Virgin Galactic Ltd.’s spacecraft designers failed to anticipate that pilots might trigger its brakes too early, leaving the ship vulnerable to the error that led to last year’s fatal crash, investigators said.
The National Transportation Safety Board focused on pilot training Tuesday in a hearing into the Oct. 31 accident that grounded Richard Branson’s space-tourism venture months before it was to start taking customers to the edge of Earth’s atmosphere. Co-pilot Michael Alsbury was killed when the vehicle was torn apart after he prematurely unlocked a braking mechanism.
The failure by Scaled Composites LLC, the craft’s designer, to consider and protect against the mistake was a probable cause of the crash, the NTSB determined. Scaled Composites knew the vehicle would be destroyed if the mechanism was deployed too early but assumed that only systems, and not humans, would cause an error, the NTSB found. The Federal Aviation Administration’s oversight also was “deficient,” the board said.
“Humans will screw up anything if you give them enough opportunity,” Robert Sumwalt, a safety board member and former commercial airline pilot, said at a Tuesday meeting to determine the cause of the crash. “It’s important to anticipate errors.”
SpaceShipTwo, Virgin’s craft, was designed to make the first stage of its flight while slung beneath a twin-hulled carrier plane, the WhiteKnightTwo. From there, the rocket-powered craft was to climb to 68 miles (109 kilometers), enabling passengers paying $250,000 to experience weightlessness and view the curvature of the earth.
The probe is the first detailed look into the new generation of space vehicles straddling the line between experimental flight and rockets. The NTSB findings “will help make the fledgling commercial space industry safer and better,” said Branson, the 65-year-old U.K. billionaire founder of Virgin Group, said in a blog post Wednesday.
The 2014 accident occurred during a test flight when the brake system, known as a “feather,” deployed about 10 seconds after SpaceShipTwo’s engine fired as pilots worked through a checklist amid the distractions of rocket flight.
Pilots are supposed to leave that system locked until the craft reaches Mach 1.4, about 920 miles an hour in near-vacuum conditions of its highest point.
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Instead Alsbury moved the feather control to “unlock” when the ship was about 0.8 Mach and gliding through heavy air, the NTSB said. Aerodynamic forces extended the feather mechanism as the vehicle moved past the speed of sound, Mach 1, and broke up.
Alsbury, who hadn’t flown since April 2013, was killed as the craft was destroyed. Pilot Peter Siebold was ejected at 50,000 feet and survived a parachute ride to earth even though he wasn’t wearing a pressurized spacesuit. The men were employees of Scaled Composites.
Pilot training was focused on the risk of unlocking the brakes too late to help the Virgin Galactic craft glide back to earth, NTSB found. In fact, Alsbury had missed the target of deploying the brake by Mach 1.8 during training four days prior to the crash, and it may have been weighing on his mind, Sumwalt said.
Scaled Composites, a Northrop Grumman Corp. unit, didn’t anticipate that pilots might unlock the brakes out of sequence and hadn’t created controls to prevent this happening, Katherine Wilson, a senior NTSB investigator, said at the meeting.
Engineers at Virgin Galactic “have already designed a mechanism to prevent the feather from being unlocked at the wrong time,” Branson said. The safety board didn’t recommend any changes to the space venture’s flight-test procedures or commercial operations, he said.
Scaled Composites, founded by aerospace designer Burt Rutan, said changes have already been made in its processes to improve safety. ‘We will continue to look for additional ways to do so,’’ the company said in an e-mail.
The safety board faulted FAA inspectors for missing the risk of human error, and recommended that the agency streamline its oversight of space ventures and create a central database modeled on an airline industry version that allows competitors to share safety-related information.
“We cannot undo what happened, but it is our hope that through this investigation we will find ways to prevent such an accident from happening again,” NTSB Chairman Christopher Hart said.