Honeywell Weather Radio 660 User Manual
®
®
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AD-54257@  
Honeywell  
AerospaceElectronic Systems  
CES–Phoenix  
P.O. Box 21111  
Phoenix, Arizona 85036–1111  
U.S.A.  
R
TO:  
HOLDERS OF THE PRIMUS 660 DIGITAL WEATHER  
RADAR SYSTEM PILOT’S MANUAL, HONEYWELL PUB.  
NO. A28–1146–111  
REVISION NO. 3 DATED AUGUST 2003  
HIGHLIGHTS  
Pages that have been revised are outlined below. Remove and insert  
the affected pages listed. The revision number has been added to the  
bottom of the revised pages and revision bars have been used to  
indicate the revised or added text. Insert this highlights letter in the  
manual in your possession ahead of page RR-1/RR-2, Record of  
Revisions. The List of Effective Pages shows the order in which to insert  
the attached new pages of front material into your manual.  
Page No.  
Title Page  
Description of Change  
Revised to reflect revision 3. Update Proprietary  
Notice. Changed S99 to S2003 and changed  
copyright from 1999 to 2003.  
RR–1/RR–1  
Revised to reflect revision 3.  
Revised to reflect revision 3.  
LEP–1 thru  
LEP–3/LEP–4  
6–1/6–2  
Removed Inc. in Honeywell in paragraph above  
figure. Replaced art in FIgure 6–1.  
Highlights  
Page 1 of 1  
August 2003  
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Honeywell  
Aerospace Electronic Systems  
CES–Phoenix  
P.O. Box 21111  
Phoenix, Arizona 85036–1111  
U.S.A.  
PRIMUSR 660 Digital Weather  
Radar System  
Pilot’s Manual  
Revised August 2003  
Printed in U.S.A.  
Pub. No. A28–1146–111–03  
February 1998  
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PROPRIETARY NOTICE  
This document and the information disclosed herein are proprietary  
data of Honeywell. Neither this document nor the information contained  
herein shall be used, reproduced, or disclosed to others without the  
written authorization of Honeywell, except to the extent required for  
installation or maintenance of recipient’s equipment.  
NOTICE – FREEDOM OF INFORMATION ACT (5 USC 552) AND  
DISCLOSURE OF CONFIDENTIAL INFORMATION GENERALLY  
(18 USC 1905)  
This document is being furnished in confidence by Honeywell. The  
information disclosed herein falls within exemption (b) (4) of 5 USC 552  
and the prohibitions of 18 USC 1905.  
All rights reserved. No part of this book, CD, or PDF may be reproduced  
or transmitted in any form or by any means, electronic or mechanical,  
including photocopying, recording, or by any information storage and  
retrieval system, without the written permission of Honeywell  
International, except where a contractual arrangement exists between  
the customer and Honeywell.  
S2003  
ASSOCIATE  
MEMBER  
E
Member of GAMA  
General Aviation  
Manufacturer’s Association  
PRIMUS and LASEREF are U.S. registered trademarks of Honeywell  
DATA NAV is a U.S. trademarks of Honeywell  
E2003 Honeywell International Inc.  
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PRIMUS 660 Digital Weather Radar System  
Record of Revisions  
Upon receipt of a revision, insert the latest revised pages and dispose  
of superseded pages. Enter revision number and date, insertion date,  
and the incorporator’s initials on the Record of Revisions. The typed  
initials H are used when Honeywell is the incorporator.  
Revision  
Number  
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Dec 1999  
Aug 2003  
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Aug 2003  
A28–1146–111  
REV 3  
Record of Revisions  
RR–1/(RR–2 blank)  
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PRIMUS 660 Digital Weather Radar System  
Record of Temporary Revisions  
Upon receipt of a temporary revision, insert the yellow temporary  
revision pages according to the filing instructions on each page. Then,  
enter the temporary revision number, issue date, and insertion date on  
this page.  
Date the  
Temporary  
Revision Was Insertion of Removal of  
Temporary  
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No.  
Incorporated  
by a Regular  
Revision  
Temporary  
Revision,  
Date/By  
Temporary  
Revision,  
Date/By  
Issue Date  
A28–1146–111  
REV 2  
Record of Temporary Revisions  
RTR–1/(RTR–2 blank)  
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PRIMUS 660 Digital Weather Radar System  
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Original  
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Normal Operation  
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Operating Controls  
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PRIMUS 660 Digital Weather Radar System  
Subheading and Page  
Revision  
Subheading and Page  
Revision  
Radar Facts (cont)  
5–13  
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(MPEL)  
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7–13  
7–14  
7–15/7–16  
In–Flight Troubelshooting  
8–1  
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PRIMUS 660 Digital Weather Radar System  
Subheading and Page  
Revision  
Subheading and Page  
Revision  
Appendix A (cont)  
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Appendix B  
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B–3  
B–4  
B–5  
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Index  
Index–1  
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Index–6  
Index–7  
Index–8  
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List of Effective Pages  
LEP–3/(LEP–4 blank)  
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PRIMUS 660 Digital Weather Radar System  
Table of Contents  
Section  
1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
Page  
1-1  
2. SYSTEM CONFIGURATIONS . . . . . . . . . . . . . . . . .  
3. OPERATING CONTROLS . . . . . . . . . . . . . . . . . . . .  
2-1  
3-1  
WI–650/660 Weather Radar Indicator Operation . . .  
WC–660 Weather Radar Controller Operation . . . . .  
3-1  
3-10  
4. NORMAL OPERATION . . . . . . . . . . . . . . . . . . . . . . .  
4-1  
Preliminary Control Settings . . . . . . . . . . . . . . . . . . .  
Standby . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
Radar Mode – Weather . . . . . . . . . . . . . . . . . . . .  
Radar Mode – Ground Mapping . . . . . . . . . . . . .  
Test Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
4-1  
4-4  
4-4  
4-5  
4-6  
5. RADAR FACTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
5-1  
Radar Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
Tilt Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
Stabilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
Dynamic Error . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
Accelerative Error . . . . . . . . . . . . . . . . . . . . . . . . .  
Antenna Mounting Error . . . . . . . . . . . . . . . . . . . .  
Wallowing (Wing Walk and Yaw) Error . . . . . . . .  
Roll Gain Error . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
Pitch Gain Error . . . . . . . . . . . . . . . . . . . . . . . . . . .  
Interpreting Weather Radar Images . . . . . . . . . . . . .  
Weather Display Calibration . . . . . . . . . . . . . . . . . . .  
Variable Gain Control . . . . . . . . . . . . . . . . . . . . . . . . .  
Rain Echo Attenuation Compensation Technique  
(REACT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
Shadowing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
Turbulence Probability . . . . . . . . . . . . . . . . . . . . .  
Hail Size Probability . . . . . . . . . . . . . . . . . . . . . . .  
Spotting Hail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
Azimuth Resolution . . . . . . . . . . . . . . . . . . . . . . . .  
Radome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
Weather Avoidance . . . . . . . . . . . . . . . . . . . . . . . . . . .  
Configurations of Individual Echoes (Northern  
Hemisphere) . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
Line Configurations . . . . . . . . . . . . . . . . . . . . . . . .  
5-1  
5-5  
5-15  
5-15  
5-15  
5-16  
5-19  
5-19  
5-22  
5-24  
5-28  
5-30  
5-31  
5-34  
5-34  
5-36  
5-37  
5-41  
5-42  
5-43  
5-47  
5-52  
A28–1146–111  
REV 2  
Table of Contents  
TC–1  
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PRIMUS 660 Digital Weather Radar System  
Table of Contents (cont)  
Section  
Page  
5. RADAR FACTS (CONT)  
Additional Hazards . . . . . . . . . . . . . . . . . . . . . . . .  
5-55  
5-56  
Ground Mapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
6. MAXIMUM PERMISSIBLE EXPOSURE LEVEL  
(MPEL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
6-1  
7-1  
7. IN–FLIGHT ADJUSTMENTS . . . . . . . . . . . . . . . . . .  
Pitch and Roll Trim Adjustments . . . . . . . . . . . . . . . .  
Level Fight Stabilization Check . . . . . . . . . . . . . .  
Roll Offset Adjustment . . . . . . . . . . . . . . . . . . . . . . . .  
Pitch Offset Adjustment . . . . . . . . . . . . . . . . . . . . . . .  
Roll Stabilization Check . . . . . . . . . . . . . . . . . . . . . . .  
Roll Gain Adjustment . . . . . . . . . . . . . . . . . . . . . . . . .  
Pitch Stabilization Check . . . . . . . . . . . . . . . . . . . . . .  
Pitch Gain Adjustment . . . . . . . . . . . . . . . . . . . . . . . .  
7-1  
7-3  
7-5  
7-8  
7-9  
7-11  
7-12  
7-15  
8. IN–FLIGHT TROUBLESHOOTING . . . . . . . . . . . . .  
8-1  
Test Mode With Text Faults Enabled . . . . . . . . . . . .  
Pilot Event Marker . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
Fault Code and Text Fault Relationships . . . . . . . . .  
8-2  
8-4  
8-5  
9. HONEYWELL PRODUCT SUPPORT . . . . . . . . . .  
9-1  
9-4  
Publication Ordering Information . . . . . . . . . . . . .  
10. ABBREVIATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . .  
10-1  
APPENDICES  
A FEDERAL AVIATION ADMINISTRATION (FAA)  
ADVISORY CIRCULARS . . . . . . . . . . . . . . . . . . . .  
A–1  
Subject: Recommended Radiation Safety Precautions  
For Ground Operation Of Airborne Weather Radar  
Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
Cancellation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
Related Reading Material . . . . . . . . . . . . . . . . . . .  
Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
Precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
A–1  
A–1  
A–1  
A–1  
A–2  
A28–1146–111  
REV 2  
Table of Contents  
TC–2  
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PRIMUS 660 Digital Weather Radar System  
Table of Contents (cont)  
A FEDERAL AVIATION ADMINISTRATION (FAA)  
ADVISORY CIRCULARS (CONT)  
Subject: Thunderstorms . . . . . . . . . . . . . . . . . . . . . .  
Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
Cancellation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
Related Reading Material . . . . . . . . . . . . . . . . . . .  
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
National Severe Storms Laboratory (NSSL)  
Thunderstorm Research . . . . . . . . . . . . . . . . . .  
A–3  
A–3  
A–3  
A–3  
A–3  
A–4  
A–10  
B ENHANCED GROUND–PROXIMITY WARNING  
SYSTEM (EGPWS) . . . . . . . . . . . . . . . . . . . . . . . . .  
B–1  
System Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
EGPWS Controls . . . . . . . . . . . . . . . . . . . . . . . . . .  
Related EGPWS System Operation . . . . . . . . . .  
EGPWS Operation . . . . . . . . . . . . . . . . . . . . . . . .  
EGPWS Display . . . . . . . . . . . . . . . . . . . . . . . . . .  
EGPWS Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
B–1  
B–1  
B–3  
B–3  
B–4  
B–6  
INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Index–1  
List of Illustrations  
Figure  
Page  
2–1 PRIMUSR 660 Configurations . . . . . . . . . . . . . . . . . .  
2-2  
2–2 Typical PRIMUSR 660 Weather Radar  
Components| . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
2-5  
3–1 Typical PRIMUSR 660 Digital  
Weather Radar Display . . . . . . . . . . . . . . . . . . . . . .  
3–2 WI–650/660 Weather Radar Indicator Front Panel  
View . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
3–3 WI–650/660 Weather Radar Indicator Display  
Screen Features . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
3–4 WC–660 Weather Radar Controller  
3-1  
3-2  
3-5  
Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
3-10  
4-3  
4–1 EFIS Test Pattern (Typical) 120° Scan Shown . . . .  
4–2 Indicator Test Pattern 120° Scan (WX), With  
TEXT FAULT Enabled . . . . . . . . . . . . . . . . . . . . . . .  
4-3  
A28–1146–111  
REV 2  
Table of Contents  
TC–3  
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PRIMUS 660 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  
5-2  
5-3  
5-4  
5-5  
5-5  
5-6  
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 Symmetrical Ground Returns . . . . . . . . . . . . . . . . . .  
5–19 Ground Return Indicating Misalignment  
5-6  
5-10  
5-10  
5-11  
5-11  
5-12  
5-12  
5-13  
5-13  
5-14  
5-14  
5-17  
(Upper Right) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
5–20 Ground Return Indicating Misalignment  
5-18  
5-18  
(Upper Left) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
5–21 Symmetrical Ground Returns – Good Roll  
Stabilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
5–22 Understabilization in a Right Turn . . . . . . . . . . . . . . .  
5–23 Overstabilization in a Right Turn . . . . . . . . . . . . . . . .  
5–24 Roll Stabilization Inoperative in a Turn . . . . . . . . . . .  
5–25 Symmetrical Ground Returns – Good Pitch  
Stabilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
5–26 Understabilized in Pitch–Up . . . . . . . . . . . . . . . . . . . .  
5–27 Overstabilized in Pitch–Up . . . . . . . . . . . . . . . . . . . . .  
5–28 Weather Radar Images . . . . . . . . . . . . . . . . . . . . . . .  
5–29 Radar and Visual Cloud Mass . . . . . . . . . . . . . . . . . .  
5–30 Squall Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
5–31 REACT ON and OFF Indications . . . . . . . . . . . . . . .  
5-20  
5-20  
5-21  
5-21  
5-22  
5-23  
5-23  
5-24  
5-26  
5-27  
5-33  
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PRIMUS 660 Digital Weather Radar System  
Table of Contents (cont)  
List of Illustrations (cont)  
Figure  
Page  
5–32 Probability of Turbulence Presence in a Weather  
Target . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
5-35  
5-37  
5-38  
5-38  
5-39  
5-40  
5-41  
5-43  
5-48  
5-49  
5-50  
5-51  
5-52  
5-53  
5-54  
5-56  
5–33 Hail Size Probability . . . . . . . . . . . . . . . . . . . . . . . . . .  
5–34 Rain Coming From Unseen Dry Hail . . . . . . . . . . . .  
5–35 Familiar Hailstorm Patterns . . . . . . . . . . . . . . . . . . . .  
5–36 Overshooting a Storm . . . . . . . . . . . . . . . . . . . . . . . .  
5–37 Short– and Long–Blind Alley . . . . . . . . . . . . . . . . . . .  
5–38 Azimuth Resolution in Weather Modes . . . . . . . . . .  
5–39 Weather Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
5–40 Typical Hook Pattern . . . . . . . . . . . . . . . . . . . . . . . . .  
5–41 V–Notch Echo, Pendant Shape . . . . . . . . . . . . . . . .  
5–42 The Classic Pendant Shape . . . . . . . . . . . . . . . . . . .  
5–43 Rain Gradients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
5–44 Crescent Shape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
5–45 Line Echo Wave Pattern (LEWP) . . . . . . . . . . . . . . .  
5–46 Bow–Shaped Line of Thunderstorms . . . . . . . . . . . .  
5–47 Ground Mapping Display . . . . . . . . . . . . . . . . . . . . . .  
