How About a combonation of the two?
I believe every time you hit a target (each bullet) you produce X amount of damage to the enemy where you hit him.
How about if you hit a freindly target, the system calculates the hits and if the total was enough to shoot the friendly plane down, you get a PNG warning. Then, if you do it again, you get a PNG status for 24 hours and are unable to load weapons during that period.
This could solve all the Kill Shooter whining and would prevent someone from getting a PNG status for a single stray bullet that happened to ping a friendly in the heat of battle. It would also prevent all those "Over the Shoulder" shooters from getting too crazy, as they would have to look out for PNG.
This should be far better than getting your ammo load instantly set to zero, or having your plane freeze in space for X seconds. The battle could still be finished, but when you tried to re-arm or start a new flight, you wold get "Sorry you are PNG for XX:XX minutes"
Also, all those PNG guys could fly goons if they still needed the AH fix.