U.S. Department 

of lranspoftation 

Federal Aviation 

Administration 

Advisory 

Circular 

Subject: Date: 11/25/88 AC No: 00-54 

PILOT WINDSHEAR GUIDE Initiated by: AFS- 200 Change: 

1 PURPOSE. This advisory circular communicates key windshear information 

relevant to flightcrews. Appendix 1 of this advisory circular is the Pilot 

Windshear Guide, which is only one section of the two-volume Windshear 

Training Aid. 

2 RELATED READING MATERIAL. The other components of the Windshear 

Training Aid are the Windshear Overview for Management, Windshear 

Substantiating Data, Example Windshear Training Program, and two training 

videos. These additional publications may be purchased from the National 

Technical Information Service, 5285 Port Royal Road, Springfield, VA 22161, 

telephone (703) 487-4650. A multimedia package, including video tapes, 

slides, 'and the Windshear Training Aid, may be purchased from the National 

Audiovisual Center, 8700 Edgeworth Drive, Capitol Heights, MD 20743-3701, 

telephone (301) 763-1896. 

3. BACKGROUND. In 1985, the Federal Aviation Administration (FAA) 

contracted with a consortium of aviation specialists from the Boeing 

Company, United Air Lines, McDonnell Douglas, Lockheed California, Aviation 

Weather Associates, and Heliwell, Inc., to study windshear. As a result, 

the Windshear Training Aid was developed. The Windshear Training Aid 

presents an effective means of training flightcrews to minimize the 

windshear threat through avoidance, cockpit recognition, and recovery 

techniques. In order to make the Pilot Windshear Guide section of the 

Windshear Training Aid available to a wide aviation audience, the guide is 

reprinted as appendix 1 to this advisory circular. 

4. UPDATING PROCEDURE. In order to ensure that the Pilot Windshear Guide 

is kept up-to-date, the FAA will host meetings for the purpose of reviewing 

new information on the subject of windshear. These meetings will be held 

approximately every 18 months and will be announced in the Federal Register. 

Technical assistance will be solicited from representatives of the original 

contract team, as w&l1 as from other qualified industry sources, in 

proposing and evaluating changes. As improvements and changes to the Pilot 

Windshear Guide occur, they will be distributed as a change to this advisory 

circular. 

a~%% 

D, C. Beaudette 

Acting Director, Flight StandardsService 

11/25/88 

APPENDIX 1, PILOT WINDSHEAR GUIDE 

AC 00-54 

Appendix 1 
AC 00-54 11]25/88 

Appendix 1 Pilot Windshear Guide-- Disclaimer 

and Indemity Notice 

The following disclaimer is'required by virtue of the contract between the 

Federal Aviation Administration and the Boeing Commercial Airplane Company. 

DISCLAIMER AND INDEMNITY NOTICE 

This document. Pilot Windshear Guide. 

and its companion documents, Windshear 

Overview For Management. Y Example Windshear Training Program,*Windshear Substantiating Data, and v?deo presentatlons “A Windshear Avoided" and "Windshear What the Crew Can Do” were=- 

pared pursuant to Federal Aviation 

Administration Prime Contract DFTAOl86-C-00005 with The Boeing Company as 

a training aid for flight in windshear 

conditions. The information contained 

herein and in the companion materials 

was derived from information originally developed for the Boeing 727, and 

provides a base-line training program 

with additional recommendations. -developed and approved by Boeing,-Douglas or Lockheed for their respective 

aircraft, regarding how that program 

might be adapted for use in specific 

commercial transport aircraft manufactured by Boeing [727, 737, 747, 757, 

and 7673, Douglas [DC-g, MD-80, and 

DC-101 and Lockheed [L-1011]. ANY USE 

OF THIS PILOT WINDSHEAR GUIDE AND ITS 

COMPANION VIDEO PRESENTATIONS "A WINDSHEAR AVOIDED" AND "WINDSHEAR -WHAT 

THE CREW CAN DO" FOR ANY PURPOSE RELATED TO AIRCRAFT OR CONDITIONS OTHER 

THAN THOSE SPECIFIED ABOVE IS NOT 

AUTHORIZED AND MAY RESULT IN IMPROPER 

AIRCRAFT OPERATION, LOSS OF AIRCRAFT 

CONTROL, INJURY AND LOSS OF AIRCRAFT 

AND LIFE. ANY USE, ADAPTATION AND/OR 

USE AFTER ADAPTATION OF THE MATERIAL 

IN THIS PILOT WINDSHEAR GUIDE AND ITS 

COMPANION VIDEO PRESENTATIONS “A WINDSHEAR AVOIDED" AND "WINDSHEAR - WHAT 

THE CREW CAN DO" BY ANY ENTITY FOR ANY 

PURPOSE RELATED TO AIRCRAFT, CONDITIONS OR TO TRAINING PROGRAMS OTHER 

THAN THOSE SPECIFIED ABOVE SHALL BE 

COMPLETELY AT THE RISK OF THE ENTITY 

RESPONSIBLE FOR USING, ADAPTING AND/OR 

USING THE ADAPTATION OF THIS PILOT 

WINDSHEAR GUIDE AND ITS COMPANION VIDEO PRESENTATIONS "A WINDSHEAR AVOIDED" 

AND "WINDSHEAR - WHAT THE CREW CAN 

DO", AND SUCH ENTITY BY SUCH USE, 

ADAPTATION AND/OR USE AFTER ADAPTATION 

ASSUMES SUCH RISK AND WAIVES AND RELEASES ALL CLAIMS IT MAY HAVE AGAINST 

THE BOEING COMPANY, MCDONNELL DOUGLAS 

CORPORATION, LOCKHEED CORPORATION, 

UNITED AIRLINES, AVIATION WEATHER 

ASSOCIATES, HELLIWELL, INC., THEIR 

DIVISIONS, SUBSIDIARIES, AFFILIATES 

AND THEIR OFFICERS, DIRECTORS, SUBCONTRACTORS AND EMPLOYEES FROM ANY LIABILITY WHATSOEVER, WHETHER BASED ON 

CONTRACT (INCLUDING BUT NOT LIMITED 

TO EXPRESS AND IMPLIED WARRANTY 

CLAIMS), TORT (INCLUDING BUT NOT LIMITED TO NEGLIGENCE AND STRICT LIABILITY CLAIMS) OR OTHERWISE, ARISING FROM 

SUCH USE, ADAPTATION AND/OR USE OF 

SUCH ADAPTATION. ANY SUCH ENTITY (INCLUDING WITHOUT LIMITATION ANY MANUFACTURER OF OTHER AIRCRAFT OR OPERATOR 

WITH ANOTHER TRAINING PROGRAM BUT NOT 

THE UNITED STATES GOVERNMENT) WHICH 

USES THIS PILOT WINDSHEAR GUIDE AND 

ITS COMPANION VIDEO PRESENTATIONS "A 

WINDSHEAR AVOIDED" AND "WINDSHEAR - 

WHAT THE CREW CAN DO" OR ADAPTS AND/OR 

USES AN ADAPTATION THEREOF WITH RESPECT TO SUCH OTHER AIRCRAFT, CONDITIONS OR TRAINING PROGRAM THEREBY 

AGREES TO INDEMNIFY AND HOLD HARMLESS 

THE BOEING COMPANY, MCDONNELL DOUGLAS 

CORPORATION, LOCKHEED CORPORATION, 

UNITED AIRLINES, AVIATION WEATHER 

ASSOCIATES, HELLIWELL, INC., THEIR 

DIVISIONS, SUBSIDIARIES AND AFFILIATES 

AND THEIR OFFICERS, DIRECTORS, AGENTS, 

SUBCONTRACTORS AND EMPLOYEES FROM ANY 

LIABILITY WHATSOEVER, WHETHER BASED ON 

CONTRACT, (INCLUDING BUT NOT LIMITED 

TO EXPRESS AND IMPLIED WARRANTY 

CLAIMS), TORT (INCLUDING BUT NOT LIMITED TO NEGLIGENCE AND STRICT LIABILITY CLAIMS) OR OTHERWISE, ARISING FROM 

SUCH USE, ADAPTATION AND/OR USE OF 

SUCH ADAPTATION. 

Notwithstanding any other provision of this contract to the contrary, the FAA shall accept the 

items delivered hereunder with the 

disclaimer affixed by Contractor 

and agrees not to remove such disclaimer for any reason whatsoever. 

ii 
11/25/88 AC oo-% 

Appendix 1 

PILOT WINDSHEAR GUIDE 

TABLE OF CONTENTS 

SECTION DESCRIPTION PAGE 

2.0 

2.1 

2.2 

2.3 

2.3.1 

2.3.2 

2.3.3 

2.3.4 

2.3.5 

2.4 

2.4.1 

2.4.2 

2.4.3 

2.4.3.1 

2.4.3.2 

2.4.4 

2.4.5 

INTRODUCTION .eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee 

OBJECTIVES eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee 

WINDSHEAR WEATHER l eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee 

LESSONS LEARNED FROM WINDSHEAR ENCOUNTERS l eeeeeeeeeeeeeeeeee 

ENCOUNTER DURING TAKEOFF - AFTER LIFTOFF l eeeeemeeeeeeee 

ENCOUNTER DURING TAKEOFF - ON RUNWAY l eeeeeeeeeeeeeeeeee 

ENCOUNTER ON APPROACH l eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee 

WINDSHEAR EFFECTS ON AIRPLANES AND SYSTEMS l eeeeeeeeeeee 

DEVELOPMENT OF WIND MODELS l eeeeeeeeeeeeeeeeeeeeeeeeeeee 

MODEL OF FLIGHT CREW ACTIONS l eeeeeeeeeeeeeeeeeeeeeeeeeeeeeee 

EVALUATE THE WEATHER l eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee 

AVOID KNOWN WINDSHEAR l eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee 

CONSIDER PRECAUTIONS l eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee 

TAKEOFF PRECAUTIONS l eeeeeeeeeeeeeeeeeeeeeeeeeeeeee 

APPROACH PRECAUTIONS l eeeeeeeeeeeeeeeeeeeeeeeeeeeee 

FOLLOW ESTABLISHED STANDARD OPERATING TECHNIQUES l eeeeee 

WINDSHEAR RECOVERY TECHNIQUES l eeemeeeeeeeeeeeeeeeeeeeee 

2e4e5e1/3 ENCOUNTER DURING TAKEOFF - AFTER LIFTOFF AND 

ENCOUNTER ON APPROACH l eeeeeeeeeeeeeeeeeeeeeeeeeeee 

2e4e 5.2 ENCOUNTER DURING TAKEOFF - ON RUNWAY l eeeeeeeeeeeee 

2e5 SUmARY eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee 

1 

1 

2 

14 

15 

19, 

22 

24 

28 

29 

30 

35 

38 

38 

41 

43 

45 

45 

49 

56 

iii 

U/25/88 AC 00-54 

Appendix 1 

2.0 INTRODUCTION 

During the period from 1964 to 1986, 

at least 32 accidents and incidents 

have occurred in which windshear was 

identified as a contributing factor. 

These accidents and incidents resulted 

in over 600 fatalities and nearly 250 

injuries. There is evidence to suggest that if undocumented "close 

calls" and general aviation statistics 

were included, these figures would be 

much higher. 

Due to the serious nature of this 

problem, the National Research Council 

was commissioned to study the windshear issue. One finding of the Council was a general lack of effective 

pilot training programs for windshear. The Council made recomnendations regarding further efforts needed 

to improve the training of pilots to 

recognize, avoid, and cope with inadvertent windshear encounters. As a 

result of these recommendations, the 

Federal Aviation Administration sponsored development of a comprehensive 

Windshear Training Aid. 

The Pilot Windshear Guide is one of 

several parts of the Windshear Training Aid. The other components are the 

Windshear Overview for Management, 

Windshear Substantiating Data, Example 

Windshear Training Program, and two 

Training Videos. 

