Telephonics MCB-RT-1601 Color Weather and Search and Rescue Radar User Manual RDR 1600

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Pilot’s Guide
RDR-1600
TABLE OF CONTENTS
PARAGRAPH
Color Weather and
Search and Rescue Radar
Command Systems Division
PAGE
1.0
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
2.0
2.1
2.2
SYSTEM CONFIGURATION . . . . . . . . . . . . . . . . . . .2
ANTENNA AND RECEIVER-TRANSMITTER . . . . . . .3
RADAR DISPLAY INDICATOR . . . . . . . . . . . . . . . . . .4
3.0
3.1
3.6
OPERATIONAL CONTROLS . . . . . . . . . . . . . . . .
FUNCTION SELECTOR – CP-113K
CONTROL PANEL . . . . . . . . . . . . . . . . . . . . . .
ANTENNA CONTROLS . . . . . . . . . . . . . . . . . . . .
DISPLAY CONTROLS . . . . . . . . . . . . . . . . . . . . .
PRIMARY MODE SELECTORS . . . . . . . . . . . . . .
SECONDARY MODE SELECTOR AND GAIN
CONTROLS . . . . . . . . . . . . . . . . . . . . . . . . . . .
ALPHANUMERICS . . . . . . . . . . . . . . . . . . . . . . .
4.0
4.1
PREFLIGHT (PFT) . . . . . . . . . . . . . . . . . . . . . . . . . .10
PREFLIGHT WARNING . . . . . . . . . . . . . . . . . . . . . .10
5.0
5.1
5.2
5.3
5.4
5.5
5.6
THEORY OF OPERATION . . . . . . . . . . . . . . . . . . . .11
GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
RADAR PRINCIPLES . . . . . . . . . . . . . . . . . . . . . . .12
WEATHER RADAR PRINCIPLES . . . . . . . . . . . . . . .13
RADAR REFLECTIVITY . . . . . . . . . . . . . . . . . . . . . .14
WEATHER DISPLAY CALIBRATION . . . . . . . . . . . .15
WEATHER ATTENUATION COMPENSATION . . . . .16
6.0
6.1
6.2
6.3
6.4
6.5
6.5.1
6.5.2
6.5.3
6.5.4
6.5.5
6.5.6
6.5.7
6.5.8
6.5.9
6.5.10
6.6
6.6.1
WEATHER OPERATIONS . . . . . . . . . . . . . . . . . . .
WEATHER MODE – WX . . . . . . . . . . . . . . . . . . . .
WEATHER ALERT MODE – WXA . . . . . . . . . . . . .
TARGET ALERT . . . . . . . . . . . . . . . . . . . . . . . . . .
WEATHER MAPPING AND INTERPRETATION . . .
OBSERVING WEATHER . . . . . . . . . . . . . . . . . . . .
Thunderstorms and Turbulence . . . . . . . . . . . . . . .
Tornadoes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Hail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Icing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Snow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Lightning and Static Discharges . . . . . . . . . . . . . . .
Range Resolution . . . . . . . . . . . . . . . . . . . . . . . . . .
Azimuth Resolution . . . . . . . . . . . . . . . . . . . . . . . .
Indicator Resolution . . . . . . . . . . . . . . . . . . . . . . . .
Short Range Displays . . . . . . . . . . . . . . . . . . . . . . .
PATH PLANNING . . . . . . . . . . . . . . . . . . . . . . . . . .
Path Planning Considerations . . . . . . . . . . . . . . . . .
3.2
3.3
3.4
3.5
TM106101
TITLE
. . .5
.5
.6
.6
.6
. . .8
. . .9
.18
.18
.19
.19
.20
.20
.21
.22
.23
.24
.24
.24
.25
.25
.26
.27
.28
.28
August 2001
TM106101(8/01)
RDR-1600 Pilot’s Guide
TABLE OF CONTENTS (CONT.)
PARAGRAPH
7.0
7.1
7.1.1
7.1.2
7.2
7.3
TITLE
PAGE
FIGURE
2-1
2.1-1
2.1-2
7.4
7.4.1
7.4.2
7.4.3
SEARCH OPERATIONS . . . . . . . . . . . . . . . .
GROUND MAPPING . . . . . . . . . . . . . . . . . . .
Looking Angle . . . . . . . . . . . . . . . . . . . . . . . .
Other Aircraft . . . . . . . . . . . . . . . . . . . . . . . . .
SEARCH MODE . . . . . . . . . . . . . . . . . . . . . .
DIFFERENCE BETWEEN WEATHER AND
SEARCH MODES . . . . . . . . . . . . . . . . . . . .
SEARCH MODES COMPARED . . . . . . . . . . .
Search 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Search 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Search 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.0
8.1
8.2
8.3
TILT MANAGEMENT . . . . . . . . . . . . . . . . . . . . .
TILT CONTROL . . . . . . . . . . . . . . . . . . . . . . . . .
TILT PERFORMANCE CHECK . . . . . . . . . . . . .
EARLY DETECTION OF ENROUTE WEATHER
. . .37
. . .37
. . .38
. . .39
9.0
9.1
9.2
9.3
ANTENNA STABILIZATION . . . . . . . . . . . . . .
LIMITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ERRORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
COMPENSATION . . . . . . . . . . . . . . . . . . . . . .
10.0
10.1
10.2
BEACON MODES . . . . . . . . . . . . . . . . . . . . . . . . . .42
BEACON FORMAT SELECTION . . . . . . . . . . . . . . .43
DO-172 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43
11.0
AC 90-80 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44
12.0
MULTIPLE INDICATORS . . . . . . . . . . . . . . . . . . . . .45
13.0
13.1
13.2
13.3
SYSTEM SPECIFICATIONS . . . . . . . . . . . . . . . .
RT-1601 RT UNIT . . . . . . . . . . . . . . . . . . . . . . . .
DA-1203A ANTENNA DRIVE ASSEMBLY . . . . . .
CP-113K CONTROL PANEL . . . . . . . . . . . . . . . .
14.0
ADVISORY CIRCULARS . . . . . . . . . . . . . . . . . . . . .48
APPENDIX . . . . . . . . . . . . . . . . . . . . . . . . . .
WARNING . . . . . . . . . . . . . . . . . . . . . . . . . . .
CAUTION . . . . . . . . . . . . . . . . . . . . . . . . . . .
MAXIMUM PERMISSIBLE EXPOSURE
LEVEL (MPEL) . . . . . . . . . . . . . . . . . . . . . .
ii
LIST OF ILLUSTRATIONS
RDR-1600 Pilot’s Guide
.31
.31
.32
.33
.33
.34
.35
.35
.36
.36
.40
.40
.40
.41
.46
.46
.46
.47
. . . . .A-1
. . . . .A-3
. . . . .A-3
. . . . .A-4
TM106101(8/01)
TITLE
PAGE
2.1-3
2.2-1
Typical System Block Diagram . . . . . . . . . . . . . .
Receiver-Transmitter . . . . . . . . . . . . . . . . . . . . . .
DA-1203A Drive Assembly with AA4512A 12”
Flat Plate Antenna . . . . . . . . . . . . . . . . . . . . . .
CP-113K Control Panel . . . . . . . . . . . . . . . . . . . .
MFD Display . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1-1
3.2-1
3.4-1
3.5-1
3.6-1
CP-113K Control Panel . . . . . . . . . . . . . . . . . . . . . .
Tilt Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Primary Mode Selectors . . . . . . . . . . . . . . . . . . . . .
Secondary Mode Selector and Gain Controls . . . . .
MFD Screen Presentations . . . . . . . . . . . . . . . . . . .
4.1-1
Preflight Warnings . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
5.2-1
5.4-1
5.6-1
Radar Transmit-Receive Timing
Reflective Levels . . . . . . . . . . . .
STC Electronically Compensates
Distance Attenuation . . . . . . .
6.1-1
6.3-1
6.5-1
6.5.3-1
6.5.3-2
6.5.3-3
6.5.3-4
6.5.8-1
6.5.10-1
6.6.1-1
6.6.1-2
6.6.1-3
Typical Weather Display . . . . . . . . . . . . . . . . . . . . . .
Weather Alert with Target Alert Display . . . . . . . . . . .
Storm Components . . . . . . . . . . . . . . . . . . . . . . . . . .
Finger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Scalloped Edge . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
U-Shaped . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Azimuth Resolution . . . . . . . . . . . . . . . . . . . . . . . . . .
Short Range Display . . . . . . . . . . . . . . . . . . . . . . . . .
Penetration of Weather . . . . . . . . . . . . . . . . . . . . . . .
Minimizing Doglegging . . . . . . . . . . . . . . . . . . . . . . .
“Blind Alley” or “Box Canyon” Situations . . . . . . . . . .
.18
.19
.20
.23
.23
.23
.23
.25
.27
.28
.29
.29
7.1-1
7.1-2
7.1.1-1
7.1.1-2
7.3-1
7.4.1-1
7.4.2-1
7.4.3-1
Over Terrain . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Over Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A Smaller Incident Angle . . . . . . . . . . . . . . . . . . .
Concentration of the Beam . . . . . . . . . . . . . . . . .
Wx and SRCH Buttons . . . . . . . . . . . . . . . . . . . .
Search 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Search 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Search 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.31
.31
.32
.32
.34
.35
.36
.36
TM106101(8/01)
.... 2
.... 3
.... 3
.... 3
.... 4
. . . . . . . . . . . . . . . . .12
. . . . . . . . . . . . . . . . .14
for
. . . . . . . . . . . . . . . . .16
RDR-1600 Pilot’s Guide
iii
Introduction
LIST OF ILLUSTRATIONS (CONT.)
