U.S. federal investigators said the descent system of Virgin Galactic's passenger spaceship was prematurely activated before last week's fatal accident.
The acting chairman of the National Transportation Safety Board, Christopher Hart, told reporters Sunday night the SpaceShip Two's co-pilot unlocked the ship's "feathering" system before it reached the proper speed.
The system is designed to decrease the spaceship's speed as it re-enters the atmosphere.
But Hart insisted it is too early to assume the feathering system played any role in the disaster.
"Again I want to emphasize that we have not determined the cause. I am not stating that this is the cause of this mishap," Hart said.
'Months of investigation'
"We have months and months of investigation to determine what the cause was. We'll be looking at training issues, we'll be looking at was there pressure to continue testing, we'll be looking at safety culture, we'll be looking at the design, the procedure. We've got many many issues to look into much more extensively before we can determine the cause," he said.
Hart said the ship's engine and propellant tanks were found intact, indicting there was no explosion.
SpaceShip Two crashed during a test flight Friday over the Mojave Desert in California, killing the co-pilot, 39-year-old Michael Alsbury. Pilot Peter Siebold ejected from the craft and parachuted to the ground but suffered serious injuries.
The ship, co-owned by British entrepreneur and adventurer Richard Branson, is designed to carry up to six passengers to the edge of space for a few minutes of weightlessness before returning to Earth.
The accident was the second suffered by a private U.S. space company last week.
Days earlier, an unmanned commercial rocket that was supposed to send a cargo ship to the International Space Station exploded seconds after liftoff from a NASA launch pad in the Atlantic Coast state of Virginia.