Low Level Windshear Alert Systems

What is Low Level Windshear?

Windshear is a rapid change in wind speed and/or direction over a short distance, either vertically or horizontally. When this occurs below 1600 ft above ground level, it is classified as low level windshear—a particular hazard during approach, landing, and initial climb.

How Do LLWAS Work?

Low level windshear alert systems aviation setups use a network of anemometers or wind sensors positioned around the airfield. These sensors continuously measure wind data and feed it to a central processor. If the system detects significant differences between sensors, it infers the presence of windshear and issues an alert. Updates are typically provided every minute to ensure information remains current and actionable.

Where and When Does Windshear Occur?

Windshear can form in various meteorological conditions:

• Thunderstorm outflows and microbursts
• Frontal boundaries and gust fronts
• Temperature inversions, especially on clear nights
• Sea breeze convergence zones
• Strong surface winds influenced by terrain

Effects on Flight

Low level windshear can cause sudden increases or decreases in airspeed, leading to uncommanded climbs or descents, and lateral deviations from the intended flight path. These effects are particularly dangerous at low altitude, where recovery time is minimal.

Alerting and Reporting

When windshear is detected, alerts are disseminated via ATIS, direct radio, or automated systems. Reports specify the affected runway and phase of flight (e.g., takeoff or landing). Pilots must be prepared to react promptly to these warnings to maintain safety.

Avoidance and Mitigation

Flight planning should consider weather reports, forecasts, and NOTAMs for windshear risk. During flight, pilots should heed all windshear warnings and be ready to execute missed approaches or go-arounds if necessary.