i thought of this one night. Just a war helicopter like a apache with a turret on the bottom that could be operated by the passenger and missiles could be operated by the driver. dosnt have to be a apache maybe a war helicopter that can carry players in the back area
for the police helicopters just a search light and a area in the middle for players
just thought this would be cool :)
Missile packs = very possible, you can mount weapons on vehicles and fire them (Aloshi's warplane proved this).
Turrets = currently not possible with the source code as is, but Badspot might be releasing that tank he's been working on in the next patch which will include a turret, so it might be possible after that (I can't wait
)
As for helicopters, someone was working on one but I can't remember who for the life of me, I read his post just yesterday too.