A failure to consider and protect against human error has been cited as a reason for the in-flight break up of SpaceShipTwo, a commercial space vehicle built by Scaled Composites for Virgin Galactic.
SpaceShipTwo broke up during a rocket-powered test flight in October 2014, seriously injuring the pilot Pete Siebold and killing co-pilot Michael Alsbury.
Investigations that immediately followed the accident found that the release mechanism on SpaceShipTwo’s “feathering” system, which creates extra drag by folding the craft’s tail fins into a near-right-angle position, was unlocked before the ship had reached the correct speed of descent.
The US National Transportation Safety Board has now determined that deployment of the feathering system represents a failure by Scaled Composites to consider and protect against the possibility of human error during the deployment of the system.
According to NTSB, the feather system was to be unlocked during the boost phase of flight at a speed of 1.4 Mach. NTSB said: “The co-pilot unlocked the feather at 0.8 Mach; once unlocked, the loads imposed on the feather were sufficient to overcome the feather actuators, allowing the feather to deploy uncommanded, which resulted in the breakup of the vehicle.”
NTSB found that Scaled Composites failed to consider the possibility that a test pilot could unlock the feather early or that this single-point human error could cause the feather to deploy uncommanded.
The Board also found that Scaled Composites failed to ensure that test pilots adequately understood the risks of unlocking the feather early.
In a statement, Christopher A. Hart, NTSB chairman said: “Manned commercial spaceflight is a new frontier, with many unknown risks and hazards.
“In such an environment, safety margins around known hazards must be rigorously established and, where possible, expanded.”
The Board has made recommendations to the US Federal Aviation Administration and the Commercial Spaceflight Federation that, if acted upon, would establish human factors guidance for commercial space operators.
A link to the abstract, which contains the findings, probable cause and recommendations can be found at the following address: http://www.ntsb.gov/news/events/Pages/2015_spaceship2_BMG.aspx