Honeywell Weather Radio 880 Users Manual PRIMUS Digital Radar System

880 to the manual 440a994a-e92c-4326-ba95-7eecdaadcbc7

2015-01-23

: Honeywell Honeywell-Honeywell-Weather-Radio-880-Users-Manual-262706 honeywell-honeywell-weather-radio-880-users-manual-262706 honeywell pdf

Open the PDF directly: View PDF .
Page Count: 161

Download
Open PDF In Browser	View PDF

Honeywell International Inc.
Commercial Electronic Systems
5353 W. Bell Rd.
Glendale, Arizona 85308-- 3912
U.S.A.
(CAGE 55939)

PRIMUSr 880 Digital Weather
Radar System

Pilot’s Guide

Printed in U.S.A.

Pub. No. A28--1146--102--03

Revised January 2006
September 1996

PRIMUSr 880 Digital Weather Radar System

Table of Contents
Section

Page

1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1-1

2. SYSTEM CONFIGURATIONS . . . . . . . . . . . . . . . . .

2-1

3. OPERATING CONTROLS . . . . . . . . . . . . . . . . . . . .

3-1

WI- 880 Weather Radar Indicator Operation . . . . . .
WC- 880 Weather Radar Controller Operation . . . .
WC- 884 Weather Radar Controller Operation . . . .
Hidden Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Forced Standby Override . . . . . . . . . . . . . . . . . . .
Roll Offset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Roll Gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pitch Offset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pitch Gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3-1
3-11
3-20
3-26
3-26
3-27
3-27
3-27
3-28

4. NORMAL OPERATION . . . . . . . . . . . . . . . . . . . . . . .

4-1

Preliminary Control Settings . . . . . . . . . . . . . . . . . . .
Standby . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Radar Mode - Weather . . . . . . . . . . . . . . . . . . . .
Radar Mode - Ground Mapping . . . . . . . . . . . . .
Test Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4-1
4-4
4-4
4-6
4-6

5. RADAR FACTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5-1

Radar Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Tilt Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stabilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Dynamic Error . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Accelerative Error . . . . . . . . . . . . . . . . . . . . . . . . .
Pitch and Roll Trim Adjustments . . . . . . . . . . . . .
Stabilization Precheck . . . . . . . . . . . . . . . . . . . . .
Roll stabilization check . . . . . . . . . . . . . . . . . . . . . . . .
Pitch offset adjustment . . . . . . . . . . . . . . . . . . . . . . . .
Roll gain adjustment . . . . . . . . . . . . . . . . . . . . . . . . . .
Pitch gain adjustment . . . . . . . . . . . . . . . . . . . . . . . . .
Interpreting Weather Radar Images . . . . . . . . . . . . .
Weather Display Calibration . . . . . . . . . . . . . . . . . . .
Variable Gain Control . . . . . . . . . . . . . . . . . . . . . . . . .

5-1
5-5
5-18
5-18
5-18
5-19
5-21
5-25
5-28
5-29
5-30
5-31
5-35
5-37

A28- 1146- 102- 00

Table of Contents
TC- 1

PRIMUSr 880 Digital Weather Radar System

Table of Contents (cont)
Section

Page

5. RADAR FACTS (cont)
Rain Echo Attenuation Compensation Technique
(REACT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Shadowing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Turbulence Probability . . . . . . . . . . . . . . . . . . . . .
Turbulence Detection Theory . . . . . . . . . . . . . . .
Turbulence Detection Operation . . . . . . . . . . . . .
Hail Size Probability . . . . . . . . . . . . . . . . . . . . . . .
Spotting Hail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Azimuth Resolution . . . . . . . . . . . . . . . . . . . . . . . .
Radome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Weather Avoidance . . . . . . . . . . . . . . . . . . . . . . . . . . .
Configurations of Individual Echoes (Northern
Hemisphere) . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Line Configurations . . . . . . . . . . . . . . . . . . . . . . . .
Additional Hazards . . . . . . . . . . . . . . . . . . . . . . . .
Ground Mapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5-37
5-40
5-40
5-42
5-45
5-47
5-48
5-53
5-54
5-55
5-60
5-65
5-68
5-69

6. MAXIMUM PERMISSIBLE EXPOSURE LEVEL
(MPEL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6-1

7. IN--FLIGHT TROUBLESHOOTING . . . . . . . . . . . . .

7--1

Test Mode With TEXT FAULTS Enabled . . . . . . . . .
Fault Code and Text Fault Relationships . . . . . . . . .

7-2
7-5

8. HONEYWELL PRODUCT SUPPORT . . . . . . . . . .

8-1

9. ABBREVIATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . .

9-1

APPENDICES
A FEDERAL AVIATION ADMINISTRATION (FAA)
ADVISORY CIRCULARS . . . . . . . . . . . . . . . . . . . .

A--1

Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cancellation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Related Reading Material . . . . . . . . . . . . . . . . . . . . . .
Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

A--1
A--1
A--1
A--2
A--2

Table of Contents
TC-- 2

A28-- 1146-- 102-- 01
REV 1

PRIMUSr 880 Digital Weather Radar System

Table of Contents (cont)
A FEDERAL AVIATION ADMINISTRATION (FAA)
ADVISORY CIRCULARS (CONT)
SUBJECT: THUNDERSTORMS . . . . . . . . . . . . . . .
Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Related Reading Material . . . . . . . . . . . . . . . . . . .
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
National Severe Storms Laboratory (NSSL)
Thunderstorm Research . . . . . . . . . . . . . . . . . .

A--4
A--4
A--4
A--4
A--4
A--11

B ENHANCED GROUND--PROXIMITY WARNING
SYSTEM (EGPWS) . . . . . . . . . . . . . . . . . . . . . . . . .
System Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . .
EGPWS Controls . . . . . . . . . . . . . . . . . . . . . . . . . .
Related EGPWS System Operation . . . . . . . . . .
EGPWS Operation . . . . . . . . . . . . . . . . . . . . . . . .
EGPWS Display . . . . . . . . . . . . . . . . . . . . . . . . . .
EGPWS Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

B--1
B--1
B--1
B--3
B--3
B--4
B--6

INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Index--1

List of Illustrations
Figure

Page
PRIMUSR

2--1
880 Configurations . . . . . . . . . . . . . . . . . .
2--2 Typical PRIMUSR 880 Weather Radar
Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3--1 Typical PRIMUSR 880 Digital Weather Radar
Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3--2 WI--880 Weather Radar Indicator Front Panel
View . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3--3 WI--880 Weather Radar Indicator Display Screen
Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3--4 WC--880 Weather Radar Controller Configurations .
3--5 WC--884 Weather Radar Controller . . . . . . . . . . . . .
4--1 Indicator Test Pattern 120° Scan (WX), With TEXT
FAULT Enabled . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4--2 EFIS Test Pattern (Typical) 120° Scan Shown
(WX) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4--3 WI--880 Indicator Test Pattern With TEXT FAULT
Enabled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A28-- 1146-- 102-- 01
REV 1

2-2
2-5
3-1
3-2
3-3
3-11
3-20
4-2
4-3
4-4

Table of Contents
TC-- 3

PRIMUSr 880 Digital Weather Radar System

Table of Contents (cont)
List of Illustrations (cont)
Figure

Page

5--1 Positional Relationship of an Airplane and Storm
Cells Ahead as Displayed on Indicator . . . . . . . . .
5--2 Antenna Beam Slicing Out Cross Section of Storm
During Horizontal Scan . . . . . . . . . . . . . . . . . . . . . .
5--3 Sea Returns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5--4 Radar Beam Illumination High Altitude
12--Inch Radiator . . . . . . . . . . . . . . . . . . . . . . . . . . .
5--5 Radar Beam Illumination High Altitude
18--Inch Radiator . . . . . . . . . . . . . . . . . . . . . . . . . . .
5--6 Radar Beam Illumination Low Altitude
12--Inch Radiator . . . . . . . . . . . . . . . . . . . . . . . . . . .
5--7 Radar Beam Illumination Low Altitude
18--Inch Radiator . . . . . . . . . . . . . . . . . . . . . . . . . . .
5--8 Ideal Tilt Angle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5--9 Earth’s Curvature . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5--10 Convective Thunderstorms . . . . . . . . . . . . . . . . . . . .
5--11 Unaltered Tilt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5--12 Proper Tilt Technique . . . . . . . . . . . . . . . . . . . . . . . . .
5--13 Tilt Management With Heading Changes . . . . . . . .
5--14 Fast Developing Thunderstorm . . . . . . . . . . . . . . . . .
5--15 Low Altitude Tilt Management . . . . . . . . . . . . . . . . . .
5--16 Antenna Size and Impact on Tilt Management . . . .
5--17 Rules of Thumb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5--18 Manual Tilt at Low Altitudes . . . . . . . . . . . . . . . . . . . .
5--19 Symmetrical Ground Returns . . . . . . . . . . . . . . . . . .
5--20 Ground Return Indicating Misalignment
(Upper Right) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5--21 Ground Return Indicating Misalignment
(Upper Left) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5--22 Roll Stabilization Inoperative . . . . . . . . . . . . . . . . . . .
5--23 Roll Offset Adjustment Display -- Initial . . . . . . . . . .
5--24 Roll Offset Adjustment Display -- Final . . . . . . . . . .
5--25 Weather Radar Images . . . . . . . . . . . . . . . . . . . . . . .
5--26 Radar and Visual Cloud Mass . . . . . . . . . . . . . . . . . .
5--27 Squall Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5--28 REACT ON and OFF Indications . . . . . . . . . . . . . . .
5--29 Probability of Turbulence Presence in a Weather
Target . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5--30 Total Return Vector . . . . . . . . . . . . . . . . . . . . . . . . . . .
5--31 No Turbulence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Table of Contents
TC-- 4

5-2
5-3
5-4
5-5
5-5
5-6
5-6
5-11
5-11
5-12
5-12
5-13
5-13
5-14
5-14
5-15
5-15
5-17
5-22
5-22
5-23
5-24
5-26
5-27
5-31
5-33
5-34
5-39
5-41
5-44
5-44

A28-- 1146-- 102-- 01
REV 1

PRIMUSr 880 Digital Weather Radar System

Table of Contents (cont)
List of Illustrations (cont)
Figure

Page

5--32 Turbulent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5--33 Weather Display With Turbulence . . . . . . . . . . . . . .
5--34 Turbulence Levels (From Airman’s Information
Manual) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5--35 Hail Size Probability . . . . . . . . . . . . . . . . . . . . . . . . . .
5--36 Rain Coming From Unseen Dry Hail . . . . . . . . . . . .
5--37 Familiar Hailstorm Patterns . . . . . . . . . . . . . . . . . . . .
5--38 Overshooting a Storm . . . . . . . . . . . . . . . . . . . . . . . .
5--39 Short-- and Long--Blind Alley . . . . . . . . . . . . . . . . . . .
5--40 Azimuth Resolution in Weather Modes . . . . . . . . . .
5--41 Weather Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5--42 Typical Hook Pattern . . . . . . . . . . . . . . . . . . . . . . . . .
5--43 V--Notch Echo, Pendant Shape . . . . . . . . . . . . . . . .
5--44 The Classic Pendant Shape . . . . . . . . . . . . . . . . . . .
5--45 Rain Gradients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5--46 Crescent Shape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5--47 Line Echo Wave Pattern (LEWP) . . . . . . . . . . . . . . .
5--48 Bow--Shaped Line of Thunderstorms . . . . . . . . . . . .
5--49 Ground Mapping Display . . . . . . . . . . . . . . . . . . . . . .

5-45
5-45
5-47
5-48
5-49
5-50
5-51
5-52
5-53
5-55
5-61
5-62
5-63
5-64
5-65
5-66
5-67
5-69

6--1 MPEL Boundary . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6-1

7--1 Fault Annunciation on Weather Indicator With TEXT
FAULT Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7--2 Fault Code on EFIS Weather Display With TEXT
FAULTS Disabled . . . . . . . . . . . . . . . . . . . . . . . . . . .
7--3 Radar Indication With Text Fault Enabled
(On Ground) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7-4

A--1 Schematic Cross Section of a Thunderstorm . . . . .

A--6

B--1 EHSI Display Over KPHX Airport With the
EGPWS Display . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B--2 EGPWS Test Display . . . . . . . . . . . . . . . . . . . . . . . . .

B--5
B--6

A28-- 1146-- 102-- 01
REV 1

7-3
7-4

Table of Contents
TC-- 5

PRIMUSr 880 Digital Weather Radar System

Table of Contents (cont)
List of Tables
Table

Page

2--1 Dual Control Mode Truth Table . . . . . . . . . . . . . . . .
2--2 PRIMUSR 880 Weather Radar Equipment List . . . .
3--1
3--2
3--3
3--4
3--5
3--6

Rainfall Rate Color Coding . . . . . . . . . . . . . . . . . . .
Target Alert Characteristics . . . . . . . . . . . . . . . . . . .
Rainfall Rate Color Coding . . . . . . . . . . . . . . . . . . .
WC--880 Controller Target Alert Characteristics . . .
WC--884 Controller Target Alert Characteristics . . .
Rainfall Rate Color Coding . . . . . . . . . . . . . . . . . . .

4--1 PRIMUSR 880 Power--Up Procedure

..........

5--1 Approximate Tilt Setting for Minimal Ground Target
Display 12--Inch Radiator . . . . . . . . . . . . . . . . . . .
5--2 Approximate Tilt Setting for Minimal Ground Target
Display 18--Inch Radiator . . . . . . . . . . . . . . . . . . .
5--3 Approximate Tilt Setting for Minimal Ground Target
Display 24--Inch Radiator . . . . . . . . . . . . . . . . . . .
5--4 Pitch and Roll Trim Adjustments Criteria . . . . . . . .
5--5 Stabilization In Straight and Level Flight Check
Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5--6 Stabilization in Turns Check Procedure . . . . . . . .
5--7 In--flight Roll Offset Adjustment Procedure . . . . . .
5--8 Pitch Offset Adjustment Procedure . . . . . . . . . . . .
5--9 Roll Gain Adjustment . . . . . . . . . . . . . . . . . . . . . . . .
5--10 Pitch Gain Adjustment . . . . . . . . . . . . . . . . . . . . . . .
5--11 Display Levels Related to VIP Levels (Typical) . .
5--12 Severe Weather Avoidance Procedures . . . . . . . .
5--13 TILT Setting for Maximal Ground Target Display
12--Inch Radiator . . . . . . . . . . . . . . . . . . . . . . . . . . .
5--14 TILT Setting for Maximal Ground Target Display
18--Inch Radiator . . . . . . . . . . . . . . . . . . . . . . . . . . .

2-3
2-4
3-4
3-7
3-13
3-17
3-21
3-24
4-1
5-8
5-9
5-10
5-20
5-21
5-23
5-25
5-28
5-29
5-30
5-36
5-60
5-70
5-71

7--1 Fault Data Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7--2 Text Faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7--3 Pilot Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7-3
7-5
7-8

B--1 EGPWS Obstacle Display Color Definitions . . . . . .

B--4

Table of Contents
TC-- 6

A28-- 1146-- 102-- 01
REV 1

PRIMUSr 880 Digital Weather Radar System

Introduction

The PRIMUSR 880 Digital Weather Radar System is a lightweight,
X- band digital radar with alphanumerics designed for weather detection
(WX) and ground mapping (GMAP).
The primary purpose of the system is to detect storms along the
flightpath and give the pilot a visual indication in color of their rainfall
intensity and turbulence content. After proper evaluation, the pilot can
chart a course to avoid these storm areas.

WARNING
THE
SYSTEM
PERFORMS
THE
FUNCTIONS
OF
WEATHER DETECTION OR GROUND MAPPING. IT SHOULD
NOT BE USED NOR RELIED UPON FOR PROXIMITY
WARNING OR ANTICOLLISION PROTECTION.
In weather detection mode, storm intensity levels are displayed in
four bright colors contrasted against a deep black background.
Areas of very heavy rainfall appear in magenta, heavy rainfall in red,
less severe rainfall in yellow, moderate rainfall in green, and little or no
rainfall in black (background). Areas of detected turbulence appear in
soft white. The antenna sweep position indicator is a yellow bar.
Range marks and identifying numerics, displayed in contrasting colors,
are provided to facilitate evaluation of storm cells.
Select the GMAP function to optimize system parameters to improve
resolution and enhance identification of small targets at short ranges.
The reflected signal from ground surfaces is displayed as magenta,
yellow, or cyan (most to least reflective).
NOTE:

Section V, Radar Facts, describes a variety of radar operating
topics. It is recommended that you read Section V, Radar
Facts, before learning the specific operational details of the
PRIMUSâ 880 Digital Weather Radar System.

A28- 1146- 102- 00

Introduction
1-1

PRIMUSr 880 Digital Weather Radar System

The radar indicator is equipped with the universal digital interface (UDI).
This feature expands the use of the radar indicator to display
information such as checklists, short and long range navigation
displays (when used with a Honeywell DATA NAV system) and
electrical discharge data from Honeywell’s LSZ- 850 Lightning Sensor
System (LSS).
NOTE:

Introduction
1-2

Refer to Honeywell Pub. 28- 1146- 54, LSZ- 850 Lightning
Sensor System Pilot’s Handbook, for more information.

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

System Configurations

The PRIMUSâ 880 Digital Weather Radar System can be operated in
many configurations to display weather or ground mapping information
on a radar indicator, electronic flight instrument system (EFIS) display,
multifunction display (MFD), or on a combination of these displays. The
various system configurations are summarized in the following
paragraphs and shown in figure 2- 1.
NOTE:

Other configurations are possible but not illustrated.

The stand- alone configuration consists of two units: receiver
transmitter antenna (RTA), and a dedicated radar indicator. In this
configuration, the radar indicator contains all the controls to operate the
PRIMUSâ 880 Digital Weather Radar System. A single or dual
Honeywell EFIS can be added to the stand- alone configuration. In such
a case the electronic horizontal situation indicator (EHSI) repeats the
data displayed on the radar indicator. System control remains with
the radar indicator.
The second system configuration uses an RTA, and single or dual
controllers. The single or dual EFIS is the radar display. Since there is
no radar indicator in this configuration, the radar system operating
controls are located on the controller. With a single controller, all cockpit
radar displays are identical.
The dual configuration gives the appearance of having two radar
systems on the aircraft. In the dual configuration, the pilot and copilot
each select independent radar mode, range, tilt, and gain settings for
display on their respective display. The dual configuration time shares
the RTA. On the right- to- left antenna scan, the system switches to the
mode, range, tilt, and gain selected by the left controller and updates
the left display. On the reverse antenna scan, the system switches to
the mode, range, tilt, and gain setting selected by the right controller
and updates the right display. Either controller can be slaved to the
other controller to show identical images on both sides of the cockpit.
NOTE:

When WAIT, SECTOR SCAN, or FORCED STANDBY are
activated, the radar operates as if in single controller
configuration. This is an exception to the ability of each pilot
to independently select modes.

A28- 1146- 102- 00

System Configurations
2-1

PRIMUSr 880 Digital Weather Radar System

RTA
WU- 880

STAND- ALONE CONFIGURATION
INDICATOR
WI- 880

SINGLE OR DUAL EFIS OPTION
EFIS ONLY CONFIGURATION
RTA
WU- 880

CONTROLLER
WC- 880
STAB

TRB
PULL
VAR
MIN

GAIN

MAX

WX
SBY
OFF

RCT
GMAP
FP
TST

RADAR

MIN

GAIN

MAX

WX
SBY
OFF

PULL
ACT

SLV

STAB

TRB
PULL
VAR

RCT
GMAP
FP
TST

RADAR

TGT

TILT

TGT
PULL
ACT

SLV

SECT
+

TILT

SECT
+
-

OPTIONAL
2ND CONTROLLER

SINGLE OR DUAL EFIS

EFIS / MFD CONFIGURATION
RTA
WU- 880

CONTROLLER
WC- 880
STAB

TRB
PULL
VAR

MIN

GAIN

MAX

WX
SBY
OFF

RCT
GMAP
FP
TST

RADAR

MIN

MFD AND
SINGLE OR DUAL EFIS

GAIN

MAX

WX
SBY
OFF

PULL
ACT

SLV

STAB

TRB
PULL
VAR

RCT
GMAP
FP
TST

RADAR

TGT

SLV

TILT

SECT
+
-

TGT
PULL
ACT

TILT

SECT
+
-

OPTIONAL
2ND CONTROLLER
AD- 46690- R2@

PRIMUSâ 880 Configurations
Figure 2- 1

System Configurations
2-2

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

The third system configuration is similar to the second except that a
Honeywell multifunction display (MFD) system is added. As before,
single or dual controllers can be used. When a single controller is used,
all displays show the same radar data. Dual controllers are used to
operate in the dual mode. The MFD can be slaved to either controller
to duplicate the data displayed on the selected side. Table 2- 1 is a truth
table for dual control modes.
Left
Controller
Mode

Right
Controller
Mode

OFF

Standby

”SLV”
Standby

Standby

OFF

Standby

”SLV”
Standby

Standby

OFF

”SLV”ON

OFF

”SLV”ON

Standby

Standby/
2

ON/2

Standby

ON/2

Standby/2

ON/2

Standby

Left Side Right Side
(NOTE 1) (NOTE 1)

RTA
Mode

Dual Control Mode Truth Table
Table 2- 1

A28- 1146- 102- 00

System Configurations
2-3

PRIMUSr 880 Digital Weather Radar System

1. ON is used to indicate any selected radar mode.

NOTES:

2. “SLV” means that displayed data is controlled by
opposite side controller.
3. XXX/2 means that display is controlled by appropriate
on--side control for the antenna sweep direction
associated with that control. (/2 implies two controllers
are on.)
4. In standby, the RTA is centered in azimuth with 15_
upward tilt. Video data is suppressed. The transmitter
is inhibited.
5. The MFD, if used, can repeat either left-- or right--side
data, depending upon external switch selection.
Equipment covered in this guide is listed in table 2--2 and shown in
figure 2--2.
Model

Unit

Part No.

Cockpit Mounted Options
WI--880

Weather Radar Indicator

7007700--401/402/
403/404

WC--880

Weather Radar Controller

7008471--4XX

WC--884

Weather Radar Controller

7006921--815/816

Remote Mounted Equipment
WU--880
NOTE:

Receiver Transmitter Antenna

7021450--801

Typically, either the indicator or one of the remote
controllers (one or two) is installed.
PRIMUSR 880 Weather Radar Equipment List
Table 2--2

System Configurations
2-4

A28-- 1146-- 102-- 03
REV 3

PRIMUSr 880 Digital Weather Radar System

WU- 880 RTA

WC- 884 CONTROLLER

WI- 880 INDICATOR

WC- 880 CONTROLLER

AD- 46691@

Typical PRIMUSâ 880 Weather Radar Components
Figure 2- 2

A28- 1146- 102- 00

System Configurations
2-5/(2-6 blank)

PRIMUSr 880 Digital Weather Radar System

Operating Controls

WI- 880 WEATHER RADAR INDICATOR OPERATION
All controls used to operate the system display shown in figure 3- 1, are
located on the WI- 880 Weather Radar Indicator front panel. There are
three basic controllers that are described in this section, they are (in
order of description):
D

WI- 880 Weather Radar Indicator

WC- 880 Weather Radar Controller

WC- 884 Weather Radar Controller.

AUTO
TILT

+1.0

30
20
1

4 T

Typical PRIMUSâ 880 Digital
Weather Radar Display
Figure 3- 1
The controls and display features of the WI- 880 Weather Radar
Indicator are indexed and identified in figure 3- 2. Brightness levels for
all legends and controls on the indicator are controlled by the dimming
bus for the aircraft panel.

A28- 1146- 102- 00

Operating Controls
3-1

PRIMUSr 880 Digital Weather Radar System

6
5
4
3

TRB
RANGE
STB

RCT

TGT

SCT

8
9

WX
SBY
OFF

GMAP
FP
TST

PULL
VAR

MIN

GAIN
MAX

BRT

TILT +
PULL
ACT

11
SBY LX
CLR
OFF
TST

BRT

AD- 46693- R1@

WI- 880 Weather Radar Indicator Front Panel View
Figure 3- 2
1

Display Area

See figure 3- 3 and the associated text which explains the alphanumeric
display.

Operating Controls
3-2

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

TARGET/TARGET ALERT:
T ARM (GREEN)
TGT ALERT (YELLOW INVERTED VIDEO)
TILT ANGLE
FAIL
NOTE STB

ALTITUDE
COMPENSATED
TILT (ACT)
ANNUNCIATION

REACT: RCT
MODE:
STBY
FSBY
WAIT
TEST
WX
WX/T
FLTPLN
GMAP

RANGE RING
MARKERS
(120- DEGREE
SCAN SHOWN)

COLOR BAR:
1 2 3 4 T WX CALIBRATED GAIN
WX VARIABLE GAIN
VAR !
1 2 3 GMAP CALIBRATED GAIN
V A R GMAP VARIABLE GAIN
NOTE:MESSAGES ARE LISTED 1 2 3 4 T WX/T CALIBRATED GAIN
WX/T VAR
VAR !
IN PRIORITY ORDER.
AD- 46694- R2@

WI- 880 Weather Radar Indicator Display Screen Features
Figure 3- 3
2

Function Switch

A rotary switch used to select the following functions:
D
D

OFF- This position turns off the radar system.
SBY (Standby) - This position places the radar system in standby,
a ready state, with the antenna scan stopped, the transmitter
inhibited, and the display memory erased. STBY, in white, is shown
in the mode field.
If SBY is selected before the initial RTA warmup period is complete
(approximately 90 seconds), the white WAIT legend is shown in
the mode field. When warmup is complete the system changes the
mode field to STBY.

