®
®
AD-54257@
Honeywell
Aerospace Electronic Systems
CES–Phoenix
P.O. Box 21111
Phoenix, Arizona 85036–111 1
U.S.A.
TO: HOLDERS OF THE PRIMUSR 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. Description of Change
Title Page 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.
LEP–1 thru
Revised to reflect revision 3.
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
Honeywell
Aerospace Electronic Systems
CES–Phoenix
P.O. Box 21111
Phoenix, Arizona 85036–111 1
U.S.A.
PRIMUSR 660 Digital Weather
Radar System
Pilot’s Manual
Printed in U.S.A. Pub. No. A28–1146–111–03 February 1998
Revised August 2003
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.
PRIMUSR 660 Digital Weather Radar System
Record of Revisions
Upon receipt of a revision, insert the latest revised pages and dispose
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and the incorporator’s initials on the Record of Revisions. The typed
initials H are used when Honeywell is the incorporator.
Revision
Number
Revision
Date
Insertion
Date
1 Aug 1999 Aug 1999 HI
2 Dec 1999 Dec 1999 HI
3 Aug 2003 Aug 2003 H
By
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REV 3 RR–1/(RR–2 blank)
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PRIMUSR 660 Digital Weather Radar System
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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
Temporary
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No. Issue Date
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Record of T emporary Revisions
REV 2 RTR–1/(RTR–2 blank)
PRIMUSR 660 Digital Weather Radar System
List of Effective Pages
Original 0. . . . Feb 1998
Revision 1. . . . Aug 1999
Revision 2. . . . Dec 1999
Revision 3. . . . Aug 2003
Subheading and Page Revision Subheading and Page Revision
Title Page H 3
Record of Revisions
RR–1/RR–2 H 3
Record of Temporary Revisions
RTR–1/RTR–2 0
List of Effective Pages
LEP–1 H 3
LEP–2 H 3
LEP–3/LEP–4 H 3
Table of Contents
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TC–2 1
TC–3 1
TC–4 1
TC–5 1
TC–6 1
TC–7/TC–8 1
Introduction
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1–2 0
System Configurations
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2–3 0
2–4 0
2–5/2–6 0
Operating Controls
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Normal Operation
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Radar Facts
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Radar Facts (cont)
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Maximum Permissible Exposure Level
(MPEL)
6–1/6–2 H 3
In–Flight Adjustments
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In–Flight Troubelshooting
8–1 0
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8–4 0
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8–8 0
Honeywell Product Support
9–1 1
9–2 1
9–3 1
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Abbreviations
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10–3/10–4 1
Appendix A
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Appendix B
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B–3 1
B–4 1
B–5 1
B–6 1
Index
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Index–2 1
Index–3 1
Index–4 1
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Index–6 1
Index–7 1
Index–8 1
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PRIMUSR 660 Digital Weather Radar System
Table of Contents
Section Page
1. INTRODUCTION 1-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2. SYSTEM CONFIGURATIONS 2-1. . . . . . . . . . . . . . . . .
3. OPERATING CONTROLS 3-1. . . . . . . . . . . . . . . . . . . .
WI–650/660 Weather Radar Indicat or Operat ion 3-1. . .
WC–660 Weather Radar Controller Operation 3-10. . . . .
4. NORMAL OPERATION 4-1. . . . . . . . . . . . . . . . . . . . . . .
Preliminary Control Settings 4-1. . . . . . . . . . . . . . . . . . .
Standby 4-4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Radar Mode – Weather 4-4. . . . . . . . . . . . . . . . . . . .
Radar Mode – Ground Mapping 4-5. . . . . . . . . . . . .
Test Mode 4-6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5. RADAR FACTS 5-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Radar Operation 5-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Tilt Management 5-5. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stabilization 5-15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Dynamic Error 5-15. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Accelerative Error 5-15. . . . . . . . . . . . . . . . . . . . . . . . .
Antenna Mounting Error 5-16. . . . . . . . . . . . . . . . . . . .
Wallowing (Wing Walk and Yaw) Error 5-19. . . . . . . .
Roll Gain Error 5-19. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pitch Gain Error 5-22. . . . . . . . . . . . . . . . . . . . . . . . . . .
Interpreting Weather Radar Images 5-24. . . . . . . . . . . . .
Weather Display Calibration 5-28. . . . . . . . . . . . . . . . . . .
Variable Gain Control 5-30. . . . . . . . . . . . . . . . . . . . . . . . .
Rain Echo Attenuation Compensation Technique
(REACT) 5-31. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Shadowing 5-34. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Turbulence Probability 5-34. . . . . . . . . . . . . . . . . . . . .
Hail Size Probability 5-36. . . . . . . . . . . . . . . . . . . . . . .
Spotting Hail 5-37. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Azimuth Resolution 5-41. . . . . . . . . . . . . . . . . . . . . . . .
Radome 5-42. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Weather Avoidance 5-43. . . . . . . . . . . . . . . . . . . . . . . . . . .
Configurations of Individual Echoes (Northern
Hemisphere) 5-47. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Line Configurations 5-52. . . . . . . . . . . . . . . . . . . . . . . .
A28–1146–111
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T able of Contents
TC–1
PRIMUSR 660 Digital Weather Radar System
Table of Contents (cont)
Section Page
5. RADAR FACTS (CONT)
Additional Hazards 5-55. . . . . . . . . . . . . . . . . . . . . . . .
Ground Mapping 5-56. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6. MAXIMUM PERMISSIBLE EXPOSURE LEVEL
(MPEL) 6-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7. IN–FLIGHT ADJUSTMENTS 7-1. . . . . . . . . . . . . . . . . .
Pitch and Roll Trim Adjustments 7-1. . . . . . . . . . . . . . . .
Level Fight Stabilization Check 7-3. . . . . . . . . . . . . .
Roll Offset Adjustment 7-5. . . . . . . . . . . . . . . . . . . . . . . .
Pitch Offset Adjustment 7-8. . . . . . . . . . . . . . . . . . . . . . .
Roll Stabilization Check 7-9. . . . . . . . . . . . . . . . . . . . . . .
Roll Gain Adjustment 7-11. . . . . . . . . . . . . . . . . . . . . . . . .
Pitch Stabilization Check 7-12. . . . . . . . . . . . . . . . . . . . . .
Pitch Gain Adjustment 7-15. . . . . . . . . . . . . . . . . . . . . . . .
8. IN–FLIGHT TROUBLESHOOTING 8-1. . . . . . . . . . . . .
Test Mode With Text Faults Enabled 8-2. . . . . . . . . . . .
Pilot Event Marker 8-4. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fault Code and Text Fault Relationships 8-5. . . . . . . . .
9. HONEYWELL PRODUCT SUPPORT 9-1. . . . . . . . . .
Publication Ordering Information 9-4. . . . . . . . . . . . .
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 A–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cancellation A–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Related Reading Material A–1. . . . . . . . . . . . . . . . . . .
