imperative, especially if the pilot must
execute a controlled descent to VMC conditions. Proper
preflight planning conducted before departure and constant
awareness of location provide an element of both comfort
(reduces stress) and information from which the pilot can
draw credible information.
In both cases, the outcomes can be successful through
systems understanding, emergency procedures training, and
correctly analyzing the risks associated with each course
of action.

Crew Resource Management (CRM)
and Single-Pilot Resource Management
(SRM)
Crew resource management (CRM) and single-pilot resource
management (SRM) is the ability for the crew or pilot to
manage all resources effectively to ensure the outcome of the
flight is successful. In general aviation, SRM will be most
often used and its focus is on the single-pilot operation. SRM
integrates the following:
•

Situational Awareness

•

Flight Deck Resource Management

•

Task Management

•

Aeronautical Decision-making (ADM) and Risk
Management

SRM recognizes the need to seek proper information from
these sources to make a valid decision. For instance, the
pilot may have to request assistance from others and be
assertive to resolve situations. Pilots should understand the
need to seek information from other sources until they have
the proper information to make the best decision. Once a
pilot has gathered all pertinent information and made the
appropriate decision, the pilot needs to perform an assessment
of the action taken.

1-14

Situational Awareness
Situational awareness is the accurate perception of
operational and environmental factors that affect the flight. It
is a logical analysis based upon the machine, external support,
environment, and the pilot. It is knowing what is going on.

Flight Deck Resource Management
CRM is the effective use of all available resources: human,
equipment, and information. It focuses on communication
skills, teamwork, task allocation, and decision-making.
While CRM often concentrates on pilots who operate in
crew environments, the elements and concepts also apply to
single-pilot operations.
Human Resources
Human resources include everyone routinely working with the
pilot to ensure flight safety. These people include, but are not
limited to: weather briefers, flight line personnel, maintenance
personnel, crew members, pilots, and air traffic personnel.
Pilots need to effectively communicate with these people.
This is accomplished by using the key components of the
communication process: inquiry, advocacy, and assertion.
Pilots must recognize the need to seek enough information
from these resources to make a valid decision. After the
necessary information has been gathered, the pilot’s decision
must be passed on to those concerned, such as air traffic
controllers, crew members, and passengers. The pilot may
have to request assistance from others and be assertive to
safely resolve some situations.
Equipment
Equipment in many of today’s aircraft includes automated
flight and navigation systems. These automatic systems, while
providing relief from many routine flight deck tasks, present a
different set of problems for pilots. The automation intended
to reduce pilot workload essentially removes the pilot from the
process of managing the aircraft, thereby reducing situational
awareness and leading to complacency. Information from
these systems needs to be continually monitored to ensure
proper situational awareness. Pilots should be thoroughly
familiar with the operation of and information provided by
all systems used. It is essential that pilots be aware not only
of equipment capabilities, but also equipment limitations in
order to manage those systems effectively and safely.
Information Workload
Information workloads and automated systems, such as
autopilots, need to be properly managed to ensure a safe

flight. The pilot flying in IMC is faced with many tasks, each
with a different level of importance to the outcome of the
flight. For example, a pilot preparing to execute an instrument
approach to an airport needs to review the approach chart,
prepare the aircraft for the approach and landing, complete
checklists, obtain information from Automatic Terminal
Information Service (ATIS) or air traffic control (ATC), and
set the navigation radios and equipment.
The pilot who effectively manages his or her workload
will complete as many of these tasks as early as possible
to preclude the possibility of becoming overloaded by last
minute changes and communication priorities in the later,
more critical stages of the approach. Figure 1-11 shows the
margin of safety is at the minimum level during this stage
of the approach. Routine tasks delayed until the last minute
can contribute to the pilot becoming overloaded and stressed,
resulting in erosion of performance.
By planning ahead, a pilot can effectively reduce workload
during critical phases of flight. If a pilot enters the final
phases of the instrument approach unprepared, the pilot
should recognize the situation, abandon the approach, and
try it again after becoming better prepared. Effective resource
management includes recognizing hazardous situations and
attitudes, decision-making to promote good judgment and
headwork, and managing the situation to ensure the safe
outcome of the IFR flight.

Task Management
Pilots have a limited capacity for information. Once
information flow exceeds the pilot’s ability to mentally
process the information any additional information will
become unattended or displace other tasks and information

already being processed. This is termed channel capacity and
once reached only two alternatives exist: shed the unimportant
tasks or perform all tasks at a less than optimal level. Like an
electrical circuit being overloaded, either the consumption
must be reduced or a circuit failure is experienced.
The pilot who effectively manages the tasks and properly
prioritizes them will have a successful flight. For example,
do not become distracted and fixate on an instrument light
failure. This unnecessary focus displaces capability and
prevents the pilot’s ability to appreciate tasks of greater
importance. By planning ahead, a pilot can effectively reduce
workload during critical phases of a flight.

Aeronautical Decision-Making (ADM)
Flying safely requires the effective integration of three
separate sets of skills. Most obvious are the basic stick-andrudder skills needed to control the airplane. Next, are skills
related to proficient operation of aircraft systems, and last,
but not least, are ADM skills.
ADM is a systematic approach to the mental process used
by pilots to consistently determine the best course of action
in response to a given set of circumstances. The importance
of learning effective ADM skills cannot be overemphasized.
While progress is continually being made in the advancement
of pilot training methods, airplane equipment and systems, and
services for pilots, accidents still occur. Despite all the changes
in technology to improve flight safety, one factor remains the
same—the human factor. While the FAA strives to eliminate
errors through training and safety programs, one fact remains:
humans make errors. It is estimated that approximately 80
percent of all aviation accidents are human factors related.

Figure 1-11. The Margin of Safety.

1-15

The ADM process addresses all aspects of decision making
in the flight deck and identifies the steps involved in good
decision making. While the ADM process will not eliminate
errors, it will help the pilot recognize errors, and in turn
enable the pilot to manage the error to minimize its effects.
These steps are:
1.

Identifying personal attitudes hazardous to safe
flight;

2.

Learning behavior modification techniques;

3.

Learning how to recognize and cope with stress;

4.

Developing risk assessment skills;

5.

Using all resources; and

6.

Evaluating the effectiveness of one’s ADM skills.

Historically, the term “pilot error” has been used to describe
the causes of these accidents. Pilot error means that an action
or decision made by the pilot was the cause, or a contributing
factor that led to the accident. This definition also includes
the pilot’s failure to make a decision or take action. From
a broader perspective, the phrase “human factors related”
more aptly describes these accidents since it is usually not a
single decision that leads to an accident, but a chain of events
triggered by a number of factors.
The poor judgment chain, sometimes referred to as the “error
chain,” is a term used to describe this concept of contributing
factors in a human factors related accident. Breaking one link
in the chain normally is all that is necessary to change the
outcome of the sequence of events.
The Decision-Making Process
An understanding of the decision-making process provides
a pilot with a foundation for developing ADM skills.
Some situations, such as engine failures, require a pilot to
respond immediately using established procedures with a
little time for detailed analysis. This is termed automatic
decision-making and is based upon training, experience, and
recognition. Traditionally, pilots have been well trained to
react to emergencies, but are not as well prepared to make
decisions requiring a more reflective response where greater
analysis is required. Typically during a flight, there is time
to examine any changes that occur, gather information, and
assess risk before reaching a decision. The steps leading to
this conclusion constitute the decision-making process.
Defining the Problem
Problem definition is the first step in the decision-making
process. Defining the problem begins with recognizing that
a change has occurred or that an expected change did not
occur. A problem is perceived first by the senses, then is
distinguished through insight and experience. One critical
1-16

error that can be made during the decision-making process
is incorrectly defining the problem. For example, a low oil
pressure reading could indicate that the engine is about to
fail and an emergency landing should be planned, or it could
mean that the oil pressure sensor has failed. The actions to be
taken in each of these circumstances would be significantly
different. One requires an immediate decision based upon
training, experience, and evaluation of the situation; whereas
the latter decision is based upon an analysis. It should be
noted that the same indication could result in two different
actions depending upon other influences.
Choosing a Course of Action
After the problem has been identified, the pilot must evaluate
the need to react to it and determine the actions that may
be taken to resolve the situation in the time available.
The expected outcome of each possible action should be
considered and the risks assessed before deciding on a
response to the situation.
Implementing the Decision and Evaluating the
Outcome
Although a decision may be reached and a course of action
implemented, the decision-making process is not complete.
It is important to think ahead and determine how the decision
could affect other phases of flight. As the flight progresses, the
pilot must continue to evaluate the outcome of the decision
to ensure that it is producing the desired result.
Improper Decision-Making Outcomes
Pilots sometimes get in trouble not because of deficient basic
skills or system knowledge, but rather because of faulty
decision-making skills. Although aeronautical decisions
may appear to be simple or routine, each individual decision
in aviation often defines the options available for the next
decision the pilot must make and the options, good or
bad, they provide. Therefore, a poor decision early on in
a flight can compromise the safety of the flight at a later
time necessitating decisions that must be more accurate and
decisive. Conversely, good decision-making early on in an
emergency provide greater latitude for options later on.
FAA Advisory Circular (AC) 60-22, defines ADM as a
systematic approach to the mental process of evaluating a
given set of circumstances and determining the best course of
action. ADM thus builds upon the foundation of conventional
decision-making, but enhances the process to decrease
the probability of pilot error. Specifically, ADM provides
a structure to help the pilot use all resources to develop
comprehensive situational awareness.

Models for Practicing ADM
Two models for practicing ADM are presented below.
Perceive, Process, Perform
The Perceive–Process–Perform (3P) model for ADM offers
a simple, practical, and systematic approach that can be
used during all phases of flight. [Figure 1-12] To use it,
the pilot will:
•

Perceive the given set of circumstances for a flight;

•

Process by evaluating their impact on flight safety;
and

•

Perform by implementing the best course of action.

loss), and probability (the likelihood that a hazard will cause
a loss). If the hazard is low ceilings, for example, the level
of risk depends on a number of other factors, such as pilot
training and experience, aircraft equipment and fuel capacity,
and others.
In the third step, the goal is to perform by taking action to
eliminate hazards or mitigate risk, and then continuously
evaluate the outcome of this action. With the example of low
ceilings at destination, for instance, the pilot can perform
good ADM by selecting a suitable alternate, knowing where
to find good weather, and carrying sufficient fuel to reach
it. This course of action would mitigate the risk. The pilot
also has the option to eliminate it entirely by waiting for
better weather.
Once the pilot has completed the 3P decision process and
selected a course of action, the process begins anew because
now the set of circumstances brought about by the course of
action requires analysis. The decision-making process is a
continuous loop of perceiving, processing and performing.

Figure 1-12. The 3P Model for Aeronautical Decision-Making.

In the first step, the goal is to develop situational awareness
by perceiving hazards, which are present events, objects, or
circumstances that could contribute to an undesired future
event. In this step, the pilot will systematically identify and
list hazards associated with all aspects of the flight: pilot,
aircraft, environment, and external pressures. It is important
to consider how individual hazards might combine. Consider,
for example, the hazard that arises when a new instrument
pilot with no experience in actual instrument conditions wants
to make a cross-country flight to an airport with low ceilings
in order to attend an important business meeting.
In the second step, the goal is to process this information
to determine whether the identified hazards constitute risk,
which is defined as the future impact of a hazard that is not
controlled or eliminated. The degree of risk posed by a given
hazard can be measured in terms of exposure (number of
people or resources affected), severity (extent of possible

The DECIDE Model
Another structured approach to ADM is the DECIDE model,
which is a six-step process intended to provide a logical
way of approaching decision-making. As in the 3P model,
the elements of the DECIDE model represent a continuous
loop process to assist a pilot in the decision-making
required when faced with a situational change that requires
judgment. [Figure 1-13C] The model is primarily focused
on the intellectual component, but can have an impact on
the motivational component of judgment as well. If a pilot
continually uses the DECIDE Model in all decision-making,
it becomes natural and results in better decisions being made
under all types of situations. The steps in this approach are
listed in Figure 1-13C.
In conventional decision-making, the need for a decision is
triggered by recognition that something has changed or an
expected change did not occur. Recognition of the change,
or lack of change, is a vital step in any decision making
process. Not noticing change in a situation can lead directly
to a mishap. [Figure 1-13A] The change indicates that an
appropriate response or action is necessary in order to modify
the situation (or, at least, one of the elements that comprise it)
and bring about a desired new situation. Therefore, situational
awareness is the key to successful and safe decision making.
At this point in the process, the pilot is faced with a need to
evaluate the entire range of possible responses to the detected
change and to determine the best course of action.
Figure 1-13B illustrates how the ADM process expands
conventional decision-making, shows the interactions of the

1-17

Figure 1-13. Decision-Making.

ADM steps, and how these steps can produce a safe outcome.
Starting with the recognition of change, and following with an
assessment of alternatives, a decision to act or not act is made,
and the results are monitored. Pilots can use ADM to enhance
their conventional decision-making process because it:
1.

Increases their awareness of the importance of attitude
in decision-making;

2.

Teaches the ability to search for and establish relevance
of information; and

3.

Increases their motivation to choose and execute actions
that ensure safety in the situational timeframe.

1-18

Hazardous Attitudes and Antidotes
Hazardous attitudes, which contribute to poor pilot judgment,
can be effectively counteracted by redirecting that hazardous
attitude so that correct action can be taken. Recognition of
hazardous thoughts is the first step toward neutralizing them.
After recognizing a thought as hazardous, the pilot should
label it as hazardous, then state the corresponding antidote.
Antidotes should be memorized for each of the hazardous
attitudes so they automatically come to mind when needed.
Each hazardous attitude along with its appropriate antidote
is shown in Figure 1-14.

3.

Invulnerability (“It won’t happen to me!”). Many
pilots feel that accidents happen to others, but never
to them. They know accidents can happen, and they
know that anyone can be affected. They never really
feel or believe that they will be personally involved.
Pilots who think this way are more likely to take
chances and increase risk.

4.

Macho (“I can do it!”). Pilots who are always trying to
prove that they are better than anyone else are thinking,
“I can do it—I’ll show them.” Pilots with this type of
attitude will try to prove themselves by taking risks in
order to impress others. This pattern is characteristic
in both men and women.

5.

Resignation (“What’s the use?”). These pilots do not
see themselves as being able to make a great deal of
difference in what happens to them. When things go
well, these pilots are apt to think it is due to good luck.
When things go badly, they may feel that someone is
out to get them, or attribute it to bad luck. The pilot
will leave the action to others, for better or worse.
Sometimes, they will even go along with unreasonable
requests just to be a “nice guy.”

Figure 1-14. The Five Antidotes to Hazardous Attitudes.

Research has identified five hazardous attitudes that can affect
a pilot’s judgment, as well as antidotes for each of these five
attitudes. ADM addresses the following:
1.

Anti-authority (“Don’t tell me!”). This attitude is
found in pilots who do not like anyone telling them
what to do. They may be resentful of having someone
tell them what to do or may regard rules, regulations,
and procedures as silly or unnecessary. However, there
is always the prerogative to question authority if it is
perceived to be in error.

2.

Impulsivity (“Do something quickly!”). This attitude
is found in pilots who frequently feel the need to do
something—anything—immediately. They do not
stop to think about what they are about to do, they do
not select the best course of action, and they do the
first thing that comes to mind.

1-19

1-20

Chapter 2

Aerodynamic
Factors
Introduction
Several factors affect aircraft performance including the
atmosphere, aerodynamics, and aircraft icing. Pilots need an
understanding of these factors for a sound basis for prediction
of aircraft response to control inputs, especially with regard
to instrument approaches, while holding, and when operating
at reduced airspeed in instrument meteorological conditions
(IMC). Although these factors are important to the pilot flying
visual flight rules (VFR), they must be even more thoroughly
understood by the pilot operating under instrument flight
rules (IFR). Instrument pilots rely strictly on instrument
indications to precisely control the aircraft; therefore, they
must have a solid understanding of basic aerodynamic
principles in order to make accurate judgments regarding
aircraft control inputs.

2-1

Figure 2-1. The Airfoil.

The Wing
To understand aerodynamic forces, a pilot needs to
understand basic terminology associated with airfoils.
Figure 2-1 illustrates a typical airfoil.
The chord line is the straight line intersecting the leading
and trailing edges of the airfoil, and the term chord refers
to the chord line longitudinal length (length as viewed from
the side).
The mean camber is a line located halfway between the
upper and lower surfaces. Viewing the wing edgewise, the
mean camber connects with the chord line at each end. The
mean camber is important because it assists in determining
aerodynamic qualities of an airfoil. The measurement of
the maximum camber; inclusive of both the displacement
of the mean camber line and its linear measurement from
the end of the chord line, provide properties useful in
evaluating airfoils.

Flight path is the course or track along which the aircraft is
flying or is intended to be flown.
The Four Forces
The four basic forces [Figure 2-3] acting upon an aircraft in
flight are lift, weight, thrust, and drag.

Lift
Lift is a component of the total aerodynamic force on an
airfoil and acts perpendicular to the relative wind. Relative
wind is the direction of the airflow with respect to an airfoil.
This force acts straight up from the average (called mean)
center of pressure (CP), which is called the center of lift. It
should be noted that it is a point along the chord line of an
airfoil through which all aerodynamic forces are considered
to act. The magnitude of lift varies proportionately with
speed, air density, shape and size of the airfoil, and angle
of attack. During straight-and-level flight, lift and weight
are equal.

Review of Basic Aerodynamics
The instrument pilot must understand the relationship
and differences between several factors that affect the
performance of an aircraft in flight. Also, it is crucial to
understand how the aircraft reacts to various control and
power changes, because the environment in which instrument
pilots fly has inherent hazards not found in visual flying. The
basis for this understanding is found in the four forces acting
on an aircraft and Newton’s Three Laws of Motion.
Relative Wind is the direction of the airflow with respect to
an airfoil.
Angle of Attack is the acute angle measured between the
relative wind, or flight path and the chord of the airfoil.
[Figure 2-2]

2-2

Figure 2-2. Angle of Attack and Relative Wind.

Figure 2-3. The Four Forces and Three Axes of Rotation.

Weight
Weight is the force exerted by an aircraft from the pull of
gravity. It acts on an aircraft through its center of gravity
(CG) and is straight down. This should not be confused
with the center of lift, which can be significantly different
from the CG. As an aircraft is descending, weight is greater
than lift.

Thrust
Thrust is a force that drives an aircraft through the air and can
be measured in thrust and/or horsepower. It is a component
that is parallel to the center of thrust and overcomes drag
providing the aircraft with its forward speed component.

Drag
Drag is the net aerodynamic force parallel to the relative
wind and is generally a sum of two components: induced
drag and parasite drag.
Induced drag
Induced drag is caused from the creation of lift and increases
with airspeed. Therefore, if the wing is not producing lift,
induced drag is zero. Conversely, induced drag increases
with airspeed.
Parasite drag
Parasite drag is all drag not caused from the production of
lift. Parasite drag is created by displacement of air by the
aircraft, turbulence generated by the airfoil, and the hindrance
of airflow as it passes over the surface of the aircraft or

components. All of these forces create drag not from the
production of lift but the movement of an object through an
air mass. Parasite drag increases with speed and includes skin
friction drag, interference drag, and form drag.
• Skin Friction Drag
Covering the entire “wetted” surface of the aircraft is a thin
layer of air called a boundary layer. The air molecules on the
surface have zero velocity in relation to the surface; however,
the layer just above moves over the stagnant molecules
below because it is pulled along by a third layer close to
the free stream of air. The velocities of the layers increase
as the distance from the surface increases until free stream
velocity is reached, but all are affected by the free stream.
The distance (total) between the skin surface and where free
stream velocity is reached is called the boundary layer. At
subsonic levels the cumulative layers are about the thickness
of a playing card, yet their motion sliding over one another
creates a drag force. This force retards motion due to the
viscosity of the air and is called skin friction drag. Because
skin friction drag is related to a large surface area its affect
on smaller aircraft is small versus large transport aircraft
where skin friction drag may be considerable.
• Interference Drag
Interference drag is generated by the collision of airstreams
creating eddy currents, turbulence, or restrictions to smooth
flow. For instance, the airflow around a fuselage and around
the wing meet at some point, usually near the wing’s root.
These airflows interfere with each other causing a greater

2-3

drag than the individual values. This is often the case when
external items are placed on an aircraft. That is, the drag of
each item individually, added to that of the aircraft, are less
than that of the two items when allowed to interfere with
one another.
• Form Drag
Form drag is the drag created because of the shape of a
component or the aircraft. If one were to place a circular
disk in an air stream, the pressure on both the top and bottom
would be equal. However, the airflow starts to break down
as the air flows around the back of the disk. This creates
turbulence and hence a lower pressure results. Because the
total pressure is affected by this reduced pressure, it creates
a drag. Newer aircraft are generally made with consideration
to this by fairing parts along the fuselage (teardrop) so that
turbulence and form drag is reduced.
Total lift must overcome the total weight of the aircraft, which
is comprised of the actual weight and the tail-down force used
to control the aircraft’s pitch attitude. Thrust must overcome
total drag in order to provide forward speed with which to
produce lift. Understanding how the aircraft’s relationship
between these elements and the environment provide proper
interpretation of the aircraft’s instruments.
Newton’s First Law, the Law of Inertia
Newton’s First Law of Motion is the Law of Inertia. It states
that a body at rest will remain at rest, and a body in motion
will remain in motion, at the same speed and in the same
direction until affected by an outside force. The force with
which a body offers resistance to change is called the force of
inertia. Two outside forces are always present on an aircraft
in flight: gravity and drag. The pilot uses pitch and thrust
controls to counter or change these forces to maintain the
desired flight path. If a pilot reduces power while in straightand-level flight, the aircraft will slow due to drag. However,
as the aircraft slows there is a reduction of lift, which causes
the aircraft to begin a descent due to gravity. [Figure 2-4]

Figure 2-4. Newton’s First Law of Motion: the Law of Inertia.

2-4

Newton’s Second Law, the Law of Momentum
Newton’s Second Law of Motion is the Law of Momentum,
which states that a body will accelerate in the same direction
as the force acting upon that body, and the acceleration
will be directly proportional to the net force and inversely
proportional to the mass of the body. Acceleration refers
either to an increase or decrease in velocity, although
deceleration is commonly used to indicate a decrease. This
law governs the aircraft’s ability to change flight path and
speed, which are controlled by attitude (both pitch and bank)
and thrust inputs. Speeding up, slowing down, entering
climbs or descents, and turning are examples of accelerations
that the pilot controls in everyday flight. [Figure 2-5]
Newton’s Third Law, the Law of Reaction
Newton’s Third Law of Motion is the Law of Reaction,
which states that for every action there is an equal and
opposite reaction. As shown in Figure 2-6, the action of
the jet engine’s thrust or the pull of the propeller lead to the
reaction of the aircraft’s forward motion. This law is also
responsible for a portion of the lift that is produced by a wing,
from the downward deflection of the airflow around it. This
downward force of the relative wind results in an equal but
opposite (upward) lifting force created by the airflow over
the wing. [Figure 2-6]

Atmosphere
The atmosphere is the envelope of air which surrounds the
Earth. A given volume of dry air contains about 78 percent
nitrogen, 21 percent oxygen, and about 1 percent other gases
such as argon, carbon dioxide, and others to a lesser degree.
Although seemingly light, air does have weight and a one
square inch column of the atmosphere at sea level weighs
approximately 14.7 pounds. About one-half of the air by
weight is within the first 18,000 feet. The remainder of the air
is spread over a vertical distance in excess of 1,000 miles.
Air density is a result of the relationship between temperature
and pressure. Air density is inversely related to temperature
and directly related to pressure. For a constant pressure to be

Figure 2-5. Newton’s Second Law of Motion: the Law of

Momentum.

maintained as temperature increases, density must decrease,
and vice versa. For a constant temperature to be maintained
as pressure increases, density must increase, and vice versa.
These relationships provide a basis for understanding
instrument indications and aircraft performance.
Layers of the Atmosphere
There are several layers to the atmosphere with the
troposphere being closest to the Earth’s surface extending to
about 60,000 feet. Following is the stratosphere, mesosphere,
ionosphere, thermosphere, and finally the exosphere. The
tropopause is the thin layer between the troposphere and
the stratosphere. It varies in both thickness and altitude but
is generally defined where the standard lapse (generally
accepted at 2° C per 1,000 feet) decreases significantly
(usually down to 1° C or less).
International Standard Atmosphere (ISA)
The International Civil Aviation Organization (ICAO)
established the ICAO Standard Atmosphere as a way
of creating an international standard for reference and
performance computations. Instrument indications and
aircraft performance specifications are derived using this
standard as a reference. Because the standard atmosphere is
a derived set of conditions that rarely exist in reality, pilots
need to understand how deviations from the standard affect
both instrument indications and aircraft performance.
In the standard atmosphere, sea level pressure is 29.92" inches
of mercury (Hg) and the temperature is 15° C (59° F). The
standard lapse rate for pressure is approximately a 1" Hg
decrease per 1,000 feet increase in altitude. The standard lapse
rate for temperature is a 2° C (3.6° F) decrease per 1,000 feet
increase, up to the top of the stratosphere. Since all aircraft
performance is compared and evaluated in the environment

Figure 2-6. Newton’s Third Law of Motion: the Law of Reaction.

of the standard atmosphere, all aircraft performance
instrumentation is calibrated for the standard atmosphere.
Because the actual operating conditions rarely, if ever, fit the
standard atmosphere, certain corrections must apply to the
instrumentation and aircraft performance. For instance, at
10,000 ISA predicts that the air pressure should be 19.92" Hg
(29.92" - 10" Hg = 19.92") and the outside temperature at -5°C
(15° C - 20° C). If the temperature or the pressure is different
than the International Standard Atmosphere (ISA) prediction
an adjustment must be made to performance predictions and
various instrument indications.

Pressure Altitude
There are two measurements of the atmosphere that affect
performance and instrument calibrations: pressure altitude
and density altitude. Pressure altitude is the height above the
standard datum pressure (SDP) (29.92" Hg, sea level under
ISA) and is used for standardizing altitudes for flight levels
(FL). Generally, flight levels are at or above 18,000 feet
(FL 180), providing the pressure is at or above 29.92"Hg.
For calculations involving aircraft performance when the
altimeter is set for 29.92" Hg, the altitude indicated is the
pressure altitude.

Density Altitude
Density altitude is pressure altitude corrected for nonstandard
temperatures, and is used for determining aerodynamic
performance in the nonstandard atmosphere. Density altitude
increases as the density decreases. Since density varies
directly with pressure, and inversely with temperature, a
wide range of temperatures may exist with a given pressure
altitude, which allows the density to vary. However, a
known density occurs for any one temperature and pressure
altitude combination. The density of the air has a significant
effect on aircraft and engine performance. Regardless of the

2-5

actual altitude above sea level an aircraft is operating at, its
performance will be as though it were operating at an altitude
equal to the existing density altitude.
If a chart is not available the density altitude can be estimated
by adding 120 feet for every degree Celsius above the ISA. For
example, at 3,000 feet pressure altitude (PA), the ISA prediction
is 9° C (15° C - [lapse rate of 2° C per 1,000 feet x 3 = 6° C]).
However, if the actual temperature is 20° C (11° C more than
that predicted by ISA) then the difference of 11° C is multiplied
by 120 feet equaling 1,320. Adding this figure to the original
3,000 feet provides a density altitude of 4,320 feet (3,000 feet
+ 1,320 feet).

Lift
Lift always acts in a direction perpendicular to the relative
wind and to the lateral axis of the aircraft. The fact that lift is
referenced to the wing, not to the Earth’s surface, is the source
of many errors in learning flight control. Lift is not always
“up.” Its direction relative to the Earth’s surface changes as
the pilot maneuvers the aircraft.
The magnitude of the force of lift is directly proportional to
the density of the air, the area of the wings, and the airspeed. It
also depends upon the type of wing and the angle of attack. Lift
increases with an increase in angle of attack up to the stalling
angle, at which point it decreases with any further increase
in angle of attack. In conventional aircraft, lift is therefore
controlled by varying the angle of attack and speed.
Pitch/Power Relationship
An examination of Figure 2-7 illustrates the relationship
between pitch and power while controlling flight path and
airspeed. In order to maintain a constant lift, as airspeed is

reduced, pitch must be increased. The pilot controls pitch
through the elevators, which control the angle of attack.
When back pressure is applied on the elevator control, the tail
lowers and the nose rises, thus increasing the wing’s angle of
attack and lift. Under most conditions the elevator is placing
downward pressure on the tail. This pressure requires energy
that is taken from aircraft performance (speed). Therefore,
when the CG is closer to the aft portion of the aircraft the
elevator downward forces are less. This results in less energy
used for downward forces, in turn resulting in more energy
applied to aircraft performance.
Thrust is controlled by using the throttle to establish or
maintain desired airspeeds. The most precise method
of controlling flight path is to use pitch control while
simultaneously using power (thrust) to control airspeed. In
order to maintain a constant lift, a change in pitch requires a
change in power, and vice versa.
If the pilot wants the aircraft to accelerate while maintaining
altitude, thrust must be increased to overcome drag. As
the aircraft speeds up, lift is increased. To prevent gaining
altitude, the pitch angle must be lowered to reduce the
angle of attack and maintain altitude. To decelerate while
maintaining altitude, thrust must be decreased to less than the
value of drag. As the aircraft slows down, lift is reduced. To
prevent losing altitude, the pitch angle must be increased in
order to increase the angle of attack and maintain altitude.

Drag Curves
When induced drag and parasite drag are plotted on a graph,
the total drag on the aircraft appears in the form of a “drag
curve.” Graph A of Figure 2-8 shows a curve based on thrust
versus drag, which is primarily used for jet aircraft. Graph B
of Figure 2-8 is based on power versus drag, and it is used
for propeller-driven aircraft. This chapter focuses on power
versus drag charts for propeller-driven aircraft.
Understanding the drag curve can provide valuable insight
into the various performance parameters and limitations of
the aircraft. Because power must equal drag to maintain a
steady airspeed, the curve can be either a drag curve or a
power required curve. The power required curve represents
the amount of power needed to overcome drag in order to
maintain a steady speed in level flight.

Figure 2-7. Relationship of Lift to Angle of Attack.

2-6

The propellers used on most reciprocating engines achieve
peak propeller efficiencies in the range of 80 to 88 percent.
As airspeed increases, the propeller efficiency increases until
it reaches its maximum. Any airspeed above this maximum
point causes a reduction in propeller efficiency. An engine
that produces 160 horsepower will have only about 80
percent of that power converted into available horsepower,

Figure 2-8. Thrust and Power Required Curves.

approximately 128 horsepower. The remainder is lost energy.
This is the reason the thrust and power available curves
change with speed.
Regions of Command
The drag curve also illustrates the two regions of command:
the region of normal command, and the region of reversed
command. The term “region of command” refers to the
relationship between speed and the power required to
maintain or change that speed. “Command” refers to the input
the pilot must give in terms of power or thrust to maintain a
new speed once reached.
The “region of normal command” occurs where power must
be added to increase speed. This region exists at speeds higher
than the minimum drag point primarily as a result of parasite
drag. The “region of reversed command” occurs where
additional power is needed to maintain a slower airspeed.
This region exists at speeds slower than the minimum drag
point (L/DMAX on the thrust required curve, Figure 2-8) and
is primarily due to induced drag. Figure 2-9 shows how one

power setting can yield two speeds, points 1 and 2. This is
because at point 1 there is high induced drag and low parasite
drag, while at point 2 there is high parasite drag and low
induced drag.

Control Characteristics
Most flying is conducted in the region of normal command:
for example, cruise, climb, and maneuvers. The region of
reversed command may be encountered in the slow-speed
phases of flight during takeoff and landing; however, for
most general aviation aircraft, this region is very small and
is below normal approach speeds.
Flight in the region of normal command is characterized
by a relatively strong tendency of the aircraft to maintain
the trim speed. Flight in the region of reversed command is
characterized by a relatively weak tendency of the aircraft to
maintain the trim speed. In fact, it is likely the aircraft exhibits
no inherent tendency to maintain the trim speed in this area.
For this reason, the pilot must give particular attention to
precise control of airspeed when operating in the slow-speed
phases of the region of reversed command.
Operation in the region of reversed command does not imply
that great control difficulty and dangerous conditions exist.
However, it does amplify errors of basic flying technique—
making proper flying technique and precise control of the
aircraft very important.
Speed Stability

Normal Command

Figure 2-9. Regions of Command.

The characteristics of flight in the region of normal command
are illustrated at point A on the curve in Figure 2-10. If the
aircraft is established in steady, level flight at point A, lift is
equal to weight, and the power available is set equal to the
power required. If the airspeed is increased with no changes
2-7

Trim
The term trim refers to employing adjustable aerodynamic
devices on the aircraft to adjust forces so the pilot does not
have to manually hold pressure on the controls. One means is
to employ trim tabs. A trim tab is a small, adjustable hinged
surface, located on the trailing edge of the elevator, aileron,
or rudder control surfaces. (Some aircraft use adjustable
stabilizers instead of trim tabs for pitch trim.) Trimming is
accomplished by deflecting the tab in the direction opposite
to that in which the primary control surface must be held.
The force of the airflow striking the tab causes the main
control surface to be deflected to a position that corrects the
unbalanced condition of the aircraft.
Figure 2-10. Region of Speed Stability.

to the power setting, a power deficiency exists. The aircraft
has a natural tendency to return to the initial speed to balance
power and drag. If the airspeed is reduced with no changes
to the power setting, an excess of power exists. The aircraft
has a natural tendency to speed up to regain the balance
between power and drag. Keeping the aircraft in proper
trim enhances this natural tendency. The static longitudinal
stability of the aircraft tends to return the aircraft to the
original trimmed condition.
An aircraft flying in steady, level flight at point C is in
equilibrium. [Figure 2-10] If the speed were increased
or decreased slightly, the aircraft would tend to remain at
that speed. This is because the curve is relatively flat and
a slight change in speed does not produce any significant
excess or deficiency in power. It has the characteristic of
neutral stability, i.e., the aircraft’s tendency is to remain at
the new speed.

Because the trim tabs use airflow to function, trim is a
function of speed. Any change in speed results in the need
to re-trim the aircraft. An aircraft properly trimmed in pitch
seeks to return to the original speed before the change. It is
very important for instrument pilots to keep the aircraft in
constant trim. This reduces the pilot’s workload significantly,
allowing attention to other duties without compromising
aircraft control.

Slow-Speed Flight
Anytime an aircraft is flying near the stalling speed or the
region of reversed command, such as in final approach for a
normal landing, the initial part of a go around, or maneuvering
in slow flight, it is operating in what is called slow-speed
flight. If the aircraft weighs 4,000 pounds, the lift produced
by the aircraft must be 4,000 pounds. When lift is less
than 4,000 pounds, the aircraft is no longer able to sustain
level flight, and consequently descends. During intentional
descents, this is an important factor and is used in the total
control of the aircraft.

Reversed Command
The characteristics of flight in the region of reversed command
are illustrated at point B on the curve in Figure 2-10. If the
aircraft is established in steady, level flight at point B, lift is
equal to weight, and the power available is set equal to the
power required. When the airspeed is increased greater than
point B, an excess of power exists. This causes the aircraft
to accelerate to an even higher speed. When the aircraft is
slowed to some airspeed lower than point B, a deficiency
of power exists. The natural tendency of the aircraft is to
continue to slow to an even lower airspeed.
This tendency toward instability happens because the
variation of excess power to either side of point B magnifies
the original change in speed. Although the static longitudinal
stability of the aircraft tries to maintain the original trimmed
condition, this instability is more of an influence because of
the increased induced drag due to the higher angles of attack
in slow-speed flight.
2-8

However, because lift is required during low speed flight
and is characterized by high angles of attack, flaps or other
high lift devices are needed to either change the camber of
the airfoil, or delay the boundary level separation. Plain
and split flaps [Figure 2-11] are most commonly used to
change the camber of an airfoil. It should be noted that with
the application of flaps, the aircraft will stall at a lower
angle of attack. The basic wing stalls at 18° without flaps
but with the application of the flaps extended (to CL-MAX
position) the new angle of attack at which point the aircraft
will stall is 15°. However, the value of lift (flaps extended
to the CL-MAX position) produces more lift than lift at 18°
on the basic wing.
Delaying the boundary layer separation is another way to
increase CL-MAX. Several methods are employed (such as
suction and use of a blowing boundary layer control), but the

most common device used on general aviation light aircraft
is the vortex generator. Small strips of metal placed along
the wing (usually in front of the control surfaces) create
turbulence. The turbulence in turn mixes high energy air from
outside the boundary layer with boundary layer air. The effect
is similar to other boundary layer devices. [Figure 2-12]
Small Airplanes
Most small airplanes maintain a speed well in excess of 1.3
times VSO on an instrument approach. An airplane with a
stall speed of 50 knots (VSO) has a normal approach speed
of 65 knots. However, this same airplane may maintain 90
knots (1.8 VSO) while on the final segment of an instrument
approach. The landing gear will most likely be extended at
the beginning of the descent to the minimum descent altitude,
or upon intercepting the glide slope of the instrument landing
system. The pilot may also select an intermediate flap setting
for this phase of the approach. The airplane at this speed has
good positive speed stability, as represented by point A on
Figure 2-10. Flying in this regime permits the pilot to make
slight pitch changes without changing power settings, and
accept minor speed changes knowing that when the pitch is
returned to the initial setting, the speed returns to the original
setting. This reduces the pilot’s workload.

If allowed to slow several knots, the airplane could enter
the region of reversed command. At this point, the airplane
could develop an unsafe sink rate and continue to lose speed
unless the pilot takes a prompt corrective action. Proper pitch
and power coordination is critical in this region due to speed
instability and the tendency of increased divergence from
the desired speed.
Large Airplanes
Pilots of larger airplanes with higher stall speeds may find the
speed they maintain on the instrument approach is near 1.3
VSO, putting them near point C [Figure 2-10] the entire time
the airplane is on the final approach segment. In this case,
precise speed control is necessary throughout the approach. It
may be necessary to temporarily select excessive, or deficient
thrust in relation to the target thrust setting in order to quickly
correct for airspeed deviations.

Aircraft are usually slowed to a normal landing speed when
on the final approach just prior to landing. When slowed to
65 knots, (1.3 VSO), the airplane will be close to point C.
[Figure 2-10] At this point, precise control of the pitch and
power becomes more crucial for maintaining the correct speed.
Pitch and power coordination is necessary because the speed
stability is relatively neutral since the speed tends to remain
at the new value and not return to the original setting. In
addition to the need for more precise airspeed control, the pilot
normally changes the aircraft’s configuration by extending
landing flaps. This configuration change means the pilot must
be alert to unwanted pitch changes at a low altitude.

Figure 2-11. Various Types of Flaps.

Figure 2-12. Vortex Generators.

2-9

For example, a pilot is on an instrument approach at 1.3
VSO, a speed near L/DMAX, and knows that a certain power
setting maintains that speed. The airplane slows several knots
below the desired speed because of a slight reduction in the
power setting. The pilot increases the power slightly, and the
airplane begins to accelerate, but at a slow rate. Because the
airplane is still in the “flat part” of the drag curve, this slight
increase in power will not cause a rapid return to the desired
speed. The pilot may need to increase the power higher
than normally needed to maintain the new speed, allow the
airplane to accelerate, then reduce the power to the setting
that maintains the desired speed.

Climbs

Turns
Like any moving object, an aircraft requires a sideward force
to make it turn. In a normal turn, this force is supplied by
banking the aircraft in order to exert lift inward, as well as
upward. The force of lift is separated into two components
at right angles to each other. [Figure 2-13] The upward
acting lift together with the opposing weight becomes the
vertical lift component. The horizontally acting lift and its
opposing centrifugal force are the horizontal lift component,
or centripetal force. This horizontal lift component is the
sideward force that causes an aircraft to turn. The equal and
opposite reaction to this sideward force is centrifugal force,
which is merely an apparent force as a result of inertia.

The ability for an aircraft to climb depends upon an excess
power or thrust over what it takes to maintain equilibrium.
Excess power is the available power over and above that
required to maintain horizontal flight at a given speed.
Although the terms power and thrust are sometimes
used interchangeably (erroneously implying they are
synonymous), distinguishing between the two is important
when considering climb performance. Work is the product of
a force moving through a distance and is usually independent
of time. Power implies work rate or units of work per unit of
time, and as such is a function of the speed at which the force
is developed. Thrust, also a function of work, means the force
which imparts a change in the velocity of a mass.
During take off, the aircraft does not stall even though it
may be in a climb near the stall speed. The reason is that
excess power (used to produce thrust) is used during this
flight regime. Therefore, it is important if an engine fails
after take off, to compensate the loss of thrust with pitch
and airspeed.
For a given weight of the aircraft, the angle of climb depends
on the difference between thrust and drag, or the excess
thrust. When the excess thrust is zero, the inclination of the
flight path is zero, and the aircraft is in steady, level flight.
When thrust is greater than drag, the excess thrust allows a
climb angle depending on the amount of excess thrust. When
thrust is less than drag, the deficiency of thrust induces an
angle of descent.
Acceleration in Cruise Flight
Aircraft accelerate in level flight because of an excess of
power over what is required to maintain a steady speed. This
is the same excess power used to climb. Upon reaching the
desired altitude with pitch being lowered to maintain that
altitude, the excess power now accelerates the aircraft to its
cruise speed. However, reducing power too soon after level
off results in a longer period of time to accelerate.

2-10

Figure 2-13. Forces In a Turn.

The relationship between the aircraft’s speed and bank angle
to the rate and radius of turns is important for instrument
pilots to understand. The pilot can use this knowledge to
properly estimate bank angles needed for certain rates of
turn, or to determine how much to lead when intercepting
a course.
Rate of Turn
The rate of turn, normally measured in degrees per second,
is based upon a set bank angle at a set speed. If either one of
these elements changes, the rate of turn changes. If the aircraft
increases its speed without changing the bank angle, the rate
of turn decreases. Likewise, if the speed decreases without
changing the bank angle, the rate of turn increases.
Changing the bank angle without changing speed also causes
the rate of turn to change. Increasing the bank angle without
changing speed increases the rate of turn, while decreasing
the bank angle reduces the rate of turn.

The standard rate of turn, 3° per second, is used as the main
reference for bank angle. Therefore, the pilot must understand
how the angle of bank varies with speed changes, such
as slowing down for holding or an instrument approach.
Figure 2-14 shows the turn relationship with reference to a
constant bank angle or a constant airspeed, and the effects on
rate of turn and radius of turn. A rule of thumb for determining
the standard rate turn is to divide the airspeed by ten and
add 7. An aircraft with an airspeed of 90 knots takes a bank
angle of 16° to maintain a standard rate turn (90 divided by
10 plus 7 equals 16°).
Radius of Turn
The radius of turn varies with changes in either speed or bank.
If the speed is increased without changing the bank angle,
the radius of turn increases, and vice versa. If the speed is
constant, increasing the bank angle reduces the radius of
turn, while decreasing the bank angle increases the radius of
turn. This means that intercepting a course at a higher speed
requires more distance, and therefore, requires a longer lead.
If the speed is slowed considerably in preparation for holding
or an approach, a shorter lead is needed than that required
for cruise flight.
Coordination of Rudder and Aileron Controls
Any time ailerons are used, adverse yaw is produced. Adverse
yaw is caused when the ailerons are deflected as a roll motion
(as in turn) is initiated. In a right turn, the right aileron is
deflected downward while the left is deflected upward. Lift
is increased on the left side and reduced on the right, resulting
in a bank to the right. However, as a result of producing lift
on the left, induced drag is also increased on the left side.
The drag causes the left wing to slow down, in turn causing
the nose of the aircraft to initially move (left) in the direction
opposite of the turn. Correcting for this yaw with rudder, when
entering and exiting turns, is necessary for precise control of
the airplane when flying on instruments. The pilot can tell if
the turn is coordinated by checking the ball in the turn-andslip indicator or the turn coordinator. [Figure 2-15]

As the aircraft banks to enter a turn, a portion of the wing’s
vertical lift becomes the horizontal component; therefore,
without an increase in back pressure, the aircraft loses altitude
during the turn. The loss of vertical lift can be offset by
increasing the pitch in one-half bar width increments. Trim
may be used to relieve the control pressures; however, if used,
it has to be removed once the turn is complete.
In a slipping turn, the aircraft is not turning at the rate
appropriate to the bank being used, and the aircraft falls to
the inside of the turn. The aircraft is banked too much for the
rate of turn, so the horizontal lift component is greater than
the centrifugal force. A skidding turn results from excess of
centrifugal force over the horizontal lift component, pulling
the aircraft toward the outside of the turn. The rate of turn
is too great for the angle of bank, so the horizontal lift
component is less than the centrifugal force.
The ball instrument indicates the quality of the turn, and
should be centered when the wings are banked. If the ball
is off of center on the side toward the turn, the aircraft is
slipping and rudder pressure should be added on that side to
increase the rate of turn or the bank angle should be reduced.
If the ball is off of center on the side away from the turn,
the aircraft is skidding and rudder pressure toward the turn
should be relaxed or the bank angle should be increased.
If the aircraft is properly rigged, the ball should be in the
center when the wings are level; use rudder and/or aileron
trim if available.
The increase in induced drag (caused by the increase in angle
of attack necessary to maintain altitude) results in a minor
loss of airspeed if the power setting is not changed.

Load Factor
Any force applied to an aircraft to deflect its flight from a
straight line produces a stress on its structure; the amount of
this force is termed load factor. A load factor is the ratio of

Figure 2-14. Turns.

2-11

Figure 2-15. Adverse Yaw.

the aerodynamic force on the aircraft to the gross weight of
the aircraft (e.g., lift/weight). For example, a load factor of 3
means the total load on an aircraft’s structure is three times
its gross weight. When designing an aircraft, it is necessary
to determine the highest load factors that can be expected in
normal operation under various operational situations. These
“highest” load factors are called “limit load factors.”
Aircraft are placed in various categories, i.e., normal, utility,
and acrobatic, depending upon the load factors they are
designed to take. For reasons of safety, the aircraft must be
designed to withstand certain maximum load factors without
any structural damage.
The specified load may be expected in terms of aerodynamic
forces, as in turns. In level flight in undisturbed air, the
wings are supporting not only the weight of the aircraft, but
centrifugal force as well. As the bank steepens, the horizontal
lift component increases, centrifugal force increases, and the
2-12

load factor increases. If the load factor becomes so great that
an increase in angle of attack cannot provide enough lift to
support the load, the wing stalls. Since the stalling speed
increases directly with the square root of the load factor, the
pilot should be aware of the flight conditions during which the
load factor can become critical. Steep turns at slow airspeed,
structural ice accumulation, and vertical gusts in turbulent
air can increase the load factor to a critical level.

Icing
One of the greatest hazards to flight is aircraft icing. The
instrument pilot must be aware of the conditions conducive to
aircraft icing. These conditions include the types of icing, the
effects of icing on aircraft control and performance, effects
of icing on aircraft systems, and the use and limitations of
aircraft deice and anti-ice equipment. Coping with the hazards
of icing begins with preflight planning to determine where
icing may occur during a flight and ensuring the aircraft is

free of ice and frost prior to takeoff. This attention to detail
extends to managing deice and anti-ice systems properly
during the flight, because weather conditions may change
rapidly, and the pilot must be able to recognize when a change
of flight plan is required.

Types of Icing
Structural Icing
Structural icing refers to the accumulation of ice on the
exterior of the aircraft. Ice forms on aircraft structures and
surfaces when super-cooled droplets impinge on them and
freeze. Small and/or narrow objects are the best collectors
of droplets and ice up most rapidly. This is why a small
protuberance within sight of the pilot can be used as an “ice
evidence probe.” It is generally one of the first parts of the
airplane on which an appreciable amount of ice forms. An
aircraft’s tailplane is a better collector than its wings, because
the tailplane presents a thinner surface to the airstream.
Induction Icing
Ice in the induction system can reduce the amount of air
available for combustion. The most common example of
reciprocating engine induction icing is carburetor ice. Most
pilots are familiar with this phenomenon, which occurs when
moist air passes through a carburetor venturi and is cooled. As
a result of this process, ice may form on the venturi walls and
throttle plate, restricting airflow to the engine. This may occur
at temperatures between 20° F (-7° C) and 70° F (21° C). The
problem is remedied by applying carburetor heat, which uses
the engine’s own exhaust as a heat source to melt the ice or
prevent its formation. On the other hand, fuel-injected aircraft
engines usually are less vulnerable to icing but still can be
affected if the engine’s air source becomes blocked with ice.
Manufacturers provide an alternate air source that may be
selected in case the normal system malfunctions.
In turbojet aircraft, air that is drawn into the engines creates
an area of reduced pressure at the inlet, which lowers the
temperature below that of the surrounding air. In marginal
icing conditions (i.e., conditions where icing is possible),
this reduction in temperature may be sufficient to cause ice
to form on the engine inlet, disrupting the airflow into the
engine. Another hazard occurs when ice breaks off and is
ingested into a running engine, which can cause damage to
fan blades, engine compressor stall, or combustor flameout.
When anti-icing systems are used, runback water also can
refreeze on unprotected surfaces of the inlet and, if excessive,
reduce airflow into the engine or distort the airflow pattern
in such a manner as to cause compressor or fan blades to
vibrate, possibly damaging the engine. Another problem
in turbine engines is the icing of engine probes used to set
power levels (for example, engine inlet temperature or engine
pressure ratio (EPR) probes), which can lead to erroneous

readings of engine instrumentation operational difficulties
or total power loss.
The type of ice that forms can be classified as clear, rime, or
mixed, based on the structure and appearance of the ice. The
type of ice that forms varies depending on the atmospheric
and flight conditions in which it forms. Significant structural
icing on an aircraft can cause serious aircraft control and
performance problems.
Clear Ice
A glossy, transparent ice formed by the relatively slow
freezing of super cooled water is referred to as clear ice.
[Figure 2-16] The terms “clear” and “glaze” have been used
for essentially the same type of ice accretion. This type of
ice is denser, harder, and sometimes more transparent than
rime ice. With larger accretions, clear ice may form “horns.”
[Figure 2-17] Temperatures close to the freezing point, large
amounts of liquid water, high aircraft velocities, and large
droplets are conducive to the formation of clear ice.

Figure 2-16. Clear Ice.

Rime Ice
A rough, milky, opaque ice formed by the instantaneous or
very rapid freezing of super cooled droplets as they strike
the aircraft is known as rime ice. [Figure 2-18] The rapid
freezing results in the formation of air pockets in the ice,
giving it an opaque appearance and making it porous and
brittle. For larger accretions, rime ice may form a streamlined
extension of the wing. Low temperatures, lesser amounts of
liquid water, low velocities, and small droplets are conducive
to the formation of rime ice.

2-13

Figure 2-17. Clear Ice Buildup.

Figure 2-18. Rime Ice.

Mixed Ice
Mixed ice is a combination of clear and rime ice formed on
the same surface. It is the shape and roughness of the ice that
is most important from an aerodynamic point of view.

on lift in cruise now, causes stall to occur at a lower angle of
attack and higher speed. Even a thin layer of ice at the leading
edge of a wing, especially if it is rough, can have a significant
effect in increasing stall speed. For large ice shapes, especially
those with horns, the lift may also be reduced at a lower angle
of attack. The accumulation of ice affects the coefficient
of drag of the airfoil. [Figure 2-19] Note that the effect is
significant even at very small angles of attack.

General Effects of Icing on Airfoils
The most hazardous aspect of structural icing is its aerodynamic
effects. [Figure 2-19] Ice alters the shape of an airfoil, reducing
the maximum coefficient of lift and angle of attack at which
the aircraft stalls. Note that at very low angles of attack, there
may be little or no effect of the ice on the coefficient of lift.
Therefore, when cruising at a low angle of attack, ice on the
wing may have little effect on the lift. However, note that the
ice significantly reduces the CL-MAX, and the angle of attack
at which it occurs (the stall angle) is much lower. Thus, when
slowing down and increasing the angle of attack for approach,
the pilot may find that ice on the wing, which had little effect

Figure 2-19. Aerodynamic Effects of Icing.

2-14

A significant reduction in CL-MAX and a reduction in the angle
of attack where stall occurs can result from a relatively small
ice accretion. A reduction of CL-MAX by 30 percent is not
unusual, and a large horn ice accretion can result in reductions
of 40 percent to 50 percent. Drag tends to increase steadily
as ice accretes. An airfoil drag increase of 100 percent is not
unusual, and for large horn ice accretions, the increase can
be 200 percent or even higher.

Ice on an airfoil can have other effects not depicted in these
curves. Even before airfoil stall, there can be changes in the
pressure over the airfoil that may affect a control surface at
the trailing edge. Furthermore, on takeoff, approach, and
landing, the wings of many aircraft are multi-element airfoils
with three or more elements. Ice may affect the different
elements in different ways. Ice may also affect the way in
which the air streams interact over the elements.

Most aircraft have a nose-down pitching moment from the
wings because the CG is ahead of the CP. It is the role of the
tailplane to counteract this moment by providing a downward
force. [Figure 2-21] The result of this configuration is
that actions which move the wing away from stall, such
as deployment of flaps or increasing speed, may increase
the negative angle of attack of the tail. With ice on the
tailplane, it may stall after full or partial deployment of flaps.
[Figure 2-22]

Ice can partially block or limit control surfaces, which
limits or makes control movements ineffective. Also, if the
extra weight caused by ice accumulation is too great, the
aircraft may not be able to become airborne and, if in flight,
the aircraft may not be able to maintain altitude. Therefore
any accumulation of ice or frost should be removed before
attempting flight.
Another hazard of structural icing is the possible uncommanded
and uncontrolled roll phenomenon, referred to as roll upset,
associated with severe in-flight icing. Pilots flying aircraft
certificated for flight in known icing conditions should be
aware that severe icing is a condition outside of the aircraft’s
certification icing envelope. Roll upset may be caused by
airflow separation (aerodynamic stall), which induces selfdeflection of the ailerons and loss of or degraded roll handling
characteristics [Figure 2-20]. These phenomena can result
from severe icing conditions without the usual symptoms of
ice accumulation or a perceived aerodynamic stall.

Figure 2-21. Downward Force on the Tailplane.

Figure 2-22. Ice on the Tailplane.

Since the tailplane is ordinarily thinner than the wing, it is a
more efficient collector of ice. On most aircraft the tailplane
is not visible to the pilot, who therefore cannot observe how
well it has been cleared of ice by any deicing system. Thus, it
is important that the pilot be alert to the possibility of tailplane
stall, particularly on approach and landing.

Piper PA-34-200T (Des Moines, Iowa)

Figure 2-20. Effect of Ice and Frost on Lift.

The pilot of this flight, which took place on January 9,
1996, said that upon crossing the runway threshold and
lowering the flaps 25°, “the airplane pitched down.” The
pilot “immediately released the flaps and added power, but
the airplane was basically uncontrollable at this point.” The
pilot reduced power and lowered the flaps before striking
the runway on its centerline and sliding 1,000 feet before
2-15

coming to a stop. The accident resulted in serious injury to
the pilot, the sole occupant.
Examination of the wreckage revealed heavy impact
damage to the airplane’s forward fuselage, engines, and
wings. Approximately one-half inch of rime ice was
observed adhering to the leading edges of the left and right
horizontal stabilizers and along the leading edge of the
vertical stabilizer.
The National Transportation Safety Board (NTSB)
determined the probable cause of the accident was the pilot’s
failure to use the airplane’s deicing system, which resulted
in an accumulation of empennage ice and a tailplane stall.
Factors relating to this accident were the icing conditions and
the pilot’s intentional flight into those known conditions.
Tailplane Stall Symptoms
Any of the following symptoms, occurring singly or in
combination, may be a warning of tailplane icing:
•

Elevator control pulsing, oscillations, or vibrations;

•

Abnormal nose-down trim change;

•

Any other unusual or abnormal pitch anomalies
(possibly resulting in pilot induced oscillations);

•

Reduction or loss of elevator effectiveness;

•

Sudden change in elevator force (control would move
nose-down if unrestrained); and

•

Sudden uncommanded nose-down pitch.

If any of the above symptoms occur, the pilot should:
•

Immediately retract the flaps to the previous setting
and apply appropriate nose-up elevator pressure;

•

Increase airspeed appropriately for the reduced flap
extension setting;

•

Apply sufficient power for aircraft configuration
and conditions. (High engine power settings may
adversely impact response to tailplane stall conditions
at high airspeed in some aircraft designs. Observe the
manufacturer’s recommendations regarding power
settings.);

•

Make nose-down pitch changes slowly, even in
gusting conditions, if circumstances allow; and

•

If a pneumatic deicing system is used, operate the
system several times in an attempt to clear the tailplane
of ice.

Once a tailplane stall is encountered, the stall condition
tends to worsen with increased airspeed and possibly may
worsen with increased power settings at the same flap

2-16

setting. Airspeed, at any flap setting, in excess of the airplane
manufacturer’s recommendations, accompanied by uncleared
ice contaminating the tailplane, may result in a tailplane stall
and uncommanded pitch down from which recovery may not
be possible. A tailplane stall may occur at speeds less than
the maximum flap extended speed (VFE).
Propeller Icing
Ice buildup on propeller blades reduces thrust for the same
aerodynamic reasons that wings tend to lose lift and increase
drag when ice accumulates on them. The greatest quantity
of ice normally collects on the spinner and inner radius of
the propeller. Propeller areas on which ice may accumulate
and be ingested into the engine normally are anti-iced rather
than deiced to reduce the probability of ice being shed into
the engine.
Effects of Icing on Critical Aircraft Systems
In addition to the hazards of structural and induction icing,
the pilot must be aware of other aircraft systems susceptible
to icing. The effects of icing do not produce the performance
loss of structural icing or the power loss of induction icing
but can present serious problems to the instrument pilot.
Examples of such systems are flight instruments, stall
warning systems, and windshields.

Flight Instruments
Various aircraft instruments including the airspeed indicator,
altimeter, and rate-of-climb indicator utilize pressures
sensed by pitot tubes and static ports for normal operation.
When covered by ice these instruments display incorrect
information thereby presenting serious hazard to instrument
flight. Detailed information on the operation of these
instruments and the specific effects of icing is presented in
Chapter 3, Flight Instruments.

Stall Warning Systems
Stall warning systems provide essential information to pilots.
These systems range from a sophisticated stall warning vane
to a simple stall warning switch. Icing affects these systems
in several ways resulting in possible loss of stall warning to
the pilot. The loss of these systems can exacerbate an already
hazardous situation. Even when an aircraft’s stall warning
system remains operational during icing conditions, it may
be ineffective because the wing stalls at a lower angle of
attack due to ice on the airfoil.

Windshields
Accumulation of ice on flight deck windows can severely
restrict the pilot’s visibility outside of the aircraft. Aircraft
equipped for flight into known icing conditions typically have
some form of windshield anti-icing to enable the pilot to see

outside the aircraft in case icing is encountered in flight. One
system consists of an electrically heated plate installed onto
the airplane’s windshield to give the pilot a narrow band of
clear visibility. Another system uses a bar at the lower end
of the windshield to spray deicing fluid onto it and prevent
ice from forming. On high performance aircraft that require
complex windshields to protect against bird strikes and
withstand pressurization loads, the heating element often is
a layer of conductive film or thin wire strands through which
electric current is run to heat the windshield and prevent ice
from forming.
Antenna Icing
Because of their small size and shape, antennas that do not lay
flush with the aircraft’s skin tend to accumulate ice rapidly.
Furthermore, they often are devoid of internal anti-icing
or deicing capability for protection. During flight in icing
conditions, ice accumulations on an antenna may cause it to
begin to vibrate or cause radio signals to become distorted
and it may cause damage to the antenna. If a frozen antenna
breaks off, it can damage other areas of the aircraft in addition
to causing a communication or navigation system failure.

Summary
Ice-contaminated aircraft have been involved in many
accidents. Takeoff accidents have usually been due to failure
to deice or anti-ice critical surfaces properly on the ground.
Proper deicing and anti-icing procedures are addressed in
two other pilot guides, Advisory Circular (AC) 120-58, Pilot
Guide: Large Aircraft Ground Deicing and AC 135-17, Pilot
Guide: Small Aircraft Ground Deicing.

The pilot of an aircraft, which is certificated for flight in
icing conditions can safely operate in the conditions for
which the aircraft was evaluated during the certification
process but should never become complacent about icing.
Even short encounters with small amounts of rough icing
can be very hazardous. The pilot should be familiar with all
information in the Aircraft Flight Manual (AFM) or Pilot’s
Operating Handbook (POH) concerning flight in icing
conditions and follow it carefully. Of particular importance
are proper operation of ice protection systems and any
airspeed minimums to be observed during or after flight
in icing conditions. There are some icing conditions for
which no aircraft is evaluated in the certification process,
such as super-cooled large drops (SLD). These subfreezing
water droplets, with diameters greater than 50 microns,
occur within or below clouds and sustained flight in these
conditions can be very hazardous. The pilot should be familiar
with any information in the AFM or POH relating to these
conditions, including aircraft-specific cues for recognizing
these hazardous conditions within clouds.
The information in this chapter is an overview of the hazards
of aircraft icing. For more detailed information refer to AC
91-74, Pilot Guide: Flight in Icing Conditions, AC 91-51A,
Effect of Icing on Aircraft Control and Airplane Deice and
Anti-Ice Systems, AC 20-73A, Aircraft Ice Protection and
AC 23.143-1, Ice Contaminated Tailplane Stall (ICTS).

The pilot of an aircraft, which is not certificated or equipped
for flight in icing conditions, should avoid all icing conditions.
The aforementioned guides provide direction on how to do
this, and on how to exit icing conditions promptly and safely
should they be inadvertently encountered.

2-17

2-18

Chapter 3

Flight Instruments
Introduction
Aircraft became a practical means of transportation when
accurate flight instruments freed the pilot from the necessity
of maintaining visual contact with the ground. Flight
instruments are crucial to conducting safe flight operations
and it is important that the pilot have a basic understanding
of their operation. The basic flight instruments required
for operation under visual flight rules (VFR) are airspeed
indicator (ASI), altimeter, and magnetic direction indicator.
In addition to these, operation under instrument flight rules
(IFR) requires a gyroscopic rate-of-turn indicator, slip-skid
indicator, sensitive altimeter adjustable for barometric
pressure, clock displaying hours, minutes, and seconds with
a sweep-second pointer or digital presentation, gyroscopic
pitch-and-bank indicator (artificial horizon), and gyroscopic
direction indicator (directional gyro or equivalent).

3-1

Aircraft that are flown in instrument meteorological conditions
(IMC) are equipped with instruments that provide attitude
and direction reference, as well as navigation instruments that
allow precision flight from takeoff to landing with limited or
no outside visual reference.
The instruments discussed in this chapter are those required
by Title 14 of the Code of Federal Regulations (14 CFR)
part 91, and are organized into three groups: pitot-static
instruments, compass systems, and gyroscopic instruments.
The chapter concludes with a discussion of how to preflight
these systems for IFR flight. This chapter addresses additional
avionics systems such as Electronic Flight Information
Systems (EFIS), Ground Proximity Warning System
(GPWS), Terrain Awareness and Warning System (TAWS),
Traffic Alert and Collision Avoidance System (TCAS),
Head Up Display (HUD), etc., that are increasingly being
incorporated into general aviation aircraft.

Pitot/Static Systems
Pitot pressure, or impact air pressure, is sensed through an
open-end tube pointed directly into the relative wind flowing
around the aircraft. The pitot tube connects to pressure
operated flight instruments such as the ASI.
Static Pressure
Other instruments depend upon accurate sampling of the
ambient still air atmospheric pressure to determine the

Figure 3-1. A Typical Electrically Heated Pitot-Static Head.

3-2

height and speed of movement of the aircraft through the
air, both horizontally and vertically. This pressure, called
static pressure, is sampled at one or more locations outside
the aircraft. The pressure of the static air is sensed at a flush
port where the air is not disturbed. On some aircraft, air is
sampled by static ports on the side of the electrically heated
pitot-static head. [Figure 3-1] Other aircraft pick up the static
pressure through flush ports on the side of the fuselage or
the vertical fin. These ports are in locations proven by flight
tests to be in undisturbed air, and they are normally paired,
one on either side of the aircraft. This dual location prevents
lateral movement of the aircraft from giving erroneous static
pressure indications. The areas around the static ports may be
heated with electric heater elements to prevent ice forming
over the port and blocking the entry of the static air.
Three basic pressure-operated instruments are found in most
aircraft instrument panels. These are the sensitive altimeter,
ASI, and vertical speed indicator (VSI). All three receive
pressures sensed by the aircraft pitot-static system. The static
ports supply pressure to the ASI, altimeter, and VSI.
Blockage Considerations
The pitot tube is particularly sensitive to blockage especially
by icing. Even light icing can block the entry hole of the pitot
tube where ram air enters the system. This affects the ASI
and is the reason most airplanes are equipped with a pitot
heating system.

Indications of Pitot Tube Blockage
If the pitot tube becomes blocked, the ASI displays inaccurate
speeds. At the altitude where the pitot tube becomes blocked,
the ASI remains at the existing airspeed and doesn’t reflect
actual changes in speed.
•

•

At altitudes above where the pitot tube became
blocked, the ASI displays a higher-than-actual
airspeed increasing steadily as altitude increases.
At lower altitudes, the ASI displays a lower-than-actual
airspeed decreasing steadily as altitude decreases.

static pressure is usually lower than outside static pressure,
selection of the alternate source may result in the following
erroneous instrument indications:
1.

Altimeter reads higher than normal,

2.

Indicated airspeed (IAS) reads greater than normal,
and

3.

VSI momentarily shows a climb. Consult the Pilot’s
Operating Handbook/Airplane Flight Manual (POH/
AFM) to determine the amount of error.

Effects of Flight Conditions
Indications from Static Port Blockage
Many aircraft also have a heating system to protect the
static ports to ensure the entire pitot-static system is clear
of ice. If the static ports become blocked, the ASI would
still function but could produce inaccurate indications. At
the altitude where the blockage occurs, airspeed indications
would be normal.
•

At altitudes above which the static ports became
blocked, the ASI displays a lower-than-actual airspeed
continually decreasing as altitude is increased.

•

At lower altitudes, the ASI displays a higher-than-actual
airspeed increasing steadily as altitude decreases.

The trapped pressure in the static system causes the altimeter
to remain at the altitude where the blockage occurred. The
VSI remains at zero. On some aircraft, an alternate static
air source valve is used for emergencies. [Figure 3-2] If
the alternate source is vented inside the airplane, where

The static ports are located in a position where the air at
their surface is as undisturbed as possible. But under some
flight conditions, particularly at a high angle of attack with
the landing gear and flaps down, the air around the static
port may be disturbed to the extent that it can cause an error
in the indication of the altimeter and ASI. Because of the
importance of accuracy in these instruments, part of the
certification tests for an aircraft is a check of position error
in the static system.
The POH/AFM contains any corrections that must be applied
to the airspeed for the various configurations of flaps and
landing gear.

Pitot/Static Instruments
Sensitive Altimeter
A sensitive altimeter is an aneroid barometer that measures
the absolute pressure of the ambient air and displays it in
terms of feet or meters above a selected pressure level.

Principle of Operation
The sensitive element in a sensitive altimeter is a stack of
evacuated, corrugated bronze aneroid capsules. [Figure 3-3]
The air pressure acting on these aneroids tries to compress
them against their natural springiness, which tries to expand
them. The result is that their thickness changes as the air
pressure changes. Stacking several aneroids increases the
dimension change as the pressure varies over the usable
range of the instrument.
Below 10,000 feet, a striped segment is visible. Above this
altitude, a mask begins to cover it, and above 15,000 feet,
all of the stripes are covered. [Figure 3-4]

Figure 3-2. A Typical Pitot-Static System.

Another configuration of the altimeter is the drum-type.
[Figure 3-5] These instruments have only one pointer that
makes one revolution for every 1,000 feet. Each number
represents 100 feet and each mark represents 20 feet. A drum,
marked in thousands of feet, is geared to the mechanism that
drives the pointer. To read this type of altimeter, first look at

3-3

Figure 3-3. Sensitive Altimeter Components.

the drum to get the thousands of feet, and then at the pointer
to get the feet and hundreds of feet.
A sensitive altimeter is one with an adjustable barometric scale
allowing the pilot to set the reference pressure from which the
altitude is measured. This scale is visible in a small window
called the Kollsman window. A knob on the instrument adjusts
the scale. The range of the scale is from 28.00" to 31.00"
inches of mercury (Hg), or 948 to 1,050 millibars.
Rotating the knob changes both the barometric scale and
the altimeter pointers in such a way that a change in the
barometric scale of 1" Hg changes the pointer indication
by 1,000 feet. This is the standard pressure lapse rate
below 5,000 feet. When the barometric scale is adjusted
to 29.92" Hg or 1,013.2 millibars, the pointers indicate the

Figure 3-4. Three-Pointer Altimeter.

3-4

pressure altitude. The pilot displays indicate altitude by
adjusting the barometric scale to the local altimeter setting.
The altimeter then indicates the height above the existing
sea level pressure.

Altimeter Errors
A sensitive altimeter is designed to indicate standard changes
from standard conditions, but most flying involves errors
caused by nonstandard conditions and the pilot must be able
to modify the indications to correct for these errors. There
are two types of errors: mechanical and inherent.
Mechanical
A preflight check to determine the condition of an altimeter
consists of setting the barometric scale to the local altimeter
setting. The altimeter should indicate the surveyed elevation

Figure 3-5. Drum-Type Altimeter.

of the airport. If the indication is off by more than 75 feet from
the surveyed elevation, the instrument should be referred
to a certificated instrument repair station for recalibration.
Differences between ambient temperature and/or pressure
causes an erroneous indication on the altimeter.
Inherent Altimeter Error
Figure 3-6 shows how nonstandard temperature affects an
altimeter. When the aircraft is flying in air that is warmer
than standard, the air is less dense and the pressure levels
are farther apart. When the aircraft is flying at an indicated
altitude of 5,000 feet, the pressure level for that altitude is
higher than it would be in air at standard temperature, and
the aircraft is higher than it would be if the air were cooler.
If the air is colder than standard, it is denser and the pressure
levels are closer together. When the aircraft is flying at an
indicated altitude of 5,000 feet, its true altitude is lower than
it would be if the air were warmer.

Cold Weather Altimeter Errors
A correctly calibrated pressure altimeter indicates true
altitude above mean sea level (MSL) when operating within
the International Standard Atmosphere (ISA) parameters of
pressure and temperature. Nonstandard pressure conditions are
corrected by applying the correct local area altimeter setting.
Temperature errors from ISA result in true altitude being
higher than indicated altitude whenever the temperature is
warmer than ISA and true altitude being lower than indicated
altitude whenever the temperature is colder than ISA.
True altitude variance under conditions of colder than ISA
temperatures poses the risk of inadequate obstacle clearance.

Under extremely cold conditions, pilots may need to add an
appropriate temperature correction determined from the chart
in Figure 3-7 to charted IFR altitudes to ensure terrain and
obstacle clearance with the following restrictions:
•

Altitudes specifically assigned by Air Traffic Control
(ATC), such as “maintain 5,000 feet” shall not be
corrected. Assigned altitudes may be rejected if the
pilot decides that low temperatures pose a risk of
inadequate terrain or obstacle clearance.

•

If temperature corrections are applied to charted
IFR altitudes (such as procedure turn altitudes, final
approach fix crossing altitudes, etc.), the pilot must
advise ATC of the applied correction.

ICAO Cold Temperature Error Table
The cold temperature induced altimeter error may be
significant when considering obstacle clearances when
temperatures are well below standard. Pilots may wish to
increase their minimum terrain clearance altitudes with a
corresponding increase in ceiling from the normal minimum
when flying in extreme cold temperature conditions. Higher
altitudes may need to be selected when flying at low terrain
clearances. Most flight management systems (FMS) with
air data computers implement a capability to compensate
for cold temperature errors. Pilots flying with these systems
should ensure they are aware of the conditions under which
the system will automatically compensate. If compensation
is applied by the FMS or manually, ATC must be informed
that the aircraft is not flying the assigned altitude. Otherwise,
vertical separation from other aircraft may be reduced
creating a potentially hazardous situation. The table in
Figure 3-7, derived from International Civil Aviation

Figure 3-6. The loss of altitude experienced when flying into an area where the air is warmer (less dense) than standard.

3-5

Figure 3-7. ICAO Cold Temperature Error Table.

Organization (ICAO) standard formulas, shows how much
error can exist when the temperature is extremely cold. To
use the table, find the reported temperature in the left column,
and then read across the top row to the height above the
airport/reporting station. Subtract the airport elevation from
the altitude of the final approach fix (FAF). The intersection
of the column and row is the amount of possible error.

charted procedure turn altitude of 1,800 feet minus the airport
elevation of 500 feet equals 1,300 feet. The altitude difference
of 1,300 feet falls between the correction chart elevations of
1,000 feet and 1,500 feet. At the station temperature of -50°C,
the correction falls between 300 feet and 450 feet. Dividing
the difference in compensation values by the difference in
altitude above the airport gives the error value per foot.

Example: The reported temperature is -10° Celsius and the
FAF is 500 feet above the airport elevation. The reported
current altimeter setting may place the aircraft as much as 50
feet below the altitude indicated by the altimeter.

In this case, 150 feet divided by 500 feet = 0.33 feet for each
additional foot of altitude above 1,000 feet. This provides a
correction of 300 feet for the first 1,000 feet and an additional
value of 0.33 times 300 feet, or 99 feet, which is rounded to
100 feet. 300 feet + 100 feet = total temperature correction
of 400 feet. For the given conditions, correcting the charted
value of 1,800 feet above MSL (equal to a height above the
reporting station of 1,300 feet) requires the addition of 400
feet. Thus, when flying at an indicated altitude of 2,200 feet,
the aircraft is actually flying a true altitude of 1,800 feet.

When using the cold temperature error table, the altitude
error is proportional to both the height above the reporting
station elevation and the temperature at the reporting
station. For IFR approach procedures, the reporting station
elevation is assumed to be airport elevation. It is important
to understand that corrections are based upon the temperature
at the reporting station, not the temperature observed at the
aircraft’s current altitude and height above the reporting
station and not the charted IFR altitude.
To see how corrections are applied, note the following
example:
Airport Elevation
496 feet
Airport Temperature
- 50° C
A charted IFR approach to the airport provides the following
data:
Minimum Procedure Turn Altitude
1,800 feet
Minimum FAF Crossing Altitude
1,200 feet
Straight-in Minimum Descent Altitude
800 feet
Circling MDA
1,000 feet
The Minimum Procedure Turn Altitude of 1,800 feet will
be used as an example to demonstrate determination of
the appropriate temperature correction. Typically, altitude
values are rounded up to the nearest 100-foot level. The

3-6

Minimum Procedure Turn Altitude
1,800 feet charted
=
2,200 feet corrected
Minimum FAF Crossing Altitude
1,200 feet charted
=
1,500 feet corrected
Straight-in MDA
800 feet charted
=
900 feet corrected
Circling MDA
1,000 feet charted
=
1,200 feet corrected

Nonstandard Pressure on an Altimeter
Maintaining a current altimeter setting is critical because the
atmosphere pressure is not constant. That is, in one location
the pressure might be higher than the pressure just a short
distance away. Take an aircraft whose altimeter setting is set
to 29.92" of local pressure. As the aircraft moves to an area
of lower pressure (Point A to B in Figure 3-8) and the pilot
fails to readjust the altimeter setting (essentially calibrating
it to local pressure), then as the pressure decreases, the
indicated altitude will be lower. Adjusting the altimeter

settings compensates for this. When the altimeter shows an
indicated altitude of 5,000 feet, the true altitude at Point A
(the height above mean sea level) is only 3,500 feet at Point
B. The fact that the altitude indication is not always true lends
itself to the memory aid, “When flying from hot to cold or
from a high to a low, look out below.” [Figure 3-8]

equipment adjusts the displayed altitudes to compensate for
local pressure differences allowing display of targets at correct
altitudes. 14 CFR part 91 requires the altitude transmitted by
the transponder to be within 125 feet of the altitude indicated
on the instrument used to maintain flight altitude.

Reduced Vertical Separation Minimum (RVSM)

Figure 3-8. Effects of Nonstandard Pressure on an Altimeter of an
Aircraft Flown into Air of Lower Than Standard Pressure (Air is
Less Dense).

Altimeter Enhancements (Encoding)
It is not sufficient in the airspace system for only the pilot
to have an indication of the aircraft’s altitude; the air traffic
controller on the ground must also know the altitude of the
aircraft. To provide this information, the aircraft is typically
equipped with an encoding altimeter.
When the ATC transponder is set to Mode C, the encoding
altimeter supplies the transponder with a series of pulses
identifying the flight level (in increments of 100 feet) at
which the aircraft is flying. This series of pulses is transmitted
to the ground radar where they appear on the controller’s
scope as an alphanumeric display around the return for the
aircraft. The transponder allows the ground controller to
identify the aircraft and determine the pressure altitude at
which it is flying.
A computer inside the encoding altimeter measures the
pressure referenced from 29.92" Hg and delivers this data to
the transponder. When the pilot adjusts the barometric scale
to the local altimeter setting, the data sent to the transponder
is not affected. This is to ensure that all Mode C aircraft are
transmitting data referenced to a common pressure level. ATC

Below 31,000 feet, a 1,000 foot separation is the minimum
required between usable flight levels. Flight levels (FLs)
generally start at 18,000 feet where the local pressure is
29.92" Hg or greater. All aircraft 18,000 feet and above use
a standard altimeter setting of 29.92" Hg, and the altitudes
are in reference to a standard hence termed FL. Between FL
180 and FL 290, the minimum altitude separation is 1,000
feet between aircraft. However, for flight above FL 290
(primarily due to aircraft equipage and reporting capability;
potential error) ATC applied the requirement of 2,000 feet of
separation. FL 290, an altitude appropriate for an eastbound
aircraft, would be followed by FL 310 for a westbound
aircraft, and so on to FL 410, or seven FLs available for flight.
With 1,000-foot separation, or a reduction of the vertical
separation between FL 290 and FL 410, an additional six
FLs become available. This results in normal flight level and
direction management being maintained from FL 180 through
FL 410. Hence the name is Reduced Vertical Separation
Minimum (RVSM). Because it is applied domestically, it is
called United States Domestic Reduced Vertical Separation
Minimum, or DRVSM.
However, there is a cost to participate in the DRVSM program
which relates to both aircraft equipage and pilot training. For
example, altimetry error must be reduced significantly and
operators using RVSM must receive authorization from the
appropriate civil aviation authority. RVSM aircraft must
meet required altitude-keeping performance standards.
Additionally, operators must operate in accordance with
RVSM policies/procedures applicable to the airspace where
they are flying.
The aircraft must be equipped with at least one automatic
altitude control—
•

Within a tolerance band of ±65 feet about an acquired
altitude when the aircraft is operated in straight-andlevel flight.

•

Within a tolerance band of ±130 feet under no
turbulent, conditions for aircraft for which application
for type certification occurred on or before April 9,
1997 that are equipped with an automatic altitude
control system with flight management/performance
system inputs.

3-7

That aircraft must be equipped with an altitude alert system
that signals an alert when the altitude displayed to the flight
crew deviates from the selected altitude by more than (in most
cases) 200 feet. For each condition in the full RVSM flight
envelope, the largest combined absolute value for residual
static source error plus the avionics error may not exceed 200
feet. Aircraft with TCAS must have compatibility with RVSM
Operations. Figure 3-9 illustrates the increase in aircraft
permitted between FL 180 and FL 410. Most noteworthy,
however, is the economization that aircraft can take advantage
of by the higher FLs being available to more aircraft.

the pressure inside the aneroid. As the aircraft ascends, the
static pressure becomes lower. The pressure inside the case
compresses the aneroid, moving the pointer upward, showing
a climb and indicating the rate of ascent in number of feet
per minute (fpm).
When the aircraft levels off, the pressure no longer changes.
The pressure inside the case becomes equal to that inside
the aneroid, and the pointer returns to its horizontal, or
zero, position. When the aircraft descends, the static
pressure increases. The aneroid expands, moving the pointer
downward, indicating a descent.
The pointer indication in a VSI lags a few seconds behind
the actual change in pressure. However, it is more sensitive
than an altimeter and is useful in alerting the pilot of an
upward or downward trend, thereby helping maintain a
constant altitude.
Some of the more complex VSIs, called instantaneous vertical
speed indicators (IVSI), have two accelerometer-actuated air
pumps that sense an upward or downward pitch of the aircraft
and instantaneously create a pressure differential. By the time
the pressure caused by the pitch acceleration dissipates, the
altitude pressure change is effective.

Dynamic Pressure Type Instruments
Airspeed Indicator (ASI)
An ASI is a differential pressure gauge that measures the
dynamic pressure of the air through which the aircraft is
flying. Dynamic pressure is the difference in the ambient
static air pressure and the total, or ram, pressure caused by
the motion of the aircraft through the air. These two pressures
are taken from the pitot-static system.

Figure 3-9. Increase in Aircraft Permitted Between FL 180 and

FL 410.

Vertical Speed Indicator (VSI)
The VSI in Figure 3-10 is also called a vertical velocity
indicator (VVI), and was formerly known as a rate-ofclimb indicator. It is a rate-of-pressure change instrument
that gives an indication of any deviation from a constant
pressure level.
Inside the instrument case is an aneroid very much like the
one in an ASI. Both the inside of this aneroid and the inside
of the instrument case are vented to the static system, but
the case is vented through a calibrated orifice that causes
the pressure inside the case to change more slowly than

3-8

Figure 3-10. Rate of Climb or Descent in Thousands of Feet Per

Minute.

The mechanism of the ASI in Figure 3-11 consists of a thin,
corrugated phosphor bronze aneroid, or diaphragm, that
receives its pressure from the pitot tube. The instrument
case is sealed and connected to the static ports. As the
pitot pressure increases or the static pressure decreases, the
diaphragm expands. This dimensional change is measured by
a rocking shaft and a set of gears that drives a pointer across
the instrument dial. Most ASIs are calibrated in knots, or
nautical miles per hour; some instruments show statute miles
per hour, and some instruments show both.

Types of Airspeed
Just as there are several types of altitude, there are multiple
types of airspeed: Indicated Airspeed (IAS), Calibrated
Airspeed (CAS), Equivalent Airspeed (EAS), and True
Airspeed (TAS).
Indicated Airspeed (IAS)
IAS is shown on the dial of the instrument, uncorrected for
instrument or system errors.
Calibrated Airspeed (CAS)
CAS is the speed at which the aircraft is moving through
the air, which is found by correcting IAS for instrument
and position errors. The POH/AFM has a chart or graph to
correct IAS for these errors and provide the correct CAS for
the various flap and landing gear configurations.

Equivalent Airspeed (EAS)
EAS is CAS corrected for compression of the air inside the
pitot tube. EAS is the same as CAS in standard atmosphere
at sea level. As the airspeed and pressure altitude increase,
the CAS becomes higher than it should be, and a correction
for compression must be subtracted from the CAS.
True Airspeed (TAS)
TAS is CAS corrected for nonstandard pressure and
temperature. TAS and CAS are the same in standard
atmosphere at sea level. Under nonstandard conditions, TAS
is found by applying a correction for pressure altitude and
temperature to the CAS.
Some aircraft are equipped with true ASIs that have a
temperature-compensated aneroid bellows inside the
instrument case. This bellows modifies the movement of
the rocking shaft inside the instrument case so the pointer
shows the actual TAS.
The TAS indicator provides both true and IAS. These
instruments have the conventional airspeed mechanism,
with an added subdial visible through cutouts in the regular
dial. A knob on the instrument allows the pilot to rotate the
subdial and align an indication of the outside air temperature
with the pressure altitude being flown. This alignment causes
the instrument pointer to indicate the TAS on the subdial.
[Figure 3-12]

Figure 3-11. Mechanism of an Airspeed Indicator.

3-9

Most high-speed aircraft are limited to a maximum Mach
number at which they can fly. This is shown on a Machmeter
as a decimal fraction. [Figure 3-13] For example, if the
Machmeter indicates .83 and the aircraft is flying at 30,000
feet where the speed of sound under standard conditions is
589.5 knots, the airspeed is 489.3 knots. The speed of sound
varies with the air temperature. If the aircraft were flying at
Mach .83 at 10,000 feet where the air is much warmer, its
airspeed would be 530 knots.

Figure 3-12. A true airspeed indicator allows the pilot to correct

IAS for nonstandard temperature and pressure.

Mach Number
As an aircraft approaches the speed of sound, the air flowing
over certain areas of its surface speeds up until it reaches the
speed of sound, and shock waves form. The IAS at which
these conditions occur changes with temperature. Therefore,
in this case, airspeed is not entirely adequate to warn the
pilot of the impending problems. Mach number is more
useful. Mach number is the ratio of the TAS of the aircraft
to the speed of sound in the same atmospheric conditions.
An aircraft flying at the speed of sound is flying at Mach
1.0. Some older mechanical Machmeters not driven from
an air data computer use an altitude aneroid inside the
instrument that converts pitot-static pressure into Mach
number. These systems assume that the temperature at any
altitude is standard; therefore, the indicated Mach number is
inaccurate whenever the temperature deviates from standard.
These systems are called indicated Machmeters. Modern
electronic Machmeters use information from an air data
computer system to correct for temperature errors. These
systems display true Mach number.

Maximum Allowable Airspeed
Some aircraft that fly at high subsonic speeds are equipped
with maximum allowable ASIs like the one in Figure 3-14.
This instrument looks much like a standard air-speed indicator,
calibrated in knots, but has an additional pointer colored red,
checkered, or striped. The maximum airspeed pointer is
actuated by an aneroid, or altimeter mechanism, that moves
it to a lower value as air density decreases. By keeping the
airspeed pointer at a lower value than the maximum pointer,
the pilot avoids the onset of transonic shock waves.

Figure 3-14. A maximum allowable airspeed indicator has a movable

pointer that indicates the never-exceed speed, which changes with
altitude to avoid the onset of transonic shock waves.

Airspeed Color Codes
The dial of an ASI is color coded to alert the pilot, at a
glance, of the significance of the speed at which the aircraft
is flying. These colors and their associated airspeeds are
shown in Figure 3-15.

Magnetism
The Earth is a huge magnet, spinning in space, surrounded
by a magnetic field made up of invisible lines of flux. These
lines leave the surface at the magnetic north pole and reenter
at the magnetic South Pole.
Figure 3-13. A Machmeter shows the ratio of the speed of sound to

the TAS the aircraft is flying.

3-10

Lines of magnetic flux have two important characteristics:
any magnet that is free to rotate will align with them, and

Figure 3-15. Color Codes for an Airspeed Indicator.

an electrical current is induced into any conductor that cuts
across them. Most direction indicators installed in aircraft
make use of one of these two characteristics.
The Basic Aviation Magnetic Compass
One of the oldest and simplest instruments for indicating
direction is the magnetic compass. It is also one of the basic
instruments required by 14 CFR part 91 for both VFR and
IFR flight.

Magnetic Compass Overview
A magnet is a piece of material, usually a metal containing
iron, which attracts and holds lines of magnetic flux.
Regardless of size, every magnet has two poles: a north
pole and a south pole. When one magnet is placed in the
field of another, the unlike poles attract each other and like
poles repel.
An aircraft magnetic compass, such as the one in Figure 3-16,
has two small magnets attached to a metal float sealed inside a
bowl of clear compass fluid similar to kerosene. A graduated

Figure 3-16. A Magnetic Compass. The vertical line is called the

scale, called a card, is wrapped around the float and viewed
through a glass window with a lubber line across it. The card
is marked with letters representing the cardinal directions,
north, east, south, and west, and a number for each 30°
between these letters. The final “0” is omitted from these
directions; for example, 3 = 30°, 6 = 60°, and 33 = 330°.
There are long and short graduation marks between the letters
and numbers, with each long mark representing 10° and each
short mark representing 5°.
Magnetic Compass Construction
The float and card assembly has a hardened steel pivot in its
center that rides inside a special, spring-loaded, hard-glass
jewel cup. The buoyancy of the float takes most of the weight
off the pivot, and the fluid damps the oscillation of the float
and card. This jewel-and-pivot type mounting allows the float
freedom to rotate and tilt up to approximately 18° angle of
bank. At steeper bank angles, the compass indications are
erratic and unpredictable.
The compass housing is entirely full of compass fluid. To
prevent damage or leakage when the fluid expands and
contracts with temperature changes, the rear of the compass
case is sealed with a flexible diaphragm, or with a metal
bellows in some compasses.
Magnetic Compass Theory of Operations
The magnets align with the Earth’s magnetic field and the
pilot reads the direction on the scale opposite the lubber line.
Note that in Figure 3-16, the pilot sees the compass card from
its backside. When the pilot is flying north as the compass
shows, east is to the pilot’s right, but on the card “33”, which
represents 330° (west of north), is to the right of north. The
reason for this apparent backward graduation is that the card
remains stationary, and the compass housing and the pilot turn
around it, always viewing the card from its backside.

lubber line.

3-11

A compensator assembly mounted on the top or bottom of the
compass allows an aviation maintenance technician (AMT)
to create a magnetic field inside the compass housing that
cancels the influence of local outside magnetic fields. This is
done to correct for deviation error. The compensator assembly
has two shafts whose ends have screwdriver slots accessible
from the front of the compass. Each shaft rotates one or two
small compensating magnets. The end of one shaft is marked
E-W, and its magnets affect the compass when the aircraft is
pointed east or west. The other shaft is marked N-S and its
magnets affect the compass when the aircraft is pointed north
or south.

Magnetic Compass Induced Errors
The magnetic compass is the simplest instrument in the
panel, but it is subject to a number of errors that must be
considered.
Variation
The Earth rotates about its geographic axis; maps and charts
are drawn using meridians of longitude that pass through the
geographic poles. Directions measured from the geographic
poles are called true directions. The north magnetic pole to
which the magnetic compass points is not collocated with
the geographic north pole, but is some 1,300 miles away;
directions measured from the magnetic poles are called
magnetic directions. In aerial navigation, the difference
between true and magnetic directions is called variation. This
same angular difference in surveying and land navigation is
called declination.

Flying in the Washington, D.C. area, for example, the variation
is 10° west. If the pilot wants to fly a true course of south (180°),
the variation must be added to this resulting in a magnetic course
to fly of 190°. Flying in the Los Angeles, CA area, the variation
is 14° east. To fly a true course of 180° there, the pilot would
have to subtract the variation and fly a magnetic course of 166°.
The variation error does not change with the heading of the
aircraft; it is the same anywhere along the isogonic line.
Deviation
The magnets in a compass align with any magnetic field.
Local magnetic fields in an aircraft caused by electrical current
flowing in the structure, in nearby wiring or any magnetized
part of the structure, conflict with the Earth’s magnetic field
and cause a compass error called deviation.
Deviation, unlike variation, is different on each heading, but it is
not affected by the geographic location. Variation error cannot
be reduced or changed, but deviation error can be minimized
when a pilot or AMT performs the maintenance task known
as “swinging the compass.”
Most airports have a compass rose, which is a series of lines
marked out on a taxiway or ramp at some location where there
is no magnetic interference. Lines, oriented to magnetic north,
are painted every 30°, as shown in Figure 3-18.

Figure 3-17 shows the isogonic lines that identify the number
of degrees of variation in their area. The line that passes near
Chicago is called the agonic line. Anywhere along this line
the two poles are aligned, and there is no variation. East of
this line, the magnetic pole is to the west of the geographic
pole and a correction must be applied to a compass indication
to get a true direction.

Figure 3-18. Utilization of a Compass Rose Aids Compensation

for Deviation Errors.

The pilot or AMT aligns the aircraft on each magnetic
heading and adjusts the compensating magnets to minimize
the difference between the compass indication and the actual
magnetic heading of the aircraft. Any error that cannot be
removed is recorded on a compass correction card, like the one
in Figure 3-19, and placed in a cardholder near the compass.
If the pilot wants to fly a magnetic heading of 120° and the
Figure 3-17. Isogonic lines are lines of equal variation.

3-12

To find the true course that is being flown when the compass
course is known:
Compass Course ± Deviation = Magnetic Course ± Variation
= True Course

Figure 3-19. A compass correction card shows the deviation

correction for any heading.

aircraft is operating with the radios on, the pilot should fly a
compass heading of 123°.
The corrections for variation and deviation must be applied
in the correct sequence and is shown below starting from the
true course desired.
Step 1: Determine the Magnetic Course
True Course (180°) ± Variation (+10°) = Magnetic Course (190°)
The Magnetic Course (190°) is steered if there is no deviation
error to be applied. The compass card must now be considered
for the compass course of 190°.
Step 2: Determine the Compass Course
Magnetic Course (190°, from step 1) ± Deviation (-2°, from
correction card) = Compass Course (188°)
NOTE: Intermediate magnetic courses between those listed on
the compass card need to be interpreted. Therefore, to steer a true
course of 180°, the pilot would follow a compass course of 188°.

Dip Errors
The lines of magnetic flux are considered to leave the Earth at
the magnetic north pole and enter at the magnetic South Pole. At
both locations the lines are perpendicular to the Earth’s surface.
At the magnetic equator, which is halfway between the poles,
the lines are parallel with the surface. The magnets in a compass
align with this field, and near the poles they dip, or tilt, the float
and card. The float is balanced with a small dip-compensating
weight, so it stays relatively level when operating in the middle
latitudes of the northern hemisphere. This dip along with this
weight causes two very noticeable errors: northerly turning error
and acceleration error.
The pull of the vertical component of the Earth’s magnetic field
causes northerly turning error, which is apparent on a heading
of north or south. When an aircraft flying on a heading of north
makes a turn toward east, the aircraft banks to the right, and the
compass card tilts to the right. The vertical component of the
Earth’s magnetic field pulls the north-seeking end of the magnet
to the right, and the float rotates, causing the card to rotate toward
west, the direction opposite the direction the turn is being made.
[Figure 3-20]
If the turn is made from north to west, the aircraft banks to the left
and the compass card tilts down on the left side. The magnetic
field pulls on the end of the magnet that causes the card to rotate
toward east. This indication is again opposite to the direction
the turn is being made. The rule for this error is: when starting

Figure 3-20. Northerly Turning Error.

3-13

Figure 3-21. The Effects of Acceleration Error.

a turn from a northerly heading, the compass indication lags
behind the turn.
When an aircraft is flying on a heading of south and begins
a turn toward east, the Earth’s magnetic field pulls on the
end of the magnet that rotates the card toward east, the same
direction the turn is being made. If the turn is made from south
toward west, the magnetic pull starts the card rotating toward
west—again, in the same direction the turn is being made. The
rule for this error is: When starting a turn from a southerly
heading, the compass indication leads the turn.
In acceleration error, the dip-correction weight causes the end
of the float and card marked N (the south-seeking end) to be
heavier than the opposite end. When the aircraft is flying at
a constant speed on a heading of east or west, the float and
card is level. The effects of magnetic dip and the weight are
approximately equal. If the aircraft accelerates on a heading
of east [Figure 3-21], the inertia of the weight holds its end of
the float back and the card rotates toward north. As soon as the
speed of the aircraft stabilizes, the card swings back to its east
indication. If, while flying on this easterly heading, the aircraft
decelerates, the inertia causes the weight to move ahead and the
card rotates toward south until the speed again stabilizes.
When flying on a heading of west, the same things happen.
Inertia from acceleration causes the weight to lag, and the
card rotates toward north. When the aircraft decelerates on a
heading of west, inertia causes the weight to move ahead and
the card rotates toward south.

3-14

Oscillation Error
Oscillation is a combination of all of the other errors, and it
results in the compass card swinging back and forth around
the heading being flown. When setting the gyroscopic
heading indicator to agree with the magnetic compass, use
the average indication between the swings.
The Vertical Card Magnetic Compass
The floating magnet type of compass not only has all the
errors just described, but also lends itself to confused reading.
It is easy to begin a turn in the wrong direction because its card
appears backward. East is on what the pilot would expect to be
the west side. The vertical card magnetic compass eliminates
some of the errors and confusion. The dial of this compass
is graduated with letters representing the cardinal directions,
numbers every 30°, and marks every 5°. The dial is rotated by
a set of gears from the shaft-mounted magnet, and the nose
of the symbolic airplane on the instrument glass represents
the lubber line for reading the heading of the aircraft from
the dial. Eddy currents induced into an aluminum-damping
cup damp oscillation of the magnet. [Figure 3-22]
The Flux Gate Compass System
As mentioned earlier, the lines of flux in the Earth’s magnetic
field have two basic characteristics: a magnet aligns with
these lines, and an electrical current is induced, or generated,
in any wire crossed by them.

Figure 3-24. The current in each of the three pickup coils changes
Figure 3-22. Vertical Card Magnetic Compass.

The flux gate compass that drives slaved gyros uses the
characteristic of current induction. The flux valve is a small,
segmented ring, like the one in Figure 3-23, made of soft
iron that readily accepts lines of magnetic flux. An electrical
coil is wound around each of the three legs to accept the
current induced in this ring by the Earth’s magnetic field. A
coil wound around the iron spacer in the center of the frame
has 400-Hz alternating current (A.C.) flowing through it.
During the times when this current reaches its peak, twice
during each cycle, there is so much magnetism produced by
this coil that the frame cannot accept the lines of flux from
the Earth’s field.

with the heading of the aircraft.

But as the current reverses between the peaks, it demagnetizes
the frame so it can accept the flux from the Earth’s field. As
this flux cuts across the windings in the three coils, it causes
current to flow in them. These three coils are connected in
such a way that the current flowing in them changes as the
heading of the aircraft changes. [Figure 3-24]
The three coils are connected to three similar but smaller coils
in a synchro inside the instrument case. The synchro rotates
the dial of a radio magnetic indicator (RMI) or a horizontal
situation indicator (HSI).
Remote Indicating Compass
Remote indicating compasses were developed to compensate
for the errors and limitations of the older type of heading
indicators. The two panel-mounted components of a typical
system are the pictorial navigation indicator and the slaving
control and compensator unit. [Figure 3-25] The pictorial
navigation indicator is commonly referred to as a HSI.

Figure 3-23. The soft iron frame of the flux valve accepts the flux

from the Earth’s magnetic field each time the current in the center
coil reverses. This flux causes current to flow in the three pickup
coils.

Figure 3-25. Pictorial Navigation Indicator (HSI Top), Slaving
Control and Compensator Unit.

3-15

The slaving control and compensator unit has a pushbutton
that provides a means of selecting either the “slaved gyro”
or “free gyro” mode. This unit also has a slaving meter
and two manual heading-drive buttons. The slaving meter
indicates the difference between the displayed heading and
the magnetic heading. A right deflection indicates a clockwise
error of the compass card; a left deflection indicates a
counterclockwise error. Whenever the aircraft is in a turn
and the card rotates, the slaving meter shows a full deflection
to one side or the other. When the system is in “free gyro”
mode, the compass card may be adjusted by depressing the
appropriate heading-drive button.
A separate unit, the magnetic slaving transmitter is mounted
remotely; usually in a wingtip to eliminate the possibility of
magnetic interference. It contains the flux valve, which is
the direction-sensing device of the system. A concentration
of lines of magnetic force, after being amplified, becomes
a signal relayed to the heading indicator unit, which is also
remotely mounted. This signal operates a torque motor in
the heading indicator unit that processes the gyro unit until
it is aligned with the transmitter signal. The magnetic slaving
transmitter is connected electrically to the HSI.
There are a number of designs of the remote indicating
compass; therefore, only the basic features of the system are
covered here. Instrument pilots must become familiar with
the characteristics of the equipment in their aircraft.
As instrument panels become more crowded and the pilot’s
available scan time is reduced by a heavier flight deck
workload, instrument manufacturers have worked toward
combining instruments. One good example of this is the
RMI in Figure 3-26. The compass card is driven by signals

Figure 3-26. Driven by signals from a flux valve, the compass card
in this RMI indicates the heading of the aircraft opposite the upper
center index mark. The green pointer is driven by the ADF.

3-16

from the flux valve, and the two pointers are driven by an
automatic direction finder (ADF) and a very high frequency
omnidirectional range (VOR).

