NTSB Discovers Possible Pilot Error in SpaceShipTwo Investigation

NTSB investigators are seen making their initial inspection of debris from the Virgin Galactic SpaceShipTwo. The debris field stresses over a fiver mile range in the Mojave desert. (Credit: Getty Images)

In a press conference at the Mojave Air and Sport Port Sunday evening, acting NTSB Chairman Christopher Hart revealed preliminary findings in the investigation of the  Virgin Galactic SpaceShipTwo test flight accident. According to Hart, review of cockpit video during the flight showed that the co-pilot Michael Alsbury turned the tail feathering lock-unlock lever to the unlocked position too early. But Hart was quick to add that the NTSB has not concluded that this represents a cause and effect, and more analysis is necessary.

“I am not stating this was the cause of this mishap,” he said. “We have months and months of investigation to determine what the cause was.”

Feathering of the tail is an action taken during re-entry at high altitude in order to increase drag and accelerate the space vehicle’s descent. The apparently unscripted action by Alsbury was taken just seconds into the flight of SpaceShipTwo when the suborbital space vehicle had reached the speed of sound, Mach 1 in the denser atmosphere at roughly 50,000 feet. However, unlocking the feathering mechanism was not followed by the second step – moving of another lever which actually rotates the twin tail sections relative to the fuselage to increase the drag for the feathering, which is like a shuttlecock effect. Two seconds after Alsbury’s action and the feathering, SpaceShipTwo experienced a catastrophic breakup.

SpaceShipTwo is shown in the feathered configuration in an earlier unpowered test flight. While the test pilots tested the feathering in the lower, denser atmosphere, the vehicles was much slower and stresses on the vehicle remained well within safety margins. (Photo Credit: Virgin Galactic)
SpaceShipTwo is shown in the feathered configuration in an earlier unpowered test flight. While the test pilots tested the feathering in the lower, denser atmosphere, the vehicles was flying much slower and stresses on the vehicle remained within safety margins. (Photo Credit: Virgin Galactic)

Feathering of the twin tail section of SpaceShiptTwo requires the pilots to execute two steps. The co-pilot Alsbury executed the first step — unlocking. According to the NTSB investigators, the unlocking of the mechanism should not have been enough to cause the feathering during the ill-fated test flight. The lock-unlock mechanism represents a safety feature. The feathering should only occur after the pilot moves a second lever which is not unlike the lever in a conventional aircraft that lowers the landing flaps to increase lift, but as with feathering, at the expense of adding more drag.

Clearly this discovery by the NTSB is turning their focus away from the rocket engine which has posed so much difficulty for Scaled Composites project life cycle of SpaceShipTwo. The propulsion system has been primarily to blame for the delays which Virgin Group founder, Richard Branson has stated stands at five years; the project development now at the 10 year mark.

Discussions in the blogosphere involving aeronautic and propulsion experts and average citizens had quickly turned to criticism of the SpaceShipTwo rocket motor. However, review of the debris appeared to show the rocket motor intact. With this NTSB finding, there is likely to be a pause and change in the focus. However, if the NTSB investigation concludes that the feathering is the cause of the accident, this may not discharge the many concerns about safety of the SpaceShipTwo propulsion system design.

Virgin Galactic CEO Richard Branson responded harshly to the criticism of the propulsion system. “I’ve never seen such irresponsible innuendo and damaging innuendo,” he told Sky News television in the UK. “The fuel tanks and the engine were intact, showing there was no explosion, despite a lot of self-proclaimed experts saying that was the cause,” he said.

The SpaceShipTwo test flight accident occurred at 10:12 AM PDT on October 31st. One day later, NTSB agents had arrived in the Mojave desert to begin the investigation. During the first press conference, Hart stated that while the investigation is expected to last most of a year, he emphasized that the telemetry recorded during the flight was comprehensive and would be instrumental to uncovering a cause and effect.

The telemetry included several video recordings from the carrier aircraft WhiteKnightTwo, from ground video cameras, and also from inside the cockpit. It is a review of the latter that showed the releasing of the feathering safety lock mechanism by Alsbury. Co-pilot Alsbury died as a result of vehicle’s breakup while the pilot, Peter Siebold, escaped or was thrown from the vehicle and parachuted to the ground. Siebold is in serious condition but conscious and speaking to family and attending physicians.

Another point of comparison between the feathering of the SpaceShipTwo tail section with conventional aircraft flaps is that flaps are given a maximum speed at which they can be safely deployed. Deployment at beyond the maximum speed risks severe mechanical stress to the airframe. The feathering that occurred during the test flight at Mach 1 and at the low altitude of the early phase of powered flight by SpaceShipTwo would also have caused sudden and severe stress and potentially the breakup of the vehicle.

NTSB’s Christopher Hart stated that a follow-up press conference would be held on Monday, November 3rd, and will provide more details regarding the NTSB discovery. Hart, during the Sunday press conference, reiterated that despite this early discovery, the investigation is still expected to take a year to conclude. Universe Today will follow with an update after the completion of the Monday press conference.

