Have you tried, using AF to hit your subject, then moving to MF and staying there during flight. Unless you are shooting on a subject very close, the DOF on the camera should hold though out your flight.
I personally don't trust the AF for anything more than registration of focus. I move to MF for flight or stills. I also check focus a lot during a flight (switching back to AF, getting confirmation then moving back to MF).
Just curious what happens if you move to MF after using AF to get focus confirmation. I have have no luck with true MF on the P4 with an iPad as you just can't see enough fine details, at least I can't.
Paul C