The educational material and training 

recommendations provided in the Windshear Training Aid were developed 

through an extensive review process to 

achieve a wide air transport industry 

consensus. The goal of the Training 

Aid is to reduce windshear related accidents and incidents by modifying 

flight crew behavior through education 

and training. 

2.1 OBJECTIVES 

The objective of the Pilot Windshear 

Guide is to summarize and communicate 

key windshear information relevant to 

flight crews. It is intended to be 

provided to pilots during windshear 

ground training and to be retained as 

a windshear information reference for 

future use. 

Avoidance is emphasized as the best 

defense against the hazards of low altitude windshear. Information to assist in recognizing and avoiding windshear is provided. However, precautions and techniques for improving 

chances of surviving an inadvertent 

windshear encounter are also discussed. Specifically, the Pilot Windshear Guide presents key findings regarding: 

1) Windshear weather, particularly 

microbursts, and clues which may 

indicate its presence, 

2) Effects of windshear on airplanes, 

3) Windshear recognition 

cockpit, an d avoidance, 

from the 

4) Precautions to take when windshear 

is suspected, 

5) 

6) 

Standard operating techniques 

lated to windshear, and 

Recovery techn iques to 

an inadve &rtent windshea 

rebe used in 

r encounter. 

Page 1 
AC 00-54 

Appendix 1 

11/25/88 

2.2 WINDSHEAR WEATHER 

Wind variations at low-altitude have 

long been recognized as a serious 

hazard to airplanes during takeoff and 

approach. These wind variations can 

result from a large variety of meteorological conditions such as: topographical conditions, temperature inversions, sea breezes, frontal systems, strong surface winds, and the 

most violent forms of wind change--the 

thunderstorm and rain shower. 

Throughout this document several terms 

are used when discussing low altitude 

wind variations. These terms are defined as follows: 

Wi ndshear - Any rapid 

di rection or velocity. 

change in wind 

Severe Windshear - A rapid change in 

wind direction or velocity causing 

airspeed changes greater than 15 knots 

or vertical speed changes greater than 

500 feet per minute. 

Increas ing Hea dwind Shear 

in whit h headw ind i ncreases 

airspeed increase. 

- Wi ndshear 

cau sing an 

Decreasing Headwind Shear - Windshear 

in which headwind decreases causing an 

airspeed loss. 

Decreasing Tailwind Shear - Windshear 

in which tailwind decreases causing an 

airspeed increase. 

Increasing Tailwind Shear - Windshear 

in which tailwind increases causing an 

airspeed loss. 

Examination of airplane accident and 

incident reports from 1959 - 1983 

identified 51 windshear-related 

events. These events are summarized 

in Figure 1. 

In order to avoid further windshear 

encounters, pilots must learn to 

recognize conditions producing windshear. As Figure 1 indicates, 2 out 

of every 3 windshear events were related to convective storms. For this 

reason, the primary focus of the Pilot 

Windshear Guide is directed toward 

windshear associated with convective 

weather conditions: thunderstorms, 

and in particular the most hazardous 

form of windshear, the microburst. 

Weather System Number of 

Windshear Events* 

Convective Storms 

(Thunderstorms, Rain/ 

Snow Showers) 

Front 

Strong Surface Winds 

Unstable (Turbulent ) Air 

Strong Winds on Top 

of Temperature Inversion 

Sea Breeze Front 

Mountain Wave 

Unknown 

Total 

*Event - accident or incident 

33 

7 

2 

2 

1 

0 

0 

6 

51 

Figure 7. Windshear events by weather system (7 959 to 7 983). 

Page 2 
11/25/88 AC 00-54 

Appendix 1 

o The Thunderstorm 

There are two basic types of thunderstorms: airmass and frontal. Airmass 

thunderstorms appear to be randomly 

distributed in‘unstable air and develop from localized heating at the 

earth's surface (Figure 2). The heated air rises and cools to form cumulus 

clouds. As the cumulus stage continues to develop, precipitation forms in 

higher portions of the cloud and 

falls. Precipitation signals the 

beginning of the mature stage and 

presence of a downdraft. After approximately an hour, the heated updraft creating the thunderstorm is cut 

off by rainfall. Heat is removed and 

the thunderstorm dissipates. Many 

thunderstorms produce an associated 

cold air gust front as a result of the 

downflow and outrush of rain-cooled 

air. These gust fronts are usually 

very turbulent and can create a serious threat to airplanes during takeoff 

and approach. 

Cumulus Stage Mature Stage Dissipating Stage 

Localized 

Surface Heating t 

Surface 

= Airflow/Circulation Cooling 

Figure 2. Airmass thunderstorm life cycle. 

Page 3 
AC 00-54 

Appendix 1 

11/25/88 

Frontal thunderstorms are usually associated with weather systems like 

fronts, converging winds, and troughs 

aloft. Frontal thunderstorms form in 

squall lines, last several hours, 

generate heavy rain and possibly hail, 

and produce strong gusty winds and 

possibly tornadoes. The principal 

distinction in formation of these more 

severe thunderstorms is the presence 

ofrge horizontal wind changes 

(speed and direction) at different 

altitudes in the thunderstorm. This 

causes the severe thunderstorm to be 

vertically tilted (Figure 3). Precipitation falls away from the heated updraft permitting a much longer storm 

development period. Resulting airflows within the storm accelerate to 

much higher vertical velocities which 

ultimately result in higher horizontal 

wind velocities at the surface. 

Airfic 

Circr 

Surface Heating LHeavy Rain and Hail 

Figure 3. Severe frontal thunderstorm anatomy. 

Page 4 
U/25/88 

The downward moving column of air, or 

downdraft, of a typical thunderstorm 

is fairly large, about 1 to 5 miles in 

diameter. Resultant outflows may produce large changes in wind speed. 

Though wind changes near the surface 

occur across an area sufficiently 

large to lessen the effect, thunderstorms always present a potential hazard to airplanes. Regardless of 

whether a thunderstorm contains windshear however, the possibility of 

heavy rain, hail, extreme turbulence, 

AC 00-54 

Appendix 1 

and tornadoes *make it critical that 

pilots avoid thunderstorms. Figure 4 

shows average annual worldwide thunderstorm days. 

Certain areas can readily be seen to 

have a high potential for windshear 

because of the high level of convective activity. Due to the lower frequency of air traffic in the highest 

threat areas (the tropics), fewer accidents have been reported in these 

regions. 

Figure Average annual worldwide thunderstorm 

threat occurs in the tropics. 

days. Note that the highest windshear 

Page 5 
AC 00-54 

Appendix 1 1x/25/88 

Examination of the worldwide windshearassociated accidents and incidents in 

Figure 5 shows that the majority of 

these have occurred in the United 

States. The greater number of accidents results from the combination of 

high convective activity and high air 

traffic density. Many more windshearassociated accidents and incidents 

have probably occurred worldwide but 

have not been recorded as such. 

I 

q3y y 

D\enverA st. LOUIS 6 

b Ckcago 

Tucson b Dallas . Chkanooga 

dago Pago 

Figure 5. 

A Microburst-related accident/incident 

Worldwide microburst-related airpiane accidents/incidents. High frequency of air 

traffic in North America combined with a high number of thunderstorm days leads 

to concentration of windshear-related accidentslincidents in United States. 

Page 6 
11125188 AC 00-54 

Appendix 1 

In fact, closer examination of the 

United States (Figure 6) shows a correlation between areas of high thunderstorm activity and a number of 

accidents. 

A Micr Doburst-related accidenthnciden 

80w 

Figure 6. Average annual continental U.S. thunderstorm days. Correlation exists between 

regions of higher thunderstorm activity and win&hear-related accidents incidents. 

Page 7 
AC 00-54 

Appendix 1 

11125188 

o The Microburst as a Windshear Threat 

Identification of concentrated, more 

powerful downdrafts--known as microbursts--has resulted from the investigation of windshear accidents and 

from meteorological research. Microbursts can occur anywhere convective 

weather conditions (thunderstorms, 

rain showers, virga) occur. Observations suggest that approximately five 

percent of all thunderstorms produce a 

microburst. 

Downdrafts associated with microbursts 

are typically only a few hundred to 

3,000 feet across. When the downdraft 

reaches the ground, it spreads out 

horizontally and may form one or more 

horizontal vortex rings around the 

downdraft (Figure 7). The outflow 

region is typically 6,000 to 12,000 

feet across. The horizontal vortices 

may extend to over 2,000 feet AGL. 

Cloud Base 

0 

Downdraft 

1 Scale 

1OOOft 

I I Xl\\ I 

Figure 7. Symmetric microburst An airplane transiting the microburst would 

experience equal headwinds and tailwinds. 

Page 8 
11/25/88 AC 00-54 

Appendix 1 

Microburst outflows are not always 

symmetric (Figure 8). Therefore, a 

significant airspeed increase may not 

occur upon entering the outflow, or 

may be much less than the subsequent 

airspeed loss experienced when exiting 

the microburst. 

Cloud Base \ 

toooft 

Approx 

LScale 

0 lOOOft 

Wind 

-Downdraft 

Horizontal 

VortexOutflow Front1 -outflowFigure 8. Asymmetric microburst. An airplane transiting the microburst from left to 

right would experience a small headwind followed by a large failwiqd. 

Page 9 
AC 00-54 

Appendix 1 

U/25/88 

More than one microburst can occur in 

the same weather system. Pilots are 

near the ground due to several microtherefore cautioned to be alert for 

bursts being embedded in one another 

(Figure 9). Conditions associated 

additional microbursts if one has already been encountered or observed. with these vortices may produce very 

If several microbursts are present, a 

powerful updrafts and roll forces in 

addition to downdrafts. 

series of horizontal vortices can form 

\ 

Microburst Series of Horizontal 

Vortices 0 

500 ft 

Figure 9. Horizontal Vortices. A series of horizontal vortices can form near the ground 

due to microbursts imbedded in one another. 

Page 10 
U/25/88 AC 00-54 

Appendix 1 

Wind speeds intensify for about 5 min- sidered significant, but an airplane 

utes after a microburst initially con- following may experience an airspeed 

tacts the ground (Figure 70). An en- change two to three times greater! 

counter during the initial stage of Microbursts typically dissipate within 

microburst development may not be con- 10 to 20 minutes after ground contact. 

Initial Ground 

Downdraft Contact 

Maximum 

Shear 

Intensity 

Dissipation 

Begins Cloud base 

I I 

5 10 

Elapsed Time (min) 

Figure 70. Evolution of a microburst. Microburst winds intensify for about 5 min 

after ground contact and typical/y dissipate about 10 to 20 min after 

ground contact. 

Page 11 
11/25/88 

AC 00-54 

Appendix 1 

Doppler radar wind measurements indicate that the wind speed change a piindicated headwind/tailwind differential velocities near 200 knots. 

lot might expect when flying through 

the average microburst at its point of 

peak intensity is about 45 knots (Figure 11). However, microburst windspeed differences of almost 100 knots 

IT IS VITAL TO RECOGNIZE THAT SOME 

MICROBURSTS CANNOT BE SUCCESSFULLY 

ESCAPED WITH ANY KNOWN TECHNIQUES! 

Note that even windshears which were 

have been measured. In fact, a severe 

event at Andrews Air Force Base (Camp 

Spring, Maryland) on August 1, 1983 

within the performance capability of 

the airplane have caused accidents. 

Number of 

Measured 

Microbursts 

(500 ft JAWS 

Doppler 

Radar Data) 

0 10 20 30 40 50 

A & Ir A JFK MSV DEN OR0 

l Maximum windshear capability of 

jet transports at heavy weight, 

for a shear encounter at a critical 

location, is 40 to 50 knots 

windspeed change 

60 70 80 90 100 

A 

DEN 

A A ep Accident/ 

DFW DEN Incident 

Windspeed -- Maximum Horizontal Windspeed Change (kt) changes 

Figure 7 7. Microburst frequency versus intensity. Accidents have occurred in windsheats 

within performance capability of airplane. Some windshears cannot be escaped 

successfully! 

