If you buy a low car, like the new Zentorno and drive under the private jet plane (with pilot in it), the plane will be flying full speed immediately!
He might just fly in one direction until he's out of sight, but sometimes he'll crash into buildings, and sometimes he'll chase you!
It's a really fun thing to do and very easy as well!
I've tried to do this in single player, but the pilot would just get out of the plane and chase you on foot, so I'm pretty sure this can only be done in Online!
Example + How to: