Golfer Payne Stewart’s jet crashed in 1999. It appears that the pilot and copilot went unconscious during the flight. Air traffic controllers were unable to communicate with the pilots, and two Air Force jets were sent to investigate.
As they pulled alongside Stewart’s jet they could not see any movement in the cockpit, but they could see that the windows were fogged up. It appears that somehow the cabin lost pressure allowing cold air from the stratosphere in the plane. After the plane ran out of fuel it plunged to the earth below.