Wind shear is an abrupt and often invisible movement of air, the most dangerous of which is the microburst. A microburst is a shaft of cold air that moves at high speed (up to 100 kph) towards the earth's surface, often from thunderstorms, spreading in all directions as it reaches the ground. Meteorologists have been able to predict certain types of wind shears (mainly those associated with warm and cold fronts, low-level jet streams, and mountains) for a number of years, but there has emerged a newly identified and treacherous type of wind shear is a downward surge of air that, striking upon the earth, spreads out in all directions. Wind shears do damage to the environment, to man-made structures, to migratory birds, and are a hazard to aviation. In aviation, wind shears play havoc with an aircraft's aerodynamics by dispersing air in all directions. An aircraft moving into this formation at low level (take off or landing) will encounter winds that will tend to lift it at first, and an unsuspecting pilot will slow the throttle. But once the plane reaches the other side of the shear, where the winds are moving with equal force in the opposite direction, it will be slowed suddenly, often to the point where the pilot cannot throttle quickly enough to avert a crash.
USA scientists blame 28 accidents, accounting for 491 deaths and 206 injuries to windshears since 1964, not including an August 1985 crash which killed 132 people and in which windshear was suspected.