6–1 MPEL Boundary . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
6-1  
7–1 Symmetrical Ground Returns . . . . . . . . . . . . . . . . . .  
7–2 Ground Return Indicating Misalignment (Right) . . .  
7–3 Ground Return Indicating Misalignment (Left) . . . .  
7–4 Roll Offset Adjustment Display – Initial . . . . . . . . . .  
7–5 Roll Offset Adjustment Display – Final . . . . . . . . . .  
7–6 Symmetrical Ground Returns, Level Flight and  
Good Roll Stabilization . . . . . . . . . . . . . . . . . . . . . .  
7–7 Understabilization in a Right Roll . . . . . . . . . . . . . . .  
7–8 Overstabilization in a Right Roll . . . . . . . . . . . . . . . .  
7–9 Level Flight and Good Pitch Stabilization . . . . . . . .  
7–10 Understabilized in Pitch Up . . . . . . . . . . . . . . . . . . . .  
7–11 Overstabilized in Pitch Up . . . . . . . . . . . . . . . . . . . . .  
7-4  
7-4  
7-5  
7-7  
7-7  
7-10  
7-10  
7-11  
7-13  
7-14  
7-14  
8–1 Fault Annunciation on Weather Indicator With  
TEXT FAULT Fields . . . . . . . . . . . . . . . . . . . . . . . . .  
8–2 Fault Code on EFIS Weather Display With  
TEXT FAULTS Disabled . . . . . . . . . . . . . . . . . . . . .  
8–3 Radar Indication With Text Fault Enabled  
(On Ground) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
8-3  
8-3  
8-4  
A–1 Schematic Cross Section of a Thunderstorm . . . . .  
A–6  
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PRIMUS 660 Digital Weather Radar System  
Table of Contents (cont)  
List of Illustrations (cont)  
Figure  
Page  
B–1 EHSI Display Over KPHX Airport With the  
EGPWS Display . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
B–2 EGPWS Test Display . . . . . . . . . . . . . . . . . . . . . . . . .  
B–5  
B–6  
List of Tables  
Table  
Page  
2–1 Dual Control Mode Truth Table . . . . . . . . . . . . . . . . .  
2–2 PRIMUSR 660 Weather Radar Equipment List . . . . .  
2-3  
2-4  
3–1 Target Alert Characteristics . . . . . . . . . . . . . . . . . . . .  
3–2 Rainfall Rate Color Coding . . . . . . . . . . . . . . . . . . . .  
3–3 WC–660 Controller Target Alert Characteristics . . .  
3–4 Rainfall Rate Color Coding . . . . . . . . . . . . . . . . . . . .  
3-4  
3-6  
3-12  
3-14  
4–1 PRIMUSR 660 Power–Up Procedure . . . . . . . . . . .  
4-1  
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 Stabilization in Straight and Level Flight Check  
Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
5–4 Stabilization in Turns Check Procedure . . . . . . . . . .  
5–5 Pitch Stabilization In–Flight Check Procedure . . . .  
5–6 Display Levels Related to dBZ Levels (Typical) . . . .  
5–7 VIP Levels Related to dBZ . . . . . . . . . . . . . . . . . . . .  
5–8 Turbulence Levels (From Airman’s Information  
Manual) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
5–9 Severe Weather Avoidance Procedures . . . . . . . . .  
5–10 TILT Setting for Maximal Ground Target Display  
12–Inch Radiator . . . . . . . . . . . . . . . . . . . . . . . . . . .  
5–11 TILT Setting for Maximal Ground Target Display  
18–Inch Radiator . . . . . . . . . . . . . . . . . . . . . . . . . . .  
5-8  
5-9  
5-17  
5-19  
5-22  
5-29  
5-30  
5-36  
5-43  
5-57  
5-58  
7-1  
7–1 Pitch and Roll Trim Adjustments Criteria . . . . . . . . .  
7–2 Stabilization in Straight and Level Flight Check  
Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
7–3 In–Flight Roll Offset Adjustment Procedure . . . . . .  
7-3  
7-5  
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PRIMUS 660 Digital Weather Radar System  
Table of Contents (cont)  
List of Tables (cont)  
Table  
Page  
7–4 Pitch Offset Adjustment Procedure . . . . . . . . . . . . .  
7–5 Roll Stabilization (While Turning) Check  
Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
7–6 Roll Gain Adjustment Procedure . . . . . . . . . . . . . . .  
7–7 Pitch Stabilization Check Procedure . . . . . . . . . . . .  
7–8 Pitch Gain Adjustment Procedure . . . . . . . . . . . . . .  
7-8  
7-9  
7-11  
7-12  
7-15  
8–1 Fault Data Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
8–2 Text Faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
8–3 Pilot Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
8-2  
8-5  
8-8  
B–1 EGPWS Obstacle Display Color Definitions . . . . . .  
B–4  
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PRIMUS 660 Digital Weather Radar System  
1. Introduction  
The PRIMUSR 660 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. 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). If selected at installation, the antenna  
sweep position indicator is a yellow band at the top of the display.  
Range marks and identifying numerics, displayed in contrasting colors,  
are provided to facilitate evaluation of storm cells.  
Selection of the GMAP function causes the system parameters to be  
optimized 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 5, Radar Facts, describes a variety of radar operating  
topics. It is recommended that you read Section 5, Radar  
Facts, before learning the specific operational details of the  
PRIMUSR 660 Digital Weather Radar System.  
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PRIMUS 660 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 NAVt system) and  
electrical discharge data from Honeywell’s LSZ–850 Lightning Sensor  
System (LSS).  
NOTE: Refer to Honeywell Pub. 28–1146–54, LSZ–850 Lightning  
Sensor System Pilot’s Handbook, for more information.  
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PRIMUS 660 Digital Weather Radar System  
2. System Configurations  
The PRIMUSR 660 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  
PRIMUSR 660 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.  
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PRIMUS 660 Digital Weather Radar System  
NOTES:  
1. 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.  
2. In the dual configuration, the pilots can use the slave  
feature to optimize the update rate of each side’s  
weather radar display to meet the needs of the  
situation. With one controller turned off, both cockpit  
displays are updated on every sweep of the radar, but  
control of the radar is only on one side. With each  
controller operating, each side has control but each  
side is updated with new radar information on every  
other sweep of the antenna.  
OFF  
RCT  
OFF  
STAB  
TGT  
SECT  
WX  
STBY  
OFF  
GMAP  
FP  
TEST  
+
PULL  
ACT  
0
PULL  
VA R  
15  
MAX  
MINGAIN  
RADAR  
SLV  
TILT  
–
OFF  
RCT  
OFF  
STAB  
TGT  
SECT  
WX  
GMAP  
FP  
TEST  
+
PULL  
ACT  
0
PULL  
VA R  
STBY  
OFF  
15  
MAX  
MINGAIN  
RADAR  
SLV  
TILT  
–
PRIMUSR 660 Configurations  
Figure 2–1  
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PRIMUS 660 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  
Left Side Right Side  
(NOTE 1) (NOTE 1)  
RTA  
Mode  
OFF  
OFF  
OFF  
OFF  
OFF  
OFF  
Standby  
”SLV”  
Standby  
Standby  
Standby  
Standby  
OFF  
Standby  
”SLV”  
Standby  
Standby  
OFF  
ON  
ON  
OFF  
ON  
”SLV” ON  
ON  
ON  
”SLV” ON  
ON/2  
ON  
ON  
ON  
Standby  
Standby/  
2
ON  
ON  
Standby  
ON  
ON/2  
ON/2  
Standby/2  
ON/2  
ON  
ON  
Standby  
Standby  
Standby  
Standby  
Standby  
Dual Control Mode Truth Table  
Table 2–1  
NOTES:  
1. ON is used to indicate any selected radar mode.  
2. “SLV” means that displayed data is controlled by  
opposite side controller. That is, the one controller that  
is operating is controlling both sweeps of the antenna.  
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.  
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PRIMUS 660 Digital Weather Radar System  
Equipment covered in this manual is listed in table 2–2 and shown in  
figure 2–2.  
Model  
Unit  
Part No.  
Cockpit Mounted Options  
WI–650/660 Weather Radar Indicator  
WC–660 Weather Radar Controller  
Remote Mounted Equipment  
WU–660 Receiver Transmitter Antenna  
7007700–VAR  
7008471–VAR  
7021450–601  
NOTES: 1. Typically, either the indicator or one of the remote controllers (one or  
two) is installed.  
2. Typical installed antenna sizes range from 12 to 18 inches in diameter.  
PRIMUSR 660 Weather Radar Equipment List  
Table 2–2  
NOTE: A WC–650 Weather Radar Controller can be installed.  
Except as noted, its operation is identical to the WC–660  
Weather Radar Controller.  
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PRIMUS 660 Digital Weather Radar System  
WU–660 RECEIVER/  
TRANSMITTER/ANTENNA  
WC–660 WEATHER RADAR  
CONTROLLER  
WI–650/660 WEATHER RADAR  
INDICATOR  
AD–51768@  
Typical PRIMUSR 660 Weather Radar Components  
Figure 2–2  
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PRIMUS 660 Digital Weather Radar System  
3. Operating Controls  
There are two basic controllers that are described in this section. They  
are (in order of description):  
D WI–650/660 Weather Radar Indicator  
D WC–660 Weather Radar Controller.  
WI–650/660 WEATHER RADAR INDICATOR  
OPERATION  
All controls used to operate the system display shown in figure 3–1, are  
located on the WI–650/660 Weather Radar Indicator front panel.  
AD–51769–R1@  
Typical PRIMUSR 660 Digital  
Weather Radar Display  
Figure 3–1  
The controls and display features of the WI–650/660 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.  
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PRIMUS 660 Digital Weather Radar System  
WI–650/660 Weather Radar Indicator Front Panel View  
Figure 3–2  
1
WX (WEATHER)  
The WX button is used to select the weather mode of operation. When  
WX is pushed, the system is fully operational and all internal  
parameters are set for enroute weather detection.  
Alphanumerics are white, and WX is displayed in the mode field.  
If WX is selected prior to the expiration of the initial RTA warm up period,  
the white WAIT legend is displayed in the mode field. In wait mode, the  
transmitter and antenna scan is inhibited and the memory is erased.  
Upon completion of the warmup period, the system automatically  
switches to WX mode.  
WX can only be selected when the function switch is in the ON position.  
2
GMP (GROUND MAPPING) OR MAP  
GMP button selects the ground mapping mode. The system is fully  
operational and all parameters are set to enhance returns from ground  
targets.  
NOTE: REACT or TGT modes are not selectable in GMP.  
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PRIMUS 660 Digital Weather Radar System  
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 the GMP is selected, the alphanumerics are  
changed to green, the GMP 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 moderated return, and  
magenta is a strong return.  
If GMP 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 GMP mode.  
GMP can only be selected when the function switch is in the ON  
position.  
3
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.  
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PRIMUS 660 Digital Weather Radar System  
4
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 3–1 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 (flight plan) modes.  
NOTE: In order to activate the target alert warning, the target must  
have the depth and range characteristics described in table  
3–1.  
Selected Range  
(NM)  
Minimum Target  
Depth (NM)  
Target Range  
(NM)  
5
5
5
5–55  
10–60  
25–75  
50–100  
100–150  
200–250  
N/A  
10  
25  
5
50  
5
100  
200  
5
5
300  
N/A  
5
FP (Flight Plan)  
5–55  
Target Alert Characteristics  
Table 3–1  
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PRIMUS 660 Digital Weather Radar System  
5
DISPLAY AREA  
See figure 3–3 and the associated text that explains the alphanumeric  
display.  
AD–51771@  
WI–650/660 Weather Radar Indicator Display Screen Features  
Figure 3–3  
6
FUNCTION SWITCH  
A rotary switch is used to select the following functions:  
D
O
F
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.
D 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 SBY.  
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PRIMUS 660 Digital Weather Radar System  
D ON – Places the system in the operational mode selected by the WX  
or MAP (GMP) button. 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.  
If ON 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 (or MAP)  
mode, as selected.  
The system, in preset gain, with WX selected, is calibrated as listed  
in table 3–2.  
Rainfall Rate  
Color  
in/hr  
mm/hr  
.04–.16  
.16–.47  
.47–2  
> 2  
1–4  
4–12  
12–50  
>5 0  
Green  
Yellow  
Red  
Magenta  
Rainfall Rate Color Coding  
Table 3–2  
D FP (Flight Plan) – The FP position puts the radar system in the flight  
plan mode, that clears the screen of radar data so ancillary data can  
be displayed. Examples of this data are:  
-
-
-
Electronic checklists  
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  
(flight plan) legend is shown in the mode field.  
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PRIMUS 660 Digital Weather Radar System  
The 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: The TGT function is inoperative when a checklist is  
displayed.  
D 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  
IN THE TEST MODE THE TRANSMITTER IS ON AND RADIATING  
X–BAND MICROWAVE ENERGY. 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, and the forced standby legend is displayed in  
the mode field.  
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).  
When in FSBY mode, you can restore normal operation by pulling the  
tilt control out, pushing it in, pulling it out, and pushing it in within three  
seconds.  
WARNING  
STANDBY OR FORCED STANDBY MODE MUST BE VERIFIED  
FOR GROUND OPERATION BY THE OPERATOR TO ENSURE  
SAFETY FOR GROUND PERSONNEL.  
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PRIMUS 660 Digital Weather Radar System  
7
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 (variance) 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 CAN BE ELIMINATED FROM THE DIS-  
PLAY 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 to allow details to be  
seen.  
Minimum gain is with the control at its full counterclockwise (ccw)  
position. Gain increases as the control is rotated cw from full ccw . At  
full clockwise (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.  
8
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_.  
WARNING  
TO AVOID FLYING UNDER OR OVER STORMS, FREQUENTLY AD-  
JUST THE TILT TO SCAN BOTH ABOVE AND BELOW YOUR  
FLIGHT LEVEL.  
Stabilization is normally ON. It can be turned OFF by pulling out the  
TILT knob. The knob is also used to operate the hidden modes. Refer  
to Section 8, In–Flight Troubleshooting  
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 STAB OFF annunciator is  
displayed on the screen.  
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PRIMUS 660 Digital Weather Radar System  
9
BRT (Brightness) or BRT/LSS (Lightning Sensor System)  
The BRT knob is a single–turn control that adjusts the brightness of the  
display. CW rotation increases display brightness and 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
O
F
F
–
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the system accumulates data in this mode.  
D
L
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operational and data is being displayed on the indicator.  
D 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.  
10 SCT (SCAN SECTOR)  
The SCT button is an alternate–action switch that is used to select  
either the normal 12 looks/minute 120_ scan or the faster update 24  
looks/minute 60_ sector scan.  
11 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.  
12 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.  
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PRIMUS 660 Digital Weather Radar System  
WC–660 WEATHER RADAR CONTROLLER OPERATION  
The controls and display features of the WC–660 Weather Radar  
Controller are indexed and identified in figure 3–4. Brightness levels for  
all legends and controls on the indicator are controlled by the dimming  
bus for the aircraft panel.  
