FOREWORD

Since 1943, low-level wind shear has been cited in a number of aircraft accidents/incidents that together have contributed to over 1 400 fatalities worldwide. Increased awareness within the aviation community of the hazardous and insidious nature of low-level wind shear has been reflected in the fact that the ICAO Council has considered it to be one of the major technical problems facing aviation.

Until the 1980s, lack of adequate operational remote-sensing equipment, the complexity of the subject, the wide range of scale of wind shear and its inherent unpredictability all conspired to hinder a complete solution to the problem which, in turn, limited the development of the necessary international Standards and Recommended Practices for the observing, reporting and forecasting of wind shear.

In 1975 there were five jet transport aircraft accidents/incidents in which wind shear was cited, one of which resulted in major loss of life.¹ The latter accident, which occurred at John F. Kennedy (JFK) International Airport, New York, on 24 June 1975, and another at Denver, Colorado, United States, on 7 August 1975, which fortunately resulted in no loss of life and occurred in an area where detailed monitoring of the wind field was possible, marked a turning point in the history of wind shear. The detailed and exhaustive analysis of the role played by wind shear in these particular accidents removed any lingering doubt regarding the real danger of wind shear. The accelerated research effort that followed, culminating in the massive Joint Airport Weather Studies (JAWS) project at Stapleton Airport, Denver, Colorado, United States, in 1982, considerably improved our understanding of the problem, particularly regarding wind shear associated with thunderstorms.

The ICAO Eighth Air Navigation Conference (Montréal, 1974)² recommended the preparation and publication of guidance material to assist all concerned to make the best possible use of the available information on wind shear. In order to assist in the preparation of this guidance material, the Low-level Wind Shear and Turbulence Study Group (WISTSG) was formed. With the assistance of the group a statement of operational requirements for observing and reporting wind shear and turbulence was developed. This statement, together with an initial list of recommended terms and their explanations and a progress report on wind shear, largely based upon circulars issued by some States, was sent as guidance to States in State letter AN 10/4.6-79/142, dated 31 August 1979.

Following the increased research effort, Amendment 64 to Annex 3 — Meteorological Service for International Air Navigation was developed and became applicable in November 1983 and included new and revised provisions for the observing and reporting of low-level wind shear. At the same time, the statement of operational requirements was slightly revised (see Appendix 1).

In 1982, the United States Subcommittees on Investigations and Oversight, and on Transportation, Aviation and Materials, of the House of Representatives’ Committee on Science and Technology held joint hearings on weather problems affecting aviation, including wind shear. Following those hearings, the Federal Aviation Administration (FAA) contracted with the National Academy of Sciences “to study the state of knowledge, alternative approaches and the consequences of wind shear alert and severe weather conditions relating to take-off and landing clearances for commercial and general aviation aircraft”. In order to accomplish this task, an ad hoc Committee for the Study of Low-Altitude^a Wind Shear and its Hazard to Aviation was formed. The Committee produced an extremely comprehensive report and a series of conclusions and recommendations¹ (see Appendix 2).

Since 1967 the FAA has had a detailed programme directed towards reducing the hazard to aviation of low-level wind shear. Under this programme, action has been taken on the recommendations made by the above-mentioned Committee and also on recommendations made on occasion by the National Transportation Safety Board (NTSB) following accident investigations. In this regard, the FAA developed an “Integrated Wind Shear Programme”, which involved close cooperation with a number of government agencies (e.g. the National Aeronautical and Space Administration (NASA), the aerospace industry, pilot associations and ICAO) and included a wind shear training aid that was published in February 1987. The programme’s objective was to further develop and refine over the next five to ten years education, training and operational procedures, surface-based and airborne wind shear detection technology and on-board flight guidance systems. In parallel, further explanation of the wind shear hazard was to be provided by continued scientific research. In 1987, with the assistance of the WISTSG, ICAO published Circular 186 on Wind Shear, the forerunner of this manual.

At the time the circular on Wind Shear (Cir 186) was published in 1987, it was stated in the foreword that “the bulk of the information on wind shear, particularly the operational aspects, is still not sufficiently mature to be translated into regulatory provisions”. Subsequent amendments to the relevant Annexes and Procedures for Air Navigation Services (PANS) to take account of the requirement to provide information on wind shear to pilots, and the fact that the original circular has been replaced by this manual, attest to the increased maturity of this subject.

Two main trends are responsible for the progress made in the past twenty years. Advances in the development of equipment to detect and warn of wind shear, both ground-based and airborne, have occurred since 1987. In particular, there have been major advances in Doppler radar and signal-processing technology, which have led to the development of highly effective, dedicated ground-based wind shear detection/warning systems. Similar advances have also produced forward-looking wind shear detection/warning systems to meet the operational requirements for airborne equipment. However, at the time of this writing, the level of deployment of such systems is much slower than expected for some airlines. The relevant ICAO regulatory documents have been amended in step with these technical developments.

In parallel with the development of wind shear detection/warning equipment, progress has been made in the training of operational personnel concerning the serious effect that wind shear can have on aircraft in flight. Especially important is the training of pilots. Excellent wind shear training aids are available that cover the explanation and recognition of wind shear and its avoidance during landing and take-off. The flying techniques recommended in order for the pilot to recover from an inadvertent encounter with wind shear are also covered. Today all pilot simulator training should include wind shear recognition, avoidance and recovery modules.

There has been a marked reduction in the past decade in the number of aircraft accidents/incidents in which wind shear was cited as a contributory factor. However, it will always be a serious hazard for aviation and a potential killer, and there must be continued vigilance and pilot training on wind shear.

^a. In this manual, the qualifying term “low-level” has been retained due to the fact that “altitude” is a defined ICAO term meaning “the vertical distance of a level, a point or an object considered as a point measured from mean sea level”. The critical issue with respect to wind shear is the effect on aircraft performance when in relatively close proximity to the ground. It is not felt that “low-level” in this context could be misconstrued as meaning low-level “in intensity”.