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Low-Altitude Wind Shear
and Its Hazard to Aviation
Report of the
Committee on Low-Altitude Wind Shear
ant! Its Hazarc! to Aviation
A Joint Study
Commission on Engineering
ant} Technical Systems
Aeronautics and Space
Engineering Boars!
National Research Council
NATIONAL ACADEMY PRESS
Washington, D.C. 1983
Commission on Physical Sciences,
Mathematics, and Resources
Atmospheric Sciences and
Climate Board
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NOTICE: The project that is the subject of this report was approved
by the Governing Board of the National Research Council, whose members
are drawn from the councils of the National Academy of Sciences, the
National Academy of Engineering, and the Institute of Medicine. The
members of the committee responsible for the report were chosen for
their special competences and with regard for appropriate balance.
This report has been reviewed by a group other than the authors
according to procedures approved by a Report Review Committee
consisting of members of the National Academy of Sciences, the
National Academy of Engineering, and the Institute of Medicine.
The National Research Council was established by the National
Academy of Sciences in 1916 to associate the broad community of science
and technology with the Academy's purposes of furthering knowledge and
of advising the federal government. The Council operates in accordance
with general policies determined by the Academy under the authority of
its congressional charter of 1863, which establishes the Academy as a
private, nonprofit, self-governing membership corporation. The Council
has become the principal operating agency of both the National Academy
of Sciences and the National Academy of Engineering in the conduct of
their services to the government, the public, and the scientific and
engineering communities. It is administered jointly by both Academies
and the Institute of Medicine. The National Academy of Engineering
and the Institute of Medicine were established in 1964 and 1970,
respectively, under the charter of the National Academy of Sciences.
This report and the study on which it is based were supported by
Contract No. OTFA01-83-C-10032 between the Federal Aviation
Administration and the National Academy of Sciences.
Library of Congress Catalog Card Number 83-63100
International Standard Book Number 0-309-03432-9
Available from
NATIONAL ACADEMY PRESS
2101 Constitution Avenue, NW
Washington, DC 20418
Printed in the United States of America
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September 29, 1983
Dr . Frank P re s s
Chairman, liational Research Council
2101 Constitution Avenue, N.W.
Washington, D.C. 20418
Dear Dr. Press:
It is my privilege to submit the report of the Committee on Low-
Altitude Wind Shear and Its Hazard to Aviation, which was established
under the terms of an agreement between the Nat tonal Academy of
Sciences and the Federal Aviation Administration (FAA). The task of
the committee was to review the state of knowledge of low-altitude
wind shear, to study the hazards of low-altitude wind variability, and
to recommend actions to reduce the hazards of wind-shear encounters
and improve flight safety. This work was directed by the terms of
Public Law 97-369, signed December 18, 1982.
The committee's principal finding confirmed that low-altitude
wind variability (or wind shear) presents an infrequent but highly
significant hazard to aircraft while landing or taking off, and that
when significant wind shears may be present, pilots should delay
takeoffs or landings or divert to alternate airports.
In the near term, risks
automating the Low-Level Wind Shear
installation at all major airports.
trained in the utilization of LLWSAS
warnings derived from forecasts
conducive to generating wind shear.
encounters or alerts by pilots to
with weather advisories remain
information for those airports that
can be reduced by improving and
Alert Sys tem (LLWSAS ~ and by its
Ground personnel must be better
da ta and in the us e 0 f wind-shear
of weather conditions that are
Voluntary reports of wind-shear
air traffic control personnel along
the only sources of wind-shear
lack LLWSAS installations.
The committee found that the education and training of most
pilots with respect to wind shear and its hazards are inadequate and
that the risk posed by wind shear can be reduced very soon by an
education campaign directed at all classes of pilots.
· . .
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Better information is required concerning the response to wind
shear of aircraft of various categories and sizes and of the effects
of piloting techniques and guidance and control systems. This
information could provide the teas is for improved pilot training to
cope with wind-shear encounters. It should be possible to design
better guidance and control aids to improve a pilot' s ability to avoid
an accident in the event of an inadvertent wind-shear encounter.
Utilization of a highly automated Doppler radar derived from the
NEXRAD system and optimized for wind-shear detect ion and located in an
airport 's terminal area would provide greatly enhanced wind-shear
detection capability and pilot warning of potential wind-shear hazards.
This would require related development of procedures for analyzing and
displaying observations and communicating warnings to ground
controllers and flight crews.
Research in a number of areas is required to help reduce the
hazards of low-altitude wind shear. Meteorological research is needed
to understand more fully all forms of wind shear and to lead to
better, more timely forecasts. Data derived from LLWSAS operations
should be recorded and analyzed, and an additional field research
program directed to measurements of wind-shear phenomena should be
undertaken at a humid southeastern location, to supplement research
done in the semi-wet north-central midwestern United States and high,
dry midwestern pi ains .