Gyroscopic Systems
Flight without reference to a visible horizon can be safely
accomplished by the use of gyroscopic instrument systems
and the two characteristics of gyroscopes, which are rigidity
and precession. These systems include attitude, heading,
and rate instruments, along with their power sources. These
instruments include a gyroscope (or gyro) that is a small wheel
with its weight concentrated around its periphery. When this
wheel is spun at high speed, it becomes rigid and resists tilting
or turning in any direction other than around its spin axis.
Attitude and heading instruments operate on the principle
of rigidity. For these instruments, the gyro remains rigid
in its case and the aircraft rotates about it. Rate indicators,
such as turn indicators and turn coordinators, operate on the
principle of precession. In this case, the gyro processes (or
rolls over) proportionate to the rate the aircraft rotates about
one or more of its axes.
Power Sources
Aircraft and instrument manufacturers have designed
redundancy in the flight instruments so that any single failure
will not deprive the pilot of the ability to safely conclude
the flight. Gyroscopic instruments are crucial for instrument
flight; therefore, they are powered by separate electrical or
pneumatic sources.

Pneumatic Systems
Pneumatic gyros are driven by a jet of air impinging on
buckets cut into the periphery of the wheel. On many aircraft
this stream of air is obtained by evacuating the instrument
case with a vacuum source and allowing filtered air to flow
into the case through a nozzle to spin the wheel.
Venturi Tube Systems
Aircraft that do not have a pneumatic pump to evacuate the
instrument case can use venturi tubes mounted on the outside
of the aircraft, similar to the system shown in Figure 3-27. Air
flowing through the venturi tube speeds up in the narrowest
part and, according to Bernoulli’s principle, the pressure
drops. This location is connected to the instrument case by
a piece of tubing. The two attitude instruments operate on
approximately 4" Hg of suction; the turn-and-slip indicator
needs only 2" Hg, so a pressure-reducing needle valve is
used to decrease the suction. Air flows into the instruments
through filters built into the instrument cases. In this system,
ice can clog the venturi tube and stop the instruments when
they are most needed.

Vacuum Pump Systems
Wet-Type Vacuum Pump
Steel-vane air pumps have been used for many years to
evacuate the instrument cases. The vanes in these pumps
are lubricated by a small amount of engine oil metered into
the pump and discharged with the air. In some aircraft the
discharge air is used to inflate rubber deicer boots on the
wing and empennage leading edges. To keep the oil from
deteriorating the rubber boots, it must be removed with an
oil separator like the one in Figure 3-28.
The vacuum pump moves a greater volume of air than is
needed to supply the instruments with the suction needed,
so a suction-relief valve is installed in the inlet side of the
pump. This spring-loaded valve draws in just enough air to
maintain the required low pressure inside the instruments,
as is shown on the suction gauge in the instrument panel.
Filtered air enters the instrument cases from a central air
filter. As long as aircraft fly at relatively low altitudes, enough
air is drawn into the instrument cases to spin the gyros at a
sufficiently high speed.
Figure 3-27. A venturi tube system that provides necessary vacuum

to operate key instruments.

Dry Air Vacuum Pump
As flight altitudes increase, the air is less dense and more air
must be forced through the instruments. Air pumps that do not
mix oil with the discharge air are used in high flying aircraft.

Figure 3-28. Single-engine instrument vacuum system using a steel-vane wet-type vacuum pump.

3-17

Steel vanes sliding in a steel housing need to be lubricated,
but vanes made of a special formulation of carbon sliding
inside carbon housing provide their own lubrication in a
microscopic amount as they wear.
Pressure Indicating Systems
Figure 3-29 is a diagram of the instrument pneumatic
system of a twin-engine general aviation airplane. Two dry
air pumps are used with filters in their inlet to filter out any
contaminants that could damage the fragile carbon vanes in
the pump. The discharge air from the pump flows through
a regulator, where excess air is bled off to maintain the
pressure in the system at the desired level. The regulated air
then flows through inline filters to remove any contamination
that could have been picked up from the pump, and from
there into a manifold check valve. If either engine should
become inoperative or either pump should fail, the check
valve isolates the inoperative system and the instruments are
driven by air from the operating system. After the air passes
through the instruments and drives the gyros, it is exhausted
from the case. The gyro pressure gauge measures the pressure
drop across the instruments.

Electrical Systems
Many general aviation aircraft that use pneumatic attitude
indicators use electric rate indicators and/or the reverse. Some

instruments identify their power source on their dial, but it
is extremely important that pilots consult the POH/AFM to
determine the power source of all instruments to know what
action to take in the event of an instrument failure. Direct
current (D.C.) electrical instruments are available in 14- or
28-volt models, depending upon the electrical system in
the aircraft. A.C. is used to operate some attitude gyros and
autopilots. Aircraft with only D.C. electrical systems can use
A.C. instruments via installation of a solid-state D.C. to A.C.
inverter, which changes 14 or 28 volts D.C. into three-phase
115-volt, 400-Hz A.C.

Gyroscopic Instruments
Attitude Indicators
The first attitude instrument (AI) was originally referred to as
an artificial horizon, later as a gyro horizon; now it is more
properly called an attitude indicator. Its operating mechanism
is a small brass wheel with a vertical spin axis, spun at a high
speed by either a stream of air impinging on buckets cut into
its periphery, or by an electric motor. The gyro is mounted in
a double gimbal, which allows the aircraft to pitch and roll
about the gyro as it remains fixed in space.
A horizon disk is attached to the gimbals so it remains in
the same plane as the gyro, and the aircraft pitches and
rolls about it. On early instruments, this was just a bar that

Figure 3-29. Twin-Engine Instrument Pressure System Using a Carbon-Vane Dry-Type Air Pump.

3-18

represented the horizon, but now it is a disc with a line
representing the horizon and both pitch marks and bank-angle
lines. The top half of the instrument dial and horizon disc
is blue, representing the sky; and the bottom half is brown,
representing the ground. A bank index at the top of the
instrument shows the angle of bank marked on the banking
scale with lines that represent 10°, 20°, 30°, 45°, and 60°.
[Figure 3-30]

that exceeded the instrument limits. Newer instruments do
not have these restrictive tumble limits; therefore, they do
not have a caging mechanism.
When an aircraft engine is first started and pneumatic or
electric power is supplied to the instruments, the gyro is
not erect. A self-erecting mechanism inside the instrument
actuated by the force of gravity applies a precessing force,
causing the gyro to rise to its vertical position. This erection
can take as long as 5 minutes, but is normally done within
2 to 3 minutes.
Attitude indicators are free from most errors, but depending
upon the speed with which the erection system functions,
there may be a slight nose-up indication during a rapid
acceleration and a nose-down indication during a rapid
deceleration. There is also a possibility of a small bank angle
and pitch error after a 180° turn. These inherent errors are
small and correct themselves within a minute or so after
returning to straight-and-level flight.
Heading Indicators
A magnetic compass is a dependable instrument used as a
backup instrument. Although very reliable, it has so many
inherent errors that it has been supplemented with gyroscopic
heading indicators.

Figure 3-30. The dial of this attitude indicator has reference lines
to show pitch and roll.

A small symbolic aircraft is mounted in the instrument case so it
appears to be flying relative to the horizon. A knob at the bottom
center of the instrument case raises or lowers the aircraft to
compensate for pitch trim changes as the airspeed changes. The
width of the wings of the symbolic aircraft and the dot in the center
of the wings represent a pitch change of approximately 2°.
For an AI to function properly, the gyro must remain
vertically upright while the aircraft rolls and pitches around
it. The bearings in these instruments have a minimum of
friction; however, even this small amount places a restraint
on the gyro producing precession and causing the gyro to tilt.
To minimize this tilting, an erection mechanism inside the
instrument case applies a force any time the gyro tilts from
its vertical position. This force acts in such a way to return
the spinning wheel to its upright position.
The older artificial horizons were limited in the amount of
pitch or roll they could tolerate, normally about 60° in pitch
and 100° in roll. After either of these limits was exceeded,
the gyro housing contacted the gimbals, applying such a
precessing force that the gyro tumbled. Because of this
limitation, these instruments had a caging mechanism that
locked the gyro in its vertical position during any maneuvers

The gyro in a heading indicator is mounted in a double gimbal,
as in an attitude indicator, but its spin axis is horizontal
permitting sensing of rotation about the vertical axis of the
aircraft. Gyro heading indicators, with the exception of slaved
gyro indicators, are not north seeking, therefore they must
be manually set to the appropriate heading by referring to
a magnetic compass. Rigidity causes them to maintain this
heading indication, without the oscillation and other errors
inherent in a magnetic compass.
Older directional gyros use a drum-like card marked in the
same way as the magnetic compass card. The gyro and the
card remain rigid inside the case with the pilot viewing the
card from the back. This creates the possibility the pilot might
start a turn in the wrong direction similar to using a magnetic
compass. A knob on the front of the instrument, below the
dial, can be pushed in to engage the gimbals. This locks the
gimbals allowing the pilot to rotate the gyro and card until
the number opposite the lubber line agrees with the magnetic
compass. When the knob is pulled out, the gyro remains rigid
and the aircraft is free to turn around the card.
Directional gyros are almost all air-driven by evacuating
the case and allowing filtered air to flow into the case and
out through a nozzle, blowing against buckets cut in the

3-19

periphery of the wheel. The Earth constantly rotates at 15°
per hour while the gyro is maintaining a position relative
to space, thus causing an apparent drift in the displayed
heading of 15° per hour. When using these instruments, it
is standard practice to compare the heading indicated on the
directional gyro with the magnetic compass at least every 15
minutes and to reset the heading as necessary to agree with
the magnetic compass.
Heading indicators like the one in Figure 3-31 work on the
same principle as the older horizontal card indicators, except
that the gyro drives a vertical dial that looks much like the
dial of a vertical card magnetic compass. The heading of the
aircraft is shown against the nose of the symbolic aircraft on
the instrument glass, which serves as the lubber line. A knob
in the front of the instrument may be pushed in and turned
to rotate the gyro and dial. The knob is spring loaded so it
disengages from the gimbals as soon as it is released. This
instrument should be checked about every 15 minutes to see
if it agrees with the magnetic compass.

Figure 3-32. Precession causes a force applied to a spinning
wheel to be felt 90° from the point of application in the direction
of rotation.

The inclinometer in the instrument is a black glass ball sealed
inside a curved glass tube that is partially filled with a liquid
for damping. This ball measures the relative strength of the
force of gravity and the force of inertia caused by a turn.
When the aircraft is flying straight-and-level, there is no
inertia acting on the ball, and it remains in the center of the
tube between two wires. In a turn made with a bank angle
that is too steep, the force of gravity is greater than the inertia
and the ball rolls down to the inside of the turn. If the turn is
made with too shallow a bank angle, the inertia is greater than
gravity and the ball rolls upward to the outside of the turn.
The inclinometer does not indicate the amount of bank, nor
does it indicate slip; it only indicates the relationship between
the angle of bank and the rate of yaw.
Figure 3-31. The heading indicator is not north seeking, but must
be set periodically (about every 15 minutes) to agree with the
magnetic compass.

Turn Indicators
Attitude and heading indicators function on the principle
of rigidity, but rate instruments such as the turn-andslip indicator operate on precession. Precession is the
characteristic of a gyroscope that causes an applied force to
produce a movement, not at the point of application, but at
a point 90° from the point of application in the direction of
rotation. [Figure 3-32]

Turn-and-Slip Indicator
The first gyroscopic aircraft instrument was the turn indicator
in the needle and ball, or turn-and-bank indicator, which
has more recently been called a turn-and-slip indicator.
[Figure 3-33]
3-20

Figure 3-33. Turn-and-Slip Indicator.

The turn indicator is a small gyro spun either by air or by
an electric motor. The gyro is mounted in a single gimbal
with its spin axis parallel to the lateral axis of the aircraft
and the axis of the gimbal parallel with the longitudinal axis.
[Figure 3-34]

Turn Coordinator
The major limitation of the older turn-and-slip indicator is that
it senses rotation only about the vertical axis of the aircraft. It
tells nothing of the rotation around the longitudinal axis, which
in normal flight occurs before the aircraft begins to turn.
A turn coordinator operates on precession, the same as the
turn indicator, but its gimbals frame is angled upward about
30° from the longitudinal axis of the aircraft. [Figure 3-34]
This allows it to sense both roll and yaw. Therefore during
a turn, the indicator first shows the rate of banking and once
stabilized, the turn rate. Some turn coordinator gyros are dualpowered and can be driven by either air or electricity.
Rather than using a needle as an indicator, the gimbal moves
a dial that is the rear view of a symbolic aircraft. The bezel
of the instrument is marked to show wings-level flight and
bank angles for a standard rate turn. [Figure 3-35]

Figure 3-34. The rate gyro in both turn-and-slip indicator and turn

coordinator.

When the aircraft yaws, or rotates about its vertical axis, it
produces a force in the horizontal plane that, due to precession,
causes the gyro and its gimbal to rotate about the gimbal’s
axis. It is restrained in this rotation plane by a calibration
spring; it rolls over just enough to cause the pointer to deflect
until it aligns with one of the doghouse-shaped marks on the
dial, when the aircraft is making a standard rate turn.
The dial of these instruments is marked “2 MIN TURN.” Some
turn-and-slip indicators used in faster aircraft are marked “4
MIN TURN.” In either instrument, a standard rate turn is being
made whenever the needle aligns with a doghouse.

Figure 3-35. A turn coordinator senses rotation about both roll

and yaw axes.

The inclinometer, similar to the one in a turn-and-slip
indicator, is called a coordination ball, which shows the
relationship between the bank angle and the rate of yaw. The
turn is coordinated when the ball is in the center, between the
marks. The aircraft is skidding when the ball rolls toward the
outside of the turn and is slipping when it moves toward the
inside of the turn. A turn coordinator does not sense pitch.
This is indicated on some instruments by placing the words
“NO PITCH INFORMATION” on the dial.

3-21

Flight Support Systems
Attitude and Heading Reference System (AHRS)
As aircraft displays have transitioned to new technology,
the sensors that feed them have also undergone significant
change. Traditional gyroscopic flight instruments have
been replaced by Attitude and Heading Reference Systems
(AHRS) improving reliability and thereby reducing cost and
maintenance.
The function of an AHRS is the same as gyroscopic systems;
that is, to determine which way is level and which way is north.
By knowing the initial heading the AHRS can determine both
the attitude and magnetic heading of the aircraft.
The genesis of this system was initiated by the development
of the ring-LASAR gyroscope developed by Kearfott located
in Little Falls, New Jersey. [Figure 3-36] Their development
of the Ring-LASAR gyroscope in the 1960s/1970s was
in support of Department of Defense (DOD) programs to
include cruise missile technology. With the precision of
these gyroscopes, it became readily apparent that they could
be leveraged for multiple tasks and functions. Gyroscopic
miniaturization has become so common that solid-state
gyroscopes are found in products from robotics to toys.
Because the AHRS system replaces separate gyroscopes,
such as those associated with an attitude indicator, magnetic
heading indicator and turn indicator these individual systems
are no longer needed. As with many systems today, AHRS
itself had matured with time. Early AHRS systems used

expensive inertial sensors and flux valves. However, today the
AHRS for aviation and general aviation in particular are small
solid-state systems integrating a variety of technology such
as low cost inertial sensors, rate gyros, and magnetometers,
and have capability for satellite signal reception.
Air Data Computer (ADC)
An Air Data Computer (ADC) [Figure 3-37] is an aircraft
computer that receives and processes pitot pressure, static
pressure, and temperature to calculate very precise altitude,
IAS, TAS, and air temperature. The ADC outputs this
information in a digital format that can be used by a variety
of aircraft systems including an EFIS. Modern ADCs
are small solid-state units. Increasingly, aircraft systems
such as autopilots, pressurization, and FMS utilize ADC
information for normal operations. NOTE: In most modern
general aviation systems, both the AHRS and ADC are
integrated within the electronic displays themselves thereby
reducing the number of units, reducing weight, and providing
simplification for installation resulting in reduced costs.

Analog Pictorial Displays
Horizontal Situation Indicator (HSI)
The HSI is a direction indicator that uses the output from
a flux valve to drive the dial, which acts as the compass
card. This instrument, shown in Figure 3-37, combines the
magnetic compass with navigation signals and a glide slope.
This gives the pilot an indication of the location of the aircraft
with relationship to the chosen course.

Figure 3-36. The Kearfott Attitude Heading Reference System (AHRS) on the left incorporates a Monolithic Ring Laser Gyro (MRLG)

(center), which is housed in an Inertial Sensor Assembly (ISA) on the right.

3-22

takes the aircraft to the selected facility. When the indicator
points to the tail of the course arrow, it shows that the course
selected, if properly intercepted and flown, takes the aircraft
directly away from the selected facility.
The glide slope deviation pointer indicates the relation of
the aircraft to the glide slope. When the pointer is below the
center position, the aircraft is above the glide slope, and an
increased rate of descent is required. In most installations,
the azimuth card is a remote indicating compass driven by
a fluxgate; however, in few installations where a fluxgate is
not installed, or in emergency operation, the heading must
be checked against the magnetic compass occasionally and
reset with the course select knob.
Figure 3-37. Air Data Computer (Collins).

In Figure 3-38, the aircraft heading displayed on the rotating
azimuth card under the upper lubber line is North or 360°.
The course-indicating arrowhead shown is set to 020; the
tail indicates the reciprocal, 200°. The course deviation bar
operates with a VOR/Localizer (VOR/LOC) navigation
receiver to indicate left or right deviations from the course
selected with the course-indicating arrow, operating in the
same manner that the angular movement of a conventional
VOR/LOC needle indicates deviation from course.

Attitude Direction Indicator (ADI)
Advances in attitude instrumentation combine the gyro
horizon with other instruments such as the HSI, thereby
reducing the number of separate instruments to which the
pilot must devote attention. The attitude direction indicator
(ADI) is an example of such technological advancement.
A flight director incorporates the ADI within its system,
which is further explained below (Flight Director System).
However, an ADI need not have command cues; however,
it is normally equipped with this feature.
Flight Director System (FDS)
A Flight Director System (FDS) combines many instruments
into one display that provides an easily interpreted
understanding of the aircraft’s flight path. The computed
solution furnishes the steering commands necessary to obtain
and hold a desired path.
Major components of an FDS include an ADI, also called
a Flight Director Indicator (FDI), an HSI, a mode selector,
and a flight director computer. It should be noted that a
flight director in use does not infer the aircraft is being
manipulated by the autopilot (coupled), but is providing
steering commands that the pilot (or the autopilot, if coupled)
follows.

Figure 3-38. Horizontal Situation Indicator (HSI).

The desired course is selected by rotating the courseindicating arrow in relation to the azimuth card by means
of the course select knob. This gives the pilot a pictorial
presentation: the fixed aircraft symbol and course deviation
bar display the aircraft relative to the selected course, as
though the pilot were above the aircraft looking down.
The TO/FROM indicator is a triangular pointer. When the
indicator points to the head of the course arrow, it shows
that the course selected, if properly intercepted and flown,

Typical flight directors use one of two display systems for
steerage. The first is a set of command bars, one horizontal
and one vertical. The command bars in this configuration
are maintained in a centered position (much like a centered
glide slope). The second uses a miniature aircraft aligned to
a command cue.
A flight director displays steerage commands to the pilot on
the ADI. As previously mentioned, the flight director receives
its signals from one of various sources and provides that to the
ADI for steerage commands. The mode controller provides
signals through the ADI to drive the steering bars, e.g., the
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pilot flies the aircraft to place the delta symbol in the V of the
steering bars. “Command” indicators tell the pilot in which
direction and how much to change aircraft attitude to achieve
the desired result.
The computed command indications relieve the pilot of
many of the mental calculations required for instrument
flight. The yellow cue in the ADI [Figure 3-39] provides all
steering commands to the pilot. It is driven by a computer that
receives information from the navigation systems, the ADC,
AHRS, and other sources of data. The computer processes this
information, providing the pilot with a single cue to follow.
Following the cue provides the pilot with the necessary three-

Figure 3-40. Components of a Typical Flight Director System.

The components of a typical flight director include the mode
controller, ADI, HSI, and annunciator panel. These units are
illustrated in Figure 3-40.
The pilot may choose from among many modes including
the HDG (heading) mode, the VOR/LOC (localizer tracking)
mode, or the AUTO Approach (APP) or G/S (automatic
capture and tracking of instrument landing system (ILS)
localizers and glide path) mode. The auto mode has a fully
automatic pitch selection computer that takes into account
aircraft performance and wind conditions, and operates once
the pilot has reached the ILS glide slope. More sophisticated
systems allow more flight director modes.

Figure 3-39. A Typical Cue That a Pilot Would Follow.

dimensional flight trajectory to maintain the desired path.
One of the first widely used flight directors was developed
by Sperry and was called the Sperry Three Axis Attitude
Reference System (STARS). Developed in the 1960s, it was
commonly found on both commercial and business aircraft
alike. STARS (with a modification) and successive flight
directors were integrated with the autopilots and aircraft
providing a fully integrated flight system.
The flight director/autopilot system described below is
typical of installations in many general aviation aircraft.

3-24

Integrated Flight Control System
The integrated flight control system integrates and merges
various systems into a system operated and controlled by one
principal component. Figure 3-41 illustrates key components
of the flight control system that was developed from the
onset as a fully integrated system comprised of the airframe,
autopilot, and flight director system. This trend of complete
integration, once seen only in large commercial aircraft, are
now becoming common in the general aviation field.

Autopilot Systems
An autopilot is a mechanical means to control an aircraft
using electrical, hydraulic, or digital systems. Autopilots can
control three axes of the aircraft: roll, pitch, and yaw. Most
autopilots in general aviation control roll and pitch.
Autopilots also function using different methods. The first
is position based. That is, the attitude gyro senses the degree
of difference from a position such as wings level, a change
in pitch, or a heading change.

Figure 3-41. The S-TEC/Meggit Corporation Integrated Autopilot Installed in the Cirrus.

Determining whether a design is position based and/or rate
based lies primarily within the type of sensors used. In order
for an autopilot to possess the capability of controlling an
aircraft’s attitude (i.e., roll and pitch), that system must be
provided with constant information on the actual attitude
of that aircraft. This is accomplished by the use of several
different types of gyroscopic sensors. Some sensors are
designed to indicate the aircraft’s attitude in the form of
position in relation to the horizon, while others indicate rate
(position change over time).
Rate-based systems use the turn-and-bank sensor for the
autopilot system. The autopilot uses rate information on
two of the aircraft’s three axes: movement about the vertical
axis (heading change or yaw) and about the longitudinal
axis (roll). This combined information from a single sensor
is made possible by the 30° offset in the gyro’s axis to the
longitudinal axis.
Other systems use a combination of both position and ratebased information to benefit from the attributes of both systems
while newer autopilots are digital. Figure 3-42 illustrates an
autopilot by Century.
Figure 3-43 is a diagram layout of a rate-based autopilot by
S-Tec, which permits the purchaser to add modular capability
form basic wing leveling to increased capability.

Flight Management Systems (FMS)
In the mid-1970s, visionaries in the avionics industry such
as Hubert Naimer of Universal, and followed by others such
as Ed King, Jr., were looking to advance the technology of
aircraft navigation. As early as 1976, Naimer had a vision

Figure 3-42. An Autopilot by Century.

of a “Master Navigation System” that would accept inputs
from a variety of different types of sensors on an aircraft
and automatically provide guidance throughout all phases
of flight.
At that time aircraft navigated over relatively short distances
with radio systems, principally VOR or ADF. For long-range
flight inertial navigation systems (INS), Omega, Doppler,
and Loran were in common use. Short-range radio systems
usually did not provide area navigation capability. Longrange systems were only capable of en route point-to-point
navigation between manually entered waypoints described
as longitude and latitude coordinates, with typical systems
containing a limited number of waypoints.

3-25

Figure 3-43. A Diagram Layout of an Autopilot by S-Tec.

The laborious process of manually entering cryptic latitude
and longitude data for each flight waypoint created high
crew workloads and frequently resulted in incorrect data
entry. The requirement of a separate control panel for each
long-range system consumed precious flight deck space and
increased the complexity of interfacing the systems with
display instruments, flight directors, and autopilots.
The concept employed a master computer interfaced with all
of the navigation sensors on the aircraft. A common control
display unit (CDU) interfaced with the master computer would
provide the pilot with a single control point for all navigation
systems, thereby reducing the number of required flight deck
panels. Management of the various individual sensors would
be transferred from the pilot to the new computer.

such a system a pilot could quickly and accurately construct
a flight plan consisting of dozens of waypoints, avoiding
the tedious typing of data and the error potential of latitude/
longitude coordinates. Rather than simply navigating pointto-point, the master system would be able to maneuver the
aircraft, permitting use of the system for terminal procedures
including departures, arrivals, and approaches. The system
would be able to automate any aspect of manual pilot
navigation of the aircraft. When the first system, called the
UNS-1, was released by Universal in 1982, it was called a
flight management system (FMS). [Figure 3-44]

Since navigation sensors rarely agree exactly about position,
Naimer believed that blending all available sensor position
data through a highly sophisticated, mathematical filtering
system would produce a more accurate aircraft position. He
called the process output the “Best Computed Position.” By
using all available sensors to keep track of position, the system
could readily provide area navigation capability. The master
computer, not the individual sensors, would be integrated into
the airplane, greatly reducing wiring complexity.
To solve the problems of manual waypoint entry, a preloaded database of global navigation information would
be readily accessible by the pilot through the CDU. Using
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Figure 3-44. A Control Display Unit (CDU) Used to Control the

Flight Management System.

An FMS uses an electronic database of worldwide
navigational data including navigation aids, airways and
intersections, Standard Instrument Departures (SIDs),
Standard Terminal Arrival Routes (STARs), and Instrument
Approach Procedures (IAPs) together with pilot input through
a CDU to create a flight plan. The FMS provides outputs to
several aircraft systems including desired track, bearing and
distance to the active waypoint, lateral course deviation and
related data to the flight guidance system for the HSI displays,
and roll steering command for the autopilot/flight director
system. This allows outputs from the FMS to command
the airplane where to go and when and how to turn. To
support adaptation to numerous aircraft types, an FMS is
usually capable of receiving and outputting both analog and
digital data and discrete information. Currently, electronic
navigation databases are updated every 28 days.
The introduction of the Global Positioning System (GPS) has
provided extremely precise position at low cost, making GPS
the dominant FMS navigation sensor today. Currently, typical
FMS installations require that air data and heading information
be available electronically from the aircraft. This limits FMS
usage in smaller aircraft, but emerging technologies allow this
data from increasingly smaller and less costly systems.
Some systems interface with a dedicated Distance Measuring
Equipment (DME) receiver channel under the control of the
FMS to provide an additional sensor. In these systems, the
FMS determines which DME sites should be interrogated
for distance information using aircraft position and the
navigation database to locate appropriate DME sites. The
FMS then compensates aircraft altitude and station altitude
with the aid of the database to determine the precise distance
to the station. With the distances from a number of sites the
FMS can compute a position nearly as accurately as GPS.
Aimer visualized three-dimensional aircraft control with
an FMS. Modern systems provide Vertical Navigation
(VNAV) as well as Lateral Navigation (LNAV) allowing
the pilot to create a vertical flight profile synchronous with
the lateral flight plan. Unlike early systems, such as Inertial
Reference Systems (IRS) that were only suitable for en route
navigation, the modern FMS can guide an aircraft during
instrument approaches.

Electronic Flight Instrument Systems
Modern technology has introduced into aviation a new
method of displaying flight instruments, such as electronic
flight instrument systems, integrated flight deck displays, and
others. For the purpose of the practical test standards, any
flight instrument display that utilizes LCD or picture tube like
displays is referred to as “electronic flight instrument display”
and/or a glass flight deck. In general aviation there is typically
a primary flight display (PFD) and a multi-function display
(MFD). Although both displays are in many cases identical,
the PFD provides the pilot instrumentation necessary for
flight to include altitude, airspeed, vertical velocity, attitude,
heading and trim and trend information.
Glass flight decks (a term coined to describe electronic flight
instrument systems) are becoming more widespread as cost
falls and dependability continually increases. These systems
provide many advantages such as being lighter, more reliable,
no moving parts to wear out, consuming less power, and
replacing numerous mechanical indicators with a single glass
display. Because the versatility offered by glass displays is
much greater than that offered by analog displays, the use
of such systems will only increase with time until analog
systems are eclipsed.

Primary Flight Display (PFD)
PFDs provide increased situational awareness to the pilot by
replacing the traditional six instruments used for instrument
flight with an easy-to-scan display that provides the horizon,
airspeed, altitude, vertical speed, trend, trim, rate of turn
among other key relevant indications. Examples of PFDs
are illustrated in Figure 3-45.
Synthetic Vision
Synthetic vision provides a realistic depiction of the aircraft
in relation to terrain and flight path. Systems such as those
produced by Chelton Flight Systems, Universal Flight
Systems, and others provide for depictions of terrain and
course. Figure 3-46 is an example of the Chelton Flight
System providing both 3-dimensional situational awareness
and a synthetic highway in the sky, representing the desired
flight path. Synthetic vision is used as a PFD, but provides
guidance in a more normal, outside reference format.

Today, an FMS provides not only real-time navigation
capability but typically interfaces with other aircraft systems
providing fuel management, control of cabin briefing and
display systems, display of uplinked text and graphic weather
data and air/ground data link communications.

3-27

Figure 3-45. Two Primary Flight Displays (Avidyne on the Left and Garmin on the Right).

Advanced Technology Systems
Automatic Dependent Surveillance—Broadcast
(ADS-B)
Although standards for Automatic Dependent Surveillance
(Broadcast) (ADS-B) are still under continuing development,
the concept is simple: aircraft broadcast a message on
a regular basis, which includes their position (such as
latitude, longitude and altitude), velocity, and possibly
other information. Other aircraft or systems can receive this
information for use in a wide variety of applications. The
key to ADS-B is GPS, which provides three-dimensional
position of the aircraft.

Figure 3-46. The benefits of realistic visualization imagery, as

illustrated by Synthetic Vision manufactured by Chelton Flight
Systems. The system provides the pilot a realistic, real-time, threedimensional depiction of the aircraft and its relation to terrain
around it.

Multi-Function Display (MFD)
In addition to a PFD directly in front of the pilot, an MFD
that provides the display of information in addition to primary
flight information is used within the flight deck. [Figure 3-47]
Information such as a moving map, approach charts, Terrain
Awareness Warning System, and weather depiction can all
be illustrated on the MFD. For additional redundancy both
the PFD and MFD can display all critical information that
the other normally presents thereby providing redundancy
(using a reversionary mode) not normally found in general
aviation flight decks.

3-28

As an simplified example, consider air-traffic radar. The radar
measures the range and bearing of an aircraft. The bearing is
measured by the position of the rotating radar antenna when it
receives a reply to its interrogation from the aircraft, and the
range by the time it takes for the radar to receive the reply.
An ADS-B based system, on the other hand, would listen
for position reports broadcast by the aircraft. [Figure 3-48]
These position reports are based on satellite navigation
systems. These transmissions include the transmitting
aircraft’s position, which the receiving aircraft processes into
usable pilot information. The accuracy of the system is now
determined by the accuracy of the navigation system, not
measurement errors. Furthermore the accuracy is unaffected
by the range to the aircraft as in the case of radar. With radar,
detecting aircraft speed changes require tracking the data and
changes can only be detected over a period of several position
updates. With ADS-B, speed changes are broadcast almost
instantaneously and received by properly equipped aircraft.

Figure 3-47. Example of a Multi-Function Display (MFD).

Figure 3-48. Aircraft equipped with Automatic Dependent Surveillance—Broadcast (ADS-B) continuously broadcast their identification,

altitude, direction, and vertical trend. The transmitted signal carries significant information for other aircraft and ground stations alike.
Other ADS-equipped aircraft receive this information and process it in a variety of ways. It is possible that in a saturated environment
(assuming all aircraft are ADS equipped), the systems can project tracks for their respective aircraft and retransmit to other aircraft
their projected tracks, thereby enhancing collision avoidance. At one time, there was an Automatic Dependent Surveillance—Addressed
(ADS-A) and that is explained in the Pilot’s Handbook of Aeronautical Knowledge.

3-29

Additionally, other information can be obtained by properly
equipped aircraft to include notices to airmen (NOTAM),
weather, etc. [Figures 3-49 and 3-50] At the present time,
ADS-B is predominantly available along the east coast of
the United States where it is matured.

Safety Systems
Radio Altimeters
A radio altimeter, commonly referred to as a radar altimeter,
is a system used for accurately measuring and displaying the
height above the terrain directly beneath the aircraft. It sends
a signal to the ground and processes the timed information.

Figure 3-49. An aircraft equipped with ADS will receive identification, altitude in hundreds of feet (above or below using + or -), direction
of the traffic, and aircraft descent or climb using an up or down arrow. The yellow target is an illustration of how a non-ADS equipped
aircraft would appear on an ADS-equipped aircraft’s display.

Figure 3-50. An aircraft equipped with ADS has the ability to upload and display weather.

3-30

Its primary application is to provide accurate absolute altitude
information to the pilot during approach and landing. In
advanced aircraft today, the radar altimeter also provides its
information to other onboard systems such as the autopilot
and flight directors while they are in the glide slope capture
mode below 200-300 feet above ground level (AGL).
A typical system consists of a receiver-transmitter (RT)
unit, antenna(s) for receiving and transmitting the signal,
and an indicator. [Figure 3-51] Category II and III precision
approach procedures require the use of a radar altimeter and
specify the exact minimum height above the terrain as a
decision height (DH) or radio altitude (RA).

Figure 3-52. Coverage Provided by a Traffic Information System.

of other aircraft [Figures 3-55, 3-56, and 3-57] and are cost
effective alternatives to TCAS equipage for smaller aircraft.
Figure 3-51. Components of a Radar Altimeter.

Traffic Advisory Systems

Traffic Information System
The Traffic Information Service (TIS) is a ground-based
service providing information to the flight deck via data
link using the S-mode transponder and altitude encoder. TIS
improves the safety and efficiency of “see and avoid” flight
through an automatic display that informs the pilot of nearby
traffic. The display can show location, direction, altitude
and the climb/descent trend of other transponder-equipped
aircraft. TIS provides estimated position, altitude, altitude
trend, and ground track information for up to several aircraft
simultaneously within about 7 NM horizontally, 3,500 feet
above and 3,500 feet below the aircraft. [Figure 3-52] This
data can be displayed on a variety of MFDs. [Figure 3-53]
Figure 3-54 displays the pictorial concept of the traffic
information system. Noteworthy is the requirement to have
Mode S and that the ground air traffic station processes the
Mode S signal.

Traffic Alert Systems
Traffic alert systems receive transponder information from
nearby aircraft to help determine their relative position to the
equipped aircraft. They provide three-dimensional location

Traffic Avoidance Systems
Traffic Alert and Collision Avoidance System (TCAS)
The TCAS is an airborne system developed by the FAA that
operates independently from the ground-based ATC system.
TCAS was designed to increase flight deck awareness of
proximate aircraft and to serve as a “last line of defense” for
the prevention of mid-air collisions.
There are two levels of TCAS systems. TCAS I was developed
to accommodate the general aviation (GA) community and
the regional airlines. This system issues traffic advisories
(TAs) to assist pilots in visual acquisition of intruder aircraft.
TCAS I provides approximate bearing and relative altitude
of aircraft with a selectable range. It provides the pilot
with traffic advisory (TA) alerting him or her to potentially
conflicting traffic. The pilot then visually acquires the traffic
and takes appropriate action for collision avoidance.
TCAS II is a more sophisticated system which provides the
same information of TCAS I. It also analyzes the projected
flight path of approaching aircraft and issues resolution
advisories (RAs) to the pilot to resolve potential mid-air
collisions. Additionally, if communicating with another
TCAS II equipped aircraft, the two systems coordinate the
resolution alerts provided to their respective flight crews.
[Figure 3-58]

3-31

Figure 3-53. Multi-Function Display (MFD).

Figure 3-54. Concept of the Traffic Information System.

3-32

Figure 3-56. A Skywatch System.
Figure 3-55. Theory of a Typical Alert System.

Figure 3-57. Alert System by Avidyne (Ryan).

3-33

While on final for landing with the landing gear inadvertently
up, the crew failed to heed the GPWS warning as the aircraft
crossed a large berm close to the threshold. In fact, the crew
attempted without success to shut the system down and attributed
the signal to a malfunction. Only after the mishap did the crew
realize the importance of the GPWS warning.

Figure 3-58. An example of a resolution advisory being provided

the pilot. In this case, the pilot is requested to climb, with 1,200
feet being the appropriate rate of ascent to avoid traffic conflict.
This visual indication plus the aural warning provide the pilot
with excellent traffic awareness that augments see and avoid
practices.

Terrain Alerting Systems
Ground Proximity Warning System (GPWS)
An early application of technology to reduce CFIT was the
GPWS. In airline use since the early 1970s, GPWS uses the
radio altimeter, speed, and barometric altitude to determine the
aircraft’s position relative to the ground. The system uses this
information in determining aircraft clearance above the Earth
and provides limited predictability about aircraft position
relative to rising terrain. It does this based upon algorithms
within the system and developed by the manufacturer for
different airplanes or helicopters. However, in mountainous
areas the system is unable to provide predictive information
due to the unusual slope encountered.
This inability to provide predictive information was evidenced
in 1999 when a DH-7 crashed in South America. The crew
had a GPWS onboard, but the sudden rise of the terrain
rendered it ineffective; the crew continued unintentionally
into a mountain with steep terrain. Another incident involved
Secretary of Commerce Brown who, along with all on board,
was lost when the crew flew over rapidly rising terrain where
the GPWS capability is offset by terrain gradient. However,
the GPWS is tied into and considers landing gear status, flap
position, and ILS glide slope deviation to detect unsafe aircraft
operation with respect to terrain, excessive descent rate,
excessive closure rate to terrain, unsafe terrain clearance while
not in a landing configuration, excessive deviation below an
ILS glide slope. It also provides advisory callouts.
Generally, the GPWS is tied into the hot bus bar of the electrical
system to prevent inadvertent switch off. This was demonstrated
in an accident involving a large four-engine turboprop airplane.
3-34

Terrain Awareness and Warning System (TAWS)
A TAWS uses GPS positioning and a database of terrain and
obstructions to provide true predictability of the upcoming
terrain and obstacles. The warnings it provides pilots are
both aural and visual, instructing the pilot to take specific
action. Because TAWS relies on GPS and a database of
terrain/obstacle information, predictability is based upon
aircraft location and projected location. The system is time
based and therefore compensates for the performance of the
aircraft and its speed. [Figure 3-59]
Head-Up Display (HUD)
The HUD is a display system that provides a projection of
navigation and air data (airspeed in relation to approach
reference speed, altitude, left/right and up/down glide slope)
on a transparent screen between the pilot and the windshield.
The concept of a HUD is to diminish the shift between
looking at the instrument panel and outside. Virtually any
information desired can be displayed on the HUD if it is
available in the aircraft’s flight computer. The display for
the HUD can be projected on a separate panel near the
windscreen or as shown in Figure 3-60 on an eye piece. Other
information may be displayed, including a runway target in
relation to the nose of the aircraft, which allows the pilot to
see the information necessary to make the approach while
also being able to see out the windshield.

Required Navigation Instrument System
Inspection
Systems Preflight Procedures
Inspecting the instrument system requires a relatively small
part of the total time required for preflight activities, but its
importance cannot be overemphasized. Before any flight
involving aircraft control by instrument reference, the pilot
should check all instruments and their sources of power
for proper operation. NOTE: The following procedures are
appropriate for conventional aircraft instrument systems.
Aircraft equipped with electronic instrument systems utilize
different procedures.

Figure 3-59. A six-frame sequence illustrating the manner in which TAWS operates. A TAWS installation is aircraft specific and provides
warnings and cautions based upon time to potential impact with terrain rather than distance. The TAWS is illustrated in an upper left
window while aircrew view is provided out of the windscreen. illustrates the aircraft in relation to the outside terrain while and
illustrate the manner in which the TAWS system displays the terrain.
is providing a caution of terrain to be traversed, while
provides an illustration of a warning with an aural and textural advisory (red) to pull up.
also illustrates a pilot taking appropriate
action (climb in this case) while illustrates that a hazard is no longer a factor.

3-35

Figure 3-60. A Head-Up Display.

Before Engine Start
1.

2.

3.

Walk-around inspection: Check the condition of all
antennas and check the pitot tube for the presence
of any obstructions and remove the cover. Check
the static ports to be sure they are free from dirt
and obstructions, and ensure there is nothing on the
structure near the ports that would disturb the air
flowing over them.
Aircraft records: Confirm that the altimeter and static
system have been checked and found within approved
limits within the past 24 calendar months. Check the
replacement date for the emergency locator transmitter
(ELT) batteries noted in the maintenance record, and
be sure they have been replaced within this time
interval.
Preflight paperwork: Check the Airport/Facility
Directory (A/FD) and all Notices to Airmen
(NOTAMs) for the condition and frequencies of all the
navigation aid (NAVAIDs) that are used on the flight.
Handbooks, en route charts, approach charts, computer
and flight log should be appropriate for the departure,
en route, destination, and alternate airports.

6.

ASI: Proper reading, as applicable. If electronic
flight instrumentation is installed, check emergency
instrument.

7.

Attitude indicator: Uncaged, if applicable. If electronic
flight instrumentation is installed, check emergency
system to include its battery as appropriate.

8.

Altimeter: Set the current altimeter setting and ensure
that the pointers indicate the elevation of the airport.

9.

VSI: Zero indication, as applicable (if electronic flight
instrumentation is installed).

10. Heading indicator: Uncaged, if applicable.
11. Turn coordinator: If applicable, miniature aircraft
level, ball approximately centered (level terrain).
12. Magnetic compass: Full of fluid and the correction
card is in place and current.
13. Clock: Set to the correct time and running.
14. Engine instruments: Proper markings and readings,
as applicable if electronic flight instrumentation is
installed.

4.

Radio equipment: Switches off.

15. Deicing and anti-icing equipment: Check availability
and fluid quantity.

5.

Suction gauge: Proper markings as applicable if
electronic flight instrumentation is installed.

16. Alternate static-source valve: Be sure it can be opened
if needed, and that it is fully closed.

3-36

17. Pitot tube heater: Check by watching the ammeter
when it is turned on, or by using the method specified
in the POH/AFM.

to the published field elevation during the preflight
instrument check.
7.

VSI: The instrument should read zero. If it does not,
tap the panel gently. If an electronic flight instrument
system is installed, consult the flight manual for proper
procedures.

8.

Engine instruments: Check for proper readings.

9.

Radio equipment: Check for proper operation and set
as desired.

After Engine Start
1.

2.

3.

4.

5.

6.

When the master switch is turned on, listen to the
gyros as they spin up. Any hesitation or unusual noises
should be investigated before flight.
Suction gauge or electrical indicators: Check the
source of power for the gyro instruments. The suction
developed should be appropriate for the instruments
in that particular aircraft. If the gyros are electrically
driven, check the generators and inverters for proper
operation.
Magnetic compass: Check the card for freedom of
movement and confirm the bowl is full of fluid.
Determine compass accuracy by comparing the
indicated heading against a known heading (runway
heading) while the airplane is stopped or taxiing
straight. Remote indicating compasses should also be
checked against known headings. Note the compass
card correction for the takeoff runway heading.
Heading indicator: Allow 5 minutes after starting
engines for the gyro to spin up. Before taxiing, or
while taxiing straight, set the heading indicator to
correspond with the magnetic compass heading. A
slaved gyrocompass should be checked for slaving
action and its indications compared with those of the
magnetic compass. If an electronic flight instrument
system is installed, consult the flight manual for proper
procedures.
Attitude indicator: Allow the same time as noted
above for gyros to spin up. If the horizon bar erects
to the horizontal position and remains at the correct
position for the attitude of the airplane, or if it begins
to vibrate after this attitude is reached and then slowly
stops vibrating altogether, the instrument is operating
properly. If an electronic flight instrument system
is installed, consult the flight manual for proper
procedures.

10. Deicing and anti-icing equipment: Check operation.
Taxiing and Takeoff
1.

Turn coordinator: During taxi turns, check the
miniature aircraft for proper turn indications. The ball
or slip/skid should move freely. The ball or slip/skid
indicator should move opposite to the direction of
turns. The turn instrument should indicate the direction
of the turn. While taxiing straight, the miniature
aircraft (as appropriate) should be level.

2.

Heading indicator: Before takeoff, recheck the heading
indicator. If the magnetic compass and deviation card
are accurate, the heading indicator should show the
known taxiway or runway direction when the airplane
is aligned with them (within 5°).

3.

Attitude indicator: If the horizon bar fails to remain
in the horizontal position during straight taxiing, or
tips in excess of 5° during taxi turns, the instrument is
unreliable. Adjust the miniature aircraft with reference
to the horizon bar for the particular airplane while on
the ground. For some tricycle-gear airplanes, a slightly
nose-low attitude on the ground gives a level flight
attitude at normal cruising speed.

Engine Shut Down
When shutting down the engine, note any abnormal
instrument indications.

Altimeter: With the altimeter set to the current reported
altimeter setting, note any variation between the
known field elevation and the altimeter indication. If
the indication is not within 75 feet of field elevation,
the accuracy of the altimeter is questionable and
the problem should be referred to a repair station
for evaluation and possible correction. Because the
elevation of the ramp or hangar area might differ
significantly from field elevation, recheck when in
the run-up area if the error exceeds 75 feet. When
no altimeter setting is available, set the altimeter
3-37

3-38

Chapter 4, Section I

Airplane Attitude
Instrument Flying
Using Analog Instrumentation
Introduction
Attitude instrument flying is defined as the control of an
aircraft’s spatial position by using instruments rather than
outside visual references. Today’s aircraft come equipped
with analog and/or digital instruments. Analog instrument
systems are mechanical and operate with numbers
representing directly measurable quantities, such as a watch
with a sweep second hand. In contrast, digital instrument
systems are electronic and operate with numbers expressed
in digits. Although more manufacturers are providing aircraft
with digital instrumentation, analog instruments remain more
prevalent. This section acquaints the pilot with the use of
analog flight instruments.

4-1

Any flight, regardless of the aircraft used or route flown,
consists of basic maneuvers. In visual flight, aircraft attitude
is controlled by using certain reference points on the aircraft
with relation to the natural horizon. In instrument flight,
the aircraft attitude is controlled by reference to the flight
instruments. Proper interpretation of the flight instruments
provides essentially the same information that outside
references do in visual flight. Once the role of each instrument
in establishing and maintaining a desired aircraft attitude is
learned, a pilot is better equipped to control the aircraft in
emergency situations involving failure of one or more key
instruments.

Learning Methods
The two basic methods used for learning attitude instrument
flying are “control and performance” and “primary and
supporting.” Both methods utilize the same instruments
and responses for attitude control. They differ in their
reliance on the attitude indicator and interpretation of other
instruments.
Attitude Instrument Flying Using the Control and
Performance Method
Aircraft performance is achieved by controlling the aircraft
attitude and power. Aircraft attitude is the relationship
of both the aircraft’s pitch and roll axes in relation to the
Earth’s horizon. An aircraft is flown in instrument flight by
controlling the attitude and power, as necessary, to produce
both controlled and stabilized flight without reference to a
visible horizon. This overall process is known as the control
and performance method of attitude instrument flying.
Starting with basic instrument maneuvers, this process can
be applied through the use of control, performance, and
navigation instruments, resulting in a smooth flight, from
takeoff to landing.

Figure 4-1. Control Instruments.

4-2

Control Instruments
The control instruments display immediate attitude and power
indications and are calibrated to permit those respective
adjustments in precise increments. In this discussion, the
term “power” is used in place of the more technically correct
term “thrust or drag relationship.” Control is determined
by reference to the attitude and power indicators. Power
indicators vary with aircraft and may include manifold
pressure, tachometers, fuel flow, etc. [Figure 4-1]

Performance Instruments
The performance instruments indicate the aircraft’s actual
performance. Performance is determined by reference to the
altimeter, airspeed or vertical speed indicator (VSI), heading
indicator, and turn-and-slip indicator. [Figure 4-2]

Navigation Instruments
The navigation instruments indicate the position of the aircraft
in relation to a selected navigation facility or fix. This group
of instruments includes various types of course indicators,
range indicators, glide-slope indicators, and bearing pointers.
[Figure 4-3] Newer aircraft with more technologically
advanced instrumentation provide blended information,
giving the pilot more accurate positional information.

Procedural Steps in Using Control and
Performance
1.

Establish an attitude and power setting on the
control instruments that results in the desired
performance. Known or computed attitude changes
and approximated power settings helps to reduce the
pilot’s workload.

2.

Trim (fine tune the control forces) until control
pressures are neutralized. Trimming for hands-off
flight is essential for smooth, precise aircraft control.

It allows a pilot to attend to other flight deck duties
with minimum deviation from the desired attitude.
3.

Cross-check the performance instruments to determine
if the established attitude or power setting is providing
the desired performance. The cross-check involves
both seeing and interpreting. If a deviation is noted,
determine the magnitude and direction of adjustment
required to achieve the desired performance.

4.

Adjust the attitude and/or power setting on the control
instruments as necessary.

Aircraft Control During Instrument Flight
Attitude Control
Proper control of aircraft attitude is the result of proper use
of the attitude indicator, knowledge of when to change the

Figure 4-2. Performance Instruments.

Figure 4-3. Flight Panel Instrumentation.

4-3

attitude, and then smoothly changing the attitude a precise
amount. The attitude reference provides an immediate, direct,
and corresponding indication of any change in aircraft pitch
or bank attitude.
Pitch Control
Changing the “pitch attitude” of the miniature aircraft or
fuselage dot by precise amounts in relation to the horizon
makes pitch changes. These changes are measured in degrees
or fractions thereof, or bar widths depending upon the type of
attitude reference. The amount of deviation from the desired
performance determines the magnitude of the correction.
Bank Control
Bank changes are made by changing the “bank attitude” or
bank pointers by precise amounts in relation to the bank scale.
The bank scale is normally graduated at 0°, 10°, 20°, 30°,
60°, and 90° and is located at the top or bottom of the attitude
reference. Normally, use a bank angle that approximates the
degrees to turn, not to exceed 30°.
Power Control
Proper power control results from the ability to smoothly
establish or maintain desired airspeeds in coordination
with attitude changes. Power changes are made by throttle
adjustments and reference to the power indicators. Power
indicators are not affected by such factors as turbulence,
improper trim, or inadvertent control pressures. Therefore,
in most aircraft little attention is required to ensure the power
setting remains constant.
Experience in an aircraft teaches a pilot approximately how
far to move the throttle to change the power a given amount.
Power changes are made primarily by throttle movement,
followed by an indicator cross-check to establish a more
precise setting. The key is to avoid fixating on the indicators

Figure 4-4. Pitch Instruments.

4-4

while setting the power. Knowledge of approximate power
settings for various flight configurations helps the pilot avoid
overcontrolling power.
Attitude Instrument Flying Using the Primary and
Supporting Method
Another basic method for teaching attitude instrument flying
classifies the instruments as they relate to control function as
well as aircraft performance. All maneuvers involve some
degree of motion about the lateral (pitch), longitudinal (bank/
roll), and vertical (yaw) axes. Attitude control is stressed in
this handbook in terms of pitch control, bank control, power
control, and trim control. Instruments are grouped as they
relate to control function and aircraft performance as pitch
control, bank control, power control, and trim.

Pitch Control
Pitch control is controlling the rotation of the aircraft about the
lateral axis by movement of the elevators. After interpreting
the pitch attitude from the proper flight instruments, exert
control pressures to effect the desired pitch attitude with
reference to the horizon. These instruments include the
attitude indicator, altimeter, VSI, and airspeed indicator.
[Figure 4-4] The attitude indicator displays a direct indication
of the aircraft’s pitch attitude while the other pitch attitude
control instruments indirectly indicate the pitch attitude of
the aircraft.
Attitude Indicator
The pitch attitude control of an aircraft controls the angular
relationship between the longitudinal axis of the aircraft and
the actual horizon. The attitude indicator gives a direct and
immediate indication of the pitch attitude of the aircraft. The
aircraft controls are used to position the miniature aircraft
in relation to the horizon bar or horizon line for any pitch
attitude required. [Figure 4-5]

Figure 4-6. Pitch Correction Using the Attitude Indicator.

Altimeter
If the aircraft is maintaining level flight, the altimeter needles
maintain a constant indication of altitude. If the altimeter
indicates a loss of altitude, the pitch attitude must be adjusted
upward to stop the descent. If the altimeter indicates a gain
in altitude, the pitch attitude must be adjusted downward to
stop the climb. [Figure 4-7] The altimeter can also indicate
the pitch attitude in a climb or descent by how rapidly the
needles move. A minor adjustment in pitch attitude may be
made to control the rate at which altitude is gained or lost.
Pitch attitude is used only to correct small altitude changes
caused by external forces, such as turbulence or up and
down drafts.

Figure 4-5. Attitude Indicator.

The miniature aircraft should be placed in the proper position
in relation to the horizon bar or horizon line before takeoff.
The aircraft operator’s manual explains this position. As soon
as practicable in level flight and at desired cruise airspeed,
the miniature aircraft should be moved to a position that
aligns its wings in front of the horizon bar or horizon line.
This adjustment can be made anytime varying loads or other
conditions indicate a need. Otherwise, the position of the
miniature aircraft should not be changed for flight at other than
cruise speed. This is to make sure that the attitude indicator
displays a true picture of pitch attitude in all maneuvers.
When using the attitude indicator in applying pitch attitude
corrections, control pressure should be extremely light.
Movement of the horizon bar above or below the miniature
aircraft of the attitude indicator in an airplane should not
exceed one-half the bar width. [Figure 4-6] If further change
is required, an additional correction of not more than one-half
horizon bar wide normally counteracts any deviation from
normal flight.

Figure 4-7. Pitch Correction Using the Altimeter.

Vertical Speed Indicator (VSI)
In flight at a constant altitude, the VSI (sometimes referred
to as vertical velocity indicator or rate-of-climb indicator)
remains at zero. If the needle moves above zero, the pitch
attitude must be adjusted downward to stop the climb and
return to level flight. Prompt adjustments to the changes in
the indications of the VSI can prevent any significant change
in altitude. [Figure 4-8] Turbulent air causes the needle to
fluctuate near zero. In such conditions, the average of the

4-5

fluctuations should be considered as the correct reading.
Reference to the altimeter helps in turbulent air because it is
not as sensitive as the VSI.
Vertical speed is represented in feet per minute (fpm).
[Figure 4-8] The face of the instrument is graduated with
numbers such as 1, 2, 3, etc. These represent thousands of
feet up or down in a minute. For instance, if the pointer is
aligned with .5 (1/2 of a thousand, or 500 fpm) the aircraft
will climb 500 feet in one minute. The instrument is
divided into two regions, one for climbing (up) and one for
descending (down).

indicated. For example, if attempting to regain lost altitude
at the rate of 500 fpm, a reading of more than 700 fpm
would indicate overcontrolling. Initial movement of the
needle indicates the trend of vertical movement. The time
for the VSI to reach its maximum point of deflection after a
correction is called lag. The lag is proportional to speed and
magnitude of pitch change. In an airplane, overcontrolling
may be reduced by relaxing pressure on the controls, allowing
the pitch attitude to neutralize. In some helicopters with
servo-assisted controls, no control pressures are apparent.
In this case, overcontrolling can be reduced by reference to
the attitude indicator.
Some aircraft are equipped with an instantaneous vertical
speed indicator (IVSI). The letters “IVSI” appear on the face
of the indicator. This instrument assists in interpretation by
instantaneously indicating the rate of climb or descent at a
given moment with little or no lag as displayed in a VSI.
Occasionally, the VSI is slightly out of calibration and
indicates a gradual climb or descent when the aircraft is in
level flight. If readjustments cannot be accomplished, the error
in the indicator should be considered when the instrument is
used for pitch control. For example, an improperly set VSI
may indicate a descent of 100 fpm when the aircraft is in
level flight. Any deviation from this reading would indicate
a change in pitch attitude.

Figure 4-8. Vertical Speed Indicator.

During turbulence, it is not uncommon to see large
fluctuations on the VSI. It is important to remember that small
corrections should be employed to avoid further exacerbating
a potentially divergent situation.
Overcorrecting causes the aircraft to overshoot the desired
altitude; however, corrections should not be so small that
the return to altitude is unnecessarily prolonged. As a guide,
the pitch attitude should produce a rate of change on the VSI
about twice the size of the altitude deviation. For example,
if the aircraft is 100 feet off the desired altitude, a 200 fpm
rate of correction would be used.
During climbs or descents, the VSI is used to change the
altitude at a desired rate. Pitch attitude and power adjustments
are made to maintain the desired rate of climb or descent on
the VSI.
When pressure is applied to the controls and the VSI shows
an excess of 200 fpm from that desired, overcontrolling is

4-6

Airspeed Indicator
The airspeed indicator gives an indirect reading of the pitch
attitude. With a constant power setting and a constant altitude,
the aircraft is in level flight and airspeed remains constant. If the
airspeed increases, the pitch attitude has lowered and should be
raised. [Figure 4-9] If the airspeed decreases, the pitch attitude
has moved higher and should be lowered. [Figure 4-10] A
rapid change in airspeed indicates a large change in pitch; a
slow change in airspeed indicates a small change in pitch.
Although the airspeed indicator is used as a pitch instrument,
it may be used in level fight for power control. Changes in
pitch are reflected immediately by a change in airspeed. There
is very little lag in the airspeed indicator.
Pitch Attitude Instrument Cross-Check
The altimeter is an important instrument for indicating pitch
attitude in level flight except when used in conditions of
exceptionally strong vertical currents, such as thunderstorms.
With proper power settings, any of the pitch attitude
instruments can be used to hold reasonably level flight
attitude. However, only the altimeter gives the exact altitude
information. Regardless of which pitch attitude control
instrument indicates a need for a pitch attitude adjustment,
the attitude indicator, if available, should be used to make the

Figure 4-9. Pitch attitude has lowered.

Figure 4-10. Pitch attitude has moved higher.

adjustment. Common errors in pitch attitude control are:

Heading Indicator
The heading indicator supplies the pertinent bank and
heading information and is considered a primary instrument
for bank.

•

Overcontrolling,

•

Improperly using power, and

•

Failing to adequately cross-check the pitch attitude
instruments and take corrective action when pitch
attitude change is needed

Bank Control
Bank control is controlling the angle made by the wing and
the horizon. After interpreting the bank attitude from the
appropriate instruments, exert the necessary pressures to move
the ailerons and roll the aircraft about the longitudinal axis.
As illustrated in Figure 4-11, these instruments include:
Attitude Indicator
As previously discussed, the attitude indicator is the only
instrument that portrays both instantly and directly the actual
flight attitude and is the basic attitude reference.

Magnetic Compass
The magnetic compass provides heading information and is
considered a bank instrument when used with the heading
indicator. Care should be exercised when using the magnetic
compass as it is affected by acceleration, deceleration in flight
caused by turbulence, climbing, descending, power changes,
and airspeed adjustments. Additionally, the magnetic compass
indication will lead and lag in its reading depending upon
the direction of turn. As a result, acceptance of its indication
should be considered with other instruments that indicate turn
information. These include the already mentioned attitude
and heading indicators as well as the turn-and-slip indicator
and turn coordinator.

Figure 4-11. Bank Instruments.

4-7

Turn Coordinator/Turn-and-Slip Indicator
Both of these instruments provide turn information.
[Figure 4-12] The turn coordinator provides both bank rate
and then turn rate once stabilized. The turn-and-slip indicator
provides only turn rate.

Figure 4-12. Turn Coordinator and Turn-and-Slip Indicator.

Power Control
A power change to adjust airspeed may cause movement
around some or all of the aircraft axes. The amount and
direction of movement depends on how much or how rapidly
the power is changed, whether single-engine or multiengine
airplane or helicopter. The effect on pitch attitude and
airspeed caused by power changes during level flight is
illustrated in Figures 4-13 and 4-14. During or immediately
after adjusting the power control(s), the power instruments
should be cross-checked to see if the power adjustment is as
desired. Whether or not the need for a power adjustment is
indicated by another instrument(s), adjustment is made by
cross-checking the power instruments. Aircraft are powered
by a variety of power plants, each power plant having
certain instruments that indicate the amount of power being
applied to operate the aircraft. During instrument flight,
these instruments must be used to make the required power
adjustments.

As illustrated in Figure 4-15, power indicator instruments
include:
Airspeed Indicator
The airspeed indicator provides an indication of power
best observed initially in level flight where the aircraft
is in balance and trim. If in level flight the airspeed is
increasing, it can generally be assumed that the power has
increased, necessitating the need to adjust power or re-trim
the aircraft.
Engine Instruments
Engine instruments, such as the manifold pressure (MP)
indicator, provide an indication of aircraft performance for a
given setting under stable conditions. If the power conditions
are changed, as reflected in the respective engine instrument
readings, there is an affect upon the aircraft performance,
either an increase or decrease of airspeed. When the propeller
rotational speed (revolutions per minute (RPM) as viewed
on a tachometer) is increased or decreased on fixed-pitch
propellers, the performance of the aircraft reflects a gain or
loss of airspeed as well.

Trim Control
Proper trim technique is essential for smooth and accurate
instrument flying and utilizes instrumentation illustrated in
Figure 4-16. The aircraft should be properly trimmed while
executing a maneuver. The degree of flying skill, which
ultimately develops, depends largely upon how well the
aviator learns to keep the aircraft trimmed.

Airplane Trim
An airplane is correctly trimmed when it is maintaining a
desired attitude with all control pressures neutralized. By
relieving all control pressures, it is much easier to maintain
the aircraft at a certain attitude. This allows more time to
devote to the navigation instruments and additional flight
deck duties.

Figure 4-13. An Increase in Power Inscreasing Airpseed Accordingly in Level Flight.

4-8

Figure 4-14. Pitch Control and Power Adjustment Required To Bring Aircraft to Level Flight.

Figure 4-15. Power Instruments.

Figure 4-16. Trim Instruments.

4-9

An aircraft is placed in trim by:
•

Applying control pressure(s) to establish a desired
attitude. Then, the trim is adjusted so that the aircraft
maintains that attitude when flight controls are
released. The aircraft is trimmed for coordinated flight
by centering the ball of the turn-and-slip indicator.

•

Moving the rudder trim in the direction where the
ball is displaced from center. Aileron trim may then
be adjusted to maintain a wings-level attitude.

•

Using balanced power or thrust when possible to aid
in maintaining coordinated flight. Changes in attitude,
power, or configuration may require trim adjustments.
Use of trim alone to establish a change in aircraft
attitude usually results in erratic aircraft control.
Smooth and precise attitude changes are best attained
by a combination of control pressures and subsequent
trim adjustments. The trim controls are aids to smooth
aircraft control.

Helicopter Trim
A helicopter is placed in trim by continually cross-checking
the instruments and performing the following:
•

Using the cyclic centering button. If the helicopter is so
equipped, this relieves all possible cyclic pressures.

•

Using the pedal adjustment to center the ball of the
turn indicator. Pedal trim is required during all power
changes and is used to relieve all control pressures
held after a desired attitude has been attained.

An improperly trimmed helicopter requires constant control
pressures, produces tension, distracts attention from crosschecking, and contributes to abrupt and erratic attitude
control. The pressures felt on the controls should be only
those applied while controlling the helicopter.
Adjust the pitch attitude, as airspeed changes, to maintain
desired attitude for the maneuver being executed. The bank
must be adjusted to maintain a desired rate of turn, and the
pedals must be used to maintain coordinated flight. Trim must
be adjusted as control pressures indicate a change is needed.
Example of Primary and Support Instruments
Straight-and-level flight at a constant airspeed means that an
exact altitude is to be maintained with zero bank (constant
heading). The primary pitch, bank, and power instruments
used to maintain this flight condition are:
•

Altimeter—supplies the most pertinent altitude
information and is primary for pitch.

•

Heading Indicator—supplies the most pertinent bank
or heading information and is primary for bank.

4-10

•

Airspeed Indicator—supplies the most pertinent
information concerning performance in level flight
in terms of power output and is primary for power.

Although the attitude indicator is the basic attitude reference,
the concept of primary and supporting instruments does not
devalue any particular flight instrument, when available, in
establishing and maintaining pitch-and-bank attitudes. It is the
only instrument that instantly and directly portrays the actual
flight attitude. It should always be used, when available, in
establishing and maintaining pitch-and-bank attitudes. The
specific use of primary and supporting instruments during
basic instrument maneuvers is presented in more detail in
Chapter 5, Airplane Basic Flight Maneuvers.

Fundamental Skills
During attitude instrument training, two fundamental flight
skills must be developed. They are instrument cross-check
and instrument interpretation, both resulting in positive
aircraft control. Although these skills are learned separately
and in deliberate sequence, a measure of proficiency in
precision flying is the ability to integrate these skills into
unified, smooth, positive control responses to maintain any
prescribed flight path.
Instrument Cross-Check
The first fundamental skill is cross-checking (also called
“scanning” or “instrument coverage”). Cross-checking is the
continuous and logical observation of instruments for attitude
and performance information. In attitude instrument flying,
the pilot maintains an attitude by reference to instruments,
producing the desired result in performance. Observing and
interpreting two or more instruments to determine attitude and
performance of an aircraft is called cross-checking. Although
no specific method of cross-checking is recommended, those
instruments that give the best information for controlling the
aircraft in any given maneuver should be used. The important
instruments are the ones that give the most pertinent
information for any particular phase of the maneuver. These
are usually the instruments that should be held at a constant
indication. The remaining instruments should help maintain
the important instruments at the desired indications, which
is also true in using the emergency panel.
Cross-checking is mandatory in instrument flying. In
visual flight, a level attitude can be maintained by outside
references. However, even then the altimeter must be checked
to determine if altitude is being maintained. Due to human
error, instrument error, and airplane performance differences
in various atmospheric and loading conditions, it is impossible
to establish an attitude and have performance remain constant
for a long period of time. These variables make it necessary

for the pilot to constantly check the instruments and make
appropriate changes in airplane attitude using cross-checking
of instruments. Examples of cross-checking are explained in
the following paragraphs.
Selected Radial Cross-Check
When the selected radial cross-check is used, a pilot spends
80 to 90 percent of flight time looking at the attitude indicator,
taking only quick glances at the other flight instruments (for
this discussion, the five instruments surrounding the attitude
indicator are called the flight instruments). With this method,
the pilot’s eyes never travel directly between the flight
instruments but move by way of the attitude indicator. The
maneuver being performed determines which instruments to
look at in the pattern. [Figure 4-17]
Inverted-V Cross-Check
In the inverted-V cross-check, the pilot scans from the
attitude indicator down to the turn coordinator, up to the
attitude indicator, down to the VSI, and back up to the attitude
indicator. [Figure 4-18]
Rectangular Cross-Check
In the rectangular cross-check, the pilot scans across
the top three instruments (airspeed indicator, attitude
indicator, and altimeter) and then drops down to scan the
bottom three instruments (VSI, heading indicator, and

turn instrument). This scan follows a rectangular path
(clockwise or counterclockwise rotation is a personal choice).
[Figure 4-19]
This cross-checking method gives equal weight to the
information from each instrument, regardless of its
importance to the maneuver being performed. However, this
method lengthens the time it takes to return to an instrument
critical to the successful completion of the maneuver.

Common Cross-Check Errors
A beginner might cross-check rapidly, looking at the
instruments without knowing exactly what to look for. With
increasing experience in basic instrument maneuvers and
familiarity with the instrument indications associated with
them, a pilot learns what to look for, when to look for it,
and what response to make. As proficiency increases, a pilot
cross-checks primarily from habit, suiting scanning rate and
sequence to the demands of the flight situation. Failure to
maintain basic instrument proficiency through practice can
result in many of the following common scanning errors,
both during training and at any subsequent time.
Fixation, or staring at a single instrument, usually occurs for
a reason, but has poor results. For example, a pilot may stare
at the altimeter reading 200 feet below the assigned altitude,
and wonder how the needle got there. While fixated on the

Figure 4-17. Radial Cross-Check.

4-11

Figure 4-18. Inverted-V Cross-Check.

Figure 4-19. Rectangular Cross-Check.

4-12

instrument, increasing tension may be unconsciously exerted
on the controls, which leads to an unnoticed heading change
that leads to more errors. Another common fixation is likely
when initiating an attitude change. For example, a shallow
bank is established for a 90° turn and, instead of maintaining
a cross-check of other pertinent instruments, the pilot stares at
the heading indicator throughout the turn. Since the aircraft is
turning, there is no need to recheck the heading indicator for
approximately 25 seconds after turn entry. The problem here
may not be entirely due to cross-check error. It may be related
to difficulties with instrument interpretation. Uncertainty
about reading the heading indicator (interpretation) or
uncertainty because of inconsistency in rolling out of turns
(control) may cause the fixation.

inadequate information. Reliance on a single instrument is
poor technique. For example, a pilot can maintain reasonably
close altitude control with the attitude indicator, but cannot
hold altitude with precision without including the altimeter
in the cross-check.

Omission of an instrument from a cross-check is another
likely fault. It may be caused by failure to anticipate
significant instrument indications following attitude
changes. For example, in a roll-out from a 180° steep turn,
straight-and-level flight is established with reference only
to the attitude indicator, and the pilot neglects to check the
heading indicator for constant heading information. Because
of precession error, the attitude indicator temporarily shows
a slight error, correctable by quick reference to the other
flight instruments.

For example, a pilot uses full power in a small airplane for a
5-minute climb from near sea level, and the attitude indicator
shows the miniature aircraft two bar widths (twice the
thickness of the miniature aircraft wings) above the artificial
horizon. [Figure 4-20] The airplane is climbing at 500 fpm
as shown on the VSI, and at airspeed of 90 knots, as shown
on the airspeed indicator. With the power available in this
particular airplane and the attitude selected by the pilot, the
performance is shown on the instruments. Now, set up the
identical picture on the attitude indicator in a jet airplane.
With the same airplane attitude as shown in the first example,
the VSI in the jet reads 2,000 fpm and the airspeed indicator
reads 300 knots.

Emphasis on a single instrument, instead of on the combination
of instruments necessary for attitude information, is an
understandable fault during the initial stages of training. It
is a natural tendency to rely on the instrument that is most
readily understood, even when it provides erroneous or

Instrument Interpretation
The second fundamental skill, instrument interpretation, requires
more thorough study and analysis. It begins by understanding
each instrument’s construction and operating principles. Then,
this knowledge must be applied to the performance of the
aircraft being flown, the particular maneuvers to be executed,
the cross-check and control techniques applicable to that
aircraft, and the flight conditions.

As the performance capabilities of the aircraft are learned,
a pilot interprets the instrument indications appropriately

Figure 4-20. Power and Attitude Equal Performance.

4-13

in terms of the attitude of the aircraft. If the pitch attitude
is to be determined, the airspeed indicator, altimeter, VSI,
and attitude indicator provide the necessary information. If
the bank attitude is to be determined, the heading indicator,
turn coordinator, and attitude indicator must be interpreted.
For each maneuver, learn what performance to expect and
the combination of instruments to be interpreted in order
to control aircraft attitude during the maneuver. It is the
two fundamental flight skills, instrument cross-check and
instrument interpretation, that provide the smooth and
seamless control necessary for basic instrument flight as
discussed at the beginning of the chapter.

4-14

Chapter 4, Section II

Airplane Attitude
Instrument Flying
Using an Electronic Flight Display
Introduction
Attitude instrument flying is defined as the control of an
aircraft’s spatial position by using instruments rather than
outside visual references. As noted in Section I, today’s
aircraft come equipped with analog and/or digital instruments.
Section II acquaints the pilot with the use of digital instruments
known as an electronic flight display (EFD).
The improvements in avionics coupled with the introduction
of EFDs to general aviation aircraft offer today’s pilot an
unprecedented array of accurate instrumentation to use in
the support of instrument flying.

4-15

Until recently, most general aviation aircraft were equipped
with individual instruments utilized collectively to safely
maneuver the aircraft by instrument reference alone. With
the release of the electronic flight display system, the
conventional instruments have been replaced by multiple
liquid crystal display (LCD) screens. The first screen is
installed in front of the left seat pilot position and is referred
to as the primary flight display (PFD). [Figure 4-21] The
second screen is positioned in approximately the center of
the instrument panel and is referred to as the multi-function
display (MFD). [Figure 4-22] The pilot can use the MFD
to display navigation information (moving maps), aircraft
systems information (engine monitoring), or should the need
arise, a PFD. [Figure 4-23] With just these two screens,
aircraft designers have been able to de-clutter instrument
panels while increasing safety. This has been accomplished
through the utilization of solid-state instruments which have
a failure rate far lower than those of conventional analog
instrumentation.
However, in the event of electrical failure, the pilot still
has emergency instruments as a backup. These instruments
either do not require electrical power, or as in the case
of many attitude indicators, they are battery equipped.
[Figure 4-24]
Pilots flying under visual flight rules (VFR) maneuver their
aircraft by reference to the natural horizon, utilizing specific

reference points on the aircraft. In order to operate the aircraft
in other than VFR weather, with no visual reference to the
natural horizon, pilots need to develop additional skills.
These skills come from the ability to maneuver the aircraft by
reference to flight instruments alone. These flight instruments
replicate all the same key elements that a VFR pilot utilizes
during a normal flight. The natural horizon is replicated on
the attitude indicator by the artificial horizon.
Understanding how each flight instrument operates and
what role it plays in controlling the attitude of the aircraft
is fundamental in learning attitude instrument flying. When
the pilot understands how all the instruments are used in
establishing and maintaining a desired aircraft attitude, the
pilot is better prepared to control the aircraft should one
or more key instruments fail or if the pilot should enter
instrument flight conditions.

Learning Methods
There are two basic methods utilized for learning attitude
instrument flying. They are “control and performance” and
“primary and supporting.” These methods rely on the same
flight instruments and require the pilot to make the same
adjustments to the flight and power controls to control aircraft
attitude. The main difference between the two methods is the
importance that is placed on the attitude indicator and the
interpretation of the other flight instruments.

Figure 4-21. Primary Flight Display (PFD) and Analog Counterparts.

4-16

Figure 4-22. Multifunction Display (MFD).

Figure 4-23. Reversionary Displays.

4-17

Figure 4-24. Emergency Back-up of the Airspeed Indicator, Attitude Indicator, and Altitude Indicator.

Control and Performance Method
Aircraft performance is accomplished by controlling the
aircraft attitude and power output. Aircraft attitude is the
relationship of its longitudinal and lateral axes to the Earth’s
horizon. When flying in instrument flight conditions, the
pilot controls the attitude of the aircraft by referencing the
flight instruments and manipulating the power output of the
engine to achieve the performance desired. This method can
be used to achieve a specific performance level enabling a
pilot to perform any basic instrument maneuver.

Figure 4-25. Control Instruments.

4-18

The instrumentation can be broken up into three different
categories: control, performance, and navigation.

Control Instruments
The control instruments depict immediate attitude and power
changes. The instrument for attitude display is the attitude
indicator. Power changes are directly reflected on the manifold
pressure gauge and the tachometer. [Figure 4-25] All three
of these instruments can reflect small adjustments, allowing
for precise control of aircraft attitude.

Figure 4-26. Performance Instruments.

In addition, the configuration of the power indicators installed
in each aircraft may vary to include the following types of
power indicators: tachometers, manifold pressure indicator,
engine pressure ratio indicator, fuel flow gauges, etc.
The control instruments do not indicate how fast the aircraft
is flying or at what altitude it is flying. In order to determine
these variables and others, a pilot needs to refer to the
performance instruments.

Performance Instruments
The performance instruments directly reflect the performance
the aircraft is achieving. The speed of the aircraft can be
referenced on the airspeed indicator. The altitude can be
referenced on the altimeter. The aircraft’s climb performance
can be determined by referencing the vertical speed indicator
(VSI). [Figure 4-26] Other performance instruments
available are the heading indicator, angle of attack indicator,
and the slip/skid indicator.

The performance instruments will most directly reflect a
change in acceleration, which is defined as change in velocity
or direction. Therefore, these instruments indicate if the
aircraft is changing airspeed, altitude, or heading, which are
horizontal, vertical, or lateral vectors.

Navigation Instruments
The navigation instruments are comprised of global
positioning system (GPS) displays and indicators, very high
frequency omnidirectional range/nondirectional radio beacon
(VOR/NDB) indicators, moving map displays, localizer, and
glide slope (GS) indicators. [Figure 4-27] The instruments
indicate the position of the aircraft relative to a selected
navigation facility or fix. Navigation instruments allow
the pilot to maneuver the aircraft along a predetermined
path of ground-based or spaced-based navigation signals
without reference to any external visual cues. The navigation
instruments can support both lateral and visual inputs.

Figure 4-27. Navigation Instruments.

4-19

The Four-Step Process Used to Change Attitude
In order to change the attitude of the aircraft, the pilot must
make the proper changes to the pitch, bank, or power settings
of the aircraft. Four steps (establish, trim, cross-check, and
adjust) have been developed in order to aid in the process.

Establish
Any time the attitude of the aircraft requires changing, the
pilot must adjust the pitch and/or bank in conjunction with
power to establish the desired performance. The changes
in pitch and bank require the pilot to reference the attitude
indicator in order to make precise changes. Power changes
should be verified on the tachometer, manifold pressure
gauge, etc. To ease the workload, the pilot should become
familiar with the approximate pitch and power changes
necessary to establish a specified attitude.

Trim
Another important step in attitude instrument flying is
trimming the aircraft. Trim is utilized to eliminate the need
to apply force to the control yoke in order to maintain the
desired attitude. When the aircraft is trimmed appropriately,
the pilot is able to relax pressure on the control yoke and
momentarily divert attention to another task at hand without
deviating from the desired attitude. Trimming the aircraft is
very important, and poor trim is one of the most common
errors instructors note in instrument students.

this process is making a larger than necessary change when
a deviation is noted. Pilots need to become familiar with the
aircraft and learn how great a change in attitude is needed to
produce the desired performance.
Applying the Four-Step Process
In attitude instrument flight, the four-step process is used to
control pitch attitude, bank attitude, and power application of
the aircraft. The EFD displays indications precisely enough
that a pilot can apply control more accurately.

Pitch Control
The pitch control is indicated on the attitude indicator which
spans the full width of the PFD. Due to the increased size of
the display, minute changes in pitch can be made and corrected
for. The pitch scale on the attitude indicator is graduated in
5-degree increments which allow the pilot to make correction
with precision to approximately 1/2 degree. The miniature
airplane utilized to represent the aircraft in conventional
attitude indicators is replaced in glass panel displays by a
yellow chevron. [Figure 4-28] Representing the nose of the
aircraft, the point of the chevron affords the pilot a much
more precise indication of the degree of pitch and allows
the pilot to make small, precise changes should the desired
aircraft performance change. When the desired performance
is not being achieved, precise pitch changes should be made
by referencing the point of the yellow chevron.

Cross-Check
Once the initial attitude changes have been made, the pilot
should verify the performance of the aircraft. Cross-checking
the control and performance instruments requires the pilot
to visually scan the instruments as well as interpret the
indications. All the instruments must be utilized collectively
in order to develop a full understanding of the aircraft attitude.
During the cross-check, the pilot needs to determine the
magnitude of any deviations and determine how much of a
change is required. All changes are then made based on the
control instrument indications.

Adjust
The final step in the process is adjusting for any deviations
that have been noted during the cross-check. Adjustments
should be made in small increments. The attitude indicator
and the power instruments are graduated in small increments
to allow for precise changes to be made. The pitch should be
made in reference to bar widths on the miniature airplane.
The bank angle can be changed in reference to the roll scale
and the power can be adjusted in reference to the tachometer,
manifold pressure gauge, etc.
By utilizing these four steps, pilots can better manage the
attitude of their aircraft. One common error associated with
4-20

Figure 4-28. The chevron’s relationship to the horizon line

indicates the pitch of the aircraft.

Bank Control
Precise bank control can be developed utilizing the roll
pointer in conjunction with the roll index displayed on the

attitude indicator. The roll index is sectioned by hash marks at
0°, 10°, 20°, 30°, 45°, 60° and the horizon line which depicts
90° of bank. [Figure 4-29] The addition of the 45° hash mark
is an improvement over conventional attitude indicators.
In addition to the roll index, the instrument pilot utilizes
the turn rate indicator to maintain the aircraft in a standard
rate turn (3° per second). Most instrument maneuvers can
be done comfortably, safely, and efficiently by utilizing a
standard rate turn.

increases, pilots begin to know approximately how much
change in throttle position is required to produce the desired
change in airspeed. Different aircraft demand differing
amounts of throttle change to produce specific performance.
It is imperative that the pilot make the specific changes on
the power instruments and allow the performance to stabilize.
Avoid the tendency to overcontrol.
One common error encountered with glass panel displays
is associated with the precision of the digital readouts.
This precision causes pilots to focus too much attention on
establishing the exact power setting.
Control and power instruments are the foundation for precise
attitude instrument flying. The keys to attitude instrument
flying are establishing the desired aircraft attitude on the
attitude indicator and selecting the desired engine output on
the power instruments. Cross-checking is the vital ingredient
in maintaining precise attitude instrument flight.
Attitude Instrument Flying—Primary and
Supporting Method
The second method for performing attitude instrument
flight is a direct extension of the control/power method.
By utilizing the primary and supporting flight instruments
in conjunction with the control and power instruments, the
pilot can precisely maintain aircraft attitude. This method
utilizes the same instruments as the control/power method;
however, it focuses more on the instruments that depict the
most accurate indication for the aspect of the aircraft attitude
being controlled. The four key elements (pitch, bank, roll,
and trim) are discussed in detail.
Similar to the control/power method, all changes to aircraft
attitude need to be made using the attitude indicator and the
power instruments (tachometer, manifold pressure gauge,
etc.). The following explains how each component of the
aircraft attitude is monitored for performance.

Pitch Control
Figure 4-29. Bank Control Index Lines.

Power Control
The power instruments indicate how much power is being
generated by the engine. They are not affected by turbulence,
improper trim, or control pressures. All changes in power
should be made with reference to power instruments and
cross-checked on performance instruments.
Power control needs to be learned from the beginning of
flight training. Attitude instrument flying demands increased
precision when it comes to power control. As experience

The pitch of the aircraft refers to the angle between the
longitudinal axis of the aircraft and the natural horizon. When
flying in instrument meteorological conditions, the natural
horizon is unavailable for reference, and an artificial horizon
is utilized in its place. [Figure 4-30] The only instrument
capable of depicting the aircraft attitude is the attitude
indicator displayed on the PFD. The attitude and heading
reference system (AHRS) is the engine that drives the attitude
display. The AHRS unit is capable of precisely tracking
minute changes in the pitch, bank, and yaw axes, thereby
making the PFD very accurate and reliable. The AHRS unit
determines the angle between the aircraft’s longitudinal
axis and the horizon line on initialization. There is no need

4-21

Figure 4-30. Pitch of the Aircraft.

or means for the pilot to adjust the position of the yellow
chevron which represents the nose of the aircraft.

Straight-and-Level Flight
In straight-and-level flight, the pilot maintains a constant
altitude, airspeed and, for the most part, heading for
extended periods of time. To achieve this, three primary
instruments need to be referenced in order to maintain these
three variables.

Primary Pitch

In addition to the primary instrument, there are also
supporting instruments that assist the pilot in cross-checking
the pitch attitude. The supporting instruments indicate trend,
but they do not indicate precise attitude indications. Three
instruments (vertical speed, airspeed, and altitude trend
tape) indicate when the pitch attitude has changed and that
the altitude is changing. [Figure 4-31] When the altitude is
constant, the VSI and altitude trend tape are not shown on
the PFD. When these two trend indicators are displayed, the
pilot is made aware that the pitch attitude of the aircraft has
changed and may need adjustment.

When the pilot is maintaining a constant altitude, the primary
instrument for pitch is the altimeter. As long as the aircraft
maintains a constant airspeed and pitch attitude, the altitude
should remain constant.
Two factors that cause the altitude to deviate are turbulence
and momentary distractions. When a deviation occurs,
a change in the pitch needs to be made on the attitude
indicator. Small deviations require small corrections while
large deviations require larger corrections. Pilots should
avoid making large corrections that result in rapid attitude
changes, for this may lead to spatial disorientation. Smooth,
timely corrections should be made to bring the aircraft back
to the desired attitude.
Pay close attention to indications on the PFD. An increase in
pitch of 2.5° produces a climb rate of 450 feet per minute (fpm).
Small deviations do not require large attitude changes.
Figure 4-31. Supporting Instruments.

A rule of thumb for correcting altitude deviations is to establish
a change rate of twice the altitude deviation, not to exceed 500
fpm. For example, if the aircraft is off altitude by 40 feet, 2 x
40 = 80 feet, so a descent of approximately 100 fpm allows
the aircraft to return to the desired altitude in a controlled,
timely fashion.
4-22

The instrument cross-check necessitates utilizing these
supporting instruments to better manage altitude control.
The VSI and trend tape provide the pilot with information
regarding the direction and rate of altitude deviations. The
pilot is thus able to make correction to the pitch attitude

before a large deviation in altitude occurs. The airspeed
indicator depicts an increase if the pitch attitude is lowered.
Conversely, when the pitch attitude increases, the pilot should
note a decrease in the airspeed.

Primary Bank
When flying in instrument meteorological conditions, pilots
maintain preplanned or assigned headings. With this in
mind, the primary instrument for bank angle is the heading
indicator. Heading changes are displayed instantaneously.
The heading indicator is the only instrument that displays the
current magnetic heading, provided that it is matched to the
magnetic compass with all deviation adjustments accounted
for. [Figure 4-32]
There are supporting instruments associated with bank as
well. The turn rate trend indicator shows the pilot when the
aircraft is changing heading. The magnetic compass is also
useful for maintaining a heading; however, it is influenced
by several errors in various phases of flight.

Primary Yaw
The slip/skid indicator is the primary instrument for yaw.
It is the only instrument that can indicate if the aircraft is

moving through the air with the longitudinal axis of the
aircraft aligned with the relative wind.

Primary Power
The primary power instrument for straight-and-level flight is
the airspeed indicator. The main focus of power is to maintain
a desired airspeed during level flight. No other instrument
delivers instantaneous indication.
Learning the primary and supporting instruments for
each variable is the key to successfully mastering attitude
instrument flying. At no point does the primary and supporting
method devalue the importance of the attitude indicator or the
power instruments. All instruments (control, performance,
primary, and supporting) must be utilized collectively.

Fundamental Skills of Attitude Instrument
Flying
When first learning attitude instrument flying, it is very
important that two major skills be mastered. Instrument crosscheck and instrument interpretation comprise the foundation
for safely maneuvering the aircraft by reference to instruments
alone. Without mastering both skills, the pilot will not be able
to maintain precise control of aircraft attitude.

Figure 4-32. Primary Bank.

4-23

Instrument Cross-Check
The first fundamental skill is cross-checking (also call
“scanning”). Cross-checking is the continuous observation of
the indications on the control and performance instruments.
It is imperative that the new instrument pilot learn to observe
and interpret the various indications in order to control
the attitude and performance of the aircraft. Due to the
configuration of some glass panel displays such as the Garmin
G1000, one or more of the performance instruments may be
located on an MFD installed to the right of the pilot’s direct
forward line of sight. [Figure 4-33]

to include the stand-by flight instruments as well as the
engine indications in the scan. Due to the size of the
attitude instrument display, scanning techniques have been
simplified because the attitude indicator is never out of
peripheral view.

How a pilot gathers the necessary information to control the
aircraft varies by individual pilot. No specific method of
cross-checking (scanning) is recommended; the pilot must
learn to determine which instruments give the most pertinent
information for any particular phase of a maneuver. With
practice, the pilot is able to observe the primary instruments
quickly and cross-check with the supporting instruments
in order to maintain the desired attitude. At no time during
instrument flying should the pilot stop cross-checking the
instrumentation.

The radial scan pattern works well for scanning the PFD. The
close proximity of the instrument tape displays necessitates
very little eye movement in order to focus in on the desired
instrument. While the eyes move in any direction, the
extended artificial horizon line allows the pilot to keep the
pitch attitude in his or her peripheral vision. This extended
horizon line greatly reduces the tendency to fixate on one
instrument and completely ignore all others. Because of
the size of the attitude display, some portion of the attitude
indicator is always visible while viewing another instrument
display on the PFD.

Scanning Techniques
Since most of the primary and supporting aircraft attitude
information is displayed on the PFD, standard scanning
techniques can be utilized. It is important to remember

Selected Radial Cross-Check
The radial scan is designed so that your eyes remain on the
attitude indicator 80–90 percent of the time. The remainder
of the time is spent transitioning from the attitude indicator
to the various other flight instruments. [Figure 4-34]

Starting the Scan
Start the scan in the center of the PFD on the yellow chevron.
Note the pitch attitude and then transition the eyes upward to
the slip/skid indicator. Ensure that the aircraft is coordinated

Figure 4-33. Note that the altitude and vertical speed tapes are slightly to the right of the pilot’s direct forward line of sight.

4-24

Figure 4-34. Selected Radial Cross-Check.

by aligning the split triangle symbol. The top of the split
triangle is referred to as the roll pointer. The lower portion of
the split triangle is the slip/skid indicator. If the lower portion
of the triangle is off to one side, step on the rudder pedal on
the same side to offset it. [Figure 4-35 NOTE: The aircraft
is not changing heading. There is no trend vector on the turn
rate indicator.]

While scanning that region, check the roll pointer and assure
that the desired degree of roll is being indicated on the bank
scale. The roll index and the bank scale remain stationary at
the top of the attitude indicator. The index is marked with
angles of 10°, 20°, 30°, 45° and 60° in both directions. If the
desired bank angle is not indicated, make the appropriate

Figure 4-35. Roll Pointer and Slip/Skid Indicator.

4-25

aileron corrections. Verify the bank angle is correct and
continue scanning back to the yellow chevron.
Scan left to the airspeed tape and verify that the airspeed is
as desired, then return back to the center of the display. Scan
right to the altimeter tape. Verify that the desired altitude is
being maintained. If it is not, make the appropriate pitch
change and verify the result. Once the desired altitude has
been verified, return to the center of the display. Transition
down to the heading indicator to verify the desired heading.
When the heading has been confirmed, scan to the center of
the display.
It is also important to include the engine indications in the
scan. Individualized scan methods may require adjustment
if engine indications are presented on a separate MFD. A
modified radial scan can be performed to incorporate these
instruments into the scan pattern. Another critical component
to include in the scan is the moving map display located on
the MFD. To aid in situational awareness and facilitate a more
centralized scan, a smaller inset map can be displayed in the
lower left corner of the PFD screen.

Trend Indicators
One improvement the glass panel displays brought to the
general aviation industry is the trend vector. Trend vectors
are magenta lines that appear on the airspeed and altitude
tapes as well as on the turn rate indicator. These magenta
lines indicate what the associated airspeed, altitude, or
heading will be in 6 seconds [Figure 4-36] if the current
rate is maintained. The trend vector is not displayed if there
is no change to the associated tape and the value remains
constant [Figure 4-37] or if there is a failure in some portion
of the system that would preclude the vector from being
determined.

Figure 4-37. Airspeed Indicators With No Trend Present.

Trend vectors are a very good source of information for the
new instrument flight rules (IFR) pilot. Pilots who utilize
good scanning techniques can pick up subtle deviations
from desired parameters and make small correction to the
desired attitude. As soon as a trend is indicated on the PFD,
a conscientious pilot can adjust to regain the desired attitude.
[Figure 4-38]

Figure 4-38. Altimeter Trend Indicators.

Figure 4-36. Airspeed Trend Indicators.

4-26

Another advancement in attitude instrument flying is the turn
rate trend indicator. As in the cases of airspeed, altitude, and
vertical speed trend indicators, the turn rate trend indicator
depicts what the aircraft’s heading will be in 6 seconds. While
examining the top of the heading indicator, notice two white
lines on the exterior of the compass rose. [Figure 4-39] These

Figure 4-39. Horizontal Situation Indicator (HSI) Trend Indicator Elongates Proportionally With the Rate of Turn.

two tick marks located on both sides of the top of the heading
indicator show half-standard rate turns as well as standard
rate turns.
In Figure 4-40, when the aircraft begins its turn to the left,
the magenta trend indicator elongates proportionally with the

rate of turn. To initiate a half-standard rate turn, position the
indicator on the first tick mark. A standard rate turn would
be indicated by the trend indicator extending to the second
tick mark. A turn rate in excess of standard rate would be
indicated by the trend indicator extending past the second tick
mark. This trend indicator shows what the aircraft’s heading
will be in 6 seconds, but is limited to indicate no more than
24° in front of the aircraft, or 4° per second. When the aircraft
exceeds a turning rate of 25° in 6 seconds, the trend indicator
has an arrowhead attached to it.
Trend indicators are very useful when leveling off at a specific
altitude, when rolling out on a heading, or when stabilizing
airspeed. One method of determining when to start to level
off from a climb or descent is to start leveling at 10 percent
of the vertical speed rate prior to the desired altitude.
As the aircraft approaches the desired altitude, adjust the
pitch attitude to keep the trend indicator aligned with the
target altitude. As the target approaches, the trend indicator
gradually shrinks until altitude stabilizes. Trend indicators
should be used as a supplement, not as a primary means of
determining pitch change.

Figure 4-40. HSI Indicator (enlargement).

4-27

Common Errors
Fixation
Fixation, or staring at one instrument, is a common error
observed in pilots first learning to utilize trend indicators.
The pilot may initially fixate on the trend indicator and make
adjustments with reference to that alone. Trend indicators are
not the only tools to aid the pilot in maintaining the desired
power or attitude; they should be used in conjunction with the
primary and supporting instruments in order to better manage
the flight. With the introduction of airspeed tapes, the pilot
can monitor airspeed to within one knot. Fixation can lead
to attempting to keep the airspeed to an unnecessarily tight
tolerance. There is no need to hold airspeed to within one
knot; the Instrument Rating Practical Test Standards (PTS)
allows greater latitude.
Omission
Another common error associated with attitude instrument
flying is omission of an instrument from the cross-check. Due
to the high reliability of the PFD and associated components,
pilots tend to omit the stand-by instruments as well as the
magnetic compass from their scans. An additional reason
for the omission is the position of the stand-by instruments.
Pilots should continue to monitor the stand-by instruments
in order to detect failures within those systems. One of the
most commonly omitted instruments from the scan is the
slip/skid indicator.

4-28

Emphasis
In initial training, placing emphasis on a single instrument
is very common and can become a habit if not corrected.
When the importance of a single instrument is elevated above
another, the pilot begins to rely solely on that instrument
for guidance. When rolling out of a 180° turn, the attitude
indicator, heading indicator, slip/skid indicator, and altimeter
need to be referenced. If a pilot omits the slip/skid indicator,
coordination is sacrificed.

Chapter 5, Section I

Airplane Basic
Flight Maneuvers
Using Analog Instrumentation
Introduction
Instrument flying techniques differ according to aircraft
type, class, performance capability, and instrumentation.
Therefore, the procedures and techniques that follow need
to be modified to suit individual aircraft. Recommended
procedures, performance data, operating limitations, and
flight characteristics of a particular aircraft are available in the
Pilot’s Operating Handbook/Airplane Flight Manual (POH/
AFM) for study before practicing the flight maneuvers.
The flight maneuvers discussed here in Chapter 5-I assume
the use of a single-engine, propeller-driven small airplane
with retractable gear and flaps and a panel with instruments
representative of those discussed earlier in Chapter 3, Flight
Instruments. With the exception of the instrument takeoff, all
of the maneuvers can be performed on “partial panel,” with the
attitude gyro and heading indicator covered or inoperative.

5-1

Figure 5-1. Pitch Attitude and Airspeed in Level Flight, Slow
Cruise Speed.

Figure 5-2. Pitch Attitude and Airspeed in Level Flight, Fast Cruise

Speed.

Straight-and-Level Flight
Pitch Control
The pitch attitude of an airplane is the angle between the
longitudinal axis of the airplane and the actual horizon. In
level flight, the pitch attitude varies with airspeed and load.
For training purposes, the latter factor can normally be
disregarded in small airplanes. At a constant airspeed, there is
only one specific pitch attitude for level flight. At slow cruise
speeds, the level flight attitude is nose high with indications
as in Figure 5-1; at fast cruise speeds, the level-flight attitude
is nose low. [Figure 5-2] Figure 5-3 shows the indications
for the attitude at normal cruise speeds. The instruments used
to determine the pitch attitude of the aircraft are the attitude
indicator, the altimeter, the vertical speed indicator (VSI),
and the airspeed indicator (ASI).

Attitude Indicator
The attitude indicator gives the direct indication of pitch
attitude. The desired pitch attitude is gained by using the
elevator control to raise or lower the miniature aircraft in
relation to the horizon bar. This corresponds to the way pitch
attitude is adjusted in visual flight by raising or lowering
the nose of the airplane in relation to the natural horizon.
However, unless the airspeed is constant, and until the
level flight attitude for that airspeed has been identified and
established, there is no way to know whether level flight as
5-2

Figure 5-3. Pitch Attitude and Airspeed in Level Flight, Normal
Cruise Speed.

indicated on the attitude indicator is resulting in level flight
as shown on the altimeter, VSI, and ASI. If the miniature
aircraft of the attitude indicator is properly adjusted on the
ground before takeoff, it shows approximately level flight at
normal cruise speed when the pilot completes the level off
from a climb. If further adjustment of the miniature aircraft
is necessary, the other pitch instruments must be used to
maintain level flight while the adjustment is made.
To practice pitch control for level flight using only the
attitude indicator, use the following exercise. Restrict the
displacement of the horizon bar to a one-half bar width, a
bar width up or down, then a one-and-one-half bar width.
One-half, one, and one-and-one-half bar width nose-high
attitudes are shown in Figures 5-4, 5-5, and 5-6.
An instructor pilot can demonstrate these normal pitch
corrections and compare the indications on the attitude
indicator with the airplane’s position to the natural horizon.

Figure 5-4. Pitch Correction for Level Flight, One-Half Bar

Width.

Pitch attitude changes for corrections to level flight by reference
to instruments are much smaller than those commonly used
for visual flight. With the airplane correctly trimmed for level
flight, the elevator displacement and the control pressures
necessary to effect these standard pitch changes are usually
very slight. The following are a few helpful hints to help
determine how much elevator control pressure is required.
First, a tight grip on the controls makes it difficult to feel
control pressure changes. Relaxing and learning to control
the aircraft usually takes considerable conscious effort during
the early stages of instrument training.
Second, make smooth and small pitch changes with positive
pressure. With practice, a pilot can make these small pitch
corrections up or down, “freezing” (holding constant) the
one-half, full, and one-and-one-half bar widths on the
attitude indicator.

Figure 5-5. Pitch Correction for Level Flight, One Bar Width.

Third, with the airplane properly trimmed for level flight,
momentarily release all pressure on the elevator control
when becoming aware of tenseness. This is a reminder that
the airplane is stable; except under turbulent conditions, it
will maintain level flight if left alone. Even when no control
change is called for, it will be difficult to resist the impulse
to move the controls. This may be one of the most difficult
initial training problems in instrument flight.

Altimeter
At constant power, any deviation from level flight (except
in turbulent air) is the result of a pitch change. Therefore,
the altimeter gives an indirect indication of the pitch attitude
in level flight, assuming constant power. Since the altitude

Figure 5-6. Pitch Correction for Level Flight, One-and-One-Half

Bar Width.

5-3

should remain constant when the airplane is in level flight,
any deviation from the desired altitude signals the need for a
pitch change. If the aircraft is gaining altitude, the nose must
be lowered. [Figures 5-7 and 5-8]

Figure 5-7. Using the Altimeter for Pitch Interpretation, a High
Altitude Means a Nose-High Pitch Attitude.

Figure 5-8. Pitch Correction Following Altitude Increase—Lower
Nose to Correct Altitude Error.