FIGURE
TITLE
1.0 INTRODUCTION
PAGE
8.1-1
8.2-1
8.3-1
Adjusting the Antenna Tilt . . . . . . . . . . . . . . . . . . . . . .37
Altitude vs. Range . . . . . . . . . . . . . . . . . . . . . . . . . . . .38
Weather Target . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39
9.1-1
Aircraft Pitching/Rolling ±30° . . . . . . . . . . . . . . . . . . . .40
10.1-1
10.2-1
Standard Beacon . . . . . . . . . . . . . . . . . . . . . . . . . . . .43
DO-172 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43
14-1
Cross-Section of a Thunderstorm . . . . . . . . . . . . . . . .50
LIST OF TABLES
TABLE
TITLE
PAGE
5.5-1
Radar Display and Thunderstorm Levels
versus Rainfall Rates . . . . . . . . . . . . . . . . . . . . . . . .15
6.5.9-1
Minimum Distinguishable Target Separation . . . . . . . .26
8.3-1
Antenna Tilt Control Settings . . . . . . . . . . . . . . . . . . . .39
In the early days of aviation, pilots were more concerned with just staying
airborne than worrying about weather. Airplanes were for fun. Pilots flew
only short hops, on clear days, and could often see their destination. There
was little need for navigation equipment. If your compass was working and
your gas held out, you could probably make it home safely. Later, as flying
came of age, thunderstorms and their associated turbulence were more of
a problem. When the weather was good, aircraft utilization was high. But
when storms were prevalent, you might take the long way home.
Today, weather radar is as much at home in the cockpit as the compass.
Corporate aircraft operators, and private pilots, as well as the airlines have
adopted weather radar with full confidence in its usefulness and reliability.
Most commercial airborne weather radars available today also provide the
pilot with one or more ancillary modes of operation and system options that
make the radar more functional and increase its versatility.
Telephonics would like to welcome you to the growing family of Telephonics
Weather Radar System owners and operators.
The RDR-1600 Color Weather Radar System is the newest advancement
of this series of radars. The RDR-1600 series radars are the most popular,
advanced capability, multi-mode radars available from any manufacturer.
The RDR-1600 provides five primary modes of operation: three air-tosurface search and detection modes, and two conventional weather avoidance modes. This lightweight digital X-band radar system provides a peak
power of 10 kW, and is primarily designed for fixed or rotary-wing aircraft
engaged in patrol, search and rescue missions, and for transporting
personnel and equipment to remote sites (e.g., off-shore oil rigs, etc.).
The system interfaces with multi-function electronic displays. The MFD is
referred to as an indicator in this manual. The RDR-1600 will also interface
with an Attitude Heading Reference System (AHRS). AHRS Pitch and Roll
data will be converted from digital ARINC 429 to analog pitch and roll data
that is used by the DA-1203A antenna drive unit for antenna stabilization.
The RDR-1600 also has the capability to receive and decode both standard
2-pulse beacon transponders and the DO-172 6-pulse transponders. This
system also provides two short ranges of 0.5 nm and 1.0 nm for search and
rescue.
This manual is designed to help you understand the RDR-1600 and its
operational procedures. Please read it carefully before operating the unit.
If you have any questions, please contact Telephonics (see back cover).
iv
RDR-1600 Pilot’s Guide
TM106101(8/01)
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RDR-1600 Pilot’s Guide
System Configuration (Cont.)
System Configuration
2.1 ANTENNA AND RECEIVER-TRANSMITTER
2.0 SYSTEM CONFIGURATION
The RT-1601 Receiver-Transmitter generates 10 KW pulses of X-band
energy. Reflected signals of weather, search and beacon modes received
by the antenna are amplified and sent to the radar display indicator.
The flat-panel antenna, which is available in diameters of 10, 12 or 18
inches scans 60 or 120 degrees. Swept by a motor-driven gear train, the
vertical component is positioned by the tilt control on the Radar Control
Panel (RCP or CP-113k). A stabilization system presents an upright radar
display while the aircraft is turning, climbing or descending.
Figure 2.1-1. ReceiverTransmitter
Figure 2-1. Typical System Block Diagram
Figure 2.1-2. DA-1203A Drive
Assembly with AA4512A 12” Flat
Plate Antenna
Figure 2.1-3. CP-113K Control Panel
RDR-1600 Pilot’s Guide
TM106101(8/01)
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RDR-1600 Pilot’s Guide
Operational Controls
System Configuration (Cont.)
2.2 RADAR DISPLAY INDICATOR
3.0 OPERATIONAL CONTROLS
3.1 FUNCTION SELECTOR – CP-113K CONTROL PANEL
OFF
Removes system power.
STBY
System is operationally ready; no display.
TEST
Displays a test pattern without transmitting, identified by
TEST and RT FAULT.
ON
System transmits in normal operation.
60°
Directs the antenna to sector scan 60° about the boresight
of the aircraft. This position will work in weather, search
(map), and beacon modes.
Figure 2.2-1. MFD Display
The MFD displays green, yellow and red moving maps of weather and
surface features.
Rainfall per hour
Ground Return
Figure 3.1-1. CP-113K Control Panel
Color
0-1 mm
No significant return
Dark
1-4 mm
Light
Green
1-12 mm
Medium
Yellow
12 mm or more
Heavy
Red
The choice of two weather modes, three search modes and antenna scan
of 60 or 120 degrees is selected by the pilot. A target alert feature is active
in the weather alert mode, and a movable track cursor helps the pilot plan
his flight around severe weather. A beacon mode enables the display of
beacon locations and a code feature identifies the beacons. Beacon
Formatting allows for the display of either standard or DO-172 type
beacons. This information can be displayed in any of eight separate ranges.
RDR-1600 Pilot’s Guide
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RDR-1600 Pilot’s Guide
Operational Controls (Cont.)
Operational Controls (Cont.)
BCN
3.2 ANTENNA CONTROLS
PULL STAB OFF
TILT
This switch is connected to the Tilt Control Knob. When
the Tilt Control Knob is pressed in, the stabilization
function is active. When this knob is pulled out, the
stabilization function is turned off.
Pressing this button will select the two Beacon type
formats to be selected. Sequentially pressing the Beacon
button will select the following beacon modes:
Beacon Only Mode
Beacon A, Beacon B, Beacon A, Beacon B, . . .
Dual Mode (Beacon/Weather or Beacon/Search)
Beacon A, Beacon B, Beacon Off, Beacon Am . . .
Adjusts antenna tilt angle.
Beacon Only Mode: If the starting mode of operation is
weather (or search), then pressing the beacon button will
place the system in Beacon/Weather (Search) mode. To
activate beacon only mode, press the weather (or search)
button to turn off weather (search) mode. To reactivate dual
mode, press either the weather or search buttons.
Figure 3.2-1. Tilt Control
Beacon A – Standard 2-pulse beacon
Beacon B – DO-172 compatible beacon
3.3 DISPLAY CONTROLS
The MFD has a brightness control to adjust the brightness of the screen.
3.4 PRIMARY MODE SELECTORS
(PUSH ON/PUSH OFF)
Wx
Selects weather mode, the primary mode of operation
(automatically selected at turn-on). Weather displayed and
Wx appear on screen. When pressed again, the weather
mode is removed. If no other mode button is active, the Wx
mode remains.
WxA
Selects weather alert mode causing red returns to flash if
the MFD is capable of performing this function. WxA
appears and Target Alert is enabled.
SRCH
Pressing this push button selects the three Search modes
in sequential cyclic manner (i.e., Search 1, Search 2,
Search 3, Search 1, Search 2, Search 3, etc.). Search
modes are as follows:
Figure 3.4-1. Primary Mode Selectors
Search 1 – Sea clutter rejection. Active on the ten-mile
range or less.
Search 2 – Short range precision mapping. Active on the
ten-mile range or less.
Search 3 – Normal surface mapping.
Beacon mode is compatible with both weather mode and
Search mode.
RDR-1600 Pilot’s Guide
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Operational Controls (Cont.)
Operational Controls (Cont.)
3.5 SECONDARY MODE SELECTOR AND GAIN CONTROLS
BCN GAIN
The Beacon Gain is a rotary potentiometer that controls the
gain of the Beacon receiver.
SRCH GAIN
The Search Gain is a rotary potentiometer that controls
the gain of the Search receiver.
CODE
Pressing this switch selects Beacon Codes in a sequential
cyclic fashion (i.e., Code 0, Code 1, Code 2, . . . Code 15
or Code 0, Code 1, Code 2, . . . Code 9) depending on
Beacon Mode selected. The selected code is annunciated
on the MFD.
3.6 ALPHANUMERICS
When DO-172 Beacon (Beacon Mode B) is selected via
the BCN button, the total of sixteen codes (0-15) can be
selected by the Code switch. Selecting a Standard twopulse Beacon (Beacon Mode A) via the BCN button, the
total of ten codes (0-9) can be selected by the Code
button. The Code button is not active unless the Beacon
mode has been selected.
Figure 3.6-1. MFD Screen Presentations
Note
+MFDs display of radar data will vary by manufacturer. Refer to the
MFD Pilot’s Guide for specific radar display.
Figure 3.5-1. Secondary Mode Selector and Gain Controls
RDR-1600 Pilot’s Guide
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RDR-1600 Pilot’s Guide
Theory of Operation
Preflight
4.0 PREFLIGHT (PFT)
5.0 THEORY OF OPERATION
4.1 PREFLIGHT WARNING
5.1 GENERAL
Test the system to verify proper operation before each flight. Rotate the
function selector from OFF to STBY. Allow system to warm up for about 100
seconds, then move the function selector to TEST. No display appears in
the STBY position and the radar does not transmit in either STBY or TEST.
The test pattern scans 120° and automatically selects the 80 mile range.
Look for distinct color bands and range marks in the order shown. Adjust
display brightness for a comfortable level. Checklist and flight log options
may be used at this time if installed.
