boeing field. downbursts downbursts can be divided into two main types macroburst: a large downburst...
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Boeing FieldBoeing Field
Downbursts
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.
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
Downburst Video
• http://www.youtube.com/watch?v=TkavH9aZue8
• http://video.google.com/videoplay?docid=5318526465028252338#
• http://www.youtube.com/watch?v=K8ilNyf5p-M
Extremely Dangerous For Aircraft Landing and Taking Off
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.
Flight trajectory (red line), winds (green arrows), and indicated airspeed of PAA 759
The following are some fatal crashes that have been The following are some fatal crashes that have been attributed to windshear/ microbursts in the vicinity of attributed to windshear/ microbursts in the vicinity of airports: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
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
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.
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
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
Joint Airport Weather Studies (JAWS)
• Major research effort between FAA and NCAR during the 1980s to understand and find ways of dealing with downbursts.
• Centered at Stapelton Airport in Denver
• Once the phenomenon was understood, proposed solution to allow warnings: terminal doppler radars and LLWAS.
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
Low Level Windshear Alert System Low Level Windshear Alert System (LLWAS)(LLWAS)
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 that detected microbursts, determined the strength in terms of headwind/tailwind gains or and located the event (on the runway, at 1, 2, or 3 nm on departure or arrival).
• 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.
Microburst “Season & Time”Microburst “Season & Time”
• The four best known downburst aviation disasters The four best known downburst aviation disasters in the U.S. happened in the summer. in the U.S. 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 afternoon or early All four happened in the late afternoon or early evening (from 4:05 to 7:43 local time)evening (from 4:05 to 7:43 local time)
Still not thereStill not there
• The threat of wind shear has been reduced The threat of wind shear has been reduced but not eliminated. It was mentioned in an but not eliminated. It was mentioned in an average of 25 National Transportation average of 25 National Transportation Safety Board accidents and incident reports Safety Board accidents and incident reports a year from 1983 through 2001. But the vast a year from 1983 through 2001. But the vast majority of cases were nonfatal and mostly majority of cases were nonfatal and mostly involved general aviation. involved general aviation.