winds hearn
TRANSCRIPT
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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.