The primary use of this radar is to aid the pilot in avoiding thunderstorms
and associated turbulence. Since each operator normally develops unique
operational procedures for use of Weather Radar, the following information
is presented for use at the operator’s discretion.
Operational techniques with the RDR-1600 Series Weather Radars are not
different than with earlier generation radars. The proficient operator
manages his antenna tilt control to achieve the best possible knowledge of
storm height, size, and relative direction of movement.
WARNING
Do not turn the radar on within 25 feet of ground personnel or
containers holding flammable or explosive material. The radar
should never be operated during refueling.
When ready to use the radar, rotate the function selector to ON position.
Figure 4.1-1. Preflight Warnings
Note
+The design of the system is such that full operation is possible
approximately two minutes after turn-on. Therefore, the pilot may
choose to leave the function switch in OFF, rather than STBY, if no
significant weather is in the immediate area of the aircraft. The life
of the magnetron transmitting tube will be extended by leaving the
system “OFF” when possible. This, in turn, will reduce the cost of
maintenance.
10
RDR-1600 Pilot’s Guide
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11
Theory of Operation (Cont.)
Theory of Operation (Cont.)
5.2 RADAR PRINCIPLES
5.3 WEATHER RADAR PRINCIPLES
Radar is fundamentally a distance measuring system using the principle of
radio echoing. The term RADAR is an acronym for Radio Detecting And
Ranging. It is a method for locating targets by using radio waves. The transmitter generates microwave energy in the form of pulses. These
pulses are then transferred to the antenna where they are focused into a
beam by the antenna. The radar beam is much like the beam of a flashlight.
The energy is focused and radiated by the antenna in such a way that it is
most intense in the center of the beam with decreasing intensity near the
edge. The same antenna is used for both transmitting and receiving. When
a pulse intercepts a target, the energy is reflected as an echo, or return
signal, back to the antenna. From the antenna, the returned signal is transferred to the receiver and processing circuits located in the receiver
transmitter unit. The echoes or returned signals are displayed on an
indicator.
Airborne weather avoidance radar, as its name implies, is for avoiding
severe weather – not for penetrating it. Whether to fly into an area of radar
echoes depends on echo intensity, spacing between the echoes, and the
capabilities of both pilot and aircraft. Remember that weather radar detects
only precipitation drops; it does not detect minute cloud droplets. Therefore,
the radar scope provides no assurance of avoiding instrument weather in
clouds and fog. Your indicator may be clear between intense echoes; this
clear area does not necessarily mean you can fly between the storms and
maintain visual sighting of them.
Radio waves travel at the speed of 300 million meters per second and thus
yield nearly instantaneous information when echoing back. Radar ranging
is a two-way process that requires 12.36 micro-seconds for the radio wave
to travel out and back for each nautical mile of target range. As shown in
the distance illustration in Figure 5.2-1, it takes 123.6 micro-seconds for a
transmitted pulse of radar energy to travel out and back from an area of
precipitation 10 nautical miles away.
The geometry of the weather radar radiated beam precludes its use for
reliable proximity warning or anti-collision protection. The beam is characterized as a cone-shaped pencil beam. It is much like that of a flashlight or
spotlight beam. It would be an event of chance, not of certainty, that such a
beam would come upon another aircraft in flight.
WARNING
Weather radar is not practical as a pilot operable collision
avoidance system. Weather analysis and avoidance are the
primary functions of the radar system.
Figure 5.2-1. Radar Transmit-Receive Timing
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Theory of Operation (Cont.)
Theory of Operation (Cont.)
5.4 RADAR REFLECTIVITY
5.5 WEATHER DISPLAY CALIBRATION
What target will reflect the radar’s pulses and thus be displayed on the
indicator?
The MFD Radar display should be calibrated to show four levels of target
intensity: Black (level 0), Green (level one), Yellow (level two) and Red
(level three). The meaning of these levels is shown in the following chart as
is their approximate relationship to the Video Integrated Processor (VIP)
intensity levels used by the National Weather Service (NWS). These levels
are valid only when (1) the Wx or WxA modes are selected; (2) the displayed returns are within the STC range of the radar (approximately 40
miles); (3) the returns are beam filling; and (4) there are no intervening
radar returns.
Only precipitation (or objects more dense than water such as earth or solid
structures) will be detected by an X-band weather radar. Therefore,
weather radar does not detect clouds, thunderstorms or turbulence directly. Instead, it detects precipitation which may be associated with dangerous
thunderstorms and turbulence. The best radar reflectors are raindrops and
wet hail. The larger the raindrop, the better it reflects. Because large drops
in a small concentrated area are characteristic of a severe thunderstorm,
the radar displays the storm as a strong echo. Drop size is the most important factor in high radar reflectivity. Generally, ice, dry snow and dry hail
have low reflective levels and often will not be displayed by the radar.
A cloud that contains only small raindrops, such a fog or drizzle, will not produce a measurable radar echo. But if the conditions should change and the
cloud begins to produce rain, it will be displayed on radar.
Table 5.5-1. Radar Display and Thunderstorm Levels
versus Rainfall Rates
Rainfall Rate
Display
Level
mm/Hr.
In./Hr
Video Integrated Processor (VIP)
Categorizations
Story
Category
VIP
Level
Rainfall Rate
Remarks
mm/Hr.
In./Hr.
Greater
than 12
Greater
than 0.5
Severe turbulence,
possible lightning
Moderate
2.5-12
0.1-0.5
Light to moderate
turbulence is
possible with
lightning
Weak
0.25-2.5
.01-0.1
Light to moderate
turbulence is
possible with
lightning
(Red)
12
0.5
Strong
(Yellow)
4-12
0.17-0.5
(Green
1-4
0.04-0.17
(Black)
Less
than 1
Less than
0.04
Figure 5.4-1. Reflective Levels
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Theory of Operation (Cont.)
Theory of Operation (Cont.)
5.6 WEATHER ATTENUATION COMPENSATION
Attenuation is an extremely important phenomenon for the weather radar
operator to understand. When a radar pulse is transmitted into the
atmosphere, it is progressively absorbed and scattered so that it loses its
ability to return to the antenna. This attenuation or weakening of the radar
pulse is caused by two primary sources, distance and precipitation. The
RDR-1600 radars have several advanced features which significantly
reduce the affects of attenuation but no airborne weather radar can eliminate them completely. It is therefore up to the operator to understand the
radar’s limitations in dealing with attenuation.
Attenuation because of distance is due to the fact that the radar energy
leaving the antenna is inversely proportional to the square of the distance.
For example, the reflected radar energy from a target 60 miles away will be
one fourth (if the target is beam filling) of the reflected energy from an
equivalent target 30 miles away. The displayed effect to the operator is that
as the storm is approached it will appear to be gaining in intensity. To compensate for distance attenuation, both Sensitivity Timing Control (STC) and
Extended STC circuitry are employed. The RDR-1600 has an STC range of
approximately 40 nautical miles and within this range the radar will electronically compensate for the effects of distance attenuation with the net
effect that targets do not appear to grow larger as the distance decreases.
Outside the STC range the Extended STC circuitry increases the displayed
intensity to more accurately represent storm intensity. The Extended STC
will not, however, totally compensate for distance attenuation and,
therefore, targets in this range can be expected to grow as the distance
decreases until reaching the STC range.
Attenuation due to precipitation is far more intense and is less predictable
than attenuation due to distance. As the radar pulses pass through moisture, some radar energy is reflected, however, much of that energy is
absorbed. If the rain is very heavy or extends for many miles, the beam may
not reach completely through the area of precipitation. The weather radar
has no way of knowing if the beam has been fully attenuated or has
reached the far side of the precipitation area. If the beam has been fully
attenuated, the radar will display a “radar shadow” which appears as an end
to the precipitation when, in fact, the heavy rain may extend for many more
miles. In the worst case, precipitation attenuation may cause the area of
heaviest precipitation to be displayed as the thinnest area of heavy precipitation. Or it may cause one cell containing heavy precipitation to totally
block or shadow a second heavy cell located behind the first cell and prevent it from being displayed on the radar.
CAUTION
Never fly into radar shadows and never believe that the full extent of
heavy rain is being seen on radar unless another cell or a ground
target can be seen beyond the heavy cell.
Proper use of the antenna tilt control can help detect radar shadows.
Attenuation can also be a problem when flying in a large area of general
rain. If the rain is moderate, the radar beam may only reach 20 or 30 miles
before it is fully attenuated. The pilot may fly along for many miles seeing
the same 20-30 miles of precipitation ahead on the radar when, actually, the
rain may extend for a great distance. In order to aid in reducing the effects
of precipitation attenuation, the RDR-1600 contains sophisticated weather
attenuation compensation circuitry. The Attenuation Compensation feature
is totally automatic and requires no pilot action to activate it. However, the
Compensation logic cannot operate until echoes are within the Sensitivity
Time Control range of approximately 40 miles. Whenever a level two
level (yellow) or level three (red) echo is displayed within the STC range,
the Compensation circuits cause the receiver gain to increase while the
antenna scans the sector containing heavy rain. The Compensation circuitry allows the radar beam to effectively look deeper into and through heavy
rain to search for possible storm cells beyond. While Attenuation
Compensation does not eliminate precipitation attenuation, it does allow the
radar to see through more rain at short ranges where every bit of weather
information possible is needed. If there is suspicion that the radar is attenuating due to precipitation, exercise extreme caution and ask the ATC
Controller what they are showing. Often the ground-based ATC radar will
have a better overall picture of a large rain area and the pilot can compare
the controller’s information with his own radar picture to avoid the strongest
cells in a general area of rain.
Figure 5.6-1. STC Electronically Compensates for
Distance Attenuation
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Weather Operations (Cont.)