WX (Weather) - This position selects the WX mode of operation.
When WX is selected, the system is fully operational and all internal
parameters are set for enroute weather detection. The
alphanumerics are white and WX is shown in the mode field.

A28- 1146- 102- 00

Operating Controls
3-3

PRIMUSr 880 Digital Weather Radar System

If WX is selected before the initial RTA warmup period is over
(approximately 90 seconds), the white WAIT legend is displayed
in the mode field. In wait mode, the transmitter and antenna scan
are inhibited and the display memory is erased. When the warmup
is complete, the system automatically switches to the WX mode.
The system, in preset gain, is calibrated as listed in table 4- 1.
Rainfall Rate

Color

in/hr

mm/hr

.04- .16

1- 4

Green

.16- .47

4- 12

Yellow

.47- 2

12- 50

Red

>5 0

Magenta

Rainfall Rate Color Coding
Table 3- 1
D

GMAP (Ground Mapping) - The GMAP position puts the radar
system in the ground mapping mode. The system is fully
operational and all parameters are set to enhance returns from
ground targets.
NOTE:

REACT, TGT, or TURB modes are not selectable in GMAP.

WARNING
WEATHER TYPE TARGETS ARE NOT CALIBRATED WHEN
THE RADAR IS IN THE GMAP MODE. BECAUSE OF THIS, DO
NOT USE THE GMAP MODE FOR WEATHER DETECTION.
As a constant reminder that GMAP is selected, the alphanumerics
are changed to green, the GMAP legend is shown in the mode field,
and the color scheme is changed to cyan, yellow, and magenta.
Cyan represents the least reflective return, yellow is a moderate
return, and magenta is a strong return.
If GMAP is selected before the initial RTA warmup period is
complete, the white WAIT legend is shown in the mode field. In wait
mode, the transmitter and antenna scan are inhibited and the
memory is erased. When the warmup period is complete, the
system automatically switches to the GMAP mode.
D

FP (Flight Plan) - The FP position puts the radar system in the flight
plan mode, which clears the screen of radar data so ancillary data
can be displayed. Examples of this data are:

Operating Controls
3-4

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

FP (Flight Plan) -- The FP position puts the radar system in the flight
plan mode, which clears the screen of radar data so ancillary data
can be displayed. Examples of this data are:
— Navigation displays
— Electrical discharge (lightning) data.
NOTE:

In the FP mode, the radar RTA is put in standby, the
alphanumerics are changed to cyan, and the FLTPLN
legend is shown in the mode field.

The target (TGT) alert mode can be used in the FP mode. With
target alert on and the FP mode selected, the target alert armed
annunciation (green TGT) is displayed. The RTA searches for a
hazardous target from 5 to 55 miles and ±7.5° of the aircraft heading.
No radar targets are displayed. If a hazardous target is detected,
the target alert armed annunciation switches to the alert
annunciation (yellow TGT). This advises the pilot that a hazardous
target is in his flightpath and the WX mode should be selected to
view it.
NOTE:
D

The TGT function is inoperative when a checklist is
displayed.

TST (Test) -- The TST position selects the radar test mode. A
special test pattern is displayed to verify system operation. The
TEST legend is shown in the mode field. Refer to Section 4, Normal
Operations, for a description of the test pattern.

WARNING
UNLESS THE SYSTEM IS IN FORCED STANDBY, THE
TRANSMITTER
IS
ON
AND
RADIATING
X--BAND
MICROWAVE ENERGY IN TEST MODE. REFER TO SECTION 6,
MAXIMUM PERMISSIBLE EXPOSURE LEVEL (MPEL), AND THE
APPENDIX, FEDERAL AVIATION ADMINISTRATION (FAA)
ADVISORY CIRCULARS, TO PREVENT POSSIBLE HUMAN BODY
DAMAGE.
FSBY (Forced Standby)
FSBY is an automatic, nonselectable radar mode. As an installation
option, the indicator can be wired to the weight--on--wheels (WOW)
squat switch. When wired, the RTA is in the FSBY mode when the
aircraft is on the ground. In FSBY mode, the transmitter and antenna
scan are both inhibited, the display memory is erased, and the FSBY
legend is displayed in the mode field. When in the FSBY mode,
pushing the STAB button 4 times within 3 seconds, restores normal
operation.
A28-- 1146-- 102-- 03
REV 3

Operating Controls
3-5

PRIMUSr 880 Digital Weather Radar System

WARNING
FORCED STANDBY MODE MUST BE VERIFIED BY THE OPERATOR
TO ENSURE SAFETY FOR GROUND PERSONNEL.
3

TGT (Target)

The TGT button is an alternate- action switch that enables and
disables the radar target alert feature. Target alert is selectable in all but
the 300- mile range. When selected, target alert monitors beyond the
selected range and 7.5° on each side of the aircraft heading. If a return
with target alert characteristics is detected in the monitored area, the
target alert legend changes from the green T armed condition to the
yellow TGT warning condition. (See the target alert characteristics in
table 3- 2 for a target description.) These annunciations advise the pilot
of potentially hazardous targets directly in front of the aircraft that are
outside the selected range. When a yellow warning is received, the pilot
should select longer ranges to view the questionable target. (Note that
target alert is inactive within the selected range.)
Selecting target alert forces the system to preset gain. Target alert can
be selected only in the WX or FP modes.
NOTE:

In order to activate the target alert warning, the target must
have the depth and range characteristics described in table
3- 2.

Operating Controls
3-6

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

Selected Range
(NM)

Minimum Target
Depth (NM)

Target Range
(NM)

5- 55

10- 60

25- 75

50- 100

100

100- 150

200

200- 250

300

N/A

FP (Flight Plan)

5- 55

Target Alert Characteristics
Table 3- 2
4

RCT (Rain Echo Attenuation Compensation Technique
(REACT))

The RCT switch is an alternate- action switch that enables and
disables REACT.
The REACT circuitry compensates for attenuation of the radar signal
as it passes through rainfall. The cyan field indicates areas where
further compensation is not possible. Any target detected within
the cyan field cannot be calibrated and should be considered
dangerous. All targets in the cyan field are displayed as fourth level
precipitation, magenta.
REACT is available in the WX mode only and selecting REACT forces
the system to preset gain. When engaged, the white RCT legend is
displayed in the REACT field.
NOTES:

1. REACT’S three main functions (attenuation
compensation, cyan field, and forcing targets to
magenta) are switched on and off with the RCT switch.
2. Refer to Section 5, Radar Facts, for a description of
REACT.

STB (Stabilization)

The STB button toggles pitch and roll stabilization ON and OFF. It is also
used with the STB adjust mode and to override forced standby.
The radar antenna is normally attitude stabilized. It automatically
compensates for roll and pitch maneuvers (refer to Section 5, Radar
Facts, for a description of stabilization). The STB OFF annunciator is
displayed on the screen.
A28- 1146- 102- 00

Operating Controls
3-7

PRIMUSr 880 Digital Weather Radar System

The radar antenna is normally attitude stabilized. It automatically
compensates for roll and pitch maneuvers (refer to Section 5, Radar
Facts, for a description of stabilization). The STB OFF annunciator is
displayed on the screen.
6

TRB (Turbulence)

The TRB switch is used to select the turbulence detection mode of
operation. The TRB mode can only be selected if the FUNCTION
switch is in the WX position and the selected range is 50 miles or less.
The weather/turbulence mode is annunciated in the mode field with the
WX/T legend. Areas of moderate or greater turbulence are shown in
soft white. The turbulence threshold is five meters per second.

WARNINGS
1. TURBULENCE CAN ONLY BE DETECTED WITHIN AREAS OF
RAINFALL. THE PRIMUSR 880 DIGITAL WEATHER RADAR
SYSTEM CANNOT DETECT CLEAR AIR TURBULENCE.
2. UNDETECTED TURBULENCE CAN EXIST WITHIN ANY
STORM CELL. REFER TO SECTION 5, RADAR FACTS, OF THIS
GUIDE FOR ADDITIONAL INFORMATION.
Selecting the 100--, 200--, or 300--mile range turns off turbulence
detection. The /T is deleted from the mode annunciation. Subsequently
selecting ranges of 50 miles or less re--engages turbulence detection.
A description of the turbulence detection capabilities and limitations is
given in Section 5 , Radar Facts, of this guide.
7

RANGE

The RANGE buttons are two momentary--contact buttons used to
select the operating range of the radar. The range selections are from
5 to 300 NM full scale. In FP mode, additional ranges of 500 and 1000
NM are available. The up arrow selects increasing ranges, and the
down arrow selects decreasing ranges. Each of the five range rings on
the display has an associated marker that annunciates its range.
8

AZ (Azimuth)

The AZ button is an alternate--action switch that enables and disables
the electronic azimuth marks. When enabled, azimuth marks at 30_
intervals are displayed. The azimuth marks are the same color as the
other alphanumerics.
9

SCT (Scan Sector)

Operating Controls
3-8

A28-- 1146-- 102-- 03
REV 3

PRIMUSr 880 Digital Weather Radar System

BRT (Brightness) or BRT/LSS (Lightning Sensor System)

The BRT knob is a single- turn control that adjusts the brightness of the
display. Clockwise (cw) rotation increases display brightness and
counterclockwise (ccw) rotation decreases brightness.
An optional BRT/LSS four- position rotary switch selects the separate
LSZ- 850 Lightning Sensor System (LSS) operating modes and the
brightness control on some models. Its LSS control switch positions are
as follows:
D

OFF - This position removes all power from the LSS.

SBY (Standby) - This position inhibits the display of LSS data, but
the system accumulates data in this mode.

LX (Lightning Sensor System) - In this position the LSS is fully
operational and data is being displayed on the indicator.

CLR/TST (Clear/Test) - In this position accumulated data is cleared
from the memory of the LSS. After 3 seconds the test mode is
initiated in the LSS. Refer to the LSZ- 850 Lightning Sensor System
Pilot’s Handbook, for a detailed description of LSS operation.

TILT

The TILT knob is a rotary control that is used to select the tilt angle of
the antenna beam with relation to the horizon. CW rotation tilts beam
upward to +15_; ccw rotation tilts beam downward to - 15_.
A digital readout of the antenna tilt angle is displayed on the CRT, with
0.5_ resolution.
D

PULL ACT (Altitude Compensated Tilt) Function - When the
TILT control knob is pulled out, the system engages the ACT. In ACT
the antenna tilt is automatically adjusted with regard to the selected
range and barometric altitude. The antenna tilt automatically
readjusts with changes in altitude and/or selected range. In ACT, the
tilt control can fine tune the autotilt setting by ±2°.
ACT is annunciated with an A following the digital tilt readout. The
digital tilt readout always shows the commanded tilt of the antenna
regardless of the tilt command source (ACT command or manual tilt
command).

WARNINGS
1.

TO AVOID FLYING UNDER OR OVER STORMS,
FREQUENTLY SELECT MANUAL TILT TO SCAN BOTH
ABOVE AND BELOW YOUR FLIGHT LEVEL.

ALWAYS USE MANUAL TILT FOR WEATHER ANALYSIS.

A28- 1146- 102- 00

Operating Controls
3-9

PRIMUSr 880 Digital Weather Radar System

GAIN

The GAIN knob is a single- turn rotary control and push/pull switch that
is used to control the receiver gain. Push in on the GAIN switch to enter
the system into the preset calibrated gain mode. Calibrated gain is the
normal mode and is used for weather avoidance. In calibrated gain, the
rotary portion of the GAIN control does nothing. In calibrated gain, the
color bar legend is labeled 1,2,3,4 in WX mode or 1,2,3 in GMAP mode.
Pull out on the GAIN switch to enter the system into the variable gain
mode with VAR displayed in the color bar. Variable gain is useful for
additional weather analysis and for ground mapping. In WX mode,
variable gain can increase receiver sensitivity over the calibrated level
to show very weak targets or it can be reduced below the calibrated
level to eliminate weak returns.

WARNING
HAZARDOUS TARGETS MAY BE ELIMINATED FROM THE DISPLAY WITH LOW SETTINGS OF VARIABLE GAIN.
In the GMAP mode, variable gain is used to reduce the level of the
typically very strong returns from ground targets.
Minimum gain is with the control at its full ccw position. Gain increases
as the control is rotated cw from full ccw . At full cw position, the gain
is at maximum.
In variable gain, the color bar legend contains the variable gain (VAR)
annunciation. Selecting RCT or TGT forces the system into calibrated
gain.

Operating Controls
3-10

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

WC- 880 WEATHER RADAR CONTROLLER
OPERATION
The controls and display features of the WC- 880 Weather Radar
Controller are indexed and identified in figure 3- 4. Brightness levels for
all legend and controls on the indicator are controlled by the dimming
bus for the aircraft panel.
7

OFF
TRB
PULL
VAR

MIN

GAIN

WX
SBY
OFF

MAX

STAB

RCT
GMAP
FP
TST

RADAR

SBY
OFF

TGT
LX
CLR
TST

LSS

SLV

SECT

PULL
ACT

TILT

+
-

2
AD- 46695- R1@

OFF
TRB
PULL
VAR

MIN

GAIN

MAX

WX
SBY
OFF

STAB

RCT
GMAP
FP
TST

RADAR

SLV

TGT
PULL
ACT

TILT

SECT
+
-

2
AD- 46696- R1@

WC- 880 Weather Radar Controller Configurations
Figure 3- 4 (cont)

A28- 1146- 102- 00

Operating Controls
3-11

PRIMUSr 880 Digital Weather Radar System

TRB
PULL
VAR

MIN

GAIN

MAX

WX
SBY
OFF

STAB

TGT

RCT
GMAP
FP
TST

RADAR

SBY
OFF

SLV

SECT
+

LX
CLR
TST

LSS

PULL
ACT

TILT

2
AD- 46697- R1@

WC- 880 Weather Radar Controller Configurations
Figure 3- 4
NOTES:

1. With a controller without built- in range control, range
is controlled from the installed EFIS navigation display
2. Controllers are available with and without the LSS
function.
3. Whenever single or dual radar controllers are used,
the radar data is displayed on the EFIS and/or an MFD
or navigation display (ND).

Operating Controls
3-12

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

RADAR

This rotary switch is used to select one of the following functions.
D

OFF - This position turns the radar system off.

SBY (Standby) - This position places the radar system in standby;
a ready state, with the antenna scan stopped, the transmitter
inhibited, and the display memory erased. STBY is displayed on the
EFIS/MFD.

WX (Weather) - This position selects the weather detection mode.
The system is fully operational and all internal parameters are set
for enroute weather detection.
If WX is selected before the initial RTA warmup period is complete
(approximately 45 to 90 seconds), the WAIT legend is displayed on
the EFIS/MFD. In WAIT mode, the transmitter and antenna scan are
inhibited and the display memory is erased. When the warmup is
complete, the system automatically switches to the WX mode.
The system, in preset gain, is calibrated as described in table 3- 3.
Rainfall Rate

Color

in/hr

mm/hr

.04- .16

1- 4

Green

.16- .47

4- 12

Yellow

.47- 2

12- 50

Red

>5 0

Magenta

Rainfall Rate Color Coding
Table 3- 3
D

RCT (Rain Echo Attenuation Compensation Technique) - This
switch position turns on RCT.
The REACT circuitry compensates for attenuation of the radar
signal as it passes through rainfall. The cyan field indicates areas
where further compensation is not possible. Any target detected
within the cyan field cannot be calibrated and should be considered
dangerous. All targets in the cyan field are displayed as 4th level
precipitation, magenta.
RCT is a submode of the WX mode and selecting RCT forces the
system to preset gain. When RCT is selected, the RCT legend is
displayed on the EFIS/MFD.

A28- 1146- 102- 00

Operating Controls
3-13

PRIMUSr 880 Digital Weather Radar System

NOTES:
1. REACT’s
three
functions
(attenuation
compensation, cyan field, and forcing targets to
magenta) are switched on and off with the RCT
switch.
2.
D

Refer to Section 5, Radar Facts, for a description
of REACT.

GMAP (Ground Mapping) - The GMAP position puts the radar
system in the Ground Mapping mode. The system is fully
operational and all parameters are set to enhance returns from
ground targets.
NOTE:

REACT, TGT, or TRB modes are not selectable in GMAP.

WARNING
WEATHER TYPE TARGETS ARE NOT CALIBRATED WHEN
THE RADAR IS IN THE GMAP MODE. BECAUSE OF THIS, DO NOT
USE THE GMAP MODE FOR WEATHER DETECTION.
As a constant reminder that GMAP is selected, the alphanumerics
are changed to green, the GMAP legend is displayed in the
mode field, and the color scheme is changed to cyan, yellow, and
magenta. Cyan represents the least reflective return, yellow is a
moderate return, and magenta is a strong return.
If GMAP is selected before the initial RTA warmup period is
complete (approximately 45 to 90 seconds), the white WAIT legend
is displayed in the mode field. In wait mode, the transmitter and
antenna scan are inhibited and the memory is erased. When the
warmup period is complete, the system automatically switches to
the GMAP mode.
D

FP (Flight Plan) - The FP position puts the radar system in the flight
plan mode, which clears the screen of radar data so ancillary data
can be displayed. Examples of this data are:
-

Navigation displays
Electrical discharge (lightning) data.

NOTE:

In the FP mode, the radar RTA is put in standby, the
alphanumerics are changed to cyan, and the FLTPLN
legend is displayed in the mode field.

Operating Controls
3-14

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

The target alert mode can be used in the FP mode. With target alert
on and the FP mode selected, the target alert armed annunciation
(green TGT) is displayed. The RTA searches for a hazardous target
from 5 to 55 miles and ±7.5 degrees of dead ahead. No radar
targets are displayed. If a hazardous target is detected, the target alert
armed annunciation switches to the alert annunciation (amber TGT).
This advises the pilot that a hazardous target is in his flightpath and he
should select the WX mode to view it.
NOTE:
D

When displaying checklist, the TGT function is inoperative.

TST (Test) - The TST position selects the radar test mode. A
special test pattern is displayed to verify system operation. The
TEST legend is displayed in the mode field. Refer to Section 4,
Normal Operations, for a description of the test pattern.

WARNING
UNLESS THE SYSTEM IS IN FORCED STANDBY, THE TRANSMITTER IS ON AND RADIATING X- BAND MICROWAVE ENERGY IN
TEST MODE. REFER TO SECTION 6, MAXIMUM PERMISSIBLE
EXPOSURE LEVEL (MPEL).
D

FSBY (Forced Standby) - FSBY is an automatic, nonselectable
radar mode. As an installation option, the indicator can be wired
to the weight- on- wheels (WOW) squat switch. When wired, the
RTA is in the FSBY mode when the aircraft is on the ground. In FSBY
mode, the transmitter and antenna scan are both inhibited, the
display memory is erased, and the FSBY legend is displayed in the
mode field. When in the FSBY mode, pushing the STAB button 4
times in 3 seconds restores normal operation.
The FSBY mode is a safety feature that inhibits the transmitter on the
ground to eliminate the X- Band microwave radiation hazard. Refer to
Section 6, Maximum Permissible Exposure Level (MPEL).

WARNING
FORCED STANDBY MODE MUST BE VERIFIED BY THE OPERATOR TO ENSURE SAFETY FOR GROUND PERSONNEL.
In installations with two radar controllers, it is only necessary to override
forced standby from one controller.
If either controller is returned to standby mode while weight is on
wheels, the system returns to the forced standby mode.
A28- 1146- 102- 00

Operating Controls
3-15

PRIMUSr 880 Digital Weather Radar System

TILT

The TILT switch is a rotary control that is used to select the tilt angle of
antenna beam with relation to the horizon. CW rotation tilts beam
upward 0_ to 15_; ccw rotation tilts beam downward 0_ to - 15_. The
range between +5_ and - 5_ is expanded for ease of setting. A digital
readout of the antenna tilt angle is displayed on the EFIS.
D

PULL ACT (Altitude Compensated Tilt) Function - When the
TILT control knob is pulled out, the system engages the ACT
(option). In ACT , the antenna tilt is automatically adjusted with
regard to the selected range and barometric altitude. The antenna
tilt automatically readjusts with changes in altitude and/or selected
range. In ACT, the tilt control can fine tune the tilt setting by ±2°.
ACT is annunciated with an A following the digital tilt readout. The
digital tilt readout always shows the commanded tilt of the antenna
regardless of the tilt command source (ACT command or manual tilt
command).

WARNINGS
1.

TO AVOID FLYING UNDER OR OVER STORMS,
FREQUENTLY SELECT MANUAL TILT TO SCAN BOTH
ABOVE AND BELOW YOUR FLIGHT LEVEL.

ALWAYS USE MANUAL TILT FOR WEATHER ANALYSIS.

SECT (Scan Sector)

The SECT switch is an alternate- action button that is used to select
either the normal 12 looks/minute 120_ scan or the faster update 24
looks/minute 60_ sector scan.
4

TGT (Target)

The TGT switch is an alternate- action, button that enables and
disables the radar target alert feature. Target alert is selectable in all but
the 300 mile range. When selected, target alert monitors beyond the
selected range and 7.5_ on each side of the aircraft heading. If a return
with certain characteristics is detected in the monitored area, the target
alert changes from the green armed condition to the yellow TGT
warning condition. This annunciation advises the pilot that a potentially
hazardous target lies directly in front and outside of the selected range.
When this warning is received, the pilot should select longer ranges to
view the questionable target. Note that target alert is inactive within the
selected range.
Operating Controls
3-16

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

Selecting target alert forces the system to preset gain. Target alert can
only be selected in the WX and FP modes.
In order to activate target alert, the target must have the depth and
range characteristics described in table 3- 4:
Selected Range
(NM)

Minimum Target
Depth (NM)

Target Range
(NM)

5- 55

10- 60

25- 75

50- 100

100

100- 150

200

200- 250

300

N/A

FP (Flight Plan)

5- 55

WC- 880 Controller Target Alert Characteristics
Table 3- 4
5

STB (Stabilization)

The STB button turns the pitch and roll stability ON and OFF. It is also
used with the STB adjust mode and to override forced standby.
NOTE:
6

Some controllers annunciate OFF when stabilization is OFF.

TRB (Turbulence Detection)

TRB is a switch used to select the turbulence detection mode of
operation. The TRB mode can only be selected if the FUNCTION
switch is in the WX or RCT positions and the selected range is 50 miles
or less. The weather/turbulence mode is annunciated in the mode field
with the WX/T legend. Areas of at least moderate turbulence are shown
in soft white. The turbulence threshold is five meters per second.

A28- 1146- 102- 00

Operating Controls
3-17

PRIMUSr 880 Digital Weather Radar System

WARNINGS
1. TURBULENCE CAN ONLY BE DETECTED WITHIN AREAS OF
RAINFALL. THE PRIMUSR 880 DIGITAL WEATHER RADAR
SYSTEM CANNOT DETECT CLEAR AIR TURBULENCE.
2. UNDETECTED TURBULENCE CAN EXIST WITHIN ANY
STORM CELL. REFER TO SECTION 5, RADAR FACTS, OF THIS
GUIDE FOR ADDITIONAL INFORMATION.
Selecting the 100, 200, or 300 mile range turns off the turbulence
detection. The /T is deleted from the mode annunciation and variable
gain is engaged if previously selected. Subsequent selection of ranges
of 50 miles or less re--engages turbulence detection.
A description of the turbulence detection capabilities and limitations of
this radar system is given in Section 5, Radar Facts, of this guide.
7

RANGE

The RANGE switches are two momentary contact buttons that are used
to select the operating range of the radar (and LSS if installed). The
system permits selection of ranges in WX mode from 5 to 300 NM full
scale. In the flight plan (FPLN) mode, additional ranges of 500 and
1000 miles are permitted. The up arrow selects increasing ranges,
while the down arrow selects decreasing ranges. One--half the
selected range is annunciated at the one--half scale range mark on the
EHSI.
NOTE:

Some Integrated avionics systems incorporate radar range
with the map display range control on a MFD/ND display.

GAIN

The GAIN is a single turn rotary control and push/pull switch that is used
to control the receiver gain. When the GAIN switch is pushed, the
system enters the preset, calibrated gain mode. Calibrated gain is the
normal mode and is used for weather avoidance. In calibrated gain, the
rotary portion of the GAIN control does nothing.
When the GAIN switch is pulled out, the system enters the variable
gain mode. Variable gain is useful for additional weather analysis and
for ground mapping. In WX mode, variable gain can increase receiver
sensitivity over the calibrated level to show weak targets or it can
be reduced below the calibrated level to eliminate weak returns.
Operating Controls
3-18

A28-- 1146-- 102-- 03
REV 3

PRIMUSr 880 Digital Weather Radar System

WARNING
LOW VARIABLE GAIN SETTINGS CAN ELIMINATE HAZARDOUS
TARGETS FROM THE DISPLAY.
In GMAP mode, variable gain is used to reduce the level of strong
returns from ground targets.
Minimum gain is attained with the control at its full ccw position. Gain
increases as the control is rotated in a cw direction from full ccw at full
cw position, the gain is at maximum.
The VAR! legend annunciates variable gain. Selecting RCT or TGT
forces the system into calibrated gain.
9

SLV (Slave)

The SLV annunciator is only used in dual controller installations. With
dual controllers, one controller can be slaved to the other by selecting
OFF on that controller only, with the RADAR mode switch. This slaved
condition is annunciated with the SLV annunciator.
In the slaved condition, both controllers must be off before the
radar system turns off.
10

LSS (Lightning Sensor System) (Option)

The LSS switch is an optional four- position rotary switch that selects
the LSS operating modes described below:
D

OFF - In this position all power is removed from the LSS.

