Making a unit firing at something, even an enemy, is some of the most difficult things on Arma because your script will always be "overridden" by Arma's engine.
Anyway, let's say you have a waypoint ("move" is the simplest and OK) to fly by the enemy car.
Let's say also, this car has a "careless" behavior just to avoid it hiding somewhere! Yes Arma engine does that!
As your blackfish has no centered gun but only fitted on side of the aircraft, it will be a pain in the b.. to obtain a clear aiming for the gunner.
What I did, and it works sometimes but not 100%, is to script something like:
0 = [] spawn {
while {alive gunship1 && alive car1} do {
group gunship1 reveal [car1,4];
gunner gunship1 lookAt car1;
gunship1 doWatch car1;
gunner gunship1 doTarget car1;
if (gunship1 aimedAtTarget [car1] > 0) then {
gunship1 fireAtTarget [car1]
};
};
};
so no chance for a shot at the target..