SpaceShipTwo Crash Was Due to Pilot Error, and a Lapse in Safety Culture
The company running the suborbital vehicle’s test program failed to pay enough attention to the possibility of human error.
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In the end it came down to a simple, but fatal, mistake. Seconds into the fourth powered test of the SpaceShipTwo commercial space vehicle over the California desert last October 31, co-pilot Michael Alsbury reached for a handle to unlock the ship’s novel “feathered” wing—the hinged assembly used during the re-entry phase of the flight. At this point the VSS Enterprise was still climbing; unlocking the feathered wing was just a precaution, in case something went wrong and the vehicle had to re-enter early.
According to procedures he had rehearsed many times, the co-pilot was supposed to unlock the feather when the vehicle hit Mach 1.4 during its rocket-boosted climb. But for some reason Alsbury unlocked it early, when the Enterprise was still at 0.8 Mach. The feathered wing started to deflect, and the resulting aerodynamic stress tore the vehicle apart, just 13 seconds after it had released from its carrier airplane. Both Alsbury and pilot Peter Siebold were thrown from the vehicle, but only Siebold, whose parachute deployed automatically, survived.
In a meeting of the National Transportation Safety Board this morning, investigators presented their initial findings as to the cause of the accident, and discussed the underlying factors that contributed to the co-pilot’s fatal error.
By all accounts, Alsbury was a scrupulous, trained professional test pilot. “Nobody was better at procedures than him,” said board member Robert Sumwalt during today’s meeting. But in those moments after separation from the carrier aircraft, he also was “experiencing high workload as a result of recalling tasks from memory while performing under time pressure and with vibration and loads that he had not recently experienced, which increased the opportunity for errors,” according to a synopsis of the NTSB report.
What’s more, even though the board found no evidence of a design flaw in the StarShipTwo vehicle itself, the Scaled Composites team running the flight test program “did not ensure that the pilots [on this flight] and other SpaceShipTwo test pilots adequately understood the risks of unlocking the feather early.” Indeed, most of the developers’ attention before the October 31 crash had been on the risk of unlocking too late. No warning system was in place to guard against the pilots’ unlocking too early, even though it was understood that such a mistake could also result in catastrophic failure.
The NTSB investigators also found fault with the FAA’s oversight of the SpaceShipTwo test program. Not only was the FAA technical staff unfamiliar with key elements of the vehicle and flight procedures, it granted a waiver for a Scaled Composites hazard analysis, even though it didn’t meet a regulatory requirement to consider human factors that might lead to an accident. The Board recommends that the FAA create a database of lessons learned from commercial space mishaps.
