If you want players to destroy a friendly vehicle (like a downed plane or chopper) without it counting as a friendly kill:
- Place the chopper or plane
- Lock it. Locking the object will prevent any player from entering it and hence making it friendly again
- Set the damage as desired
- Place an enemy unit on the map, and make its spawn probability zero
- drag and drop the unit into the pilot seat of the plane or chopper
This will make the object hostile, even though the dummy pilot will not spawn. It will mean you don’t get friendly fire score, and AI will not engage you.