The moment you disable a helicopter or a jet with a accurate AA-missle (or others) and it crashes this now shows as an action caused by the the pilot.
It seems more logical that vehicles that receive critical damage by someone and crashes because of this critical damage should be "credited" to the person doing the damage.
A certain unfairness goes to the pilot now since he gets marked a teamkiller when he was transporting soldiers across the map and was unable to crashland his vehicle after his vehicle got disabled.