NTSB releases report on SpaceShipTwo accident
On Oct. 31, 2014, Virgin Galactic’s SpaceShipTwo crashed near Koehn Dry Lake in California, killing co-pilot Michael Alsbury. What has followed since the time of the accident has been a detailed investigation into what caused the crash, the findings of which have now been released.The National Transportation Safety Board (NTSB) has released its report on what it believes was the reason that SpaceShipTwo disintegrated during the test flight. According to the NTSB and what has been known almost from the beginning, Alsbury prematurely deployed the feathering system, causing the spacecraft to break up. The spacecraft’s pilot, Peter Siebold, survived the crash.
SpaceShipTwo was constructed by Scaled Composites for Richard Branson’s Virgin Galactic, following up on the successful flights of SpaceShipOne which was Scaled Composites’ entry in the Ansari X-PRIZE.
Where SpaceShipOne carried a single pilot on its suborbital flights, SpaceShipTwo is designed to carry up to six passengers and two pilots on suborbital flights. A crewed, doubled-hulled mothership, White Knight Two, carries SpaceShipTwo to launch altitude and then releases it. The SpaceShipTwo crash took place during the first flight to use a new type of fuel based on nylon plastic grains.
The feathering mechanism was designed by Scaled Composites aerospace designer Burt Rutan to control the re-entry. The wings can rotate up to 65 degrees, increasing atmospheric drag. The feathering mechanism is meant to be engaged when the spacecraft achieves Mach 1.4, but Alsbury engaged the mechanism at Mach 0.8.
According to the NTSB report, it states: “Afterward, the aerodynamic and inertial loads imposed on the feather flap assembly were sufficient to overcome the feather actuators, which were not designed to hold the feather in the retracted position during the transonic region. As a result, the feather extended uncommanded, causing the catastrophic structural failure.”
Christopher Hart, acting chairman of the NTSB, said: “Our investigation was greatly aided by the abundance of data available, including cockpit video telemetry. As our investigators will explain, in addition to incorporating information provided by the pilot, we were able to see the actions of flight crew members, and learn with a high degree of certainty the events that resulted in the breakup.”
Hart further emphasized: “The NTSB is not a regulator, and we have no power to require changes. We identify the causes of accidents in all modes of transportation and make safety recommendations which, if acted upon, can help prevent recurrences. However, more than 80% of our recommendations are acted upon favorably, contributing to a high standard of transportation safety today, and pointing toward even safer transportation tomorrow.”
The NTSB report concluded that a number of safety issues contributed to the accident. For instance, “Scaled did not emphasize human factors in the design, operational procedures, hazard analysis, and simulator training for SS2.”
Specifically, the report points out that Scaled did not consider human error as a possible cause for incorrect feathering deployment, and therefore “missed opportunities to identify design and/or operational factors that could have mitigated the catastrophic consequences of a single human error during a high workload phase of flight.”
Also the pre-application process for an experimental permit can be up to two years long, with the initial request sent to the Federal Aviation Administration Office of Commercial Space Transportation (FAA/AST) after the spacecraft had already been designed and manufactured. Therefore, it would be difficult and expensive for Scaled to implement design changes should the FAA/AST conclude that changes are warranted.
There was also insufficient interaction between the FAA/AST and Scaled during the experimental permit evaluation process. According to the report, “[…] some FAA/AST technical staff members reported that their questions that did not directly relate to public safety were filtered by FAA/AST management to reduce the burden on Scaled.”
“The test flight was subject to oversight by the Federal Aviation Administration. The FAA’s oversight role in commercial space is different from its oversight role in aviation. For commercial space, the FAA does not certify the vehicle. It only certifies the launch, focusing mainly on public safety. Nonetheless, many of the safety issues that we will hear about today arose not from the novelty of a space launch test-flight, but from human factors that were already known elsewhere in transportation,” Hart said.
The report went on to state that the renewal of the SpaceShipTwo experimental permit overlooked the presence of tasks that, if the pilots performed them incorrectly or at the wrong time, could lead to catastrophe, and that FAA/AST inspectors were not sufficiently familiar with Scaled’s operations. The report mentioned that in 2010, the FAA/AST had compiled a database of “mishap lessons learned”, but that this database has not been fully developed.
The report concluded that Scaled needed to improve its emergency response planning, noting that the emergency response helicopter was not positioned near Mojave Airport, where Scaled conducted its flight test.
Another factor mentioned in the report was that the pilots were conducting a large number of tasks under time pressure and from memory, while experiencing vibration not previously experienced, and that Scaled did not emphasize the danger of unlocking the feathering system prematurely.
“We cannot undo what happened, but it is our hope that through this investigation we will find ways to prevent such an accident from happening again, thereby helping to improve the safety of manned commercial space flight,” Hart said.
Video courtesy of Virgin Galactic/NTSB
Collin R. Skocik has been captivated by space flight since the maiden flight of space shuttle Columbia in April of 1981. He frequently attends events hosted by the Astronaut Scholarship Foundation, and has met many astronauts in his experiences at Kennedy Space Center. He is a prolific author of science fiction as well as science and space-related articles. In addition to the Voyage Into the Unknown series, he has also written the short story collection The Future Lives!, the science fiction novel Dreams of the Stars, and the disaster novel The Sunburst Fire. His first print sale was Asteroid Eternia in Encounters magazine. When he is not writing, he provides closed-captioning for the hearing impaired. He lives in Atlantic Beach, Florida.