Page 12 
11/25/88 AC 00-54 

Appendix 1 

Microbursts can be associated with 

both heavy rain, as in thunderstorm 

conditions, and much lighter precipitation associated with convective 

clouds. Microbursts have occurred in 

relatively dry conditions of light 

rain or virga (precipitation that 

evaporates before reaching the earth's 

surface). The formation of a dry microburst is illustrated in Figure 12. 

In this example, air below a cloud 

base (up to approximately 15,000 feet 

AGL) is very dry. Precipitation from 

higher convective clouds falls into 

low humidity air and evaporates. This 

evaporative cooling causes the air to 

plunge downward. As the evaporative 

cooling process continues, the downdraft accelerates. Pilots are therefore cautioned not to fly beneath convective clouds producing virga conditions. 

. 

Cloud Base A 

lOooft 

Approx 

LScale 

0 lOOOft 

Figure 72. Dry microburst formation. Evaporation of rain below cloud base (virga) 

causes intense cooling of rainshaft air and subsequent cold air plunge. 

Page 13 
AC 00-54 

Appendix 1 

11/25/88 

2.3 LESSONS LEARNED FROM WINDSHEAR 

ENCOUNTERS 

Analysis of past windshear accidents 

and incidents has taught valuable lessons regarding windshear recognition 

and flight path control. Engineering 

studies and flight simulator evaluations have been conducted as well to 

gather additional information. The 

resulting lessons learned form a basis 

for the recommended precautions and 

techniques in this document. 

The primary lesson learned is that the 

best defense against windshear is to 

avoid it altogether. This is especially important because shears will 

exist which are beyond the capability 

of any pilot or airplane. In most 

windshear accidents, several. cluesLLWAS alerts, weather reports, visual 

signs--were present that would have 

alerted the flight crew to the presence of a windshear threat. In all 

instances, however, these clues were 

either not recognized or not acted 

upon. Flight crews must seek and heed 

signs alerting them to the need for 

avoidance. 

Other lessons were also learned regarding windshear recognition and 

pilot technique should the avoidance 

process fail. These lessons are summarized as follows: 

Windshear Recoqnition 

o Recognition of windshear encounter 

is difficult and is usually complicated by marginal weather 

o Time available for recognition and 

recovery is short (as little as 5 

seconds) 

o Flight crew coordination is essential for prompt windshear recognition and recovery 

Pilot Techniaue 

o Flight path must be controlled 

with pitch attitude (unusual stick 

forces may be required as a result) 

o Lower than normal airspeed may 

have to be accepted to counter 

lift loss 

In reaching these conclusions, three 

types of windshear encounters which 

have resulted in an accident or incident were examined: an encounter during takeoff after liftoff, an encounter during takeoff on the runway, and 

an encounter during approach. Details 

of these encounters and the lessons 

1 earned are described in Sections 

2.3.1 through 2.3.3. Following this, 

Section 2.3.4 presents the lessons 

learned regarding effects of windshear 

on airplanes and airplane systems. 

Section 2.3.5 describes the impact of 

these lessons on simulator training. 

Page 14 
11125188 AC 00-54 

Appendix 1 

2.3.1 ENCOUNTER DURING TAKEOFF - AFTER off the runway (Figure 13). For the 

LIFTOFF first 5 seconds after liftoff the 

takeoff appeared normal, but the airIn a typical accident studied, the plane crashed off the end of the runairplane encountered an increasing way about 20 seconds after liftoff. 

tailwind shear shortly after lifting 

3 

~ 

2 

1 4 

Runway 

Figure 13. Windshear encounter during takeoff after liftoff. (1) Takeoff initially appeared 

normal. (2) Windshear encountered just after liftoff. (3) Airspeed decrease resulted 

in pitch attitude reduction. (4) Aircraft crashed off departure end of runway 

20 set after liftoff. 

Page 15 
AC 00-54 

Appendix 1 

II/25188 

In many events involving after-liftoff 

windshear encounters, early trends in 

airspeed, pitch attitude, vertical 

speed and altitude appeared normal. 

In this example, the airplane encountered windshear before stabilized 

climb was established which caused 

difficulty in detecting onset of 

shear. As the airspeed decreased, 

pitch attitude was reduced to regain 

trim airspeed (Figure 14). By reducing pitch attitude, available performance capability was not utilized and 

the airplane lost altitude. As terrequired on some airplanes). Corrective action, however, was too late to 

prevent ground contact since the downward flight path was well established. 

Reducing pitch attitude to regain lost 

airspeed, or allowing attitude to decrease in response to lost airspeed, 

is the result of past training emphasis on airspeed control. Successful 

recovery from an inadvertent windshear 

encounter requires maintaining or increasing pitch attitude and accepting 

lower than usual airspeed. Unusual 

and unexpected stick 

quired to counter 

pitching tendencies 

and lift loss. 

forces may be renatural airplane 

due to airspeed 

rain bec'ame a factor, recovery to initial pitch attitude was initiated. 

This required unusually high stick 

force (up to 30 pounds of pull may be 

Microburst w 

Normal Climb 

,ing 

Figure 74. Windshear effects on flight path. Microburst reduces airspeed and lift at 

normal attitude which results in pitch down tendency to regain airspeed. 

Page 16 
11/25/88 AC 00-54 

Appendix 1 

To counter the loss of airspeed and flight path degradation be prevented 

lift resulting from windshear, pitch (Figure 15). Once the airplane begins 

attitude must not be allowed to fall to deviate from the intended flight 

below the normal range. Only by prop- path and high descent rates develop, 

erly controlling pitch attitude and it takes additional time and altitude 

accepting reduced airspeed can to change flight path direction. 

Pitch Down 

Lack of Proper Pitch Control 

Microburst w 

Controlled Pitch Attitude 

Figure 75. Pitch control effects on flight path. Control of pitch attitude and 

acceptance of reduced airspeed results in improved flight path. 

Page 17 
AC 00-54 

Appendix 1 

U/25/88 

In the windshear encounter cited earlier, available airplane performance 

capability may not have been used because of two factors: lack of timely 

recognition and inappropriate or inadequate response. Rapidly deteriorating climb performance may not be 

apparent to the crew unless all appropriate vertical flight path instruments are closely monitored. 

300 

200 

Altitude 

(fi) 

Only 5 to 15 seconds may be available 

to recognize and respond to a windshear encounter (Figure 16). It is 

therefore of great importance that a 

windshear encounter be recognized as 

soon as possible. Timely recognition 

of windshear requires effective crew 

coordination and appropriate callouts 

by the pilot not flying. 

Normal )(( 

0 

0 5 10 15 20 25 

Time From Liftoff (set) 

Figure 76. lime available to respond to windshear encounter. Takeoff initia//y appeared normal. 

Additional time is required to arrest descent. Result: only 5 to 15 set may be 

available for recognition and recovery. 

Page 18 
11/25/88 AC 00-54 

Appendix 1 

2.3.2 ENCOUNTER DURING TAKEOFF - ON 

RUNWAY 

Analysis of a typical accident where 

an increasing tailwind shear was encountered during takeoff ground roll 

showed that initial indications appeared normal (Figure 17). Due to the 

increasing tailwind shear however, the 

airplane did not reach VR until 

nearing the end of the runway. As the 

airplane lifted off, the tailwind continued increasing, preventing any further airspeed increase. The airplane 

contacted an obstacle off the departure end of the runway. 

Runway 

Figure 17. Windshear encounter during takeoff on runway. (7) Takeoff initially appeared 

normal. (2) Airspeed buildup slowed due to windshear. (3) Airplane reached 

VR near end of runway, lifted off but failed to climb. (4) Airplane contacted 

obstacle off departure end of runway. 

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AC 00-54 

Appendix 1 

11/25/88 

Less-than-normal airspeed, due to takeoff attitude 

windshear encounter, resulted in re- 

(Figure 18). In 

turn, inability to lift off soon 

duced available lift at normal enough to clear obstacles resulted. 

Lift 

t 

f 

Runway 

Normal Takeoff 

Runway 

Windshear Encounter 

Figure 78. Win&hear effects on liftoff. Microburst reduces airspeed and iii? at 

normal attitude that results in inability to lift off. 

Page 20 
U/25/88 AC 00-54 

Appendix 1 

An additional factor is the difficulty 

of recognizing deteriorating airplane 

performance. Timely recognition of a 

windshear encounter on the runway may 

be difficult since the only indication 

may be a slower than normal airspeed 

increase. The presence of gusts may 

mask abnormal airspeed build-up. Time 

available to respond effectively to a 

windshear may be as little as 5 

seconds from the initial encounter. 

Effective crew coordination, particularly standard callouts, is essential 

in routine operations to develop habit 

patterns required to ensure timely 

recognition of degrading performance. 

Full thrust may be required to provide 

additional performance, particularly 

if reduced thrust takeoff procedures 

have been used. 

If there is insufficient runway left 

to accelerate to normal takeoff speed, 

and inadequate runway to stop, liftoff 

and safe climb may require rotation at 

speeds less than normal rotation speed 

(VR). In this case, additional pitch 

attitude may be required to achieve 

sufficient lift (Figure 19). In traditional training, crews are frequently cautioned not to rotate at speeds 

less than VR to avoid high pitch attitudes that could result in aft body 

contact. In a windshear encounter, 

rotation toward normal takeoff pitch 

attitude at lower than normal airspeed 

may be required to lift off in the remaining runway. This may result in 

aft body contact. To deal with an inadvertent windshear encounter, the 

pilot must be prepared to apply techniques which differ from those ordinarily used. 

Microburst N 

Runway 

Normal Takeoff Attitude 

Runway 

increased Pitch Attitude 

Figure 19. Pitch attitude effects on liftoff. Increased pitch attitude generates 

lift required for liftoff. 

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U/25/88 

2.3.3 ENCOUNTER ON APPROACH 

Analysis of a typical windshear encounter on approach provided evidence 

of an increasing downdraft and tailwind 

along the approach flight path (Figure 

20). The airplane lost airspeed, 

dropped below the target glidepath, 

and contacted the ground short of the 

runway threshold. 

Figure 20. Windshear encounter during approach. (1) Approach initially appeared normal. 

(2) Increasing downdraft and tailwind encountered at transition. (3) Airspeed 

decrease combified with reduced visual cues resulted in pitch attitude 

reduction. (4) Airplane crashed short of approach end of runway. 

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11/25/88 AC 00-54 

Appendix 1 

Reduced airspeed, as the airplane encountered the windshear, resulted in 

decreased lift. This loss of lift increased the descent rate (Figure 21). 

The natural nose-down pitch response 

of the airplane to low airspeed caused 

additional altitude loss. Pitch attitude increase and recovery initiation 

were not used soon enough to prevent 

ground contact. 

Lack of timely and appropriate 

response--affected by weather conditions, inadequate crew coordination 

and limited recognition time--was a 

significant factor in delaying recovery initiation. Gradual application of thrust during approach may 

have masked the initial decreasing 

airspeed trend. Poor weather conditions caused increased workload and 

complicated the approach. Transition 

from instruments to exterior visual 

references may have detracted from instrument scan. Inadequate crew coordination may have resulted in failure 

to be aware of flight path degradation. A stabilized approach with 

clearly defined callouts is essential 

to aid in recognition of unacceptable 

flight path trends and the need to 

initiate recovery. 

\ Runway Normal Approach 

Glide Path 

Figure 27. 

Descending 

Glide Path 

Below 

. 

\ Runway 

Windshear Encounter 

.Windshear effects on flight path on 1 approach. Microburst reduces airspeed and 

lift at normal attitude which results in pitch down tendency to regain airspeed. 

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11/25/88 

2.3.4 WINDSHEAR EFFECTS ON AIRPLANES 

AND SYSTEMS 

Windshear Effects on Airblanes 

0 Headwi nd/Tailwind Shear Response 

The various components of windshear 

have unique effects on airplane performance. In addition, the magnitude 

of the shear depends on the flight 

path through the microburst. 

An increasing headwind (or decreasing 

tailwind) shear increases indicated 

airspeed and thus increases performance. The airplane will tend to pitch 

up to regain trim airspeed. An additional consideration is that this type 

of shear may reduce normal deceleration during flare which could cause 

overrun. 

