Oh and don't worry, they won't be suspicious at all of a clown with a knife getting on the plane. They'll know your beef is not with anyone on the plane.
"A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?"