Microbursts are when thunderstorm winds are concentrated into a small area and then crash to the ground violently. Microbursts have been responsible for airplane crashes and for damage to buildings that resemble a tornado.
These bursts of wind develop when dry air is entrained into a thunderstorm and then it evaporates some of the raindrops in the storm. Evaporation is a cooling process and when the raindrops evaporate a cold pool of air is the result.
This pocket of air is colder than the surrounding air and is also heavier and because of this the colder air collapses rapidly to the ground. If the microburst slams to the ground straight on, the wind will spread out like a drop of water splashing on the cement. After the microburst hits the ground, it spreads out and eventually the air begins to rise again. This can give airline pilots problems, especially when landing.
Delta flight 191 crashed at Dallas/Ft Worth International Airport on August 2, 1985. Only 30 passengers out of the 163 survived the crash. What tends to happen is when an airplane is landing it runs into a head wind, which forces the plane to rise. The pilot will then compensate for this and point the noise of the plain towards the ground.
Then the airplane hits the down draft portion of the microburst, lift is lost, and the plane could crash. Today, pilots are trained for this and microburst can be detected ahead of time before the plane lands.