Background A–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Precautions A–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
T able of Contents
TC–2
A28–1146–111
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PRIMUSR 660 Digital Weather Radar System
Table of Contents (cont)
A FEDERAL AVIATION ADMINISTRATION (FAA)
ADVISORY CIRCULARS (CONT)
Subject: Thunderstorms A–3. . . . . . . . . . . . . . . . . . . . . .
Purpose A–3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cancellation A–3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Related Reading Material A–3. . . . . . . . . . . . . . . . . . .
General A–3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Hazards A–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
National Severe Storms Laboratory (NSSL)
Thunderstorm Research A–10. . . . . . . . . . . . . . . . . .
B ENHANCED GROUND–PROXIMITY WARNING
SYSTEM (EGPWS) B–1. . . . . . . . . . . . . . . . . . . . . . . . .
System Operation B–1. . . . . . . . . . . . . . . . . . . . . . . . . . . .
EGPWS Controls B–1. . . . . . . . . . . . . . . . . . . . . . . . . .
Related EGPWS System Operation B–3. . . . . . . . . .
EGPWS Operation B–3. . . . . . . . . . . . . . . . . . . . . . . .
EGPWS Display B–4. . . . . . . . . . . . . . . . . . . . . . . . . .
EGPWS Test 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 3-1. . . . . . . . . . . . . . . . . . . . . .
3–2WI–650/660 Weather Radar Indicator Front Panel
View 3-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3–3WI–650/660 Weather Radar Indicator Display
Screen Features 3-5. . . . . . . . . . . . . . . . . . . . . . . . . . . .
3–4WC–660 Weather Radar Controller
Configurations 3-10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4–1 EFIS Test Pattern (Typical) 120° Scan Shown 4-3. . . .
4–2 Indicator Test Pattern 120° Scan (WX), With
TEXT FAULT Enabled 4-3. . . . . . . . . . . . . . . . . . . . . . .
A28–1146–111
REV 2
T able of Contents
TC–3
PRIMUSR 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. . . . . . . . .
5–2 Antenna Beam Slicing Out Cross Section of Storm
During Horizontal Scan 5-3. . . . . . . . . . . . . . . . . . . . . .
5–3 Sea Returns 5-4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5–4 Radar Beam Illumination High Altitude
12–Inch Radiator 5-5. . . . . . . . . . . . . . . . . . . . . . . . . . .
5–5 Radar Beam Illumination High Altitude
18–Inch Radiator 5-5. . . . . . . . . . . . . . . . . . . . . . . . . . .
5–6 Radar Beam Illumination Low Altitude
12–Inch Radiator 5-6. . . . . . . . . . . . . . . . . . . . . . . . . . .
5–7 Radar Beam Illumination Low Altitude
18–Inch Radiator 5-6. . . . . . . . . . . . . . . . . . . . . . . . . . .
5–8 Ideal Tilt Angle 5-10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5–9 Earth’s Curvature 5-10. . . . . . . . . . . . . . . . . . . . . . . . . . . .
5–10 Convective Thunderstorms 5-11. . . . . . . . . . . . . . . . . . . .
5–11 Unaltered Tilt 5-11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5–12 Proper Tilt Technique 5-12. . . . . . . . . . . . . . . . . . . . . . . . .
5–13 Tilt Management With Heading Changes 5-12. . . . . . . .
5–14 Fast Developing Thunderstorm 5-13. . . . . . . . . . . . . . . . .
5–15 Low Altitude Tilt Management 5-13. . . . . . . . . . . . . . . . . .
5–16 Antenna Size and Impact on Tilt Management 5-14. . . .
5–17 Rules of Thumb 5-14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5–18 Symmetrical Ground Returns 5-17. . . . . . . . . . . . . . . . . .
5–19 Ground Return Indicating Misalignment
(Upper Right) 5-18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5–20 Ground Return Indicating Misalignment
(Upper Left) 5-18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5–21 Symmetrical Ground Returns – Good Roll
Stabilization 5-20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5–22 Understabilization in a Right Turn 5-20. . . . . . . . . . . . . . .
5–23 Overstabilization in a Right Turn 5-21. . . . . . . . . . . . . . . .
5–24 Roll Stabilization Inoperative in a Turn 5-21. . . . . . . . . . .
5–25 Symmetrical Ground Returns – Good Pitch
Stabilization 5-22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5–26 Understabilized in Pitch–Up 5-23. . . . . . . . . . . . . . . . . . . .
5–27 Overstabilized in Pitch–Up 5-23. . . . . . . . . . . . . . . . . . . . .
5–28 Weather Radar Images 5-24. . . . . . . . . . . . . . . . . . . . . . .
5–29 Radar and Visual Cloud Mass 5-26. . . . . . . . . . . . . . . . . .
5–30 Squall Line 5-27. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5–31 REACT ON and OFF Indications 5-33. . . . . . . . . . . . . . .
T able of Contents
TC–4
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PRIMUSR 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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5–33 Hail Size Probability 5-37. . . . . . . . . . . . . . . . . . . . . . . . . .
5–34 Rain Coming From Unseen Dry Hail 5-38. . . . . . . . . . . .
5–35 Familiar Hailstorm Patterns 5-38. . . . . . . . . . . . . . . . . . . .
5–36 Overshooting a Storm 5-39. . . . . . . . . . . . . . . . . . . . . . . .
5–37 Short– and Long–Blind Alley 5-40. . . . . . . . . . . . . . . . . . .
5–38 Azimuth Resolution in Weather Modes 5-41. . . . . . . . . .
5–39 Weather Display 5-43. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5–40 Typical Hook Pattern 5-48. . . . . . . . . . . . . . . . . . . . . . . . .
5–41 V–Notch Echo, Pendant Shape 5-49. . . . . . . . . . . . . . . .
5–42 The Classic Pendant Shape 5-50. . . . . . . . . . . . . . . . . . .
5–43 Rain Gradients 5-51. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5–44 Crescent Shape 5-52. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5–45 Line Echo Wave Pattern (LEWP) 5-53. . . . . . . . . . . . . . .
5–46 Bow–Shaped Line of Thunderstorms 5-54. . . . . . . . . . . .
5–47 Ground Mapping Display 5-56. . . . . . . . . . . . . . . . . . . . . .
6–1 MPEL Boundary 6-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7–1 Symmetrical Ground Returns 7-4. . . . . . . . . . . . . . . . . .
7–2 Ground Return Indicating Misalignment (Right) 7-4. . .
7–3 Ground Return Indicating Misalignment (Left) 7-5. . . .
7–4 Roll Offset Adjustment Display – Initial 7-7. . . . . . . . . .
7–5 Roll Offset Adjustment Display – Final 7-7. . . . . . . . . .
7–6 Symmetrical Ground Returns, Level Flight and
Good Roll Stabilization 7-10. . . . . . . . . . . . . . . . . . . . . .
