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Windshear in Aviation: Understanding the Invisible Threat

Few weather phenomena pose as serious a hazard to aviation as windshear. Unlike turbulence that can be anticipated near mountains or thunderstorms, windshear is often sudden, invisible, and powerful enough to overwhelm even the most capable aircraft. For pilots, especially during takeoff and landing, recognizing and respecting windshear is essential to safe flight.



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What is Windshear?

Windshear is defined as a sudden change in wind speed and/or direction over a short distance. This change can occur horizontally or vertically, and at any altitude.


While windshear can happen anywhere, it is particularly dangerous at low altitudes, where an aircraft has little time and space to recover. A rapid shift from headwind to tailwind during climbout or final approach can rob an airplane of lift, causing a sudden sink that may lead to controlled flight into terrain (CFIT).


Types of Windshear

1. Low-Level Windshear

Low-level windshear is typically defined as occurring below 2,000 feet AGL, where aircraft are most vulnerable. It can be caused by:

  • Frontal Boundaries: Strong cold fronts and warm fronts can create sharp wind shifts.

  • Temperature Inversions: A layer of warm air above cooler air can trap wind changes, leading to shear.

  • Obstacles and Terrain: Buildings, hangars, or natural terrain can create localized shear around airports.

  • Thunderstorms: The strongest and most hazardous source, particularly near downdrafts and outflow boundaries.

Impact on Pilots:

  • On takeoff, an aircraft may encounter a strong headwind that suddenly shifts to a tailwind, reducing airspeed and climb performance.

  • On approach, a sudden loss of headwind component can cause the airplane to sink rapidly below the glide path.


2. Microbursts: The Deadliest Form of Windshear

A microburst is an intense, localized downdraft of air from a thunderstorm that spreads out rapidly upon hitting the ground. Microbursts can generate winds in excess of 100 knots and last for 5 to 15 minutes.

  • Structure of a Microburst:

    1. Strong downdraft hits the ground.

    2. Air spreads outward in all directions, producing an initial headwind.

    3. As the aircraft flies through, the headwind suddenly turns into a tailwind.

  • Effects on Aircraft:

    • Initial headwind may cause the aircraft to balloon upward, tricking pilots into reducing power or pitch.

    • The sudden transition to tailwind then causes a rapid loss of lift, often when the aircraft is already at low altitude.

    • Even maximum thrust may not be enough to recover in time.

  • Notorious Accidents:Several high-profile accidents in the 1970s and 1980s—such as Delta Air Lines Flight 191 (1985)—were caused by microbursts. These tragedies led to major advancements in detection and pilot training.


Detection and Avoidance

Ground-Based Systems

  • Low-Level Windshear Alert Systems (LLWAS): Installed at many airports to detect sudden changes in wind between sensors.

  • Terminal Doppler Weather Radar (TDWR): Detects microbursts and gust fronts near airports.

  • Weather Forecasts and SIGMETs: Provide warnings of potential windshear conditions.


Cockpit Systems

  • Airborne Weather Radar: Can identify thunderstorm cells, allowing pilots to avoid convective areas where microbursts are likely.

  • Predictive Windshear Systems: Many modern aircraft use radar to detect hazardous wind patterns ahead of the aircraft, providing alerts before entry.


Pilot Response to Windshear

Pilots are trained to follow strict procedures when encountering or anticipating windshear:

  • Before Takeoff:

    • Review weather reports and forecasts for windshear advisories.

    • Delay takeoff if thunderstorms or gust fronts are near the departure path.

  • During Approach or Landing:

    • Be alert for rapid airspeed, vertical speed, or ground speed changes.

    • If windshear is reported or suspected, consider a diversion.

  • If Encountered:

    • Apply maximum available thrust immediately.

    • Maintain pitch attitude as directed by aircraft-specific windshear guidance.

    • Do not attempt to regain lost airspeed until safely clear.

    • Avoid abrupt configuration changes (gear/flaps) that could worsen the situation.


Key Takeaways

  • Windshear is a rapid change in wind direction or speed that can occur at any altitude but is most dangerous close to the ground.

  • Low-level windshear often occurs near fronts, inversions, or terrain, and poses a major hazard on takeoff and landing.

  • Microbursts are the most violent form of windshear, with powerful downdrafts and wind shifts capable of overwhelming aircraft.

  • Detection technology and pilot training have dramatically improved safety, but avoidance remains the best defense.


Final Thoughts

For pilots, windshear is one of those hazards that demands respect. It cannot be seen, and it often provides little to no warning. But with an understanding of how it forms, how it affects aircraft, and how to respond, aviators can make informed decisions that keep themselves and their passengers safe.


In aviation, knowledge is power—and when it comes to windshear, it’s also protection.



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