This is a script-heavy non-ideal solution, but should work:
Use eventhandlers on planes (or a looping monitoring script) that always keeps their damage set to zero (undamaged). And keep an array of plane objects and corresponding damage values, to track what the damage should be for each plane (each time a plane is hit, add the damage to the damage array value). Your script can then destroy the plane, or disable it with a very high damage score, when the damage array value reaches some threshold.
If you want damaged planes to smoke, you could add an effect when the damage array value reaches some threshold.
This would allow the game engine to think "no support needed", but the planes are still not invincible, because you are managing their damage via scripts.
If this works for you, I want another Oscar for my mantle!