Any rapid or large airspeed increase, 

particularly near convective weather 

conditions, should be viewed as a possible indication of a forthcoming airspeed decrease. Thus a large airspeed 

increase may be reason for discontinuing the approach. However, since microbursts are often asymmetric and the 

headwind may not always be present, 

headwind shears must not be relied 

upon to provide early indications of 

subsequent tailwind shears. 

pared! 

Be preIn contrast to shears which increase 

airspeed, an increasing tailwind (or 

decreasing headwind) shear will decrease indicated airspeed and performance capability. Due to airspeed 

loss, the airplane may tend to pitch 

down to regain trim speed. 

0 Vertical Windshear Response 

Vertical winds exist in every microburst and increase in intensity with 

altitude. Such winds usually reach 

peak intensity at heights greater than 

500 feet above the ground. Downdrafts 

with speeds greater than 3,000 feet 

per minute can exist in the center of 

a strong microburst. The severity of 

the downdraft the airplane encounters 

depends on both the altitude and lateral proximity to the center of the 

microburst. 

Perhaps more critical than sustained 

downdrafts, short duration reversals 

in vertical winds can exist due to the 

horizontal vortices associated with 

microbursts. This is shown in Figure 22. 

\ 

Microburst 

Series of Horizontal 

Vortices 

500 ft 

ft 

Figure 22. Encounter with microburst horizontal vortices. Rapid updraft downdraft variations 

due to horizontal vortices can cause uncommanded pitch changes and may 

result in momentary stick shaker activation well above normal stick shaker speeds. 

Page 24 
11/25/88 AC 00-54 

Appendix 1 

An airplane flying through horizontal 

vortices as shown on the previous page 

experiences alternating updrafts and 

downdrafts causing pitch changes without pilot input. These vertical winds 

result in airplane angle-of-attack 

fluctuations which, if severe enough, 

may result in momentary stick shaker 

actuation or airframe shudder at 

speeds well above normal, 

Vertical winds, like those associated 

with horizontal vortices, were considered in development of the recovery 

procedure. The most significant impact of rapidly changing vertical 

winds is to increase pilot workload 

during the recovery. The higher workload results from attention to momentary stick shaker actuation and uncommanded pitch attitude changes from 

rapid changes in vertical wind. 

0 Crosswind Shear Response 

A crosswind shear tends to cause the 

airplane to roll and/or yaw. Large 

crosswind shears may require large or 

rapid control wheel inputs. These 

shears may result in significantly increased workload and distraction. In 

addition, if an aircraft encounters a 

horizontal vortex, severe roll forces 

may require up to full control wheel 

inpu t to coun teract the roll and maintain airc raft control. 

0 Turbulence Effects 

Turbulence may be quite intense in 

weather conditions associated with 

windshear. Effects of turbulence can 

mask changing airspeed trends and 

delay recognition of severe windshear. Turbulence may also tend to 

discourage use of available airplane 

pitch attitude during a recovery by 

causing random stick shaker activity. 

These effects can significantly increase pilot workload and distraction. 

0 Rain Effects 

Accident *investigations and the study 

of windshear have shown that some 

forms of windshear are accompanied by 

high rates of rainfall. NASA research 

is underway to determine if high rainfall rates contribute to a loss of 

airplane performance. The results 

available to date are inconclusive. 

However, because rain may serve as a 

warning of severe windshear, areas of 

heavy rain should be avoided. High 

rates of rainfall also cause significant increases in cockpit noise 

levels, making crew coordination and 

pilot concentration more difficult. 

Page 25 
AC 00-54 11/25/88 

Appendix 1 

0 Basic Aerodynamics 

The pilot has direct control over airplane pitch attitude which in turn 

acts to change the flight path. The 

angle-of-attack will change with pitch 

attitude resulting in a modified 

flight path angle. These three angles 

are related as follows: 

Pitch = Angle of + Flight 

Attitude Attack Path Angle 

0 Airplane Performance 

Transport category airplanes have considerable climb capability at speeds 

below normal reference values. As 

seen in Figure 23 for typical takeoff 

climb performance, a rate-of-climb of 

1500 FPM is possible even at stick 

shaker speeds. 

0 Airplane Stability 

As mentioned earlier, typical longiRate-of2500 

Climb 

(ft/min) 1500 

tudinal stability characteristics tend 

to pitch the airplane up with increasing airspeed and down with decreasing 

airspeed. Thrust changes in response 

to these airspeed variations may also 

affect stability. In airplanes with 

underwing-mounted engines, there is an 

additional tendency to pitch up as 

thrust increases, and pitch down as 

thrust decreases. This tendency may 

become more pronounced at low speeds. 

0 Stall and Stall Warning 

Airplane stall occurs when further increases in angle-of-attack produce no 

further increase in lift. In order to 

prevent inadvertent entry into this 

flight region, stall warning devices 

(stick shakers, stick pushers, stall 

warning horns) are installed on airplanes. In addition, having clean, 

smooth wing leading edges will help 

prevent both early onset of stall buffet as well as rolloff tendency prior 

to stall. 

Shaker I 

I 

I 

I 

130 150 

Airspeed (kt) 

Figure 23. Typical takeoff Me-of-climb capability. Significant climb capability exists 

even at stick shaker airspeeds. 

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11/25/88 AC 00-54 

Appendix 1 

Windshear Effects OK Systems 

0 Altimeters 

During cal louts and instrument scan in 

a windshear, use of radio and/or barometric altimeters must be tempered by 

the characteristics of each. Since 

radio altitude is subject to terrain 

contours, the indicator may show a 

climb or descent due to falling or 

rising terrain, respectively. The 

barometric altimeter may also provide 

distorted indications due to pressure 

variations within the microburst. 

0 Vertical Speed Indicators 

The vertical speed indicator (VSI) 

should not be solely relied upon to 

Vertical 

Speed 

(ft/min) 

provide accurate vertical speed information. Due to instrument lags, 

indications may be several seconds 

behind actual airplane rate of climb/ 

descent and, in some situations, may 

indicate a climb after the airplane 

has started descending (Figure 24). 

Vertical speed indicators driven by an 

Inertial Reference Unit (IRU) show 

significant improvement over other 

type instruments but still have some 

lag. 

In addition, gust-induced pitot static 

pressure variations within the microburst may introduce further VSI inaccuracies. Due to such lags and 

errors, all vertical flight path 

instruments should be crosschecked to 

verify climb/descent trends. 

- Actual Vertical Speed 

. . . . Inertial- 

-400 

t 

Airplane Is’ 

Descending 

-800 - 

Instruments 

Lag .and 

Erroneously 

Indicate Climb 

8 12 16 20 24 28 32 36 40 44 48 

Time (set) 

Figure 24. VSI error during takeoff windshear encounter. VSi may lag actual flight path changes. 

Page 27 
AC 00-54 

Appendix 1 

11/25/88 

0 Stick Shaker 

Stick shaker is activated by angle of 

attack. Consequently, rapidly changing vertical winds or maneuvering will 

vary the attitude and airspeed at 

which stick shaker occurs. With a 

properly functioning stall warning 

system and undamaged alpha vanes, 

stick shaker will normally activate 

below the stall angle of attack, thus 

providing a warning prior to stall. 

0 Cockpit Angle of Attack Indicators 

Angle of attack indicators do provide 

useful indications of margin to stick 

shaker; however, they may not provide 

effective guidance in a windshear environment since angle of attack is 

controlled indirectly through pitch 

attitude adjustments. In an actual 

windshear encounter where rapidly 

changing vertical winds cause rapid 

angle of attack fluctuations independent of pilot input, the lack of direct 

control over angle of attack limits 

its usefulness as a guiding parameter. 

2.3.5 DEVELOPMENT OF WIND MODELS 

The lessons learned from windshear accident investigations, engineering 

analyses, and flight simulator studies 

have provided insight for development 

of simulator windshear models for pilot training. Through these efforts, 

it was determined that the essential 

elements which must be taught include: 

1) Recognition of windshear encounter, 

2) Flight at speeds significantly 

less than those speeds typically 

exposed to in training, and 

3) Use of pitch attitude rather than 

airspeed control to recover. 

A simple model presenting a significant windshear threat requiring use of 

prompt corrective attitude control is 

sufficient to teach these elements. 

Once the basics of recognition and recovery are understood, more complex 

models may be useful. 

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Appendix 1 

2.4 MODEL OF FLIGHT CREW ACTIONS 

Due to the serious threat imposed by 

infrequent windshear encounters, an 

orderly set of actions is necessary to 

increase flight crew awareness of 

weather conditions that produce windshear (Figure 25). Additionally, certain operating practices have been developed that improve the chances of 

surviving a windshear encounter. In ' 

past windshear accidents, certain of 

these actions were frequently missing, 

thereby reducing crew effectiveness in 

dealing with the situation. The model 

of flight crew actions must be incorporated into day-to-day operations to 

ensure such actions are available and 

easily recalled when needed. 

The recommended procedures in this 

section have been developed for 

Boeing, Douglas, and Lockheed jet 

transport airplanes.' Use of these 

procedures for other types of airplanes is not appropriate until verified with the respective airframe 

manufacturer. 

1 Evaluate the Weather JJ 

I 

No 

Avoid Known Windshear 

Follow Standard . 

- Operating Techniques m 

i 

[ Windshear Recovery Technique 1 

r ---m --me 1 

L Report the Encounter J w--m---mm 

Figure 25. Model of flight crew actions. 

Page 29 
AC 00-54 

Appendix 1 

11125188 

2.4.1 EVALUATE THE WEATHER 

The weather evaluation process that 

follows was developed after careful 

analyses of several windshear-related 

accidents. In each accident that 

occurred, several potential windshear 

indicators were present, but a clear, 

definitive choice to divert or delay 

was not made. The windshear indicators are meant to be cumulative. The 

more indicators present, the more 

crews should consider delaying departure or approach. Only through an increased awareness of potential windshear indicators and a proper weather rl 

evaluation routine will flight crews 

be best prepared to avoid microburst 

windshear. 

Every windshear accident has occurred 

on a typical day, to a typical crew, 

on a typical takeoff or approach. Too 

many times a number of clues were 

present, acknowledged by the crew, but 

not accepted as potential indicators 

of windshear. The weather evaluation 

process must continue during the takeoff and climbout and throughout the 

approach and landing. If some of the 

indicators are present, this continual 

searching may lead to early recognition of the potential for a windshear 

encounter. 

If convective cloud conditions are 

present and/or if thunderstorms appear 

likely, the potential for windshear 

and microburst activity exists. Even 

if there are only subtle signs of convective weather, such as weak cumulus 

cloud forms, suspect the possibility 

of microbursts, particularly if the 

air is hot and dry. 

The following weather information 

should be examined for any potential 

windshear conditions affecting the 

flight: . 

1) Terminal Forecasts 

An examination of terminal forecasts is recommended. Study o. 

the following two terminal forecasts demonstrates what to look 

for: 

YNG FT AMD 1 101815 18202 C45 5KN 

80 OVC 2018635 LLWS OCNL C20 OVC 

3RW-/TRW-Z= OVC 3214625 

- OVC 2RW-/TRW-. 09Z IFR 

CIG RW TRW WND. 

HUF FT AMD 2 COR 101815 17452 C30 

BKN 2020635 OCNL Cl2 OVC 3TRW CHC 

C4 X 1/2T+RW+AG55. - 222 m OVC 

QTRW- 2420630SLGT CHC C4 

XmTRW+G50. OlZ Cl6 OVC 2918628 

CHC 4RW-, 042 Cl8 BKN 3016 BKN 

OCNL SCT. 09Z VFR.. 

Note that for Youngstown, Ohio the 

forecast is calling for LLWS-low 

level (altitude) windshear. While 

thunderstorms exist in the forecast, pilots are given an additional "LLWS" clue.' 

In the terminal forecast for Terre 

Haute, Indiana, LLWS does not 

appear. However, the chance of 

severe thunderstorm, heavy rain 

showers, hail, and wind gusts to 

55 knots, suggest the potential 

for microbursts if actual thunderstorm conditions are encountered. 

