Yes, you are right. I first tried that. I figured out what is going on.

The issue is that you can't park AI jets down at the military hanger at the North end of the Altis airbase. If you do, the AI will take the plane across the grass to the South end of the stip to takeoff. There is a tower in the way of this, and the jets get stuck.

If you park the jets at the South end it works fine.