Airplane mishaps very preventable˙̇

I watched a program about how two planes collided in air.  One pilot had rested his foot up and apparently clicked off the on-board radar.  His plane lost a tip of a wing, but was OK.  The other plane, a 737 I think, tumbled and broke up in the air.

Oh, it was the transponder that was clicked off.  I remember now.  Transponders broadcast that the plane exists and so other planes can pick up on it as they approach.