Weather Operations
6.2 WEATHER ALERT MODE – WXA
6.0 WEATHER OPERATIONS
6.1 WEATHER MODE – WX
The RDR-1600 will provide you with target information to a greater degree
than ever possible on previous generation weather radars. With a 240 nm
maximum display range, you will have plenty of time to plan weather avoid-
In Weather Alert mode, WxA, you will see a standard weather presentation
displayed in Green, Yellow and Red, except that the red returns flash
between black and red to draw your attention to the heavier activity.
6.3 TARGET ALERT
In Weather Alert Mode, WxA, the words TGT ALRT flash if red returns exist
within 25 miles beyond the displayed range.
ance maneuvers.
Figure 6.3-1. Weather Alert with Target Alert Display
Figure 6.1-1. Typical Weather Display
By pressing the “WX” button on the face of the indicator, you will see a standard weather presentation. Different levels of precipitation are displayed in
Green, Yellow and Red. Use the range up/down buttons to select the
desired full scale range distance to be displayed. See Paragraph 8.0 for
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Weather Operations (Cont.)
Weather Operations (Cont.)
6.4 WEATHER MAPPING AND INTERPRETATION
6.5.1 Thunderstorms and Turbulence
This section contains general information on use of the radar for weather
interpretation. Review of this information will assist the pilot.
The RDR-1600 weather radar can give you a clue to the presence of
turbulence. Areas of the display where the colors change rapidly over a
short distance represent steep rainfall gradients, which are usually associated with severe turbulence.
6.5 OBSERVING WEATHER
A weather radar is only as good as the operator’s interpretation of the
echoes that are displayed on the radar indicator. The pilot must combine his
knowledge of how radar works and its limitations with such things as the
prevailing weather pattern, the geographic location, and his personal experience in order to make a sound interpretation of the displayed targets.
As a starting point, the operator should read FAA Advisory Circular number
00-24B, Subject: Thunderstorms. It is also highly recommended that the
operator take advantage of one of the commercially available weather radar
seminars.
Turbulence may be divided into two basic types:
(1) clear-air turbulence. It is not possible to detect clear-air turbulence
with this type of radar.
(2) turbulence associated with thunderstorms and precipitation. This
type is most common. Weather radar is most helpful to the pilot
with this type.
Weather guidance is now available from ground radar stations in some
areas. However, this system suffers in comparison with the airborne
weather radar when the weather is clearly visible on the pilot’s indicator,
instantly available for the pilot to act upon, considering his immediate
circumstances and future flight planning.
The strong up and down drafts in a thunderstorm create very large raindrops which are usually displayed on a radar as level three.
The probability of turbulence in these strong vertical gusts is great. The
National Severe Storms Laboratory (NSSL) has found that the intensity
level of the precipitation reflection correlates with the degree of turbulence
found in a thunderstorm. The most severe turbulence in the storm,
however, may not be at the same place that gives the greatest radar reflectivity.
The rate of change in rainfall rate laterally within a storm is called the rain
gradient. This change will appear on the indicator as a change from green
to yellow to red. If the rainfall rate increases from level one to three in a
short distance, the rain gradient is steep and severe turbulence is often
present. Avoid any storm with a steep rain gradient by an extra margin and
especially avoid flying near the portion of the storm with the steepest
gradient.
Figure 6.5-1. Storm Components
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Weather Operations (Cont.)
Weather Operations (Cont.)
6.5.2 Tornadoes
6.5.3 Hail
It is possible that conclusive methods of detecting tornadoes with airborne
radar may eventually be developed. However, evidence collected to date
indicates tornadoes may be detected if the following echoes are observed:
Hail usually has a film of water on its surface; consequently, a hailstone is
often reflected as a very large water particle. Because of the film and
because hail stones usually are larger than raindrops, thunderstorms with
large amounts of wet hail return stronger signals than those with rain.
Although wet hail is an excellent reflector of radar energy, some hail shafts
are extremely small (100 yards or less). These narrow shafts make poor
radar targets.
1. A hook-shaped pendant which may be 5 or more miles long and in the
general shape of the numeral 6 strongly suggests the presence of a
major tornado, especially if the pendant is a bright one and if it projects
from the southwest quadrant (northeast quadrant in the southern hemisphere) of a major thunderstorm moving eastward. The pendant may be
lost in ground clutter when viewed on the indicator and in some cases
might not be much more than a blunt projection or scalloped edge of the
parent thunderstorm echo.
2. A crescent-shaped indentation on the side of a major thunderstorm echo
3 to 7 miles long is another possible identifier of an active or potential
tornado in the vicinity.
3. The best procedure is to make wider than usual detours around sharpedged thunderstorms and especially those which show projections or
crescent-shaped indentations.
Hail shafts are usually identified with four different characteristics patterns:
(1) fingers and protrusions, (2) hooks, (3) scalloped edges on the cloud outline and (4) U-shaped cloud edges 3 to 7 miles across.
These echoes appear quite suddenly and along any edge of the storm outline. They also change in intensity and shape in a matter of seconds, and
for this reason careful monitoring of the display is essential. It must be
noted that weak or fuzzy projections are not normally associated with hail;
however, such echoes should be watched closely for signs of rapid intensification.
The 40-mile operating range seems best and, with occasional up-tilt to
check for fresh hail from above, generally good results can be obtained.
Note
+It takes an experienced eye to identify “hooks” and “fingers” and
other radar echo characteristics which can indicate hail or tornadoes. However, the pilot can be sure that any echo with very
ragged edges or rapid changes in shape or intensity will contain
severe turbulence.
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Figure 6.5.3-1. Finger
Figure 6.5.3-2. Hook
Figure 6.5.3.3. Scalloped
Edge
Figure 6.5.3-4. U-Shaped
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Weather Operations (Cont.)
Weather Operations (Cont.)
6.5.4 Icing
6.5.7 Range Resolution
There is reason to believe that the radar will be of assistance in locating
areas of heavy icing conditions. However, weather radar has not yet proved
its ability to distinguish between super-cooled water droplets and ice crystals, since both are usually quite small. Needless to say, the operational
problem in each case would be different. In the first case icing would definitely exist but in the second case the pure crystals would offer no danger.
The ability of the radar system to resolve closely spaced targets in range
depends on transmitter pulse width. In long range modes, the RDR-1600
can distinguish objects spaced as close as 0.19 nm (385 yds.) apart. In
Search 1 (SR1) and Search 2 (SR2) modes on ranges of 20 miles and
below, the resolution is improved to 0.04 nm (80 yds.).
1. It should be remembered, however, that super-cooled water and ice
crystals can co-exist. In each case the radar echo would be small or
even nil due to the minute size of the free water particles. At this time, it
appears fairly certain that radar is not going to give warning of cloud icing
unless it happens to be involved with active precipitation at the time.
When precipitation is occurring, however, the areas of maximum ice
exposure should appear as sandy or grainy echoes.
2. An icing condition that the radar might possibly detect is the intermittent
moderate or heavy icing condition associated with unstable air lifted by
frontal action or orographic effects. In this situation, the cumulus cells
are hidden by surrounding cloud layers but could be spotted by radar.
This would be of assistance in avoiding the moderate-to-heavy icing
which occasionally occurs in cumulus clouds.
6.5.8 Azimuth Resolution
The ability of the radar to resolve adjacent targets in azimuth depends on
antenna beam width and range to the target. The diameter of the radiated
beam increases as it gets further from the antenna. Larger antennas have
narrower beam widths and, therefore, produce better ground mapping and
weather pictures.
Targets separated by a distance less than the beam diameter will merge
and appear on the indicator as one.
WARNING
Thunderstorm icing can be extremely hazardous.
6.5.5 Snow
Dry snowfall has not been detected with any success on weather radar.
However, a characteristic sandy or grainy echo identifies the presence of
steady moderate-to-heavy wet snow. Such echoes are not readily obvious
and require a little study of the display before they can be seen.
6.5.6 Lightning and Static Discharges
Lightning and static discharges could scatter the display momentarily.
However, the general presentation is unaffected and should return to
normal within 1 scan.
Figure 6.5.8-1. Azimuth Resolution
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Weather Operations (Cont.)
Weather Operations (Cont.)
6.5.9 Indicator Resolution
6.5.10 Short Range Displays
The resolution of the indicator depends on the number of display bits on the
screen. A typical screen matrix is composed of 256 bits horizontally by 256
bits vertically. The display resolution is equal to 1/256 times the display
range as shown in Table 6.5.9-1. The lower the range, the better the
resolution.
The RDR-1600 allows the selection of full-scale ranges of 1.0 nm and
0.5 nm in Search Modes.
Table 6.5.9-1. Minimum Distinguishable Target Separation
Resolution
Range (nm)
Miles
Feet
2.0
0.008
48
14.8
5.0
0.02
122
37.0
10.0
0.04
243
74.1
20.0
0.08
486
148.2
40.0
0.16
972
296.3
80.0
0.31
1884
574.1
These unique short range selections are especially useful during
approaches and surveillance operations, because it keeps the target from
getting lost in the clutter at the vertex of the display.
When operating in either short range mode, certain features become
unavailable. They are: Moving Map with Waypoints, BeaconTrac and
Beacon Identification. All other modes are still accessible.
Meters
Figure 6.5.10-1. Short Range Display
In the weather mode, the RDR-1600 is unable to ascertain radar returns
from close in. On the short range displays, the RDR-1600 paints a red arc
in this range to depict the dead band area, as shown in Figure 6.5.10-1.
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Weather Operations (Cont.)
Weather Operations (Cont.)
6.6 PATH PLANNING
Remember to plan a deviation path early. Simply skirting the red portion of
a cell is not enough. Plan an avoidance path for all weather echoes which
appear beyond 100 miles since this indicates they are quite intense.
