The loads on the airplane built up beyond the structural limits, and the X-15-3 aircraft broke up at approximately 62,000 feet and about 3,800 feet-per-second speed…
The X-15 is a famous and significant part of aviation history. Its purpose was to fly high and fast, testing the machine and subjecting pilots to conditions that future astronauts would face. It made the first manned flights to the edges of space and was the world’s first piloted aircraft to reach hypersonic speeds, or more than five times the speed of sound. The X-15 was an important tool for developing spaceflight in the 1960s, and pilots flying above 50 miles altitude in the X-15 earned astronaut wings.
Three X-15s were built, and they made 199 flights between 1959-1968. The program was a joint U.S. Air Force/Navy/NASA project.
On almost every flight of the X-15, some type of technical problem or failure occurred, sometimes multiple problems on the same flight. It is remarkable that only one pilot, Mike Adams, lost his life during the whole X-15 program of 199 flights.
As told by John Anderson and Richard Passman in their book X-15 The World’s Fastest Rocket Plane and the Pilots who Ushered in the Space Age, Mike Adams was the twelfth (and last) pilot in the X-15 program.
On Nov. 15, 1967, Michael Adams, veteran pilot with six previous X-15 flights, entered the aircraft for a flight to evaluate a guidance display and to conduct several experiments. He had spent more than 21 hours practicing the specifics of this flight in the simulator. The drop at about 10 a.m. and 45,000 feet was normal, and he climbed to 266,000 feet. While the aircraft climbed to higher altitude after launch, an electrical disturbance caused the MH-96 dampers to trip out. Adams reset the dampers. He then switched the sideslip indicator to a vernier attitude control mode to more accurately control the experiments. He planned to reset this back to indicate yaw angle when returning to base in order to see his sideslip during approach to landing. But this instrument change prevented him from seeing that the airplane was yawing at a critical time in the flight.
After burnout, as he soared upward, he conducted a wing-rocking experiment, in which the rocking became excessive as he approached his peak altitude, 266,000 feet. His yaw had drifted to 15 degrees, and he was unaware of this because his instrument was inadvertently set to show pitch attitude, not yaw. About 15 seconds later, the airplane was yawing wildly and Adams communicated to Pete Knight that “the airplane seems squirrelly.” He soon after stated that he was in a spin, subjected to high accelerations. Since little was known about the hypersonic spin characteristics of the airplane, the ground crew was not able to offer advice. According to the ground data that was later correlated with the flight data, when Adams recovered, he was yawed 90 degrees, flying upside down, and descending at supersonic speed.
Adams pulled out of the spin, and he probably would have had a successful landing except that the MH-96, the Minneapolis-Honeywell adaptive flight control system, was on and locked in, causing the airplane to oscillate between its limits, up and down, preventing Adams from correcting his attitude and flying his way home. The loads on the airplane built up beyond the structural limits, and the X-15-3 aircraft broke up at approximately 62,000 feet and about 3,800 feet-per-second speed. It crashed to the desert floor near Johannesburg, California. There was talk about Adams having slight vertigo, which may have contributed to his not noticing the yaw buildup or resetting the yaw indicator to the yaw setting.
Adams’s death shows the dangers of flight testing a new aircraft in previously untested regions of flight, and of flying experiments in which certain research-data measuring instruments may have caused an electrical disturbance that affected the MH-96 from operating at its top quality and in conditions it was not designed for. Any and all these things may have influenced the accident.
Because his flight was above 50 miles high, Adams was posthumously awarded an astronaut rating. For the X-15 program, the tragedy was a blight, but it was the only casualty in 199 flights. Since the objectives for the airplane had been accomplished, the accident was a major reason for the termination of the X-15 program. There were only seven subsequent flights.
Photo credit: NASA