Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 11
1
Introduction
Low-altitude wind variability, or wind shear,* has long been
recognized as a potential hazard to aircraft landing and taking off.
Although wind shear can result from a number of basically different
meteorological conditions, pilots have been trained to avoid
thunderstorms in particular because of often associated severe wind
variability and turbulence near the ground and aloft.
It has recently been recognized that small, short-lived downdrafts,
called microbursts, are serious hazards to aircraft during landings
and takeoffs. In some microbursts the air carried downward strikes
the ground and spreads out in a shal low layer--sometimes only a few
hundred feet in thicknes s. The parent cloud from which the microburst
descends is a convective one but one that has not necessarily grown to
thunderstorm size and strength.
Thunderstorm outflow and accompanying downdrafts, some of the
scale and intensity that have recently been named microbursts and
downbursts, were identified by the Thunderstorm Pro ject nearly 40
years ago (Byers and graham, 1949~. Such outflows and downdrafts were
newly emphasized as the cause of some serious accidents after a
quantitative analysis of the winds encountered by Eastern Airlines
Flight 66 while landing at John F. Kennedy International Airport on
June 24, 1975. Analysis of the flight recorder data from another
aircraft operating in the immediate vicinity provided a wind model
considered to be very similar to that encountered by EAL Flight 66.
A detailed map of the wind-shear patterns at the time of the crash
was constructed from an analysis of available data, including meteoro-
logical satellite photographs and surface weather observations and
measurements (Fujita, 1976; Lewellen et al., 1976~. The analysis
provided valuable insight into the characteristics of violent downburst
-Inless specified otherwise in this report, wind shear is the differ-
ence of wind velocity at two points divided by the distance between
the two points.
11
OCR for page 12
cells within thunderstorms, the need to detect their presence as early
as possible, and the need for immediate communication of warnings to
air traffic controllers and flight crews in the vicinity.
Incident/Accident Records
\
In 197 7 the FAA conduc ted a s tudy o f NTSB repor t s on a ircraf t
accidents and incidents related to low-altitude wind shear that
occurred from 1964 through 1975 (Shrager, 1977~. More than 59,000
reports were reviewed, covering all classes of civil aircraft and
flight operations. About one-third of the accidents or incidents,
more than 19 ,000, occurred during terminal area operations. Only 25
accidents or incidents involving large aircraft (more than 12,500
pounds) were identified in which low-altitude wind shear could have
been a contributing factor. Of these 25 cases, 23 occurred during
approach or landing and only 2 during takeof f .
Table 1 lists 27 U.S. aircraft accidents or incidents that
occurred from 1964 to 1982 and that are at tributed to low-al titude
wind shear. The list includes most of the 25 cases identified by the
FAA. Some were omitted because, on further examination, they could
not be attributed to wind shear. The table does include
wind-shear-re lated accidents or incidents that have oc curred s ince
1976, including 2 during 1982.
In 1981 general aviation aircraft numbered more than 200,000 and
flew more than 40 million hours (compared with 3,973 aircraft and 8
million flight hours for air carriers). General aviation operations
accounted for 662 fatal accidents from all causes, with 1,265
fatalities (FAA, 1981~. Informal accident cause/factor statistics
from the NTSB for 1981 indicate that weather caused or was a related
factor in 40 percent (289 cases) of the U.S. general aviation
accidents. Of these, wind shear was reportedly the cause of one fatal
accident and was a factor in two. It should be noted that the NTSB
generally investigates only those general aviation accidents that
result in a fatality, and not all of those attributed to weather were
analyzed by trained meteorologists. Low-altitude wind variability may
have been a factor in some of these.
In 1975, NASA, in cooperation with the FAA, instituted the Aviation
Safety Reporting System (ASRS), whereby safety-related incidents
involving aircraft operations are submitted voluntarily and treated
anonymously, with the expectation that potential flight safety problems
may be identified and corrective action suggested. A total of 26
reports have been indexed as wind shear related out of nearly 21,600
reports received since May 1, 1978. Of these, 17 appear to involve
wind shear as a primary factor.
12
OCR for page 13
A recent study (Anderson and Clark, 1981) of the effects of wind
shear on aircraft operations and flight safety in Australia, including
an extensive survey of pilots, concluded that wind shear was a causal
or contributory factor in numerous aircraft accidents in Australia and
elsewhere and that inadequate knowledge of wind structure and of the
resulting effects on aircraft operations constitutes a flight safety
hazard. Furthermore, the term wind shear is subject to various
-
interpretations among pilots, and specific definitions are often
misunderstood. Pilot judgments as to the aircraft types most suscep-
tible to wind shear were not readily explicable in terms of aircraft
size, landing speed, or wing loading. The use of standard terminology
and improved training for pilots and air traffic controllers was
recommended, along with research on optimal piloting techniques during
wind-shear encounters.