OFF  
RCT  
OFF  
STAB  
TGT  
SECT  
+
15  
–
0
AD–51772@  
WC–660 Weather Radar Controller Configurations  
Figure 3–4  
NOTES:  
1. A WC–650 Weather Radar Controller can be installed  
in the aircraft. Consult the aircraft installed equipment  
configuration listing for details. Except as noted,  
operation of the WC–650 Weather Radar Controller is  
identical to the WC–660 Weather Radar Controller.  
2. Controllers are available with and without the LSS  
function.  
3. When single or dual radar controllers are used, the  
radar data is displayed on the EFIS, and/or an MFD or  
navigation display (ND).  
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PRIMUS 660 Digital Weather Radar System  
1
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.  
2
RCT (RAIN ECHO ATTENUATION COMPENSATION  
TECHNIQUE REACT))  
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 fourth 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.  
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. Refer to Section 5, Radar Facts, for a description of  
REACT.  
3
STAB (STABILIZATION)  
The STAB button turns the pitch and roll stability ON and OFF. It is also  
used with the hidden modes.  
NOTE: Some controllers annunciate OFF when stabilization is OFF.  
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PRIMUS 660 Digital Weather Radar System  
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.  
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 3–3.  
Selected Range  
(NM)  
Minimum Target  
Depth (NM)  
Target Range  
(NM)  
5
5
5
5–55  
10–60  
25–75  
50–100  
100–150  
200–250  
N/A  
10  
25  
5
50  
5
100  
200  
5
5
300  
N/A  
5
FP (Flight Plan)  
5–55  
WC–660 Controller Target Alert Characteristics  
Table 3–3  
NOTE: When on the ground, in FSBY mode, pushing STAB  
four times in three seconds, overrides forced standby.  
5
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.  
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PRIMUS 660 Digital Weather Radar System  
6
TILT  
The TILT knob 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
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between +5_ and –5_ is expanded for ease of setting. A digital readout  
of the antenna tilt angle is displayed on the EFIS.  
WARNING  
TO AVOID FLYING UNDER OR OVER STORMS, FREQUENTLY  
ADJUST THE TILT TO SCAN BOTH ABOVE AND BELOW YOUR  
FLIGHT LEVEL.  
7
LSS (LIGHTNING SENSOR SYSTEM) (OPTIONAL)  
The LSS switch is an optional four–position rotary switch that selects  
the LSS operating modes described below:  
D
O
F
F
–
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,
but the LSS still accumulates data.  
D
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operational and it displays LSS data on the indicator.  
D 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.  
8
SLV (SLAVE) (DUAL INSTALLATIONS ONLY)  
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. The slave mode  
allows one controller to set the modes of the RTA for both sweep  
directions. In the slave mode, all EFIS WX displays are indentical and  
updated on each sweep.  
With dual controllers, both controllers must be off before the radar  
system turns off.  
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PRIMUS 660 Digital Weather Radar System  
9
RADAR  
This rotary switch is used to select one of the following functions.  
D
O
F
F
–
T
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.
D STBY (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.  
D 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 3–4.  
Rainfall Rate  
Color  
in/hr  
mm/hr  
.04–.16  
.16–.47  
.47–2  
> 2  
1–4  
4–12  
12–50  
>5 0  
Green  
Yellow  
Red  
Magenta  
Rainfall Rate Color Coding  
Table 3–4  
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 or TGT 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.  
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PRIMUS 660 Digital Weather Radar System  
As a constant reminder that GMAP is selected, 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.  
NOTE: Some installations have controllers that have a WX/GMAP  
select switch. In this case, the radar mode switch provides an  
ON selection. The separate WX/GMAP switch is used to  
select either WX (weather) or GMAP (ground mapping).  
D FP (Flight Plan) – The FP position puts the radar system in the flight  
plan mode, that clears the screen of radar data. This allows the radar  
controller to select a range for display (on EFIS) of mapping  
information at very long ranges.  
NOTE: In the FP mode, the radar RTA is put in standby, and the  
FLTPLN legend is displayed in the mode field.  
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: When displaying checklist, the TGT function is inoperative.  
D 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 Operation, for a description of the test pattern.  
WARNING  
IN THE TEST MODE, THE TRANSMITTER IS ON AND RADIATING  
X–BAND MICROWAVE ENERGY. REFER TO SECTION 6, MAXI-  
MUM PERMISSIBLE EXPOSURE LEVEL (MPEL).  
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PRIMUS 660 Digital Weather Radar System  
FSBY (FORCED STANDBY)  
FSBY is an automatic, nonselectable radar mode. As an installation  
option, the RTA 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 four times in three seconds restores normal operation.  
NOTE: If a WC–650 Weather Radar Controller is installed, FSBY is  
overridden by simultaneously pushing both range arrow  
buttons.  
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  
STANDBY OR FORCED STANDBY MODE MUST BE VERIFIED IN  
GROUND OPERATIONS 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.  
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.  
WARNING  
LOW VARIABLE GAIN SETTINGS CAN ELIMINATE HAZARDOUS  
TARGETS FROM THE DISPLAY.  
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PRIMUS 660 Digital Weather Radar System  
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.  
NOTE: Some controllers have a preset position on the rotary knob.  
Rotating the knob to PRESET provides calibrated gain  
functions. Rotating the knob out of the PRESET position  
allows variable gain operation.  
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PRIMUS 660 Digital Weather Radar System  
4. Normal Operation  
PRELIMINARY CONTROL SETTINGS  
Table 4–1 gives the power–up procedure for the PRIMUSR 660 Digital  
Weather Radar System.  
Step  
Procedure  
1
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  
2
Take the following precautions if the radar system is 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.  
D Do not operate the radar system during aircraft refueling or  
during refueling operations within 100 feet (30 meters).  
D 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  
manual.)  
D Operating personnel should be familiar with FAA AC  
20–68B, which is reproduced in Appendix A of this  
manual.  
3
4
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, as shown in figure 4–1.  
PRIMUSR 660 Power–Up Procedure  
Table 4–1 (cont)  
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PRIMUS 660 Digital Weather Radar System  
Step  
Procedure  
5
When power is first applied, the radar is in WAIT for  
approximately 90 seconds to allow the magnetron to warm  
up. Power interruptions 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
7
After the warm–up, select the test mode and verify that the  
test pattern is displayed, as shown in figure 4–2. If the  
radar is being used with an EFIS, the test pattern is similar.  
The antenna position indicator (API) is shown as a yellow  
arc at the top of the display.  
NOTE: The API (a strap option) paints and unpaints on alternate sweeps to  
supply a continuous indication of picture bus activity. The color of the  
text does not change on alternate sweeps.  
Verify that the azimuth marks, target alert (TGT), and  
sector scan controls are operational.  
PRIMUSR 660 Power–Up Procedure  
Table 4–1  
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PRIMUS 660 Digital Weather Radar System  
TGT OR VAR ANNUNCIATOR  
:
TGT:  
TARGET ALERT  
– GREEN–SELECTED  
– AMBER TGT DETECTED  
P660 WX  
MODE  
ANNUNCIATIONS  
WX RANGE  
RINGS  
(WHITE)  
:
VAR:  
VARIABLE GAIN (AMBER)  
STBY (GREEN)  
TEST (GREEN)  
WX (GREEN)  
RCT (GREEN)  
GMAP (GREEN)  
WAIT (AMBER)  
FAIL ”N” (AMBER)  
FPLN  
TGT ALERT ON:  
RED  
TGT ALERT OFF:  
BLACK AND  
NOISE BAND  
DTRK  
MAG1  
TGT  
FMS1  
130 NM  
321  
315  
TEST  
+11  
TEXT AREA  
GRAY  
ANTENNA  
V
TILT  
ANGLE  
VOR1  
VOR2  
MAGENTA  
BLUE  
50  
REACT OFF:  
BLACK  
HDG  
319  
REACT ON:  
CYAN  
GSPD  
260 KTS  
25  
15  
YELLOW  
RED  
WX RANGE  
ANNUNCIATOR  
(WHITE)  
GREEN  
1. IF THE BITE DETECTS A FAULT IN TEST MODE, FAIL ”N” WILL BE SHOWN.  
”N” IS A FAULT CODE.  
NOTES:  
2. ANY FAULT CODE CAN ALSO BE DISPLAYED IN THE MAINTENANCE MODE.  
IN THAT CASE, IT REPLACES THE ANTENNA TILT ANGLE.  
AD–51774@  
EFIS Test Pattern (Typical) 120_ Scan Shown  
Figure 4–1  
AD–51773@  
Indicator Test Pattern 120_ Scan (WX),  
With TEXT FAULT Enabled  
Figure 4–2  
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PRIMUS 660 Digital Weather Radar System  
NOTES:  
1. Refer to the specific EFIS manual for a detailed  
description.  
2. The example shown is for installations with TEXT  
FAULT disabled.  
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 manual.  
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 or  
target alert (TGT) is selected.  
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.  
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PRIMUS 660 Digital Weather Radar System  
In the absence of intervening targets, the range at which the cyan field  
starts is approximately 290 NM with a 12–inch antenna. For the 18–inch  
antenna, the cyan field starts beyond 300 NM and therefore is not seen  
if there are no intervening targets.  
The RCT feature includes attenuation compensation (Refer to Section  
5, Radar Facts, 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 extended sensitivity time control  
(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.  
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 sensitivity time control (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.  
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PRIMUS 660 Digital Weather Radar System  
Test Mode  
The PRIMUSR 660 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 black/green/yellow/red/cyan/white/  
magenta/blue 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):  
- 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 8, In–Flight Troubleshooting.)  
D 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).  
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PRIMUS 660 Digital Weather Radar System  
5. Radar Facts  
RADAR OPERATION  
R
The PRIMUS 660 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.  
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PRIMUS 660 Digital Weather Radar System  
AIRCRAFT HEADING  
100  
80  
60  
+0.6  
40  
WX  
20  
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  
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.  
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PRIMUS 660 Digital Weather Radar System  
THUNDERSTORM  
ANTENNA  
TRANSMITTER  
INDICATOR  
SWEEP ORIGIN  
THUNDERSTORM  
SCAN  
AD–17716–R2@  
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.  
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PRIMUS 660 Digital Weather Radar System  
When the antenna is tilted downward for ground mapping, two  
phenomena can 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  
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PRIMUS 660 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 that is  
equivalent to sea level in altitude. The pilot must make adjustments for  
the effects of mountainous terrain.  
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  
41,800 FT  
60,000  
50,000  
ZERO TILT  
7.9  
20,000 FT  
20,000 FT  
10,500 FT  
10,500 FT  
CENTER OF RADAR BEAM  
30,000  
20,000  
41,800 FT  
10,000  
0
25  
50  
0
100  
RANGE NAUTICAL MILES  
AD–35693@  
Radar Beam Illumination High Altitude  
12–Inch Radiator  
Figure 5–4  
80,000  
70,000  
60,000  
50,000  
ZERO TILT  
7,400 FT  
7,400 FT  
29,000 FT  
29,000 FT  
14,800 FT  
CENTER OF RADAR BEAM  
14,800 FT  
30,000  
20,000  
5.6  
10,000  
0
0
25  
50  
RANGE NAUTICAL MILES  
100  
AD–17717–R1@  
Radar Beam Illumination High Altitude  
18–Inch Radiator  
Figure 5–5  
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PRIMUS 660 Digital Weather Radar System  
Radar Beam Illumination Low Altitude  
12–Inch Radiator  
Figure 5–6  
AD54258@  
Radar Beam Illumination Low Altitude  
18–Inch Radiator  
Figure 5–7  
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PRIMUS 660 Digital Weather Radar System  
Tables 5–1 and 5–2 give the approximate tilt settings that the ground  
targets begin to be displayed on the image periphery for 12– and  
18–inch radiators. The range that the 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.  
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.  
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PRIMUS 660 Digital Weather Radar System  
RANGE  
SCALE  
(NM)  
LINE OF  
SIGHT  
(NM)  
5
10  
25  
50 100 200 300  
ALTITUDE  
(FEET)  
40,000  
–12 –4  
–10 –3  
–1  
+1  
+1  
+1  
246  
35,000  
30,000  
25,000  
20,000  
15,000  
10,000  
5,000  
0
230  
213  
195  
174  
151  
123  
87  
–8  
–6  
–4  
–2  
–0  
+2  
–2  
–1  
0
0
+1  
+1  
+2  
+2  
–11  
–6  
+1  
+2  
+2  
–5  
–1  
4,000  
3,000  
2,000  
1,000  
–4  
–2  
0
0
+2  
+3  
+3  
+3  
+3  
+3  
+3  
78  
67  
55  
+1  
+2  
+3  
+2  
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: The line of sight distance is nominal. Atmospheric conditions  
and terrain offset this value.  
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PRIMUS 660 Digital Weather Radar System  
RANGE  
SCALE  
(MILES)  
LINE OF  
5
10  
25  
50 100 200  
SIGHT  
(MILES)  
ALTITUDE  
(FEET)  
40,000  
–13 –5  
–11 –4  
–2  
–1  
–1  
0
–1  
0
246  
230  
35,000  
30,000  
25,000  
20,000  
15,000  
10,000  
5,000  
–9  
–7  
–5  
–3  
–2  
–1  
–1  
0
0
213  
195  
0
174  
–12 –3  
151  
+1  
+1  
–7  
–2  
–1  
0
123  
+1  
+2  
+2  
+2  
87  
–7  
–5  
–3  
–1  
+1  
4,000  
–1 +1  
+1  
78  
3,000  
0
67  
2,000  
+1 +2  
+2 +2  
55  
39  
1,000  
AD–35711@  
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.  
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PRIMUS 660 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  
windshear 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 as shown in 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  
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PRIMUS 660 Digital Weather Radar System  
D 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  
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PRIMUS 660 Digital Weather Radar System  
D 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  
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PRIMUS 660 Digital Weather Radar System  
D 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 (GSPD), 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: The pilot should have freeze level information as a part of  
the flight planning process.  
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PRIMUS 660 Digital Weather Radar System  
D 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.  
AD–46703@  
Antenna Size and Impact on Tilt Management  
Figure 5–16  
NOTE: The 10– and 24–inch antennas are shown for illustration  
purposes only.  
D 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  
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PRIMUS 660 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 that, 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.  
NOTE: LASEREFR vertical reference systems do not suffer from  
these acceleration effects.  
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PRIMUS 660 Digital Weather Radar 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.  
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 let the gyroscope 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.  
Antenna Mounting Error  
If the radar consistently displays more ground returns on one side or the  
other during level flight over level ground, the antenna is probably  
scanning on a slight diagonal, rather than level with the earth. The usual  
cause is that the radar antenna is physically mounted slightly rotated  
from the vertical axis of the aircraft. The procedure in table 5–3 and  
figures 5–18, 5–19, and 5–20 can help you identify this type of problem.  
On a vertical gyro equipped aircraft, the condition could be caused by  
mistrim flying one wing low. The gyro erects to this condition and the  
stabilization is not able to compensate.  
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PRIMUS 660 Digital Weather Radar System  
LEVEL FLIGHT STABILIZATION CHECK  
Check stabilization in level flight using the procedure in table 5–3.  