7–7 Understabilization in a Right Roll 7-10. . . . . . . . . . . . . . .
7–8 Overstabilization in a Right Roll 7-11. . . . . . . . . . . . . . . .
7–9 Level Flight and Good Pitch Stabilization 7-13. . . . . . . .
7–10 Understabilized in Pitch Up 7-14. . . . . . . . . . . . . . . . . . . .
7–11 Overstabilized in Pitch Up 7-14. . . . . . . . . . . . . . . . . . . . .
8–1 Fault Annunciation on Weather Indicator With
TEXT FAULT Fields 8-3. . . . . . . . . . . . . . . . . . . . . . . . .
8–2 Fault Code on EFIS Weather Display With
TEXT FAULTS Disabled 8-3. . . . . . . . . . . . . . . . . . . . .
8–3 Radar Indication With Text Fault Enabled
(On Ground) 8-4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A–1 Schematic Cross Section of a Thunderstorm A–6. . . . .
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TC–5
PRIMUSR 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–5. . . . . . . . . . . . . . . . . . . . . . . . . . . .
B–2 EGPWS Test Display B–6
Table Page
2–1 Dual Control Mode Truth Table 2-3. . . . . . . . . . . . . . . . .
2–2PRIMUSR 660 Weather Radar Equipment Lis t 2-4. . . . .
3–1 Target Alert Characteristics 3-4. . . . . . . . . . . . . . . . . . . .
3–2 Rainfall Rate Color Coding 3-6. . . . . . . . . . . . . . . . . . . .
3–3WC–660 Controller Target Alert Characteristics 3-12. . .
3–4 Rainfall Rate Color Coding 3-14. . . . . . . . . . . . . . . . . . . .
4–1 PRIMUSR 660 Power–Up Procedure 4-1. . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . .
List of Tables
5–1 Approximate Tilt Setting for Minimal Ground Target
Display 12–Inch Radiator 5-8. . . . . . . . . . . . . . . . . . . .
5–2 Approximate Tilt Setting for Minimal Ground Target
Display 18–Inch Radiator 5-9. . . . . . . . . . . . . . . . . . . .
5–3 Stabilization in Straight and Level Flight Check
Procedure 5-17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5–4 Stabilization in Turns Check Procedure 5-19. . . . . . . . . .
5–5 Pitch Stabilization In–Flight Check Procedure 5-22. . . .
5–6 Display Levels Related to dBZ Levels (Typical) 5-29. . . .
5–7 VIP Levels Related to dBZ 5-30. . . . . . . . . . . . . . . . . . . .
5–8 Turbulence Levels (From Airman’s Information
Manual) 5-36. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5–9 Severe Weather Avoidance Procedures 5-43. . . . . . . . .
5–10 TILT Setting for Maximal Ground Target Display
12–Inch Radiator 5-57. . . . . . . . . . . . . . . . . . . . . . . . . . .
5–11 TILT Setting for Maximal Ground Target Display
18–Inch Radiator 5-58. . . . . . . . . . . . . . . . . . . . . . . . . . .
7–1 Pitch and Roll Trim Adjustments Criteria 7-1. . . . . . . . .
7–2 Stabilization in Straight and Level Flight Check
Procedure 7-3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7–3In–Flight Roll Offset Adjustment Procedure 7-5. . . . . .
T able of Contents
TC–6
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Table of Contents (cont)
List of Tables (cont)
Table Page
7–4 Pitch Offset Adjustment Procedure 7-8. . . . . . . . . . . . .
7–5 Roll Stabilization (While Turning) Check
Procedure 7-9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7–6 Roll Gain Adjustment Procedure 7-11. . . . . . . . . . . . . . .
7–7 Pitch Stabilization Check Procedure 7-12. . . . . . . . . . . .
7–8 Pitch Gain Adjustment Procedure 7-15. . . . . . . . . . . . . .
8–1 Fault Data Fields 8-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8–2 Text Faults 8-5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8–3 Pilot Messages 8-8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B–1 EGPWS Obstacle Display Color Definitions B–4. . . . . .
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PRIMUSR 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 weat her 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 ANTICOLL IS I O N PRO T E CT I O N.
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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Introduction
PRIMUSR 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.
Introduction
1-2
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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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System Configurations
PRIMUSR 660 Digital Weather Radar System
NOTES: 1. When W AIT, 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.
System Configurations
2-2
PRIMUSR 660 Configurations
Figure 2–1
OFF OFF
RCT
PULL
STBY FP
VAR
MAXMIN
OFF OFF
RCT STAB TGT SECT
PULL
STBY FP
VAR
MAXMIN
STAB
TGT SECT
GMAPWX
TESTOFF
GMAPWX
TESTOFF
A28–1146–111
PULL
ACT
0
TILTSLVRADARGAIN
PULL
ACT
0
TILTSLVRADARGAIN
+
15
–
+
15
–
REV 2
PRIMUSR 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
(NOTE 1)
Right Side
(NOTE 1)
Mode
OFF OFF OFF OFF OFF
OFF Standby ”SLV”
Standby Standby
Standby
Standby OFF Standby ”SLV”
Standby
Standby
OFF ON ”SLV” ON ON ON
ON OFF ON ”SLV” ON ON
Standby ON Standby/
ON/2 ON
2
ON Standby ON/2 Standby/2 ON
ON ON ON/2 ON/2 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. “SL V” means that displayed data is controlled by
opposite side cont roller. That is, the one controller that
is operating is controlling bot h sweeps of the antenna.
3. XXX/2 means that display is controlled by appropriate
on–side control for the antenna sweep direction
associated wit h that control. (/2 implies two controllers
are ON.)
4. In standby, the RTA is centered in azimuth with 15_
upward tilt. Video data is suppr essed. The transmitter
is inhibited.
5. The MF D, if used, can repeat either left– or right–side
data, depending upon external switch selection.
RTA
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PRIMUSR 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 7007700–VAR
WC–660 Weather Radar Controller 7008471–VAR
Remote Mounted Equipment
WU–660 Receiver Transmitter Antenna 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.
System Configurations
2-4
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WI–650/660 WEATHER RADAR
INDICATOR
PRIMUSR 660 Digital Weather Radar System
WU–660 RECEIVER/
TRANSMITTER/ANTENNA
WC–660 WEATHER RADAR
CONTROLLER
AD–51768@
Typical PRIMUSR 660 Weather Radar Components
Figure 2–2
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System Configurations
PRIMUSR 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):
WI–650/660 Weather Radar Indicator
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.
AUTO
TILT
2134
T
10
+1.0
50
40
30
20
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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Operating Controls
PRIMUSR 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.
Operating Controls
3-2
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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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Operating Controls
PRIMUSR 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
FP (Flight Plan) 5 5–55
Operating Controls
3-4
(NM)
Minimum Target
Depth (NM)
Target Range
(NM)
5 5 5–55
10 5 10–60
25 5 25–75
50 5 50–100
100 5 100–150
200 5 200–250
300 N/A N/A
Target Alert Characteristics
Table 3–1
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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:
OFF– This position turns off the radar system.