In the United Kingdom the Royal Aircraft Establishment has
undertaken a program to extract wind-shear data from records obtained
from 10 Boeing 747 aircraft operated throughout the world by British
Airways. (Haynes, 1980; Woodfield and Woods, 1981~. This is a
continuing effort to obtain wind information on strong wind-shear
events during approach and landing. Time histories of wind velocities
and aircraft reactions to interesting events are identified and
analyzed. The results may lead to statistics on the probabilities of
encountering wind shears and criteria for testing and evaluating
autopilots and onboard wind-shear detection systems.
The rarity and lack of a reliable statistical data base on wind-
shear-related accidents, shear encounters, or even the frequency of
occurrence of potentially hazardous wind shears does not diminish the
importance or severity of the safety problem. The potentially catas-
trophic consequences of an encounter during takeoff or approach and
landing require that wind shear always be taken into account as a
primary safety consideration when weather conditions are such that
strong wind shears may be present. The widespread lack of appreciation
among pilots, traffic controllers, and aircraft operations personnel
of the seriousness of the possible safety hazards has exacerbated the
problem.
Reports by the NTSB of investigations of air carrier accidents at
least partly attributable to wind shear have resulted in a series of
specific safety recommendations by the NTSB to the FAA. These recom-
mendations are routinely considered and acted on by the FAA and
followed up by the NTSB. Together with other FAA activities, these
have contributed to a compendium of FAA actions with respect to wind
shear. The NTSB's report of the investigation of the Pan American
World Airways Flight 759 accident that occurred on July 9, 1982,
contained 14 recommendations for priority and longer-term action
intended to improve safety in wind-shear weather conditions (NTSB,
1983).
13
OCR for page 14
u - ~
At
Go
At
1
in
~9
~ -
· -
cd
H ~
in
Cal ~
in . -
u 3
· - ~
~ U
C) ~
¢ U
U ¢
1
~ o
Cal ,
o
u
o,
Cat
to
to
tD
oo
Or)
CD
o o
~ N
CD CD
J J
· ~
US
Cat
14
CO
Lo
OCR for page 15
in ~
lo ~
to to
in
in
rn
O Lit
in
a,
~ -
o~
Lr)
en
en
or
ID
15
Cot
·^ ·^
~ .^ ,_
Go ~ ,_
Do ~ .
o
. -
cd a) u
Cal V ~ ~ ~
a) ~ ~ cat
V C)~-
v
¢
~C:= ~
cn O
~ ~o ~ ~ C'
¢ o
¢ ~ C~ ~
U
~ ~ C~
o ~ U _' ~
C0~ - · -
·^
~: ~ o
~ u, ~ a
U =,
U =~ -
a~ ~ ~ 3
~ . - _~ ~ o
3 ~ U.
· ^
cn ¢
E~ ~ r~ .= 0
~z ~ a~ ~ ~
~ ~, `_
C~ ~ ^~ .^
cn oo co
S~ _'
.^ .^ ~ s"
~o `~^ o
~ ,_ ~ oo
c~ ~ ~ a)
a) ~ ct ~ a'
C~ U ~ ~ ~
~ U' - ~ - C)
U) 3 ;4
~^~
_, ~ ~
·-
cn
C~
cn
OCR for page 16
FAA Wind-Shear Program Activities
In 19 71 the FAA inn' fated a program to work on the prob lem of wind
shear in coordination with other organizations working in the field.
Several areas of investigation were addressed, including wind-shear
forecasting techniques and means of detecting the presence of wind
shear with both ground-based and airborne instrumentation.
A multiphased research and development program was undertaken to
investigate and develop cockpit displays, instrumentation, and
operational procedures for assisting a pilot in the event of a
wind-shear encounter. The project involved development of wind-shear
models and evaluation of cockpit instrumentation, various cockpit
instrument panel display configurations, and flight-path management
systems in moving-base simulations of the flight of various large
transport airplanes in wind shear. The results have been published in
a series of reports (e.g., Foy, 1979~.
In 1976 a wind-shear detection system called the Low-Level Wind
Shear Alert System (LLWSAS) was developed (Goff, 1980) , and instal-
lations are now in operational use at 59 ma jor airports ~ see Table 2 ~ .
Also, the FAA published an advisory circular (AC 00-50 ), entitled Low
Level Wind Shear, dated April 18, 1976, intended to provide guidance
for recognizing the possibilities of hazardous wind-shear situations
and piloting techniques for recovery from wind-shear encounters.
Detailed research on the nature and characteristics of downbursts,
sponsored by the FAA together with the NWS, NSF, and NASA has been
undertaken. Project NIMROD conducted by the University of Chicago in
the north-central midwestern United States during 19 78-19 79 and the
JAWS Project in the Denver area during the surfer of 1982 have provided
extensive new knowledge on the meteorological characteristics of wind
shear required for more realistic computer modeling of wind-shear
fields for flight simulation, instrument design and development, and
system certification.
