Wind shear is a difference in either wind speed or direction over a fairly short distance in the atmosphere. Wind shear can be divided into two different types: horizontal and vertical wind shear.
Wind shear
Aircraft hazards
If an aircraft enters an area with wind shear, its movement adapts to the suddenly changed wind direction and strength only with a delay. This means that, depending on the wind direction, the wings initially experience additional lift or loss of lift due to increasing or decreasing airflow. Horizontal wind shear can occur at the gaps of hill chains and large rows of buildings, as well as being the result of a microburst (downdraft, or vertical wind shear), which is deflected into a horizontal direction (outflow) at ground level.
The driving force is large differences in air pressure, with the wind movement acting as a counterbalance. Near the ground, this weather phenomenon is a potential hazard both during take-off and landing of aircraft.
Examples
In December 1992, a McDonnell Douglas DC-10 on Martinair Flight 495 crashed due to wind shear at Faro. Another example is Lufthansa Flight 2904. The Airbus A320 was caught by wind shear during landing in Warsaw in September 1993 and subsequently taxied beyond the end of the rain-soaked runway. In August 1985, Delta Air Lines Flight 191 was struck by wind shear. This forced the Lockheed L-1011 TriStar to the ground and it moved across a highway, killing a motorist before exploding near the Dallas airport. 134 people died, only 29 survived. That flight sparked intense research into early detection of wind shear. They can now be detected in part by ground-based Doppler radar or LIDAR. On board, they can usually only be detected by the Ground Proximity Warning System (Mode 7) when flying in.
See also
- Shear layer
- Downburst
- Down gust