Wind shear is a sudden change in wind speed, direction, or both over a short distance. In aviation, it matters most during takeoff and landing, when aircraft fly low and slow with little margin for error. A plane flying through wind shear can gain or lose airspeed rapidly, sometimes dozens of knots in seconds, making it one of the most dangerous weather hazards pilots face near the ground.
How Wind Shear Works
Wind shear comes in two forms. Vertical wind shear is a change in wind speed or direction as you move up or down through the atmosphere. You might have calm winds at the surface and a 40-knot breeze at 1,000 feet. Horizontal wind shear is a change at the same altitude, where wind conditions differ sharply across a short lateral distance. In practice, pilots often encounter both at once.
The concern isn’t the wind itself. Planes handle strong, steady winds without trouble. The danger is the rapid transition. When an aircraft passes through a shear zone, its airspeed (the speed of air flowing over the wings, which generates lift) changes faster than the plane can accelerate or decelerate. For a few critical seconds, the aircraft may not have enough lift to maintain altitude.
What Causes It
Several weather phenomena produce wind shear, but the most dangerous is the microburst. A microburst is a column of rapidly sinking air that hits the ground and fans outward in all directions. The entire event, from the start of the downdraft to the dissipation of intense shear, lasts only 15 to 20 minutes. The shear reaches peak intensity within about 5 minutes of the downdraft striking the surface. Wind speed differentials within a microburst can reach 80 knots, roughly 90 miles per hour of difference across just a few kilometers.
A microburst is especially treacherous because it creates a trap. A plane flying through one initially encounters a headwind, which temporarily increases airspeed and lift. The pilot may even think conditions are favorable. Then the aircraft hits the downdraft at the center, losing altitude, followed by a tailwind on the other side that slashes airspeed. This sequence, headwind to downdraft to tailwind, can push a plane toward the ground at the worst possible moment.
Thunderstorms are the most common source of microbursts, but wind shear also comes from frontal boundaries, where different air masses collide. Temperature inversions, which often form on clear nights when the ground cools rapidly, create layers of air moving at different speeds and directions. Mountain waves, generated when wind is forced over a ridge, can produce strong gusts and shear on the downwind side that extend across nearby runways. Even the outflow boundary from a distant storm can create shear at an airport with clear skies overhead.
Why Takeoff and Landing Are Most Vulnerable
Low-level wind shear, defined as a change of 10 knots or more per 100 feet in a layer more than 200 feet thick, occurs within 2,000 feet of the surface. This is precisely where aircraft are configured for approach or have just left the runway, flying at their slowest speeds with the least room to recover.
On approach, a shear from headwind to tailwind causes airspeed to drop, the nose to pitch down, and the aircraft to sink below its intended glide path. If the pilot raises the nose to compensate, airspeed drops even further. Adding engine power helps, but jet engines take several seconds to spool up to full thrust. In those seconds, the aircraft may touch down short of the runway, too slow, and too hard.
The opposite scenario is also problematic. If calm conditions suddenly shift to a headwind, airspeed spikes, the nose pitches up, and the plane balloons above the glide path. It lands long, potentially running off the end of the runway. Neither outcome is survivable at the extreme end.
How Airports Detect Wind Shear
Modern airports use layered detection systems. The Low-Level Windshear Alert System, or LLWAS, is a network of pole-mounted wind sensors positioned on and around the runway. These sensors feed real-time wind speed and direction data to a central station inside the control facility, which runs algorithms to identify hazardous patterns like microbursts and gust fronts. When the system detects a threat, it generates alerts that air traffic controllers relay directly to pilots.
Terminal Doppler Weather Radar (TDWR) provides a more detailed picture. Designed specifically to scan for low-altitude hazards, TDWR has a range resolution of 150 meters for wind data, nearly twice as fine as standard weather radar. It covers an area up to 90 kilometers from the airport and can detect wind shifts over runways, shear along approach and departure corridors, and downbursts before they reach the surface. Together, LLWAS and TDWR give controllers and pilots advance warning that would have been unavailable a few decades ago.
Onboard systems add a final layer. Most commercial aircraft carry predictive wind shear radar that scans ahead of the flight path and alerts the crew with both visual and audio warnings, giving them seconds to react before entering a shear zone.
What Pilots Do During a Wind Shear Encounter
The FAA’s wind shear recovery procedure centers on two priorities: maximum thrust and controlled pitch. If a pilot encounters shear after liftoff or during approach, the immediate response is to push the engines to full power, disengaging autothrottle if needed. Overboost (pushing engines beyond normal limits) is acceptable if the alternative is hitting the ground.
Simultaneously, the pilot pitches the nose up toward 15 degrees. This is not intuitive. In normal flying, pulling the nose up at low speed risks a stall. But in a wind shear escape, maintaining or gaining altitude matters more. Pilots are trained to use intermittent stick shaker activation (the vibration warning that a stall is near) as the upper pitch limit. If the plane shakes, they hold. If it stops shaking, they pitch up further. Flaps and landing gear stay where they are until the aircraft has safely cleared the shear.
If wind shear is detected while the plane is still rolling down the runway, pilots rotate at normal speed toward 15 degrees. If the normal rotation speed hasn’t been reached and only 2,000 feet of runway remain, they rotate anyway and increase pitch beyond 15 degrees if necessary to get airborne. The overriding principle is that pitch control, not thrust alone, is the most important factor in surviving a wind shear encounter.
How Wind Shear Gets Reported
Pilots report wind shear through a system called PIREPs (pilot weather reports). Any airspeed fluctuation of 10 knots or more within 2,000 feet of the surface triggers an urgent report, classified as UUA. Fluctuations below 10 knots are filed as routine. A typical report might read “LLWS +/-15 KT SFC-008 DURC RY22 JFK,” meaning the pilot experienced 15-knot fluctuations between the surface and 800 feet during approach to runway 22 at JFK.
These reports feed into the broader weather briefing system, so subsequent pilots approaching the same airport receive timely warnings. Combined with LLWAS alerts and TDWR data, this creates a real-time picture of shear conditions that simply didn’t exist before the 1990s. The result has been a dramatic reduction in wind shear accidents, transforming what was once one of aviation’s deadliest hazards into one that is well understood, actively monitored, and survivable when encountered.