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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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