Step  
Procedure  
1
Trim the aircraft for straight and level flight in smooth,  
clear air over level terrain.  
2
3
Select the 50–mile range.  
Rotate the tilt control until a band of ground returns  
starts at the 40 NM range arc.  
4
After several antenna sweeps, verify that ground  
returns are equally displayed (figure 5–18). 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.  
Stabilization in Straight and Level Flight Check Procedure  
Table 5–3  
NOTE: Refer to Section 7, In–Flight Adjustments, for procedures to  
adjust pitch and roll offsets.  
Symmetrical Ground Returns  
Figure 5–18  
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PRIMUS 660 Digital Weather Radar System  
100  
80  
60  
40  
20  
wx  
AD–17721–R2@  
Ground Return Indicating Misalignment (Upper Right)  
Figure 5–19  
100  
80  
60  
40  
20  
wx  
AD–17722–R2@  
Ground Return Indicating Misalignment (Upper Left)  
Figure 5–20  
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PRIMUS 660 Digital Weather Radar System  
Wallowing (Wing Walk and Yaw) Error  
A condition where the greatest intensity of ground targets wanders  
around the screen over a period of several minutes should not be  
confused with antenna mounting error. This phenomenon is caused by  
the tendency for many aircraft to slowly wallow (roll and yaw axes  
movement) with a cycle time of several minutes. The erection circuits  
of the gyro chasing the wallow can intensify the effect of wandering  
ground targets. IRS–equipped aircraft are less likely to show this  
condition.  
Roll Gain Error  
If, when the aircraft is in a turn, you see ground returns on one side or  
the other that are not present in level flight, the roll gain is most likely  
misadjusted. The procedure in table 5–4, and figures 5–21, 5–22, and  
5–23 can help you identify this type of problem. Figure 5–24 shows a  
total lack of roll stabilization in a turn.  
ROLL STABILIZATION (WHILE TURNING) CHECK  
Once proper operation is established in level flight, verify stabilization  
in a turn using this procedure.  
Step  
Procedure  
1
2
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. See figure  
5–24.  
3
4
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. See figure 5–23.  
NOTE: Proper radar operation in turns depends on the accuracy and stability of the  
installed attitude source.  
Stabilization in Turns Check Procedure  
Table 5–4  
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PRIMUS 660 Digital Weather Radar System  
Symmetrical Ground Returns – Good Roll Stabilization  
Figure 5–21  
100  
80  
60  
40  
20  
wx  
AD–17721–R2@  
Understabilization in a Right Turn  
Figure 5–22  
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PRIMUS 660 Digital Weather Radar System  
100  
80  
60  
40  
20  
wx  
AD–17722–R2@  
Overstabilization in a Right Turn  
Figure 5–23  
100  
80  
60  
40  
20  
wx  
AD–17723–R2@  
Roll Stabilization Inoperative in a Turn  
Figure 5–24  
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PRIMUS 660 Digital Weather Radar System  
Pitch Gain Error  
If the aircraft is in a pitch maneuver and you see ground returns that are  
not present in level flight, the pitch gain is most likely misadjusted. The  
procedure in table 5–5 and figures 5–25, 5–26, and 5–27 can help you  
identify this type of problem.  
PITCH STABILIZATION CHECK  
Once proper operation of the roll stabilization is established, verify pitch  
stabilization using the procedure in table 5–5 and figures 5–25, 5–26,  
and 5–27.  
Step  
Procedure  
1
2
3
Complete the steps listed in table 5–3.  
Place the aircraft between 5 and 10° pitch up.  
Note the radar display. If it is correctly stabilized, there  
is very little change in the ground returns.  
4
5
If the display of ground returns resembles figure 5–26,  
the radar is understabilized.  
If the display of ground returns resembles figure 5–27,  
the radar is overstabilized.  
Pitch Stabilization In–Flight Check Procedure  
Table 5–5  
Symmetrical Ground Returns – Good Pitch Stabilization  
Figure 5–25  
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PRIMUS 660 Digital Weather Radar System  
100  
80  
60  
40  
20  
GMAP  
AD–53797@  
Understabilized in Pitch–Up  
Figure 5–26  
100  
80  
60  
40  
GMAP  
20  
AD–53798@  
Overstabilized in Pitch–Up  
Figure 5–27  
Refer to Section 7, In–Flight Adjustments, for adjustment procedures.  
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PRIMUS 660 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 that  
these conditions are associated.  
The weather radar can see water best in its liquid form, as shown in  
figure 5–28 (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  
SMALL DRY HAIL  
AD–46704–R1@  
DRY SNOW – VERY POOR  
Weather Radar Images  
Figure 5–28  
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PRIMUS 660 Digital Weather Radar System  
The following are some truths about weather and flying, as shown in  
figure 5–29.  
D Turbulence results when two air masses at different temperatures  
and/or pressures meet.  
D This meeting can form a thunderstorm.  
D The thunderstorm produces rain.  
D The radar displays rain (thus revealing the turbulence).  
D 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.  
D In the thunderstorm’s mature stage, radar echoes are sharp and  
clear. Hail occurs most frequently early in this stage.  
D 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 5–30, 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.  
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PRIMUS 660 Digital Weather Radar System  
VISIBLE CLOUD MASS  
RAIN AREA  
(ONLY THIS IS  
VISIBLE ON RADAR)  
RED ZONE  
WITHIN  
RAIN AREA  
RED LEVEL*  
0
20  
40  
60  
80  
NAUTICAL MILES  
AD–12057–R3@  
Radar and Visual Cloud Mass  
Figure 5–29  
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.  
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PRIMUS 660 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 5–30, 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.  
GROWING  
AREAS OF MAXIMUM TURBULENCE  
CELLS  
DECAYING  
CELLS  
MATURE CELLS  
OUTLINE OF RAIN AREA VISIBLE TO RADAR  
BEST DETOUR  
AD–12058–R1@  
Squall Line  
Figure 5–30  
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PRIMUS 660 Digital Weather Radar System  
WEATHER DISPLAY CALIBRATION  
Ground based Nexrad radars of the National Weather Service display  
rainfall levels in dBZ, a decibel scaling of an arbitrary reflectivity factor  
(Z). The formula for determining dBZ is: dBZ = 16 log R + 23, where R  
is the rainfall rate in millimeters per hour. The Nexrad radar displays  
rainfall in 15 color coded levels of 5 dBZ per step.  
There is a close correspondence in rainfall rates between the colors in  
the PRIMUSR airborne radars and color families in a Nexrad display. To  
help the pilot in comparing them, table 5–6 shows PRIMUSR radar  
colors, rainfall rates, and dBZ.  
The dBZ rainfall intensity scale replaces the video integrated processor  
(VIP) intensity scale used in the previous generation ground based  
radars. Table 5–7 compares the classic VIP levels, rainfall rates, and  
storm categories with the new dBZ levels. Refer to Section 6 of FAA  
Advisory Circular AC–00–24B for additional information on VIP levels.  
Table 5–6 also shows maximum calibrated range for each color level.  
This is the maximum range where the indicated rainfall rate can be  
detected if there is no intervening radar signal attenuation caused by  
other precipitation. Beyond calibrated range, the precipitation appears  
at a lower color level than it actually is. For example, (with a 12–inch  
antenna) a red level storm can appear as a green level at 200 miles, as  
you fly closer it becomes yellow, and then red at 130 miles. As covered  
in the RCT description, intervening 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 that 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.  
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PRIMUS 660 Digital Weather Radar System  
300 NAUTICAL MILES  
MAXIMUM  
CALIBRATE  
D RANGE  
(NM) 10–IN  
AND 12–IN  
MAXIMUM  
CALIBRATE  
D RANGE  
(NM) 18–IN  
MAXIMUM  
CALIBRATE  
D RANGE  
(NM) 24–IN  
FLAT–PLATE  
RAINFALL  
RATE  
MM/HR  
RAINFALL  
RATE  
IN./HR  
DISPLAY  
LEVEL  
dBZ  
FLAT–PLATE FLAT–PLATE  
GREATER  
THAN  
300  
4
GREATER  
THAN  
50  
GREATER  
THAN  
2
GREATER  
THAN  
53  
GREATER  
THAN  
(MAGENTA  
)
232  
130  
90  
300  
190  
130  
3
(RED)  
12 – 50  
4 – 12  
1 – 4  
0.5 – 2  
40 – 53  
33 – 40  
23 – 33  
230  
160  
2
(YELLOW  
0.17 – 0.5  
0.04 – 0.17  
1
(GREEN)  
55  
–
80  
–
100  
–
0
LESS THAN  
1
LESS THAN  
0.04  
LESS THAN  
23  
(BLACK)  
Display Levels Related to dBZ Levels (Typical)  
Table 5–6  
WARNING  
THE RADAR IS CALIBRATED FOR CONVECTIVE WEATHER.  
STRATIFORM STORMS AT OR NEAR THE FREEZING LEVEL  
CAN SHOW HIGH REFLECTIVITY. DO NOT PENETRATE SUCH  
TARGETS.  
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PRIMUS 660 Digital Weather Radar System  
Rainfall rate in  
Storm  
Category  
VIP Level  
dBZ Level  
mm/hr  
6
Greater than  
125  
Extreme  
Greater than  
57  
5
4
3
2
1
50 – 125  
25 – 50  
Intense  
Very Strong  
Strong  
50 – 57  
45 – 50  
40 – 45  
29 – 40  
13 – 29  
12 – 25  
2.5 – 12  
0.25 – 2.5  
Moderate  
Weak  
VIP Levels Related to dBZ  
Table 5–7  
VARIABLE GAIN CONTROL  
The PRIMUSR 660 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.  
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PRIMUS 660 Digital Weather Radar System  
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.  
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.  
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PRIMUS 660 Digital Weather Radar System  
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 give invalid  
indications.  
Any target detected inside a cyan area is automatically forced to a  
magenta color indicating maximum severity. Figure 5–31 shows the  
same storm with REACT OFF and with REACT ON.  
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PRIMUS 660 Digital Weather Radar System  
AD–51778–R1@  
With REACT Selected  
AD–54262@  
Without REACT  
REACT ON and OFF Indications  
Figure 5–31  
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PRIMUS 660 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 5–32. This graph  
shows the following:  
D There is a 100% probability of light turbulence occurring in any area  
of rain  
D 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  
D 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  
D 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  
D 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 CAN 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.  
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PRIMUS 660 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.  
LEVEL 1  
GREEN  
LEVEL 2  
YELLOW  
LEVEL 3  
RED  
LEVEL 4  
MAGENTA  
LIGHT  
100%  
90%  
80%  
70%  
60%  
50%  
40%  
30%  
20%  
10%  
0%  
(4 mm / Hr)  
(12 mm / Hr)  
(50 mm / Hr)  
RAINFALL RATE  
AD–15357–R3@  
Probability of Turbulence Presence  
in a Weather Target  
Figure 5–32  
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PRIMUS 660 Digital Weather Radar System  
Turbulence levels are listed and described in table 5–8.  
REACTION INSIDE  
AIRCRAFT  
INTENSITY  
AIRCRAFT REACTION  
Turbulence that momentarily causes  
Occupants can feel a slight  
slight, erratic changes in altitude and/or strain against seat belts or  
LIGHT  
attitude (pitch, roll, yaw).  
shoulder straps. Unsecured  
objects can be displaced  
slightly.  
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.  
MODERATE  
SEVERE  
Turbulence that causes large abrupt  
changes in altitude and/or attitude. It  
usually causes large variations in  
indicated airspeed. Aircraft can be  
momentarily out of control.  
Occupants are forced  
violently against seat belts  
or shoulder straps.  
Unsecured objects are  
tossed about.  
Turbulence Levels (From Airman’s Information Manual)  
Table 5–8  
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 5–33. 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.  
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PRIMUS 660 Digital Weather Radar System  
100%  
80%  
60%  
40%  
20%  
0%  
1/4” HAIL  
1/2” HAIL  
3/4” AND LAGER HAIL  
LEVEL 2  
YELLOW  
LEVEL 3  
RED  
LEVEL 4  
MAGENTA  
AD–15358–R1@  
Hail Size Probability  
Figure 5–33  
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.  
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 5–34. At lower altitudes,  
the reverse is sometimes true. The radar can be scanning below a rapidly  
developing storm cell, that 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.  
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PRIMUS 660 Digital Weather Radar System  
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 5–35. 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 5–34  
FINGER  
HOOK  
U–SHAPE  
AD–35713@  
Familiar Hailstorm Patterns  
Figure 5–35  
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PRIMUS 660 Digital Weather Radar System  
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 5–36. 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.  
OVERFLYING A STORM  
HAIL  
AD–12061–R1@  
Overshooting a Storm  
Figure 5–36  
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PRIMUS 660 Digital Weather Radar System  
Another example of the pilot’s importance in helping the radar serve its  
safety/comfort purpose is shown in figure 5–37. 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.  
THE BLIND ALLEY  
40  
20  
20  
SHORT RANGE  
LONG RANGE  
AD–12062–R1@  
Short– and Long–Blind Alley  
Figure 5–37  
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PRIMUS 660 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 that the 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  
60  
A
40  
20  
INDICATOR DISPLAY A  
50  
40  
30  
20  
B
10  
INDICATOR DISPLAY B  
AD–35705@  
Azimuth Resolution in Weather Modes  
Figure 5–38  
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PRIMUS 660 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, that 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.  
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PRIMUS 660 Digital Weather Radar System  
WEATHER AVOIDANCE  
Figure 5–39 illustrates a typical weather display in WX mode.  
Recommended procedures when using the radar for weather  
avoidance are given in table 5–9. The procedures are given in bold face,  
explanations of the procedure follow in normal type face.  
AD–51780@  
Weather Display  
Figure 5–39  
Step  
Procedure  
1
Keep TGT alert enabled when using short ranges to be  
alerted if a new storm cell develops in the aircraft’s  
flightpath.  
2
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. SIG-  
NIFICANT WEATHER CAN NOT BE DISPLAYED.  
Severe Weather Avoidance Procedures  
Table 5–9 (cont)  
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PRIMUS 660 Digital Weather Radar System  
Step  
Procedure  
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 can NOT BE  
DETECTED.  
4
5
For brief periods 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.  
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 that was fully within the beam at 100 NM  
gradually passes out of and under the radar beam.  
6
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 can 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.  
Severe Weather Avoidance Procedures  
Table 5–9 (cont)  
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PRIMUS 660 Digital Weather Radar System  
Step  
Procedure  
7
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 often contain severe  
weather. Although nearby, slower moving echoes can  
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.  
8
9
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.  
Avoid all rapidly growing storms by 20 miles.  
When severe storms and rapid development are evident,  
the intensity of the radar return can increase by a huge  
factor in a matter of minutes. Moreover, the summit of the  
storm cells can 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.  
10  
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 can indicate the  
storm is severe. There are several causes of erratic  
motion. They can 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 can  
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!  
Severe Weather Avoidance Procedures  
Table 5–9 (cont)  
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PRIMUS 660 Digital Weather Radar System  
Step  
Procedure  
10  
(cont)  
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  
3. Interaction With Other Storms. A thunderstorm that is  
located between another storm and its moisture source  
can cause the blocked storm to have erratic motion.  
