The VSS Enterprise crash occurred on October 31, 2014, when VSS Enterprise, a SpaceShipTwo experimental spaceflight test vehicle operated by Virgin Galactic, suffered a catastrophic in-flight breakup during a test flight and crashed in the Mojave Desert near Cantil, California. Co-pilot Michael Alsbury was killed and pilot Peter Siebold was seriously injured. The National Transportation Safety Board later concluded that the breakup was caused by Alsbury's premature unlocking of the air brake device used for atmospheric re-entry. The NTSB said other important factors in the accident were inadequate design safeguards, poor pilot training and lack of rigorous oversight by the Federal Aviation Administration (FAA).
Accident
On the day of the accident, Enterprise was performing a test flight – powered flight 4 (PF04) – in which it was dropped from the WhiteKnightTwo carrier aircraft, VMS Eve, after taking off from the Mojave Air and Space Port. The test flight was the aircraft's first powered flight in nine months, and was to include the first flight testing of a new, more powerful and steadier-thrust hybrid rocket engine whose fuel grain was composed of nylon instead of rubber. The flight was the aircraft's 55th, and its 35th free flight. VSS Enterprise was crewed by pilot Peter Siebold and co-pilot Michael Alsbury. According to the NTSB briefing, SpaceShipTwo (SS2) dropped from the mother ship as planned and fired its new hybrid rocket engine normally. About eleven seconds later, the space plane violently broke apart, substantially giving the appearance of an explosion, and creating a 35-mile-long (55-kilometer) debris field. Witnesses reported seeing a parachute before the aircraft crashed. Alsbury was killed in the crash. Siebold survived with serious injuries and was transported to Antelope Valley Hospital in nearby Lancaster. The carrier aircraft, VMS Eve, landed safely. There was initial conjecture from some industry experts that the new rocket engine was at fault, but this was quickly disproved when the craft's engine and propellant tanks were recovered intact; indicating there was no explosion due to either the solid (nylon-based) or liquid (nitrous oxide) components of the hybrid engine. A preliminary investigation and cockpit video subsequently indicated that the feathering system, the ship's air-braking descent device, deployed too early. Two seconds later, while still under rocket propulsion, the craft disintegrated. The feathering system requires two levers to operate. The system was unlocked by Michael Alsbury, but the feathering control was not moved, indicating an uncommanded feathering as "that action alone should not have been enough to pivot the tails upright" according to the NTSB. The feathering system had been deliberately deployed at supersonic speeds during earlier powered flight tests of SS2, but previous activation either occurred in thinner air at higher altitudes, or at much lower speeds than the flight on October 31. Regarding the possibility of pilot error being the proximate cause of the crash, acting NTSB chairman Christopher Hart said: "We are not ruling anything out. We are looking at all of these issues to determine what was the root cause of this mishap … We are looking at a number of possibilities, including that possibility (of pilot error)." The incident resulted in the first fatality on a spacecraft in flight since the Space Shuttle Columbia disaster in 2003. The survival of pilot Peter Siebold also marks the first time in history that anyone has survived the destruction of a spacecraft during a flight when others on board have died. Investigators were initially puzzled about how Siebold managed to get out of the rocket plane and parachute to the ground from an altitude of roughly 50,000 feet (15,000 meters), where the atmosphere is virtually devoid of oxygen. On November 7, Siebold told investigators that the aircraft broke up around him. He was still strapped into his seat. He released the straps and his parachute later deployed automatically. Siebold was not wearing a pressure suit.
Aircraft The vehicle in the accident, VSS Enterprise, registration N339SS, was the sole Scaled Composites Model 339 SpaceShipTwo test vehicle. It was the first of the five SpaceShipTwo craft planned by Virgin Galactic. Since October 2010, VSS Enterprise had flown 20 captive flights while remaining attached to its WhiteKnightTwo carrier aircraft, 31 unpowered glide-to-landing tests, and three rocket-powered test flights. There were several performance issues during the ship engine's development in 2012 and 2013. A rocket-powered test flight of SpaceShipTwo took place on April 29, 2013, with an engine burn of 16 seconds duration. The brief flight began at an altitude of 47,000 feet (14,000 m), and reached a maximum altitude of 55,000 feet (17,000 m) and a speed of Mach 1.2 (920 mph or 1,480 km/h). A second SS2 vehicle, VSS Unity, was rolled out in February 2016.
Investigation
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