Game Version number: 1.3.0.18
Modded: No

Objects like smoke grenades (when thrown) and supplies (when dropped, physically appearing in the world) collide with helicopters blade, breaking them. It's very easy for people to grief pilots by throwing smoke grenades on the main rotor to break it, or dropping the supplies from the helicopter (which spawns them on top of the main rotor first) to break the main rotor.