The U.S. National Transportation Safety Board (NTSB) says that a co-pilot error was the cause of failure of the Virgin Galactic’s SpaceShipTwo spacecraft over the Mojave Desert in October 2014.

The spacecraft broke apart during a powered test flight, killing co-pilot Michael Alsbury and critically injuring pilot Peter Siebold.

NTSB Go-Team inspects a tail section of the VSS2 spacecraft. Source: wikipedia.com The NTSB investigation identified the manufacturers failure to anticipate the potential of such a mistake as being partly responsible.

The NTSB says that Albury was found to have unlocked the spacecraft’s feathering system shortly after SpaceShipTwo separated from its mother-ship and fired its hybrid rocket engine. According to the NTSB, during the feathering procedure, a pilot will unlock then deploy the stabilizers. These rotate the two tail booms upward to create drag and slow the craft as it aligns into a “belly-up” position before re-entry into the atmosphere.

The procedure was designed to be used as a form of descent only. In the accident, however, NTSB says it appears that Alsbury unlocked the feathers while the spacecraft was still accelerating. The breakup occurred after the craft passed Mach 1—the speed of sound.

The report, read by NTSB Chairman Christopher Hart, indicates the unlocking of the feathering system was activated too early. This caused the plane to encounter an excessive amount of air resistance and ultimately led to its disintegration.

The board also suggested that Scaled Composites, the manufacturers, was partly responsible for the crash, due to its “failure to consider and protect against the possibility that a single human error could result in a catastrophic hazard to the SpaceShipTwo vehicle.”

The feathering system had been used during 10 prior test flights when it first began in April 2013.

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