The original LLWAS system ( LLWAS I ) was developed by the Federal Aviation Administration ( FAA ) in 1976 in response to the 1975 Eastern Air Lines Flight 66 windshear accident in New York . LLWAS I used a center field anemometer along with five pole mounted anemometers sited around the periphery of a single runway . It was installed at 110 FAA towered airports between 1977 and 1987 . Windshear was detected using a simple vector difference algorithm , triggering an alarm when the magnitude of the difference vector between the center field anemometer and any of the five remotes exceeded 15 knots . The LLWAS II deployment included software and hardware upgrades to the existing LLWAS I to improve the windshear detection and reduce false alarms . Between 1988 and 1991 , all of the LLWAS I systems were upgraded to be LLWAS II compliant . Windshear deployment studies conducted from 1989 through 1994 determined at which LLWAS-II sites weather exposure justified upgrade to a weather radar ( Terminal Doppler Weather Radar ( TDWR ) or Weather Systems Processor ( WSP ) ) an LLWAS Network Expansion ( LLWAS-NE ) or LLWAS-Relocate/Sustain ( LLWAS-RS ) upgrade , singly or in combination . By 2005 all LLWAS-II had been decommissioned for one of these replacement wind shear detection systems or for two in combination . The LLWAS-NE added the ability to cover more than a single runway , using up to 32 remote stations to provide runway specific alerts for parallel and crossing runways at ten large airports in combination with TDWR . The LLWAS-RS further upgrades service at 40 remaining LLWAS-2 operating sites ( not justified for a radar solution ) to employ LLWAS-NE algorithms and extend service life by 20 years , in part by adding ultrasonic anemometers with no moving parts . 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
USAir Flight 1016
USAir Flight 1016
Low-level windshear alert system