Dry microbursts are somewhat more 

difficult to recognize. When flying in regions of low humidity 

near the surfaces any convective 

cloud is a likely microburst producer. Examination of the terminal forecast for convective activity-rain, thunderstorms, etc.--is 

good practice. 

Page 30 
U/25/88 

2) Hourly Sequence Reports 

Hourly sequence reports should be 

inspected for windshear cluesthunderstorms, rainshowers, or 

blowing dust. The temperature and 

dew point spread should be examined for large differences, i.e. 30 

to 50 degrees Fahrenheit, indicating low humidity. Additional 

signs such as warming trends, 

gusty winds, cumulonimbus clouds, 

etc., should be noted. 

In the example shown below, evidence of blowing dust, large temperature/dewpoint spread, gusting 

winds, and thunderstorms (without 

rain) is present. These signs 

3) 

provide a strong indication that 

windshear may be present. 

MS0 SA 2152 SOBKN 800VC 12TBD 

007/83/45/1715G30/974 VSBY W3 m/2 

Severe Weather Watch Reports 

A check for issuance of an aviation severe weather watch should 

be made. In the following example, a line of thunderstorms approaching severe limits are forecast. Severe convective weather 

is a prime source for microbursts. 

TSTMS FCST TO APCH SVR LIMITS THIS 

mN AND tRY EVE TO THE RT OF A LN 

FM YUM IPL RIV BUR 15 W SDB BFL 

IYK EED YUM. 

AC 00-54 

Appendix 1 

Page 31 
AC 00-54. 

Appendix 1 

11/25/88 

4) LLWAS Reports 

LLWAS (Low Level Windshear Alert 

System) - Presently installed at 

110 airports in the U.S., this 

system is designed to detect wind 

shifts between outlying stations 

and a reference centerfield station (Figure 26). If an LLWAS 

alert (triggered by wind speed 

and/or direction differential) 

occurs, it indicates the presence 

of something shear-like, though 

not necessarily indicative of magnitude or location. However, the 

absence of an alert does not 

necessarily indicate that it is 

safe to proceed! 

LLWAS information is available by 

request anytime, but will be proE) LLWAS coverage only exists near 

vided by controllers whenever an 

the runways and typically does 

LLWAS alert is in progress. 

not extend beyond the middle 

marker: 

LLWAS in its present form has some 

limitations: 

A) shear magnitude may be seriously underestimated, 

B) trees, buildings and other surface obstructions may disrupt 

or limit the flow of air near 

the sensors, 

C) location and spacing of sensors 

may allow microburst development to go entirely undetected--particularly in the 

early stages (Figure 26), 

0) because the sensors are on the 

ground, microburst development 

which has not yet reached the 

surface will not be detected, 

and 

WINDSHEAR ALERTS. 2 QUADRANTS. 

CENTERFIELD WIND 210 AT 14. WEST 

BOUNDARY WIND 140 AT 22. NORTHEAST BOUNDARY WIND 270 AT 24. 

Even with these limitations, LLWAS 

can provide useful information 

about winds around the airport. 

0 LLWAS Stations 

- Runways 

Figure 26. Undetected microburst due to tide LLWAS station spacing. 

Page 32 
11125188 AC 00-54 

Appendix 1 

5) SIGMETS 

SIGMETS, particularly CONVECTIVE 

SIGMETS, may provide essential 

clues. In the example, the CONVECTIVE SIGMET warns of scattered 

embedded thunderstorms, some 

reaching level 5 intensity, indicating a potential for windshear. 

ATTENTION ALL AIRCRAFT, CONVECTIVE 

SIGMET CHARLIE ONE FROM mE VICIN 

mF ELMIRA TO PHILLIPSBURG: 

SCATTERED EMBEDDED THUNDERSTORMS 

:ZATONE KNm A 

FEW INTENSE LEVEL FIVE CELLS, 'MAXIMUM- - FIVE 

ZERO. 

6) Visual Clues from the Cockpit 

The value of recognizing microbursts by visual clues from the 

cockpit cannot be overemphaiized. 

Pilots must remember that microbursts occur only in the presence 

of convective weather indicated by 

cumulus-type clouds, thunderstorms, rain showers, and virga. 

(Note that other types of windshear can occur in the 

convective weather. 1 

absence of 

Microburst windshear can often be 

identified by some obvious visual 

clues such as heavy rain (in a dry 

or moist environment). This is 

particularly true if the rain is 

accompanied by curling outflow, a 

ring of blowing dust or localized 

dust in general, flying debris, 

virga, a rain core with rain diverging away horizontally from the 

rain core, or tornadic features 

(funnel clouds, tornados). At 

night, lightning may be the only 

visual clue. Pilots must become 

aware that these visual clues are 

often the on1 

the presence -+ o 

means to identify 

se windshear. 

7) PIREPS 

PIREPS are extremely important indicators in microburst windshear 

situations. Reports of sudden 

airspeed changes in the airport 

approach orlanding corridors provide indication of the presence of 

windshear. 

"Miami Tower, PIREP, Flight 126 

encountered windshear on final, 

loss of 20 knots at 300 feet approaching middle marker runway 27 

right, Douglas MD-80." 

In international weather reports, 

windshear observations or reports 

from pilots may be included at the 

end of routine and special weather 

reports. 

N 

. ..WS WRNG B727 REPORTED MOD WS 

ON APCH RW 34 AT 1610" 

In the above example, a Boeing 727 

on approach to Runway 34 reported 

moderate windshear at 1610 hours. 

Page 33 
AC 00-54 

Appendix 1 

11/25/88 

8) Airborne Weather Radar 

The use of airborne weather radar 

to detect convective cells should 

be considered a matter of routine. Weather radar provides 

extremely useful information for 

the avoidance of thunderstorms in 

the airport terminal area, but. 

cannot directly detect windshear. 

Pilots have become adept at avoiding thunderstorms while enroute 

and at altitude. However, relatively little emphasis has been 

placed on their use near the 

terminal area. Most heavy rain 

thunderstorms near the airport can 

be detected with conventional 

weather radar by a careful use of 

tilt control to scan above the 

intended flight altitude (15,000 

to 20,000 feet). The subject of 

the proper use of tilt control for 

this purpose should be studied in 

available radar manuals and 

bulletins. 

Pilots should understand that 

heavy precipitation, as seen on 

their radar and associated with 

convective clouds, indicates the 

possibility of microbursts; however, 'the absence of strong returns must not be depended upon to 

indicate a safe situation. Potentially hazardous dry microburst 

conditions may only produce weak 

radar returns. 

Another significant aspect of 

weather radar use is attenuation. 

Attenuation is caused by heavy 

rainfall reducing the ability of 

the radar signal to penetrate, 

causing the radar to present an 

incomplete picture of the weather 

area. In the terminal area, comparison of ground returns to 

weather echoes is a useful technique to identify when attenuation 

is occurring. Tilt the antenna 

down and observe ground returns 

around the radar echo. With very 

heavy intervening rain, ground returns behind the echo will not be 

present. This area lacking ground 

returns is referred to as a shadow 

and may indicate a larger area of 

precipitation than is shown on the 

indicator. Areas of shadowing 

should be avoided. 

Turbulence Doppler radars starting 

to become available to flight 

crews provide an additional clue 

to the presence of microbursts. 

If, in the departure/arrival segment of the airport vicinity, turbulence indications are present in 

mid-levels of convective cloud 

systems (e.g., 15,000 to 20,000 

feet) and low humidity conditions 

exist (large temperature/dewpoint 

spread), the situation is prime 

for microburst formation. Pilots 

should be particularly cautious 

when they observe this indication. 

Page 34 
11/25/88 AC 00-54 

Appendix 1 

2.4.2 AVOID KNOWN WINDSHEAR 

The importance of avoiding severe 

windshear and microbursts cannot be 

over-emphasized. Microburst windshears have been measured which are 

beyond the capability of transport 

category airplanes and the most highly 

skilled pilots. Recall from Figure 11 

that even windshears which were within 

the performance capability of the airplane have caused accidents. Avoidance may only involve delaying departure or approach for 10 to 20 minutes 

since this is the typical time required for microburst dissipation. 

Even though significant emphasis on 

simulator training is recommended in 

pilot training curriculums, avoidance 

must be the first line of defense. 

Simulators are valuable for teaching 

windshear recognition and recovery. 

However, pilots are cautioned not to 

develop the impression that real-world 

windshear encounters can be successfully negotiated simply because they 

have received simulator training. In 

an airplane, complicating factors 

(i.e. turbulence, precfpitation noise, 

instrument errors, etc.) may make 

shears much more difficult than in a 

simulator. In addition, simulator motion systems are limited in their capability to reproduce all the dynamics 

of an actual windshear encounter. 

Remember, some windshears cannot be 

escaped using any known techniques. 

Therefore, above all, AVOID, AVOID, 

AVOID! 

Unfortunately, there are no universal 

quantitative windshear avoidance criteria that provide unambiguous 

go/no-go decision guidelines. There 

is no assured detection and warning 

system in operation which can measure 

windshear intensity along a specific 

flight path. However, a summary of 

the weather evaluation factors which 

can be helpful in avoiding windshear 

is shown in Table 1 on the following 

page, 

Page 35 
AC 00-54 

Appendix 1 

11/25/88 

TABLE 1 

MICROBURST WINDSHEAR PROBABILITY GUIDELINES 

OBSERVATION PROBABILITY 

OF WINDSHEAR 

PRESENCE OF CONVECTIVE WEATHER NEAR INTENDED FLIGHT PATH: 

With localized strong winds (Tower reports or 

observed blowing dust, rings of dust, 

tornado-l i ke features, etc. ) l **e*eeee*eeee*ee*eeeeee* HIGH 

With heavy precipitation (Observed or radar 

indications of contour, red or attenuation shadow) . . . HIGH 

With rainshower l eeeeee*e*e**eeeeeeeeeeeeeeeeeeeeeeeee MEDIUM 

With lightning l eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee MEDIUM 

With virga l *eeeeeeeeeeeo*eeeeeeeeeeeeeeeeeeeeeeeeeeee MEDIUM 

With moderate or 

B 

reater turbulence (reported or 

radar indications l eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee MEDIUM 

With temperature/dew point spread between 

30 and 50 degrees fahrenheit l eeeeeeeemeeeeeeeeeeeeeee MEDIUM 

ONBOARD WINDSHEAR DETECTION SYSTEM ALERT (Reported 

or observed) l eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee HIGH 

PIREP OF AIRSPEED LOSS OR GAIN: 

- 15 knots or greater l eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee 

- Less than 15 knots l eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee 

HIGH 

MEDIUM 

LLWAS ALERT/WIND VELOCITY CHANGE 

- 20 knots or greater l eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeem HIGH 

- Less than 20 knots l eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee MEDIUM 

FORECAST OF CONVECTIVE WEATHER l eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee LOW 

NOTE: These guidelines apply to operations in the airport vicinity (within 

3 miles of the point of takeoff or landing along the intended flight 

path and below 1000 feet AGL)e The clues should be considered cumulative. If more than one is observed the probability weighting 

shoul d be increased, The hazard increases with proximity to the 

convective weather, Weather assessment should be made continuously, 

CAUTION: CURRENTLY NO QUANTITATIVE MEANS EXISTS FOR DETERMINING THE PRESENCE 

OR INTENSITY OF MICROBURST WINDSHEAR, PILOTS ARE URGED TO EXERCISE 

CAUTION IN DETERMINING A COURSE OF ACTION, 

Page 36 
11125188 AC 00-54 

Appendix 1 

Table 1, designed specifically for 

convective weather (thunderstorm, 

rainshower, virga), provides a subjective evaluation of various observational clues to aid in making appropriate real time avoidance decisions. 

The observation weighting is categorized according to the following scale: 

HIGH PROBABILITY: 

Critical attention need be given to 

this observation. A decision to avoid 

(e.g. divert or delay) is appropriate. 

