Sixty-one years ago this week, USAF Major William F. “Pete” Knight made an emergency landing in X-15 No. 1 at Mud Lake, Nevada. Knight somehow managed to save the hypersonic aircraft following a complete loss of electrical power as the vehicle passed through 107,000 feet during the climb.
The famed X-15 Program conducted 199 flights between June 1959 and October 1968. North American Aviation (NAA) built three (3) X-15 aircraft. Twelve (12) men from NAA, USAF and NASA flew the X-15. Eight (8) pilots received astronaut wings for flying the X-15 beyond 250,000 feet. One (1) aircraft and one (1) pilot were lost during flight test.
The X-15 flew as fast as 4,520 mph (Mach 6.7) and as high as 354,200 feet. The basic airframe measured 50 feet in length, featured a wing span of 22 feet and had a gross weight of 33,000 pounds. The type’s Reaction Motors XLR-99 rocket engine burned anhydrous ammonia and liquid oxygen to produce a sea level thrust of 57,000 pounds. The X-15 used both 3-axis aerodynamic and ballistic flight controls.
An X-15 mission was fast-paced. Flight time from B-52 drop to unpowered landing was typically 10 to 12 minutes in duration. The pilot wore a full pressure suit and experienced 6 to 7 G’s during pull-out from max altitude. There really was no such thing as a routine X-15 mission. However, all X-15 missions had one factor in common; high danger.
On Thursday, 29 June 1967, X-15 No. 1 (S/N 56-6670) made its 73rd and the X-15 Program’s 184th free flight. Launch took place at 1828 UTC as the NASA B-52B launch aircraft (S/N 52-0008) flew at Mach 0.82 and 40,000 feet near Smith Ranch, Nevada. Knight, making his 10th X-15 flight, quickly ignited the XLR-99 and started the climb upstairs.
The X-15 was performing well and Knight was enjoying the flight until 67.6 seconds into a planned 87 second XLR-99 burn. That’s when the engine suddenly quit. A couple of heartbeats later, the Stability Augmentation System (SAS) failed, the Auxiliary Power Units (APU’s) ceased operating, the X-15’s generators stopped functioning and the cockpit lights went out. This was the total hit; a complete power failure.
Pete Knight was now just along for the ride. No thrust to power the aircraft. No electrical power to run onboard systems. No hydraulics to move flight controls. Even the reaction controls appeared inoperative. The X-15 continued upward, but it wallowed aimlessly in the low dynamic pressure of high altitude flight. At this point, Knight considered taking his chances and punching-out.
The X-15 went over the top at 173,000 feet. On the way downhill, Knight was able to get some electrical power from the emergency battery. This meant that he now had some hydraulic power and could utilize the X-15’s flight control surfaces. Knight next tried to fire-up the APU’s. The right APU would not respond. The left APU fired, but the its generator would not engage.
As the X-15 descended and the dynamic pressure built-up, Knight was able to maneuver his stricken X-15. He headed for Mud Lake in a sustained 6-G turn. As he leveled off at 45,000 feet, Knight instinctively knew he could now make the east shore of the Nevada dry lake. But it was tough work to fly the X-15. Knight ended-up using both hands to fly the airplane; one hand on the side stick and one hand on the center stick.
While Knight was trying to get his airplane down on the ground in one piece, only he and his Maker knew his whereabouts. The X-15 flight test team certainly didn’t, since Knight’s radio, telemetry and radar transponder were now inop. Further, the X-15 was not being skinned tracked at the time of the electrical anomaly. Just before he touched-down at Mud Lake, Knight’s X-15 was spotted by NASA’s Bill Dana who was flying a F-104N chase aircraft.
Pete Knight made a good landing at Mud Lake. The X-15 slid to a stop. After a struggle with the release mechanism, he managed to get the canopy open. Hot and soaked with perspiration, Knight somehow removed his own helmet. A ground crewman usually did that for him. But there were no flight support people at his X-15 landing site on this day.
As he attempted to get out of the X-15 cockpit, Knight pulled an emergency release. To his surprise, the headrest blew off, bounced off the canopy and smacked him square in the head. Undeterred, Knight got out of the cockpit and onto terra firma. In the meantime, a Lockheed C-130 Hercules had landed at Mud Lake. Wearily, Pete Knight got onboard and returned to Edwards Air Force Base.
Post-flight investigation revealed that the most probable source of the X-15’s electrical failure was arcing in a flight experiment system. This system had been connected to the X-15’s primary electrical bus. The solution was to connect flight experiments to the secondary electrical bus.
Reflecting on Knight’s amazing recovery from almost certain disaster, long-time NASA flight test manager Paul Bickle claimed the fete was among the most impressive of the X-15 Program. Indeed, it was Pete Knight’s clearly uncommon piloting skill and calmness under pressure that gave him the edge.