Thunderstorms, Tornadoes, and Microbursts, oh my!

How are microbursts developed and what are their hazards to aviation? How could one microburst bring down a Boeing 737?

An ordinary thunderstorm goes through a relatively constant cycle of development. It goes through a cumulus stage, where warm, humid air rises and condenses into a single cumulus cloud or cluster of cumulus clouds. A mature stage, the most intense stage, brings precipitation and gust fronts. A dissipating stage which occurs when the updrafts weaken and the gust front moves away from the storm and no longer enhances the updrafts. Downbursts occur under an intense thunderstorm where downdrafts can become concentrated and hit the ground in a concentrated manner, then divert outwards horizontally. A downburst with winds spanning less than 4 km is termed a microburst. In spite of its small size, an intense microburst can induce damaging straight-line winds well over 100 knots (Ahrens and Henson, 2018). Microbursts can cause damage such as uprooted and fallen trees and even building damage if it's strong enough.

Microbursts can be extremely hazardous to aircraft flying at lower levels because of the horizontal wind shear. If an aircraft were to fly into a microburst, it would first encounter a headwind which would generate extra lift and cause the aircraft to climb. The aircraft would then encounter a downdraft or tailwind, and this downward air can be strong enough to force an aircraft to accelerate toward the ground. Areas that experience regular thunderstorms have radar systems that are able to predict low-level wind shear so that more severe conditions can be anticipated and avoided.

On January 18, 2001, a Boeing-737 encountered microburst wind shear at 0729 EST while conducting a go-around from runway 19 during an intense thunderstorm... As the aircraft passed 1,000 ft during the landing approach, it encountered rain and some isolated hail. The approach lighting for runway 19 was visible to the crew, and the pilot in command elected to continue the approach. At about 500 ft, the weather deteriorated rapidly, and the aircraft encountered hail and turbulence. The pilot in command discontinued the approach and applied go-around engine thrust...The crew then diverted the aircraft to another airport where it landed without further incident (Editor, 2017).

References

Ahrens, C. D., & Henson, R. (2018). Meteorology Today: Introductory Weather Climate & Environment, 12th Edition. Mason, OH: Cengage Learning.

Editor. (2017, February 27). Qantas – BOEING b737-400 (vh-tjx). Retrieved https://www.aviation-accidents.net/qantas-boeing-b737-400-vh-tjx/

Storm Chasers. (2019, August 11). https://youtu.be/57GsZ50n7Jg