SBY (Standby) – This position places the radar system in standby,
a ready state, with the antenna scan stopped, the transmitter
inhibited, and the display memory erased. STBY, in white, is shown
in the mode field.
If SBY is selected before the initial RTA warmup period is complete
(approximately 90 seconds), the white W AIT legend is shown in the
mode field. When warmup is complete, the system changes the
mode field to SBY.
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Operating Controls
PRIMUSR 660 Digital Weather Radar System
Á
Á
Á
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
in/hr mm/hr
Color
.04–.16 1–4 Green
.16–.47 4–12 Yellow
.47–2 12–50 Red
> 2
ÁÁÁÁ
>5 0
ÁÁÁ
ББББББББ
Magenta
Rainfall Rate Color Coding
Table 3–2
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.
Operating Controls
3-6
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PRIMUSR 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.
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 GRO UND PERSO NNEL .
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Operating Controls
PRIMUSR 660 Digital Weather Radar System
7 GAIN
The GAI N knob is a single–turn rot ary control and push/pull switch that
is used to cont rol the receiver gain. Push in on the GAIN switch to enter
the syst em int o the preset calibrated gain mode. Calibrated gain is the
normal mode and is used for weather av oidance. In calibrated gain, the
rotary portion of the GAI N 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 increas e rec eiver sensitiv ity 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 DISPLAY WITH LOW SETTINGS OF VARIABLE GAIN.
In the GMAP mode, variable gain is used to reduce the level of the
typically very strong returns from ground targets 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 int o 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 ADJUST 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 des cription of stabilization). The STAB OFF annunc iator is
displayed on the screen.
Operating Controls
3-8
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PRIMUSR 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:
OFF – This position removes all power from the LSS.
SBY (Standby) – This position inhibits the display of LSS data, but
the system accumulates data in this mode.
LX (Lightning Sensor System) – In this position the LSS is fully
operational and data is being displayed on the indicator.
CLR/TST (Clear/Test) – In this position accumulated data is cleared
from the memory of the LSS. After 3 seconds the test mode is
initiated in the LSS. Refer to the LSZ–850 Lightning Sensor System
Pilot’s Handbook, for a detailed description of LSS operation.
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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Operating Controls
°
PRIMUSR 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 OFF
RCT STAB TGT SECT
+
0
15
–
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).
Operating Controls
3-10
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PRIMUSR 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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PRIMUSR 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 s elected
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 out side of the selected range. When this war ning is
received, the pilot should select longer ranges to view the quest ionable
target. Note that target aler t 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 5–55
10 5 10–60
25 5 25–75
50 5 50–100
100 5 100–150
200 5 200–250
300 N/A N/A
FP (Flight Plan) 5 5–55
WC–660 Controller Target Alert Characteristics
Table 3–3
NOTE: When on the ground, in FSBY mode, pushing STAB
four times in t hree seconds, o verrides forced s tandby .
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.
Operating Controls
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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 to 15; ccw rotation tilts beam downward 0 to –15. The range
between +5 and –5 is expanded for ease of setting. A digital readout
of the antenna tilt angle is displayed on the EFI S.
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:
OFF – In this position all power is removed from the LSS.
SBY (Standby) –In this position the display of LSS data is inhibited,
but the LSS still accumulates data.
LX (Lightning Sensor System) –In this position the LSS is fully
operational and it displays LSS data on the indicator.
CLR/TST (Clear/Test) –In this position, accumulated data is
cleared from the memory of the LSS. After 3 seconds the test mode
is initiated in the LSS.
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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Operating Controls
PRIMUSR 660 Digital Weather Radar System
Á
9 RADAR
This rotary switch is used to select one of the following functions.
OFF – This position turns off the radar system.
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.
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
in/hr mm/hr
Color
.04–.16 1–4 Green
.16–.47 4–12 Yellow
ÁÁÁÁ
.47–2 12–50 Red
> 2
>5 0
Magenta
Rainfall Rate Color Coding
Table 3–4
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 select able in GM AP.
WARNING
WEATHER TYPE TARGETS ARE NOT CALIBRATED WHEN
THE RADAR IS IN THE GMAP MODE. BECAUSE OF THIS, DO NOT
USE THE GMAP MODE FOR WEATHER DETECTION.
Operating Controls
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PRIMUSR 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).
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 display ed in the mode field.
The target alert mode can be used in the FP mode. Wit h 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 annunciat ion (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.
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, MAXIMUM PERMISSIBLE EXPOSURE LEVEL (MPEL).
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Operating Controls
PRIMUSR 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 S TAB
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.
Operating Controls
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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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Operating Controls
PRIMUSR 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 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.
4 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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Normal Operation
PRIMUSR 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 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.
7 Verify that the azimuth marks, target alert (TGT), and
sector scan controls are operational.
Normal Operation
4-2
PRIMUSR 660 Power–Up Procedure
Table 4–1
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P660 WX
MODE
ANNUNCIATIONS
STBY (GREEN)
TEST (GREEN)
WX (GREEN)
RCT (GREEN)
GMAP (GREEN)
WAIT (AMBER)
FAIL ”N” (AMBER)
FPLN
ANTENNA
REACT OFF:
REACT ON:
TILT
ANGLE
BLACK
CYAN
RED
WX RANGE
RINGS
(WHITE)
DTRK
315
TEST
+11
VOR1
VOR2
HDG
319
PRIMUSR 660 Digital Weather Radar System
TGT OR VAR ANNUNCIATOR
:
TGT:
TARGET ALERT
– GREEN–SELECTED
– AMBER TGT DETECTED
:
VAR:
VARIABLE GAIN (AMBER)
TGT ALERT ON:
RED
MAG1
50
25
15
321
TGT FMS1
130 NM
260 KTS
V
GSPD
TGT ALERT OFF:
BLACK AND
NOISE BAND
TEXT AREA
GRAY
MAGENTA
BLUE
YELLOW
WX RANGE
ANNUNCIATOR
(WHITE)
1.2.IF THE BITE DETECTS A FAULT IN TEST MODE, FAIL ”N” WILL BE SHOWN.
NOTES:
”N” IS A FAULT CODE.
ANY FAULT CODE CAN ALSO BE DISPLAYED IN THE MAINTENANCE MODE.
IN THAT CASE, IT REPLACES THE ANTENNA TILT ANGLE.
EFIS Test Pattern (Typical) 120_ Scan Shown
Figure 4–1
Indicator Test Pattern 120_ Scan (WX),
With TEXT FAULT Enabled
Figure 4–2
GREEN
AD–51774@
AD–51773@
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PRIMUSR 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.
Normal Operation
4-4
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PRIMUSR 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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Normal Operation
PRIMUSR 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).
