US investigators say they have not ruled out the possibility of pilot error on board the doomed Virgin Galactic spaceship, as they revealed that a safety device to slow the craft's descent was deployed early.
SpaceShipTwo co-pilot Michael Alsbury (39) died when the aircraft crashed in the Mojave Desert in California on Friday.
Surviving pilot Peter Siebold (43) was alert and speaking with family members and medical staff in hospital, his employer, Scaled Composites, said.
The National Transportation Safety Board (NTSB), which is leading the probe into the crash, said investigators found that the spaceship's "feathering" system - which lifts and rotates the tail to create drag - was activated before the craft reached the appropriate speed.
The system of deployment is a two-step process, but Christopher Hart, acting chairman of the NTSB, said that, while the co-pilot unlocked the system, the second step occurred "without being commanded".
"After it was unlocked, the feathers moved into the deployed position and two seconds later we saw disintegration," he told a press conference.
Mr Hart said investigators would look at a wide range of issues including training, the spacecraft's design and whether there was pressure to continue testing.
Asked whether investigators were "edging" towards the possibility of pilot error, Mr Hart replied: "We're not edging towards anything. We're not ruling anything out.
"We're looking at all of these issues to determine what was the root cause of this mishap. We are looking at a number of possibilities."
Investigators are also looking at video from within the spaceship and from the ground and there were a number of eyewitness accounts, he added.
Virgin Galactic, owned by Richard's Branson's Virgin Group and Aabar Investments PJS of Abu Dhabi, plans to fly passengers to altitudes more than 62 miles (100km) above Earth. The company, which sells seats on each prospective journey for 250,000 US dollars (£156,000), has denied reports that it ignored safety warnings ahead of the test flight crash.
In a statement, the company said: "At Virgin Galactic, we are dedicated to opening the space frontier, while keeping safety as our 'North Star'. This has guided every decision we have made over the past decade, and any suggestion to the contrary is categorically untrue."
Geoff Daly, an engineer, has filed complaints with several American government agencies over the use of nitrous oxide to power the spaceship's engine.
"Something is wrong here," said Mr Daly. "We offered to talk, give our experience. It was either ignored or totally dismissed."
Carolynne Campbell-Knight, a co-partner of Knights Arrow, an engineering project, said she had expressed concerns over safety some years ago, urging the company to "go away and do something they might be good at like selling mobile phones".