Research is also needed to determine the effects of heavy rain,
which often accompanies wind shear, on aircraft aerodynamic character-
istics. Research on airborne wind-shear detection systems should be
continued, in view of the benefits that could be provided by a small-
sized, lightweight, airborne wind-shear detector.
There appears to be no single solution to all hazards caused by
wind shear. To help ensure that all feasible steps are undertaken to
minimize its risks, however, it is recommended that the FAA establish
an integrated program to maintain a sustained effort for coping with
all aspects of low-altitude wind shear in aircraft operations and to
minimize its hazards to flight safety.
Sincerely,
:1~, · cams ~
/ John W. Townsend
Cha irman
JWT/lds
1V
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Committee on Low-Altit?~de Wind Shear and
Its Hazard to Aviation
JOHN W. TOWNSEND, JR., President, Fairchild Space Company,
Committee Chairman
PANEL ON AIRCRAFT PERFORMANCE AND OPERATIONS
-
KENNETH F. HOLTBY, Senior Vice President, The Boeing Company,
Chairman
IRVING L. ASHKENAS, Vice President and Technical Director,
Systems Technology, Inc.
JOHN W. CONNOLLY, Director, Government Affairs, Alden Electronics
Company, Inc.
ROBERT S. CRUMP, Captain and Vice President, Flight Standards and
Training, United Airlines
JOHN H. ENDERS, President, Flight Safety Foundation, Inc.
J. ROGER FLEMING, Vice President, Operations, Air Transport
Association
WILLIAM M. FLENER, Director, Government Relations, National Business
Aircraft Association, Inc.
ROBERT P. HARPER, JR., Department Head, Flight Research Department,
Calspan Corporation
MARK E. KIRCHNER, Director, Engineering Technology, Boeing
Commercial Airplane Company
WILLIAM W. MELVIN, Captain, Delta Airlines; Chairman, Airworthiness
and Performance Committee, Air Line Pilots Association
HARVEY O. NAY, Director of Engineering, Piper Aircraft Corporation
ROBERT F. STENGEL, Professor and Director, Flight Research
Laboratory, Princeton University
CLIVE A. WHITMORE, Aerodynamics Division Engineer,
Lockheed-California Company
PANEL ON LOW-ALTITUDE WIND VARIABILITY
LOUIS J. BATTAN, Professor, Institute of Atmospheric Physics,
University of Arizona, Chairman
ELBERT W. FRIDAY, JR., Deputy Assistant Administrator for Weather
Services, National Weather Service
v
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TETSUYA T. FUJITA, Professor, University of Chicago
KENNETH M. CLOVER, Air Force Geophysics Laboratory, Air Force System
Command, Hanscom Air Force Base
WILLIAM H. HOOKE, Chief, Sea State Studies Program Area, Wave
Propagation Laboratory, National Oceanic and Atmospheric
Administration
EDWIN KESSLER III, Director, National Severe Storms Laboratory,
National Oceanic and Atmospheric Administration
JOHN McCARTHY, National Center for Atmospheric Research
ROBERT J. SERAFIN, Director, Atmospheric Technology Division,
National Center for Atmospheric Research
DANIEL F. SOWA, Superintendent of Meteorology, Northwest Orient
Airlines
DONALD L. VEAL, President, University of Wyoming
LIAISON REPRESENTATIVES
~ _
NEAL BLAKE, Deputy Associate Administrator for Engineering and
Development, Federal Aviation Administration
WILLIAM LAYNOR, Deputy Director, Bureau of Technology, National
Transportation Safety Board
GREGORY D. SALOTTOLO, Senior Meteorologist, National Transportation
Safety Board
ALLAN R. TOBIASON, Aeronautical Systems Division, National
Aeronautics and Space Administration
COL. PAUL D. TRY (USAF), Director, Environmental and Life Sciences
Office of Deputy Under Secretary, Research and Advanced Technology,
U.S. Department of Defense
NRC STAFF
ALBERT J. EVANS, Executive Director, Aeronautics and Space
Engineering Board, Commission on Engineering and Technical Systems
JOHN S. PERRY, Executive Secretary, Board on Atmospheric Sciences
and Climate, Commission on Physical Science, Mathematics,
and Resources
JEROME TEPLITZ, Consultant, Aeronautics and Space Engineering Board
FRED D. WHITE, Staff Officer, Board on Atmospheric Sciences
and Climate
LAURA D'SA, Administrative Assistant
V1
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Contents
PREFACE
EXECUTIVE SUMMARY
1. INTRODUCTION
Incident/Accident Records
FAA Wind-Shear Program Activities
2. LOW-ALTITUDE WIND SHEAR
The Nature of Low-Altitude Wind Shear
Ground-Based Sensing of Low-Altitude Wind Shear
Airborne Remote Sensing of Wind Shear
Interpretation and Communication to Air Traffic
Controllers and Pilots
Wind-Shear Prediction
National Weather Service Interaction with
the Federal Aviation Administration