Normal Operation
4-6
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5. Radar Facts
RADAR OPERATION
The PRIMUSR 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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Radar Facts
PRIMUSR 660 Digital Weather Radar System
AIRCRAFT HEADING
WX
100
80
60
+0.6
40
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.
Radar Facts
5-2
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PRIMUSR 660 Digital Weather Radar System
ANTENNA
TRANSMITTER
INDICATOR
SWEEP ORIGIN
SCAN
THUNDERSTORM
THUNDERSTORM
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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Radar Facts
PRIMUSR 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
Radar Facts
5-4
CALM WATER OR WATER WITH
SWELLS DOES NOT PROVIDE
GOOD RETURN.
WIND DIRECTION AT
SURFACE OF WATER
Sea Returns
Figure 5–3
CHOPPY WATER PROVIDES
GOOD RETURN FROM
DOWNWIND SIDE OF WAVES
PATCH
OF SEA
RETURNS
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PRIMUSR 660 Digital Weather Radar System
Î
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
60,000
50,000
30,000
20,000
ELEVATION IN FEET
10,000
0
0
ZERO TILT
7.9
10,500 FT
10,500 FT
25 50
RANGE NAUTICAL MILES
20,000 FT
20,000 FT
CENTER OF RADAR BEAM
41,800 FT
41,800 FT
100
AD–35693@
Radar Beam Illumination High Altitude
12–Inch Radiator
Figure 5–4
80,000
70,000
60,000
50,000
30,000
20,000
ELEVATION IN FEET
10,000
ZERO TILT
5.6
0
02550
7,400 FT
14,800 FT
CENTER OF RADAR BEAM
14,800 FT
7,400 FT
RANGE NAUTICAL MILES
29,000 FT
29,000 FT
100
AD–17717–R1@
Radar Beam Illumination High Altitude
18–Inch Radiator
Figure 5–5
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Radar Facts
PRIMUSR 660 Digital Weather Radar System
Radar Beam Illumination Low Altitude
12–Inch Radiator
Figure 5–6
Radar Facts
5-6
AD54258@
Radar Beam Illumination Low Altitude
18–Inch Radiator
Figure 5–7
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PRIMUSR 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.
A28–1146–111
REV 2 5-7
Radar Facts
PRIMUSR 660 Digital Weather Radar System
RANGE
SCALE
(NM)
ALTITUDE
(FEET)
40,000
35,000
30,000
25,000
20,000
15,000
10,000
5,000
4,000
3,000
2,000
1,000 +3
510
–5
–4
–2
0
+2
(TILT LIMITED
25 50 100 200 300
–12
–10
–8
REGION)
–6
–4
–2
–11
–0
–6
+2
–1
+2
0
+3
+1
+3 +3
+2
+3
–1+1
–4
0+1
–3
–2
+1–1
0+1
+1 +2
+2+2
+2
+3
+3
LINE OF
SIGHT
(NM)
246
230
+10
213
195
174
151
123
87
78
(LINE OF SIGHT LIMITED REGION)
67
55
39
AD–29830–R2@
Approximate Tilt Setting for Minimal Ground Target Display
12–Inch Radiator
Table 5–1
Tilt angles shown are approximate. Where the tilt angle is not listed, the
operator must exercise good judgment.
NOTE: The line of sight distance is nominal. Atmospheric conditions
and terrain offset this value.
Radar Facts
5-8
A28–1146–111
REV 2
ALTITUDE
(FEET)
RANGE
SCALE
(MILES)
PRIMUSR 660 Digital Weather Radar System
5 10 25 50 100 200
LINE OF
(MILES)
SIGHT
40,000
35,000
30,000
25,000
20,000
15,000
10,000
5,000
4,000
3,000
2,000
1,000 +1 +2 +2
–7
–5
–3
–1
–13 –5 –2 –1
–11 –4
REGION)
(TILT LIMITED
–5 –10
–12
–3 –1
–7
–2
0
–1
+1
0
+1
+1 +2 +2
–2–7
+1
+2
+2
246
0
–1
–1–9 –3
0
+1
+10–1
(LINE OF
230
0
213
195
174
151
123
87
78
67
55
SIGHT LIMITED REGION)
39
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.
A28–1146–111
REV 2 5-9
Radar Facts
PRIMUSR 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
Radar Facts
5-10
A28–1146–111
REV 2
PRIMUSR 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
A28–1146–111
REV 2 5-11
Radar Facts
PRIMUSR 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.
Radar Facts
5-12
DISPLAY BEFORE
TURN
DISPLAY AFTER
TURN
THUNDERSTORM WAS OUT
OF DISPLAY BEFORE TURN
AND IS NOW UNDER BEAM
AD–30429@
Tilt Management With Heading Changes
Figure 5–13
A28–1146–111
REV 2
PRIMUSR 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 4 00 k t g roundspeed ( GSPD), a f ast d eveloping t hunderstorm
that spawns 67 NM in front of the aircraft can be large enough to
damage the aircraft by the time it arrives at the st orm.
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.
A28–1146–111
REV 2 5-13
Radar Facts
PRIMUSR 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.
Radar Facts
5-14
TILT
BEAM WIDTH
AD–35702@
Rules of Thumb
Figure 5–17
A28–1146–111
REV 2
PRIMUSR 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.
A28–1146–111
REV 2 5-15
Radar Facts
PRIMUSR 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.
Radar Facts
5-16
A28–1146–111
REV 2
PRIMUSR 660 Digital Weather Radar System
Á
Á
Á
Á
Á
Á
Á
Á
LEVEL FLIGHT STABILIZATION CHECK
Check stabilization in level flight using the procedure in table 5–3.
Step Procedure
1
ÁÁ
Trim the aircraft for straight and level flight in smooth,
clear air over level terrain.
ББББББББББББББББ
2 Select the 50–mile range.
3 Rotate the tilt control until a band of ground returns
starts at the 40 NM range arc.
4
ÁÁ
ÁÁ
ÁÁ
After several antenna sweeps, verify that ground
returns are equally displayed (figure 5–18). If returns
ББББББББББББББББ
are only on one side of the radar screen or uneven
ББББББББББББББББ
across the radar screen, a misalignment of the radar
ББББББББББББББББ
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
A28–1146–111
REV 2 5-17
Radar Facts
PRIMUSR 660 Digital Weather Radar System
40
wx
20
Ground Return Indicating Misalignment (Upper Right)
Figure 5–19
100
80
60
AD–17721–R2@
100
40
wx
20
Ground Return Indicating Misalignment (Upper Left)
Figure 5–20
Radar Facts
5-18
80
60
AD–17722–R2@
A28–1146–111
REV 2
PRIMUSR 660 Digital Weather Radar System
Á
Á
Á
Á
Á
Á
Á
Á
Á
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
ÁÁ
2
ÁÁ
3
ÁÁ
4
ÁÁ
NOTE: Proper radar operation in turns depends on the accuracy and stability of the
БББББББББББББББББББ
Place the aircraft in 20° roll to the right.