The most intense echoes are severe thunderstorms. Remember that hail
may fall several miles from the cloud, and hazardous turbulence may
extend as much as 20 miles from the storm. Avoid the most intense echoes
by at least 20 miles, that is, echoes should be separated by at least 40
miles before you fly between them. As echoes diminish in intensity, you can
reduce the distance by which you avoid them.
6.6.1 Path Planning Considerations
Figure 6.6.1-2. Minimizing Doglegging
Cells beyond 75 miles are areas of substantial rainfall; do not wait for
red to appear. Plan and execute evasive action quickly to minimize
“doglegging.”
• Avoid cells containing red areas by at least 20 miles.
• Do not deviate downwind unless absolutely necessary. Your chances of
encountering severe turbulence and damaging hail are greatly reduced
by selecting the upwind side of the storm.
• If looking for a corridor, remember corridors between two cells containing
red areas should be at least 40 miles wide from the outer fringes of the
radar echo.
Note
+Do not approach a storm cell containing red any closer than 20 nm.
Echoes should be separated by at least 40 nm before attempting
to fly between them.
Figure 6.6.1-3. “Blind Alley” or “Box Canyon” Situations
Figure 6.6.1-1. Penetration of Weather
When a complete detour is impractical, penetration of weather patterns may
be required. Avoid adjacent cells by at least 20 miles.
A “Blind Alley” or “Box Canyon” situation can be very dangerous when viewing the short ranges. Periodically switch to longer range displays to
observe distant conditions. As shown above, the short-range returns show
an obvious corridor between two areas of heavy rainfall, but the long-range
setting shows a larger area of heavy rainfall.
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Search Operations
Weather Operations (Cont.)
Above all, remember: Never regard any thunderstorm as LIGHT, even when
radar observers report the echoes are of light intensity. Avoiding thunderstorms is the best policy.
DON’T attempt to preflight plan a course between closely
space echoes.
DON’T land or take off in the face of a thunderstorm in the
projected flight path. A sudden wind shift or low level turbulence could cause loss of control.
7.0 SEARCH OPERATIONS
7.1 GROUND MAPPING
A secondary objective of the radar system is gathering and presentation of
terrain data. This data is represented in the form of a topographical map
that can be employed as a supplement to standard navigation procedures.
Target quality affects the indicator display in various situations. Use of the
SRCH gain control and TILT knob will often improve picture contrast so
specific ground targets are more readily recognizable.
DON’T attempt to fly under a thunderstorm even if you can see
through to the other side. Turbulence under the storm could be
severe.
DON’T try to navigate between thunderstorms that cover 6/10
or more of the display. Fly around the storm system by a wide
margin.
DON’T fly without airborne radar into a cloud mass containing
scattered embedded thunderstorms. Scattered thunderstorms
not embedded usually can be circumnavigated.
Figure 7.1-1. Over Terrain
Illumination of terrain results in a “diffused” reflection of the beam. A portion
of this reflected energy is scattered back toward the antenna resulting in the
prominent display of land features as well as lakes, large rivers, shore lines
and ships.
DO avoid by at least 20 miles any thunderstorm identified as
severe or giving an intense radar echo. This is especially true
under the anvil of a large cumulonimbus.
DO clear the top of a known or suspected severe thunderstorm
by at least 10,000 feet altitude. This may exceed the altitude
capability of the aircraft.
DO remember that vivid and frequent lightning indicates a
severe thunderstorm.
DO regard as severe any thunderstorm with tops 35,000 feet
or higher whether the top is visually sighted or determined by
radar.
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Figure 7.1-2. Over Water
Calm water or water with swells does not provide good returns. The energy is reflected in a forward scatter angle with inadequate portions being
returned. The resulting display is “no target”. Choppy water provides better
returns from the downwind side of the waves. The resulting display is a
target whose intensity will vary with the degree to choppiness.
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Search Operations (Cont.)
Search Operations (Cont.)
7.1.1 Looking Angle
7.1.2 Other Aircraft
The incident angle at which the terrain is illuminated has a direct bearing on
the detectable range and the area of illumination. A large incident angle
gives the radar system a smaller detectable range of operation (due to a
minimized reflection of direct radar energy). However, the illuminated area
“A” is larger.
Tests show that only with extremely careful observation at relatively short
ranges can other aircraft be detected by this type of radar equipment. The
character of this echo is such that this type of radar system cannot be
considered adequate for this purpose.
7.2 SEARCH MODE
An advantage of this radar system is the enhancement of short range
mapping capability. This facilitates locating specific targets on land or sea
and provides a navigational map as a supplement to standard navigation
procedures.
Figure 7.1.1-1. A Smaller Incident Angle
A smaller incident angle gives the radar a larger detectable range of operation because of an increase of direct radar energy reflected from the
target to the antenna. The area of illumination (“A”) is smaller.
Figure 7.1.1-2. Concentration of the Beam
Concentration of the beam energy on the small area of terrain increases the
magnitude of the echo intercepted by the antenna. The resulting detectable
range is therefore increased for mountainous terrain; the maximum
distance at which this terrain can be monitored is greater because of the
more direct reflection (or radar echo) produced. Illuminating the backslope
of hills stretches the area of coverage beyond the flat terrain coverage.
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Search Operations (Cont.)
Search Operations (Cont.)
7.3 DIFFERENCE BETWEEN WEATHER AND SEARCH MODES
7.4 SEARCH MODES COMPARED
In weather modes, the receiver gain is preset and cannot be changed by
the pilot. In the search modes, the pilot controls receiver gain with the
SRCH knob on the indicator front panel for best display resolution.
Additionally, in search modes on ranges below 10 miles, the transmitter
pulse is changed to enhance target resolution.
In the photographs below, the aircraft is flying southwest along the Florida
Keys. Florida’s marshy coast is on the right and the islands are in the center of the screen. Strong boat target returns are on the left. Tilt and search
gain are adjusted for optimum display. Note that in SRCH 3, the land
masses blend together while in SRCH 2 and SRCH 1, a small boat (arrow)
target can be extracted from heavy seas.
When operating in weather or search modes, both weather and ground
returns can appear on the screen at the same time.
7.4.1 Search 3
Conventional ground map mode. Beyond 10 mile range, SR1 and SR2 are
the same as SR3.
The radar’s long range mapping compatibility may be used to recognize
known, well defined targets such as mountains, lakes, rivers, or cities. Use
of gain and tilt controls will often improve picture quality.
Figure 7.3-1. Wx and SRCH Buttons
Figure 7.4.1-1. Search 3
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Tilt Management
Search Operations (Cont.)
7.4.2 Search 2
8.0 TILT MANAGEMENT
Short range precision mapping on ranges of 10 miles or less.
8.1 TILT CONTROL
One of the most important factors in improving your expertise in using your
radar is antenna tilt management. Control of the vertical movement of the
antenna, and hence the radar beam, is through the antenna tilt knob.
Proper antenna tilt management provides information of the storm’s
approximate size and relative direction of movement.
The correct procedure for weather avoidance is to aim the antenna directly
at the storm, not above it, or at the ground. The tilt control permits positioning the antenna in small increments up or down, to keep the antenna
intersecting the storm area. Also, changes in pitch attitude can be compensated for by adjusting the antenna tilt.
Figure 7.4.2-1. Search 2
7.4.3 Search 1
Sea clutter rejection effect on ranges of 10 miles or less.
Figure 8.1-1. Adjusting the Antenna Tilt
Figure 7.4.3-1. Search 1
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Tilt Management (Cont.)
Tilt Management (Cont.)
8.2 TILT PERFORMANCE CHECK
8.3 EARLY DETECTION OF ENROUTE WEATHER
A good performance check of your radar system in flight is to lower the tilt
slowly and observe the maximum range of solid ground returns. As a rule
of thumb, this range in miles should approximate the square root of your
operational altitude.
To set the Antenna Tilt to optimize the radar’s ability to quickly identify
significant weather, follow these steps:
1. Select the Wx (Weather) or WxA (Weather Alert) mode of operation.
Adjust brightness control as desired.
2. Select the 40 or 80 nm range.
3. Adjust the Antenna Tilt control down until the entire display is filled with
ground returns.
4. Slowly work the Antenna Tilt up so that ground returns are painted on or
about the outer one third of the indicator area.
5. Watch the strongest returns seen on the display. if, as they are
approached, they become weaker and fade out after working back inside
the near limit of the general ground return pattern, they are probably
ground returns or insignificant weather. If they continue strong after
working down into the lower half of the indicator, you are approaching a
hazardous storm or storms, and should deviate immediately.
6. Examine the area behind strong targets. If radar shadows are detected,
you are approaching a hazardous storm or storms, and should deviate
immediately. Regardless of the aircraft’s altitude, if weather is being
detected, move the Antenna Tilt control up and down in small increments
until the return object is optimized. At that angle, the most active vertical
level of the storm is being displayed.
Figure 8.2-1. Altitude vs. Range
Note
For example, at 5,000 ft. the maximum displayed ground target range
should be about 70 nautical miles. You should perform this test on every
flight. Don’t wait until you’re penetrating severe weather to discover that
your system is not providing optimum performance.
+The TILT position in
If the radar is operating normally when you reach cruising altitude, select
the longest display range and lower the antenna tilt until ground targets are
displayed. Now, slowly raise the tilt until the ground returns disappear. This
will give you the optimum tilt setting for your cruise altitude. Each time a
new range is selected, however, the tilt control must be readjusted, down
for a shorter range, and up for a longer one.
Table 8.3-1. Antenna Tilt Control Settings
Step 4 should be that
shown in the chart.
The exact setting will
depend upon the aircraft’s pitch altitude
and the flatness of
the terrain.
