United Airlines flight 736, a Douglas DC-7, crashed following a mid-air collision with a USAF North American F-100F Super Sabre near Arden, NV, USA, killing all 49 occupants on both aircraft. Flight UA736, a Douglas DC-7, took off from Los Angeles, California at 07:37 on an IFR flight to New York-Idlewild Airport with a planned cruising altitude of FL210. At about 07:45 a US Air Force North American F-100F-5-NA Super Sabre fighter (56-3755) took off from Nellis Air Force Base on an instrument training flight. During the exercise the flight was executing a simulated jet penetration in the area of Las Vegas, NV. At 08:30 the fighter plane pilot reported that they were descending from FL280 near the KRAM radio station. At the same time, United flight 736 was approaching the Las Vegas VOR. Both aircraft collided at FL210, 9 miles south west of the Las Vegas VOR station on Victor Airway 8. Initial contact occurred between the leading edge of the DC-7 right wing and the leading edge of the F-100 right wing, 132 inches outboard of the aircraft centreline. It was determined that the DC-7 was flying at about 312 knots on a 23 degree heading and the F-100 at 444 knots on a 145 degree heading. Assuming a small descent angle of the F-100, the closure speed was about 665 knots. Both planes crashed out of control. PROBABLE CAUSE: “A high rate of near head-on closure at high altitude; human and cockpit limitations; and the failure of Nellis Air Force Base and the Civil Aeronautics Administration to take every measure to reduce a known collision exposure.”