Sometimes you die and you don't want to. Its part of the game. Many soldiers and airmen will happily remind you it is also part of war.
Really, while FSO is intended to be more realistic than MA, you can't expect absolute realism, it simply will never happen...
At the end of the day, your job and everyone elses is to win the frame. IF that means shooting someone on the rearm, or on takeoff or landing, I would do it. As was frequently done in the real war.
I think it is silly to expect immunity from enemy fire at any time in Aces High... The one way it is most realistic is that it is a chaotic warzone...
There was a line in Band of Brothers that pretty much summed it up... "The reason you're still scared and the Captain isn't, is that you still expect to survive..."