Antenna Tilt Angle
Altitude (ft)
5,000
10,000
15,000
20,000
25,000
30,000
35,000
40,000
10”
+7.0°
6.0°
5.5°
4.5°
4.0°
3.5°
3.0°
2.5°
12”
+6.0°
5.0°
4.0°
3.5°
3.0°
2.5°
2.0°
1.5°
18”
+5.0°
4.0°
3.0°
2.5°
2.0°
1.5°
1.0°
0.5°
Line-of-Sight
Range (SM)
87
123
150
174
194
213
230
246
Figure 8.3-1. Weather Target
If target is shown at or beyond the line-of-sight range listed above, the
chances are good that it is a weather target.
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Antenna Stabilization (Cont.)
Antenna Stabilization
9.0 ANTENNA STABILIZATION
9.3 COMPENSATION
Airborne radar antennas are stabilized to preserve a normal cockpit display
when the aircraft is climbing, descending or turning. When the aircraft
departs from straight and level flight, the stabilization system automatically
adjusts the antenna position to compensate for the change. Both limits and
errors associated with antenna stabilization are important to the pilot.
There are some compensations the pilot can use for antenna stabilization
errors. When the system has been operating properly in level flight, the pilot
may be able to correct for ground return showing on one side and not the
other by tilting the antenna up until all ground returns are cleared. During
takeoff, the pilot can raise the antenna tilt to clear the ground returns
caused by gyro acceleration error, then as the airplane stops accelerating,
readjust the antenna tilt back toward level. Adjusting antenna tilt is also the
remedy for ground returns that appear because of gyro precession in a prolonged turn. Good operating practices include:
9.1 LIMITS
The limits of antenna stabilization are different for climbing or descending
and turning while climbing or descending. For straight ahead climbs and
descents, the limits are simply the mechanical stops at 30 degrees. When
turning, the tilt and bank angles determine the stabilization limits (the rule
of thumb is a total of 30 degrees) so moderate turns combined with moderate climbs and descents will stay within limits.
• Adjust radar and obtain weather picture before takeoff
• Compensate antenna tilt for gyro precession
• Evaluate weather in the immediate sphere of operation
• Do not “over-scan” weather targets
• During excessive aircraft maneuvers, recognize the limitations of
stabilization
Figure 9.1-1. Aircraft Pitching/Rolling ±30°
9.2 ERRORS
There are two sources of stabilization errors: acceleration and drift.
Accelerations and decelerations cause the gyro to precess in pitch. The
pilot may not notice a small temporary discrepancy between the altitude
indicator and visible horizon, but on the radar screen the antenna pitch precession will appear as an exaggeration of the desired tilt. Drift errors
(appearing on the attitude indicators pitch and roll precession accumulate
in turns) disappear slowly after the aircraft returns to straight and level.
Gyro precession errors directly affect radar stabilization and the quality of
the return displayed on the screen.
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Beacon Mode (Cont.)
Beacon Mode
10.0 BEACON MODES
10.1 BEACON FORMAT SELECTION
In the Beacon (BCN) mode, the RDR-1600 can interrogate, receive and display signals from fixed transponder beacons on all ranges. The beacon
itself is displayed as curved “slashes”, with the position of the beacon
located approximately in the center of the closest slash.
The RDR-1600 will always display all beacon signals on the screen as they
respond to the radar interrogation, regardless of the format selection.
The RDR-1600 will also display the bearing and radar distance to any
selected beacon; this information is displayed in the lower left corner of the
indicator display.
For greater flexibility, the beacon mode may be operated alone or in combination with the weather or search modes.
To identify a particular beacon and place an identification number beside it,
you must first identify whether the beacon is the standard or DO-172
format. This is accomplished by observing the beacon responses.
If the beacon is of the standard format, there will always be only 2 “slashes” on the display spaced 7 nm apart or more. The RDR-1600 can identify
any one of nine standard beacons in this mode.
Figure 10.1-1. Standard Beacon
10.2 DO-172
A selected beacon utilizing the DO-172 format will have two framing “slashes” which are positioned approximately 2 nm apart. Within these two
“frames” will be a combination of up to four slashes. Varying the combinations of the inner slashes makes it possible to identify any one of fifteen different DO-172 beacon codes. This feature is especially beneficial when
operating in areas of multiple beacon activity.
Figure 10.2-1. DO-172
After the beacon type has been identified and the proper format selected,
the operator may now select the desired beacon number by pressing the
COURSE/CODE (CRS CODE) button the proper number of times.
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Multiple Indicators
Course Bearing Cursor (Cont.)
11.0 AC 90-80
12.0 MULTIPLE INDICATORS
The FAA allows lower minimums in radar approaches to clusters of rigs,
when both the radar altimeter and “course bearing cursor” are operating
and are used as described in AC 90-80. For details on minimum approach
heights and distances, refer to FAA AC 90-80.
An additional MFD unit, is required for multiple indicator installations.
• Operating modes
Note
+Advisory Circular AC 90-80, Approval of Offshore Standard
Approach Procedures. . .can be downloaded from www.faa.gov in
Adobe Acrobat format.
Click on:
• Search and beacon gain
• Antenna tilt angle
• Antenna scan angle
• Beacon code
• Aviation Support and Regulation, then
• Guidance, Reference, Advisory, then
• Index of FAA Advisory Circulars (AC)
All indicators independently control:
• Display range
Go to the search engine at the bottom of the AC page and enter
the title in quotations to find the AC.
44
Since all controls for the radar system are located on the control panel, both
MFD observers will see the same display.
RDR-1600 Pilot’s Guide
TM106101(8/01)
• Desired brightness level
The RDR-1600 will perform dual scan operation when the range of indicator No. 1 (or 2) is greater than or equal to 20 nm and indicator No. 2 (or 1)
is less than or equal to 10 nm, and the mode of operation is either search
1 or search 2. In this situation, the short range will use a short transmitted
pulse, and the long range will use a long transmitted pulse. This is an
incompatible situation in that the transmitter cannot transmit both a long
and short pulse at the same time. In this situation, indicator No. 1 will be
updated on the right to left sweep of the antenna, and indicator No. 2 will
be updated on the left to right sweep of the antenna.
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System Specifications (Cont.)
System Specifications
13.3 CP-113K CONTROL PANEL
13.0 SYSTEM SPECIFICATIONS
Environmental Qualification:
DO-160A Env. Cat.
F1A/PKS/XXXXXXABABA
Frequency: 9375 MHz Xmit/Rec; 9310 MHz BCN REC
Altitude:
55,000 feet
RF Power Output: 10 KW Peak Power
Temperature:
-20 degrees C. to +55 degrees C.
(-4 degrees F. to +131 degrees F.)
Cooling:
May be required as determined by ambient
temperature range in aircraft cockpit.
Altitude: 50,000 ft.
Mounting:
Panel mounted, DZUS.
Temperature: -50°C to +55°C
Weight:
1.7 lbs. maximum (0.77 kg)
Size: 5”w x 6-1/4”h x 13-7/8”d (1/2 ATRI)
TSO:
C63c
13.1 RT-1601 RT UNIT
PRF/Pulse Width: Short Range Search 1500 P.P.S./0.2 sec
Long Range Search and Beacon; 200 P.P.S./2.35 sec
Weight: 16 lbs. (7.26 kg)
Overall Dimensions
TSO: C63c
13.2 DA-1203A ANTENNA DRIVE ASSEMBLY
Reflector Size: 10”, 12”, or 18” Flat Plate
Height:
2.25 inches maximum (57.2 mm)
Width:
5.75 inches maximum (146.0 mm)
Length:
6.5 inches maximum (165.1 mm)
Input Power
Scan Angle: 120° or 60°
Tilt Angle: ±15°
Scan Rate: 28°/sec
Stabilization Accuracy: ±1°
Altitude: 50,000 ft.
Temperature: -50°C to +55°C
Weight: 10”, 0.88 lbs. (4 Kgs), 12”; 1.1 lbs. (0.498 Kgs), 18”; 2.2 lbs.
(1.0 Kgs)
Voltage
+28 Vdc inputs per DO-160A
Category B. Two inputs available.
Power Draw Using
+28 Vdc Lighting
Power Bus
2.5 watts maximum electrical power drain
from +28 Vdc power bus plus 7.5 watts
maximum lighting power drain from
+28 Vdc lighting bus.
Power Draw using 5 Vac,
400 Hz Lighting
Power Bus
10 watts maximum electrical and lighting
input power drain from +28 Vdc power bus.
One milliamp power drain from 5 Vac
lighting bus (reference).
Drive Assembly: 6.5 lbs. (2.95 Kgs)
Counterbalanced Drive Assembly: 9.5 lbs. (4.32 Kgs)
TSO: C63b
46
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Advisory Circulars (Cont.)
Advisory Circulars
AC 00-24B
1/20/83
b. Tornadoes.
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
Washington, D.C.
Subject: THUNDERSTORMS
Date: 1/20/83
Initiated by: AFO-260
AC No.: 00-24B
Change:
1. PURPOSE. This advisory circular describes the hazards of thunderstorms to aviation and offers guidance to help prevent accidents caused
by thunderstorms.
2, CANCELLATION. Advisory Circular 00-24A, dated June 23, 1978, is
canceled.
3. RELATED READING MATERIAL. Advisory Circulars 00-6A, Aviation
Weather, 00-45B, Aviation Weather Services, 00-50A, Low Level Wind
Shear.
4. GENERAL. We all know what a thunderstorm looks like. Much has
been written about the mechanics and life cycles of thunderstorms. They
have been studied for many years; and while much has been learned, the
studies continue because much is not known. Knowledge and weather
radar have modified our attitudes toward thunderstorms, but one rule continues to be true - any storm recognizable as a thunder-storm should be
considered hazardous until measurements have shown it to be safe. That
means safe for you and your aircraft. Almost any thunderstorm can spell
disaster for the wrong combination of aircraft and pilot.
