FAA Airline Transport Pilot (ATM)Meteorology and Weather ServicesHard
An airport's Low-Level Wind Shear Alert System (LLWAS) issues an alert to air traffic control indicating wind shear on the approach end of the active runway. What does this ground-based system primarily use to detect the wind shear condition?
- APilot reports (PIREPs) collected exclusively from departing flights
- BSatellite-based temperature and moisture soundings updated hourly
- CAirborne Doppler radar carried aboard arriving aircraft transmitting data to the tower
- DA network of surface wind sensors positioned around the airport perimeter that compares wind vectors between sites
Show answer & explanationAnswer & explanation
Correct answer: D. A network of surface wind sensors positioned around the airport perimeter that compares wind vectors between sites
LLWAS relies on a network of anemometers, typically 5 to 32 sensors, placed around the airfield including near the runways. The system compares the wind vector at a centerfield sensor to those at the perimeter sensors; a significant difference indicates wind shear and triggers an alert to the tower.
Why the other options are wrong
- A. LLWAS operates continuously via sensors, not by relying on pilot reports.
- B. Satellite soundings are unrelated to LLWAS, which is a surface-based sensor network.
- C. Airborne Doppler radar describes systems like TDWR or onboard predictive wind shear radar, not LLWAS.
Low-Level Wind Shear Alert System (LLWAS)
A ground-based network of anemometers around an airport that detects wind shear by comparing wind vector differences between a centerfield sensor and perimeter sensors, alerting ATC and pilots.
- Uses 5 to 32 wind sensors depending on airport configuration
- Compares centerfield wind vector to remote sensor sites
- Complements airborne and Terminal Doppler Weather Radar (TDWR) wind shear detection
Memory trick: LLWAS = a ring of wind gauges 'listening' for mismatched winds around the field