SBY - In this position the display of LSS data is inhibited, but the LSS
still accumulates data.

LX - In this position the LSS is fully operational and it displays LSS
data on the indicator.

CLR/TST - In this position, accumulated data is cleared from the
memory of the LSS. After 3 seconds the test mode is initiated in the
LSS.

A28- 1146- 102- 00

Operating Controls
3-19

PRIMUSr 880 Digital Weather Radar System

WC- 884 WEATHER RADAR CONTROLLER
OPERATION
The controls and display features of the WC- 884 Weather Radar
Controller are indexed and identified in figure 3- 5. Brightness levels for
all legend and controls on the indicator are controlled by the dimming
bus for the aircraft panel.
Whenever single or dual radar controllers are used, the radar data is
displayed on the EFIS, MFD, or NAV display.
1

BRT
TGT
PULL VAR

MIN

GAIN

MAX

STAB

TEST
STBY
OFF

WX
GMAP

MODE

SLV

RCT

TRB
100 PULL ACT
200

50
25
10

300

FPLN

RANGE

TILT

AD- 46698- R2@

WC- 884 Weather Radar Controller
Figure 3- 5
1

BRT (Brightness)

The BRT switch is a rotary control that is used to set the radar (raster)
brightness on the EFIS display.
2

TGT (Target Alert)

The TGT switch is an alternate- action, button that enables and
disables the radar target alert feature. Target alert is selectable in all but
the 300- mile range. When selected, target alert monitors beyond the
selected range and 7.5_ on each side of the aircraft heading. If a return
with certain characteristics is detected in the monitored area, the target
alert changes from the green armed condition to the amber TGT
warning condition. (Refer to the target alert characteristics in table 3- 5
for a target description.) The amber TGT alerts the pilot as to potentially
hazardous targets directly in front and outside of the selected range.
When the alert is given, the pilot should select longer ranges to view
the questionable target. Target alert is inactive within the selected
range.
Operating Controls
3-20

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

Selecting target alert forces the system into preset gain. Target alert
can be selected in the WX and FP modes.
To activate target alert, the target must have the depth and range
characteristics described in table 3- 5:
Selected Range
(NM)

Minimum Target
Depth (NM)

Target Range
(NM)

10- 60

25- 75

50- 100

100

100- 150

200

200- 250

300

N/A

FP (Flight Plan)

5- 55

WC- 884 Controller Target Alert Characteristics
Table 3- 5
3

STB (Stabilization)

The STAB button is a that turns the pitch and roll stabilization ON and
OFF.
This radar is normally attitude stabilized. It automatically compensates
for roll and pitch maneuvers (refer to Section 5, Radar Facts, for a
description of stabilization). The amber STB annunciator appears
on the screen. It is also used with the STB adjust mode, and to override
forced standby.
4

RCT (Rain Echo Attenuation Compensation Technique)

Selecting RCT forces the system to preset gain. When RCT is selected,
the green REACT legend is displayed in the mode field. The RCT
circuitry compensates for attenuation of the radar signal as it passes
through rainfall. The cyan field indicates areas where further
compensation is not possible. Any target detected within the cyan field
cannot be calibrated and should be considered dangerous. All targets
in the cyan field are displayed as fourth level precipitation, magenta.
NOTE:

Refer to Section 5, Radar Facts, for a description of REACT.

A28- 1146- 102- 00

Operating Controls
3-21

PRIMUSr 880 Digital Weather Radar System

TRB (Turbulence Detection)

TRB switch is used to select the turbulence detection mode of
operation. The TRB mode can only be selected if the MODE switch is
in the WX position and the selected range is 50 miles or less. The
weather/turbulence mode is annunciated in the mode field with the
green WX/T legend. Areas of at least moderate turbulence are shown
in soft white.
CAUTION
TURBULENCE CAN ONLY BE DETECTED WITHIN AREAS OF
RAINFALL. THE PRIMUSR 880 DIGITAL WEATHER RADAR
SYSTEM DOES NOT DETECT CLEAR AIR TURBULENCE.

WARNING
UNDETECTED TURBULENCE CAN EXIST WITHIN ANY STORM
CELL. REFER TO SECTION 5, RADAR FACTS, OF THIS GUIDE
FOR ADDITIONAL INFORMATION.
Selecting the 100--, 200--, or 300--mile range turns off the turbulence
detection. The /T is deleted from the mode annunciation and variable
gain is engaged if previously selected. Subsequent selection of ranges
of 50 miles or less re--engages turbulence detection.
A description of the turbulence detection capabilities and limitations can
be found in Section 5, Radar Facts, of this guide.
6

TILT

The TILT switch is a rotary control used to select tilt angle of antenna
beam with relation to the horizon. CW rotation tilts beam upward to
+15_; ccw rotation tilts beam downward to --15_.
A digital readout of the antenna tilt angle is displayed on the EFIS.
D

PULL ACT (Altitude Compensated Tilt) Function -- When the
TILT control knob is pulled out, the system engages the ACT
(option). In ACT, the antenna tilt is automatically adjusted with
regard to the selected range and barometric altitude. The antenna
tilt automatically readjusts with changes in altitude and/or selected
range. In ACT, the tilt control can fine tune the tilt setting by ±2°.
ACT is annunciated with an A following the digital tilt legend. The
digital tilt readout always shows the commanded tilt of the antenna
regardless of the tilt command source (ACT command or manual tilt
command).

Operating Controls
3-22

A28-- 1146-- 102-- 03
REV 3

PRIMUSr 880 Digital Weather Radar System

WARNINGS
1.

TO AVOID FLYING UNDER OR OVER STORMS,
FREQUENTLY SELECT MANUAL TILT TO SCAN BOTH
ABOVE AND BELOW YOUR FLIGHT LEVEL.

ALWAYS USE MANUAL TILT FOR WEATHER ANALYSIS.

RANGE

RANGE is a rotary control used to select one of six ranges (10, 25, 50,
100, 200, and 300 NM). The seventh position of the range switch is flight
plan mode. Selecting FPLN blanks the radar information from the EFIS
display and the mode annunciation flashes if a radiating mode is
selected. The EFIS is set to a range determined by the installation.
Target alert can be used in the FPLN mode. With target alert on in the
FPLN mode, the target alert armed annunciation (green TGT) is displayed.
The RTA becomes active and starts searching for a hazardous target
from 5 to 55 miles and ±7.5_ dead ahead. No radar targets are displayed.
If a hazardous target is detected, the target alert armed annunciation
switches to the alert annunciation (amber TGT). This advisory indicates
that a hazardous target is in the aircraft’s flightpath and the WX mode
should be selected.
8

SLV (Slave)

The SLV annunciator is a dead front annunciator that is only used in dual
controller installations. With dual controllers, one controller can be
slaved to the other by selecting the RADAR mode switch to OFF on that
controller, only. This slaved condition is annunciated with the SLV
annunciator.
In the slaved condition both controllers must be off before the radar
system turns off.
9

MODE

The MODE switch is a rotary switch used to select one of the following
functions:
D
D

OFF - In this position the radar system is turned off.
STBY - In this position the radar system is placed in standby; a
ready state, with the antenna scan stopped, the transmitter
inhibited, and the display memory erased. STBY, in green, is
displayed in the mode field.
If STBY is selected before the initial RTA warmup period is complete
(approximately 45 - 90 seconds), the flashing WAIT legend is
displayed in the mode field.

A28- 1146- 102- 00

Operating Controls
3-23

PRIMUSr 880 Digital Weather Radar System

When the warmup is complete, the system changes the mode field
from WAIT to STBY.
D

TEST- This position selects the radar test mode. A test pattern is
displayed to verify that system operates. The green TEST legend
is displayed in the mode field. Refer to Section 4, Normal
Operation, for a description of the test pattern.

WARNING
UNLESS THE SYSTEM IS IN FORCED STANDBY, THE TRANSMITTER IS ON AND RADIATING X- BAND MICROWAVE ENERGY IN
TEST MODE. REFER TO SECTION 6, MAXIMUM PERMISSIBLE EXPOSURE LEVEL (MPEL).
D

WX - In this position, the radar system is fully operational and all
internal parameters are set for enroute weather detection.
If WX is selected before the initial RTA warmup period is complete, a
flashing WAIT legend is displayed. In WAIT mode, the transmitter
and antenna scan are inhibited and the memory is erased. When the
warmup is complete, the system automatically switches to the WX
mode and a green WX is displayed in mode field.
The system, in preset gain, is calibrated given in table NO TAG.
Rainfall Rate

Color

in/hr

mm/hr

.04- .16

1- 4

Green

.16- .47

4- 12

Yellow

.47- 2

12- 50

Red

>5 0

Magenta

Rainfall Rate Color Coding
Table 3- 6
D

GMAP - Selecting GMAP places the radar system in the ground
mapping mode. The system is fully operational and all internal
parameters are set to enhance returns from ground targets. RCT
compensation is inactive.

WARNING
WEATHER TYPE TARGETS ARE NOT CALIBRATED WHEN
THE RADAR IS IN THE GMAP MODE. BECAUSE OF THIS, DO
NOT USE THE GMAP MODE FOR WEATHER DETECTION.
Operating Controls
3-24

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

When GMAP is selected, a green GMAP legend is displayed and the
color scheme is changed to cyan, yellow, magenta. Cyan
represents the least reflective return, yellow is a moderate return,
and magenta is a strong return.
If GMAP is selected before the initial RTA warmup period is
complete, a flashing WAIT legend is displayed. In WAIT mode, the
transmitter and antenna scan are inhibited and the memory is
erased. When the warmup is complete, the system automatically
switches to the GMAP mode.

WARNING
THE SYSTEM PERFORMS ONLY THE FUNCTIONS OF WEATHER
DETECTION OR GROUND MAPPING. IT CANNOT BE RELIED
UPON FOR PROXIMITY WARNING OR ANTICOLLISION
PROTECTION.
D

FSBY - Forced standby is an automatic, nonselectable radar
mode. As an installation option, the controllers can be wired to the
WOW squat switch. When wired, the RTA is in the forced standby
mode when the aircraft is on the ground. In the forced standby
mode, the transmitter and antenna scan are both inhibited, the
memory is erased, and the amber FSBY legend is displayed in the
mode field. When in the forced standby mode, pushing the STAB
button 4 times in 3 seconds, exits the mode.
FSBY mode is a safety feature that inhibits the transmitter on the
ground to eliminate the X- band microwave radiation hazard. Refer
to Section 6, Maximum Permissible Exposure Level (MPEL).
NOTE:

In dual installations, overriding the forced standby using
the TGT button is done on only one controller.

WARNING
FORCED STANDBY MODE MUST BE VERIFIED BY THE OPERATOR
TO ENSURE SAFETY FOR GROUND PERSONNEL.
10

GAIN

The GAIN is a single- turn rotary control and push/pull switch that is
used to control the receiver gain. When the GAIN switch is pushed, the
system enters the preset, calibrated gain mode. Calibrated gain is the
normal mode and is used for weather avoidance. In calibrated gain, the
rotary portion of the GAIN control does nothing.
When the GAIN switch is pulled out, the system enters the variable gain
mode. Variable gain is useful for additional weather analysis and for
ground mapping. In WX mode, variable gain can increase receiver
sensitivity over the calibrated level to show weak targets or it can be
reduced below the calibrated level to eliminate weak returns.
A28- 1146- 102- 00

Operating Controls
3-25

PRIMUSr 880 Digital Weather Radar System

WARNING
WHEN LOW SETTINGS OF VARIABLE GAIN ARE USED,
HAZARDOUS TARGETS CAN BE ELIMINATED FROM
THE DISPLAY.
In the GMAP mode, variable gain is used to reduce the level of the
typically very strong returns from ground targets.
Minimum gain is with the control at its full ccw position. Gain increases
as the control is rotated in a cw direction from full ccw. At the full cw
position, the gain is at maximum.
The VAR legend annunciates variable gain. Selecting RCT or TGT forces
the system into preset gain. Preset gain is not annunciated.

HIDDEN MODES
The PRIMUSâ 880 has five hidden modes that are summarized as
follows:
D

Forced Standby (FSBY) Override

Roll Offset

Roll Gain (NOTE)

Pitch Offset (NOTE)

Pitch Gain (NOTE).

NOTE:

At the time of installation, the programming strap STAB TRIM
ENABLE, determines if the roll and pitch gain, and pitch offset
adjustment features are available. Consult the aircraft
installation information to determine the installed
configuration.

Forced Standby Override
D

Function - Forced standby places the radar in a standby mode
on the ground that prevents the radar from radiating and
therefore, exposing ground personnel to radiation exposure.
This mode is annunciated as FSBY (STBY on EFIS) in systems
where mode annunciations are made.

Entry Method - Power up aircraft on the ground or land the
aircraft with the radar powered.

Exit Method - Push the STAB button 4 times within 3 seconds
on radar indicator or on controller.

Operating Controls
3-26

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

Roll Offset
D

Function - Roll offset permits exact compensation of the
antenna roll to eliminate the effects of small errors in the aircraft
radar installation. Constantly lopsided ground returns can be
eliminated. (Refer to Section 5, Radar Facts, table 5- 5.)

Entry Method - Using only one controller that is in the WX and
variable gain modes, select RCT OFF. Push STB 4 times within
3 seconds. Verify that VAR and RCT are not displayed.
D

Control - The GAIN control is used to adjust the roll offset.
Exit Method - Push STAB (once) to continue with the next
adjustment.

Roll Gain
D

Function - Roll gain corrects the installation at bank angles over
20°, for unsymmetrical radar displays.

Entry Method - Selected by sequencing through the roll offset
and pitch offset menus with the STAB button. (Refer to Section
5, Radar Facts, table 5- 9.)
D

Control - Pull GAIN knob out and use it.
Exit Method - Push STAB (once) to continue with the next
adjustment.

Pitch Offset
D

Function - Adjusts the pitch attitude of the antenna to allow
radar returns, in straight and level flight, to conform to the radar
range rings.

Entry Method - Selected by sequencing through the roll offset
menu with the STAB button. (Refer to Section 5, Radar Facts,
table 5- 8.)
D

Control - Pull the GAIN knob out and use it.
Exit Method - Push STAB (once) to continue with the next
adjustment.

Pitch Gain
D

Function - Adjusts the gain if the radar display is in pitch so that
the contour lines track the range lines at higher pitch attitudes.

A28- 1146- 102- 00

Operating Controls
3-27

PRIMUSr 880 Digital Weather Radar System

Entry Method - Selected by sequencing through the roll offset,
pitch offset, and roll gain menus with the STAB button. (Refer to
Section 5, Radar Facts, table 5- 10.)

D
D

Control - Pull the GAIN knob out and use it.
Exit Method - Push the GAIN knob in. Push STAB to exit and
save settings.

NOTES:

1. If installation is configured only for roll offset
adjustment, pushing the STB button saves and exits
after the roll offset adjustment is made.
2. Upon exiting, stabilization may be either OFF or ON
depending on how many times it was pushed during
the procedure. Be sure to set stabilization OFF or ON
as desired.
3. If upon entering the adjustment mode, no changes are
desired, keep the gain knob pushed in and repeatedly
push STAB until the mode is exited.

Operating Controls
3-28

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

Normal Operation

PRELIMINARY CONTROL SETTINGS
Table 4--1 gives the proper power--up procedure for the PRIMUSR 880
Digital Weather Radar System.
Step

Procedure

Verify that the system controls are in the positions
described below before powering up the radar system:
Mode control: Off
GAIN control: Preset Position
TILT control:
+15

Take the following precautions, if the radar system will be
operated in any mode other than standby or forced
standby while the aircraft is on the ground:
D

Direct nose of aircraft so that antenna scan sector is
free of large metallic objects such as hangars or
other aircraft for a minimum distance of 100 feet (30
meters), and tilt the antenna fully upwards.

Do not operate the radar system during aircraft
refueling or during refueling operations within 100
feet (30 meters).
Do not operate the radar if personnel are standing
too close to the 120_ forward sector of aircraft.
(Refer to Section 6, Maximum Permissible
Exposure Level, in this guide.)
Operating personnel should be familiar with FAA AC
20--68B, which is reproduced in Appendix A of this
guide.

If the system is being used with an EFIS display,
power--up by selecting the weather display on the
EHSI. Apply power to the radar system using either
the indicator or controller power controls.

Select either Standby or Test mode.
PRIMUSR 880 Power--Up Procedure
Table 4--1 (cont)

A28-- 1146-- 102-- 03
REV 3

Normal Operation
4-1

PRIMUSr 880 Digital Weather Radar System

Step

Procedure

When power is first applied the radar is in WAIT for
approximately 90 seconds to allow the magnetron to
warm up. Power sequences ON- OFF- ON lasting less
than 3 seconds result in a 6- second wait period.
NOTE:

If forced standby is incorporated, it is necessary
to exit forced standby.

WARNING
OUTPUT POWER IS RADIATED IN TEST MODE.
6

After the warm- up, select the Test mode and verify
that the test pattern is displayed as shown in figure
4- 1. If the radar is being used with an EFIS, the test
pattern is similar to that shown in figures 4- 2 and 4- 3.
Verify that the yellow antenna position indicator (API)
is shown at the top of the display.

Verify that the azimuth marks, target alert (TGT), and
sector scan controls are operational.
PRIMUSâ 880 Power- Up Procedure
Table 4- 1

Indicator Test Pattern 120_ Scan (WX),
With TEXT FAULT Enabled
Figure 4- 1
Normal Operation
4-2

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

TGT OR VAR ANNUNCIATOR
TGT::

P880 WX
MODE
ANNUNCIATIONS

WX RANGE
RINGS
(WHITE)

DTRK

315

VAR::

MAG1

321

TARGET ALERT
-- GREEN--SELECTED
-- AMBER TGT DETECTED
VARIABLE GAIN (AMBER)

TGT

FMS1
130 NM

TEST
+11

TEXT AREA

ANTENNA
TILT
ANGLE

V
VOR1
VOR2
HDG

319

GRAY
MAGENTA

BLUE
25
15

GSPD
260 KTS

YELLOW

RED

WX RANGE
ANNUNCIATOR
(WHITE)
NOTES:

GREEN

1. IF THE BITE DETECTS A FAULT IN TEST MODE, FAIL ”N” WILL BE SHOWN.
”N” IS A FAULT CODE
2. ANY FAULT CODE CAN ALSO BE DISPLAYED IN THE MAINTENANCE MODE.
IN THAT CASE, IT REPLACES THE ANTENNA TILT ANGLE.

NOTES:

AD--46700--R2@

1. Refer to the specific EFIS document for a detailed
description.
2. The example shown is for installations with TEXT
FAULT disabled.

EFIS Test Pattern (Typical) 120_ Scan Shown (WX)
Figure 4--2

A28-- 1146-- 102-- 03
REV 3

Normal Operation
4-3

PRIMUSr 880 Digital Weather Radar System

WI--880 Indicator Test Pattern With TEXT FAULT Enabled
Figure 4--3

Standby
When Standby is selected, and the radar is not in dual control mode
(refer to table 2--1, dual control mode truth table, for dual control
operation), the antenna is stowed in a tilt--up position and is neither
scanning nor transmitting.
Standby should be selected when the pilot wants to keep power applied
to the radar without transmitting.

Radar Mode -- Weather
For purposes of weather avoidance, pilots should familiarize
themselves with FAA Advisory Circular AC 00--24B (1--20--83).Subject:
“Thunderstorms.” The advisory circular is reproduced in Appendix A of
this guide.
To help the pilot categorize storms as described in the advisory circular
referenced above, the radar receiver gain is calibrated in the WX mode
with the GAIN control in the preset position. The radar is not calibrated
when variable gain is being used, but calibration is restored if RCT,
TRB, or target alert (TGT) is selected.

Normal Operation
4-4

A28-- 1146-- 102-- 03
REV 3

PRIMUSr 880 Digital Weather Radar System

To aid in target interpretation, targets are displayed in various colors.
Each color represents a specific target intensity. The intensity levels
chosen are related to the National Weather Service (NWS) video
integrated processor (VIP) levels.
In the WX mode, the system displays five levels as black, green, yellow,
red, and magenta in increasing order of intensity.
If RCT is selected, the radar receiver adjusts the calibration
automatically to compensate for attenuation losses as the radar pulse
passes through weather targets on its way to illuminate other targets.
There is a maximum extent to which calibration can be adjusted. When
this maximum value is reached, REACT compensation ceases. At this
point, a cyan field is added to the display to indicate that no further
compensation is possible.
In the absence of intervening targets, the range at which the cyan field
starts is approximately 290° with a 12--inch antenna. For the 18-- and
24--inch antennas, the cyan field starts beyond 300 NM and therefore
will not be seen if there are no intervening targets.
The RCT feature includes attenuation compensation (Refer to Section
5, Radar Facts, of this guide for a description of attenuation
compensation.). Rainfall causes attenuation and attenuation
compensation modifies the color calibration to maintain calibration
regardless of the amount of attenuation. Modifying the color calibration
results in a change in the point where calibration can no longer keep the
radar system calibrated for red level targets. The heavier the rainfall,
the greater the attenuation and the shorter the range where XSTC runs
out of control. Therefore, the range at which the cyan
background starts varies depending on the amount of attenuation. The
greater the attenuation, the closer the start of the cyan field.
The radar’s calibration includes a nominal allowance for radome losses.
Excessive losses in the radome seriously affect radar calibration. One
possible means of verification are signal returns from known targets.
Honeywell recommends that the pilot report evidence of weak returns
to ensure that radome performance is maintained at a level that does
not affect radar calibration.
Target alert can be selected in any WX range. The target alert circuit
monitors for hazardous targets within 7.5_ of the aircraft centerline.

A28-- 1146-- 102-- 03
REV 3

Normal Operation
4-5

PRIMUSr 880 Digital Weather Radar System

Radar Mode - Ground Mapping
NOTE:

Refer to Tilt Management in Section 5, Radar Facts, for
additional information on the use of tilt control.

Ground- mapping operation is selected by setting the controls
to GMAP. The TILT control is turned down until a usable amount of
navigable terrain is displayed. The degree of down- tilt depends on the
aircraft altitude and the selected range.
The receiver STC characteristics are altered to equalize ground- target
reflection versus range. As a result, selecting preset GAIN generally
creates the desired mapping display. However, the pilot can control the
gain manually (by selecting manual gain and rotating the GAIN control)
to help achieve an optimum display.
With experience, the pilot can interpret the color display patterns that
indicate water regions, coast lines, hilly or mountainous regions, cities,
or even large structures. A good learning method is to practice
ground- mapping during flights in clear visibility where the radar display
can be visually compared with the terrain.

TEST MODE
The PRIMUSâ 880 Digital Weather Radar System has a self- test mode
and a maintenance function.
In the self- test (TST) mode a special test pattern is displayed as
illustrated earlier in this section. The functions of this pattern are as
follows:
D

Color Bands - A series of green/yellow/red/magenta/white bands,
indicate that the signal to color conversion circuits are operating
normally.

The maintenance function lets the pilot or the line maintenance
technician determine the major fault areas. The fault data can be
displayed in one of two ways (selected at the time of installation):
D

TEXT FAULT - A plain English text indicating the failure is placed
in the test band.

Fault code - A fault code is displayed, refer to the maintenance
manual for an explanation.

The indicator or EFIS display indicates a fault as noted below.
D

Dedicated Radar Indicator - A FAIL annunciation is shown at the
top left corner of the test pattern. It indicates that the built- in test
equipment (BITE) circuitry is detecting a malfunction. The exact
nature of the malfunction can be seen by selecting TEST. (Refer to
Section 7, In- Flight Troubleshooting.)

Normal Operation
4-6

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

EFIS/MFD/ND - Faults are normally shown when test is selected.
NOTES:

1. Some weather failures on EFIS are annunciated
with an amber WX.
2. Some EFIS installations can power up with an
amber WX if weather radar is turned off.
3. If the fault code option is selected, they are shown
with the FAIL annunciation (e.g., FAIL 13).

A28- 1146- 102- 00

Normal Operation
4-7/(4-8 blank)

PRIMUSr 880 Digital Weather Radar System

Radar Facts

RADAR OPERATION
The PRIMUSâ 880 Digital Weather Radar works on an echo principle.
The radar sends out short bursts of electromagnetic energy that travel
through space as a radio wave. When the traveling wave of energy
strikes a target, some of the energy reflects back to the radar receiver.
Electronic circuits measure the elapsed time between the transmission
and the reception of the echo to determine the distance to the target
(range). Because the antenna beam is scanning right and left in
synchronism with the sectoring sweep on the indicator, the bearing of
the target is found, as shown in figure 5- 1.
The indicator with the radar is called a plan- position indicator (PPI)
type. When an architect makes a drawing for a house, one of the views
he generally shows is a plan view, a diagram of the house as viewed
from above. The PPI aboard an airplane presents a cross sectional
picture of the storm as though viewed from above. In short, it is NOT
a horizon view of the storm cells ahead but rather a MAP view. This
positional relationship of the airplane and the storm cells, as displayed
by the indicator, is shown in figure 5- 1.

