SpaceShipTwo Accident Comparison
SpaceShipTwo Accident ComparisonVideo Credit: ©Virgin Galactic (silent)
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On October 31, 2014, at approximately 10:07 PDT, Scaled Composites’ SpaceShipTwo flight test vehicle, SS2-001 (N339SS) experienced a serious in-flight anomaly during a rocket-powered test flight approximately 13 seconds after release that resulted in the destruction of the vehicle and the death of the copilot. The pilot survived after successfully parachuting to the ground. No other persons were injured in the air or on the ground.
The accident occurred during the program’s 55th overall and fourth powered test flight (PF-04) of SpaceShipTwo. Scaled Composites, the vehicle’s designer and builder, held an experimental launch permit from the Federal Aviation Administration’s Office of Space Transportation (FAA- AST) to conduct the vehicle’s rocket-powered test flights. Scaled Composites, a wholly-owned subsidiary of the Northrop Grumman Corporation, was under contract with Virgin Galactic (VG) and The Spaceship Company (TSC) to carry out SpaceShipTwo’s developmental flight test program, maintaining both operational control and safety oversight. At the time of the accident, SpaceShipTwo was piloted by two Scaled Composites test pilots.
The mishap test flight, designated PF-04, had three primary objectives:
1) Expand SpaceShipTwo’s powered flight envelope utilizing a 38-second rocket burn to attain approximately 135,000 feet above mean sea level (MSL) and Mach 2.00;
2) Conduct the first supersonic feathered re-entry of SpaceShipTwo;
3) Conduct the first flight using an alternative, polyamide-based hybrid rocket motor fuel that was essentially structurally identical to previously flown motors.
The Probable Cause of this accident was the copilot’s unlocking of SpaceShipTwo’s feather locks at 0.92 Mach, approximately 14 seconds prior to the flight manual minimum speed of 1.4 Mach.
Although normal checklist procedures maintained the feather locks in the locked position until after obtaining a minimum speed of 1.4 Mach, the mishap copilot prematurely unlocked the system at approximately 0.92 Mach. This premature unlocking was indisputably confirmed by telemetric, in-cockpit video and audio data. At this speed, lift from the horizontal tails well exceeded the feather actuator’s ability to prevent a rapid aerodynamic extension of the feather system. These forces caused the feather to rapidly extend without any further pilot action or mechanical malfunction.
A thorough review of the mishap flight data conclusively determined that there were no misleading indications on the pilot displays and that all flight data were accurately displayed to the aircrew.
Extension of the feather while in boosted flight under these conditions imparted over 9g’s of pitch up acceleration forces on the spaceship. These forces exceeded SpaceShipTwo’s designed structural load capability and resulted in its in-flight breakup.
The Contributing Causes of the accident were:
• Feather Lock system design. The Feather Lock system design did not have an automatic
mechanical inhibit to prevent premature movement of the feather system.
• Crew Resource Management. Scaled Composites’ aircrew procedures did not require a challenge/response protocol prior to moving the feather lock handle.
Read more at the NTSB site https://www.ntsb.gov/investigations/pa…