Sometimes the blocking of moisture is effective enough  
to cause the thunderstorm to dissipate.  
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 can 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 5–9 (cont)  
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PRIMUS 660 Digital Weather Radar System  
Step  
Procedure  
11  
Never continue flight towards or into a radar shadow  
or the blue REACT field.  
WARNING  
STORMS SITUATED BEHIND INTERVENING RAINFALL  
CAN BE MORE SEVERE THAN DEPICTED ON THE DIS-  
PLAY.  
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 forms fingers that point  
toward the stronger cells.  
Severe Weather Avoidance Procedures  
Table 5–9  
Configurations of Individual Echoes (Northern  
Hemisphere)  
Sometimes a large echo develops configurations that 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 5–40 shows a hook echo.  
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PRIMUS 660 Digital Weather Radar System  
N
AD–15560–R1@  
Typical Hook Pattern  
Figure 5–40  
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.  
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.  
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PRIMUS 660 Digital Weather Radar System  
AVOID V–NOTCH BY 20 MILES  
A large isolated echo sometimes has the configuration that is shown  
in figure 5–41. 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 5–41.  
N
v
s
echo movement  
AD–15561–R1@  
V–Notch Echo, Pendant Shape  
Figure 5–41  
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PRIMUS 660 Digital Weather Radar System  
AVOID PENDANT BY 20 MILES  
The pendant shape shown in figure 5–42, 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)  
D The average width of the hail swath is over 12.5 miles (20.2 km)  
D Sixty percent produce funnel clouds or tornadoes.  
The classic pendant shape echo is shown in figure 5–42. Note the  
general pendant shape, the hook, and the steep rain gradient. This  
storm is extremely dangerous and must be avoided.  
STORM MOTION  
N
AD–35706@  
The Classic Pendant Shape  
Figure 5–42  
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PRIMUS 660 Digital Weather Radar System  
AVOID STEEP RAIN GRADIENTS BY 20 MILES  
Figure 5–43 shows steep rain gradients. Refer to the paragraph,  
Interpreting Weather Radar Images, in this section, for a detailed  
explanation of weather images.  
AD–51781–R1@  
Rain Gradients  
Figure 5–43  
AVOID ALL CRESCENT SHAPED ECHOES BY 20 MILES  
A crescent shaped echo, shown in figure 5–44, 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.  
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PRIMUS 660 Digital Weather Radar System  
50  
40  
30  
20  
10  
AD–22161–R1@  
Crescent Shape  
Figure 5–44  
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.  
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PRIMUS 660 Digital Weather Radar System  
AVOID LINE ECHO WAVE PATTERNS (LEWP) BY 20 MILES  
One portion of a line can accelerate and cause the line to  
assume a wave–like configuration. Figure 5–45 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 5–45  
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.  
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PRIMUS 660 Digital Weather Radar System  
AVOID BOW–SHAPED LINE OF ECHOES BY 20 MILES  
Sometimes a fast moving, broken to solid thunderstorm line becomes  
bow–shaped, as shown in figure 5–46. 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  
can accelerate to speeds in excess of 70 knots within an hour.  
S
N
VIP 1  
100 mi  
VIP 3  
VIP 5  
AD–15563–R1@  
Bow–Shaped Line of Thunderstorms  
Figure 5–46  
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PRIMUS 660 Digital Weather Radar System  
Additional Hazards  
TURBULENCE VERSUS DISTANCE FROM STORM CORE  
The stronger the return, the further the turbulence is 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–wind side. The air rising in a tornado  
can contribute to a downwind area of strong echoes, while the tornado  
itself can or can 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.  
Appendix A, Federal Aviation Administration (FAA) Advisory Circulars,  
of this manual contains several advisory circulars. It is recommended  
that you become familiar with them.  
A28–1146–111  
Radar Facts  
5-55  
REV 2  
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PRIMUS 660 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 5–47. Turn the TILT  
control down until the desired amount of terrain is displayed. The  
degree of down–tilt depends upon the type of terrain, aircraft altitude,  
and selected range. Tables 5–10 and 5–11 show tilt settings for maximal  
ground target display at selected ranges.  
AD–51782–R1@  
Ground Mapping Display  
Figure 5–47  
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.  
A28–1146–111  
REV 2  
Radar Facts  
5-56  
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PRIMUS 660 Digital Weather Radar System  
RANGE  
SCALE  
(NM)  
LINE OF  
SIGHT  
(NM)  
10  
25  
50 100 200  
–12 –8  
ALTITUDE  
(FEET)  
40,000  
246  
230  
213  
195  
174  
151  
123  
87  
–11  
–10 –7  
–8  
35,000  
30,000  
25,000  
20,000  
15,000  
10,000  
5,000  
–13 –9  
–11 –8  
–10 –7  
–7  
–6  
–6  
–5  
–13 –8  
–6  
–5  
–5  
–5  
–4  
–9  
–8  
–7  
–6  
–5  
–6  
–6  
–5  
–5  
–4  
4,000  
78  
3,000  
67  
2,000  
55  
39  
1,000  
TILT Setting for Maximal Ground Target Display  
12–Inch Radiator  
Table 5–10  
NOTE: The line of sight distance is nominal. Atmospheric conditions  
and terrains offset this value.  
A28–1146–111  
Radar Facts  
5-57  
REV 2  
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PRIMUS 660 Digital Weather Radar System  
RANGE  
SCALE  
(MILES)  
LINE OF  
SIGHT  
(MILES)  
5
10  
25  
50 100 200  
ALTITUDE  
(FEET)  
40,000  
–11 –7  
–6  
–5  
–5  
246  
230  
213  
195  
174  
151  
123  
87  
–10  
–9  
–8  
–7  
–6  
–5  
–4  
–4  
–3  
–3  
–7  
–6  
–6  
–5  
–5  
–4  
35,000  
30,000  
25,000  
20,000  
15,000  
10,000  
5,000  
–8  
–12 –7  
–8  
–7  
–6  
–5  
–4  
–7  
–5  
–4  
–4  
–3  
–12  
–11  
–8  
4,000  
78  
3,000  
67  
2,000  
–6  
55  
39  
1,000  
–5  
AD–12041@  
TILT Setting for Maximal Ground Target Display  
18–Inch Radiator  
Table 5–11  
NOTE: The line of sight distance is nominal. Atmospheric conditions  
and terrains offset this value.  
A28–1146–111  
REV 2  
Radar Facts  
5-58  
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PRIMUS 660 Digital Weather Radar System  
6. 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  
2
exposure levels equal or exceed 10 mW/cm , 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  
manual.  
The IEEE Standard for Safety Level with Respect to Human Exposure  
to Radio Frequency Electronic Fields 3kHz to 300 GHz (IEEE  
C95.1–1991), recommends an exposure level of no more than 6  
2
mW/cm .  
2
Honeywell recommends that operators follow the 6 mW/cm standard.  
Figure 6–1 shows MPEL for both exposure levels.  
MPEL Boundary  
Figure 6–1  
A28–1146–111  
REV 3  
Maximum Permissible Exposure Level (MPEL)  
6-1/(6-2 blank)  
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PRIMUS 660 Digital Weather Radar System  
7. In–Flight Adjustments  
PITCH AND ROLL TRIM ADJUSTMENTS  
The PRIMUSR 660 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, 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  
7–1.  
Effect On Ground  
Return Display (Over  
Level Terrain)  
Trim  
Adjustment  
Flight Condition  
Roll offset  
Straight and level  
Straight and level  
Nonsymmetrical display  
Pitch offset  
Ground displays do not  
follow contour of range  
arcs.  
Roll gain  
Constant roll angle  
>20°  
Nonsymmetrical display  
Pitch gain  
Constant pitch angle Ground displays do not  
>5°  
follow contour of range  
arcs.  
NOTE: Generally, it is recommended to perform trim adjustments only if noticeable  
effects are being observed.  
Pitch and Roll Trim Adjustments Criteria  
Table 7–1  
A28–1146–111  
REV 2  
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7-1  
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PRIMUS 660 Digital Weather Radar System  
NOTES:  
1. Depending on the installation, not all of the  
adjustments shown in table 7–1 are available. If STAB  
TRIM ENABLE programming pin is open, only the roll  
offset adjustment is available. If STAB TRIM ENABLE  
programming pin 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 7–2, and can be done  
in the sequence of first finishing one adjustment, then  
proceeding to do the next by pushing the STAB button.  
4. The in–flight stabilization adjustment range is limited.  
If you cannot achieve a satisfactory adjustment  
in–flight, a ground adjustment is required.  
5. Proper radar stabilization depends on the accuracy  
and stability of the installed attitude source.  
6. The procedures in tables 7–3, 7–4, 7–6, and 7–8 that  
instruct you to “push the STAB button” assume that  
you are using a controller rather than an indicator. If  
you are using an indicator, pulling the TILT knob out or  
pushing it in is equal to pushing the STAB button on a  
controller.  
7. When you finish the in–flight stabilization procedures,  
the STAB can be OFF ( stab light on), an additional  
push of the button is required to turn stab back on.  
A28–1146–111  
REV 2  
In–Flight Adjustments  
7-2  
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PRIMUS 660 Digital Weather Radar System  
Level Fight Stabilization Check  
Follow the procedure in table 7–2 to determine if you need to perform  
the roll offset adjustment.  
Step  
Procedure  
1
Trim the aircraft for straight and level flight in smooth, clear  
air over level terrain at an altitude of at least 10,000 feet  
AGL.  
2
3
Select the 50–mile range and GMAP mode.  
Adjust the tilt control until your radar display shows a solid  
band of ground returns starting at the 40–mile range arc.  
4
After several antenna sweeps, verify that ground returns  
follow the range arc closely and are equally displayed on  
both sides as shown in figure 7–1. If the ground returns are  
not equally displayed on both sides (see examples in  
figures 7–2 and 7–3), perform the roll offset adjustment  
shown in table 7–3.  
Stabilization in Straight and Level Flight Check Procedure  
Table 7–2  
NOTE: A condition where the strongest ground targets move from  
side to side over a period of several minutes, can be caused  
by the gyro erection circuits chasing a slow wingwalk in the  
flightpath. Roll offset adjustment cannot compensate for this  
condition.  
A28–1146–111  
REV 2  
In–Flight Adjustments  
7-3  
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PRIMUS 660 Digital Weather Radar System  
Symmetrical Ground Returns  
Figure 7–1  
100  
80  
60  
40  
20  
wx  
AD–17721–R2@  
Ground Return Indicating Misalignment (Right)  
Figure 7–2  
A28–1146–111  
REV 2  
In–Flight Adjustments  
7-4  
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PRIMUS 660 Digital Weather Radar System  
100  
80  
60  
40  
20  
wx  
AD–17722–R2@  
Ground Return Indicating Misalignment (Left)  
Figure 7–3  
ROLL OFFSET ADJUSTMENT  
You can make an in–flight adjustment when level flight stabilization  
errors are detected. This procedure is done by either the WC–660  
Weather Radar Controller or the WI–650/660 Weather Radar Indicator.  
During this procedure, described in table 7–3, the GAIN control acts as  
roll offset control. After the procedure the GAIN control reverts to acting  
as a gain control.  
Step  
Procedure  
1
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.  
2
3
Fly to an altitude of 10,000 feet above ground level (AGL),  
or greater.  
Set range to 50 NM.  
In–Flight Roll Offset Adjustment Procedure  
Table 7–3 (cont)  
A28–1146–111  
REV 2  
In–Flight Adjustments  
7-5  
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PRIMUS 660 Digital Weather Radar System  
Step  
Procedure  
4
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 40 NM.  
5
6
Select STAB (STB) 4 times within 3 seconds. A display  
with text instructions is displayed. See figure 7–4. The  
radar unit is in the roll offset adjustment mode.  
Pull out the GAIN knob to make a roll offset adjustment.  
See figure 7–5 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.  
7
8
9
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.  
Push the STAB (STB) button to exit, or to go to the next  
menu (pitch offset), if the full stab trim mode is enabled in  
your installation.  
NOTE: 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 7–3  
A28–1146–111  
REV 2  
In–Flight Adjustments  
7-6  
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PRIMUS 660 Digital Weather Radar System  
WX  
AD–51776@  
Roll Offset Adjustment Display – Initial  
Figure 7–4  
WX  
AD–51777–R1@  
Roll Offset Adjustment Display – Final  
Figure 7–5  
A28–1146–111  
In–Flight Adjustments  
7-7  
REV 2  
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PRIMUS 660 Digital Weather Radar System  
PITCH OFFSET ADJUSTMENT  
This in–flight adjustment is 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 7–4.  
Step  
Procedure  
1
If two controllers are installed, one must be turned off.  
If an indicator is used, the procedure is the same as given  
below.  
2
3
4
Fly to an altitude of 10,000 feet AGL or greater.  
Set range to 50 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 40 NM.  
5
6
7
8
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.  
9
When change is completed, push in the GAIN knob. The  
display returns to the previous message.  
10  
Push the STAB (STB) button to go to the next menu (roll  
gain).  
Pitch Offset Adjustment Procedure  
Table 7–4  
A28–1146–111  
REV 2  
In–Flight Adjustments  
7-8  
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PRIMUS 660 Digital Weather Radar System  
ROLL STABILIZATION CHECK  
Once proper operation in level flight has been established, you can  
verify correct roll stabilization using the procedures in table 7–5.  
Step  
Procedure  
1
Trim the aircraft for straight and level flight in smooth, clear  
air over level terrain at an altitude of at least 10,000 feet  
AGL.  
2
3
Select the 50–mile range and GMAP mode.  
Adjust the TILT control until your radar display shows a  
solid band of ground returns starting at the 40–mile range  
arc. See figure 7–6.  
4
5
6
7
Place the aircraft in a 20–degree (or greater) roll to the  
right. If there is little change to the arc of ground returns,  
the roll stabilization is good.  
If ground returns come in closer on the right side and go  
out on the left side, the roll is understabilized. See figure  
7–7.  
If the ground returns go out on the right side and come in  
closer on the left side, the roll is overstabilized. See figure  
7–8.  
If the roll is understabilized or overstabilized, you can  
perform an in–flight roll gain adjustment as shown in table  
7–6.  
Roll Stabilization (While Turning) Check Procedure  
Table 7–5  
A28–1146–111  
REV 2  
In–Flight Adjustments  
7-9  
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PRIMUS 660 Digital Weather Radar System  
Symmetrical Ground Returns, Level Flight  
and Good Roll Stabilization  
Figure 7–6  
100  
80  
60  
40  
20  
wx  
AD–17721–R2@  
Understabilization in a Right Roll  
Figure 7–7  
A28–1146–111  
REV 2  
In–Flight Adjustments  
7-10  
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PRIMUS 660 Digital Weather Radar System  
100  
80  
60  
40  
20  
wx  
AD–17722–R2@  
Overstabilization in a Right Roll  
Figure 7–8  
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  
7–6.  
Step  
Procedure  
1
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.  
