LOS ANGELES -- The NTSB-led investigation team probing the cause of the Oct. 31 crash of Virgin Galactic's SpaceShipTwo says 2 sec. before beginning to break up in midair, the vehicle's two moveable tail booms unexpectedly began to deploy into a "feathering" position.

Revealing the findings, NTSB Chairman Christopher Hart says camera footage and telemetry show that around 9 sec. after ignition of the hybrid rocket, the mechanism that controls the stowage of the moving tails moved from "lock" to "unlock." Hart adds that as the vehicle accelerated through about Mach 1, the co-pilot was seen to move the locking handle. Normal procedure is to unlock the feathers after Mach 1.4 so that aerodynamic forces do not prematurely extend the mechanism.

In normal operations the feathering device is designed to be activated outside of the sensible atmosphere before the vehicle begins its descent. In addition to the locking mechanism, the feathering device requires the activation of a second handle. The feather system acts like a shuttlecock and was originally conceived by Scaled Composite designer Burt Rutan as a carefree re-entry method for recovery of SpaceShipOne. The feathering system was deliberately deployed supersonically as a part of earlier powered flight tests of SS2. However, in each previous deployment, activation either occurred in thinner air at higher altitudes, or during unpowered flights at much slower speeds than the ill-fated flight on Oct 31.

Although not commenting on whether the uncommanded deployment led to the overstressing of the structure and the subsequent inflight breakup, Hart says the data is a "statement of fact rather than a statement of cause." The feathering system was first used on a powered flight during the second rocket-propelled sortie on Sept. 5, 2013, when SS2 reached Mach 1.43 and an apogee of 69,000 ft.

The NTSB also reports that the fuel and oxidizer tanks as well as the hybrid rocket motor were all intact and showed no signs of burn through or of "being breached." The findings support photographic evidence of the mishap which clearly indicated a successful ignition and continuing rocket burn before the catastrophic structural breakup.

The flight was the fourth powered test of SS2 and the first to use a new plastic-based fuel aimed at a more powerful, smoother acceleration. While the switch to the new fuel led to speculation that this would form the initial focus for the investigation, the latest findings now indicate the inquiry will shift to the inadvertent deployment of the feathering mechanism and the impact of excessive aerodynamic loads on the structure.