A28- 1146- 102- 00

Radar Facts
5-1

PRIMUSr 880 Digital Weather Radar System

AIRCRAFT HEADING

100

+0.6

AD- 12055- R2@

Positional Relationship of an Airplane and
Storm Cells Ahead as Displayed on Indicator
Figure 5- 1
The drawing is laid out to simulate the face of the indicator with the
semicircular range marks. To derive a clearer concept of the picture that
the indicator presents, imagine that the storm is a loaf of sliced bread
standing on end. From a point close to the surface of earth, it towers
to a high- altitude summit. Without upsetting the loaf of bread, the radar
removes a single slice from the middle of the loaf, and places this slice
flat upon the table. Looking at the slice of bread from directly above, a
cross section of the loaf can be seen in its broadest dimension. In the
same manner, the radar beam literally slices out a horizontal cross
section of the storm and displays it as though the viewer was looking
Radar Facts
5-2

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

at it from above, as shown in figure 5- 2. The height of the slice selected
for display depends upon the altitude and also upon the upward or
downward TILT adjustment made to the antenna.

Antenna Beam Slicing Out Cross Section of Storm
During Horizontal Scan
Figure 5- 2
Weather radar can occasionally detect other aircraft, but it is not
designed for this purpose and should never be considered a
collision- avoidance device. Nor is weather radar specifically designed
as a navigational aid, but it can be used for ground mapping by tilting
the antenna downward. Selecting the GMAP mode enhances returns
from ground targets.

A28- 1146- 102- 00

Radar Facts
5-3

PRIMUSr 880 Digital Weather Radar System

When the antenna is tilted downward for ground mapping, two
phenomena may occur that can confuse the pilot. The first is called ”The
Great Plains Quadrant Effect”that is seen most often when flying over
the great plains of central United States. In this region, property lines
(fences), roads, houses, barns, and power lines tend to be laid out in
a stringent north- south/east- west orientation. As a result, radar
returns from these cardinal points of the compass tend to be more
intense than returns from other directions and the display shows these
returns as bright north/south/east/west spokes overlaying the ground
map.
The second phenomenon is associated with radar returns from water
surfaces (generally called sea clutter), as shown in figure 5- 3. Calm
water reflects very low radar returns since it directs the radar pulses
onward instead of backward (i.e. the angle of incidence from mirrored
light shone on it at an angle). The same is true when viewing choppy
water from the upwind side. The downwind side of waves, however, can
reflect a strong signal because of the steeper wave slope. A relatively
bright patch of sea return, therefore, indicates the direction of surface
winds.
REFLECTION

CALM WATER OR WATER WITH
SWELLS DOES NOT PROVIDE
GOOD RETURN.

CHOPPY WATER PROVIDES
GOOD RETURN FROM
DOWNWIND SIDE OF WAVES
WIND DIRECTION AT
SURFACE OF WATER

PATCH
OF SEA
RETURNS

AD- 12056- R2@

Sea Returns
Figure 5- 3
Radar Facts
5-4

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

TILT MANAGEMENT
The pilot can use tilt management techniques to minimize ground
clutter when viewing weather targets.
Assume the aircraft is flying over relatively smooth terrain which is
equivalent to sea level in altitude. The pilot must make adjustments for
the effects of mountainous terrain.

ELEVATION IN FEET

The figures below help to visualize the relationship between tilt angle,
flight altitude, and selected range. Figures 5- 4 and 5- 5 show the
distance above and below aircraft altitude that is illuminated by the
flat- plate radiator during level flight with 0_ tilt. Figures 5- 6 and 5- 7
show a representative low altitude situation, with the antenna adjusted
for 2.8_ up- tilt.
80,000
70,000
60,000

41,800 FT

ZERO TILT

50,000

10,500 FT

30,000

10,500 FT

7.9

20,000

20,000 FT
CENTER OF RADAR BEAM
20,000 FT
41,800 FT

10,000
0
0

50
RANGE NAUTICAL MILES

100
AD- 35693@

Radar Beam Illumination High Altitude
12- Inch Radiator
Figure 5- 4

ELEVATION IN FEET

80,000
70,000
ZERO TILT

60,000

7,400 FT

50,000
30,000

5.6

20,000
10,000
0

7,400 FT

29,000 FT
14,800 FT
CENTER OF RADAR BEAM
14,800 FT
29,000 FT

50
RANGE NAUTICAL MILES

100
AD- 17717- R1@

Radar Beam Illumination High Altitude
18- Inch Radiator
Figure 5- 5
A28- 1146- 102- 00

Radar Facts
5-5

PRIMUSr 880 Digital Weather Radar System

ELEVATION IN FEET

40,000
ANTENNA ADJUSTED
FOR 2.8 UPTILT

30,000

20,900 FT
20,000
10,500 FT

7.9

4,200 FT

10,000

20,900 FT

10,500 FT
1.15

4,200 FT

5,000

30
40
50
RANGE NAUTICAL MILES

AD- 17718- R1@

Radar Beam Illumination Low Altitude
12- Inch Radiator
Figure 5- 6

ELEVATION IN FEET

40,000
ANTENNA ADJUSTED
FOR 2.8 UPTILT
30,000
14,000 FT
20,000
3,000 FT
10,000

14,000 FT

7,400 FT

5,000
0

7,400 FT

5.6

3,000 FT
0

RANGE NAUTICAL MILES

AD- 17719@

Radar Beam Illumination Low Altitude
18- Inch Radiator
Figure 5- 7

Radar Facts
5-6

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

Tables 5- 1 and 5- 2 give the approximate tilt settings at which ground
targets begin to be displayed on the image periphery for 12- and
18- inch radiators. The range at which ground targets can be observed
is affected by the curvature of the earth, the distance from the aircraft
to the horizon, and altitude above the ground. As the tilt control is
rotated downward, ground targets first appear on the display at less
than maximum range.
NOTE:

Operation with a 24- inch radiator is similar.

To find the ideal tilt angle after the aircraft is airborne, adjust the TILT
control so that groundclutter does not interfere with viewing of weather
targets. Usually, this can be done by tilting the antenna downward in 1_
increments until ground targets begin to appear at the display periphery.
Ground returns can be distinguished from strong storm cells by
watching for closer ground targets with each small downward increment
of tilt. The more the downward tilt, the closer the ground targets that
are displayed.
When ground targets are displayed, move the tilt angle upward in 1_
increments until the ground targets begin to disappear. Proper tilt
adjustment is a pilot judgment, but typically the best tilt angle lies where
ground targets are barely visible or just off the radar image.
Tables 5- 1 and 5- 2 give the approximate tilt settings required for
different altitudes and ranges. If the altitude changes or a different
range is selected, adjust the tilt control as required to minimize ground
returns.

A28- 1146- 102- 00

Radar Facts
5-7

PRIMUSr 880 Digital Weather Radar System

RANGE
SCALE
(NM)

100

200

- 12

-4

-1

- 10

-3

-8

-2

-6

-1

-4

300

LINE OF
SIGHT
(NM)

35,000
30,000
25,000
20,000
15,000

- 11

-2

10,000

-6

-0

-1

5,000

-5

4,000

-4

3,000

-2

2,000

1,000

246
(LINE OF SIGHT LIMITED REGION)

40,000

(TILT LIMITED
REGION)

ALTITUDE
(FEET)
230
213
195
174
151
123
87
78
67
55
39
AD- 29830- R2@

Approximate Tilt Setting for Minimal Ground Target Display
12- Inch Radiator
Table 5- 1
Tilt angles shown are approximate. Where the tilt angle is not listed, the
operator must exercise good judgment.
NOTE:
Radar Facts
5-8

The line of sight distance is nominal. Atmospheric conditions
and terrain offset this value.
A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

RANGE
SCALE
(NM)

100

- 12

-8

- 11

-8

- 10

-7

- 13

-9

-7

- 11

-8

-6

- 10

-7

-6
-5

200

ALTITUDE
(FEET)

30,000
25,000
20,000
15,000
10,000

- 13

-8

-6

5,000

-9

-6

-5

4,000

-8

-6

-5

3,000

-7

-5

2,000

-6

-5

-4

1,000

-5

-4

246
(LINE OF SIGHT LIMITED REGION)

35,000

(TILT LIMITED
REGION)

40,000

LINE OF
SIGHT
(NM)

230
213
195
174
151
123
87
78
67
55
39
AD- 35710@

Approximate Tilt Setting for Minimal Ground Target Display
18- Inch Radiator
Table 5- 2
Tilt angles shown are approximate. Where the tilt angle is not listed, the
operator must exercise good judgment.
NOTE:

The line of sight distance is nominal. Atmospheric conditions
and terrain offset this value.

A28- 1146- 102- 00

Radar Facts
5-9

PRIMUSr 880 Digital Weather Radar System

Range
Scale
(NM)
Altitude
(Feet)

100

200

40,000

-6

-3

-2

246

35,000

-5

-2

230
213

0.5

1.0

2.5

-4

-2

-8

-3

-1

-6

-2

-1

30,000
(TILT LIMITED
REGION)

25,000
20,000

-4

-1

-8

-2

-8

-3

15,000
10,000
5,000

-6

-2

-9

-4

-1

4,000
3,000

500

-7

195
174
151
123
87
78
67

-6

-2

-7

-2

-3

2,000
1,000

(LINE OF SIGHT LIMITED REGION)

Line of
Sight
(NM)

27
AD- 50232@

Approximate Tilt Setting for Minimal Ground Target Display
24- Inch Radiator
Table 5- 3
Tilt angles shown are approximate. Where the tilt angle is not listed,
the operator must exercise good judgement.
NOTE:

Radar Facts
5-10

The line of sight distance is nominal. Atmospheric
conditions and terrain offset this value.

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

Tilt management is often misunderstood. It is crucial to safe operation
of airborne weather radar. If radar tilt angles are not properly managed,
weather targets can be missed or underestimated.
The upper levels of convective storms are the most dangerous because
of the probability of violent windshears and large hail. But hail and
winshear are not very reflective because they lack reflective liquid
water.
The figures that follow show the relationship between flight situations
and the correct tilt angle. The first describes a high altitude situation; the
second describes a low altitude situation.
D

The ideal tilt angle shows a few ground targets at the edge of the
display (see figure 5- 8).
GROUND
RETURN

AD- 35694@

Ideal Tilt Angle
Figure 5- 8
D

Earth’s curvature can be a factor if altitude is low enough, or if the
selected range is long enough, as shown in figure 5- 9.
GROUND
RETURN

AD- 35695@

Earth’s Curvature
Figure 5- 9
A28- 1146- 102- 00

Radar Facts
5-11

PRIMUSr 880 Digital Weather Radar System

Convective thunderstorms become much less reflective above the
freezing level. This reflectivity decreases gradually over the first
5000 to 10,000 feet above the freezing level, as shown in figure
5- 10.

FREEZING LEVEL

AD- 35696@

Convective Thunderstorms
Figure 5- 10
The aircraft in figure 5- 10 has a clear radar indication of the
thunderstorm, probably with a shadow in the ground returns behind
it.
D

If the tilt angle shown in figure 5- 11 is not altered, the thunderstorm
appears to weaken as the aircraft approaches it.

FREEZING LEVEL

AD- 35697@

Unaltered Tilt
Figure 5- 11

Radar Facts
5-12

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

Proper tilt management demands that tilt be changed continually
when approaching hazardous weather so that ground targets are
not painted by the radar beam, as shown in figure 5- 12.

FREEZING
LEVEL

AD- 35698@

Proper Tilt Technique
Figure 5- 12
D

After heading changes in a foul weather situation, the pilot should
adjust the tilt to see what was brought into the aircraft’s flightpath by
the heading changes, as shown in figure 5- 13.

DISPLAY BEFORE
TURN

DISPLAY AFTER
TURN

THUNDERSTORM WAS OUT
OF DISPLAY BEFORE TURN
AND IS NOW UNDER BEAM
AD- 30429@

Tilt Management With Heading Changes
Figure 5- 13
A28- 1146- 102- 00

Radar Facts
5-13

PRIMUSr 880 Digital Weather Radar System

Under the right conditions, a dangerous thunder bumper can
develop in 10 minutes, and can in fact spawn and mature under the
radar beam as the aircraft approaches it, as shown in figure 5- 14.
If flying at 400 kt groundspeed, a fast developing thunderstorm that
spawns 67 NM in front of the aircraft can be large enough to damage
the aircraft by the time it arrives at the storm.
THUNDERSTORM MATURES
AS IT APPROACHES

FREEZING
LEVEL

AD- 35699@

Fast Developing Thunderstorm
Figure 5- 14
D

At low altitude, the tilt should be set as low as possible to get ground
returns at the periphery only as shown in figure 5- 15.

CORRECT

WRONG

FREEZING
LEVEL

AD- 35700@

Low Altitude Tilt Management
Figure 5- 15
Excess up- tilt should be avoided as it can illuminate weather above
the freezing level.
NOTE:
Radar Facts
5-14

The pilot should have freeze level information as a part of
the flight planning process.
A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

The antenna size used on the aircraft alters the best tilt settings by
about 1_. However, tilt management is the same for either size, as
shown in figure 5- 16.
10- IN. ANTENNA
HAS 10 BEAM

12- IN. ANTENNA
HAS 7.9 BEAM
18- IN. ANTENNA
HAS 5.6 BEAM
24- IN. ANTENNA
HAS 4.2 BEAM

Antenna Size and Impact on Tilt Management
Figure 5- 16
NOTE:
D

A 10- inch antenna is shown for illustration purposes only.

Some of the rules of thumb are described below and shown in figure
5- 17.
-

A 1_ look down angle looks down 100 ft per mile
Bottom of beam is 1/2 beam width below tilt setting
A 12- inch antenna grazes the ground at 100 NM if set to 0_ tilt
at 40,000 ft.
TILT

BEAM WIDTH

AD- 35702@

Rules of Thumb
Figure 5- 17

A28- 1146- 102- 00

Radar Facts
5-15

PRIMUSr 880 Digital Weather Radar System

ALTITUDE COMPENSATED TILT (ACT)
The PRIMUSâ 880 Digital Weather Radar has an ACT feature that can
be selected by pulling out the tilt control knob. This feature is
annunciated on the radar display by adding an A suffix to the tilt readout.
While in ACT or manual tilt the digital tilt readout always shows the
actual (true) tilt of the antenna.
In ACT, the antenna tilt is automatically adjusted with regard to the
selected range and the aircraft’s barometric attitude. ACT adjusts the
tilt to show a few ground targets at the edge of the display. In ACT, the
ideal setting can be adjusted ± 2°to accommodate terrain height or
pilot preferences.
NOTE:

Since ACT uses air data computer barometric altitude to
adjust the tilt, operating near high altitude airports or even
high terrain can result in a lower than desired tilt angle. In such
cases, use of the manual tilt is recommended.

To calculate the tilt angle, the weather radar uses the air data
computer’s barometric altitude with reference to an assumed ground
level of 2000 feet above sea level. This assumed ground level is a factor
during low altitude flight, especially when flying in mountainous areas.
The ground targets that are usually at the edge of the display tend to
migrate to the middle of the display. This also happens when longer
ranges (200 NM to 300 NM) are selected and the altitude is such that
the earth’s curvature is a factor.
In ACT the range control can be used to sweep the beam along the
ground to look for storms at various ranges, as shown in figure 5- 18.
ACT is best suited for high altitude operation while in the weather
surveillance mode; i.e., aircraft is in cruise and there is no weather
within 100 NM. The operator can then use the range control to
frequently sweep the beam down to avoid overflying any fast
developing storms.
At lower altitudes, manual tilt should be used to frequently sweep above
and below the flight level to avoid flying under or over storms, as shown
in figure 5- 18. Manual tilt should also be used exclusively when
analyzing weather.
NOTE:

Radar Facts
5-16

The radar system does not have enough information to be
able to tilt the beam into the wet, lower portions of cells by
itself. The operator must manage tilt dynamically or manually
to locate and analyze weather. ACT simply adjusts the beam
to the earth’s surface at the selected maximum range. Also,
it assumes that the surface is at 2000 feet above sea level.
A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

50
100

NM
AD- 35703@

Manual Tilt at Low Altitudes
Figure 5- 18

A28- 1146- 102- 00

Radar Facts
5-17

PRIMUSr 880 Digital Weather Radar System

STABILIZATION
The purpose of the stabilization system is to hold the elevation of the
antenna beam relative to the earth’s surface constant at all azimuths,
regardless of aircraft bank and pitch maneuvers. The stabilization
system uses the aircraft attitude source as a reference.
Several sources of error exist in any stabilization system.

Dynamic Error
Dynamic error is the basis of the stabilization system. Stabilization is
a corrective process. It logically follows that there must first be some
error to correct. In stabilization, this error is called dynamic. An
example of dynamic error occurs when a gust lifts the right wing and the
pilot instinctively raises the right aileron and lowers the left. In this
action, the pilot detects a changing (dynamic) error in aircraft attitude
and corrects it.
As the gust lifts the wing, the aircraft attitude source sends a continuous
stream of attitude change information to stabilization circuits which, in
turn, control the motors that raise and lower the beam. In short, a
dynamic error in aircraft attitude (as seen by the radar) is detected, and
the antenna attitude is corrected for it. Extremely small errors of less
than 1_ can be detected and compensated. However, the point is
ultimately reached where dynamic error is too small to be detected.
Without detection, there is no compensation.

Accelerative Error
One of the most common forms of error seen in a radar- antenna
stabilization system results from forces of acceleration on the aircraft
equipped with a vertical gyroscope. Acceleration forces result from
speeding up, slowing down, or turning. Radar stabilization
accuracy depends upon the aircraft vertical gyroscope. Therefore,
any gyroscopic errors accumulated through acceleration are
automatically imparted to the antenna stabilization system.
A vertical gyroscope contains a gravity- sensitive element, a
heavily dampened pendulous device that enables the gyro to erect
itself to earth gravity at the rate of approximately 2_/min. The pendulous
device is unable to differentiate between earth gravity and an
acceleration force. It tends to rest at a false- gravity position where the
forces of gravity and acceleration are equal. As long as the
acceleration force persists, the gyroscope precesses toward a
false- gravity position at the rate of approximately 2_/min. The radar
follows the gyroscope into error at the same rate. When the
acceleration force ceases, the gyroscope precesses back to true
gravity erection at the same rate.
Radar Facts
5-18

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

Some vertical gyroscopes have provisions for deactivating the
roll- erection torque motor (whenever the airplane banks more
than approximately 6_) to reduce the effect of lateral
acceleration during turns. To some extent, stabilization error is
displayed in the radar image after any speed change and/or turn
condition. If the stabilization system seems to be in error because the
radar begins ground mapping on one side and not the other, or
because it appears that the tilt adjustment has slipped, verify
that aircraft has been in nonturning, constant- speed flight long enough
to allow the gyroscope to erect on true earth gravity.
When dynamic and acceleration errors are taken into account,
maintaining accuracy of 1/2 of 1_ or less is not always possible. Adjust
the antenna tilt by visually observing the ground return. Then, slowly
tilt the antenna upward until terrain clutter no longer enters the display,
except at the extreme edges. If ground display is observed on one side
but not on the other, the stabilization system is somewhat in error, but
it is probably impossible to adjust it more accurately.

Pitch and Roll Trim Adjustments
The PRIMUSâ 880 is delivered from the Honeywell factory or repair
facility adjusted for correct pitch and roll stabilization and should be
ready for use. However, due to the tolerances of some vertical
reference sources, you may elect to make a final adjustment whenever
the radar or vertical reference is replaced on the aircraft, or if
stabilization problems are observed in flight.
The four trim adjustments and their effects are summarized in table
5- 4.

A28- 1146- 102- 00

Radar Facts
5-19

PRIMUSr 880 Digital Weather Radar System

Trim Adjustment

Flight Condition

Effect On Ground
Return Display
(Over Level
Terrain)

Roll offset

Straight and level

Nonsymmetrical
display

Pitch offset

Straight and level

Ground displays do
not follow contour of
range arcs.

Roll gain

Constant roll angle
>20°

Nonsymmetrical
display

Pitch gain

Constant pitch angle
>5°

Ground displays do
not follow contour of
range arcs.

Generally, it is recommended to perform trim adjustments only if
noticeable effects are being observed.
Pitch and Roll Trim Adjustments Criteria
Table 5- 4
NOTES:

1. Depending on the installation, not all of the
adjustments shown in table 5- 4 are available. If STAB
TRIM ENABLE programming strap is open, only the
roll offset adjustment is available. If STAB TRIM
ENABLE is grounded, all four adjustments are
available. Consult the installation configuration
information for details.
2. After any adjustment procedure is completed, monitor
the ground returns displayed by the radar during
several pitch and roll maneuvers. Verify that the
ground returns stay somewhat constant during
changes in aircraft orientations. If not, repeat the
adjustment procedure.
3. After the trim adjustment feature is selected, more
than one adjustment can be made. They are available
in the sequence shown in table 5- 4, and can be done
in the sequence of first finishing one adjustment, then
proceeding to do the next by pushing the STAB button.

Radar Facts
5-20

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

Stabilization Precheck
Prior to performing any of the adjustment procedures, conduct the
precheck procedures listed in tables 5- 5 and 5- 6.
LEVEL FLIGHT STABILIZATION CHECK
Check stabilization in level flight using the procedure in table 5- 5.
Step

Procedure

Trim the aircraft for straight and level flight in smooth,
clear air over level terrain.

Select the 50- mile range.

Rotate the tilt control upward until all ground returns
disappear.

Rotate the tilt downward until ground returns just begin
to show.

After several antenna sweeps, verify that ground
returns are equally displayed (figure 5- 19). If returns
are only on one side of the radar screen or uneven
across the radar screen, a misalignment of the radar
antenna mounting is indicated. This problem can be
corrected by means of the roll offset function before
proceeding (figures 5- 20 and 5- 21).

Refer to the roll offset adjustment procedure in table
5- 7.

Stabilization In Straight and Level Flight Check Procedure
Table 5- 5

A28- 1146- 102- 00

Radar Facts
5-21

PRIMUSr 880 Digital Weather Radar System

GMAP

10
5
AD- 17720- R1@

Symmetrical Ground Returns
Figure 5- 19

GMAP

10
5
AD- 17721- R1@

Ground Return Indicating Misalignment (Upper Right)
Figure 5- 20

Radar Facts
5-22

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

15
10

GMAP
5

AD- 17722- R1@

Ground Return Indicating Misalignment (Upper Left)
Figure 5- 21

ROLL STABILIZATION CHECK
Once proper operation is established in level flight, verify stabilization
in a turn using the procedure in table 5- 6.
Procedure

Step
1

Place the aircraft in 20°roll to the right.

Note the radar display. It should contain appreciably no
more returns than found during level flight. Figure 5- 22
indicates that roll stabilization is inoperative.

If returns display on the right side of radar indicator;
the radar system is understabilizing.

Targets on the left side of the radar display indicate the
system is Overstabilizing. Refer to table 5- 9 for roll
gain adjustment.

NOTE:

Proper radar operation in turns depends on the accuracy
and stability of the installed attitude source.
Stabilization in Turns Check Procedure
Table 5- 6

A28- 1146- 102- 00

Radar Facts
5-23

PRIMUSr 880 Digital Weather Radar System

In prolonged turns, gyro precession can occur that is tracked by the
stabilization system and appears as undesirable ground targets on the
indicator. For example, a 1°precession error (which would probably not
be noticed on the gyro horizon) moves the antenna beam
approximately 10,500 feet at a point 100 NM from the aircraft, If ground
targets between 50 and 80 NM depending on aircraft altitude and the
actual setting of the tilt control.

15
10

GMAP
5

AD- 17723- R1@

Roll Stabilization Inoperative
Figure 5- 22

Radar Facts
5-24

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

ROLL STABILIZATION CHECK
You can make an in- flight adjustment when level flight stabilization
errors are detected. This procedure is done by either the WC- 880 or
WC- 884 Weather Radar Controller or the WI- 880 Weather Radar
Indicator. During this procedure, described in table 5- 7, the GAIN
control acts as roll offset control. After the procedure the GAIN control
reverts to acting as a gain control.

Step

Procedure

If two controllers are installed, one must be turned off.
If an indicator is used as the controller, the procedure
is the same as given below.

Fly to an altitude of 10,000 feet above ground level
(AGL), or greater.

Set range to 25 NM.

Adjust the tilt down until a solid band of ground returns
are shown on the screen. Then adjust the tilt until the
green region of the ground returns start at about 20
NM.

On the WC controller, select RCT OFF.

Select STAB (STB) 4 times within 3 seconds. A
display with text instructions will be displayed. See
figure 5- 23. The radar unit is in the roll offset
adjustment mode.

Pull out the GAIN knob to make a roll offset
adjustment. See figure 5- 24 for a typical display. The
offset range is from - 2.0°to +2.0°and is adjustable by
the GAIN knob. The polarity of the GAIN knob is such
that clockwise rotation of the knob causes the antenna
to move down when scanning on the right side.

While flying straight and level, adjust the GAIN knob
until ground clutter display is symmetrical.

