NTSB: Uncommanded Feathering Occurred on SS2

Christopher Hart, acting chairman of the National Transportation Safety Board (NTSB), said this evening (November 2) that investigators determined today as a matter of fact — not necessarily cause — that “uncommanded feathering” took place on SpaceShipTwo (SS2) after it dropped away from its carrier aircraft and fired its rocket engine.  The engine, fuel tanks and oxidizer tank were all recovered today and all are intact with no signs of burn-through or of being breached.

SS2 crashed on October 31, killing co-pilot Michael Alsbury, seriously injuring pilot Peter Siebold, and destroying the spaceplane.  SS2 was built by Scaled Composites and owned by Richard Branson’s Virgin Galactic, a business created to take anyone who can afford a $250,000 ticket on a brief, suborbital flight to space.

Until now, speculation has focused on a new fuel used on this test flight, but the facts released by Hart tonight cast a very different light on what may have happened.  He stressed repeatedly however that these are facts, not a judgment about the cause of the accident.

Feathering is a technique used after the vehicle reaches apogee (its highest altitude) to increase drag as it returns to Earth.  The pilots need to take two steps in order to deploy the feathers (tail booms):  the lock/unlock handle must be moved from lock to unlock, and the feathering handle then must be moved to the feather position.  The lock/unlock handle is not supposed to be moved to the unlock position until the vehicle reaches Mach 1.4.

In this case, however, telemetry and video from a camera inside the cockpit show that the co-pilot moved the lock/unlock handle to the unlock position when the vehicle was approximately at Mach 1.0 instead of Mach 1.4.  The second step, moving the feathering handle to the feather position, never took place.  Hart therefore described this as “uncommanded feathering.”

Until then, the mission was proceeding normally.  SS2 dropped away from its WhiteKnightTwo carrier aircraft and fired its rocket engine. The engine fired for 9 seconds at which point telemetry and video showed that the lever was moved from lock to unlock and two seconds later the feathers deployed even though the feather handle was not moved to the feather position.  Shortly thereafter, telemetry was lost and the vehicle disintegrated.

The bottom line of these facts, then, is that the lock/unlock handle was moved prematurely, the second step ordinarily needed to deploy the feathers — moving the feathering handle — did not occur, the feathers deployed nonetheless, and the vehicle broke apart shortly thereafter.

Stressing again that these are facts, not a determination of cause, he said months of investigation lie ahead and the NTSB will be looking at training issues, whether there was pressure to continue testing, the safety culture, design, procedures, and many other issues.

Hart said the NTSB would hold another press briefing tomorrow, time TBD.