SpaceShipTwo's wings changed position prematurely and seemingly without full pilot input shortly before it broke apart in flight, the National Transportation Safety Board said last night. The vehicle's two tail wings are supposed to be moved by pilots into a vertical position once the craft hits a certain speed, but the NTSB found that the wings were moved before it had hit that speed. The craft was traveling at approximately Mach 1.0 when the wings were raised into the "feathering" position, which is meant to create drag and reduce speed, but the deployment shouldn't have occurred until at least Mach 1.4.
"We have months and months of investigation to determine what the cause was."
It appears that pilots only gave one of the two commands necessary to deploy the wings, though the command they did give was issued earlier than launch procedures call for. To deploy the wings, pilots must both move a handle from a "lock" position to an "unlock" position and then move another handle into a "feathering" position. Around Mach 1.0, a pilot moved the "lock" handle into the "unlock" position. Two seconds later, the wings moved into the feathering position, though the feathering handle had not been activated.
The NTSB is not yet ready to declare the cause of the accident and emphasizes that these events did not necessarily contribute to the ship's destruction. It is, however, investigating the potential for pilot error, and these details suggest that there may have been a mechanical error as well. "We have months and months of investigation to determine what the cause was," says NTSB acting chair Christopher Hart. "We'll be looking at training issues; we'll be looking at [whether there was] pressure to continue testing; we'll be looking at safety culture, the design, the procedure. We've got many, many issues to look into much more extensively before we can determine the cause."
There has also been some speculation that a new type of fuel being tested during SpaceShipTwo's flight contributed to the accident, but the NTSB notes that the ship's engine, fuel tank, and oxidizer tank have all been recovered "in tact" with no signs of burn through or having been breached.