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Wow! Tracking points! This will be very useful indeed!

The mod is definitely incomplete (no autopilot, automatically changes character to Michael, etc), but one way to work around it for now is when flying, keep the plane level, then select the 'Freeze Vehicle' option in Simple Trainer (other trainers may have this too). Then you can go ahead and activate it with F10 and change your character to whatever you want with the trainer. The plane would be sitting still, though, and it would be nice to be able to walk around when the plane is actually flying around, but I guess this is all we can do for now to be able to walk around while in the air.