I think the problem is that the visual you see doesn't always accurately reflect the degree of damage.
Sometimes a rather minor amount of damage seems to trigger a big visual damage. In this case the plane remains flyable.
It's been discussed before, both here and in gameplay I think. You might do a search because I don't remember if HTC said anything in those threads or not.
It's just one of those "things" to me. Sometimes I get home, sometimes I don't.
Oh, yeah... you do use rudder and aileron trim to help out with wing damage?