1.) Take an MH-9 Pawnee up to 500m on auto hover.
2.) Disable autohover.
3.) Induce engine failure by setting fuel in the aircraft to zero. (vehicle player setFuel 0)
4.) Point nose of chopper down and reduce collective to nearly zero.
5.) Pull nose back up, try to get vertical airspeed as close to -30m/s as possible.
6.) Keep chopper as level as you can with collective at nearly zero.
7.) Chopper should begin to flip out and velocity will increase to insane values, throwing the helicopter across the map or into the ground.
I also caused the game to hard crash due to this bug; the IAS increased to a value that couldn't be contained by the digital display number for the IAS, I'm assuming that maybe the airspeed of the chopper caused some sort of variable overflow or something, dunno. All I know is that one second my airspeed was very high, and the next I get the "ArmA 3 is not responding" box.
Explained further and illustrated in this video:
https://www.youtube.com/watch?v=Q2GYE5v7oPM