Weather related Aviation Crashes

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Weather related Aviation Crashes Deaths in 2004
by Type of Operation

• Crashes 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 deadly one-two punch of
microbursts aircraft level off when they
encounter headwinds, then find themselves pushed
to the ground by intense downdrafts and tailwinds.
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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

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Eastern Air Lines 66 June 24, 1975 New York
Kennedy Airport 112 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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Flight trajectory (red line), winds (green
arrows), and indicated airspeed of PAA 759
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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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USAir 1016 July 2, 1994 Charlotte/Douglas
Airport Crashed on landing 37 killed 25
injured McDonnell Douglas DC-9
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Downbursts
Microburst
Dry Microburst

• Damaging winds less than 2.5 miles in diameter

• Accompanied by little or no rainfall

Wet Microburst

• Damaging winds less than 2.5 miles in diameter

• Accompanied by very heavy rainfall and perhaps
  hail

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August 1, 1983 the strongest microburst recorded
at an airport was observed at Andrews Air Force
Base in Washington DC. The wind speeds may have
exceeded 150 mph in this microburst. The peak
gust was recorded 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-offs the pilot experiences a headwind
and increased aircraft performance followed by a
short period of decreased headwind a downdraft
and finally a strong tailwind
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During landings the airplane begins the descent
flying into a strong headwind a downdraft and
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. Damaging winds, 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 small horizontal scale, an intense
  microburst could induce damaging winds as high as
  168 mph.

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Macroburst
Wisconsin on the 4th of July, 1977, with winds
that were estimated to exceed 115 mph, and
completely flattening thousands of acres of
forest
Microburst
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The Terminal Doppler Weather Radar (TDWR) is now
deployed at 44 major airports. The TDWR mission
is to provide wind shear detection 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 disasters
  in the U.S. happened in the summer.
• (1 in June, 2 in July, 1 in August)
• All four happened in the late afternoon or early
  evening (from 405 to 743 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 Transportation Safety Board accident and
  incident reports a year from 1983 through 2001.
  But the vast majority of cases were nonfatal and
  mostly involved general aviation.