Definition
A ground-based system installed at certain airports that uses a network of wind sensors positioned around the airfield to detect sudden changes in wind speed or direction near the surface. When the system detects a significant difference between sensors, it alerts air traffic controllers, who then pass wind shear warnings to pilots arriving or departing.
Plain English
A set of wind sensors around an airport that watches for sudden, dangerous wind changes near the ground and warns the tower so they can warn pilots.
Context Anchor
Pilots encounter LLWAS information in tower reports, airport weather discussions, and alerts given before takeoff or landing.
Derivation
“Shear” comes from the idea of cutting or sliding. In weather, wind shear means nearby layers or areas of air are moving differently, as if the wind pattern has been sharply split or shifted.
Why Pilots Care
Wind shear can cause abrupt loss of airspeed and altitude near the ground, a known factor in approach and departure accidents; early detection allows pilots to delay or adjust the flight path.
Grounding Statement
Picture an airplane just above the runway flying from one patch of wind into another patch that is moving a different speed or direction.
Intuition Check
“Low level” does not mean a minor alert. Here it means the wind change is close to the ground, where takeoffs and landings happen.
Example Sentence 1
Tower advised, "LLWAS alert, north boundary wind two-seven-zero at fifteen, south boundary wind one-five-zero at twenty-five," so we elected to go around and hold until conditions stabilized.
Example Sentence 2
We reviewed the current LLWAS status as part of our departure weather package before engine start.