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
Eastern Air Lines Flight 66
Eastern Air Lines Flight 66
Low-level windshear alert system