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A difference in wind speed and direction over a relatively
short distance in the atmosphere
Delta Air Lines Flight 191 was a regularly scheduled service from Fort Lauderdale-Hollywood International Airport, Florida to Los Angeles International Airport, California, by way of Dallas-Fort Worth International Airport. On the afternoon of August 2, 1985, the plane crashed when it hit a microburst while landing at DFW, killing 8 of the 11 crew members and 126 of the 152 passengers on board, and one person on the ground. Two people later died 30 days or more after the crash, bringing the total fatalities to 137.
Description of what it is: Air mass wind shear - This type of wind shear occurs at night under fair weather conditions in the absence of strong fronts and/or strong surface pressure gradients. We know with radiational cooling, the ground will cool faster than the overlying air mass. If the cooling is strong enough, a nocturnal inversion results.
•Dangers of it: low level wind shear
•How to minimize or avoid: It is the pilot’s responsibility to obtain a pre-flight weather briefing. Any ATC reported weather information, along with periodic contacts with Flight Watch
while airborne, will supplement what was learned during the pre-flight briefing.
Description of what it is: Jet streams are fast flowing, narrow air currents
•Dangers of it: Associated with jet streams is a phenomenon known as clear-air
turbulence (CAT), caused by vertical and horizontal wind shear connected to the jet
streams.The CAT is strongest on the cold air side of the jet stream, next to and just underneath
the axis of the jet stream. Clear-air turbulence can cause aircraft to plunge and so present a
passenger safety hazard that has caused fatal accidents.
•How to minimize or avoid: It is the pilot’s responsibility to obtain a pre-flight weather
briefing. Any ATC reported weather information, along with periodic contacts with Flight Watch
while airborne, will supplement what was learned during the pre-flight briefing.
Jet Stream Fatality: On December 28, 1997, United Airlines Flight 826 was a Boeing
747-100 flying from Narita International Airport, Japan to Honolulu International Airport in
Hawaii. Two hours into the flight, at 9400 meters (31,000 ft), the plane received reports of
severe clear-air turbulence in the area and the seat belt sign was turned on. Moments later, the
aircraft suddenly dropped around 30 meters (100 ft), seriously injuring 15 passengers and 3 crew members, although there was no structural damage to the aircraft. The plane turned
around and landed safely back in Tokyo, but it was not put back in service since it had been
scheduled to be retired in early 1998. One passenger died of her injuries after landing in Tokyo.
Description of what it is: Jet streams are fast flowing, narrow air currents
•Dangers of it: Associated with jet streams is a phenomenon known as clear-air
turbulence (CAT), caused by vertical and horizontal wind shear connected to the jet
streams.The CAT is strongest on the cold air side of the jet stream, next to and just underneath
the axis of the jet stream. Clear-air turbulence can cause aircraft to plunge and so present a
passenger safety hazard that has caused fatal accidents.
•How to minimize or avoid: It is the pilot’s responsibility to obtain a pre-flight weather
briefing. Any ATC reported weather information, along with periodic contacts with Flight Watch
while airborne, will supplement what was learned during the pre-flight briefing.
Jet Stream Fatality: On December 28, 1997, United Airlines Flight 826 was a Boeing
747-100 flying from Narita International Airport, Japan to Honolulu International Airport in
Hawaii. Two hours into the flight, at 9400 meters (31,000 ft), the plane received reports of
severe clear-air turbulence in the area and the seat belt sign was turned on. Moments later, the
aircraft suddenly dropped around 30 meters (100 ft), seriously injuring 15 passengers and 3 crew members, although there was no structural damage to the aircraft. The plane turned
around and landed safely back in Tokyo, but it was not put back in service since it had been
scheduled to be retired in early 1998. One passenger died of her injuries after landing in Tokyo.