Push in the GAIN knob. When the GAIN knob is
pushed in, the display returns to the previous
message.
In- flight Roll Offset Adjustment Procedure
Table 5- 7 (cont)

A28- 1146- 102- 00

Radar Facts
5-25

PRIMUSr 880 Digital Weather Radar System

Step
10
NOTE:

Procedure
Push the STAB (STB) button to go to the next menu
(pitch offset).
Once set, the roll compensation is stored in nonvolatile memory in
the RTA. It is remembered when the system is powered down.

In- flight Roll Offset Adjustment Procedure
Table 5- 7

Roll Offset Adjustment Display - Initial
Figure 5- 23

Radar Facts
5-26

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

Roll Offset Adjustment Display - Final
Figure 5- 24

A28- 1146- 102- 00

Radar Facts
5-27

PRIMUSr 880 Digital Weather Radar System

PITCH OFFSET ADJUSTMENT
This in- flight adjustment in made in straight and level flight when the
ground returns do not follow the contours of the radar display range
arcs. The procedure is listed in table 5- 8.
Step

Procedure

If two controllers are installed, one must be turned off.
If an indicator is used, the procedure is the same as
given below.

Fly to an altitude of 10,000 feet AGL or greater.

Set range to 25 NM.

Adjust the tilt down until a solid band of ground returns
are shown on the screen. Then adjust the tilt until the
green region of the ground returns start at about 20
NM.

Select RCT OFF.

Select STAB (STB) 4 times within 3 seconds. The roll
offset display is shown.

From the roll offset entry menu, push the STAB (STB)
button once more to bring up the pitch offset entry
menu.

To change the pitch offset value, pull out the GAIN
knob and rotate it. The offset range is from - 2.0°to
+2.0° .

When flying straight and level, adjust so the contour of
the ground returns follow the contour of the range arcs
as closely as possible.

When change is completed, push in the GAIN knob.
The display returns to the previous message.

Push the STAB (STB) button to go to the next menu
(roll gain).
Pitch Offset Adjustment Procedure
Table 5- 8

Radar Facts
5-28

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

ROLL GAIN ADJUSTMENT
This in- flight adjustment is made in a bank when the ground returns do
not remain symmetrical during turns. The procedure is listed in table
5- 9.
Step

Procedure

If two controllers are installed, one must be turned off.
If an indicator is used as the controller, the procedure
is the same as given below.

Fly to an altitude of 10,000 feet AGL or greater.

Set range to 25 NM.

Adjust the tilt down until a solid band of ground returns
are shown on the screen. Then adjust the tilt until the
green region of the ground returns start at about 20
NM.

On the WC controller, select variable gain (pull), WX,
and REACT OFF. VAR shows on the display

Select STAB (STB) 4 times within 3 seconds. A
display with text instructions is shown.

From the roll offset entry menu, push the STAB (STB)
button twice more to bring up the roll gain entry menu.

To change the roll gain value, pull out the GAIN knob
and rotate it. The roll gain adjustment range is from 90
to 110%.

While flying with a steady roll angle of 10 to 20°, adjust
for symmetrical display of ground returns.

When change is completed, push in the GAIN knob.
The display returns to the previous message.

Push the STAB (STB) button to go to the next menu
(pitch gain).
Roll Gain Adjustment
Table 5- 9

A28- 1146- 102- 00

Radar Facts
5-29

PRIMUSr 880 Digital Weather Radar System

PITCH GAIN ADJUSTMENT
This in- flight adjustment is made in a bank when the ground returns do
not follow the contours of the range arcs during turns. The procedure
is listed in table 5- 10.
Step

Procedure

If two controllers are installed, one must be turned off.
If an indicator is used as the controller, the procedure
is the same as given below.

Fly to an altitude of 10,000 feet AGL or greater.

Set range to 25 NM.

Adjust the tilt down until a solid band of ground returns
are shown on the screen. Then adjust the tilt until the
green region of the ground returns start at about 20
NM.

On the WC controller, select variable gain (pull), WX
and REACT OFF. VAR shows on the display.

Push STAB (STB) 4 times within 3 seconds. A display
with text instruction is shown.

From the roll offset entry menu, push the STAB (STB)
button 3 more times to bring up the pitch gain entry
menu.

To change the pitch gain value, pull out the GAIN knob
and rotate it. The pitch gain adjustment range is from
90 to 110%.

While flying with a steady pitch angle of >5°, adjust so
the contour of the ground returns follow the contour of
the range arcs as closely as possible.

When change is completed, push in the GAIN knob.
The display returns to the previous message.

Push the STAB button to exit the mode and save the
value in nonvolatile memory.
Pitch Gain Adjustment
Table 5- 10

Radar Facts
5-30

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

INTERPRETING WEATHER RADAR IMAGES
From a weather standpoint, hail and turbulence are the principal
obstacles to a safe and comfortable flight. Neither of these conditions
is directly visible on radar. The radar shows only the rainfall patterns
with which these conditions are associated.
The weather radar can see water best in its liquid form, as shown in
figure 5- 25 (not water vapor; not ice crystals; not hail when small and
perfectly dry). It can see rain, wet snow, wet hail, and dry hail when its
diameter is about 8/10 of the radar wavelength or larger. (At X- band,
this means that dry hail becomes visible to the radar at about 1- in.
diameter.)
REFLECTIVE LEVELS

WILL NOT REFLECT

WET HAIL - GOOD

VAPOR

RAIN - GOOD
ICE CRYSTALS
WET SNOW - GOOD

DRY HAIL - POOR

DRY SNOW - VERY POOR

SMALL DRY HAIL

AD- 46704- R1@

Weather Radar Images
Figure 5- 25

A28- 1146- 102- 00

Radar Facts
5-31

PRIMUSr 880 Digital Weather Radar System

The following are some truths about weather and flying, as shown in
figure 5- 26.
D

Turbulence results when two air masses at different temperatures
and/or pressures meet.

This meeting can form a thunderstorm.

The thunderstorm produces rain.

The radar displays rain (thus revealing the turbulence).

In the thunderstorm’s cumulus stage, echoes appear on the display
and grow progressively larger and sharper. The antenna can be tilted
up and down in small increments to maximize the echo pattern.

In the thunderstorm’s mature stage, radar echoes are sharp and
clear; hail occurs most frequently early in this stage.

In the thunderstorm’s dissipating stage, the rain area is largest and
shows best with a slight downward antenna tilt.

Radar can be used to look inside the precipitation area to spot zones
of present and developing turbulence. Some knowledge of meteorology
is required to identify these areas as being turbulent. The most
important fact is that the areas of maximum turbulence occur where
the most abrupt changes from light or no rain to heavy rain occur. The
term applied to this change in rate is rain gradient. The greater the
change in rainfall rate, the steeper the rain gradient. The steeper the
rain gradient, the greater the accompanying turbulence. More
important, however, is another fact: Storm cells are not static or stable,
but are in a constant state of change. While a single thunderstorm
seldom lasts more than an hour, a squall line, shown in figure 5- 27 can
contain many such storm cells developing and decaying over a much
longer period. A single cell can start as a cumulus cloud only 1 mile in
diameter, rise to 15,000 ft, grow within 10 minutes to 5 miles in
diameter and tower to an altitude of 60,000 feet or more. Therefore,
weather radar should not be used to take flash pictures of weather, but
to keep weather under continuous surveillance.

Radar Facts
5-32

A28- 1146- 102- 00

RAINFALL RATE

PRIMUSr 880 Digital Weather Radar System

RED LEVEL*

40
60
NAUTICAL MILES

80
AD- 12057- R2@

Radar and Visual Cloud Mass
Figure 5- 26
As masses of warm, moist air are hurled upward to meet the colder air
above, the moisture condenses and builds into raindrops heavy
enough to fall downward through the updraft. When this precipitation is
heavy enough, it can reverse the updraft. Between these downdrafts
(shafts of rain), updrafts continue at tremendous velocities. It is not
surprising, therefore, that the areas of maximum turbulence are near
these interfaces between updraft and downdraft. Keep these facts in
mind when tempted to crowd a rain shaft or to fly over an
innocent- looking cumulus cloud.

A28- 1146- 102- 00

Radar Facts
5-33

PRIMUSr 880 Digital Weather Radar System

To find a safe and comfortable route through the precipitation area,
study the radar image of the squall line while closing in on the
thunderstorm area. In the example shown in figure 5- 27, radar
observation shows that the rainfall is steadily diminishing on the left
while it is very heavy in two mature cells (and increasing rapidly in a third
cell) to the right. The safest and most comfortable course lies to the left
where the storm is decaying into a light rain. The growing cell on the
right should be given a wide berth.

AREAS OF MAXIMUM TURBULENCE
DECAYING
CELLS

GROWING
CELLS

MATURE CELLS

OUTLINE OF RAIN AREA VISIBLE TO RADAR
BEST DETOUR

AD- 12058- R1@

Squall Line
Figure 5- 27

Radar Facts
5-34

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

WEATHER DISPLAY CALIBRATION
Ground based radar observers of the National Weather Service (NWS)
currently use video integrator processor (VIP) levels in reporting
thunderstorm intensity levels. These radar echo intensity levels are on
a scale of one to six. Refer to Section 6 of FAA Advisory Circular
AC- 00- 24B for additional details.
To assist the pilot in categorizing storms in accordance with VIP levels,
the indicator display colors represent calibrated rainfall rates in WX and
preset calibrated gain. The relationship between the 4- color
calibrations and the VIP levels is shown in table 5- 11.
As covered in the RCT description, intervening attenuating rainfall
reduces the calibrated range and the radar can incorrectly depict the
true cell intensity.
The radar calibration includes a nominal allowance for radome losses.
Excessive losses in the radome seriously affect radar calibration. One
possible means of verification is signal returns from known ground
targets. It is recommended that you report evidence of weak returns to
ensure that radome performance is maintained at a level that does not
affect radar calibration.
To test for a performance loss, note the distance at which the aircraft’s
base city, a mountain, or a shoreline can be painted from a given
altitude. When flying in familiar surroundings, verify that landmarks can
still be painted at the same distances.
Any loss in performance results in the system not painting the reference
target at the normal range.

A28- 1146- 102- 00

Radar Facts
5-35

PRIMUSr 880 Digital Weather Radar System

REFLECTIVITY
DISPLAY
LEVEL

RAINFALL
RATE
MM/HR

4
(MAGENTA)

GREATER
THAN
50

VERY
STRONG
3
(RED)

12 - 50

25 - 50
(1 - 2)

STRONG

12 - 25
(0.5 - 1)

MODERATE

2.5 - 12
(0.1 - 0.5)

WEAK

0.25 - 2.5
(0.01 - 0.1)

0.5 - 2

2
(YELLOW)

4 - 12

0.17 - 0.5

1
(GREEN)

1- 4

0.04 - 0.17

0
(BLACK)

300 NM
MAXIMUM*

MAXIMUM*

PROCESSOR
RAINFALL VIDEO INTEGRATED
CALIBRATED CALIBRATED CALIBRATED
CATEGORIZATIONS
RANGE (NM) RANGE (NM) RANGE (NM)
RATE
RAINFALL
STORM
VIP
24- IN
18- IN
12- IN
RATE- MM/HR
IN./HR
CATEGORY
LEVEL
FLAT- PLATE FLAT- PLATE FLAT- PLATE
(IN./HR)
GREATER
THAN
EXTREME
6
125
GREATER
(5)
THAN
232
>300
>300
2
50 - 125
INTENSE
5
(2 - 5)

LESS THAN LESS THAN
1
0.04

130

190

230

130

160

100

* THE THRESHOLD FOR THE VIP LEVELS CAN BE REALIZED WHEN THERE IS NO INTERVENING RADAR
SIGNAL ATTENUATION. WITH RCT SELECTED, RCT BLUE FIELD OCCURS WHEN THE MINIMUM RED
LEVEL DETECTED IS BELOW SYSTEM SENSITIVITY.
AD- 17926- R5@

Display Levels Related to VIP Levels (Typical)
Table 5- 11
NOTE:

Radar Facts
5-36

The radar is calibrated for convective weather.
Stratiform storms at or near the freezing level can show high
reflectivity. Do not penetrate such targets.

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

VARIABLE GAIN CONTROL
The PRIMUSâ 880 Digital Weather Radar variable gain control is a
single turn rotary control and a push/pull switch that is used to control
the radar’s receiver gain. With the switch pushed in, the system is in the
preset, calibrated gain mode. In calibrated gain, the rotary control does
nothing.
When the GAIN switch is pulled out, the system enters the variable gain
mode. Variable gain is useful for additional weather analysis. In the WX
mode, variable gain can increase receiver sensitivity over the calibrated
level to show very weak targets or it can be reduced below the
calibrated level to eliminate weak returns.

WARNING
LOW VARIABLE GAIN SETTINGS CAN ELIMINATE HAZARDOUS
TARGETS.

RAIN ECHO ATTENUATION COMPENSATION
TECHNIQUE (REACT)
Honeywell’s REACT feature has three separate, but related functions.
D

Attenuation Compensation - As the radar energy travels through
rainfall, the raindrops reflect a portion of the energy back toward the
airplane. This results in less energy being available to detect
raindrops at greater ranges. This process continues throughout the
depth of the storm, resulting in a phenomenon known as
attenuation. The amount of attenuation increases with an increase
in rainfall rate and with an increase in the range traveled through the
rainfall (i.e., heavy rain over a large area results in high levels of
attenuation, while light rain over a small area results in low levels of
attenuation).
Storms with high rainfall rates can totally attenuate the radar energy
making it impossible to see a second cell hidden behind the first cell.
In some cases, attenuation can be so extreme that the total depth
of a single cell cannot be shown.
Without some form of compensation, attenuation causes a single
cell to appear to weaken as the depth of the cell increases.

A28- 1146- 102- 00

Radar Facts
5-37

PRIMUSr 880 Digital Weather Radar System

Honeywell has incorporated attenuation compensation that adjusts
the receiver gain by an amount equal to the amount of attenuation.
That is, the greater the amount of attenuation, the higher the receiver
gain and thus, the more sensitive the receiver. Attenuation
compensation continuously calibrates the display of weather targets,
regardless of the amount of attenuation.
With attenuation compensation, weather target calibration is
maintained throughout the entire range of a single cell. The
cell behind a cell remains properly calibrated, making proper
calibration of weather targets at long ranges possible.
D

Cyan REACT Field - From the description of attenuation, it can be
seen that high levels of attenuation (caused by cells with heavy
rainfall) causes the attenuation compensation circuitry to increase
the receiver gain at a fast rate.
Low levels of attenuation (caused by cells with low rainfall rates)
cause the receiver gain to increase at a slower rate.
The receiver gain is adjusted to maintain target calibration. Since
there is a maximum limit to receiver gain, strong targets (high
attenuation levels) cause the receiver to reach its maximum gain
value in a short time/short range. Weak or no targets (low
attenuation levels) cause the receiver to reach its maximum gain
value in a longer time/longer range. Once the receiver reaches its
maximum gain value, weather targets can no longer be calibrated.
The point where red level weather target calibration is no longer
possible is highlighted by changing the background field from black
to cyan.
Any area of cyan background is an area where attenuation has
caused the receiver gain to reach its maximum value, so further
calibration of returns is not possible. Extreme caution is
recommended in any attempt to analyze weather in these
cyan areas. The radar cannot display an accurate picture of what
is in these cyan areas. Cyan areas should be avoided.
NOTE:

If the radar is operated such that ground targets are
affecting REACT, they could cause REACT to provide
invalid indications.

Any target detected inside a cyan area is automatically forced to a
magenta color indicating maximum severity. Figure 5- 28 shows the
same storm with REACT OFF and with REACT ON.

Radar Facts
5-38

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

With REACT Selected

REACT
REACT ON and OFF Indications
Figure 5- 28

A28- 1146- 102- 00

Radar Facts
5-39

PRIMUSr 880 Digital Weather Radar System

Shadowing
An operating technique similar to the REACT blue field is shadowing. To
use the shadowing technique, tilt the antenna down until ground is being
painted just in front of the storm cell(s). An area of no ground returns
behind the storm cell has the appearance of a shadow behind the cell.
This shadow area indicates that the storm cell has totally attenuated the
radar energy and the radar cannot show any additional targets (WX or
ground) behind the cell. The cell that produces a radar shadow is a very
strong and dangerous cell. It should be avoided by 20 miles.

WARNING
DO NOT FLY INTO THE SHADOW BEHIND THE CELL.

Turbulence Probability
The graph of turbulence probability is shown in figure 5- 29. This graph
shows the following:
D

There is a 100% probability of light turbulence occurring in any area
of rain.

A level one storm (all green) has virtually no chance of containing
severe or extreme turbulence but has between a 5% and 20%
chance that moderate turbulence exists.

A level two storm (one containing green and yellow returns) has
virtually no probability of extreme turbulence but has a 20% to 40%
chance of moderate turbulence and up to a 5% chance of severe
turbulence.

A level three storm (green, yellow, and red radar returns) has a 40%
to 85% chance of moderate turbulence, a 5% to 10% chance of
severe turbulence, and a slight chance of extreme turbulence.

A level four storm (one with a magenta return) has moderate
turbulence, a 10% to 50% chance of severe turbulence, and a slight
to 25% chance of extreme turbulence.

WARNING
THE AREAS OF TURBULENCE MAY NOT BE ASSOCIATED WITH
THE MAXIMUM RAINFALL AREAS. THE PROBABILITIES OF
TURBULENCE ARE STATED FOR THE ENTIRE STORM AREA,
NOT JUST THE HEAVY RAINFALL AREAS.
Radar Facts
5-40

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

Although penetrating a storm with a red (level three) core appears to be
an acceptable risk, it is not. At the lower end of the red zone, there is
no chance of extreme turbulence, a slight chance of severe turbulence,
and a 40% chance of moderate turbulence. However, the radar lumps
all of the rainfall rates between 12 mm to 50 mm per hour into one group
- a level three (red). Once the rainfall rate reaches the red threshold,
it masks any additional information about the rainfall rate until the
magenta threshold is reached. A red return covers a range of
turbulence probabilities and the worst case must be assumed,
especially since extreme, destructive turbulence is born in the red zone.
Therefore, once the red threshold is reached, the risk in penetration
becomes totally unacceptable.
Likewise, once the magenta threshold is reached, it must be
assumed that more severe weather is being masked.

100%

LEVEL 1
GREEN
LIGHT

LEVEL 2
YELLOW

LEVEL 3
RED

LEVEL 4
MAGENTA

TURBULENCE PROBABILITY

90%
80%
70%
60%
50%
40%
30%
20%
10%
0%

(4 mm / Hr)

(12 mm / Hr)

(50 mm / Hr)

RAINFALL RATE

AD- 15357- R2@

Probability of Turbulence Presence
in a Weather Target
Figure 5- 29

A28- 1146- 102- 00

Radar Facts
5-41

PRIMUSr 880 Digital Weather Radar System

Turbulence Detection Theory
The PRIMUSâ 880 Digital Weather Radar uses a turbulence detection
technique called Pulse Pair Processing (PPP). The PPP technique
used in the new PRIMUSâ 880 Digital Weather Radar is adapted from
the proven technique used in the earlier PRIMUSâ Weather Radars.
In the turbulence detection mode of operation, the PRIMUSâ 880 Digital
Weather Radar transmits about 1400 pulses per second with a power
of 10 kW. The pulse pair processor compares the returns from
successive pulses to determine the presence of turbulence (i.e.,
the return from pulse one is compared to the return from pulse two,
pulse two’s return is compared to pulse three’s, and so on). Since the
processor is comparing the returns from two subsequent pulses (a
pair), it was given the name pulse pair processor.
To perform the comparison, the radar first divides the selected range
into 128 equal parts with each part called a range bin. The radar
compares the return data in each range bin for the first pulse with the
return data in each range bin for the second pulse. For example, the
data returned from pulse one in range bin 34 is compared to the data
returned from pulse two in range bin 34. This process continues
throughout the entire area covered by the radar (all range bins) and a
turbulence decision is made for each range bin. When turbulence is
detected in any bin, the color of that bin is made white.
The return data being compared is the total return vector (TRV). TRV
is the vector sum of the return from each raindrop contained within the
range bin. In other words, the first pulse TRV of range bin 34 is
compared to the TRV for pulse two in range bin 34. A total return vector
is shown in figure 5- 30.
In the simplified example of figure 5- 30, the range bin contains
five raindrops of equal size that are at slightly different ranges. The
amplitudes of the returns from the raindrops (vector length) are identical
because all the drops are equal in size, but the phase (vector rotation)
of the individual returns varies because of the variation in the range of
the raindrops. The radar does not see the individual returns, rather it
sees the total return vector which is the vector sum of the returns from
all the individual raindrops. In reality, the range bin could contain
thousands and thousands of raindrops which means that a longer chain
of vectors are summed, but the result is still one total return vector.

Radar Facts
5-42

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

With the very short time between radar pulses when in the turbulence
mode (one pulse every .0008 second), little or no turbulence results in
little or no change in the size or position of the raindrops. This results
in little or no change in the individual returns from each raindrop and a
commensurate little or no change in the total return vector. Therefore,
when there is little or no difference between two subsequent total return
vectors in the same range bin, there is little or no turbulence in that
range bin. This is illustrated by comparing figures 5- 30 and 5- 31.
If turbulence is present in the precipitation, there is a significant change in
the raindrop size and/or position between the subsequent radar pulses.
This difference results in a change in the individual return vectors from
each raindrop and a commensurate change in the total return vector.
Therefore, if there is a significant difference between pairs of total return
vectors for the same range bin, that bin contains turbulence and is
displayed in white. This is illustrated by comparing figures 5- 30 and 5- 32.
The presence of turbulence is detected by comparing the amplitude of
subsequent total return vectors.
To measure raindrop motion, the turbulence detection circuitry measures
the raindrop motion directly toward and away from the antenna. Raindrop
motion that is perpendicular to the antenna does not produce any doppler
effect and cannot be measured by the turbulence detection circuitry. For
this reason, there can be areas of turbulence not detectable by radar, or
the displayed areas of turbulence can change from antenna scan to
antenna scan as the turbulence throws the raindrops in various directions.

WARNING
AREAS OF TURBULENCE
DETECTED BY THE RADAR.

A28- 1146- 102- 00

CAN

NOT

ALWAYS

Radar Facts
5-43

PRIMUSr 880 Digital Weather Radar System

Total Return Vector
Figure 5- 30

AD- 17726- R1@

No Turbulence
Figure 5- 31

Radar Facts
5-44

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

TURBULENT
AD- 17727- R1@

Turbulent
Figure 5- 32

Turbulence Detection Operation
With the radar in the WX mode and with 50 miles or less range selected,
pushing the TRB switch turns on the turbulence detection mode. Areas
of detected turbulence are displayed in soft white, as shown in figure
5- 33. Soft white is a high contrast shade of white that has a slight gray
appearance.

Weather Display With Turbulence
Figure 5- 33
If any range greater than 50 miles is selected, turbulence detection turns
off and remains off until 50 miles or less is reselected. Similarly, if any
mode other than WX is selected, turbulence detection turns off.
A28- 1146- 102- 00

Radar Facts
5-45

PRIMUSr 880 Digital Weather Radar System

Mode annunciation for the turbulence detection mode is the /T legend
that is added to the WX annunciation. The resultant annunciation is
WX/T for weather and turbulence. The color bar legend on the
dedicated radar indicator includes a T within a soft white square
whenever turbulence detection is turned on. EFIS/MFD does not have
a color bar legend.
The PRIMUSâ 880 Digital Weather Radar measures the motion of
raindrops to determine areas of turbulence. The radar must detect
precipitation before it can detect turbulence. It cannot detect clear air
turbulence.

WARNING
THE PRIMUSâ 880 DIGITAL WEATHER RADAR CAN ONLY DETECT
TURBULENCE WITHIN AREAS OF PRECIPITATION. IT CANNOT DETECT CLEAR AIR TURBULENCE.
The turbulence detection threshold is moderate turbulence. That is, any
area of raindrop motion that is detected as moderate, severe, or
extreme turbulence is displayed in white. Areas shown as turbulent are
at least moderate turbulence and can be severe, extreme, or
combinations of the three levels of turbulence. All three must be
avoided.
Turbulence is most accurately measured within ? 30_ of straight
ahead. Turbulence measurements outside this area experience
reduced accuracy. The reduced accuracy results from the effects of the
antenna scan angle and aircraft motion. Levels of turbulence are
described in the Airman’s Information Manual and are shown in figure
5- 34.

Radar Facts
5-46

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

INTENSITY

AIRCRAFT REACTION

REACTION INSIDE
AIRCRAFT

Turbulence that momentarily causes
slight, erratic changes in altitude and/or
attitude (pitch, roll, yaw).

Occupants may feel a slight
strain against seat belts or
shoulder straps. Unsecured
objects may be displaced
slightly.

MODERATE

Turbulence that is similar to light
turbulence but of greater intensity.
Changes in altitude and/or attitude
occur but the aircraft remains in
positive control at all times. It usually
causes variations in indicated
airspeed.

Occupants feel definite
strains against seat belts or
shoulder straps. Unsecured
objects are dislodged.

SEVERE

Turbulence that causes large abrupt
changes in altitude and/or attitude. It
usually causes large variations in
indicated airspeed. Aircraft may be
momentarily out of control.

