WASHINGTON — As the U.S. National Transportation Safety Board (NTSB) wraps up the on-scene portion of its investigation into the fatal crash of SpaceShipTwo, officials said Nov. 3 that they planned to expand their work to include an analysis of human factors that may have contributed to the accident.
At a press conference held late Nov. 3 at the Mojave Air and Space Port in California, NTSB Acting Chairman Christopher Hart said investigators had established a “human performance” group to work alongside groups studying debris, data and other information about the Oct. 31 accident.
That group, Hart said, will examine “the interface between the flight crew and the vehicle, to look at issues such as displays, checklist design and other issues.”
The decision to add human factors analysis to the investigation came a day after the NTSB revealed that SpaceShipTwo’s co-pilot, Michael Alsbury, had unlocked the vehicle’s feathering mechanism prematurely. That mechanism is designed to raise the vehicle’s twin tail booms during re-entry to provide increased drag and stability.
Hart said at a Nov. 2 briefing that seconds after Alsbury unlocked the feather, it started to deploy, although the pilots had not moved the handle to engage it. Soon afterward, telemetry and video from SpaceShipTwo were lost.
According to a specific timeline of events Hart read at the Nov. 3 briefing, the feather went from locked to unlocked between eight and 10 seconds after engine ignition, as SpaceShipTwo accelerated from Mach 0.94 to Mach 1.02. “Soon after that, the feather itself soon began to deploy,” he said, with telemetry cut off 13 seconds after engine ignition.
At the Nov. 3 briefing, Hart appeared to back away from statements the previous day identifying Alsbury as the pilot who unlocked the feathering mechanism. Hart said it was the pilot sitting in the right-hand seat in the SpaceShipTwo cockpit who unlocked it, but could not confirm that this person was the co-pilot.
Shortly after the briefing ended, NTSB posted on its Twitter account a clarification of Hart’s comments: “[T]he copilot, who was in right seat, moved the lock/unlock handle into unlock position; he did not survive [the] accident.” Scaled Composites announced Nov. 1 that Alsbury was the co-pilot of the flight and was the person who died in the accident.
The pilot of SpaceShipTwo, Peter Siebold, was injured in the accident and has not yet been interviewed by NTSB investigators. “We will work with his medical care and his family to arrange that interview when he’s ready,” Hart said.
Although the NTSB has stopped short of blaming the accident on the premature unlocking of the feathering mechanism, Virgin Galactic went further in a statement issued early Nov. 4.
“The NTSB indicated that the lock/unlock lever was pulled prematurely based on recorded speed at the time, and they have suggested that subsequent aerodynamic forces then deployed the feathering mechanism, which resulted in the in-flight separation of the wings and vehicle,” the company said in the statement.
Virgin Galactic also said in the statement that it planned to continue construction of a second SpaceShipTwo at the company’s Mojave factory. The second SpaceShipTwo is currently about 65 percent complete.
At a media tour of the factory in October, Virgin Galactic executives said that second SpaceShipTwo would be ready for test flights in 2015 and commercial service in 2016. The company’s Nov. 4 statement gave no timeline for completing the vehicle.
The Nov. 3 NTSB briefing is the last planned in this phase of the investigation. “The on-scene portion of the investigation will be closing within a few days,” Hart said at the briefing. The overall investigation will continue for up to 12 months, with the NTSB providing updates from Washington “as events warrant.”