Wind shear is a sudden change in wind speed, direction, or both over a short distance. It occurs horizontally, vertically, or in both planes at once.
How It Works#
Wind shear forms when two air masses with different speeds or directions meet. The boundary between them creates a zone where wind conditions shift rapidly. This shift can be gradual or nearly instantaneous.
The most dangerous form is low-level wind shear (LLWS), which occurs below 2,000 feet AGL (above ground level). At this altitude, pilots have little time and little room to recover from an unexpected change in performance.
Microbursts are an especially severe type. A microburst is a concentrated downdraft that spreads outward when it hits the ground. An aircraft flying through one first encounters a strong headwind that boosts lift, then almost immediately hits a tailwind that destroys it. The entire event can last under two minutes.
Wind shear also appears near jet streams, frontal boundaries, mountain waves, and temperature inversions. An inversion is a layer where warm air sits above cool air, trapping the cooler air below. The wind speed difference across an inversion layer can be dramatic.
Example in Aviation#
A Boeing 737 is on final approach to land. The tower reports calm winds at the surface. Unknown to the crew, a microburst sits directly on the runway centerline. At 800 feet, the aircraft suddenly gains 15 knots of airspeed as it enters the headwind. Thirty seconds later, it loses 25 knots as the tailwind takes over. The aircraft sinks rapidly below the glidepath. The crew applies full thrust and executes a go-around.
This scenario mirrors the conditions behind several fatal accidents in the 1970s and 1980s, which drove the FAA to mandate onboard wind shear warning systems and ground-based detection equipment at major airports.
Why It Matters#
Wind shear is a leading weather-related cause of aviation accidents, particularly during takeoff and landing. Pilots train specifically to recognize the warning signs and respond with the correct escape maneuver: full power, pitch to a target attitude, and accept any airspeed loss while climbing away.
Understanding wind shear is not optional knowledge. It appears on FAA written exams, in instrument and commercial training, and in every airline initial training program. Recognizing it early, and acting decisively, is what separates a close call from a catastrophe.
Key Takeaways#
- Wind shear is a rapid change in wind speed or direction over a short distance.
- Low-level wind shear below 2,000 feet AGL is the most dangerous form.
- Microbursts can flip from headwind to tailwind in under two minutes.
- The correct escape maneuver uses full power and a fixed pitch attitude.
- Ground-based detection systems and onboard alerts exist at most major airports.