The AI can fly on its own, small tutorial here!

I found out just now that you can make the AI fly on its own. You'll need the Cessna Skyhawk mod and a fair amount of skill.
1. Start in the cessna plane, then spawn a new vehicle, it should be the default one and it should spawn under the left wing. You ought to be in control of the pickup, park it behind the plane as per the pic.

2. This bit has to be done quickly, change the AI to flee, start driving and when it is about 50m away change the ai mode to chase. This makes the AI brake, which is the control to pull up in the Cessna.

3. Keep driving, and watch that birdy fly!!

4. Take pretty pictures.

Have fun!

 

It's the flee, then chase combination I think. If you are directly behind it when chase is enabled the AI slams on the "Brakes" which pulls up in the plane, ergo flight! Or at least, that's my theory...