aviation and downbursts douglas cain jamie gudmestad aviation program nws midland
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Aviation and DownburstsAviation and Downbursts
Douglas CainJamie GudmestadAviation ProgramNWS Midland
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Things you should know about Things you should know about DownburstsDownbursts
• Are caused by shower or thunderstorm outflow
• Strong out-rush of damaging winds
• Can be very hazardous to aircraft
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Weather related Aviation Crashes Weather related Aviation Crashes & Deaths in 2004 by Type of & Deaths in 2004 by Type of
OperationOperation Crashes DeathsCrashes Deaths Scheduled Airlines 1 13Scheduled Airlines 1 13
Air Taxi, Commuter 12 29Air Taxi, Commuter 12 29
General Aviation 98 198General Aviation 98 198
Totals 111 240Totals 111 240
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Downburst!
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Downbursts most dangerous to Downbursts most dangerous to aviation aviation
On take offOn take off
On landingOn landing
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During take-offsthe 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 landingsthe 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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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 can be Divided into Downbursts can be Divided into Two Main TypesTwo 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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Wisconsin on the 4th of July, 1977, with winds that were estimated to exceed 115 mph, and completely flattening thousands of acres of forest
MacroburstMacroburst
MicroburstMicroburst
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DownburstsDownbursts
MicroburstMicroburst
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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Dry Microburst Sounding
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Wet Microburst
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Signs a Downburst may be Signs a Downburst may be OccurringOccurring
Thunderstorm Thunderstorm RainshowerRainshower Blowing dustBlowing dust VirgaVirga RainfootRainfoot
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Dry vs. Wet Microburst Characteristics
Characteristic Dry Microburst Wet Mircoburst
Location of Highest Probability
Precipitation
Cloud Bases
Features below Cloud Base
Primary Catalyst
Environment below Cloud Base
Surface Outflow Pattern
West
Little or none
As high as 500 mb
Virga
Evaporative cooling
Deep dry layer/low relative humidity/dry adiabatic lapse rate
Omni-directional
Southeast
Moderate or heavy
Usually below 850 mb
Shafts of strong precipitation reaching the ground
Downward transport of higher momentum/precipitation loading
Shallow dry layer/high relative humidity/moist adiabatic lapse rate
Gusts of the direction of the mid-level wind
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The following are some fatal crashes that The following are some fatal crashes that have been attributed to windshear/ have been attributed to windshear/ microbursts in the vicinity of airports:microbursts in the vicinity of airports:
Eastern Airlines Flight 66 Eastern Airlines Flight 66 Pan Am Flight 759 Pan Am Flight 759 Delta Airlines Flight 191 Delta Airlines Flight 191 USAir Flight 1016 USAir Flight 1016
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Eastern Air Lines 66June 24, 1975
New York – Kennedy Airport
112 killed
12 injured
Crashed while landing
Boeing 727
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Pan Am 759July 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 8 of 11 crew members and 128 of the 152 passengers killed,152 passengers killed,1 person on ground killed 1 person on ground killed Lockheed L-1011
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USAir 1016July 2, 1994
Charlotte/Douglas Airport
Crashed on landing
37 killed
25 injured
McDonnell Douglas DC-9
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Is the Situation Getting Is the Situation Getting Better or Worse?Better or Worse?
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Fatalities Associated with U.S. Aviation Wind Shear Accidents
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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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In the 1980s, research conducted at the National Center for Atmospheric Research (NCAR), indicated that microburst windshear was very dangerous to aircraft below 1000 ft. Several major accidents during the 1980s also implicated windshear as a factor.
Low Level Windshear Alert System Low Level Windshear Alert System (LLWAS)(LLWAS)
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Microburst “Season & Time”Microburst “Season & Time”
The four best known downburst The four best known downburst aviation disasters in the U.S. aviation disasters in the U.S. happened in the summer. happened in the summer.
(1 in June, 2 in July, 1 in August)(1 in June, 2 in July, 1 in August)
All four happened in the late All four happened in the late afternoon or early evening (from afternoon or early evening (from 4:05 to 7:43 local time)4:05 to 7:43 local time)
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Still not ThereStill not There
The threat of wind shear has been The threat of wind shear has been reduced but not eliminated. It was reduced but not eliminated. It was mentioned in an average of 25 mentioned in an average of 25 National Transportation Safety Board National Transportation Safety Board accident and incident reports a year accident and incident reports a year from 1983 through 2001. But the from 1983 through 2001. But the vast majority of cases were nonfatal vast majority of cases were nonfatal and mostly involved general aviation. and mostly involved general aviation.
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So What Days have High So What Days have High
Likelihood of Downbursts? Likelihood of Downbursts?
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This is a morning sounding, what kind of microburst would you expect in the afternoon?
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The End!The End!
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Aviation and DownburstsAviation and Downbursts
Douglas CainDouglas Cain
Jamie GudmestadJamie Gudmestad
Aviation ProgramAviation Program
NWS MidlandNWS Midland