5. HAZARDS. A thunderstorm packs just about every weather hazard
know to aviation into one vicious bundle. Although the hazards occur in
numerous combinations, let us look at the most hazardous combination of
thunderstorms, the squall line, then we will examine the hazards individually.
a. Squall Lines. A squall line is a narrow band of active thunderstorms. Often it develops on or ahead of a cold front in moist, unstable air,
but it may develop in unstable air far removed from any front. The line
may be too long to detour easily and too wide and severe to penetrate. It
often contains steady-state thunderstorms and presents the single most
intense weather hazard to aircraft. It usually forms rapidly, generally
reaching maximum intensity during the late afternoon and the first few
hours of darkness.
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(1) The most violent thunderstorms draw air into their cloud bases
with great vigor. If the incoming air has any initial rotating motion, it often
forms an extremely concentrated vortex from the surface well into the
cloud. Meteorologists have estimated that wind in such a vortex can
exceed 200 knots; pressure inside the vortex is quite low. The strong
winds gather dust and debris and the low pressure generates a funnelshaped cloud extending downward from the cumulonimbus base. If the
cloud does not reach the surface, it is a "funnel cloud"; if it touches a land
surface, it is a "tornado."
(2) Tornadoes occur with both isolated and squall line thunderstorms. Reports for forecasts of tornadoes indicate that atmospheric conditions are favorable for violent turbulence. An aircraft entering a tornado
vortex is almost certain to suffer structural damage. Since the vortex
extends well into the cloud, any pilot inadvertently caught on instruments
in a severe thunderstorm could encounter a hidden vortex.
(3) Families of tornadoes have been observed as appendages of
the main cloud extending several miles outward from the area of lightning
and precipitation. Thus, any cloud connected to a severe thunderstorm
carries a threat of violence.
c. Turbulence.
(1) Potentially hazardous turbulence is present in all thunderstorms,
and a severe thunderstorm can destroy an aircraft. Strongest turbulence
within the cloud occurs with shear between updrafts and downdrafts.
Outside the cloud, shear turbulence has been encountered several thousand feet above and 20 miles laterally from a severe storm. A low level
turbulent area is the shear zone associated with the gust front. Often, a
"roll cloud" on the leading edge of a storm marks the top of the eddies in
this shear and it signifies an extremely turbulent zone. Gust fronts often
move far ahead (up to 15 miles) of associated precipitation. The gust front
causes a rapid and sometimes drastic change in surface wind ahead of
an approaching storm. Advisory Circular 00-50A, "Low Level Wind Shear,"
explains in greater detail the hazards associated with gust fronts. Figure
A-1 shows a schematic cross section of a thunderstorm with areas outside the cloud where turbulence may be encountered.
(2) It is almost impossible to hold a constant altitude in a thunderstorm, and maneuvering in an attempt to do so provides greatly increased
stress on the aircraft. It is understandable that the speed of the aircraft
determines the rate of turbulence encounters. Stresses are least if the aircraft is held in a constant attitude and allowed to "ride the waves." To
date, we have no sure way to pick "soft spots" in a thunderstorm.
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Advisory Circulars (Cont.)
Advisory Circulars (Cont.)
AC 00-24B
1/20/83
d. Icing.
(1) Updrafts in a thunderstorm support abundant liquid water with
relatively large droplet sizes; and when carried above the freezing level,
the water becomes supercooled. When the temperature in the upward
current cools to about -15°C, much of the remaining water vapor sublimates as ice crystals; and above this level, at lower temperatures, the
amount of supercooled water decreases.
(2) Supercooled water freezes on impact with an aircraft. Clear
icing can occur at any altitude above the freezing level; but at high levels,
icing from smaller droplets may be rime or mixed rime and clear. The
abundance of large, supercooled water droplets makes clear icing very
rapid between 0°C and -15°C and encounters can be frequent in a cluster
of cells. Thunderstorm icing can be extremely hazardous.
AC 00-24B
1/20/83
(2) As hailstones fall through air whose temperature is above 0°C,
they begin to melt and precipitation may reach the ground as either hail or
rain. Rain at the surface does not mean the absence of hail aloft. You
should anticipate possible hail with any thunderstorm, especially beneath
the anvil of a large cumulonimbus. Hailstones larger than one-half inch in
diameter can significantly damage an aircraft in a few seconds.
f. Low Ceiling and Visibility. Generally, visibility is near zero within a
thunderstorm cloud. Ceiling and visibility also may be restricted in precipitation and dust between the cloud base and the ground. The restrictions
create the same problem as all ceiling and visibility restrictions; but the
hazards are increased many fold when associated with the other thunderstorm hazards of turbulence, hail, and lightning which make precision
instrument flying virtually impossible.
g. Effect on Altimeters. Pressure usually falls rapidly with the approach of a thunderstorm, then rises sharply with the onset of the first
gust and arrival of the cold downdraft and heavy rain showers, falling
back to normal as the storm moves on. This cycle of pressure change
may occur in 15 minutes. If the pilot does not receive a corrected altimeter
setting, the altimeter may be more than 100 feet in error.
h. Lightning. A lightning strike can puncture the skin of an aircraft and
can damage communications and electronic navigational equipment.
Lightning has been suspected of igniting fuel vapors causing explosion;
however, serious accidents due to lightning strikes are extremely rare.
Nearby lightning can blind the pilot rendering him momentarily unable to
navigate either by instrument or by visual reference. Nearby lightning can
also induce permanent errors in the magnetic compass. Lightning discharges, even distant ones, can disrupt radio communications on low and
medium frequencies. Though lightning intensity and frequency have no
simple relationship to other storm parameters, severe storms, as a rule,
have a high frequency of lightning.
i. Engine Water Ingestion.
Figure 14-1. Cross-Section of a Thunderstorm
e. Hail.
(1) Hail competes with turbulence as the greatest thunderstorm
hazard to aircraft. Supercooled drops above the freezing level begin to
freeze. Once a drop has frozen, other drops latch on and freeze to it, so
the hailstone grows - sometimes into a huge iceball. Large hail occurs
with severe thunderstorms with strong updrafts that have built to great
heights. Eventually, the hailstones fall, possible some distance from the
storm core. Hail may be encountered in clear air several miles from dark
thunderstorm clouds.
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(1) Turbine engines have a limit on the amount of water they can
ingest. Updrafts are present in many thunderstorms, particularly those in
the developing stages. If the updraft velocity in the thunderstorm
approaches or exceeds the terminal velocity of the falling raindrops, very
high concentrations of water may occur. It is possible that these concentrations can be in excess of the quantity of water turbine engines are
designed to ingest. Therefore, severe thunderstorms may contain areas of
high water concentration which could result in flame-out and/or structural
failure of one or more engines.
(2) At the present time, there is no known operational procedure
that can completely eliminate the possibility of engine damage/flameout
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Advisory Circulars (Cont.)
Advisory Circulars (Cont.)
AC 00-24B
1/20/83
during massive water ingestion. Although the exact mechanism of these
water-induced engine stalls has not bee determined, it is felt that thrust
changes may have an adverse effect on engine stall margins in the presence of massive water ingestion.
(3) Avoidance of severe storm systems is the only measure assured to be effective in preventing exposure to this type of multiple engine
damage/flameout. During an unavoidable encounter with severe storms
with extreme precipitation, the best known recommendation is to follow
the severe turbulence penetration procedure contained in the approved
airplane flight manual with special emphasis on avoiding thrust changes
unless excessive airspeed variations occur.
6. WEATHER RADAR.
a. Weather radar detects droplets of precipitation size. Strength of the
radar return (echo) depends on drop size and number. The greater the
number of drops, the stronger is the echo; and the larger the drops, the
stronger is the echo. Drop size determines echo intensity to a much
greater extent that does drop number. Hailstones usually are covered with
a film of water and, therefore, act as huge water droplets giving the
strongest of all echoes.
b. Numerous methods have been used in an attempt to categorize the
intensity of a thunderstorm. To standardize thunderstorm language
between weather radar operators and pilots, the use of Video Integrator
Processor (VIP) levels is being promoted.
c. The National Weather Service (NWS) radar observer is able to
objectively determine storm intensity levels with VIP equipment. These
radar echo intensity levels are on a scale of one to six. If the maximum
VIP Levels are 1 "weak" and 2 "moderate," then light to moderate turbulence is possible with lightning. VIP Level 3 is "strong" and severe turbulence is possible with lightning. VIP Level 4 is "very strong" and severe
turbulence is likely with lightning. VIP Level 5 is "intense" with severe turbulence, lightning, hail likely, and organized surface wind gusts. VIP Level
6 is "extreme' with severe turbulence, lightning, large hail, extensive surface wind gusts, and turbulence.
d. Thunderstorms build and dissipate rapidly. Therefore, do not
attempt to plan a course between echoes. The best use of ground radar
information is to isolate general areas and coverage of echoes. You must
avoid individual storms from in-flight observations either by visual sighting
or by airborne radar. It is better to avoid the whole thunderstorm area than
to detour around individual storms unless they are scattered.
e. Airborne weather avoidance radar is, as its name implies, for avoiding severe weather - not for penetrating it. Whether to fly into an area of
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AC 00-24B
1/20/83
radar echoes depends on echo intensity, spacing between the echoes,
and the capabilities of you and your aircraft. Remember that weather
radar detects only precipitation drops; it does not detect turbulence.
Therefore, the radar scope provides no assurance of avoiding turbulence.