2
3
4
Fly to an altitude of 10,000 feet AGL or greater.  
Set range to 50 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 40 NM.  
5
Select STAB (STB) 4 times within 3 seconds. A display  
with text instructions for roll offset is shown.  
Roll Gain Adjustment Procedure  
Table 7–6 (cont)  
A28–1146–111  
REV 2  
In–Flight Adjustments  
7-11  
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PRIMUS 660 Digital Weather Radar System  
Step  
Procedure  
6
From the roll offset entry menu, push the STAB (STB)  
button twice more to bring up the roll gain entry menu.  
7
8
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 at least 20°, adjust  
for symmetrical display of ground returns at the 40–NM  
range arc..  
9
When change is completed, push in the GAIN knob. The  
display returns to the previous message.  
10  
Push the STAB (STB) button to go to the next menu (pitch  
gain).  
Roll Gain Adjustment Procedure  
Table 7–6  
PITCH STABILIZATION CHECK  
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  
7–7.  
Step  
Procedure  
1
Trim the aircraft for straight and level flight in smooth, clear  
air over level terrain at an altitude of at least 10,000 feet  
AGL.  
2
3
Select the 50–mile range and GMAP mode.  
Adjust the TILT control until your radar display shows a  
solid band of ground returns starting at the 40–mile range  
arc. See figure 7–9.  
4
Place the aircraft between 5 and 10° pitch up. If there is  
little change to the arc of ground returns, the pitch  
stabilization is good.  
Pitch Stabilization Check Procedure  
Table 7–7 (cont)  
A28–1146–111  
REV 2  
In–Flight Adjustments  
7-12  
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PRIMUS 660 Digital Weather Radar System  
Step  
Procedure  
5
If the display of ground returns goes out in range, the pitch  
is understabilized. See figure 7–10.  
6
7
If the display of ground returns comes in closer in range,  
the pitch is overstabilized. See figure 7–11.  
If the pitch is understabilized or overstabilized, you can  
wish to perform an in–flight pitch gain adjustment as  
shown in table 7–8.  
Pitch Stabilization Check Procedure  
Table 7–7  
Level Flight and Good Pitch Stabilization  
Figure 7–9  
A28–1146–111  
REV 2  
In–Flight Adjustments  
7-13  
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PRIMUS 660 Digital Weather Radar System  
100  
80  
60  
40  
WX  
20  
AD–53802@  
Understabilized in Pitch Up  
Figure 7–10  
Overstabilized in Pitch Up  
Figure 7–11  
A28–1146–111  
REV 2  
In–Flight Adjustments  
7-14  
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PRIMUS 660 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 7–8.  
Step  
Procedure  
1
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.  
2
3
4
Fly to an altitude of 10,000 feet AGL or greater.  
Set range to 50 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 40 NM.  
5
6
7
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%.  
8
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.  
9
When change is completed, push in the GAIN knob. The  
display returns to the previous message.  
10  
Push the STAB button to exit the mode and save the value  
in nonvolatile memory.  
Pitch Gain Adjustment Procedure  
Table 7–8  
A28–1146–111  
REV 2  
In–Flight Adjustments  
7-15/(7-16 blank)  
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PRIMUS 660 Digital Weather Radar System  
8. In–Flight Troubleshooting  
The PRIMUSR 660 Digital Weather Radar System can provide  
troubleshooting information on one of two formats:  
D Fault codes  
D 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 as well as fault codes  
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.  
D Display, indicator, or RTA malfunction  
D FAIL annunciation on weather indicator or EFIS display.  
If the feature TEXT FAULTS is enabled, the radar test pattern area  
displays plain 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.  
The PRIMUSR 660 also contains a feature called “Pilot Event Marker”  
that enables the pilot to record a full set of BITE parameters at any time,  
typically if the radar seems to be malfunctioning.  
NOTES:  
1. In some EFIS installations, radar failures are only  
annunciated with an amber WX if faults are not  
enabled..  
2. In EFIS installations, with TEXT FAULTS enabled, the  
fault codes are also presented as part of the FAIL  
annunciation (e.g., FAIL 13).  
A28–1146–111  
REV 2  
In–Flight Troubleshooting  
8-1  
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PRIMUS 660 Digital Weather Radar System  
TEST MODE WITH TEXT FAULTS ENABLED  
When airborne, if the radar is switched to TEST mode, any current  
faults are displayed.  
When on the ground (weight on wheels active) and the radar is switched  
to TEST mode, any current faults are displayed, followed by up to 32  
faults from the last 10 power on cycles. The historic faults are displayed  
going from the most recent to the oldest and are cycled every two  
antenna sweeps (approximately 8 seconds). The POC number  
indicates how many power on counts back into the history the fault  
occurred. After the last fault, an END OF LIST message is displayed.  
To recycle through the list again, exit and re–enter the TEST mode.  
Table 8–1 describes the six fault data fields that are displayed in figure  
8–1.  
Field No.  
Description  
Pilot message  
1
2
3
4
5
6
Line maintenance message  
Fault code/power–on count  
Fault name  
Transmit ON/OFF  
Strap code  
NOTES: 1. If airborne, only fault fields 1, 2, and 3 are  
displayed.  
2. Airborne, only the current faults are displayed.  
3. Strap codes indicate the configuration that was  
done at the time of installation. Refer to the  
System Description and Installation manual for  
further explanation.  
Fault Data Fields  
Table 8–1  
A28–1146–111  
REV 2  
In–Flight Troubleshooting  
8-2  
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PRIMUS 660 Digital Weather Radar System  
FAULT  
DISPLAY  
MESSAGE  
DIVIDER  
100  
PILOT  
MESSAGE  
FIELD  
LINE  
MAINTENANCE  
MESSAGE  
FAULT CODE/  
POWER ON  
COUNT  
80  
FAULT  
NAME  
TRANSMIT  
ON/OFF  
60  
40  
TEST  
STRAP  
CODE  
20  
1
2
3
4
AD–46709@  
WEATHER INDICATOR  
Fault Annunciation on Weather Indicator  
With TEXT FAULT Fields  
Figure 8–1  
Figure 8–2 shows the fault codes displayed on EFIS with text faults  
disabled.  
Fault Code on EFIS Weather Display  
With TEXT FAULTS Disabled  
Figure 8–2  
A28–1146–111  
REV 2  
In–Flight Troubleshooting  
8-3  
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PRIMUS 660 Digital Weather Radar System  
Radar Indication With Text Fault Enabled (On Ground)  
Figure 8–3  
PILOT EVENT MARKER  
At any time a full set of BITE parameters can be recorded by going in  
and out of variable gain four times (pull GAIN knob for VAR, push for  
preset, pull for VAR, and push for preset) within three seconds. There  
is no annunciation on the display after this operation.  
This feature can be useful if the radar appears to be malfunctioning and  
a fail annunciation is not shown on the display. If the pilot event marker  
is used, it is best to record several sets of data during the period of  
misoperation. Refer to the PRIMUSR 660 System Description and  
Installation Manual for information on constructing an interconnect  
cable for accessing this information.  
A28–1146–111  
REV 2  
In–Flight Troubleshooting  
8-4  
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PRIMUS 660 Digital Weather Radar System  
FAULT CODE AND TEXT FAULT RELATIONSHIPS  
Table 8–2 lists the relationship between:  
D Fault codes (FC)  
D Pilot/Maintenance (MAINT) Messages  
D Fault Name/type/description/cross reference (XREF).  
PILOT  
MSG  
LINE  
MAINT  
FC  
XREF  
FAULT DESCRIPTION  
FAULT NAME  
FAULT TYPE  
4808  
4809  
4810  
Startup Code CRC  
IOP Code CRC  
DSP Code CRC  
01  
FLASH CRC  
RADAR  
FAIL  
PULL  
RTA  
POWER ON  
4904  
4905  
4846  
4903  
CONFIG Table CRC  
FPGA Firmware CRC  
2V ADC Reference  
IOP Ready  
CONTINUOUS  
IOP  
IOP  
RADAR  
FAIL  
PULL  
RTA  
02  
4908  
4910  
4913  
INT ARINC 429  
Loopback  
POWER ON  
Spurious ARINC  
Interrupt  
CONTINUOUS  
RADAR  
FAIL  
PULL  
RTA  
ARINC 429 INT  
Coupling  
IOP  
POWER ON  
POWER ON  
POWER ON  
4806  
4811  
4842  
EEPROM Timer CRC  
EEPROM POC  
FLASH CRC  
RADAR  
FAIL  
PULL  
RTA  
STAB Trim CRC  
EEPROM  
IOP  
REDO  
STAB  
TRIM  
REDO  
STAB  
TRIM  
03  
04  
POWER ON  
POWER ON  
4912  
Calibration CRC  
RADAR  
FAIL  
PULL  
RTA  
4812  
4818  
IOP Mailbox  
DSP Mailbox  
MAILBOX RAM  
RADAR  
FAIL  
PULL  
RTA  
Text Faults  
Table 8–2 (cont)  
A28–1146–111  
REV 2  
In–Flight Troubleshooting  
8-5  
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PRIMUS 660 Digital Weather Radar System  
PILOT  
MSG  
LINE  
MAINT  
FC  
XREF  
FAULT DESCRIPTION  
FAULT NAME  
FAULT TYPE  
4813  
4814  
4815  
4828  
4906  
4847  
Timing FPGA RAM  
Timing FPGA REG  
IO FPGA RAM  
FPGA Download  
IO FPGA REG  
FPGA  
RADAR  
FAIL  
PULL  
RTA  
POWER ON  
05  
06  
07  
STC Monitor  
STC DAC  
RADAR  
FAIL  
PULL  
RTA  
POWER ON  
4830  
HVPS Monitor  
HVPS MON  
RADAR  
FAIL  
PULL  
RTA  
CONTINUOUS  
4816  
4817  
4855  
4900  
DSP RAM  
DSP Video RAM  
DSP Watchdog  
POWER ON  
CONTINUOUS  
10  
Mailbox Miscompare  
DSP  
RADAR  
FAIL  
PULL  
RTA  
4901  
4902  
DSP HOLDA Asserted  
POWER ON  
LATCHED  
DSP HOLDA Not  
Asserted  
4825  
4827  
4829  
4831  
Filament Monitor  
Severe Magnetron  
PFN Trim Monitor  
Pulse Width  
MAGNETRON  
RADAR  
FAIL  
PULL  
RTA  
11  
HVPS MON  
CONTINUOUS  
CONTINUOUS  
12  
13  
PULSE WIDTH  
RADAR  
UNCAL  
PULL  
RTA  
4832  
4833  
Elevation Error  
Azimuth Error  
EL POSITION  
AZ POSITION  
TILT  
UNCAL  
CHK  
RADOME  
/RTA  
CONTINUOUS  
CONTINUOUS  
14  
AZIMUTH  
UNCAL  
CHK  
RADOME  
/RTA  
15  
16  
4836  
4837  
Over TEMP  
OVER–TEMP  
RADAR  
CAUTION  
PULL  
RTA  
CONTINUOUS  
CONTINUOUS  
XMITTER Power  
XMTR POWER  
RADAR  
UNCAL  
PULL  
RTA  
CHK  
CNTL  
SRC  
CHK  
CNTL  
SRC  
4839  
4911  
No SCI Control  
20  
NO CNTL IN  
PROBE  
No ARINC 429 Control  
Text Faults  
Table 8–2 (cont)  
A28–1146–111  
REV 2  
In–Flight Troubleshooting  
8-6  
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PRIMUS 660 Digital Weather Radar System  
PILOT  
MSG  
LINE  
MAINT  
FC  
XREF  
FAULT DESCRIPTION  
FAULT NAME  
FAULT TYPE  
4840  
AGC Limiting  
PICTURE  
UNCAL  
CONTINUOUS  
21  
22  
AGC  
PULL  
RTA  
4927  
4928  
4841  
AGC RX DAC Monitor  
AGC TX DAC Monitor  
Selftest OSC Failure  
RADAR  
FAIL  
POWER ON  
RCVR  
SELF–TEST  
PICTURE  
UNCAL  
PULL  
RTA  
CONTINUOUS  
CONTINUOUS  
4843  
4845  
4929  
4930  
4848  
Multiple AFC Unlocks  
AFC Sweeping  
SPOKING  
LIKELY  
24  
27  
AFC  
PULL  
RTA  
AFC RX DAC Monitor  
AFC Trim DAC Monitor  
AHRS/IRS Source  
RADAR  
FAIL  
POWER ON  
NO STAB SRC  
STAB  
UNCAL  
CHK ATT  
SRC  
INSTALLATION  
4852  
4853  
Analog STAB REF  
Scan Switch Off  
34  
35  
SCAN SWITCH  
XMIT SWITCH  
SCAN  
SWITCH  
CHK  
SWITCH  
INSTALLATION  
INSTALLATION  
4854  
4914  
XMIT Switch Off  
XMIT  
SWITCH  
CHK  
SWITCH  
Invalid  
Altitude/Airspeed/STAB  
Strapping  
INVALID  
STRAPS  
RADAR  
UNCAL  
CHK  
STRAPS  
36  
POWER ON  
4915  
4916  
Invalid Controller  
Source Strapping  
Config1 Database  
Version/Size Mismatch  
IOP  
RADAR  
FAIL  
PULL  
RTA  
Text Faults  
Table 8–2  
A28–1146–111  
REV 2  
In–Flight Troubleshooting  
8-7  
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PRIMUS 660 Digital Weather Radar System  
Table 8–3 describes the pilot messages.  
Pilot MSG  
Description  
RADAR FAIL  
The radar is currently inoperable and should not be  
relied upon. It needs 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 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.  
TILT UNCAL  
An error in the antenna position system has been  
detected. The displayed tilt angle setting could be  
incorrect. This can also cause ground spoking.  
Have the RTA checked at the next opportunity.  
SPOKING LIKELY A problem has been detected that can 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 can occur. This can be  
due either to the RTA or the source of pitch and roll  
information to the RTA.  
SCAN SWITCH  
XMIT SWITCH  
The SCAN SWITCH located on the RTA is off,  
disabling the antenna scan. Check at the next  
opportunity.  
The XMIT switch located on the RTA is off, disabling  
the transmitter. Check at the next opportunity.  
Pilot Messages  
Table 8–3  
A28–1146–111  
REV 2  
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8-8  
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PRIMUS 660 Digital Weather Radar System  
9. Honeywell Product Support  
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 9000 spare  
components assures that your 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.  
When contacting a Honeywell Dealer or Customer Support Center for  
service under the SPEXR program, the following information regarding  
the unit and the aircraft are required:  
D Complete part number with dash number of faulty unit  
D Complete serial number of faulty unit  
D Aircraft type, serial number and registration number  
D Aircraft Owner  
D Reported complaint with faulty unit  
D Service requested (Exchange or Rental)  
D Ship to address  
D Purchase order number.  