Occupants are forced
violently against seat belts
or shoulder straps.
Unsecured objects are
tossed about.

LIGHT

Turbulence Levels
(From Airman’s Information Manual)
Figure 5- 34

Hail Size Probability
Whenever the radar shows a red or magenta target, the entire storm cell
should be considered extremely hazardous and must not be
penetrated. Further support for this statement comes from the hail
probability graph shown in figure 5- 35. The probability of destructive
hail starts at a rainfall rate just above the red level three threshold.
Like precipitation, the red and magenta returns should be considered
as a mask over more severe hail probabilities.
By now, it should be clear that the only safe way to operate in areas of
thunderstorm activity is to AVOID ALL CELLS THAT HAVE RED OR
MAGENTA RETURNS.

A28- 1146- 102- 00

Radar Facts
5-47

PRIMUSr 880 Digital Weather Radar System

100%

1/4”HAIL

RELATIVE FREQUENCY

80%

60%

40%

1/2”HAIL

20%

3/4”AND LAGER HAIL
0%

LEVEL 2
YELLOW

LEVEL 3
RED

LEVEL 4
MAGENTA
AD- 15358- R1@

Hail Size Probability
Figure 5- 35

Spotting Hail
As previously stated, dry hail is a poor reflector, and therefore
generates deceptively weak or absent radar returns. When flying above
the freezing level, hail can be expected in regions above and around wet
storm cells found at lower altitudes. The hail is carried up to the
tropopause by strong vertical winds inside the storm. In large storms,
these winds can easily exceed 200 kt, making them very dangerous.
Since the core of such a storm is very turbulent, but largely icy, the red
core on the radar display is weak or absent and highly mobile. The
storm core can be expected to change shapes with each antenna scan.

Radar Facts
5-48

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

On reaching the tropopause, the hail is ejected from the storm and falls
downward to a point where it is sucked back into the storm. When the
hail falls below the freezing level, however, it begins to melt and form
a thin surface layer of liquid detectable by radar. A slight downward tilt
of the antenna toward the warmer air shows rain coming from unseen
dry hail that is directly in the flightpath, as shown in figure 5- 36. At lower
altitudes, the reverse is sometimes true; the radar may be scanning
below a rapidly developing storm cell, from which the heavy rain
droplets have not had time to fall through the updrafts to the flight level.
Tilting the antenna up and down regularly produces the total weather
picture.
Using a tilt setting that has the radar look into the area of maximum
reflectivity (5000 to 20,000 ft) gives the strongest radar picture.
However the tilt setting must not be left at this setting. Periodically, the
pilot should look up and down from this setting to see the total picture
of the weather in the flightpath.
Often, hailstorms generate weak but characteristic patterns like those
shown in figure 5- 37. Fingers or hooks of cyclonic winds that radiate
from the main body of a storm usually contain hail. A U shaped pattern
is also (frequently) a column of dry hail that returns no signal but is
buried in a larger area of rain that does return a strong signal. Scalloped
edges on a pattern also indicate the presence of dry hail bordering
a rain area. Finally, weak or fuzzy protuberances are not
always associated with hail, but should be watched closely; they
can change rapidly.

DRY HAIL

BEAM IN
DOWNWARD
TILT POSITION
WET HAIL
AND RAIN

AD- 12059- R1@

Rain Coming From Unseen Dry Hail
Figure 5- 36
A28- 1146- 102- 00

Radar Facts
5-49

PRIMUSr 880 Digital Weather Radar System

FINGER

HOOK

U- SHAPE
AD- 35713@

Familiar Hailstorm Patterns
Figure 5- 37
The more that is learned about radar, the more the pilot is an
all- important part of the system. The proper use of controls is essential
to gathering all pertinent weather data. The proper interpretation of that
data (the displayed patterns) is equally important to safety and comfort.
This point is illustrated again in figure 5- 38. When flying at higher
altitudes, a storm detected on the long- range setting can
disappear from the display as it is approached. The pilot should not be
fooled into believing the storm has dissipated as the aircraft approaches
it. The possibility exists that the radiated energy is being directed from
the aircraft antenna above the storm as the aircraft gets closer. If this
is the case, the weather shows up again when the antenna is tilted
downward as little as 1_. Assuming that a storm has dissipated during
the approach can be quite dangerous; if this is not the case, the
turbulence above a storm can be as severe as that inside it.

Radar Facts
5-50

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

OVERFLYING A STORM

HAIL

AD- 12061- R1@

Overshooting a Storm
Figure 5- 38
Another example of the pilot’s importance in helping the radar serve its
safety/comfort purpose is shown in figure 5- 39. This is the blind alley
or box canyon situation. Pilots can find themselves in this situation if
they habitually fly with the radar on the short range. The short- range
returns show an obvious corridor between two areas of heavy rainfall,
but the long- range setting shows the trap. Both the near and far
weather zones could be avoided by a short- term course change of
about 45_ to the right. Always switch to long range before entering such
a corridor.

A28- 1146- 102- 00

Radar Facts
5-51

PRIMUSr 880 Digital Weather Radar System

THE BLIND ALLEY

20
LONG RANGE

SHORT RANGE
AD- 12062- R1@

Short- and Long- Blind Alley
Figure 5- 39

Radar Facts
5-52

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

Azimuth Resolution
When two targets, such as storms, are closely adjacent at the
same range, the radar displays them as a single target, as shown in
figure 5- 38. However, as the aircraft approaches the targets, they
appear to separate. In the illustration, the airplane is far away from the
targets at position A. At this distance, the beam width is spreading. As
the beam scans across the two targets, there is no point at which beam
energy is not reflected, either by one target or the other, because the
space between the targets is not wide enough to pass the beam width.
In target position B, the aircraft is closer to the same two targets; the
beam width is narrower, and the targets separate on the display.

100

80
A

INDICATOR DISPLAY A

50
40

INDICATOR DISPLAY B

AD- 35705@

Azimuth Resolution in Weather Modes
Figure 5- 40

A28- 1146- 102- 00

Radar Facts
5-53

PRIMUSr 880 Digital Weather Radar System

RADOME
Ice or water on the radome does not generally cause radar failure, but
it hampers operation. The radome is constructed of materials that pass
the radar energy with little attenuation. Ice or water increases the
attenuation making the radar appear to have less sensitivity. Ice can
cause refractive distortion, a condition characterized by loss of image
definition. If the ice should cause reverberant echoes within the
radome, the condition might be indicated by the appearance of
nonexisting targets.
The radome can also cause refractive distortion, which would make it
appear that the TILT control was out of adjustment, or that bearing
indications were somewhat erroneous.
A radome with ice or water trapped within its walls can cause significant
attenuation and distortion of the radar signals. This type of attenuation
cannot be detected by the radar, even with REACT on, but it can, in
extreme cases, cause blind spots. If a target changes significantly in
size, shape, or intensity as aircraft heading or attitude change, the
radome is probably the cause.

Radar Facts
5-54

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

WEATHER AVOIDANCE
Figure 5- 41 illustrates a typical weather display in WX mode.
Recommended procedures when using the radar for weather
avoidance are given in table 5- 12. The procedures are given in bold
face, explanations of the procedure follow in normal type face.

Weather Display
Figure 5- 41

A28- 1146- 102- 00

Radar Facts
5-55

PRIMUSr 880 Digital Weather Radar System

Step

Procedure

Keep TGT alert enabled when using short ranges to
be alerted if a new storm cell develops in the
aircraft’s flightpath.

Keep the gain in preset. The gain control should be
in preset except for brief periods when variable gain
is used for detailed analysis. Immediately after the
analysis, switch back to preset gain.

WARNING
DO NOT LEAVE THE RADAR IN VARIABLE GAIN. SIGNIFICANT WEATHER MAY NOT BE DISPLAYED.
3

Any storm with reported tops at or greater than
20,000 feet must be avoided by 20 NM.

WARNING
DRY HAIL CAN BE PREVALENT AT HIGHER ALTITUDES WITHIN, NEAR, OR ABOVE STORM CELLS,
AND SINCE ITS RADAR REFLECTIVITY IS
POOR, IT MAY NOT BE DETECTED.
4

Use increased gain (rotate GAIN control to its
maximum cw position) when flying near storm tops.
This helps display the normally weaker returns that
could be associated with hail.
Severe Weather Avoidance Procedures
Table 5- 12 (cont)

Radar Facts
5-56

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

Step

Procedure

When flying at high altitudes, tilt downward
frequently to avoid flying above storm tops.
Studies by the National Severe Storms Laboratory (NSSL)
of Oklahoma have determined that thunderstorms
extending to 60,000 ft show little variation of turbulence
intensity with altitude.
Ice crystals are poor reflectors. Rain water at the lower
altitudes produce a strong echo, however at higher
altitudes, the nonreflective ice produces a week echo as
the antenna is tilted up. Therefore, though the intensity
of the echo diminishes with altitude, it does not mean
the severity of the turbulence has diminished.
NOTE:

If the TILT control is left in a fixed position at
the higher flight levels, a storm detected at
long range can appear to become weaker
and actually disappear as it is approached.
This occurs because the storm cell which
was fully within the beam at 100 NM gradually
passes out of and under the radar beam.

When flying at low altitudes rotate tilt upward
frequently to avoid flying under a thunderstorm.
There is some evidence that maximum turbulence exists
at middle heights in storms (20,000 to 30,000 ft); however,
turbulence beneath a storm is not to be minimized.
However, the lower altitude may be affected by strong
outflow winds and severe turbulence where thunderstorms
are present. The same turbulence considerations that
apply to high altitude flight near storms apply to low
altitude flight.

Avoid all rapidly moving echoes by 20 miles.
A single thunderstorm echo, a line of echoes, or a
cluster of echoes moving 40 knots or more will often
contain severe weather. Although nearby, slower moving
echoes may contain more intense aviation hazards, all
rapidly moving echoes warrant close observation. Fast
moving, broken to solid line echoes are particularly
disruptive to aircraft operations.

Avoid, the entire cell if any portion of the cell is red
or magenta by 20 NM.
The stronger the radar return, the greater the frequency
and severity of turbulence and hail.
Severe Weather Avoidance Procedures
Table 5- 12 (cont)

A28- 1146- 102- 00

Radar Facts
5-57

PRIMUSr 880 Digital Weather Radar System

Step

Procedure

Avoid all rapidly growing storms by 20 miles.
When severe storms and rapid development are evident,
the intensity of the radar return may increase by a huge
factor in a matter of minutes. Moreover, the summit of the
storm cells may grow at 7000 ft/min. The pilot cannot
expect a flightpath through such a field of strong storms
separated by 20 to 30 NM to be free of severe
turbulence.

Avoid all storms showing erratic motion by 20
miles.
Thunderstorms tend to move with the average wind that
exists between the base and top of the cloud. Any motion
differing from this is considered erratic and may indicate
the storm is severe. There are several causes of erratic
motion. They may act individually or in concert. Three of
the most important causes of erratic motion are:
1. Moisture Source. Thunderstorms tend to grow toward
a layer of very moist air (usually south or southeast in
the U.S.) in the lowest 1500 to 5000 ft above the earth’s
surface. Moist air generates most of the energy for the
storm’s growth and activity. Thus, a thunderstorm may
tend to move with the average wind flow around it, but
also grow toward moisture. When the growth toward
moisture is rapid, the echo motion often appears
erratic. On at least one occasion, a thunderstorm echo
moved in direct opposition to the average wind!
2. Disturbed Wind Flow. Sometimes thunderstorm
updrafts block winds near the thunderstorm and act
much like a rock in a shallow river bed. This pillar of
updraft forces the winds outside the storm to flow
around the storm instead of carrying it along. This also
happens in wake eddies that often form downstream of
the blocking updraft

10
(cont)

3. Interaction With Other Storms. A thunderstorm that is
located between another storm and its moisture source
may cause the blocked storm to have erratic motion.
Sometimes the blocking of moisture is effective enough
to cause the thunderstorm to dissipate.
Severe Weather Avoidance Procedures
Table 5- 12 (cont)

Radar Facts
5-58

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

Step

Procedure
Three of the most common erratic motions are:
1. Right Turning Echo. This is the most frequently
observed erratic motion. Sometimes a thunderstorm
echo traveling the same direction and speed as nearby
thunderstorm echoes, slows, and turns to the right of its
previous motion. The erratic motion may last an hour or
more before it resumes its previous motion. The storm
should be considered severe while this erratic motion
is in progress.
2. Splitting Echoes. Sometimes a large (20- mile or
larger diameter) echo splits into two echoes. The
southernmost echo often slows, turns to the right of its
previous motion, and becomes severe with large hail
and extreme turbulence.
If a tornado develops, it is usually at the right rear
portion of the southern echo. When the storm weakens,
it usually resumes its original direction of movement.
The northern echo moves left of the mean wind,
increases speed and often produces large hail and
extreme turbulence.
3. Merging Echoes. Merging echoes sometimes
become severe, but often the circulation of the
merging cells interfere with each other preventing
intensification. The greatest likelihood of aviation
hazards is at the right rear section of the echo.
Severe Weather Avoidance Procedures
Table 5- 12 (cont)

A28- 1146- 102- 00

Radar Facts
5-59

PRIMUSr 880 Digital Weather Radar System

Step
11

Procedure
Never continue flight towards or into a radar
shadow or the blue REACT field.

WARNING
STORMS SITUATED BEHIND INTERVENING RAINFALL MAY BE MORE SEVERE THAN DEPICTED ON
THE DISPLAY.
If the radar signal can penetrate a storm, the target
displayed seems to cast a shadow with no visible
returns. This indicates that the storm contains a great
amount of rain, that attenuates the signal and prevents
the radar from seeing beyond the cell under observation.
The REACT blue field shows areas where attenuation
could be hiding severe weather. Both the shadow and
the blue field are to be avoided by 20 miles. Keep the
REACT blue field turned on. The blue field will form
fingers that point towards the stronger cells.
Severe Weather Avoidance Procedures
Table 5- 12

Configurations of Individual Echoes (Northern
Hemisphere)
Sometimes a large echo will develop configurations which are
associated with particularly severe aviation hazards. Several of these
are discussed below.
AVOID HOOK ECHOES BY 20 MILES
The hook is probably the best known echo associated with severe
weather. It is an appendage of a thunderstorm echo and usually only
appears on weather radars. Figure 5- 42 shows a hook echo.

Radar Facts
5-60

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

AD- 15560- R1@

Typical Hook Pattern
Figure 5- 42
The hooks are located at the right rear side of the thunderstorm echo’s
direction of movement (usually the southwest quadrant).
The hook is not the tornado echo! A small scale low pressure area is
centered at the right rear side of the thunderstorm echo near its edge.
The low usually ranges from about 3 to 10 miles in diameter.
Precipitation is drawn around the low’s cyclonic circulation to form the
characteristic hook shape. Tornadoes form within the low near hook.
According to statistics from the NSSL, almost 60 percent of all observed
hook echoes have tornadoes associated with them. A tornado is always
suspected when a hook echo is seen.
A hook can form with no tornadoes and vice versa. However, when a
bona fide hook is observed on a weather radar, moderate or greater
turbulence, strong shifting surface winds, and hail are often nearby and
aircraft should avoid them.

A28- 1146- 102- 00

Radar Facts
5-61

PRIMUSr 880 Digital Weather Radar System

There are many patterns on radar that resemble hook echoes but are
not associated with severe weather. Severe weather hook echoes last
at least 5 minutes and are less than 25 miles in diameter. The favored
location for hook echoes is to the right rear of a large and strong cell,
however, in rare cases tornadoes occur with hooks in other parts of the
cell.
AVOID V- NOTCH BY 20 MILES
A large isolated echo will sometimes have the configuration that is
shown in figure 5- 43. This echo is called V- notch or flying eagle
although some imagination may be needed by the reader to see
the eagle. V- notch echoes are formed by the wind pattern at the
leading edge (left front) of the echo. Thunderstorm echoes with
V- notches are often severe, containing strong gusty winds, hail,
or funnel clouds, but not all V- notches indicate severe weather. Again,
severe weather is most likely at S in figure 5- 43.

N
v
s echo movement
AD- 15561- R1@

V- Notch Echo, Pendant Shape
Figure 5- 43

Radar Facts
5-62

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

AVOID PENDANT BY 20 MILES
The pendant shape shown in figure 5- 44, represents one of the
most severe storms - the supercell. One study concluded that, in
supercells:
D

The average maximum size of hail is over 2 inches (5.3 cm)

The average width of the hail swath is over 12.5 miles (20.2 km)

Sixty percent produce funnel clouds or tornadoes.

The classic pendant shape echo is shown in figure 5- 44. Note the
general pendant shape, the hook, and the steep rain gradient. This
storm is extremely dangerous and must be avoided.

STORM MOTION

AD- 35706@

The Classic Pendant Shape
Figure 5- 44

A28- 1146- 102- 00

Radar Facts
5-63

PRIMUSr 880 Digital Weather Radar System

AVOID STEEP RAIN GRADIENTS BY 20 MILES
Figure 5- 45 shows steep rain gradients. Refer to the paragraph,
Interpreting Weather Radar Images, this section, for a detailed
explanation of weather images.

Rain Gradients
Figure 5- 45
AVOID ALL CRESCENT SHAPED ECHOES BY 20 MILES
A crescent shaped echo, shown in figure 5- 46, with its tips pointing
away from the aircraft indicates a storm cell that has attenuated the
radar energy to the point where the entire storm cell is not displayed.
This is especially true if the trailing edge is very crisp and well defined
with what appears to be a steep rain gradient.
When REACT is selected, the area behind the steep rain gradient fills
in with cyan.

Radar Facts
5-64

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

30
20
10
AD- 22161- R1@

Crescent Shape
Figure 5- 46

Line Configurations
AVOID THUNDERSTORM ECHOES AT THE SOUTH END OF A
LINE OR AT A BREAK IN A LINE BY 20 MILES
The echo at the south end of a line of echoes is often severe and so too
is the storm on the north side of a break in line. Breaks frequently fill in
and are particularly hazardous for this reason. Breaks should be
avoided unless they are 40 miles wide. This is usually enough room to
avoid thunderstorm hazards.
The above two locations favor severe thunderstorm formation since these
storms have less competition for low level moisture than others nearby.

A28- 1146- 102- 00

Radar Facts
5-65

PRIMUSr 880 Digital Weather Radar System

AVOID LINE ECHO WAVE PATTERNS (LEWP) BY 20 MILES
One portion of a line may accelerate and cause the line to
assume a wave- like configuration. Figure 5- 47 is an example of an
LEWP. The most severe weather is likely at S. LEWPs form solid or
nearly solid lines that are dangerous to aircraft operations and
disruptive to normal air traffic flow.

N
S

AD- 15562- R1@

Line Echo Wave Pattern (LEWP)
Figure 5- 47
The S indicates the location of the greatest hazards to aviation. The
next greatest probability is anywhere along the advancing (usually east
or southeast) edge of the line.

Radar Facts
5-66

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

AVOID BOW- SHAPED LINE OF ECHOES BY 20 MILES
Sometimes a fast moving, broken to solid thunderstorm line will
become bow- shaped as shown in figure 5- 48. Severe weather is most
likely along the bulge and at the north end, but severe weather can
occur at any point along the line. Bow- shaped lines are particularly
disruptive to aircraft operations because they are broken to solid and
may accelerate to speeds in excess of 70 knots within an hour.

VIP 1
100 mi

VIP 3

VIP 5
AD- 15563- R1@

Bow- Shaped Line of Thunderstorms
Figure 5- 48

A28- 1146- 102- 00

Radar Facts
5-67

PRIMUSr 880 Digital Weather Radar System

Additional Hazards
TURBULENCE VERSUS DISTANCE FROM STORM CORE
The stronger the return, the further the turbulence will be encountered
from the storm core at any altitude. Severe turbulence is often found in
the tenuous anvil cloud 15 to 20 miles downwind from a severe storm
core. Moreover, the storm cloud is only the visible portion of a turbulent
system whose up and down drafts often extend outside of the storm
proper.
TURBULENCE VERSUS DISTANCE FROM STORM EDGE
Severe clear- air turbulence can occur near a storm, most often on the
downwind side. Tornadoes are located in a variety of positions with
respect to associated echoes, but many of the most intense and
enduring occur on the up- relative- windside. The air rising in a tornado
can contribute to a downwind area of strong echoes, while the tornado
itself may or may not return an echo. Echo hooks and appendages,
though useful indexes of tornadoes, are not infallible guides.
The appearance of a hook warns the pilot to stay away, but just because
the tornado cannot be seen is no assurance that there is no tornado
present.
Expect severe turbulence up to 20 NM away from severe storms; this
turbulence often has a well- defined radar echo boundary. This
distance decreases somewhat with weaker storms that display
less well- defined echo boundaries.
The last section of this manual contains several advisory circulars. It is
recommended that the pilot become familiar with them.

Radar Facts
5-68

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

GROUND MAPPING
Ground mapping operation is selected with the GMAP button An
example of ground map display is shown in figure 5- 49. Turn the TILT
control down until the desired amount of terrain is displayed. The
degree of down- tilt will depend upon the type of terrain, aircraft altitude,
and selected range. Tables 5- 13 and 5- 5 show tilt settings for maximal
ground target display at selected ranges.

Ground Mapping Display
Figure 5- 49
For the low ranges (5, 10, 25, and 50 NM), the transmitter pulsewidth is
narrowed and the receiver bandwidth is widened to enhance the
identification of small targets. In addition, the receiver STC characteristics
are altered to better equalize ground target reflections versus range. As
a result, the preset gain position is generally used to display the desired
map. The pilot can manually decrease the gain to eliminate unwanted
clutter.

A28- 1146- 102- 00

Radar Facts
5-69

PRIMUSr 880 Digital Weather Radar System

RANGE
SCALE
(NM)

100

- 12

-8

- 11

-8

- 10

-7

- 13

-9

-7

- 11

-8

-6

- 10

-7

-6
-5

200

ALTITUDE
(FEET)

30,000
25,000
20,000
15,000
10,000

- 13

-8

-6

5,000

-9

-6

-5

4,000

-8

-6

-5

3,000

-7

-5

2,000

-6

-5

-4

1,000

-5

-4

246
(LINE OF SIGHT LIMITED REGION)

35,000

(TILT LIMITED
REGION)

40,000

LINE OF
SIGHT
(NM)

230
213
195
174
151
123
87
78
67
55
39
AD- 35710@

TILT Setting for Maximal Ground Target Display
12- Inch Radiator
Table 5- 13
NOTE:
Radar Facts
5-70

The line of sight distance is nominal. Atmospheric conditions
and terrain will offset this value.
A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

RANGE
SCALE
(MILES)

100

200

LINE OF
SIGHT
(MILES)

- 13

-5

-2

-1

246

- 11

-4

-1

230

213

35,000
30,000
25,000

-9

-3

-1

-7

-2

195
174

-5

-1

15,000

- 12

-3

-1

10,000

-7

-1

5,000

-7

-2

4,000

-5

-1

3,000

-3

2,000

-1

1,000

20,000

(LINE OF
SIGHT LIMITED REGION)

40,000

(TILT LIMITED
REGION)

ALTITUDE
(FEET)

151
123
87
78
67
55
39
AD- 35711@

TILT Setting for Maximal Ground Target Display
18- Inch Radiator
Table 5- 14
NOTES:

1. The line of sight distance is nominal. Atmospheric
conditions and terrain will offset this value.
2. Tilt management for 24- inch radiator installation
operates in a similar manner.

A28- 1146- 102- 00

Radar Facts
5-71/(5-72 blank)

PRIMUSr 880 Digital Weather Radar System

Maximum Permissible Exposure
Level (MPEL)

Heating and radiation effects of weather radar can be hazardous to life.
Personnel should remain at a distance greater than R from the radiating
antenna in order to be outside of the envelope in which radiation
exposure levels equal or exceed 10 mW/cm2, the limit recommended
in FAA Advisory Circular AC No. 20--68B, August 8, 1980, Subject:
Recommended Radiation Safety Precautions for Ground Operation of
Airborne Weather Radar. The radius, R, to the maximum permissible
exposure level boundary is calculated for the radar system on the basis
of radiator diameter, rated peak--power output, and duty cycle. The
greater of the distances calculated for either the far--field or near--field
is based on the recommendations outlined in AC No. 20--68B. The
advisory circular is reproduced without Appendix 1 in Appendix A of this
guide.
The American National Standards Institute (ANSI), in their document
ANSI C95.1--1982, recommends an exposure level of no more than
5 mW/cm2.
Honeywell recommends that operators follow the 5 mW/cm2 standard.
Figure 6--1 shows MPEL for both exposure levels.

MPEL Boundary
Figure 6--1

A28-- 1146-- 102-- 03
REV 3

Maximum Permissible Exposure Level (MPEL)
6-1/(6-2 blank)

PRIMUSr 880 Digital Weather Radar System

In- Flight Troubleshooting

The PRIMUSÒ 880 Digital Weather Radar System can provide
troubleshooting information on one of two formats:
D

Fault codes

Text faults.

The selection is made at the time of installation. This section describes
access and use of this information.
If the fault codes option is selected, they are shown in place of the tilt
angle. The text fault option provides English text in the radar test pattern
areas.
Critical functions in the receiver transmitter antenna (RTA) are
continuously monitored. Each fault condition has a corresponding
2- digit fault code (FC). Additionally, a fault name, a pilot message, and
a line maintenance message are associated with each fault condition.
Faults can be accessed on the ground, or while airborne. The following
conditions indicate that fault information is being displayed:
D

Display, indicator, or RTA malfunction

FAIL annunciation on weather indicator or EFIS display.

