One of the most hazardous forms of windshear is a microburst. A microburst is a concentrated, powerful, downdraft, that is typically a few hundred to 3,000 feet across. When a downdraft reaches the ground, it spreads out and forms a series of vortex rings.

Microbursts occur near convective storms. They are severe downdrafts that hit the ground with such severity that they bouce back up creating a strong updraft. If you're landing as you fly into it, you first encounter the updrafts. This will normally cause the pilot to pull back power in order to maintain the glide path to landing. The next thing that occurs is that the plane encounters the severe downdrafts; and, with the power back, the plane is even more susceptible to the downdrafts and begins to sink towards the ground. Even if the pilot reacts instantly and goes to full power, most planes don't have the power to climb out of the downdrafts. If you are taking off into one, it can either cause you to pitch up and possibly stall, or it will simply slam you into the ground.

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Curator: Tom.Benson@grc.nasa.gov
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