Sure, you could opt to use an aircraft's weapons when in an aircraft. Or, you can use the altitude to your advantage as a sniper, as sSantzuu does here in Battlefield 3. One of these options is more impressive, if not more dangerous than the other!
I wonder which is more difficult—sniping while falling from an aircraft, or sniping a pilot from the ground?
Battlefield 3 End Game - HelicopterSniper [sSantzuu]