In May 1977 the FAA amended Part 121 of the Federal Aviation
Regulations [FAR 121.601 (b) ~ to require air carriers to adopt an
approved system for obtaining weather forecasts and reports of adverse
weather conditions, including low-altitude wind shear, at each airport
used in their operations. In support of this rule, FAA inspectors were
directed to ensure that the air carriers provided pilot training for
adverse weather operations, applying the information on wind-shear
hazards contained in the FAA's Advisory Circular AC 00-50 .
In 1979 the FAA published an updated advisory circular (AC 00-50A,
dated 1/23/79 ~ and developed a pilot training film to provide detailed
information, guidance, and training to cope with wind shear during
takeoff or landing operations, based on newly acquired data. In May
1979 the FAA issued an advance notice of proposed rulemaking (NPRM
79-11 ) to invite public discussion and to solicit comments as to the
16
OCR for page 17
TABLE 2 Location of Low-Level Wind Shear
Alert System (LLWSAS) Installations
IN OPERATION (59 UNITS)
Albuquerque, NM
Atlanta, GA
Baltimore, MD
Birmingham, AL
Boston, MA
Buffalo, NY
Charlotte, NC
Chicago (O'Hare),
Cincinnati, OH
Cleveland (Hopkins), OH
Columbus, OH
Dallas/Ft. Worth, TX
Dayton, OH
Denver, CO
Des Moines, IA
Detroit (Metro. ), MI
Ft. Lauderdale (Ins. ) , FL
Houston (Int.), TX
Houston, TX
TX
TO Be INSTALLED (51 UNITS)
Indianapolis (Int.), IN
Jackson, MS
Jacksonville, FL
Kansas City (Int.), MO
Knoxville, TN
Las Vegas, NV
Little Rock, AR
Los Angeles, CA
Louisville, KY
Memphis (Int.), TN
Miami, FL
Milwaukee, WI
Minneapolis (Int.), MN
Mobile, AL
Nashville, TN
New Orleans, LA
New York (Kennedy) NY
New York (LaGuardia)
Newark (Int.), NJ
Norfolk, VA
Oklahoma City, OK
Omaha, NE
Orlando (Int.), FL
Philadelphia (Int.), PA
Phoenix, AZ
Pittsburgh (Int.), PA
Raleigh-Durham, NC
Roanoke, VA
Rochester, NY
St. Louis (Int.), MO
Salt Lake City, UT
San Antonio, TX
San Juan, PR
Sarasota, FL
Tampa, FL
Tulsa, OK
Washington (Dulles), VA
NY Washington, (National), VA
W. Palm Beach, FL
Wichita, KS
Albany, NY Fayetteville, NC Montgomery, AL
Asheville, NC Fort Smith, AR Pensacola, FL
Augusta, GA Fort Myers, FL Peoria, IL
Austin, TX Grand Rapids, MI Richmond, VA
Baton Rouge, LA Green Bay, WI Rochester, MN
Billings, MT Greensboro, NC San Francisco, CA
Bristol, TN Greer, SC Savannah, FA
Cedar Rapids, LA Honolulu Oahu, HI Shreveport, LA
Charleston, SC Huntsville, AL Sioux City, LA
Charleston, WV Lansing, MI Sioux Falls, SD
Chattanooga, TN Lexington, KY Springfield (Capitol), IL
Colo Spgs, CO Lincoln, NE Springfield, MO
Columbia, SC Lubbock, TX Syracuse, NY
Columbus, GA Madison, WI Tallahassee, FL
Dallas-Love, TX Midland, TX Toledo, OH -~
Daytona Beach, PL Moline, IL Tuscon, AZ
E1 Paso, TX Monroe, LA Windsor Locks, CT
Source: FAA. 1983
17
OCR for page 18
need to amend FAR 121 to require large air carrier aircraft to utilize
wind-shear detection equipment or to take other actions to provide
practical, effective, and reliable detection of hazardous wind shears.
No regulatory action has yet been taken directly in response to this
proposal. In this connection, however, the FAA has prepared an
advisory circular presenting criteria for operational approval of
airborne wind-shear alerting and flight guidance systems and wind-shear
detection and avoidance systems.
These proposed criteria, including presently available
mathematical models of a variety of wind-shear and turbulence fields,
are intended to permit FAA acceptance of concepts designed to enable
pilots to recognize the presence of wind shear, to optimize their
reactions, and to fully utilize the performance capabilities of their
aircraf t to cope with a wind-shear hazard that may be encountered .
The circular provides that the wind-shear models will be updated as
new data become available. This advisory circular is currently under
review, preparatory to its adoption.
Air traff ic control procedures used by the FAA relative to wind
shear include the use of meteorological forecasts, surface and
upper-air weather and weather radar observations, voluntary pilot
reports (PIREPs ~ of wind-shear encounters, and LLWSAS.
18
Representative terms from entire chapter:
wind shears
