On 9 May 1952, Major Neil H. Lathrop (chief of Flight Test Operations at Edwards) took 686 up on a functional test flight. He took off from Edwards AFB at 0753, escorted by a F-86 chase aircraft. After approximately 20 minutes, the chase was relieved of his duties, and returned to base. Lathrop continued his test mission for about 10 more minutes. He then called the tower and requested permission to make some low-altitude, high-speed flybys over the South Base Runway for the benefit of a motion picture crew that was filming activities at the Air Force Flight Test Center.

Permission was granted, and Lathrop made his first pass from west to east. After two more passes were completed, he reversed course. Lathrop initiated a pass from east to west, at a slightly lower speed. His altitude was approximately equal to the height of the control tower. As the aircraft passed the western end of the ramp area, the pilot raised the nose of the XB-51 slightly, and initiated an aileron roll to the right. The roll appeared normal until the aircraft became inverted. At this point, the XB-51 appeared to "dish out" of the roll, striking the ground in a left-wing-low, slightly nose-down attitude. The crash was followed by an explosion and fire, completely destroying the aircraft and killing Major Lathrop. The cause of the accident was attributed to pilot error.