If the feature TEXT FAULTS is enabled, the radar test pattern area will
display plan English text fault information. If it is not enabled, only the
fault code is shown (one at a time) on the indicator or EFIS display.

A28- 1146- 102- 00

In- Flight Troubleshooting
7-1

PRIMUSr 880 Digital Weather Radar System

NOTES:

1. FC installations with a radar indicator can display
stored faults for the current power- on cycle and nine
previous cycles. Installations with radar displayed on
the electronic flight instrument system (EFIS) do not
display stored faults.
2. In FC installation, that use a radar indicator, when the
storage memory is full, the indicator fault storage
deletes the oldest power- on fault codes to make room
for the newest.
3. In EFIS installations, some weather failures are only
annunciated with an amber WX.
4. In EFIS installations, with TEXT FAULTS enabled, the
fault codes are also presented as part of the FAIL
annunciation (e.g., FAIL 13).

Test Mode With TEXT FAULTS Enabled
Upon entering test mode, the most recent fault is displayed, cycling to
the oldest fault in the eligible list of faults. Upon reaching the last fault
an END OF LIST message is displayed. To recycle through the list
again, exit and re- enter TEST mode.

In- Flight Troubleshooting
7-2

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

Table 7- 1 describes the six fault data fields that are displayed in figure
7- 1.
Field No.

Description

Pilot Message

Line Maintenance Message

Fault Code/Power- on Code

Fault Name

Transmit ON/OFF

Strap Code
1. If airborne, only fault fields 1, 2, and 3 are
displayed.

NOTES:

2. Airborne, only the current faults are displayed.
3. Strap codes indicate the installation configuration
that was done at the time of installation. Refer to
the System Description and Installation manual for
further explanation.

Fault Data Fields
Table 7- 1
The last 32 faults from the last 10 power- on cycles are cycled every two
antenna sweeps (approximately 8 seconds).

0.0

PILOT
MESSAGE
FIELD

100

FAULT
DISPLAY
MESSAGE
DIVIDER
LINE
MAINTENANCE
MESSAGE

FAULT CODE/
POWER ON
COUNT

FAULT
NAME

TRANSMIT
ON/OFF
60

RCT/T
1

40
3

WEATHER INDICATOR

STRAP
CODE
AD- 46709@

Fault Annunciation on Weather Indicator With TEXT FAULT
Fields
Figure 7- 1
A28- 1146- 102- 00

In- Flight Troubleshooting
7-3

PRIMUSr 880 Digital Weather Radar System

Figure 7- 2 shows the fault codes displayed on EFIS with text faults
disabled.

DTRK

315

MAG1

FAIL
22

321

TGT

FMS1
130 NM

V
VOR1
50
VOR2
HDG

319

25
15

GSPD
260 KTS

AD- 35708- R1@

Fault Code on EFIS Weather Display
With TEXT FAULTS Disabled
Figure 7- 2

Radar Indication With Text Fault Enabled (On Ground)
Figure 7- 3

In- Flight Troubleshooting
7-4

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

Fault Code and Text Fault Relationships
Table 7- 2 lists the relationship between:
D

Fault codes (FC)

Pilot/Maintenance Messages

Fault Name/type/description/cross reference (XREF).

XREF

FAULT DESCRIPTION

4808

Startup Code CRC

4809

IOP Code CRC

4810

DSP Code CRC

4904

Config Table CRC

4905

FPGA Firmware CRC

4846

2V ADC Reference

4903

IOP Ready

4908

Int ARINC 429
Loopback

4910

Spurious ARINC
Interrupt

4913

ARINC 429 In Coupling

4806

EEPROM Timer CRC

4811

EEPROM POC

4842

Stab Trim CRC

4912

Calibration CRC

4812

IOP Mailbox

4818

DSP Mailbox

4813

Timing FPGA RAM

4814

Timing FPGA REG

4815

IO FPGA RAM

FAULT NAME

PILOT
MSG

LINE
MAINT

FAULT TYPE

FLASH CRC

RADAR
FAIL

PULL
RTA

POWER ON

IOP

RADAR
FAIL

PULL
RTA

CONTINUOUS

POWER ON

IOP

RADAR
FAIL

PULL
RTA

CONTINUOUS

IOP

RADAR
FAIL

PULL
RTA

POWER ON

FLASH CRC

POWER ON
RADAR
FAIL

PULL
RTA

POWER ON

EEPROM

REDO
STAB
TRIM

IOP

RADAR
FAIL

PULL
RTA

MAILBOX RAM

RADAR
FAIL

PULL
RTA

POWER ON

FPGA

RADAR
FAIL

PULL
RTA

POWER ON

Text Faults
Table 7- 2 (cont)
A28- 1146- 102- 00

In- Flight Troubleshooting
7-5

PRIMUSr 880 Digital Weather Radar System

XREF

FAULT DESCRIPTION

4828

FPGA Download

FAULT NAME

PILOT
MSG

LINE
MAINT

FAULT TYPE

4906

IO FPGA REG

4847

STC Monitor

STC DAC

RADAR
FAIL

PULL
RTA

POWER ON

4830

HVPS Monitor

HVPS MON

RADAR
FAIL

PULL
RTA

CONTINUOUS

4816

DSP RAM

4817

DSP Video RAM

POWER ON

4855

DSP Watchdog

CONTINUOUS

4900

Mailbox Miscompare

4901

DSP Holda Asserted

4902

DSP Holda not
Asserted

DSP

RADAR
FAIL

PULL
RTA
POWER ON

4825

Filament Monitor

4827

Severe Magnetron

MAGNETRON

4829

PFN Trim Monitor

HVPS MON

4831

Pulse Width

PULSE WIDTH

RADAR
UNCAL

PULL
RTA

CONTINUOUS

4832

Elevation Error

EL POSITION

TILT
UNCAL

CHK
RADOME
/RTA

CONTINUOUS

4833

Azimuth Error

AZ POSITION

AZIMUTH
UNCAL

CHK
RADOME
/RTA

CONTINUOUS

4836

Over Temp

OVER- TEMP

RADAR
CAUTION

PULL
RTA

CONTINUOUS

4837

Xmitter Power

XMTR POWER

RADAR
UNCAL

PULL
RTA

CONTINUOUS

4839

No SCI Control

4911

No ARINC 429 Control

NO CNTL IN

CHK
CNTL
SRC

PROBE

4840

AGC Limiting

4927

AGC Rx DAC Monitor

4928

AGC Tx DAC Monitor

RADAR
FAIL

PULL
RTA

CONTINUOUS

PICTURE
UNCAL
AGC

LATCHED

RADAR
FAIL

CONTINUOUS
PULL
RTA

POWER ON

Text Faults
Table 7- 2 (cont)
In- Flight Troubleshooting
7-6

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

XREF

FAULT DESCRIPTION

FAULT NAME

PILOT
MSG

4841

Selftest OSC Failure

RCVR
SELF- TEST

PICTURE
UNCAL

4843

Multiple AFC Unlocks

4845

AFC Sweeping

LINE
MAINT

FAULT TYPE

PULL
RTA

CONTIUOUS

SPOKING
LIKELY
AFC

CONTINUOUS
PULL
RTA

4929

AFC DAC Monitor

4930

AFC Trim DAC Monitor

4848

AHRS/IRS Source

HS 429

STAB
UNCAL

CHK ATT
SRC

INSTALLATION

4849

DADC Source

LS 429

TURB
UNCAL

CHK ADC

INSTALLATION

4852

Analog Stab Ref

STAB REF

STAB
UNCAL

CHK ATT
SRC

INSTALLATION

4853

Scan Switch Off

SCAN SWITCH

SCAN
SWITCH

CHK
SWITCH

INSTALLATION

4854

Xmit Switch Off

XMIT SWITCH

XMIT
SWITCH

CHK
SWITCH

INSTALLATION

4914

Invalid
altitude/airspeed/stab
strapping

INVALID
STRAPS

RADAR
UNCAL

CHK
STRAPS

4915

Invalid controller source
strapping

4916

Config1 database
version/size mismatch

RADAR
FAIL

POWER ON

IOP

RADAR
FAIL

PULL
RTA

Text Faults
Table 7- 2

A28- 1146- 102- 00

In- Flight Troubleshooting
7-7

PRIMUSr 880 Digital Weather Radar System

Table 7- 3 describes the pilot messages.
Pilot MSG
RADAR FAIL

Description
The radar is currently inoperable and should not be
relied upon. It will need to be replaced or repaired at
the next opportunity.

RADAR CAUTION A failure has been detected that can compromise the
calibration accuracy of the radar. Information from the
radar should be used only for advisory purposes such
as ground mapping for navigation.
PICTURE UNCAL

TILT UNCAL

TURB UNCAL

SPOKING LIKELY

The radar functions are ok, but receiver calibration is
degraded. Color level calibration should be assumed
to be incorrect.
Have the RTA checked at the next opportunity.
An error in the antenna position system has been
detected. The displayed tilt angle setting could be
incorrect. This may also cause ground spoking.
Have the RTA checked at the next opportunity.
A problem has been detected with the turbulence
detection hardware. Assume turbulence display to be
inaccurate. Nonturbulence modes should be
functioning properly.
Have the RTA checked at the next opportunity.
A problem has been detected which may cause
spoking to occur.
Have the system checked at the next opportunity.

STAB UNCAL

An error in the antenna positioning system has been
detected. Groundspoking, or excessive ground
returns during roll maneuvers may occur. This may be
due either to the RTA or the source of pitch and roll
information to the RTA.

NO AUTOTILT

No altitude information is available to make the
altitude compensated tilt calculation. Otherwise, the
unit may be operated as normal. Have system
(including altitude source) checked at the next
opportunity.

SCAN SWITCH

The SCAN SWITCH located on the RTA is off,
disabling the antenna scan. Check at the next
opportunity.

XMIT SWITCH

The XMIT switch located on the RTA is off, disabling
the transmitter. Check at the next opportunity.

Pilot Messages
Table 7- 3

In- Flight Troubleshooting
7-8

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

Honeywell Product Support

The Honeywell SPEXR program for corporate operators provides an
extensive exchange and rental service that complements a worldwide
network of support centers. An inventory of more than 9,000 spare
components assures that the Honeywell equipped aircraft will be
returned to service promptly and economically. This service is available
both during and after warranty.
The aircraft owner/operator is required to ensure that units provided
through this program have been approved in accordance with their
specific maintenance requirements.
All articles are returned to Reconditioned Specifications limits when
they are processed through a Honeywell repair facility. All articles are
inspected by quality control personnel to verify proper workmanship
and conformity to Type Design and to certify that the article meets all
controlling documentation. Reconditioned Specification criteria are on
file at Honeywell facilities and are available for review. All exchange
units are updated with the latest performance reliability MODs on an
attrition basis while in the repair cycle.
For more information regarding the SPEX program, including
maintenance, pricing, warranty, support, and access to an electronic
copy of the Exchange/Rental Program for Corporate Operators, Pub.
No. A65--8200--001, you can go to the Honeywell web site at:
http://www.avionicsservices.com/home.jsp

A28-- 1146-- 102-- 03
REV 3

Honeywell Product Support
8-1

PRIMUSr 880 Digital Weather Radar System

CUSTOMER SUPPORT
Honeywell Aerospace Online Technical Publications
Web Site
Go to the Honeywell Online Technical Publications Web site at
https://pubs.cas.honeywell.com/ to:
D

Download or view publications online

Order a publication

Tell Honeywell of a possible data error in a publication.

Customer Response Center (CRC)
If you do not have access to the Honeywell Online Technical
Publications Web site, send an e--mail message or a fax, or speak to
a person at the CRC:
D

E--mail: cas--publications--distribution@honeywell.com

Fax: 1--602--822--7272

Phone: 1--877--484--2979 (USA)

Phone: 1--602--436--0272 (International).

Also, the CRC is available if you need to:
D

Identify a change of address, telephone number, or e--mail address

Make sure that you get the next revision of this guide.

Honeywell Product Support
8-2

A28-- 1146-- 102-- 03
REV 3

PRIMUSr 880 Digital Weather Radar System

Abbreviations

Acronyms and abbreviations used in this guide are defined as follows:
ABBREVIATION

EQUIVALENT

AC
ACT
ADC
AFC
AGC
AGL
AHRS
ANLG
ANSI
API
ATT
AZ

Advisory Circular
Altitude Compensated Tilt
Air Data Computer
Automatic Flight Control
Automatic Gain Control
Above Ground Level
Attitude Heading Reference System
Analog
American National Standards Institute
Antenna Position Indicator
Attitude
Azimuth

BITE
BRT

Built--in Test Equipment
Brightness

ccw
CHK
CLR
CNTL
CONFIG
CRC
CRT
cw

Counterclockwise
Check
Clear
Control
Configuration
Cyclic Redundancy Check
Cathode Ray Tube
Clockwise

DADC
DSP

Digital Air Data Computer
Display

EFIS
EGPWS
EHSI
EL

Electronic Flight Instrument System
Enhanced Ground--Proximity Warning System
Electronic Horizontal Situation Indicator
Elevation

FAA
FC

Federal Aviation Administration
Fault Code

A28-- 1146-- 102-- 03
REV 3

Abbreviations
9-1

PRIMUSr 880 Digital Weather Radar System

FLTPLN, FP,
FPLN
FMS
FPGA
FSBY
ft

Flight Management System
Field--Programmable Gate Array
Forced Standby
Feet

GCR
GMAP
GPS

Ground Clutter Reduction
Ground Mapping
Global Positioning System

hr
HVPS

hour
High Voltage Power Supply

INHIB
IO
IOP
IN
IRS

Inhibit
Input/Output
Inoperative
Inch
Inertial Reference System

kt, kts

Knot(s)

LEWP
LSS, LX

Line Echo Wave Pattern
Lightning Sensor System

MFD
mm
MON
MPEL

Multifunction Display
millimeter
Monitor
Maximum Permissible Exposure Level

NAV
ND
NM
NSSL
NWS

Navigation
Navigation Display
Nautical Miles
National Severe Storms Laboratory
National Weather Service

OSC

Oscillator

PPI
PPP

Plan--Position Indicator
Pulse Pair Processing

Abbreviations
9-2

Flight Plan

A28-- 1146-- 102-- 01
REV 1

PRIMUSr 880 Digital Weather Radar System

RCT, REACT
RCVR
RTA

Rain Echo Attenuation Compensation Technique
Receiver
Receiver Transmitter Antenna

SBY,STBY
SCI
SCT, SECT
SECT
SLV
SPEX
SRC
STAB
STC

Standby
Serial Control Interface
Scan Sector
Sector Scan
Slave
Spares Exchange
Source
Stabilization
Sensitivity Timing Control

TCAS
TERR
TGT
TRB
TRV
TST
TURB

Traffic Alert and Crew Alerting System
Terrain
Target
Turbulence
Total Return Vector
Test
Turbulence

UDI
UNCAL

Universal Digital Interface
Uncalibration

VAR
VIP

Variable, Variance
Video Integrated Processor

WOW
WX

Weight--on--Wheels
Weather

XMIT, XMTR
XSTC

Transmitter
Extended Sensitivity Timing Control

A28-- 1146-- 102-- 01
REV 1

Abbreviations
9-3/(9-4 blank)

PRIMUSr 880 Digital Weather Radar System

Appendix A

Federal Aviation Administration
(FAA) Advisory Circulars
NOTE:

This section contains a word- for- word transcription of the
contents of the following FAA advisory circulars:

AC 20- 68B

AC 00- 24B.

SUBJECT: RECOMMENDED RADIATION SAFETY
PRECAUTIONS
FOR
GROUND
OPERATION OF AIRBORNE WEATHER
RADAR
Purpose
This circular sets forth recommended radiation safety precautions to be
taken by personnel when operating airborne weather radar on the
ground.

Cancellation
AC 20- 66A, dated April 11, 1975, is cancelled.

Related Reading Material
Barnes and Taylor, radiation Hazards and Protection (London: George
Newnes Limited, 1963), p. 211.
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.
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.
A28- 1146- 102- 00

Federal Aviation Administration (FAA) Advisory Circulars
A- 1

PRIMUSr 880 Digital Weather Radar System

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 the testis.

Precautions
Management and supervisory personnel should establish procedures
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.
GENERAL
D

Airborne weather radar should be operated on the ground only by
qualified personnel.

Installed airborne radar should not be operated while other aircraft
is in the 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:
D

Personnel should never stand nearby and in front of a 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 Appendix 1 or the graphs of figures 1 and
2. 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 10 milliwatts per square centimeter.

Personnel should be advised to avoid the end of an open waveguide
unless the radar is turned off.

Personnel should be advised to avoid looking into a waveguide, or
into the open end of a coaxial connector or line connector to a radar
transmitter output, as severe eye damage may result.

Federal Aviation Administration (FAA) Advisory Circulars
A- 2

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

Personnel should be advised that when high 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 pulser, oscillator, clipper, or rectifier tubes, as well as
magnetrons.

COMBUSTIBLE MATERIALS
To prevent possible fuel ignition, an insulated airborne weather radar
should not be operated while an aircraft is being refueled or defueled.
M.C. Beard
Director of Airworthiness.

A28- 1146- 102- 00

Federal Aviation Administration (FAA) Advisory Circulars
A- 3

PRIMUSr 880 Digital Weather Radar System

SUBJECT: THUNDERSTORMS
Purpose
This advisory circular describes the hazards of thunderstorms to
aviation and offers guidance to help prevent accidents caused by
thunderstorms.
Cancellation
Advisory Circular 00- 24A, dated
June 23, 1978, is cancelled.

Related Reading Material
Advisory Circulars, 00- 6A, Aviation Weather, 090- 45B, Aviation
Weather Services, 00- 50A, Low Level Wind Shear.

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 attitudes toward thunderstorms, but one rule continues
to be true - any storm recognizable as a thunderstorm 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.

Hazards
A thunderstorm packs just about every weather hazard known to
aviation into one vicious bundle. Although the hazards occur in
numerous combinations, let us look at the most hazardous combination
of thunderstorm, the squall line, then we will examine the hazards
individually.
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.
Federal Aviation Administration (FAA) Advisory Circulars
A- 4

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

TORNADOES
D

The most violent thunderstorms draw 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 funnel shaped cloud extending downward from the cumulonimbus
base. If the cloud does not reach the surface, it is a funnel cloud;
if it touches the land surface, it is a tornado.

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.

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.

TURBULENCE
D

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 thunderstorm. 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 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 1 shows a schematic cross section of a thunderstorm
with areas outside the cloud where turbulence may be encountered.

It is almost impossible to hold a constant altitude in a thunderstorm,
and maneuvering in an attempt to do so produces 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.

A28- 1146- 102- 00

Federal Aviation Administration (FAA) Advisory Circulars
A- 5

PRIMUSr 880 Digital Weather Radar System

ICING
D

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 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.

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 with rime and clear.
The abundance of large, supercooled droplets makes clear icing
very rapid between O _C and - 15 _C and encounters can be
frequent in a cluster of cells. Thunderstorm icing can be extremely
hazardous.

MOTION OF STORM
DRY AIR
INFLOW

WARM AIR INFLOW
COLD

AIR

WAKE

OUTFLOW

WARM AIR
INFLOW

WAKE
COLD
AIR
OUTFLOW

NAUTICAL MILES
0

GUST FRONT
15

AD- 37561@

Schematic Cross Section of a Thunderstorm
Figure A- 1

Federal Aviation Administration (FAA) Advisory Circulars
A- 6

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

HAIL
D

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, possibly some
distance from the storm core. Hail may be encountered in clear air
several miles from dark thunderstorm clouds.

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.

LOW CEILING AND VISIBILITY
Generally, visibility is near zero within a thunderstorm cloud. Ceiling
and visibility may also 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 other thunderstorm hazards
of turbulence, hail, and lightning which make precision instrument flying
virtually impossible.
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.

A28- 1146- 102- 00

Federal Aviation Administration (FAA) Advisory Circulars
A- 7

PRIMUSr 880 Digital Weather Radar System

LIGHTNING
A lightning strike can puncture the skin of an aircraft and can damage
communication 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 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.
WEATHER RADAR
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 than 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.
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.
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 wind gusts, and turbulence.
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.
Federal Aviation Administration (FAA) Advisory Circulars
A- 8

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

Airborne weather avoidance radar is, as its name implies, 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 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 avoidance
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 does not mean you can fly.
Remember that while hail always gives a radar echo, it may fall several
miles from the nearest 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.
DO’S AND DON’TS OF THUNDERSTORM FLYING
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:
D

Don’t land or take off in the face of an approaching thunderstorm. A
sudden gust front of low level turbulence could cause loss of control.

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.

Don’t fly without airborne radar into a cloud mass containing
scattered embedded thunderstorms. Scattered thunderstorms not
embedded, usually can be visually circumnavigated.

Don’t trust the visual appearance to be a reliable indicator of the
turbulence inside a thunderstorm.

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 circumnavigate the entire area if the area has 6/1 thunderstorm
coverage.

Do remember that vivid and frequent lightning indicates the
probability of a severe thunderstorm.

Do regard as extremely hazardous, any thunderstorm with tops
35,000 feet or higher, whether the top is visually sighted or
determined by radar.

A28- 1146- 102- 00

Federal Aviation Administration (FAA) Advisory Circulars
A- 9

PRIMUSr 880 Digital Weather Radar System

If you cannot avoid penetrating a thunderstorm, the following are some
do’s BEFORE entering the storm.
D

Tighten your safety belt, put on your shoulder harness if you have
one, and secure all loose objects.

Plan and hold your course to take you through the storm in a
minimum time.

To avoid the most critical icing, establish a penetration altitude below
the freezing level or above the level of - 15 _C.

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.

Establish power settings for turbulence penetration airspeed
recommended in your aircraft manual.

Turn up cockpit lights to highest intensity to lessen temporary
blindness from lightning.

If using automatic pilot, disengage altitude hold mode and speed
hold mode. The automatic altitude and airspeed controls will
increase maneuvers of the aircraft thus increasing structural stress.

If using airborne radar, tilt the antenna up and down occasionally.
This will permit you to detect other thunderstorm activity at altitudes
other than the one being flown.

Following are some do’s and don’ts during thunderstorm penetration.
D

Do keep your eyes on your instruments. Looking outside the cockpit
can increase danger of temporary blindness from lightning.

Don’t change power settings; maintain settings
recommended turbulence penetration airspeed.

Do maintain constant attitude; let the aircraft ride the waves.
Maneuvers in trying to maintain constant altitude increase stress on
the aircraft.

Don’t turn back once you are in a 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.

Federal Aviation Administration (FAA) Advisory Circulars
A- 10

for

the

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

National Severe Storms Laboratory (NSSL)
Thunderstorm Research
The NSSL has, since 1964, been the focal point of our thunderstorm
research. In- flight conditions obtained from thunderstorm penetration
by controlled, especially equipped high performance aircraft are
compared by the NSSL with National Weather Service (NWS) type
ground- based radar and with newly developed doppler radar. The
following comments are based on NSSL’s interpretation of information
and experience from this research.
RELATIONSHIP BETWEEN TURBULENCE AND REFLECTIVITY
Weather radar reflects precipitation such as rain and hail, turbulence.
It has been found, however, that the intensity level of the precipitation
reflection does correlate with the degree of turbulence in a
thunderstorm. The most severe turbulence is not necessarily found at
the same place that gives the greatest radar reflection.
RELATIONSHIP BETWEEN TURBULENCE AND ALTITUDE
The NSSL studies of thunderstorms extending to 60,000 feet show little
variation of turbulence intensity with altitude.
TURBULENCE AND ECHO INTENSITY ON NWS RADAR (WSR- 57)
The frequency and severity of turbulence increases with radar reflectivity,
a measure of the intensity of echoes from storm targets at a standard
range. Derived gust velocities exceeding 2,100 feet per minute (classified
as severe turbulence) are commonly encountered in level 3 storms. In
level 2 storms, gusts of intensity between 1,200 and 2,100 feet per minute
(classified as moderate turbulence) are encountered approximately once
for each 10 nautical miles of thunderstorm flight.
TURBULENCE IN RELATION TO DISTANCE FROM STORM CORE
NSSL data indicates that the frequency and severity of turbulence
encounters decrease slowly with distance from storm cores. Significantly,
the data indicates that within 20 miles from the center of severe storm
cores, moderate to severe turbulence is encountered at any altitude about
one- fifth as often as in the cores of Level 3 or greater thunderstorms.
Further, the data indicates that moderate turbulence is encountered at any
altitude up to 10 miles from the center of level 2 thunderstorms. SEVERE
TURBULENCE IS OFTEN FOUND IN TENUOUS ANVIL CLOUDS 15
TO 20 MILES DOWNWIND FROM SEVERE STORM CORES. Our
findings agree with meteorological reasoning that THE STORM CLOUD
IS ONLY THE VISIBLE PORTION OF A TURBULENT SYSTEM
WHOSE UPDRAFTS AND DOWN- DRAFTS OFTEN EXTEND
OUTSIDE OF THE STORM PROPER.
A28- 1146- 102- 00

Federal Aviation Administration (FAA) Advisory Circulars
A- 11

PRIMUSr 880 Digital Weather Radar System

TURBULENCE IN RELATION TO DISTANCE FROM THE STORM
EDGE
THE CLEAR AIR ON THE INFLOW SIDE OF A STORM IS A PLACE
WHERE SEVERE TURBULENCE OCCURS. At the edge of a cloud, the
mixing of cloudy and clear air often produces strong temperature gradients
associated with rapid variation of vertical velocity. Tornado activity is found
in a wide range of spacial relationships to the strong echoes with which
they are commonly associated, but many of the most intense and enduring
tornadoes occur on the south to west edges of severe storms. The
tornado itself is often associated with only a weak echo. Echo hooks and
appendages are useful qualitative indicators of tornado occurrence but are
by no means infallible guides. Severe turbulence should be anticipated up
to 20 miles from the radar edge of severe storms; these often have a
well- defined radar echo boundary.
The distance decreases to
approximately 10 miles with weaker storms which may sometimes have
indefinite radar echo boundaries. THEREFORE, AIRBORNE RADAR IS
A PARTICULARLY USEFUL AID FOR PILOTS IN MAINTAINING A
SAFE DISTANCE FROM SEVERE STORMS.
TURBULENCE ABOVE STORM TOPS
Flight data shows a relationship between turbulence above storm tops
and the airspeed of upper tropospheric winds. WHEN THE WINDS AT
STORM TOP EXCEED 100 KNOTS, THERE ARE TIMES WHEN
SIGNIFICANT TURBULENCE MAY BE EXPERIENCED AS MUCH
AS 10,000 FEET ABOVE THE CLOUD TOPS. THIS VALUE MAY BE
DECREASED 1,000 FEET FOR EACH 10- KNOT REDUCTION OF
WIND SPEED. This is especially important for clouds whose height
exceeds the height of the tropopause. It should be noted that flight
above severe thunderstorms is an academic consideration for today’s
civil aircraft in most cases, since these storms usually extend up to
40,000 feet and above.
TURBULENCE BELOW CLOUD BASE
While there is little evidence that maximum turbulence exists at middle
heights in storms (FL 200- 300), turbulence beneath a storm is not to
be minimized. This is especially true when the relative humidity is low
in any air layer between the surface and 15,000 feet. Then the lower
altitudes may be characterized by strong outflowing winds and severe
turbulence where thunderstorms are present. Therefore, THE SAME
TURBULENCE CONSIDERATIONS WHICH APPLY TO FLIGHT AT
HIGH ALTITUDES NEAR STORMS APPLY TO LOW LEVELS AS
WELL.