3. AIRCRAFT PERFORMANCE AND OPERATIONS
Wind-Shear Warnings
Cockpit Procedures and Training
Performance in Wind Shear
Guidance and Control Aids
4. CONCLUSIONS
5. RECOMMENDATIONS
General
Detection and Prediction
Aircraft Peformance and Operations
Research
V11
1X
1
11
12
15
19
19
33
44
46
48
48
51
51
53
60
72
79
85
85
86
87
89
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APPENDIXE S
A . WIND-SHEAR P IREP S
B. EXAMPLE OF A MODERN WIND-SHEAR PENETRATION SYSTEM
C . REFERENCES AND BIBL IOGRAPHY
91
93
97
D. GLOS SARY OF ACRONYMS AND ABBREVIATIONS USED IN THE TEXT 111
· · ~
V111
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Preface
On July 9, 1982, Pan American World Airways Flight 759 crashed
shortly after taking off from New Orleans International Airport.
One-hundred forty-five persons on board the airplane and eight persons
on the ground died. The crash was attributed by the National
Transportation Safety Board to strong low-altitude wind shears
produced by isolated yet heavy thunderstorms in the vicinity of the
airport.
One month later, the Subcommittees on Investigations and Oversight
and on Transportation, Aviation, and Materials of the U.S. House of
Representative's Committee on Science and Technology held joint
hearings on weather problems affecting aviation. The hearings
addressed the current technical capability to detect hazardous weather
phenomena, such as wind shear, and the extent of its hazard to
aircraft takeoff and landing operations. Subsequent to these
hearings, P.L. 97-369 was passed in December 1982 requiring the
Federal Aviation Administration (FAA) to contract with the National
Academy of Sciences (NAS) "to study the state of knowledge,
alternative approaches and the consequences of wind-shear alert and
severe weather condition standards relating to takeoff and landing
clearances for commercial and general aviation aircraft." The law
also specified that the study be completed within 6 months.
Under the terms of an agreement between NAS and the FAA signed on
March 17, 1983, the study was also to review what is known about
low-altitude wind shear and wind variability, how it is detected and
measured, and how warnings are communicated to pilots and air traffic
controllers. Furthermore, the study was to address the adequacy of
pilot training on what to do when wind shear is encountered and to
evaluate the implications for aircraft design, construction, and
flight operations.
To conduct the study, NAS created an ad hoc Committee for the Study
of Low-Altitude Wind Shear and Its Hazard to Aviation. The committee
was established under the National Research Council's Commission on
Engineering and Technical Systems (GETS) and Commission on Physical
1X
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(CPSMR). The committee was
Panel on Low-Altitude Wind
knowledge on low-altitude wind
and Prediction. The nanel was
Sciences, Mathematics, and
divided into two panels. First, the
Variability, was to review the state of
shear, including detection, measurement,
also asked to recommend changes and improvements in wind-shear warning
techniques and procedures as well as required research and development
relating to wind shear. A second Panel on Aircraft Performance and
Operations was asked to review hazards of low-altitude wind shear to
commercial and general aviation operations. This panel was to consider
the diversity of aircraft design and performance characteristics, air
traffic control procedures, and pilot training and practices. The
panel was also asked to recommend changes to improve flight safety in
the event of encounters with hazardous wind shears, including research
and development.
Resources
The committee's charge was accomplished by means of three meetings
of the full committee and of each of its two panels in Washington,
D.C., from April through July 1983. In addition, each panel met
separately in May. The Panel on Low-Altitude Wind Variability met at
the National Center for Atmospheric Research in Boulder, Colorado, and
the Panel on Aircraft Peformance and Onerations met at the National
-
. .
.% ~ . ~ .
~ ~ _ ~ &_ _ ~ 1 ~ _ _ I _ ~ %~ A ~ A ~ T _ _ _ ~ _ __ ~ ~ __ _ ~ ~ ~
Aeronautics and space Admlnlstratlon's kNAbA) Langley Kesearcn center
in Hampton, Virginia.
work the committee received generous cooperation
Throughout its ~ .
from the FAA, NASA, the National Transportation Safety Board, the U.S.
Air Force, the National Oceanic and Atmospheric Administration, and
the National Center for Atmospheric Research.
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