This is quite difficult to reproduce as it seems to rely on a number of factors, such as PHYSX, client connection to the server and type of mission.
However, this seems most common on Wasteland, Invade & Annex, Domination and Life servers, where a large group of players bundle into a helicopter, the get-in animation seems to cause the problem and cause the player to 'glitch' into the rotors of the aircraft and cause it to become disabled (MROT collision).