Aviation and DownburstsAviation and Downbursts

Douglas CainJamie GudmestadAviation ProgramNWS Midland

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

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

Downburst!

Downbursts most dangerous to Downbursts most dangerous to aviation aviation

On take offOn take off

On landingOn landing

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

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

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.

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.

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

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

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.

Dry Microburst Sounding

Wet Microburst

Signs a Downburst may be Signs a Downburst may be OccurringOccurring

Thunderstorm Thunderstorm RainshowerRainshower Blowing dustBlowing dust VirgaVirga RainfootRainfoot

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

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

Eastern Air Lines 66June 24, 1975

New York – Kennedy Airport

112 killed

12 injured

Crashed while landing

Boeing 727

Pan Am 759July 9, 1982

New Orleans Airport

145 passenger/crew killed

8 on ground killed

Crashed after takeoff

Boeing 727

Flight trajectory (red line), winds (green arrows), and indicated airspeed of PAA 759

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

USAir 1016July 2, 1994

Charlotte/Douglas Airport

Crashed on landing

37 killed

25 injured

McDonnell Douglas DC-9

Is the Situation Getting Is the Situation Getting Better or Worse?Better or Worse?

Fatalities Associated with U.S. Aviation Wind Shear Accidents

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

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)

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)

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.

So What Days have High So What Days have High

Likelihood of Downbursts? Likelihood of Downbursts?

This is a morning sounding, what kind of microburst would you expect in the afternoon?

The End!The End!

Aviation and DownburstsAviation and Downbursts

Douglas CainDouglas Cain

Jamie GudmestadJamie Gudmestad

Aviation ProgramAviation Program

NWS MidlandNWS Midland