The radar scope also does not provide assurance of avoiding instrument
weather from clouds and fog. Your scope may be clear between intense
echoes; this clear area does not necessarily mean you can fly between
the storms and maintain visual sighting of them.
f. Remember that while hail always gives a radar echo, it may fall
several miles from the nearest visible cloud and hazardous turbulence
may extend to as much as 20 miles from the echo edge. Avoid intense or
extreme level echoes by at least 20 miles; that is, such echoes should be
separated by at least 40 miles before you fly between them. With weaker
echoes you can reduce the distance by which you avoid them.
7. DO'S AND DON'TS OF THUNDERSTORM FLYING.
a. Above all, remember this: never regard any thunderstorm lightly
even when radar observers report the echoes are of light intensity.
Avoiding thunderstorms is the best policy. Following are some do's and
don'ts of thunderstorm avoidance:
(1) Don't land or takeoff in the face of an approaching thunderstorm. A sudden gust front of low level turbulence could cause loss of
control.
(2) Don't attempt to fly under a thunderstorm even if you can see
through to the other side. Turbulence and wind shear under the storm
could be disastrous.
(3) Don't fly without airborne radar into a cloud mass containing
scattered embedded thunderstorms. Scattered thunderstorms not embedded usually can be visually circumnavigated.
(4) Don't trust the visual appearance to be a reliable indicator of the
turbulence inside a thunderstorm.
(5) Do avoid by at least 20 miles any thunderstorm identified as
severe or giving an intense radar echo. This is especially true under the
anvil of a large cumulonimbus.
(6) Do circumnavigate the entire area if the area has 6/10 thunderstorm coverage.
(7) Do remember that vivid and frequent lightning indicates the
probability of a severe thunderstorm.
(8) Do regard as extremely hazardous any thunderstorm with tops
35,000 feet or higher whether the top is visually sighted or determined by
radar.
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Advisory Circulars (Cont.)
Advisory Circulars (Cont.)
AC 00-24B
1/20/83
b. If you cannot avoid penetrating a thunderstorm, following are some
do's BEFORE entering the storm:
(1) Tighten your safety belt, put on your shoulder harness if you
have one, and secure all loose objects.
(2) Plan and hold your course to take you through the storm in a
minimum time.
ADVISORY CIRCULAR
AC 20-68B
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration, Washington, D.C.
Recommended radiation safety precautions for ground operation of
airborne weather radar.
Initiated by: AFO-512
(3) To avoid the most critical icing, establish a penetration altitude
below the freezing level or above the level of -15°C.
PURPOSE
(4) Verify that pitot-heat is on and turn on carburetor heat or jet
engine anti-ice. Icing can be rapid at any altitude and cause almost instantaneous power failure and/or loss of airspeed indication.
This circular sets forth recommended radiation safety precautions to be
taken by personnel when operating airborne weather radar on the ground.
(5) Establish power settings for turbulence penetration airspeed recommended in your aircraft manual.
CANCELLATION
AC 20-68A, dated April 11, 1975, is canceled.
(6) Turn up cockpit lights to highest intensity to lessen temporary
blindness from lightning.
RELATED READING MATERIAL
(7) If using automatic pilot, disengage altitude hold mode and speed
hold mode. The automatic altitude and speed controls will increase
maneuvers of the aircraft thus increasing structural stress.
• Barnes and Taylor, Radiation Hazards and Protection (London: George
Newnes Limited, 1963), p. 211.
(8) If using airborne radar, tilt the antenna up and down occasionally. This will permit you to detect other thunderstorm activity at altitudes
other then the one being flown.
c. Following are some do's and don'ts during the thunderstorm penetration:
(1) Do keep your eyes on your instruments. Looking outside the
cockpit can increase danger of temporary blindness from lightning.
(2) Don't change power settings; maintain settings for the recommended turbulence penetration airspeed.
(3) Do maintain constant attitude; let the aircraft "ride the waves."
Maneuvers in trying to maintain constant altitude increase stress on the
aircraft.
(4) Don't turn back once you are in the thunderstorm. A straight
course through the storm most likely will get you out of the hazards most
quickly. In addition, turning maneuvers increase stress on the aircraft.
RDR-1600 Pilot’s Guide
• Mumford, W.W., “Some technical aspects of microwave radiation hazards”, Proceedings of the IRE, Washington, U.S. Government Printing
Office, February 1961, pp. 427-447.
BACKGROUND
Dangers from ground operation of airborne weather radar include the
possibility of human body damage and ignition of combustible materials by
radiated energy. Low tolerance parts of the body include the eyes and
testes.
PRECAUTIONS
Management and supervisory personnel should establish procedure for
advising personnel of dangers from operating airborne weather radars on
the ground. Precautionary signs should be displayed in affected areas to
alert personnel of ground testing.
WILLIAM T. BRENNAN
Acting Director of Flight Operations
54
• U.S. Department of Health, Education and Welfare, Public Health
Service, Consumer Protection and Environmental Health Service,
“Environmental health microwaves, ultraviolet radiation and radiation
from lasers and television receivers – An Annotated Bibliography”, FS
2.300: RH-35, Washington, U.S. Government Printing Office, pp. 56-57.
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Advisory Circulars (Cont.)
General
• Airborne weather radar should be operated on the ground only by qualified personnel.
• Installed airborne radar should not be operated while the aircraft is in a
hangar or other enclosure unless the radar transmitter is not operating,
or the energy is directed toward an absorption shield which dissipates
the radio frequency energy. Otherwise, radiation within the enclosure can
be reflected throughout the area.
Body Damage. To prevent possible human body damage, the following precautions should be taken:
• Personnel should never stand nearby and in front of radar antenna which
is transmitting. When the antenna is not scanning, the danger increases.
• A recommended safe distance from operating airborne weather radars
should be established. A safe distance can be determined by using the
equations in the Appendix. This criterion is now accepted by many industrial organizations and is based on limiting exposure of humans to an
average power density not greater than 1 milliwatt per square centimeter.
• Personnel should be advised to avoid the end of an open wave guide
unless the radar is turned off.
• Personnel should be advised to avoid looking into a wave guide, or into
the open end of a coaxial connector or line connector to a radar transmitter output, as severe eye damage may result.
• Personnel should be advised that when power radar transmitters are
operated out of their protective cases, X-rays may be emitted. Stray
X-rays may emanate from the glass envelope-type pulsar, oscillator,
clipper, or rectifier tubes, as well as magnetrons.
Combustible Materials. To prevent possible fuel ignition, an
installed airborne weather radar should not be operated while an
aircraft is being refueled or defueled.
M.C. Beard
Director of Airworthiness
AC 20-68B
56
8/8/80
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Appendix
APPENDIX
SAFE DISTANCE DETERMINATION
The following information can be used in establishing a minimum safe distance from the antenna for personnel near an operating airborne weather
radar.
NEAR FIELD/FAR FIELD INTERSECTION
The distance to the near field/far field intersection can be computed by:
Ri = Gλ
8π
where Ri=intersection distance from the antenna (in meters)
= Wave length (in meters)
= Antenna gain
DISTANCE TO 1 MW/CM2 SAFE LIMIT
For a far field power density of 1 mw/cm2, the distance (in meters) from
the antenna may be calculated by:
Rs =
GP
40π
where Rs=the minimum safe distance in meters.
P = Transmitted average power in watts.
G = Antenna gain
PROCEDURES
The above formulas may be used to determine the minimum safe distance.
In either case, the following procedures apply:
a. Determine the distance (Ri) to the near field/far field intersection (paragraph 1)
b. Determine the distance (Rs) to 1 mw/cm2 power density
c. If the distance (Rs) determined in item b is less than (Ri) found in item a,
use distance (Ri) as the minimum safe distance
d. If the distance (Rs) determined in item b is greater than (Ri) found in item
a, use distance (Rs) as the minimum safe distance
TM106101(8/01)
RDR-1600 Pilot’s Guide
A-1
Appendix (Cont.)
Appendix (Cont.)
EXAMPLE
The following is typical data for the airborne weather radar.
Antenna Diameter: 18 inches = 45.6 cm
Transmitter Frequency: 9375 +30 MHz
Wave Length: 3.2 cm
Pulse Length: 2.5 microseconds (search)
Pulse Repetition: 200 Hz
Peak Power: 10 kilowatts
Average Power: 5 watts (search)
Antenna Gain: 1250 (31 dB)
Calculations
(1) Distance (Ri) to the near field/far field intersection
CAUTION
Ri = Gλ
8π
Maintain prescribed safe distance when standing in front of radiating
antenna.
Ri = (1250 x 0.032)
8π
Never expose eyes or any part of the body to an unterminated wave
guide.
=1.6 meters = 5.25 feet
(2) Distance (Rs) to 1 mw/cm2 safe limit
Rs =
GP
40π
(1250)(5)
40π
= 7.05 meters = 23.1 feet
The distance (Rs) is greater than (Ri), therefore, the minimum safe distance
is 23.1 feet.
A-2
RDR-1600 Pilot’s Guide
TM106101(8/01)
TM106101(8/01)
RDR-1600 Pilot’s Guide
A-3
Appendix (Cont.)
MAXIMUM PERMISSIBLE EXPOSURE LEVEL (MPEL)
In order to avoid the envelope in which the radiation level exceeds the U.S.
Government standard of 1 mW per square centimeter, all personnel should
remain beyond the distance indicated in the illustration below. The distance
to the MPEL boundary is calculated upon the basis of the largest antenna
available with the RDR-1600 system, rated output power of the transmitter
and in the non-rotating or boresight position of the antenna. With a
scanning beam, the power density at the MPEL boundary is significantly
reduced.
Command Systems Division
Copyright 2001
Telephonics
TM106101(8/01)
A-4
RDR-1600 Pilot’s Guide
TM106101(8/01)
815 Broad Hollow Road, Farmingdale, NY 11735
Phone: 1 (631) 755-7004 • Fax: 1 (877) 577-7701
www.telephonics.com

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