The rate of movement of the altimeter needle is as important
as its direction of movement in maintaining level flight
without the use of the attitude indicator. An excessive pitch
deviation from level flight results in a relatively rapid change
of altitude; a slight pitch deviation causes a slow change.
Thus, if the altimeter needle moves rapidly clockwise, assume
a considerable nose-high deviation from level flight attitude.
Conversely, if the needle moves slowly counterclockwise to
indicate a slightly nose-low attitude, assume that the pitch
correction necessary to regain the desired altitude is small.
As the altimeter is added to the attitude indicator in a crosscheck, a pilot will learn to recognize the rate of movement
of the altimeter needle for a given pitch change as shown on
the attitude indicator.
To practice precision control of pitch in an airplane without
an attitude indicator, make small pitch changes by visual
reference to the natural horizon, and note the rate of
movement of the altimeter. Note what amount of pitch change
gives the slowest steady rate of change on the altimeter. Then
practice small pitch corrections by accurately interpreting
and controlling the rate of needle movement.

5-4

An instructor pilot can demonstrate an excessive nose-down
deviation (indicated by rapid movement of the altimeter
needle) and then, as an example, show the result of improper
corrective technique. The normal impulse is to make a
large pitch correction in a hurry, but this inevitably leads
to overcontrolling. The needle slows down, then reverses
direction, and finally indicates an excessive nose-high
deviation. The result is tension on the controls, erratic control
response, and increasingly extreme control movements. The
correct technique, which is slower and smoother, will return
the airplane to the desired attitude more quickly, with positive
control and no confusion.
When a pitch error is detected, corrective action should be
taken promptly, but with light control pressures and two
distinct changes of attitude: (1) a change of attitude to stop
the needle movement and (2) a change of attitude to return
to the desired altitude.
When the altimeter indicates an altitude deviation, apply
just enough elevator pressure to decrease the rate of needle
movement. If it slows down abruptly, ease off some of the
pressure until the needle continues to move, but ease off
slowly. Slow needle movement means the airplane attitude
is close to level flight. Add slightly more corrective pressure
to stop the direction of needle movement. At this point level
flight is achieved; a reversal of needle movement means
the aircraft has passed through it. Relax control pressures
carefully, continuing to cross-check since changing airspeed
will cause changes in the effectiveness of a given control
pressure. Next, adjust the pitch attitude with elevator pressure
for the rate of change of altimeter needle movement that is
correlated with normal pitch corrections, and return to the
desired altitude.
As a rule of thumb, for errors of less than 100 feet, use a half
bar width correction. [Figures 5-9 and 5-10] For errors in
excess of 100 feet, use an initial full bar width correction.
[Figures 5-11 and 5-12] Practice predetermined altitude
changes using the altimeter alone, then in combination with
the attitude indicator.

Vertical Speed Indicator (VSI)
The VSI, like the altimeter, gives an indirect indication of
pitch attitude and is both a trend and a rate instrument. As
a trend instrument, it shows immediately the initial vertical
movement of the airplane, which disregarding turbulence
can be considered a reflection of pitch change. To maintain
level flight, use the VSI in conjunction with the altimeter and
attitude indicator. Note any positive or negative trend of the
needle from zero and apply a very light corrective elevator

pressure. As the needle returns to zero, relax the corrective
pressure. If control pressures have been smooth and light, the
needle reacts immediately and slowly, and the altimeter shows
little or no change of altitude. As a rate instrument, the VSI
requires consideration of lag characteristics.

Figure 5-9. Altitude Error, Less Than 100 Feet.

Figure 5-10. Pitch Correction, Less Than 100 Feet—One-Half Bar
Low to Correct Altitude Error.

Figure 5-11. Altitude Error, Greater Than 100 Feet.

Lag refers to the delay involved before the needle attains a
stable indication following a pitch change. Lag is directly
proportional to the speed and magnitude of a pitch change.
If a slow, smooth pitch change is initiated, the needle moves
with minimum lag to a point of deflection corresponding
to the extent of the pitch change, and then stabilizes as the
aerodynamic forces are balanced in the climb or descent.
A large and abrupt pitch change produces erratic needle
movement, a reverse indication, and introduces greater time
delay (lag) before the needle stabilizes. Pilots are cautioned
not to chase the needle when flight through turbulent
conditions produces erratic needle movements. The apparent
lag in airspeed indications with pitch changes varies greatly
among different airplanes and is due to the time required for
the airplane to accelerate or decelerate when the pitch attitude
is changed. There is no appreciable lag due to the construction
or operation of the instrument. Small pitch changes, smoothly
executed, result in an immediate change of airspeed.
When using the VSI as a rate instrument and combining it
with the altimeter and attitude indicator to maintain level
flight, a pilot should know that the amount the altimeter
needle moves from the desired altitude governs the rate which
should be used to return to that altitude. A rule of thumb is
to make an attitude change that will result in a vertical-speed
rate approximately double the error in altitude. For example,
if altitude is off by 100 feet, the rate of return to the desired
altitude should be approximately 200 feet per minute (fpm).
If it is off by more than 100 feet, the correction should
be correspondingly greater, but should never exceed the
optimum rate of climb or descent for the airplane at a given
airspeed and configuration.
A deviation of more than 200 fpm from the desired rate
of return is considered overcontrolling. For example, if
attempting to change altitude by 200 feet, a rate in excess of
400 fpm indicates overcontrolling.

Figure 5-12. Pitch Correction, Greater Than 100 Feet—One Bar

When returning to an altitude, the VSI is the primary pitch
instrument. Occasionally, the VSI is slightly out of calibration
and may indicate a climb or descent when the airplane is in
level flight. If the instrument cannot be adjusted, take the
error into consideration when using it for pitch control. For

Correction Initially.

5-5

example, if the needle indicates a descent of 200 fpm while
in level flight, use this indication as the zero position.

Airspeed Indicator (ASI)
The ASI presents an indirect indication of the pitch attitude.
In non-turbulent conditions with a constant power setting and
pitch attitude, airspeed remains constant. [Figure 5-13] As the
pitch attitude lowers, airspeed increases, and the nose should
be raised. [Figure 5-14] As the pitch attitude rises, airspeed
decreases, and the nose should be lowered. [Figure 5-15] A
rapid change in airspeed indicates a large pitch change, and
a slow change of airspeed indicates a small pitch change.
Constant Airspeed

Constant Pitch

Figure 5-13. Constant Power Plus Constant Pitch Equals Constant

Speed.
Increased Airspeed

Decreased Pitch

Figure 5-14. Constant Power Plus Decreased Pitch Equals
Increased Airspeed.
Decreased Airspeed

Increased Pitch

Pitch control in level flight is a question of cross-check and
interpretation of the instrument panel for the instrument
information that enables a pilot to visualize and control pitch
attitude. Regardless of individual differences in cross-check
technique, all pilots should use the instruments that give the
best information for controlling the airplane in any given
maneuver. Pilots should also check the other instruments
to aid in maintaining the primary instruments at the desired
indication.
As noted previously, the primary instrument is the one
that gives the most pertinent information for a particular
maneuver. It is usually the one that should be held at a
constant indication. Which instrument is primary for pitch
control in level flight, for example? This question should
be considered in the context of specific airplane, weather
conditions, pilot experience, operational conditions, and other
factors. Attitude changes must be detected and interpreted
instantly for immediate control action in high-performance
airplanes. On the other hand, a reasonably proficient
instrument pilot in a slower airplane may rely more on the
altimeter for primary pitch information, especially if it is
determined that too much reliance on the attitude indicator
fails to provide the necessary precise attitude information.
Whether the pilot decides to regard the altimeter or the
attitude indicator as primary depends on which approach will
best help control the attitude. In this handbook, the altimeter
is normally considered as the primary pitch instrument during
level flight.
Bank Control
The bank attitude of an airplane is the angle between the
airplane’s wings and the natural horizon. To maintain a
straight-and-level flight path, the wings of the airplane are
kept level with the horizon (assuming the airplane is in
coordinated flight). The instruments used for bank control
are the attitude indicator, the heading indicator, and the
turn coordinator. Figure 5-16 illustrates coordinated flight.
The aircraft is banked left with the attitude indicator and
turn coordinator indicating the bank. The heading indicator
indicates a left turn by apparent clockwise rotation of the
compass card behind the airplane silhouette.

Attitude Indicator

Figure 5-15. Constant Power Plus Increased Pitch Equals

Decreased Airspeed.

5-6

The attitude indicator shows any change in bank attitude
directly and instantly and is, therefore, a direct indicator. On
the standard attitude indicator, the angle of bank is shown
pictorially by the relationship of the miniature aircraft to the
artificial horizon bar, and by the alignment of the pointer with
the banking scale at the top of the instrument. On the face of
the standard three-inch instrument, small angles of bank can
be difficult to detect by reference to the miniature aircraft,
especially if leaning to one side or changing a seating position

and predictable, but the obvious advantage of the attitude
indicator is an immediate indication of both pitch attitude
and bank attitude in a single glance. Even with the precession
errors associated with many attitude indicators, the quick
attitude presentation requires less visual effort and time for
positive control than other flight instruments.

Heading Indicator
The bank attitude of an aircraft in coordinated flight is shown
indirectly on the heading indicator, since banking results in
a turn and change in heading. Assuming the same airspeed
in both instances, a rapid movement of the heading indicator
(azimuth card in a directional gyro) indicates a large angle
of bank, whereas slow movement reflects a small angle of
bank. Note the rate of movement of the heading indicator
and compare it to the attitude indicator’s degrees of bank.
The attitude indicator’s precession error makes a precise
check of heading information necessary in order to maintain
straight flight.

Figure 5-16. Instruments Used for Bank Control.

slightly. The position of the scale pointer is a good check
against the apparent miniature aircraft position. Disregarding
precession error, small deviations from straight coordinated
flight can be readily detected on the scale pointer. The
banking index may be graduated as shown in Figure 5-17,
or it may be graduated in 30° increments.
The instrument depicted in Figure 5-17 has a scale pointer
that moves in the same direction of bank shown by the
miniature aircraft. In this case, the aircraft is in a left 15°
bank. Precession errors in this instrument are common

Figure 5-17. Bank Interpretation with the Attitude Indicator.

When deviations from straight flight are noted on the heading
indicator, correct to the desired heading using a bank angle no
greater than the number of degrees to be turned. In any case,
limit bank corrections to a bank angle no greater than that
required for a standard rate turn. Use of larger bank angles
requires a very high level of proficiency, and normally results
in overcontrolling and erratic bank control.

Turn Coordinator
The miniature aircraft of the turn coordinator gives an indirect
indication of the bank attitude of the airplane. When the
miniature aircraft is level, the airplane is in straight flight.
When the miniature airplane is aligned with one of the
alignment marks and the aircraft is rolling to the left or right
the indication represents the roll rate, with the alignment
marks indicating a roll of 3° per second in the direction of
the miniature aircraft. This can be seen in level flight when
a bank is introduced either to the left or the right. The turn
coordinator’s indicator will indicate the rolling motion
although there is no turn being made. Conversely, a pedal
input to the right or left causes the aircraft to turn momentarily
about its vertical axis (with no rolling motion) with an
indication of turn on the turn coordinator. After the turn
becomes stabilized and the aircraft is no longer rolling, the
turn coordinator displays the rate of turn with the alignment
marks equaling a turn of 3° per second. The turn coordinator
is able to display both roll and turn parameters because its
electrically powered gyroscope is canted at an angle. As a
result, the turn-and-slip indicator provides both roll and turn
indications. Autopilots in general aviation today use this
instrument in determining both roll and turn information.
After the completion of a turn, return to straight flight is
accomplished by coordinated aileron and rudder pressure to
5-7

level the miniature aircraft. Include the miniature aircraft in
the cross-check and correct for even the smallest deviations
from the desired position. When this instrument is used to
maintain straight flight, control pressures must be applied
very lightly and smoothly.
The ball of the turn coordinator is actually a separate
instrument, conveniently located under the miniature aircraft
because the two instruments are used together. The ball
instrument indicates the quality of the turn. If the ball is off
center, the airplane is slipping or skidding. That is, if the
coordinator’s miniature airplane is tilted right and the ball is
displaced to the right, the aircraft is in a skid. [Figure 5-18] If
however, the miniature airplane is tilted to the right with the
ball off-center to the left, the aircraft is in a slip. [Figure 5-19]
If the wings are level and the airplane is properly trimmed,
the ball will remain in the center, and the airplane will be
in straight flight. If the ball is not centered, the airplane is
improperly trimmed.

rudder, right ball/right rudder), use aileron as necessary for
bank control, and retrim.
To trim the airplane using only the turn coordinator, use
aileron pressure to level the miniature aircraft and rudder
pressure to center the ball. Hold these indications with control
pressures, gradually releasing them while applying rudder
trim sufficient to relieve all rudder pressure. Apply aileron
trim, if available, to relieve aileron pressure. With a full
instrument panel, maintain a wings level attitude by reference
to all available instruments while trimming the airplane.

Turn-and-Slip Indicator (Needle and Ball)
Unlike the turn coordinator that provides three indications
(roll, turn, and trim), the turn-and-slip indicator provides
two: turn-rate and trim. Although the turn-and-slip indicator
needle provides an indication of turn only, it provides an
indirect indication of aircraft attitude when used with roll
indicators such as a heading indicator or magnetic compass.
As with the turn coordinator (after stabilizing from a roll),
when the turn-and-slip indicator’s needle is aligned with the
alignment marks the aircraft is in a standard turn of 3° per
second or 360° in 2 minutes.
The ball of the turn-and-bank indicator provides important
trim in the same manner that the ball in the turn coordinator
does. Figures 5-18 and 5-19 provide a comparison of the
two instruments.

Figure 5-18. Skid Indication.

Figure 5-19. Slip Indication.

To maintain straight-and-level flight with proper trim, note
the direction of ball displacement. If the ball is to the left of
center and the left wing is low, apply left rudder pressure
to center the ball and correct the slip. At the same time
apply right aileron pressure as necessary to level the wings,
cross-checking the heading indicator and attitude indicator
while centering the ball. If the wings are level and the ball is
displaced from the center, the airplane is skidding. Note the
direction of ball displacement, and use the same corrective
technique as for an indicated slip. Center the ball (left ball/left

5-8

Power Control
Power produces thrust which, with the appropriate angle of
attack of the wing, overcomes the forces of gravity, drag,
and inertia to determine airplane performance.
Power control must be related to its effect on altitude and
airspeed, since any change in power setting results in a change
in the airspeed or the altitude of the airplane. At any given
airspeed, the power setting determines whether the airplane
is in level flight, in a climb, or in a descent. If the power is
increased in straight-and-level flight and the airspeed held
constant, the airplane climbs. If power is decreased while
the airspeed is held constant, the airplane descends. On the
other hand, if altitude is held constant, the power applied will
determine the airspeed.
The relationship between altitude and airspeed determines the
need for a change in pitch or power. If the airspeed is not the
desired value, always check the altimeter before deciding that
a power change is necessary. Think of altitude and airspeed
as interchangeable; altitude can be traded for airspeed by
lowering the nose, or convert airspeed to altitude by raising
the nose. If altitude is higher than desired and airspeed is

Figure 5-20. Airspeed Low and Altitude High—Lower Pitch.

low, or vice versa, a change in pitch alone may return the
airplane to the desired altitude and airspeed. [Figure 5-20] If
both airspeed and altitude are high or if both are low, then a
change in both pitch and power is necessary in order to return
to the desired airspeed and altitude. [Figure 5-21]
For changes in airspeed in straight-and-level flight, pitch,
bank, and power must be coordinated in order to maintain
constant altitude and heading. When power is changed to
vary airspeed in straight-and-level flight, a single-engine,
propeller-driven airplane tends to change attitude around all
axes of movement. Therefore, to maintain constant altitude
and heading, apply various control pressures in proportion
to the change in power. When power is added to increase
airspeed, the pitch instruments indicate a climb unless
forward elevator control pressure is applied as the airspeed
changes. With an increase in power, the airplane tends to
yaw and roll to the left unless counteracting aileron and
rudder pressures are applied. Keeping ahead of these changes
requires increasing cross-check speed, which varies with the
type of airplane and its torque characteristics, the extent of
power and speed change involved.

Power Settings
Power control and airspeed changes are much easier when
approximate power settings necessary to maintain various
airspeeds in straight-and-level flight are known in advance.
However, to change airspeed by any appreciable amount, the
common procedure is to underpower or overpower on initial
power changes to accelerate the rate of airspeed change.

(For small speed changes, or in airplanes that decelerate or
accelerate rapidly, overpowering or underpowering is not
necessary.)
Consider the example of an airplane that requires 23"
mercury (Hg) of manifold pressure to maintain a normal
cruising airspeed of 120 knots, and 18" Hg of manifold
pressure to maintain an airspeed of 100 knots. The reduction
in airspeed from 120 knots to 100 knots while maintaining
straight-and-level flight is discussed below and illustrated in
Figures 5-22, 5-23, and 5-24.
Instrument indications, prior to the power reduction, are
shown in Figure 5-22. The basic attitude is established and
maintained on the attitude indicator. The specific pitch,
bank, and power control requirements are detected on these
primary instruments:
Altimeter—Primary Pitch
Heading Indicator—Primary Bank
Airspeed Indicator—Primary Power
Supporting pitch-and-bank instruments are shown in
Figure 5-23. Note that the supporting power instrument is
the manifold pressure gauge (or tachometer if the propeller
is fixed pitch). However, when a smooth power reduction to
approximately 15" Hg (underpower) is made, the manifold
pressure gauge becomes the primary power instrument.
[Figure 5-23] With practice, power setting can be changed
with only a brief glance at the power instrument, by sensing

Figure 5-21. Airspeed and Altitude High—Lower Pitch and Reduce Power.

5-9

Figure 5-22. Straight-and-Level Flight (Normal Cruising Speed).

Figure 5-23. Straight-and-Level Flight (Airspeed Decreasing).

5-10

the movement of the throttle, the change in sound, and the
changes in the feel of control pressures.
As thrust decreases, increase the speed of the cross-check
and be ready to apply left rudder, back-elevator, and aileron
control pressure the instant the pitch-and-bank instruments
show a deviation from altitude and heading. As proficiency
is obtained, a pilot learns to cross-check, interpret, and
control the changes with no deviation of heading and altitude.
Assuming smooth air and ideal control technique, as airspeed
decreases, a proportionate increase in airplane pitch attitude
is required to maintain altitude. Similarly, effective torque
control means counteracting yaw with rudder pressure.
As the power is reduced, the altimeter is primary for pitch,
the heading indicator is primary for bank, and the manifold
pressure gauge is momentarily primary for power (at 15"
Hg in this example). Control pressures should be trimmed
off as the airplane decelerates. As the airspeed approaches
the desired airspeed of 100 knots, the manifold pressure
is adjusted to approximately 18" Hg and becomes the
supporting power instrument. The ASI again becomes
primary for power. [Figure 5-24]

Airspeed Changes in Straight-and-Level Flight
Practice of airspeed changes in straight-and-level flight provides
an excellent means of developing increased proficiency in all
three basic instrument skills, and brings out some common

errors to be expected during training in straight-and-level flight.
Having learned to control the airplane in a clean configuration
(minimum drag conditions), increase proficiency in crosscheck and control by practicing speed changes while extending
or retracting the flaps and landing gear. While practicing, be
sure to comply with the airspeed limitations specified in the
POH/AFM for gear and flap operation.
Sudden and exaggerated attitude changes may be necessary
in order to maintain straight-and-level flight as the landing
gear is extended and the flaps are lowered in some airplanes.
The nose tends to pitch down with gear extension, and when
flaps are lowered, lift increases momentarily (at partial flap
settings) followed by a marked increase in drag as the flaps
near maximum extension.
Control technique varies according to the lift and drag
characteristics of each airplane. Accordingly, knowledge of
the power settings and trim changes associated with different
combinations of airspeed, gear and flap configurations will
reduce instrument cross-check and interpretation problems.
For example, assume that in straight-and-level flight
instruments indicate 120 knots with power at 23" Hg/2,300
revolutions per minute (rpm), gear and flaps up. After
reduction in airspeed, with gear and flaps fully extended,
straight-and-level flight at the same altitude requires 25"
Hg manifold pressure/2,500 rpm. Maximum gear extension
speed is 115 knots; maximum flap extension speed is 105

Figure 5-24. Straight-and-Level Flight (Reduced Airspeed Stabilized).

5-11

1.

Maintain rpm at 2,500, since a high power setting will
be used in full drag configuration.

2.

Reduce manifold pressure to 10" Hg. As the airspeed
decreases, increase cross-check speed.

Changes in attitude, power, or configuration will require a
trim adjustment in most cases. Using trim alone to establish
a change in aircraft attitude invariably leads to erratic aircraft
control. Smooth and precise attitude changes are best attained
by a combination of control pressures and trim adjustments.
Therefore, when used correctly, trim adjustment is an aid to
smooth aircraft control.

3.

Make trim adjustments for an increased angle of attack
and decrease in torque.

Common Errors in Straight-and-Level Flight

knots. Airspeed reduction to 95 knots, gear and flaps down,
can be made in the following manner:

4.

Lower the gear at 115 knots. The nose may tend to
pitch down and the rate of deceleration increases.
Increase pitch attitude to maintain constant altitude,
and trim off some of the back-elevator pressures.
If full flaps are lowered at 105 knots, cross-check,
interpretation, and control must be very rapid. A
simpler technique is to stabilize attitude with gear
down before lowering the flaps.

5.

Since 18" Hg manifold pressure will hold level
flight at 100 knots with the gear down, increase
power smoothly to that setting until the ASI shows
approximately 105 knots, and retrim. The attitude
indicator now shows approximately two-and-a-half
bar width nose-high in straight-and-level flight.

6.

Actuate the flap control and simultaneously increase
power to the predetermined setting (25" Hg) for the
desired airspeed, and trim off the pressures necessary
to hold constant altitude and heading. The attitude
indicator now shows a bar width nose-low in straightand-level flight at 95 knots.

Proficiency in straight-and-level flight is attained when a
pilot can consistently maintain constant altitude and heading
with smooth pitch, bank, power, and trim control during the
pronounced changes in aircraft attitude.
Trim Technique
Proper trim technique is essential for smooth and precise
aircraft control during all phases of flight. By relieving all
control pressures, it is much easier to hold a given attitude
constant, and devote more attention to other flight deck
duties.
An aircraft is trimmed by applying control pressures to
establish a desired attitude, then adjusting the trim so the
aircraft will maintain that attitude when the flight controls are
released. Trim the aircraft for coordinated flight by centering
the ball of the turn-and-slip indicator, by using rudder trim in
the direction the ball is displaced from the center. Differential
power control on multiengine aircraft is an additional factor
affecting coordinated flight. Use balanced power or thrust,
when possible, to aid in maintaining coordinated flight.

5-12

Pitch
Pitch errors usually result from the following faults:
1.

Improper adjustment of the attitude indicator’s
miniature aircraft to the wings level attitude.
Following the initial level off from a climb, check the
attitude indicator and make any necessary adjustment
in the miniature aircraft for level flight indication at
normal cruise airspeed.

2.

Insufficient cross-check and interpretation of pitch
instruments. For example, the airspeed indication is
low. The pilot, believing a nose-high attitude exists,
applies forward pressure without noting that a low
power setting is the cause of the airspeed discrepancy.
Increase cross-check speed to include all relevant
instrument indications before making a control input.

3.

Uncaging the attitude indicator (if caging feature is
present) when the airplane is not in level flight. The
altimeter and heading indicator must be stabilized with
airspeed indication at normal cruise before pulling
out the caging knob, to obtain correct indications in
straight-and-level flight at normal cruise airspeed.

4.

Failure to interpret the attitude indicator in terms of
the existing airspeed.

5.

Late pitch corrections. Pilots commonly like to leave
well enough alone. When the altimeter indicates a 20
foot error, there is a reluctance to correct it, perhaps
because of fear of overcontrolling. If overcontrolling
is the anticipated error, practice small corrections and
find the cause of overcontrolling. If any deviation is
tolerated, errors will increase.

6.

Chasing the vertical speed indications. This tendency
can be corrected by proper cross-check of other
pitch instruments, as well as by increasing overall
understanding of instrument characteristics.

7.

Using excessive pitch corrections for the altimeter
evaluation. Rushing a pitch correction by making a
large pitch change usually aggravates the existing
error, saving neither time nor effort.

8.

9.

Failure to maintain established pitch corrections, a
common error associated with cross-check and trim
errors. For example, having established a pitch change
to correct an altitude error, there is a tendency to
slow down the cross-check, waiting for the airplane
to stabilize in the new pitch attitude. To maintain
the attitude, continue to cross-check and trim off the
pressures.
Fixations during cross-check. After initiating a
heading correction, for example, there is a tendency
to become preoccupied with bank control and miss
errors in pitch attitude. Likewise, during an airspeed
change, unnecessary gazing at the power instrument
is common. A small error in power setting is of less
consequence than large altitude and heading errors.
The airplane will not decelerate any faster by staring
at the manifold pressure gauge.

Power
Power errors usually result from the following faults:
1.

Failure to know the power settings and pitch attitudes
appropriate to various airspeeds and airplane
configurations.

2.

Abrupt use of throttle.

3.

Failure to lead the airspeed when making power
changes. For example, during airspeed reduction in
level flight, especially with gear and flaps extended,
adjust the throttle to maintain the slower speed before
the airspeed actually reaches the desired speed.
Otherwise, the airplane will decelerate to a speed
lower than that desired, resulting in additional power
adjustments. The amount of lead depends upon how
fast the airplane responds to power changes.

4.

Fixation on airspeed or manifold pressure instruments
during airspeed changes, resulting in erratic control
of both airspeed and power.

Heading
Heading errors usually result from the following faults:
Failure to cross-check the heading indicator, especially
during changes in power or pitch attitude.

Trim

2.

Misinterpretation of changes in heading, with resulting
corrections in the wrong direction.

1.

3.

Failure to note and remember a preselected heading.

Improper adjustment of seat or rudder pedals for
comfortable position of legs and feet. Tension in the
ankles makes it difficult to relax rudder pressures.

4.

Failure to observe the rate of heading change and its
relation to bank attitude.

2.

5.

Overcontrolling in response to heading changes,
especially during changes in power settings.

Confusion about the operation of trim devices, which
differ among various airplane types. Some trim wheels
are aligned appropriately with the airplane’s axes;
others are not. Some rotate in a direction contrary to
what is expected.

6.

Anticipating heading changes with premature
application of rudder control.

3.

7.

Failure to correct small heading deviations. Unless
zero error in heading is the goal, a pilot will tolerate
larger and larger deviations. Correction of a 1° error
takes a lot less time and concentration than correction
of a 20° error.

Faulty sequence in trim technique. Trim should be
used not as a substitute for control with the wheel
(stick) and rudders, but to relieve pressures already
held to stabilize attitude. As proficiency is gained,
little conscious effort will be required to trim off the
pressures as they occur.

4.

Excessive trim control. This induces control pressures
that must be held until the airplane is trimmed
properly. Use trim frequently and in small amounts.

5.

Failure to understand the cause of trim changes. Lack
of understanding the basic aerodynamics related to
basic instrument skills will cause a pilot to continually
lag behind the airplane.

1.

8.

9.

Correcting with improper bank attitude. If correcting
a 10° heading error with 20° of bank, the airplane
will roll past the desired heading before the bank
is established, requiring another correction in the
opposite direction. Do not multiply existing errors
with errors in corrective technique.

Trim errors usually result from the following faults:

Failure to note the cause of a previous heading error
and thus repeating the same error. For example, the
airplane is out of trim, with a left wing low tendency.
Repeated corrections for a slight left turn are made,
yet trim is ignored.

10. Failure to set the heading indicator properly or failure
to uncage it.
5-13

Straight Climbs and Descents
Climbs
For a given power setting and load condition, there is only
one attitude that will give the most efficient rate of climb.
The airspeed and climb power setting that will determine this
climb attitude are given in the performance data found in the
POH/AFM. Details of the technique for entering a climb vary
according to airspeed on entry and the type of climb (constant
airspeed or constant rate) desired. (Heading and trim control
are maintained as discussed in Straight-and-Level Flight.)

Entry
To enter a constant-airspeed climb from cruising airspeed,
raise the miniature aircraft to the approximate nose-high
indication for the predetermined climb speed. The attitude
will vary according to the type of airplane. Apply light backelevator pressure to initiate and maintain the climb attitude.
The pressures will vary as the airplane decelerates. Power
may be advanced to the climb power setting simultaneously
with the pitch change, or after the pitch change is established
and the airspeed approaches climb speed. If the transition
from level flight to climb is smooth, the VSI will show an
immediate trend upward, continue to move slowly, and
then stop at a rate appropriate to the stabilized airspeed and
attitude. (Primary and supporting instruments for the climb
entry are shown in Figure 5-25.)

Figure 5-25. Climb Entry for Constant Airspeed Climb.

5-14

Once the airplane stabilizes at a constant airspeed and attitude,
the ASI is primary for pitch and the heading indicator remains
primary for bank. [Figure 5-26] Monitor the tachometer or
manifold pressure gauge as the primary power instrument to
ensure the proper climb power setting is being maintained. If
the climb attitude is correct for the power setting selected, the
airspeed will stabilize at the desired speed. If the airspeed is
low or high, make an appropriately small pitch correction.
To enter a constant airspeed climb, first complete the airspeed
reduction from cruise airspeed to climb speed in straightand-level flight. The climb entry is then identical to entry
from cruising airspeed, except that power must be increased
simultaneously to the climb setting as the pitch attitude is
increased. Climb entries on partial panel are more easily
and accurately controlled if entering the maneuver from
climbing speed.
The technique for entering a constant rate climb is very
similar to that used for entry to a constant-airspeed climb
from climb airspeed. As the power is increased to the
approximate setting for the desired rate, simultaneously
raise the miniature aircraft to the climbing attitude for the
desired airspeed and rate of climb. As the power is increased,
the ASI is primary for pitch control until the vertical speed
approaches the desired value. As the vertical speed needle
stabilizes, it becomes primary for pitch control and the ASI
becomes primary for power control. [Figure 5-27]

Figure 5-26. Stabilized Climb at Constant Airspeed.

Figure 5-27. Stabilized Climb at Constant Rate.

5-15

Pitch and power corrections must be promptly and closely
coordinated. For example, if the vertical speed is correct, but
the airspeed is low, add power. As the power is increased,
the miniature aircraft must be lowered slightly to maintain
constant vertical speed. If the vertical speed is high and the
airspeed is low, lower the miniature aircraft slightly and note
the increase in airspeed to determine whether or not a power
change is also necessary. [Figure 5-28] Familiarity with the
approximate power settings helps to keep pitch and power
corrections at a minimum.

Leveling Off
To level off from a climb and maintain an altitude, it is
necessary to start the level off before reaching the desired
altitude. The amount of lead varies with rate of climb and
pilot technique. If the airplane is climbing at 1,000 fpm, it will
continue to climb at a decreasing rate throughout the transition
to level flight. An effective practice is to lead the altitude by
10 percent of the vertical speed shown (500 fpm/ 50-foot lead,
1,000 fpm/100-foot lead).
To level off at cruising airspeed, apply smooth, steady
forward-elevator pressure toward level flight attitude for the
speed desired. As the attitude indicator shows the pitch change,
the vertical speed needle will move slowly toward zero, the
altimeter needle will move more slowly, and the airspeed will
show acceleration. [Figure 5-29] When the altimeter, attitude

Figure 5-28. Airspeed Low and Vertical Speed High—Reduce Pitch.

5-16

indicator, and VSI show level flight, constant changes in
pitch and torque control will have to be made as the airspeed
increases. As the airspeed approaches cruising speed, reduce
power to the cruise setting. The amount of lead depends upon
the rate of acceleration of the airplane.
To level off at climbing airspeed, lower the nose to the pitch
attitude appropriate to that airspeed in level flight. Power
is simultaneously reduced to the setting for that airspeed
as the pitch attitude is lowered. If power reduction is at a
rate proportionate to the pitch change, airspeed will remain
constant.
Descents
A descent can be made at a variety of airspeeds and attitudes
by reducing power, adding drag, and lowering the nose
to a predetermined attitude. The airspeed will eventually
stabilize at a constant value. Meanwhile, the only flight
instrument providing a positive attitude reference, is the
attitude indicator. Without the attitude indicator (such as
during a partial panel descent), the ASI, the altimeter, and
the VSI will show varying rates of change until the airplane
decelerates to a constant airspeed at a constant attitude.
During the transition, changes in control pressure and trim,
as well as cross-check and interpretation, must be accurate
to maintain positive control.

Figure 5-29. Level Off at Cruising Speed.

Entry
The following method for entering descents is effective
with or without an attitude indicator. First, reduce airspeed
to a selected descent airspeed while maintaining straightand-level flight, then make a further reduction in power
(to a predetermined setting). As the power is adjusted,
simultaneously lower the nose to maintain constant airspeed,
and trim off control pressures.
During a constant airspeed descent, any deviation from the
desired airspeed calls for a pitch adjustment. For a constant
rate descent, the entry is the same, but the VSI is primary for
pitch control (after it stabilizes near the desired rate), and the
ASI is primary for power control. Pitch and power must be
closely coordinated when corrections are made, as they are
in climbs. [Figure 5-30]

Leveling Off
The level off from a descent must be started before reaching
the desired altitude. The amount of lead depends upon the
rate of descent and control technique. With too little lead, the
airplane will tend to overshoot the selected altitude unless
technique is rapid. Assuming a 500 fpm rate of descent, lead
the altitude by 100–150 feet for a level off at an airspeed
higher than descending speed. At the lead point, add power to
the appropriate level flight cruise setting. [Figure 5-31] Since
the nose will tend to rise as the airspeed increases, hold
forward elevator pressure to maintain the vertical speed at

the descending rate until approximately 50 feet above the
altitude, and then smoothly adjust the pitch attitude to the
level flight attitude for the airspeed selected.
To level off from a descent at descent airspeed, lead the desired
altitude by approximately 50 feet, simultaneously adjusting
the pitch attitude to level flight and adding power to a setting
that will hold the airspeed constant. [Figure 5-32] Trim off
the control pressures and continue with the normal straightand-level flight cross-check.
Common Errors in Straight Climbs and Descents
Common errors result from the following faults:
1.

Overcontrolling pitch on climb entry. Until the pitch
attitudes related to specific power settings used in
climbs and descents are known, larger than necessary
pitch adjustments are made. One of the most difficult
habits to acquire during instrument training is to
restrain the impulse to disturb a flight attitude until
the result is known. Overcome the inclination to
make a large control movement for a pitch change,
and learn to apply small control pressures smoothly,
cross-checking rapidly for the results of the change,
and continuing with the pressures as instruments show
the desired results. Small pitch changes can be easily
controlled, stopped, and corrected; large changes are
more difficult to control.

5-17

Figure 5-30. Constant Airspeed Descent, Airspeed High—Reduce Power.

Figure 5-31. Level Off Airspeed Higher Than Descent Airspeed.

5-18

Figure 5-32. Level Off at Descent Airspeed.

2.

Failure to vary the rate of cross-check during speed,
power, or attitude changes or climb or descent
entries.

3.

Failure to maintain a new pitch attitude. For example,
raising the nose to the correct climb attitude, and as
the airspeed decreases, either overcontrol and further
increase the pitch attitude, or allow the nose to lower. As
control pressures change with airspeed changes, crosscheck must be increased and pressures readjusted.

4.

Failure to trim off pressures. Unless the airplane is
trimmed, there will be difficulty in determining whether
control pressure changes are induced by aerodynamic
changes or by the pilot’s own movements.

5.

Failure to learn and use proper power settings.

6.

Failure to cross-check both airspeed and vertical speed
before making pitch or power adjustments.

7.

Improper pitch and power coordination on slow-speed
level offs, due to slow cross-check of airspeed and
altimeter indications.

8.

Failure to cross-check the VSI against the other pitch
control instruments, resulting in chasing the vertical
speed.

9.

Failure to note the rate of climb or descent to determine
the lead for level offs, resulting in overshooting or
undershooting the desired altitude.

10. Ballooning (allowing the nose to pitch up) on level
offs from descents, resulting from failure to maintain
descending attitude with forward-elevator pressure as
power is increased to the level flight cruise setting.
11. Failure to recognize the approaching straight-and-level
flight indications as level off is completed. Maintain
an accelerated cross-check until positively established
in straight-and-level flight.

Turns
Standard Rate Turns
A standard rate turn is one in which the pilot will do a
complete 360° circle in two minutes, or 3° per second. A
standard rate turn, although always 3° per second, will
require higher angles of bank as airspeed increases. To enter a
standard rate level turn, apply coordinated aileron and rudder
pressures in the desired direction of turn. Pilots commonly
roll into turns at a much too rapid rate. During initial training
in turns, base control pressures on the rate of cross-check
and interpretation. Maneuvering an airplane faster than
the capability to keep up with the changes in instrument
indications only creates the need to make corrections.
A rule of thumb to determine the approximate angle of bank
required for a standard rate turn is to use 15 percent of the
true airspeed. A simple way to determine this amount is to

5-19

divide the airspeed by 10 and add one-half the result. For
example, at 100 knots, approximately 15° of bank is required
(100 ÷ 10 = 10 + 5 = 15); at 120 knots, approximately 18°
of bank is needed for a standard rate turn.
On the roll-in, use the attitude indicator to establish
the approximate angle of bank, and then check the turn
coordinator’s miniature aircraft for a standard rate turn
indication or the aircraft’s turn-and-bank indicator. Maintain
the bank for this rate of turn, using the turn coordinator’s
miniature aircraft as the primary bank reference and the
attitude indicator as the supporting bank instrument.
[Figure 5-33] Note the exact angle of bank shown on
the banking scale of the attitude indicator when the turn
coordinator indicates a standard rate turn.
During the roll-in, check the altimeter, VSI, and attitude
indicator for the necessary pitch adjustments as the vertical
lift component decreases with an increase in bank. If constant
airspeed is to be maintained, the ASI becomes primary for
power, and the throttle must be adjusted as drag increases. As
the bank is established, trim off the pressures applied during
pitch and power changes.
To recover to straight-and-level flight, apply coordinated
aileron and rudder pressures opposite to the direction of the
turn. Strive for the same rate of roll-out used to roll into the
turn; fewer problems will be encountered in estimating the
lead necessary for roll-out on exact headings, especially on

Figure 5-33. Standard Rate Turn, Constant Airspeed.

5-20

partial panel maneuvers. Upon initiation of the turn recovery,
the attitude indicator becomes the primary bank instrument.
When the airplane is approximately level, the heading
indicator is the primary bank instrument as in straight-andlevel flight. Pitch, power, and trim adjustments are made as
changes in vertical lift component and airspeed occur. The
ball should be checked throughout the turn, especially if
control pressures are held rather than trimmed off.
Some airplanes are very stable during turns, requiring only
slight trim adjustments that permit hands-off flight while the
airplane remains in the established attitude. Other airplanes
require constant, rapid cross-check and control during turns to
correct overbanking tendencies. Due to the interrelationship
of pitch, bank, and airspeed deviations during turns, crosscheck must be fast in order to prevent an accumulation of
errors.
Turns to Predetermined Headings
As long as an airplane is in a coordinated bank, it continues
to turn. Thus, the roll-out to a desired heading must be started
before the heading is reached. The amount of lead varies with
the relationship between the rate of turn, angle of bank, and
rate of recovery. For small heading changes, use a bank angle
that does not exceed the number of degrees to be turned.
Lead the desired heading by one-half the number of degrees
of bank used. For example, if a 10° bank is used during a
change in heading, start the roll-out 5° before reaching the
desired heading. For larger changes in heading, the amount

of lead varies since the angle of bank for a standard rate turn
varies with the true airspeed.
Practice with a lead of one-half the angle of bank until the
precise lead a given technique requires is determined. If
rates of roll-in and roll-out are consistent, the precise amount
of lead suitable to a particular roll-out technique can be
determined.
Timed Turns
A timed turn is a turn in which the clock and the turn
coordinator are used to change heading by a specific number
of degrees in a given time. For example, in a standard rate turn
(3° per second), an airplane turns 45° in 15 seconds; in a half
standard rate turn, the airplane turns 45° in 30 seconds.
Prior to performing timed turns, the turn coordinator should
be calibrated to determine the accuracy of its indications.
[Figure 5-34] Establish a standard rate turn as indicated by
the turn coordinator, and as the sweep-second hand of the
clock passes a cardinal point (12, 3, 6, 9), check the heading
on the heading indicator. While holding the indicated rate
of turn constant, note the indicated heading changes at 10
second intervals. If the airplane turns more than or less than
30° in that interval, a respectively larger or smaller deflection
of the miniature aircraft of the turn coordinator is necessary
to produce a standard rate turn. After calibrating the turn
coordinator during turns in each direction, note the corrected
deflections, if any, and apply them during all timed turns.

The same cross-check and control technique is used in making
a timed turn that is used to execute turns to predetermined
headings, except the clock is substituted for the heading
indicator. The miniature aircraft of the turn coordinator is
primary for bank control, the altimeter is primary for pitch
control, and the ASI is primary for power control. Start the
roll-in when the clock’s second hand passes a cardinal point,
hold the turn at the calibrated standard rate indication (or
half-standard rate for small heading changes), and begin the
roll-out when the computed number of seconds has elapsed.
If the rates of roll-in and roll-out are the same, the time taken
during entry and recovery does not need to be considered in
the time computation.
Practice timed turns with a full instrument panel and check
the heading indicator for the accuracy of turns. If the turns are
executed without the gyro heading indicator, use the magnetic
compass at the completion of the turn to check turn accuracy,
taking compass deviation errors into consideration.
Compass Turns
In most small airplanes, the magnetic compass is the only
direction-indicating instrument independent of other airplane
instruments and power sources. Because of its operating
characteristics, called compass errors, pilots are prone to
use it only as a reference for setting the heading indicator,
but knowledge of magnetic compass characteristics permits
full use of the instrument to turn the airplane to correct and
maintain headings.

Figure 5-34. Turn Coordinator Calibration.

5-21

Remember the following points when making turns to
magnetic compass headings or when using the magnetic
compass as a reference for setting the heading indicator:
1.

If on a north heading and a turn is started to the east
or west, the compass indication lags, or indicates a
turn in the opposite direction.

2.

If on a south heading and a turn is started toward the
east or west, the compass indication precedes the turn,
indicating a greater amount of turn than is actually
occurring.

3.

When on an east or west heading, the compass
indicates correctly when starting a turn in either
direction.

4.

If on an east or west heading, acceleration results in
a north turn indication; deceleration results in a south
turn indication.

5.

When maintaining a north or south heading, no error
results from diving, climbing, or changing airspeed.

With an angle of bank between 15° and 18°, the amount of
lead or lag to be used when turning to northerly or southerly
headings varies with, and is approximately equal to, the
latitude of the locality over which the turn is being made.
When turning to a heading of north, the lead for roll-out must
include the number of degrees of change of latitude, plus the
lead normally used in recovery from turns. During a turn to
a south heading, maintain the turn until the compass passes
south the number of degrees of latitude, minus normal rollout lead. [Figure 5-35]
For example, when turning from an easterly direction to
north, where the latitude is 30°, start the roll-out when the
compass reads 37° (30° plus one-half the 15° angle of bank,
or whatever amount is appropriate for the rate of roll-out).
When turning from an easterly direction to south, start the
roll-out when the magnetic compass reads 203° (180° plus
30° minus one-half the angle of bank). When making similar
turns from a westerly direction, the appropriate points at
which to begin the roll-out would be 323° for a turn to north,
and 157° for a turn to south.
When turning to a heading of east or west from a northerly
direction, start the roll-out approximately 10° to 12° before
the east or west indication is reached. When turning to an
east or west heading from a southerly direction, start the
rollout approximately 5° before the east or west indication
is reached. When turning to other headings, the lead or lag
must be interpolated.
Abrupt changes in attitude or airspeed and the resulting erratic
movements of the compass card make accurate interpretations

5-22

Figure 5-35. North and South Turn Error.

of the instrument very difficult. Proficiency in compass turns
depends on knowledge of compass characteristics, smooth
control technique, and accurate bank-and-pitch control.
Steep Turns
For purposes of instrument flight training in conventional
airplanes, any turn greater than a standard rate is considered
steep. [Figure 5-36] The exact angle of bank at which a
normal turn becomes steep is unimportant. What is important
is learning to control the airplane with bank attitudes in
excess of those normally used on instruments. Practicing
steep turns will not only increase proficiency in the basic
instrument flying skills, but also enable smooth, quick, and
confident reactions to unexpected abnormal flight attitudes
under instrument flight conditions.
Pronounced changes occur in the effects of aerodynamic
forces on aircraft control at progressively greater bank
attitudes. Skill in cross-check, interpretation, and control is
increasingly necessary in proportion to the amount of these
changes, though the techniques for entering, maintaining, and
recovering from the turn are the same in principle for steep
turns as for shallower turns.
Enter a steep turn in the same way as a shallower turn, but
prepare to cross-check rapidly as the turn steepens. Because
of the greatly reduced vertical lift component, pitch control
is usually the most difficult aspect of this maneuver. Unless

immediately noted and corrected with a pitch increase, the
loss of vertical lift results in rapid movement of the altimeter,
vertical speed, and airspeed needles. The faster the rate of
bank change, the more suddenly the lift changes occur. If
a cross-check is fast enough to note the immediate need

for pitch changes, smooth, steady back elevator pressure
will maintain constant altitude. However, overbanking
to excessively steep angles without adjusting pitch as the
bank changes occur, requires increasingly stronger elevator
pressure. The loss of vertical lift and increase in wing loading
finally reach a point at which further application of backelevator pressure tightens the turn without raising the nose.
How does a pilot recognize overbanking and low pitch
attitude? What should a pilot do to correct them? If a rapid
downward movement of the altimeter needle or vertical speed
needle, together with an increase in airspeed, is observed
despite application of back elevator pressure, the airplane is in
a diving spiral. [Figure 5-37] Immediately shallow the bank
with smooth and coordinated aileron and rudder pressures,
hold or slightly relax elevator pressure, and increase the crosscheck of the attitude indicator, altimeter, and VSI. Reduce
power if the airspeed increase is rapid. When the vertical
speed trends upward, the altimeter needle will move slower
as the vertical lift increases. When the elevator is effective in
raising the nose, hold the bank attitude shown on the attitude
indicator and adjust elevator control pressures smoothly for
the nose-high attitude appropriate to the bank maintained.
If pitch control is consistently late on entries to steep turns,
rollout immediately to straight-and-level flight and analyze
possible errors. Practice shallower turns initially and learn the
attitude changes and control responses required, then increase
the banks as a quicker and more accurate cross-check and
control techniques are developed.

Figure 5-36. Steep Left Turn.

The power necessary to maintain constant airspeed increases
as the bank and drag increase. With practice, the power

Figure 5-37. Diving Spiral.

5-23

settings appropriate to specific bank attitudes are learned, and
adjustments can be made without undue attention to airspeed
and power instruments. During training in steep turns, as in
any other maneuver, attend to the most important tasks first.
Keep the pitch attitude relatively constant, and more time can
be devoted to cross-check and instrument interpretation.
During recovery from steep turns to straight-and-level
flight, elevator and power control must be coordinated with
bank control in proportion to the changes in aerodynamic
forces. Back elevator pressures must be released and power
decreased. The common errors associated with steep turns are
the same as those discussed later in this section. Remember,
errors are more exaggerated, more difficult to correct, and
more difficult to analyze unless rates of entry and recovery
are consistent with the level of proficiency in the three basic
instrument flying skills.
Climbing and Descending Turns
To execute climbing and descending turns, combine the
technique used in straight climbs and descents with the various
turn techniques. The aerodynamic factors affecting lift and
power control must be considered in determining power
settings, and the rate of cross-check and interpretation must be
increased to enable control of bank as well as pitch changes.
Change of Airspeed During Turns
Changing airspeed during turns is an effective maneuver
for increasing proficiency in all three basic instrument
skills. Since the maneuver involves simultaneous changes
in all components of control, proper execution requires
rapid cross-check and interpretation as well as smooth

Figure 5-38. Change of Airspeed During Turn.

5-24

control. Proficiency in the maneuver will also contribute
to confidence in the instruments during attitude and power
changes involved in more complex maneuvers. Pitch and
power control techniques are the same as those used during
changes in airspeed in straight-and-level flight.
The angle of bank necessary for a given rate of turn is
proportional to the true airspeed. Since the turns are executed
at a standard rate, the angle of bank must be varied in direct
proportion to the airspeed change in order to maintain a
constant rate of turn. During a reduction of airspeed, decrease
the angle of bank and increase the pitch attitude to maintain
altitude and a standard rate turn.
The altimeter and turn coordinator indications should remain
constant throughout the turn. The altimeter is primary for
pitch control and the miniature aircraft of the turn coordinator
is primary for bank control. The manifold pressure gauge (or
tachometer) is primary for power control while the airspeed
is changing. As the airspeed approaches the new indication,
the ASI becomes primary for power control.
Two methods of changing airspeed in turns may be used. In the
first method, airspeed is changed after the turn is established.
[Figure 5-38] In the second method, the airspeed change is
initiated simultaneously with the turn entry. The first method
is easier, but regardless of the method used, the rate of crosscheck must be increased as power is reduced. As the airplane
decelerates, check the altimeter and VSI for necessary pitch
changes and the bank instruments for required bank changes.
If the miniature aircraft of the turn coordinator indicates a
deviation from the desired deflection, adjust the bank. Adjust

pitch attitude to maintain altitude. When approaching the
desired airspeed, pitch attitude becomes primary for power
control and the manifold pressure gauge (or tachometer) is
adjusted to maintain the desired airspeed. Trim is important
throughout the maneuver to relieve control pressures.

Bank
1.

Overcontrolling, resulting in overbanking upon turn
entry, overshooting and undershooting headings, as
well as aggravated pitch, airspeed, and trim errors.

Until control technique is very smooth, frequent cross-check
of the attitude indicator is essential to prevent overcontrolling
and to provide approximate bank angles appropriate to the
changing airspeeds.

2.

Fixation on a single bank instrument. On a 90° change
of heading, for example, leave the heading indicator
out of the cross-check for approximately 20 seconds
after establishing a standard rate turn, since at 3°
per second the turn will not approach the lead point
until that time has elapsed. Make the cross-check
selective, checking only what needs to be checked at
the appropriate time.

3.

Failure to check for precession of the horizon bar
following recovery from a turn. If the heading
indicator shows a change in heading when the attitude
indicator shows level flight, the airplane is turning. If
the ball is centered, the attitude gyro has precessed;
if the ball is not centered, the airplane may be in a
slipping or skidding turn. Center the ball with rudder
pressure, check the attitude indicator and heading
indicator, stop the heading change if it continues, and
retrim.

4.

Failure to use the proper degree of bank for the amount
of heading change desired. Rolling into a 20° bank
for a heading change of 10° will normally overshoot
the heading. Use the bank attitude appropriate to the
amount of heading change desired.

5.

Failure to remember the heading to which the aircraft
is being turned. This fault is likely when rushing the
maneuver.

6.

Turning in the wrong direction, due to misreading or
misinterpreting the heading indicator, or to confusion
regarding the location of points on the compass. Turn
in the shortest direction to reach a given heading,
unless there is a specific reason to turn the long way
around. Study the compass rose and visualize at least
the positions of the eight major points around the
azimuth. A number of methods can be used to make
quick computations for heading changes. For example,
to turn from a heading of 305° to a heading of 110°,
would a pilot turn right or left for the shortest way
around? Subtracting 200 from 305 and adding 20,
gives 125° as the reciprocal of 305°; therefore, execute
the turn to the right. Likewise, to figure the reciprocal
of a heading less than 180°, add 200 and subtract 20.
Computations are done more quickly using multiples
of 100s and 10s than by adding or subtracting 180°
from the actual heading; therefore, the method
suggested above may save time and confusion.

Bank and heading errors result from the following faults:

Common Errors in Turns

Pitch
Pitch errors result from the following faults:
1.

Preoccupation with bank control during turn entry
and recovery. If 5 seconds are required to roll into a
turn, check the pitch instruments as bank pressures
are initiated. If bank control pressure and rate of bank
change are consistent, a sense of the time required
for an attitude change will be developed. During the
interval, check pitch, power, and trim—as well as
bank—controlling the total attitude instead of one
factor at a time.

2.

Failure to understand or remember the need for
changing the pitch attitude as the vertical lift
component changes, resulting in consistent loss of
altitude during entries.

3.

Changing the pitch attitude before it is necessary. This
fault is very likely if a cross-check is slow and rate
of entry too rapid. The error occurs during the turn
entry due to a mechanical and premature application
of back-elevator control pressure.

4.

Overcontrolling the pitch changes. This fault
commonly occurs with the previous error.

5.

Failure to properly adjust the pitch attitude as the
vertical lift component increases during the roll-out,
resulting in consistent gain in altitude on recovery to
headings.

6.

Failure to trim during turn entry and following turn
recovery (if turn is prolonged).

7.

Failure to maintain straight-and-level cross-check
after roll-out. This error commonly follows a perfectly
executed turn.

8.

Erratic rates of bank change on entry and recovery,
resulting from failure to cross-check the pitch
instruments with a consistent technique appropriate
to the changes in lift.

5-25

7.

Failure to check the ball of the turn coordinator when
interpreting the instrument for bank information. If the
roll rate is reduced to zero, the miniature aircraft of
the turn coordinator indicates only direction and rate
of turn. Unless the ball is centered, do not assume the
turn is resulting from a banked attitude.

Power
Power and airspeed errors result from the following faults:
1.

Failure to cross-check the ASI as pitch changes are
made.

2.

Erratic use of power control. This may be due to
improper throttle friction control, inaccurate throttle
settings, chasing the airspeed readings, abrupt or
overcontrolled pitch-and-bank changes, or failure
to recheck the airspeed to note the effect of a power
adjustment.

3.

Poor coordination of throttle control with pitch-andbank changes, associated with slow cross-check or
failure to understand the aerodynamic factors related
to turns.

Approach to Stall
Practicing approach to stall recoveries in various airplane
configurations should build confidence in a pilot’s ability to
control the airplane in unexpected situations. Approach to
stall should be practiced from straight flight and from shallow
banks. The objective is to practice recognition and recovery
from the approach to a stall.
Prior to stall recovery practice, select a safe altitude above
the terrain, an area free of conflicting air traffic, appropriate
weather, and the availability of radar traffic advisory
service.
Approaches to stalls are accomplished in the following
configurations:
1.

Takeoff configuration—should begin from level flight
near liftoff speed. Power should be applied while
simultaneously increasing the angle of attack to induce
an indication of a stall.

2.

Clean configuration—should begin from a reduced
airspeed, such as pattern airspeed, in level flight.
Power should be applied while simultaneously
increasing the angle of attack to induce an indication
of a stall.

3.

Approach or landing configuration—should be
initiated at the appropriate approach or landing
airspeed. The angle of attack should be smoothly
increased to induce an indication of a stall.

Trim
Trim errors result from the following faults:
1.

Failure to recognize the need for a trim change due
to slow cross-check and interpretation. For example,
a turn entry at a rate too rapid for a cross-check leads
to confusion in cross-check and interpretation, with
resulting tension on the controls.

2.

Failure to understand the relationship between trim
and attitude/power changes.

3.

Chasing the vertical speed needle. Overcontrolling
leads to tension and prevents sensing the pressures to
be trimmed off.

4.

Failure to trim following power changes.

Errors During Compass Turns
In addition to the faults discussed above, the following errors
connected with compass turns should be noted:
1.

Faulty understanding or computation of lead and
lag.

2.

Fixation on the compass during the roll-out. Until
the airplane is in straight-and-level unaccelerated
flight, it is unnecessary to read the indicated heading.
Accordingly, after the roll-out, cross-check for
straight-and-level flight before checking the accuracy
of the turn.

5-26

Recoveries should be prompt in response to a stall warning
device or an aerodynamic indication by smoothly reducing
the angle of attack and applying maximum power, or as
recommended by the POH/AFM. The recovery should be
completed without an excessive loss of altitude, and on a
predetermined heading, altitude, and airspeed.

Unusual Attitudes and Recoveries
An unusual attitude is an airplane attitude not normally
required for instrument flight. Unusual attitudes may
result from a number of conditions, such as turbulence,
disorientation, instrument failure, confusion, preoccupation
with flight deck duties, carelessness in cross-checking,
errors in instrument interpretation, or lack of proficiency in
aircraft control. Since unusual attitudes are not intentional
maneuvers during instrument flight, except in training, they
are often unexpected, and the reaction of an inexperienced
or inadequately trained pilot to an unexpected abnormal
flight attitude is usually instinctive rather than intelligent

and deliberate. This individual reacts with abrupt muscular
effort, which is purposeless and even hazardous in turbulent
conditions, at excessive speeds, or at low altitudes. However,
with practice, the techniques for rapid and safe recovery from
unusual attitudes can be mastered.
When an unusual attitude is noted during the cross-check,
the immediate problem is not how the airplane got there, but
what it is doing and how to get it back to straight-and-level
flight as quickly as possible.
Recognizing Unusual Attitudes
As a general rule, any time an instrument rate of movement
or indication other than those associated with the basic
instrument flight maneuvers is noted, assume an unusual
attitude and increase the speed of cross-check to confirm the
attitude, instrument error, or instrument malfunction.
Nose-high attitudes are shown by the rate and direction of
movement of the altimeter needle, vertical speed needle, and
airspeed needle, as well as the immediately recognizable
indication of the attitude indicator (except in extreme
attitudes). [Figure 5-39] Nose-low attitudes are shown
by the same instruments, but in the opposite direction.
[Figure 5-40]

Recovery from Unusual Attitudes
In moderate unusual attitudes, the pilot can normally
reorient by establishing a level flight indication on the
attitude indicator. However, the pilot should not depend on
this instrument if the attitude indicator is the spillable type,
because its upset limits may have been exceeded or it may
have become inoperative due to mechanical malfunction.
If it is the nonspillable-type instrument and is operating
properly, errors up to 5° of pitch-and-bank may result and its
indications are very difficult to interpret in extreme attitudes.
As soon as the unusual attitude is detected, the recommended
recovery procedures stated in the POH/AFM should be
initiated. If there are no recommended procedures stated in
the POH/AFM, the recovery should be initiated by reference
to the ASI, altimeter, VSI, and turn coordinator.
Nose-High Attitudes
If the airspeed is decreasing, or below the desired airspeed,
increase power (as necessary in proportion to the observed
deceleration), apply forward elevator pressure to lower the
nose and prevent a stall, and correct the bank by applying
coordinated aileron and rudder pressure to level the
miniature aircraft and center the ball of the turn coordinator.
The corrective control applications are made almost
simultaneously, but in the sequence given above. A level
pitch attitude is indicated by the reversal and stabilization

Figure 5-39. Unusual Attitude—Nose-High.

5-27

Figure 5-40. Unusual Attitude—Nose-Low.

of the ASI and altimeter needles. Straight coordinated flight
is indicated by the level miniature aircraft and centered ball
of the turn coordinator.
Nose-Low Attitudes
If the airspeed is increasing, or is above the desired airspeed,
reduce power to prevent excessive airspeed and loss of
altitude. Correct the bank attitude with coordinated aileron
and rudder pressure to straight flight by referring to the turn
coordinator. Raise the nose to level flight attitude by applying
smooth back elevator pressure. All components of control
should be changed simultaneously for a smooth, proficient
recovery. However, during initial training a positive,
confident recovery should be made by the numbers, in the
sequence given above. A very important point to remember
is that the instinctive reaction to a nose-down attitude is to
pull back on the elevator control.
After initial control has been applied, continue with a
fast cross-check for possible overcontrolling, since the
necessary initial control pressures may be large. As the rate
of movement of altimeter and ASI needles decreases, the
attitude is approaching level flight. When the needles stop
and reverse direction, the aircraft is passing through level
flight. As the indications of the ASI, altimeter, and turn
coordinator stabilize, incorporate the attitude indicator into
the cross-check.
5-28

The attitude indicator and turn coordinator should be checked
to determine bank attitude and then corrective aileron
and rudder pressures should be applied. The ball should
be centered. If it is not, skidding and slipping sensations
can easily aggravate disorientation and retard recovery. If
entering the unusual attitude from an assigned altitude (either
by an instructor or by air traffic control (ATC) if operating
under instrument flight rules (IFR)), return to the original
altitude after stabilizing in straight-and-level flight.
Common Errors in Unusual Attitudes
Common errors associated with unusual attitudes include
the following faults:
1.

Failure to keep the airplane properly trimmed. A flight
deck interruption when holding pressures can easily
lead to inadvertent entry into unusual attitudes.

2

Disorganized flight deck. Hunting for charts, logs,
computers, etc., can seriously distract attention from
the instruments.

3.

Slow cross-check and fixations. The impulse is to
stop and stare when noting an instrument discrepancy
unless a pilot has trained enough to develop the skill
required for immediate recognition.

4.

Attempting to recover by sensory sensations other than
sight. The discussion of disorientation in Chapter 1,
Human Factors, indicates the importance of trusting
the instruments.

5.

Failure to practice basic instrument skills. All of the
errors noted in connection with basic instrument skills
are aggravated during unusual attitude recoveries until
the elementary skills have been mastered.

Instrument Takeoff
Competency in instrument takeoffs will provide the
proficiency and confidence necessary for use of flight
instruments during departures under conditions of low
visibility, rain, low ceilings, or disorientation at night. A
sudden rapid transition from “visual” to “instrument” flight
can result in serious disorientation and control problems.
Instrument takeoff techniques vary with different types of
airplanes, but the method described below is applicable
whether the airplane is single- or multiengine; tricycle gear
or conventional gear.
Align the airplane with the centerline of the runway with
the nosewheel or tailwheel straight. Lock the tailwheel, if so
equipped, and hold the brakes firmly to avoid creeping while
preparing for takeoff. Set the heading indicator with the nose
index on the 5° mark nearest the published runway heading
to allow instant detection of slight changes in heading during
the takeoff. Make certain that the instrument is uncaged (if it
has a caging feature) by rotating the knob after uncaging and
checking for constant heading indication. If using an electric
heading indicator with a rotatable needle, rotate the needle
so that it points to the nose position, under the top index.
Advance the throttle to an rpm that will provide partial rudder
control. Release the brakes, advancing the power smoothly
to takeoff setting.
During the takeoff roll, hold the heading constant on the
heading indicator by using the rudder. In multiengine,
propeller-driven airplanes, also use differential throttle to
maintain direction. The use of brakes should be avoided,
except as a last resort, as it usually results in overcontrolling
and extending the takeoff roll. Once the brakes are released,
any deviation in heading must be corrected instantly.
As the airplane accelerates, cross-check both heading
indicator and ASI rapidly. The attitude indicator may precess
to a slight nose-up attitude. As flying speed is approached
(approximately 15–25 knots below takeoff speed), smoothly
apply elevator control for the desired takeoff attitude on the
attitude indicator. This is approximately a two bar width
climb indication for most small airplanes.

Continue with a rapid cross-check of heading indicator and
attitude indicator as the airplane leaves the ground. Do not
pull it off; let it fly off while holding the selected attitude
constant. Maintain pitch-and-bank control by referencing
the attitude indicator, and make coordinated corrections in
heading when indicated on the heading indicator. Crosscheck the altimeter and VSI for a positive rate of climb
(steady clockwise rotation of the altimeter needle, and the VSI
showing a stable rate of climb appropriate to the airplane).
When the altimeter shows a safe altitude (approximately 100
feet), raise the landing gear and flaps, maintaining attitude by
referencing the attitude indicator. Because of control pressure
changes during gear and flap operation, overcontrolling is
likely unless the pilot notes pitch indications accurately and
quickly. Trim off control pressures necessary to hold the
stable climb attitude. Check the altimeter, VSI, and airspeed
for a smooth acceleration to the predetermined climb speed
(altimeter and airspeed increasing, vertical speed stable). At
climb speed, reduce power to climb setting (unless full power
is recommended for climb by the POH/AFM and trim).
Throughout the instrument takeoff, cross-check and
interpretation must be rapid, and control positive and smooth.
During liftoff, gear and flap retraction, power reduction, and
the changing control reactions demand rapid cross-check,
adjustment of control pressures, and accurate trim changes.
Common Errors in Instrument Takeoffs
Common errors during the instrument takeoff include the
following:
1.

Failure to perform an adequate flight deck check
before the takeoff. Pilots have attempted instrument
takeoffs with inoperative airspeed indicators (pitot
tube obstructed), gyros caged, controls locked,
and numerous other oversights due to haste or
carelessness.

2.

Improper alignment on the runway. This may result
from improper brake application, allowing the airplane
to creep after alignment, or from alignment with the
nosewheel or tailwheel cocked. In any case, the result
is a built-in directional control problem as the takeoff
starts.

3.

Improper application of power. Abrupt application
of power complicates directional control. Add power
with a smooth, uninterrupted motion.

4.

Improper use of brakes. Incorrect seat or rudder pedal
adjustment, with feet in an uncomfortable position,
frequently cause inadvertent application of brakes and
excessive heading changes.

5-29

5.

Overcontrolling rudder pedals. This fault may be
caused by late recognition of heading changes, tension
on the controls, misinterpretation of the heading
indicator (and correcting in the wrong direction),
failure to appreciate changing effectiveness of rudder
control as the aircraft accelerates, and other factors. If
heading changes are observed and corrected instantly
with small movement of the rudder pedals, swerving
tendencies can be reduced.

6.

Failure to maintain attitude after becoming airborne.
If the pilot reacts to seat-of-the-pants sensations when
the airplane lifts off, pitch control is guesswork.
The pilot may either allow excessive pitch or apply
excessive forward elevator pressure, depending on the
reaction to trim changes.

7.

8.

Inadequate cross-check. Fixations are likely during trim
changes, attitude changes, gear and flap retractions,
and power changes. Once an instrument or a control
input is applied, continue the cross-check and note the
effect during the next cross-check sequence.
Inadequate interpretation of instruments. Failure to
understand instrument indications immediately indicates
that further study of the maneuver is necessary.

Figure 5-41. Racetrack Pattern (Entire Pattern in Level Flight).

NOTE: This pattern is an exercise combining use of the clock
with basic maneuvers.
Procedure Turn
A procedure turn is a maneuver that facilitates:
•

A reversal in flight direction.

•

A descent from an initial approach fix or assigned
altitude to a permissible altitude (usually the procedure
turn altitude).

•

An interception of the inbound course at a sufficient
distance allowing the aircraft to become aligned with
the final approach.

Basic Instrument Flight Patterns
Flight patterns are basic maneuvers, flown by sole reference
to the instruments rather than outside visual clues, for the
purpose of practicing basic attitude flying. The patterns
simulate maneuvers encountered on instrument flights
such as holding patterns, procedure turns, and approaches.
After attaining a reasonable degree of proficiency in basic
maneuvers, apply these skills to the various combinations of
individual maneuvers. The following practice flight patterns
are directly applicable to operational instrument flying.
Racetrack Pattern
1.

Time 3 minutes straight-and-level flight from A to B.
[Figure 5-41] During this interval, reduce airspeed to
the holding speed appropriate for the aircraft.

2.

Start a 180° standard rate turn to the right at B. Roll-out
at C on the reciprocal of the heading originally used
at A.

3.

Time a 1 minute straight-and-level flight from C to D.

4.

Start a 180° standard rate turn to the right at D, rollingout on the original heading.

5.

Fly 1 minute on the original heading, adjusting
the outbound leg so that the inbound segment is 1
minute.

5-30

Procedure turn types include the 45° turn, the 80/260 turn, and
the teardrop turn. All of these turns are normally conducted no
more than 10 nautical miles (NM) from the primary airport.
The procedure turn altitude generally provides a minimum
of 1,000' obstacle clearance in the procedure turn area (not
necessarily within the 10 NM arc around the primary airport).
Turns may have to be increased or decreased but should not
exceed 30° of a bank angle.
Standard 45° Procedure Turn
1.

Start timing at point A (usually identified on approach
procedures by a fix). For example, fly outbound on a
heading of 360° for a given time (2 minutes, in this
example). [Figure 5-42]

2.

After flying outbound for 2 minutes (point B), turn left
45° to a heading of 315° using a standard rate turn.
After roll-out and stabilizing, fly this new heading
of 315° for 40 seconds and the aircraft will be at the
approximate position of C.

2.

At B, enter a left standard rate turn of 80° to a heading
of 280°.

3.

At the completion of the 80° turn to 280° (Point C),
immediately turn right 260°, rolling-out on a heading
of 180° (Point D) and also the reciprocal of the entry
heading.

Teardrop Patterns
There are three typical teardrop procedure turns. A 30°, 20°,
and a 10° teardrop pattern. The below steps indicate actions
for all three starting on a heading of 360°. [Figure 5-44]
1.

Figure 5-42. Standard Procedure Turn (Entire Pattern in Level

Flight).

3.

At point C, turn 225° right (using a standard rate turn)
which will provide a heading of 180°. The timing is
such that in a no wind environment, the pilot will be
aligned with the final approach course of 180° at D.
Wind conditions, however must be considered during
the execution of the procedure turn. Compensating
for wind may result in changes to outbound time,
procedure turn heading and/or time and minor changes
in the inbound turn.

80/260 Procedure Turn
1.

Start timing at point A (usually identified on approach
procedures by a fix). For example, fly outbound on a
heading of 360° for 2 minutes. [Figure 5-43]

2.

At point B (after stabilizing on the outbound course)
turn left:
•

30° to a heading of 330° and time for 1 minute

•

20° to a heading of 340° and time for 2 minutes

•

10° to a heading of 350° and time for 3 minutes

After the appropriate time above (Point C), make a
standard rate turn to the right for:
•

30° teardrop—210° to the final course heading
of 180° (Point D)

•

20° teardrop—200° to the final course heading
of 180° (Point D)

•

10° teardrop—190° to the final course heading
of 180° (Point D)

By using the different teardrop patterns, a pilot is afforded the
ability to manage time more efficiently. For instance, a 10°
pattern for 3 minutes provides about three times the distance

Figure 5-43. 80/260 Procedure Turn (Entire Pattern in Level

Flight).

Figure 5-44. Teardrop Pattern (Entire Pattern in Level Flight).

5-31

(and time) than a 30° pattern. Pattern selection should be
based upon an individual assessment of the procedure turn
requirements to include wind, complexity, the individual
preparedness, etc.

Pattern II
Steps:
1.

At A, start timing for 2 minutes from A to B; reduce
airspeed to approach speed. [Figure 5-46]

Circling Approach Patterns

2.

At B, make a standard rate turn to the left for 45°.

Pattern I

3.

At the completion of the turn, time for 1 minute to
C.

4.

At C, turn right for 180° to D; fly for 1-1/2 minutes
to E, lowering the landing gear and flaps.

5.

At E, turn right for 180°, rolling-out at F.

6.

At F, enter a 500 fpm rate descent. At the end of a 500
foot descent, enter a straight constant-airspeed climb,
retracting gear and flaps.

1.

At A, start timing for 2 minutes from A to B; reduce
airspeed to approach speed. [Figure 5-45]

2.

At B, make a standard rate turn to the left for 45°.

3.

At the completion of the turn, time for 45 seconds to
C.

4.

At C, turn to the original heading; fly 1 minute to D,
lowering the landing gear and flaps.

5.

At D, turn right 180°, rolling-out at E on the reciprocal
of the entry heading.

6.

At E, enter a 500 fpm rate descent. At the end of a 500
foot descent, enter a straight constant-airspeed climb,
retracting gear and flaps.

Figure 5-46. Circling Approach Pattern II (Imaginary Runway).

Figure 5-45. Circling Approach Pattern I (Imaginary Runway).

5-32

Chapter 5, Section II

Airplane Basic
Flight Maneuvers
Using an Electronic Flight Display
Introduction
The previous chapters have laid the foundation for instrument
flying. The pilot’s ability to use and interpret the information
displayed and apply corrective action is required to maneuver
the aircraft and maintain safe flight. A pilot must recognize
that each aircraft make and model flown may require a
different technique. Aircraft weight, speed, and configuration
changes require the pilot to vary his or her technique in order
to perform successful attitude instrument flying. A pilot must
become familiar with all sections of the Pilot’s Operating
Handbook/Airplane Flight Manual (POH/AFM) prior to
performing any flight maneuver.
Chapter 5–II describes basic attitude instrument flight
maneuvers and explains how to perform each one by
interpreting the indications presented on the electronic
flight display (EFD). In addition to normal flight maneuvers,
“partial panel” flight will be addressed. With the exception of
the instrument takeoff, all flight maneuvers can be performed
on “partial panel” with the Attitude Heading Reference
System (AHRS) unit simulated or rendered inoperative.

5-33

Straight-and-Level Flight
Pitch Control
The pitch attitude of an airplane is the angle between the
longitudinal axis of the airplane and the actual horizon.
In level flight, the pitch attitude varies with airspeed and
load. For training purposes, the latter factor can normally
be disregarded in small airplanes. At a constant airspeed,
there is only one specific pitch attitude for level flight. At
slow cruise speeds, the level flight attitude is nose-high with
indications as in Figure 5-47; at fast cruise speeds, the level
flight attitude is nose-low. [Figure 5-48] Figure 5-49 shows
the indications for the attitude at normal cruise speeds.

The instruments that directly or indirectly indicate pitch on
the Primary Flight Display (PFD) are the attitude indicator,
altimeter, vertical speed indicator (VSI), airspeed indicator
(ASI), and both airspeed and altitude trend indicators.

Attitude Indicator
The attitude indicator gives the pilot a direct indication of
the pitch attitude. The increased size of the attitude display
on the EFD system greatly increases situational awareness
for the pilot. Most attitude indicators span the entire width
of the PFD screen.
The aircraft pitch attitude is controlled by changing the
deflection of the elevator. As the pilot pulls back on the
control yoke causing the elevator to rise, the yellow chevron
will begin to show a displacement up from the artificial
horizon line. This is caused by the AHRS unit sensing the
changing angle between the longitudinal plane of the earth
and the longitudinal axis of the aircraft.
The attitude indicator displayed on the PFD screen is a
representation of outside visual cues. Rather than rely on
the natural horizon visible during visual flight rules (VFR)
flight, the pilot must rely on the artificial horizon of the
PFD screen.
During normal cruise airspeed, the point of the yellow
chevron (aircraft symbol) will be positioned on the artificial
horizon. Unlike conventional attitude indicators, the EFD
attitude indicator does not allow for manipulating the position
of the chevron in relationship to the artificial horizon. The
position is fixed and therefore will always display the pitch
angle as calculated by the AHRS unit.

Figure 5-47. Pitch Attitude and Airspeed in Level Flight, Slow

Cruise Speed.

Figure 5-48. Pitch Attitude Decreasing and Airspeed Increasing—Indicates Need to Increase Pitch.

5-34

must smoothly and precisely manipulate the elevator control
forces in order to change the pitch attitude.
To master the ability to smoothly control the elevator, a pilot
must develop a very light touch on the control yoke. The
thumb and two fingers are normally sufficient to move the
control yoke. The pilot should avoid griping the yoke with
a full fist. When a pilot grips the yoke with a full fist, there
is a tendency to apply excess pressures, thus changing the
aircraft attitude.
Practice making smooth, small pitch changes both up and
down until precise corrections can be made. With practice
a pilot will be able to make pitch changes in 1° increments,
smoothly controlling the attitude of the aircraft.

Figure 5-49. Various Pitch Attitudes (Right), Aircraft Shown in

Level Flight.

The attitude indicator only shows pitch attitude and does
not indicate altitude. A pilot should not attempt to maintain
level flight using the attitude indicator alone. It is important
for the pilot to understand how small displacements both up
and down can affect the altitude of the aircraft. To achieve
this, the pilot should practice increasing the pitch attitude
incrementally to become familiar with how each degree of
pitch changes the altitude. [Figures 5-50 and 5-51] In both
cases, the aircraft will slow and gain altitude.
The full height of the chevron is approximately 5° and
provides an accurate reference for pitch adjustment. It is
imperative that the pilot make the desired changes to pitch
by referencing the attitude indicator and then trimming off
any excess control pressures. Relieving these pressures will
allow for a more stabilized flight and will reduce pilot work
load. Once the aircraft is trimmed for level flight, the pilot

Figure 5-50. Pitch Indications for Various Attitudes (1° through 5°).

The last step in mastering elevator control is trim. Trimming
the aircraft to relieve any control pressures is essential
for smooth attitude instrument flight. To accomplish this,
momentarily release the control yoke. Note which way the
aircraft pitch attitude wants to move. Grasp the control yoke
again and then reapply the pressure to return the attitude
to the previous position. Apply trim in the direction of the
control pressure. Small applications of trim will make large
changes in the pitch attitude. Be patient and make multiple
changes to trim, if necessary.
Once the aircraft is in trim, relax on the control yoke as
much as practicable. When pressure is held on the yoke,
unconscious pressures are applied to the elevator and ailerons
which displaces the aircraft from its desired flight path. If the
aircraft is in trim, in calm, non-turbulent air, a pilot should be
able to release the control yoke and maintain level flight for
extended periods of time. This is one of the hardest skills to
learn prior to successfully flying in instrument meteorological
conditions (IMC).

Figure 5-51. Pitch Illustrated at 10°.

5-35

Altimeter
At constant power, any deviation from level flight (except
in turbulent air) must be the result of a pitch change. If the
power is constant, the altimeter gives an indirect indication
of the pitch attitude in level flight. Since the altitude should
remain constant when the airplane is in level flight, any
deviation from the desired altitude signals the need for a
pitch change. For example, if the aircraft is gaining altitude,
the nose must be lowered.

During instrument flight with limited instrumentation, it is
imperative that only small and precise control inputs are
made. Once a needle movement is indicated denoting a
deviation in altitude, the pilot needs to make small control
inputs to stop the deviation. Rapid control movements will
only compound the deviation by causing an oscillation effect.
This type of oscillation can quickly cause the pilot to become
disoriented and begin to fixate on the altitude. Fixation on
the altimeter can lead to a loss of directional control as well
as airspeed control.

In the PFD, as the pitch starts to change, the altitude trend
indicator on the altitude tape will begin to show a change
in the direction of displacement. The rate at which the trend
indicator grows and the altimeter numbers change aids the
pilot in determining how much of a pitch change is necessary
to stop the trend.

As a general rule of thumb, for altitude deviations less than
100 feet, utilize a pitch change of 1°, which equates to 1/5 of
the thickness of the chevron. Small incremental pitch changes
will allow the performance to be evaluated and will eliminate
overcontrolling of the aircraft.

As a pilot becomes familiar with a specific aircraft’s
instruments, he or she learns to correlate pitch changes,
altimeter tapes, and altitude trend indicators. By adding the
altitude tape display and the altitude trend indicator into the
scan along with the attitude indicator, a pilot starts to develop
the instrument cross-check.

Instrumentation needs to be utilized collectively, but
failures will occur which leave the pilot with only limited
instrumentation. That is why partial panel flying training
is important. If the pilot understands how to utilize each
instrument independently, no significant change is encountered
in carrying out the flight when other instruments fail.

Partial Panel Flight

VSI Tape

One important skill to practice is partial panel flight by
referencing the altimeter as the primary pitch indicator.
Practice controlling the pitch by referencing the altitude
tape and trend indicator alone without the use of the attitude
indicator. Pilots need to learn to make corrections to altitude
deviations by referencing the rate of change of the altitude
tape and trend indicator. When operating in IMC and in a
partial panel configuration, the pilot should avoid abrupt
changes to the control yoke. Reacting abruptly to altitude
changes can lead to large pitch changes and thus a larger
divergence from the initial altitude.

The VSI tape provides for an indirect indication of pitch
attitude and gives the pilot a more immediate indication of a
pending altitude deviation. In addition to trend information,
the vertical speed also gives a rate indication. By using the
VSI tape in conjunction with the altitude trend tape, a pilot
will have a better understanding of how much of a correction
needs to be made. With practice, the pilot will learn the
performance of a particular aircraft and know how much
pitch change is required in order to correct for a specific
rate indication.

When a pilot is controlling pitch by the altitude tape and
altitude trend indicators alone, it is possible to overcontrol the
aircraft by making a larger than necessary pitch correction.
Overcontrolling will cause the pilot to move from a nosehigh attitude to a nose-low attitude and vice versa. Small
changes to pitch are required to insure prompt corrective
actions are taken to return the aircraft to its original altitude
with less confusion.
When an altitude deviation occurs, two actions need to be
accomplished. First, make a smooth control input to stop
the needle movement. Once the altitude tape has stopped
moving, make a change to the pitch attitude to start back to
the entry altitude.

5-36

Unlike older analog VSIs, new glass panel displays have
instantaneous VSIs. Older units had a lag designed into the
system that was utilized to indicate rate information. The
new glass panel displays utilize a digital air data computer
that does not indicate a lag. Altitude changes are shown
immediately and can be corrected for quickly.
The VSI tape should be used to assist in determining what
pitch changes are necessary to return to the desired altitude.
A good rule of thumb is to use a vertical speed rate of change
that is double the altitude deviation. However, at no time
should the rate of change be more than the optimum rate of
climb or descent for the specific aircraft being flown. For
example, if the altitude is off by 200 feet from the desired
altitude, then a 400 feet per minute (fpm) rate of change

would be sufficient to get the aircraft back to the original
altitude. If the altitude has changed by 700 feet, then doubling
that would necessitate a 1,400 fpm change. Most aircraft
are not capable of that, so restrict changes to no more than
optimum climb and descent. An optimum rate of change
would vary between 500 and 1,000 fpm.
One error the instrument pilot encounters is overcontrolling.
Overcontrolling occurs when a deviation of more than
200 fpm is indicated over the optimum rate of change. For
example, an altitude deviation of 200 feet is indicated on the
altimeter, a vertical speed rate of 400 feet should be indicated
on the gauge. If the vertical speed rate showed 600 fpm (200
more than optimum), the pilot would be overcontrolling the
aircraft.
When returning to altitude, the primary pitch instrument
is the VSI tape. If any deviation from the desired vertical
speed is indicated, make the appropriate pitch change using
the attitude indicator.
As the aircraft approaches the target altitude, the vertical
speed rate can be slowed in order to capture the altitude in a
more stabilized fashion. Normally within 10 percent of the
rate of climb or descent from the target altitude, begin to
slow the vertical speed rate in order to level off at the target
altitude. This will allow the pilot to level at the desired altitude
without rapid control inputs or experiencing discomfort due
to G-load.

indicating 1 knot changes in airspeed and also capable of
projecting airspeed trends.
When flying by reference to flight instruments alone, it
is imperative that all of the flight instruments be crosschecked for pitch control. By cross-checking all pitch related
instruments, the pilot can better visualize the aircraft attitude
at all times.
As previously stated, the primary instrument for pitch is the
instrument that gives the pilot the most pertinent information
for a specific parameter. When in level flight and maintaining
a constant altitude, what instrument shows a direct indication
of altitude? The only instrument that is capable of showing
altitude is the altimeter. The other instruments are supporting
instruments that are capable of showing a trend away from
altitude, but do not directly indicate an altitude.
The supporting instruments forewarn of an impending
altitude deviation. With an efficient cross-check, a proficient
pilot will be better able to maintain altitude.
Bank Control
This discussion assumes the aircraft is being flown in
coordinated flight which means the longitudinal axis of the
aircraft is aligned with the relative wind. On the PFD, the
attitude indicator shows if the wings are level. The turn rate
indicator, slip/skid indicator, and the heading indicator also
indicate whether or not the aircraft is maintaining a straight
(zero bank) flight path.

Airspeed Indicator (ASI)
The ASI presents an indirect indication of the pitch attitude.
At a constant power setting and pitch attitude, airspeed
remains constant. As the pitch attitude lowers, airspeed
increases, and the nose should be raised.
As the pitch attitude is increased, the nose of the aircraft will
raise, which will result in an increase in the angle of attack
as well as an increase in induced drag. The increased drag
will begin to slow the momentum of the aircraft which will
be indicated on the ASI. The airspeed trend indicator will
show a trend as to where the airspeed will be in 6 seconds.
Conversely, if the nose of the aircraft should begin to fall, the
angle of attack as well as induced drag will decrease.
There is a lag associated with the ASI when using it as a pitch
instrument. It is not a lag associated with the construction
of the ASI, but a lag associated with momentum change.
Depending on the rate of momentum change, the ASI may not
indicate a pitch change in a timely fashion. If the ASI is being
used as the sole reference for pitch change, it may not allow
for a prompt correction. However, if smooth pitch changes
are executed, modern glass panel displays are capable of

Attitude Indicator
The attitude indicator is the only instrument on the PFD that
has the capability of displaying the precise bank angle of the
aircraft. This is made possible by the display of the roll scale
depicted as part of the attitude indicator.
Figure 5-52 identifies the components that make up the
attitude indicator display. Note that the top of the display
is blue, representing sky, the bottom is brown, depicting
dirt, and the white line separating them is the horizon. The
lines parallel to the horizon line are the pitch scale which is
marked in 5° increments and labeled every 10°. The pitch
scale always remains parallel to the horizon.
The curved line in the blue area is the roll scale. The triangle
on the top of the scale is the zero index. The hash marks on
the scale represent the degree of bank. [Figure 5-53] The
roll scale always remains in the same position relative to
the horizon line.

5-37

Figure 5-53. Attitude Indicator Showing a 15° left bank.

Figure 5-52. Attitude Indicator.

The roll pointer indicates the direction and degree of bank.
[Figure 5-53] The roll pointer is aligned with the aircraft
symbol. The roll pointer indicates the angle of the lateral axis
of the aircraft compared to the natural horizon. The slip/skid
indicator will show if the longitudinal axis of the aircraft is
aligned with the relative wind, which is coordinated flight. With
the roll index and the slip/skid indicator aligned, any deflection,
either right or left of the roll index will cause the aircraft to turn
in that direction. With the small graduations on the roll scale, it
is easy to determine the bank angle within approximately 1°. In
coordinated flight, if the roll index is aligned with the roll pointer,
the aircraft is achieving straight flight.
An advantage of EFDs is the elimination of the precession
error. Precession error in analog gauges is caused by forces
being applied to a spinning gyro. With the new solid state
instruments, precession error has been eliminated.

between the rate at which the HSI changes heading displays
and the amount of bank angle required to meet that rate of
change. A very small rate of heading change means the bank
angle is small, and it will take more time to deviate from the
desired straight flight path. A larger rate of heading change
means a greater bank angle will happen at a faster rate.

Heading Indicator
The heading indicator is the large black box with a white
number that indicates the magnetic heading of the aircraft.
[Figure 5-54] The aircraft heading is displayed to the nearest
degree. When this number begins to change, the pilot should
be aware that straight flight is no longer being achieved.

Turn Rate Indicator
The turn rate indicator gives an indirect indication of bank. It is
a magenta trend indicator capable of displaying half-standard
as well as standard rate turns to both the left and right. The
turn indicator is capable of indicating turns up to 4° per second
by extending the magenta line outward from the standard
rate mark. If the rate of turn has exceeded 4° per second, the

Since the attitude indicator is capable of showing precise
pitch and bank angles, the only time that the attitude indicator
will be a primary instrument is when attempting to fly at a
specific bank angle or pitch angle. Other times, the attitude
instrument can be thought of as a control instrument.

Horizontal Situation Indicator (HSI)
The HSI is a rotating 360° compass card that indicates
magnetic heading. The HSI is the only instrument that is
capable of showing exact headings. The magnetic compass
can be used as a backup instrument in case of an HSI failure;
however, due to erratic, unstable movements, it is more likely
to be used a supporting instrument.
In order for the pilot to achieve the desired rate of change,
it is important for him or her to understand the relationship
5-38

Figure 5-54. Slip/Skid and Turn Rate Indicator.

magenta line can not precisely indicate where the heading
will be in the next 6 seconds, the magenta line freezes and an
arrowhead will be displayed. This alerts the pilot to the fact
that the normal range of operation has been exceeded.

Slip/Skid Indicator
The slip/skid indicator is the small portion of the lower
segmented triangle displayed on the attitude indicator. This
instrument depicts whether the aircraft’s longitudinal axis is
aligned with the relative wind. [Figure 5-54]
The pilot must always remember to cross-check the roll index
to the roll pointer when attempting to maintain straight flight.
Any time the heading remains constant and the roll pointer and
the roll index are not aligned, the aircraft is in uncoordinated
flight. To make a correction, the pilot should apply rudder
pressure to bring the aircraft back to coordinated flight.
Power Control
Power produces thrust which, with the appropriate angle of
attack of the wing, overcomes the forces of gravity, drag,
and inertia to determine airplane performance.

and heading, apply various control pressures in proportion
to the change in power. When power is added to increase
airspeed, the pitch instruments indicate a climb unless
forward-elevator control pressure is applied as the airspeed
changes. With an increase in power, the airplane tends to
yaw and roll to the left unless counteracting aileron and
rudder pressures are applied. Keeping ahead of these changes
requires increasing cross-check speed, which varies with the
type of airplane and its torque characteristics, the extent of
power and speed change involved.

Power Settings
Power control and airspeed changes are much easier when
approximate power settings necessary to maintain various
airspeeds in straight-and-level flight are known in advance.
However, to change airspeed by any appreciable amount, the
common procedure is to underpower or overpower on initial
power changes to accelerate the rate of airspeed change. (For
small speed changes, or in airplanes that decelerate or accelerate
rapidly, overpowering or underpowering is not necessary.)

Power control must be related to its effect on altitude and
airspeed, since any change in power setting results in a change
in the airspeed or the altitude of the airplane. At any given
airspeed, the power setting determines whether the airplane
is in level flight, in a climb, or in a descent. If the power is
increased in straight-and-level flight and the airspeed held
constant, the airplane will climb; if power is decreased while
the airspeed is held constant, the airplane will descend. On
the other hand, if altitude is held constant, the power applied
will determine the airspeed.
The relationship between altitude and airspeed determines the
need for a change in pitch or power. If the airspeed is off the
desired value, always check the altimeter before deciding that
a power change is necessary. Think of altitude and airspeed
as interchangeable; altitude can be traded for airspeed by
lowering the nose, or convert airspeed to altitude by raising
the nose. If altitude is higher than desired and airspeed is
low, or vice versa, a change in pitch alone may return the
airplane to the desired altitude and airspeed. [Figure 5-55] If
both airspeed and altitude are high or if both are low, then a
change in both pitch and power is necessary in order to return
to the desired airspeed and altitude. [Figure 5-56]
For changes in airspeed in straight-and-level flight, pitch,
bank, and power must be coordinated in order to maintain
constant altitude and heading. When power is changed to
vary airspeed in straight-and-level flight, a single-engine,
propeller-driven airplane tends to change attitude around all
axes of movement. Therefore, to maintain constant altitude

Figure 5-55. An aircraft decreasing in airspeed while gaining

altitude. In this case, the pilot has decreased pitch.

Figure 5-56. Figure shows both an increase in speed and altitude

where pitch adjustment alone is insufficient. In this situation, a
reduction of power is also necessary.

5-39

Consider the example of an airplane that requires 23" of
manifold pressure (Hg) to maintain a normal cruising airspeed
of 120 knots, and 18" Hg to maintain an airspeed of 100 knots.
The reduction in airspeed from 120 knots to 100 knots while
maintaining straight-and-level flight is discussed below and
illustrated in Figures 5-57, 5-58, and 5-59.
Instrument indications, prior to the power reduction, are
shown in Figure 5-57. The basic attitude is established and
maintained on the attitude indicator. The specific pitch,
bank, and power control requirements are detected on these
primary instruments:
Altimeter—Primary Pitch
Heading Indicator—Primary Bank
Airspeed Indicator—Primary Power
Supporting pitch and bank instruments are shown in
Figure 5-57. Note that the supporting power instrument is
the manifold pressure gauge (or tachometer if the propeller
is fixed pitch). However, when a smooth power reduction to
approximately 15" Hg (underpower) is made, the manifold
pressure gauge becomes the primary power instrument.
[Figure 5-58] With practice, power setting can be changed
with only a brief glance at the power instrument, by sensing
the movement of the throttle, the change in sound, and the
changes in the feel of control pressures.
As the thrust decreases, increase the speed of the cross-check
and be ready to apply left rudder, back-elevator, and aileron
control pressure the instant the pitch-and-bank instruments

Figure 5-57. Straight-and-Level Flight (Normal Cruising Speed).

5-40

show a deviation from altitude and heading. As proficiency
is obtained, a pilot will learn to cross-check, interpret, and
control the changes with no deviation of heading and altitude.
Assuming smooth air and ideal control technique, as airspeed
decreases, a proportionate increase in airplane pitch attitude
is required to maintain altitude. Similarly, effective torque
control means counteracting yaw with rudder pressure.
As the power is reduced, the altimeter is primary for pitch,
the heading indicator is primary for bank, and the manifold
pressure gauge is momentarily primary for power (at 15"
Hg in Figure 5-58). Control pressures should be trimmed
off as the airplane decelerates. As the airspeed approaches
the desired airspeed of 100 knots, the manifold pressure
is adjusted to approximately 18" Hg and becomes the
supporting power instrument. The ASI again becomes
primary for power. [Figure 5-58]

Airspeed Changes in Straight-and-Level Flight
Practice of airspeed changes in straight-and-level flight
provides an excellent means of developing increased
proficiency in all three basic instrument skills, and brings
out some common errors to be expected during training
in straight-and-level flight. Having learned to control the
airplane in a clean configuration (minimum drag conditions),
increase proficiency in cross-check and control by practicing
speed changes while extending or retracting the flaps and
landing gear. While practicing, be sure to comply with the
airspeed limitations specified in the POH/AFM for gear and
flap operation.

Figure 5-58. Straight-and-Level Flight (Airspeed Decreasing).

Figure 5-59. Straight-and-Level Flight (Reduced Airspeed Stabilized).

5-41

Sudden and exaggerated attitude changes may be necessary
in order to maintain straight-and-level flight as the landing
gear is extended and the flaps are lowered in some airplanes.
The nose tends to pitch down with gear extension, and when
flaps are lowered, lift increases momentarily (at partial flap
settings) followed by a marked increase in drag as the flaps
near maximum extension.
Control technique varies according to the lift and drag
characteristics of each airplane. Accordingly, knowledge of
the power settings and trim changes associated with different
combinations of airspeed, gear, and flap configurations will
reduce instrument cross-check and interpretation problems.
[Figure 5-60]
For example, assume that in straight-and-level flight
instruments indicate 120 knots with power at 23" Hg
manifold pressure/2,300 revolutions per minute (rpm), gear
and flaps up. After reduction in airspeed, with gear and flaps
fully extended, straight-and-level flight at the same altitude
requires 25" Hg manifold pressure/2,500 rpm. Maximum
gear extension speed is 115 knots; maximum flap extension
speed is 105 knots. Airspeed reduction to 95 knots, gear and
flaps down, can be made in the following manner:
1.

Maintain rpm at 2,500, since a high power setting will
be used in full drag configuration.

Figure 5-60. Cross-check Supporting Instruments.

5-42

2.

Reduce manifold pressure to 10" Hg. As the airspeed
decreases, increase cross-check speed.

3.

Make trim adjustments for an increased angle of attack
and decrease in torque.

4.

Lower the gear at 115 knots. The nose may tend to
pitch down and the rate of deceleration increases.
Increase pitch attitude to maintain constant altitude,
and trim off some of the back-elevator pressures.
If full flaps are lowered at 105 knots, cross-check,
interpretation, and control must be very rapid. A
simpler technique is to stabilize attitude with gear
down before lowering the flaps.

5.

Since 18" Hg manifold pressure will hold level
flight at 100 knots with the gear down, increase
power smoothly to that setting as the ASI shows
approximately 105 knots, and retrim. The attitude
indicator now shows approximately two-and-a-half
bar width nose-high in straight-and-level flight.

6.

Actuate the flap control and simultaneously increase
power to the predetermined setting (25" Hg) for the
desired airspeed, and trim off the pressures necessary
to hold constant altitude and heading. The attitude
indicator now shows a bar width nose-low in straightand-level flight at 95 knots.

Trim Technique
Trim control is one of the most important flight habits to
cultivate. Trimming refers to relieving any control pressures
that need to be applied by the pilot to the control surfaces to
maintain a desired flight attitude. The desired result is for the
pilot to be able to take his or her hands off the control surfaces
and have the aircraft remain in the current attitude. Once the
aircraft is trimmed for hands-off flight, the pilot is able to
devote more time to monitoring the flight instruments and
other aircraft systems.
In order to trim the aircraft, apply pressure to the control surface
that needs trimming and roll the trim wheel in the direction
pressure is being held. Relax the pressure that is being applied to
the control surface and monitor the primary instrument for that
attitude. If the desired performance is achieved, fly hands off. If
additional trimming is required, redo the trimming steps.
An aircraft is trimmed for a specific airspeed, not pitch attitude
or altitude. Any time an aircraft changes airspeed there is a
need to re-trim. For example, an aircraft is flying at 100 knots
straight-and-level. An increase of 50 rpm will cause the airspeed
to increase. As the airspeed increases, additional lift will be
generated and the aircraft will climb. Once the additional thrust
has stabilized at some higher altitude, the airspeed will again
stabilize at 100 knots.

This demonstrates how trim is associated with airspeed and
not altitude. If the initial altitude is to be maintained, forward
pressure would need to be applied to the control wheel while
the trim wheel needs to be rolled forward to eliminate any
control pressures. Rolling forward on the trim wheel is equal
to increasing for a trimmed airspeed. Any time the airspeed
is changed, re-trimming will be required. Trimming can be
accomplished during any transitional period; however, prior
to final trimming, the airspeed must be held constant. If the
airspeed is allowed to change, the trim will not be adjusted
properly and the altitude will vary until the airspeed for which
the aircraft is trimmed is achieved.
Common Errors in Straight-and-Level Flight

Pitch
Pitch errors usually result from the following errors:
1.

Improper adjustment of the yellow chevron (aircraft
symbol) on the attitude indicator.
Corrective Action: Once the aircraft has leveled off and
the airspeed has stabilized, make small corrections to
the pitch attitude to achieve the desired performance.
Cross-check the supporting instruments for validation.

2.

Insufficient cross-check and interpretation of pitch
instruments. [Figure 5-61]

Figure 5-61. Insufficient cross-check. The problem is power and not nose-high. In this case, the pilot decreased pitch inappropriately.

5-43

Example: The airspeed indication is low. The pilot,
believing a nose-high pitch attitude exists, applies
forward pressure without noting that a low power setting
is the cause of the airspeed discrepancy.
Corrective Action: Increase the rate of cross-check of all
the supporting flight instruments. Airspeed and altitude
should be stabilized before making a control input.
3.

Corrective Action: The pilot should initiate a pitch
change and then immediately trim the aircraft to
relieve any control pressures. A rapid cross-check
should be established in order to validate the desired
performance is being achieved.
6.

Devoting an unequal amount of time to one instrument
either for interpretation or assigning too much
importance to an instrument. Equal amounts of time
should be spent during the cross-check to avoid an
unnoticed deviation in one of the aircraft attitudes.

Acceptance of deviations.
Example: A pilot has an altitude range of ±100 feet
according to the practical test standards for straight-and
level-flight. When the pilot notices that the altitude has
deviated by 60 feet, no correction is made because the
altitude is holding steady and is within the standards.

Example: A pilot makes a correction to the pitch
attitude and then devotes all of the attention to the
altimeter to determine if the pitch correction is
valid. During this time, no attention is paid to the
heading indicator which shows a turn to the left.
[Figure 5-62]

Corrective Action: The pilot should cross-check the
instruments and, when a deviation is noted, prompt
corrective actions should be taken in order to bring the
aircraft back to the desired altitude. Deviations from
altitude should be expected but not accepted.
4.

Corrective Action: Small, smooth corrections should
be made in order to recover to the desired altitude
(0.5° to 2° depending on the severity of the deviation).
Instrument flying is comprised of small corrections to
maintain the aircraft attitude. When flying in IMC,
a pilot should avoid making large attitude changes
in order to avoid loss of aircraft control and spatial
disorientation.
5.

Failure to Maintain Pitch Corrections.
Pitch changes need to be made promptly and held for
validation. Many times pilots will make corrections
and allow the pitch attitude to change due to not
trimming the aircraft. It is imperative that any time a
pitch change is made; the trim is readjusted in order to
eliminate any control pressures that are being held. A
rapid cross-check will aid in avoiding any deviations
from the desired pitch attitude.
Example: A pilot notices a deviation in altitude. A
change in the pitch attitude is accomplished but no
adjustment to the trim is made. Distractions cause
the pilot to slow the cross-check and an inadvertent
reduction in the pressure to the control column
commences. The pitch attitude then changes, thus
complicating recovery to the desired altitude.

