A co-pilot’s fatal mistake that led to the break-up of SpaceShipTwo represented a single-point failure that could have been addressed long before the crash last October, the National Transportation Safety Board (NTSB) said on 28 July.
A required hazard analysis completed by Scaled Composites failed to anticipate that a single mistake by the co-pilot could lead to an inflight break-up, the NTSB says.
The US Federal Aviation Administration’s office of commercial space transportation, meanwhile, concluded that Scaled’s hazard analysis was incomplete, but issued the company an unsolicited waiver, reasoning that pilot training and experience mitigated the risk of human error, the NTSB says.
“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,” says NTSB chairman Christopher Hart, opening the board’s first ever hearing on the crash of a manned commercial spacecraft.
The 31 October flight was piloted by Peter Siebold, who survived, and co-pilot Michael Alsbury, who was killed instantly when SpaceShipTwo broke up.
SpaceShipTwo was carried to an altitude of around 46,000ft by WhiteKnightTwo, a twin-boomed mothership, and released. Siebold then correctly commanded Alsbury to fire the SpaceShipTwo rocket motor.
But Alsbury next made a tragic mistake by unlocking the spacecraft’s twin-boomed feathers. He was already in a stressful position, trying to remember several critical tasks that must be performed in a short period. It’s not clear if he remembered a three-year-old training lesson that warned pilots that aerodynamic forces would overwhelm the feathers if they were unlocked too early.
Alsbury more likely was aware that if he somehow forgot to unlock the feathers by the time the vehicle reached Mach 1.8, the flight would have to be aborted. Mere seconds after unlocking the feathers, the SpaceShipTwo pitched up suddenly as aerodynamic forces spun the vehicle beyond its structural design limits, leading to complete structural failure.
Richard Branson, founder of Virgin Galactic, says that the company’s engineers have designed a “mechanism to prevent the feather from being unlocked at the wrong time”.
“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 says.