MEDIUM PROBABILITY: 

Cons idera 

avoi ding. 

ti on should be given to 

Prec autions are a PProPri ate. 

LOW PROBABILITY: 

Consideration should be given to this 

observation, but a decision to avoid 

is not generally indicated. 

The guidelines in Table 1 apply to 

operations in the airport vicinity 

(within 3 miles of takeoff or landing 

along the intended flight path below 

1000 feet AGL). Although encountering 

weather conditions described in Table 

1 above 1000 feet may be less critical 

in terms of flight path, such encounters may present other significant 

weather related risks. Pilots are 

therefore urged to exercise caution 

when determining a course of action. 

Use of Table 1 should not replace 

sound judgement in making avoidance 

decisions. 

Windshear clues should be considered 

cumulative. The probability for each 

single observation is given. However, 

if more than one windshear clue is 

observed, the total probability rating 

may be increased to reflect the total 

set of observations. 

Example: 

Nearing destination, VIRGA is seen 

descending from high based clouds over 

the airfield (MEDIUM PROBABILITY). 

Commencing approach, a PIREP is received indicating that another flight 

just experienced a 10 knot airspeed 

loss on final approach to the same 

airport (MEDIUM PROBABILITY). Therefore, it would be appropriate to raise 

the total avoidance decision weighting 

to HIGH PROBABILITY (indicating a 

decision to avoid is appropriate). 

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11125188 

2.4.3 CONSIDER PRECAUTIONS 

Avoidance is the best precaution. 

However, there are situations when 

windshear clues do not clearly dictate 

delaying, but can be interpreted to 

mean that conditions are right for 

windshear activity. In these instances, pilots should consider the 

next step of flight crew actions, the 

use of precautions. 

A number of precautionary techniques 

have been developed which crews can 

take to lessen the effect of windshear 

should an unsuspected severe windshear 

be encountered on takeoff or approach. These precautions include 

consideration of thrust setting, runway selection, flap selection, airspeed, use of autopilot, autothrottle 

and flight director. They were developed by detailed analysis and piloted 

simulation of several microburst windshear encounters. In many cases, 

tradeoffs were involved and no "best" 

recommendation for all conditions 

could be developed. 

Use of precautions along with even the 

best recovery piloting skills cannot 

guarantee a successful escape from 

many microburst windshears. It is important to realize that the recommended precautions each have a relatively small effect on the outcome of 

an inadvertent windshear encounter. 

Therefore, use of precautions should 

not replace sound pilot judgment in 

deciding whether or not it is safe to 

proceed. Use of precautions should 

not bias a go/no-go decision in the go 

direction. 

2.4.3.1 TAKEOFF PRECAUTIONS 

0 Thrust Setting 

Maximum rated takeoff thrust should be 

used for takeoff. This shortens the 

takeoff roll and reduces overrun exposure. Full thrust also provides the 

best rate of climb, thus increasing 

altitude available for recovery if required. Lastly, full thrust takeoffs 

may eliminate resetting thrust in a 

recovery, thereby maximizing acceleration capability and reducing crew 

workload. 

0 Runway Selection 

Use the longest suitable runway that 

avoids suspected areas of windshear. 

The choice of a suitable runway involves consideration of exposure to 

obstacles after liftoff and crosswind 

and tailwind limitations. This assures maximum runway available to accelerate to rotation speed and may result in more ground clearance at the 

end of the runway and during the climb 

profile. Should the decision be made 

to reject the takeoff, more runway is 

available on which to stop the airplane. 

0 Takeoff Flap Selection 

The choice of takeoff flap setting is 

dependent on the airplane type. The 

following flap settings should be considered unless limited by obstacle 

clearance and/or climb gradient: 

Airplane Takeoff 

Type Flap Setting 

0727 15 

0737 5 to 15 

6747 20 

0757 20 

0767 20 

DC-9-10 

DC-9-20,.30,-40,050 

MD-80 

DC-10 

10 or 20 

5 or 15 

5 to 15 

5 to 20 

L-1011 10 to 22 

Studies of available takeoff flap settings showed that the greater flap 

setting provided best performance for 

windshear encounters on the runway. 

However, lesser flap settings showed 

Page 38 
11125188 AC 00-54 

Appendix 1 

the best performance for in-air windshear encounters. The takeoff flap 

settings in the table offered somewhat 

better performance over a wide range 

of conditions; however, it must be 

pointed out that the performance difference between flap settings is small. 

0 Increased airspeed 

Increased airspeed at rotation improves the ability of the airplane to 

negotiate a windshear encountered 

after liftoff. Increased airspeed improves the flight path, reduces potential exposure to flight near stick 

shaker speeds, and reduces pilot workload. 

Delaying rotation to a higher airspeed 

may appear to increase the risk of 

overrunning available runway. However, because of the manner in which 

increased rotation speed is calculated, it is simply using the runway 

as if the aircraft was loaded to the 

field length limit weight for that 

runway, If the takeoff is at field 

length limit conditions, the risk of 

overrunning the available runway is 

increased because there ,is no extra 

runway available. The overrun exposure is also increased if the windshear reduces the airspeed below the 

minimum airspeed required for liftoff 

at the maximum available (body contact) attitude. However, initiating 

rotation no later than 2000 feet from 

the end of the usable runway surface 

reduces the probability of overrun and 

maximizes the available energy after 

liftoff. 

If increased VR is to be used, the 

technique for scheduling and using increased rotation airspeed is: 

1) Determine Vl, V 

speeds for s 

and V2 

actua airplane 

gross weight and flap setting. 

Set airspeed bugs to these 

values in the normal manner. 

2) Determine field length limit 

maximum weight and corresponding VR for selected runway. 

3) If field length limit VR is 

greater than actual 

weight VR, 

gross 

use the higher 

VR (up to 20 knots in excess 

of actual gross weight VR) 

for takeoff. Airspeed bugs 

should not be reset to the 

higher speeds. 

4) Rotate to normal initial climb 

attitude at the increased VR 

and maintain this attitude. 

This technique produces a 

higher initial climb speed 

which slowly bleeds off to the 

normal initial climb speed. 

WARNING: If windshear is encountered 

at or beyond the actual 

gross weight (bug) VR, do 

not attempt to accelerate to 

the increased VR, but rotate without hesitation; In 

no case should rotation be 

delayed beyond 2,000 feet 

from the end of the usable 

runway surface. (See Section 2.4.5 Recovery Techniques) 

If increased airspeed was not used 

prior to liftoff, accelerating to 

higher than normal airspeed after 

liftoff is not recommended. Reducing 

pitch attitude at low altitude to 

accelerate might produce a hazard if 

windshear is encountered. 

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11125188 

0 Flight Director 

Do not use speed-referenced flight 

directors unless they are equipped 

with windshear recovery guidance. 

WARNING: A speed-referenced flight 

- director which does not have 

windshear recovery guidance 

may command a pitch attitude 

change to follow target 

airspeeds regardless of 

flight path degradation. 

This guidance may be in 

conflict with the proper 

procedures for windshear 

recovery. Such flight directors must be disregarded 

if a recovery is required 

and, time permitting, 

switched off by the Pilot 

Not Flying (PNF). 

Some flight directors are equipped 

with a selectable pitch attitude 

mode. If normal procedures utilize 

this feature, the selectable pitch 

attitude mode may be effectively used 

in a windshear encounter provided the 

selected attitude is within the acceptable range. However, if an attitude other then the selected attitude 

becomes necessary, the flight director 

should be disregarded, and time permitting, switched off by the PNF. 

Takeoff Precautions 

Nse maximum rated takeoff thrust 

l Use longest suitable runway 

l Consider using recommended flap setting 

l Consider using increased rotation airspeed 

l Do not use speed referenced flight director 

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2.4.3.2 APPROACH PRECAUTIONS considered: 

0 Stabilized Approach 

During some normal operations, stabilized approaches are not achieved 

prior to 500 feet AGL. However, in a 

potential windshear environment, a 

stabilized approach should be established no later than 1,000 feet AGL to 

improve windshear recognition capability. 

Airplane 

Type 

0727 

0737 

0747 

0757 

0767 

0 Thrust Management 

Minimize thrust reductions. Rather 

than immediately compensating for an 

airspeed increase by reducing thrust, 

a brief pause to evaluate speed trends 

is prudent. If a tailwind shear 

occurs and recovery is initiated, the 

additional airspeed and earlier availability. of thrust (due to engines accelerating from a higher RPM) will be 

advantageous. If autothrottles are 

engaged, assure inappropriate thrust 

reductions do not occur. In the absence of a tailwind shear, this procedure may result in a higher than 

normal approach speed which may have 

to be accounted for on landing. 

DC-9 * 

MD-80 28 

DC-JO 35 

L-1011 33 

* Minimum flap setting authorized for 

particular model. 

Studies of windshear encounters using 

all available landing flap settings 

showed that the flap settings recommended above provided the best overall 

recovery performance for a wide range 

of windshears. 

0 Increased Airspeed 

0 Runway'Selection 

Use the most suitable runway that 

avoids the area of suspected windshear 

and is compatible with crosswind and 

tailwind limitations. A longer runway 

provides the greatest margin for increased ground roll due to unanticipated winds and possible resulting 

high ground speed at touchdown. A 

precision (instrument) approach and 

other aids to glide path monitoring 

(VASI, etc.) are also desirable as 

they can enhance windshear recognition 

by providing timely, accurate flight 

path deviation information. 

Increased airspeed on approach improves climb performance capability 

and reduces the potential for flight 

at stick shaker during recovery from 

an inadvertent windshear encounter. 

If available landing field length permits, airspeed may be increased up to 

a maximum of 20 knots. This increased 

speed should be maintained to flare. 

Touchdown must occur within the normal 

touchdown zone-do not allow the airplane to float down the runway. 

0 Landing Flap Selection 

The choice of landing flap setting is 

dependent on airplane type. The 

following flap settings should be 

As many variables are involved, it is 

not practical to provide exact guidance on the effect of 20 knots extra 

speed on actual stopping distance. 

Wind can be a major factor since stopping distance is affected by groundspeed rather than airspeed. If increased airspeed is used and an increasing performance shear is encountered, a go-around may be necessary 

due to insufficient landing field 

Landing 

Flap Setting 

30 

30 

25 or 30 

30 

30 

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length for the higher approach speed. 

Furthermore, if a pilot can be reasonably certain that wind changes (due to 

topography or unique local conditions) 

will not result in decreasing performance, it may be inappropriate to use 

increased approach speed. 

Other factors affecting stopping distance such as availability and effectiveness of thrust reversers, tire and 

brake condition, runway surface conditions, etc., must also be taken into 

consideration. On a dry runway with 

no adverse factors present, landing 

field length may accommodate 20 knots 

extra speed at touchdown In other 

cases greater field length may be 

required. If in doubt, use the 

longest suitable runway which does not 

expose the airplane to greater hazard 

from possible shear. 

WARNING: Increased touchdown speeds 

increase stopping distance. 

An additional 20 knots at 

touchdown can increase stopping distance by as much as 

Approach Precautions 

25 percent and in some cases 

may exceed brake energy 

limits. 

0 Flight Director and/or Autopilot 

and Autothrottles 

During approach it is desirable to 

utilize the flight director, autopilot 

and autothrottles to the maximum extent practical, These systems may relieve pilot workload, allowing the 

crew more time to monitor instruments 

and weather conditions. However, use 

of autoflight systems, and in particular the autothrottle, only provide 

benefits if properly monitored. In 

the absence of proper monitoring, 

these systems mqy mask onset of shear 

through lack of pilot awareness of 

control inputs being made. 

Furthermore, not a71 autoflight systems perform well in gusty or turbulent conditions. The autopilot and/or 

the autothrottle should be disconnected when continued use appears 

counter-productive. 

l Stabilize approach rio later than 1000 ft AGL 

l Minimize thrust reductions 

l Use most suitable runway 

l Consider using recommended flap setting 

l Consider using increased approach speed 

l Use autoflight systems during approach 

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2.4.4 FOLLOW ESTABLISHED STANDARD 

OPERATING TECHNIQUES 

In an effort to aid crews with the 

early recognition of a windshear encounter, a series of recommendations 

were formulated under the general 

heading of Standard Operating Techniques (SOT's). These SOT's fall into 

two general headings of crew awareness 

and crew coordination. 

