When the co-pilot of Virgin Galactic’s SpaceshipTwo prematurely unlocked the feathering -- or braking system on the spacecraft it set off a chain of events that lead to a chain of events that brought the ship down.
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That was but one of the findings released today by the National Transportation Safety Board which has ben investigating the Virgin Galactic crash 10 months ago that killed the copilot and badly injured the pilot.
“The National Transportation Safety Board determines that the probable cause of this accident was [the spacecraft’s builder] Scaled Composites’ failure to consider and protect against the possibility that a single human error could result in a catastrophic hazard to the SpaceShipTwo vehicle. This failure set the stage for the copilot’s premature unlocking of the feather system as a result of time pressure and vibration and loads that he had not recently experienced, which led to uncommanded feather extension and the subsequent aerodynamic overload and in-flight breakup of the vehicle,” the NTSP stated.
“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, thereby helping to improve the safety of manned commercial space flight,” said Christopher Hart, Chairman of the NTSB in a hearing on the crash today. “These two test pilots took on an uncommon challenge: testing technologies for manned commercial space flight, which is still in its infancy. Human space flight is subject to unique hazards, and test-pilots work in an environment in which unknown hazards might emerge.”
Hart went on to say that while spaceflight can encounter unknown hazards, it is of utmost importance to incorporate as much as possible of what is known: the lessons that have already been learned from other, more developed modes of transportation.
“Many of the safety issues that we will hear about today arose not from the novelty of a space launch test-flight, but from human factors that were already known elsewhere in transportation,” Hart stated.
Some of the NTSB crash findings included:
- Although the copilot made the required 0.8 Mach callout at the correct point in the flight, he incorrectly unlocked the feather immediately afterward instead of waiting until SpaceShipTwo reached the required speed of 1.4 Mach.
- The unlocking of the feather during the transonic region resulted in uncommanded feather operation because the external aerodynamic loads on the feather flap assembly were greater than the capability of the feather actuators to hold the assembly in the unfeathered position with the locks disengaged.
- The pilot and copilot were properly certificated and qualified. Fatigue and medical and pathological issues were not factors in this accident. The recovered vehicle components showed no evidence of any structural, system, or rocket motor failures before the in-flight breakup.
- Although Scaled Composites’ systems safety analysis (SSA)correctly identified that uncommanded feather operation would be catastrophic during the boost phase of flight and that multiple independent system failures had to occur to result in this hazard, the SSA process was inadequate because it resulted in an analysis that failed to (1) identify that a single human error could lead to unintended feather operation during the boost phase and (2) consider the need to more rigorously verify and validate the effectiveness of the planned mitigation measures.
- By not considering human error as a potential cause of uncommanded feather extension on the SpaceShipTwo vehicle, Scaled Composites missed opportunities to identify the design and/or operational requirements that could have mitigated the consequences of human error during a high workload phase of flight.
- Scaled Composites did not ensure that the accident pilots and other SpaceShipTwo test pilots adequately understood the risks of unlocking the feather early.
- Human factors should be emphasized in the design, operational procedures, hazard analysis, and flight crew simulator training for a commercial space vehicle to reduce the possibility that human error during operations could lead to a catastrophic event.
- The Federal Aviation Administration Office of Commercial Space Transportation’s evaluations of Scaled Composites’ initial and first renewal of the SpaceShipTwo experimental permit application were deficient because the evaluations failed to recognize that Scaled Composites’ hazard analysis did not meet regulatory requirements to identify hazards caused by human error
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