TWO-time US Open golf champ Payne Stewart was among five people killed when a Lear Jet crashed in the South Dakota hills on Monday after apparently flying out of control for 2400km at high altitude above the southern states of America. Air force F-16 fighter jets were scrambled to intercept the private plane as it flew north-west, but were unable to detect any sign of life behind the aircraft windows, which had frosted over, suggesting the cabin may have suffered a sudden loss of air pressure.