On the one hand, I’m pretty sure that act of crashing a plane isn’t illegal by itself and there isn’t a regulation that states you must get approval or coordinate with the FAA prior to a crash. But even if you manage to set things up so that you aren’t endangering the public, the moment you leave a flying plane unattended you have turned it into a UAV, and you almost certainly break the FAA’s rules on UAV operations. So if you’re going to crash a plane intentionally you have to ride it all the way to the ground :)