Probe clears SpaceShipTwo design, faults Scaled for oversights
Sen—Investigators probing the mid-air breakup of Virgin Galactic’s SpaceShipTwo determined that co-pilot Michael Alsbury made a fatal mistake that cost him his life, but blamed manufacturer Scaled Composites for a gaping oversight in recognizing the potential safety issue.
“Scaled Composite’s failure to consider and protect against human error and the co-pilot’s premature unlocking of the spaceship’s feather system as a result of time pressure and vibration and loads that he had not recently experienced,” caused the Oct. 31, 2014 breakup of SpaceShipTwo as it was making its fourth powered test flight over California’s Mojave Desert, the National Transportation Safety Board said Tuesday.
Alsbury, 39, unlocked SpaceShipTwo’s rotating tail boom early, before the ship had even broken the sound barrier and before atmospheric forces were strong enough to keep the so-called “feathering system” from rotating forward on its own. With SpaceShipTwo scooting along at about Mach 0.8, the tail flipped, creating gravitational forces far in excess of what the vehicle was designed to withstand.
Alsbury died in the crash, while pilot Peter Siebold was jettisoned out of the disintegrating ship. He managed to parachute to safety, but was seriously injured.
Pilot Pete Siebold parachutes to safety, though seriously injured, after the breakup of SpaceShipTwo. Image credit: Virgin Galactic
A better understanding of the consequences of releasing the tail early could have prevented the mistake, the NTSB determined.
"Scaled did not consider that a pilot would induce that kind of failure," said NTSB lead investigator Lorenda Ward.
“Would a single-point mechanical failure with catastrophic consequences be acceptable? It would not, so why would a single-point human failure be acceptable?” added board member Robert Sumwalt.
It wasn’t just Scaled, a wholly owned subsidiary of Northrop Grumman Corp., that failed the pilots and the SpaceShipTwo project.
The Federal Aviation Administration, which oversees commercial spaceflight in the United States, rushed to grant permission for Scaled’s test flights of SpaceShipTwo and did so without understanding how a single human error could lead to fatal consequences.
In separate statements and reports filed to the NTSB and released on Tuesday, Virgin Galactic, an offshoot of Richard Branson's Virgin Group, and Scaled Composites said changes were being made to recognize all potential single-point failures, such as the feather release procedure. That issue specifically has been addressed by the addition of an extra mechanical device to prevent unlocking the tail early.
“Contrary to some initial speculation, the NTSB made clear that the spaceship Scaled Composites had designed, built and then flew for us was performing exactly as it should have. We can therefore be certain that among other things, the rocket motor was working perfectly, the vehicle’s airframe performed as it had been designed, and the cockpit displays were all fully functional,” Branson said in a statement.
“In short, the NTSB has been able to confirm its initial statements as to the cause of the accident: that the feather, a unique system used for the spaceship’s safe re-entry from space, was manually and prematurely unlocked by Scaled’s pilot,” he said.
“With the investigation completed, Virgin Galactic can now focus fully on the future with a clean bill of health and a strengthened resolve to achieve its goals,” Branson added.