Even by modern day standards, the X-15 was a remarkably safe aircraft given the goals it was designed to achieve. Be it skill, experience, or just plain luck, the engineer’s design stood up to everything thrown at it right up until Michael Adams launched on flight 191.
Adams was a highly qualified pilot. His X-15 selection letter places him first in a group of people who were already amoung the best in the USAF.
He had six X-15 flights behind him and the X-15 had been flying for 8 years when he strapped into the cockpit in November 1967.
He launched from the B-52, lit the rocket, and nosed up, heading for 250,000ft. Above 85,000ft he had an electrical problem that took some of his attention and degraded his control of the aircraft, but he elected to continue the mission. This wasn’t a cavalier act, aircraft are complex machines and failures happen, not all of them require the mission to be aborted. Besides the X-15 had telemetry and engineers on the ground were monitoring what was happening. Highly experienced fellow X-15 pilot, Pete Knight, was the mission controller in the control room. Everyone agreed to continue.
The X-15 peaked, Adams started his test points and found the aircraft sensitive to handle. What he didn’t notice as the aircraft began to descend was that the aircraft had turned – it was now at right angles to its direction of travel. In the rarified atmosphere above 200,000ft this made little difference, but he was soon to start reentering the earth’s atmosphere where the environment would be far less forgiving to his alignment error.
In the control room, the telemetry data looked normal. Pete Knight radioed that Adams looked “in good shape.”
At 230,000ft, the air pressure on the sideways X-15 built dramatically. Seconds later, at Mach 5, Adams radioed back that he was in a spin.
I can only imagine the shock in the control room. On the ground all they they saw were small pitch and roll oscillation – heading was not part of the telemetry data. They knew which way the aircraft was moving, but had no way to know which way it was pointing. Worse, there was no established spin recovery technique for the X-15.
The X-15 flew like a brick when it was gliding, but a spinning aircraft isn’t flying, it’s falling, and Adams was falling at 150,000ft/min – that’s about the height of Everest every ten seconds. He was higher than 99% of the earth’s atmosphere but he had only a little over a minute before he would reach the ground.
With Adams’s piloting skills, he managed to get the X-15 out of the spin. He was flying again, but he was upside down, at mach 4.7, and diving at 40 degrees. His first response was to roll upright and pull up. It’s the correct maneuver, and it shows he wasn’t disoriented despite the spin. Unfortunately, a pitch stability system stepped in, not just inhibiting his control of the aircraft but also causing a severe oscillation. The oscillation started bad and grew. Chase planes went into afterburner, heading for all the alternate landing locations, desperate to offer all the assistance a second set of eyeballs could. No one saw the X-15 flying.
At 65,000ft the oscillations reached 15g and the airframe succumbed. One of the chase pilots saw smoke northwest of Cuddeback. It was just ten and a half minutes since Adams had launched from the B-52. The debris spread over 50 square miles. He did not survive.
Perhaps because of the then recent loss of the Apollo 1 crew, the incident wasn’t heavily reported. Major Adams was posthumously awarded Air Force astronaut wings, but it took NASA until 1991 to add his name to the Astronaut Memorial. I would defend NASA for much that they do, but that is something for which I think they should be ashamed. In 2004, thanks to the efforts of an Eagle Scout Candidate, John Bodylski, a monument was erected where the cockpit fell, near Randsburg, California, the dedication reads as below.
The accident investigation board concluded that Adams had not interpreted his instruments correctly (specifically his heading indicator) and possibly suffered vertigo. Vertigo seems hard to believe as he had completed six flights without a problem. What’s more he recovered from a hypersonic spin, and was sufficiently oriented to attempt the correct maneuver to pull out of his hellish dive, only the stability system defeated him.
The big issue to me was that heading was not part of the telemetry. Spin recovery procedures hadn’t been developed for the aircraft, making heading vital. It was added as a result of the crash. If that single piece of information had been available to the ground crew they could have alerted him the moment it happened, preventing the whole scenario. Hindsight is always 20/20.
It’s often said, “that’s why we do flight test.” Fortunately the vast majority of those times when it is said have happier endings than Michael Adams’s case. There were many examples where the engineers design of the X-15 allowed it and its pilot to get back home even with unexpected events.
For example, the X-15 encountered temperatures that caused expansion and deformation of its metal surface. Several times the deformation to the nose section of the aircraft caused a gap to open around the front landing gear door. Thirteen hundred degree air blasted into the wheel well, disintegrating the tire and causing the metal remains of the wheel to be deployed – all at mach 4. Given the effort that went into the design of the vehicles hypersonic stability, you might expect very bad things to happen, bit no. Robert Rushworth reported it generated “an awful bang and yaw,” which is probably an understatement, but in each case the pilot went on to a safe (if rough) landing. The “that’s why we do flight test” lesson learned here was to pay attention to the sealing of gaps, especially around the moving surfaces. It was a lesson that influenced the design of the Space Shuttle.
Another event is described in the video below (which was recorded prior to Michael Adams’s accident). The engine failed to ignite and just twenty seconds from the drop, you can hear the decision for pilot, Jack McKay, to abort to the Mud Lake landing zone. You can see why they put in so much time in the simulator before each flight, there was no time to debate what to do when they were up in the air.
On landing, the aircraft rolled over and the ground crews had to dig around the canopy for Jack to escape. The picture of the aircraft looks horrific, and he was injured, but he recovered to fly the X-15 again.
So, it’s hard to say with the loss of Michael Adams, but in its harsh environment the X-15 was remarkable safe, withstanding unplanned events and still making it home.
I don’t know about you, but if aircraft have undefinable qualities, that’s the one I want the most.
This post was written with reference to several fascinating resources:
Scott Kaczorowski’s West Mojave Aviation Archeology (thanks for the image of Adams’s Memorial)