In this Saturday, Nov. 1, 2014, file photo, wreckage lies near the site where a Virgin Galactic space tourism rocket, SpaceShipTwo, exploded and crashed in Mojave, Calif. The surviving pilot of the Virgin Galactic spaceship that tore apart over the Mojave Desert was thrown clear of the disintegrating craft and did not know his co-pilot had prematurely unlocked the re-entry braking system, federal investigators said Wednesday, Nov. 12, 2014. (AP Photo/Ringo H.W. Chiu, File)

The pilot of the Virgin Galactic spaceship that tore apart over the Mojave Desert didn't know his co-pilot had prematurely unlocked its brakes, despite protocol requiring the co-pilot to announce the step.

Pilot Peter Siebold told the National Transportation Safety Board that he wasn't aware co-pilot Mike Alsbury unlocked the before the rocket was done accelerating. Seconds later, SpaceShipTwo began to disintegrate.

An agency spokesman said Wednesday that protocol was to announce the unlocking. It's not clear if Siebold didn't hear it, or Alsbury never voiced it.

Spokesman Eric Weiss says the safety board plans to analyze audio from the flight starting next week.

The Oct. 31 crash killed the co-pilot and injured Siebold.

It could take a year for the NTSB to determine the 's cause.

  • This undated file photo released Saturday, Nov. 1, 2014, by Scaled Composites, shows Peter Siebold, the Director of Flight Operations at Scaled Composites. Siebold was piloting SpaceShipTwo on Friday, Oct. 31, 2014, when it exploded in flight. Siebold the surviving pilot of the Virgin Galactic spaceship that tore apart over the Mojave Desert was thrown clear of the disintegrating craft and did not know his co-pilot had prematurely unlocked the re-entry braking system, federal investigators said Wednesday, Nov. 12, 2014. (AP Photo/Scaled Composites,File)

  • This undated file photo released Saturday, Nov. 1, 2014, by Scaled Composites, shows Michael Alsbury, who was killed while co-piloting the test flight of Virgin Galactic SpaceShipTwo on Friday, Oct. 31, 2014. The surviving pilot of the Virgin Galactic spaceship that tore apart over the Mojave Desert was thrown clear of the disintegrating craft and did not know his co-pilot Alsbury had prematurely unlocked the re-entry braking system, federal investigators said Wednesday, Nov. 12, 2014. (AP Photo/Scaled Composites,File)