Low-level windshear alert system

A low-level windshear alert system (LLWAS) measures average surface wind speed and direction using a network of remote sensor stations, situated near runways and along approach or departure corridors at an airport.

Arriving aircraft on descent, generally within six nautical miles of touchdown will fly within this low level, maintaining a glide slope and may lack recovery altitude sufficient to avoid a stall or flight-into-terrain if caught unaware by a microburst.

Air traffic controller (ATC) users at local, ground and departure positions in the ATCT relay the LLWAS runway specific alerts to pilots via voice radio communication.

LLWAS wind shear and microburst alerts assist pilots during busy times on final approach and on departure, often when heavy traffic, low ceilings, obstructions to vision, and moderate to heavy precipitation add to the difficulty in determining in just a few seconds whether mounting wind and weather hazards should be risked or avoided.

The LLWAS-RS program began in response to the National Transportation Safety Board (NTSB) investigation of the USAir Flight 1016 accident at Charlotte, North Carolina, in 1994.

From that accident, a determination was made that LLWAS-II must regain and retain its original capability, often degraded by tree growth and airport construction such as hangars that obstruct or deflect wind near LLWAS remote station sensors.