Updated: Nov 15, 2021
The X-15 Rocket Plane program suffered a major setback on this day in aviation history when the third built X-15 (BuNo. 56-6672) broke up in flight killing the pilot, Major Michael J. Adams of the US Air Force, it was the 7th flight for Adams in the X-15 and the 65th flight for the airframe.
With Major Adams his wife and mother visiting the Nasa Control room at Edwards Air Force base the X-15 was carried aloft by a Boeing B-52. The NB-52B Stratofortress was specially modified to carry X-15 aircraft up launch altitude, for this flight it was "Balls 8" (BuNo. 52-008 under command of Colonel Joe Cotton.
The flight had taken off at 9:12 local time and had headed north to the test area over the Delamar Dry Lake, Nevada.
As the rescue plane was a little late arriving on station the Honeywell MH-96 Auto Flight Control System (AFCS) had to be reset to correct for the change of the suns position in the sky.
But finally, at 10:30 PST the X-15 was launched, and a second later Adams started the XLR99-RM-1 Rocket engine. During the engine burn (which lasted 82.3 seconds) the aircraft accelerated to Mach 5.20 (3,617 mph / 5,821 kph) and climbed to an altitude of 266,000 feet (81,077 meters). During the climb, the computer of the Inertial Flight Data System had failed. Following the flight profile as briefed Adams ran into some control issues causing the aircraft to yaw left and right alternatively with the yaw angle as well as the pitch angle increasing. At an altitude of 230.000 feet (70.104 meters) the pitch had increased to 40° nose up and yaw had increased to 90° to the right of its flight path. Also, control in the roll axis became more and more difficult and the aircraft was rolling at 20° per second. The aircraft entered a spin at a speed of Mach 5.
The X-15 56-6672 climbing away after a launch from a B-52 (not the accident flight)
After a 'fight' with the aircraft, Adams managed to get the aircraft out of the spin at an altitude of 118.000 feet (35.967 meters), however, the aircraft was inverted at Mach 4.7 with a negative pitch of 45°. The AFCS however now started causing oscillations in the pitch and roll causing the G-loading on the airframe to increase up to 15 g's! At 62.000 feet (18.898 meters) at a speed of Mach 3.93, the aircraft broke apart when the structure could not handle the load any longer. The aircraft crashed in a remote area, close to the village of Randsburg, killing Major Adams. He would be the only pilot killed in the X-15 program.
The crash was investigated and the accident board found that the cockpit instrumentation had been functioning properly, and concluded that Adams had lost control of the X-15 as a result of a combination of distraction, misinterpretation of his instrumentation display, and possible vertigo. The reprogramming early in the flight of the Honeywell MH-96 Auto Flight Control System (AFCS), due to the delay caused by the late arrival of the rescue aircraft, degraded the overall effectiveness of the aircraft's control system and further added to the pilot workload.