Just an odd thought, what if there's still a penalty, but a little different than killshooter... bear with me a moment on this idea of lunacy =)
Instead of killshooter, what do you think of this...
The friendly hit takes damage as he would if were enemy. The shooter, upon landing gets 0 perks (or negative if they die), 0 towards score, does NOT display on the bar if they land multiple kills, and takes a time penalty before next allowed takeoff such as 5 minutes for first offense, 60 minutes for 2nd offense, 3 hours for 3rd offense for any vehicles with ENY under 40.
This way, the friendly would still go down, which is realistic. The shooter would be penalized and get nothing positive for the kill (ESPECIALLY no "name in lights" notification), and now are limited to taking planes which, while may be somewhat effective, are not "uber" aircraft, putting him at a disadvantage.
This way, if the guy GETTING shot down was shot down because he was too agressive (i.e. diving within the gun path), he is penalized by losing his plane. The Shooter is penalized as well, and the overly agressive will now understand they have to keep themselves in check if they want to pilot specific planes. Mistakes will still happen, but I think this can be an incentive to both not TK (team kill), but also not get in the way of someone else's shot.