D If faulty unit is IN WARRANTY:  
-
-
Type of warranty (NEW PRODUCT or Exchange)  
Date warranty started  
D If faulty unit is covered under a Maintenance Contract:  
-
-
-
Type of contract  
Contract date  
Plan ID number  
D If faulty unit is NOT IN WARRANTY, provide billing address  
A28–1146–111  
REV 2  
Honeywell Product Support  
9-1  
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PRIMUS 660 Digital Weather Radar System  
The Honeywell Support Centers listed below will assist with processing  
exchange/rental orders.  
24–HOUR EXCHANGE/RENTAL SUPPORT CENTERS  
U.S.A. – DALLAS  
800–872–7739  
972–402–4300  
CANADA – OTTAWA  
800–267–9947  
613–728–4681  
ENGLAND – BASINGSTOKE  
44–1256–72–2200  
AUSTRALIA – TULLAMARINE  
61–3–9330–1411  
FRANCE – TOULOUSE  
33–0–5–6171–9662  
GERMANY – AOA GAUTING  
0172–8207300 (in Germany)  
49–172–8207300 (outside Germany)  
SINGAPORE  
65–542–1313  
CUSTOMER SUPPORT CENTERS – NORTH AMERICA  
Dallas Support Center  
Honeywell Inc.  
Canada Support Center  
Honeywell Inc.  
Commercial Aviation Systems  
7825 Ridgepoint Dr.  
IRVING, TX 75063  
TEL: 972–402–4300  
FAX: 972–402–4999  
Commercial Aviation Systems  
3 Hamilton Avenue North  
OTTAWA, ONTARIO, K1Y 4J4  
TEL: 613–728–4681  
FAX: 613–728–7084  
Minneapolis Support Center  
Honeywell Inc.  
Ohio Support Center  
Honeywell Inc.  
Commercial Aviation Systems  
8840 Evergreen Boulevard  
MINNEAPOLIS, MN 55433–6040  
TEL: 612–957–4051  
Commercial Aviation Systems  
8370 Dow Circle  
STRONGSVILLE, OH 44136  
TEL: 440–243–8877  
FAX: 440–243–1954  
FAX: 612–957–4698  
Central Support Center  
Honeywell Inc.  
Commercial Aviation Systems  
1830 Industrial Avenue  
WICHITA, KS 67216  
TEL: 316–522–8172  
FAX: 316–522–2693  
Northwest Support Center  
Honeywell Inc.  
Commercial Aviation Systems  
4150 Lind Avenue Southwest  
RENTON, WA 98055  
TEL: 425–251–9511  
TLX: 320033  
FAX: 425–243–1954  
A28–1146–111  
REV 2  
Honeywell Product Support  
9-2  
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PRIMUS 660 Digital Weather Radar System  
CUSTOMER SUPPORT CENTERS – NORTH AMERICA (CONT)  
Miami Support Center  
Honeywell Inc.  
Commercial Aviation Systems  
7620 N.W. 25th Street  
Bldg. C Unit 6  
MIAMI, FL 33122  
TEL: 305–436–8722  
FAX: 305–436–8532  
CUSTOMER SUPPORT CENTERS – REST OF THE WORLD  
United Kingdom Support Center  
Honeywell Avionics Systems Ltd  
Edison Road, Ringway North  
BASINGSTOKE, HANTS,  
RG21 6QD  
France Support Center  
Honeywell Aerospace  
1 Rue Marcel–Doret, B.P.14  
31701 BLAGNAC CEDEX,  
FRANCE (Toulouse)  
TEL:33–5–6212–1500  
FAX: 33–5–6130–0258  
AOG: 33–5–6171–9662  
TLX: 521635F  
ENGLAND  
TEL:44–1256–72–2200  
FAX:44–1256–72–2201  
AOG: 44–1256–72–2200  
TLX: 51–858067  
Singapore Support Center  
Honeywell Aerospace Pte. Ltd.  
2 Loyang Crescent  
Australia Support Center  
Honeywell Ltd.  
Trade Park Drive  
SINGAPORE 1750  
TULLAMARINE, 3043, VICTORIA  
AUSTRALIA (Melbourne)  
TEL: 61–3–9330–1411  
FAX: 61–3–9330–3042  
AOG: 61–3–9330–1411  
TLX: 37586 HWLTUL  
TEL: 65–542–1313  
FAX: 65–542–1212  
AOG: 65–542–1313  
TLX: RS 56969 HWLSSC  
Germany Support Center  
AOA Apparatebau Gauting GmbH  
Ammerseestrasse 45–49  
D82131 Gauting  
GERMANY  
TEL: 49–89–89317–0  
FAX: 49–89–89317–183  
After Hours AOG Service:  
0172–8207300 (in Germany)  
49–172–8207300 (outside Germany)  
TLX: 0521702  
A28–1146–111  
REV 2  
Honeywell Product Support  
9-3  
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PRIMUS 660 Digital Weather Radar System  
PUBLICATION ORDERING INFORMATION  
Additional copies of this manual can be obtained by contacting:  
Honeywell Inc.  
P.O. Box 29000  
Business and Commuter Aviation Systems  
Phoenix, Arizona 85038–9000  
Attention: Publication Distribution, Dept. M/S V19A1  
Telephone No.:  
FAX:  
E–MAIL  
(602) 436–6900  
(602) 436–1588  
CAS–publications distribution@  
CAS.honeywell.com  
A28–1146–111  
REV 2  
Honeywell Product Support  
9-4  
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PRIMUS 660 Digital Weather Radar System  
10. Abbreviations  
Abbreviations used in this manual are defined as follows:  
TERMS  
DEFINITION  
AC  
Advisory Circular  
ADC  
AFC  
AGC  
AGL  
AHRS  
API  
Air Data Computer  
Automatic Flight Control  
Automatic Gain Control  
Above Ground Level  
Attitude Heading Reference System  
Antenna Position Indicator  
Azimuth  
AZ  
BITE  
BRT  
Built–in Test Equipment  
Brightness  
ccw  
CHK  
CLR  
Counterclockwise  
Check  
Clear  
CNTL  
CONFIG  
CRC  
cw  
Control  
Configuration  
Cyclic Redundancy Check  
Clockwise  
DAC  
DSP  
Digital to Analog Converter  
Display  
EEPROM  
Electrically Erasable Programmable  
Read–Only Memory  
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  
FLTPLN, FP,  
FPLN  
FMS  
FPGA  
FSBY  
Flight Plan  
Flight Management System  
Field–Programmable Gate Array  
Forced Standby  
A28–1146–111  
REV 2  
Abbreviations  
10-1  
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PRIMUS 660 Digital Weather Radar System  
TERMS  
DEFINITION  
ft  
Feet, Foot  
GMAP, GMP  
GPS  
GSPD  
Ground Mapping  
Global Positioning System  
Groundspeed  
HOLDA  
HVPS  
Hold Acknowledge  
High Voltage Power Supply  
INHIB  
INT  
IO  
IOP  
IRS  
Inhibit  
Interrupt  
Input/Output  
Inoperative  
Inertial Reference System  
kt  
Knot(s)  
LEWP  
LSS, LX  
Line Echo Wave Patterns  
Lightning Sensor System  
MAINT  
MFD  
MON  
MPEL  
MSG  
Maintenance  
Multifunction Display  
Monitor  
Maximum Permissible Exposure Level  
Message  
N/A  
Not Applicable  
NAV  
ND  
NM  
Navigation  
Navigation Display  
Nautical Mile  
NSSL  
NWS  
National Severe Storms Laboratory  
National Weather Service  
OSC  
Oscillator  
PFN  
POC  
PPI  
Pulse Forming Network  
Power on Count  
Plan–Position Indicator  
RCT, REACT  
RCVR  
Rain Echo Attenuation Compensation Technique  
Receiver  
A28–1146–111  
REV 2  
Abbreviations  
10-2  
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PRIMUS 660 Digital Weather Radar System  
TERMS  
DEFINITION  
Register  
Receiver Transmitter Antenna  
Receiver  
REG  
RTA  
RX  
SBY, STBY  
SCI  
SCT, SECT  
SLV  
Standby  
Serial Control Interface  
Scan Sector  
Slave  
SPEX  
STAB, STB  
STC  
Spares Exchange  
Stabilization  
Sensitivity Time Control  
TCAS  
TEMP  
TERR  
TGT  
Traffic Alert and Crew Alerting System  
Temperature  
Terrain  
Target  
TST  
Test  
TX  
Transmitter  
UDI  
UNCAL  
Universal Digital Interface  
Uncalibration  
VAR  
VIP  
Variance  
Video Integrated Processor  
WOW  
WX  
Weight–on–Wheels  
Weather  
XMIT, XMITTER, Transmitter  
XMTR  
XREF  
XSTC  
Cross Reference  
Extended Sensitivity Time Control  
A28–1146–111  
REV 2  
Abbreviations  
10-3/(10-4 blank)  
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PRIMUS 660 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:  
D AC 20–68B  
D 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.  
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.  
A28–1146–111  
REV 2  
Federal Aviation Administration (FAA) Advisory Circulars  
A–1  
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PRIMUS 660 Digital Weather Radar System  
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.  
D 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.  
D 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.  
D Personnel should be advised to avoid the end of an open waveguide  
unless the radar is turned off.  
D 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.  
D 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.  
A28–1146–111  
REV 2  
Federal Aviation Administration (FAA) Advisory Circulars  
A–2  
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PRIMUS 660 Digital Weather Radar System  
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.  
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.  
A28–1146–111  
REV 2  
Federal Aviation Administration (FAA) Advisory Circulars  
A–3  
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PRIMUS 660 Digital Weather Radar System  
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.  
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.  
D 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.  
D 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.  
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PRIMUS 660 Digital Weather Radar System  
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.  
D 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.  
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.  
D 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.  
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PRIMUS 660 Digital Weather Radar System  
COLD  
10  
0
5
15  
Schematic Cross Section of a Thunderstorm  
Figure A–1  
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.  
D 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.  
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PRIMUS 660 Digital Weather Radar System  
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.  
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.  
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PRIMUS 660 Digital Weather Radar System  
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.  
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.  
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PRIMUS 660 Digital Weather Radar System  
D 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.  
D Don’t fly without airborne radar into a cloud mass containing  
scattered embedded thunderstorms. Scattered thunderstorms not  
embedded, usually can be visually circumnavigated.  
D Don’t trust the visual appearance to be a reliable indicator of the  
turbulence inside a thunderstorm.  
D 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.  
D Do circumnavigate the entire area if the area has 6/1 thunderstorm  
coverage.  
D Do remember that vivid and frequent lightning indicates the  
probability of a severe thunderstorm.  
D Do regard as extremely hazardous, any thunderstorm with tops  
35,000 feet or higher, whether the top is visually sighted or  
determined by radar.  
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.  
D Plan and hold your course to take you through the storm in a  
minimum time.  
D To avoid the most critical icing, establish a penetration altitude below  
the freezing level or above the level of –15 _C.  
D 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.  
D Establish power settings for turbulence penetration airspeed  
recommended in your aircraft manual.  
D Turn up cockpit lights to highest intensity to lessen temporary  
blindness from lightning.  
D If using automatic pilot, disengage altitude hold mode and speed  
hold mode. The automatic altitude and airspeed controls of the  
aircraft increase maneuvers, thus increasing structural stress.  
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PRIMUS 660 Digital Weather Radar System  
D 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.  
D Don’t change power settings; maintain settings for the  
recommended turbulence penetration airspeed.  
D Do maintain constant attitude; let the aircraft ride the waves.  
Maneuvers in trying to maintain constant altitude increase stress on  
the aircraft.  
D 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.  
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. 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.  
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PRIMUS 660 Digital Weather Radar System  
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.  
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.  
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PRIMUS 660 Digital Weather Radar System  
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.  
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.  
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PRIMUS 660 Digital Weather Radar System  
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 FLIGHTPATH 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.  
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.  
D 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.  
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PRIMUS 660 Digital Weather Radar System  
Appendix B  
Enhanced Ground–Proximity  
Warning System (EGPWS)  
The AlliedSignal 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 data base 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 AlliedSignal recommended controls.  
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PRIMUS 660 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.  
D 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.  
D 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.  
D TERR (Terrain) – The TERR annunciator indicates that the  
annunciator lamp power is on. It does not indicate the operational  
status of the system.  
D 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 AlliedSignal publication for details.  
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PRIMUS 660 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 O 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 AlliedSignal EGPWS  
operating manual.  
