[••• ĤБĶБM •••]

Create a Dini INT that actually saves your plane model, and when the player connects, load he's plane - And OnPlayerStateChange, just add that if player's model and the keys are the same of the vehicle or not, if the same, let the player enter it - If not, remove the player from the vehicle.

That's it, just script it. It's really really really easy!