[Suhiir]

Aircraft just plain don't have the capability to perform air-to-air combat as that's totally outside the scope of WinSPMBT plus there is never more then one aircraft on map at the same time.
On rare occasions aircraft do attack helos, but its merely because that's what they saw first and the helo had been stationary the previous turn.

On top of which there's no way to designate a specific target for aircraft in WinSPMBT.

Until they get about 3-4 armor helos are pretty fragile, in fact with 0 armor (as most have) it's often argued too fragile. Once they get 4 armor they become very very difficult to damage with MPADs or even .50 cals, one of the things that makes Hinds and Apaches so "fun".