5-44

Corrective Action: The pilot should monitor all
instrumentation during the cross-check. Do not fixate
on one instrument waiting for validation. Continue to
scan all instruments to avoid allowing the aircraft to
begin a deviation in another attitude.

Overcontrolling—Excessive Pitch Changes.
Example: A pilot notices a deviation in altitude. In an
attempt to quickly return to altitude, the pilot makes a
large pitch change. The large pitch change destabilizes
the attitude and compounds the error.

Fixation During Cross-Check.

Heading
Heading errors usually result from but are not limited to the
following errors:
1.

Failure to cross-check the heading indicator, especially
during changes in power or pitch attitude.

2.

Misinterpretation of changes in heading, with resulting
corrections in the wrong direction.

3.

Failure to note and remember a preselected heading.

4.

Failure to observe the rate of heading change and its
relation to bank attitude.

5.

Overcontrolling in response to heading changes,
especially during changes in power settings.

6.

Anticipating heading changes with premature
application of rudder pressure.

7.

Failure to correct small heading deviations. Unless
zero error in heading is the goal, a pilot will tolerate
larger and larger deviations. Correction of a 1° error
takes far less time and concentration than correction
of a 20° error.

8.

Correcting with improper bank attitude. If correcting
a 10° heading error with a 20° bank correction, the
aircraft will roll past the desired heading before the
bank is established, requiring another correction in
the opposite direction. Do not multiply existing errors
with errors in corrective technique.

Figure 5-62. The pilot has fixated on pitch and altitude, leaving bank indications unattended. Note the trend line to the left.

9.

Failure to note the cause of a previous heading error
and thus repeating the same error. For example, the
airplane is out of trim, with a left wing low tendency.
Repeated corrections for a slight left turn are made,
yet trim is ignored.

Power
Power errors usually result from but are not limited to the
following errors:
1.

Failure to become familiar with the aircraft’s specific
power settings and pitch attitudes.

2.

Abrupt use of throttle.

3.

Failure to lead the airspeed when making power
changes, climbs or descents.
Example: When leveling off from a descent, increase
the power in order to avoid the airspeed from bleeding
off due to the decrease in momentum of the aircraft.
If the pilot waits to bring in the power until after the
aircraft is established in the level pitch attitude, the
aircraft will have already decreased below the speed
desired which will require additional adjustment in
the power setting.

4.

Fixation on airspeed tape or manifold pressure
indications during airspeed changes, resulting in

erratic control of airspeed, power, as well as pitch and
bank attitudes.

Trim
Trim errors usually result from the following faults:
1.

Improper adjustment of seat or rudder pedals for
comfortable position of legs and feet. Tension in the
ankles makes it difficult to relax rudder pressures.

2.

Confusion about the operation of trim devices, which
differ among various airplane types. Some trim wheels
are aligned appropriately with the airplane’s axes;
others are not. Some rotate in a direction contrary to
expectations.

3.

Failure to understand the principles of trim and that
the aircraft is being trimmed for airspeed, not a pitch
attitude.

4.

Faulty sequence in trim techniques. Trim should be
utilized to relieve control pressures, not to change
pitch attitudes. The proper trim technique has the pilot
holding the control wheel first and then trimming to
relieve any control pressures. Continuous trim changes
will be required as the power setting is changed.
Utilize the trim continuously, but in small amounts.

5-45

Straight Climbs and Descents
Each aircraft will have a specific pitch attitude and airspeed
that corresponds to the most efficient climb rate for a specified
weight. The POH/AFM contains the speeds that will produce
the desired climb. These numbers are based on maximum
gross weight. Pilots must be familiar with how the speeds will
vary with weight so they can compensate during flight.
Entry

Constant Airspeed Climb From Cruise Airspeed
To enter a constant airspeed climb from cruise airspeed,
slowly and smoothly apply aft elevator pressure in order
to raise the yellow chevron (aircraft symbol) until the tip
points to the desired degree of pitch. [Figure 5-63] Hold
the aft control pressure and smoothly increase the power
to the climb power setting. This increase in power may be

Figure 5-63. Constant Airspeed Climb From Cruise Airspeed.

5-46

initiated either prior to initiating the pitch change or after
having established the desired pitch setting. Consult the
POH/AFM for specific climb power settings if anything other
than a full power climb is desired. Pitch attitudes will vary
depending on the type of aircraft being flown. As airspeed
decreases, control forces will need to be increased in order
to compensate for the additional elevator deflection required
to maintain attitude. Utilize trim to eliminate any control
pressures. By effectively using trim, the pilot will be better
able to maintain the desired pitch without constant attention.
The pilot is thus able to devote more time to maintaining an
effective scan of all instrumentation.
The VSI should be utilized to monitor the performance of the
aircraft. With a smooth pitch transition, the VSI tape should
begin to show an immediate trend upward and stabilize on a

rate of climb equivalent to the pitch and power setting being
utilized. Depending on current weight and atmospheric
conditions, this rate will be different. This will require the
pilot to be knowledgeable of how weight and atmospheric
conditions affect aircraft performance.
Once the aircraft is stabilized at a constant airspeed and pitch
attitude, the primary flight instrument for pitch will be the ASI
and the primary bank instrument will be the heading indicator.
The primary power instrument will be the tachometer or the
manifold pressure gauge depending on the aircraft type. If the
pitch attitude is correct, the airspeed should slowly decrease
to the desired speed. If there is any variation in airspeed,
make small pitch changes until the aircraft is stabilized at
the desired speed. Any change in airspeed will require a trim
adjustment.

Constant Airspeed Climb from Established Airspeed
In order to enter a constant airspeed climb, first complete the
airspeed reduction from cruise airspeed to climb airspeed.
Maintain straight-and-level flight as the airspeed is reduced.
The entry to the climb is similar to the entry from cruise
airspeed with the exception that the power must be increased
when the pitch attitude is raised. [Figure 5-64] Power added
after the pitch change will show a decrease in airspeed due
to the increased drag encountered. Power added prior to a
pitch change will cause the airspeed to increase due to the
excess thrust.

Constant Rate Climbs
Constant rate climbs are very similar to the constant airspeed
climbs in the way the entry is made. As power is added,

Figure 5-64. Constant-Airspeed Climb From Established Airspeed.

5-47

smoothly apply elevator pressure to raise the yellow chevron
to the desired pitch attitude that equates to the desired vertical
speed rate. The primary instrument for pitch during the initial
portion of the maneuver is the ASI until the vertical speed
rate stabilizes and then the VSI tape becomes primary. The
ASI then becomes the primary instrument for power. If any
deviation from the desired vertical speed is noted, small
pitch changes will be required in order to achieve the desired
vertical speed. [Figure 5-65]
When making changes to compensate for deviations in
performance, pitch, and power, pilot inputs need to be
coordinated to maintain a stable flight attitude. For instance,
if the vertical speed is lower than desired but the airspeed is
correct, an increase in pitch will momentarily increase the
vertical speed. However, the increased drag will quickly
start to degrade the airspeed if no increase in power is made.
A change to any one variable will mandate a coordinated
change in the other.
Conversely, if the airspeed is low and the pitch is high, a
reduction in the pitch attitude alone may solve the problem.
Lower the nose of the aircraft very slightly to see if a power
reduction is necessary. Being familiar with the pitch and
power settings for the aircraft aids in achieving precise
attitude instrument flying.

Figure 5-65. Constant Rate Climbs.

5-48

Leveling Off
Leveling off from a climb requires a reduction in the pitch
prior to reaching the desired altitude. If no change in pitch
is made until reaching the desired altitude, the momentum
of the aircraft causes the aircraft to continue past the desired
altitude throughout the transition to a level pitch attitude. The
amount of lead to be applied depends on the vertical speed
rate. A higher vertical speed requires a larger lead for level
off. A good rule of thumb to utilize is to lead the level off
by 10 percent of the vertical speed rate (1,000 fpm ÷ 10 =
100 feet lead).
To level off at the desired altitude, refer to the attitude display
and apply smooth forward elevator pressure toward the desired
level pitch attitude while monitoring the VSI and altimeter
tapes. The rates should start to slow and airspeed should
begin to increase. Maintain the climb power setting until the
airspeed approaches the desired cruise airspeed. Continue to
monitor the altimeter to maintain the desired altitude as the
airspeed increases. Prior to reaching the cruise airspeed, the
power must be reduced to avoid overshooting the desired
speed. The amount of lead time that is required depends on
the speed at which the aircraft accelerates. Utilization of the
airspeed trend indicator can assist by showing how quickly
the aircraft will arrive at the desired speed.

To level off at climbing airspeed, lower the nose to the
appropriate pitch attitude for level flight with a simultaneous
reduction in power to a setting that will maintain the desired
speed. With a coordinated reduction in pitch and power there
should be no change in the airspeed.
Descents
Descending flight can be accomplished at various airspeeds
and pitch attitudes by reducing power, lowering the nose to
a pitch attitude lower than the level flight attitude, or adding
drag. Once any of these changes have been made, the airspeed
will eventually stabilize. During this transitional phase, the
only instrument that will display an accurate indication of
pitch is the attitude indicator. Without the use of the attitude
indicator (such as in partial panel flight), the ASI tape, the VSI
tape, and the altimeter tape will show changing values until

the aircraft stabilizes at a constant airspeed and constant rate
of descent. The altimeter tape continues to show a descent.
Hold pitch constant and allow the aircraft to stabilize. During
any change in attitude or airspeed, continuous application of
trim is required to eliminate any control pressures that need
to be applied to the control yoke. An increase in the scan rate
during the transition is important since changes are being
made to the aircraft flight path and speed. [Figure 5-66]
Entry
Descents can be accomplished with a constant rate, constant
airspeed or a combination. The following method can
accomplish any of these with or without an attitude indicator.
Reduce the power to allow the aircraft to decelerate to the
desired airspeed while maintaining straight-and-level flight.
As the aircraft approaches the desired airspeed, reduce the

Figure 5-66. The top image illustrates a reduction of power and descending at 500 fpm to an altitude of 5,000 feet. The bottom image

illustrates an increase in power and the initiation of leveling off.

5-49

power to a predetermined value. The airspeed continues to
decrease below the desired airspeed unless a simultaneous
reduction in pitch is performed. The primary instrument
for pitch is the ASI tape. If any deviation from the desired
speed is noted, make small pitch corrections by referencing
the attitude indicator and validate the changes made with the
airspeed tape. Utilize the airspeed trend indicator to judge if
the airspeed will be increasing and at what rate. Remember
to trim off any control pressures.

Common Errors in Straight Climbs and Descents
Climbing and descending errors usually result from but are
not limited to the following errors:
1.

Overcontrolling pitch on beginning the climb.
Aircraft familiarization is the key to achieving precise
attitude instrument flying. Until the pilot becomes
familiar with the pitch attitudes associated with
specific airspeeds, the pilot must make corrections
to the initial pitch settings. Changes do not produce
instantaneous and stabilized results; patience must be
maintained while the new speeds and vertical speed
rates stabilize. Avoid the temptations to make a change
and then rush into making another change until the
first one is validated. Small changes will produce more
expeditious results and allow for a more stabilized
flight path. Large changes to pitch and power are
more difficult to control and can further complicate
the recovery process.

2.

Failure to increase the rate of instrument cross-check.
Any time a pitch or power change is made, an increase
in the rate a pilot cross-checks the instrument is
required. A slow cross-check can lead to deviations
in other flight attitudes.

3.

Failure to maintain new pitch attitudes. Once a
pitch change is made to correct for a deviation, that
pitch attitude must be maintained until the change
is validated. Utilize trim to assist in maintaining the
new pitch attitude. If the pitch is allowed to change,
it is impossible to validate whether the initial pitch
change was sufficient to correct the deviation. The
continuous changing of the pitch attitude delays the
recovery process.

4.

Failure to utilize effective trim techniques. If control
pressures have to be held by the pilot, validation of
the initial correction will be impossible if the pitch
is allowed to vary. Pilots have the tendency to either
apply or relax additional control pressures when
manually holding pitch attitudes. Trim allows the
pilot to fly without holding pressure on the control
yoke.

5.

Failure to learn and utilize proper power settings. Any
time a pilot is not familiar with an aircraft’s specific
pitch and power settings, or does not utilize them, a
change in flight paths will take longer. Learn pitch
and power settings in order to expedite changing the
flight path.

6.

Failure to cross-check both airspeed and vertical speed
prior to making adjustments to pitch and or power. It is
possible that a change in one may correct a deviation
in the other.

The entry procedure for a constant rate descent is the same
except the primary instrument for pitch is the VSI tape.
The primary instrument for power will be the ASI. When
performing a constant rate descent while maintaining
a specific airspeed, coordinated use of pitch and power
will be required. Any change in pitch directly affects the
airspeed. Conversely, any change in airspeed will have a
direct impact on vertical speed as long as the pitch is being
held constant.

Leveling Off
When leveling off from a descent with the intention of
returning to cruise airspeed, first start by increasing the
power to cruise prior to increasing the pitch back toward
the level flight attitude. A technique used to determine
how soon to start the level off is to lead the level off by an
altitude corresponding to 10 percent of the rate of descent.
For example, if the aircraft is descending at 1,000 fpm, start
the level off 100 feet above the level off altitude. If the pitch
attitude change is started late, there is a tendency to overshoot
the desired altitude unless the pitch change is made with
a rapid movement. Avoid making any rapid changes that
could lead to control issues or spatial disorientation. Once
in level pitch attitude, allow the aircraft to accelerate to the
desired speed. Monitor the performance on the airspeed and
altitude tapes. Make adjustments to the power in order to
correct any deviations in the airspeed. Verify that the aircraft
is maintaining level flight by cross-checking the altimeter
tape. If deviations are noticed, make an appropriate smooth
pitch change in order to arrive back at desired altitude. Any
change in pitch requires a smooth coordinated change to the
power setting. Monitor the airspeed in order to maintain the
desired cruise airspeed.
To level off at a constant airspeed, the pilot must again
determine when to start to increase the pitch attitude toward
the level attitude. If pitch is the only item that is changing,
airspeed varies due to the increase in drag as the aircraft’s
pitch increases. A smooth coordinated increase in power will
need to be made to a predetermined value in order to maintain
speed. Trim the aircraft to relieve any control pressure that
may have to be applied.

5-50

7.

Uncoordinated use of pitch and power during level
offs. During level offs, both pitch and power settings
need to be made in unison in order to achieve the
desired results. If pitch is increased before adding
power, additional drag will be generated thereby
reducing airspeed below the desired value.

8.

Failure to utilize supporting pitch instruments which
will lead to chasing the VSI. Always utilize the attitude
indicator as the control instrument on which to change
the pitch.

9.

Failure to determine a proper lead time for level off
from a climb or descent. Waiting too long can lead to
overshooting the altitude.

10. Ballooning—Failure to maintain forward control
pressure during level off as power is increased.
Additional lift is generated causing the nose of the
aircraft to pitch up.

Turns
Standard Rate Turns
The previous sections have addressed flying straight-andlevel as well as climbs and descents. However, attitude
instrument flying is not accomplished solely by flying in
a straight line. At some point, the aircraft will need to be
turned to maneuver along victor airways, global positioning
system (GPS) courses, and instrument approaches. The
key to instrument flying is smooth, controlled changes to
pitch and bank. Instrument flying should be a slow but
deliberate process that takes the pilot from departure airport
to destination airport without any radical flight maneuvers.
A turn to specific heading should be made at standard rate.
Standard rate is defined as a turning rate of 3° per second
which will yield a complete 360° turn in 2 minutes. A
turning rate of 3° per second will allow for a timely heading
change, as well as allowing the pilot sufficient time to crosscheck the flight instruments and avoid drastic changes to
the aerodynamic forces being exerted on the aircraft. At no
time should the aircraft be maneuvered faster than the pilot
is comfortable cross-checking the flight instruments. Most
autopilots are programmed to turn at standard rate.

Establishing A Standard Rate Turn
In order to initiate a standard rate turn, approximate the
bank angle and then establish that bank angle on the attitude
indicator. A rule of thumb to determine the approximate angle
of bank is to use 15 percent of the true airspeed. A simple
way to determine this amount is to divide the airspeed by
10 and add one-half the result. For example, at 100 knots,
approximately 15° of bank is required (100/10 = 10 + 5 =
15); at 120 knots, approximately 18° of bank is needed for a

standard-rate turn. Cross-check the turn rate indicator, located
on the HSI, to determine if that bank angle is sufficient to
deliver a standard rate turn. Slight modifications may need
to be made to the bank angle in order to achieve the desired
performance. The primary bank instrument in this case is the
turn rate indicator since the goal is to achieve a standard rate
turn. The turn rate indicator is the only instrument that can
specifically indicate a standard rate turn. The attitude indicator
is used only to establish a bank angle (control instrument) but
can be utilized as a supporting instrument by cross-checking
the bank angle to determine if the bank is greater or less than
what was calculated.
As the aircraft rolls into the bank, the vertical component of
lift will begin to decrease. [Figure 5-67] As this happens,
additional lift must be generated to maintain level flight.
Apply aft control pressure on the yoke sufficient to stop any
altitude loss trend. With the increase in lift that needs to be
generated, additional induced drag will also be generated.
This additional drag will cause the aircraft to start to
decelerate. To counteract this, apply additional thrust by
adding power to the power lever. Once altitude and airspeed
is being maintained, utilize the trim wheel to eliminate any
control forces that need to be held on the control column.
When rolling out from a standard rate turn, the pilot needs
to utilize coordinated aileron and rudder and roll-out to a
wings level attitude utilizing smooth control inputs. The
roll-out rate should be the same as the roll-in rate in order to
estimate the lead necessary to arrive at the desired heading
without over- or undershooting.
During the transition from the turn back to straight flight, the
attitude indicator becomes the primary instrument for bank.
Once the wings are level, the heading indicator becomes
the primary instrument for bank. As bank decreases, the
vertical component increases if the pitch attitude is not
decreased sufficiently to maintain level flight. An aggressive
cross-check keeps the altimeter stationary if forward control
pressure is applied to the control column. As the bank angle is
decreased, the pitch attitude should be decreased accordingly
in order to arrive at the level pitch attitude when the aircraft
reaches zero bank. Remember to utilize the trim wheel to
eliminate any excess control forces that would otherwise
need to be held.

Common Errors
1.

One common error associated with standard rate turns
is due to pilot inability to hold the appropriate bank
angle that equates to a standard rate. The primary bank
instrument during the turn is the turn rate indicator;
however the bank angle varies slightly. With an

5-51

Figure 5-67. Standard Rate Turn—Constant Airspeed.

aggressive cross-check, a pilot should be able to
minimize errors arising from over- or underbanking.
2.

Another error normally encountered during standard
rate turns is inefficient or lack of adequate crosschecking. Pilots need to establish an aggressive
cross-check in order to detect and eliminate all
deviations from altitude, airspeed, and bank angle
during a maneuver.

3.

Fixation is a major error associated with attitude
instrument flying in general. Pilots training for their
instrument rating tend to focus on what they perceive
to be the most important task at hand and abandon
their cross-check by applying all of their attention to
the turn rate indicator. A modified radial scan works
well to provide the pilot with adequate scanning of all
instrumentation during the maneuver.

Turns to Predetermined Headings
Turning the aircraft is one of the most basic maneuvers that a
pilot learns during initial flight training. Learning to control
the aircraft, maintaining coordination, and smoothly rolling
out on a desired heading are all keys to proficient attitude
instrument flying.
EFDs allow the pilot to better utilize all instrumentation during
all phases of attitude instrument flying by consolidating all
5-52

traditional instrumentation onto the PFD. The increased size
of the attitude indicator, which stretches the entire width
of the multi-function display (MFD), allows the pilot to
maintain better pitch control while the introduction of the
turn rate indicator positioned directly on the compass rose
aids the pilot in determining when to begin a roll-out for the
desired heading.
When determining what bank angle to utilize when making a
heading change, a general rule states that for a small heading
change, do not use a bank angle that is greater than the total
number of degrees of change needed. For instance, if a heading
change of 20° is needed, a bank angle of not more than 20° is
required. Another rule of thumb that better defines the bank
angle is half the total number of degrees of heading change
required, but never greater than standard rate. The exact bank
angle that equates to a standard rate turn varies due to true
airspeed.
With this in mind and the angle of bank calculated, the next
step is determining when to start the roll-out process. For
example:
An aircraft begins a turn from a heading of 030° to a heading
of 120°. With the given airspeed, a standard rate turn has
yielded a 15° bank. The pilot wants to begin a smooth

coordinated roll-out to the desired heading when the heading
indicator displays approximately 112°. The necessary
calculations are:
15° bank (standard rate) ÷ 2 = 7.5°
120° – 7.5° = 112.5°
By utilizing this technique the pilot is better able to judge if
any modifications need to be made to the amount of lead once
the amount of over- or undershooting is established.
Timed Turns
Timed turns to headings are performed in the same fashion
with an EFD as with an analog equipped aircraft. The
instrumentation used to perform this maneuver is the turn rate
indicator as well as the clock. The purpose of this maneuver
is to allow the pilot to gain proficiency in scanning as well
as to further develop the pilot’s ability to control the aircraft
without standard instrumentation.
Timed turns become essential when controlling the aircraft
with a loss of the heading indicator. This may become
necessary due to a loss of the AHRS unit or the magnetometer.
In any case, the magnetic compass will still be available for
navigation. The reason for timed turns instead of magnetic
compass turns is the simplicity of the maneuver. Magnetic
compass turns require the pilot to take into account various
errors associated with the compass; timed turns do not.
Prior to initiating a turn, determine if the standard rate
indication on the turn rate indicator will actually deliver a
3° per second turn. To accomplish this, a calibration must
be made. Establish a turn in either direction at the indicated
standard rate. Start the digital timer as the compass rolls past
a cardinal heading. Stop the timer once the compass card
rolls through another cardinal heading. Roll wings level and
compute the rate of turn. If the turn rate indicator is calibrated
and indicating correctly, 90° of heading change should take
30 seconds. If the time taken to change heading by 90° is
more or less than 30 seconds, then a deflection above or
below the standard rate line needs to be made to compensate
for the difference. Once the calibration has been completed
in one direction, proceed to the opposite direction. When
both directions have been calibrated, apply the calibrated
calculations to all timed turns.
In order to accomplish a timed turn, the amount of heading
change needs to be established. For a change in heading from
120° to a heading of 360°, the pilot calculates the difference
and divides that number by 3. In this case, 120° divided by
3° per second equals 40 seconds. This means that it would
take 40 seconds for an aircraft to change heading 120° if that
aircraft were held in a perfect standard rate turn. Timing for

the maneuver should start as the aircraft begins rolling into
the standard rate turn. Monitor all flight instruments during
this maneuver. The primary pitch instrument is the altimeter.
The primary power instrument is the ASI and the primary
bank instrument is the turn rate indicator.
Once the calculated time expires, start a smooth coordinated
roll-out. As long as the pilot utilizes the same rate of roll-in as
roll-out, the time it takes for both will not need to be included
in the calculations. With practice the pilot should level the
wings on the desired heading. If any deviation has occurred,
make small corrections to establish the correct heading.
Compass Turns
The magnetic compass is the only instrument that requires
no other source of power for operation. In the event of an
AHRS or magnetometer failure, the magnetic compass is
the instrument the pilot uses to determine aircraft heading.
For a more detailed explanation on the use of the magnetic
compass, see page 5-21.
Steep Turns
For the purpose of instrument flight training, a steep turn is
defined as any turn in excess of standard rate. A standard rate
turn is defined as 3° per second. The bank angle that equates
to a turn rate of 3° per second varies according to airspeed.
As airspeed increases, the bank angle must be increased.
The exact bank angle that equates to a standard rate turn is
unimportant. Normal standard rate turn bank angles range
from 10° to 20°. The goal of training in steep turn maneuvers
is pilot proficiency in controlling the aircraft with excessive
bank angles.
Training in excessive bank angles will challenge the pilot in
honing cross-checking skills and improve altitude control
throughout a wider range of flight attitudes. Although the
current instrument flight check practical test standards (PTS)
do not call for a demonstration of steep turns on the certification
check flight, this does not eliminate the need for the instrument
pilot-in-training to demonstrate proficiency to an instructor.
Training in steep turns teaches the pilot to recognize and to
adapt to rapidly changing aerodynamic forces that necessitate
an increase in the rate of cross-checking all flight instruments.
The procedures for entering, maintaining and exiting a steep
turn are the same as for shallower turns. Proficiency in
instrument cross-check and interpretation is increased due to
the higher aerodynamic forces and increased speed at which
the forces are changing.

5-53

Performing the Maneuver
To enter a steep turn to the left, roll into a coordinated 45°
bank turn to the left. An advantage that glass panel displays
have over analog instrumentation is a 45° bank indication on
the roll scale. This additional index on the roll scale allows
the pilot to precisely roll into the desired bank angle instead
of having to approximate it as is necessary with analog
instrumentation. [Figure 5-68]

generate a greater and greater differential in lift compared
to the inboard wing. As the bank angle continues to progress
more and more steeply past 45°, the two components of lift
(vertical and horizontal) become inversely proportionate.
Once the angle has exceeded 45°, the horizontal component
of lift is now the greater force. If altitude should continue to
decrease and the pilot only applies back yoke pressure, the
aircraft’s turn radius begins to tighten due to the increased
horizontal force. If aft control pressure continues to increase,
there will come a point where the loss of the vertical
component of lift and aerodynamic wing loading prohibits
the nose of the aircraft from being raised. Any increase in
pitch only tightens the turning radius.
The key to successfully performing a steep turn by reference
to instruments alone is the thorough understanding of the
aerodynamics involved, as well as a quick and reliable crosscheck. The pilot should utilize the trim to avoid holding
control forces for any period of time. With time and practice,
a flight instructor can demonstrate how to successfully fly
steep turns with and without the use of trim. Once the aircraft
is trimmed for the maneuver, accomplishing the maneuver
will be virtually a hands-off effort. This allows additional
time for cross-checking and interpreting the instruments.

Figure 5-68. Steep Left Turn.

As soon as the bank angle increases from level flight, the
vertical component of lift begins to decrease. If the vertical
component of lift is allowed to continue to decrease, a
pronounced loss of altitude is indicated on the altimeter along
with the VSI tape, as well as the altitude trend indicator.
Additionally, the airspeed will begin to increase due to
the lowered pitch attitude. It is very important to have a
comprehensive scan developed prior to training in steep
turns. Utilization of all of the trend indicators, as well the
VSI, altimeter, and ASI, is essential in learning to fly steep
turns by reference to instruments alone.
In order to avoid a loss of altitude, the pilot begins to
slowly increase back pressure on the control yoke in order
to increase the pitch attitude. The pitch change required is
usually no more than 3° to 5°, depending on the type of
aircraft. As the pilot increases back pressure, the angle of
attack increases, thus increasing the vertical component of
lift. When a deviation in altitude is indicated, proper control
force corrections need to be made. During initial training
of steep turns, pilots have a tendency to overbank. Over
banking is when the bank angle exceeds 50°. As the outboard
wing begins to travel faster through the air it will begin to
5-54

It is imperative when correcting for a deviation in altitude,
that the pilot modify the bank angle ±5° in order to vary the
vertical component of lift, not just adjust back pressure. These
two actions should be accomplished simultaneously.
During the recovery from steep turns to straight-and-level
flight, aft control forces must be varied with the power control
to arrive back at entry altitude, heading and airspeed.
Steps:
1.

Perform clearing turns.

2.

Roll left into a 45° bank turn and immediately begin to
increase the pitch attitude by approximately 3° to 5°.

3.

As the bank rolls past 30°, increase power to maintain
the entry airspeed.

4.

Apply trim to eliminate any aft control wheel forces.

5.

Begin rolling out of the steep turn approximately 20°
prior to the desired heading.

6.

Apply forward control pressure and place the pitch
attitude in the level cruise pitch attitude.

7.

Reduce power to the entry power setting to maintain
the desired airspeed.

8.

Re-trim the aircraft as soon as practical or continue
into a right hand steep turn and continue from step 3.

9.

Once the maneuver is complete, establish cruise flight
and accomplish all appropriate checklist items.

One problem with analog gauges is that the attitude indicator
displays a complete blue or brown segment when the pitch
attitude is increased toward 90° nose-up or nose-down.

Unusual Attitude Recovery Protection
Unusual attitudes are some of the most hazardous situations
for a pilot to be in. Without proper recovery training
on instrument interpretation and aircraft control, a pilot
can quickly aggravate an abnormal flight attitude into a
potentially fatal accident.

With the EFDs, the attitude indicator is designed to retain a
portion of both sky and land representation at all times. This
improvement allows the pilot to always know the quickest
way to return to the horizon. Situational awareness is greatly
increased.

Analog gauges require the pilot to scan between instruments
to deduce the aircraft attitude. Individually, these gauges
lack the necessary information needed for a successful
recovery.

NOTE: The horizon line starts moving downward at
approximately 47° pitch up. From this point on, the brown
segment will remain visible to show the pilot the quickest
way to return to the level pitch attitude. [Figure 5-69]

EFDs have additional features to aid in recognition and
recovery from unusual flight attitudes. The PFD displays
all the flight instruments on one screen. Each instrument is
superimposed over a full-screen representation of the attitude
indicator. With this configuration, the pilot no longer needs
to transition from one instrument to another.

NOTE: The horizon line starts moving upward at
approximately 27° pitch down. From this point on, the blue
segment will remain visible to show the pilot the quickest
way to return to the level pitch attitude. [Figure 5-70]

The new unusual attitude recovery protection allows the pilot
to be able to quickly determine the aircraft’s attitude and make
a safe, proper and prompt recovery. Situational awareness is
increased by the introduction of the large full-width artificial
horizon depicted on the PFD. This now allows for the attitude
indicator to be in view during all portions of the scan.

It is imperative to understand that the white line on the
attitude indicator is the horizon line. The break between the
blue and brown symbols is only a reference and should not
be thought of as the artificial horizon.
Another important advancement is the development of the
unusual attitude recovery protection that is built into the PFD
software and made capable by the AHRS. In the case of a nosehigh unusual attitude, the unusual attitude recovery protection
displays red chevrons which point back to the horizon line.

Figure 5-69. Unusual Attitude Recovery Protection. Note the brown horizon line is visible at the bottom.

5-55

Figure 5-70. Horizon line starts moving upward at 27°. Note that the blue sky remains visible at 17° nose-down.

These chevrons are positioned at 50° up on the attitude indicator.
The chevrons appear when the aircraft approaches a nose-high
attitude of 30°. The software automatically de-clutters the PFD
leaving only airspeed, heading, attitude, altimeter, VSI tape,
and the trend vectors. The de-cluttered information reappears
when the pitch attitude falls below 25°.
For nose-low unusual attitudes, the chevrons are displayed
when the pitch exceeds 15° nose-down. If the pitch continues
to decrease, the unusual attitude recovery protection declutters the screen at 20° nose-down. The de-cluttered
information reappears when the pitch increases above 15°.
Additionally, there are bank limits that trigger the unusual
attitude protection. If the aircraft’s bank increases beyond
60°, a continuation of the roll index occurs to indicate the
shortest direction to roll the wings back to level. At 65°, the
PFD de-clutters. All information reappears when the bank
decreases below 60°.
In Figure 5-71, the aircraft has rolled past 60°. Observe the
white line that continues from the end of the bank index.
This line appears to indicate the shortest distance back to
wings level.
When experiencing a failure of the AHRS unit, all unusual
attitude protection is lost. The failure of the AHRS results
in the loss of all heading and attitude indications on the PFD.
In addition, all modes of the autopilot, except for roll and
altitude hold, are lost.
5-56

The following picture series represents how important this
technology is in increasing situational awareness, and how
critical it is in improving safety.
Figure 5-72 shows the unusual attitude protection with
valid AHRS and air data computer (ADC) inputs. The
bright red chevrons pointing down to the horizon indicate
a nose-high unusual attitude that can be easily recognized
and corrected.
NOTE: The red chevrons point back to the level pitch attitude.
The trend indicators show where the airspeed and altitude will
be in 6 seconds. The trend indicator on the heading indicator
shows which direction the aircraft is turning. The slip/skid
indicator clearly shows if the aircraft is coordinated. This
information helps the pilot determine which type of unusual
attitude the aircraft has taken.
Now look at Figure 5-73. The display shows the same
airspeed as the picture above; however, the AHRS unit has
failed. The altimeter and the VSI tape are the only clear
indications that the aircraft is in a nose-high attitude. The
one key instrument that is no longer present is the slip/skid
indicator. There is not a standby turn coordinator installed
in the aircraft for the pilot to reference.
The magnetic compass indicates a heading is being
maintained; however, it is not as useful as a turn coordinator
or slip/skid indicator.

Figure 5-71. Aircraft Rolled Past 60°.

Figure 5-72. Unusual Attitude Protection With Valid AHRS.

5-57

Figure 5-73. AHRS Unit Failed.

Figure 5-74 depicts an AHRS and ADC failure. In this failure
scenario, there are no indications of the aircraft’s attitude. The
manufacturer recommends turning on the autopilot which is
simply a wing leveler.

aircraft can specify if an autopilot is to be installed. Extreme
caution should be utilized when flying an EFD equipped
aircraft without an autopilot in IMC with an AHRS and
ADC failure.

With a failure of the primary instrumentation on the PFD, the
only references available are the stand-by instruments. The
standby instrumentation consists of an analog ASI, attitude
indicator, altimeter, and magnetic compass. There is no
standby turn coordinator installed.

The autopilot should be utilized to reduce workload, which
affords the pilot more time to monitor the flight. Utilization
of the autopilot also decreases the chances of entry into an
unusual attitude.

In extreme nose-high or nose-low pitch attitudes, as well
as high bank angles, the analog attitude indicator has the
potential to tumble, rendering it unusable.
Autopilot Usage
The autopilot is equipped with inputs from a turn coordinator
installed behind the MFD screen. This turn coordinator is
installed solely for the use of the autopilot to facilitate the
roll mode. Roll mode, which is simply a wing leveler. This
protection will always be available, barring a failure of the
turn coordinator (to aid the pilot if the aircraft attains an
unusual attitude).
NOTE: The pilot is not able to gain access to the turn
coordinator. This instrument is installed behind the MFD
panel. [Figure 5-75]
Most EFD equipped aircraft are coming from the factory
with autopilots installed. However, the purchaser of the
5-58

Flying an EFD equipped aircraft without the use of an
autopilot has been shown to increase workload and decrease
situational awareness for pilots first learning to flying the
new system.

Common Errors Leading to Unusual Attitudes
The following errors have the potential to disrupt a pilot’s
situational awareness and lead to unusual attitudes.
1.

Improper trimming techniques. A failure to keep the
aircraft trimmed for level flight at all times can turn
a momentary distraction into an emergency situation
if the pilot stops cross-checking.

2.

Poor crew resource management (CRM) skills. Failure
to perform all single-pilot resource management
duties efficiently. A major cause of CRM related
accidents comes from the failure of the pilot to
maintain an organized flight deck. Items that are
being utilized for the flight portion should be neatly
arranged for easy access. A disorganized flight deck

Figure 5-74. AHRS ADC Failure.

Figure 5-75. This autopilot requires roll information from a turn coordinator.

5-59

can lead to a distraction that causes the pilot to cease
cross-checking the instruments long enough to enter
an unusual attitude.

a modification to the maneuver; therefore, always obtain
training on any new equipment to be used.

3.

Fixation is displayed when a pilot focuses far too
much attention on one instrument because he or
she perceives something is wrong or a deviation is
occurring. It is important for the instrument pilot to
remember that a cross-check of several instruments
for corroboration is more valuable than checking a
single instrument.

4.

Attempting to recover by sensory sensations other
than sight. Recovery by instinct almost always leads
to erroneous corrections due to the illusions that are
prevalent during instrument flight.

5.

Failure to practice basic attitude instrument flying.
When a pilot does not fly instrument approach
procedures or even basic attitude instrument flying
maneuvers for long periods of time, skill levels
diminish. Pilots should avoid flying in IMC if they are
not proficient. They should seek a qualified instructor
to receive additional instruction prior to entry into
IMC.

In order to accomplish an instrument takeoff, the aircraft
needs to be maneuvered on the centerline of the runway facing
the direction of departure with the nose or tail wheel straight.
Assistance from the instructor may be necessary if the pilot
has been taxiing while wearing a view limiting device. Lock
the tail wheel, if so equipped, and hold the brakes firmly to
prevent the aircraft from creeping. Cross-check the heading
indicator on the PFD with the magnetic compass and adjust
for any deviations noted on the compass card. Set the heading
to the nearest 5° mark closest to the runway heading. This
allows the pilot to quickly detect any deviations from the
desired heading and allows prompt corrective actions during
the takeoff roll. Using the omnibearing select (OBS) mode
on the GPS, rotate the OBS selector until the needle points
to the runway heading. This adds additional situational
awareness during the takeoff roll. Smoothly apply power to
generate sufficient rudder authority for directional control.
Release the brakes and continue to advance the power to the
takeoff setting.

Instrument Takeoff
The reason for learning to fly by reference to instruments
alone is to expand a pilot’s abilities to operate an aircraft
in visibility less than VFR. Another valuable maneuver
to learn is the instrument takeoff. This maneuver requires
the pilot to maneuver the aircraft during the takeoff roll by
reference to flight instruments alone with no outside visual
reference. With practice, this maneuver becomes as routine
as a standard rate turn.
The reason behind practicing instrument takeoffs is to reduce
the disorientation that can occur during the transitional phase
of quickly moving the eyes from the outside references inside
to the flight instruments.
One EFD system currently offers what is trademarked as
synthetic vision. Synthetic vision is a three-dimensional
computer-generated representation of the terrain that lies
ahead of the aircraft. The display shows runways as well
as a depiction of the terrain features based on a GPS terrain
database. Similar to a video game, the display generates a
runway the pilot can maneuver down in order to maintain
directional control. As long as the pilot tracks down the
computer-generated runway, the aircraft will remain aligned
with the actual runway.
Not all EFD systems have such an advanced visioning system.
With all other systems, the pilot needs to revert to the standard
procedures for instrument takeoffs. Each aircraft may require
5-60

As soon as the brakes are released, any deviation in heading
needs to be corrected immediately. Avoid using brakes to
control direction as this increases the takeoff roll, as well as
provides the potential of overcontrolling the aircraft.
Continuously cross-check the ASI and the heading indicator
as the aircraft accelerates. As the aircraft approaches 15-25
knots below the rotation speed, smoothly apply aft elevator
pressure to increase the pitch attitude to the desired takeoff
attitude (approximately 7° for most small airplanes). With
the pitch attitude held constant, continue to cross-check the
flight instruments and allow the aircraft to fly off of the
runway. Do not pull the aircraft off of the runway. Pulling
the aircraft off of the runway imposes left turning tendencies
due to P-Factor, which will yaw the aircraft to the left and
destabilize the takeoff.
Maintain the desired pitch and bank attitudes by referencing
the attitude indicator and cross-check the VSI tape for an
indication of a positive rate of climb. Take note of the magenta
6-second altimeter trend indicator. The trend should show
positive. Barring turbulence, all trend indications should
be stabilized. The airspeed trend indicator should not be
visible at this point if the airspeed is being held constant. An
activation of the airspeed trend indicator shows that the pitch
attitude is not being held at the desired value and, therefore,
the airspeed is changing. The desired performance is to be
climbing at a constant airspeed and vertical speed rate. Use
the ASI as the primary instrument for the pitch indication.

Once the aircraft has reached a safe altitude (approximately
100 feet for insufficient runway available for landing should
an engine failure occur) retract the landing gear and flaps
while referencing the ASI and attitude indicator to maintain
the desired pitch. As the configuration is changed, an increase
in aft control pressure is needed in order to maintain the
desired pitch attitude. Smoothly increase the aft control
pressure to compensate for the change in configuration.
Anticipate the changes and increase the rate of cross-check.
The airspeed tape and altitude tape increases while the VSI
tape is held constant. Allow the aircraft to accelerate to the
desired climb speed. Once the desired climb speed is reached,
reduce the power to the climb power setting as printed in
the POH/AFM. Trim the aircraft to eliminate any control
pressures.

5.

Overcontrolling rudder pedals. This fault may be
caused by late recognition of heading changes, tension
on the controls, misinterpretation of the heading
indicator (and correcting in the wrong direction),
failure to appreciate changing effectiveness of rudder
control as the aircraft accelerates, and other factors. If
heading changes are observed and corrected instantly
with small movement of the rudder pedals, swerving
tendencies can be reduced.

6.

Failure to maintain attitude after becoming airborne.
If the pilot reacts to seat-of-the-pants sensations when
the airplane lifts off, pitch control is guesswork.
The pilot may either allow excessive pitch or apply
excessive forward-elevator pressure, depending on
the reaction to trim changes.

Common Errors in Instrument Takeoffs
Common errors associated with the instrument takeoff
include, but are not limited to, the following:

7.

Inadequate cross-check. Fixations are likely during the
trim changes, attitude changes, gear and flap retractions,
and power changes. Once an instrument or a control
input is applied, continue the cross-check and note the
effect control during the next cross-check sequence.

8.

Inadequate interpretation of instruments. Failure
to understand instrument indications immediately
indicates that further study of the maneuver is
necessary.

1.

Failure to perform an adequate flight deck check
before the takeoff. Pilots have attempted instrument
takeoff with inoperative airspeed indicators (pitot
tube obstructed), controls locked, and numerous
other oversights due to haste or carelessness. It is
imperative to cross-check the ASI as soon as possible.
No airspeed will be indicated until 20 knots of true
airspeed is generated in some systems.

2.

Improper alignment on the runway. This may result
from improper brake applications, allowing the
airplane to creep after alignment, or from alignment
with the nosewheel or tailwheel cocked. In any case,
the result is a built-in directional control problem as
the takeoff starts.

3.

Improper application of power. Abrupt applications of
power complicate directional control. Power should be
applied in a smooth and continuous manner to arrive
at the takeoff power setting within approximately 3
seconds.

4.

Improper use of brakes. Incorrect seat or rudder pedal
adjustment, with feet in an uncomfortable position,
frequently causes inadvertent application of brakes
and excessive heading changes.

Basic Instrument Flight Patterns
After attaining a reasonable degree of proficiency in basic
maneuvers, apply these skills to the various combinations
of individual maneuvers. The practice flight patterns,
beginning on page 5-30, are directly applicable to operational
instrument flying.

5-61

5-62

Chapter 6

Helicopter Attitude
Instrument Flying
Introduction
Attitude instrument flying in helicopters is essentially visual
flying with the flight instruments substituted for the various
reference points on the helicopter and the natural horizon.
Control changes, required to produce a given attitude by
reference to instruments, are identical to those used in
helicopter visual flight rules (VFR) flight, and pilot thought
processes are the same. Basic instrument training is intended to
be a building block toward attaining an instrument rating.

6-1

Flight Instruments
When flying a helicopter with reference to the flight
instruments, proper instrument interpretation is the basis
for aircraft control. Skill, in part, depends on understanding
how a particular instrument or system functions, including
its indications and limitations (see Chapter 3, Flight
Instruments). With this knowledge, a pilot can quickly
interpret an instrument indication and translate that
information into a control response.

Instrument Flight
To achieve smooth, positive control of the helicopter during
instrument flight, three fundamental skills must be developed.
They are instrument cross-check, instrument interpretation,
and aircraft control.
Instrument Cross-Check
Cross-checking, sometimes referred to as scanning, is the
continuous and logical observation of instruments for attitude
and performance information. In attitude instrument flying,
an attitude is maintained by reference to the instruments,
which produces the desired result in performance. Due to
human error, instrument error, and helicopter performance
differences in various atmospheric and loading conditions,
it is difficult to establish an attitude and have performance

remain constant for a long period of time. These variables
make it necessary to constantly check the instruments and
make appropriate changes in the helicopter’s attitude. The
actual technique may vary depending on what instruments
are installed and where they are installed, as well as pilot
experience and proficiency level. This discussion concentrates
on the six basic flight instruments. [Figure 6-1]
At first, there may be a tendency to cross-check rapidly,
looking directly at the instruments without knowing exactly
what information is needed. However, with familiarity and
practice, the instrument cross-check reveals definite trends
during specific flight conditions. These trends help a pilot
control the helicopter as it makes a transition from one flight
condition to another.
When full concentration is applied to a single instrument, a
problem called fixation is encountered. This results from a
natural human inclination to observe a specific instrument
carefully and accurately, often to the exclusion of other
instruments. Fixation on a single instrument usually results
in poor control. For example, while performing a turn, there
is a tendency to watch only the turn-and-slip indicator instead
of including other instruments in the cross-check. This
fixation on the turn-and-slip indicator often leads to a loss of
altitude through poor pitch-and-bank control. Look at each

Figure 6-1. In most situations, the cross-check pattern includes the attitude indicator between the cross-check of each of the other
instruments. A typical cross-check might progress as follows: attitude indicator, altimeter, attitude indicator, vertical speed indicator,
attitude indicator, heading indicator, attitude indicator, and so on.

6-2

instrument only long enough to understand the information
it presents, and then proceed to the next one. Similarly, too
much emphasis can be placed on a single instrument, instead
of relying on a combination of instruments necessary for
helicopter performance information. This differs from fixation
in that other instruments are included in a cross-check, but too
much attention is placed on one particular instrument.
During performance of a maneuver, there is sometimes
a failure to anticipate significant instrument indications
following attitude changes. For example, during level off
from a climb or descent, a pilot may concentrate on pitch
control, while forgetting about heading or roll information.
This error, called omission, results in erratic control of
heading and bank.
In spite of these common errors, most pilots can adapt well to
flight by instrument reference after instruction and practice.
Many find that they can control the helicopter more easily
and precisely by instruments.
Instrument Interpretation
The flight instruments together give a picture of what is
happening. No one instrument is more important than the
next; however, during certain maneuvers or conditions,
those instruments that provide the most pertinent and useful
information are termed primary instruments. Those which
back up and supplement the primary instruments are termed
supporting instruments. For example, since the attitude
indicator is the only instrument that provides instant and
direct aircraft attitude information, it should be considered
primary during any change in pitch or bank attitude. After
the new attitude is established, other instruments become
primary, and the attitude indicator usually becomes the
supporting instrument.
Aircraft Control
Controlling a helicopter is the result of accurately interpreting
the flight instruments and translating these readings
into correct control responses. Aircraft control involves
adjustment to pitch, bank, power, and trim in order to achieve
a desired flight path.
Pitch attitude control is controlling the movement of
the helicopter about its lateral axis. After interpreting
the helicopter’s pitch attitude by reference to the pitch
instruments (attitude indicator, altimeter, airspeed
indicator, and vertical speed indicator (VSI)), cyclic control
adjustments are made to affect the desired pitch attitude. In
this chapter, the pitch attitudes depicted are approximate
and vary with different helicopters.

Bank attitude control is controlling the angle made by the
lateral tilt of the rotor and the natural horizon, or the movement
of the helicopter about its longitudinal axis. After interpreting
the helicopter’s bank instruments (attitude indicator, heading
indicator, and turn indicator), cyclic control adjustments are
made to attain the desired bank attitude.
Power control is the application of collective pitch with
corresponding throttle control, where applicable. In straightand-level flight, changes of collective pitch are made to
correct for altitude deviation if the error is more than 100
feet, or the airspeed is off by more than 10 knots. If the error
is less than that amount, a pilot should use a slight cyclic
climb or descent.
In order to fly a helicopter by reference to the instruments, it
is important to know the approximate power settings required
for a particular helicopter in various load configurations and
flight conditions.
Trim, in helicopters, refers to the use of the cyclic centering
button, if the helicopter is so equipped, to relieve all
possible cyclic pressures. Trim also refers to the use of pedal
adjustment to center the ball of the turn indicator. Pedal trim
is required during all power changes.
The proper adjustment of collective pitch and cyclic friction
helps a pilot relax during instrument flight. Friction should
be adjusted to minimize overcontrolling and to prevent
creeping, but not applied to such a degree that control
movement is limited. In addition, many helicopters equipped
for instrument flight contain stability augmentation systems
or an autopilot to help relieve pilot workload.

Straight-and-Level Flight
Straight-and-level unaccelerated flight consists of maintaining
the desired altitude, heading, airspeed, and pedal trim.
Pitch Control
The pitch attitude of a helicopter is the angular relation of
its longitudinal axis to the natural horizon. If available, the
attitude indicator is used to establish the desired pitch attitude.
In level flight, pitch attitude varies with airspeed and center of
gravity (CG). At a constant altitude and a stabilized airspeed,
the pitch attitude is approximately level. [Figure 6-2]

Attitude Indicator
The attitude indicator gives a direct indication of the pitch
attitude of the helicopter. In visual flight, attain the desired
pitch attitude by using the cyclic to raise and lower the nose

6-3

Figure 6-2. The flight instruments for pitch control are the airspeed indicator, attitude indicator, altimeter, and vertical speed

indicator.

of the helicopter in relation to the natural horizon. During
instrument flight, follow exactly the same procedure in
raising or lowering the miniature aircraft in relation to the
horizon bar.
There is some delay between control application and resultant
instrument change. This is the normal control lag in the
helicopter and should not be confused with instrument lag.
The attitude indicator may show small misrepresentations
of pitch attitude during maneuvers involving acceleration,
deceleration, or turns. This precession error can be detected
quickly by cross-checking the other pitch instruments.
If the miniature aircraft is properly adjusted on the ground, it
may not require readjustment in flight. If the miniature aircraft
is not on the horizon bar after level off at normal cruising
airspeed, adjust it as necessary while maintaining level flight
with the other pitch instruments. Once the miniature aircraft
has been adjusted in level flight at normal cruising airspeed,
leave it unchanged so it gives an accurate picture of pitch
attitude at all times.

Altimeter
The altimeter gives an indirect indication of the pitch
attitude of the helicopter in straight-and-level flight. Since
the altitude should remain constant in level flight, deviation
from the desired altitude indicates a need for a change in
pitch attitude and power as necessary. When losing altitude,
raise the pitch attitude and adjust power as necessary. When
gaining altitude, lower the pitch attitude and adjust power
as necessary. Indications for power changes are explained
in the next paragraph.
The rate at which the altimeter moves helps to determine pitch
attitude. A very slow movement of the altimeter indicates
a small deviation from the desired pitch attitude, while a

When making initial pitch attitude corrections to maintain
altitude, the changes of attitude should be small and smoothly
applied. The initial movement of the horizon bar should not
exceed one bar width high or low. [Figure 6-3] If a further
adjustment is required, an additional correction of one-half bar
normally corrects any deviation from the desired altitude. This
one-and-one-half bar correction is normally the maximum
pitch attitude correction from level flight attitude.
After making the correction, cross-check the other pitch
instruments to determine whether the pitch attitude change
is sufficient. If additional correction is needed to return to
altitude, or if the airspeed varies more than 10 knots from
that desired, adjust the power.

6-4

Figure 6-3. The initial pitch correction at normal cruise is one bar
width or less.

fast movement of the altimeter indicates a large deviation
from the desired pitch attitude. Make any corrective action
promptly, with small control changes. Also, remember that
movement of the altimeter should always be corrected by
two distinct changes. The first is a change of attitude to stop
the altimeter movement; the second is a change of attitude to
return smoothly to the desired altitude. If altitude and airspeed
are more than 100 feet and 10 knots low, respectively, apply
power in addition to an increase of pitch attitude. If the
altitude and airspeed are high by more than 100 feet and 10
knots, reduce power and lower the pitch attitude.
There is a small lag in the movement of the altimeter;
however, for all practical purposes, consider that the altimeter
gives an immediate indication of a change, or a need for
change in pitch attitude. Since the altimeter provides the
most pertinent information regarding pitch in level flight, it
is considered primary for pitch.

Vertical Speed Indicator (VSI)
The VSI gives an indirect indication of the pitch attitude of
the helicopter and should be used in conjunction with the
other pitch instruments to attain a high degree of accuracy
and precision. The instrument indicates zero when in level
flight. Any movement of the needle from the zero position
shows a need for an immediate change in pitch attitude to
return it to zero. Always use the VSI in conjunction with
the altimeter in level flight. If a movement of the VSI is
detected, immediately use the proper corrective measures
to return it to zero. If the correction is made promptly, there
is usually little or no change in altitude. If the needle of the
VSI does not indicate zero, the altimeter indicates a gain or
loss of altitude.
The initial movement of the vertical speed needle is
instantaneous and indicates the trend of the vertical movement
of the helicopter. A period of time is necessary for the VSI to
reach its maximum point of deflection after a correction has
been made. This time element is commonly referred to as
instrument lag. The lag is directly proportional to the speed
and magnitude of the pitch change. When employing smooth
control techniques and small adjustments in pitch attitude are
made, lag is minimized, and the VSI is easy to interpret.
Overcontrolling can be minimized by first neutralizing the
controls and allowing the pitch attitude to stabilize, then
readjusting the pitch attitude by noting the indications of the
other pitch instruments.
Occasionally, the VSI may be slightly out of calibration.
This could result in the instrument indicating a slight climb
or descent even when the helicopter is in level flight. If the
instrument cannot be calibrated properly, this error must be

taken into consideration when using the VSI for pitch control.
For example, if a descent of 100 feet per minute (fpm) is the
vertical speed indication when the helicopter is in level flight,
use that indication as level flight. Any deviation from that
reading would indicate a change in attitude.

Airspeed Indicator
The airspeed indicator gives an indirect indication of
helicopter pitch attitude. With a given power setting and
pitch attitude, the airspeed remains constant. If the airspeed
increases, the nose is too low and should be raised. If the
airspeed decreases, the nose is too high and should be
lowered. A rapid change in airspeed indicates a large change
in pitch attitude, and a slow change in airspeed indicates a
small change in pitch attitude. There is very little lag in the
indications of the airspeed indicator. If, while making attitude
changes, there is some lag between control application and
change of airspeed, it is most likely due to cyclic control lag.
Generally, a departure from the desired airspeed, due to an
inadvertent pitch attitude change, also results in a change in
altitude. For example, an increase in airspeed due to a low
pitch attitude results in a decrease in altitude. A correction in
the pitch attitude regains both airspeed and altitude.
Bank Control
The bank attitude of a helicopter is the angular relation of
its lateral axis to the natural horizon. To maintain a straight
course in visual flight, keep the lateral axis of the helicopter
level with the natural horizon. Assuming the helicopter is in
coordinated flight, any deviation from a laterally level attitude
produces a turn. [Figure 6-4]

Attitude Indicator
The attitude indicator gives a direct indication of the bank
attitude of the helicopter. For instrument flight, the miniature
aircraft and the horizon bar of the attitude indicator are
substituted for the actual helicopter and the natural horizon.
Any change in bank attitude of the helicopter is indicated
instantly by the miniature aircraft. For proper interpretation
of this instrument, imagine being in the miniature aircraft. If
the helicopter is properly trimmed and the rotor tilts, a turn
begins. The turn can be stopped by leveling the miniature
aircraft with the horizon bar. The ball in the turn-and-slip
indicator should always be kept centered through proper
pedal trim.
The angle of bank is indicated by the pointer on the banking
scale at the top of the instrument. [Figure 6-5] Small bank
angles, which may not be seen by observing the miniature
aircraft, can easily be determined by referring to the banking
scale pointer.

6-5

Figure 6-4. The flight instruments used for bank control are the attitude, heading, and turn indicators.

Pitch-and-bank attitudes can be determined simultaneously
on the attitude indicator. Even though the miniature aircraft
is not level with the horizon bar, pitch attitude can be
established by observing the relative position of the miniature
aircraft and the horizon bar.
The attitude indicator may show small misrepresentations
of bank attitude during maneuvers that involve turns. This
precession error can be detected immediately by closely
cross-checking the other bank instruments during these
maneuvers. Precession is normally noticed when rolling
out of a turn. If, upon completion of a turn, the miniature
aircraft is level and the helicopter is still turning, make a

small change of bank attitude to center the turn needle and
stop the movement of the heading indicator.

Heading Indicator
In coordinated flight, the heading indicator gives an indirect
indication of a helicopter’s bank attitude. When a helicopter is
banked, it turns. When the lateral axis of a helicopter is level,
it flies straight. Therefore, in coordinated flight when the
heading indicator shows a constant heading, the helicopter is
level laterally. A deviation from the desired heading indicates
a bank in the direction the helicopter is turning. A small angle
of bank is indicated by a slow change of heading; a large angle
of bank is indicated by a rapid change of heading. If a turn
is noticed, apply opposite cyclic until the heading indicator

Figure 6-5. The banking scale at the top of the attitude indicator indicates varying degrees of bank. In this example, the helicopter is

banked approximately 15° to the right.

6-6

indicates the desired heading, simultaneously ensuring the
ball is centered. When making the correction to the desired
heading, do not use a bank angle greater than that required
to achieve a standard rate turn. In addition, if the number
of degrees of change is small, limit the bank angle to the
number of degrees to be turned. Bank angles greater than
these require more skill and precision in attaining the desired
results. During straight-and-level flight, the heading indicator
is the primary reference for bank control.

Turn Indicator
During coordinated flight, the needle of the turn-and-slip
indicator gives an indirect indication of the bank attitude
of the helicopter. When the needle is displaced from the
vertical position, the helicopter is turning in the direction of
the displacement. Thus, if the needle is displaced to the left,
the helicopter is turning left. Bringing the needle back to
the vertical position with the cyclic produces straight flight.
A close observation of the needle is necessary to accurately
interpret small deviations from the desired position.
Cross-check the ball of the turn-and-slip indicator to determine
if the helicopter is in coordinated flight. [Figure 6-6] If
the rotor is laterally level and pedal pressure properly
compensates for torque, the ball remains in the center. To
center the ball, level the helicopter laterally by reference to
the other bank instruments, then center the ball with pedal
trim. Torque correction pressures vary as power changes are
made. Always check the ball after such changes.

Common Errors During Straight-and-Level Flight
1.

Failure to maintain altitude

2.

Failure to maintain heading

3.

Overcontrolling pitch and bank during corrections

4.

Failure to maintain proper pedal trim

5.

Failure to cross-check all available instruments

Power Control During Straight-and-Level Flight
Establishing specific power settings is accomplished through
collective pitch adjustments and throttle control, where
necessary. For reciprocating-powered helicopters, power
indication is observed on the manifold pressure gauge.
For turbine-powered helicopters, power is observed on the
torque gauge. (Although most Instrument Flight Rules (IFR)certified helicopters are turbine powered, depictions within
this chapter use a reciprocating-powered helicopter as this
is where training is most likely conducted.)
At any given airspeed, a specific power setting determines
whether the helicopter is in level flight, in a climb, or in a
descent. For example, cruising airspeed maintained with
cruising power results in level flight. If a pilot increases the
power setting and holds the airspeed constant, the helicopter
climbs. Conversely, if the pilot decreases power and holds
the airspeed constant, the helicopter descends.

Figure 6-6. Coordinated flight is indicated by centering of the ball.

6-7

If the altitude is held constant, power determines the airspeed.
For example, at a constant altitude, cruising power results
in cruising airspeed. Any deviation from the cruising power
setting results in a change of airspeed. When power is added
to increase airspeed, the nose of the helicopter pitches up and
yaws to the right in a helicopter with a counterclockwise main
rotor blade rotation. [Figure 6-7] When power is reduced to
decrease airspeed, the nose pitches down and yaws to the
left. [Figure 6-8] The yawing effect is most pronounced in
single-rotor helicopters, and is absent in helicopters with
counter-rotating rotors. To counteract the yawing tendency
of the helicopter, apply pedal trim during power changes.
To maintain a constant altitude and airspeed in level flight,
coordinate pitch attitude and power control. The relationship
between altitude and airspeed determines the need for a
change in power and/or pitch attitude. If the altitude is
constant and the airspeed is high or low, change the power to
obtain the desired airspeed. During the change in power, make
an accurate interpretation of the altimeter, then counteract
any deviation from the desired altitude by an appropriate
change of pitch attitude. If the altitude is low and the airspeed
is high, or vice versa, a change in pitch attitude alone may
return the helicopter to the proper altitude and airspeed. If
both airspeed and altitude are low, or if both are high, changes
in both power and pitch attitude are necessary.

various airspeeds at which the helicopter is flown. When the
airspeed is to be changed by any appreciable amount, adjust
the power so that it is over or under that setting necessary
to maintain the new airspeed. As the power approaches the
desired setting, include the manifold pressure in the crosscheck to determine when the proper adjustment has been
accomplished. As the airspeed is changing, adjust the pitch
attitude to maintain a constant altitude. A constant heading
should be maintained throughout the change. As the desired
airspeed is approached, adjust power to the new cruising
power setting and further adjust pitch attitude to maintain
altitude. The instrument indications for straight-and-level
flight at normal cruise and during the transition from normal
cruise to slow cruise are illustrated in Figures 6-9 and 6-10.
After the airspeed stabilizes at slow cruise, the attitude
indicator shows an approximate level pitch attitude.
The altimeter is the primary pitch instrument during level
flight, whether flying at a constant airspeed or during a
change in airspeed. Altitude should not change during
airspeed transitions, and the heading indicator remains the
primary bank instrument. Whenever the airspeed is changed
by an appreciable amount, the manifold pressure gauge is
momentarily the primary instrument for power control.
When the airspeed approaches the desired reading, the
airspeed indicator again becomes the primary instrument
for power control.

To make power control easy when changing airspeed, it is
necessary to know the approximate power settings for the

Figure 6-7. Flight instrument indications in straight-and-level flight with power increasing.

6-8

Figure 6-8. Flight instrument indications in straight-and-level flight with power decreasing.

Figure 6-9. Flight instrument indications in straight-and-level flight at normal cruise speed.

6-9

Figure 6-10. Flight instrument indications in straight-and-level flight with airspeed decreasing.

To produce straight-and-level flight, the cross-check of the
pitch-and-bank instruments should be combined with the
power control instruments. With a constant power setting, a
normal cross-check should be satisfactory. When changing
power, the speed of the cross-check must be increased to
cover the pitch-and-bank instruments adequately. This is
necessary to counteract any deviations immediately.
Common Errors During Airspeed Changes
1.

Improper use of power

2.

Overcontrolling pitch attitude

3.

Failure to maintain heading

4.

Failure to maintain altitude

5.

Improper pedal trim

Straight Climbs (Constant Airspeed and
Constant Rate)
For any power setting and load condition, there is only
one airspeed that gives the most efficient rate of climb.
To determine this, consult the climb data for the type of
helicopter being flown. The technique varies according to
the airspeed on entry and whether a constant airspeed or
constant rate climb is made.

6-10

Entry
To enter a constant airspeed climb from cruise airspeed when
the climb speed is lower than cruise speed, simultaneously
increase power to the climb power setting and adjust pitch
attitude to the approximate climb attitude. The increase in
power causes the helicopter to start climbing and only very
slight back cyclic pressure is needed to complete the change
from level to climb attitude. The attitude indicator should
be used to accomplish the pitch change. If the transition
from level flight to a climb is smooth, the VSI shows an
immediate upward trend and then stops at a rate appropriate
to the stabilized airspeed and attitude. Primary and supporting
instruments for climb entry are illustrated in Figure 6-11.
When the helicopter stabilizes at a constant airspeed and
attitude, the airspeed indicator becomes primary for pitch.
The manifold pressure continues to be primary for power and
should be monitored closely to determine if the proper climb
power setting is being maintained. Primary and supporting
instruments for a stabilized constant airspeed climb are shown
in Figure 6-12.
The technique and procedures for entering a constant rate
climb are very similar to those previously described for a
constant airspeed climb. For training purposes, a constant

Figure 6-11. Flight instrument indications during climb entry for a constant-airspeed climb.

Figure 6-12. Flight instrument indications in a stabilized constant-airspeed climb.

6-11

rate climb is entered from climb airspeed. Use the rate
appropriate for the particular helicopter being flown.
Normally, in helicopters with low climb rates, 500 fpm is
appropriate. In helicopters capable of high climb rates, use
a rate of 1,000 fpm.
To enter a constant rate climb, increase power to the
approximate setting for the desired rate. As power is
applied, the airspeed indicator is primary for pitch until the
vertical speed approaches the desired rate. At this time, the
VSI becomes primary for pitch. Change pitch attitude by
reference to the attitude indicator to maintain the desired
vertical speed. When the VSI becomes primary for pitch, the
airspeed indicator becomes primary for power. Primary and
supporting instruments for a stabilized constant rate climb are
illustrated in Figure 6-13. Adjust power to maintain desired
airspeed. Pitch attitude and power corrections should be
closely coordinated. To illustrate this, if the vertical speed
is correct but the airspeed is low, add power. As power is
increased, it may be necessary to lower the pitch attitude
slightly to avoid increasing the vertical rate. Adjust the pitch
attitude smoothly to avoid overcontrolling. Small power
corrections are usually sufficient to bring the airspeed back
to the desired indication.
Level Off
The level off from a constant airspeed climb must be started
before reaching the desired altitude. Although the amount

of lead varies with the type of helicopter being flown and
pilot technique, the most important factor is vertical speed.
As a rule of thumb, use 10 percent of the vertical velocity
as the lead point. For example, if the rate of climb is 500
fpm, initiate the level off approximately 50 feet before the
desired altitude. When the proper lead altitude is reached, the
altimeter becomes primary for pitch. Adjust the pitch attitude
to the level flight attitude for that airspeed. Cross-check the
altimeter and VSI to determine when level flight has been
attained at the desired altitude. If cruise airspeed is higher
than climb airspeed, leave the power at the climb power
setting until the airspeed approaches cruise airspeed, and
then reduce it to the cruise power setting. The level off from
a constant rate climb is accomplished in the same manner as
the level off from a constant airspeed climb.

Straight Descents (Constant Airspeed
and Constant Rate)
A descent may be performed at any normal airspeed the
helicopter can attain, but the airspeed must be determined
prior to entry. The technique is determined by the type of
descent, a constant airspeed or a constant rate.
Entry
If airspeed is higher than descending airspeed, and a constant
airspeed descent is desired, reduce power to a descent
power setting and maintain a constant altitude using cyclic
pitch control. This slows the helicopter. As the helicopter

Figure 6-13. Flight Instrument Indications in a Stabilized Constant-Rate Climb.

6-12

approaches the descending airspeed, the airspeed indicator
becomes primary for pitch and the manifold pressure is
primary for power. Holding the airspeed constant causes the
helicopter to descend. For a constant rate descent, reduce the
power to the approximate setting for the desired rate. If the
descent is started at the descending airspeed, the airspeed
indicator is primary for pitch until the VSI approaches the
desired rate. At this time, the VSI becomes primary for
pitch, and the airspeed indicator becomes primary for power.
Coordinate power and pitch attitude control as previously
described on page 6-10 for constant rate climbs.
Level Off
The level off from a constant airspeed descent may be
made at descending airspeed or at cruise airspeed, if this is
higher than descending airspeed. As in a climb level off, the
amount of lead depends on the rate of descent and control
technique. For a level off at descending airspeed, the lead
should be approximately 10 percent of the vertical speed. At
the lead altitude, simultaneously increase power to the setting
necessary to maintain descending airspeed in level flight. At
this point, the altimeter becomes primary for pitch, and the
airspeed indicator becomes primary for power.
To level off at an airspeed higher than descending airspeed,
increase the power approximately 100 to 150 feet prior to
reaching the desired altitude. The power setting should be that
which is necessary to maintain the desired airspeed in level
flight. Hold the vertical speed constant until approximately
50 feet above the desired altitude. At this point, the altimeter
becomes primary for pitch and the airspeed indicator becomes
primary for power. The level off from a constant rate descent
should be accomplished in the same manner as the level off
from a constant airspeed descent.
Common Errors During Straight Climbs and
Descents

of bank required for a standard rate turn is to use 15 percent
of the airspeed. A simple way to determine this amount is
to divide the airspeed by 10 and add one-half the result. For
example, at 60 knots approximately 9° of bank is required
(60 ÷ 10 = 6, 6 + 3 = 9); at 80 knots approximately 12° of
bank is needed for a standard rate turn.
To enter a turn, apply lateral cyclic in the direction of the
desired turn. The entry should be accomplished smoothly,
using the attitude indicator to establish the approximate bank
angle. When the turn indicator indicates a standard rate turn,
it becomes primary for bank. The attitude indicator now
becomes a supporting instrument. During level turns, the
altimeter is primary for pitch, and the airspeed indicator is
primary for power. Primary and supporting instruments for a
stabilized standard rate turn are illustrated in Figure 6-14. If
an increase in power is required to maintain airspeed, slight
forward cyclic pressure may be required since the helicopter
tends to pitch up as collective pitch is increased. Apply pedal
trim, as required, to keep the ball centered.
To recover to straight-and-level flight, apply cyclic in the
direction opposite the turn. The rate of roll-out should be the
same as the rate used when rolling into the turn. As the turn
recovery is initiated, the attitude indicator becomes primary
for bank. When the helicopter is approximately level, the
heading indicator becomes primary for bank as in straightand-level flight. Cross-check the airspeed indicator and ball
closely to maintain the desired airspeed and pedal trim.
Turn to a Predetermined Heading
A helicopter turns as long as its lateral axis is tilted;
therefore, the recovery must start before the desired heading
is reached. The amount of lead varies with the rate of turn
and piloting technique.

Turns

As a guide, when making a 3° per second rate of turn, use a
lead of one-half the bank angle. For example, if using a 12°
bank angle, use half of that, or 6°, as the lead point prior to the
desired heading. Use this lead until the exact amount required
by a particular technique can be determined. The bank angle
should never exceed the number of degrees to be turned.
As in any standard rate turn, the rate of recovery should be
the same as the rate of entry. During turns to predetermined
headings, cross-check the primary and supporting pitch, bank,
and power instruments closely.

Turns made by reference to the flight instruments should
be made at a precise rate. Turns described in this chapter
are those not exceeding a standard rate of 3° per second
as indicated on the turn-and-slip indicator. True airspeed
determines the angle of bank necessary to maintain a standard
rate turn. A rule of thumb to determine the approximate angle

Timed Turns
A timed turn is a turn in which the clock and turn-and-slip
indicator are used to change heading a definite number of
degrees in a given time. For example, using a standard rate
turn, a helicopter turns 45° in 15 seconds. Using a half-

1.

Failure to maintain heading

2.

Improper use of power

3.

Poor control of pitch attitude

4.

Failure to maintain proper pedal trim

5.

Failure to level off on desired altitude

6-13

Figure 6-14. Flight Instrument Indications in a Standard-Rate Turn to the Left.

standard rate turn, the helicopter turns 45° in 30 seconds.
Timed turns can be used if the heading indicator becomes
inoperative.
Prior to performing timed turns, the turn coordinator should
be calibrated to determine the accuracy of its indications.
To do this, establish a standard rate turn by referring to the
turn-and-slip indicator. Then, as the sweep second hand of
the clock passes a cardinal point (12, 3, 6, or 9), check the
heading on the heading indicator. While holding the indicated
rate of turn constant, note the heading changes at 10-second
intervals. If the helicopter turns more or less than 30° in
that interval, a smaller or larger deflection of the needle is
necessary to produce a standard rate turn. After the turnand-slip indicator has been calibrated during turns in each
direction, note the corrected deflections, if any, and apply
them during all timed turns.
Use the same cross-check and control technique in making
timed turns that is used to make turns to a predetermined
heading, but substitute the clock for the heading indicator.
The needle of the turn-and-slip indicator is primary for bank
control, the altimeter is primary for pitch control, and the
airspeed indicator is primary for power control. Begin the
roll-in when the clock’s second hand passes a cardinal point;
hold the turn at the calibrated standard rate indication, or
half-standard rate for small changes in heading; then begin
the roll-out when the computed number of seconds has
elapsed. If the roll-in and roll-out rates are the same, the time
6-14

taken during entry and recovery need not be considered in
the time computation.
If practicing timed turns with a full instrument panel, check
the heading indicator for the accuracy of the turns. If executing
turns without the heading indicator, use the magnetic compass
at the completion of the turn to check turn accuracy, taking
compass deviation errors into consideration.
Change of Airspeed in Turns
Changing airspeed in turns is an effective maneuver for
increasing proficiency in all three basic instrument skills.
Since the maneuver involves simultaneous changes in all
components of control, proper execution requires a rapid
cross-check and interpretation, as well as smooth control.
Proficiency in the maneuver also contributes to confidence in
the instruments during attitude and power changes involved
in more complex maneuvers.
Pitch and power control techniques are the same as those
used during airspeed changes in straight-and-level flight.
As discussed previously, the angle of bank necessary for a
given rate of turn is proportional to the true airspeed. Since
the turns are executed at standard rate, the angle of bank
must be varied in direct proportion to the airspeed change in
order to maintain a constant rate of turn. During a reduction
of airspeed, decrease the angle of bank and increase the pitch
attitude to maintain altitude and a standard rate turn.

Altimeter and turn indicator readings should remain constant
throughout the turn. The altimeter is primary for pitch control,
and the turn needle is primary for bank control. Manifold
pressure is primary for power control while the airspeed is
changing. As the airspeed approaches the new indication, the
airspeed indicator becomes primary for power control.
Two methods of changing airspeed in turns may be used.
In the first method, airspeed is changed after the turn is
established. In the second method, the airspeed change
is initiated simultaneously with the turn entry. The first
method is easier, but regardless of the method used, the rate
of cross-check must be increased as power is reduced. As
the helicopter decelerates, check the altimeter and VSI for
needed pitch changes, and the bank instruments for needed
bank changes. If the needle of the turn-and-slip indicator
shows a deviation from the desired deflection, change the
bank. Adjust pitch attitude to maintain altitude. When the
airspeed approaches that desired, the airspeed indicator
becomes primary for power control. Adjust the power to
maintain the desired airspeed. Use pedal trim to ensure the
maneuver is coordinated.
Until control technique is very smooth, frequently crosscheck the attitude indicator to keep from overcontrolling
and to provide approximate bank angles appropriate for the
changing airspeeds.
Compass Turns
The use of gyroscopic heading indicators makes heading
control very easy. However, if the heading indicator fails
or the helicopter is not equipped with one, use the magnetic
compass for heading reference. When making compass-only
turns, a pilot needs to adjust for the lead or lag created by
acceleration and deceleration errors so that the helicopter
rolls out on the desired heading. When turning to a heading
of north, the lead for the roll-out must include the number of
degrees of latitude plus the lead normally used in recovery
from turns. During a turn to a south heading, maintain the
turn until the compass passes south the number of degrees
of latitude, minus the normal roll-out lead. For example,
when turning from an easterly direction to north, where the
latitude is 30°, start the roll-out when the compass reads
37° (30° plus one-half the 15° angle of bank, or whatever
amount is appropriate for the rate of roll-out). When turning
from an easterly direction to south, start the roll-out when
the magnetic compass reads 203° (180° plus 30° minus onehalf the angle of bank). When making similar turns from a
westerly direction, the appropriate points at which to begin
the roll-out would be 323° for a turn to north, and 157° for
a turn to south.

30° Bank Turn
A turn using 30° of bank is seldom necessary or advisable
in instrument meteorological conditions (IMC), and is
considered an unusual attitude in a helicopter. However, it
is an excellent maneuver to practice to increase the ability to
react quickly and smoothly to rapid changes of attitude. Even
though the entry and recovery techniques are the same as for
any other turn, it is more difficult to control pitch because
of the decrease in vertical lift as the bank increases. Also,
because of the decrease in vertical lift, there is a tendency
to lose altitude and/or airspeed. Therefore, to maintain a
constant altitude and airspeed, additional power is required.
Do not initiate a correction, however, until the instruments
indicate the need for one. During the maneuver, note the
need for a correction on the altimeter and VSI, check the
attitude indicator, and then make the necessary adjustments.
After making a change, check the altimeter and VSI again to
determine whether or not the correction was adequate.
Climbing and Descending Turns
For climbing and descending turns, the techniques described
previously for straight climbs, descents, and standard rate
turns are combined. For practice, simultaneously turn and
start the climb or descent. The primary and supporting
instruments for a stabilized constant airspeed left climbing
turn are illustrated in Figure 6-15. The level off from a
climbing or descending turn is the same as the level off from
a straight climb or descent. To return to straight-and-level
flight, stop the turn and then level off, or level off and then
stop the turn, or simultaneously level off and stop the turn.
During climbing and descending turns, keep the ball of the
turn indicator centered with pedal trim.
Common Errors During Turns
1.

Failure to maintain desired turn rate

2.

Failure to maintain altitude in level turns

3.

Failure to maintain desired airspeed

4.

Variation in the rate of entry and recovery

5.

Failure to use proper lead in turns to a heading

6.

Failure to properly compute time during timed turns

7.

Failure to use proper leads and lags during the compass
turns

8.

Improper use of power

9.

Failure to use proper pedal trim

6-15

Unusual Attitudes
Any maneuver not required for normal helicopter instrument
flight is an unusual attitude and may be caused by any one
or combination of factors such as turbulence, disorientation,
instrument failure, confusion, preoccupation with flight deck
duties, carelessness in cross-checking, errors in instrument
interpretation, or lack of proficiency in aircraft control. Due
to the instability characteristics of the helicopter, unusual
attitudes can be extremely critical. As soon as an unusual
attitude is detected, make a recovery to straight-and-level
flight as soon as possible with a minimum loss of altitude.
To recover from an unusual attitude, a pilot should correct
bank-and-pitch attitude and adjust power as necessary. All
components are changed almost simultaneously, with little
lead of one over the other. A pilot must be able to perform
this task with and without the attitude indicator. If the
helicopter is in a climbing or descending turn, adjust bank,
pitch, and power. The bank attitude should be corrected
by referring to the turn-and-slip indicator and attitude
indicator. Pitch attitude should be corrected by reference to
the altimeter, airspeed indicator, VSI, and attitude indicator.
Adjust power by referring to the airspeed indicator and
manifold pressure.
Since the displacement of the controls used in recovery from
unusual attitudes may be greater than those used for normal
flight, make careful adjustments as straight-and-level flight

is approached. Cross-check the other instruments closely to
avoid overcontrolling.
Common Errors During Unusual Attitude
Recoveries
1.

Failure to make proper pitch correction

2.

Failure to make proper bank correction

3.

Failure to make proper power correction

4.

Overcontrolling pitch and/or bank attitude

5.

Overcontrolling power

6.

Excessive loss of altitude

Emergencies
Emergencies during instrument flight are handled similarly
to those occurring during VFR flight. A thorough knowledge
of the helicopter and its systems, as well as good aeronautical
knowledge and judgment, is the best preparation for
emergency situations. Safe operations begin with preflight
planning and a thorough preflight inspection. Plan a route
of flight to include adequate landing sites in the event of an
emergency landing. Make sure all resources, such as maps,
publications, flashlights, and fire extinguishers are readily
available for use in an emergency.
During any emergency, first fly the aircraft. This means ensure
the helicopter is under control, and determine emergency

Figure 6-15. Flight Instrument Indications for a Stabilized Left Climbing Turn at a Constant Airspeed.

6-16

landing sites. Then perform the emergency checklist memory
items, followed by items written in the rotorcraft flight
manual (RFM). When all these items are under control, notify
air traffic control (ATC). Declare any emergency on the last
assigned ATC frequency. If one was not issued, transmit on
the emergency frequency 121.5. Set the transponder to the
emergency squawk code 7700. This code triggers an alarm
or special indicator in radar facilities.
When experiencing most in-flight emergencies, such as low
fuel or complete electrical failure, land as soon as possible.
In the event of an electrical fire, turn off all nonessential
equipment and land immediately. Some essential electrical
instruments, such as the attitude indicator, may be required
for a safe landing. A navigation radio failure may not require
an immediate landing if the flight can continue safely. In
this case, land as soon as practical. ATC may be able to
provide vectors to a safe landing area. For specific details
on what to do during an emergency, refer to the RFM for
the helicopter.
Autorotations
Both straight-ahead and turning autorotations should be
practiced by reference to instruments. This training ensures
prompt corrective action to maintain positive aircraft control
in the event of an engine failure.
To enter autorotation, reduce collective pitch smoothly to
maintain a safe rotor RPM and apply pedal trim to keep the
ball of the turn-and-slip indicator centered. The pitch attitude
of the helicopter should be approximately level as shown by
the attitude indicator. The airspeed indicator is the primary
pitch instrument and should be adjusted to the recommended
autorotation speed. The heading indicator is primary for bank
in a straight-ahead autorotation. In a turning autorotation, a
standard rate turn should be maintained by reference to the
needle of the turn-and-slip indicator.

Common Errors During Autorotations
1.

Uncoordinated entry due to improper pedal trim

2.

Poor airspeed control due to improper pitch attitude

3.

Poor heading control in straight-ahead autorotations

4.

Failure to maintain proper rotor RPM

5.

Failure to maintain a standard rate turn during turning
autorotations

servo fails. If a cyclic servo fails, a pilot may want to land
immediately because the workload increases tremendously. If
an antitorque or collective servo fails, continuing to the next
suitable landing site might be possible.

Instrument Takeoff
The procedures and techniques described here should be
modified as necessary to conform to those set forth in the
operating instructions for the particular helicopter being
flown. During training, instrument takeoffs should not
be attempted except when receiving instruction from an
appropriately certificated, proficient flight instructor pilot.
Adjust the miniature aircraft in the attitude indicator, as
appropriate, for the aircraft being flown. After the helicopter
is aligned with the runway or takeoff pad, to prevent forward
movement of a helicopter equipped with a wheel-type landing
gear, set the parking brakes or apply the toe brakes. If the
parking brake is used, it must be unlocked after the takeoff
has been completed. Apply sufficient friction to the collective
pitch control to minimize overcontrolling and to prevent
creeping. Excessive friction should be avoided since it limits
collective pitch movement.
After checking all instruments for proper indications, start
the takeoff by applying collective pitch and a predetermined
power setting. Add power smoothly and steadily to gain
airspeed and altitude simultaneously and to prevent settling to
the ground. As power is applied and the helicopter becomes
airborne, use the antitorque pedals initially to maintain the
desired heading. At the same time, apply forward cyclic to
begin accelerating to climbing airspeed. During the initial
acceleration, the pitch attitude of the helicopter, as read on the
attitude indicator, should be one- to two-bar widths low. The
primary and supporting instruments after becoming airborne
are illustrated in Figure 6-16. As the airspeed increases to the
appropriate climb airspeed, adjust pitch gradually to climb
attitude. As climb airspeed is reached, reduce power to the
climb power setting and transition to a fully coordinated
straight climb.
During the initial climb out, minor heading corrections
should be made with pedals only until sufficient airspeed is
attained to transition to fully coordinated flight. Throughout
the instrument takeoff, instrument cross-check and
interpretations must be rapid and accurate, and aircraft control
positive and smooth.

Servo Failure
Most helicopters certified for single-pilot IFR flight are required
to have autopilots, which greatly reduces pilot workload. If an
autopilot servo fails, however, resume manual control of the
helicopter. The amount of workload increase depends on which
6-17

Figure 6-16. Flight Instrument Indications During an Instrument Takeoff.

Common Errors During Instrument Takeoffs
1.

Failure to maintain heading

2.

Overcontrolling pedals

3.

Failure to use required power

4.

Failure to adjust pitch attitude as climbing airspeed is
reached

Changing Technology
Advances in technology have brought about changes in
the instrumentation found in all types of aircraft, including
helicopters. Electronic displays commonly referred to as
“glass cockpits” are becoming more common. Primary flight
displays (PFDs) and multi-function displays (MFDs) are
changing not only what information is available to a pilot
but also how that information is displayed.

6-18

Illustrations of technological advancements in instrumentation
are described as follows. In Figure 6-17, a typical PFD
depicts an aircraft flying straight-and-level at 3,000
feet and 100 knots. Figure 6-18 illustrates a nose-low
pitch attitude in a right turn. MFDs can be configured to
provide navigation information such as the moving map in
Figure 6-19 or information pertaining to aircraft systems as
in Figure 6-20.

Figure 6-17. PFD Indications During Straight-and-Level Flight.

Figure 6-18. PFD Indications During a Nose-Low Pitch Attitude in a Right Turn.

6-19

Figure 6-19. MFD Display of a Moving Map.

Figure 6-20. MFD Display of Aircraft Systems.

6-20

Chapter 7

Navigation
Systems
Introduction
This chapter provides the basic radio principles applicable to
navigation equipment, as well as an operational knowledge
of how to use these systems in instrument flight. This
information provides the framework for all instrument
procedures, including standard instrument departure
procedures (SIDS), departure procedures (DPs), holding
patterns, and approaches, because each of these maneuvers
consists mainly of accurate attitude instrument flying and
accurate tracking using navigation systems.

7-1

Basic Radio Principles
A radio wave is an electromagnetic (EM) wave with
frequency characteristics that make it useful. The wave
will travel long distances through space (in or out of the
atmosphere) without losing too much strength. An antenna
is used to convert electric current into a radio wave so it can
travel through space to the receiving antenna, which converts
it back into an electric current for use by a receiver.
How Radio Waves Propagate
All matter has a varying degree of conductivity or resistance
to radio waves. The Earth itself acts as the greatest resistor
to radio waves. Radiated energy that travels near the ground
induces a voltage in the ground that subtracts energy from the
wave, decreasing the strength of the wave as the distance from
the antenna becomes greater. Trees, buildings, and mineral
deposits affect the strength to varying degrees. Radiated
energy in the upper atmosphere is likewise affected as the
energy of radiation is absorbed by molecules of air, water,
and dust. The characteristics of radio wave propagation vary
according to the signal frequency and the design, use, and
limitations of the equipment.

Ground Wave
A ground wave travels across the surface of the Earth. You
can best imagine a ground wave’s path as being in a tunnel
or alley bounded by the surface of the Earth and by the
ionosphere, which keeps the ground wave from going out
into space. Generally, the lower the frequency, the farther
the signal will travel.

due to the varying amount of the sun’s radiation reaching it
(night/day and seasonal variations, sunspot activity, etc.). The
sky wave is, therefore, unreliable for navigation purposes.
For aeronautical communication purposes, the sky wave
(HF) is about 80 to 90 percent reliable. HF is being gradually
replaced by more reliable satellite communication.

Space Wave
When able to pass through the ionosphere, radio waves
of 15 MHz and above (all the way up to many GHz), are
considered space waves. Most navigation systems operate
with signals propagating as space waves. Frequencies above
100 MHz have nearly no ground or sky wave components.
They are space waves, but (except for global positioning
system (GPS)) the navigation signal is used before it reaches
the ionosphere so the effect of the ionosphere, which can
cause some propagation errors, is minimal. GPS errors
caused by passage through the ionosphere are significant
and are corrected for by the GPS receiver system.
Space waves have another characteristic of concern to users.
Space waves reflect off hard objects and may be blocked if
the object is between the transmitter and the receiver. Site
and terrain error, as well as propeller/rotor modulation error
in very high omnidirectional range (VOR) systems is caused
by this bounce. Instrument landing system (ILS) course
distortion is also the result of this phenomenon, which led
to the need for establishment of ILS critical areas.

Ground waves are usable for navigation purposes because
they travel reliably and predictably along the same route
day after day, and are not influenced by too many outside
factors. The ground wave frequency range is generally from
the lowest frequencies in the radio range (perhaps as low as
100 Hz) up to approximately 1,000 kHz (1 MHz). Although
there is a ground wave component to frequencies above this,
up to 30 MHz, the ground wave at these higher frequencies
loses strength over very short distances.

Sky Wave
The sky wave, at frequencies of 1 to 30 MHz, is good for
long distances because these frequencies are refracted or
“bent” by the ionosphere, causing the signal to be sent back
to Earth from high in the sky and received great distances
away. [Figure 7-1] Used by high frequency (HF) radios in
aircraft, messages can be sent across oceans using only 50
to 100 watts of power. Frequencies that produce a sky wave
are not used for navigation because the pathway of the signal
from transmitter to receiver is highly variable. The wave is
“bounced” off of the ionosphere, which is always changing

7-2

Figure 7-1. Ground, Space, and Sky Wave Propogation.

Generally, space waves are “line of sight” receivable, but
those of lower frequencies will “bend” somewhat over the
horizon. The VOR signal at 108 to 118 MHz is a lower
frequency than distance measuring equipment (DME) at 962
to 1213 MHz. Therefore, when an aircraft is flown “over the
horizon” from a VOR/DME station, the DME will normally
be the first to stop functioning.
Disturbances to Radio Wave Reception
Static distorts the radio wave and interferes with normal
reception of communications and navigation signals. Lowfrequency airborne equipment such as automatic direction
finder (ADF) and LORAN are particularly subject to static
disturbance. Using very high frequency (VHF) and ultrahigh frequency (UHF) frequencies avoids many of the
discharge noise effects. Static noise heard on navigation
or communication radio frequencies may be a warning of
interference with navigation instrument displays. Some of
the problems caused by precipitation static (P-static) are:
•

Complete loss of VHF communications.

•

Erroneous magnetic compass readings.

•

Aircraft flying with one wing low while using the
autopilot.

•

High-pitched squeal on audio.

•

Motorboat sound on audio.

•

Loss of all avionics.

•

Inoperative very-low frequency (VLF) navigation
system.

•

Erratic instrument readouts.

•

Weak transmissions and poor radio reception.

•

St. Elmo’s Fire.

NDB Components
The ground equipment, the NDB, transmits in the frequency
range of 190 to 535 kHz. Most ADFs will also tune the AM
broadcast band frequencies above the NDB band (550 to
1650 kHz). However, these frequencies are not approved
for navigation because stations do not continuously identify
themselves, and they are much more susceptible to sky
wave propagation especially from dusk to dawn. NDB
stations are capable of voice transmission and are often used
for transmitting the automated weather observing system
(AWOS). The aircraft must be in operational range of the
NDB. Coverage depends on the strength of the transmitting
station. Before relying on ADF indications, identify the
station by listening to the Morse code identifier. NDB stations
are usually two letters or an alpha-numeric combination.

ADF Components
The airborne equipment includes two antennas, a receiver,
and the indicator instrument. The “sense” antenna (nondirectional) receives signals with nearly equal efficiency
from all directions. The “loop” antenna receives signals
better from two directions (bidirectional). When the loop
and sense antenna inputs are processed together in the ADF
radio, the result is the ability to receive a radio signal well in
all directions but one, thus resolving all directional ambiguity.
The indicator instrument can be one of four kinds: fixedcard ADF, rotatable compass-card ADF, or radio magnetic

Traditional Navigation Systems
Nondirectional Radio Beacon (NDB)
The nondirectional radio beacon (NDB) is a ground-based
radio transmitter that transmits radio energy in all directions.
The ADF, when used with an NDB, determines the bearing
from the aircraft to the transmitting station. The indicator
may be mounted in a separate instrument in the aircraft
panel. [Figure 7-2] The ADF needle points to the NDB
ground station to determine the relative bearing (RB) to the
transmitting station. It is the number of degrees measured
clockwise between the aircraft’s heading and the direction
from which the bearing is taken. The aircraft’s magnetic
heading (MH) is the direction the aircraft is pointed with
respect to magnetic north. The magnetic bearing (MB) is the
direction to or from a radio transmitting station measured
relative to magnetic north.
Figure 7-2. ADF Indicator Instrument and Receiver.

7-3

indicator (RMI) with either one needle or dual needle. Fixedcard ADF (also known as the relative bearing indicator (RBI))
always indicates zero at the top of the instrument, with the
needle indicating the RB to the station. Figure 7-3 indicates
an RB of 135°; if the MH is 045°, the MB to the station is
180°. (MH + RB = MB to the station.)
The movable-card ADF allows the pilot to rotate the
aircraft’s present heading to the top of the instrument so
that the head of the needle indicates MB to the station and
the tail indicates MB from the station. Figure 7-4 indicates
a heading of 045°, MB to the station of 180°, and MB from
the station of 360°.
The RMI differs from the movable-card ADF in that it
automatically rotates the azimuth card (remotely controlled
by a gyrocompass) to represent aircraft heading. The RMI
has two needles, which can be used to indicate navigation
information from either the ADF or the VOR receiver. When
a needle is being driven by the ADF, the head of the needle
indicates the MB TO the station tuned on the ADF receiver.
The tail of the needle is the bearing FROM the station. When
a needle of the RMI is driven by a VOR receiver, the needle
indicates where the aircraft is radially with respect to the
VOR station. The needle points to the bearing TO the station,
as read on the azimuth card. The tail of the needle points to
the radial of the VOR the aircraft is currently on or crossing.
Figure 7-5 indicates a heading of 005°, the MB to the station
is 015°, and the MB from the station is 195°.

Figure 7-3. Relative bearing (RB) on a fixed-card indicator. Note
that the card always indicates 360°, or north. In this case, the
relative bearing to the station is 135° to the right. If the aircraft
were on a magnetic heading of 360°, then the magnetic bearing
(MB) would also be 135°.

7-4

Function of ADF
The ADF can be used to plot your position, track inbound
and outbound, and intercept a bearing. These procedures
are used to execute holding patterns and nonprecision
instrument approaches.
Orientation
The ADF needle points TO the station, regardless of aircraft
heading or position. The RB indicated is thus the angular
relationship between the aircraft heading and the station,
measured clockwise from the nose of the aircraft. Think of
the nose/tail and left/right needle indications, visualizing the
ADF dial in terms of the longitudinal axis of the aircraft.
When the needle points to 0°, the nose of the aircraft points
directly to the station; with the pointer on 210°, the station
is 30° to the left of the tail; with the pointer on 090°, the
station is off the right wingtip. The RB alone does not indicate
aircraft position. The RB must be related to aircraft heading
in order to determine direction to or from the station.
Station Passage
When you are near the station, slight deviations from
the desired track result in large deflections of the needle.
Therefore, it is important to establish the correct drift
correction angle as soon as possible. Make small heading
corrections (not over 5°) as soon as the needle shows a
deviation from course, until it begins to rotate steadily toward
a wingtip position or shows erratic left/right oscillations. You

Figure 7-4. Relative bearing (RB) on a movable-card indicator. By
placing the aircraft’s magnetic heading (MH) of 045° under the
top index, the relative bearing (RB) of 135° to the right will also
be the magnetic bearing (no wind conditions) which will take you
to the transmitting station.

Tracking
Tracking uses a heading that will maintain the desired track
to or from the station regardless of crosswind conditions.
Interpretation of the heading indicator and needle is done to
maintain a constant MB to or from the station.

Figure 7-5. Radio magnetic indicator (RMI). Because the aircraft’s
magnetic heading is automatically changed, the relative bearing
(RB), in this case 095°, will indicate the magnetic bearing (095°)
to the station (no wind conditions) and the magnetic heading that
will take you there.

are abeam a station when the needle points 90° off your track.
Hold your last corrected heading constant and time station
passage when the needle shows either wingtip position or
settles at or near the 180° position. The time interval from
the first indications of station proximity to positive station
passage varies with altitude—a few seconds at low levels to
3 minutes at high altitude.
Homing
The ADF may be used to “home” in on a station. Homing
is flying the aircraft on any heading required to keep the
needle pointing directly to the 0° RB position. To home in
on a station, tune the station, identify the Morse code signal,
and then turn the aircraft to bring the ADF azimuth needle to
the 0° RB position. Turns should be made using the heading
indicator. When the turn is complete, check the ADF needle
and make small corrections as necessary.
Figure 7-6 illustrates homing starting from an initial MH of
050° and an RB of 300°, indicating a 60° left turn is needed
to produce an RB of zero. Turn left, rolling out at 50° minus
60° equals 350°. Small heading corrections are then made
to zero the ADF needle.
If there is no wind, the aircraft will home to the station on a
direct track over the ground. With a crosswind, the aircraft
will follow a circuitous path to the station on the downwind
side of the direct track to the station.

To track inbound, turn to the heading that will produce a zero
RB. Maintain this heading until off-course drift is indicated
by displacement of the needle, which will occur if there is a
crosswind (needle moving left = wind from the left; needle
moving right = wind from the right). A rapid rate of bearing
change with a constant heading indicates either a strong
crosswind or close proximity to the station or both. When
there is a definite (2° to 5°) change in needle reading, turn
in the direction of needle deflection to intercept the initial
MB. The angle of interception must be greater than the
number of degrees of drift, otherwise the aircraft will slowly
drift due to the wind pushing the aircraft. If repeated often
enough, the track to the station will appear circular and the
distance greatly increased as compared to a straight track.
The intercept angle depends on the rate of drift, the aircraft
speed, and station proximity. Initially, it is standard to double
the RB when turning toward your course.
For example, if your heading equals your course and the
needle points 10° left, turn 20° left, twice the initial RB.
[Figure 7-7] This will be your intercept angle to capture the
RB. Hold this heading until the needle is deflected 20° in
the opposite direction. That is, the deflection of the needle
equals the interception angle (in this case 20°). The track has
been intercepted, and the aircraft will remain on track as long
as the RB remains the same number of degrees as the wind
correction angle (WCA), the angle between the desired track
and the heading of the aircraft necessary to keep the aircraft
tracking over the desired track. Lead the interception to avoid
overshooting the track. Turn 10° toward the inbound course.
You are now inbound with a 10° left correction angle.
NOTE: In Figure 7-7, for the aircraft closest to the station, the
WCA is 10° left and the RB is 10° right. If those values do
not change, the aircraft will track directly to the station. If you
observe off-course deflection in the original direction, turn
again to the original interception heading. When the desired
course has been re-intercepted, turn 5° toward the inbound
course, proceeding inbound with a 15° drift correction. If the
initial 10° drift correction is excessive, as shown by needle
deflection away from the wind, turn to parallel the desired
course and let the wind drift you back on course. When the
needle is again zeroed, turn into the wind with a reduced
drift correction angle.

7-5

Figure 7-6. ADF Homing With a Crosswind.

7-6

Figure 7-7. ADF Tracking Inbound.

7-7

To track outbound, the same principles apply: needle moving
left = wind from the left, needle moving right = wind from the
right. Wind correction is made toward the needle deflection.
The only exception is while the turn to establish the WCA is
being made, the direction of the azimuth needle deflections is
reversed. When tracking inbound, needle deflection decreases
while turning to establish the WCA, and needle deflection
increases when tracking outbound. Note the example of
course interception and outbound tracking in Figure 7-8.
Intercepting Bearings
ADF orientation and tracking procedures may be applied to
intercept a specified inbound or outbound MB. To intercept
an inbound bearing of 355°, the following steps may be used.
[Figure 7-9]
1.

2.

3.

4.

5.

Determine your position in relation to the station by
paralleling the desired inbound bearing. In this case,
turn to a heading of 355°. Note that the station is to
the right front of the aircraft.
Determine the number of degrees of needle deflection
from the nose of the aircraft. In this case, the needle’s
RB from the aircraft’s nose is 40° to the right. A rule
of thumb for interception is to double this RB amount
as an interception angle (80°).
Turn the aircraft toward the desired MB the number of
degrees determined for the interception angle which
as indicated (in two above) is twice the initial RB
(40°), or in this case 80°. Therefore, the right turn will
be 80° from the initial MB of 355°, or a turn to 075°
magnetic (355° + 80° + 075°).
Maintain this interception heading of 075° until the
needle is deflected the same number of degrees “left”
from the zero position as the angle of interception
080°, (minus any lead appropriate for the rate at which
the bearing is changing).
Turn left 80° and the RB (in a no wind condition and
with proper compensation for the rate of the ADF
needle movement) should be 0°, or directly off the
nose. Additionally, the MB should be 355° indicating
proper interception of the desired course.

NOTE: The rate of an ADF needle movement or any bearing
pointer for that matter will be faster as aircraft position
becomes closer to the station or waypoint (WP).
Interception of an outbound MB can be accomplished by the
same procedures as for the inbound intercept, except that
it is necessary to substitute the 180° position for the zero
position on the needle.

7-8

Operational Errors of ADF
Some of the common pilot-induced errors associated with
ADF navigation are listed below to help you avoid making
the same mistakes. The errors are:
1.

Improper tuning and station identification. Many pilots
have made the mistake of homing or tracking to the
wrong station.

2.

Positively identifying any malfunctions of the RMI
slaving system or ignoring the warning flag.

3.

Dependence on homing rather than proper tracking.
This commonly results from sole reliance on the ADF
indications, rather than correlating them with heading
indications.

4.

Poor orientation, due to failure to follow proper steps
in orientation and tracking.

5.

Careless interception angles, very likely to happen if
you rush the initial orientation procedure.

6.

Overshooting and undershooting predetermined MBs,
often due to forgetting the course interception angles
used.

7.

