Wind Shear
Aircraft safety is a major concern in aviation; in General Aviation, Military and Commercial Aviation, where passengers in airliners rely on the safe systems and qualified pilots. Each time there is an accident or a minor incident in aviation the NTSB looks to find out what the cause was. One of the most dangerous situations in aviation besides mid-collisions and near misses; is Windshear.
The occurs win the normal relative airflow change greatly in speed or direction as you either as change altitude or are simply flying forward and all of a sudden the wind is going a different way. Most experienced pilots have experienced this many times in their careers. In fact you may have noticed this phenomena yourself in a parking lot, it happens all the time. Have you ever observed or noticed flagpoles, which are quarter mile apart. One flag is blowing one direction and another is blowing a different direction. Yet they should be blowing the same way right? Indeed they should, but they are not always are they. Sometimes this is due to terrain and sometimes it is due to buildings in the way, while other times you are simply witnessing the exact problem pilots encounter when they try to fly through such situations.
