Pilot error, an in-flight braking system that wasn’t sufficiently fail-safe, and lapses in training and the regulatory process contributed to the fatal breakup of Virgin Galactic’s SpaceShipTwo rocket plane during a test flight last October, according to the National Transportation Safety Board.
Tuesday’s findings, issued in conjunction with an NTSB hearing on the accident in Washington, D.C., mark the end of the agency’s nine-month-long investigation – and close a dark chapter in Virgin Galactic’s decade-long effort to send passengers to the edge of space. The company says it’s addressing the factors raised during the investigation as it builds a second SpaceShipTwo in a hangar at California’s Mojave Air and Space Port.
During the hearing, acting NTSB Chairman Christopher Hart said the accident and its aftermath may also lead to changes in the way that the Federal Aviation Administration regulates the commercial spaceflight industry – although he stressed that the NTSB is “not a regulator.”
“It is our objective … to identify actions that the FAA and the industry can take to collaboratively improve the safety of commercial spaceflight in the future,” Hart said.
Tuesday’s documents flesh out the factors behind the Oct. 31 tragedy, which left co-pilot Mike Alsbury dead and pilot Pete Siebold injured.
SpaceShipTwo broke up just seconds after it separated from its WhiteKnightTwo carrier airplane and lit up its hybrid rocket motor, 47,000 feet above the Mojave Desert. The NTSB said video and data showed that Alsbury prematurely pulled a lever to unlock SpaceShipTwo’s braking system.
The system is designed to angle or “feather” the wings, like a badminton shuttlecock, to slow down the craft during its descent. The wing-feathering system shouldn’t have moved until a second lever was pulled – but because it was unlocked while the craft was still accelerating at transonic speeds through the atmosphere, extreme aerodynamic loads forced it to spring open at the wrong time. The NTSB said the resulting stresses led to the breakup.
In documents submitted to the NTSB, Virgin Galactic said the next SpaceShipTwo will be equipped with an “automatic mechanical inhibit” that will keep the braking system from being unlocked or locked during safety-critical phases of a flight.
The NTSB also addressed factors that contributed to Alsbury pulling the lever too soon. Investigator Katherine Wilson said that vibrations inside the cockpit “could have increased the co-pilot’s stress,” and she noted that pilots did not experience those vibrations during training sessions on a flight simulator. The investigators also noted that training materials didn’t put enough emphasis on the risk of unlocking the braking system too early.
According to the NTSB, Siebold told investigators that he didn’t know Alsbury had pulled the unlocking lever. To respond to a concern about pilot communications, Virgin Galactic said it’s adding specific warnings and “challenge-and-response” callouts to cockpit procedures.
The fatal test occurred just as Virgin Galactic and its partner, Mojave-based Scaled Composites, were entering a crucial phase of SpaceShipTwo’s development program. The program was thought to be just months away from sending the rocket plane beyond the boundary of outer space, opening the way for commercial operations.
Over the past decade, about 700 customers have paid as much as $250,000 each to reserve seats on SpaceShipTwo. Virgin Galactic says about two dozen customers have sought refunds in the wake of the accident.
Scaled Composites built the first SpaceShipTwo, which was a scaled-up version of the SpaceShipOne craft that captured the $10 million Ansari X Prize in 2004. When last October’s accident occurred, Scaled was still in charge of the test program for SpaceShipTwo, and Alsbury and Siebold worked as test pilots for Scaled.
During Tuesday’s hearing, NTSB investigators suggested that human factors and emergency procedures were not sufficiently considered during the licensing process for the first SpaceShipTwo. “In its SS2 hazard analysis, Scaled did not account for the possibility that a pilot might prematurely unlock the feather system, allowing the feather to extend under conditions that would cause a catastrophic failure of the vehicle structure,” the NTSB said in an online summary..
The investigators said that the FAA’s inspectors weren’t familiar enough with Scaled’s procedures, and that the FAA issued some waivers to permit requirements even though Scaled didn’t ask for them. To remedy such lapses, the investigators said the FAA should assign inspectors to focus more fully on specific space vehicles. The NTSB also recommended that the FAA work with the Commercial Spaceflight Federation to develop better guidelines for taking human factors into account when designing and operating space vehicles. (Check the NTSB’s summary for additional recommendations.)
The president of the Commercial Spaceflight Federation, Eric Stallmer, said in a statement that he welcomed the NTSB’s report and pledged to follow through on the recommendations. “We cannot undo the unfortunate events that transpired last October,” Stallmer said, “but we will successfully apply, and in some cases have already applied, the lessons learned to make our entire industry better and safer as a result.”
In the future, Scaled will have less of a role in SpaceShipTwo’s development. The second rocket plane is being built by The Spaceship Company, or TSC, which is fully owned by Virgin Galactic. When construction is completed, the craft and its WhiteKnightTwo carrier airplane will be flown by Virgin Galactic pilots under different procedures.
“While it is good to have passed this milestone and be able to focus on the future, we are acutely aware that it does not alter the fact that this was at heart a human tragedy,” Virgin Galactic’s billionaire founder, Richard Branson, said in a statement released after Tuesday’s hearing. “Our thoughts go out again today to the family, friends and colleagues of Mike Alsbury.”