Failure to maintain selected headings. Any heading
change is accompanied by an ADF needle change.
The instruments must be read in combination before
any interpretation is made.

8.

Failure to understand the limitations of the ADF and
the factors that affect its use.

9.

Overcontrolling track corrections close to the station
(chasing the ADF needle), due to failure to understand
or recognize station approach.

10. Failure to keep the heading indicator set so it agrees
with the magnetic compass.
Very High Frequency Omnidirectional Range
(VOR)
VOR is the primary navigational aid (NAVAID) used by civil
aviation in the National Airspace System (NAS). The VOR
ground station is oriented to magnetic north and transmits
azimuth information to the aircraft, providing 360 courses
TO or FROM the VOR station. When DME is installed with
the VOR, it is referred to as a VOR/DME and provides both
azimuth and distance information. When military tactical air
navigation (TACAN) equipment is installed with the VOR,
it is known as a VORTAC and provides both azimuth and
distance information.

Figure 7-8. ADF Interception and Tracking Outbound.

7-9

the aircraft altitude, class of facility, location of the facility,
terrain conditions within the usable area of the facility, and
other factors. Above and beyond certain altitude and distance
limits, signal interference from other VOR facilities and a
weak signal make it unreliable. Coverage is typically at least
40 miles at normal minimum instrument flight rules (IFR)
altitudes. VORs with accuracy problems in parts of their
service volume are listed in Notices to Airmen (NOTAMs)
and in the Airport/Facility Directory (A/FD) under the name
of the NAVAID.

VOR Components
The ground equipment consists of a VOR ground station,
which is a small, low building topped with a flat white disc,
upon which are located the VOR antennas and a fiberglass
cone-shaped tower. [Figure 7-11] The station includes an
automatic monitoring system. The monitor automatically
turns off defective equipment and turns on the standby
transmitter. Generally, the accuracy of the signal from the
ground station is within 1°.

Figure 7-9. Interception of Bearing.

VOR facilities are aurally identified by Morse code, or
voice, or both. The VOR can be used for ground-to-air
communication without interference with the navigation
signal. VOR facilities operate within the 108.0 to 117.95 MHz
frequency band and assignment between 108.0 and 112.0

The courses oriented FROM the station are called radials. The
VOR information received by an aircraft is not influenced
by aircraft attitude or heading. [Figure 7-10] Radials can
be envisioned to be like the spokes of a wheel on which the
aircraft is on one specific radial at any time. For example,
aircraft A (heading 180°) is inbound on the 360° radial; after
crossing the station, the aircraft is outbound on the 180°
radial at A1. Aircraft B is shown crossing the 225° radial.
Similarly, at any point around the station, an aircraft can be
located somewhere on a specific VOR radial. Additionally,
a VOR needle on an RMI will always point to the course
that will take you to the VOR station where conversely the
ADF needle points to the station as a RB from the aircraft. In
the example above, the ADF needle at position A would be
pointed straight ahead, at A1 to the aircraft’s 180° position
(tail) and at B, to the aircraft’s right.
The VOR receiver measures and presents information to
indicate bearing TO or FROM the station. In addition to the
navigation signals transmitted by the VOR, a Morse code
signal is transmitted concurrently to identify the facility, as
well as voice transmissions for communication and relay of
weather and other information.
VORs are classified according to their operational uses. The
standard VOR facility has a power output of approximately
200 watts, with a maximum usable range depending upon
7-10

Figure 7-10. VOR Radials.

Omnibearing Selector (OBS)
The desired course is selected by turning the OBS knob until
the course is aligned with the course index mark or displayed
in the course window.
Course Deviation Indicator (CDI)
The deviation indicator is composed of an instrument face
and a needle hinged to move laterally across the instrument
face. The needle centers when the aircraft is on the selected
radial or its reciprocal. Full needle deflection from the center
position to either side of the dial indicates the aircraft is 12°
or more off course, assuming normal needle sensitivity. The
outer edge of the center circle is 2° off course; with each dot
representing an additional 2°.
Figure 7-11. VOR Transmitter (Ground Station).

MHz is in even-tenth increments to preclude any conflict
with ILS localizer frequency assignment, which uses the
odd tenths in this range.

TO/FROM Indicator
The TO/FROM indicator shows whether the selected course
will take the aircraft TO or FROM the station. It does not
indicate whether the aircraft is heading to or from the
station.

The airborne equipment includes an antenna, a receiver, and
the indicator instrument. The receiver has a frequency knob to
select any of the frequencies between 108.0 to 117.95 MHz.
The On/Off/volume control turns on the navigation receiver
and controls the audio volume. The volume has no effect on
the operation of the receiver. You should listen to the station
identifier before relying on the instrument for navigation.

Flags or Other Signal Strength Indicators
The device that indicates a usable or an unreliable signal may
be an “OFF” flag. It retracts from view when signal strength
is sufficient for reliable instrument indications. Alternately,
insufficient signal strength may be indicated by a blank or
OFF in the TO/FROM window.

VOR indicator instruments have at least the essential
components shown in the instrument illustrated in
Figure 7-12.

The indicator instrument may also be a horizontal situation
indicator (HSI) which combines the heading indicator
and CDI. [Figure 7-13] The combination of navigation
information from VOR/Localizer (LOC) or from LORAN
or GPS, with aircraft heading information provides a visual
picture of the aircraft’s location and direction. This decreases
pilot workload especially with tasks such as course intercepts,
flying a back-course approach, or holding pattern entry. (See

Figure 7-12. The VOR Indicator Instrument.

Figure 7-13. A Typical Horizontal Situation Indicator (HSI).

7-11

Chapter 3, Flight Instruments, for operational characteristics.)
[Figure 7-14]

due to the radiation pattern of the station’s antenna, and
because the resultant of the opposing reference and variable
signals is small and constantly changing.

Function of VOR
Orientation
The VOR does not account for the aircraft heading. It only
relays the aircraft direction from the station and will have the
same indications regardless of which way the nose is pointing.
Tune the VOR receiver to the appropriate frequency of the
selected VOR ground station, turn up the audio volume, and
identify the station’s signal audibly. Then, rotate the OBS
to center the CDI needle and read the course under or over
the index.
In Figure 7-12, 360° TO is the course indicated, while in
Figure 7-15, 180° TO is the course. The latter indicates that
the aircraft (which may be heading in any direction) is, at this
moment, located at any point on the 360° radial (line from the
station) except directly over the station or very close to it, as
between points I and S in Figure 7-15. The CDI will deviate
from side to side as the aircraft passes over or nearly over
the station because of the volume of space above the station
where the zone of confusion exists. This zone of confusion is
caused by lack of adequate signal directly above the station

The CDI in Figure 7-15 indicates 180°, meaning that the
aircraft is on the 180° or the 360° radial of the station. The TO/
FROM indicator resolves the ambiguity. If the TO indicator is
showing, then it is 180° TO the station. The FROM indication
indicates the radial of the station the aircraft is presently on.
Movement of the CDI from center, if it occurs at a relatively
constant rate, indicates the aircraft is moving or drifting off the
180°/360° line. If the movement is rapid or fluctuating, this
is an indication of impending station passage (the aircraft is
near the station). To determine the aircraft’s position relative
to the station, rotate the OBS until FROM appears in the
window, and then center the CDI needle. The index indicates
the VOR radial where the aircraft is located. The inbound (to
the station) course is the reciprocal of the radial.
If the VOR is set to the reciprocal of the intended course,
the CDI will reflect reverse sensing. To correct for needle
deflection, turn away from the needle. To avoid this reverse
sensing situation, set the VOR to agree with the intended
course.

Figure 7-14. An HSI display as seen on the pilot’s primary flight display (PFD) on an electronic flight instrument. Note that only attributes

related to the HSI are labeled.

7-12

Figure 7-15. CDI Interpretation. The CDI as typically found on analog systems (right) and as found on electronic flight instruments

(left).

7-13

A single NAVAID will allow a pilot to determine the aircraft’s
position relative to a radial. Indications from a second
NAVAID are needed in order to narrow the aircraft’s position
down to an exact location on this radial.

than 90° (45° x 2 = 090°). 205° + 090° = 295° for the
intercept)
4.

Rotate the OBS to the desired radial or inbound
course.

Tracking TO and FROM the Station
To track to the station, rotate the OBS until TO appears, then
center the CDI. Fly the course indicated by the index. If the CDI
moves off center to the left, follow the needle by correcting
course to the left, beginning with a 20° correction.

5.

Turn to the interception heading.

6.

Hold this heading constant until the CDI center, which
indicates the aircraft is on course. (With practice in
judging the varying rates of closure with the course
centerline, pilots learn to lead the turn to prevent
overshooting the course.)

When flying the course indicated on the index, a left
deflection of the needle indicates a crosswind component
from the left. If the amount of correction brings the needle
back to center, decrease the left course correction by half. If
the CDI moves left or right now, it should do so much more
slowly, and smaller heading corrections can be made for the
next iteration.

7.

Turn to the MH corresponding to the selected
course, and follow tracking procedures inbound or
outbound.

Keeping the CDI centered will take the aircraft to the station.
To track to the station, the OBS value at the index is not
changed. To home to the station, the CDI needle is periodically
centered, and the new course under the index is used for the
aircraft heading. Homing will follow a circuitous route to the
station, just as with ADF homing.

Course interception is illustrated in Figure 7-16.

VOR Operational Errors
Typical pilot-induced errors include:
1.

Careless tuning and identification of station.

2.

Failure to check receiver for accuracy/sensitivity.

3.

Turning in the wrong direction during an orientation.
This error is common until visualizing position rather
than heading.

To track FROM the station on a VOR radial, you should
first orient the aircraft’s location with respect to the station
and the desired outbound track by centering the CDI needle
with a FROM indication. The track is intercepted by either
flying over the station or establishing an intercept heading.
The magnetic course of the desired radial is entered under the
index using the OBS and the intercept heading held until the
CDI centers. Then the procedure for tracking to the station is
used to fly outbound on the specified radial.

4.

Failure to check the ambiguity (TO/FROM) indicator,
particularly during course reversals, resulting
in reverse sensing and corrections in the wrong
direction.

5.

Failure to parallel the desired radial on a track
interception problem. Without this step, orientation
to the desired radial can be confusing. Since pilots
think in terms of left and right of course, aligning the
aircraft position to the radial/course is essential.

Course Interception
If the desired course is not the one being flown, first orient
the aircraft’s position with respect to the VOR station and the
course to be flown, and then establish an intercept heading.
The following steps may be used to intercept a predetermined
course, either inbound or outbound. Steps 1–3 may be omitted
when turning directly to intercept the course without initially
turning to parallel the desired course.

6.

Overshooting and undershooting radials on interception
problems.

7.

Overcontrolling corrections during tracking, especially
close to the station.

8.

Misinterpretation of station passage. On VOR
receivers not equipped with an ON/OFF flag, a
voice transmission on the combined communication
and navigation radio (NAV/COM) in use for VOR
may cause the same TO/FROM fluctuations on the
ambiguity meter as shown during station passage.
Read the whole receiver—TO/FROM, CDI, and
OBS—before you make a decision. Do not utilize a
VOR reading observed while transmitting.

9.

Chasing the CDI, resulting in homing instead of
tracking. Careless heading control and failure to
bracket wind corrections make this error common.

1.

Turn to a heading to parallel the desired course, in the
same direction as the course to be flown.

2.

Determine the difference between the radial to be
intercepted and the radial on which the aircraft is
located (205° – 160° = 045°).

3.

Double the difference to determine the interception
angle, which will not be less than 20° nor greater

7-14

Figure 7-16. Course Interception (VOR).

7-15

VOR Accuracy
The effectiveness of the VOR depends upon proper use and
adjustment of both ground and airborne equipment.
The accuracy of course alignment of the VOR is generally
plus or minus 1°. On some VORs, minor course roughness
may be observed, evidenced by course needle or brief flag
alarm. At a few stations, usually in mountainous terrain,
the pilot may occasionally observe a brief course needle
oscillation, similar to the indication of “approaching station.”
Pilots flying over unfamiliar routes are cautioned to be on
the alert for these vagaries, and in particular, to use the TO/
FROM indicator to determine positive station passage.

To use the VOT service, tune in the VOT frequency 108.0
MHz on the VOR receiver. With the CDI centered, the
OBS should read 0° with the TO/FROM indication showing
FROM or the OBS should read 180° with the TO/FROM
indication showing TO. Should the VOR receiver operate an
RMI, it would indicate 180° on any OBS setting.
A radiated VOT from an appropriately rated radio repair
station serves the same purpose as an FAA VOT signal, and
the check is made in much the same manner as a VOT with
some differences.

Certain propeller revolutions per minute (RPM) settings
or helicopter rotor speeds can cause the VOR CDI to
fluctuate as much as plus or minus 6°. Slight changes to
the RPM setting will normally smooth out this roughness.
Pilots are urged to check for this modulation phenomenon
prior to reporting a VOR station or aircraft equipment for
unsatisfactory operation.

The frequency normally approved by the Federal
Communications Commission (FCC) is 108.0 MHz;
however, repair stations are not permitted to radiate the
VOR test signal continuously. The owner or operator of the
aircraft must make arrangements with the repair station to
have the test signal transmitted. A representative of the repair
station must make an entry into the aircraft logbook or other
permanent record certifying to the radial accuracy and the
date of transmission.

VOR Receiver Accuracy Check

Certified Checkpoints

VOR system course sensitivity may be checked by noting
the number of degrees of change as the OBS is rotated to
move the CDI from center to the last dot on either side. The
course selected should not exceed 10° or 12° either side. In
addition, Title 14 of the Code of Federal Regulations (14
CFR) part 91 provides for certain VOR equipment accuracy
checks, and an appropriate endorsement, within 30 days prior
to flight under IFR. To comply with this requirement and to
ensure satisfactory operation of the airborne system, use the
following means for checking VOR receiver accuracy:

Airborne and ground checkpoints consist of certified radials
that should be received at specific points on the airport surface
or over specific landmarks while airborne in the immediate
vicinity of the airport. Locations of these checkpoints are
published in the A/FD.

1.

VOR test facility (VOT) or a radiated test signal from
an appropriately rated radio repair station.

2.

Certified checkpoints on the airport surface.

3.

Certified airborne checkpoints.

VOR Test Facility (VOT)
The Federal Aviation Administration (FAA) VOT transmits
a test signal which provides users a convenient means to
determine the operational status and accuracy of a VOR
receiver while on the ground where a VOT is located.
Locations of VOTs are published in the A/FD. Two means of
identification are used. One is a series of dots and the other is
a continuous tone. Information concerning an individual test
signal can be obtained from the local flight service station
(FSS.) The airborne use of VOT is permitted; however, its
use is strictly limited to those areas/altitudes specifically
authorized in the A/FD or appropriate supplement.

7-16

Should an error in excess of ±4° be indicated through use of
a ground check, or ±6° using the airborne check, IFR flight
shall not be attempted without first correcting the source of
the error. No correction other than the correction card figures
supplied by the manufacturer should be applied in making
these VOR receiver checks.
If a dual system VOR (units independent of each other except
for the antenna) is installed in the aircraft, one system may
be checked against the other. Turn both systems to the same
VOR ground facility and note the indicated bearing to that
station. The maximum permissible variation between the two
indicated bearings is 4°.
Distance Measuring Equipment (DME)
When used in conjunction with the VOR system, DME makes
it possible for pilots to determine an accurate geographic
position of the aircraft, including the bearing and distance
TO or FROM the station. The aircraft DME transmits
interrogating radio frequency (RF) pulses, which are received
by the DME antenna at the ground facility. The signal triggers
ground receiver equipment to respond to the interrogating

aircraft. The airborne DME equipment measures the elapsed
time between the interrogation signal sent by the aircraft and
reception of the reply pulses from the ground station. This
time measurement is converted into distance in nautical miles
(NM) from the station.

Altitude
Some DMEs correct for slant-range error.

Function of DME

Some DME receivers provide a groundspeed in knots by
monitoring the rate of change of the aircraft’s position relative
to the ground station. Groundspeed values are accurate only
when tracking directly to or from the station.

A DME is used for determining the distance from a ground
DME transmitter. Compared to other VHF/UHF NAVAIDs,
a DME is very accurate. The distance information can be
used to determine the aircraft position or flying a track that
is a constant distance from the station. This is referred to as
a DME arc.

DME Components

DME Arc

VOR/DME, VORTAC, ILS/DME, and LOC/DME
navigation facilities established by the FAA provide course
and distance information from collocated components under
a frequency pairing plan. DME operates on frequencies
in the UHF spectrum between 962 MHz and 1213 MHz.
Aircraft receiving equipment which provides for automatic
DME selection assures reception of azimuth and distance
information from a common source when designated VOR/
DME, VORTAC, ILS/DME, and LOC/DME are selected.
Some aircraft have separate VOR and DME receivers, each
of which must be tuned to the appropriate navigation facility.
The airborne equipment includes an antenna and a receiver.

There are many instrument approach procedures (IAPs) that
incorporate DME arcs. The procedures and techniques given
here for intercepting and maintaining such arcs are applicable
to any facility that provides DME information. Such a facility
may or may not be collocated with the facility that provides
final approach guidance.

The pilot-controllable features of the DME receiver
include:

As an example of flying a DME arc, refer to Figure 7-17 and
follow these steps:
1.

Track inbound on the OKT 325° radial, frequently
checking the DME mileage readout.

2.

A 0.5 NM lead is satisfactory for groundspeeds of 150
knots or less; start the turn to the arc at 10.5 miles. At
higher groundspeeds, use a proportionately greater
lead.

Channel (Frequency) Selector
Many DMEs are channeled by an associated VHF radio, or
there may be a selector switch so a pilot can select which
VHF radio is channeling the DME. For a DME with its
own frequency selector, use the frequency of the associated
VOR/DME or VORTAC station.
On/Off/Volume Switch
The DME identifier will be heard as a Morse code identifier
with a tone somewhat higher than that of the associated VOR
or LOC. It will be heard once for every three or four times
the VOR or LOC identifier is heard. If only one identifier is
heard about every 30 seconds, the DME is functional, but
the associated VOR or LOC is not.
Mode Switch
The mode switch selects between distance (DIST) or distance
in NMs, groundspeed, and time to station. There may also
be one or more HOLD functions which permit the DME to
stay channeled to the station that was selected before the
switch was placed in the hold position. This is useful when
you make an ILS approach at a facility that has no collocated
DME, but there is a VOR/DME nearby.
Figure 7-17. DME Arc Interception.

7-17

3.

Continue the turn for approximately 90°. The roll-out
heading will be 055° in a no wind condition.

4.

During the last part of the intercepting turn, monitor
the DME closely. If the arc is being overshot (more
than 1.0 NM), continue through the originally planned
roll-out heading. If the arc is being undershot, roll-out
of the turn early.

The procedure for intercepting the 10 DME when outbound
is basically the same, the lead point being 10 NM minus 0.5
NM, or 9.5 NM.
When flying a DME arc with wind, it is important to keep a
continuous mental picture of the aircraft’s position relative to
the facility. Since the wind-drift correction angle is constantly
changing throughout the arc, wind orientation is important.

Figure 7-18. Using DME and RMI To Maintain an Arc.

7-18

In some cases, wind can be used in returning to the desired
track. High airspeeds require more pilot attention because of
the higher rate of deviation and correction.
Maintaining the arc is simplified by keeping slightly inside
the curve; thus, the arc is turning toward the aircraft and
interception may be accomplished by holding a straight
course. When outside the curve, the arc is “turning away”
and a greater correction is required.
To fly the arc using the VOR CDI, center the CDI needle
upon completion of the 90° turn to intercept the arc. The
aircraft’s heading will be found very near the left or right
side (270° or 90° reference points) of the instrument. The
readings at that side location on the instrument will give
primary heading information while on the arc. Adjust the
aircraft heading to compensate for wind and to correct for

distance to maintain the correct arc distance. Recenter the
CDI and note the new primary heading indicated whenever
the CDI gets 2°–4° from center.
With an RMI, in a no wind condition, pilots should
theoretically be able to fly an exact circle around the facility
by maintaining an RB of 90° or 270°. In actual practice,
a series of short legs are flown. To maintain the arc in
Figure 7-18, proceed as follows:
1.

2.

With the RMI bearing pointer on the wingtip reference
(90° or 270° position) and the aircraft at the desired
DME range, maintain a constant heading and allow the
bearing pointer to move 5°–10° behind the wingtip.
This will cause the range to increase slightly.
Turn toward the facility to place the bearing pointer
5–10° ahead of the wingtip reference, and then
maintain heading until the bearing pointer is again
behind the wingtip. Continue this procedure to
maintain the approximate arc.

3.

If a crosswind causes the aircraft to drift away from
the facility, turn the aircraft until the bearing pointer is
ahead of the wingtip reference. If a crosswind causes
the aircraft to drift toward the facility, turn until the
bearing is behind the wingtip.

4.

As a guide in making range corrections, change the RB
10°–20° for each half-mile deviation from the desired
arc. For example, in no-wind conditions, if the aircraft
is 1/2 to 1 mile outside the arc and the bearing pointer
is on the wingtip reference, turn the aircraft 20° toward
the facility to return to the arc.

Without an RMI, orientation is more difficult since there is
no direct azimuth reference. However, the procedure can be
flown using the OBS and CDI for azimuth information and
the DME for arc distance.

Intercepting Lead Radials
A lead radial is the radial at which the turn from the arc to the
inbound course is started. When intercepting a radial from
a DME arc, the lead will vary with arc radius and ground
speed. For the average general aviation aircraft, flying arcs
such as those depicted on most approach charts at speeds
of 150 knots or less, the lead will be under 5°. There is no
difference between intercepting a radial from an arc and
intercepting it from a straight course.
With an RMI, the rate of bearing movement should be
monitored closely while flying the arc. Set the course of the
radial to be intercepted as soon as possible and determine
the approximate lead. Upon reaching this point, start the
intercepting turn. Without an RMI, the technique for radial

interception is the same except for azimuth information,
which is available only from the OBS and CDI.
The technique for intercepting a localizer from a DME arc
is similar to intercepting a radial. At the depicted lead radial
(LR 070° or LR 084° in Figures 7-19, 7-20, and 7-21), a
pilot having a single VOR/LOC receiver should set it to the
localizer frequency. If the pilot has dual VOR/LOC receivers,
one unit may be used to provide azimuth information and the
other set to the localizer frequency. Since these lead radials
provide 7° of lead, a half-standard rate turn should be used
until the LOC needle starts to move toward center.

DME Errors
A DME/DME fix (a location based on two DME lines of
position from two DME stations) provides a more accurate
aircraft location than using a VOR and a DME fix.
DME signals are line-of-sight; the mileage readout is the
straight line distance from the aircraft to the DME ground
facility and is commonly referred to as slant range distance.
Slant range refers to the distance from the aircraft’s antenna
to the ground station (A line at an angle to the ground
transmitter. GPS systems provide distance as the horizontal
measurement from the WP to the aircraft. Therefore, at 3,000
feet and 0.5 miles the DME (slant range) would read 0.6 NM
while the GPS distance would show the actual horizontal
distance of .5 DME. This error is smallest at low altitudes
and/or at long ranges. It is greatest when the aircraft is closer
to the facility, at which time the DME receiver will display
altitude (in NM) above the facility. Slant range error is
negligible if the aircraft is one mile or more from the ground
facility for each 1,000 feet of altitude above the elevation of
the facility.
Area Navigation (RNAV)
Area navigation (RNAV) equipment includes VOR/DME,
LORAN, GPS, and inertial navigation systems (INS). RNAV
equipment is capable of computing the aircraft position,
actual track, groundspeed, and then presenting meaningful
information to the pilot. This information may be in the form
of distance, cross-track error, and time estimates relative to
the selected track or WP. In addition, the RNAV equipment
installations must be approved for use under IFR. The Pilot’s
Operating Handbook/Airplane Flight Manual (POH/AFM)
should always be consulted to determine what equipment is
installed, the operations that are approved, and the details of
equipment use. Some aircraft may have equipment that allows
input from more than one RNAV source, thereby providing
a very accurate and reliable navigation source.

7-19

Figure 7-19. An aircraft is displayed heading southwest to intercept the localizer approach, using the 16 NM DME Arc off of ORM.

7-20

Figure 7-20. The same aircraft illustrated in Figure 7-19 shown on the ORM radial near TIGAE intersection turning inbound for the

localizer.

7-21

Figure 7-21. Aircraft is illustrated inbound on the localizer

course.

Figure 7-22. RNAV Computation.

7-22

VOR/DME RNAV

4.

RNAV/APPR (approach mode) with linear deviation
of ±1.25 NM as full scale CDI deflection.

5.

WP select control. Some units allow the storage of more
than one WP; this control allows selection of any WP
in storage.

6.

Data input controls. These controls allow user input
of WP number or ident, VOR or LOC frequency, WP
radial and distance.

VOR RNAV is based on information generated by the present
VORTAC or VOR/DME system to create a WP using an
airborne computer. As shown in Figure 7-22, the value of
side A is the measured DME distance to the VOR/DME. Side
B, the distance from the VOR/DME to the WP, and angle 1
(VOR radial or the bearing from the VORTAC to the WP)
are values set in the flight deck control. The bearing from
the VOR/DME to the aircraft, angle 2, is measured by the
VOR receiver. The airborne computer continuously compares
angles 1 and 2 and determines angle 3 and side C, which is
the distance in NMs and magnetic course from the aircraft
to the WP. This is presented as guidance information on the
flight deck display.

While DME groundspeed readout is accurate only when
tracking directly to or from the station in VOR/DME mode,
in RNAV mode the DME groundspeed readout is accurate on
any track.

VOR/DME RNAV Components

Function of VOR/DME RNAV

Although RNAV flight deck instrument displays vary among
manufacturers, most are connected to the aircraft CDI with a
switch or knob to select VOR or RNAV guidance. There is
usually a light or indicator to inform the pilot whether VOR
or RNAV is selected. [Figure 7-23] The display includes the
WP, frequency, mode in use, WP radial and distance, DME
distance, groundspeed, and time to station.

The advantages of the VOR/DME RNAV system stem from
the ability of the airborne computer to locate a WP wherever it
is convenient, as long as the aircraft is within reception range
of both nearby VOR and DME facilities. A series of these
WPs make up an RNAV route. In addition to the published
routes, a random RNAV route may be flown under IFR if it is
approved by air traffic control (ATC). RNAV DPs and standard
terminal arrival routes (STARs) are contained in the DP and
STAR booklets.

Figure 7-23. Onboard RNAV receivers have changed significantly.
Originally, RNAV receivers typically computed combined data
from VOR, VORTAC, and/or DME. That is generally not the case
now. Today, GPS such as the GNC 300 and the Bendix King KLS
88 LORAN receivers compute waypoints based upon embedded
databases and aircraft positional information.

Most VOR/DME RNAV systems have the following airborne
controls:
1.

Off/On/Volume control to select the frequency of the
VOR/DME station to be used.

2.

MODE select switch used to select VOR/DME mode,
with:

3.

a.

Angular course width deviation (standard VOR
operation); or

b.

Linear cross-track deviation as standard (±5 NM
full scale CDI).

VOR/DME RNAV approach procedure charts are also
available. Note in the VOR/DME RNAV chart excerpt shown
in Figure 7-24 that the WP identification boxes contain the
following information: WP name, coordinates, frequency,
identifier, radial distance (facility to WP), and reference facility
elevation. The initial approach fix (IAF), final approach fix
(FAF), and missed approach point (MAP) are labeled.
To fly a route or to execute an approach under IFR, the RNAV
equipment installed in the aircraft must be approved for the
appropriate IFR operations.
In vertical navigation (VNAV) mode, vertical guidance is
provided, as well as horizontal guidance in some installations. A
WP is selected at a point where the descent begins, and another
WP is selected where the descent ends. The RNAV equipment
computes the rate of descent relative to the groundspeed; on
some installations, it displays vertical guidance information
on the GS indicator. When using this type of equipment
during an instrument approach, the pilot must keep in mind
that the vertical guidance information provided is not part of
the nonprecision approach. Published nonprecision approach
altitudes must be observed and complied with, unless otherwise
directed by ATC.

RNAV mode, with direct to WP with linear cross-track
deviation of ±5 NM.

7-23

Figure 7-24. VOR/DME RNAV Rwy 25 Approach (Excerpt).

To fly to a WP using RNAV, observe the following procedure
[Figure 7-25]:
1.

Select the VOR/DME frequency.

2.

Select the RNAV mode.

3.

Select the radial of the VOR that passes through the WP
(225°).

4.

Select the distance from the DME to the WP (12
NM).

5.

Check and confirm all inputs, and center the CDI needle
with the TO indicator showing.

6.

Maneuver the aircraft to fly the indicated heading
plus or minus wind correction to keep the CDI needle
centered.

7.

The CDI needle will indicate distance off course of 1
NM per dot; the DME readout will indicate distance in
NM from the WP; the groundspeed will read closing
speed (knots) to the WP; and the time to station (TTS)
will read time to the WP.

VOR/DME RNAV Errors
The limitation of this system is the reception volume.
Published approaches have been tested to ensure this is not
a problem. Descents/approaches to airports distant from the
VOR/DME facility may not be possible because, during
the approach, the aircraft may descend below the reception
altitude of the facility at that distance.

Figure 7-25. Aircraft/DME/Waypoint Relationship.

7-24

Long Range Navigation (LORAN)
LORAN uses a network of land-based transmitters to provide
an accurate long-range navigation system. The FAA and the
United States Coast Guard (USCG) arranged the stations
into chains. The signal from station is a carefully structured
sequence of brief RF pulses centered at 100 kHz. At that
frequency, signals travel considerable distances as ground
waves, from which accurate navigation information is
available. The airborne receiver monitors all of the stations
within the selected chain, then measures the arrival time
difference (TD) between the signals. All of the points having
the same TD from a station pair create a line of position

pilots. When the LORAN receiver is turned on and position
is determined, absolute accuracy applies. Typical LORAN
absolute accuracy will vary from about 0.1 NM to as much
as 2.5 NM depending on distance from the station, geometry
of the TD LOP crossing angles, terrain and environmental
conditions, signal-to-noise ratio (signal strength), and some
design choices made by the receiver manufacturer.
Although LORAN use diminished with the introduction
of Global Navigation Satellite Systems such as the United
States’ GPS, its use has since increased. Three items aided
in this resurgence:
•

In 1996, a commission called the Gore Commission
evaluated GPS’ long-term use as a sole navigation
aid. Although GPS was hailed originally as the
eventual sole NAVAID, which would replace the need
for most currently existing NAVAIDs by the year
2020, the Commission questioned single-link failure
potential and its effect on the NAS. For this reason,
the forecasted decommissioning of the VOR has been
amended and their expectant lifecycle extended into
the future. Additionally, the use of LORAN continues
to be evaluated for facilitating carrying GPS corrective
timing signals.

•

The GPS is controlled by the DOD presenting certain
unforecasted uncertainties for commercial use on an
uninterrupted basis.

Figure 7-26. A control panel from a military aircraft after LORAN

was first put into use. The receiver is remotely mounted and weighs
over 25 pounds. Its size is about six times that of the LORAN fully
integrated receiver.

(LOP). The aircraft position is determined at the intersection
of two or more LOPs. Then the computer converts the
known location to latitude and longitude coordinates.
[Figure 7-26]
While continually computing latitude/longitude fixes, the
computer is able to determine and display:
1.

Track over the ground since last computation;

2.

Groundspeed by dividing distance covered since last
computation by the time since last computation (and
averaging several of these);

3.

Distance to destination;

4.

Destination time of arrival; and

5.

Cross-track error.

The Aeronautical Information Manual (AIM) provides a
detailed explanation of how LORAN works. LORAN is
a very accurate navigation system if adequate signals are
received. There are two types of accuracy that must be
addressed in any discussion of LORAN accuracy.
Repeatable accuracy is the accuracy measured when a user
notes the LORAN position, moves away from that location,
then uses the LORAN to return to that initial LORAN
position. Distance from that initial position is the error.
Propagation and terrain errors will be essentially the same as
when the first position was taken, so those errors are factored
out by using the initial position. Typical repeatable accuracy
for LORAN can be as good as 0.01 NM, or 60 feet, if the
second position is determined during the day and within a
short period of time (a few days).
Absolute accuracy refers to the ability to determine present
position in space independently, and is most often used by

As a result of these and other key factors, it was determined that
LORAN would remain. In recognition of GPS vulnerabilities
as a GNSS, there are plans to maintain other systems that
could provide en route and terminal accuracy such as LORAN.
Therefore as LORAN is further modernized it’s a possibility
that it may be used to augment GPS and provide backup to
GPS during unlikely but potential outages. Or if combined
with GPS and other systems such as newer miniaturized lowcost inertial navigation systems (INS), superior accuracy and
seamless backup will always be available.

LORAN Components
The LORAN receiver incorporates a radio receiver, signal
processor, navigation computer, control/display, and antenna.
When turned on, the receivers go through an initialization
or warm-up period, then inform the user they are ready to
be programmed. LORAN receivers vary widely in their
appearance, method of user programming, and navigation
information display. Therefore, it is necessary to become
familiar with the unit, including programming and output
interpretation. The LORAN operating manual should be in the
aircraft at all times and available to the pilot. IFR-approved
LORAN units require that the manual be aboard and that the
pilot be familiar with the unit’s functions, before flight.
7-25

Function of LORAN
After initialization, select for the present location WP
(the airport), and select GO TO in order to determine if
the LORAN is functioning properly. Proper operation is
indicated by a low distance reading (0 to 0.5 NM). The
simplest mode of navigation is referred to as GO TO: you
select a WP from one of the databases and choose the
GO TO mode. Before use in flight, verify that the latitude
and longitude of the chosen WP is correct by reference to
another approved information source. An updatable LORAN
database that supports the appropriate operations (e.g., en
route, terminal, and instrument approaches) is required when
operating under IFR.

Operational Errors
Some of the typical pilot-induced errors of LORAN operation
are:
1.

Use of a nonapproved LORAN receiver for IFR
operations. The pilot should check the aircraft’s POH/
AFM LORAN supplement to be certain the unit’s
functions are well understood (this supplement must
be present in the aircraft for approved IFR operations).
There should be a copy of FAA Form 337, Major
Repair and Alteration, present in the aircraft’s records,
showing approval of use of this model LORAN for
IFR operations in this aircraft.

2.

Failure to double-check the latitude/longitude values
for a WP to be used. Whether the WP was accessed
from the airport, NDB, VOR, or intersection database,
the values of latitude and longitude should still be
checked against the values in the A/FD or other
approved source. If the WP data is entered in the user
database, its accuracy must be checked before use.

3.

Attempting to use LORAN information with degraded
signals.

In addition to displaying bearing, distance, time to the WP,
and track and speed over the ground, the LORAN receiver
may have other features such as flight planning (WP
sequential storage), emergency location of several nearest
airports, vertical navigation capabilities, and more.

LORAN Errors
System Errors
LORAN is subject to interference from many external
sources, which can cause distortion of or interference with
LORAN signals. LORAN receiver manufacturers install
“notch filters” to reduce or eliminate interference. Proximity
to 60 Hz alternating current power lines, static discharge,
P-static, electrical noise from generators, alternators, strobes,
and other onboard electronics may decrease the signalto-noise ratio to the point where the LORAN receiver’s
performance is degraded.

Advanced Technologies
Global Navigation Satellite System (GNSS)
The Global Navigation Satellite System (GNSS) is a
constellation of satellites providing a high-frequency signal
which contains time and distance that is picked up by a
receiver thereby. [Figure 7-27] The receiver which picks up
multiple signals from different satellites is able to triangulate
its position from these satellites.

Proper installation of the antenna, good electrical bonding,
and an effective static discharge system are the minimum
requirements for LORAN receiver operation. Most receivers
have internal tests that verify the timing alignment of the
receiver clock with the LORAN pulse, and measure and
display signal-to-noise ratio. A signal will be activated to alert
the pilot if any of the parameters for reliable navigation are
exceeded on LORAN sets certified for IFR operations.
LORAN is most accurate when the signal travels over sea
water during the day and least accurate when the signal
comes over land and large bodies of fresh water or ice at
night; furthermore, the accuracy degrades as distance from
the station increases. However, LORAN accuracy is generally
better than VOR accuracy.

7-26

Figure 7-27. A typical example (GNS 480) of a stand-alone GPS

receiver and display.

Three GNSSs exist today: the GPS, a United States system;
the Russian GNSS (GLONASS); and Galileo, a European
system.
1.

GLONASS is a network of 24 satellites, which can be
picked up by any GLONASS receiver, allowing the
user to pinpoint their position.

2.

Galileo is a network of 30 satellites that continuously
transmit high-frequency radio signals containing time
and distance data that can be picked up by a Galileo
receiver with operational expectancy by 2008.

3.

The GPS came on line in 1992 with 24 satellites, and
today utilizes 30 satellites.

Global Positioning System (GPS)
The GPS is a satellite-based radio navigation system, which
broadcasts a signal that is used by receivers to determine
precise position anywhere in the world. The receiver tracks
multiple satellites and determines a measurement that is then
used to determine the user location. [Figure 7-28]

fully meets the civil requirements for use as the primary
means of navigation in oceanic airspace and certain remote
areas. Properly certified GPS equipment may be used as a
supplemental means of IFR navigation for domestic en route,
terminal operations, and certain IAPs. Navigational values,
such as distance and bearing to a WP and groundspeed, are
computed from the aircraft’s current position (latitude and
longitude) and the location of the next WP. Course guidance
is provided as a linear deviation from the desired track of a
Great Circle route between defined WPs.
GPS may not be approved for IFR use in other countries.
Prior to its use, pilots should ensure that GPS is authorized
by the appropriate countries.

GPS Components
GPS consists of three distinct functional elements: space,
control, and user.
The space element consists of over 30 Navstar satellites. This
group of satellites is called a constellation. The satellites
are in six orbital planes (with four in each plane) at about
11,000 miles above the Earth. At least five satellites are
in view at all times. The GPS constellation broadcasts a
pseudo-random code timing signal and data message that the
aircraft equipment processes to obtain satellite position and
status data. By knowing the precise location of each satellite
and precisely matching timing with the atomic clocks on
the satellites, the aircraft receiver/processor can accurately
measure the time each signal takes to arrive at the receiver
and, therefore, determine aircraft position.
The control element consists of a network of ground-based
GPS monitoring and control stations that ensure the accuracy
of satellite positions and their clocks. In its present form, it
has five monitoring stations, three ground antennas, and a
master control station.

Figure 7-28. Typical GPS Satellite Array.

The Department of Defense (DOD) developed and deployed
GPS as a space-based positioning, velocity, and time system.
The DOD is responsible for operation of the GPS satellite
constellation, and constantly monitors the satellites to ensure
proper operation. The GPS system permits Earth-centered
coordinates to be determined and provides aircraft position
referenced to the DOD World Geodetic System of 1984
(WGS-84). Satellite navigation systems are unaffected
by weather and provide global navigation coverage that

The user element consists of antennas and receiver/processors
on board the aircraft that provide positioning, velocity,
and precise timing to the user. GPS equipment used while
operating under IFR must meet the standards set forth in
Technical Standard Order (TSO) C-129 (or equivalent); meet
the airworthiness installation requirements; be “approved” for
that type of IFR operation; and be operated in accordance with
the applicable POH/AFM or flight manual supplement.
An updatable GPS database that supports the appropriate
operations (e.g., en route, terminal, and instrument
approaches) is required when operating under IFR. The
aircraft GPS navigation database contains WPs from the

7-27

geographic areas where GPS navigation has been approved
for IFR operations. The pilot selects the desired WPs from
the database and may add user-defined WPs for the flight.
Equipment approved in accordance with TSO C-115a, visual
flight rules (VFR), and hand-held GPS systems do not meet
the requirements of TSO C-129 and are not authorized for
IFR navigation, instrument approaches, or as a principal
instrument flight reference. During IFR operations, these
units (TSO C-115a) may be considered only an aid to
situational awareness.
Prior to GPS/WAAS IFR operation, the pilot must review
appropriate NOTAMs and aeronautical information. This
information is available on request from an Automated
Flight Service Station. The FAA will provide NOTAMs to
advise pilots of the status of the WAAS and level of service
available.

Function of GPS
GPS operation is based on the concept of ranging and
triangulation from a group of satellites in space which act
as precise reference points. The receiver uses data from a
minimum of four satellites above the mask angle (the lowest
angle above the horizon at which it can use a satellite).
The aircraft GPS receiver measures distance from a satellite
using the travel time of a radio signal. Each satellite transmits
a specific code, called a course/acquisition (CA) code, which
contains information about satellite position, the GPS system
time, and the health and accuracy of the transmitted data.
Knowing the speed at which the signal traveled (approximately
186,000 miles per second) and the exact broadcast time,
the distance traveled by the signal can be computed from
the arrival time. The distance derived from this method of
computing distance is called a pseudo-range because it is not
a direct measurement of distance, but a measurement based
on time. In addition to knowing the distance to a satellite, a
receiver needs to know the satellite’s exact position in space,
its ephemeris. Each satellite transmits information about its
exact orbital location. The GPS receiver uses this information
to establish the precise position of the satellite.
Using the calculated pseudo-range and position information
supplied by the satellite, the GPS receiver/processor
mathematically determines its position by triangulation
from several satellites. The GPS receiver needs at least four
satellites to yield a three-dimensional position (latitude,
longitude, and altitude) and time solution. The GPS receiver
computes navigational values (distance and bearing to
a WP, groundspeed, etc.) by using the aircraft’s known
latitude/longitude and referencing these to a database built
into the receiver.
7-28

The GPS receiver verifies the integrity (usability) of the
signals received from the GPS constellation through receiver
autonomous integrity monitoring (RAIM) to determine if a
satellite is providing corrupted information. RAIM needs
a minimum of five satellites in view, or four satellites and
a barometric altimeter baro-aiding to detect an integrity
anomaly. For receivers capable of doing so, RAIM needs
six satellites in view (or five satellites with baro-aiding)
to isolate a corrupt satellite signal and remove it from the
navigation solution.
Generally, there are two types of RAIM messages. One
type indicates that there are not enough satellites available
to provide RAIM and another type indicates that the RAIM
has detected a potential error that exceeds the limit for the
current phase of flight. Without RAIM capability, the pilot
has no assurance of the accuracy of the GPS position.
Aircraft using GPS navigation equipment under IFR for
domestic en route, terminal operations, and certain IAPs,
must be equipped with an approved and operational alternate
means of navigation appropriate to the flight. The avionics
necessary to receive all of the ground-based facilities
appropriate for the route to the destination airport and any
required alternate airport must be installed and operational.
Ground-based facilities necessary for these routes must also
be operational. Active monitoring of alternative navigation
equipment is not required if the GPS receiver uses RAIM for
integrity monitoring. Active monitoring of an alternate means
of navigation is required when the RAIM capability of the
GPS equipment is lost. In situations where the loss of RAIM
capability is predicted to occur, the flight must rely on other
approved equipment, delay departure, or cancel the flight.

GPS Substitution
IFR En Route and Terminal Operations
GPS systems, certified for IFR en route and terminal
operations, may be used as a substitute for ADF and DME
receivers when conducting the following operations within
the United States NAS.
1.

Determining the aircraft position over a DME fix. This
includes en route operations at and above 24,000 feet
mean sea level (MSL) (FL 240) when using GPS for
navigation.

2.

Flying a DME arc.

3.

Navigating TO/FROM an NDB/compass locator.

4.

Determining the aircraft position over an NDB/compass
locator.

5.

Determining the aircraft position over a fix defined by
an NDB/compass locator bearing crossing a VOR/LOC
course.

6.

Holding over an NDB/compass locator.

facility is the DME facility which is charted as the one
used to establish the DME fix. If this facility is not in
the airborne database, it is not authorized for use.

GPS Substitution for ADF or DME
3.

This equipment must be installed in accordance with
appropriate airworthiness installation requirements
and operated within the provisions of the applicable
POH/AFM, or supplement.

If the fix is identified by a five-letter name which is not
contained in the GPS airborne database, or if the fix is
not named, select the facility establishing the DME fix
or another named DME fix as the active GPS WP.

4.

The required integrity for these operations must be
provided by at least en route RAIM, or equivalent.

When selecting the named fix as the active GPS WP,
a pilot is over the fix when the GPS system indicates
the active WP.

5.

If selecting the DME providing facility as the active
GPS WP, a pilot is over the fix when the GPS distance
from the active WP equals the charted DME value, and
the aircraft is established on the appropriate bearing
or course.

Using GPS as a substitute for ADF or DME is subject to the
following restrictions:
1.

2.
3.

4.

5.

6.

7.

WPs, fixes, intersections, and facility locations to be
used for these operations must be retrieved from the
GPS airborne database. The database must be current.
If the required positions cannot be retrieved from the
airborne database, the substitution of GPS for ADF
and/or DME is not authorized
Procedures must be established for use when RAIM
outages are predicted or occur. This may require the
flight to rely on other approved equipment or require
the aircraft to be equipped with operational NDB and/or
DME receivers. Otherwise, the flight must be rerouted,
delayed, canceled, or conducted under VFR.
The CDI must be set to terminal sensitivity (1 NM)
when tracking GPS course guidance in the terminal
area.
A non-GPS approach procedure must exist at the
alternate airport when one is required. If the non-GPS
approaches on which the pilot must rely require DME
or ADF, the aircraft must be equipped with DME or
ADF avionics as appropriate.
Charted requirements for ADF and/or DME can be met
using the GPS system, except for use as the principal
instrument approach navigation source.

NOTE: The following provides guidance, which is not
specific to any particular aircraft GPS system. For specific
system guidance, refer to the POH/AFM, or supplement, or
contact the system manufacturer.

To Fly a DME Arc:
1.

Verify aircraft GPS system integrity monitoring
is functioning properly and indicates satisfactory
integrity.

2.

Select from the airborne database the facility providing
the DME arc as the active GPS WP. The only
acceptable facility is the DME facility on which the arc
is based. If this facility is not in your airborne database,
you are not authorized to perform this operation.

3.

Maintain position on the arc by reference to the GPS
distance instead of a DME readout.

To Navigate TO or FROM an NDB/Compass
Locator:
1.

Verify aircraft GPS system integrity monitoring
is functioning properly and indicates satisfactory
integrity.

2.

Select the NDB/compass locator facility from the
airborne database as the active WP. If the chart depicts
the compass locator collocated with a fix of the same
name, use of that fix as the active WP in place of the
compass locator facility is authorized.

3.

Select and navigate on the appropriate course to or
from the active WP.

To Determine Aircraft Position Over a DME Fix:
1.

Verify aircraft GPS system integrity monitoring
is functioning properly and indicates satisfactory
integrity.

2.

If the fix is identified by a five-letter name which is
contained in the GPS airborne database, select either
the named fix as the active GPS WP or the facility
establishing the DME fix as the active GPS WP. When
using a facility as the active WP, the only acceptable

To Determine Aircraft Position Over an NDB/
Compass Locator:
1.

Verify aircraft GPS system integrity monitoring
is functioning properly and indicates satisfactory
integrity.

7-29

2.

3.

Select the NDB/compass locator facility from the
airborne database. When using an NDB/compass
locator, the facility must be charted and be in the
airborne database. If the facility is not in the airborne
database, pilots are not authorized to use a facility WP
for this operation.
A pilot is over the NDB/compass locator when the
GPS system indicates arrival at the active WP.

To Determine Aircraft Position Over a Fix Made up
of an NDB/Compass Locator Bearing Crossing a
VOR/LOC Course:
1.

Verify aircraft GPS system integrity monitoring
is functioning properly and indicates satisfactory
integrity.

2.

A fix made up by a crossing NDB/compass locator
bearing is identified by a five-letter fix name. Pilots
may select either the named fix or the NDB/compass
locator facility providing the crossing bearing to
establish the fix as the active GPS WP. When using
an NDB/compass locator, that facility must be charted
and be in the airborne database. If the facility is not
in the airborne database, pilots are not authorized to
use a facility WP for this operation.

3.

When selecting the named fix as the active GPS WP,
pilot is over the fix when the GPS system indicates
the pilot is at the WP.

4.

When selecting the NDB/compass locator facility
as the active GPS WP, pilots are over the fix when
the GPS bearing to the active WP is the same as
the charted NDB/compass locator bearing for the
fix flying the prescribed track from the non-GPS
navigation source.

To Hold Over an NDB/Compass Locator:
1.

Verify aircraft GPS system integrity monitoring
is functioning properly and indicates satisfactory
integrity.

2.

Select the NDB/compass locator facility from the
airborne database as the active WP. When using a
facility as the active WP, the only acceptable facility
is the NDB/compass locator facility which is charted.
If this facility is not in the airborne database, its use
is not authorized.

3.

Select nonsequencing (e.g., “HOLD” or “OBS”) mode
and the appropriate course in accordance with the
POH/AFM, or supplement.

4.

Hold using the GPS system in accordance with the
POH/AFM, or supplement.

7-30

IFR Flight Using GPS
Preflight preparations should ensure that the GPS is properly
installed and certified with a current database for the type
of operation. The GPS operation must be conducted in
accordance with the FAA-approved POH/AFM or flight
manual supplement. Flightcrew members must be thoroughly
familiar with the particular GPS equipment installed in the
aircraft, the receiver operation manual, and the POH/AFM
or flight manual supplement. Unlike ILS and VOR, the
basic operation, receiver presentation to the pilot and some
capabilities of the equipment can vary greatly. Due to these
differences, operation of different brands, or even models
of the same brand of GPS receiver under IFR should not be
attempted without thorough study of the operation of that
particular receiver and installation. Using the equipment in
flight under VFR conditions prior to attempting IFR operation
will allow further familiarization.
Required preflight preparations should include checking
NOTAMs relating to the IFR flight when using GPS as a
supplemental method of navigation. GPS satellite outages
are issued as GPS NOTAMs both domestically and
internationally. Pilots may obtain GPS RAIM availability
information for an airport by specifically requesting GPS
aeronautical information from an automated flight service
station (AFSS) during preflight briefings. GPS RAIM
aeronautical information can be obtained for a 3-hour
period: the estimated time of arrival (ETA), and 1 hour
before to 1 hour after the ETA hour, or a 24-hour time frame
for a specific airport. FAA briefers will provide RAIM
information for a period of 1 hour before to 1 hour after
the ETA, unless a specific timeframe is requested by the
pilot. If flying a published GPS departure, the pilot should
also request a RAIM prediction for the departure airport.
Some GPS receivers have the capability to predict RAIM
availability. The pilot should also ensure that the required
underlying ground-based navigation facilities and related
aircraft equipment appropriate to the route of flight, terminal
operations, instrument approaches for the destination, and
alternate airports/heliports will be operational for the ETA.
If the required ground-based facilities and equipment will
not be available, the flight should be rerouted, rescheduled,
canceled, or conducted under VFR.
Except for programming and retrieving information from
the GPS receiver, planning the flight is accomplished in a
similar manner to conventional NAVAIDs. Departure WP,
DP, route, STAR, desired approach, IAF, and destination
airport are entered into the GPS receiver according to the
manufacturer’s instructions. During preflight, additional
information may be entered for functions such as ETA, fuel
planning, winds aloft, etc.

When the GPS receiver is turned on, it begins an internal
process of test and initialization. When the receiver is
initialized, the user develops the route by selecting a WP
or series of WPs, verifies the data, and selects the active
flight plan. This procedure varies widely among receivers
made by different manufacturers. GPS is a complex system,
offering little standardization between receiver models. It is
the pilot’s responsibility to be familiar with the operation of
the equipment in the aircraft.
The GPS receiver provides navigational values such as track,
bearing, groundspeed, and distance. These are computed from
the aircraft’s present latitude and longitude to the location of
the next WP. Course guidance is provided between WPs. The
pilot has the advantage of knowing the aircraft’s actual track
over the ground. As long as track and bearing to the WP are
matched up (by selecting the correct aircraft heading), the
aircraft is going directly to the WP.

GPS Instrument Approaches
There is a mixture of GPS overlay approaches (approaches
with “or GPS” in the title) and GPS stand-alone approaches
in the United States.

While conducting these IAPs, ground-based NAVAIDs are
not required to be operational and associated aircraft avionics
need not be installed, operational, turned on, or monitored;
however, monitoring backup navigation systems is always
recommended when available.
Pilots should have a basic understanding of GPS approach
procedures and practice GPS IAPs under visual meteorological
conditions (VMC) until thoroughly proficient with all
aspects of their equipment (receiver and installation) prior
to attempting flight in instrument meteorological conditions
(IMC). [Figure 7-29]
All IAPs must be retrievable from the current GPS database
supplied by the manufacturer or other FAA-approved
source. Flying point to point on the approach does not
assure compliance with the published approach procedure.
The proper RAIM sensitivity will not be available and the
CDI sensitivity will not automatically change to 0.3 NM.
Manually setting CDI sensitivity does not automatically
change the RAIM sensitivity on some receivers. Some
existing nonprecision approach procedures cannot be coded
for use with GPS and will not be available as overlays.

NOTE: GPS instrument approach operations outside the
United States must be authorized by the appropriate country
authority.

Figure 7-29. A GPS Stand-Alone Approach.

7-31

GPS approaches are requested and approved by ATC using
the GPS title, such as “GPS RWY 24” or “RNAV RWY
35.” Using the manufacturer’s recommended procedures, the
desired approach and the appropriate IAF are selected from
the GPS receiver database. Pilots should fly the full approach
from an initial approach waypoint (IAWP) or feeder fix unless
specifically cleared otherwise. Randomly joining an approach
at an intermediate fix does not ensure terrain clearance.
When an approach has been loaded in the flight plan, GPS
receivers will give an “arm” annunciation 30 NM straight
line distance from the airport/heliport reference point. The
approach mode should be “armed” when within 30 NM
distance so the receiver will change from en route CDI
(±5 NM) and RAIM (±2 NM) sensitivity to ±1 NM terminal
sensitivity. Where the IAWP is within 30 NM, a CDI
sensitivity change will occur once the approach mode is
armed and the aircraft is within 30 NM. Where the IAWP
is beyond the 30 NM point, CDI sensitivity will not change
until the aircraft is within 30 NM even if the approach is
armed earlier. Feeder route obstacle clearance is predicated
on the receiver CDI and RAIM being in terminal CDI
sensitivity within 30 NM of the airport/heliport reference
point; therefore, the receiver should always be armed no later
than the 30 NM annunciation.
Pilots should pay particular attention to the exact operation
of their GPS receivers for performing holding patterns and in
the case of overlay approaches, operations such as procedure
turns. These procedures may require manual intervention
by the pilot to stop the sequencing of WPs by the receiver
and to resume automatic GPS navigation sequencing once
the maneuver is complete. The same WP may appear in the
route of flight more than once and consecutively (e.g., IAWP,
final approach waypoint (FAWP), missed approach waypoint
(MAWP) on a procedure turn). Care must be exercised to
ensure the receiver is sequenced to the appropriate WP for
the segment of the procedure being flown, especially if one
or more fly-over WPs are skipped (e.g., FAWP rather than
IAWP if the procedure turn is not flown). The pilot may need
to sequence past one or more fly-overs of the same WP in
order to start GPS automatic sequencing at the proper place
in the sequence of WPs.
When receiving vectors to final, most receiver operating
manuals suggest placing the receiver in the nonsequencing
mode on the FAWP and manually setting the course. This
provides an extended final approach course in cases where
the aircraft is vectored onto the final approach course outside
of any existing segment which is aligned with the runway.
Assigned altitudes must be maintained until established on a
published segment of the approach. Required altitudes at WPs
outside the FAWP or step-down fixes must be considered.

7-32

Calculating the distance to the FAWP may be required in
order to descend at the proper location.
When within 2 NM of the FAWP with the approach mode
armed, the approach mode will switch to active, which results
in RAIM and CDI sensitivity changing to the approach
mode. Beginning 2 NM prior to the FAWP, the full scale
CDI sensitivity will change smoothly from ±1 NM to ±0.3
NM at the FAWP. As sensitivity changes from ±1 NM to
±0.3 NM approaching the FAWP, and the CDI not centered,
the corresponding increase in CDI displacement may give
the impression the aircraft is moving further away from the
intended course even though it is on an acceptable intercept
heading. If digital track displacement information (cross-track
error) is available in the approach mode, it may help the pilot
remain position oriented in this situation. Being established
on the final approach course prior to the beginning of the
sensitivity change at 2 NM will help prevent problems in
interpreting the CDI display during ramp-down. Requesting
or accepting vectors, which will cause the aircraft to intercept
the final approach course within 2 NM of the FAWP, is not
recommended.
Incorrect inputs into the GPS receiver are especially critical
during approaches. In some cases, an incorrect entry can
cause the receiver to leave the approach mode. Overriding
an automatically selected sensitivity during an approach
will cancel the approach mode annunciation. If the approach
mode is not armed by 2 NM prior to the FAWP, the approach
mode will not become active at 2 NM prior to the FAWP and
the equipment will flag. In these conditions, the RAIM and
CDI sensitivity will not ramp down, and the pilot should not
descend to minimum descent altitude (MDA), but fly to the
MAWP and execute a missed approach. The approach active
annunciator and/or the receiver should be checked to ensure
the approach mode is active prior to the FAWP.
A GPS missed approach requires pilot action to sequence the
receiver past the MAWP to the missed approach portion of
the procedure. The pilot must be thoroughly familiar with
the activation procedure for the particular GPS receiver
installed in the aircraft and must initiate appropriate action
after the MAWP. Activating the missed approach prior to the
MAWP will cause CDI sensitivity to change immediately to
terminal (±1 NM) sensitivity, and the receiver will continue
to navigate to the MAWP. The receiver will not sequence past
the MAWP. Turns should not begin prior to the MAWP. If
the missed approach is not activated, the GPS receiver will
display an extension of the inbound final approach course and
the along track distance (ATD) will increase from the MAWP
until it is manually sequenced after crossing the MAWP.

Missed approach routings in which the first track is via a
course rather than direct to the next WP require additional
action by the pilot to set the course. Being familiar with all
of the required inputs is especially critical during this phase
of flight.

of less than 100 feet. Satellite atomic clock inaccuracies,
receiver/processors, signals reflected from hard objects
(multi-path), ionospheric and tropospheric delays, and
satellite data transmission errors may cause small position
errors or momentary loss of the GPS signal.

Departures and Instrument Departure Procedures
(DPs)

System Status

The GPS receiver must be set to terminal (±1 NM) CDI
sensitivity and the navigation routes contained in the database
in order to fly published IFR charted departures and DPs.
Terminal RAIM should be provided automatically by the
receiver. (Terminal RAIM for departure may not be available
unless the WPs are part of the active flight plan rather than
proceeding direct to the first destination.) Certain segments
of a DP may require some manual intervention by the pilot,
especially when radar vectored to a course or required to
intercept a specific course to a WP. The database may not
contain all of the transitions or departures from all runways
and some GPS receivers do not contain DPs in the database.
It is necessary that helicopter procedures be flown at 70 knots
or less since helicopter departure procedures and missed
approaches use a 20:1 obstacle clearance surface (OCS),
which is double the fixed-wing OCS. Turning areas are based
on this speed also. Missed approach routings in which the
first track is via a course rather than direct to the next WP
require additional action by the pilot to set the course. Being
familiar with all of the required inputs is especially critical
during this phase of flight.

GPS Errors
Normally, with 30 satellites in operation, the GPS
constellation is expected to be available continuously
worldwide. Whenever there are fewer than 24 operational
satellites, GPS navigational capability may not be available
at certain geographic locations. Loss of signals may also
occur in valleys surrounded by high terrain, and any time
the aircraft’s GPS antenna is “shadowed” by the aircraft’s
structure (e.g., when the aircraft is banked).
Certain receivers, transceivers, mobile radios, and portable
receivers can cause signal interference. Some VHF
transmissions may cause “harmonic interference.” Pilots
can isolate the interference by relocating nearby portable
receivers, changing frequencies, or turning off suspected
causes of the interference while monitoring the receiver’s
signal quality data page.

The status of GPS satellites is broadcast as part of the data
message transmitted by the GPS satellites. GPS status
information is also available by means of the United States
Coast Guard navigation information service: (703) 3135907, or on the internet at http://www.navcen.uscg.gov/.
Additionally, satellite status is available through the Notice
to Airmen (NOTAM) system.
The GPS receiver verifies the integrity (usability) of the
signals received from the GPS constellation through receiver
autonomous integrity monitoring (RAIM) to determine if
a satellite is providing corrupted information. At least one
satellite, in addition to those required for navigation, must
be in view for the receiver to perform the RAIM function;
thus, RAIM needs a minimum of five satellites in view, or
four satellites and a barometric altimeter (baro-aiding) to
detect an integrity anomaly. For receivers capable of doing
so, RAIM needs six satellites in view (or five satellites with
baro-aiding) to isolate the corrupt satellite signal and remove
it from the navigation solution.
RAIM messages vary somewhat between receivers; however,
there are two most commonly used types. One type indicates
that there are not enough satellites available to provide
RAIM integrity monitoring and another type indicates that
the RAIM integrity monitor has detected a potential error
that exceeds the limit for the current phase of flight. Without
RAIM capability, the pilot has no assurance of the accuracy
of the GPS position.
Selective Availability. Selective Availability (SA) is a method
by which the accuracy of GPS is intentionally degraded.
This feature is designed to deny hostile use of precise GPS
positioning data. SA was discontinued on May 1, 2000,
but many GPS receivers are designed to assume that SA
is still active. New receivers may take advantage of the
discontinuance of SA based on the performance values in
ICAO Annex 10, and do not need to be designed to operate
outside of that performance.

GPS position data can be affected by equipment characteristics
and various geometric factors, which typically cause errors

7-33

GPS Familiarization
Pilots should practice GPS approaches under visual
meteorological conditions (VMC) until thoroughly proficient
with all aspects of their equipment (receiver and installation)
prior to attempting flight by IFR in instrument meteorological
conditions (IMC). Some of the tasks which the pilot should
practice are:
1.

Utilizing the receiver autonomous integrity monitoring
(RAIM) prediction function;

2.

Inserting a DP into the flight plan, including setting
terminal CDI sensitivity, if required, and the conditions
under which terminal RAIM is available for departure
(some receivers are not DP or STAR capable);

3.

Programming the destination airport;

4.

Programming and flying the overlay approaches
(especially procedure turns and arcs);

5.

Changing to another approach after selecting an
approach;

6.

Programming and flying “direct” missed
approaches;

7.

Programming and flying “routed” missed
approaches;

8.

Entering, flying, and exiting holding patterns,
particularly on overlay approaches with a second WP
in the holding pattern;

9.

Programming and flying a “route” from a holding
pattern;

10. Programming and flying an approach with radar
vectors to the intermediate segment;
11. Indication of the actions required for RAIM failure
both before and after the FAWP; and
12. Programming a radial and distance from a VOR (often
used in departure instructions).
Differential Global Positioning Systems (DGPS)
Differential global positioning systems (DGPS) are designed
to improve the accuracy of global navigation satellite systems
(GNSS) by measuring changes in variables to provide satellite
positioning corrections.
Because multiple receivers receiving the same set of satellites
produce similar errors, a reference receiver placed at a known
location can compute its theoretical position accurately and
can compare that value to the measurements provided by the
navigation satellite signals. The difference in measurement
between the two signals is an error that can be corrected by
providing a reference signal correction.
As a result of this differential input accuracy of the
7-34

satellite system can be increased to meters. The Wide Area
Augmentation System (WAAS) and Local Area Augmentation
System (LAAS) are examples of differential global positioning
systems.
Wide Area Augmentation System (WAAS)
The WAAS is designed to improve the accuracy, integrity,
and availability of GPS signals. WAAS allows GPS to be
used, as the aviation navigation system, from takeoff through
Category I precision approaches. The International Civil
Aviation Organization (ICAO) has defined Standards for
satellite-based augmentation systems (SBAS), and Japan
and Europe are building similar systems that are planned
to be interoperable with WAAS: EGNOS, the European
Geostationary Navigation Overlay System, and MSAS,
the Japanese Multifunctional Transport Satellite (MTSAT)
Satellite-based Augmentation System. The result will be a
worldwide seamless navigation capability similar to GPS but
with greater accuracy, availability, and integrity.
Unlike traditional ground-based navigation aids, WAAS
will cover a more extensive service area in which surveyed
wide-area ground reference stations are linked to the WAAS
network. Signals from the GPS satellites are monitored by
these stations to determine satellite clock and ephemeris
corrections. Each station in the network relays the data to a
wide-area master station where the correction information is
computed. A correction message is prepared and uplinked to
a geostationary satellite (GEO) via a ground uplink and then
broadcast on the same frequency as GPS to WAAS receivers
within the broadcast coverage area. [Figure 7-30]
In addition to providing the correction signal, WAAS
provides an additional measurement to the aircraft receiver,
improving the availability of GPS by providing, in effect,
an additional GPS satellite in view. The integrity of GPS is
improved through real-time monitoring, and the accuracy
is improved by providing differential corrections to reduce
errors. [Figure 7-31] As a result, performance improvement
is sufficient to enable approach procedures with GPS/WAAS
glide paths. At this time the FAA has completed installation of
25 wide area ground reference systems, two master stations,
and four ground uplink stations.

General Requirements
WAAS avionics must be certified in accordance with
TSO-C145A, Airborne Navigation Sensors Using the GPS
Augmented by the WAAS; or TSO-146A for stand-alone
systems. GPS/WAAS operation must be conducted in
accordance with the FAA-approved aircraft flight manual
(AFM) and flight manual supplements. Flight manual
supplements must state the level of approach procedure that
the receiver supports.

Figure 7-30. WAAS Satellite Representation.

7-35

Figure 7-31. WAAS Satellite Representation.

Instrument Approach Capabilities
WAAS receivers support all basic GPS approach functions
and will provide additional capabilities with the key benefit
to generate an electronic glide path, independent of ground
equipment or barometric aiding. This eliminates several
problems such as cold temperature effects, incorrect altimeter
setting or lack of a local altimeter source, and allows approach
procedures to be built without the cost of installing ground
stations at each airport. A new class of approach procedures
which provide vertical guidance requirements for precision
approaches has been developed to support satellite navigation
use for aviation applications. These new procedures called
Approach with Vertical Guidance (APV) include approaches
such as the LNAV/VNAV procedures presently being flown
with barometric vertical navigation.
Local Area Augmentation System (LAAS)
LAAS is a ground-based augmentation system which uses
a GPS reference facility located on or in the vicinity of
the airport being serviced. This facility has a reference
receiver that measures GPS satellite pseudo-range and
timing and retransmits the signal. Aircraft landing at
LAAS-equipped airports are able to conduct approaches to
Category I level and above for properly equipped aircraft.
[Figures 7-32 and 7-33]
Inertial Navigation System (INS)
Inertial Navigation System (INS) is a system that navigates
precisely without any input from outside of the aircraft. It is
fully self-contained. The INS is initialized by the pilot, who
enters into the system the exact location of the aircraft on the
ground before the flight. The INS is also programmed with
WPs along the desired route of flight.

7-36

Figure 7-32. LAAS Representation.

it is working but may be subject to short and periodic outages.
INS is made more accurate because it is continually updated
and continues to function with good accuracy if the GPS has
moments of lost signal.

Instrument Approach Systems
Most navigation systems approved for en route and terminal
operations under IFR, such as VOR, NDB, and GPS, may
also be approved to conduct IAPs. The most common
systems in use in the United States are the ILS, simplified
directional facility (SDF), localizer directional aid (LDA),
and microwave landing system (MLS). These systems
operate independently of other navigation systems. There are
new systems being developed, such as WAAS and LAAS.
Other systems have been developed for special use.
Figure 7-33. LAAS Representation.

INS Components
INS is considered a stand-alone navigation system, especially
when more than one independent unit is onboard. The
airborne equipment consists of an accelerometer to measure
acceleration—which, when integrated with time, gives
velocity—and gyros to measure direction.
Later versions of the INS, called inertial reference systems
(IRS) utilize laser gyros and more powerful computers;
therefore, the accelerometer mountings no longer need to
be kept level and aligned with true north. The computer
system can handle the added workload of dealing with the
computations necessary to correct for gravitational and
directional errors. Consequently, these newer systems are
sometimes called strap down systems, as the accelerometers
and gyros are strapped down to the airframe, rather than being
mounted on a structure that stays fixed with respect to the
horizon and true north.

INS Errors
The principal error associated with INS is degradation of
position with time. INS computes position by starting with
accurate position input which is changed continuously as
accelerometers and gyros provide speed and direction inputs.
Both accelerometers and gyros are subject to very small
errors; as time passes, those errors probably accumulate.
While the best INS/IRS display errors of 0.1 to 0.4 NM after
flights across the North Atlantic of 4 to 6 hours, smaller and
less expensive systems are being built that show errors of 1
to 2 NM per hour. This accuracy is more than sufficient for
a navigation system that can be combined with and updated
by GPS. The synergy of a navigation system consisting of an
INS/IRS unit in combination with a GPS resolves the errors
and weaknesses of both systems. GPS is accurate all the time

Instrument Landing Systems (ILS)
The ILS system provides both course and altitude guidance
to a specific runway. The ILS system is used to execute
a precision instrument approach procedure or precision
approach. [Figure 7-34] The system consists of the following
components:
1.

A localizer providing horizontal (left/right) guidance
along the extended centerline of the runway.

2.

A glide slope (GS) providing vertical (up/down)
guidance toward the runway touchdown point, usually
at a 3° slope.

3.

Marker beacons providing range information along
the approach path.

4.

Approach lights assisting in the transition from
instrument to visual flight.

The following supplementary elements, though not specific
components of the system, may be incorporated to increase
safety and utility:
1.

Compass locators providing transition from en route
NAVAIDs to the ILS system and assisting in holding
procedures, tracking the localizer course, identifying
the marker beacon sites, and providing a FAF for ADF
approaches.

2.

DME collocated with the GS transmitter providing
positive distance-to-touchdown information or DME
associated with another nearby facility (VOR or standalone), if specified in the approach procedure.

ILS approaches are categorized into three different types of
approaches based on the equipment at the airport and the
experience level of the pilot. Category I approaches provide
for approach height above touchdown of not less than 200 feet.
Category II approaches provide for approach to a height above

7-37

Figure 7-34. Instrument Landing Systems.

7-38

touchdown of not less than 100 feet. Category III approaches
provide lower minimums for approaches without a decision
height minimum. While pilots need only be instrument rated
and the aircraft be equipped with the appropriate airborne
equipment to execute Category I approaches, Category II
and III approaches require special certification for the pilots,
ground equipment, and airborne equipment.

ILS Components
Ground Components
The ILS uses a number of different ground facilities. These
facilities may be used as a part of the ILS system, as well as
part of another approach. For example, the compass locator
may be used with NDB approaches.
Localizer
The localizer (LOC) ground antenna array is located on the
extended centerline of the instrument runway of an airport,
located at the departure end of the runway to prevent it from
being a collision hazard. This unit radiates a field pattern,
which develops a course down the centerline of the runway
toward the middle markers (MMs) and outer markers
(OMs), and a similar course along the runway centerline in
the opposite direction. These are called the front and back
courses, respectively. The localizer provides course guidance,
transmitted at 108.1 to 111.95 MHz (odd tenths only),
throughout the descent path to the runway threshold from a
distance of 18 NM from the antenna to an altitude of 4,500
feet above the elevation of the antenna site. [Figure 7-35]

The localizer course width is defined as the angular
displacement at any point along the course between a full
“fly-left” (CDI needle fully deflected to the left) and a full
“fly-right” indication (CDI needle fully deflected to the right).
Each localizer facility is audibly identified by a three-letter
designator, transmitted at frequent regular intervals. The ILS
identification is preceded by the letter “I” (two dots). For
example, the ILS localizer at Springfield, Missouri transmits
the identifier ISGF. The localizer includes a voice feature on
its frequency for use by the associated ATC facility in issuing
approach and landing instructions.
The localizer course is very narrow, normally 5°. This
results in high needle sensitivity. With this course width,
a full-scale deflection shows when the aircraft is 2.5° to
either side of the centerline. This sensitivity permits accurate
orientation to the landing runway. With no more than onequarter scale deflection maintained, the aircraft will be
aligned with the runway.
Glide Slope (GS)
GS describes the systems that generate, receive, and indicate
the ground facility radiation pattern. The glide path is the
straight, sloped line the aircraft should fly in its descent from
where the GS intersects the altitude used for approaching the
FAF, to the runway touchdown zone. The GS equipment
is housed in a building approximately 750 to 1,250 feet
down the runway from the approach end of the runway, and
between 400 and 600 feet to one side of the centerline.

Figure 7-35. Localizer Coverage Limits.

7-39

The course projected by the GS equipment is essentially the
same as would be generated by a localizer operating on its
side. The GS projection angle is normally adjusted to 2.5°
to 3.5° above horizontal, so it intersects the MM at about
200 feet and the OM at about 1,400 feet above the runway
elevation. At locations where standard minimum obstruction
clearance cannot be obtained with the normal maximum GS
angle, the GS equipment is displaced farther from the approach
end of the runway if the length of the runway permits; or, the
GS angle may be increased up to 4°.

Compass Locator
Compass locators are low-powered NDBs and are received
and indicated by the ADF receiver. When used in conjunction
with an ILS front course, the compass locator facilities are
collocated with the outer and/or MM facilities. The coding
identification of the outer locator consists of the first two
letters of the three-letter identifier of the associated LOC.
For example, the outer locator at Dallas/Love Field (DAL) is
identified as “DA.” The middle locator at DAL is identified
by the last two letters “AL.”

Unlike the localizer, the GS transmitter radiates signals only
in the direction of the final approach on the front course. The
system provides no vertical guidance for approaches on the
back course. The glide path is normally 1.4° thick. At 10
NM from the point of touchdown, this represents a vertical
distance of approximately 1,500 feet, narrowing to a few feet
at touchdown.

Approach Lighting Systems (ALS)
Normal approach and letdown on the ILS is divided into two
distinct stages: the instrument approach stage using only radio
guidance, and the visual stage, when visual contact with the
ground runway environment is necessary for accuracy and
safety. The most critical period of an instrument approach,
particularly during low ceiling/visibility conditions, is the
point at which the pilot must decide whether to land or
execute a missed approach. As the runway threshold is
approached, the visual glide path will separate into individual
lights. At this point, the approach should be continued by
reference to the runway touchdown zone markers. The ALS
provides lights that will penetrate the atmosphere far enough
from touchdown to give directional, distance, and glide path
information for safe visual transition.

Marker Beacons
Two VHF marker beacons, outer and middle, are normally
used in the ILS system. [Figure 7-36] A third beacon, the
inner, is used where Category II operations are certified. A
marker beacon may also be installed to indicate the FAF on
the ILS back course.

Figure 7-36. Localizer receiver indications and aircraft

Visual identification of the ALS by the pilot must be
instantaneous, so it is important to know the type of ALS
before the approach is started. Check the instrument approach
chart and the A/FD for the particular type of lighting facilities
at the destination airport before any instrument flight. With
reduced visibility, rapid orientation to a strange runway can
be difficult, especially during a circling approach to an airport
with minimum lighting facilities, or to a large terminal airport
located in the midst of distracting city and ground facility
lights. Some of the most common ALS systems are shown
in Figure 7-37.

displacement.

The OM is located on the localizer front course 4–7 miles
from the airport to indicate a position at which an aircraft, at
the appropriate altitude on the localizer course, will intercept
the glide path. The MM is located approximately 3,500 feet
from the landing threshold on the centerline of the localizer
front course at a position where the GS centerline is about 200
feet above the touchdown zone elevation. The inner marker
(IM), where installed, is located on the front course between
the MM and the landing threshold. It indicates the point at
which an aircraft is at the decision height on the glide path
during a Category II ILS approach. The back-course marker,
where installed, indicates the back-course FAF.

7-40

A high-intensity flasher system, often referred to as “the
rabbit,” is installed at many large airports. The flashers consist
of a series of brilliant blue-white bursts of light flashing in
sequence along the approach lights, giving the effect of a ball
of light traveling towards the runway. Typically, “the rabbit”
makes two trips toward the runway per second.
Runway end identifier lights (REIL) are installed for rapid and
positive identification of the approach end of an instrument
runway. The system consists of a pair of synchronized
flashing lights placed laterally on each side of the runway
threshold facing the approach area.

Figure 7-37. Precision and Nonprecision ALS Configuration.

The visual approach slope indicator (VASI) gives visual
descent guidance information during the approach to a
runway. The standard VASI consists of light bars that
project a visual glide path, which provides safe obstruction
clearance within the approach zone. The normal GS angle
is 3°; however, the angle may be as high as 4.5° for proper
obstacle clearance. On runways served by ILS, the VASI
angle normally coincides with the electronic GS angle.
Visual left/right course guidance is obtained by alignment
with the runway lights. The standard VASI installation
consists of either 2-, 3-, 4-, 6-, 12-, or 16-light units arranged
in downwind and upwind light bars. Some airports serving
long-bodied aircraft have three-bar VASIs which provide two
visual glidepaths to the same runway. The first glide path
encountered is the same as provided by the standard VASI.

The second glide path is about 25 percent higher than the first
and is designed for the use of pilots of long-bodied aircraft.
The basic principle of VASI is that of color differentiation
between red and white. Each light projects a beam having
a white segment in the upper part and a red segment in the
lower part of the beam. From a position above the glide path
the pilot sees both bars as white. Lowering the aircraft with
respect to the glide path, the color of the upwind bars changes
from white to pink to red. When on the proper glide path,
the landing aircraft will overshoot the downwind bars and
undershoot the upwind bars. Thus the downwind (closer)
bars are seen as white and the upwind bars as red. From a
position below the glide path, both light bars are seen as
red. Moving up to the glide path, the color of the downwind
7-41

The localizer and GS warning flags disappear from view on
the indicator when sufficient voltage is received to actuate the
needles. The flags show when an unstable signal or receiver
malfunction occurs.

Figure 7-38. Standard two-bar VASI.

bars changes from red to pink to white. When below the
glide path, as indicated by a distinct all-red signal, a safe
obstruction clearance might not exist. A standard two-bar
VASI is illustrated in Figure 7-38.

ILS Airborne Components
Airborne equipment for the ILS system includes receivers
for the localizer, GS, marker beacons, ADF, DME, and the
respective indicator instruments.
The typical VOR receiver is also a localizer receiver with
common tuning and indicating equipment. Some receivers
have separate function selector switches, but most switch
between VOR and LOC automatically by sensing if odd
tenths between 108 and 111.95 MHz have been selected.
Otherwise, tuning of VOR and localizer frequencies is
accomplished with the same knobs and switches, and the CDI
indicates “on course” as it does on a VOR radial.
Though some GS receivers are tuned separately, in a typical
installation the GS is tuned automatically to the proper
frequency when the localizer is tuned. Each of the 40 localizer
channels in the 108.10 to 111.95 MHz band is paired with a
corresponding GS frequency.
When the localizer indicator also includes a GS needle, the
instrument is often called a cross-pointer indicator. The
crossed horizontal (GS) and vertical (localizer) needles are
free to move through standard five-dot deflections to indicate
position on the localizer course and glide path.
When the aircraft is on the glide path, the needle is horizontal,
overlying the reference dots. Since the glide path is much
narrower than the localizer course (approximately 1.4° from
full up to full down deflection), the needle is very sensitive
to displacement of the aircraft from on-path alignment. With
the proper rate of descent established upon GS interception,
very small corrections keep the aircraft aligned.

7-42

The OM is identified by a low-pitched tone, continuous dashes
at the rate of two per second, and a purple/blue marker beacon
light. The MM is identified by an intermediate tone, alternate
dots and dashes at the rate of 95 dot/dash combinations per
minute, and an amber marker beacon light. The IM, where
installed, is identified by a high-pitched tone, continuous dots
at the rate of six per second, and a white marker beacon light.
The back-course marker (BCM), where installed, is identified
by a high-pitched tone with two dots at a rate of 72 to 75 twodot combinations per minute, and a white marker beacon light.
Marker beacon receiver sensitivity is selectable as high or low
on many units. The low-sensitivity position gives the sharpest
indication of position and should be used during an approach.
The high-sensitivity position provides an earlier warning that
the aircraft is approaching the marker beacon site.
ILS Function
The localizer needle indicates, by deflection, whether the
aircraft is right or left of the localizer centerline, regardless of
the position or heading of the aircraft. Rotating the OBS has
no effect on the operation of the localizer needle, although
it is useful to rotate the OBS to put the LOC inbound course
under the course index. When inbound on the front course, or
outbound on the back course, the course indication remains
directional. (See Figure 7-39, aircraft C, D, and E.)
Unless the aircraft has reverse sensing capability and it is in
use, when flying inbound on the back course or outbound
on the front course, heading corrections to on-course are
made opposite the needle deflection. This is commonly
described as “flying away from the needle.” (See Figure 7-39,
aircraft A and B.) Back course signals should not be used
for an approach unless a back course approach procedure
is published for that particular runway and the approach is
authorized by ATC.
Once you have reached the localizer centerline, maintain
the inbound heading until the CDI moves off center. Drift
corrections should be small and reduced proportionately as
the course narrows. By the time you reach the OM, your drift
correction should be established accurately enough on a wellexecuted approach to permit completion of the approach,
with heading corrections no greater then 2°.
The heaviest demand on pilot technique occurs during
descent from the OM to the MM, when you maintain
the localizer course, adjust pitch attitude to maintain the

Figure 7-39. Localizer Course Indications. To follow indications displayed in the aircraft, start from A and proceed through E.

7-43

proper rate of descent, and adjust power to maintain proper
airspeed. Simultaneously, the altimeter must be checked
and preparation made for visual transition to land or for a
missed approach. You can appreciate the need for accurate
instrument interpretation and aircraft control within the ILS
as a whole, when you notice the relationship between CDI
and glide path needle indications, and aircraft displacement
from the localizer and glide path centerlines.
Deflection of the GS needle indicates the position of the
aircraft with respect to the glide path. When the aircraft is
above the glide path, the needle is deflected downward. When
the aircraft is below the glide path, the needle is deflected
upward. [Figure 7-40]
ILS Errors
The ILS and its components are subject to certain errors,
which are listed below. Localizer and GS signals are subject to
the same type of bounce from hard objects as space waves.
1.

Reflection. Surface vehicles and even other aircraft
flying below 5,000 feet above ground level (AGL)
may disturb the signal for aircraft on the approach.

2.

False courses. In addition to the desired course, GS
facilities inherently produce additional courses at

higher vertical angles. The angle of the lowest of these
false courses will occur at approximately 9°–12°. An
aircraft flying the LOC/GS course at a constant altitude
would observe gyrations of both the GS needle and GS
warning flag as the aircraft passed through the various
false courses. Getting established on one of these
false courses will result in either confusion (reversed
GS needle indications) or in the need for a very high
descent rate. However, if the approach is conducted
at the altitudes specified on the appropriate approach
chart, these false courses will not be encountered.

Marker Beacons
The very low power and directional antenna of the marker
beacon transmitter ensures that the signal will not be received
any distance from the transmitter site. Problems with signal
reception are usually caused by the airborne receiver not
being turned on, or by incorrect receiver sensitivity.
Some marker beacon receivers, to decrease weight and cost,
are designed without their own power supply. These units
utilize a power source from another radio in the avionics
stack, often the ADF. In some aircraft, this requires the
ADF to be turned on in order for the marker beacon receiver
to function, yet no warning placard is required. Another

Figure 7-40. Illustrates a GS receiver indication and aircraft displacement. An analog system is on the left and the same indication on
the Garmin PFD on the right.

7-44

source of trouble may be the “High/Low/Off” three-position
switch, which both activates the receiver and selects receiver
sensitivity. Usually, the “test” feature only tests to see if
the light bulbs in the marker beacon lights are working.
Therefore, in some installations, there is no functional way
for the pilot to ascertain the marker beacon receiver is actually
on except to fly over a marker beacon transmitter, and see if
a signal is received and indicated (e.g., audibly, and visually
via marker beacon lights).

Operational Errors
1.

Failure to understand the fundamentals of ILS ground
equipment, particularly the differences in course
dimensions. Since the VOR receiver is used on the
localizer course, the assumption is sometimes made
that interception and tracking techniques are identical
when tracking localizer courses and VOR radials.
Remember that the CDI sensing is sharper and faster
on the localizer course.

2.

Disorientation during transition to the ILS due to poor
planning and reliance on one receiver instead of on all
available airborne equipment. Use all the assistance
available; a single receiver may fail.

3.

Disorientation on the localizer course, due to the first
error noted above.

4.

Incorrect localizer interception angles. A large
interception angle usually results in overshooting,
and possible disorientation. When intercepting,
if possible, turn to the localizer course heading
immediately upon the first indication of needle
movement. An ADF receiver is an excellent aid to
orient you during an ILS approach if there is a locator
or NDB on the inbound course.

centerline up to an angle 7° above the horizontal. The angle
of convergence of the final approach course and the extended
runway centerline must not exceed 30°. Pilots should note
this angle since the approach course originates at the antenna
site, and an approach continued beyond the runway threshold
would lead the aircraft to the SDF offset position rather than
along the runway centerline.
The course width of the SDF signal emitted from the
transmitter is fixed at either 6° or 12°, as necessary, to provide
maximum flyability and optimum approach course quality.
A three-letter identifier is transmitted in code on the SDF
frequency; there is no letter “I” (two dots) transmitted before
the station identifier, as there is with the LOC. For example,
the identifier for Lebanon, Missouri, SDF is LBO.
Localizer Type Directional Aid (LDA)
The LDA is of comparable utility and accuracy to a localizer
but is not part of a complete ILS. The LDA course width is
between 3° and 6° and thus provides a more precise approach
course than an SDF installation. Some LDAs are equipped
with a GS. The LDA course is not aligned with the runway,
but straight-in minimums may be published where the angle
between the runway centerline and the LDA course does not
exceed 30°. If this angle exceeds 30°, only circling minimums
are published. The identifier is three letters preceded by “I”
transmitted in code on the LDA frequency. For example, the
identifier for Van Nuys, California, LDA is I-BUR.

Chasing the CDI and glide path needles, especially
when you have not sufficiently studied the approach
before the flight.

Microwave Landing System (MLS)
The MLS provides precision navigation guidance for exact
alignment and descent of aircraft on approach to a runway.
It provides azimuth, elevation, and distance. Both lateral
and vertical guidance may be displayed on conventional
course deviation indicators or incorporated into multipurpose
flight deck displays. Range information can be displayed
by conventional DME indicators and also incorporated into
multipurpose displays. [Figure 7-41]

Simplified Directional Facility (SDF)
The SDF provides a final approach course similar to the ILS
localizer. The SDF course may or may not be aligned with
the runway and the course may be wider than a standard
ILS localizer, resulting in less precision. Usable off-course
indications are limited to 35° either side of the course
centerline. Instrument indications in the area between 35°
and 90° from the course centerline are not controlled and
should be disregarded.

The system may be divided into five functions, which are
approach azimuth, back azimuth, approach elevation, range;
and data communications. The standard configuration of
MLS ground equipment includes an azimuth station to
perform functions as indicated above. In addition to providing
azimuth navigation guidance, the station transmits basic data,
which consists of information associated directly with the
operation of the landing system, as well as advisory data on
the performance of the ground equipment.

The SDF must provide signals sufficient to allow satisfactory
operation of a typical aircraft installation within a sector
which extends from the center of the SDF antenna system
to distances of 18 NM covering a sector 10° either side of

Approach Azimuth Guidance

5.

The azimuth station transmits MLS angle and data on one
of 200 channels within the frequency range of 5031 to 5091

7-45

increased operational efficiency in terms of direct routings
and track-keeping accuracy, have resulted in the concept
of required navigation performance—a statement of the
navigation performance accuracy necessary for operation
within a defined airspace. RNP can include both performance
and functional requirements, and is indicated by the RNP type.
These standards are intended for designers, manufacturers,
and installers of avionics equipment, as well as service
providers and users of these systems for global operations.
The minimum aviation system performance specification
(MASPS) provides guidance for the development of airspace
and operational procedures needed to obtain the benefits of
improved navigation capability. [Figure 7-42]

Figure 7-41. MLS Coverage Volumes, 3-D Representation.

MHz. The equipment is normally located about 1,000 feet
beyond the stop end of the runway, but there is considerable
flexibility in selecting sites. For example, for heliport
operations the azimuth transmitter can be collocated with
the elevation transmitter. The azimuth coverage extends
laterally at least 40° on either side of the runway centerline
in a standard configuration, in elevation up to an angle of 15°
and to at least 20,000 feet, and in range to at least 20 NM.
MLS requires separate airborne equipment to receive and
process the signals from what is normally installed in general
aviation aircraft today. It has data communications capability,
and can provide audible information about the condition
of the transmitting system and other pertinent data such as
weather, runway status, etc. The MLS transmits an audible
identifier consisting of four letters beginning with the letter
M, in Morse code at a rate of at least six per minute. The
MLS system monitors itself and transmits ground-to-air data
messages about the system’s operational condition. During
periods of routine or emergency maintenance, the coded
identification is missing from the transmissions. At this time
there are only a few systems installed.

The RNP type defines the total system error (TSE) that
is allowed in lateral and longitudinal dimensions within
a particular airspace. The TSE, which takes account of
navigation system errors (NSE), computation errors, display
errors and flight technical errors (FTE), must not exceed the
specified RNP value for 95 percent of the flight time on any
part of any single flight. RNP combines the accuracy standards
laid out in the ICAO Manual (Doc 9613) with specific
accuracy requirements, as well as functional and performance
standards, for the RNAV system to realize a system that
can meet future air traffic management requirements. The
functional criteria for RNP address the need for the flight paths
of participating aircraft to be both predictable and repeatable
to the declared levels of accuracy. More information on RNP
is contained in subsequent chapters.
The term RNP is also applied as a descriptor for airspace,
routes, and procedures (including departures, arrivals,
and IAPs). The descriptor can apply to a unique approach
procedure or to a large region of airspace. RNP applies to
navigation performance within a designated airspace, and
includes the capability of both the available infrastructure
(navigation aids) and the aircraft.
RNP type is used to specify navigation requirements for the
airspace. The following are ICAO RNP Types: RNP-1.0,
RNP-4.0, RNP-5.0, and RNP-10.0. The required performance
is obtained through a combination of aircraft capability and
the level of service provided by the corresponding navigation
infrastructure. From a broad perspective:

Required Navigation Performance

Aircraft Capability + Level of Service = Access

RNP is a navigation system that provides a specified level
of accuracy defined by a lateral area of confined airspace
in which an RNP-certified aircraft operates. The continuing
growth of aviation places increasing demands on airspace
capacity and emphasizes the need for the best use of the
available airspace. These factors, along with the accuracy of
modern aviation navigation systems and the requirement for

In this context, aircraft capability refers to the airworthiness
certification and operational approval elements (including
avionics, maintenance, database, human factors, pilot
procedures, training, and other issues). The level of service
element refers to the NAS infrastructure, including published
routes, signal-in-space performance and availability, and air

7-46

Figure 7-42. Required Navigation Performance.

7-47

traffic management. When considered collectively, these
elements result in providing access. Access provides the
desired benefit (airspace, procedures, routes of flight, etc.).
RNP levels are actual distances from the centerline of the
flight path, which must be maintained for aircraft and obstacle
separation. Although additional FAA-recognized RNP
levels may be used for specific operations, the United States
currently supports three standard RNP levels:
•

RNP 0.3 – Approach

•

RNP 1.0 – Departure, Terminal

•

RNP 2.0 – En route

RNP 0.3 represents a distance of 0.3 NM either side of a
specified flight path centerline. The specific performance
that is required on the final approach segment of an
instrument approach is an example of this RNP level. At
the present time, a 0.3 RNP level is the lowest level used in
normal RNAV operations. Specific airlines, using special
procedures, are approved to use RNP levels lower than
RNP 0.3, but those levels are used only in accordance with
their approved operations specifications (OpsSpecs). For
aircraft equipment to qualify for a specific RNP type, it
must maintain navigational accuracy at least 95 percent of
the total flight time.

Flight Management Systems (FMS)
A flight management system (FMS) is not a navigation
system in itself. Rather, it is a system that automates the
tasks of managing the onboard navigation systems. FMS may
perform other onboard management tasks, but this discussion
is limited to its navigation function.
FMS is an interface between flight crews and flight-deck
systems. FMS can be thought of as a computer with a large
database of airport and NAVAID locations and associated
data, aircraft performance data, airways, intersections,

DPs, and STARs. FMS also has the ability to accept and
store numerous user-defined WPs, flight routes consisting
of departures, WPs, arrivals, approaches, alternates, etc.
FMS can quickly define a desired route from the aircraft’s
current position to any point in the world, perform flight
plan computations, and display the total picture of the flight
route to the crew.
FMS also has the capability of controlling (selecting) VOR,
DME, and LOC NAVAIDs, and then receiving navigational
data from them. INS, LORAN, and GPS navigational data
may also be accepted by the FMS computer. The FMS may
act as the input/output device for the onboard navigation
systems, so that it becomes the “go-between” for the crew
and the navigation systems.
Function of FMS
At startup, the crew programs the aircraft location, departure
runway, DP (if applicable), WPs defining the route, approach
procedure, approach to be used, and routing to alternate. This
may be entered manually, be in the form of a stored flight
plan, or be a flight plan developed in another computer and
transferred by disk or electronically to the FMS computer.
The crew enters this basic information in the control/display
unit (CDU). [Figure 7-43]
Once airborne, the FMS computer channels the appropriate
NAVAIDs and takes radial/distance information, or
channels two NAVAIDs, taking the more accurate distance
information. FMS then indicates position, track, desired
heading, groundspeed and position relative to desired track.
Position information from the FMS updates the INS. In more
sophisticated aircraft, the FMS provides inputs to the HSI,
RMI, glass flight deck navigation displays, head-up display
(HUD), autopilot, and autothrottle systems.

Figure 7-43. Typical Display and Control Unit(s) in General Aviation. The Universal UNS-1 (left) controls and integrates all other

systems. The Avidyne (center) and Garmin systems (right) illustrate and are typical of completely integrated systems. Although the
Universal CDU is not typically found on smaller general aviation aircraft, the difference in capabilities of the CDUs and stand-alone
sytems is diminishing each year.

7-48

Head-Up Display (HUD)
The HUD is a display system that provides a projection of
navigation and air data (airspeed in relation to approach
reference speed, altitude, left/right and up/down GS) on a
transparent screen between the pilot and the windshield. Other
information may be displayed, including a runway target in
relation to the nose of the aircraft. This allows the pilot to see
the information necessary to make the approach while also
being able to see out the windshield, which diminishes the
need to shift between looking at the panel to looking outside.
Virtually any information desired can be displayed on the

HUD if it is available in the aircraft’s flight computer, and
if the display is user definable. [Figure 7-44]

Radar Navigation (Ground Based)
Radar works by transmitting a pulse of RF energy in a specific
direction. The return of the echo or bounce of that pulse from
a target is precisely timed. From this, the distance traveled
by the pulse and its echo is determined and displayed on a
radar screen in such a manner that the distance and bearing to
this target can be instantly determined. The radar transmitter
must be capable of delivering extremely high power levels
toward the airspace under surveillance, and the associated
radar receiver must be able to detect extremely small signal
levels of the returning echoes.
The radar display system provides the controller with a maplike presentation upon which appear all the radar echoes
of aircraft within detection range of the radar facility. By
means of electronically generated range marks and azimuthindicating devices, the controller can locate each radar target
with respect to the radar facility, or can locate one radar target
with respect to another.
Another device, a video-mapping unit, generates an actual
airway or airport map and presents it on the radar display
equipment. Using the video-mapping feature, the air traffic
controller not only can view the aircraft targets, but can see
these targets in relation to runways, navigation aids, and
hazardous ground obstructions in the area. Therefore, radar
becomes a NAVAID, as well as the most significant means
of traffic separation.
In a display presenting perhaps a dozen or more targets, a
primary surveillance radar system cannot identify one specific
radar target, and it may have difficulty “seeing” a small target
at considerable distance—especially if there is a rain shower
or thunderstorm between the radar site and the aircraft. This
problem is solved with the Air Traffic Control Radar Beacon
System (ATCRBS), sometimes called secondary surveillance
radar (SSR), which utilizes a transponder in the aircraft. The
ground equipment is an interrogating unit, in which the beacon
antenna is mounted so it rotates with the surveillance antenna.
The interrogating unit transmits a coded pulse sequence that
actuates the aircraft transponder. The transponder answers the
coded sequence by transmitting a preselected coded sequence
back to the ground equipment, providing a strong return signal
and positive aircraft identification, as well as other special data
such as aircraft altitude.

Figure 7-44. Example of a Head-Up Display (top) and a Head-Down
Display (bottom). The head-up display presents information in front
of the pilot along his/her normal field of view while a head-down
display may present information beyond the normal head-up field
of view.

Functions of Radar Navigation
The radar systems used by ATC are air route surveillance
radar (ARSR), airport surveillance radar (ASR), and precision
approach radar (PAR) and airport surface detection equipment
7-49

(ASDE). Surveillance radars scan through 360° of azimuth
and present target information on a radar display located in
a tower or center. This information is used independently or
in conjunction with other navigational aids in the control of
air traffic.
ARSR is a long-range radar system designed primarily to cover
large areas and provide a display of aircraft while en route
between terminal areas. The ARSR enables air route traffic
control center (ARTCC) controllers to provide radar service
when the aircraft are within the ARSR coverage. In some
instances, ARSR may enable ARTCC to provide terminal radar
services similar to but usually more limited than those provided
by a radar approach control.
ASR is designed to provide relatively short-range coverage in
the general vicinity of an airport and to serve as an expeditious
means of handling terminal area traffic through observation
of precise aircraft locations on a radarscope. Nonprecision
instrument approaches are available at airports that have an
approved surveillance radar approach procedure. ASR provides
radar vectors to the final approach course and then azimuth
information to the pilot during the approach. In addition to
range (distance) from the runway, the pilot is advised of MDA,
when to begin descent, and when the aircraft is at the MDA. If
requested, recommended altitudes will be furnished each mile
while on final.
PAR is designed to be used as a landing aid displaying range,
azimuth, and elevation information rather than as an aid for
sequencing and spacing aircraft. PAR equipment may be
used as a primary landing aid, or it may be used to monitor
other types of approaches. Two antennas are used in the PAR
array, one scanning a vertical plane, and the other scanning
horizontally. Since the range is limited to 10 miles, azimuth to
20°, and elevation to 7°, only the final approach area is covered.
The controller’s scope is divided into two parts. The upper half
presents altitude and distance information, and the lower half
presents azimuth and distance.
PAR is a system in which a controller provides highly accurate
navigational guidance in azimuth and elevation to a pilot. Pilots
are given headings to fly to direct them to and keep their aircraft
aligned with the extended centerline of the landing runway.
They are told to anticipate glide path interception approximately
10–30 seconds before it occurs and when to start descent.
The published decision height (DH) is given only if the pilot
requests it. If the aircraft is observed to deviate above or below
the glide path, the pilot is given the relative amount of deviation
by use of terms “slightly” or “well” and is expected to adjust
the aircraft’s rate of descent/ascent to return to the glide path.
Trend information is also issued with respect to the elevation
of the aircraft and may be modified by the terms “rapidly” and

7-50

“slowly” (e.g., “well above glide path, coming down rapidly”).
Range from touchdown is given at least once each mile. If an
aircraft is observed by the controller to proceed outside of
specified safety zone limits in azimuth and/or elevation and
continue to operate outside these prescribed limits, the pilot will
be directed to execute a missed approach or to fly a specified
course unless the pilot has the runway environment (runway,
approach lights, etc.) in sight. Navigational guidance in azimuth
and elevation is provided to the pilot until the aircraft reaches
the published decision altitude (DA)/DH. Advisory course and
glide path information is furnished by the controller until the
aircraft passes over the landing threshold, at which point the
pilot is advised of any deviation from the runway centerline.
Radar service is automatically terminated upon completion of
the approach.

Airport Surface Detection Equipment
Radar equipment is specifically designed to detect all principal
features on the surface of an airport, including aircraft and
vehicular traffic, and to present the entire image on a radar
indicator console in the control tower. It is used to augment
visual observation by tower personnel of aircraft and/or
vehicular movements on runways and taxiways.
Radar Limitations
1.

It is very important for the aviation community to
recognize the fact that there are limitations to radar
service and that ATC controllers may not always be able
to issue traffic advisories concerning aircraft which are
not under ATC control and cannot be seen on radar.

