There are many different reasons why airplanes crash. The two main ones are of course during take off and landing. For the most part take offs are relativity easy and safe. There are a number of things that can go wrong of course. A couple of examples would be rubber malfunction, or failure for the yoke to lift, and possibly a sudden burst from on engine or turbine. Landing, being slightly more dangerous also has its risks. The plane can pitch downward from a sudden gust of wind, the landing gear could fail or the ailerons could tip the plane on its side. While in the air its even harder to bring down a plane. Turbulence is experienced in practically every flight, if the winds are strong enough the plane can pitch over and crash or in extreme circumstances break the wings or tail. Lighting also hits planes frequently usually with little effect. Most lightning strikes are absorbed by the plane and the instruments in the plane might malfunction slightly. Still, the lightning could short circuit the engines or props and light them on fire bringing the plane down. There are many things that cause airplane crashes but they rarely happen and airplanes are still a very safe way of travel for anyone.