1. Boeing Field 1

2. Downbursts

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4. 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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7. Wet microburst photo taken by Bill Bunting. A series of three sides.
Downburst Hazards. Downburst winds can exceed 100 mph and are capable of doing the same damage as a weak to strong tornado. Rapidly shifting wind direction and changes in visibility pose problems to mobile spotters. 7

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9. Strongest winds occur in the curl.
Heavy rains and flooding are likely when you see something like this. Don’t drive your vehicle into something like this. 9

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13. Downbursts Microburst Dry Microburst Wet 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 13

14. Downburst Video http://www.youtube.com/watch?v=TkavH9aZue8

15. Extremely Dangerous For Aircraft Landing and Taking Off

16. 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. 16

17. Flight trajectory (red line), winds (green arrows), and indicated airspeed of PAA 75917

18. Eastern Airlines Flight 66 Pan Am Flight 759 Delta Airlines Flight 191
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 18

19. Eastern Air Lines 66 June 24, 1975 New York – Kennedy Airport
112 killed
12 injured
Crashed while landing
Boeing 727 19

20. Pan Am 759 July 9, 1982 New Orleans Airport 145 passenger/crew killed
8 on ground killed
Crashed after takeoff
Boeing 727 20

21. 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 21

22. USAir 1016 July 2, 1994 Charlotte/Douglas Airport Crashed on landing
37 killed
25 injured
McDonnell Douglas DC-9 22

23. 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. 23

24. the pilot experiences a headwind and increased aircraft performance
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 24

25. the airplane begins the descent flying into a strong headwind
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 25

26. 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 26

27. 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.

28. 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

29. Low Level Windshear Alert System (LLWAS)

30. 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.

32. 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 4:05 to 7:43 local time)

33. 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 accidents and incident reports a year from 1983 through But the vast majority of cases were nonfatal and mostly involved general aviation.