2.

The characteristics of radio waves are such that they
normally travel in a continuous straight line unless
they are “bent” by abnormal atmospheric phenomena
such as temperature inversions; reflected or attenuated
by dense objects such as heavy clouds, precipitation,
ground obstacles, mountains, etc.; or screened by high
terrain features.

3.

Primary radar energy that strikes dense objects will be
reflected and displayed on the operator’s scope, thereby
blocking out aircraft at the same range and greatly
weakening or completely eliminating the display of
targets at a greater range.

4.

Relatively low altitude aircraft will not be seen if they
are screened by mountains or are below the radar beam
due to curvature of the Earth.

5.

The amount of reflective surface of an aircraft will
determine the size of the radar return. Therefore, a small
light airplane or a sleek jet fighter will be more difficult
to see on primary radar than a large commercial jet or
military bomber.

6.

All ARTCC radar in the conterminous United States and
many ASR have the capability to interrogate Mode C
and display altitude information to the controller from
appropriately equipped aircraft. However, a number of
ASR do not have Mode C display capability; therefore,
altitude information must be obtained from the pilot.

7-51

7-52

Chapter 8

The National
Airspace System
Introduction
The National Airspace System (NAS) is the network of
United States airspace: air navigation facilities, equipment,
services, airports or landing areas, aeronautical charts,
information/services, rules, regulations, procedures, technical
information, manpower, and material. Included are system
components shared jointly with the military. The system’s
present configuration is a reflection of the technological
advances concerning the speed and altitude capability of jet
aircraft, as well as the complexity of microchip and satellitebased navigation equipment. To conform to international
aviation standards, the United States adopted the primary
elements of the classification system developed by the
International Civil Aviation Organization (ICAO).
This chapter is a general discussion of airspace classification;
en route, terminal, and approach procedures; and operations
within the NAS. Detailed information on the classification
of airspace, operating procedures, and restrictions is found
in the Aeronautical Information Manual (AIM).

8-1

Airspace Classification
Airspace in the United States [Figure 8-1] is designated as
follows:
1.

Class A. Generally, airspace from 18,000 feet mean
sea level (MSL) up to and including flight level (FL)
600, including the airspace overlying the waters
within 12 nautical miles (NM) of the coast of the
48 contiguous states and Alaska. Unless otherwise
authorized, all pilots must operate their aircraft under
instrument flight rules (IFR).

2.

Class B. Generally, airspace from the surface to 10,000
feet MSL surrounding the nation’s busiest airports in
terms of airport operations or passenger enplanements.
The configuration of each Class B airspace area is
individually tailored, consists of a surface area and two
or more layers (some Class B airspace areas resemble
upside-down wedding cakes), and is designed to
contain all published instrument procedures once
an aircraft enters the airspace. An air traffic control
(ATC) clearance is required for all aircraft to operate
in the area, and all aircraft that are so cleared receive
separation services within the airspace.

3.

4.

8-2

Class C. Generally, airspace from the surface to
4,000 feet above the airport elevation (charted
in MSL) surrounding those airports that have an
operational control tower, are serviced by a radar
approach control, and have a certain number of IFR
operations or passenger enplanements. Although the
configuration of each Class C area is individually
tailored, the airspace usually consists of a surface
area with a 5 NM radius, an outer circle with a 10 NM
radius that extends from 1,200 feet to 4,000 feet above
the airport elevation and an outer area. Each aircraft
must establish two-way radio communications with
the ATC facility providing air traffic services prior
to entering the airspace and thereafter maintain those
communications while within the airspace.
Class D. Generally, that airspace from the surface
to 2,500 feet above the airport elevation (charted
in MSL) surrounding those airports that have an
operational control tower. The configuration of
each Class D airspace area is individually tailored
and when instrument procedures are published,
the airspace will normally be designed to contain
the procedures. Arrival extensions for instrument
approach procedures (IAPs) may be Class D or Class
E airspace. Unless otherwise authorized, each aircraft
must establish two-way radio communications with
the ATC facility providing air traffic services prior
to entering the airspace and thereafter maintain those
communications while in the airspace.

5.

Class E. Generally, if the airspace is not Class A, B,
C, or D, and is controlled airspace, then it is Class E
airspace. Class E airspace extends upward from either
the surface or a designated altitude to the overlying
or adjacent controlled airspace. When designated as a
surface area, the airspace will be configured to contain
all instrument procedures. Also in this class are federal
airways, airspace beginning at either 700 or 1,200 feet
above ground level (AGL) used to transition to and
from the terminal or en route environment, and en
route domestic and offshore airspace areas designated
below 18,000 feet MSL. Unless designated at a lower
altitude, Class E airspace begins at 14,500 MSL over
the United States, including that airspace overlying the
waters within 12 NM of the coast of the 48 contiguous
states and Alaska, up to but not including 18,000 feet
MSL, and the airspace above FL 600.

6.

Class G. Airspace not designated as Class A, B, C, D,
or E. Class G airspace is essentially uncontrolled by
ATC except when associated with a temporary control
tower.

Special Use Airspace
Special use airspace is the designation for airspace in which
certain activities must be confined, or where limitations
may be imposed on aircraft operations that are not part
of those activities. Certain special use airspace areas can
create limitations on the mixed use of airspace. The special
use airspace depicted on instrument charts includes the
area name or number, effective altitude, time and weather
conditions of operation, the controlling agency, and the chart
panel location. On National Aeronautical Charting Group
(NACG) en route charts, this information is available on one
of the end panels.
Prohibited areas contain airspace of defined dimensions
within which the flight of aircraft is prohibited. Such areas
are established for security or other reasons associated with
the national welfare. These areas are published in the Federal
Register and are depicted on aeronautical charts. The area is
charted as a “P” followed by a number (e.g., “P-123”).
Restricted areas are areas where operations are hazardous to
nonparticipating aircraft and contain airspace within which
the flight of aircraft, while not wholly prohibited, is subject
to restrictions. Activities within these areas must be confined
because of their nature, or limitations may be imposed upon
aircraft operations that are not a part of those activities, or
both. Restricted areas denote the existence of unusual, often
invisible, hazards to aircraft (e.g., artillery firing, aerial

Figure 8-1. Airspace Classifications.

8-3

gunnery, or guided missiles). IFR flights may be authorized
to transit the airspace and are routed accordingly. Penetration
of restricted areas without authorization from the using
or controlling agency may be extremely hazardous to the
aircraft and its occupants. ATC facilities apply the following
procedures when aircraft are operating on an IFR clearance
(including those cleared by ATC to maintain visual flight
rules (VFR)-On-Top) via a route that lies within joint-use
restricted airspace:
1.

If the restricted area is not active and has been released
to the Federal Aviation Administration (FAA), the
ATC facility will allow the aircraft to operate in the
restricted airspace without issuing specific clearance
for it to do so.

2.

If the restricted area is active and has not been
released to the FAA, the ATC facility will issue a
clearance which will ensure the aircraft avoids the
restricted airspace.

Restricted areas are charted with an “R” followed by a
number (e.g., “R-5701”) and are depicted on the en route
chart appropriate for use at the altitude or FL being flown.
Warning areas are similar in nature to restricted areas;
however, the United States government does not have sole
jurisdiction over the airspace. A warning area is airspace of
defined dimensions, extending from 12 NM outward from
the coast of the United States, containing activity that may
be hazardous to nonparticipating aircraft. The purpose of
such areas is to warn nonparticipating pilots of the potential
danger. A warning area may be located over domestic or
international waters or both. The airspace is designated with
a “W” followed by a number (e.g., “W-123”).
Military operations areas (MOAs) consist of airspace with
defined vertical and lateral limits established for the purpose
of separating certain military training activities from IFR
traffic. Whenever an MOA is being used, nonparticipating
IFR traffic may be cleared through an MOA if IFR separation
can be provided by ATC. Otherwise, ATC will reroute or
restrict nonparticipating IFR traffic. MOAs are depicted on
sectional, VFR terminal area, and en route low altitude charts
and are not numbered (e.g., “Boardman MOA”).
Alert areas are depicted on aeronautical charts with an
“A” followed by a number (e.g., “A-123”) to inform
nonparticipating pilots of areas that may contain a high
volume of pilot training or an unusual type of aerial activity.
Pilots should exercise caution in alert areas. All activity
within an alert area shall be conducted in accordance with
regulations, without waiver, and pilots of participating
aircraft, as well as pilots transiting the area, shall be equally
responsible for collision avoidance.
8-4

Military Training Routes (MTRs) are routes used by military
aircraft to maintain proficiency in tactical flying. These routes
are usually established below 10,000 feet MSL for operations
at speeds in excess of 250 knots. Some route segments may
be defined at higher altitudes for purposes of route continuity.
Routes are identified as IFR (IR), and VFR (VR), followed by
a number. MTRs with no segment above 1,500 feet AGL are
identified by four number characters (e.g., IR1206, VR1207,
etc.). MTRs that include one or more segments above 1,500
feet AGL are identified by three number characters (e.g.,
IR206, VR207). IFR Low Altitude En Route Charts depict
all IR routes and all VR routes that accommodate operations
above 1,500 feet AGL. IR routes are conducted in accordance
with IFR regardless of weather conditions.
Temporary flight restrictions (TFRs) are put into effect
when traffic in the airspace would endanger or hamper air
or ground activities in the designated area. For example, a
forest fire, chemical accident, flood, or disaster-relief effort
could warrant a TFR, which would be issued as a Notice to
Airmen (NOTAM).
National Security Areas (NSAs) consist of airspace with
defined vertical and lateral dimensions established at
locations where there is a requirement for increased security
and safety of ground facilities. Flight in NSAs may be
temporarily prohibited by regulation under the provisions of
Title 14 of the Code of Federal Regulations (14 CFR) part 99
and prohibitions will be disseminated via NOTAM.
Federal Airways
The primary means for routing aircraft operating under IFR
is the federal airways system.
Each federal airway is based on a centerline that extends from
one NAVAID/waypoint/fix/intersection to another NAVAID/
waypoint/fix/intersection specified for that airway. A federal
airway includes the airspace within parallel boundary lines
four NM to each side of the centerline. As in all instrument
flight, courses are magnetic, and distances are in NM. The
airspace of a federal airway has a floor of 1,200 feet AGL,
unless otherwise specified. A federal airway does not include
the airspace of a prohibited area.
Victor airways include the airspace extending from 1,200 feet
AGL up to, but not including 18,000 feet MSL. The airways
are designated on Sectional and IFR low altitude en route
charts with the letter “V” followed by a number (e.g., “V23”).
Typically, Victor airways are given odd numbers when oriented
north/south and even numbers when oriented east/west. If more
than one airway coincides on a route segment, the numbers are
listed serially (e.g., “V287-495-500”). [Figure 8-2]

Figure 8-2. Victor Airways and Charted IFR Altitudes.

Jet routes exist only in Class A airspace, from 18,000 feet
MSL to FL 450, and are depicted on high-altitude en route
charts. The letter “J” precedes a number to label the airway
(e.g., J12).
RNAV routes have been established in both the low-altitude
and the high-altitude structures in recent years and are
depicted on the en route low and high chart series. High
altitude RNAV routes are identified with a “Q” prefix (except
the Q-routes in the Gulf of Mexico) and low altitude RNAV
routes are identified with a “T” prefix. RNAV routes and data
are depicted in aeronautical blue.
In addition to the published routes, a random RNAV route may
be flown under IFR if it is approved by ATC. Random RNAV
routes are direct routes, based on area navigation capability,
between waypoints defined in terms of latitude/longitude

coordinates, degree-distance fixes, or offsets from established
routes/airways at a specified distance and direction.
Radar monitoring by ATC is required on all random
RNAV routes. These routes can only be approved in a radar
environment. Factors that will be considered by ATC in
approving random RNAV routes include the capability to
provide radar monitoring, and compatibility with traffic
volume and flow. ATC will radar monitor each flight;
however, navigation on the random RNAV route is the
responsibility of the pilot.
Other Routing
Preferred IFR routes have been established between
major terminals to guide pilots in planning their routes of
flight, minimizing route changes and aiding in the orderly
management of air traffic on federal airways. Low and high

8-5

altitude preferred routes are listed in the Airport/Facility
Directory (A/FD). To use a preferred route, reference the
departure and arrival airports; if a routing exists for your
flight, then airway instructions will be listed.
Tower En Route Control (TEC) is an ATC program that
uses overlapping approach control radar services to provide
IFR clearances. By using TEC, a pilot is routed by airport
control towers. Some advantages include abbreviated filing
procedures and reduced traffic separation requirements. TEC
is dependent upon the ATC’s workload, and the procedure
varies among locales.
The latest version of Advisory Circular (AC) 90-91, North
American Route Program (NRP), provides guidance to users
of the NAS for participation in the NRP. All flights operating
at or above FL 290 within the conterminous United States
and Canada are eligible to participate in the NRP, the primary
purpose of which is to allow operators to plan minimum time/
cost routes that may be off the prescribed route structure. NRP
aircraft are not subject to route-limiting restrictions (e.g.,
published preferred IFR routes) beyond a 200 NM radius of
their point of departure or destination.

other side of the folded chart. Information concerning MTRs
is also included on the chart cover. The en route charts are
revised every 56 days.
When the NACG en route chart is unfolded, the legend is
displayed and provides information concerning airports,
NAVAIDs, communications, air traffic services, and
airspace.
Airport Information
Airport information is provided in the legend, and the symbols
used for the airport name, elevation, and runway length are
similar to the sectional chart presentation. Associated city
names are shown for public airports only. FAA identifiers are
shown for all airports. ICAO identifiers are also shown for
airports outside of the contiguous United States. Instrument
approaches can be found at airports with blue or green
symbols, while the brown airport symbol denotes airports
that do not have instrument approaches. Stars are used to
indicate the part-time nature of tower operations, ATIS
frequencies, part-time or on request lighting facilities, and
part-time airspace classifications. A box after an airport name
with a “C” or “D” inside indicates Class C and D airspace,
respectively, per Figure 8-3.

IFR En Route Charts
The objective of IFR en route flight is to navigate within the
lateral limits of a designated airway at an altitude consistent
with the ATC clearance. Your ability to fly instruments
safely and competently in the system is greatly enhanced by
understanding the vast array of data available to the pilot on
instrument charts. The NACG maintains and produces the
charts for the United States government.
En route high-altitude charts provide aeronautical information
for en route instrument navigation (IFR) at or above 18,000
feet MSL. Information includes the portrayal of Jet and
RNAV routes, identification and frequencies of radio aids,
selected airports, distances, time zones, special use airspace,
and related information. Established Jet routes from 18,000
feet MSL to FL 450 use NAVAIDs not more than 260 NM
apart. The charts are revised every 56 days.
To effectively depart from one airport and navigate en route
under instrument conditions a pilot needs the appropriate IFR
en route low-altitude chart(s). The IFR low altitude en route
chart is the instrument equivalent of the Sectional chart. When
folded, the cover of the NACG en route chart displays an
index map of the United States showing the coverage areas.
Cities near congested airspace are shown in black type and
their associated area chart is listed in the box in the lower
left-hand corner of the map coverage box. Also noted is an
explanation of the off-route obstruction clearance altitude
(OROCA). The effective date of the chart is printed on the
8-6

Charted IFR Altitudes
The minimum en route altitude (MEA) ensures a navigation
signal strong enough for adequate reception by the aircraft
navigation (NAV) receiver and obstacle clearance along the
airway. Communication is not necessarily guaranteed with
MEA compliance. The obstacle clearance, within the limits of
the airway, is typically 1,000 feet in non-mountainous areas
and 2,000 feet in designated mountainous areas. MEAs can
be authorized with breaks in the signal coverage; if this is the
case, the NACG en route chart notes “MEA GAP” parallel
to the affected airway. MEAs are usually bidirectional;
however, they can be single-directional. Arrows are used to
indicate the direction to which the MEA applies.
The minimum obstruction clearance altitude (MOCA), as
the name suggests, provides the same obstruction clearance
as an MEA; however, the NAV signal reception is ensured
only within 22 NM of the closest NAVAID defining the route.
The MOCA is listed below the MEA and indicated on NACG
charts by a leading asterisk (e.g., “*3400”—see Figure 8-2,
V287 at bottom left).
The minimum reception altitude (MRA) identifies the lowest
altitude at which an intersection can be determined from an
off-course NAVAID. If the reception is line-of-sight based,
signal coverage will only extend to the MRA or above.
However, if the aircraft is equipped with distance measuring
equipment (DME) and the chart indicates the intersection can

Figure 8-3. En Route Airport Legend.

be identified with such equipment, the pilot could define the
fix without attaining the MRA. On NACG charts, the MRA
is indicated by the symbol
and the altitude preceded by
“MRA” (e.g., “MRA 9300”). [Figure 8-2]
The minimum crossing altitude (MCA) will be charted when
a higher MEA route segment is approached. The MCA is
usually indicated when a pilot is approaching steeply rising
terrain, and obstacle clearance and/or signal reception is
compromised. In this case, the pilot is required to initiate
a climb so the MCA is reached by the time the intersection
is crossed. On NACG charts, the MCA is indicated by the
symbol
, and the Victor airway number, altitude, and
the direction to which it applies (e.g. “V24 8000 SE”).
The maximum authorized altitude (MAA) is the highest
altitude at which the airway can be flown with assurance
of receiving adequate navigation signals. Chart depictions
appear as “MAA-15000.”
When an MEA, MOCA, and/or MAA change on a segment
other than at a NAVAID, a sideways “T”
is depicted
on the chart. If there is an airway break without the symbol,
one can assume the altitudes have not changed (see the upper
left area of Figure 8-2). When a change of MEA to a higher
MEA is required, the climb may commence at the break,
ensuring obstacle clearance. [Figure 8-4]

Navigation Features

Types of NAVAIDs
Very high frequency omnidirectional ranges (VORs) are the
principal NAVAIDs that support the Victor and Jet airways.
Many other navigation tools are also available to the pilot.
For example, nondirectional beacons (NDBs) can broadcast
signals accurate enough to provide stand-alone approaches,
and DME allows the pilot to pinpoint a reporting point on the
airway. Though primarily navigation tools, these NAVAIDs
can also transmit voice broadcasts.
Tactical air navigation (TACAN) channels are represented
as the two- or three-digit numbers following the three-letter
identifier in the NAVAID boxes. The NACG terminal
procedures provide a frequency-pairing table for the
TACAN-only sites. On NACG charts, very-high frequencies
and ultra-high frequencies (VHF/UHF) NAVAIDs (e.g.,
VORs) are depicted in black, while low frequencies and
medium frequencies (LF/MF) are depicted as brown.
[Figure 8-5]

Identifying Intersections
Intersections along the airway route are established by a
variety of NAVAIDs. An open triangle
indicates the
location of an ATC reporting point at an intersection. If the
triangle is solid,
a report is compulsory. [Figure 8-4]

8-7

Figure 8-4. Legend From En Route Low Attitude Chart, Air Traffic Services and Airspace Information Section.

8-8

Figure 8-5. Legend From En Route Low Attitude Chart.

8-9

NDBs, localizers, and off-route VORs are used to establish
intersections. NDBs are sometimes collocated with
intersections, in which case passage of the NDB would mark
the intersection. A bearing to an off-route NDB also can
provide intersection identification. A localizer course used to
identify an intersection is depicted by a feathered arrowhead
symbol on the en route chart.
If feathered markings appear on the left-hand side of the
arrowhead,
a back course (BC)
signal is transmitted. On NACG en route charts, the localizer
symbol is only depicted to identify an intersection.
Off-route VORs remain the most common means of
identifying intersections when traveling on an airway. Arrows
depicted next to the intersection
indicate the NAVAID to
be used for identification. Another means of identifying an
intersection is with the use of DME. A hollow arrowhead
indicates DME is authorized for intersection identification. If
the DME mileage at the intersection is a cumulative distance
of route segments, the mileage is totaled and indicated by
a D-shaped symbol with a mileage number inside.
[Figure 8-4] Approved IFR GPS units can also be used to
report intersections.

Other Route Information
DME and GPS provide valuable route information concerning
such factors as mileage, position, and groundspeed. Even
without this equipment, information is provided on the
charts for making the necessary calculations using time and
distance. The en route chart depicts point-to-point distances
on the airway system. Distances from VOR to VOR are
charted with a number inside of a box.
To differentiate
distances when two airways coincide, the word “TO” with the
three-letter VOR identifier appear to the left of the distance
boxes.
VOR changeover points (COPs) are depicted on the charts by
this symbol:
The numbers indicate the distance at which
to change the VOR frequency. The frequency change might
be required due to signal reception or conflicting frequencies.
If a COP does not appear on an airway, the frequency should
be changed midway between the facilities. A COP at an
intersection may indicate a course change.
Occasionally an “x” will appear at a separated segment of
an airway that is not an intersection. The “x” is a mileage
breakdown or computer navigation fix and may indicate a
course change.
Today’s computerized system of ATC has greatly reduced
the need for holding en route. However,
published holding patterns are still found on
charts at junctures where ATC has deemed it Holding Pattern
8-10

necessary to enable traffic flow. When a holding pattern is
charted, the controller may provide the holding direction and
the statement “as published.” [Figure 8-4]
Boundaries separating the jurisdiction of Air Route Traffic
Control Centers (ARTCC) are depicted on charts with blue
serrations.
The name
NAME
Name
of the controlling facility is printed on the
000.0
000.0
corresponding side of the division line.
ARTCC remote sites are depicted as blue serrated boxes
and contain the center name, sector name, and the sector
frequency. [Figure 8-4]

Weather Information and Communication Features
En route NAVAIDs also provide weather information and
serve communication functions.
When a NAVAID is shown as a
shadowed box, an automated flight
service station (AFSS) of the same
name is directly associated with the facility. If an AFSS is
located without an associated NAVAID, the shadowed box is
smaller and contains only the name and identifier. The AFSS
frequencies are provided above the
box. (Frequencies 122.2 and 255.4,
and emergency frequencies 121.5 and
243.0 are not listed.)
A Remote Communications Outlet (RCO) associated with
a NAVAID is designated by a thinlined box with the controlling AFSS
frequency above the box, and the
name under the box. Without an
associated facility, the thin-lined
RCO box contains the AFSS name
and remote frequency.
Automated Surface Observing Station (ASOS), Automated
Weather Observing Station (AWOS), Hazardous Inflight
Weather Advisory Service
(HIWAS) and Transcribed
Weather Broadcast (TWEB) are
continuously transmitted over
selected NAVAIDs and depicted in the NAVAID box. ASOS/
AWOS are depicted by a white “A”, HIWAS by a “H” and
TWEB broadcasts by a “T” in a solid black circle in the upper
right or left corner.

New Technologies
Technological advances have made multifunction displays
and moving maps more common in newer aircraft. Even older
aircraft are being retrofitted to include “glass” in the flight
deck. [Figure 8-6] Moving maps improve pilot situational
awareness by providing a picture of aircraft location in

Figure 8-6. Moving Map Display.

relation to NAVAIDS, waypoints, airspace, terrain, and
hazardous weather. GPS systems can be certified for terminal
area and en route use as well as approach guidance.
Additional breakthroughs in display technology are the new
electronic chart systems or electronic flight bags that facilitate
the use of electronic documents in the general aviation
flight deck. [Figure 8-7] An electronic chart or flight bag
is a self-powered electronic library that stores and displays
en route charts and other essential documents on a screen.
These electronic devices can store the digitized United States
terminal procedures, en route charts, the complete airport
facility directory, in addition to Title 14 of the Code of Federal
Regulations (14 CFR) and the AIM. Full touch-screen based
computers allow pilots to view airport approach and area
charts electronically while flying. It replaces paper charts as
well as other paper materials including minimum equipment
lists (MELs), standard operating procedures (SOPs), standard
instrument departures (SIDs), standard terminal arrival
routes (STARs), checklists, and flight deck manuals. As with
paper flight publications, the electronic database needs to be
current to provide accurate information regarding NAVAIDS,
waypoints, and terminal procedures. Databases are updated
every 28 days and are available from various commercial
vendors. Pilots should be familiar with equipment operation,
capabilities, and limitations prior to use.

Figure 8-7. Example of an Electronic Flight Bag.

8-11

Terminal Procedures Publications

Instrument Approach Procedure (IAP)
While the en route charts provide the information necessary Charts
to safely transit broad regions of airspace, the United States
Terminal Procedures Publication (TPP) enables pilots to
guide their aircraft in the airport area. Whether departing or
arriving, these procedures exist to make the controllers’ and
pilots’ jobs safer and more efficient. Available in booklets
by region (published by NACG), the TPP includes approach
procedures, STARs, Departure Procedures (DPs), and airport
diagrams.
Departure Procedures (DPs)
There are two types of DPs, Obstacle Departure Procedures
(ODP) and SIDs. [Figure 8-8] Both types of DPs provide
obstacle clearance protection to aircraft in instrument
meteorological conditions (IMC), while reducing
communications and departure delays. DPs are published in
text and/or charted graphic form. Regardless of the format, all
DPs provide a way to depart the airport and transition to the
en route structure safely. When possible, pilots are strongly
encouraged to file and fly a DP at night, during marginal
visual meteorological conditions (VMC) and IMC.
All DPs provide obstacle clearance provided the aircraft
crosses the end of the runway at least 35 feet AGL; climbs
to 400 feet above airport elevation before turning; and climbs
at least 200 feet per nautical mile (FPNM), unless a higher
climb gradient is specified to the assigned altitude. ATC may
vector an aircraft off a previously assigned DP; however, the
200 FPNM or the FPNM specified in the DP is required.
Textual ODPs are listed by city and airport in the IFR
Take-Off Minimums and DPs Section of the TPP. SIDs are
depicted in the TPP following the approach procedures for
the airport.
Standard Terminal Arrival Routes (STARs)
STARs depict prescribed routes to transition the instrument
pilot from the en route structure to a fix in the terminal area
from which an instrument approach can be conducted. If a
pilot does not have the appropriate STAR, write “No STAR”
in the flight plan. However, if the controller is busy, the pilot
might be cleared along the same route and, if necessary,
the controller will have the pilot copy the entire text of the
procedure.
STARs are listed alphabetically at the beginning of the
NACG booklet. Figure 8-9 shows an example of a STAR, and
the legend for STARs and DPs printed in NACG booklets.

8-12

The IAP chart provides the method to descend and land safely
in low visibility conditions. The FAA establishes an IAP
after thorough analyses of obstructions, terrain features, and
navigational facilities. Maneuvers, including altitude changes,
course corrections, and other limitations, are prescribed in the
IAP. The approach charts reflect the criteria associated with
the United States Standard for Terminal Instrument Approach
Procedures (TERPs), which prescribes standardized methods
for use in designing instrument flight procedures.
In addition to the NACG, other governmental and corporate
entities produce approach procedures. The United States
military IAPs are established and published by the
Department of Defense and are available to the public
upon request. Special IAPs are approved by the FAA for
individual operators and are not available to the general
public. Foreign country standard IAPs are established and
published according to the individual country’s publication
procedures. The information presented in the following
sections will highlight features of the United States Terminal
Procedures Publications.
The instrument approach chart is divided into six main
sections, which include the margin identification, pilot
briefing (and notes), plan view, profile view, landing
minimums, and airport diagram. [Figure 8-10] An
examination of each section follows.
Margin Identification
The margin identification, at the top and bottom of the chart,
depicts the airport location and procedure identification.
The civil approach plates are organized by city, then airport
name and state. For example, Orlando Executive in Orlando,
Florida is alphabetically listed under “O” for Orlando.
Military approaches are organized by airport name first.
The chart’s amendment status appears below the city and state
in the bottom margin. The amendment number is followed
by the five-digit julian-date of the last chart change.“05300”
is read, “the 300th day of 2005”. At the center of the top
margin is the FAA chart reference number and the approving
authority. At the bottom center, the airport’s latitude and
longitude coordinates are provided.

8-13

Figure 8-8. Obstacle Departure Procedures (ODP) and Standard Instrument Departures (SID).

8-14

Figure 8-9. DP Chart Legend and STAR.

Figure 8-10. Instrument Approach Chart.

8-15

The procedure chart title (top and bottom margin area of
Figure 8-10) is derived from the type of navigational facility
providing final approach course guidance. A runway number
is listed when the approach course is aligned within 30º of the
runway centerline. This type of approach allows a straightin landing under the right conditions. The type of approach
followed by a letter identifies approaches that do not have
straight-in landing minimums. Examples include procedure
titles at the same airport, which have only circling minimums.
The first approach of this type created at the airport will be
labeled with the letter A, and the lettering will continue in
alphabetical order (e.g., “VOR-A or “LDA-B”). The letter
designation signifies the expectation is for the procedure to
culminate in a circling approach to land. As a general rule,
circling-only approaches are designed for one of the two
following reasons:
•

The final approach course alignment with the runway
centerline exceeds 30º.

•

The descent gradient is greater than 400 feet per
NM from the FAF to the threshold crossing height
(TCH). When this maximum gradient is exceeded, the
circling-only approach procedure may be designed to
meet the gradient criteria limits.

Further information on this topic can be found in the
Instrument Procedures Handbook, Chapter 5, under Approach
Naming Conventions.
To distinguish between the left, right, and center runways, an
“L,” “R,” or “C” follows the runway number (e.g., “ILS RWY
16R”). In some cases, an airport might have more than one
circling approach, shown as VOR-A, VOR/DME-B, etc.
More than one navigational system separated by a slash
indicates more than one type of equipment is required to
execute the final approach (e.g., VOR/DME RWY 31). More
than one navigational system separated by “or” indicates either
type of equipment may be used to execute the final approach
(e.g., VOR or GPS RWY 15). Multiple approaches of the same
type, to the same runway and using the same guidance, have
an additional letter from the end of the alphabet, number, or
term in the title (e.g., ILS Z RWY 28, SILVER ILS RWY
28, or ILS 2 RWY 28). VOR/DME RNAV approaches are
identified as VOR/DME RNAV RWY (runway number).
Helicopters have special IAPs, designated with COPTER in
the procedure identification (e.g., COPTER LOC/DME 25L).
Other types of navigation systems may be required to execute
other portions of the approach prior to intercepting the final
approach segment or during the missed approach.
The Pilot Briefing
The pilot briefing is located at the top of the chart and
provides the pilot with information required to complete the
8-16

published approach procedure. Included in the pilot briefing
are the NAVAID providing approach guidance, its frequency,
the final approach course, and runway information. A notes
section contains additional procedural information. For
example, a procedural note might indicate restrictions for
circling maneuvers. Some other notes might concern a local
altimeter setting and the resulting change in the minimums.
The use of RADAR may also be noted in this section.
Additional notes may be found in the plan view.
When a triangle containing a “T” ( ) appears in the notes
section, it signifies the airport has nonstandard IFR takeoff
minimums. Pilots should refer to the DPs section of the TPP
to determine takeoff minimums.
When a triangle containing an “A” ( ) appears in the notes
section, it signifies the airport has nonstandard IFR alternate
minimums. Civil pilots should refer to the Alternate Minimums
Section of the TPP to determine alternate minimums. Military
pilots should refer to appropriate regulations.
) appears in
When a triangle containing an “A” NA (
the notes area, it signifies that Alternate Minimums are Not
Authorized due to unmonitored facility or the absence of
weather reporting service.
Communication frequencies are listed in the order in which
they would be used during the approach. Frequencies for
weather and related facilities are included, where applicable,
such as automatic terminal information service (ATIS),
automated surface observing system (ASOS), automated
weather observation system (AWOS), and AFSSs.
The Plan View
The plan view provides a graphical overhead view of the
procedure, and depicts the routes that guide the pilot from
the en route segments to the initial approach fix (IAF).
[Figure 8-10] During the initial approach, the aircraft has
departed the en route phase of flight and is maneuvering
to enter an intermediate or final segment of the instrument
approach. An initial approach can be made along prescribed
routes within the terminal area, which may be along an arc,
radial, course, heading, radar vector, or a combination thereof.
Procedure turns and high altitude teardrop penetrations
are initial approach segments. Features of the plan view,
including the procedure turn, obstacle elevation, minimum
safe altitude (MSA), and procedure track, are depicted in
Figure 8-11. Terrain will be depicted in the plan view portion
of all IAPs if the terrain within the plan view exceeds 4,000
feet above the airport elevation, or if within a 6 nautical mile
radius of the airport reference point the terrain rises at least
2,000 feet above the airport elevation.

8-17

Figure 8-11. IAP Plan View and Symbol Legends.

Some NACG charts contain a reference or distance circle
with a specified radius (10 NM is most common). Normally,
approach features within the plan view are shown to scale;
however, only the data within the reference circle is always
drawn to scale.
Concentric dashed circles, or concentric rings around the
distance circle, are used when the information necessary to
the procedure will not fit to scale within the limits of the plan
view area. They serve as a means to systematically arrange
this information in its relative position outside and beyond
the reference circle. These concentric rings are labeled en
route facilities and feeder facilities.
The primary airport depicted in the plan view is drawn with
enough detail to show the runway orientation and final
approach course alignment. Airports other than the primary
approach airport are not normally depicted in the NACG
plan view.
Known spot elevations are indicated on the plan view with a
dot in MSL altitude. The largest dot and number combination
indicates the highest elevation. An inverted “V” with a dot
in the center depicts an obstacle.
The highest obstacle is
indicated with a bolder, larger version of the same symbol.
[Figure 8-11]
The MSA circle appears in the plan view, except in approaches
for which the Terminal Arrival Area (TAA) format is used or
appropriate NAVAIDs (e.g., VOR or NDB)
are unavailable. The MSA is provided for
emergency purposes only and guarantees
1,000 feet obstruction clearance in the sector
indicated with reference to the bearings in the
circle. For conventional navigation systems,
the MSA is normally based on the primary omnidirectional
facility (NAVAID) on which the IAP is predicated. The MSA
depiction on the approach chart contains the facility identifier
of the NAVAID used to determine the MSA altitudes. For
RNAV approaches, the MSA is based on the runway waypoint
for straight-in approaches, or the airport waypoint for circling
approaches. For GPS approaches, the MSA center header will
be the missed approach waypoint. The MSL altitudes appear
in boxes within the circle, which is typically a 25 NM radius
unless otherwise indicated. The MSA circle header refers to
the letter identifier of the NAVAID or waypoint that describes
the center of the circle.
NAVAIDs necessary for the completion of the instrument
procedure include the facility name, letter identifier, and
Morse code sequence. They may also furnish the frequency,
Morse code, and channel. A heavy-lined NAVAID box depicts
the primary NAVAID used for the approach. An “I” in front

8-18

of the NAVAID identifier (in Figure 8-11, “I-AVL”) listed in
the NAVAID box indicates a localizer. The requirement for
an ADF, DME, or RADAR in the approach is noted in the
plan view.
Intersections, fixes, radials, and course lines describe route
and approach sequencing information. The main procedure
or final approach course is a thick, solid line.
A
DME arc, which is part of the main procedure course, is
also represented as a thick, solid line.
A feeder
route is depicted with a medium line
and provides
heading, altitude, and distance information. (All three
components must be designated on the chart to provide a
navigable course.) Radials, such as lead radials, are shown
by thin lines.
The missed approach track is drawn
using a thin, hash marked line with a directional arrow.
A visual flight path segment
appears as a thick dashed line with a directional arrow.
IAFs are charted IAF when associated with
a NAVAID or when freestanding.
The missed approach holding pattern track is represented with
a thin-dashed line. When collocated, the missed approach
holding pattern and procedure turn holding pattern are
indicated as a solid, black line. Arrival holding patterns are
depicted as thin, solid lines.

Terminal Arrival Area (TAA)
The design objective of the TAA procedure is to provide
a transition method for arriving aircraft with GPS/RNAV
equipment. TAAs will also eliminate or reduce the need
for feeder routes, departure extensions, and procedure
turns or course reversal. The TAA is controlled airspace
established in conjunction with the standard or modified
RNAV approach configurations.
The standard TAA has three areas: straight-in, left base, and
right base. The arc boundaries of the three areas of the TAA
are published portions of the approach and allow aircraft to
transition from the en route structure direct to the nearest
IAF. When crossing the boundary of each of these areas or
when released by ATC within the area, the pilot is expected
to proceed direct to the appropriate waypoint IAF for the
approach area being flown. A pilot has the option in all areas
of proceeding directly to the holding pattern.
The TAA has a “T” structure that normally provides a NoPT
for aircraft using the approach. [Figure 8-12] The TAA
provides the pilot and air traffic controller with an efficient
method for routing traffic from the en route to the terminal
structure. The basic “T” contained in the TAA normally
aligns the procedure on runway centerline, with the missed

8-19

Figure 8-12. Basic “T” Design of Terminal Arrival Area (TAA) and Legend.

approach point (MAP) located at the threshold, the FAF 5
NM from the threshold, and the intermediate fix (IF) 5 NM
from the FAF.
In order to accommodate descent from a high en route altitude
to the initial segment altitude, a hold in lieu of a procedure
turn provides the aircraft with an extended distance for the
necessary descent gradient. The holding pattern constructed
for this purpose is always established on the center IAF
waypoint. Other modifications may be required for parallel
runways, or special operational requirements. When
published, the RNAV chart will depict the TAA through
the use of icons representing each TAA associated with the
RNAV procedure. These icons are depicted in the plan view
of the approach, generally arranged on the chart in accordance
with their position relative to the aircraft’s arrival from the
en route structure.
Course Reversal Elements in Plan View and
Profile View
Course reversals included in an IAP are depicted in one of
three different ways: a 45°/180° procedure turn, a holding
pattern in lieu of procedure turn, or a teardrop procedure.
The maneuvers are required when it is necessary to reverse
direction to establish the aircraft inbound on an intermediate
or final approach course. Components of the required
procedure are depicted in the plan view and the profile view.
The maneuver must be completed within the distance and
at the minimum altitude specified in the profile view. Pilots
should coordinate with the appropriate ATC facility relating
to course reversal during the IAP.

the procedure turn is made. [Figure 8-13] Headings are
provided for course reversal using the 45° procedure turn.
However, the point at which the turn may be commenced,
and the type and rate of turn is left to the discretion of the
pilot. Some of the options are the 45° procedure turn, the
racetrack pattern, the teardrop procedure turn, or the 80°/260°
course reversal. The absence of the procedure turn barbed
arrow in the plan view indicates that a procedure turn is
not authorized for that procedure. A maximum procedure
turn speed of not greater than 200 knots indicated airspeed
(KIAS) should be observed when turning outbound over the
IAF and throughout the procedure turn maneuver to ensure
staying within the obstruction clearance area. The normal
procedure turn distance is 10 NM. This may be reduced to
a minimum of 5 NM where only Category A or helicopter
aircraft are operated, or increased to as much as 15 NM to
accommodate high performance aircraft. Descent below the
procedure turn altitude begins after the aircraft is established
on the inbound course.
The procedure turn is not required when the symbol “NoPT”
appears, when radar vectoring to the final approach is
provided, when conducting a timed approach, or when the
procedure turn is not authorized. Pilots should contact the
appropriate ATC facility when in doubt if a procedure turn
is required.

Holding in Lieu of Procedure Turn
A holding pattern in lieu of a procedure turn may be specified
for course reversal in some procedures. [Figure 8-14] In such
cases, the holding pattern is established over an intermediate
fix or a final approach fix (FAF). The holding pattern distance

Procedure Turns
A procedure turn barbed arrow
indicates
the direction or side of the outbound course on which

Figure 8-13. 45° Procedure Turn.

8-20

Figure 8-14. Holding in Lieu of Procedure Turn.

or time specified in the profile view must be observed.
Maximum holding airspeed limitations as set forth for all
holding patterns apply. The holding pattern maneuver is
completed when the aircraft is established on the inbound
course after executing the appropriate entry. If cleared for
the approach prior to returning to the holding fix and the
aircraft is at the prescribed altitude, additional circuits of the
holding pattern are neither necessary nor expected by ATC.
If pilots elect to make additional circuits to lose excessive
altitude or to become better established on course, it is their
responsibility to advise ATC upon receipt of their approach
clearance. When holding in lieu of a procedure turn, the
holding pattern must be followed, except when RADAR
VECTORING to the final approach course is provided or
when NoPT is shown on the approach course.

Teardrop Procedure
When a teardrop procedure turn is depicted and a course
reversal is required, unless otherwise authorized by ATC,
this type of procedure must be executed. [Figure 8-15] The
teardrop procedure consists of departure from an IAF on the
published outbound course followed by a turn toward and
intercepting the inbound course at or prior to the intermediate
fix or point. Its purpose is to permit an aircraft to reverse
direction and lose considerable altitude within reasonably
limited airspace. Where no fix is available to mark the
beginning of the intermediate segment, it shall be assumed
to commence at a point 10 NM prior to the FAF. When the
facility is located on the airport, an aircraft is considered to
be on final approach upon completion of the penetration turn.
However, the final approach segment begins on the final
approach course 10 NM from the facility.

The Profile View
The profile view is a depiction of the procedure from the side
and illustrates the vertical approach path altitudes, headings,
distances, and fixes. [Figures 8-10, 8-11, and 8-12] The
view includes the minimum altitude and the maximum
distance for the procedure turn, altitudes over prescribed
fixes, distances between fixes, and the missed approach
procedure. The profile view aids in the pilot’s interpretation
of the IAP. The profile view is not drawn to scale.
[Figures 8-10, 8-11, 8-12, and 8-16]
The precision approach glide slope (GS) intercept altitude
is a minimum altitude for GS interception after completion
of the procedure turn, illustrated by an altitude number and
“zigzag” line. It applies to precision approaches, and except
where otherwise prescribed, also applies as a minimum
altitude for crossing the FAF when the GS is inoperative
or not used. Precision approach profiles also depict the GS
angle of descent, threshold-crossing height (TCH), and GS
altitude at the outer marker (OM).
For nonprecision approaches, a final descent is initiated and
the final segment begins at either the FAF or the final approach
point (FAP). The FAF is identified by use of the Maltese cross
[Figure 8-11] When no FAF
symbol in the profile view.
is depicted, the final approach point is the point at which the
aircraft is established inbound on the final approach course.
[Figure 8-16]
Stepdown fixes in nonprecision procedures are provided
between the FAF and the airport for authorizing a lower
minimum descent altitude (MDA) after passing an
obstruction. Stepdown fixes can be identified by NAVAID,
NAVAID fix, waypoint or radar, and are depicted by a hash
marked line. Normally, there is only one stepdown fix
between the FAF and the MAP, but there can be several.
If the stepdown fix cannot be identified for any reason, the
minimum altitude at the stepdown fix becomes the MDA for
the approach. However, circling minimums apply if they are
higher than the stepdown fix minimum altitude, and a circling
approach is required.
The visual descent point (VDP) is a defined point on
the final approach course of a nonprecision straight-in
approach procedure. A normal descent from the MDA to
the runway touchdown point may be commenced, provided
visual reference is established. The VDP is identified on
the profile view of the approach chart by the symbol “V.”
[Figure 8-12]

Figure 8-15. Teardrop Procedure.

The MAP varies depending upon the approach flown. For
the ILS, the MAP is at the decision altitude/decision height
(DA/DH). For nonprecision procedures, the pilot determines
8-21

8-22

Figure 8-16. More IAP Profile View Features.

the MAP by timing from FAF when the approach aid is away
from the airport, by a fix or NAVAID when the navigation
facility is located on the field, or by waypoints as defined
by GPS or VOR/DME RNAV. The pilot may execute the
MAP early, but pilots should, unless otherwise cleared by
ATC, fly the IAP as specified on the approach plate to the
MAP at or above the MDA or DA/DH before executing a
turning maneuver.
A complete description of the missed approach procedure
appears in the pilot briefing section. [Figure 8-16] Icons
indicating what is to be accomplished at the MAP are located
in the profile view. When initiating a missed approach, the
pilot will be directed to climb straight ahead (e.g., “Climb to
2,000”) or commence a turning climb to a specified altitude
(e.g., “Climbing right turn to 2,000”). In some cases, the
procedure will direct the pilot to climb straight ahead to
an initial altitude, then turn or enter a climbing turn to the
holding altitude (e.g., “Climb to 900, then climbing right turn
to 2,500 direct ABC VOR and hold”).
When the missed approach procedure specifies holding at
a facility or fix, the pilot proceeds according to the missed
approach track and pattern depicted on the plan view. An
alternate missed approach procedure may also be issued by
ATC. The textual description will also specify the NAVAID(s)
or radials that identify the holding fix.
The profile view also depicts minimum, maximum,
recommended, and mandatory block altitudes used in
approaches. The minimum altitude is depicted with the altitude
underscored.
On final approach, aircraft are required
to maintain an altitude at or above the depicted altitude until
reaching the subsequent fix. The maximum altitude will be
depicted with the altitude overscored,
and aircraft
must remain at or below the depicted altitude. Mandatory
altitudes will be depicted with the altitude both underscored
and overscored,
and altitude is to be maintained at the
depicted value. Recommended altitudes are advisory altitudes
and are neither over- nor underscored. When an over- or
underscore spans two numbers, a mandatory block altitude is
indicated, and aircraft are required to maintain altitude within
the range of the two numbers. [Figures 8-11 and 8-12]
The Vertical Descent Angle (VDA) found on nonprecision
approach charts provides the pilot with information required
to establish a stabilized approach descent from the FAF
or stepdown fix to the threshold crossing height (TCH).
[Figure 8-17] Pilots can use the published angle and
estimated or actual ground speed to find a target rate of descent
using the rate of descent table in the back of the TPP.

Figure 8-17. Vertical Descent Angle (VDA).

Landing Minimums
The minimums section sets forth the lowest altitude and
visibility requirements for the approach, whether precision
or nonprecision, straight-in or circling, or radar vectored.
When a fix is incorporated in a nonprecision final segment,
two sets of minimums may be published, depending upon
how the fix can be identified. Two sets of minimums may
also be published when a second altimeter source is used
in the procedure. The minimums ensure that final approach
obstacle clearance is provided from the start of the final
segment to the runway or MAP, whichever occurs last. The
same minimums apply to both day and night operations unless
different minimums are specified in the Notes section of the
pilot briefing. Published circling minimums provide obstacle
clearance when pilots remain within the appropriate area of
protection. [Figure 8-18]
Minimums are specified for various aircraft approach
categories based upon a value 1.3 times the stalling speed
of the aircraft in the landing configuration at maximum
certified gross landing weight. If it is necessary to maneuver
at speeds in excess of the upper limit of a speed range for a
category, the minimums for the next higher category should
be used. For example, an aircraft that falls into category A,
but is circling to land at a speed in excess of 91 knots, should
use approach category B minimums when circling to land.
[Figure 8-19]
The minimums for straight-in and circling appear directly
under each aircraft category. [Figure 8-19] When there is
no solid division line between minimums for each category
on the rows for straight-in or circling, the minimums apply
to the two or more categories.
The terms used to describe the minimum approach altitudes
differ between precision and nonprecision approaches.

8-23

8-24

Figure 8-18. IAP Profile Legend.

8-25

Figure 8-19. Descent Rate Table.

8-26

Figure 8-20. Terms/Landing Minima Data.

Precision approaches use decision height (DH), which
is referenced to the height above threshold elevation
(HAT). Nonprecision approaches use MDA, referenced
to “feet MSL.” The MDA is also referenced to HAT for
straight-in approaches, or height above airport (HAA) for
circling approaches. On NACG charts, the figures listed
parenthetically are for military operations and are not used
in civil aviation.

in no case may it be reduced to less than 1/4 mile or 1,200
feet RVR.

Visibility figures are provided in statute miles or runway
visual range (RVR), which is reported in hundreds of feet.
RVR is measured by a transmissometer, which represents the
horizontal distance measured at points along the runway. It
is based on the sighting of either high intensity runway lights
or on the visual contrast of other targets, whichever yields
the greater visual range. RVR is horizontal visual range, not
slant visual range, and is used in lieu of prevailing visibility
in determining minimums for a particular runway. It is
illustrated in hundreds of feet if less than a mile (i.e., “24”
is an RVR of 2,400 feet). [Figures 8-19 and 8-20]

Airport Sketch /Airport Diagram
The airport sketch, located on the bottom right side of the
chart, includes many helpful features. IAPs for some of the
larger airports devote an entire page to an airport diagram.
Airport sketch information concerning runway orientation,
lighting, final approach bearings, airport beacon, and
obstacles all serve to guide the pilot in the final phases of
flight. See Figure 8-21 for a legend of airport diagram/airport
sketch features (see also Figure 8-10 for an example of an
airport diagram).

Visibility figures are depicted after the DA/DH or MDA in the
minimums section. If visibility in statute miles is indicated,
an altitude number, hyphen, and a whole or fractional
number appear; for example, 530-1, which indicates “530
feet MSL” and 1 statute mile visibility. This is the descent
minimum for the approach. The RVR value is separated
from the minimum altitude with a slash, such as “1065/24,”
which indicates 1,065 feet MSL and an RVR of 2,400 feet.
If RVR is prescribed for the procedure, but not available, a
conversion table is used to provide the equivalent visibility
in this case, of 1/2 statute mile visibility. [Figure 8-20] The
conversion table is also available in the TPP.
When an alternate airport is required, standard IFR alternate
minimums apply. For aircraft other than helicopters, precision
approach procedures require a 600-feet ceiling and two
statute miles visibility; nonprecision approaches require an
800-feet ceiling and two statute miles visibility. Helicopter
alternate minimums are a ceiling that is 200 feet above the
minimum for the approach to be flown and visibility of at
least one statute mile, but not less than the minimum visibility
for the approach to be flown. When a black triangle with a
white “A” appears in the notes section of the pilot briefing,
it indicates non-standard IFR alternate minimums exist for
the airport. If an “NA” appears after the “A,”
then
alternate minimums are not authorized. This information is
found in the beginning of the TPP.
In addition to the COPTER approaches, instrument-equipped
helicopters may fly standard approach procedures. The
required visibility minimum may be reduced to one-half the
published visibility minimum for category A aircraft, but

Two terms are specific to helicopters. Height above landing
(HAL) means height above a designated helicopter landing
area used for helicopter IAPs. “Point in space approach”
refers to a helicopter IAP to a MAP more than 2,600 feet
from an associated helicopter landing area.

The airport elevation is indicated in a separate box at the
top left of the airport sketch. The touchdown zone elevation
(TDZE), which is the highest elevation within the first 3,000
feet of the runway, is designated at the approach end of the
procedure’s runway.
Beneath the airport sketch is a time and speed table when
applicable. The table provides the distance and the amount
of time required to transit the distance from the FAF to the
MAP for selected groundspeeds.
The approach lighting systems and the visual approach lights
are depicted on the airport sketch. White on black symbols
are used for identifying pilot-controlled lighting (PCL).
Runway lighting aids are also noted (e.g., REIL, HIRL), as
is the runway centerline lighting (RCL). [Figure 8-22]
The airport diagram shows the paved runway configuration
in solid black, while the taxiways and aprons are shaded
gray. Other runway environment features are shown, such
as the runway identification, dimensions, magnetic heading,
displaced threshold, arresting gear, usable length, and slope.
Inoperative Components
Certain procedures can be flown with inoperative components.
According to the Inoperative Components Table, for
example, an ILS approach with a malfunctioning Medium
Intensity Approach Lighting System with Runway Alignment
Indicator Lights (MALSR = MALS with RAIL) can be
flown if the minimum visibility is increased by 1/4 mile.
[Figure 8-23] A note in this section might read, “Inoperative
Table does not apply to ALS or HIRL Runway 13L.”

8-27

8-28

Figure 8-21. Airport Legend and Diagram.

8-29

Figure 8-22. Approach Lighting Legend.

Figure 8-23. IAP Inoperative Components Table.

8-30

8-31

Figure 8-24. RNAV Instrument Approach Charts.

RNAV Instrument Approach Charts
To avoid unnecessary duplication and proliferation of
approach charts, approach minimums for unaugmented
GPS, Wide Area Augmentation System (WAAS), Local
Area Augmentation System (LAAS), will be published
on the same approach chart as lateral navigation/vertical
navigation (LNAV/VNAV). Other types of equipment may
be authorized to conduct the approach based on the minima
notes in the front of the TPP approach chart books. Approach
charts titled “RNAV RWY XX” may be used by aircraft
with navigation systems that meet the required navigational
performance (RNP) values for each segment of the approach.
[Figure 8-24]
The chart may contain as many as four lines of approach
minimums: global landing system (GLS), WAAS and LAAS,
LNAV/VNAV, LNAV, and circling. LNAV/VNAV is an
instrument approach with lateral and vertical guidance with
integrity limits similar to barometric vertical navigation
(BARO VNAV).
RNAV procedures that incorporate a final approach stepdown
fix may be published without vertical navigation on a separate
chart also titled RNAV. During a transition period when GPS
procedures are undergoing revision to a new title, both RNAV
and GPS approach charts and formats will be published. ATC
clearance for the RNAV procedure will authorize a properly
certificated pilot to utilize any landing minimums for which
the aircraft is certified.
Chart terminology will change slightly to support the new
procedure types:
1.

8-32

DA replaces the term DH. DA conforms to the
international convention where altitudes relate to
MSL and heights relate to AGL. DA will eventually
be published for other types of IAPs with vertical
guidance, as well. DA indicates to the pilot that the
published descent profile is flown to the DA (MSL),
where a missed approach will be initiated if visual
references for landing are not established. Obstacle
clearance is provided to allow a momentary descent
below DA while transitioning from the final approach to
the missed approach. The aircraft is expected to follow
the missed approach instructions while continuing
along the published final approach course to at least
the published runway threshold waypoint or MAP (if
not at the threshold) before executing any turns.

2.

MDA will continue to be used only for the LNAV and
circling procedures.

3.

Threshold crossing height (TCH) has been traditionally
used in precision approaches as the height of the GS
above threshold. With publication of LNAV/VNAV
minimums and RNAV descent angles, including
graphically depicted descent profiles, TCH also
applies to the height of the “descent angle,” or glide
path, at the threshold. Unless otherwise required for
larger type aircraft, which may be using the IAP, the
typical TCH will be 30 to 50 feet.

The minima format changes slightly:
1.

Each line of minima on the RNAV IAP will be titled
to reflect the RNAV system applicable (e.g., GLS,
LNAV/VNAV, and LNAV). Circling minima will
also be provided.

2.

The minima title box will also indicate the nature of
the minimum altitude for the IAP. For example: DA
will be published next to the minima line title for
minimums supporting vertical guidance, and MDA
will be published where the minima line supports only
lateral guidance. During an approach where an MDA
is used, descent below MDA is not authorized.

3.

Where two or more systems share the same minima,
each line of minima will be displayed separately.

For more information concerning government charts, the
NACG can be contacted by telephone, or via their internet
address at:
National Aeronautical Charting Group
Telephone 800-626-3677
http://naco.faa.gov/

Chapter 9

The Air Traffic
Control System
Introduction
This chapter covers the communication equipment,
communication procedures, and air traffic control (ATC)
facilities and services available for a flight under instrument
flight rules (IFR) in the National Airspace System (NAS).

9-1

Communication Equipment
Navigation/Communication (NAV/COM)
Equipment
Civilian pilots communicate with ATC on frequencies in
the very high frequency (VHF) range between 118.000 and
136.975 MHz. To derive full benefit from the ATC system,
radios capable of 25 kHz spacing are required (e.g., 134.500,
134.575, 134.600). If ATC assigns a frequency that cannot
be selected, ask for an alternative frequency.
Figure 9-1 illustrates a typical radio panel installation,
consisting of a communications transceiver on the left and a
navigational receiver on the right. Many radios allow the pilot
to have one or more frequencies stored in memory and one
frequency active for transmitting and receiving (called simplex

Figure 9-1. Typical NAV/COM Installation.

Figure 9-2. Audio Panel.

9-2

operation). It is possible to communicate with some automated
flight service stations (AFSS) by transmitting on 122.1 MHz
(selected on the communication radio) and receiving on a
VHF omnidirectional range (VOR) frequency (selected on
the navigation radio). This is called duplex operation.
An audio panel allows a pilot to adjust the volume of the
selected receiver(s) and to select the desired transmitter.
[Figure 9-2] The audio panel has two positions for receiver
selection, cabin speaker, and headphone (some units might
have a center “off” position). Use of a hand-held microphone
and the cabin speaker introduces the distraction of reaching
for and hanging up the microphone. A headset with a boom
microphone is recommended for clear communications. The
microphone should be positioned close to the lips to reduce

Figure 9-4. Combination GPS-Com Unit.

select the appropriate communications frequency for that
location in the communications radio.
Radar and Transponders
ATC radars have a limited ability to display primary returns,
which is energy reflected from an aircraft’s metallic structure.
Their ability to display secondary returns (transponder replies
to ground interrogation signals) makes possible the many
advantages of automation.

Figure 9-3. Boom Microphone, Headset, and Push-To-Talk

Switch.

the possibility of ambient flight deck noise interfering with
transmissions to the controller. Headphones deliver the
received signal directly to the ears; therefore, ambient noise
does not interfere with the pilot’s ability to understand the
transmission. [Figure 9-3]
Switching the transmitter selector between COM1 and
COM2 changes both transmitter and receiver frequencies.
It is necessary only when a pilot wants to monitor one
frequency while transmitting on another. One example is
listening to automatic terminal information service (ATIS)
on one receiver while communicating with ATC on the
other. Monitoring a navigation receiver to check for proper
identification is another reason to use the switch panel.
Most audio switch panels also include a marker beacon
receiver. All marker beacons transmit on 75 MHz, so there
is no frequency selector.
Figure 9-4 illustrates an increasingly popular form of
NAV/COM radio; it contains a global positioning system
(GPS) receiver and a communications transceiver. Using its
navigational capability, this unit can determine when a flight
crosses an airspace boundary or fix and can automatically

A transponder is a radar beacon transmitter/receiver installed
in the instrument panel. ATC beacon transmitters send out
interrogation signals continuously as the radar antenna
rotates. When an interrogation is received by a transponder, a
coded reply is sent to the ground station where it is displayed
on the controller’s scope. A reply light on the transponder
panel flickers every time it receives and replies to a radar
interrogation. Transponder codes are assigned by ATC.
When a controller asks a pilot to “ident” and the ident button
is pushed, the return on the controller’s scope is intensified for
precise identification of a flight. When requested, briefly push
the ident button to activate this feature. It is good practice
for pilots to verbally confirm that they have changed codes
or pushed the ident button.

Mode C (Altitude Reporting)
Primary radar returns indicate only range and bearing from
the radar antenna to the target; secondary radar returns can
display altitude, Mode C, on the control scope if the aircraft
is equipped with an encoding altimeter or blind encoder. In
either case, when the transponder’s function switch is in the
ALT position the aircraft’s pressure altitude is sent to the
controller. Adjusting the altimeter’s Kollsman window has
no effect on the altitude read by the controller.
Transponders, when installed, must be ON at all times when
operating in controlled airspace; altitude reporting is required
by regulation in Class B and Class C airspace and inside a
30-mile circle surrounding the primary airport in Class B
airspace. Altitude reporting should also be ON at all times.

9-3

Communication Procedures
Clarity in communication is essential for a safe instrument
flight. This requires pilots and controllers to use terms that
are understood by both—the Pilot/Controller Glossary in the
Aeronautical Information Manual (AIM) is the best source of
terms and definitions. The AIM is revised twice a year and
new definitions are added, so the glossary should be reviewed
frequently. Because clearances and instructions are comprised
largely of letters and numbers, a phonetic pronunciation guide
has been developed for both. [Figure 9-5]

ground communication outlets (GCOs), and by using duplex
transmissions through navigational aids (NAVAIDs). The
best source of information on frequency usage is the Airport/
Facility Directory (A/FD) and the legend panel on sectional
charts also contains contact information.

ATCs must follow the guidance of the Air Traffic Control
Manual when communicating with pilots. The manual
presents the controller with different situations and prescribes
precise terminology that must be used. This is advantageous
for pilots because once they have recognized a pattern
or format they can expect future controller transmissions
to follow that format. Controllers are faced with a wide
variety of communication styles based on pilot experience,
proficiency, and professionalism.
Pilots should study the examples in the AIM, listen to
other pilots communicate, and apply the lessons learned
to their own communications with ATC. Pilots should ask
for clarification of a clearance or instruction. If necessary,
use plain English to ensure understanding, and expect the
controller to reply in the same way. A safe instrument flight
is the result of cooperation between controller and pilot.

Communication Facilities
The controller’s primary responsibility is separation of
aircraft operating under IFR. This is accomplished with ATC
facilities which include the AFSS, airport traffic control tower
(ATCT), terminal radar approach control (TRACON), and
air route traffic control center (ARTCC).
Automated Flight Service Stations (AFSS)
A pilot’s first contact with ATC is usually through AFSS,
either by radio or telephone. AFSSs provide pilot briefings,
receive and process flight plans, relay ATC clearances,
originate Notices to Airmen (NOTAMs), and broadcast
aviation weather. Some facilities provide En Route Flight
Advisory Service (EFAS), take weather observations,
and advise United States Customs and Immigration of
international flights.
Telephone contact with Flight Service can be obtained
by dialing 1-800-WX-BRIEF. This number can be used
anywhere in the United States and connects to the nearest
AFSS based on the area code from which the call originates.
There are a variety of methods of making radio contact:
direct transmission, remote communication outlets (RCOs),

9-4

Figure 9-5. Phonetic Pronunciation Guide.

The briefer sends a flight plan to the host computer at
the ARTCC (Center). After processing the flight plan,
the computer will send flight strips to the tower, to the
radar facility that will handle the departure route, and to
the Center controller whose sector the flight first enters.
Figure 9-6 shows a typical strip. These strips are delivered
approximately 30 minutes prior to the proposed departure
time. Strips are delivered to en route facilities 30 minutes
before the flight is expected to enter their airspace. If a
flight plan is not opened, it will “time out” 2 hours after the
proposed departure time.
When departing an airport in Class G airspace, a pilot receives
an IFR clearance from the AFSS by radio or telephone. It
contains either a clearance void time, in which case an aircraft
must be airborne prior to that time, or a release time. Pilots
should not take-off prior to the release time. Pilots can help
the controller by stating how soon they expect to be airborne.
If the void time is, for example, 10 minutes past the hour and
an aircraft is airborne at exactly 10 minutes past the hour,
the clearance is void—a pilot must take off prior to the void
time. A specific void time may be requested when filing a
flight plan.
ATC Towers
Several controllers in the tower cab are involved in handling
an instrument flight. Where there is a dedicated clearance
delivery position, that frequency is found in the A/FD and
on the instrument approach chart for the departure airport.
Where there is no clearance delivery position, the ground
controller performs this function. At the busiest airports, pretaxi clearance is required; the frequency for pre-taxi clearance
can be found in the A/FD. Taxi clearance should be requested
not more than 10 minutes before proposed taxi time.
It is recommended that pilots read their IFR clearance back to
the clearance delivery controller. Instrument clearances can
be overwhelming when attempting to copy them verbatim,
but they follow a format that allows a pilot to be prepared
when responding “Ready to copy.” The format is: clearance
limit (usually the destination airport); route, including any

departure procedure; initial altitude; frequency (for departure
control); and transponder code. With the exception of the
transponder code, a pilot knows most of these items before
engine start. One technique for clearance copying is writing
C-R-A-F-T.
Assume an IFR flight plan has been filed from Seattle,
Washington to Sacramento, California via V-23 at 7,000
feet. Traffic is taking off to the north from Seattle-Tacoma
(Sea-Tac) airport and, by monitoring the clearance delivery
frequency, a pilot can determine the departure procedure
being assigned to southbound flights. The clearance limit
is the destination airport, so write “SAC” after the letter C.
Write “SEATTLE TWO – V23” after R for Route, because
departure control issued this departure to other flights. Write
“7” after the A, the departure control frequency printed on
the approach charts for Sea-Tac after F, and leave the space
after the letter T blank—the transponder code is generated by
computer and can seldom be determined in advance. Then,
call clearance delivery and report “Ready to copy.”
As the controller reads the clearance, check it against what
is already written down; if there is a change, draw a line
through that item and write in the changed item. Chances
are the changes are minimal, and most of the clearance is
copied before keying the microphone. Still, it is worthwhile
to develop clearance shorthand to decrease the verbiage that
must be copied (see Appendix 1).
Pilots are required to have either the text of a departure
procedure (DP) or a graphic representation (if one is
available), and should review it before accepting a clearance.
This is another reason to find out ahead of time which DP is
in use. If the DP includes an altitude or a departure control
frequency, those items are not included in the clearance.
The last clearance received supersedes all previous clearances.
For example, if the DP says “Climb and maintain 2,000 feet,
expect higher in 6 miles,” but upon contacting the departure
controller a new clearance is received: “Climb and maintain
8,000 feet,” the 2,000 feet restriction has been canceled. This
rule applies in both terminal and Center airspace.

Figure 9-6. Flight Strip.

9-5

When reporting ready to copy an IFR clearance before the
strip has been received from the Center computer, pilots
are advised “clearance on request.” The controller initiates
contact when it has been received. This time can be used for
taxi and pre-takeoff checks.
The local controller is responsible for operations in the Class
D airspace and on the active runways. At some towers,
designated as IFR towers, the local controller has vectoring
authority. At visual flight rules (VFR) towers, the local
controller accepts inbound IFR flights from the terminal radar
facility and cannot provide vectors. The local controller also
coordinates flights in the local area with radar controllers.
Although Class D airspace normally extends 2,500 feet above
field elevation, towers frequently release the top 500 feet to
the radar controllers to facilitate overflights. Accordingly,
when a flight is vectored over an airport at an altitude that
appears to enter the tower controller’s airspace, there is no
need to contact the tower controller—all coordination is
handled by ATC.
The departure radar controller may be in the same building
as the control tower, but it is more likely that the departure
radar position is remotely located. The tower controller will
not issue a takeoff clearance until the departure controller
issues a release.
Terminal Radar Approach Control (TRACON)
TRACONs are considered terminal facilities because they
provide the link between the departure airport and the en route
structure of the NAS. Terminal airspace normally extends 30
nautical miles (NM) from the facility, with a vertical extent

Figure 9-7. Combined Radar and Beacon Antenna.

9-6

of 10,000 feet; however, dimensions vary widely. Class B
and Class C airspace dimensions are provided on aeronautical
charts. At terminal radar facilities the airspace is divided
into sectors, each with one or more controllers, and each
sector is assigned a discrete radio frequency. All terminal
facilities are approach controls and should be addressed
as “Approach” except when directed to do otherwise (e.g.,
“Contact departure on 120.4”).
Terminal radar antennas are located on or adjacent to the
airport. Figure 9-7 shows a typical configuration. Terminal
controllers can assign altitudes lower than published
procedural altitudes called minimum vectoring altitudes
(MVAs). These altitudes are not published or accessible to
pilots, but are displayed at the controller’s position, as shown
in Figure 9-8. However, when pilots are assigned an altitude
that seems to be too low, they should query the controller
before descending.
When a pilot accepts a clearance and reports ready for takeoff,
a controller in the tower contacts the TRACON for a release.
An aircraft is not cleared for takeoff until the departure
controller can fit the flight into the departure flow. A pilot may
have to hold for release. When takeoff clearance is received,
the departure controller is aware of the flight and is waiting
for a call. All of the information the controller needs is on
the departure strip or the computer screen there is no need to
repeat any portion of the clearance to that controller. Simply
establish contact with the facility when instructed to do so by
the tower controller. The terminal facility computer picks up
the transponder and initiates tracking as soon as it detects the

Figure 9-8. Minimum Vectoring Altitude Chart.

assigned code. For this reason, the transponder should remain
on standby until takeoff clearance has been received.
The aircraft appears on the controller’s radar display as a
target with an associated data block that moves as the aircraft
moves through the airspace. The data block includes aircraft
identification, aircraft type, altitude, and airspeed.
A TRACON controller uses Airport Surveillance Radar
(ASR) to detect primary targets and Automated Radar
Terminal Systems (ARTS) to receive transponder signals; the
two are combined on the controller’s scope. [Figure 9-9]
At facilities with ASR-3 equipment, radar returns from
precipitation are not displayed as varying levels of intensity,
and controllers must rely on pilot reports and experience
to provide weather avoidance information. With ASR-9
equipment, the controller can select up to six levels of
intensity. Light precipitation does not require avoidance
tactics but precipitation levels of moderate, heavy or
extreme should cause pilots to plan accordingly. Along
with precipitation the pilot must additionally consider the
temperature, which if between -20° and +5° C will cause icing
even during light precipitation. The returns from higher levels
of intensity may obscure aircraft data blocks, and controllers
may select the higher levels only on pilot request. When
uncertainty exists about the weather ahead, ask the controller
if the facility can display intensity levels—pilots of small
aircraft should avoid intensity levels 3 or higher.
Tower En Route Control (TEC)
At many locations, instrument flights can be conducted
entirely in terminal airspace. These TEC routes are generally
for aircraft operating below 10,000 feet, and they can be
found in the A/FD. Pilots desiring to use TEC should include
that designation in the remarks section of the flight plan.
Pilots are not limited to the major airports at the city pairs
listed in the A/FD. For example, a tower en route flight from
an airport in New York (NYC) airspace could terminate
at any airport within approximately 30 miles of Bradley
International (BDL) airspace, such as Hartford (HFD).
[Figure 9-10]
A valuable service provided by the automated radar
equipment at terminal radar facilities is the Minimum Safe
Altitude Warnings (MSAW). This equipment predicts an
aircraft’s position in 2 minutes based on present path of
flight—the controller issues a safety alert if the projected
path encounters terrain or an obstruction. An unusually
rapid descent rate on a nonprecision approach can trigger
such an alert.

Air Route Traffic Control Center (ARTCC)
ARTCC facilities are responsible for maintaining separation
between IFR flights in the en route structure. Center radars
(Air Route Surveillance Radar (ARSR)) acquire and track
transponder returns using the same basic technology as
terminal radars. [Figure 9-11]
Earlier Center radars display weather as an area of slashes
(light precipitation) and Hs (moderate rainfall), as illustrated
in Figure 9-12. Because the controller cannot detect higher
levels of precipitation, pilots should be wary of areas showing
moderate rainfall. Newer radar displays show weather as
three levels of blue. Controllers can select the level of weather
to be displayed. Weather displays of higher levels of intensity
can make it difficult for controllers to see aircraft data blocks,
so pilots should not expect ATC to keep weather displayed
continuously.
Center airspace is divided into sectors in the same manner
as terminal airspace; additionally, most Center airspace is
divided by altitudes into high and low sectors. Each sector
has a dedicated team of controllers and a selection of radio
frequencies, because each Center has a network of remote
transmitter/receiver sites. All Center frequencies can be found
in the back of the A/FD in the format shown in Figure 9-13;
they are also found on en route charts.
Each ARTCC’s area of responsibility covers several states;
when flying from the vicinity of one remote communication
site toward another, expect to hear the same controller on
different frequencies.
Center Approach/Departure Control
The majority of airports with instrument approaches do not
lie within terminal radar airspace, and when operating to
or from these airports pilots communicate directly with the
Center controller. Departing from a tower-controlled airport,
the tower controller provides instructions for contacting the
appropriate Center controller. When departing an airport
without an operating control tower, the clearance includes
instructions such as “Upon entering controlled airspace,
contact Houston Center on 126.5.” Pilots are responsible
for terrain clearance until reaching the controller’s MVA.
Simply hearing “Radar contact” does not relieve a pilot of
this responsibility.
If obstacles in the departure path require a steeper-thanstandard climb gradient (200 FPNM), then the controller
advises the pilot. However, it is the pilot’s responsibility to
check the departure airport listing in the A/FD to determine if
there are trees or wires in the departure path. When in doubt,
ask the controller for the required climb gradient.

9-7

Figure 9-9. The top image is a display as seen by controllers in an Air Traffic Facility. The one illustrated is an ARTS III (Automated

Radar Terminal System). The display shown provides an explanation of the symbols in the graphic. The lower figure is an example of
the Digital Bright Radar Indicator Tower Equipment (DBRITE) screen as seen by tower personnel. It provides tower controllers with
a visual display of the airport surveillance radar, beacon signals, and data received from ARTS III. The display shown provides an
explanation of the symbols in the graphic.

9-8

Figure 9-10. A Portion of the New York Area Tower En Route List. (From the A/FD)

9-9

Figure 9-11. Center Radar Displays.

Figure 9-12. A Center Controller’s Scope.

A common clearance in these situations is “When able,
proceed direct to the Astoria VOR…” The words “when able”
mean to proceed to the waypoint, intersection, or NAVAID
when the pilot is able to navigate directly to that point using
onboard available systems providing proper guidance, usable
signal, etc. If provided such guidance while flying VFR, the
pilot remains responsible for terrain and obstacle clearance.
Using the standard climb gradient, an aircraft is 2 miles
from the departure end of the runway before it is safe to
turn (400 feet above ground level (AGL)). When a Center
controller issues a heading, a direct route, or says “direct
when able,” the controller becomes responsible for terrain
and obstruction clearance.
Another common Center clearance is “Leaving (altitude)
fly (heading) or proceed direct when able.” This keeps the
terrain/obstruction clearance responsibility in the flight deck
until above the minimum IFR altitude. A controller cannot
issue an IFR clearance until an aircraft is above the minimum
IFR altitude unless it is able to climb in VFR conditions.
On a Center controller’s scope, 1 NM is about 1/28 of an inch.
When a Center controller is providing Approach/Departure
control services at an airport many miles from the radar
antenna, estimating headings and distances is very difficult.
Controllers providing vectors to final must set the range on
their scopes to not more than 125 NM to provide the greatest
possible accuracy for intercept headings. Accordingly, at
locations more distant from a Center radar antenna, pilots
should expect a minimum of vectoring.

Figure 9-13. Center Symbology.

9-10

ATC Inflight Weather Avoidance
Assistance
ATC Radar Weather Displays
ATC radar systems are able to display areas of precipitation
by sending out a beam of radio energy that is reflected back to
the radar antenna when it strikes an object or moisture which
may be in the form of rain drops, hail, or snow. The larger
the object, or the denser its reflective surface, the stronger the
return will be. Radar weather processors indicate the intensity
of reflective returns in terms of decibels with respect to the
radar reflectively factor (dBZ).
ATC systems cannot detect the presence or absence of
clouds. ATC radar systems can often determine the intensity
of a precipitation area, but the specific character of that area
(snow, rain, hail, VIRGA, etc.) cannot be determined. For
this reason, ATC refers to all weather areas displayed on
ATC radar scopes as “precipitation.”
All ATC facilities using radar weather processors with the
ability to determine precipitation intensity describes the
intensity to pilots as:
1. “LIGHT”

(< 30 dBZ)

2. “MODERATE”

(30 to 40 dBZ)

3. “HEAVY”

(>40 to 50 dBZ)

4. “EXTREME”

(>50 dBZ)

ARTCC controllers do not use the term “LIGHT” because
their systems do not display “LIGHT” precipitation
intensities. ATC facilities that, due to equipment limitations,
cannot display the intensity levels of precipitation, will
describe the location of the precipitation area by geographic
position, or position relative to the aircraft. Since the intensity
level is not available, the controller states, “INTENSITY
UNKNOWN.”
ARTCC facilities normally use a Weather and Radar
Processor (WARP) to display a mosaic of data obtained from
multiple NEXRAD sites. The WARP processor is only used
in ARTCC facilities.
There is a time delay between actual conditions and those
displayed to the controller. For example, the precipitation
data on the ARTCC controller’s display could be up to 6
minutes old. When the WARP is not available, a secondary
system, the narrowband ARSR is utilized. The ARSR system
can display two distinct levels of precipitation intensity that
is described to pilots as “MODERATE” (30 to 40 dBZ) and
“HEAVY to EXTREME” (>40 dBZ).

ATC radar systems cannot detect turbulence. Generally,
turbulence can be expected to occur as the rate of rainfall or
intensity of precipitation increases. Turbulence associated
with greater rates of rainfall/precipitation is normally more
severe than any associated with lesser rates of rainfall/
precipitation. Turbulence should be expected to occur near
convective activity, even in clear air. Thunderstorms are a
form of convective activity that implies severe or greater
turbulence. Operation within 20 miles of thunderstorms
should be approached with great caution, as the severity of
turbulence can be markedly greater than the precipitation
intensity might indicate.
Weather Avoidance Assistance
ATC’s first duty priority is to separate aircraft and issue
safety alerts. ATC provides additional services to the extent
possible, contingent upon higher priority duties and other
factors including limitations of radar, volume of traffic,
frequency congestion, and workload. Subject to the above
factors/limitations, controllers issue pertinent information
on weather or chaff areas; and if requested, assist pilots, to
the extent possible, in avoiding areas of precipitation. Pilots
should respond to a weather advisory by acknowledging the
advisory and, if desired, requesting an alternate course of
action, such as:
1.

Request to deviate off course by stating the direction
and number of degrees or miles needed to deviate from
the original course;

2.

Request a change of altitude; or

3.

Request routing assistance to avoid the affected
area. Because ATC radar systems cannot detect the
presence or absence of clouds and turbulence, such
assistance conveys no guarantee that the pilot will not
encounter hazards associated with convective activity.
Pilots wishing to circumnavigate precipitation areas
by a specific distance should make their desires
clearly known to ATC at the time of the request for
services. Pilots must advise ATC when they can
resume normal navigation.

IFR pilots shall not deviate from their assigned course or
altitude without an ATC clearance. Plan ahead for possible
course deviations because hazardous convective conditions
can develop quite rapidly. This is important to consider
because the precipitation data displayed on ARTCC radar
scopes can be up to 6 minutes old and thunderstorms can
develop at rates exceeding 6,000 feet per minute (fpm). When
encountering weather conditions that threaten the safety of
the aircraft, the pilot may exercise emergency authority as

9-11

stated in 14 CFR part 91, section 91.3 should an immediate
deviation from the assigned clearance be necessary and time
does not permit approval by ATC.
Generally, when weather disrupts the flow of air traffic,
greater workload demands are placed on the controller.
Requests for deviations from course and other services
should be made as far in advance as possible to better assure
the controller’s ability to approve these requests promptly.
When requesting approval to detour around weather activity,
include the following information to facilitate the request:
1.

The proposed point where detour commences;

2.

The proposed route and extent of detour (direction
and distance);

3.

The point where original route will be resumed;

4.

Flight conditions (IMC or VMC);

5.

Whether the aircraft is equipped with functioning
airborne radar; and

6.

Any further deviation that may become necessary.

Approach Control Facility
An approach control facility is a terminal ATC facility
that provides approach control service in the terminal area.
Services are provided for arriving and departing VFR and
IFR aircraft and, on occasion, en route aircraft. In addition,
for airports with parallel runways with ILS or LDA
approaches, the approach control facility provides monitoring
of the approaches.

Approach Control Advances
Precision Runway Monitor (PRM)
Over the past few years, a new technology has been installed
at airports that permits a decreased separation distance
between parallel runways. The system is called a Precision
Runway Monitor (PRM) and is comprised of high-update
radar, high-resolution ATC displays, and PRM-certified
controllers. [Figure 9-14]

To a large degree, the assistance that might be rendered
by ATC depends upon the weather information available
to controllers. Due to the extremely transitory nature of
hazardous weather, the controller’s displayed precipitation
information may be of limited value.
Obtaining IFR clearance or approval to circumnavigate
hazardous weather can often be accommodated more readily
in the en route areas away from terminals because there
is usually less congestion and, therefore, greater freedom
of action. In terminal areas, the problem is more acute
because of traffic density, ATC coordination requirements,
complex departure and arrival routes, and adjacent airports.
As a consequence, controllers are less likely to be able to
accommodate all requests for weather detours in a terminal
area. Nevertheless, pilots should not hesitate to advise
controllers of any observed hazardous weather and should
specifically advise controllers if they desire circumnavigation
of observed weather.
Pilot reports (PIREPs) of flight conditions help define the
nature and extent of weather conditions in a particular area.
These reports are disseminated by radio and electronic means
to other pilots. Provide PIREP information to ATC regarding
pertinent flight conditions, such as:
1.

Turbulence;

2.

Visibility;

3.

Cloud tops and bases; and

4.

The presence of hazards such as ice, hail, and
lightning.

9-12

Figure 9-14. High Resolution ATC Displays Used in PRM.

Precision Runway Monitor (PRM) Radar
The PRM uses a Monopulse Secondary Surveillance Radar
(MSSR) that employs electronically scanned antennas.
Because the PRM has no scan rate restrictions, it is capable
of providing a faster update rate (up to 0.5 second) over
conventional systems, thereby providing better target
presentation in terms of accuracy, resolution, and track
prediction. The system is designed to search, track, process,
and display SSR-equipped aircraft within airspace of over
30 miles in range and over 15,000 feet in elevation. Visual
and audible alerts are generated to warn controllers to take
corrective actions.

Figure 9-15. Aircraft Management Using PRM. (Note the no transgression zone (NTZ) and how the aircraft are separated.)

PRM Benefits
Typically, PRM is used with dual approaches with centerlines
separated less than 4,300 feet but not less than 3,000 feet
(under most conditions). [Figure 9-15] Separating the two
final approach courses is a No Transgression Zone (NTZ)
with surveillance of that zone provided by two controllers,
one for each active approach. The system tracking software
provides PRM monitor controllers with aircraft identification,
position, speed, projected position, as well as visual and
aural alerts.

Control Sequence
The IFR system is flexible and accommodating if pilots do
their homework, have as many frequencies as possible written
down before they are needed, and have an alternate in mind
if the flight cannot be completed as planned. Pilots should
familiarize themselves with all the facilities and services
available along the planned route of flight. [Figure 9-16]
Always know where the nearest VFR conditions can be
found, and be prepared to head in that direction if the situation
deteriorates.

A typical IFR flight, with departure and arrival at airports
with control towers, would use the ATC facilities and services
in the following sequence:
1.

AFSS: Obtain a weather briefing for a departure,
destination and alternate airports, and en route
conditions, and then file a flight plan by calling
1-800-WX-BRIEF.

2.

ATIS: Preflight complete, listen for present conditions
and the approach in use.

3.

Clearance Delivery: Prior to taxiing, obtain a departure
clearance.

4.

Ground Control: Noting that the flight is IFR, receive
taxi instructions.

5.

Tower: Pre-takeoff checks complete, receive clearance
to takeoff.

6.

Departure Control: Once the transponder “tags up”
with the ARTS, the tower controller instructs the pilot
to contact Departure to establish radar contact.
9-13

7.

ARTCC: After departing the departure controller’s
airspace, aircraft is handed off to Center, who
coordinates the flight while en route. Pilots may
be in contact with multiple ARTCC facilities; they
coordinate the hand-offs.

8.

EFAS/HIWAS: Coordinate with ATC before
leaving their frequency to obtain inflight weather
information.

9.

ATIS: Coordinate with ATC before leaving their
frequency to obtain ATIS information.

10. Approach Control: Center hands off to approach
control where pilots receive additional information
and clearances.
11. Tower: Once cleared for the approach, pilots are
instructed to contact tower control; the flight plan is
canceled by the tower controller upon landing.
A typical IFR flight, with departure and arrival at airports
without operating control towers, would use the ATC
facilities and services in the following sequence:
1.

AFSS: Obtain a weather briefing for departure,
destination, and alternate airports, and en route
conditions, and then file a flight plan by calling
1-800-WX-BRIEF. Provide the latitude/longitude
description for small airports to ensure that Center is
able to locate departure and arrival locations.

2.

AFSS or UNICOM: ATC clearances can be filed and
received on the UNICOM frequency if the licensee
has made arrangements with the controlling ARTCC;
otherwise, file with AFSS via telephone. Be sure all
preflight preparations are complete before filing. The
clearance includes a clearance void time. Pilots must
be airborne prior to the void time.

9-14

3.

ARTCC: After takeoff, establish contact with Center.
During the flight, pilots may be in contact with
multiple ARTCC facilities; ATC coordinates the handoffs.

4.

EFAS/HIWAS: Coordinate with ATC before
leaving their frequency to obtain in-flight weather
information.

5.

Approach Control: Center hands off to approach
control where pilots receive additional information and
clearances. If a landing under visual meteorological
conditions (VMC) is possible, pilots may cancel their
IFR clearance before landing.

Letters of Agreement (LOA)
The ATC system is indeed a system, and very little happens
by chance. As a flight progresses, controllers in adjoining
sectors or adjoining Centers coordinate its handling by
telephone or by computer. Where there is a boundary between
the airspace controlled by different facilities, the location and
altitude for hand-off is determined by Letters of Agreement
(LOA) negotiated between the two facility managers. This
information is not available to pilots in any Federal Aviation
Administration (FAA) publication. For this reason, it is good
practice to note on the en route chart the points at which handoffs occur. Each time a flight is handed-off to a different
facility, the controller knows the altitude and location—this
was part of the hand-off procedure.

Figure 9-16. ATC Facilities, Services, and Radio Call Signs.

9-15

9-16

Chapter 10

IFR Flight
Introduction
This chapter is a discussion of conducting a flight under
instrument flight rules (IFR). It also explains the sources for
flight planning, the conditions associated with instrument
flight, and the procedures used for each phase of IFR flight:
departure, en route, and approach. The chapter concludes
with an example of an IFR flight which applies many of the
procedures discussed in the chapter.

10-1

Sources of Flight Planning Information
The following resources are available for a pilot planning a
flight conducted under instrument flight rules (IFR).
National Aeronautical Charting Group (NACG)
publications:
•

IFR en route charts

•

area charts

•

United States (U.S.) Terminal Procedures Publications
(TPP)

Notices to Airmen Publication (NTAP)
The NTAP is a publication containing current Notices to
Airmen (NOTAMs) which are essential to the safety of flight,
as well as supplemental data affecting the other operational
publications listed. It also includes current Flight Data Center
(FDC) NOTAMs, which are regulatory in nature, issued to
establish restrictions to flight or to amend charts or published
instrument approach procedures (IAPs).

•

AIM

•

Airport/Facility Directory (A/FD)

POH/AFM
The POH/AFM contain operating limitations, performance,
normal and emergency procedures, and a variety of other
operational information for the respective aircraft. Aircraft
manufacturers have done considerable testing to gather and
substantiate the information in the aircraft manual. Pilots should
refer to it for information relevant to a proposed flight.

•

Notices to Airmen Publication (NTAP) for flight
planning in the National Airspace System (NAS)

IFR Flight Plan

The Federal Aviation Administration (FAA) publications:

Pilots should also consult the Pilot’s Operating Handbook/
Airplane Flight Manual (POH/AFM) for flight planning
information pertinent to the aircraft to be flown.
A review of the contents of all the listed publications will help
determine which material should be referenced for each flight.
As a pilot becomes more familiar with these publications, the
flight planning process becomes quicker and easier.
Aeronautical Information Manual (AIM)
The AIM provides the aviation community with basic
flight information and air traffic control (ATC) procedures
used in the United States NAS. An international version
called the Aeronautical Information Publication contains
parallel information, as well as specific information on the
international airports used by the international community.
Airport/Facility Directory (A/FD)
The A/FD contains information on airports, communications,
and navigation aids pertinent to IFR flight. It also includes
very-high frequency omnidirectional range (VOR) receiver
checkpoints, automated flight service station (AFSS), weather
service telephone numbers, and air route traffic control center
(ARTCC) frequencies. Various special notices essential
to flight are also included, such as land-and-hold-short
operations (LAHSO) data, the civil use of military fields,
continuous power facilities, and special flight procedures.
In the major terminal and en route environments, preferred
routes have been established to guide pilots in planning their
routes of flight, to minimize route changes, and to aid in the
orderly management of air traffic using the federal airways.
The A/FD lists both high and low altitude preferred routes.

10-2

As specified in Title 14 of the Code of Federal Regulations
(14 CFR) part 91, no person may operate an aircraft in
controlled airspace under IFR unless that person has filed an
IFR flight plan. Flight plans may be submitted to the nearest
AFSS or air traffic control tower (ATCT) either in person,
by telephone (1-800-WX-BRIEF), by computer (using the
direct user access terminal system (DUATS)), or by radio
if no other means are available. Pilots should file IFR flight
plans at least 30 minutes prior to estimated time of departure
to preclude possible delay in receiving a departure clearance
from ATC. The AIM provides guidance for completing
and filing FAA Form 7233-1, Flight Plan. These forms are
available at flight service stations (FSSs), and are generally
found in flight planning rooms at airport terminal buildings.
[Figure 10-1]
Filing in Flight
IFR flight plans may be filed from the air under various
conditions, including:
1.

A flight outside controlled airspace before proceeding
into IFR conditions in controlled airspace.

2.

A VFR flight expecting IFR weather conditions en
route in controlled airspace.

In either of these situations, the flight plan may be filed with
the nearest AFSS or directly with the ARTCC. A pilot who
files with the AFSS submits the information normally entered
during preflight filing, except for “point of departure,”
together with present position and altitude. AFSS then
relays this information to the ARTCC. The ARTCC will
then clear the pilot from present position or from a specified
navigation fix.

A pilot who files directly with the ARTCC reports present
position and altitude, and submits only the flight plan
information normally relayed from the AFSS to the ARTCC.
Be aware that traffic saturation frequently prevents ARTCC
personnel from accepting flight plans by radio. In such
cases, a pilot is advised to contact the nearest AFSS to file
the flight plan.
Cancelling IFR Flight Plans
An IFR flight plan may be cancelled any time a pilot is
operating in VFR conditions outside Class A airspace by
stating “cancel my IFR flight plan” to the controller or air-toground station. After cancelling an IFR flight plan, the pilot
should change to the appropriate air-to-ground frequency,
transponder code as directed, and VFR altitude/flight level.
ATC separation and information services (including radar
services, where applicable) are discontinued when an IFR
flight plan is cancelled. If VFR radar advisory service is
desired, a pilot must specifically request it. Be aware that
other procedures may apply when cancelling an IFR flight
plan within areas such as Class C or Class B airspace.
When operating on an IFR flight plan to an airport with
an operating control tower, a flight plan is cancelled

automatically upon landing. If operating on an IFR flight
plan to an airport without an operating control tower, the
pilot is responsible for cancelling the flight plan. This can
be done by telephone after landing if there is no operating
FSS or other means of direct communications with ATC.
When there is no FSS or air-to-ground communications are
not possible below a certain altitude, a pilot may cancel an
IFR flight plan while still airborne and able to communicate
with ATC by radio. If using this procedure, be certain the
remainder of the flight can be conducted under VFR. It is
essential that IFR flight plans be cancelled expeditiously. This
allows other IFR traffic to utilize the airspace.

Clearances
An ATC clearance allows an aircraft to proceed under
specified traffic conditions within controlled airspace for the
purpose of providing separation between known aircraft.
Examples
A flight filed for a short distance at a relatively low altitude
in an area of low traffic density might receive a clearance
as follows:
“Cessna 1230 Alpha, cleared to Doeville airport direct,
cruise 5,000.”

Figure 10-1. Flight Plan Form.

10-3

The term “cruise” in this clearance means a pilot is authorized
to fly at any altitude from the minimum IFR altitude up to and
including 5,000 feet, and may level off at any altitude within
this block of airspace. A climb or descent within the block may
be made at the pilot’s discretion. However, once a pilot reports
leaving an altitude within the block, the pilot may not return to
that altitude without further ATC clearance.
When ATC issues a cruise clearance in conjunction with an
unpublished route, an appropriate crossing altitude will be
specified to ensure terrain clearance until the aircraft reaches a
fix, point, or route where the altitude information is available.
The crossing altitude ensures IFR obstruction clearance to
the point at which the aircraft enters a segment of a published
route or IAP.
Once a flight plan is filed, ATC will issue the clearance with
appropriate instructions, such as the following:
“Cessna 1230 Alpha is cleared to Skyline airport via
the Crossville 055 radial, Victor 18, maintain 5,000.
Clearance void if not off by 1330.”

navigation equipment and be ready for departure before
requesting an IFR clearance.
Once the clearance is accepted, a pilot is required to comply
with ATC instructions. A clearance different from that issued
may be requested if the pilot considers another course of action
more practicable or if aircraft equipment limitations or other
considerations make acceptance of the clearance inadvisable.
A pilot should also request clarification or amendment, as
appropriate, any time a clearance is not fully understood
or considered unacceptable for safety of flight. The pilot is
responsible for requesting an amended clearance if ATC issues
a clearance that would cause a pilot to deviate from a rule or
regulation or would place the aircraft in jeopardy.
Clearance Separations
ATC will provide the pilot on an IFR clearance with separation
from other IFR traffic. This separation is provided:
1.

Vertically—by assignment of different altitudes.

2.

Longitudinally—by controlling time separation between
aircraft on the same course.

3.

Laterally—by assignment of different flight paths.

4.

By radar—including all of the above.

Or a more complex clearance, such as:
“Cessna 1230 Alpha is cleared to Wichita Mid-continent
airport via Victor 77, left turn after takeoff, proceed
direct to the Oklahoma City VORTAC. Hold west on
the Oklahoma City 277 radial, climb to 5,000 in holding
pattern before proceeding on course. Maintain 5,000 to
CASHION intersection. Climb to and maintain 7,000.
Departure control frequency will be 121.05, Squawk
0412.”
Clearance delivery may issue the following “abbreviated
clearance” which includes a departure procedure (DP):
“Cessna 1230 Alpha, cleared to La Guardia as filed,
RINGOES 8 departure Phillipsburg transition, maintain
8,000. Departure control frequency will be 120.4,
Squawk 0700.”
This clearance may be readily copied in shorthand as follows:
“CAF RNGO8 PSB M80 DPC 120.4 SQ 0700.”

ATC does not provide separation for an aircraft operating:
1.

Outside controlled airspace.

2.

On an IFR clearance:
a)

With “VFR-On-Top” authorized instead of a
specific assigned altitude.

b) Specifying climb or descent in “VFR conditions.”
c)

At any time in VFR conditions, since uncontrolled
VFR flights may be operating in the same
airspace.

In addition to heading and altitude assignments, ATC will
occasionally issue speed adjustments to maintain the required
separations. For example:
“Cessna 30 Alpha, slow to 100 knots.”

The information contained in this DP clearance is abbreviated
using clearance shorthand (see appendix 1). The pilot should
know the locations of the specified navigation facilities, together
with the route and point-to-point time, before accepting the
clearance.

A pilot who receives speed adjustments is expected to maintain
that speed plus or minus 10 knots. If for any reason the pilot
is not able to accept a speed restriction, the pilot should advise
ATC.

The DP enables a pilot to study and understand the details
of a departure before filing an IFR flight plan. It provides
the information necessary to set up communication and

At times, ATC may also employ visual separation techniques
to keep aircraft safely separated. A pilot who obtains visual
contact with another aircraft may be asked to maintain visual
separation or to follow the aircraft. For example:

10-4

“Cessna 30 Alpha, maintain visual separation with that
traffic, climb and maintain 7,000.”
The pilot’s acceptance of instructions to maintain visual
separation or to follow another aircraft is an acknowledgment
that the aircraft will be maneuvered as necessary, to maintain
safe separation. It is also an acknowledgment that the pilot
accepts the responsibility for wake turbulence avoidance.
In the absence of radar contact, ATC will rely on position
reports to assist in maintaining proper separation. Using the data
transmitted by the pilot, the controller follows the progress of
each flight. ATC must correlate the pilots’ reports to provide
separation; therefore, the accuracy of each pilot’s report can
affect the progress and safety of every other aircraft operating
in the area on an IFR flight plan.

ODPs are found in section C of each booklet published
regionally by the NACG, TPP, along with “IFR Take-off
Minimums” while SIDs are collocated with the approach
procedures for the applicable airport. Additional information
on the development of DPs can be found in paragraph 5-2-7
of the AIM. However, the following points are important
to remember.
1.

The pilot of IFR aircraft operating from locations
where DP procedures are effective may expect an ATC
clearance containing a DP. The use of a DP requires
pilot possession of at least the textual description of the
approved DP.

2.

If a pilot does not possess a preprinted DP or for any other
reason does not wish to use a DP, he or she is expected
to advise ATC. Notification may be accomplished by
filing “NO DP” in the remarks section of the filed flight
plan, or by advising ATC.

3.

If a DP is accepted in a clearance, a pilot must comply
with it.

Departure Procedures (DPs)
Instrument departure procedures are preplanned instrument
flight rule (IFR) procedures, which provide obstruction
clearance from the terminal area to the appropriate en route
structure and provide the pilot with a way to depart the airport
and transition to the en route structure safely. Pilots operating
under 14 CFR part 91 are strongly encouraged to file and fly a
DP when one is available. [Figure 10-2]
There are two types of DPs, Obstacle Departure Procedures
(ODP), printed either textually or graphically, and Standard
Instrument Departures (SID), always printed graphically. All
DPs, either textual or graphic, may be designed using either
conventional or RNAV criteria. RNAV procedures will have
RNAV printed in the title, e.g., SHEAD TWO DEPARTURE
(RNAV).
Obstacle Departure Procedures (ODP)
ODPs provide obstruction clearance via the least onerous route
from the terminal area to the appropriate en route structure. ODPs
are recommended for obstruction clearance and may be flown
without ATC clearance unless an alternate departure procedure
(SID or radar vector) has been specifically assigned by ATC.
Graphic ODPs will have (OBSTACLE) printed in the procedure
title, e.g., GEYSR THREE DEPARTURE (OBSTACLE),
CROWN ONE DEPARTURE (RNAV)(OBSTACLE).
Standard Instrument Departures
Standard Instrument Departures (SID) are air traffic control
(ATC) procedures printed for pilot/controller use in graphic
form to provide obstruction clearance and a transition from
the terminal area to the appropriate en route structure. SIDs
are primarily designed for system enhancement and to reduce
pilot/controller workload. ATC clearance must be received
prior to flying a SID.

Radar Controlled Departures
On IFR departures from airports in congested areas, a pilot
will normally receive navigational guidance from departure
control by radar vector. When a departure is to be vectored
immediately following takeoff, the pilot will be advised before
takeoff of the initial heading to be flown. This information is
vital in the event of a loss of two-way radio communications
during departure.
The radar departure is normally simple. Following takeoff,
contact departure control on the assigned frequency when
advised to do so by the control tower. At this time departure
control verifies radar contact, and gives headings, altitude, and
climb instructions to move an aircraft quickly and safely out of
the terminal area. A pilot is expected to fly the assigned headings
and altitudes until informed by the controller of the aircraft’s
position with respect to the route given in the clearance, whom
to contact next, and to “resume own navigation.”
Departure control will provide vectors to either a navigation
facility, or an en route position appropriate to the departure
clearance, or transfer to another controller with further radar
surveillance capabilities. [Figure 10-2]
A radar controlled departure does not relieve the pilot of
responsibilities as pilot-in-command. Be prepared before
takeoff to conduct navigation according to the ATC clearance,
with navigation receivers checked and properly tuned. While
under radar control, monitor instruments to ensure continuous
orientation to the route specified in the clearance, and record
the time over designated checkpoints.

10-5

Figure 10-2. Departure Procedure (DP).

10-6

Departures From Airports Without an Operating
Control Tower
When departing from airports that have neither an operating
tower nor an FSS, a pilot should telephone the flight plan to the
nearest ATC facility at least 30 minutes before the estimated
departure time. If weather conditions permit, depart VFR and
request IFR clearance as soon as radio contact is established
with ATC.
If weather conditions make it undesirable to fly VFR, telephone
clearance request. In this case, the controller would probably
issue a short-range clearance pending establishment of radio
contact, and might restrict the departure time to a certain period.
For example:
“Clearance void if not off by 0900.”

Position Reports
Position reports are required over each compulsory reporting
point (shown on the chart as a solid triangle) along the route
being flown regardless of altitude, including those with
a VFR-on-top clearance. Along direct routes, reports are
required of all IFR flights over each point used to define
the route of flight. Reports at reporting points (shown as an
open triangle) are made only when requested by ATC. A
pilot should discontinue position reporting over designated
reporting points when informed by ATC that the aircraft
is in “RADAR CONTACT.” Position reporting should be
resumed when ATC advises “RADAR CONTACT LOST”
or “RADAR SERVICE TERMINATED.”
Position reports should include the following items:
1.

Identification

2.

Position

3.

Time

4.

Altitude or flight level (include actual altitude or flight
level when operating on a clearance specifying VFRon-top)

Procedures en route will vary according to the proposed route,
the traffic environment, and the ATC facilities controlling
the flight. Some IFR flights are under radar surveillance and
controlled from departure to arrival, and others rely entirely
on pilot navigation.

