AT THE AIRPORT...Windshear Prediction

Another dangerous situation for aircraft is windshear. Windshear has been blamed for over 30 aircraft accidents in the U.S., and the loss of hundreds of lives. After a bad windshear accident in 1985, the Federal Aviation Administration (FAA) and NASA began to work together to find a way to predict windshear, and to give pilots enough warning to take preventive action.

Windshear is a sudden shift in wind direction and speed. The microburst is the most dangerous form of windshear. A microburst is a column of cool air that creates intense downdrafts and powerful, swirling winds near the ground. If a slow moving airplane, especially one taking off or landing, passes through a microburst, the winds can cause it to lose control and plunge toward the ground.

The system that became the first in airline service is the Doppler microwave radar. It sends a radio wave ahead of the aircraft to "bounce" off of raindrops in the thunderstorm and return to the instrument. A computer measures the Doppler shift (the difference in wavelength frequency between the outbound wave and the returning signal) and tells the pilot the speed of the winds in a windshear. The pilot can then avoid the area, or adjust the speed and/or altitude of the plane.

Flight tests of the system began in 1991. Like the lightning protection project, NASA had the job of flying into thunderstorms -- 131 thunderstorms to be exact. (Anybody looking for a fun NASA career?!) These tests showed that the forward looking Doppler radar was able to provide pilots with 20-40 seconds of warning of upcoming micobursts.

In November 1994, a Continental Airlines flight was the first to carry the new windshear detection and warning system.

NASA has helped to make air travel safer for passengers and crews all over the world. Many American airlines are using the system, plus Swissair (Switzerland), Alitalia (Italy), Iberia (Spain), and Kuwait Airways.