Microburst on Delta Aircraft Accident 8/2/1985

A microburst is a very localized column of sinking air, producing damaging divergent and straight-line winds at the surface that are similar to but distinguishable from tornadoes which generally have convergent damage. There are two types of microbursts: wet microbursts and dry microbursts. They go through three stages in their life cycle: the downburst, outburst, and cushion stages. The scale and suddenness of a microburst makes it a great danger to aircraft due to the low-level wind shear caused by its gust front, with several fatal crashes having been attributed to the phenomenon over the past several decades.

A microburst often has high winds that can knock over fully grown trees. They usually last for a couple of seconds.

Danger to aircraft
The scale and suddenness of a microburst makes it a great danger to aircraft, particularly those at low altitude which are taking off and landing. The following are some fatal crashes and/or aircraft incidents that have been attributed to microbursts in the vicinity of airports:

• Eastern Air Lines Flight 66, John F. Kennedy International Airport – June 24, 1975
• Pan Am Flight 759, New Orleans International Airport – July 9, 1982
• Delta Air Lines Flight 191, Dallas-Fort Worth International Airport – August 2, 1985
• Martinair Flight 495, Faro Airport – December 21, 1992
• USAir Flight 1016, Charlotte/Douglas International Airport – July 2, 1994
• Goodyear Blimp (Stars and Stripes), Coral Springs, Florida – June 16, 2005
• One-Two-GO Airlines Flight 269, Phuket International Airport – September 16, 2007

A microburst often causes aircraft to crash when they are attempting to land (the above mentioned Pan Am flight is a notable exception). The microburst is an extremely powerful gust of air that, once hitting the ground, spreads in all directions. As the aircraft is coming in to land, the pilots try to slow the plane to an appropriate speed. When the microburst hits, the pilots will see a large spike in their airspeed, caused by the force of the headwind created by the microburst. A pilot inexperienced with microbursts would try to decrease the speed. The plane would then travel through the microburst, and fly into the tailwind, causing a sudden decrease in the amount of air flowing across the wings. The decrease in airflow over the wings of the aircraft causes a drop in the amount of lift produced. This decrease in lift combined with a strong downward flow of air can cause the thrust required to remain at altitude to exceed what is available.