5.

Type of flight plan (not required in IFR position reports
made directly to ARTCCs or approach control)

6.

ETA and name of next reporting point

7.

The name only of the next succeeding reporting point
along the route of flight

Where ATC has no jurisdiction, it does not issue an IFR
clearance. It has no control over the flight, nor does the pilot
have any assurance of separation from other traffic.

8.

Pertinent remarks

This would authorize departure within the allotted period and
permit a pilot to proceed in accordance with the clearance. In
the absence of any specific departure instructions, a pilot would
be expected to proceed on course via the most direct route.

En Route Procedures

ATC Reports
All pilots are required to report unforecast weather conditions
or other information related to safety of flight to ATC. The
pilot-in-command of each aircraft operated in controlled
airspace under IFR shall report as soon as practical to ATC any
malfunctions of navigational, approach, or communication
equipment occurring in flight:

En route position reports are submitted normally to
the ARTCC controllers via direct controller-to-pilot
communications channels, using the appropriate ARTCC
frequencies listed on the en route chart.
Whenever an initial contact with a controller is to be followed
by a position report, the name of the reporting point should
be included in the call-up. This alerts the controller that such
information is forthcoming. For example:

1.

Loss of VOR, tactical air navigation (TACAN) or
automatic direction finder (ADF) receiver capability.

“Atlanta Center, Cessna 1230 Alpha at JAILS
intersection.”

2.

Complete or partial loss of instrument landing system
(ILS) receiver capability.

“Cessna 1230 Alpha Atlanta Center.”

3.

Impairment of air-to-ground communications
capability.

The pilot-in-command shall include within the report
(1) Aircraft identification, (2) Equipment affected, (3) Degree
to which the pilot to operate under IFR within the ATC
system is impaired, and (4) Nature and extent of assistance
desired from ATC.

“Atlanta Center, Cessna 1230 Alpha at JAILS
intersection, 5,000, estimating Monroeville at
1730.”
Additional Reports
In addition to required position reports, the following reports
should be made to ATC without a specific request.

10-7

1. At all times:
a)

When vacating any previously assigned altitude
or flight level for a newly assigned altitude or
flight level

b) When an altitude change will be made if operating
on a clearance specifying VFR-on-top
c)

When unable to climb/descend at a rate of at least
500 feet per minute (fpm)

d) When an approach has been missed (Request
clearance for specific action (to alternative
airport, another approach, etc.))
e)

f)

Change in average true airspeed (at cruising
altitude) when it varies by 5 percent or ten knots
(whichever is greater) from that filed in the flight
plan
The time and altitude upon reaching a holding fix
or point to which cleared

g) When leaving any assigned holding fix or point
NOTE - The reports in (f) and (g) may be omitted
by pilots of aircraft involved in instrument
training at military terminal area facilities when
radar service is being provided.
h) Any loss in controlled airspace of VOR,
TACAN, ADF, low frequency navigation
receiver capability, GPS anomalies while using
installed IFR-certified GPS/GNSS receivers,
complete or partial loss of ILS receiver capability,
or impairment of air/ground communications
capability. Reports should include aircraft
identification, equipment affected, degree to
which the capability to operate under IFR in
the ATC system is impaired, and the nature and
extent of assistance desired from ATC.
i)
2.

Any information relating to the safety of flight.

When not in radar contact:
a)

When leaving the final approach fix inbound
on final approach (nonprecision approach), or
when leaving the outer marker or fix used in lieu
of the outer marker inbound on final approach
(precision approach).

b) A corrected estimate at any time it becomes
apparent that an estimate as previously submitted
is in error in excess of 3 minutes.
Any pilot who encounters weather conditions that have not
been forecast, or hazardous conditions which have been
forecast, is expected to forward a report of such weather
to ATC.

10-8

Planning the Descent and Approach
ATC arrival procedures and flight deck workload are affected
by weather conditions, traffic density, aircraft equipment,
and radar availability.
When landing at an airport with approach control services
and where two or more IAPs are published, information on
the type of approach to expect will be provided in advance of
arrival or vectors will be provided to a visual approach. This
information will be broadcast either on automated terminal
information service (ATIS) or by a controller. It will not be
furnished when the visibility is 3 miles or more and the ceiling
is at or above the highest initial approach altitude established
for any low altitude IAP for the airport.
The purpose of this information is to help the pilot plan arrival
actions; however, it is not an ATC clearance or commitment
and is subject to change. Fluctuating weather, shifting
winds, blocked runway, etc., are conditions that may result
in changes to the approach information previously received.
It is important for a pilot to advise ATC immediately if he
or she is unable to execute the approach or prefers another
type of approach.
If the destination is an airport without an operating control
tower, and has automated weather data with broadcast
capability, the pilot should monitor the automated surface
observing system/automated weather observing system
(ASOS/AWOS) frequency to ascertain the current weather for
the airport. ATC should be advised that weather information
has been received and what the pilot’s intentions are.
When the approach to be executed has been determined, the
pilot should plan for and request a descent to the appropriate
altitude prior to the initial approach fix (IAF) or transition
route depicted on the IAP. When flying the transition route,
a pilot should maintain the last assigned altitude until ATC
gives the instructions “cleared for the approach.” Lower
altitudes can be requested to bring the transition route
altitude closer to the required altitude at the initial approach
fix. When ATC uses the phrase “at pilot’s discretion” in the
altitude information of a clearance, the pilot has the option
to start a descent at any rate, and may level off temporarily
at any intermediate altitude. However, once an altitude has
been vacated, return to that altitude is not authorized without
a clearance. When ATC has not used the term “at pilot’s
discretion” nor imposed any descent restrictions, initiate
descent promptly upon acknowledgment of the clearance.
Descend at an optimum rate (consistent with the operating
characteristics of the aircraft) to 1,000 feet above the assigned
altitude. Then attempt to descend at a rate of between 500 and

1,500 fpm until the assigned altitude is reached. If at anytime
a pilot is unable to maintain a descent rate of at least 500 fpm,
advise ATC. Also advise ATC if it is necessary to level off
at an intermediate altitude during descent. An exception to
this is when leveling off at 10,000 feet mean sea level (MSL)
on descent, or 2,500 feet above airport elevation (prior to
entering a Class B, Class C, or Class D surface area) when
required for speed reduction.
Standard Terminal Arrival Routes (STARs)
Standard terminal arrival routes (as described in Chapter
8) have been established to simplify clearance delivery
procedures for arriving aircraft at certain areas having high
density traffic. A STAR serves a purpose parallel to that of a
DP for departing traffic. [Figure 10-3] The following points
regarding STARs are important to remember:
1.

All STARs are contained in the TPP, along with the
IAP charts for the destination airport. The AIM also
describes STAR procedures.

2.

If the destination is a location for which STARs
have been published, a pilot may be issued a
clearance containing a STAR whenever ATC deems
it appropriate. To accept the clearance, a pilot must
possess at least the approved textual description.

3.

It is the pilot’s responsibility to either accept or refuse
an issued STAR. If a STAR will not or cannot be used,
advise ATC by placing “NO STAR” in the remarks
section of the filed flight plan or by advising ATC.

4.

If a STAR is accepted in a clearance, compliance is
mandatory.

Substitutes for Inoperative or Unusable
Components
The basic ground components of an ILS are the localizer,
glide slope, outer marker, middle marker, and inner marker
(when installed). A compass locator or precision radar may
be substituted for the outer or middle marker. Distance
measuring equipment (DME), VOR, or nondirectional beacon
(NDB) fixes authorized in the standard IAP or surveillance
radar may be substituted for the outer marker.
Additionally, IFR-certified global positioning system (GPS)
equipment, operated in accordance with Advisory Circular
(AC) 90-94, Guidelines for Using Global Positioning System
Equipment for IFR En Route and Terminal Operations and
for Nonprecision Instrument Approaches in the United
States National Airspace System, may be substituted for
ADF and DME equipment, except when flying NDB IAP.
Specifically, GPS can be substituted for ADF and DME
equipment when:
1.

2.

Navigating TO/FROM an NDB;

3.

Determining the aircraft position over an NDB;

4.

Determining the aircraft position over a fix made up
of a crossing NDB bearing;

5.

Holding over an NDB;

6.

Determining aircraft position over a DME fix.

Holding Procedures
Depending upon traffic and weather conditions, holding may
be required. Holding is a predetermined maneuver which
keeps aircraft within a specified airspace while awaiting
further clearance from ATC. A standard holding pattern
uses right turns, and a nonstandard holding pattern uses left
turns. The ATC clearance will always specify left turns when
a nonstandard pattern is to be flown.
Standard Holding Pattern (No Wind)
In a standard holding pattern with no winds, [Figure 10-4] the
aircraft follows the specified course inbound to the holding
fix, turns 180° to the right, flies a parallel straight course
outbound for 1 minute, turns 180° to the right, and flies the
inbound course to the fix.
Standard Holding Pattern (With Wind)
A standard symmetrical holding pattern cannot be flown
when winds exist. In those situations, the pilot is expected
to:
1.

Compensate for the effect of a known wind except
when turning.

2.

Adjust outbound timing to achieve a 1-minute (1-1/2
minutes above 14,000 feet) inbound leg.

Figure 10-5 illustrates the holding track followed with a left
crosswind. The effect of wind is counteracted by applying
drift corrections to the inbound and outbound legs and by
applying time allowances to the outbound leg.
Holding Instructions
If an aircraft arrives at a clearance limit before receiving
clearance beyond the fix, ATC expects the pilot to maintain
the last assigned altitude and begin holding in accordance
with the charted holding pattern. If no holding pattern is
charted and holding instructions have not been issued, enter
a standard holding pattern on the course on which the aircraft
approached the fix and request further clearance as soon
as possible. Normally, when no delay is anticipated, ATC
will issue holding instructions at least 5 minutes before the

Flying a DME arc;

10-9

Figure 10-3. Standard Terminal Arrival Route (STAR).

10-10

5.

Direction of turn, if left turns are to be made, because
the pilot requests or the controller considers it
necessary.

6.

Time to expect-further-clearance (EFC) and any
pertinent additional delay information.

ATC instructions will also be issued whenever:
1.

It is determined that a delay will exceed 1 hour.

2.

A revised EFC is necessary.

3.

In a terminal area having a number of navigation
aids and approach procedures, a clearance limit may
not indicate clearly which approach procedures will
be used. On initial contact, or as soon as possible
thereafter, approach control will advise the pilot of
the type of approach to expect.

4.

Ceiling and/or visibility is reported as being at or
below the highest “circling minimums” established
for the airport concerned. ATC will transmit a report
of current weather conditions and subsequent changes,
as necessary.

5.

An aircraft is holding while awaiting approach
clearance, and the pilot advises ATC that reported
weather conditions are below minimums applicable
to the operation. In this event, ATC will issue suitable
instructions to aircraft desiring either to continue
holding while awaiting weather improvement or
proceed to another airport.

Figure 10-4. Standard Holding Pattern—No Wind.

Standard Entry Procedures
The entry procedures given in the AIM evolved from
extensive experimentation under a wide range of operational
conditions. The standardized procedures should be followed
to ensure that an aircraft remains within the boundaries of
the prescribed holding airspace.

Figure 10-5. Drift Correction in Holding Pattern.

estimated arrival at the fix. Where a holding pattern is not
charted, the ATC clearance will specify the following:
1.

Direction of holding from the fix in terms of the eight
cardinal compass points (N, NE, E, SE, etc.)

2.

Holding fix (the fix may be omitted if included at the
beginning of the transmission as the clearance limit)

3.

Radial, course, bearing, airway, or route on which the
aircraft is to hold.

4.

Leg length in miles if DME or area navigation
(RNAV) is to be used (leg length will be specified in
minutes on pilot request or if the controller considers
it necessary).

When a speed reduction is required, start the reduction when
3 minutes or less from the holding fix. Cross the holding fix
initially at or below the maximum holding airspeed (MHA).
The purpose of the speed reduction is to prevent overshooting
the holding airspace limits, especially at locations where
adjacent holding patterns are close together.
All aircraft may hold at the following altitudes and maximum
holding airspeeds:
Altitude Mean Sea Level (MSL)

Airspeed (KIAS)

Up to 6,000 feet

200

6,001 – 14,000 feet

230

14,001 feet and above

265

10-11

The following are exceptions to the maximum holding
airspeeds:
1.

2.

Holding patterns from 6,001 to 14,000 feet may
be restricted to a maximum airspeed of 210 knots
indicated airspeed (KIAS). This nonstandard pattern
is depicted by an icon.
Holding patterns may be restricted to a maximum
airspeed of 175 KIAS. This nonstandard pattern is
depicted by an icon. Holding patterns restricted to
175 KIAS are generally found on IAPs applicable to
category A and B aircraft only.

3.

Holding patterns at Air Force airfields only—310
KIAS maximum, unless otherwise depicted.

4.

Holding patterns at Navy airfields only—230 KIAS
maximum, unless otherwise depicted.

5.

The pilot of an aircraft unable to comply with
maximum airspeed restrictions should notify ATC.

While other entry procedures may enable the aircraft to
enter the holding pattern and remain within protected
airspace, the parallel, teardrop, and direct entries are the
procedures for entry and holding recommended by the FAA.
Additionally, paragraph 5-3-7 in the AIM should be reviewed.
[Figure 10-6]
1.

2.

Parallel Procedure. When approaching the holding
fix from anywhere in sector (a), the parallel entry
procedure would be to turn to a heading to parallel the
holding course outbound on the nonholding side for
1 minute, turn in the direction of the holding pattern
through more than 180°, and return to the holding fix
or intercept the holding course inbound.
Teardrop Procedure. When approaching the holding
fix from anywhere in sector (b), the teardrop entry
procedure would be to fly to the fix, turn outbound to
a heading for a 30° teardrop entry within the pattern

(on the holding side) for a period of 1 minute, then
turn in the direction of the holding pattern to intercept
the inbound holding course.
3.

Direct Entry Procedure. When approaching the
holding fix from anywhere in sector (c), the direct
entry procedure would be to fly directly to the fix and
turn to follow the holding pattern.

A pilot should make all turns during entry and while holding at:
1.

3° per second, or

2.

30° bank angle, or

3.

A bank angle provided by a flight director system.

Time Factors
The holding pattern entry time reported to ATC is the initial
time of arrival over the fix. Upon entering a holding pattern,
the initial outbound leg is flown for 1 minute at or below
14,000 feet MSL, and for 1-1/2 minutes above 14,000
feet MSL. Timing for subsequent outbound legs should be
adjusted as necessary to achieve proper inbound leg time.
The pilot should begin outbound timing over or abeam the
fix, whichever occurs later. If the abeam position cannot
be determined, start timing when the turn to outbound is
completed. [Figure 10-7]
Time leaving the holding fix must be known to ATC before
succeeding aircraft can be cleared to the vacated airspace.
Leave the holding fix:
1.

When ATC issues either further clearance en route or
approach clearance;

2.

As prescribed in 14 CFR part 91 (for IFR operations;
two-way radio communications failure, and
responsibility and authority of the pilot-in-command);
or

3.

After the IFR flight plan has been cancelled, if the
aircraft is holding in VFR conditions.

DME Holding
The same entry and holding procedures apply to DME
holding, but distances (nautical miles) are used instead of
time values. The length of the outbound leg will be specified
by the controller, and the end of this leg is determined by
the DME readout.

Approaches

Figure 10-6. Holding Pattern Entry Procedures.

10-12

Compliance With Published Standard Instrument
Approach Procedures
Compliance with the approach procedures shown on the
approach charts provides necessary navigation guidance
information for alignment with the final approach courses,

5.

Otherwise directed by ATC.

Instrument Approaches to Civil Airports
Unless otherwise authorized, when an instrument letdown to
an airport is necessary, the pilot should use a standard IAP
prescribed for that airport. IAPs are depicted on IAP charts
and are found in the TPP.
ATC approach procedures depend upon the facilities available
at the terminal area, the type of instrument approach executed,
and the existing weather conditions. The ATC facilities,
navigation aids (NAVAIDs), and associated frequencies
appropriate to each standard instrument approach are given
on the approach chart. Individual charts are published for
standard approach procedures associated with the following
types of facilities:

Figure 10-7. Holding—Outbound Timing.

as well as obstruction clearance. Under certain conditions, a
course reversal maneuver or procedure turn may be necessary.
However, this procedure is not authorized when:
1.

The symbol “NoPT” appears on the approach course
on the plan view of the approach chart.

2.

Radar vectoring is provided to the final approach
course.

3.

A holding pattern is published in lieu of a procedure
turn.

4.

Executing a timed approach from a holding fix.

1.

Nondirectional beacon (NDB)

2.

Very-high frequency omnirange (VOR)

3.

Very-high frequency omnirange with distance
measuring equipment (VORTAC or VOR/DME)

4.

Localizer (LOC)

5.

Instrument landing system (ILS)

6.

Localizer-type directional aid (LDA)

7.

Simplified directional facility (SDF)

8.

Area navigation (RNAV)

9.

Global positioning system (GPS)

An IAP can be flown in one of two ways: as a full approach
or with the assistance of radar vectors. When the IAP is flown
as a full approach, pilots conduct their own navigation using
the routes and altitudes depicted on the instrument approach
chart. A full approach allows the pilot to transition from
the en route phase, to the instrument approach, and then to
a landing with minimal assistance from ATC. This type of
procedure may be requested by the pilot but is most often
used in areas without radar coverage. A full approach also
provides the pilot with a means of completing an instrument
approach in the event of a communications failure.
When an approach is flown with the assistance of radar vectors,
ATC provides guidance in the form of headings and altitudes
which position the aircraft to intercept the final approach.
From this point, the pilot resumes navigation, intercepts the
final approach course, and completes the approach using the
IAP chart. This is often a more expedient method of flying
the approach, as opposed to the full approach, and allows
ATC to sequence arriving traffic. A pilot operating in radar
contact can generally expect the assistance of radar vectors
to the final approach course.

10-13

Approach to Airport Without an Operating Control
Tower

Approach to an Airport With an Operating Tower,
With an Approach Control

Figure 10-8 shows an approach procedure at an airport
without an operating control tower. When approaching
such a facility, the pilot should monitor the AWOS/ASOS
if available for the latest weather conditions. When direct
communication between the pilot and controller is no longer
required, the ARTCC or approach controller will issue a
clearance for an instrument approach and advise “change to
advisory frequency approved.” When the aircraft arrives on
a “cruise” clearance, ATC will not issue further clearance
for approach and landing.

Where radar is approved for approach control service, it is
used to provide vectors in conjunction with published IAPs.
Radar vectors can provide course guidance and expedite
traffic to the final approach course of any established IAP.
Figure 10-9 shows an IAP chart with maximum ATC
facilities available.

If an approach clearance is required, ATC will authorize
the pilot to execute his or her choice of standard instrument
approach (if more than one is published for the airport)
with the phrase “Cleared for the approach” and the
communications frequency change required, if any. From
this point on, there will be no contact with ATC. The pilot
is responsible for closing the IFR flight plan before landing,
if in VFR conditions, or by telephone after landing.

Approach control facilities that provide this radar service
operate in the following manner:
1.

Arriving aircraft are either cleared to an outer fix most
appropriate to the route being flown with vertical
separation and, if required, given holding information;
or,

2.

When radar hand-offs are effected between ARTCC
and approach control, or between two approach
control facilities, aircraft are cleared to the airport, or
to a fix so located that the hand-off will be completed
prior to the time the aircraft reaches the fix.
a)

Unless otherwise authorized by ATC, a pilot is expected to
execute the complete IAP shown on the chart.

Approach to Airport With an Operating Tower,
With No Approach Control
When an aircraft approaches an airport with an operating
control tower, but no approach control, ATC will issue
a clearance to an approach/outer fix with the appropriate
information and instructions as follows:
1.

Name of the fix

2.

Altitude to be maintained

3.

Holding information and expected approach clearance
time, if appropriate

4.

Instructions regarding further communications,
including:
a)

b) After hand-off to approach control, an aircraft
is vectored to the appropriate final approach
course.
3.

Radar vectors and altitude/flight levels are issued
as required for spacing and separating aircraft; do
not deviate from the headings issued by approach
control.

4.

Aircraft are normally informed when it becomes
necessary to be vectored across the final approach
course for spacing or other reasons. If approach
course crossing is imminent and the pilot has not
been informed that the aircraft will be vectored across
the final approach course, the pilot should query the
controller. The pilot is not expected to turn inbound on
the final approach course unless an approach clearance
has been issued. This clearance is normally issued with
the final vector for interception of the final approach
course, and the vector enables the pilot to establish the
aircraft on the final approach course prior to reaching
the final approach fix.

5.

Once the aircraft is established inbound on the final
approach course, radar separation is maintained with
other aircraft, and the pilot is expected to complete
the approach using the NAVAID designated in the
clearance (ILS, VOR, NDB, GPS, etc.) as the primary
means of navigation.

facility to be contacted

b) time and place of contact
c)

frequency/ies to be used

If ATIS is available, a pilot should monitor that frequency
for information such as ceiling, visibility, wind direction and
velocity, altimeter setting, instrument approach, and runways
in use prior to initial radio contact with the tower. If ATIS is
not available, ATC will provide weather information from
the nearest reporting station.

10-14

When the radar hand-offs are utilized, successive
arriving flights may be handed off to approach
control with radar separation in lieu of vertical
separation.

Figure 10-8. Monroeville, AL (MVC) VOR or GPS Rwy 3 Approach: An Approach Procedure at an Airport Without an Operating

Control Tower.

10-15

Figure 10-9. Gulfport, MS (GPT) ILS or LOC Rwy 14 Approach: An Instrument Procedure Chart With Maximum ATC Facilities

Available.

10-16

6.

After passing the final approach fix inbound, the
pilot is expected to proceed direct to the airport and
complete the approach, or to execute the published
missed approach procedure.

7.

Radar service is automatically terminated when the
landing is completed or when the pilot is instructed to
change to advisory frequency at uncontrolled airports,
whichever occurs first.

Radar Approaches
With a radar approach, the pilot receives course and altitude
guidance from a controller who monitors the progress of the
flight with radar. This is an option should the pilot experience
an emergency or distress situation.
The only airborne radio equipment required for radar
approaches is a functioning radio transmitter and receiver.
The radar controller vectors the aircraft to align it with the
runway centerline. The controller continues the vectors to
keep the aircraft on course until the pilot can complete the
approach and landing by visual reference to the surface.
There are two types of radar approaches: Precision (PAR)
and Surveillance (ASR).
A radar approach may be given to any aircraft upon request
and may be offered to pilots of aircraft in distress or to expedite
traffic; however, an ASR might not be approved unless
there is an ATC operational requirement, or in an unusual
or emergency situation. Acceptance of a PAR or ASR by a
pilot does not waive the prescribed weather minimums for the
airport or for the particular aircraft operator concerned. The

decision to make a radar approach when the reported weather
is below the established minimums rests with the pilot.
PAR and ASR minimums are published on separate pages
in the FAA Terminal Procedures Publication (TPP).
Figure 10-10.
Precision Approach (PAR) is one in which a controller
provides highly accurate navigational guidance in azimuth
and elevation to a pilot.
The controller gives the pilot headings to fly that direct the
aircraft to, and keep the aircraft aligned with, the extended
centerline of the landing runway. The pilot is told to anticipate
glide path interception approximately 10 to 30 seconds before
it occurs and when to start descent. The published decision
height (DH) will be given only if the pilot requests it. If
the aircraft is observed to deviate above or below the glide
path, the pilot is given the relative amount of deviation by
use of terms “slightly” or “well” and is expected to adjust
the aircraft’s rate of descent/ascent to return to the glide
path. Trend information is also issued with respect to the
elevation of the aircraft and may be modified by the terms
“rapidly” and “slowly”; e.g., “well above glide path, coming
down rapidly.”
Range from touchdown is given at least once each mile. If
an aircraft is observed by the controller to proceed outside
of specified safety zone limits in azimuth and/or elevation
and continue to operate outside these prescribed limits, the
pilot will be directed to execute a missed approach or to fly a

Figure 10-10. Radar Instrument Approach Minimums for Troy, AL.

10-17

specified course unless the pilot has the runway environment
(runway, approach lights, etc.) in sight. Navigational
guidance in azimuth and elevation is provided to the pilot
until the aircraft reaches the published DH. Advisory course
and glide path information is furnished by the controller
until the aircraft passes over the landing threshold. At this
point the pilot is advised of any deviation from the runway
centerline. Radar service is automatically terminated upon
completion of the approach.
Surveillance Approach (ASR) is one in which a controller
provides navigational guidance in azimuth only.
The controller furnishes the pilot with headings to fly to
align the aircraft with the extended centerline of the landing
runway. Since the radar information used for a surveillance
approach is considerably less precise than that used for a
precision approach, the accuracy of the approach will not
be as great and higher minimums will apply. Guidance in
elevation is not possible but the pilot will be advised when to
commence descent to the Minimum Descent Altitude (MDA)
or, if appropriate, to an intermediate step-down fix Minimum
Crossing Altitude and subsequently to the prescribed MDA.
In addition, the pilot will be advised of the location of the
Missed Approach Point (MAP) prescribed for the procedure
and the aircraft’s position each mile on final from the runway,
airport or heliport or MAP, as appropriate.
If requested by the pilot, recommended altitudes will be
issued at each mile, based on the descent gradient established
for the procedure, down to the last mile that is at or above
the MDA. Normally, navigational guidance will be provided
until the aircraft reaches the MAP.

Radar Monitoring of Instrument Approaches
PAR facilities operated by the FAA and the military services
at some joint-use (civil and military) and military installations
monitor aircraft on instrument approaches and issue radar
advisories to the pilot when weather is below VFR minimums
(1,000 and 3), at night, or when requested by a pilot. This
service is provided only when the PAR Final Approach
Course coincides with the final approach of the navigational
aid and only during the operational hours of the PAR. The
radar advisories serve only as a secondary aid since the pilot
has selected the navigational aid as the primary aid for the
approach.
Prior to starting final approach, the pilot will be advised of
the frequency on which the advisories will be transmitted.
If, for any reason, radar advisories cannot be furnished, the
pilot will be so advised.
Advisory information, derived from radar observations,
includes information on:
1.

Passing the final approach fix inbound (nonprecision
approach) or passing the outer marker or fix used
in lieu of the outer marker inbound (precision
approach).

2.

Trend advisories with respect to elevation and/or
azimuth radar position and movement will be
provided.

3.

If, after repeated advisories, the aircraft proceeds
outside the PAR safety limit or if a radical deviation is
observed, the pilot will be advised to execute a missed
approach unless the prescribed visual reference with
the surface is established.

Radar service is automatically terminated at the completion
of a radar approach.

Radar service is automatically terminated upon completion
of the approach. [Figure 10-11]

No-Gyro Approach is available to a pilot under radar control
who experiences circumstances wherein the directional gyro or
other stabilized compass is inoperative or inaccurate. When this
occurs, the pilot should so advise ATC and request a no-gyro
vector or approach. The pilot of an aircraft not equipped with a
directional gyro or other stabilized compass who desires radar
handling may also request a no-gyro vector or approach. The
pilot should make all turns at standard rate and should execute
the turn immediately upon receipt of instructions. For example,
“TURN RIGHT,” “STOP TURN.” When a surveillance or
precision approach is made, the pilot will be advised after the
aircraft has been turned onto final approach to make turns at
half standard rate.

Timed Approaches From a Holding Fix
Timed approaches from a holding fix are conducted when
many aircraft are waiting for an approach clearance. Although
the controller will not specifically state “timed approaches
are in progress,” the assigning of a time to depart the FAF
inbound (nonprecision approach), or the outer marker or
fix used in lieu of the outer marker inbound (precision
approach), indicates that timed approach procedures are
being utilized.

10-18

Figure 10-11. ILS RWY 7 Troy, AL.

10-19

In lieu of holding, the controller may use radar vectors to the
final approach course to establish a distance between aircraft
that will ensure the appropriate time sequence between the
FAF and outer marker, or fix used in lieu of the outer marker
and the airport. Each pilot in the approach sequence will
be given advance notice of the time they should leave the
holding point on approach to the airport. When a time to
leave the holding point is received, the pilot should adjust
the flight path in order to leave the fix as closely as possible
to the designated time.
Timed approaches may be conducted when the following
conditions are met:
1.

A control tower is in operation at the airport where
the approaches are conducted.

2.

Direct communications are maintained between the
pilot and the Center or approach controller until the
pilot is instructed to contact the tower.

3.

If more than one missed approach procedure is
available, none require a course reversal.

4.

If only one missed approach procedure is available,
the following conditions are met:
a)

Course reversal is not required; and

b) Reported ceiling and visibility are equal to or
greater than the highest prescribed circling
minimums for the IAP.
5.

When cleared for the approach, pilots should not
execute a procedure turn.

Approaches to Parallel Runways
Procedures permit ILS instrument approach operations to dual
or triple parallel runway configurations. A parallel approach
is an ATC procedure that permits parallel ILS approach to
airports with parallel runways separated by at least 2,500
feet between centerlines. Wherever parallel approaches
are in progress, pilots are informed that approaches to both
runways are in use.
Simultaneous approaches are permitted to runways:
1.

With centerlines separated by 4,300 to 9,000 feet;

2.

That are equipped with final monitor controllers;

3.

That require radar monitoring to ensure separation
between aircraft on the adjacent parallel approach
course.

The approach procedure chart will include the note
“simultaneous approaches authorized RWYS 14L and 14R,”
identifying the appropriate runways. When advised that
simultaneous parallel approaches are in progress, pilots must

10-20

advise approach control immediately of malfunctioning or
inoperative components.
Parallel approach operations demand heightened pilot
situational awareness. The close proximity of adjacent
aircraft conducting simultaneous parallel approaches
mandates strict compliance with all ATC clearances and
approach procedures. Pilots should pay particular attention
to the following approach chart information: name and
number of the approach, localizer frequency, inbound course,
glide slope intercept altitude, DA/DH, missed approach
instructions, special notes/procedures, and the assigned
runway location and proximity to adjacent runways. Pilots
also need to exercise strict radio discipline, which includes
continuous monitoring of communications and the avoidance
of lengthy, unnecessary radio transmissions.
Side-Step Maneuver
ATC may authorize a side-step maneuver to either one of
two parallel runways that are separated by 1,200 feet or less,
followed by a straight-in landing on the adjacent runway.
Aircraft executing a side-step maneuver will be cleared
for a specified nonprecision approach and landing on the
adjacent parallel runway. For example, “Cleared ILS runway
7 left approach, side-step to runway 7 right.” The pilot is
expected to commence the side-step maneuver as soon as
possible after the runway or runway environment is in sight.
Landing minimums to the adjacent runway will be based on
nonprecision criteria and therefore higher than the precision
minimums to the primary runway, but will normally be lower
than the published circling minimums.
Circling Approaches
Landing minimums listed on the approach chart under
“CIRCLING” apply when it is necessary to circle the airport,
maneuver for landing, or when no straight-in minimums are
specified on the approach chart. [Figure 10-11]
The circling minimums published on the instrument approach
chart provide a minimum of 300 feet of obstacle clearance in
the circling area. [Figure 10-12] During a circling approach,
the pilot should maintain visual contact with the runway of
intended landing and fly no lower than the circling minimums
until positioned to make a final descent for a landing. It is
important to remember that circling minimums are only
minimums. If the ceiling allows it, fly at an altitude that
more nearly approximates VFR traffic pattern altitude. This
will make any maneuvering safer and bring the view of the
landing runway into a more normal perspective.
Figure 10-13 shows patterns that can be used for circling
approaches. Pattern “A” can be flown when the final approach

runway is sighted in time for a turn to downwind leg. If the
runway is sighted too late for a turn to downwind, fly pattern
“D.” Regardless of the pattern flown, the pilot must maneuver
the aircraft to remain within the designated circling area.
Refer to section A (“Terms and Landing Minima Data”) in
the front of each TPP for a description of circling approach
categories.
The criteria for determining the pattern to be flown are
based on personal flying capabilities and knowledge of the
performance characteristics of the aircraft. In each instance,
the pilot must consider all factors: airport design, ceiling and
visibility, wind direction and velocity, final approach course
alignment, distance from the final approach fix to the runway,
and ATC instructions.

Figure 10-12. Circling Approach Area Radii.

IAP Minimums
Pilots may not operate an aircraft at any airport below
the authorized MDA or continue an approach below the
authorized DA/DH unless:
1.

The aircraft is continuously in a position from which
a descent to a landing on the intended runway can
be made at a normal descent rate using normal
maneuvers;

2.

The flight visibility is not less than that prescribed for
the approach procedure being used; and

3.

At least one of the following visual references for
the intended runway is visible and identifiable to the
pilot:
a)

Approach light system

b) Threshold
c)

Threshold markings

d) Threshold lights
e)

Runway end identifier lights (REIL)

f)

Visual approach slope indicator (VASI)

g) Touchdown zone or touchdown zone markings
h) Touchdown zone lights

Figure 10-13. Circling Approaches.

course intersects the runway centerline at less than a 90°
angle, and the runway is in sight early enough to establish a
base leg. If the runway becomes visible too late to fly pattern
“A,” circle as shown in “B.” Fly pattern “C” if it is desirable
to land opposite the direction of the final approach, and the

i)

Runway or runway markings

j)

Runway lights

Missed Approaches
A missed approach procedure is formulated for each
published instrument approach and allows the pilot to return
to the airway structure while remaining clear of obstacles.
The procedure is shown on the approach chart in text and
graphic form. Since the execution of a missed approach
occurs when the flight deck workload is at a maximum, the

10-21

procedure should be studied and mastered before beginning
the approach.
When a missed approach procedure is initiated, a climb pitch
attitude should be established while setting climb power.
Configure the aircraft for climb, turn to the appropriate
heading, advise ATC that a missed approach is being
executed, and request further clearances.
If the missed approach is initiated prior to reaching the
missed approach point (MAP), unless otherwise cleared by
ATC, continue to fly the IAP as specified on the approach
chart. Fly to the MAP at or above the MDA or DA/DH before
beginning a turn.
If visual reference is lost while circling-to-land from an
instrument approach, execute the appropriate missed
approach procedure. Make the initial climbing turn toward
the landing runway and then maneuver to intercept and fly
the missed approach course.
Pilots should immediately execute the missed approach
procedure:
1.

Whenever the requirements for operating below DA/
DH or MDA are not met when the aircraft is below
MDA, or upon arrival at the MAP and at any time
after that until touchdown;

2.

Whenever an identifiable part of the airport is not visible
to the pilot during a circling maneuver at or above MDA;
or

3.

When so directed by ATC.

Landing
According to 14 CFR part 91, no pilot may land when the flight
visibility is less than the visibility prescribed in the standard
IAP being used. ATC will provide the pilot with the current
visibility reports appropriate to the runway in use. This may be
in the form of prevailing visibility, runway visual value (RVV),
or runway visual range (RVR). However, only the pilot can
determine if the flight visibility meets the landing requirements
indicated on the approach chart. If the flight visibility meets
the minimum prescribed for the approach, then the approach
may be continued to a landing. If the flight visibility is less than
that prescribed for the approach, then the pilot must execute a
missed approach, regardless of the reported visibility.
The landing minimums published on IAP charts are based on
full operation of all components and visual aids associated
with the instrument approach chart being used. Higher
minimums are required with inoperative components or
visual aids. For example, if the ALSF-1 approach lighting
system were inoperative, the visibility minimums for an ILS
10-22

would need to be increased by one-quarter mile. If more
than one component is inoperative, each minimum is raised
to the highest minimum required by any single component
that is inoperative. ILS glide slope inoperative minimums
are published on instrument approach charts as localizer
minimums. Consult the “Inoperative Components or Visual
Aids Table” (printed on the inside front cover of each TPP),
for a complete description of the effect of inoperative
components on approach minimums.

Instrument Weather Flying
Flying Experience
The more experience a pilot has in VFR and IFR flight,
the more proficient a pilot becomes. VFR experience can
be gained by flying in terminal areas with high traffic
activity. This type of flying forces the pilot to polish the
skill of dividing his or her attention between aircraft control,
navigation, communications, and other flight deck duties.
IFR experience can be gained through night flying which
also promotes both instrument proficiency and confidence.
The progression from flying at night under clear, moonlit
conditions to flying at night without moonlight, natural
horizon, or familiar landmarks teaches a pilot to trust the
aircraft instruments with minimal dependence upon what
can be seen outside the aircraft. It is a pilot’s decision to
proceed with an IFR flight or to wait for more acceptable
weather conditions.

Recency of Experience
Currency as an instrument pilot is an equally important
consideration. No person may act as pilot in command of an
aircraft under IFR or in weather conditions less than VFR
minimums unless he or she has met the requirements of part
91. Remember, these are minimum requirements.

Airborne Equipment and Ground Facilities
Regulations specify minimum equipment for filing an IFR
flight plan. It is the pilot’s responsibility to determine the
adequacy of the aircraft and navigation/communication
(NAV/COM) equipment for the proposed IFR flight.
Performance limitations, accessories, and general condition
of the equipment are directly related to the weather, route,
altitude, and ground facilities pertinent to the flight, as well
as to the flight deck workload.
Weather Conditions
In addition to the weather conditions that might affect a
VFR flight, an IFR pilot must consider the effects of other
weather phenomena (e.g., thunderstorms, turbulence, icing,
and visibility).

Turbulence
Inflight turbulence can range from occasional light bumps
to extreme airspeed and altitude variations that make aircraft
control difficult. To reduce the risk factors associated with
turbulence, pilots must learn methods of avoidance, as
well as piloting techniques for dealing with an inadvertent
encounter.
Turbulence avoidance begins with a thorough preflight weather
briefing. Many reports and forecasts are available to assist
the pilot in determining areas of potential turbulence. These
include the Severe Weather Warning (WW), SIGMET (WS),
Convective SIGMET (WST), AIRMET (WA), Severe Weather
Outlook (AC), Center Weather Advisory (CWA), Area Forecast
(FA), and Pilot Reports (UA or PIREPs). Since thunderstorms
are always indicative of turbulence, areas of known and forecast
thunderstorm activity will always be of interest to the pilot. In
addition, clear air turbulence (CAT) associated with jet streams,
strong winds over rough terrain, and fast moving cold fronts are
good indicators of turbulence.
Pilots should be alert while in flight for the signposts of
turbulence. For example, clouds with vertical development
such as cumulus, towering cumulus, and cumulonimbus are
indicators of atmospheric instability and possible turbulence.
Standing lenticular clouds lack vertical development but
indicate strong mountain wave turbulence. While en route,
pilots can monitor hazardous inflight weather advisory

service (HIWAS) broadcast for updated weather advisories,
or contact the nearest AFSS or En Route Flight Advisory
Service (EFAS) for the latest turbulence-related PIREPs.
To avoid turbulence associated with strong thunderstorms,
circumnavigate cells by at least 20 miles. Turbulence may
also be present in the clear air above a thunderstorm. To
avoid this, fly at least 1,000 feet above the top for every 10
knots of wind at that level, or fly around the storm. Finally,
do not underestimate the turbulence beneath a thunderstorm.
Never attempt to fly under a thunderstorm. The possible
results of turbulence and wind shear under the storm could
be disastrous.
When moderate to severe turbulence is encountered, aircraft
control is difficult, and a great deal of concentration is
required to maintain an instrument scan. [Figure 10-14] Pilots
should immediately reduce power and slow the aircraft to
the recommended turbulence penetration speed as described
in the POH/AFM. To minimize the load factor imposed on
the aircraft, the wings should be kept level and the aircraft’s
pitch attitude should be held constant. The aircraft is allowed
to fluctuate up and down, because maneuvering to maintain
a constant altitude only increases the stress on the aircraft.
If necessary, the pilot should advise ATC of the fluctuations
and request a block altitude clearance. In addition, the power
should remain constant at a setting that will maintain the
recommended turbulence penetration airspeed.

Figure 10-14. Maintaining an instrument scan in severe turbulence can be difficult.

10-23

The best source of information on the location and intensity
of turbulence are PIREPs. Therefore, pilots are encouraged to
familiarize themselves with the turbulence reporting criteria
found in the AIM, which also describes the procedure for
volunteering PIREPs relating to turbulence.

Structural Icing
The very nature of flight in Instrument Meteorological
Conditions means operating in visible moisture such as clouds.
At the right temperatures, this moisture can freeze on the
aircraft, causing increased weight, degraded performance, and
unpredictable aerodynamic characteristics. Understanding,
avoidance, and early recognition followed by prompt action
are the keys to avoiding this potentially hazardous situation.
Structural icing refers to the accumulation of ice on the exterior
of the aircraft and is broken down into three classifications:
rime ice, clear ice, and mixed ice. For ice to form, there must
be moisture present in the air, and the air must be cooled to
a temperature of 0° C (32° F) or less. Aerodynamic cooling
can lower the surface temperature of an airfoil and cause ice
to form on the airframe even though the ambient temperature
is slightly above freezing.
Rime ice forms if the droplets are small and freeze immediately
when contacting the aircraft surface. This type of ice usually
forms on areas such as the leading edges of wings or struts.
It has a somewhat rough-looking appearance and a milkywhite color.

by the aircraft, the first course of action should be to leave
the area of visible moisture. This might mean descending
to an altitude below the cloud bases, climbing to an altitude
that is above the cloud tops, or turning to a different course.
If this is not possible, then the pilot must move to an altitude
where the temperature is above freezing. Pilots should report
icing conditions to ATC and request new routing or altitude
if icing will be a hazard. Refer to the AIM for information
on reporting icing intensities.

Fog
Instrument pilots must learn to anticipate conditions leading
to the formation of fog and take appropriate action early in
the progress of the flight. Before a flight, close examination
of current and forecast weather should alert the pilot to the
possibility of fog formation. When fog is a consideration,
pilots should plan adequate fuel reserves and alternate
landing sites. En route, the pilot must stay alert for fog
formation through weather updates from EFAS, ATIS, and
ASOS/AWOS sites.
Two conditions will lead to the formation of fog. Either the
air is cooled to saturation, or sufficient moisture is added
to the air until saturation occurs. In either case, fog can
form when the temperature/dewpoint spread is 5° or less.
Pilots planning to arrive at their destination near dusk with
decreasing temperatures should be particularly concerned
about the possibility of fog formation.

Volcanic Ash
Clear ice is usually formed from larger water droplets or
freezing rain that can spread over a surface. This is the most
dangerous type of ice since it is clear, hard to see, and can
change the shape of the airfoil.
Mixed ice is a mixture of clear ice and rime ice. It has the
bad characteristics of both types and can form rapidly. Ice
particles become embedded in clear ice, building a very rough
accumulation. The table in Figure 10-15 lists the temperatures
at which the various types of ice will form.

Figure 10-15. Temperature Ranges for Ice Formation.

Structural icing is a condition that can only get worse.
Therefore, during an inadvertent icing encounter, it is
important the pilot act to prevent additional ice accumulation.
Regardless of the level of anti-ice or deice protection offered
10-24

Volcanic eruptions create volcanic ash clouds containing
an abrasive dust that poses a serious safety threat to flight
operations. Adding to the danger is the fact that these ash
clouds are not easily discernible from ordinary clouds when
encountered at some distance from the volcanic eruption.
When an aircraft enters a volcanic ash cloud, dust particles
and smoke may become evident in the cabin, often along with
the odor of an electrical fire. Inside the volcanic ash cloud,
the aircraft may also experience lightning and St. Elmo’s fire
on the windscreen. The abrasive nature of the volcanic ash
can pit the windscreens, thus reducing or eliminating forward
visibility. The pitot-static system may become clogged,
causing instrument failure. Severe engine damage is probable
in both piston and jet-powered aircraft.
Every effort must be made to avoid volcanic ash. Since
volcanic ash clouds are carried by the wind, pilots should plan
their flights to remain upwind of the ash-producing volcano.
Visual detection and airborne radar are not considered
a reliable means of avoiding volcanic ash clouds. Pilots
witnessing volcanic eruptions or encountering volcanic
ash should immediately pass this information along in
the form of a pilot report. The National Weather Service

monitors volcanic eruptions and estimates ash trajectories.
This information is passed along to pilots in the form of
SIGMETs.
As for many other hazards to flight, the best source of
volcanic information comes from PIREPs. Pilots who witness
a volcanic eruption or encounter volcanic ash in flight
should immediately inform the nearest agency. Volcanic
Ash Forecast Transport and Dispersion (VAFTAD) charts
are also available; these depict volcanic ash cloud locations
in the atmosphere following an eruption, and also forecast
dispersion of the ash concentrations over 6- and 12-hour time
intervals. See AC 00-45, Aviation Weather Services.

Thunderstorms
A thunderstorm packs just about every weather hazard known
to aviation into one vicious bundle. Turbulence, hail, rain,
snow, lightning, sustained updrafts and downdrafts, and icing
conditions are all present in thunderstorms. Do not take off in
the face of an approaching thunderstorm or fly an aircraft that is
not equipped with thunderstorm detection in clouds or at night
in areas of suspected thunderstorm activity. [Figure 10-16]
There is no useful correlation between the external visual
appearance of thunderstorms and the severity or amount of
turbulence or hail within them. All thunderstorms should be

considered hazardous, and thunderstorms with tops above
35,000 feet should be considered extremely hazardous.
Weather radar, airborne or ground based, will normally
reflect the areas of moderate to heavy precipitation (radar
does not detect turbulence). The frequency and severity of
turbulence generally increases with the radar reflectivity
closely associated with the areas of highest liquid water
content of the storm. A flight path through an area of strong
or very strong radar echoes separated by 20 to 30 miles or
less may not be considered free of severe turbulence.
The probability of lightning strikes occurring to aircraft is
greatest when operating at altitudes where temperatures are
between -5 ° C and +5 ° C. In addition, an aircraft flying in the
clear air near a thunderstorm is also susceptible to lightning
strikes. Thunderstorm avoidance is always the best policy.

Wind Shear
Wind shear can be defined as a change in wind speed and/or
wind direction in a short distance. It can exist in a horizontal
or vertical direction and occasionally in both. Wind shear can
occur at all levels of the atmosphere but is of greatest concern
during takeoffs and landings. It is typically associated
with thunderstorms and low-level temperature inversions;
however, the jet stream and weather fronts are also sources
of wind shear.
As Figure 10-17 illustrates, while an aircraft is on an
instrument approach, a shear from a tailwind to a headwind
causes the airspeed to increase and the nose to pitch up with
a corresponding balloon above the glide path. A shear from
a headwind to a tailwind has the opposite effect, and the
aircraft will sink below the glide path.
A headwind shear followed by a tailwind/downdraft shear is
particularly dangerous because the pilot has reduced power
and lowered the nose in response to the headwind shear. This
leaves the aircraft in a nose-low, power-low configuration
when the tailwind shear occurs, which makes recovery more
difficult, particularly near the ground. This type of wind
shear scenario is likely while making an approach in the
face of an oncoming thunderstorm. Pilots should be alert for
indications of wind shear early in the approach phase and be
ready to initiate a missed approach at the first indication. It
may be impossible to recover from a wind shear encounter
at low altitude.

Figure 10-16. A thunderstorm packs just about every weather hazard

To inform pilots of hazardous wind shear activity, some
airports have installed a Low-Level Wind Shear Alert
System (LLWAS) consisting of a centerfield wind indicator
and several surrounding boundary-wind indicators. With

known to aviation into one vicious bundle.

10-25

Figure 10-17. Glide slope Deviations Due to Wind Shear Encounter.

this system, controllers are alerted of wind discrepancies
(an indicator of wind shear possibility) and provide this
information to pilots. A typical wind shear alert issued to a
pilot would be:
“Runway 27 arrival, wind shear alert, 20 knot loss 3
mile final, threshold wind 200 at 15”
In plain language, the controller is advising aircraft arriving
on runway 27 that at about 3 miles out they can expect a
wind shear condition that will decrease their airspeed by 20
knots and possibly encounter turbulence. Additionally, the
airport surface winds for landing runway 27 are reported as
200° at 15 knots.
Pilots encountering wind shear are encouraged to pass along
pilot reports. Refer to AIM for additional information on
wind shear PIREPs.
VFR-On-Top
Pilots on IFR flight plans operating in VFR weather
conditions may request VFR-on-top in lieu of an assigned
altitude. This permits them to select an altitude or flight level
of their choice (subject to any ATC restrictions).
Pilots desiring to climb through a cloud, haze, smoke, or
other meteorological formation and then either cancel their
IFR flight plan or operate VFR-on-top may request a climb
to VFR-on-top. The ATC authorization will contain a top
report (or a statement that no top report is available) and a
request to report upon reaching VFR-on-top. Additionally,
the ATC authorization may contain a clearance limit, routing,
and an alternative clearance if VFR-on-top is not reached by
a specified altitude.
A pilot on an IFR flight plan, operating in VFR conditions,
may request to climb/descend in VFR conditions. When
operating in VFR conditions with an ATC authorization to

10-26

“maintain VFR-on-top/maintain VFR conditions,” pilots on
IFR flight plans must:
1.

Fly at the appropriate VFR altitude as prescribed in 14
CFR part 91.

2.

Comply with the VFR visibility and distance-fromcloud criteria in 14 CFR part 91.

3.

Comply with instrument flight rules applicable to this
flight (minimum IFR altitudes, position reporting, radio
communications, course to be flown, adherence to ATC
clearance, etc.).

Pilots operating on a VFR-on-top clearance should advise
ATC before any altitude change to ensure the exchange of
accurate traffic information.
ATC authorization to “maintain VFR-on-top” is not intended
to restrict pilots to operating only above an obscuring
meteorological formation (layer). Rather, it permits operation
above, below, between layers, or in areas where there is no
meteorological obstruction. It is imperative pilots understand,
however, that clearance to operate “VFR-on-top/VFR
conditions” does not imply cancellation of the IFR flight
plan.
Pilots operating VFR-on-top/VFR conditions may receive
traffic information from ATC on other pertinent IFR or
VFR aircraft. However, when operating in VFR weather
conditions, it is the pilot’s responsibility to be vigilant to see
and avoid other aircraft.
This clearance must be requested by the pilot on an IFR flight
plan. VFR-on-top is not permitted in certain areas, such as
Class A airspace. Consequently, IFR flights operating VFRon-top must avoid such airspace.

VFR Over-The-Top
VFR over-the-top must not be confused with VFR-ontop. VFR-on-top is an IFR clearance that allows the pilot
to fly VFR altitudes. VFR over-the-top is strictly a VFR
operation in which the pilot maintains VFR cloud clearance
requirements while operating on top of an undercast layer.
This situation might occur when the departure airport and the
destination airport are reporting clear conditions, but a low
overcast layer is present in between. The pilot could conduct
a VFR departure, fly over the top of the undercast in VFR
conditions, then complete a VFR descent and landing at the
destination. VFR cloud clearance requirements would be
maintained at all times, and an IFR clearance would not be
required for any part of the flight.

Conducting an IFR Flight
To illustrate some of the concepts introduced in this chapter,
follow along on a typical IFR flight from the Birmingham
International Airport (BHM), Birmingham, Alabama to
Gulfport-Biloxi International Airport (GPT), Gulfport,
Mississippi. [Figure 10-18] For this trip, a Cessna 182
with a call sign of N1230A will be flown. The aircraft is
equipped with dual navigation and communication radios, a
transponder, and a GPS system approved for IFR en route,
terminal, and approach operations.
Preflight
The success of the flight depends largely upon the
thoroughness of the preflight planning. The evening before
the flight, pay close attention to the weather forecast and
begin planning the flight.
The Weather Channel indicates a large, low-pressure system
has settled in over the Midwest, pulling moisture up from
the Gulf of Mexico and causing low ceilings and visibility
with little chance for improvement over the next couple of
days. To begin planning, gather all the necessary charts and
materials, and verify everything is current. This includes en
route charts, approach charts, DPs, STAR charts, the GPS
database, as well as an A/FD, some navigation logs, and the
aircraft’s POH/AFM. The charts cover both the departure
and arrival airports and any contingency airports that will
be needed if the flight cannot be completed as planned. This
is also a good time for the pilot to consider recent flight
experience, pilot proficiency, fitness, and personal weather
minimums to fly this particular flight.
Check the A/FD to become familiar with the departure and
arrival airport, and check for any preferred routing between
BHM and GPT. Next, review the approach charts and any
DP or STAR that pertains to the flight. Finally, review the en
route charts for potential routing, paying close attention to the
minimum en route and obstacle clearance altitudes.

After this review, select the best option. For this flight, the
Birmingham Three Departure [Figure 10-2] to Brookwood
VORTAC, V 209 to Kewanee VORTAC, direct to Gulfport
using GPS would be a logical route. An altitude of 4,000 feet
meets all the regulatory requirements and falls well within
the performance capabilities of the aircraft.
Next, call 1-800-WX-BRIEF to obtain an outlook-type
weather briefing for the proposed flight. This provides
forecast conditions for departure and arrival airports, as well
as the en route portion of the flight including forecast winds
aloft. This also is a good opportunity to check the available
NOTAMs.
The weather briefer confirms the predictions of the weather
channel giving forecast conditions that are at or near
minimum landing minimums at both BHM and GPT for
the proposed departure time. The briefer provides NOTAM
information for GPT indicating that the localizer to runway
32 is scheduled to be out of service and that runway 18/36 is
closed until further notice. Also check for temporary flight
restrictions (TFRs) along the proposed route.
After receiving a weather briefing, continue flight planning
and begin to transfer some preliminary information onto
the navigation log, listing each fix along the route and the
distances, frequencies, and altitudes. Consolidating this
information onto an organized navigation log will keep the
workload to a minimum during the flight.
Next, obtain a standard weather briefing online for the
proposed route. A check of current conditions indicates
low IFR conditions at both the departure airport and the
destination, with visibility of one-quarter mile:
SURFACE WEATHER OBSERVATIONS
METAR KBHM 111155Z VRB04KT ¼ SM FG –RA VV004
06/05 A2994 RMK A02 SLP140
METAR KGPT 111156Z 24003KT ¼ SM FG OVC001 08/07
A2962 RMK A02 SLP033
The small temperature/dewpoint spread is causing the low
visibility and ceilings. Conditions should improve later in
the day as temperatures increase. A check of the terminal
forecast confirms this theory:
TERMINAL FORECASTS
TAF KBHM 111156Z 111212 VRB04KT ¼ SM FG VV004
TEMPO1316 ¾ SM OVC004
FM1600 VRB05KT 2SM BR OVC007 TEMPO 1720 3SM
DZ BKN009
10-27

10-28

Figure 10-18. Route Planning.

FM2000 22008KT 3SM –RA OVC015 TEMP 2205 3SM
–RA OVC025 FM0500 23013KT P6SM OVC025

TS IMPLY SEV OR GTR TURB SEV ICE LLWS AND
IFR CONDS.

FM0800 23013KT P6SM BKN030 PROB40 1012 2SM BR
OVC030

NON MSL HGHTS DENOTED BY AGL OR CIG.

TAF KGPT 111153Z 111212 24004KT ¼ SM FG OVC001
BECMG 1317 3SM BR 0VC004
FM1700 24010KT 4SM –RA OVC006 FM0400 24010 5SM
SCT080 TEMPO 0612 P6SM SKC

A recheck of NOTAMs for Gulfport confirms that the
localizer to runway 32 is out of service until further notice
and runway 18/36 is closed. If runway 6 is planned for the
departure, confirm that the climb restriction for the departure
can be met.
GPT 12/006 GPT LOC OS UFN

In addition to the terminal forecast, the area forecast also
indicates gradual improvement along the route. Since the
terminal forecast only provides information for a 5-mile
radius around a terminal area, checking the area forecast
provides a better understanding of the overall weather picture
along the route, as well as potential hazards:

GPT 12/008 GPT MIRL RWY 18/36 OS UFN
Since the weather is substantially better to the east, Pensacola
Regional Airport is a good alternate with current conditions
and a forecast of marginal VFR.

SYNOPSIS AND VFR CLOUDS/WEATHER FORECASTS
SYNOPSIS… AREA OF LOW PRESSURE CNTD OV AL
RMNG GENLY STNRY BRNGNG MSTR AND WD SPRD
IFR TO E TN. ALF…LOW PRES TROF ACRS CNTR PTN
OF THE DFW FA WILL GDLY MOV EWD DURG PD.

METAR KPNS 111150Z 21010Z 3SM BKN014 OVC025
09/03 A2973

NRN LA, AR, NRN MS
SWLY WND THRUT THE PD. 16Z CIG OVC006. SCT
–SHRA. OTLK… IFR SRN ½ … CIG SCT – BKN015
TOPS TO FL250 SWLY WND THRUT THE PD. 17Z AGL
BKN040. OTLK…MVFR CIG VIS.

FM1700 23010KT 4SM –RA OVC030

LA MS CSTL WTRS
CIG OVC001 – OVC006. TOPS TO FL240. VIS ¼ - ¾ SM
FG. SWLY WND. 16Z CIG OVC010 VIS 2 SM BR. OCNL
VIS 3-5SM –RN BR OVC009. OTLK…MVFR CIG VIS.
FL
CIG BKN020 TOPS TO FL180. VIS 1–3 SM BR. SWLY
WND. 18Z BRK030. OTLK…MVFR CIG.
At this time, there are no SIGMETs or PIREPs reported.
However, there are several AIRMETs, one for IFR
conditions, one for turbulence that covers the entire route,
and another for icing conditions which covers an area just
north of the route:
WAUS44 KKCI 111150
DFWS WA 0111150
AIRMET SIERRA FOR IFR VALID UNTIL 111800
AIRMET IFR...OK TX LA AR MS AL FL

TAF KPNS 111152Z 111212 22010KT 3 SM BR OVC020
BECMG 1317 4 SM BR OVC025

FM 0400 25014KT 5SM OVC050 TEMPO1612 P6SM
OVC080
If weather minimums are below a pilot’s personal minimums,
a delay in departure to wait for improved conditions is
a good decision. This time can be used to complete the
navigation log which is the next step in planning an IFR
flight. [Figure 10-19]
Use the POH/AFM to compute a true airspeed, cruise power
setting, and fuel burn based on the forecast temperatures
aloft and cruising pressure altitude. Also, compute weightand-balance information and determine takeoff and landing
distances. There will be a crosswind if weather conditions
require a straight-in landing on runway 14 at GPT. Therefore,
compute the landing distance assuming a 10-knot crosswind
and determine if the runway length is adequate to allow
landing. Determine the estimated flight time and fuel burn
using the winds aloft forecast and considering Pensacola
Regional Airport as an alternate airport. With full tanks, the
flight can be made nonstop with adequate fuel for flight to
the destination, alternate, and the reserve requirement.
Next, check the surface analysis chart which shows where the
pressure systems will be found. The weather depiction chart
shows areas of IFR conditions and can be used to find areas

10-29

Figure 10-19. Navigation Log.

of improving conditions. These charts provide information
a pilot will need should a diversion to VFR conditions be
required. For this flight, the radar depicts precipitation along
the route, and the latest satellite photo confirms what the
weather depiction chart showed.
When the navigation log is finished, complete the flight plan
in preparation for filing with flight service. [Figure 10-20]

10-30

Call an AFSS for an updated weather briefing, Birmingham
INTL airport is now reporting 700 overcast with 3 miles
visibility, and Gulfport-Biloxi is now 400 overcast with 2
miles visibility. The alternate, Pensacola Regional Airport,
continues to report adequate weather conditions with 2,000
overcast and 3 miles visibility in light rain.

Figure 10-20. Flight Plan Form.

Several pilot reports have been submitted for light icing
conditions; however, all the reports are north of the route
of flight and correspond to the AIRMET that was issued
earlier. No pilot reports have included cloud tops, but the
area forecast predicted cloud tops to flight level 240. Since
the weather conditions appear to be improving, a flight plan
can be filed using the completed form.

within the preceding 30 days. Turn on the master switch and
pitot heat, and quickly check the heating element before it
becomes too hot. Then, complete the rest of the walk-around
procedure. Since this will be a flight in actual IFR conditions,
place special emphasis on IFR equipment during the walkaround, including the alternator belt and antennas. After
completing the preflight, organize charts, pencils, paper, and
navigation log in the flight deck for quick, easy access. This
is also the time to enter the planned flight into the GPS.

Analyze the latest weather minimums to determine if they
exceed personal minimums. With the absence of icing
reported along the route and steadily rising temperatures,
structural icing should not be a problem. Make a note to
do an operational check of the pitot heat during preflight
and to take evasive action immediately should even light
icing conditions be encountered in flight. This may require
returning to BHM or landing at an intermediate spot before
reaching GPT. The go/no-go decision will be constantly
reevaluated during the flight.

Departure
After starting the engine, tune in ATIS and copy the
information to the navigation log. The conditions remain the
same as the updated weather briefing with the ceiling at 700
overcast, and visibility at 3 miles. Call clearance delivery to
receive a clearance:

Once at the airport, conduct a thorough preflight inspection.
A quick check of the logbooks indicates all airworthiness
requirements have been met to conduct this IFR flight
including an altimeter, static, and transponder test within
the preceding 24 calendar months. In addition, a log on
the clipboard indicates the VOR system has been checked

“Cessna 1230A is cleared to Gulfport-Biloxi via the
Birmingham Three Departure, Brookwood, Victor
209 Kewanee then direct Mindo, Gulfport. Climb and
maintain 4,000. Squawk 0321.”

“Clearance Delivery, Cessna 1230A IFR to Gulfport
Biloxi with information Kilo, ready to copy.”

10-31

Read back the clearance and review the DP. Although a
departure frequency was not given in the clearance, note that
on the DP, the departure control frequency is listed as 123.8
for the southern sector. Since a departure from runway 24
is anticipated, note the instruction to climb to 2,100 prior
to turning. After tuning in the appropriate frequencies and
setting up navigation equipment for the departure routing,
contact ground control (noting that this is IFR) and receive
the following clearance:
“Cessna 1230A taxi to runway 24 via taxiway
Mike.”
Read back the clearance and aircraft call sign. After a review
of the taxi instructions on the airport diagram, begin to taxi
and check the flight instruments for proper indications.
Hold short of runway 24 and complete the before takeoff
checklist and engine run-up. Advise the tower when ready
for takeoff. The tower gives the following clearance:
“Cessna 30A cleared for takeoff runway 24.
Caution wake turbulence from 737 departing to the
northwest.”
Taxi into position. Note the time off on the navigation log,
verify that the heading indicator and magnetic compass are
in agreement, the transponder is in the ALT position, all the
necessary lights, equipment, and pitot heat are on. Start the
takeoff roll. To avoid the 737’s wake turbulence, make note
of its lift off point and take off prior to that point.
En Route
After departure, climb straight ahead to 2,100 feet as directed
by the Birmingham Three Departure. While continuing a
climb to the assigned altitude of 4,000 feet, the following
instructions are received from the tower:
“Cessna 30A contact Departure.”
Acknowledge the clearance and contact departure on the
frequency designated by the DP. State the present altitude
so the departure controller can check the encoded altitude
against indicated altitude:
“Birmingham Departure Cessna 1230A climbing
through 2,700 heading 240.”
Departure replies:
“Cessna 30A proceed direct to Brookwood and resume
own navigation. Contact Atlanta Center on 134.05.”
Acknowledge the clearance, contact Atlanta Center and
proceed direct to Brookwood VORTAC, using the IFRapproved GPS equipment. En route to Kewanee, VORTAC
Atlanta Center issues the following instructions:
10-32

“Cessna 1230A contact Memphis Center on
125.975.”
Acknowledge the instructions and contact Memphis Center
with aircraft ID and present altitude. Memphis Center
acknowledges contact:
“Cessna 1230A, Meridian altimeter is 29.87. Traffic
at your 2 o’clock and 6 miles is a King Air at 5,000
climbing to 12,000.”
Even when on an IFR flight plan, pilots are still responsible
for seeing and avoiding other aircraft. Acknowledge the call
from Memphis Center and inform them of negative contact
with traffic due to IMC.
“Roger, altimeter setting 29.87. Cessna 1230A is in
IMC negative contact with traffic.”
Continue the flight, and at each fix note the arrival time on
the navigation log to monitor progress.
To get an update of the weather at the destination and issue
a pilot report, contact the FSS servicing the area. To find
the nearest AFSS, locate a nearby VOR and check above
the VOR information box for a frequency. In this case, the
nearest VOR is Kewanee VORTAC which lists a receiveonly frequency of 122.1 for Greenwood FSS. Request a
frequency change from Memphis and then attempt to contact
Greenwood on 122.1 while listening over the Kewanee
VORTAC frequency of 113.8:
“Greenwood Radio Cessna 1230A receiving on
frequency 113.8, over.”
“Cessna 30A, this is Greenwood, go ahead.”
“Greenwood Radio, Cessna 30A is currently 30 miles
south of the Kewanee VORTAC at 4,000 feet en
route to Gulfport. Requesting an update of en route
conditions and current weather at GPT, as well as
PNS.”
“Cessna 30A, Greenwood Radio, current weather at
Gulfport is 400 overcast with 3 miles visibility in light
rain. The winds are from 140 at 7 and the altimeter
is 29.86. Weather across your route is generally IFR
in light rain with ceilings ranging from 300 to 1,000
overcast with visibilities between 1 and 3 miles.
Pensacola weather is much better with ceilings now
at 2,500 and visibility 6 miles. Checking current
NOTAMs at GPT shows the localizer out of service
and runway 18/36 closed.”

“Roger, Cessna 30A copies the weather. I have a
PIREP when you are ready to copy.”
“Cessna 30A go ahead with your PIREP.”
“Cessna 30A is a Cessna 182 located on the Kewanee
195° radial at 30 miles level at 4,000 feet. I am
currently in IMC conditions with a smooth ride.
Outside air temperature is plus 1° Celsius. Negative
icing.”
“Cessna 30A thank you for the PIREP.”
With the weather check and PIREP complete, return to
Memphis Center:
“Memphis Center, Cessna 1230A is back on your
frequency.”
“Cessna 1230A, Memphis Center, roger, contact
Houston Center now on frequency 126.8.”
“Roger, contact Houston Center frequency 126.8,
Cessna 1230A.”
“Houston Center, Cessna 1230A level at 4,000
feet.”

will affect the sensitivity of the CDI. Tune in the VORTAC
frequency of 109.0 on the number one navigation radio, and
set in the final approach course of 133° on the OBS. This
setup will help with situational awareness should the GPS
lose signal.
“Cessna 30A your position is 7 miles from MINDO,
maintain 3,000 feet until MINDO, cleared for the GPS
runway 14 approach.”
Read back the clearance and concentrate on flying the aircraft.
At MINDO descend to 2,000 as depicted on the approach
chart. At BROWA turn to the final approach course of
133°. Just outside the Final Approach Way Point (FAWP)
AVYUM, the GPS will change to the approach mode and
the CDI will become even more sensitive. Gulfport approach
control issues instructions to contact Gulfport tower:
“Cessna 30A contact Tower on 123.7.”
“123.7, Cessna 30A.”
“Tower, Cessna 1230A outside AVYUM on the GPS
runway 14.”
“Cessna 30A Gulfport Tower, the ceiling is now 600
overcast and the visibility is 4 miles.”
“Cleared to land runway 14, Cessna 30A.”

“Cessna 30A, Houston Center area altimeter 29.88.”
Arrival
40 miles north of Gulfport, tune in ATIS on number two
communication radio. The report reveals there has been no
change in the weather and ATIS is advertising ILS runway
14 as the active approach.
Houston Center completes a hand off to Gulfport approach
control with instructions to contact approach:
“Gulfport Approach, Cessna 1230A level 4,000 feet
with information TANGO. Request GPS Runway 14
approach.”
“Cessna 30A, Gulfport Approach, descend and
maintain 3,000 feet.”

Continue the approach, complete the appropriate checklists,
cross AVYUM, and begin the final descent. At 700 feet MSL
visual contact with the airport is possible. Slow the aircraft
and configure it to allow a normal descent to landing. As
touch down is completed, Gulfport Tower gives further
instructions:
“Cessna 30A turn left at taxiway Bravo and contact
ground on 120.4.”
“Roger, Cessna 30A.”
Taxi clear of the runway and complete the appropriate
checklists. The Tower will automatically cancel the IFR
flight plan.

“Descend to 3,000, Cessna 30A.”
Begin a descent to 3,000 and configure your navigation
radios for the approach. The GPS will automatically change
from the en route mode to the terminal mode. This change
10-33

10-34

Chapter 11

Emergency
Operations
Introduction
Changing weather conditions, air traffic control (ATC), the
aircraft, and the pilot are all variables that make instrument
flying an unpredictable and challenging operation. The safety
of the flight depends upon the pilot’s ability to manage these
variables while maintaining positive aircraft control and
adequate situational awareness. This chapter discusses the
recognition and suggested remedies for such abnormal and
emergency events related to unforecasted, adverse weather;
aircraft system malfunctions; communication/navigation
system malfunctions; and loss of situational awareness.

11-1

Unforecast Adverse Weather
Inadvertent Thunderstorm Encounter
A pilot should avoid flying through a thunderstorm of any
intensity. However, certain conditions may be present that
could lead to an inadvertent thunderstorm encounter. For
example, flying in areas where thunderstorms are embedded
in large cloud masses may make thunderstorm avoidance
difficult, even when the aircraft is equipped with thunderstorm
detection equipment. Therefore, pilots must be prepared to
deal with an inadvertent thunderstorm penetration. At the
very least, a thunderstorm encounter subjects the aircraft to
turbulence that could be severe. The pilot and passengers
should tighten seat belts and shoulder harnesses and secure
any loose items in the cabin.
As with any emergency, the first order of business during
an inadvertent thunderstorm encounter must be to fly the
aircraft. The pilot workload is heavy; therefore, increased
concentration is necessary to maintain an instrument scan.
If a pilot inadvertently enters a thunderstorm, it is better to
maintain a course straight through the thunderstorm rather
than turning around. A straight course minimizes the amount
of time in the thunderstorm and turning maneuvers only
increase structural stress on the aircraft.
Reduce power to a setting that maintains a speed at the
recommended turbulence penetration speed as described in the
Pilot’s Operating Handbook/Airplane Flight Manual (POH/
AFM), and try to minimize additional power adjustments.
Concentrate on maintaining a level attitude while allowing
airspeed and altitude to fluctuate. Similarly, if using the
autopilot, disengage the altitude hold and speed hold modes,
as they only increase the aircraft’s maneuvering—thereby
increasing structural stress.
During a thunderstorm encounter, the potential for icing
also exists. As soon as possible, turn on anti-icing/deicing
equipment and carburetor heat, if equipped. Icing can be
rapid at any altitude and may lead to power failure and/or
loss of airspeed indication.
Lightning is also present in a thunderstorm and can
temporarily blind a pilot. To reduce this risk, turn up flight
deck lights to the highest intensity, concentrate on the flight
instruments, and resist the urge to look outside.
Inadvertent Icing Encounter
Because icing is unpredictable in nature, pilots may find
themselves in icing conditions even though they have done
everything practicable to avoid it. In order to stay alert to this
possibility while operating in visible moisture, pilots should
monitor the outside air temperature (OAT).

11-2

The effects of ice on aircraft are cumulative—thrust is
reduced, drag increases, lift lessens, and weight increases.
The results are an increase in stall speed and a deterioration
of aircraft performance. In extreme cases, two to three inches
of ice can form on the leading edge of the airfoil in less than
5 minutes. It takes only 1/2 inch of ice to reduce the lifting
power of some aircraft by 50 percent and increases the
frictional drag by an equal percentage.
A pilot can expect icing when flying in visible precipitation,
such as rain or cloud droplets, and the temperature is
between +02 and -10° Celsius. When icing is detected, a
pilot should do one of two things, particularly if the aircraft
is not equipped with deicing equipment: leave the area of
precipitation or go to an altitude where the temperature is
above freezing. This “warmer” altitude may not always be
a lower altitude. Proper preflight action includes obtaining
information on the freezing level and the above-freezing
levels in precipitation areas.
If neither option is available, consider an immediate landing
at the nearest suitable airport. Even if the aircraft is equipped
with anti-icing/deicing equipment, it is not designed to allow
aircraft to operate indefinitely in icing conditions. Antiicing/deicing equipment gives a pilot more time to get out of
the icing conditions. Report icing to ATC and request new
routing or altitude. Be sure to report the type of aircraft, and
use the following terms when reporting icing to ATC:
1.

Trace. Ice becomes perceptible. Rate of accumulation
is slightly greater than sublimation. Deicing/anti-icing
equipment is not utilized unless encountered for an
extended period of time (over 1 hour).

2.

Light. The rate of accumulation may create a problem
if flight is prolonged in this environment (over 1
hour). Occasional use of deicing/anti-icing equipment
removes/prevents accumulation. It does not present a
problem if deicing/anti-icing equipment is used.

3.

Moderate. The rate of accumulation is such that even
short encounters become potentially hazardous and
use of deicing/anti-icing equipment or flight diversion
is necessary.

4.

Severe. The rate of accumulation is such that deicing/
anti-icing equipment fails to reduce or control the
hazard. Immediate flight diversion is necessary.

Early ice detection is critical and is particularly difficult during
night flight. Use a flashlight to check for ice accumulation on
the wings. At the first indication of ice accumulation, take
action to get out of the icing conditions. Refer to the POH/
AFM for the proper use of anti-icing/deicing equipment.

Figure 11-1. St. Elmo’s Fire is harmless but may affect both communication and navigation radios, especially the lower frequencies

such as those used on the ADF.

Precipitation Static
Precipitation static, often referred to as P-static, occurs
when accumulated static electricity is discharged from the
extremities of the aircraft. This discharge has the potential
to create problems for the instrument pilot. These problems
range from the serious, such as erroneous magnetic compass
readings and the complete loss of very high frequency (VHF)
communications to the annoyance of high-pitched audio
squealing and St. Elmo’s fire. [Figure 11-1]
Precipitation static is caused when an aircraft encounters
airborne particles during flight (e.g., rain or snow),
and develops a negative charge. It can also result from
atmospheric electric fields in thunderstorm clouds. When
a significant negative voltage level is reached, the aircraft
discharges it, which can create electrical disturbances. This
electrical discharge builds with time as the aircraft flies in
precipitation. It is usually encountered in rain, but snow can
cause the same effect. As the static buildup increases, the
effectiveness of both communication and navigation systems
decreases to the point of potential unusability.
To reduce the problems associated with P-static, the pilot
should ensure the aircraft’s static wicks are properly maintained
and accounted for. Broken or missing static wicks should be
replaced before an instrument flight. [Figure 11-2]

Aircraft System Malfunctions
Preventing aircraft system malfunctions that might lead
to an inflight emergency begins with a thorough preflight

Figure 11-2. One example of a static wick installed on aircraft

control surface to bleed off static charges built up during flight.
This will prevent static buildup and St. Elmo’s fire by allowing
the static electricity to dissipate harmlessly.

11-3

inspection. In addition to those items normally checked
prior to a visual flight rules (VFR) flight, pilots intending to
fly under instrument flight rules (IFR) should pay particular
attention to the alternator belt, antennas, static wicks, antiicing/deicing equipment, pitot tube, and static ports.
During taxi, verify the operation and accuracy of all flight
instruments. In addition, during the run-up, verify that the
operation of the pneumatic system(s) is within acceptable
parameters. It is critical that all systems are determined to be
operational before departing into IFR conditions.
Electronic Flight Display Malfunction
When a pilot becomes familiar and comfortable with the
new electronic displays, he or she also tends to become more
reliant on the system. The system then becomes a primary
source of navigation and data acquisition instead of the
supplementary source of data as initially intended.
Complete reliance on the moving map for navigation becomes
a problem during a failure of one, more, or all of the flight
display screens. Under these conditions, the systems revert to
a composite mode (called reversionary), which eliminates the
moving map display and combines the PFD with the engine

indicating system. [Figure 11-3] If a pilot has relied on the
display for navigation information and situational awareness,
he or she lacks any concept of critical data such as the aircraft’s
position, the nearest airport, or proximity to other aircraft.
The electronic flight display is a supplementary source of
navigation data and does not replace en route charts. To
maintain situational awareness, a pilot must follow the flight
on the en route chart while monitoring the PFD. It is important
for the pilot to know the location of the closest airport as
well as surrounding traffic relative to the location of his or
her aircraft. This information becomes critical should the
electronic flight display fail.
For the pilot who utilizes the electronic database as a
substitute for the Airport Facilities Directory, screen failure
or loss of electrical power can mean the pilot is no longer
able to access airport information. Once the pilot loses the
ability to call up airport information, aeronautical decisionmaking is compromised.
Alternator/Generator Failure
Depending upon the aircraft being flown, an alternator failure
is indicated in different ways. Some aircraft use an ammeter

Figure 11-3. G1000 PFD display in normal mode and in the reversionary mode activated upon system failure.

11-4

Figure 11-4. Ammeter (left) and Loadmeter (right).

that indicates the state of charge or discharge of the battery.
[Figure 11-4] A positive indication on the ammeter indicates
a charge condition; a negative indication reveals a discharge
condition. Other aircraft use a load meter to indicate the load
being carried by the alternator. [Figure 11-4]
Sometimes an indicator light is also installed in the aircraft to
alert the pilot to an alternator failure. On some aircraft such
as the Cessna 172, the light is located on the lower left side
making it difficult to see its illumination if charts are open
Ensure that these safety indicators are visible during flight.
When a loss of the electrical charging system is experienced,
the pilot has approximately 40 minutes of battery life
remaining before the system fails entirely. The time
mentioned is an approximation and should not be relied upon
as specific to all aircraft. In addition, the battery charge that
exists in a battery may not be full, altering the time available
before electrical exhaustion occurs. At no time should a pilot
consider continuing a flight once the electrical charging
system has failed. Land at the nearest suitable airport.

consider pulling circuit breakers to isolate those pieces of
equipment from the electrical system. Maximum time of
useful voltage may be between 30 and 40 minutes and is
influenced by many factors, which degrade the useful time.
Loss of Alternator/Generator for Electronic Flight
Instrumentation
With the increase in electrical components being installed
in modern technically advanced aircraft, the power supply
and the charging system need increased attention and
understanding. Traditional round dial aircraft do not rely
as heavily on electrical power for the primary six-pack
instrumentation. Modern electronic flight displays utilize the
electrical system to power the AHRS, ADC, engine indicating
system (EIS), etc. A loss of an alternator or generator was
considered an abnormality in traditionally equipped aircraft;

Techniques for Electrical Usage

Master Battery Switch
One technique for conserving the main battery charge is
to fly the aircraft to the airport of intended landing while
operating with minimal power. If a two-position battery
master/alternator rocker switch [Figure 11-5] is installed, it
can be utilized to isolate the main battery from the electrical
system and conserve power.

Operating on the Main Battery
While en route to the airport of intended landing, reduce the
electrical load as much as practical. Turn off all unnecessary
electrical items such as duplicate radios, non-essential
lighting, etc. If unable to turn off radios, lights, etc. manually,

Figure 11-5. Double Rocker Switch Seen on Many Aircraft.

11-5

however, a failure of this magnitude is considered an
emergency in technically advanced aircraft.
Due to the increased demand for electrical power, it is
necessary for manufacturers to install a standby battery in
conjunction with the primary battery. The standby battery is
held in reserve and kept charged in case of a failure of the
charging system and a subsequent exhaustion of the main
battery. The standby battery is brought online when the main
battery voltage is depleted to a specific value, approximately
19 volts. Generally, the standby battery switch must be in the
ARM position for this to occur but pilots should refer to the
aircraft flight manual for specifics on an aircraft’s electrical
system. The standby battery powers the essential bus and
allows the primary flight display (PFD) to be utilized.
The essential bus usually powers the following
components:
1.

AHRS (Attitude and Heading Reference System)

2.

ADC (Air Data Computer)

3.

PFD (Primary Flight Display)

4.

Navigation Radio #1

5.

Communication Radio #1

6.

Standby Indicator Light

once the standby battery has exhausted its charge, the flight
deck may become very dark depending on what time of
day the failure occurs. The priority during this emergency
situation is landing the aircraft as soon as possible without
jeopardizing safety.
A standby attitude indicator, altimeter, airspeed indicator
(ASI) and magnetic compass are installed in each aircraft
for use when the PFD instrumentation is unavailable.
[Figure 11-7] These would be the only instruments left
available to the pilot. Navigation would be limited to pilotage
and dead reckoning unless a hand-held transceiver with a
GPS/navigation function is onboard.
Once an alternator failure has been detected, the pilot must
reduce the electrical load on the battery and land as soon as
practical. Depending upon the electrical load and condition
of the battery, there may be sufficient power available for
45 minutes of flight—or for only a matter of minutes. Pilots
should also know which systems on the aircraft are electric and
those that continue to operate without electrical power. Pilots
can attempt to troubleshoot alternator failure by following
the established alternator failure procedure published in the
POH/AFM. If the alternator cannot be reset, advise ATC of
the situation and inform them of the impending electrical
failure.

Techniques for Electrical Usage

Analog Instrument Failure

Standby Battery

A warning indicator or an inconsistency between indications
on the attitude indicator and the supporting performance

One technique for conserving the main battery charge is
to fly the aircraft to the airport of intended landing while
using the standby battery. A two-position battery master/
alternator rocker switch is installed on most aircraft with
electronic flight displays, which can be utilized to isolate
the main battery from the electrical system. By switching the
MASTER side off, the battery is taken offline and the standby
battery comes online to power the essential bus. However,
the standby battery switch must be in the ARM position for
this to occur. [Figure 11-6] Utilization of the standby battery
first reserves the main battery for use when approaching to
land. With this technique, electrical power may be available
for the use of flaps, gear, lights, etc. Do not rely on any power
to be available after the standby battery has exhausted itself.
Once the charging system has failed, flight with a powered
electrical system is not guaranteed.

Operating on the Main Battery
While en route to the airport of intended landing, reduce the
electrical load as much as practical. Turn off all unnecessary
electrical items such as duplicate radios, non-essential
lighting, etc. If unable to turn off radios, lights, etc., manually,
consider pulling circuit breakers to isolate those pieces of
equipment from the electrical system. Keep in mind that
11-6

Figure 11-6. Note the double rocker switch and the standby battery

switch in this aircraft. The standby battery must be armed to work
correctly; arming should be done prior to departure.

Figure 11-7. Emergency Instrumentation Available to the Pilot on Electronic Flight Instrumented Aircraft.

instruments usually identifies system or instrument failure.
Aircraft control must be maintained while identifying the
failed component(s). Expedite the cross-check and include
all flight instruments. The problem may be individual
instrument failure or a system failure affecting multiple
instruments.

supplied by a vacuum pump mechanically driven off the
engine. Occasionally these pumps fail, leaving the pilot with
inoperative attitude and heading indicators.

One method of identification involves an immediate
comparison of the attitude indicator with the rate-of-turn
indicator and vertical speed indicator (VSI). Along with
providing pitch-and-bank information, this technique
compares the static system with the suction or pressure system
and the electrical system. Identify the failed component(s)
and use the remaining functional instruments to maintain
aircraft control.

Figure 11-8 illustrates inoperative vacuum driven attitude
and heading indicators which can fail progressively. As the
gyroscopes slow down they may wander, which, if connected
to the autopilot and/or flight director, can cause incorrect
movement or erroneous indications. In Figure 11-8, the
aircraft is actually level and at 2,000 feet MSL. It is not in
a turn to the left which the pilot may misinterpret if he or
she fails to see the off or failed flags. If that occurs, the pilot
may transform a normally benign situation into a hazardous
situation. Again, good decision-making by the pilot only
occurs after a careful analysis of systems.

Attempt to restore the inoperative component(s) by checking
the appropriate power source, changing to a backup or
alternate system, and resetting the instrument if possible.
Covering the failed instrument(s) may enhance a pilot’s
ability to maintain aircraft control and navigate the aircraft.
Usually, the next step is to advise ATC of the problem and,
if necessary, declare an emergency before the situation
deteriorates beyond the pilot’s ability to recover.

Many small aircraft are not equipped with a warning system
for vacuum failure; therefore, the pilot should monitor the
system’s vacuum/pressure gauge. This can be a hazardous
situation with the potential to lead the unsuspecting pilot into
a dangerous unusual attitude which would require a partial
panel recovery. It is important that pilots practice instrument
flight without reference to the attitude and heading indicators
in preparation for such a failure.

Pneumatic System Failure

Pitot/Static System Failure

One possible cause of instrument failure is a loss of the
suction or pressure source. This pressure or suction is

A pitot or static system failure can also cause erratic and
unreliable instrument indications. When a static system
11-7

Figure 11-8. Vacuum Failure.

problem occurs, it affects the ASI, altimeter, and the VSI.
In most aircraft, provisions have been made for the pilot to
select an alternate static source. Check the POH/AFM for
the location and operation of the alternate static source. In
the absence of an alternate static source, in an unpressurized
aircraft, the pilot could break the glass on the VSI. The VSI
is not required for instrument flight, and breaking the glass
provides the altimeter and the ASI a source of static pressure.
This procedure could cause additional instrument errors.

3.

In the absence of an assigned route, by the route
that ATC has advised may be expected in a further
clearance; or

4.

In the absence of an assigned route or a route that ATC
has advised may be expected in a further clearance,
by the route filed in the flight plan.

The pilot should maintain the highest of the following
altitudes or flight levels for the route segment being flown:

Communication/Navigation System
Malfunction

1.

The altitude or flight level assigned in the last ATC
clearance received;

Avionics equipment has become very reliable, and the
likelihood of a complete communications failure is remote.
However, each IFR flight should be planned and executed in
anticipation of a two-way radio failure. At any given point
during a flight, the pilot must know exactly what route to fly,
what altitude to fly, and when to continue beyond a clearance
limit. Title 14 of the Code of Federal Regulations (14 CFR)
part 91 describes the procedures to be followed in case of a
two-way radio communications failure. If operating in VFR
conditions at the time of the failure, the pilot should continue
the flight under VFR and land as soon as practicable. If the
failure occurs in IFR conditions, or if VFR conditions cannot
be maintained, the pilot must continue the flight:

2.

The minimum altitude (converted, if appropriate, to
minimum flight level as prescribed in part 91 for IFR
operations); or

3.

The altitude or flight level ATC has advised may be
expected in a further clearance.

1.

Along the route assigned in the last ATC clearance
received;

2.

If being radar vectored, by the direct route from the
point of radio failure to the fix, route, or airway specified
in the vector clearance;

11-8

In addition to route and altitude, the pilot must also plan the
progress of the flight to leave the clearance limit.
1.

When the clearance limit is a fix from which an
approach begins, commence descent or descent
and approach as close as possible to the expectfurther-clearance time if one has been received. If an
expect-further-clearance time has not been received,
commence descent or descent and approach as close as
possible to the estimated time of arrival as calculated
from the filed or amended (with ATC) estimated time
en route.

2.

If the clearance limit is not a fix from which an
approach begins, leave the clearance limit at the
expect-further-clearance time if one has been received.
If no expect-further-clearance time has been received,
leave the clearance limit upon arrival over it, and
proceed to a fix from which an approach begins and
commence descent or descent and approach as close as
possible to the estimated time of arrival as calculated
from the filed or amended (with ATC) estimated time
en route. [Figure 11-8]

While following these procedures, set the transponder to
code 7600 and use all means possible to reestablish two-way
radio communication with ATC. This includes monitoring
navigational aids (NAVAIDs), attempting radio contact with
other aircraft, and attempting contact with a nearby automated
flight service station (AFSS).

GPS Nearest Airport Function
Procedures for accessing the nearest airport information
vary by the type of display installed in an aircraft. Pilots can
obtain information relative to the nearest airport by using the
PFD, MFD, or the nearest function on the GPS receiver. The
following examples are based on a popular system. Pilots
should become familiar with the operational characteristics
of the equipment to be used.

Nearest Airports Using the PFD
With the advancements in electronic databases, diverting to
alternate airports has become easier. Simply by pressing a soft
key on the PFD, pilots can access information for up to 25 of
the nearest airports that meet the criteria set in the systems
configuration page. [Figure 11-9] Pilots are able to specify
what airports are acceptable for their aircraft requirements
based on landing surface and length of runway.
When the text box opens, the flashing cursor is located over
the nearest airport that meets the criteria set in the auxiliary
setup page as shown in Figure 11-10. Scrolling through the
25 airports is accomplished by turning the outer FMS knob,
which is located on the lower right corner of the display
screen. Turning the FMS knob clockwise moves the blinking
cursor to the next closest airport. By continuing to turn the
knob, the pilot is able to scroll through all 25 nearest airports.
Each airport box contains the information illustrated in
Figure 11-11, which the pilot can utilize to determine which
airport best suits their individual needs.

Additional Information for a Specific Airport
In addition to the information that is presented on the first
screen, the pilot can view additional information as shown in
Figure 11-12 by highlighting the airport identifier and then
pressing the enter key.

Figure 11-9. The default soft key menu that is displayed on the PFD contains a “NRST” (Nearest Airport) soft key. Pressing this soft

key opens a text box which displays the nearest 25 airports.

11-9

From this menu or the previous default nearest airport screen,
the pilot is able to activate the Direct-To function, which
provides a direct GPS course to the airport. In addition,
the pilot can auto-tune communication frequencies by
highlighting the appropriate frequency and then pressing
the enter key. The frequency is placed in the stand-by box
of either COM1 or COM2, whichever frequency has the
cyan box around it.
Nearest Airports Using the MFD
A second way to determine the nearest airport is by
referencing the NRST Page Group located on the MFD. This
method provides additional information to the pilot; however,
it may require additional steps to view. [Figure 11-13]

Navigating the MFD Page Groups
Figure 11-10. An enlargement of the box shown in the lower right

of Figure 11-9. Note that KGNV would be flashing.

Most display systems are designed for ease of navigation
through the different screens on the MFD. Notice the
various page groups in the lower right-hand corner of the
MFD screen. Navigation through these four page groups
is accomplished by turning the outer FMS knob clockwise.
[Figure 11-14]
Within each page group are specific pages that provide
additional information pertaining to that specific group. Once
the desired page group and page is selected, the MFD remains
in that configuration until the page is changed or the CLR
button is depressed for more than 2 seconds. Holding the CLR
button returns the display to the default moving map page.

Nearest Airport Page Group

Figure 11-11. Information shown on the nearest airport page.

The nearest airport page contains specific areas of interest
for the airport selected. [Figure 11-15] The pilot is furnished
information regarding runways, frequencies, and types of
approaches available.

Nearest Airports Page Soft Keys
Figure 11-16 illustrates four specific soft keys that allow
the pilot to access independent windows of the airport page.
Selection of each of these windows can also be accomplished
by utilizing the MENU hard key.
The soft keys and functions are as follows: Scroll through
each section with the cursor, then press enter to accept the
selection.
1.

Figure 11-12. Information shown on the additional information

page that will aid the pilot in making a more informed decision
about which airport to choose when diverting.

11-10

APT. Allows the user access to scroll through the
25 nearest airports. The white arrow indicates which
airport is selected. The INFORMATION window
is slaved to the white arrow. The INFORMATION
window decodes the airport identifier. Scroll through
the 25 airports by turning the outer FMS knob.

Figure 11-13. The MFD is another means of viewing the nearest airports.

2.

RNWY. Moves the cursor into the Runways section
and allows the user to scroll through the available
runways at a specific airport that is selected in
conjunction with the APT soft key. A green arrow
indicates additional runways to view.

3.

FREQ. Moves the cursor into the Frequencies section
and allows the pilot to highlight and auto-tune the
frequency into the selected standby box.

4.

APR. Moves the cursor into the Approach section and
allows the pilot to review approaches and load them
into the flight plan. When the APR soft key is selected,
an additional soft key appears. The LD APR (Load
Approach) soft key must be pressed once the desired
instrument approach procedure has been highlighted.
Once the soft key is pressed, the screen changes to the
PROC Page Group. From this page the pilot is able to
choose the desired approach, the transition, and choose
the option to activate the approach or just load it into
the flight plan.

end of the SA spectrum is a pilot who is knowledgeable of
every aspect of the flight; consequently, this pilot’s decisionmaking is proactive. With good SA, this pilot is able to make
decisions well ahead of time and evaluate several different
options. On the other end of the SA spectrum is a pilot who
is missing important pieces of the puzzle: “I knew exactly
where I was when I ran out of fuel.” Consequently, this
pilot’s decision-making is reactive. With poor SA, a pilot

Situational Awareness
Situational awareness (SA) is not simply a mental picture of
aircraft location; rather, it is an overall assessment of each
element of the environment and how it affects a flight. On one

Figure 11-14. Page Groups. As the FMS outer knob is rotated, the

current page group is indicated by highlighting the specific group
indicator. Notice that the MAP page group is highlighted.

11-11

Figure 11-15. The page group of nearest airports has been selected.

lacks a vision of future events and is forced to make decisions
quickly, often with limited options.
During a typical IFR flight, a pilot operates at varying levels
of SA. For example, a pilot may be cruising to his or her
destination with a high level of SA when ATC issues an
unexpected standard terminal arrival route (STAR). Since the
pilot was not expecting the STAR and is not familiar with it,
SA is lowered. However, after becoming familiar with the
STAR and resuming normal navigation, the pilot returns to
a higher level of SA.
Factors that reduce SA include: distractions, unusual or
unexpected events, complacency, high workload, unfamiliar
situations, and inoperative equipment. In some situations, a
loss of SA may be beyond a pilot’s control. For example, a
pneumatic system failure and associated loss of the attitude
and heading indicators could cause a pilot to find his or her
aircraft in an unusual attitude. In this situation, established
procedures must be used to regain SA.
Pilots should be alert to a loss of SA anytime they are in a
reactive mindset. To regain SA, reassess the situation and
seek additional information from other sources, such as the
navigation instruments or ATC.

11-12

Summary
Electronic flight displays have been dramatically improved
regarding how information is displayed and what information
is available to a pilot. With only the push of a button, a pilot
is able to access information that was traditionally contained
in multiple publications. (Electronic databases have replaced
paper manuals and reduced the clutter in the flight deck.)
Multi-Function Displays (MFD) are capable of displaying
moving maps that mirror sectional charts. These detailed
displays depict all airspace including permanent temporary
flight restrictions (TFRs).
In fact, MFDs have become so descriptive that many pilots
fall into the trap of relying solely on the moving maps for
navigation. In addition, pilots are drawing upon the database
to familiarize themselves with departure and destination
airport information.
Pilots are relying heavily on the electronic database for their
flight planning and have moved away from the traditional
method of cross-country flight planning. It is imperative
to understand that the electronic flight display adds to the
overall quality of the flight experience, but can also lead to

Figure 11-16. The four soft keys at the bottom of the MFD are airport (A), runway (B), frequency (C), and approach (D).

11-13

catastrophe if not utilized properly. At no time is the moving
map meant to substitute for a VFR sectional or Low Altitude
En Route chart.
Traffic Avoidance
Electronic flight displays have the capability of displaying
transponder-equipped aircraft on the MFD as well as the
inset map on the PFD. However, due to the limitations of the
systems, not all traffic is displayed. Some TIS units display
only eight intruding targets within the service volume. The
normal service volume has altitude limitations of 3,500 feet
below the aircraft to 3,500 feet above the aircraft. The lateral
limitation is 7 NM. [Figure 11-17] Pilots unfamiliar with the
limitations of the system may rely on the aural warnings to
alert them to approaching traffic.

Figure 11-17. The Area Surrounding the Aircraft for Coverage

Using TIS.

Figure 11-18. A Typical Display on Aircraft MFD When Using TIS.

11-14

In addition to an outside visual scan of traffic, a pilot should
incorporate any Traffic Information electronically displayed
such as TIS. This innovation in traffic alerting reinforces and
adds synergy to the ability to see and avoid. However, it is
an aid and not a replacement for the responsibilities of the
pilot. Systems such as TIS provide a visual representation
of nearby traffic and displays a symbol on the moving map
display with relative information about altitude, vertical
trends, and direction of flight. [Figure 11-18]

It is important to remember that most systems display only a
specific maximum number of targets allowed. Therefore, it
does not mean that the targets displayed are the only aircraft
in the vicinity. The system displays only the closest aircraft.
In addition, the system does not display aircraft that are not
equipped with transponders. The display may not show any
aircraft; however, a Piper Cub with no transponder could be
flying in the area. TIS coverage can be sporadic and is not
available in some areas of the United States. Traffic advisory
software is to be utilized only for increased situational
awareness and not the sole means of traffic avoidance. There is
no substitute for a good visual scan of the surrounding sky.

11-15

11-16

Appendix A
Clearance Shorthand

The following shorthand system is recommended by the
Federal Aviation Administration (FAA). Applicants for the
instrument rating may use any shorthand system, in any
language, which ensures accurate compliance with air traffic
control (ATC) instructions. No shorthand system is required
by regulation and no knowledge of shorthand is required for
the FAA Knowledge Test; however, because of the vital need
for reliable communication between the pilot and controller,
clearance information should be unmistakably clear.
The following symbols and contractions represent words
and phrases frequently used in clearances. Most are used
regularly by ATC personnel. By practicing this shorthand,
omitting the parenthetical words, you will be able to copy
long clearances as fast as they are read.
RH RV V18 40 SQ 0700 DPC 120.4
Example: CAF
Cleared as filed, maintain runway heading for radar vector
to Victor 18, climb to 4,000, squawk 0700, departure control
frequency is 120.4.
Words and Phrases
Shorthand
Above ..........................................................................ABV
Above (Altitude, Hundreds of Feet) ............................... 70
Adjust speed to 250 knots ......................................... 250 K
Advise .........................................................................ADZ
After (Passing) ..................................................................<
Airway (Designation)................................................... V26
Airport .............................................................................. A
Alternate Instructions ...................................................... ( )
Altitude 6,000–17,000 .............................................60-170
And................................................................................... &
Approach ........................................................................ AP
Approach Control........................................................ APC
Area Navigation .......................................................RNAV
Arriving ..............................................................................
At..................................................................................... @
At or Above....................................................................
At or Below ....................................................................
(ATC) Advises ...............................................................CA
(ATC) Clears or Cleared .................................................. C
(ATC) Requests .............................................................CR

Back Course ...................................................................BC
Bearing ...........................................................................BR
Before (Reaching, Passing) ...............................................>
Below .......................................................................... BLO
Below (Altitude, Hundreds of Feet)................................ 70
Center .......................................................................... CTR
Clearance Void if Not Off By (Time) .............................v<
Cleared as Filed........................................................... CAF
Cleared to Airport ............................................................ A
Cleared to Climb/Descend at Pilot’s Discretion ............ PD
Cleared to Cross ............................................................... X
Cleared to Depart From the Fix ....................................... D
Cleared to the Fix ..............................................................F
Cleared to Hold and Instructions Issued .......................... H
Cleared to Land .................................................................L
Cleared to the Outer Marker ............................................ O
Climb to (Altitude, Hundreds of Feet) ........................... 70
Contact Approach .......................................................... CT
Contact (Denver) Approach Control ............................ (den
Contact (Denver) Center ............................................(DEN
Course ..........................................................................CRS
Cross ................................................................................ X
Cruise .............................................................................
Delay Indefinite............................................................ DLI
Depart (Direction, if Specified)................................ T ( )
Departure Control ....................................................... DPC
Descend To (Altitude, Hundreds of Feet) ...................... 70
Direct..............................................................................DR
Direction (Bound)
Eastbound ................................................................... EB
Westbound .................................................................WB
Northbound.................................................................NB
Southbound................................................................. SB
Inbound........................................................................ IB
Outbound ....................................................................OB
DME Fix (Mile) ............................................................
Each................................................................................EA
Enter Control Area .......................................................
Estimated Time of Arrival .......................................... ETA
Expect ............................................................................EX
Expect-Further-Clearance ............................................EFC
A-1

Fan Marker .................................................................... FM
Final ..................................................................................F
Final Approach............................................................... FA
Flight Level .................................................................... FL
Flight Planned Route.................................................... FPR
For Further Clearance .................................................. FFC
For Further Headings ...................................................FFH
From .............................................................................. FM
Ground ....................................................................... GND
GPS Approach .............................................................GPS
Heading ...................................................................... HDG
Hold (Direction) .......................................................... H-W
Holding Pattern ............................................................
ILS Approach ................................................................ ILS
Increase Speed 30 Knots ........................................... +30 K
Initial Approach .................................................................I
Instrument Departure Procedure .................................... DP
Intersection.................................................................... XN
Join or Intercept Airway/Jet Route/Track or Course ........
Left Turn After Takeoff ...................................................
Locator Outer Marker ................................................ LOM
Magnetic ..........................................................................M
Maintain ........................................................................
Maintain VFR Conditions On Top ............................. VFR
Middle Compass Locator .............................................. ML
Middle Marker ............................................................. MM
Missed Approach ..........................................................MA
Nondirectional Beacon Approach ...............................NDB
Out of (Leave) Control Area ........................................
Outer Marker .................................................................OM
Over (Station)..............................................................OKC
On Course ......................................................................OC
Precision Approach Radar .......................................... PAR
Procedure Turn............................................................... PT
Radar Vector ..................................................................RV
Radial (080° Radial) .................................................. 080R

A-2

Reduce Speed 20 Knots .............................................-20 K
Remain This Frequency ...............................................RTF
Remain Well to Left Side .............................................. LS
Remain Well to Right Side ............................................ RS
Report Crossing .............................................................RX
Report Departing............................................................RD
Report Leaving............................................................... RL
Report on Course .....................................................R-CRS
Report Over....................................................................RO
Report Passing ............................................................... RP
Report Reaching.............................................................RR
Report Starting Procedure Turn .................................RSPT
Reverse Course ..............................................................RC
Right Turn After Takeoff .................................................
Runway Heading............................................................RH
Runway (Number) .....................................................RY18
Squawk........................................................................... SQ
Standby .....................................................................STBY
Straight-in Approach........................................................SI
Surveillance Radar Approach ..................................... ASR
Takeoff (Direction) ................................................... T N
Tower ................................................................................Z
Turn Left ........................................................................ TL
Turn Right ...................................................................... TR
Until ................................................................................... /
Until Advised (By)........................................................ UA
Until Further Advised ................................................. UFA
VFR Conditions On Top ..............................................OTP
Via ................................................................................ VIA
Victor (Airway Number).............................................. V14
Visual Approach ........................................................... VA
VOR ..............................................................................
VOR Approach ..............................................................VR
VORTAC ......................................................................
While in Control Area ..................................................