The need for emphasis on SOT's came 

from recognition that in most takeoff 

windshear accidents, the airplane 

pitch attitude was reduced below the 

attitude that would maintain level 

flight. This was done when the airplane was already descending toward 

the ground and indicates lack of 

flight path awareness on the part of 

the crews involved. This lack of 

awareness was also observed during 

piloted simulator studies of windshear 

encounters. Traditional training programs and routine flying may not have 

reinforced proper flight path control 

and concern for altitude loss. However, flight path control should be 

the primary focus, when dealing with 

windshear. XCHNIQUES sucti AS STRICT 

ADHERENCE TO AIRSPEED MUST BE MODIFIED 

IN FAVOR OF MAINTAINING FLIGHT PATH BY 

CONTROLLING PITCH ATTITUDE. 

The SOT's that follow emphasize flight 

path and pitch attitude for operations 

near the ground. Following SOT's results in better crew performance during day-to-day operations, as well as 

during windshear encounters. In both 

takeoff and approach to landing, crew 

awareness and coordination are vital 

for timely windshear recognition, particularly at night or in marginal 

weather conditions. 

0 Crew Awareness 

It is important for crews to remain 

alert for any change in conditions, 

remembering that windshear can be 

quick to form and to dissipate. The 

shears that proved to be most deadly 

are those which caught crews by surprise. 

Crews should be aware of normal vertical flight path indications so that 

windshear induced deviations are more 

readily recognized. On takeoff, this 

would include attitude, climb rate, 

and airspeed buildup. On approach, 

airspeed, attitude, descent rate and 

throttle position provide valuable information. Awareness of these indications assures that flight path degradation is recognized as soon as possible. 

During takeoff and approach, be alert 

for airspeed fluctuations. Such fluctuations may be the first indication 

of windshear. Control column forces 

significantly different than those expected during a normal takeoff or 

go-around may result if airspeed is 

below target or airspeed buildup is 

low during rotation and liftoff. Vertical flight path displays should be 

used to crosscheck flight director 

commands. 

During takeoff while at relatively low 

altitude (below 1000 feet), the SOT's 

require awareness and use- of normal 

climbout pitch attitude and less emhasis on strict airspeed m. 

k- the all-engine initial climb 

pitch attitude. Rotate at the normal 

rotation rate to this attitude for all 

takeoffs. Minimize pitch attitude reductions in response to low airspeed 

until terrain and obstruction clkarante is assured. 

On approach, avoid large thrust reductions or trim changes in response to 

sudden airspeed increases as an airspeed decrease may follow. Closely 

monitor vertical flight path instruments, such as vertical speed, altimeters and glideslope displacement. In 

addition, comparison of groundspeed 

and airspeed indications can provide 

additional information for timely 

Page 43 
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windshear recognition. When potential 

for windshear exists, achieve a stabilized approach no later than 1,000 

feet AGL. 

High workload and distractions in the 

approach phase, particularly in marginal weather, may divert attention 

away from instruments that provide 

early recognition of flight path deterioration. Additionally, gradual 

application of thrust on approach may 

mask a decreasing airspeed trend. 

Crews should be prepared to execute 

the recommended recovery procedure immediately if deviations from target 

conditions in excess of the following 

occur: 

Takeoff/Approach 

1) +15 knots indicated airspeed 

2) +500 FPM vertical speed 

3) +5" pitch attitude 

Approach 

1) +l dot 91 ideslope displacement 

2) Unusual throttle position for a 

. . significant period of time. 

These values should be considered as 

guidelines only. Exact criteria cannot be established. In certain instances where significant rates of 

change occur, it' may be necessary to 

initiate recovery before any of the 

above criteria are exceeded. " Other 

situations may exist where brief excursions, particularly in airspeed, 

resulting from known or anticipated 

local wind effects may not be an indication of significant hazard. The 

pilot flying (PF) is responsible for 

assessing the situation and using 

sound judgment to determine the safest 

course of action. 

0 Crew Coordination 

The PF should focus attention on flying the airplane. In a windshear encounter, appropriate action should be 

taken in response to callouts. 

The PNF should focus attention on airspeed, vertical speed, altitude, pitch 

attitude, glidepath deviation and 

thrust. If any significant deviations 

from normal indications are detected, 

the PNF should imnediately call out 

the deviation. Callouts in the cockpit should be standardized and easy to 

understand to ensure timely recognition. 

EXAMPLE: 

"Vertical speed 1200 down--airspeed 

115 decreasing--glideslope one dot 

low.)) 

STANDARD OPERATING TECHNIQUES SUMMARY 

0 Takeoff 

o Know normal attitudes, climb 

rates, airspeed build-up. 

o Know/use all-engine initial 

climb attitude. 

o Make continuous rotation at 

normal rate. 

o Crosscheck flight director commands. 

o Minimize pitch attitude reductions. 

o Monitor vertical flight path 

instruments, call out deviations (PNF). 

o Know recovery decision guidelines. 

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0 Approach 

o Know normal attitudes, descent 

rates, airspeeds, throttle 

position. 

o Crosscheck flight director commands. 

o Avoid large thrust reductions. 

o Monitor vertical flight path 

instruments, call out deviations (PNF). 

o Know recovery decision guidelines. 

2.4.5 WINDSHEAR RECOVERY TECHNIQUE 

The primary recovery technique objective is to keep the airplane flying as 

long as possible in hope of exiting 

the shear. A wide variety of techniques were considered to establish 

the one best meeting this objective. 

The best results were achieved by 

pitching toward an initial target attitude while using necessary thrust. 

Several factors were considered in 

developing this technique. 

Studies show windshear encounters 

occur infrequently and that only a few 

seconds are available to initiate a 

successful recovery. Additionally, 

during high stress situations pilot 

instrument scan typically becomes very 

limited--in extreme cases, to only one 

instrument. Lastly, recovery skills 

will not be exercised .on a day-to-day 

basis. These factors dictated that 

the recovery technique must not only 

be effective, but simple, easily recalled, and have general applicability. 

Extensive analysis and pilot evaluations were conducted. Al though a 

range of recovery attitudes (including 

15" and the range of all-engine initial climb attitudes) provides good 

recovery capability for a wide variety 

of windshears, 15 was chosen as the 

initial target pitch attitude for both 

takeoff and approach. Additional advantages of 15" initial target pitch 

attitude are that it is easily recalled in emergency situations and it 

is prominently displayed on attitude 

director indicators. 

Note: 1) L-1011 target attitudes: 

Takeoff = 17.5O 

Approach = 15" 

2) Operators using pre-calculated target pitch attitudes 

such as all-engine attitude 

for normal takeoffs and 

go-arounds may use these attitudes in place of the recommended initial target recovery attitude. 

While other more complex techniques 

may make slightly better use of airplane performance, these techniques do 

not meet simplicity and ease of recall 

requirements. Evaluations showed that 

the recommended technique provides a 

simple, effective means of recovering 

from a windshear encounter. 

A detailed discussion of the recommended recovery technique follows. 

Recovery both during takeoff after 

liftoff and during approach is discussed together in the following section since the technique for both situations is identical. The recovery 

technique for encounters during takeoff on runway is presented later. 

2.4.5.1/3 ENCOUNTER DURING TAKEOFF - 

AFTER LIFTOFF 

and 

ENCOUNTER ON APPROACH 

Windshear recognition is crucial to 

making a timely recovery decision. 

The recommended recovery procedure 

should be initiated any time the 

flight path is threatened below 1000 

Page 45 
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Appendix 1 

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feet AGL on takeoff or approach. The 

guidelines for unacceptable flight 

path degradation are repeated below: 

o Takeoff/Approach 

required to avoid ground contact. 

When airplane safety has been ensured, 

adjust thrust to maintain engine parameters within specified limits. 

o PITCH 

7) +15 knots indicated airspeed 

2) +500 FPM vertical speed 

3) +5" bitch attitude 

The pitch control technique for recovery from a windshear encounter 

after liftoff or on approach is as 

follows: 

0 Approach 

1) +1 dot glideslope displacement 

2) Unusual throttle position for a 

significant period of time. 

Again, these should be considered as 

guidelines since exact criteria cannot 

be established.- In every case, it is 

the responsibility of the pilot flying 

to assess the situation and use sound 

judgement in determining the safest 

course of action. In certain instances where significant rates of 

change occur, it may be necessary to 

initiate recovery before any of the 

above are exceeded. 

If windshear is inadve rten tlY 

coun tered afte lr liftoff or on 

enappreach, immediately initiate the recomnended recovery technique. If on 

approach, do not attempt to land. 

(However, if on approach and an increasing performance shear is encountered, a normal go-around, rather than 

the recovery maneuver, may be accompl ished.) 

The technique for 

windshear encounter 

recovery from 

after liftoff 

a 

or 

during approach is the same for both 

cases. This technique is described as 

follows: 

o THRUST 

Aggressively apply necessary thrust to 

ensure adequate airplane performance. 

Disengage the autothrottle if necessary. Avoid engine overboost unless 

o At a normal pitch rate, increase or decrease pitch attitude as necessary toward an 

inMa 

15O. 

target attitude of 

The autopilot/flight 

director should be turned off 

by the PNF unless specifically 

designed for operations in 

windshear, or unless using a 

pitch selectable flight director with desired attitude commanded. 

o Always respect stick shaker. 

Use intermittent stick shaker 

as the upper pitch limit. In a 

severe shear, stick shaker may 

occur below 15" pitch attitude. 

o If attitude has been limited to 

less than 15" to stop stick 

shaker, increase attitude 

toward 15" as soon as stick 

shaker stops. 

o If vertical flight path or altitude loss is still unacceptable after reaching 15', further 

increase pitch attitude smoothly in small increments. 

0 Control pitch in a smooth, 

steady manner (in approximately 

2 degree increments) to avoid 

excessive overshoot/undershoot 

of desired attitude. 

o Once the airplane is climbing 

and ground contact is no longer 

an immediate concern, airspeed 

should be increased by cautious 

reductions inpitch attitude. 

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o CONFIGLRATION 

Maintain flap and gear position until 

terrain clearance is assured. Although a small performance increase is 

available after landing gear retraction, initial performance degradation 

may occur when landing gear doors open 

for retraction. While extending flaps 

during a recovery after liftoff may 

result in a performance benefit, it is 

not a recommended technique because: 

1) Accidentally retracting flaps 

(the usual direction of movement) has a large adverse impact on performance. 

2) If landing gear retraction had 

been initiated prior to recognition of the encounter, extending flaps beyond a takeoff 

flap setting might result in a 

continuous warning horn which 

distracts the crew. 

0 ADDITIONAL CONSIDERATIONS 

If autopilot/flight director systems 

specifically designed for operation in 

windshear are engaged during approach, 

they should be used during the recovery maneuver. These systems may 

aid in recovery from an inadvertent 

windshear encounter. However, due to 

limited time available to recognize 

and respond, do not engage the autopilot or autothrottle if these systems 

were not engaged prior to recovery. 

WARNING: A flight director and/or 

autoflight system which is 

not specifically designed 

for operation in windshear 

may command a pitch attitude 

change 'to follow target airspeeds or a fixed pitch attitude regardless of flight 

path degradation. This 

guidance may be in conflict 

with the proper procedures 

for windshear recovery. 

Such systems must be disregarded if recovery is required and, time permitting, 

switched off by the PNF. 

Use of autopilot control wheel steering (CWS) has not been fully evaluated 

for its effectiveness in a windshear 

encounter. * One consideration regarding CWS is that it is usually a single 

channel autopilot mode and as such has 

reduced control authority. In any 

case, if CWS is used during a windshear encounter, its use should be 

discontinued if it produces difficulty 

in achieving the desired attitude. 

