1. Start attached rotor_breaking_repro.VR mission in editor
2. After mission starts, activate "Ejects unit" action to have all units eject out of helicopter.
3. In most cases this causes rotor to get destroyed and engine to instantly stop making helicopter fall down with more and more increasing speed.
If fails, try again, it should happen most of the time.
Repro video: http://youtu.be/vlgCoydiM8k