Probably never, because then a plane could intentialy ram you by ripping it's wings off.
Just so I have this idea correct, you wan't more realism by only having collisions when the plane you collide with is flying straight?
I Can just see the after action report.
But sir, I didn't think he would turn into me, so it's his fault that we collided, me doing a 6 g turn in a sissors had no effect on us colliding. That bloody german should have been more carefull. Can you build these spitfires so I can just fly threw the 109's? Those bloody eng. should design stronger planes. And sir they should also put in an auto pilot that automaticly avoids collision, so I don't have to watch out for collisions my self. I realy think there should be a general order sent to all friendly planes to please make sure they don't run into me, because I realy feel the entire sky is mine, and I should be able to fly how,when, and where ever I wish.
HiTech