ББББББББББББББББ
Note the radar display. It should contain appreciably no
more returns than found during level flight. See figure
ББББББББББББББББ
5–24.
If returns display on the right side of radar indicator;
ББББББББББББББББ
the radar system is understabilizing.
Targets on the left side of the radar display indicate the
ББББББББББББББББ
system is overstabilizing. See figure 5–23.
installed attitude source.
Stabilization in Turns Check Procedure
Table 5–4
A28–1146–111
REV 2 5-19
Radar Facts
PRIMUSR 660 Digital Weather Radar System
Symmetrical Ground Returns – Good Roll Stabilization
Figure 5–21
100
Radar Facts
5-20
wx
Understabilization in a Right Turn
Figure 5–22
80
60
40
20
AD–17721–R2@
A28–1146–111
REV 2
wx
PRIMUSR 660 Digital Weather Radar System
100
80
60
40
20
AD–17722–R2@
Overstabilization in a Right Turn
Figure 5–23
100
80
60
40
wx
20
AD–17723–R2@
Roll Stabilization Inoperative in a Turn
Figure 5–24
A28–1146–111
REV 2 5-21
Radar Facts
PRIMUSR 660 Digital Weather Radar System
Á
Á
Á
Á
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
ÁÁÁ
4
ÁÁÁ
5
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
БББББББББББББББ
is very little change in the ground returns.
If the display of ground returns resembles figure 5–26,
the radar is understabilized.
БББББББББББББББ
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
Radar Facts
5-22
A28–1146–111
REV 2
GMAP
PRIMUSR 660 Digital Weather Radar System
100
80
60
40
20
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.
A28–1146–111
REV 2 5-23
Radar Facts
PRIMUSR 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
RAIN – GOOD
WET SNOW – GOOD
DRY HAIL – POOR
DRY SNOW – VERY POOR
Weather Radar Images
Figure 5–28
VAPOR
ICE CRYSTALS
SMALL DRY HAIL
AD–46704–R1@
Radar Facts
5-24
A28–1146–111
REV 2
PRIMUSR 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 thunder storm’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.
A28–1146–111
REV 2 5-25
Radar Facts
PRIMUSR 660 Digital Weather Radar System
VISIBLE CLOUD MASS
RED ZONE
WITHIN
RAIN AREA
RAIN AREA
(ONLY THIS IS
VISIBLE ON RADAR)
RAINFALL RATE
60 8040200
NAUTICAL MILES
RED LEVEL*
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.
Radar Facts
5-26
A28–1146–111
REV 2
PRIMUSR 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 i s 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.
DECAYING
CELLS
AREAS OF MAXIMUM TURBULENCE
MATURE CELLS
OUTLINE OF RAIN AREA VISIBLE TO RADAR
BEST DETOUR
Squall Line
Figure 5–30
GROWING
CELLS
AD–12058–R1@
A28–1146–111
REV 2 5-27
Radar Facts
PRIMUSR 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 PRIMUS
R
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.
Radar Facts
5-28
A28–1146–111
REV 2
DISPLAY
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
Á
LEVEL
RAINFALL
RATE
MM/HR
RAINFALL
RATE
IN./HR
PRIMUSR 660 Digital Weather Radar System
300 NAUTICAL MILES
MAXIMUM
dBZ
CALIBRATE
D RANGE
(NM) 10–IN
AND 12–IN
FLAT–PLATE
MAXIMUM
CALIBRATE
D RANGE
(NM) 18–IN
FLAT–PL ATE
MAXIMUM
CALIBRATE
D RANGE
(NM) 24–IN
FLAT–PL ATE
4
(MAGENTA
Á
)
3
Á
(RED)
Á
2
(YELLOW
Á
1
(GREEN)
Á
0
Á
(BLACK)
Á
GREATER
THAN
ÁÁ
50
ÁÁ
12 – 50
ÁÁ
4 – 12
ÁÁ
1 – 4
ÁÁ
LESS THAN
ÁÁ
1
ÁÁ
GREATER
THAN
ÁÁ
2
ÁÁ
0.5 – 2
ÁÁ
0.17 – 0.5
ÁÁ
0.04 – 0.17
ÁÁ
LESS THAN
ÁÁ
0.04
ÁÁ
GREATER
THAN
ÁÁ
53
ÁÁ
40 – 53
ÁÁ
33 – 40
ÁÁ
23 – 33
ÁÁ
LESS THAN
ÁÁ
23
ÁÁ
ÁÁ
232
ÁÁ
130
ÁÁ
90
ÁÁ
55
ÁÁ
–
ÁÁ
ÁÁ
GREATER
THAN
ÁÁ
300
ÁÁ
190
ÁÁ
130
ÁÁ
80
ÁÁ
–
ÁÁ
ÁÁ
GREATER
THAN
ÁÁ
300
ÁÁ
230
ÁÁ
160
ÁÁ
100
ÁÁ
–
ÁÁ
ÁÁ
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.
A28–1146–111
REV 2 5-29
Radar Facts
PRIMUSR 660 Digital Weather Radar System
Á
Á
Á
Á
Á
Á
Á
Á
VIP Level
ÁÁÁÁ
6
5
ÁÁÁÁ
4
3
2
1
Rainfall rate in
mm/hr
Greater than
ÁÁÁÁ
125
50 – 125
25 – 50
ÁÁÁÁ
12 – 25
2.5 – 12
0.25 – 2.5
Storm
Category
Extreme
ÁÁÁÁ
Intense
Very Strong
ÁÁÁÁ
Strong
Moderate
Weak
dBZ Level
Greater than
ÁÁÁÁ
57
50 – 57
45 – 50
ÁÁÁÁ
40 – 45
29 – 40
13 – 29
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 i n 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. Variab le gai n 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.
Radar Facts
5-30
A28–1146–111
REV 2
PRIMUSR 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 t he amount of attenuat ion.
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.
A28–1146–111
REV 2 5-31
Radar Facts
PRIMUSR 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.
Radar Facts
5-32
A28–1146–111
REV 2
PRIMUSR 660 Digital Weather Radar System
With REACT Selected
AD–51778–R1@
AD–54262@
Without REACT
REACT ON and OFF Indications
Figure 5–31
A28–1146–111
REV 2 5-33
Radar Facts
PRIMUSR 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 unt il ground is
being painted just in front of the storm cell(s). An area of no ground
returns behind the storm cell has t he 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 (W X or ground) behind the cell. The cell that produces a radar
shadow is a very st rong 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.
Radar Facts
5-34
A28–1146–111
REV 2
PRIMUSR 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.
