1. Helicopter can be destroyed by anybody as long as it's empty. Once the first person gets in, they're automatically the pilot, and the pilot's team can't destroy the helicopter. The pilot determines who controls the helicopter, and nobody can get into a helicopter controlled by the other team.
2. One pilot, 3 passengers. Passengers can fire their weapons and drop grenades. Any occupant can jump in or out at any time. The pilot has a fixed machine gun that points where the chopper points. It has unlimited ammo but has to cool down if it overheats.
3. Vehicles spawn in waves in random locations on either side. Each team has 2 helicopters, and when a helicopter "dies", it has to wait for the next wave to respawn. If a helicopter is captured by the enemy, it will still respawn on the friendly side, but only after it "dies".
4. Any occupant can be killed individually. If the pilot dies or leaves the helicopter, it starts to crash, taking damage when it lands according to how far it fell. However, any passenger can take the pilot's position by pressing a hotkey.
5. If the pilot dies or leaves, but the helicopter is still occupied, the helicopter is still controlled by the passenger's team. The helicopter must be cleared before the other team can pilot it.
6. The helicopter should be extremely tough, so that the best way for a single player to destroy it is by trying to shoot all the occupants. However, two or more players working together should be able to bring it down by brute force using SMGs.
EDIT: 7. The helicopter body should be made of different pieces (i.e. main body, tail, rotor), and different parts of the helicopter should have different armor levels. Hitting different parts should do damage to those parts independently, and if any critical part reaches 100% damage, the whole helicopter is destroyed.