Appendix B
Instrument Training Lesson Guide

Introduction

Lesson 2—Preflight preparation and
Flight instructors may use this guide in the development of flight by reference to instruments
lesson plans. The lessons are arranged in a logical learning
sequence and use the building-block technique. Each lesson
includes ground training appropriate to the flight portion of
the lesson. It is vitally important that the flight instructor brief
the student on the objective of the lesson and how it will be
accomplished. Debriefing the student’s performance is also
necessary to motivate further progress. To ensure steady
progress, student pilots should master the objective of each
lesson before advancing to the next lesson. Lessons should
be arranged to take advantage of each student’s knowledge
and skills.
Flight instructors must monitor progress closely during
training to guide student pilots in how to properly divide
their attention. The importance of this division of attention
or “cross-check” cannot be overemphasized. Cross-check and
proper instrument interpretation are essential components
of “attitude instrument flying” that enables student pilots to
accurately visualize the aircraft’s attitude at all times.
When possible, each lesson should incorporate radio
communications, basic navigation, and emergency procedures
so the student pilot is exposed to the entire IFR experience
with each flight. Cross-reference the Instrument Training
Lesson Guide with this handbook and the Instrument
Practical Test Standards for a comprehensive instrument
rating training program.

Lesson 1—Ground and flight evaluation
of student’s knowledge and performance
Aircraft systems
Aircraft performance
Preflight planning
Use of checklists
Basic flight maneuvers
Radio communications procedures
Navigation systems

Ground Training
Instrument system preflight procedures
Attitude instrument flying
Fundamental instrument skills
Instrument cross-check techniques
Flight Training
Aircraft and instrument preflight inspection
Use of checklists
Fundamental instrument skills
Basic flight maneuvers
Instrument approach (demonstrated)
Postflight procedures

Lesson 3—Flight instruments and human
factors
Ground Training
Human factors
Flight instruments and systems
Aircraft systems
Navigation instruments and systems
Flight Training
Aircraft and instrument preflight inspection
Radio communications
Checklist procedures
Attitude instrument flying
Fundamental instrument skills
Basic flight maneuvers
Spatial disorientation demonstration
Navigation systems
Postflight procedures

Lesson 4—Attitude instrument flying
Ground Training
Human factors
Flight instruments and systems

B-1

Aircraft systems
Navigation instruments and systems
Attitude instrument flying
Fundamental instrument skills
Basic flight maneuvers
Flight Training
Aircraft and instrument preflight inspection
Checklist procedures
Radio communications
Attitude instrument flying
Fundamental instrument skills
Basic flight maneuvers
Spatial disorientation
Navigation
Postflight procedures

Lesson 7—Recovery from unusual
attitudes
Ground Training
Attitude instrument flying
ATC system
NAS overview
Flight Training
Preflight
Aircraft and instrument preflight inspection
Checklist procedures
Radio communications
Instrument takeoff
Navigation
Partial panel practice
Recovery from unusual attitudes
Postflight procedures

Lesson 5—Aerodynamic factors and
basic flight maneuvers

Lesson 8—Navigation systems

Ground Training
Basic aerodynamic factors
Basic instrument flight patterns
Emergency procedures

Ground Training
ATC clearances
Departure procedures
IFR en route charts

Flight Training
Aircraft and instrument preflight inspection
Checklist procedures
Radio communications
Basic instrument flight patterns
Emergency procedures
Navigation
Postflight procedures

Flight Training
Aircraft and instrument preflight inspection
Checklist procedures
Radio communications
Intercepting and tracking
Holding
Postflight procedures

Lesson 6—Partial panel operations
Ground Training
ATC system
Flight instruments
Partial panel operations
Flight Training
Aircraft and instrument preflight inspection
Checklist procedures
Radio communications
Basic instrument flight patterns
Emergency procedures
Partial panel practice
Navigation
Postflight procedures

B-2

Lesson 9—Review and practice
Ground Training
Aerodynamic factors
Flight instruments and systems
Attitude instrument flying
Navigation systems
NAS
ATC
Emergency procedures
Flight Training
Aircraft and instrument preflight inspection
Checklist procedures
Radio communications
Review and practice as determined by the flight instructor

Instrument takeoff
Radio communications
Navigation systems
Emergency procedures
Postflight procedures

Instrument approach
Missed approach
Approach to a landing
Postflight procedures

Lessons 22 and 23—Review and practice
Lessons 10 through 19—Orientation,
intercepting, tracking, and holding using
each navigation system installed in the
aircraft
Ground Training
Preflight planning
Navigation systems
NAS
ATC
Emergencies

Ground Training
Human factors
Aerodynamic factors
Flight instruments and systems
Attitude instrument flying
Basic flight maneuvers
Navigation systems
NAS
ATC
Emergency operations

Flight Training
Aircraft and instrument preflight inspection
Checklist procedures
Radio communications
Departure procedures
En route navigation
Terminal operations
Partial panel operation
Instrument approach
Missed approach
Approach to a landing
Postflight procedures

Flight Training
Aircraft and instrument preflight inspection
Checklist procedures
Radio communications
Review and practice as determined by the flight instructor
Instrument takeoff
Partial panel operations
Unusual attitude recoveries
Radio communications
Navigation systems
Emergency procedures
Postflight procedures

Lessons 20 and 21—Cross-country
flights

Lessons 24 and subsequent—Practical
test preparation

Ground Training
Preflight planning
Aircraft performance
Navigation systems
NAS
ATC
Emergencies

Ground Training
Title 14 of the Code of Federal Regulations (14 CFR) parts
61, 71, 91, 95, and 97
Instrument Flying Handbook
Practical test standards
Administrative requirements
Equipment requirements
Applicant’s requirements

Flight Training
Emergency procedures
Partial panel operation
Aircraft and instrument preflight inspection
Checklist procedures
Radio communications
Departure procedures
En route navigation
Terminal operations

Flight Training
Review and practice until the student can consistently
perform all required tasks in accordance with the appropriate
practical test standards.
NOTE: It is the recommending instructor’s responsibility to
ensure that the applicant meets 14 CFR part 61 requirements
and is prepared for the practical test, including: training,
knowledge, experience, and the appropriate instructor
endorsements.

B-3

Glossary
Absolute accuracy. The ability to determine present position
in space independently, and is most often used by pilots.
Absolute altitude. The actual distance between an aircraft
and the terrain over which it is flying.
Absolute pressure. Pressure measured from the reference
of zero pressure, or a vacuum.
A.C. Alternating current.
Acceleration error. A magnetic compass error apparent when
the aircraft accelerates while flying on an easterly or westerly
heading, causing the compass card to rotate toward North.
Accelerometer. A part of an inertial navigation system
(INS) that accurately measures the force of acceleration in
one direction.
ADF. See automatic direction finder.
ADI. See attitude director indicator.

Agonic line. An irregular imaginary line across the surface of
the Earth along which the magnetic and geographic poles are in
alignment, and along which there is no magnetic variation.
Aircraft approach category. A performance grouping of
aircraft based on a speed of 1.3 times the stall speed in the
landing configuration at maximum gross landing weight.
Air data computer (ADC). An aircraft computer that
receives and processes pitot pressure, static pressure, and
temperature to calculate very precise altitude, indicated
airspeed, true airspeed, and air temperature.
AIRMET. Inflight weather advisory issued as an amendment
to the area forecast, concerning weather phenomena of
operational interest to all aircraft and that is potentially
hazardous to aircraft with limited capability due to lack of
equipment, instrumentation, or pilot qualifications.
Airport diagram. The section of an instrument approach
procedure chart that shows a detailed diagram of the
airport. This diagram includes surface features and airport
configuration information.

ADM. See aeronautical decision-making.
ADS–B. See automatic dependent surveillance–broadcast.
Adverse yaw. A flight condition at the beginning of a turn in
which the nose of the aircraft starts to move in the direction
opposite the direction the turn is being made, caused by the
induced drag produced by the downward-deflected aileron
holding back the wing as it begins to rise.
Aeronautical decision-making (ADM). A systematic
approach to the mental process used by pilots to consistently
determine the best course of action in response to a given
set of circumstances.

Airport/Facility Directory (A/FD). An FAA publication
containing information on all airports, communications,
and NAVAIDs.
Airport surface detection equipment (ASDE). Radar
equipment specifically designed to detect all principal
features and traffic on the surface of an airport, presenting the
entire image on the control tower console; used to augment
visual observation by tower personnel of aircraft and/or
vehicular movements on runways and taxiways.
Airport surveillance radar (ASR). Approach control
radar used to detect and display an aircraft’s position in the
terminal area.

A/FD. See Airport/Facility Directory.

G-1

Airport surveillance radar approach. An instrument
approach in which ATC issues instructions for pilot
compliance based on aircraft position in relation to the final
approach course and the distance from the end of the runway
as displayed on the controller’s radar scope.
Air route surveillance radar (ARSR). Air route traffic
control center (ARTCC) radar used primarily to detect
and display an aircraft’s position while en route between
terminal areas.
Air route traffic control center (ARTCC). Provides ATC
service to aircraft operating on IFR flight plans within
controlled airspace and principally during the en route phase
of flight.
Airspeed indicator. A differential pressure gauge that
measures the dynamic pressure of the air through which the
aircraft is flying. Displays the craft’s airspeed, typically in
knots, to the pilot.
Air traffic control radar beacon system (ATCRBS).
Sometimes called secondary surveillance radar (SSR), which
utilizes a transponder in the aircraft. The ground equipment is
an interrogating unit, in which the beacon antenna is mounted
so it rotates with the surveillance antenna. The interrogating
unit transmits a coded pulse sequence that actuates the aircraft
transponder. The transponder answers the coded sequence by
transmitting a preselected coded sequence back to the ground
equipment, providing a strong return signal and positive
aircraft identification, as well as other special data.
Airway. An airway is based on a centerline that extends from
one navigation aid or intersection to another navigation aid
(or through several navigation aids or intersections); used
to establish a known route for en route procedures between
terminal areas.
Alert area. An area in which there is a high volume of pilot
training or an unusual type of aeronautical activity.
Almanac data. Information the global positioning system
(GPS) receiver can obtain from one satellite which describes
the approximate orbital positioning of all satellites in the
constellation. This information is necessary for the GPS
receiver to know what satellites to look for in the sky at a
given time.

Alternate static source valve. A valve in the instrument static
air system that supplies reference air pressure to the altimeter,
airspeed indicator, and vertical speed indicator if the normal
static pickup should become clogged or iced over.
Altimeter setting. Station pressure (the barometric pressure
at the location the reading is taken) which has been corrected
for the height of the station above sea level.
AME. See aviation medical examiner.
Amendment status. The circulation date and revision
number of an instrument approach procedure, printed above
the procedure identification.
Ammeter. An instrument installed in series with an electrical
load used to measure the amount of current flowing through
the load.
Aneroid. The sensitive component in an altimeter or
barometer that measures the absolute pressure of the air.
It is a sealed, flat capsule made of thin disks of corrugated
metal soldered together and evacuated by pumping all of
the air out of it.
Aneroid barometer. An instrument that measures the
absolute pressure of the atmosphere by balancing the weight
of the air above it against the spring action of the aneroid.
Angle of attack. The acute angle formed between the
chord line of an airfoil and the direction of the air striking
the airfoil.
Anti-ice. Preventing the accumulation of ice on an aircraft
structure via a system designed for that purpose.
Approach lighting system (ALS). Provides lights that will
penetrate the atmosphere far enough from touchdown to give
directional, distance, and glide path information for safe
transition from instrument to visual flight.
Area chart. Part of the low-altitude en route chart series,
this chart furnishes terminal data at a larger scale for
congested areas.
Area navigation (RNAV). Allows a pilot to fly a selected
course to a predetermined point without the need to overfly
ground-based navigation facilities, by using waypoints.

ALS. See approach lighting system.
ARSR. See air route surveillance radar.
Alternate airport. An airport designated in an IFR flight
plan, providing a suitable destination if a landing at the
intended airport becomes inadvisable.

G-2

ARTCC. See air route traffic control center.

ASDE. See airport surface detection equipment.
ASOS. See automated surface observing station.
ASR. See airport surveillance radar.

Automatic direction finder (ADF). Electronic navigation
equipment that operates in the low- and medium-frequency
bands. Used in conjunction with the ground-based
nondirectional beacon (NDB), the instrument displays the
number of degrees clockwise from the nose of the aircraft
to the station being received.

ATC. Air Traffic Control.
ATCRBS. See air traffic control radar beacon system.
ATIS. See automatic terminal information service.
Atmospheric propagation delay. A bending of the
electromagnetic (EM) wave from the satellite that creates
an error in the GPS system.
Attitude and heading reference systems (AHRS). System
composed of three-axis sensors that provide heading, attitude,
and yaw information for aircraft. AHRS are designed to
replace traditional mechanical gyroscopic flight instruments
and provide superior reliability and accuracy.
Attitude director indicator (ADI). An aircraft attitude
indicator that incorporates flight command bars to provide
pitch and roll commands.
Attitude indicator. The foundation for all instrument flight,
this instrument reflects the airplane’s attitude in relation to
the horizon.
Attitude instrument flying. Controlling the aircraft by
reference to the instruments rather than by outside visual
cues.
Autokinesis. Nighttime visual illusion that a stationary light
is moving, which becomes apparent after several seconds of
staring at the light.
Automated Weather Observing System (AWOS).
Automated weather reporting system consisting of various
sensors, a processor, a computer-generated voice subsystem,
and a transmitter to broadcast weather data.
Automated Surface Observing Station (ASOS). Weather
reporting system which provides surface observations every
minute via digitized voice broadcasts and printed reports.
Automatic dependent surveillance–broadcast (ADS-B). A
device used in aircraft that repeatedly broadcasts a message
that includes position (such as latitude, longitude, and
altitude), velocity, and possibly other information.

Automatic terminal information service (ATIS). The
continuous broadcast of recorded non-control information in
selected terminal areas. Its purpose is to improve controller
effectiveness and relieve frequency congestion by automating
repetitive transmission of essential but routine information.
Aviation medical examiner (AME). A physician with
training in aviation medicine designated by the Civil
Aerospace Medical Institute (CAMI).
AWOS. See automated weather observing system.
Azimuth card. A card that may be set, gyroscopically
controlled, or driven by a remote compass.
Back course (BC). The reciprocal of the localizer course
for an ILS. When flying a back-course approach, an aircraft
approaches the instrument runway from the end at which the
localizer antennas are installed.
Baro-aiding. A method of augmenting the GPS integrity
solution by using a non-satellite input source. To ensure that
baro-aiding is available, the current altimeter setting must
be entered as described in the operating manual.
Barometric scale. A scale on the dial of an altimeter to which
the pilot sets the barometric pressure level from which the
altitude shown by the pointers is measured.
BC. See back course.
Block altitude. A block of altitudes assigned by ATC to
allow altitude deviations; for example, “Maintain block
altitude 9 to 11 thousand.”
Cage. The black markings on the ball instrument indicating
its neutral position.
Calibrated. The instrument indication compared with a
standard value to determine the accuracy of the instrument.
Calibrated orifice. A hole of specific diameter used to delay
the pressure change in the case of a vertical speed indicator.

G-3

Calibrated airspeed. The speed at which the aircraft
is moving through the air, found by correcting IAS for
instrument and position errors.
CAS. Calibrated airspeed.
CDI. Course deviation indicator.
Changeover point (COP). A point along the route or
airway segment between two adjacent navigation facilities
or waypoints where changeover in navigation guidance
should occur.
Circling approach. A maneuver initiated by the pilot to
align the aircraft with a runway for landing when a straightin landing from an instrument approach is not possible or is
not desirable.
Class A airspace. Airspace from 18,000 feet MSL up to and
including FL 600, including the airspace overlying the waters
within 12 NM of the coast of the 48 contiguous states and
Alaska; and designated international airspace beyond 12 NM
of the coast of the 48 contiguous states and Alaska within areas
of domestic radio navigational signal or ATC radar coverage,
and within which domestic procedures are applied.
Class B airspace. Airspace from the surface to 10,000 feet
MSL surrounding the nation’s busiest airports in terms of
IFR operations or passenger numbers. The configuration of
each Class B airspace is individually tailored and consists
of a surface area and two or more layers, and is designed to
contain all published instrument procedures once an aircraft
enters the airspace. For all aircraft, an ATC clearance is
required to operate in the area, and aircraft so cleared receive
separation services within the airspace.
Class C airspace. Airspace from the surface to 4,000 feet
above the airport elevation (charted in MSL) surrounding
those airports having an operational control tower, serviced
by radar approach control, and having a certain number of IFR
operations or passenger numbers. Although the configuration
of each Class C airspace area is individually tailored, the
airspace usually consists of a 5 NM radius core surface area
that extends from the surface up to 4,000 feet above the airport
elevation, and a 10 NM radius shelf area that extends from
1,200 feet to 4,000 feet above the airport elevation.
Class D airspace. Airspace from the surface to 2,500 feet
above the airport elevation (charted in MSL) surrounding
those airports that have an operational control tower. The
configuration of each Class D airspace area is individually
tailored, and when instrument procedures are published, the
airspace is normally designed to contain the procedures.

G-4

Class E airspace. Airspace that is not Class A, Class B, Class
C, or Class D, and is controlled airspace.
Class G airspace. Airspace that is uncontrolled, except
when associated with a temporary control tower, and has
not been designated as Class A, Class B, Class C, Class D,
or Class E airspace.
Clean configuration. A configuration in which all flight
control surfaces have been placed to create minimum drag.
In most aircraft this means flaps and gear retracted.
Clearance. ATC permission for an aircraft to proceed under
specified traffic conditions within controlled airspace, for the
purpose of providing separation between known aircraft.
Clearance delivery. Control tower position responsible for
transmitting departure clearances to IFR flights.
Clearance limit. The fix, point, or location to which an
aircraft is cleared when issued an air traffic clearance.
Clearance on request. An IFR clearance not yet received
after filing a flight plan.
Clearance void time. Used by ATC, the time at which the
departure clearance is automatically canceled if takeoff has
not been made. The pilot must obtain a new clearance or
cancel the IFR flight plan if not off by the specified time.
Clear ice. Glossy, clear, or translucent ice formed by the
relatively slow freezing of large, supercooled water droplets.
Compass course. A true course corrected for variation and
deviation errors.
Compass locator. A low-power, low- or medium-frequency
(L/MF) radio beacon installed at the site of the outer or middle
marker of an ILS.
Compass rose. A small circle graduated in 360° increments,
printed on navigational charts to show the amount of
compass variation at different locations, or on instruments
to indicate direction.
Computer navigation fix. A point used to define a
navigation track for an airborne computer system such as
GPS or FMS.
Concentric rings. Dashed-line circles depicted in the plan
view of IAP charts, outside of the reference circle, that show
en route and feeder facilities.

Cone of confusion. A cone-shaped volume of airspace
directly above a VOR station where no signal is received,
causing the CDI to fluctuate.
Control and performance. A method of attitude instrument
flying in which one instrument is used for making attitude
changes, and the other instruments are used to monitor the
progress of the change.
Control display unit. A display interfaced with the master
computer, providing the pilot with a single control point
for all navigations systems, thereby reducing the number of
required flight deck panels.
Controlled airspace. An airspace of defined dimensions
within which ATC service is provided to IFR and VFR flights
in accordance with the airspace classification. It includes
Class A, Class B, Class C, Class D, and Class E airspace.
Control pressures. The amount of physical exertion on the
control column necessary to achieve the desired attitude.
Convective weather. Unstable, rising air found in
cumiliform clouds.
Convective SIGMET. Weather advisory concerning
convective weather significant to the safety of all aircraft,
including thunderstorms, hail, and tornadoes.
Coordinated flight. Flight with a minimum disturbance of
the forces maintaining equilibrium, established via effective
control use.
COP. See changeover point.
Coriolis illusion. The illusion of rotation or movement in an
entirely different axis, caused by an abrupt head movement,
while in a prolonged constant rate turn that has ceased
stimulating the brain’s motion sensing system.
Crew resource management (CRM). The effective
use of all available resources—human, hardware, and
information.
Critical areas. Areas where disturbances to the ILS localizer
and glide slope courses may occur when surface vehicles or
aircraft operate near the localizer or glide slope antennas.
CRM. See crew resource management.

Cruise clearance. An ATC clearance issued to allow a
pilot to conduct flight at any altitude from the minimum
IFR altitude up to and including the altitude specified in the
clearance. Also authorizes a pilot to proceed to and make an
approach at the destination airport.
Current induction. An electrical current being induced into,
or generated in, any conductor that is crossed by lines of flux
from any magnet.
DA. See decision altitude.
D.C. Direct current.
Dark adaptation. Physical and chemical adjustments of the
eye that make vision possible in relative darkness.
Deceleration error. A magnetic compass error that occurs
when the aircraft decelerates while flying on an easterly
or westerly heading, causing the compass card to rotate
toward South.
Decision altitude (DA). A specified altitude in the precision
approach, charted in feet MSL, at which a missed approach
must be initiated if the required visual reference to continue
the approach has not been established.
Decision height (DH). A specified altitude in the precision
approach, charted in height above threshold elevation,
at which a decision must be made either to continue the
approach or to execute a missed approach.
Deice. The act of removing ice accumulation from an
aircraft structure.
Density altitude. Pressure altitude corrected for nonstandard
temperature. Density altitude is used in computing the
performance of an aircraft and its engines.
Departure procedure (DP). Preplanned IFR ATC departure,
published for pilot use, in textual and graphic format.
Deviation. A magnetic compass error caused by local
magnetic fields within the aircraft. Deviation error is different
on each heading.
DGPS. Differential global positioning system.
DH. See decision height.

Cross-check. The first fundamental skill of instrument flight,
also known as “scan,” the continuous and logical observation
of instruments for attitude and performance information.

G-5

Differential Global Positioning System (DGPS). A system
that improves the accuracy of Global Navigation Satellite
Systems (GNSS) by measuring changes in variables to
provide satellite positioning corrections.
Direct indication. The true and instantaneous reflection of
aircraft pitch-and-bank attitude by the miniature aircraft,
relative to the horizon bar of the attitude indicator.

Duplex. Transmitting on one frequency and receiving on a
separate frequency.
Eddy currents. Current induced in a metal cup or disc when
it is crossed by lines of flux from a moving magnet.
EFAS. See En Route Flight Advisory Service.
EFC. See expect-further-clearance.

Direct User Access Terminal System (DUATS). A system
that provides current FAA weather and flight plan filing
services to certified civil pilots, via personal computer,
modem, or telephone access to the system. Pilots can request
specific types of weather briefings and other pertinent data
for planned flights.

Electronic flight display (EFD). For the purpose of
standardization, any flight instrument display that uses
LCD or other image-producing system (Cathode Ray Tube
[CRT], etc.)

Distance circle. See reference circle.

Elevator illusion. The sensation of being in a climb or
descent, caused by the kind of abrupt vertical accelerations
that result from up- or downdrafts.

Distance measuring equipment (DME). A pulse-type
electronic navigation system that shows the pilot, by an
instrument-panel indication, the number of nautical miles
between the aircraft and a ground station or waypoint.
DME. See distance measuring equipment.
DME arc. A flight track that is a constant distance from the
station or waypoint.
DOD. Department of Defense.
Doghouse. A turn-and-slip indicator dial mark in the shape
of a doghouse.
Domestic Reduced Vertical Separation Minimum
(DRVSM). Additional flight levels between FL 290 and FL
410 to provide operational, traffic, and airspace efficiency.
Double gimbal. A type of mount used for the gyro in an
attitude instrument. The axes of the two gimbals are at right
angles to the spin axis of the gyro, allowing free motion in
two planes around the gyro.

Emergency. A distress or urgent condition.
Emphasis error. The result of giving too much attention
to a particular instrument during the cross-check, instead of
relying on a combination of instruments necessary for attitude
and performance information.
EM wave. Electromagnetic wave.
Encoding altimeter. A special type of pressure altimeter
used to send a signal to the air traffic controller on the ground,
showing the pressure altitude the aircraft is flying.
En route facilities ring. Depicted in the plan view of IAP
charts, a circle which designates NAVAIDs, fixes, and
intersections that are part of the en route low altitude airway
structure.
En Route Flight Advisory Service (EFAS). An en route
weather-only AFSS service.
En route high-altitude charts. Aeronautical charts for en
route instrument navigation at or above 18,000 feet MSL.

DP. See departure procedure.
Drag. The net aerodynamic force parallel to the relative
wind, usually the sum of two components: induced drag
and parasite drag.
Drag curve. The curve created when plotting induced drag
and parasite drag.
DUATS. See direct user access terminal system.

G-6

En route low-altitude charts. Aeronautical charts for en
route IFR navigation below 18,000 feet MSL.
Equivalent airspeed. Airspeed equivalent to CAS in
standard atmosphere at sea level. As the airspeed and pressure
altitude increase, the CAS becomes higher than it should be,
and a correction for compression must be subtracted from
the CAS.

Expect-further-clearance (EFC). The time a pilot can
expect to receive clearance beyond a clearance limit.

Flight path. The line, course, or track along which an aircraft
is flying or is intended to be flown.

FAA. Federal Aviation Administration.

Flight patterns. Basic maneuvers, flown by reference to the
instruments rather than outside visual cues, for the purpose
of practicing basic attitude flying. The patterns simulate
maneuvers encountered on instrument flights such as holding
patterns, procedure turns, and approaches.

FAF. See final approach fix.
False horizon. Inaccurate visual information for aligning the
aircraft, caused by various natural and geometric formations
that disorient the pilot from the actual horizon.
Federal airways. Class E airspace areas that extend upward
from 1,200 feet to, but not including, 18,000 feet MSL, unless
otherwise specified.
Feeder facilities. Used by ATC to direct aircraft to
intervening fixes between the en route structure and the
initial approach fix.
Final approach. Part of an instrument approach
procedure in which alignment and descent for landing are
accomplished.
Final approach fix (FAF). The fix from which the IFR
final approach to an airport is executed, and which identifies
the beginning of the final approach segment. An FAF is
designated on government charts by a Maltese cross symbol
for nonprecision approaches, and a lightning bolt symbol for
precision approaches.
Fixating. Staring at a single instrument, thereby interrupting
the cross-check process.
FL. See flight level.
Flight configurations. Adjusting the aircraft control surfaces
(including flaps and landing gear) in a manner that will
achieve a specified attitude.
Flight director indicator (FDI). One of the major components
of a flight director system, it provides steering commands that
the pilot (or the autopilot, if coupled) follows.

Flight strips. Paper strips containing instrument flight
information, used by ATC when processing flight plans.
FMS. See flight management system.
Form drag. The drag created because of the shape of a
component or the aircraft.
Fundamental skills. Pilot skills of instrument cross-check,
instrument interpretation, and aircraft control.
Glide slope (GS). Part of the ILS that projects a radio beam
upward at an angle of approximately 3° from the approach
end of an instrument runway. The glide slope provides
vertical guidance to aircraft on the final approach course for
the aircraft to follow when making an ILS approach along
the localizer path.
Glide slope intercept altitude. The minimum altitude of an
intermediate approach segment prescribed for a precision
approach that ensures obstacle clearance.
Global landing system (GLS). An instrument approach with
lateral and vertical guidance with integrity limits (similar to
barometric vertical navigation (BRO VNAV).
Global navigation satellite systems (GNSS). Satellite
navigation systems that provide autonomous geo-spatial
positioning with global coverage. It allows small electronic
receivers to determine their location (longitude, latitude, and
altitude) to within a few meters using time signals transmitted
along a line of sight by radio from satellites.
GNSS. See global navigation satellite systems.

Flight level (FL). A measure of altitude (in hundreds of feet)
used by aircraft flying above 18,000 feet with the altimeter
set at 29.92" Hg.

Global positioning system (GPS). Navigation system
that uses satellite rather than ground-based transmitters for
location information.

Flight management system (FMS). Provides pilot and crew
with highly accurate and automatic long-range navigation
capability, blending available inputs from long- and shortrange sensors.

G-7

Goniometer. As used in radio frequency (RF) antenna
systems, a direction-sensing device consisting of two fixed
loops of wire oriented 90° from each other, which separately
sense received signal strength and send those signals to two
rotors (also oriented 90°) in the sealed direction-indicating
instrument. The rotors are attached to the direction-indicating
needle of the instrument and rotated by a small motor until
minimum magnetic field is sensed near the rotors.
GPS. See global positioning system.
GPS Approach Overlay Program. An authorization for
pilots to use GPS avionics under IFR for flying designated
existing nonprecision instrument approach procedures, with
the exception of LOC, LDA, and SDF procedures.

Head-up display (HUD). A special type of flight viewing
screen that allows the pilot to watch the flight instruments
and other data while looking through the windshield of the
aircraft for other traffic, the approach lights, or the runway.
Height above airport (HAA). The height of the MDA above
the published airport elevation.
Height above landing (HAL). The height above a designated
helicopter landing area used for helicopter instrument
approach procedures.
Height above touchdown elevation (HAT). The DA/DH or
MDA above the highest runway elevation in the touchdown
zone (first 3,000 feet of the runway).

Graveyard spiral. The illusion of the cessation of a turn
while still in a prolonged, coordinated, constant rate turn,
which can lead a disoriented pilot to a loss of control of the
aircraft.

HF. High frequency.

Great circle route. The shortest distance across the surface
of a sphere (the Earth) between two points on the surface.

HIWAS. See Hazardous Inflight Weather Advisory
Service.

Ground proximity warning system (GPWS). A system
designed to determine an aircraft’s clearance above the Earth
and provides limited predictability about aircraft position
relative to rising terrain.

Holding. A predetermined maneuver that keeps aircraft
within a specified airspace while awaiting further clearance
from ATC.

Groundspeed. Speed over the ground, either closing speed to
the station or waypoint, or speed over the ground in whatever
direction the aircraft is going at the moment, depending upon
the navigation system used.
GS. See glide slope.
GWPS. See ground proximity warning system.
HAA. See height above airport.

Hg. Abbreviation for mercury, from the Latin
hydrargyrum.

Holding pattern. A racetrack pattern, involving two turns
and two legs, used to keep an aircraft within a prescribed
airspace with respect to a geographic fix. A standard pattern
uses right turns; nonstandard patterns use left turns.
Homing. Flying the aircraft on any heading required to keep
the needle pointing to the 0° relative bearing position.
Horizontal situation indicator (HSI). A flight navigation
instrument that combines the heading indicator with a CDI,
in order to provide the pilot with better situational awareness
of location with respect to the courseline.

HAL. See height above landing.
HSI. See horizontal situation indicator.
HAT. See height above touchdown elevation.
HUD. See head-up display.
Hazardous attitudes. Five aeronautical decision-making
attitudes that may contribute to poor pilot judgment:
antiauthority, impulsivity, invulnerability, machismo, and
resignation.
Hazardous Inflight Weather Advisory Service (HIWAS).
Service providing recorded weather forecasts broadcast to
airborne pilots over selected VORs.

G-8

Human factors. A multidisciplinary field encompassing the
behavioral and social sciences, engineering, and physiology,
to consider the variables that influence individual and
crew performance for the purpose of optimizing human
performance and reducing errors.

Hypoxia. A state of oxygen deficiency in the body sufficient
to impair functions of the brain and other organs.

Induction icing. A type of ice in the induction system that
reduces the amount of air available for combustion. The most
commonly found induction icing is carburetor icing.

IAF. See initial approach fix.
IAP. See instrument approach procedures.
IAS. See indicated airspeed.
ICAO. See International Civil Aviation Organization.
Ident. Air Traffic Control request for a pilot to push
the button on the transponder to identify return on the
controller’s scope.

Inertial navigation system (INS). A computer-based
navigation system that tracks the movement of an aircraft
via signals produced by onboard accelerometers. The initial
location of the aircraft is entered into the computer, and all
subsequent movement of the aircraft is sensed and used to
keep the position updated. An INS does not require any inputs
from outside signals.
Initial approach fix (IAF). The fix depicted on IAP charts
where the instrument approach procedure (IAP) begins unless
otherwise authorized by ATC.

IFR. See instrument flight rules.
ILS. See instrument landing system.
ILS categories. Categories of instrument approach
procedures allowed at airports equipped with the following
types of instrument landing systems:
ILS Category I: Provides for approach to a height
above touchdown of not less than 200 feet, and with
runway visual range of not less than 1,800 feet.
ILS Category II: Provides for approach to a height
above touchdown of not less than 100 feet and with
runway visual range of not less than 1,200 feet.
ILS Category IIIA: Provides for approach without
a decision height minimum and with runway visual
range of not less than 700 feet.
ILS Category IIIB: Provides for approach without
a decision height minimum and with runway visual
range of not less than 150 feet.
ILS Category IIIC: Provides for approach without a
decision height minimum and without runway visual
range minimum.

Inoperative components. Higher minimums are prescribed
when the specified visual aids are not functioning; this
information is listed in the Inoperative Components Table found
in the United States Terminal Procedures Publications.
INS. See inertial navigation system.
Instantaneous vertical speed indicator (IVSI). Assists in
interpretation by instantaneously indicating the rate of climb
or descent at a given moment with little or no lag as displayed
in a vertical speed indicator (VSI).
Instrument approach procedures (IAP). A series of
predetermined maneuvers for the orderly transfer of an
aircraft under IFR from the beginning of the initial approach
to a landing or to a point from which a landing may be
made visually.
Instrument flight rules (IFR). Rules and regulations
established by the Federal Aviation Administration to govern
flight under conditions in which flight by outside visual
reference is not safe. IFR flight depends upon flying by
reference to instruments in the flight deck, and navigation is
accomplished by reference to electronic signals.

IMC. See instrument meteorological conditions.
Indicated airspeed (IAS). Shown on the dial of the
instrument airspeed indicator on an aircraft. Directly related
to calibrated airspeed (CAS), IAS includes instrument errors
and position error.
Indirect indication. A reflection of aircraft pitch-and-bank
attitude by the instruments other than the attitude indicator.
Induced drag. Drag caused by the same factors that produce
lift; its amount varies inversely with airspeed. As airspeed
decreases, the angle of attack must increase, in turn increasing
induced drag.

Instrument landing system (ILS). An electronic system
that provides both horizontal and vertical guidance to a
specific runway, used to execute a precision instrument
approach procedure.
Instrument meteorological conditions (IMC).
Meteorological conditions expressed in terms of visibility,
distance from clouds, and ceiling less than the minimums
specified for visual meteorological conditions, requiring
operations to be conducted under IFR.

G-9

Instrument takeoff. Using the instruments rather than
outside visual cues to maintain runway heading and execute
a safe takeoff.
Interference drag. Drag generated by the collision of
airstreams creating eddy currents, turbulence, or restrictions
to smooth flow.
International Civil Aviation Organization (ICAO). The
United Nations agency for developing the principles and
techniques of international air navigation, and fostering planning
and development of international civil air transport.

Land as soon as practical. ATC instruction to pilot. The
landing site and duration of flight are at the discretion of the
pilot. Extended flight beyond the nearest approved landing
area is not recommended.
Land immediately. ATC instruction to pilot. The urgency
of the landing is paramount. The primary consideration is
to ensure the survival of the occupants. Landing in trees,
water, or other unsafe areas should be considered only as
a last resort.
LDA. See localizer-type directional aid.

International standard atmosphere (IAS). A model of
standard variation of pressure and temperature.

Lead radial. The radial at which the turn from the DME arc
to the inbound course is started.

Inversion illusion. The feeling that the aircraft is tumbling
backwards, caused by an abrupt change from climb to straightand-level flight while in situations lacking visual reference.

Leans, the. A physical sensation caused by an abrupt
correction of a banked attitude entered too slowly to
stimulate the motion sensing system in the inner ear. The
abrupt correction can create the illusion of banking in the
opposite direction.

Inverter. A solid-state electronic device that converts D.C.
into A.C. current of the proper voltage and frequency to
operate A.C. gyro instruments.
Isogonic lines. Lines drawn across aeronautical charts to
connect points having the same magnetic variation.

Lift. A component of the total aerodynamic force on an airfoil
and acts perpendicular to the relative wind.
Lines of flux. Invisible lines of magnetic force passing
between the poles of a magnet.

IVSI. See instantaneous vertical speed indicator.
L/MF. See low or medium frequency.
Jet route. A route designated to serve flight operations from
18,000 feet MSL up to and including FL 450.
Jet stream. A high-velocity narrow stream of winds, usually
found near the upper limit of the troposphere, which flows
generally from west to east.

LMM. See locator middle marker.
Load factor. The ratio of a specified load to the total weight
of the aircraft. The specified load is expressed in terms of
any of the following: aerodynamic forces, inertial forces, or
ground or water reactions.

KIAS. Knots indicated airspeed.
Kollsman window. A barometric scale window of a
sensitive altimeter used to adjust the altitude for the
altimeter setting.
LAAS. See local area augmentation system.
Lag. The delay that occurs before an instrument needle attains
a stable indication.
Land as soon as possible. ATC instruction to pilot. Land
without delay at the nearest suitable area, such as an open
field, at which a safe approach and landing is assured.

G-10

Loadmeter. A type of ammeter installed between the generator
output and the main bus in an aircraft electrical system.
LOC. See localizer.
Local area augmentation system (LAAS). A differential
global positioning system (DGPS) that improves the accuracy
of the system by determining position error from the GPS
satellites, then transmitting the error, or corrective factors,
to the airborne GPS receiver.

Localizer (LOC). The portion of an ILS that gives left/right
guidance information down the centerline of the instrument
runway for final approach.
Localizer-type directional aid (LDA). A NAVAID used
for nonprecision instrument approaches with utility and
accuracy comparable to a localizer but which is not a part
of a complete ILS and is not aligned with the runway. Some
LDAs are equipped with a glide slope.
Locator middle marker (LMM). Nondirectional radio
beacon (NDB) compass locator, collocated with a middle
marker (MM).
Locator outer marker (LOM). NDB compass locator,
collocated with an outer marker (OM).
LOM. See locator outer marker.
Long range navigation (LORAN). An electronic
navigational system by which hyperbolic lines of position
are determined by measuring the difference in the time of
reception of synchronized pulse signals from two fixed
transmitters. LORAN A operates in the 1750 to 1950 kHz
frequency band. LORAN C and D operate in the 100 to 110
kHz frequency band.
LORAN. See long range navigation.
Low or medium frequency. A frequency range between
190–535 kHz with the medium frequency above 300
kHz. Generally associated with nondirectional beacons
transmitting a continuous carrier with either a 400 or 1,020
Hz modulation.
Lubber line. The reference line used in a magnetic compass
or heading indicator.

Mandatory altitude. An altitude depicted on an instrument
approach chart with the altitude value both underscored and
overscored. Aircraft are required to maintain altitude at the
depicted value.
Mandatory block altitude. An altitude depicted on an
instrument approach chart with two underscored and
overscored altitude values between which aircraft are
required to maintain altitude.
MAP. See missed approach point.
Margin identification. The top and bottom areas on an
instrument approach chart that depict information about
the procedure, including airport location and procedure
identification.
Marker beacon. A low-powered transmitter that directs its
signal upward in a small, fan-shaped pattern. Used along the
flight path when approaching an airport for landing, marker
beacons indicate both aurally and visually when the aircraft
is directly over the facility.
Maximum altitude. An altitude depicted on an instrument
approach chart with overscored altitude value at which or
below aircraft are required to maintain altitude.
Maximum authorized altitude (MAA). A published altitude
representing the maximum usable altitude or flight level for
an airspace structure or route segment.
MB. See magnetic bearing.
MCA. See minimum crossing altitude.
MDA. See minimum descent altitude.
MEA. See minimum en route altitude.

MAA. See maximum authorized altitude.
Mach number. The ratio of the true airspeed of the aircraft
to the speed of sound in the same atmospheric conditions,
named in honor of Ernst Mach, late 19th century physicist.

Mean sea level. The average height of the surface of the
sea at a particular location for all stages of the tide over a
19-year period.
MFD. See multi-function display.

Mach meter. The instrument that displays the ratio of the
speed of sound to the true airspeed an aircraft is flying.
Magnetic bearing (MB). The direction to or from a radio
transmitting station measured relative to magnetic north.

MH. See magnetic heading.
MHz. Megahertz.

Magnetic heading (MH). The direction an aircraft is pointed
with respect to magnetic north.

G-11

Microwave landing system (MLS). A precision instrument
approach system operating in the microwave spectrum which
normally consists of an azimuth station, elevation station,
and precision distance measuring equipment.
Mileage breakdown. A fix indicating a course change
that appears on the chart as an “x” at a break between two
segments of a federal airway.
Military operations area (MOA). Airspace established for
the purpose of separating certain military training activities
from IFR traffic.
Military training route (MTR). Airspace of defined vertical
and lateral dimensions established for the conduct of military
training at airspeeds in excess of 250 knots indicated airspeed
(KIAS).

Minimum vectoring altitude (MVA). An IFR altitude lower
than the minimum en route altitude (MEA) that provides
terrain and obstacle clearance.
Minimums section. The area on an IAP chart that displays the
lowest altitude and visibility requirements for the approach.
Missed approach. A maneuver conducted by a pilot when an
instrument approach cannot be completed to a landing.
Missed approach point (MAP). A point prescribed in each
instrument approach at which a missed approach procedure
shall be executed if the required visual reference has not
been established.
Mixed ice. A mixture of clear ice and rime ice.
MLS. See microwave landing system.

Minimum altitude. An altitude depicted on an instrument
approach chart with the altitude value underscored. Aircraft are
required to maintain altitude at or above the depicted value.

MM. Middle marker.
MOA. See military operations area.

Minimum crossing altitude (MCA). The lowest allowed
altitude at certain fixes an aircraft must cross when proceeding
in the direction of a higher minimum en route altitude
(MEA).
Minimum descent altitude (MDA). The lowest altitude (in
feet MSL) to which descent is authorized on final approach,
or during circle-to-land maneuvering in execution of a
nonprecision approach.

MOCA. See minimum obstruction clearance altitude.
Mode C. Altitude reporting transponder mode.
MRA. See minimum reception altitude.
MSA. See minimum safe altitude.
MSL. See mean sea level.

Minimum en route altitude (MEA). The lowest published
altitude between radio fixes that ensures acceptable
navigational signal coverage and meets obstacle clearance
requirements between those fixes.
Minimum obstruction clearance altitude (MOCA). The
lowest published altitude in effect between radio fixes on VOR
airways, off-airway routes, or route segments, which meets
obstacle clearance requirements for the entire route segment
and which ensures acceptable navigational signal coverage
only within 25 statute (22 nautical) miles of a VOR.
Minimum reception altitude (MRA). The lowest altitude
at which an airway intersection can be determined.
Minimum safe altitude (MSA). The minimum altitude
depicted on approach charts which provides at least 1,000 feet
of obstacle clearance for emergency use within a specified
distance from the listed navigation facility.

G-12

MTR. See military training route.
Multi-function display (MFD). Small screen (CRT or LCD)
in an aircraft that can be used to display information to the
pilot in numerous configurable ways. Often an MFD will be
used in concert with a Primary Flight Display.
MVA. See minimum vectoring altitude.
NACG. See National Aeronautical Charting Group.
NAS. See National Airspace System.
National Airspace System (NAS). The common network of
United States airspace—air navigation facilities, equipment
and services, airports or landing areas; aeronautical charts,
information and services; rules, regulations and procedures,
technical information; and manpower and material.

National Aeronautical Charting Group (NACG). A
Federal agency operating under the FAA, responsible for
publishing charts such as the terminal procedures and en
route charts.

Notice to Airmen (NOTAM). A notice filed with an aviation
authority to alert aircraft pilots of any hazards en route or at
a specific location. The authority in turn provides means of
disseminating relevant NOTAMs to pilots.

National Route Program (NRP). A set of rules and
procedures designed to increase the flexibility of user flight
planning within published guidelines.

NRP. See National Route Program.

National Security Area (NSA). Areas consisting of airspace of
defined vertical and lateral dimensions established at locations
where there is a requirement for increased security and safety
of ground facilities. Pilots are requested to voluntarily avoid
flying through the depicted NSA. When it is necessary to
provide a greater level of security and safety, flight in NSAs
may be temporarily prohibited. Regulatory prohibitions are
disseminated via NOTAMs.

NTSB. See National Transportation Safety Board.

NSA. See National Security Area.

NWS. National Weather Service.
Obstacle departure procedures (ODP). Obstacle clearance
protection provided to aircraft in instrument meteorological
conditions (IMC).
ODP. See obstacle departure procedures.

National Transportation Safety Board (NTSB). A United
States Government independent organization responsible for
investigations of accidents involving aviation, highways,
waterways, pipelines, and railroads in the United States.
NTSB is charged by congress to investigate every civil
aviation accident in the United States.
NAVAID. Naviagtional aid.
NAV/COM. Navigation and communication radio.
NDB. See nondirectional radio beacon.
NM. Nautical mile.
NOAA. National Oceanic and Atmospheric Administration.
No-gyro approach. A radar approach that may be used in
case of a malfunctioning gyro-compass or directional gyro.
Instead of providing the pilot with headings to be flown,
the controller observes the radar track and issues control
instructions “turn right/left” or “stop turn,” as appropriate.
Nondirectional radio beacon (NDB). A ground-based radio
transmitter that transmits radio energy in all directions.
Nonprecision approach. A standard instrument approach
procedure in which only horizontal guidance is provided.
No procedure turn (NoPT). Term used with the appropriate
course and altitude to denote that the procedure turn is not
required.

OM. Outer marker.
Omission error. The failure to anticipate significant
instrument indications following attitude changes; for
example, concentrating on pitch control while forgetting
about heading or roll information, resulting in erratic control
of heading and bank.
Optical illusion. A misleading visual image. For the
purpose of this handbook, the term refers to the brain’s
misinterpretation of features on the ground associated
with landing, which causes a pilot to misread the spatial
relationships between the aircraft and the runway.
Orientation. Awareness of the position of the aircraft and
of oneself in relation to a specific reference point.
Otolith organ. An inner ear organ that detects linear
acceleration and gravity orientation.
Outer marker. A marker beacon at or near the glide slope
intercept altitude of an ILS approach. It is normally located
four to seven miles from the runway threshold on the
extended centerline of the runway.
Overcontrolling. Using more movement in the control
column than is necessary to achieve the desired pitch-and
bank condition.
Overpower. To use more power than required for the purpose
of achieving a faster rate of airspeed change.

NoPT. See no procedure turn.

G-13

P-static. See precipitation static.
PAPI. See precision approach path indicator.
PAR. See precision approach radar.
Parasite drag. Drag caused by the friction of air moving
over the aircraft structure; its amount varies directly with
the airspeed.
PFD. See primary flight display.

Precipitation static (P-static). A form of radio interference
caused by rain, snow, or dust particles hitting the antenna and
inducing a small radio-frequency voltage into it.
Precision approach. A standard instrument approach
procedure in which both vertical and horizontal guidance
is provided.
Precision approach path indicator (PAPI). A system of
lights similar to the VASI, but consisting of one row of lights
in two- or four-light systems. A pilot on the correct glide slope
will see two white lights and two red lights. See VASI.

PIC. See pilot-in-command.
Pilot-in-command (PIC). The pilot responsible for the
operation and safety of an aircraft.
Pilot report (PIREP). Report of meteorological phenomena
encountered by aircraft.
Pilot’s Operating Handbook/Airplane Flight Manual
(POH/AFM). FAA-approved documents published by the
airframe manufacturer that list the operating conditions for
a particular model of aircraft.
PIREP. See pilot report.
Pitot pressure. Ram air pressure used to measure airspeed.
Pitot-static head. A combination pickup used to sample pitot
pressure and static air pressure.
Plan view. The overhead view of an approach procedure on
an instrument approach chart. The plan view depicts the routes
that guide the pilot from the en route segments to the IAF.
POH/AFM. See Pilot’s Operating Handbook/Airplane
Flight Manual.
Point-in-space approach. A type of helicopter instrument
approach procedure to a missed approach point more than
2,600 feet from an associated helicopter landing area.
Position error. Error in the indication of the altimeter, ASI,
and VSI caused by the air at the static system entrance not
being absolutely still.

Precision approach radar (PAR). A type of radar used
at an airport to guide an aircraft through the final stages of
landing, providing horizontal and vertical guidance. The
radar operator directs the pilot to change heading or adjust
the descent rate to keep the aircraft on a path that allows it
to touch down at the correct spot on the runway.
Precision runway monitor (PRM). System allows
simultaneous, independent Instrument Flight Rules (IFR)
approaches at airports with closely spaced parallel runways.
Preferred IFR routes. Routes established in the major
terminal and en route environments to increase system
efficiency and capacity. IFR clearances are issued based on
these routes, listed in the A/FD except when severe weather
avoidance procedures or other factors dictate otherwise.
Pressure altitude. Altitude above the standard 29.92" Hg
plane.
Prevailing visibility. The greatest horizontal visibility
equaled or exceeded throughout at least half the horizon
circle (which is not necessarily continuous).
Primary and supporting. A method of attitude instrument
flying using the instrument that provides the most direct
indication of attitude and performance.
Primary flight display (PFD). A display that provides
increased situational awareness to the pilot by replacing the
traditional six instruments used for instrument flight with
an easy-to-scan display that provides the horizon, airspeed,
altitude, vertical speed, trend, trim, rate of turn among other
key relevant indications.

Position report. A report over a known location as
transmitted by an aircraft to ATC.

PRM. See precision runway monitor.

Precession. The characteristic of a gyroscope that causes an
applied force to be felt, not at the point of application, but
90° from that point in the direction of rotation.

Procedure turn. A maneuver prescribed when it is necessary
to reverse direction to establish an aircraft on the intermediate
approach segment or final approach course.

G-14

Profile view. Side view of an IAP chart illustrating the vertical
approach path altitudes, headings, distances, and fixes.
Prohibited area. Designated airspace within which flight of
aircraft is prohibited.
Propeller/rotor modulation error. Certain propeller RPM
settings or helicopter rotor speeds can cause the VOR course
deviation indicator (CDI) to fluctuate as much as ±6°. Slight
changes to the RPM setting will normally smooth out this
roughness.
Rabbit, the. High-intensity flasher system installed at many
large airports. The flashers consist of a series of brilliant
blue-white bursts of light flashing in sequence along the
approach lights, giving the effect of a ball of light traveling
towards the runway.
Radar. Radio Detection And Ranging.
Radar approach. The controller provides vectors while
monitoring the progress of the flight with radar, guiding
the pilot through the descent to the airport/heliport or to a
specific runway.
Radials. The courses oriented from a station.
Radio or radar altimeter. An electronic altimeter that
determines the height of an aircraft above the terrain by
measuring the time needed for a pulse of radio-frequency
energy to travel from the aircraft to the ground and return.
Radio frequency (RF). A term that refers to alternating
current (AC) having characteristics such that, if the current is
input to antenna, an electromagnetic (EM) field is generated
suitable for wireless broadcasting and/or communications.

Ranging signals. Transmitted from the GPS satellite, these
allow the aircraft’s receiver to determine range (distance)
from each satellite.
RB. See relative bearing.
RBI. See relative bearing indicator.
RCO. See remote communications outlet.
Receiver autonomous integrity monitoring (RAIM).
A system used to verify the usability of the received GPS
signals and warns the pilot of any malfunction in the
navigation system. This system is required for IFR-certified
GPS units.
Recommended altitude. An altitude depicted on an
instrument approach chart with the altitude value neither
underscored nor overscored. The depicted value is an
advisory value.
Receiver-transmitter (RT). A system that receives and
transmits a signal and an indicator.
Reduced vertical separation minimum (RVSM). Reduces
the vertical separation between flight level (FL) 290–410
from 2,000 feet to 1,000 feet and makes six additional FLs
available for operation. Also see DRVSM.
Reference circle (also, distance circle). The circle depicted
in the plan view of an IAP chart that typically has a 10 NM
radius, within which chart the elements are drawn to scale.
Regions of command. The “regions of normal and reversed
command” refers to the relationship between speed and the
power required to maintain or change that speed in flight.
REIL. See runway end identifier lights.

Radio magnetic indicator (RMI). An electronic navigation
instrument that combines a magnetic compass with an ADF
or VOR. The card of the RMI acts as a gyro-stabilized
magnetic compass, and shows the magnetic heading the
aircraft is flying.
Radio wave. An electromagnetic wave (EM wave) with
frequency characteristics useful for radio transmission.
RAIM. See receiver autonomous integrity monitoring.
Random RNAV routes. Direct routes, based on area
navigation capability, between waypoints defined in terms
of latitude/longitude coordinates, degree-distance fixes, or
offsets from established routes/airways at a specified distance
and direction.

Relative bearing (RB). The angular difference between the
aircraft heading and the direction to the station, measured
clockwise from the nose of the aircraft.
Relative bearing indicator (RBI). Also known as the fixedcard ADF, zero is always indicated at the top of the instrument
and the needle indicates the relative bearing to the station.
Relative wind. Direction of the airflow produced by an object
moving through the air. The relative wind for an airplane in
flight flows in a direction parallel with and opposite to the
direction of flight; therefore, the actual flight path of the
airplane determines the direction of the relative wind.

G-15

Remote communications outlet (RCO). An unmanned
communications facility that is remotely controlled by air
traffic personnel.
Required navigation performance (RNP). A specified level
of accuracy defined by a lateral area of confined airspace in
which an RNP-certified aircraft operates.
Restricted area. Airspace designated under 14 CFR part
73 within which the flight of aircraft, while not wholly
prohibited, is subject to restriction.
Reverse sensing. The VOR needle appearing to indicate the
reverse of normal operation.

SA. See selective availability.
St. Elmo’s Fire. A corona discharge which lights up the aircraft
surface areas where maximum static discharge occurs.
Satellite ephemeris data. Data broadcast by the GPS
satellite containing very accurate orbital data for that
satellite, atmospheric propagation data, and satellite clock
error data.
Scan. The first fundamental skill of instrument flight, also
known as “cross-check;” the continuous and logical observation
of instruments for attitude and performance information.
SDF. See simplified directional facility.

RF. Radio frequency.
Rhodopsin. The photosensitive pigments that initiate the
visual response in the rods of the eye.
Rigidity. The characteristic of a gyroscope that prevents its
axis of rotation tilting as the Earth rotates.
Rime ice. Rough, milky, opaque ice formed by the
instantaneous freezing of small supercooled water droplets.
Risk. The future impact of a hazard that is not eliminated
or controlled.

Selective availability (SA). A satellite technology permitting
the Department of Defense (DOD) to create, in the interest
of national security, a significant clock and ephemeris error
in the satellites, resulting in a navigation error.
Semicircular canal. An inner ear organ that detects angular
acceleration of the body.
Sensitive altimeter. A form of multipointer pneumatic
altimeter with an adjustable barometric scale that allows the
reference pressure to be set to any desired level.
SIDS. See standard instrument departure procedures.

RMI. See radio magnetic indicator.
RNAV. See area navigation.

SIGMET. The acronym for Significant Meteorological
information. A weather advisory issued concerning weather
significant to the safety of all aircraft.

RNP. See required navigation performance.
Runway end identifier lights (REIL). A pair of synchronized
flashing lights, located laterally on each side of the runway
threshold, providing rapid and positive identification of the
approach end of a runway.
Runway visibility value (RVV). The visibility determined
for a particular runway by a transmissometer.
Runway visual range (RVR). The instrumentally derived
horizontal distance a pilot should be able to see down the
runway from the approach end, based on either the sighting
of high-intensity runway lights, or the visual contrast of
other objects.
RVR. See runway visual range.
RVV. See runway visibility value.

G-16

Signal-to-noise ratio. An indication of signal strength
received compared to background noise, which is a measure
of how adequate the received signal is.
Simplex. Transmission and reception on the same
frequency.
Simplified directional facility (SDF). A NAVAID used
for nonprecision instrument approaches. The final approach
course is similar to that of an ILS localizer; however, the
SDF course may be offset from the runway, generally not
more than 3°, and the course may be wider than the localizer,
resulting in a lower degree of accuracy.
Single-pilot resource management (SRM). The ability for
crew or pilot to manage all resources effectively to ensure
the outcome of the flight is successful.

Situational awareness. Pilot knowledge of where the aircraft
is in regard to location, air traffic control, weather, regulations,
aircraft status, and other factors that may affect flight.

Standard instrument departure procedures (SIDS).
Published procedures to expedite clearance delivery and to
facilitate transition between takeoff and en route operations.

Skidding turn. An uncoordinated turn in which the rate of
turn is too great for the angle of bank, pulling the aircraft to
the outside of the turn.

Standard rate turn. A turn in which an aircraft changes its
direction at a rate of 3° per second (360° in 2 minutes) for
low- or medium-speed aircraft. For high-speed aircraft, the
standard rate turn is 1-1/2° per second (360° in 4 minutes).

Skin friction drag. Drag generated between air molecules
and the solid surface of the aircraft.
Slant range. The horizontal distance from the aircraft antenna
to the ground station, due to line-of-sight transmission of the
DME signal.
Slaved compass. A system whereby the heading gyro is
“slaved to,” or continuously corrected to bring its direction
readings into agreement with a remotely located magnetic
direction sensing device (usually this is a flux valve or flux
gate compass).
Slipping turn. An uncoordinated turn in which the aircraft
is banked too much for the rate of turn, so the horizontal lift
component is greater than the centrifugal force, pulling the
aircraft toward the inside of the turn.
Small airplane. An airplane of 12,500 pounds or less
maximum certificated takeoff weight.
Somatogravic illusion. The misperception of being
in a nose-up or nose-down attitude, caused by a rapid
acceleration or deceleration while in flight situations that
lack visual reference.
Spatial disorientation. The state of confusion due to
misleading information being sent to the brain from various
sensory organs, resulting in a lack of awareness of the aircraft
position in relation to a specific reference point.
Special use airspace. Airspace in which flight activities are
subject to restrictions that can create limitations on the mixed
use of airspace. Consists of prohibited, restricted, warning,
military operations, and alert areas.
SRM. See single-pilot resource management.

Standard service volume (SSV). Defines the limits of the
volume of airspace which the VOR serves.
Standard terminal arrival route (STAR). A preplanned
IFR ATC arrival procedure published for pilot use in graphic
and/or textual form.
STAR. See standard terminal arrival route.
Static longitudinal stability. The aerodynamic pitching
moments required to return the aircraft to the equilibrium
angle of attack.
Static pressure. Pressure of air that is still, or not moving,
measured perpendicular to the surface of the aircraft.
Steep turns. In instrument flight, any turn greater than standard
rate; in visual flight, anything greater than a 45° bank.
Stepdown fix. The point after which additional descent is
permitted within a segment of an IAP.
Strapdown system. An INS in which the accelerometers
and gyros are permanently “strapped down” or aligned with
the three axes of the aircraft.
Stress. The body’s response to demands placed upon it.
Structural icing. The accumulation of ice on the exterior
of the aircraft.
Suction relief valve. A relief valve in an instrument vacuum
system required to maintain the correct low pressure inside
the instrument case for the proper operation of the gyros.
Synchro. A device used to transmit indications of angular
movement or position from one location to another.

SSR. See secondary surveillance radar.
SSV. See standard service volume.

Synthetic vision. A realistic display depiction of the aircraft
in relation to terrain and flight path.

Standard holding pattern. A holding pattern in which all
turns are made to the right.

G-17

TAA. See terminal arrival area.
TACAN. See tactical air navigation.
Tactical air navigation (TACAN). An electronic navigation
system used by military aircraft, providing both distance and
direction information.
TAWS. See terrain awareness and warning system.
TCAS. See traffic alert collision avoidance system.

Terrain Awareness and Warning System (TAWS). A
timed-based system that provides information concerning
potential hazards with fixed objects by using GPS positioning
and a database of terrain and obstructions to provide true
predictability of the upcoming terrain and obstacles.
TFR. See temporary flight restriction.
Threshold crossing height (TCH). The theoretical height
above the runway threshold at which the aircraft’s glide
slope antenna would be if the aircraft maintains the trajectory
established by the mean ILS glide slope or MLS glide path.

TCH. See threshold crossing height.
TDZE. See touchdown zone elevation.

Thrust (aerodynamic force). The forward aerodynamic
force produced by a propeller, fan, or turbojet engine as it
forces a mass of air to the rear, behind the aircraft.

TEC. See Tower En Route Control.
Technique. The manner in which procedures are executed.
Temporary flight restriction (TFR). Restriction to flight
imposed in order to:

Time and speed table. A table depicted on an instrument
approach procedure chart that identifies the distance from the
FAF to the MAP, and provides the time required to transit
that distance based on various groundspeeds.

1.

Protect persons and property in the air or on the
surface from an existing or imminent flight associated
hazard;

Timed turn. A turn in which the clock and the turn
coordinator are used to change heading a definite number of
degrees in a given time.

2.

Provide a safe environment for the operation of
disaster relief aircraft;

TIS. See traffic information service.

3.

Prevent an unsafe congestion of sightseeing aircraft
above an incident;

4.

Protect the President, Vice President, or other public
figures; and,

Title 14 of the Code of Federal Regulations (14 CFR).
The federal aviation regulations governing the operation of
aircraft, airways, and airmen.

5.

Provide a safe environment for space agency
operations.
Pilots are expected to check appropriate NOTAMs during
flight planning when conducting flight in an area where a
temporary flight restriction is in effect.
Tension. Maintaining an excessively strong grip on the control
column, usually resulting in an overcontrolled situation.
Terminal Instrument Approach Procedure (TERP).
Prescribes standardized methods for use in designing
instrument flight procedures.
Terminal arrival area (TAA). A procedure to provide a
new transition method for arriving aircraft equipped with
FMS and/or GPS navigational equipment. The TAA contains
a “T” structure that normally provides a NoPT for aircraft
using the approach.
TERP. See terminal instrument approach procedure.

G-18

Touchdown zone elevation (TDZE). The highest elevation
in the first 3,000 feet of the landing surface, TDZE is
indicated on the instrument approach procedure chart when
straight-in landing minimums are authorized.
Tower En Route Control (TEC). The control of IFR en route
traffic within delegated airspace between two or more adjacent
approach control facilities, designed to expedite traffic and
reduce control and pilot communication requirements.
TPP. See United States Terminal Procedures Publication.
Tracking. Flying a heading that will maintain the desired track
to or from the station regardless of crosswind conditions.
Traffic Alert Collision Avoidance System (TCAS).
An airborne system developed by the FAA that operates
independently from the ground-based Air Traffic Control
system. Designed to increase flight deck awareness of
proximate aircraft and to serve as a “last line of defense” for
the prevention of mid-air collisions.

Traffic information service (TIS). A ground-based service
providing information to the flight deck via data link using
the S-mode transponder and altitude encoder to improve the
safety and efficiency of “see and avoid” flight through an
automatic display that informs the pilot of nearby traffic.
Transcribed Weather Broadcast (TWEB). Meteorological
and aeronautical data recorded on tapes and broadcast over
selected NAVAIDs. Generally, the broadcast contains routeoriented data with specially prepared NWS forecasts, inflight
advisories, and winds aloft. It also includes selected current
information such as weather reports (METAR/SPECI),
NOTAMs, and special notices.
Transponder. The airborne portion of the ATC radar
beacon system.
Transponder code. One of 4,096 four-digit discrete codes
ATC assigns to distinguish between aircraft.
Trend. Immediate indication of the direction of aircraft
movement, as shown on instruments.
Trim. Adjusting the aerodynamic forces on the control
surfaces so that the aircraft maintains the set attitude without
any control input.
TWEB. See Transcribed Weather Broadcast.
True airspeed. Actual airspeed, determined by applying a
correction for pressure altitude and temperature to the CAS.
UHF. See ultra-high frequency.
Ultra-high frequency (UHF). The range of electromagnetic
frequencies between 962 MHz and 1213 MHz.
Uncaging. Unlocking the gimbals of a gyroscopic instrument,
making it susceptible to damage by abrupt flight maneuvers
or rough handling.
Underpower. Using less power than required for the purpose
of achieving a faster rate of airspeed change.
United States Terminal Procedures Publication (TPP).
Booklets published in regional format by the NACO that
include DPs, STARs, IAPs, and other information pertinent
to IFR flight.

User-defined waypoints. Waypoint location and other data
which may be input by the user, this is the only GPS database
information that may be altered (edited) by the user.
Variation. Compass error caused by the difference in
the physical locations of the magnetic north pole and the
geographic north pole.
VASI. See visual approach slope indicator.
VDP. See visual descent point.
Vectoring. Navigational guidance by assigning headings.
Venturi tube. A specially shaped tube attached to the outside
of an aircraft to produce suction to allow proper operation
of gyro instruments.
Vertical speed indicator (VSI). A rate-of-pressure change
instrument that gives an indication of any deviation from a
constant pressure level.
Very-high frequency (VHF). A band of radio frequencies
falling between 30 and 300 MHz.
Very-high frequency omnidirectional range (VOR).
Electronic navigation equipment in which the flight deck
instrument identifies the radial or line from the VOR station,
measured in degrees clockwise from magnetic north, along
which the aircraft is located.
Vestibule. The central cavity of the bony labyrinth of the ear,
or the parts of the membranous labyrinth that it contains.
VFR. See visual flight rules.
VFR-on-top. ATC authorization for an IFR aircraft to operate
in VFR conditions at any appropriate VFR altitude.
VFR over-the-top. A VFR operation in which an aircraft
operates in VFR conditions on top of an undercast.
Victor airways. Airways based on a centerline that extends
from one VOR or VORTAC navigation aid or intersection,
to another navigation aid (or through several navigation aids
or intersections); used to establish a known route for en route
procedures between terminal areas.

Unusual attitude. An unintentional, unanticipated, or
extreme aircraft attitude.

G-19

Visual approach slope indicator (VASI). A visual aid of
lights arranged to provide descent guidance information
during the approach to the runway. A pilot on the correct
glide slope will see red lights over white lights.

Warning area. An area containing hazards to any aircraft
not participating in the activities being conducted in the
area. Warning areas may contain intensive military training,
gunnery exercises, or special weapons testing.

Visual descent point (VDP). A defined point on the final
approach course of a nonprecision straight-in approach
procedure from which normal descent from the MDA to the
runway touchdown point may be commenced, provided the
runway environment is clearly visible to the pilot.

Waypoint. A designated geographical location used for route
definition or progress-reporting purposes and is defined in
terms of latitude/longitude coordinates.

Visual flight rules (VFR). Flight rules adopted by the
FAA governing aircraft flight using visual references. VFR
operations specify the amount of ceiling and the visibility the
pilot must have in order to operate according to these rules.
When the weather conditions are such that the pilot can not
operate according to VFR, he or she must use instrument
flight rules (IFR).

Weather and radar processor (WARP). A device that
provides real-time, accurate, predictive and strategic weather
information presented in an integrated manner in the National
Airspace System (NAS).

Visual meteorological conditions (VMC). Meteorological
conditions expressed in terms of visibility, distance from
cloud, and ceiling meeting or exceeding the minimums
specified for VFR.

Wide area augmentation system (WAAS). A differential
global positioning system (DGPS) that improves the accuracy
of the system by determining position error from the GPS
satellites, then transmitting the error, or corrective factors,
to the airborne GPS receiver.

WCA. See wind correction angle.

Weight. The force exerted by an aircraft from the pull of
gravity.

VMC. See visual meteorological conditions.
VOR. See very-high frequency omnidirectional range.
VORTAC. A facility consisting of two components, VOR
and TACAN, which provides three individual services: VOR
azimuth, TACAN azimuth, and TACAN distance (DME) at
one site.
VOR test facility (VOT). A ground facility which emits a
test signal to check VOR receiver accuracy. Some VOTs are
available to the user while airborne, while others are limited
to ground use only.
VOT. See VOR test facility.
VSI. See vertical speed indicator.
WAAS. See wide area augmentation system.

G-20

Wind correction angle (WCA). The angle between the
desired track and the heading of the aircraft necessary to
keep the aircraft tracking over the desired track.
Work. A measurement of force used to produce movement.
Zone of confusion. Volume of space above the station where
a lack of adequate navigation signal directly above the VOR
station causes the needle to deviate.

Index
A
above ground level .............................3-31, 7-44, 8-2, 9-10
absolute accuracy .........................................................7-25
acceleration in cruise flight ..........................................2-10
acute fatigue .............................................. 1-11, 1-12, 1-13
additional reports .........................................................10-7
adjust ............................................................................4-20
advanced technologies .................................................7-26
advanced technology systems ......................................3-28
adverse yaw ........................................................ 2-11, 2-12
aeronautical decision-making (ADM)1-1, 1-12, 1-15, 1-17
aeronautical information manual (AIM) .............. 9-4, 10-2
agonic line ....................................................................3-12
air data computer (ADC) .............................................3-22
air route surveillance radar (ARSR) .................... 7-49, 9-7
air route traffic control center (ARTC) 7-50, 9-4, 9-7, 10-2
air traffic control (ATC) .............................. 1-15, 9-1, 11-1
inflight weather avoidance assistance ......................9-11
radar weather displays ..............................................9-11
air traffic control radar beacon system (ATCRBS)......7-49
air traffic control towers .................................................9-5
aircraft approach categories .........................................8-23
aircraft control ................................................................6-3
aircraft system malfunctions ........................................11-3
airplane trim ...................................................................4-8
airport diagram .............................................................8-27
airport information .........................................................8-6
airport sketch................................................................8-27
airport surface detection equipment (ASDE) ..... 7-49, 7-50
airport surveillance radar (ASR) .......................... 7-49, 9-7
Airport/Facility Directory (A/FD) .......1-9, 7-10, 8-6, 10-2
airspace classification.....................................................8-1
class A through G .......................................................8-2
airspeed color codes .....................................................3-10
airspeed
indicated .....................................................................3-9
indicator ..............................................4-6, 5-5, 5-37, 6-5
calibrated ....................................................................3-9
equivalent ...................................................................3-9
true ..............................................................................3-9

airspeed changes
common errors..........................................................6-10
airspeed indicators .................................... 4-26, 5-29, 5-61
maximum allowable airspeed ...................................3-10
alcohol ..........................................................................1-12
alternate airport ............................................................8-27
alternator/generator failure...........................................11-5
altimeter ............................................................... 5-36, 6-4
amendment status .........................................................8-12
analog pictorial displays ..............................................3-22
anti-ice..........................................................................2-12
approach lighting systems (ALS ..................................7-40
approach to stall ...........................................................5-26
altimeter
errors...........................................................................3-4
cold weather ...............................................................3-5
enhancements (encoding) ...........................................3-7
analog instrument failure .............................................11-6
angle of attack ........................................................ 2-2, 2-6
approach azimuth guidance..........................................7-45
approach control advances ...........................................9-12
approach control facility ..............................................9-12
approach to airport
without an operating control tower ........................10-14
with control tower, no approach control ................10-14
with control tower and approach control................10-14
approaches..................................................................10-12
missed .....................................................................10-21
parallel runways .....................................................10-20
radar ........................................................................10-17
timed, from a holding fix ........................................10-18
area navigation (RNAV) ..............................................7-19
arrival .........................................................................10-33
atmosphere .....................................................................2-4
layers of the atmosphere .............................................2-5
attitude and heading reference system (AHRS) ...........3-22
attitude director indicator (ADI) ..................................3-23

I-1

attitude
indicator ....... 4-4, 4-5, 4-7, 5-2, 5-6, 5-34, 5-37, 6-3, 6-5
control.........................................................................4-3
instrument flying ....................................... 4-1, 4-21, 6-1
autokinesis......................................................................1-7
automated flight service stations (AFSS).......................9-4
automated radar terminal systems (ARTS) ....................9-7
automated surface observing station (ASOS) ..............8-10
automated terminal information service (ATIS) ..........10-8
automated weather observing station (AWOS) ...........8-10
automatic dependent surveillance-broadcast (ADS-B) 3-28
automatic direction finder (ADF)................ 3-16, 7-3, 10-7
function of ..................................................................7-4
operational errors........................................................7-8
automatic terminal information service (ATIS) . 1-15, 8-16
automatic weather observing system (AWOS) ..............7-3
autopilot systems..........................................................3-24
autorotations.................................................................6-17
common errors....................................................6-17
azimuth card ...................................................................7-4

B
back courses (BC) ........................................................7-39
bank control .......................... 4-4, 4-7, 4-20, 5-6, 5-37, 6-5
baro-aiding ...................................................................7-28
barometric vertical navigation (BARO VNAV) ..........8-32
basic aerodynamics (review of) .....................................2-2
relative wind ...............................................................2-2
angle of attack ............................................................2-2
basic instrument flight patterns .......................... 5-30, 5-61
basic radio principles .....................................................7-2
blockage considerations .................................................3-2
indications of pitot tube blockage ..............................3-3
indications from static port blockage .........................3-3
effects of flight conditions ..........................................3-3

C
calibrated .............................................................. 5-2, 6-14
calibrated orifice.............................................................3-8
center approach/departure control..................................9-7
certified checkpoints ....................................................7-16
changeover points (COPs) ...........................................8-10
changing technology ....................................................6-18
charted IFR altitudes ......................................................8-6
chronic fatigue .............................................................1-13
circling approaches ....................................................10-20
circling approach pattern..............................................5-32
class D airspace ...................................................... 8-2, 9-6
clean configuration .......................................................5-11
clear ice ............................................................ 2-13, 10-24

I-2

clearances .....................................................................10-3
separations ................................................................10-4
clearance delivery ........................................................10-4
clearance on request .......................................................9-6
clearance void time ........................................................9-5
climbing
while accelerating .......................................................1-8
while turning ..............................................................1-8
climbs ................................................................. 2-10, 5-14
common errors
fixation ......................................................................4-27
omission ...................................................................4-28
emphasis ...................................................................4-28
communication equipment .............................................9-2
communication facilities ................................................9-4
communication procedures ............................................9-4
communication/navigation system malfunction ..........11-8
compass
course .......................................................................3-13
locator ............................................................. 7-28, 7-40
turns ....................................................... 5-21, 5-53, 6-15
compass rose ...................................................... 3-12, 5-25
computer navigation fix ...............................................8-10
concentric rings ............................................................8-18
conducting an IFR flight ............................................10-27
constant airspeed climb
from cruise airspeed .................................................5-46
from established airspeed .........................................5-47
constant rate climbs......................................................5-47
control
characteristics .............................................................2-7
and performance .........................................................4-2
instruments ....................................................... 4-2, 4-18
sequence ...................................................................9-13
control display unit (CDU) ..........................................3-26
control pressures ............................................................5-3
coordinated............................................................. 5-6, 6-5
coordination of rudder and aileron controls .................2-11
coriolis illusion...............................................................1-6
course interception .......................................................7-14
course reversal elements
plan view ..................................................................8-20
profile view ...............................................................8-20
crew resource management (CRM) .............................1-14
critical areas ...................................................................7-2
cross-check ........................................................... 4-3, 4-20
common errors..........................................................4-11
cruise clearance ............................................................10-4
current induction ..........................................................3-15

D
dark adaptation ...............................................................1-3
DECIDE model ............................................................1-17
decision height (DH) ................................. 3-31, 7-50, 8-21
deice .............................................................................2-13
density altitude ...............................................................2-5
departure ....................................................................10-31
departure procedures (DPs)................7-1, 7-33, 8-12, 10-5
instrument .................................................................7-33
departures
airports without an operating control tower .............10-7
radar controlled ........................................................10-5
descents .............................................................. 5-16, 5-49
deviation.......................................................................3-12
differential global positioning systems (DGPS) ..........7-34
direct indication ............................................ 5-2, 5-34, 6-3
directional ....................................................................7-42
distance circle...............................................................8-18
distance measuring equipment (DME) ................ 7-16, 8-7
arc .............................................................................7-17
components...............................................................7-17
errors.........................................................................7-19
function of ................................................................7-17
diving
or rolling beyond the vertical plane............................1-8
while turning ..............................................................1-8
DOD .............................................................................3-22
doghouse ......................................................................3-21
domestic reduced vertical
separation minimum (DRVSM) ...........................3-7
double gimbal...............................................................3-18
drag ................................................................................2-3
drag curves .....................................................................2-6
dry air vacuum pump ...................................................3-17
duplex.............................................................................9-2
dynamic pressure type instruments ................................3-8

E
ears .................................................................................1-4
otolith organs .................................................. 1-4, 1-5
semicircular canals .................................................1-4
eddy currents ........................................................ 2-3, 3-14
electrical systems .........................................................3-18
electronic flight display (EFD).......................................4-1
electronic flight instrument systems.............................3-27
elevator illusion..............................................................1-6
emergencies..................................................................6-16
en route............................................................. 10-7, 10-32
en route flight advisory service (EFAS).........................9-4
en route high-altitude charts...........................................8-6
en route procedures ......................................................10-7

encoding altimeter ..........................................................3-7
entry .................................................5-14, 5-46, 5-49, 6-10
equipment.....................................................................1-14
eyes ................................................................................1-2

F
false horizon ...................................................................1-7
fatigue ..........................................................................1-12
featureless terrain illusion ..............................................1-9
federal airways ...............................................................8-4
feeder facilities .............................................................8-18
feet per minute (fpm) .....................................................4-6
filing in flight ...............................................................10-2
final approach fix (FAF)...............................................7-23
final approach waypoint (FAWP) ................................7-32
flight director indicator (FDI) ......................................3-23
flight instruments .......................................... 2-16, 3-1, 6-2
flight levels (FL) ............................................................3-7
flight management systems (FMS) ..............................3-25
function of ................................................................7-48
flight patterns ...............................................................5-30
flight planning information, sources ............................10-2
flight strips .....................................................................9-5
flight support systems ..................................................3-22
flight path ............................................................... 2-2, 2-6
four step process used to change attitude .....................4-20
flux gate compass .........................................................3-14
flying experience ........................................................10-22
fog ...................................................................... 1-9, 10-24
form drag........................................................................2-4
four forces ......................................................................2-2
fundamental skills
of attitude instrument flying .....................................4-24
instrument cross-check .............................................4-10
instrument flight .........................................................6-2

G
glide slope ....................................................................7-39
glide slope intercept altitude ......................................10-20
global landing system (GLS) .......................................8-32
global navigation satellite system (GNSS) ..................7-26
global positioning system (GPS) ....................... 3-27, 7-27
components...............................................................7-27
errors.........................................................................7-33
familiarization ..........................................................7-34
function of ................................................................7-28
instrument approaches ..............................................7-31
nearest airport function.............................................11-9
substitution ...............................................................7-28
graveyard spiral ..............................................................1-6
ground lighting illusions ................................................1-9
I-3

ground proximity warning system (GPWS) ................3-34
ground speed ................................................................7-19
ground wave ...................................................................7-2
gyroscopic systems, power sources .............................3-16
pneumatic systems....................................................3-16
vacuum pump systems .............................................3-17
gyroscopic instruments
attitude indicator .......................................................3-18

H
hazard identification .....................................................1-13
hazardous attitudes .......................................................1-18
and antidotes .............................................................1-18
Hazardous Inflight Weather Advisory Service
(HIWAS) ......................................................................8-10
haze ................................................................................1-9
head up display (HUD) ...................................... 3-34, 7-49
heading ............................................................... 5-13, 5-44
heading indicators ........................ 3-19, 4-7, 5-7, 5-38, 6-6
height above airport (HAA) .........................................8-27
height above landing (HAL) ........................................8-27
height above threshold elevation (HAT)......................8-27
helicopter trim ..............................................................4-10
holding .........................................................................10-9
DME .......................................................................10-13
instructions .............................................................10-10
patterns .......................................................................7-1
procedures ..............................................................10-10
homing ...........................................................................7-5
horizontal situation indicator (HSI) ................... 3-22, 5-38
human
factors .........................................................................1-1
resources ...................................................................1-14

I
IAP minimums ...........................................................10-21
ICAO cold temperature error table ................................3-6
ICAO Standard Atmosphere ..........................................2-5
icing..............................................................................2-12
types of .....................................................................2-13
identifying intersections .................................................8-7
IFR en route and terminal operations...........................7-28
IFR en route charts .........................................................8-6
IFR flight plan ..............................................................10-2
canceling...................................................................10-3
IFR Flight using GPS ...................................................7-30
illusions leading to spatial disorientation.......................1-5
IMSAFE Checklist .......................................................1-13
indirect indication ........................................... 5-3, 5-6, 6-4
induced drag ...................................................................2-3
induction icing .............................................................2-13
I-4

inertia navigation systems (INS) ..................................7-36
components...............................................................7-37
errors.........................................................................7-37
initial approach fix (IAF) .......................... 7-23, 8-16, 8-18
inoperative components ...............................................8-27
instantaneous vertical speed indicator (IVSI) ........ 3-8, 4-6
instrument
approach capabilities ................................................7-36
approach systems......................................................7-37
cross-check .............................................. 4-10, 4-24, 6-2
instrument approach procedures (IAPs)...... 7-17, 8-2, 8-12
instrument approach procedures, compliance with ....10-12
instrument approaches
to civil airports .......................................................10-13
radar monitoring of.................................................10-18
instrument flight .............................................................6-2
instrument flight rules (IFR) ................................ 3-1, 10-1
instrument interpretation ................................................6-3
instrument landing systems (ILS) ................................7-37
components...............................................................7-39
errors.........................................................................7-44
function.....................................................................7-42
instrument takeoffs.................................... 5-29, 5-60, 6-17
common errors....................................... 5-29, 5-61, 6-18
instrument weather flying ..........................................10-22
integrated flight control system....................................3-24
intercepting lead radials ...............................................7-19
interference drag ............................................................2-3
international civil aviation organization (ICAO) ... 2-5, 8-1
international standard atmosphere (ISA) .......................2-5
inversion illusion............................................................1-6
inverted-V cross-check ................................................4-11
inverter .........................................................................3-18
isogonic lines ...............................................................3-12

J
jet routes .........................................................................8-5

K
Kollsman window .................................................. 3-4, 9-3

L
lag........................................................................... 5-5, 6-5
land as soon as possible ...............................................6-17
land as soon as practical ...............................................6-17
land immediately..........................................................6-17
landing........................................................................10-22
landing minimums .......................................................8-23
large airplanes ..............................................................2-10
Law of Inertia .................................................................2-9

Law of Momentum ........................................................2-4
Law of Reaction .............................................................2-4
layers of the atmosphere ................................................2-5
lead radial .....................................................................7-19
leans, the ........................................................................1-5
learning methods
control and performance................................... 4-2, 4-17
primary and supporting ..............................................4-2
letters of agreement (LOA) ..........................................9-14
leveling off .......................................5-16, 5-17, 5-48, 5-50
lift ........................................................................... 2-2, 2-6
lines of magnetic flux ...................................................3-11
load factor ....................................................................2-11
local area augmentation system (LAAS) ........... 7-36, 8-32
localizer (LOC) ............................................................7-39
localizer type directional aid (LDA) ............................7-45
long range navigation (LORAN) ......................... 7-3, 7-24
components...............................................................7-25
errors.........................................................................7-26
function of ................................................................7-26
loss of alternator/generator for electronic flight
instrumentation ............................................................11-5
lubber line ....................................................................3-11

M
mach number................................................................3-10
machmeters ..................................................................3-10
magnetic compass, basic aviation ................................3-11
induced errors ...........................................................3-12
magnetic bearing (MB) ..................................................7-3
magnetic heading (MH) .................................................7-3
magnetism ....................................................................3-10
margin identification ....................................................8-12
marker beacons ......................................... 7-37, 7-40, 7-44
maximum authorized altitude (MAA) ...........................8-7
mean sea level (MSL) ..................................................10-9
medical factors .............................................................1-12
acute fatigue..............................................................1-12
alcohol ......................................................................1-12
chronic fatigue ..........................................................1-13
fatigue .......................................................................1-12
microwave landing system (MLS) ...............................7-45
middle markers (MMs) ................................................7-39
mileage breakdown ......................................................8-10
military operations areas (MOAs) .................................8-4
military training routes (MTRs) .....................................8-4
minimum crossing altitude (MCA) ................................8-7
minimum descent altitude (MDA) ..................... 7-32, 8-21
minimum en route altitude (MEA) ................................8-6
minimum obstruction clearance altitude (MOCA) ........8-6
minimum reception altitude (MRA) ..............................8-6

minimum safe altitude (MSA) ........................... 8-16, 8-18
minimum vectoring altitudes (MVAs) ...........................9-6
minimums section ........................................................8-23
missed approach point (MAP) .....................................7-23
missed approach procedure ..........................................8-23
missed approach waypoint (MAHWP) ........................7-32
mixed ice ......................................................................2-14
Mode C...........................................................................3-7
altitude reporting ........................................................9-3
models for practicing ADM
perceive, process, perform .......................................1-17
DECIDE model, the .................................................1-17
monopulse secondary surveillance radar (MSSR) .......9-12
multi-function display (MFD)................. 3-27, 3-28, 11-12
navigating page groups...........................................11-10
nearest airports, using .............................................11-10

N
National Aeronautical Charting Group (NACG) ...........8-2
National Airspace System (NAS) .......................... 8-1, 9-1
National Security Areas (NSA) .....................................8-4
National Transportation Safety Board (NTSB .............2-16
nautical miles (NM) .....................................................7-17
navigation/communication (NAV/COM) equipment .........
................................................................................ 9-2, 9-3
navigation features .........................................................8-7
navigation instruments ......................................... 4-2, 4-19
nearest airport page group ..........................................11-10
nearest airports page soft keys ...................................11-10
nerves .............................................................................1-5
new technologies..........................................................8-10
Newton’s First Law of Motion Law of Inertia...............2-4
Newton’s Second Law of Motion Law of Momentum ..2-4
Newton’s Third Law of Motion Law of Reaction .........2-4
no-gyro approach .......................................................10-18
nondirectional beacon (NDB) ................................ 7-3, 8-7
nonprecision approach ...................................................9-7
nonstandard pressure on an altimeter .............................3-6
normal command ...........................................................2-7
North American Route Program (NRP) .........................8-6
nose high attitudes........................................................5-27
nose low attitudes.........................................................5-28
notices to airmen (NOTAM) ................................ 7-10, 8-4

O
obstical clearance surface ............................................7-32
obstacle departure procedures (ODP) ..........................8-12
off-route obstruction clearance altitude (OROCA .........8-6
operating on the main battery ......................................11-5
operational errors .........................................................7-45
optical illusions ..............................................................1-9
I-5

featureless terrain illusion ..........................................1-9
fog...............................................................................1-9
ground lighting illusions.............................................1-9
haze.............................................................................1-9
how to prevent landing errors due to optical illusions ....
....................................................................................1-9
runway width illusion .................................................1-9
runway and terrain slopes illusion ..............................1-9
water refraction ..........................................................1-9
orientation ......................................................................1-2
oscillation error ............................................................3-14
otolith organs ......................................................... 1-4, 1-5
outer markers (OMs) ....................................................7-39
outside air temperature (OAT) .....................................11-2
overcontrolling ................................................ 4-7, 5-4, 6-3
overpower ......................................................................5-9

P
parasite drag ...................................................................2-3
partial panel flight ........................................................5-36
performance instruments ...................................... 4-2, 4-19
physiological and psychological factors ......................1-11
pilot briefing .................................................................8-12
Pilot’s Operating Handbook/Airplane Flight
Manual (POH/AFM) ......................................................3-3
pilot/static instruments ...................................................3-3
pilot/static systems .........................................................3-2
failure .......................................................................11-7
pitch control ............................ 4-4, 4-20-21, 5-2, 5-34, 6-3
pitch/power relationship.................................................2-6
pitot pressure ..................................................................3-2
pitot-static head ..............................................................3-2
plan view ......................................................................8-16
course reversal elements...........................................8-20
planning the descent and approach ..............................10-8
preflight ........................................................................10-2
profile view ..................................................................8-21
pneumatic systems .......................................................3-16
failure .......................................................................11-7
POH/AFM ....................................................................10-2
position
error ............................................................................3-3
reports .......................................................................10-7
postural considerations...................................................1-7
power................................................2-10, 5-13, 5-25, 5-45
control....................................... 4-4, 4-8, 4-21, 5-8, 5-39
settings .............................................................. 5-9, 5-39
precession.....................................................................3-16
error .................................................................... 5-7, 6-6
precipitation static (P-static) ........................................11-3
precision approach .......................................................7-37
I-6

precision approach path indicator (PAPI) ....................1-10
precision approach radar (PAR)....................... 7-49, 10-17
precision runway monitor (PRM) ................................9-12
RADAR ....................................................................9-12
benefits .....................................................................9-12
preferred IFR routes .......................................................8-5
pressure
altitude ................................................................ 2-5, 9-3
density ........................................................................2-5
indicating systems ....................................................3-18
preventing landing errors due to optical illusions ..........1-9
primary
bank ..........................................................................4-23
pitch ..........................................................................4-22
power ........................................................................4-23
yaw ...........................................................................4-23
primary and supporting method ........................... 4-4, 4-21
primary flight display (PFD) ........................................3-27
additional information for specific airport .............11-11
nearest airports, using .............................................11-10
procedure turn .................................................... 7-32, 8-20
holding in lieu of ......................................................8-20
standard 45° ..............................................................5-30
80/260 .......................................................................5-31
profile view ..................................................................8-21
propeller icing ..............................................................2-16
propeller/rotor modulation error ....................................7-2

R
racetrack pattern ...........................................................5-30
radar ..............................................................................9-3
limitations .................................................................7-50
transponders ...............................................................9-3
radar controlled departures ..........................................10-5
radar navigation (ground based) ..................................7-49
functions of ...............................................................7-49
radials ...........................................................................7-10
radio altimeter ..............................................................3-30
radio frequency (RF .....................................................7-16
radio magnetic indicator (RMI) ........................... 3-15, 7-4
radio wave ......................................................................7-2
radius of turn ................................................................2-11
rate of turns ..................................................................2-10
receiver autonomous integrity monitoring (RAIM) .....7-28
receiver-transmitter (RT) .............................................3-31
rectangular cross-check ................................................4-11
reduced vertical separation minimum (RVSM) .............3-7
reference circle .............................................................8-18

regions of command.......................................................2-7
normal command ........................................................2-7
reversed command......................................................2-8
relative bearing (RB)......................................................7-3
relative wind........................................................... 2-2, 2-4
remote communications outlet (RCO) .........................8-10
remote indicating compass ...........................................3-15
repeatable accuracy ......................................................7-25
required navigation performance .................................7-46
required navigation instrument system inspection .......3-34
reversal of motion ..........................................................1-8
RNAV instrument approach charts ..............................8-32
reversed command .........................................................2-8
reverse sensing .............................................................7-12
rhodopsin........................................................................1-2
rigidity ..........................................................................3-16
rime ice.........................................................................2-13
risk................................................................................1-13
risk analysis..................................................................1-13
RNAV (See area navigation) runway width
illusion ................................................................. 1-9, 1-10
and terrain slopes illusion ................................. 1-9, 1-10
runway end identifier lights (REIL) .............................7-40
runway visual range (RVR) ............................. 8-27, 10-22
runway visual value (RVV) .......................................10-22

S
safety systems ..............................................................3-30
scanning techniques .....................................................4-24
selected radial cross-check ................................. 4-11, 4-24
selective availability (SA) ............................................7-33
semicircular canals .........................................................1-4
sensitive altimeter ..........................................................3-3
principle of operation .................................................3-3
sensory systems for orientation......................................1-2
servo failure .................................................................6-17
side-step maneuver.....................................................10-20
simplex ...........................................................................9-2
simplified directional facility (SDF) ............................7-45
single-pilot resource management (SRM) ...................1-14
situational awareness ....................................... 1-14, 11-11
skin friction drag ............................................................2-3
sky wave.........................................................................7-2
slip/skid indicator .........................................................5-39
slow-speed flight ............................................................2-8
small airplanes ...............................................................2-9
somatogravic illusion .....................................................1-6
space wave .....................................................................7-2
spatial disorientation ......................................................1-2
coping with spatial disorientation ..............................1-8
demonstration of spatial disorientation ......................1-7

special use airspace ........................................................8-2
speed stability.................................................................2-7
St. Elmo’s Fire ..................................................... 7-3, 11-3
stall warning systems ...................................................2-16
standard entry procedures ..........................................10-11
standard holding pattern
no wind .....................................................................10-9
with wind ..................................................................10-9
standard instrument departure procedures (SID) .........10-5
standard rate of turn .................................. 2-11, 5-19, 5-51
establishing ...............................................................5-51
common errors..........................................................5-51
standard terminal arrival routes (STAR)............ 8-12, 10-9
standby battery .............................................................11-6
static longitudinal stability .............................................2-8
static pressure .................................................................3-2
steep turns .......................................................... 5-22, 5-53
stepdown fixes..............................................................8-21
straight-and-level flight ........................4-22, 5-2, 5-34, 6-3
airspeed changes ............................................. 5-11, 5-40
common errors............................................................6-7
power control during ..................................................6-7
straight climbs and descents............................... 5-14, 5-46
common errors....................................... 5-17, 5-50, 6-13
stress.............................................................................1-11
structural icing ................................................ 2-13, 10-24
suction relief valve .......................................................3-17
synchro .........................................................................3-15
synthetic vision ............................................................3-27
system status ................................................................7-33
systems preflight procedures
before engine start ....................................................3-36
after engine start .......................................................3-37
taxiing and takeoff ....................................................3-37
engine shut down ......................................................3-37

T
tactical air navigation (TACAN) .................. 7-8, 8-7, 10-7
tailplane stall symptoms...............................................2-16
task management ..........................................................1-15
teardrop
patterns .....................................................................5-31
procedure ..................................................................8-21
techniques ......................................................................5-1
for electrical usage ......................................... 11-5, 11-6
master battery switch ................................................11-5
operating on the main battery ......................... 11-5, 11-6
temporary flight restrictions (TFRs) ..............................8-4
tension ................................................................ 4-10, 4-13
terminal arrival area (TAA) .........................................8-18
terminal instrument approach procedures (TERPs) .....8-12
I-7

Terminal Procedures Publications (TPP) .....................8-12
terminal radar approach control (TRACON) .................9-6
terrain alerting systems ................................................3-34
terrain awareness and warning systems (TAWS) ........3-34
threshold crossing height (TCH)..................................8-32
thrust ......................................................2-2, 2-3, 2-6, 2-10
thunderstorm encounter, inadvertent ...........................11-2
thunderstorms................................................... 9-11, 10-25
tilting to right or left.......................................................1-8
time factors.................................................................10-12
time and speed table .....................................................8-27
timed turns ................................................ 5-21, 5-53, 6-13
Title 14 of the Code of Federal Regulations
(14 CFR) ..................1-12, 3-2, 7-16, 8-4, 8-11, 10-2, 11-8
touch down zone elevation (TDZE) .............................8-27
Tower En Route Control (TEC) ............................. 8-6, 9-7
tracking ..........................................................................7-5
to and from the station ..............................................7-14
Traditional navigation systems ......................................7-3
traffic
advisory systems ......................................................3-31
alert systems .............................................................3-31
alert and collision avoidance system (TCAS) ..........3-31
avoidance ................................................................11-14
avoidance systems ....................................................3-31
information system (TIS) .........................................3-31
transcribed weather broadcast (TWEB) .......................8-10
transponder.....................................................................9-3
codes ...........................................................................9-3
trend indicators.............................................................4-26
trim ................. 2-8, 4-8, 4-10, 4-20, 5-12, 5-13, 5-26, 5-45
control............................................................... 4-8, 5-43
turbulence...................................................................10-23
turn indicator ........................................................ 3-20, 6-7
turn rate indicator .........................................................5-38
turn-and-slip indicator .......................................... 3-20, 5-8
turns..................................................2-10, 5-19, 5-51, 6-13
change of airspeed .......................................... 5-24, 6-14
climbing and descending ................................ 5-24, 6-15
common errors................................................ 5-25, 6-15
compass ................................................. 5-21, 5-53, 6-15
coordinator ................................................ 3-21, 4-8, 5-7
to predetermined headings .................... 5-20, 5-52, 6-13
radius of ....................................................................2-11
rate of........................................................................2-10
standard rate .......................................... 2-11, 5-19, 5-51
steep ..........................................................................5-22
timed ...................................................... 5-21, 5-53, 6-13
turn-and-slip indicator ................................... 3-20, 4-8, 5-8
types of icing ................................................................2-13
types of NAVAIDS ........................................................8-7

I-8

U
ultra high frequency (UHF) ...........................................7-3
uncaging .......................................................................5-29
underpower ..................................................................5-39
unforecast adverse weather ..........................................11-2
unusual attitude .................................................. 5-26, 6-16
common errors....................................... 5-28, 5-58, 6-16
recognizing ...............................................................5-27
recovery from ................................................. 5-26, 5-55

V
vacuum pump systems .................................................3-17
variation .......................................................................3-12
vectoring ........................................................................9-6
venturi tubes .................................................................3-16
vertical card magnetic compass ...................................3-14
vertical speed indicator (VSI) ..................3-8, 4-5, 5-4, 6-5
very high frequency (VHF) ............................................9-2
very high frequency omni-directional
range (VOR)...................................................................7-8
accuracy ....................................................................7-16
function of ................................................................7-12
operational errors......................................................7-14
receiver accuracy check ...........................................7-16
vestibular ......................................................... 1-2, 1-4, 1-5
vestibular illusions .........................................................1-5
VFR Over-The-Top ...................................................10-27
VFR-On-Top ..............................................................10-26
Victor airways ................................................................8-4
visual approach slope indicator (VASI) .......................7-41
visual descent point (VDP) ..........................................8-21
visual flight rules (VFR) ........................2-1, 3-1, 4-16, 6-1
visual illusions ...............................................................1-7
visual meteorological conditions
(VMC) ................................................1-3, 7-31, 7-34, 9-14
volcanic ash................................................................10-24
VOR/DME RNAV .......................................................7-23
components...............................................................7-23
errors.........................................................................7-24
function of ................................................................7-23
VOR test facility (VOT) ..............................................7-16
VMC (See visual meteorological conditions)

W
water refraction ..............................................................1-9
waypoint.........................................................................7-8
weather and radar processor (WARP) .........................9-11
weather avoidance assistance .......................................9-11
weather conditions .....................................................10-22
weather information and communication features .......8-10

weight..................................................................... 2-2, 2-3
wet type vacuum pump ................................................3-17
wide area augmentation system (WAAS) ....................7-34
windshields ........................................................ 2-16, 2-17
wing, the.........................................................................2-2
wind correction angle (WCA) ........................................7-5
wind shear ..................................................................10-25
work .............................................................................2-10

Z
zone of confusion .........................................................7-12

I-9



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