100%
90%
80%
70%
60%
50%
40%
30%
TURBULENCE PROBABILITY
20%
10%
0%
LEVEL 1
GREEN
LIGHT
(4 mm / Hr) (12 mm / Hr) (50 mm / Hr)
LEVEL 2
YELLOW
RAINFALL RATE
LEVEL 3
RED
Probability of Turbulence Presence
in a Weather Target
Figure 5–32
LEVEL 4
MAGENTA
AD–15357–R3@
A28–1146–111
Radar Facts
REV 2 5-35
PRIMUSR 660 Digital Weather Radar System
Á
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Turbulence levels are listed and described in table 5–8.
REACTION INSIDE
INTENSITY AIRCRAFT REACTION
AIRCRAFT
ÁÁÁ
LIGHT
ÁÁÁ
ÁÁÁ
ÁÁÁ
MODERATE
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
SEVERE
ÁÁÁ
ÁÁÁ
Turbulence that momentarily causes
ББББББББ
slight, erratic changes in altitude and/or
attitude (pitch, roll, yaw).
ББББББББ
ББББББББ
Turbulence that is similar to light
turbulence but of greater intensity.
ББББББББ
Changes in altitude and/or attitude
occur but the aircraft remains in
ББББББББ
positive control at all times. It usually
ББББББББ
causes variations in indicated
airspeed.
ББББББББ
Turbulence that causes large abrupt
ББББББББ
changes in altitude and/or attitude. It
usually causes large variations in
ББББББББ
indicated airspeed. Aircraft can be
ББББББББ
momentarily out of control.
Occupants can feel a slight
ББББББ
strain against seat belts or
shoulder straps. Unsecured
ББББББ
objects can be displaced
ББББББ
slightly.
Occupants feel definite
strains against seat belts or
ББББББ
shoulder straps. Unsecured
objects are dislodged.
ББББББ
ББББББ
ББББББ
Occupants are forced
ББББББ
violently against seat belts
or shoulder straps.
ББББББ
Unsecured objects are
ББББББ
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.
Radar Facts
5-36
A28–1146–111
REV 2
100%
80%
60%
PRIMUSR 660 Digital Weather Radar System
1/4” HAIL
40%
RELA TIVE FREQUENCY
20%
0%
LEVEL 2
YELLOW
1/2” HAIL
LEVEL 3
RED
3/4” AND LAGER HAIL
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 dece p t i v e l y w e a k o r 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 tr opopause, the hail is eject ed 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 u p a nd d own
regularly produces the total weather pic ture.
A28–1146–111
REV 2 5-37
Radar Facts
PRIMUSR 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 colum n of dry hail that retur ns 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
Radar Facts
5-38
WET HAIL
AND RAIN
Rain Coming From Unseen Dry Hail
Figure 5–34
Familiar Hailstorm Patterns
Figure 5–35
AD–12059–R1@
U–SHAPEHOOKFINGER
AD–35713@
A28–1146–111
REV 2
PRIMUSR 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
A28–1146–111
REV 2 5-39
Radar Facts
PRIMUSR 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
Radar Facts
5-40
LONG RANGE
Short– and Long–Blind Alley
40
20
Figure 5–37
20
SHORT RANGE
AD–12062–R1@
A28–1146–111
REV 2
PRIMUSR 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
A
INDICA TOR DISPLAY A
B
INDICA TOR DISPLAY B
20
10
AD–35705@
Azimuth Resolution in Weather Modes
Figure 5–38
40
20
60
50
40
30
A28–1146–111
REV 2 5-41
Radar Facts
PRIMUSR 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.
Radar Facts
5-42
A28–1146–111
REV 2
PRIMUSR 660 Digital Weather Radar System
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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
Á
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Á
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A28–1146–111
REV 2 5-43
БББББББББББББББББ
alerted if a new storm cell develops in the aircraft’s
flightpath.
БББББББББББББББББ
2
Keep the gain in preset. The gain control should be in
preset except for brief periods when variable gain is used
БББББББББББББББББ
for detailed analysis. Immediately after the analysis, switch
БББББББББББББББББ
back to preset gain.
БББББББББББББББББ
БББББББББББББББББ
БББББББББББББББББ
DO NOT LEAVE THE RADAR IN VARIABLE GAIN. SIGNIFICANT WEATHER CAN NOT BE DISPLAYED.
БББББББББББББББББ
Severe Weather Avoidance Procedures
WARNING
Table 5–9 (cont)
Radar Facts
PRIMUSR 660 Digital Weather Radar System
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Step Procedure
3
Any storm with reported tops at or greater than 20,000 feet
ÁÁ
ÁÁ
ÁÁ
ÁÁ
ÁÁ
ÁÁ
ÁÁ
ÁÁ
ÁÁ
ÁÁ
ÁÁ
ÁÁ
ÁÁ
ÁÁ
ÁÁ
ÁÁ
ÁÁ
ÁÁ
ÁÁ
must be avoided by 20 NM.
ББББББББББББББББ
ББББББББББББББББ
ББББББББББББББББ
DRY HAIL CAN BE PREVALENT A T HIGHER ALTITUDES
ББББББББББББББББ
WITHIN, NEAR, OR ABOVE STORM CELLS, AND SINCE
ББББББББББББББББ
ITS RADAR REFLECTIVITY IS POOR, IT can NOT BE
DETECTED.
ББББББББББББББББ
4
For brief periods use increased gain (rotate GAIN control
to its maximum cw position) when flying near storm tops.
ББББББББББББББББ
This helps display the normally weaker returns that could
be associated with hail.
ББББББББББББББББ
5
When flying at high altitudes, tilt downward frequently
to avoid flying above storm tops.
ББББББББББББББББ
Studies by the National Severe Storms Laborat or y (NSSL)
ББББББББББББББББ
of Oklahoma have determined that thunderstorms
extending to 60,000 ft show little variation of turbulence
ББББББББББББББББ
intensity wit h altitude.
ББББББББББББББББ
Ice crystals are poor reflectors. Rain water at the lower
ББББББББББББББББ
altitudes produce a strong echo, however at higher
altitudes, the nonreflective ice produces a week echo as
ББББББББББББББББ
the antenna is tilted up. Therefore, though the intensity of
ББББББББББББББББ
the echo diminishes with altitude, it does not mean the
severity of the turbulence has diminished.
ББББББББББББББББ
NOTE: If the TILT control is left in a fixed position at the higher flight
ББББББББББББББББ
levels, a storm detected at long range can appear to become
weaker and actually disappear as it is approached. This occurs
ББББББББББББББББ
because the storm cell that was fully within the beam at 100 NM
ББББББББББББББББ
gradually passes out of and under the radar beam.
WARNING
6
ÁÁ
ÁÁ
ÁÁ
ÁÁ
ÁÁ
ÁÁ
Radar Facts
5-44
When flying at low altitudes rotate tilt upward
ББББББББББББББББ
frequently to avoid flying under a thunderstorm.
There is some evidence that maximum tur bulence exists at
ББББББББББББББББ
middle heights in st orms (20,000 to 30,000 ft); however,
turbulence beneath a storm is not to be minimized.
