Pilot unlocked the feathering, and the mechanism then malfunction, activating itself, without the feathering handle being pulled

Investigators revealed this week that it was a combination of a dangerous mistake and the failure of a secondary system that triggered the deadly crash of Virgin Galactic's SpaceShip Two space plane last week.
I. Investigation Commences
The U.S. National Transportation Safety Board (NTSB) -- an agency most commonly associated with federal investigations into serious defects affecting the consumer automotive industry -- was called upon to investigate the tragic crash of Virgin Galactic's VSS Enterprise.
Among the Congressionally delegated duties of the NTSB is to investigation aviation accidents, and on the day of the crash -- Oct. 31 -- announced that it would be conducting a full-fledged investigation into the failure.

VSS wreckage
The broken remains of the VSS Enterprise were found in the Californian desert hours after the crash on Friday.  One pilot perished in the crash, the other parachuted to safety. [Image Source: AP]

The NTSB assigned Lorenda Ward, a senior investigator, to lead the team looking into the cause of the crash.  Ms. Ward had previously served as the principal investigator for the NTSB during the Boeing Comp.'s (BA) 787 Dreamliner battery fire problems, flying out to Japan's Kagawa prefecture in Jan. 2013 to investigate one of the incidents.

Ms. Ward headed a team of 15 federal investigators, 13 of which traveled to Mojave, Calif. where Virgin Galactic subsidiary The Spaceship Comp. has a factory.  The Californian desert city is also home to the hangar housing the VMS Eve WhiteKnight Two flying launch platform, which escaped damage in Friday's incident. Among the items revealed by investigators was the deceased pilot's identity -- Michael Tyner Alsbury, 39.  He was actually the co-pilot for the flight, according to the NTSB.  He was seated in the craft's right-hand side copilot seat and was responsible for an apparent erroneous action that contributed to the failure.
The pilot of the craft was Peter Siebold, 43.  Seated in the left-hand pilot's seat, Mr. Siebold suffered "moderate" injuries during the mishap but managed to parachute out of the plummeting spaceplane.  Landing in the desert field, he was airlifted to the hospital.
Both pilots reportedly had two years of experience flying the Scaled Composites and Virgin Galactic derived design.  Both pilots held Bachelor of Sciences degrees in aerospace engineering from Californian colleges.  They were technically employees of Scaled Composites, who were contracted by Virgin Galactic for the flight.
II. Cause of Failure Determined -- and It's Surprising
Ms. Ward and fellow investigators traveled to Mojave, Calif. where Virgin Galactic subsidiary The Spaceship Comp. has a factory.  
A part of the Mojave Air and Space Port in California, The Spaceship Comp.'s Final Assembly, Integration and Test Hangar (FAITH) opened in 2011.  Since then, the $8M USD hangar has served as the final assembly and testing site for Virgin Galactic's second (and now sole surviving) SpaceShipTwo plane, the VSS Voyager.  It also housed the preexisting SpaceShip Two, VSS Enterprise (lost in the crash), and the sole WhiteKnight Two plane, VMS Eve.
This weekend FAITH took a more somber role, housing the remains of the VSS Enterprise.
The NTSB inspected those remains and has come to initial conclusions about what happened.  And the results are somewhat surprising.
The failed launch was the first test of a new thermoplastic fuel -- a polyamide compound -- that replaced the rubbery hydroxyl-terminated polybutadiene (HTPB) fuel used in previous launches.  As a result many speculated that the crash might have been triggered by a failed rocket ignition.  But in this week's press briefings, the NTSB's inspection of fuel tanks and other engine remains in the wreckage revealed that the burn was clean and failure free.

Virgin Galactic summarizes:

Based on information they have released about their investigation to date, the NTSB has recovered the intact engine and rocket propulsion fuel tanks with no signs of burn through or mid-air explosion. This definitively dismisses the premature and inaccurate speculation that the problem was related to the engine or the fuel.

So what did go wrong?  It turns out that the craft's feathering mechanism -- which tilts the wings to slow the plane's descent as it falls back to Earth on the return leg of the flight -- activated erroneously during the rocket-powered acceleration, subjecting the craft to immense amounts of drag.  The craft tour apart sending the pilots flying into the desert sky and sending the craft's remains plummeting back to Earth.
The feathering mechanism is supposed to be a two-stage process.  The first step is to unlock the feathering mechanism, which is done via a lever on the dash.  The copilot -- Mr. Alsbury -- for some reason pulled the lever during the ascent, unlocking the feathering. But in a curious twist, evidence indicates he never pulled the separate handle to activate feathering -- the second stage required during normal operation.

VSS Feathering
The VSS Enterprise is shown feathering in this image.  The erroneous activation doomed the craft.
[Image Source: Virgin Galactic]

Instead, the feathering mechanism appears to have malfunctoned and activated itself, with tragic results.

Virgin Galactic summarizes:

The NTSB also evaluated the vehicle’s feathering mechanism, which is the unique technology that turns the wing booms into position for re-entry. The NTSB indicated that the lock/unlock lever was pulled prematurely based on recorded speed at the time, and they have suggested that subsequent aerodynamic forces then deployed the feathering mechanism, which resulted in the in-flight separation of the wings and vehicle. At this time, the NTSB investigation is still ongoing and no cause has yet been determined – these are purely facts based on initial findings. We are all determined to understand the cause of the accident and to learn all we can.

While it can't undo the tragedy, this is somewhat good news for Virgin Galactic as it dispels broader fears of the craft's integrity.  While dangers remain, Virgin Galactic can now focus its efforts into redesigning the feathering mechanism to prevent future failures.  It still has one SpaceShip Two -- VSS Voyager.  And if it plays its cards right, its vision of commercial spaceflight tourism may survive.

Sources: Virgin Galactic, NTSB on YouTube, NTSB on Twitter

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