Well your right it's not really realistic for the pilot to switch planes, but for some reason it is possible for the gunner.
The only reason why you would want to switch the pilot is if your pilot is wounded or one of your engines is out and the plane handles like crap (maybe a few more reasons), but basically EskimoJoe is right, you would want to switch only if you made a mistake. However if the drone pilot gets a PW (Pilot Wound) your are not effected by it, but if your main pilot gets a PW you are. So I figured perhaps make the pilot equal to the gunners and allow the pilot to do the same.