The aircraft that flew to the edge of space
The North American X-15 was a rocket-powered research aircraft flown by NASA and the United States Air Force, with support from the Navy, from 1959 to 1968. Carried under the wing of a modified B-52 bomber and dropped at altitude, it climbed on a rocket engine to speeds and heights no other winged aircraft had reached. Three X-15s were built. In total the programme made 199 flights, and it produced a great deal of data on high-speed flight, heating and control that fed into the space programme.
In 1967 the programme was in its late phase. The year had already included a speed record: in October, the pilot William Knight flew an X-15 to about Mach 6.7, which remains a record for a piloted winged aircraft. The X-15 was still a hazardous machine, and its flights were treated as experiments with real risk.
Michael Adams and the final flight
Major Michael J. Adams was an Air Force test pilot who had joined the X-15 programme and had been selected earlier for the Air Force’s Manned Orbiting Laboratory programme, which was later cancelled. On 15 November 1967 he flew the programme’s Flight 191 in the X-15 numbered three. The planned flight was to reach a very high altitude, around 250,000 feet or more, and to carry a set of scientific experiments.
After the aircraft was released from the B-52 over Nevada, Adams ignited the engine and climbed steeply. He reached a peak altitude of roughly 80 kilometres, around 50 miles, which is above the line the US Air Force used to award astronaut wings. That is short of the 100 kilometres often used as the boundary of space internationally, but it was above the American threshold.
What went wrong
Near the top of the climb, an electrical problem with one of the experiments reportedly interfered with the aircraft’s systems. Adams also seems to have become distracted and to have allowed the aircraft’s nose to swing away from the proper heading, with the X-15 yawing sideways relative to its direction of travel. As it began to descend, the aircraft entered a spin.
The X-15 was recovered from the spin into a steep dive. But its flight control system, which was designed to adapt its response, appears to have made matters worse. As the aircraft descended it began to oscillate violently, and the loads on the structure became too great. The aircraft broke up at high speed several miles above the ground over the desert of California. Adams did not escape and was killed.
Wreckage was spread across a wide area, and the accident board later reviewed the data from the aircraft’s instruments and from ground tracking.
The investigation
The board concluded that the accident resulted from a combination of factors rather than one cause. The electrical disturbance, the pilot’s attention and the way the flight control system behaved in the unusual condition all contributed. Details in different accounts vary somewhat, and the specific order of events is best treated as an outline, not a precise sequence.
The case later led to discussion of the workload on pilots flying such demanding profiles and of how automatic control systems interact with a pilot in an emergency.
Remembered
Adams was the only X-15 pilot to die in the programme, which took place across nearly a decade of risky flying. In 1991 his name was added to the Astronaut Memorial at the Kennedy Space Center, and he was recognised as having earned astronaut wings through the flight. The aircraft number three was destroyed. The other two airframes had remaining flights, though one had been rebuilt after an earlier accident, and the programme continued for less than another year. The last flight took place in October 1968.
Why it fits into 1967
The year of 1967 saw the loss of Apollo 1’s crew in January and of Soyuz 1’s cosmonaut Vladimir Komarov in April. The death of Adams in November added a third fatal accident at the frontier of flight. It was a reminder that the move from the atmosphere to space was risky, and that the margin for error was thin.
The X-15’s legacy was practical. Pilots including Neil Armstrong had flown it before becoming astronauts, and its data on re-entry heating, control at the edge of the atmosphere and human performance helped shape later spacecraft. Flight 191 is remembered as a loss at the end of a successful programme.