Update: One Survivor, One Fatality in Virgin Galactic’s SpaceShipTwo Flight Accident

One of two tail sections (empennage) of SpaceShiipTwo lies on the Mojave desert moments after its breakup during test flight. (Credit: Mojave Rescue & Emergency Response Team)

Officials from Virgin Galactic and Scaled Composites have confirmed one of the pilots was killed and another was injured in a major anomaly during a test flight of SpaceShipTwo today (Friday, October 31). The names of the pilots have not yet been released. During a hastily-called press conference, officials said launch of the WhiteKnightTwo plane carrying SpaceShipTwo occurred at 9:20 am PDT this morning and at 10:10 am, SpaceShipTwo (SS2) was released for its test flight to the edge of the atmosphere and space. Two minutes into its flight, SpaceShipTwo encountered an anomaly. Officials had no immediate cause but the rocket motor is the first point of concern.

During the press conference, it was stated that the rocket motor called RocketMotorTwo (RM2) had itself been flown in four previous flights but this was the first flight of version 2 now using a nylon-type plastic called thermoplastic polyamide, replacing the rubber-based fuel used by SpaceShipOne; ultimately too problematic for the SS2 design. Participating in the press conference were executives Kevin Mickey, CEO of Scaled Composites, George Whitesides, CEO of Virgin Galactic and Stu Witt, chief executive of Mojave Air and Space Port. They emphasized that the nylon-based rocket fuel and engine had been thoroughly tested on the ground and they were confident of its readiness for in-flight testing.

WhiteKnightTwo and SpaceShipTwo in flight during test prior to release of the experimental space vehicle. (Photo Credit: Virgin Galactic)
WhiteKnightTwo and SpaceShipTwo in flight during test prior to release of the experimental space vehicle. (Photo Credit: Virgin Galactic)

Within seconds of release, SpaceShipTwo’s engine ignited for flight. Two minutes into the powered flight would have permitted considerable time for SpaceShipTwo to gain altitude and speed. The pilots were not wearing pressure suits, only masks providing supplemental oxygen. At 50,000 feet and more, conditions are equivalent to space, and fluids in the human body begin to boil – turn from liquid to gas. The velocity of the surrounding jetstream upon breakup or ejection would have caused loss of their masks and any oxygen possibly carried with them.

Scaled Composites did not state during the press conference at what altitude the accident occurred. Based on the time of the accident – 2 minutes into powered flight – the vehicle could have been anywhere from 40,000 feet (12 km) to as high as 200,000 feet (60 km). It is more likely that, for this first flight of the nylon-based propellant, the trajectory was left shallow or the full potential of the motor not tested.

SpaceShipTwo does not have ejection seats but is equipped with an escape hatch. The fuselage is fully pressurized for the pilots and planned paying customers. It is not yet determined if the test pilots escaped from the hatch or were thrown from the vehicle after its mid-air breakup.

It is standard practice for any test pilot in an experimental vehicle to be wearing a parachute. SpaceShipTwo would be no exception. Furthermore, being aware of the flight conditions and escaping from a vehicle at high altitude, the chutes very likely had automatic mechanisms to deploy, assuming unconsciousness.

The press conference did not provide further details. At noon time PST, it did not seem evident that the rescue teams knew the conditions of the crew. Rescue teams at the Mojave airport supporting Scaled Composites were prepared and were quickly dispatched. The debris field was located but some more time was required to find both test pilots.

“We do know one of the crew members was met by emergency responders, treated on the scene, and transported to Antelope Valley Hospital,” said Witt at the press conference. “We also know that we have one fatality.”

During the press conference, Scaled Composite and Virgin Galactic executives emphasized their grief and concern for the surviving pilot, the families and friends. The Mojave desert-based companies are a tight knit group and a loss is certainly extremely personal to every team member. The executives did also emphasize once again that “space is hard.” This was first stated by President Kennedy during his famous speech at Rice University. Those words were echoed earlier this week when Orbital Sciences Antares rocket exploded seconds into flight and the leaders of lost payloads were also quick to state the same. The Scaled Composites expressed during the press conference that they remain determined and committed and now in honor of a fallen test pilot and another fighting for his life.

A SpaceShipTwo solid rocket motor is tested on a stand in the Mojave desert. Recent delays led Scaled Composites to swtich from a rubber-based fuel to one chemically similar to nylon. (Photo Credit: Virgin Galactic)
A SpaceShipTwo solid rocket motor is tested on a stand in the Mojave desert. Recent delays led Scaled Composites to swtich from a rubber-based fuel to one chemically similar to nylon. (Photo Credit: Virgin Galactic)

Now a accident investigation begins. The FAA and NSTB will be involved. The investigation of this type of accident will takes months. For Scaled Composites who is effectively responsible and the owner of the flight systems will be analyzing their telemetry and are now forced to consider if the new rocket fuel is worthy of flight or whether they will turn to another solid fuel for SpaceShiptTwo. Sir Richard Branson, owner of the Virgin Group including Galactic has stated that they are five years behind schedule and most of this is attributed to engine development troubles. Company executives stated during the press conference that Branson is expected in Mojave within 24 hours.

Correction: November 1, 2014

In the original article of October 31, 2014, released immediately after the first press conference in the aftermath of the fatal test flight accident, it was stated that the rocket engine in the test flight was using thermoset plastic similar to nylon. The article is now corrected. The rocket fuel of version 2 of RocketMotorTwo is a thermoplastic polyamide which is similar to nylon.