X-15 accidents and the end of the program

The X-15 flew 199 times and took one pilot's life in flight. Two accidents shaped the program: the Mud Lake landing in 1962 and the loss of Michael Adams in 1967.

9 November 1962: Mud Lake

After an engine failure, Jack McKay landed X-15-2 on Mud Lake, Nevada. The landing gear collapsed and he was seriously injured. McKay later retired because of his injuries. The airframe was rebuilt as the X-15A-2, which went on to fly Mach 6.7.

8 June 1966: Joe Walker

Joe Walker, who held the altitude record, was killed in a mid-air collision during a formation flight with an XB-70. That was not an X-15 flight but it took one of the program's most experienced pilots.

15 November 1967: Flight 191

Major Michael Adams, on his seventh X-15 flight, was released from NB-52B over Delamar Dry Lake in X-15-3 (56-6672). He reached about 266,000 ft, above NASA's 80 km definition of space but below the 100 km line. The aircraft carried seven experiments.

An electrical disturbance early in the flight distracted Adams and degraded his control. As the aircraft climbed it drifted off heading, which the ground team could not see. It entered a spin at about 70,000 m. Adams recovered at about 36,000 m, but the aircraft went into an inverted dive, and the adaptive flight control system's high gain caused increasingly violent pitch oscillations. The X-15 broke apart about 10 minutes 35 seconds after launch. Adams was killed and the aircraft was destroyed.

The accident board concluded that Adams lost control through distraction, misreading his instruments and possible vertigo. It recommended a telemetered heading indicator in the control room and medical screening of pilot candidates for vertigo sensitivity. NASA added a ground-based attitude indicator so controllers could see real-time flight data. A monument was erected at the crash site near Johannesburg, California, on 8 May 2004. Adams was awarded astronaut wings posthumously and his name is on the Space Mirror Memorial.

After flight 191

X-15-3 was gone, leaving X-15-1 and the X-15A-2. Several pilots and engineers left the program. Flights continued and the series ended on 24 October 1968, when Bill Dana flew flight 199. A 200th flight planned for 21 November 1968 was cancelled on 20 December.

The board's recommendations, a ground-based attitude display for controllers and vertigo screening for pilot candidates, were practical changes to how flights were monitored and how pilots were chosen. For what the program achieved overall, see the X-15 legacy.