The co-pilot of the SpaceShipTwo rocket that crashed into the California desert Friday may have executed a braking maneuver at the wrong time and speed, the chief investigator of the accident said Sunday.

While stressing that they have not determined the cause of the crash, the acting director of the National Transportation Safety Board also suggested that so far there was no sign of an engine failure, fire or explosion. The craft, which was part of entrepreneur Richard Branson’s “Virgin Galactic” dream of ferrying rich people into space, crashed seconds after it was released from the carrier plane that had flown it aloft.

The fuel tanks and the engine were recovered intact with no signs of burning, said Christopher A. Hart, acting chairman of the NTSB.

The findings described yesterday, however, at least hint at the possibility of pilot error or a malfunction of the system designed to create drag as the rocket reenters the atmosphere. A braking action, at a lower altitude where the air is dense, could conceivably have jolted or stressed the rocket causing it to break up. The braking system–which relies on the tailfins folding into a “feathered” configuration to create drag–is supposed to be deployed before the plane enters the atmosphere and then retract.

The SpaceShipTwo, a narrow craft designed to whisk wealthy adventure-seekers into suborbital space, crashed early Friday — just seconds after separating from its carrier plane during a midair launch tens of thousands of feet above the Mojave Desert. It was the first time the engines used a new type of plastic-based fuel, splitting from the rubber-based solid fuel that propelled its predecessor, the SpaceShipOne, and nearly all previous tests.

The carrier plane is designed to ascend to 50,000 feet and then release SpacShipTwo, which is then supposed to reach a sub-orbital altitude of 328,000 feet before beginning its descent.

The craft has two tailfins designed to rotate upward and forward to slow the plane on its way down when it hits a speed of Mach 1.4. The effect has been compared with the feathers of a shuttlecock in badminton. In this flight, however, the “feathers” were deployed at Mach 1.0, Hart said, calling the sequence of events an “uncommanded feather.”

U.S. transportation officials say the co-pilot of the Virgin Galactic space plane that crashed unlocked its wing tip "feathers" early and that pilot error has not been ruled out. (Reuters)

Two actions are required in succession to deploy the feathers, Hart said. First, a handle must be moved manually from the “locked” to “unlocked” position. And then a second lever deploys the feathers and slows the spacecraft to prevent it from burning up on reentry.

Hart said that, nine seconds after SpaceShipTwo was released from the carrier plane, the co-pilot did indeed shift the first handle to the unlocked position. The second lever was never pulled, he said. If the system were operating properly, the feathers should not have been deployed.

But two seconds after the co-pilot shifted the first handle, the feathers were deployed. There’s no data after that point, he said, suggesting that’s when SpaceShipTwo malfunctioned or broke up.

“There’s much more that we don’t know,” he said when asked if there was pilot error. “I’m not saying this was the cause,” he stressed repeatedly.

The co-pilot, Michael Alsbury, died in the crash. The pilot, Peter Siebold, survived after being pulled from the wreckage. Hart would not comment on any interviews the investigators have conducted so far with witnesses or those involved in the flight.

SpaceShipTwo was the industry’s glossiest showpiece, with Virgin Galactic owner Richard Branson saying he wanted to be one of the first passengers when flights began as early as next year. More than 700 celebrities and spacefaring hopefuls have paid up to $250,000 each for flight aboard the rocket plane. They were promised a few minutes of weightlessness at the edge of space.