Winds Hearn

7/28/2019 Winds Hearn

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Weather related Aviation Crashes &

Deaths in 2004 by Type of OperationCrashes Deaths

Scheduled Airlines 1 13

Air Taxi, Commuter 12 29

General Aviation 98 198

Totals 111 240


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Boeing Field


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Research by NCAR and collaborators in the 1980s uncovered the deadlyone-two punch of microbursts: aircraft level off when they encounter

headwinds, then find themselves pushed to the ground by intensedowndrafts and tailwinds.


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http://en.wikipedia.org/wiki/Image:Microburst_%28NSSL%29.jpg


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http://en.wikipedia.org/wiki/Image:Microburst_%28NSSL%29.jpg


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Downbursts most dangerous to

aviation On take off

On landing


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The following are some fatal crashes that have been

attributed to windshear/ microbursts in the vicinity of

airports:

Eastern Airlines Flight 66

Pan Am Flight 759 Delta Airlines Flight 191

USAir Flight 1016
http://en.wikipedia.org/wiki/Eastern_Airlines_Flight_66http://en.wikipedia.org/wiki/Pan_Am_Flight_759http://en.wikipedia.org/wiki/Delta_Airlines_Flight_191http://en.wikipedia.org/wiki/USAir_Flight_1016http://en.wikipedia.org/wiki/USAir_Flight_1016http://en.wikipedia.org/wiki/Delta_Airlines_Flight_191http://en.wikipedia.org/wiki/Pan_Am_Flight_759http://en.wikipedia.org/wiki/Eastern_Airlines_Flight_66


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Eastern Air Lines 66

June 24, 1975

New York

Kennedy Airport112 killed

12 injured

Crashed while landing

Boeing 727


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Pan Am 759

July 9, 1982

New Orleans Airport

145 passenger/crew killed

8 on ground killed

Crashed after takeoff

Boeing 727


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Flighttrajectory(red line), winds (green arrows), and indicated airspeed of PAA 759
http://www-das.uwyo.edu/~geerts/cwx/notes/chap08/mb_1.gif


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Delta 191

August 2, 1985

Dallas-Fort Worth Airport

Crashed on landing

8 of 11 crew members and 128 of the

152 passengers killed,1 person on ground killed

Lockheed L-1011


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USAir1016

July 2, 1994

Charlotte/Douglas AirportCrashed on landing

37 killed

25 injured

McDonnell Douglas DC-9


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Downbursts

Microburst

Dry Microburst

Damaging winds less than2.5 miles in diameter

Accompanied by little orno rainfall

Wet Microburst

Damaging winds less than2.5 miles in diameter

Accompanied by very heavyrainfall and perhaps hail


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August 1, 1983 the strongest microburst recorded at an airport wasobserved at Andrews Air Force Base in Washington DC. The wind speedsmay have exceeded 150 mph in this microburst. The peak gust wasrecorded at 211 PM 7 minutes after Air Force One, with the President

on board, landed on the same runway.


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During take-offsthe pilot experiences a headwind and increased aircraft performance

followed by a short period of decreased headwinda downdraft

and finally a strong tailwind


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During landings

the airplane begins the descentflying into a strong headwind

a downdraftand finally a strong tailwind

represents the extreme situation just prior to impact


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Downbursts can be Divided into

Two Main Types

MACROBURST: A large downburst with its outburst winds

extending greater than 2.5 miles horizontal dimension. Damagingwinds, lasting 5 to 30 minutes, could be as high as 134 mph.

MICROBURST: A small downburst with its outburst,

damaging winds extending 2.5 miles or less. In spite of its smallhorizontal scale, an intense microburst could induce damaging winds

as high as 168 mph.


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Wisconsin on the 4th of July, 1977,

with winds that were estimated toexceed 115 mph, and completelyflattening thousands of acres of forest

Macroburst

Microburst


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The Terminal Doppler Weather Radar (TDWR) is now deployed at 44major airports. The TDWR mission is to provide wind sheardetection services to air traffic controllers and supervisors


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Low Level Windshear Alert System

(LLWAS)


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LLWAS

In 1983, the FAA asked NCAR to develop a version of LLWAS that could detect microbursts.

Between 1983 and 1988, NCAR developed and tested a new LLWAS system, called enhanced

LLWAS or LLWAS-Network Expansion that detected microbursts, determined the strength in terms

of headwind/tailwind gains or losses (in knots) and located the event (on the runway, at 1, 2, or 3

nm on departure or arrival). The system was designed to provide alerts specific to each runway

operation. It was designed to have a probability of detection of 90 percent or greater and a false

alarm rate of 10 percent or less.

This system was later improved and is now called the Phase-3 LLWAS. A typical Phase-3 LLWAS

will have enough sensors to be spaced 2-km apart (~1 nm apart) and cover out to 2 nm from the

end of each major runway. The largest LLWAS is at Denver International Airport. It has 32 wind

sensors. Most Phase-3 systems have between 12 and 16 wind sensors. A siting evaluation is done

for each airport to determine the network geometry since it depends on terrain, # of runways,obstructions, etc.


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Microburst Season & Time

The four best known downburst aviation disastersin the U.S. happened in the summer.

(1 in June, 2 in July, 1 in August)

All four happened in the late afternoon or earlyevening (from 4:05 to 7:43 local time)


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Still not There

The threat of wind shear has been reduced

but not eliminated. It was mentioned in an

average of 25 National TransportationSafety Board accident and incident reports a

year from 1983 through 2001. But the vast

majority of cases were nonfatal and mostlyinvolved general aviation.

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