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PRIMUS 660 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  
Color  
AGL  
2000 or more above the aircraft High density red  
1000 – 2000 above the aircraft  
0–1000 above the aircraft  
High density yellow dot pattern  
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  
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PRIMUS 660 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  
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PRIMUS 660 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  
A28–1146–111  
REV 2  
Enhanced Ground–Proximity Warning System (EGPWS)  
B–6  
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PRIMUS 660 Digital Weather Radar System  
Index  
A
E
Abbreviations, 10-1  
Effect on altimeters, A–7  
Enhanced ground–proximity warning  
system (EGPWS), B–1  
annunciators, B–2  
FAIL, B–2  
Accelerative Error, 5-15  
Additional hazards, 5-55  
turbulence versus distance from  
storm core, 5-55  
turbulence versus distance from  
storm edge, 5-55  
INHIB, B–2  
ON, B–2  
Altitude, A–10  
TERR, B–2  
relationship between turbulence  
and altitude, A–10  
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  
Antenna mounting error, 5-16  
level flight stabilization check, 5-17  
stabilization in straight and  
level flight check procedure,  
5-17  
Azimuth resolution, 5-41  
EGPWS operation, B–3  
related EGPWS system  
operation, B–3  
C
Equipment list, 2-4  
cockpit mounted options, 2-4  
remote mounted, 2-4  
Errors, 5-15  
Cockpit mounted equipment, 2-4  
Configurations of individual echoes  
(northern hemisphere), 5-47  
avoid all crescent shaped echoes  
by 20 miles, 5-51  
accelerative, 5-15  
antenna mounting error, 5-16  
level flight stabilization check,  
5-17  
avoid hook echoes by 20 miles,  
5-47  
avoid pendant by 20 miles, 5-50  
avoid steep rain gradients by 20  
miles, 5-51  
dynamic, 5-15  
pitch gain, 5-22  
pitch stabilization check, 5-22  
roll gain, 5-19  
avoid V–notch by 20 miles, 5-49  
Customer support centers , 9-2  
North America, 9-2  
roll stabilization (while turning)  
check, 5-19  
Rest of the World, 9-3  
stabilization in turns check  
procedure, 5-19  
wallowing (wing walk and yaw),  
5-19  
Exchange and rental service, 9-1  
Extrapolation to different climbs,  
A–13  
D
Do’s and don’ts of thunderstorm  
flying, A–8  
Dynamic Error, 5-15  
desert areas, A–13  
tropical–humid climates, A–13  
A28–1146–111  
REV 2  
Index  
Index–1  
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PRIMUS 660 Digital Weather Radar System  
Index (cont)  
Hail size probability, 5-36  
Honeywell product support, 9-1  
customer support centers, 9-2,  
North America, 9-2  
F
Fault code and text fault  
relationships, 8-5  
pilot messages, 8-8  
Federal Aviation Administration  
(FAA) Advisory Circulars  
recommended radiation safety  
precautions for ground  
operation of airborne weather  
radar, A–1  
Rest of the World, 9-3  
publication ordering information,  
9-4  
I
background, A–1  
cancellation, A–1  
precautions, A–2  
Icing, A–5  
In–flight adjustments, 7-1  
pitch and roll trim adjustments, 7-1  
level flight stabilization check,  
7-3  
purpose, A–1  
related reading material, A–1  
Thunderstorms, A–3  
cancellation, A–3  
pitch gain adjustment, 7-15  
adjustment procedure, 7-15  
pitch offset adjustment, 7-8  
adjustment procedure, 7-8  
pitch stabilization check, 7-12  
check procedure, 7-12  
roll gain adjustment, 7-11  
adjustment procedure, 7-11  
roll offset adjustment, 7-5  
adjustment procedure, 7-5  
roll stabilization check, 7-9  
while turning check  
general, A–3  
hazards, A–4  
national severe storms  
laboratory (NSSL)  
thunderstorm research, A–10  
purpose, A–3  
related reading material, A–3  
G
Gain adjustment, 7-11  
pitch, 7-15  
procedure, 7-9  
in–flight troubleshooting, 8-1  
fault code and text fault  
relationships, 8–1, 8-5  
pilot messages, 8-8  
adjustment procedure, 7-15  
roll, 7-11  
adjustment procedure, 7-11  
Ground mapping, 5-56  
TILT setting for maximal ground  
target display, 5-57  
pilot event marker, 8-1, 8-4  
test mode with TEXT FAULTS  
enabled, 8-2  
12–inch radiator, 5-57  
18–inch radiator, 5-58  
fault data fields, 8-2  
Interpreting weather radar images,  
5-24  
radar and visual cloud mass, 5-26  
squall line, 5-27  
H
Hail, A–6  
Hail in thunderstorms, A–12  
weather radar images, 5-24  
Introduction, 1-1  
A28–1146–111  
REV 2  
Index  
Index–2  
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PRIMUS 660 Digital Weather Radar System  
Index (cont)  
relationship between turbulence  
and reflectivity, A–10  
L
turbulence above storm tops,  
A–11  
Level flight stabilization check, 5-17,  
7-3  
turbulence and echo intensity on  
NWS radar (WSR–57), A–11  
turbulence below cloud base,  
A–12  
stabilization in straight and level  
flight check  
procedure, 5-17, 7-3  
Lightning, A–7  
turbulence in relation to distance  
from storm core, A–11  
turbulence in relation to distance  
from the storm edge, A–11  
use of airborne radar, A–13  
visual appearance of storm and  
associated turbulence with  
them , A–12  
Line configurations, 5-52  
avoid bow–shaped line of echoes  
by 20 miles, 5-54  
avoid line echo wave patterns  
(LEWP) by 20 miles, 5-53  
avoid thunderstorm echoes at the  
south end of a line or at a break  
in a line by 20 miles, 5-52  
Low ceiling and visibility, A–7  
Normal operation, 4-1  
preliminary control settings, 4-1  
power–up procedure, 4-1  
radar mode –– ground  
mapping, 4-5  
M
radar mode –– weather, 4-4  
standby, 4-4  
test mode, 4-6  
Maximum permissible exposure  
level (MPEL), 6-1  
Maximum storm tops, A–12  
Modification of criteria when severe  
storms and rapid development are  
evident, A–13  
color bands, 4-6  
dedicated radar indicator, 4-6  
EFIS/MFD/ND, 4-6  
O
N
National severe storms laboratory  
(NSSL) thunderstorm  
Offset adjustment, 7-5  
pitch, 7-8  
research, A–10  
extrapolation to different climbs,  
A–13  
adjustment procedure, 7-8  
roll, 7-5  
adjustment procedure, 7-5  
Operating controls, 3-1  
weather radar controller  
operation, WC–660, 3-10  
GAIN, 3-16  
desert areas, A–13  
tropical–humid climates, A–13  
hail in thunderstorms, A–12  
maximum storm tops, A–12  
modification of criteria when  
severe storms and rapid  
development are evident, A–13  
relationship between turbulence  
and altitude, A–10  
LSS (lightning sensor system)  
(optional), 3-13  
RADAR, 3-14  
rainfall rate color coding, 3-14  
RANGE, 3-11  
A28–1146–111  
REV 2  
Index  
Index–3  
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PRIMUS 660 Digital Weather Radar System  
Index (cont)  
weather radar controller  
operation, WC–660 (cont)  
RCT (rain echo attenuation  
compensation technique  
(REACT)), 3-11  
pitch stabilization check, 5-22  
Pitch offset adjustment, 7-8  
adjustment procedure, 7-8  
Pitch stabilization check, 7-12  
check procedure, 7-12  
SECT (scan sector), 3-12  
SLV (slave) (dual installations  
only), 3-13  
STAB (stabilization), 3-11  
target alert characteristics,  
3-12  
Preliminary control settings, 4-1  
power–up procedure, 4-1  
radar mode – ground mapping,  
4-5  
radar mode – weather, 4-4  
standby, 4-4  
TGT (target), 3-12  
TILT, 3-13  
weather radar indicator operation,  
WI–650/660, 3-1  
Procedures  
in–flight roll offset adjustment, 7-5  
pitch gain adjustment, 7-15  
pitch offset adjustment, 7-8  
pitch stabilization check, 7-12  
power–up, 4-1  
roll gain adjustment, 7-11  
roll stabilization (while turning)  
check, 7-9  
AZ (azimuth), 3-9  
BRT (brightness) or BRT/LSS  
(lightning sensor  
system), 3-9  
display area, 3-5  
function switch, 3-5  
GAIN, 3-8  
GMP (ground mapping)  
button MAP, 3-2  
Rainfall rate color coding, 3-6  
RANGE, 3-9  
severe weather avoidance, 5-43  
stabilization in straight and level  
flight check, 5-17, 7-3  
stabilization in turns check, 5-19  
Publication ordering information, 9-4  
RCT (rain echo attenuation  
compensation technique  
(REACT)), 3-3  
R
SCT (scan sector), 3-9  
target alert characteristics,  
3-4  
TGT (target), 3-4  
TILT, 3-8  
Radar facts  
ground mapping, 5-56  
TILT setting for maximal  
ground target display, 5-57  
interpreting weather radar  
images, 5-24  
WX (weather) button, 3-2  
radar and visual cloud mass,  
5-26  
squall line, 5-27  
P
weather radar images, 5-24  
radar operation, 5-1  
phenomenas, 5-4  
radome, 5-42  
rain echo attenuation  
compensation technique  
(react), 5-31  
Pilot event marker, 8-4  
Pitch and roll trim adjustments, 7-1  
level flight stabilization check, 7-3  
Pitch gain adjustment, 7-15  
adjustment procedure, 7-15  
Pitch gain error, 5-22  
A28–1146–111  
REV 2  
Index  
Index–4  
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PRIMUS 660 Digital Weather Radar System  
Index (cont)  
azimuth resolution, 5-41  
hail size probability, 5-36  
shadowing, 5-34  
related reading material, A–1  
Reflectivity, A–10  
relationship between turbulence  
and reflectivity, A–10  
spotting hail, 5-37  
turbulence probability, 5-34  
stabilization, 5-15  
Relationship between turbulence  
and altitude, A–10  
accelerative error, 5-15  
antenna mounting error, 5-16  
dynamic error, 5-15  
pitch gain error, 5-22  
roll gain error, 5-19  
Remote mounted equipment, 2-4  
Roll gain adjustment, 7-11  
adjustment procedure, 7-11  
Roll offset adjustment, 7-5  
adjustment procedure, 7-5  
Roll stabilization check, 7-9  
while turning check procedure, 7-9  
wallowing (wing walk and  
yaw) error, 5-19  
tilt management, 5-5  
tilt setting for minimal ground  
target display, 5-8  
S
variable gain control, 5-30  
weather avoidance, 5-43  
additional hazards, 5-55  
configurations of individual  
echoes (northern  
Shadowing, 5-34  
Spotting hail, 5-37  
Squall lines, A–4  
Stabilization, 5-15  
hemisphere), 5-47  
accelerative error, 5-15  
antenna mounting error, 5-16  
level flight stabilization check,  
5-17  
line configurations, 5-52  
severe weather avoidance  
procedures, 5-43  
weather display calibration, 5-28  
Radiation Safety Precautions, A–1  
Radome, 5-42  
Rain echo attenuation  
compensation technique  
(REACT), 5-31  
dynamic error, 5-15  
pitch gain error, 5-22  
pitch stabilization check, 5-22  
roll gain error, 5-19  
roll stabilization (while turning)  
check, 5-19  
related functions, 5-31  
attenuation compensation,  
5-31  
wallowing (wing walk and yaw)  
error, 5-19  
Stabilization check, 7-9  
Pitch, 7-12  
cyan REACT field, 5-31  
Recommended radiation safety  
precautions for ground operation  
of airborne weather radar, A–1  
background, A–1  
Check procedure, 7-12  
Roll, 7-9  
While turning check  
procedure, 7-9  
cancellation, A–1  
precautions, A–2  
Support centers, 9-2  
customer support centers, 9-2  
North America, 9-2  
Rest of the World, 9-3  
24–hour exchange/rental support  
centers, 9-2  
body damage, A–2  
combustible materials, A–3  
general, A–2  
purpose, A–1  
A28–1146–111  
REV 2  
Index  
Index–5  
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PRIMUS 660 Digital Weather Radar System  
Index (cont)  
System configurations, 2-1  
dual configuration, 2-1  
dual control mode truth table, 2-3  
equipment list, 2-4  
relationship between  
turbulence and altitude,  
A–10  
relationship between  
turbulence and reflectivity,  
A–10  
cockpit mounted options, 2-4  
remote mounted, 2-4  
stand–alone, 2-1  
turbulence above storm tops,  
A–11  
turbulence and echo intensity  
on NWS radar (WSR–57),  
A–11  
T
Test mode, 4-6  
turbulence below cloud base,  
A–12  
color bands, 4-6  
dedicated radar indicator, 4-6  
EFIS/MFD/ND, 4-6  
Test mode with TEXT FAULTS  
enabled, 8-2  
Thunderstorms, A–3  
Cancellation, A–3  
turbulence in relation to  
distance from the storm  
edge, A–11  
turbulence in relation to  
distance from storm core,  
A–11  
general, A–3  
hazards, A–4  
use of airborne radar, A–13  
visual appearance of storm  
and associated turbulence  
with them, A–12  
do’s and don’ts of  
thunderstorm flying, A–8  
effect on altimeters, A–7  
hail, A–6  
icing, A–5  
lightning, A–7  
low ceiling and visibility, A–7  
schematic cross section of a  
thunderstorm, A–6  
squall lines, A–4  
purpose, A–3  
related reading material, A–3  
Tilt management, 5-5  
tilt setting for minimal ground  
target display, 5-8  
12–inch radiator, 5-8  
18–inch radiator, 5-9  
Tornadoes, A–4  
tornadoes, A–4  
turbulence, A–5  
Trim adjustments, 7-1  
Turbulence  
weather radar, A–7  
national severe storms laboratory  
(NSSL) thunderstorm research,  
A–10  
above storm tops, A–11  
and echo intensity on NWS radar  
(WSR–57), A–11  
below cloud base, A–12  
in relation to distance from storm  
core, A–11  
extrapolation to different  
climbs, A–13  
hail in thunderstorms, A–12  
maximum storm tops, A–12  
modification of criteria when  
severe storms and rapid  
development are evident,  
A–13  
in relation to distance from the  
storm edge, A–11  
relationship between turbulence  
and altitude, A–10  
relationship between turbulence  
and reflectivity, A–10  
A28–1146–111  
REV 2  
Index  
Index–6  
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PRIMUS 660 Digital Weather Radar System  
Index (cont)  
versus distance from storm core,  
5-55  
avoid hook echoes by 20  
miles, 5-47  
versus distance from storm edge,  
5-55  
avoid pendant by 20 miles,  
5-50  
visual appearance of storm and  
associated turbulence with  
them , A–12  
avoid steep rain gradients by  
20 miles, 5-51  
avoid v–notch by 20 miles,  
5-49  
Turbulence probability, 5-34  
turbulence levels (from airman’s  
information manual), 5-36  
24–hour exchange/rental support  
centers, 9-2  
line configurations, 5-52  
avoid bow–shaped line of  
echoes by 20 miles, 5-54  
avoid line echo wave patterns  
(LEWP) by 20 miles, 5-53  
avoid thunderstorm echoes at  
the south end of a line or at  
a break in a line by 20  
miles, 5-52  
U
Use of airborne radar, A–13  
severe weather avoidance  
procedures, 5-43  
Weather display calibration, 5-28  
Weather radar, A–7  
Weather radar controller operation,  
WC–660, 3-10  
V
Variable gain control, 5-30  
Visual appearance of storm and  
associated turbulence with them ,  
A–12  
GAIN, 3-16  
LSS (lightning sensor system)  
(optional), 3-13  
CLR/TST (clear/test), 3-13  
LX (lightning sensor system),  
3-13  
W
OFF, 3-13  
SBY (standby), 3-13  
RADAR, 3-14  
Wallowing (wing walk and yaw)  
error, 5-19  
Warranty, 9-1  
FP (flight plan), 3-15  
GMAP (ground mapping),  
3-14  
Weather avoidance, 5-43  
additional hazards, 5-55  
turbulence versus distance  
from storm core, 5-55  
turbulence versus distance  
from storm edge, 5-55  
configurations of individual  
echoes (northern hemisphere),  
5-47  
OFF, 3-14  
rainfall rate color coding, 3-14  
STBY (standby), 3-14  
TST (test), 3-15  
WX (weather), 3-14  
RANGE, 3-11  
RCT (rain echo attenuation  
compensation technique  
(REACT)), 3-11  
avoid all crescent shaped  
echoes by 20 miles, 5-51  
SECT (scan sector), 3-12  
A28–1146–111  
REV 2  
Index  
Index–7  
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PRIMUS 660 Digital Weather Radar System  
Index (cont)  
Weather radar controller operation,  
WC–660 (cont)  
SLV (slave) (dual installations  
only), 3-13  
STAB (stabilization), 3-11  
target alert characteristics, 3-12  
TGT (target), 3-12  
TILT, 3-13  
Weather radar indicator operation,  
WI–650/660, 3-1  
AZ (azimuth), 3-9  
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  
display area, 3-5  
display screen features, 3-5  
function switch, 3-5  
FP (flight plan), 3-6  
FSBY (forced standby), 3-7  
OFF, 3-5  
ON, 3-6  
SBY (standby), 3-5  
TST (test), 3-7  
GAIN, 3-8  
GMP (ground mapping) button or  
MAP, 3-2  
rainfall rate color coding, 3-6  
RANGE, 3-9  
RCT (rain echo attenuation  
compensation technique  
(REACT)), 3-3  
SCT (scan sector), 3-9  
TGT (target), 3-4  
target alert characteristics,  
3-4  
TILT, 3-8  
WX (weather) button, 3-2  
A28–1146–111  
REV 2  
Index  
Index–8  
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