Encounters with UFO's have on rare occasions resulted in the disappearance of an airplane and its pilot, never to be seen again. What happened to these pilots? Were they captured or killed? When space ships disappear, winking out in the sky in an instant, they are essentially moving into another density. We have explained that density switching has its dangers, and if the ship is programmed to switch with its surrounding airspace, the switch takes the pilot and plane with it. Thus the pilot finds himself suddenly in a 4th Density existence, without atmosphere to breathe. This is a quick and painless death for the startled pilots, who have little chance to sort it out before they lose consciousness.