Some flight directors are equipped 

with a selectable pitch attitude 

mode. If normal procedures utilize 

this feature, the selectable pitch attitude mode may Be effectively used in 

a windshear encounter provided the selected attitude is within the acceptable range; However, if an attitude 

other than the selected attitude becomes necessary, the flight director 

should be disregarded, and time permitting, switched off by the PNF. 

Avoid stabilizer trim changes in response to short term windshear-produced airspeed/stick force changes. 

However, stabilizer trim should be 

used to trim out stick force due to 

thrust application. 

Throughout recovery, the PNF should 

call out vertical flight path deviations using the barometric altimeter, 

radio altimeter, or vertical speed 

indicator as appropriate. For example, 

"sinking 500, altitude ZOO, climbing 

400, altitude 300, etc." 

Operators of airplanes requiring a 

flight engineer may incorporate the 

second officer into the callout 

process. 

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Rapidly changing winds may cause rapid 2 

excursions in pitch and roll with 

little or no pilot input as well as 

varying the attitude for stick shaker 3 

activation. 

Altjtude at which shear was encountered 

Location of shear with respect to 

runway in use 

following may not have the performance 

required to recover from the same 

windshear encounter. The wi ndshear 

also may be increasing in intensity 

making flight through it even more 

dangerous. 

As soon as possible, report the enPilots and controllers 

must be aware that their timely accounter to the tower. 

tions may prevent a pending disaster--SECONDS MAY SAVE LIVES! 

The airplane 

The 

pilot report for windshear encounters 

should contain the following information: 

Airplane type 

5) Use the term PIREP to encourage 

rebroadcast of the report to other 

aircraft 

4 

Critical remarks are also helpful in 

establishing windshear severity (e.g. II 

. ..maximum thrust required", "...almost contacted terrain", etc.). 

EXAMPLE: 

"San Francisco Tower, PIREP, Flight 

126 encountered windshear on final, 

loss of 20 knots at 300 feet approaching middle marker runway 27 right, 

Douglas MD-80." 

1) Maximum loss or gain of airspeed 

After Liftoff/On Approach Windshear 

Recovery Technique 

l Apply necessary thrust 

l PITCH 

l Adjust toward 15” 

l Increase beyond 15’ if required to 

ensure acceptable flight path 

l Always respect stick shaker 

l CONFIGURATION 

0 Maintain existing configuration 

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2.4.5.2 ENCOUNTER DURING TAKEOFF - 

ON RUNWAY 

Recognition of windshear is difficult 

during takeoff roll since airspeed is 

changing rapidly. In addition to 

visual clues described previously, unusual airspeed fluctuations, slow or 

erratic airspeed build-up may be indications of a windshear encounter. 

IV, = 130kt 1 

The go/no-go criteria based on engine 

failure decision speed (Vl) may not 

be valid for windshear conditions 

since groundspeed can be much higher 

than airspeed (Figure 27). It therefore may not be possible to stop the 

airplane on the runway during a rejected takeoff. The ability to lift 

off is a function of airspeed; the 

ability to stop is largely a function 

of ground speed. 

A Microburst 

Indicated 

Airspeed 

Reaches VI 

I 

Insufficient 

Stopping 

Distance 

G Remains! 

Runway 

GS=8Okt c/s= 13okt 

Normal VI Distance 

Figure 27. Windshear effects on go/no-go decision point. VI decision speed may 

not be attained until insufficient runway remains to aboR takeoff. 

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11125188 

Prior to Vr 

The takeoff should be rejected if unacceptable airspeed variations occur 

below indicated Vl and the pilot 

decides that there is sufficient runway remaining to stop the airplane. 

After Vl 

The takeoff must be continued if Vl 

has been reached. 

o THRUST 

Aggressively apply necessary thrust to 

ensure adequate airplane performance. 

Avoid engine overboost unless necessary to ensure airplane safety. When 

airplane safety has been ensured, adjust thrust to maintain engine parameters within specified limits. 

Overboost thrust alone, however, is 

NOT sufficient to offset the effects 

of an inadvertent windshear encounter. Proper pitch attitude control is the most important factor in 

recovery from windshear.' 

o PITCH 

When VR is reached, rotate at normal 

rate toward 15" pitch attitude. In 

severe windshear encounters, however, 

VR might not be reached and the option to reject the takeoff may not 

exist. If this is the case, rotation 

must be initiated no later than 2,000 

feet from the end of the usable surface (Figure 28). 

Note: Transport category airplanes 

typically can lift off 5 to 10 

knots prior to 

727, 

VR (except 

which cannot lift off 

prior to VR). 

Results in Overrun 

Figure 28. Win&hear effects on rotation decision. Win&hear effects may force rotation 

3tspeeds below I/R. Rotation should begin no later than 2000 ft from runway 

departure end. 

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Pitch attitude and rotation rate 

should not be restricted to avoid aft 

in the available runway. Once airbody contact since all available pitch 

borne, follow the After Liftoff Recovery Technique discussed earlier. 

attitude may be required to lift off 

Takeoff (On Runway) Recovery Technique 

l THRUST 

* Apply necessary thrust 

o PITCH 

l Rotate toward 15O (no later than 

2000 ft remaining) 

0 increase beyond 15’ if required to 

lift off 

Note: After liftoff follow after liftoff recovery technique 

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The runway remaining during takeoff 

can be identified on runways having 

appropriate marking and lighting. 

While the markings discussed are usually to assist landing aircraft, they 

can also be used to determine runway 

remaining during a takeoff. 

Figure 29 illustrates the markings and 

lighting typical of FAA and ICAO precision approach runways. For an airplane departing from left to right in 

the figure, the first pair of single 

hash marks on either side of the centerline indicates 3,000 feet of runway 

remaining (i.e. 1,000 feet until rotation must be initiated). As takeoff 

continues, the 2,000 feet remaining 

point is denoted by the first pair of 

double- hash marks encountered. Note 

that the spacing of al 1 hash marks is 

in 500 foot intervals from the departure end threshold. 

Another indication of runway remaining 

may be the runway lighting. FAA/ICAO 

precision approach runways (Figure 29) 

have edge lights which are yellow 

rather than white for the last 2,000 

feet of runway when viewed in the 

takeoff direction. In addition, centerline lighting can be used to identify the amount of runway remaining. 

The crew in an airplane taking off 

from left'to right in the figure would 

see white centerline lights until 

3,000 feet from the end of the runway 

(1,000 feet until rotation must take 

place). From 3,000 feet to the 1,000 

feet remaining point the centerline 

lights alternate white and red. The 

centerline lights are all red for the 

last 1,000 feet of runway. A line of 

red lights perpendicular to the runway 

indicate the end of usable runway surface. 

Centerline and 

Edge Lighting 

0 White 

Nighttime - Approximate Feet Remaining @Red 

3000 2000 1000 Q Yellow 

+ 

0 d 0 0 0 Q Q Q 0 4 Q Q Q Q 

r--6 0 0 1 Q Q Q Q 1 Q Q Q Q Q 

3000 2000 1000 

Daytime - Approximate Feet Remaining 

Figure 29. FAA /CA0 precision approach runway markings and lighting. 

Page 52 
U/25/88 AC 00-54 

Appendix 1 

Figure 30 illustrates the markings on 

an FAA non-precision approach runway. 

the runway threshold. For runways 

with these markings, pilot judgement 

The main indicator of distance remain- and/or familiarity with specific feaing on these runways is the fixed dis- tures along the runway are required to 

tance markings on either side of cen- estimate 

terline approximately 1,000 feet from 

the 2,000 feet remaining 

point. 

Centerline and 

Edge Lighting 

0 White 

ORed 

Approximate Feet Remaining 

0 0 0 0 0 0 0 0 0 0 0 0 0 0 I 

0 ‘0 0 0 0 0 0 0 0 0 0 0 0 0 

Figure 30. FAA nonprecision approach funway markings and lighting. 

Page 53 
11125188 

AC 00-54 

Appendix 1 

Runway markings and lighting on an 

ICAO non-precision runway are shown in 

Figure 31. This figure represents the 

optimum configuration that might appear. Most ICAO non-precision approach runways would include some, but 

not necessarily all of these features. 

ICAO non-precision runways have single 

hash marks on either side of runway 

0 

centerline at intervals of approximately 500 feet (150 meters) starting 

from the runway threshold. Fixed distance markers may also be present approximately 1,000 feet (300 meters) 

from the threshold. In addition, runway edge lights may be color coded 

similar to precision approach runways 

with yellow rather than white lights 

for approximately the last 2,000 feet 

(600 meters) of the runway. 

Centerline and 

Edge Lighting 

0 White 

Nighttime - Approximate Feet Remaining l Red 

2000 Q Yellow 

+ 

0 0 0 0 Q a Q 0 0 Q CD a Q 

I 0 

010 0 0 01’) Q Q 0 A Q 0 Q Q Q 

3000 2000 1 0 

Daytime - Approximate Feet Remaining 

Figure 37. /CA0 nonprecision approach runway markings and lighting. 

Page 54 
11125188 AC 00-54 

Appendix 1 

0 Other Recovery Techniques 

Many windshear recovery techniques 

were evaluated while establishing the 

technique recommended above. The 

techniques below are NOT recommended 

since they may reduce the chances for 

surviving a windshear encounter. 

0 cAttempting to maintain target airspeed- does not utilize full climb 

capability of the airplane. 

0 Attempting to pitch directly to 

stick shaker does not maximize use 

of available airplane energy, and 

results in a degraded flight path 

and increased exposure to stall. 

0 Attempting to fly at best 

Lift/Drag angle-of-attack does not 

utilize the short-term maximum 

gradient capability of the airplane. 

0 Retracting flaps during approach 

recovery (per the normal go-around 

procedure) reduces margins to 

stick shaker and has an adverse 

impact on initial climb capability 

of the airplane. 

0 

0 

Use of inertial reference ground 

speed emphasizes control of speed 

which is contrary to the recommended recovery technique. In 

addition, this technique is oriented toward compensating for the 

windshear and continuing the approach rather than immediately 

initiating the recovery maneuver. 

While this technique is not appropriate for microburst encounters, 

it may be suitable for use in 

other types of windshears. 

Use of "dive" technique (lowering 

airplane nose in attempt to accelerate then pull up at some predetermined minimum altitude) exposes 

the airplane to potentially higher 

intensity horizontal winds, produces lower minimum recovery altitudes, requires high pitch rates 

and complicates the recovery procedure. 

Page 55 

Again, best recovery results are 

achieved by properly controlling pitch 

attitude 'in conjunction with thrust 

application. 

.- -. -. -- 
AC 00-54 

Appendix 1 

11/25/88 

2.5 SUMMARY 

This document has presented the latest 

air transport industry findings on 

windshear education and training. As 

with any learning, however, it must 

produce changes in attitude and behavior if it is to be effective. 

Changes in attitude are necessary to 

heighten crew awareness of clues which 

indicate the presence of windshear. 

In past windshear accidents, significant clues apparently went unnoticed, 

Recall again that the best defense 

against the low altitude windshear 

haiard is to avoid it altogether. 

This is especially important since 

shears exist that are beyond the capability of any pilot or airplane. 

Since present weather information 

sources and detection systems cannot 

infallibly detect windshear, flight 

crews must be ever alert for the signals which will permit avoidance. 

Behavior changes are also necessary. 

These changes involve appropriate 

pilot technique should the windshear 

avoidance process fail. 

As was discussed in this Pilot Windshear Guide, some of the techniques 

presented regarding pitch attitude and 

airspeed control differ from those 

ordinarily used. However, the recommended techniques have been rigorously 

studied and evaluated for their effectiveness. Pilots must be prepared to 

apply these techniques and take decisive action should the need arise. 

It is recognized that the value of 

this training will be challenged given 

the infrequency of its required use. 

Like many other piloting skills, windshear training will not be exercised 

daily and periodic recurrency training 

will be required to maintain proficiency. Through this process the knowledge and skills pertaining to windshear recognition, avoidance, and recovery will be available and ready for 

use when required. 

Page 56 

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