ББББББББББББББББ
However, the lower altitude can be affected by strong
ББББББББББББББББ
outflow winds and severe tur bulenc e where thunderst or m s
are present. The same turbulence consider at ions that
ББББББББББББББББ
apply to high altitude flight near storms apply to low
ББББББББББББББББ
altitude flight .
Severe Weather Avoidance Procedures
Table 5–9 (cont)
A28–1146–111
REV 2
PRIMUSR 660 Digital Weather Radar System
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Step Procedure
7
Avoid all rapidly moving echoes by 20 miles.
A single thunderstorm echo, a line of echoes, or a cluster
Á
Á
Á
Á
Á
Á
БББББББББББББББББ
of echoes moving 40 knots or more often contain severe
weather. Although nearby, slower moving echoes can
БББББББББББББББББ
contain more intense aviation hazards, all rapidly moving
БББББББББББББББББ
echoes warrant close observation. Fast moving, broken–
to solid–line echoes are particularly disruptive to aircraft
БББББББББББББББББ
operations.
8
Avoid, the entire cell if any portion of the cell is red or
БББББББББББББББББ
magenta by 20 NM.
The stronger the radar return, the greater the frequency
БББББББББББББББББ
and severity of turbulence and hail.
9
Avoid all rapidly growing storms by 20 miles.
Á
Á
Á
Á
Á
10
БББББББББББББББББ
When severe storms and rapid development ar e evident,
БББББББББББББББББ
the intensity of the radar return can increase by a huge
factor in a matter of minutes. Moreover, the summit of the
БББББББББББББББББ
storm cells can grow at 7000 ft / m in. The pilot cannot
БББББББББББББББББ
expect a flightpat h through such a field of strong storms
separated by 20 to 30 NM to be free of severe turbulence.
БББББББББББББББББ
Avoid all storms showing erratic motion by 20 miles.
Á
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A28–1146–111
REV 2 5-45
БББББББББББББББББ
Thunderstorms tend to mov e with the average wind that
exists between the bas e and top of the cloud. Any motion
БББББББББББББББББ
differing from this is cons ider ed erratic and can indicate the
БББББББББББББББББ
storm is severe. There are several causes of errat ic
motion. They can act indiv idually or in concert. Three of
БББББББББББББББББ
the most im port ant causes of err at ic mot ion are:
БББББББББББББББББ
1. Moisture Source. Thunderstorms tend to grow toward a
layer of very moist air (usually south or southeast in the
БББББББББББББББББ
U.S.) in the lowest 1500 to 5000 ft above the earth’s
БББББББББББББББББ
surface. Moist air generates most of the energy for the
БББББББББББББББББ
storm’s growth and activity. Thus, a thunderstorm can
tend to move with the average wind flow around it, but
БББББББББББББББББ
also grow toward moisture. When the growth toward
БББББББББББББББББ
moisture is rapid, the echo motion often appears erratic.
On at least one occasion, a thunderstorm echo moved in
БББББББББББББББББ
direct opposition to the average wind!
БББББББББББББББББ
Severe Weather Avoidance Procedures
Table 5–9 (cont)
Radar Facts
PRIMUSR 660 Digital Weather Radar System
Á
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Step Procedure
10
(cont)
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Radar Facts
5-46
2. Disturbed Wind Flow. Sometimes thunderstorm
updrafts block winds near the thunderstorm and act much
ББББББББББББББББ
like a rock in a shallow river bed. This pillar of updraft
forces the winds outside the storm to flow around the
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storm instead of carrying it along. This also happens in
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wake eddies that often form downstream of the blocking
ББББББББББББББББ
updraft
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3. Interaction With Other Storms. A thunderstorm that is
ББББББББББББББББ
located between another storm and its moisture source
ББББББББББББББББ
can cause the blocked storm to have erratic motion.
Sometimes the blocking of moisture is effective enough
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to caus e the thunderstorm to dissipat e.
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Three of the most common erratic motions are:
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ББББББББББББББББ
1. Right Turning Echo. This is the most frequently
observed erratic motion. Sometimes a thunderstorm
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echo traveling the same direction and speed as nearby
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thunderstorm echoes, slows, and turns to the right of its
previous motion. The erratic motion can last an hour or
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more before it resumes its previous motion. The storm
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should be considered severe while this erratic motion is
ББББББББББББББББ
in progress.
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2. Splitting Echoes. Sometimes a large (20–mile or larger
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diameter) echo splits into two echoes. The southernmost
echo often slows, turns to the right of its previous motion,
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and becomes severe with large hail and extreme
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turbulence.
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If a tornado develops, it is usually at the right rear portion
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of the southern echo. When the storm weakens, it usually
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resumes its original direction of movement. The northern
echo moves left of the mean wind, increases speed and
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often produces large hail and extreme turbulence.
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3. Merging Echoes. Merging echoes sometimes become
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severe, but often the circulation of the merging cells
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interfere with each other preventing intensification. The
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greatest likelihood of aviation hazards is at the right rear
section of the echo.
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Severe Weather Avoidance Procedures
Table 5–9 (cont)
A28–1146–111
REV 2
PRIMUSR 660 Digital Weather Radar System
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Step Procedure
11
Never continue flight towards or into a radar shadow
or the blue REACT field.
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БББББББББББББББББ
БББББББББББББББББ
БББББББББББББББББ
STORMS SITUATED BEHIND INTERVENING RAINFALL
БББББББББББББББББ
CAN BE MORE SEVERE THAN DEPICTED ON THE DIS-
БББББББББББББББББ
PLAY.
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If the radar signal can penetrate a storm, the target
displayed seems to cast a shadow with no visible returns.
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This indicates that the storm contains a great amount of
rain, that attenuates the signal and prevents the radar from
БББББББББББББББББ
seeing beyond the cell under observation.
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The REACT blue field shows areas where attenuation
could be hiding severe weather. Both the shadow and the
БББББББББББББББББ
blue field are to be avoided by 20 miles. Keep the REACT
БББББББББББББББББ
blue field turned on. The blue field forms fingers that point
toward the stronger cells.
БББББББББББББББББ
WARNING
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.
A28–1146–111
REV 2 5-47
Radar Facts
PRIMUSR 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.
Radar Facts
5-48
A28–1146–111
REV 2
PRIMUSR 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
A28–1146–111
REV 2 5-49
Radar Facts
PRIMUSR 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
Radar Facts
5-50
AD–35706@
The Classic Pendant Shape
Figure 5–42
A28–1146–111
REV 2
PRIMUSR 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.
A28–1146–111
REV 2 5-51
Radar Facts
PRIMUSR 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.
Radar Facts
5-52
A28–1146–111
REV 2
PRIMUSR 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.
A28–1146–111
REV 2 5-53
Radar Facts
PRIMUSR 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
Radar Facts
5-54
VIP 5
AD–15563–R1@
Bow–Shaped Line of Thunderstorms
Figure 5–46
A28–1146–111
REV 2
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