Federal Aviation Administration (FAA) Advisory Circulars
A- 12

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

MAXIMUM STORM TOPS
Photographic data indicates that the maximum height attained by
thunderstorm clouds is approximately 63,000 feet. Such very tall storm
tops have not been explored by direct means, but meteorological
judgments indicate the probable existence of large hail and strong
vertical drafts to within a few thousand feet of the top of these isolated
stratosphere- penetrating storms.
THEREFORE, IT APPEARS
IMPORTANT TO AVOID SUCH VERY TALL STORMS AT ALL
ALTITUDES.
HAIL IN THUNDERSTORMS
The occurrence of HAIL IS MUCH MORE CLEARLY IDENTIFIED WITH
THE INTENSITY OF ECHOES THAN IS TURBULENCE. AVOIDANCE
OF MODERATE AND SEVERE STORMS SHOULD ALWAYS BE
ASSOCIATED WITH THE AVOIDANCE OF DAMAGING HAIL.
VISUAL APPEARANCE OF STORM AND ASSOCIATED
TURBULENCE WITH THEM
On numerous occasions, flight at NSSL have indicated that NO
USEFUL CORRELATION EXISTS BETWEEN THE EXTERNAL
VISUAL APPEARANCE OF THUNDERSTORMS AND THE
TURBULENCE AND HAIL WITHIN THEM.
MODIFICATION OF CRITERIA WHEN SEVERE STORMS AND
RAPID DEVELOPMENT ARE EVIDENT
During severe storm situations, radar echo intensities may grow by a
factor of ten each minute, and cloud tops by 7,000 feet per minute.
THEREFORE, NO FLIGHT PATH THROUGH A FIELD OF STRONG
OR VERY STRONG STORMS SEPARATED BY 20- 30 MILES OR
LESS MAY BE CONSIDERED TO REMAIN FREE FROM SEVERE
TURBULENCE.

A28- 1146- 102- 00

Federal Aviation Administration (FAA) Advisory Circulars
A- 13

PRIMUSr 880 Digital Weather Radar System

EXTRAPOLATION TO DIFFERENT CLIMBS
General comment: Severe storms are associated with an atmospheric
stratification marked by large values of moisture in low levels, relative
dryness in middle levels, and strong wind shear. It is well known that
this stratification of moisture permits excessive magnitudes of
convective instability to exist for an indefinite period until rapid
overturning of air is triggered by a suitable disturbance. Regions of the
atmosphere which are either very dry or very moist throughout
substantial depths cannot harbor great convective instability. Rather,
a more nearly neutral thermal stratification is maintained, partially
through a process of regular atmospheric overturning.
D

Desert Areas - In desert areas, storms should be avoided on the
same basis as described in the above paragraphs. While nonstorm
turbulence may, in general, be expected more frequently over desert
areas during daylight hours than elsewhere, THE SAME
TURBULENCE CONSIDERATIONS PREVAIL IN THE VICINITY
OF THUNDERSTORMS.

Tropical- Humid Climates - When the atmosphere is moist and only
slightly unstable though a great depth, strong radar echoes may be
received from towering clouds which do not contain vertical velocities
as strong as those from storms over the U.S. plains. Then it is a matter
of the pilot being informed with respect to the general atmospheric
conditions accompanying storms, for it is well known that
PRACTICALLY
ALL
GEOGRAPHIC
AREAS
HAVING
THUNDERSTORMS ARE OCCASIONALLY VISITED BY SEVERE
ONES.

USE OF AIRBORNE RADAR
Airborne radar is a valuable tool; HOWEVER, ITS USE IS
PRINCIPALLY AS AN INDICATOR OF STORM LOCATIONS FOR
AVOIDANCE PURPOSES WHILE ENROUTE.

Federal Aviation Administration (FAA) Advisory Circulars
A- 14

A28- 1146- 102- 00

PRIMUSr 880 Digital Weather Radar System

Appendix B

Enhanced Ground--Proximity
Warning System (EGPWS)
The Mark VII EGPWS combines information from aircraft navigation
equipment (i.e., flight management system (FMS), inertial reference
system (IRS), global positioning system (GPS), radio altimeter) with a
stored terrain database that alerts the pilot to potentially dangerous
ground proximity.
In addition to the verbal alert, the EGPWS can display the terrain data
on the weather radar indicator. Depending on the installation, the pilot
pushes a button to display the terrain, or the terrain data is automatically
displayed when a Terrain Alert occurs.

SYSTEM OPERATION
To display the EGPWS, the weather system can be in any mode except
OFF. When the EGPWS is active, the indicator range up and down
arrows control the EGPWS display range. The AZ button on the
indicator is also active and the azimuth lines can be displayed or
removed.
The other radar controls do not change the terrain display, but if they
are used while the EGPWS is displayed, they control the radar receiver
transmitter antenna (RTA), and the effect is displayed when the system
returns to the radar display.

EGPWS Controls
The typical EGPWS installation has remotely mounted push button
controls and status annunciators that are related to the display on the
radar indicator. The paragraphs below give a functional description of
the recommended controls.

A28-- 1146-- 102-- 03
REV 3

Enhanced Ground-- Proximity Warning System (EGPWS)
B-- 1

Use or disclosure of the information on this page is subject to the restrictions on the title page of this document.

PRIMUSr 880 Digital Weather Radar System

PUSH BUTTON CONTROLS
The following remotely mounted push buttons control the EGPWS
display:
D

INHIB (Inhibit) Button -- When active, the push on/push off INHIB
button prevents terrain data from being displayed on the radar
indicator. When the button is active, the INHIB annunciator lights.

ON (Terrain) Button -- When active, the push on/push off ON button
displays terrain on the radar indicator.

ANNUNCIATORS
The following annunciators are displayed on the radar indicator to
indicate EGPWS operation:
D

FAIL -- The FAIL annunciator indicates that the EGPWS has failed.

INHIB -- The INHIB annunciator indicates that the INHIB push
button has been pushed and is active. When INHIB is annunciated,
EGPWS is not displayed on the radar indicator, and the aural
annunciators do not sound.
NOTE:

The FAIL and INHIB annunciators are often incorporated
into the INHIB push button.

TERR (Terrain) -- The TERR annunciator indicates that the
annunciator lamp power is on. It does not indicate the operational
status of the system.

ON -- The ON annunciator indicates that the radar indicator is
displaying terrain. This ON push button lamp is lit if the ON push
button has been pushed and is active, or if an actual Terrain Alert
is indicated by the EGPWS system and the terrain is automatically
displayed.
NOTE:

The TERR and ON annunciators are often incorporated
into the ON push button.

Some installation may not contain all of these controls and
annunciators, or they may have different names. Most EGPWS
installations have additional controls and/or annunciators (i.e., TEST).
Refer to the appropriate publication for details.

Enhanced Ground-- Proximity Warning System (EGPWS)
B-- 2

A28-- 1146-- 102-- 03
REV 3

Use or disclosure of the information on this page is subject to the restrictions on the title page of this document.

PRIMUSr 880 Digital Weather Radar System

Related EGPWS System Operation
Some installations may have a DATA--NAV (navigation display, and/or
checklist), lightning sensor system (LSS), and/or traffic alert and crew
alerting system (TCAS) that already share the radar indicator’s display
by way of the Universal Digital Interface (UDI) connector. These
systems have priority for access to the radar display screen. These
systems data may be overlaid on the EGPWS display, or they may
simply override the EGPWS display.

EGPWS Operation
The EGPWS system may vary, depending on the installed controls and
software level of the EGPWS computer.
In some installations, the EGPWS display on the radar indicator is
manually operated. It is only displayed if the pilot pushes the ON button,
and it is removed if the pilot pushes the ON button a second time.
In some installations, the EGPWS display has a pop--up mode in which
the terrain display is automatically displayed when the EGPWS system
detects a terrain alert situation.
The pilot can remove the ground display from the radar indicator, or
prevent the EGPWS system from displaying ground on the radar
indicator by pushing the INHIB button.
The ↑ and ↓ range buttons on the radar indicator control the range of
the ground display. The radar indicator AZ button is active, and can
display or remove azimuth buttons. The other radar controls do not
change the ground display, but if they are used while EGPWS is
displayed, they control the radar RTA and the effects of any changes
are seen when the radar image is re--displayed.
For additional information, refer to the appropriate EGPWS operating
manual.

A28-- 1146-- 102-- 03
REV 3

Enhanced Ground-- Proximity Warning System (EGPWS)
B-- 3

Use or disclosure of the information on this page is subject to the restrictions on the title page of this document.

PRIMUSr 880 Digital Weather Radar System

EGPWS Display
The EGPWS displays is shown as variable dot patterns in green,
yellow, or red. The density and color is a function of how close the
terrain is relative to the aircraft altitude above ground level (AGL), refer
to table B--1. Terrain/obstacle alerts are shown by painting the
threatening terrain as solid or red. Terrain that is more than 2000 feet
below the aircraft is not displayed. Areas where terrain data is not
available are shown in magenta.
Elevation of Terrain in Feet
AGL

Color

2000 or more above the aircraft

High density red

1000 -- 2000 above the aircraft

High density yellow dot pattern

0--1000 above the aircraft

Medium Density yellow Dot
Pattern

0--1000 below the aircraft

Medium density green dot
pattern

1000 -- 2000 below the aircraft

Low density green dot pattern

2000 or more below the aircraft

black

Unknown terrain

Magenta

NOTE: Caution terrain (60 second warning) is displayed as solid yellow. Warning
obstacle (30 second warning) is displayed as solid red.

EGPWS Obstacle Display Color Definitions
Table B--1

Enhanced Ground--Proximity Warning System (EGPWS)
B--4

A28--1146--102--01
REV 1

PRIMUSr 880 Digital Weather Radar System

Figure B--1 shows the EGPWS over KPHX airport at 2000 feet mean
sea level heading north. The terrain shows the mountains to the north
of Phoenix.

AD--62964@

EHSI Display Over KPHX Airport
With the EGPWS Display
Figure B--1

A28--1146--102--01
REV 1

Enhanced Ground--Proximity Warning System (EGPWS)
B--5

PRIMUSr 880 Digital Weather Radar System

EGPWS Test
When the EGPWS is selected for display, it can be tested. Push the
remote mounted EGPWS TEST button to display the test format shown
in figure B--2.

AD--63056@

EGPWS Test Display
Figure B--2

Enhanced Ground--Proximity Warning System (EGPWS)
B--6

A28--1146--102--01
REV 1

PRIMUSr 880 Digital Weather Radar System

Index
A
Abbreviations, 9-1
Accelerative error, 5-18
Altitude compensated tilt, 5-16

C
Categorizing storms, 5-35

D
Dynamic error, 5-18

F
Federal Aviation Administration
(FAA) Advisory Circulars
recommended radiation safety
precautions for ground
operation of airborne weather
radar, A--1
background, A--2
cancellation, A--1
precautions, A--2
purpose, A--1
related reading material, A--1
thunderstorms, A--4
general, A--4
hazards, A--4
national severe storms
laboratory (NSSL) thunder-storm research, A--11
purpose, A--4
related reading material, A--4

E
Enhanced ground--proximity
warning system (EGPWS), B--1
annunciators, B--2
FAIL, B--2
INHIB, B--2
ON, B--2
TERR, B--2
displays, B--4
obstacle display color
definitions, B--4
EGPWS test, B--6
push buttons controls, B--2
INHIB button, B--2
ON (terrain) button, B--2
system operation, B--1
controls, B--1
EGPWS operation, B--3
related EGPWS system
operation, B--3

A28--1146--102--01
REV 1

H
Hidden modes, 3-26
forced standby
entry method, 3-27
exit method, 3-27
function, 3-26
roll offset, 3-26, 3-27, 3-28
entry method, 3-27
exit method, 3-27
function, 3-27
use, 3-27
Honeywell product support, 8-1
24--hour exchange/rental support
centers, 8-2
customer support centers, 8-2
North America, 8-2
Rest of the world, 8-3
publication ordering information,
8-4

Index
Index--1

PRIMUSr 880 Digital Weather Radar System

Index (cont)
I

power--up procedure, 4-1
radar mode ---- ground
mapping, 4-6
radar mode ---- weather, 4-4
standby, 4-4
test mode, 4-6
color bands, 4-7
dedicated radar indicator, 4-7
fault code, 4--7
EFIS/MFD/ND, 4-7
noise band, 4-6
target alert block, 4-6
text fault, 4--6

In--flight troubleshooting, fault
access
fault data fields, 7-3
pilot messages, 7-5
test mode with TEXT FAULTS
enabled, 7-2
text faults, 7-5
Interpreting weather radar images,
5-31

N
National severe storms laboratory
(NSSL) thunderstorm
research, A--11
extrapolation to different climbs,
A--14
hail in thunderstorms, A--13
maximum storm tops, A--13
modification of criteria when
severe storms and rapid
development are evident, A--13
relationship between turbulence
and altitude, A--11
relationship between turbulence
and reflectivity, A--11
turbulence above storm tops,
A--12
turbulence and echo intensity on
NWS radar (WSR--57), A--11
turbulence below cloud base,
A--12
turbulence in relation to distance
from the storm edge, A--12
turbulence in relation to distance
from storm core, A--11
use of airborne radar, A--14
visual appearance of storm and
associated turbulence with
them, A--13
Normal operation
preliminary control settings, 4-1
Index
Index--2

O
Operating controls
hidden modes, 3-26
roll offset, 3-26, 3-27, 3-28
WC--884 Weather radar controller
operation, 3-20
BRT (brightness), 3-20
controller target alert
characteristics, 3-21
gain, 3-25
mode, 3-23
range, 3-23
RCT (rain echo attenuation
compensation technique),
3-21
SLV (slave), 3-23
STAB (stabilization), 3-21
TGT (target alert), 3-20
TILT, 3-22
TRB (turbulence detection),
3-21
Weather radar controller
operation, 3-11
controller target alert
characteristics, 3-17
gain, 3-18
LSS (lightning sensor system)
(option), 3-19
radar, 3-13
A28--1146--102--01
REV 1

PRIMUSr 880 Digital Weather Radar System

Index (cont)
range, 3-18
SECT (scan sector), 3-16
SLV (slave), 3-19
STB (stabilization), 3-17
TGT (target), 3-16
Tilt, 3-16
TRB (turbulence detection),
3-17
WI--880 Weather radar indicator
operation, 3-1
AZ (azimuth), 3-8
BRT (brightness) or BRT/LSS
(lightning sensor system),
3-9
display area, 3-2
function switch, 3-3
gain, 3-10
range, 3-8
RCT (rain echo attenuation
compensation technique),
3-7
SCT (scan sector), 3-8
STAB (stabilization), 3-7
target alert characteristics,
3-7
TGT (target), 3-6
tilt, 3-9
TRB (turbulence), 3-8

P
Pitch and roll trim adjustments, 5-19
Preliminary control settings, 4-1
Radar mode ---- ground mapping,
4-6
power--up procedure, 4-1
radar mode ---- weather, 4-4
standby, 4-4
Procedures
in--flight roll offset adjustment
procedure, 5-26
pitch gain adjustment, 5-30
pitch offset adjustment
procedure, 5-28
A28--1146--102--01
REV 1

PRIMUSR 880 power--up
procedure, 4-2
roll gain adjustment, 5-29
severe weather avoidance
procedures, 5-60
stabilization in straight and level
flight check procedure, 5-21
stabilization in turns check
procedure, 5-23

R
Radar facts
additional comments, 5-68
turbulence versus distance
from storm core, 5-68
turbulence versus distance
from storm edge, 5-68
configurations of individual
echoes (Northern Hemisphere),
5-60
avoid all crescent shaped
echoes by 20 miles, 5-64
avoid hook echoes by 20
miles, 5-60
avoid pendant by 20 miles,
5-63
avoid steep rain gradients by
20 miles, 5-64
avoid V--notch by 20 miles,
5-62
ground mapping, 5-69
interpreting weather radar
images, 5-31
line configurations, 5-65
avoid bow--shaped line of
echoes by 20 miles, 5-67
avoid line echo wave patterns
(LEWP) by 20 miles, 5-66
avoid thunderstorm echoes at
the south end of a line or at
a break in a line by 20
miles, 5-65
radar operation, 5-1
radome, 5-54
Index
Index--3

PRIMUSr 880 Digital Weather Radar System

Index (cont)
Radar facts (cont)
rain echo attenuation
compensation technique
(REACT), 5-37
azimuth resolution, 5-53
hail size probability, 5-47
shadowing, 5-40
spotting hail, 5-48
turbulence detection
operation, 5-45
turbulence detection theory,
5-42
turbulence probability, 5-40
stabilization, 5-18
accelerative error, 5-18
dynamic error, 5-18
tilt management, 5-5
variable gain control, 5-37
weather avoidance, 5-55
severe weather avoidance
procedures, 5-60
weather display calibration, 5-35
Radar Images, 5-31
Radar operation, 5-1
Radiation Safety Precautions, A--1
Radome, 5-54
Rain echo attenuation
compensation technique
(REACT), 5-37
Recommended radiation safety
precautions for ground operation
of airborne weather radar, A--1
background, A--2
cancellation, A--1
precautions, A--2
body damage, A--2
combustible materials, A--3
general, A--2
purpose, A--1
related reading material, A--1

S
Shadowing, 5-40
Stabilization, 5-18
Index
Index--4

pitch gain adjustment, 5-30
pitch offset adjustment, 5-28
roll gain adjustment, 5-29
roll stabilization check, 5-23, 5-25
variable gain control, 5-37
Stabilization precheck, 5-21
System configurations, 2-1, 2-2

T
Test mode, 4-6
color bands, 4-7
dedicated radar indicator, 4-7
fault code, 4--7
EFIS/MFD/ND, 4-7
noise band, 4-6
target alert block, 4-6
text fault, 4--6
Thunderstorms, A--4
effect on altimeters, A--7
extrapolation to different climbs,
A--14
general, A--4
hail, A--7
hail in, A--13
hazards of, A--4
effect on altimeters, A--7
hail, A--7
do’s and don’ts of
thunderstorm flying, A--9
icing, A--6
lightning, A--8
low ceiling and visibility, A--7
schematic cross section of a
thunderstorm, A--6
squall lines, A--4
tornadoes, A--5
turbulence, A--5
weather radar, A--8
icing, A--6
lightning, A--8
low ceiling and visibility, A--7
maximum storm tops, A--13
A28--1146--102--01
REV 1

PRIMUSr 880 Digital Weather Radar System

Index (cont)
National severe storms laboratory
(NSSL) thunderstorm research,
A--11
extrapolation to different
climbs, A--14
hail in thunderstorms, A--13
maximum storm tops, A--13
modification of criteria when
severe storms and rapid
development are evident,
A--13
relationship between
turbulence and altitude,
A--11
relationship between
turbulence and reflectivity,
A--11
turbulence above storm tops,
A--12
turbulence and echo intensity
on NWS radar (WSR--57),
A--11
turbulence below cloud base,
A--12
turbulence in relation to
distance from the storm
edge, A--12
turbulence in relation to
distance from storm core,
A--11
use of airborne radar, A--14
visual appearance of storm
and associated turbulence
with them, A--13
purpose, A--4
related reading material, A--4
squall line, A--4
thunderstorm flying, A--9
thunderstorm research, A--11
tornadoes, A--5
turbulence, A--5
above storm tops, A--12
and altitude, A--11
and echo intensity on NWS
radar, A--11
A28--1146--102--01
REV 1

in relation to distance from
storm core, A--11
and reflectivity, A--11
below cloud base, A--12
in relation to distance from the
storm edge, A--12
visual appearance, A--13
Tilt management, 5-5

V
Variable gain control, 5-37

W
WC--884 Weather radar controller
operation, 3-20
mode, 3-23
FSBY, 3-25
GMAP, 3-24
OFF, 3-23
Rainfall rate color coding,
3-24
STBY, 3-23
WX, 3-24
tilt, 3-22
PULL ACT (altitude
compensated tilt) function,
3-22
Weather avoidance, 5-55
Weather display calibration, 5-35
Weather radar controller operation,
3-11
LSS (lightning sensor system)
(option), 3-19
CLR/TST, 3-19
LX, 3-19
Off, 3-19
SBY, 3-19
radar, 3-13
FP (flight plan), 3-14
FSBY (forced standby), 3-15
GMAP (ground mapping),
3-14
Index
Index--5

PRIMUSr 880 Digital Weather Radar System

Index (cont)
Weather radar controller operation
(cont)
OFF, 3-13
Rainfall rate color coding,
3-13
RCT (rain Echo attenuation
compensation technique),
3-13
SBY (standby), 3-13
TST (test), 3-15
WX (weather), 3-13
tilt, 3-16
PULL ACT (altitude
compensated tilt) function,
3-16
WI--880 Weather radar indicator
operation, 3-1
BRT (brightness) or BRT/LSS
(lightning sensor system), 3-9
CLR/TST (clear/test), 3-9
LX (lightning sensor system),
3-9
OFF, 3-9
SBY (standby) , 3-9
function switch, 3-3
FP (flight plan), 3-5
FSBY (forced standby), 3-5
GMAP (ground mapping), 3-4
OFF, 3-3
rainfall rate color coding, 3-4
SBY (standby), 3-3
TST (test), 3-5
WX (weather), 3-3
tilt, 3-9
PULL ACT (altitude
compensated tilt) function,
3-9

Index
Index--6

A28--1146--102--01
REV 1

Source Exif Data:

File Type                       : PDF
File Type Extension             : pdf
MIME Type                       : application/pdf
PDF Version                     : 1.5
Linearized                      : Yes
Has XFA                         : No
XMP Toolkit                     : 3.1-701
About                           : uuid:5653297a-bea5-4bae-acc7-ec7ca0024be3
Keywords                        : PRIMUS 880
Producer                        : Acrobat PDFWriter 3.0 for Windows NT; modified using iText 5.0.0_SNAPSHOT by 1T3XT
Modify Date                     : 2010:01:08 12:06:39-05:00
Create Date                     : 1996:12:09 09:13:09Z
Creator Tool                    : Interleaf Print Cancel Box
Metadata Date                   : 2010:01:08 12:06:39-05:00
Document ID                     : uuid:d3ccd5f5-9483-40dc-8bf3-c9ce8a62d644
Instance ID                     : uuid:2c592d93-a99f-447f-b4ea-34b58ea9c4f6
Format                          : application/pdf
Title                           : PRIMUS 880 Digital Weather Radar System
Creator                         : BCAS
Description                     : A28-1146-102, Rev 1
Subject                         : PRIMUS 880
Page Mode                       : UseOutlines
Page Count                      : 161
Author                          : BCAS

EXIF Metadata provided by EXIF.tools

Honeywell Weather Radio 880 Users Manual PRIMUS Digital Radar System

880 to the manual 440a994a-e92c-4326-ba95-7eecdaadcbc7

Navigation menu

Versions of this User Manual:

Views

Navigation