Virgin Galactic crash: Pilots' actions analysed
Investigators probing the Virgin SpaceShipTwo accident have established a "human performance" team to help them understand the actions of the pilots.
The new group will look at how the men interacted with the vehicle, and the design and layout of the systems they used to control the craft.
SpaceShipTwo broke apart just seconds after igniting its rocket engine for a test outing above California on Friday.
Pilot Peter Siebold parachuted clear; co-pilot Michael Alsbury was killed.
Their ill-fated flight was to be part of a series of sorties that Sir Richard Branson's Virgin Galactic company hoped would finally lead to a commercial passenger service to sub-orbital space being introduced next year.
US National Transportation Safety Board acting chairman Christopher Hart told reporters in his final on-site briefing in Mojave that investigators were still waiting to interview Mr Siebold, who was seriously injured.
Mr Hart added a few more details to the information he put in the public domain on Sunday, when he revealed the vehicle's descent system was activated prematurely.
This "feathering" technology, which is designed to slow and orientate the craft on its return to Earth, should not have been unlocked so early in the flight, and certainly should not have engaged at the time it did - on an accelerating ascent.
Mr Hart laid out a detailed timeline for SpaceShipTwo's last catastrophic moments.
The vehicle, he said, was dropped from its carrier aircraft, WhiteKnightTwo, at an altitude of almost 50,000ft at 10:07:19 US Pacific time.
The ship's hybrid rocket motor was then ignited just a couple of seconds later, at 10:07:21.
Eight seconds after that (10:07:29), the vehicle was travelling just under the speed of sound (Mach 0.94). Two further seconds into the flight (10:07:31), it was travelling at Mach 1.02.
It is in that period between Mach 0.94 and Mach 1.02 that Michael Alsbury is seen on recovered cockpit video moving a lever to unlock the feathering system - an action that in the pilots' checklist was not called for until the vehicle had reached Mach 1.4.
Investigators have previously described how the feathering system then deployed, apparently "uncommanded" by the pilots. It is probable that aerodynamic forces deployed the mechanism, resulting in the break-up of the ship. This is timed at 10:07:34 - the instant at which video and telemetry were lost.
One line of inquiry will be to ascertain whether the pilots were getting the correct information on their cockpit display throughout this critical period.
Mr Hart also revealed that small, lightweight pieces of wreckage have been found up to 30-35 miles (55km) northeast of the crash site in the Mojave desert.
His investigators expect to finish their work at the site in the next few days.
The largest item of wreckage, a piece of fuselage and wing, will be cut into smaller pieces to be transported away for further analysis.
Mr Hart said the NTSB's full report would take many months to produce.
"It may be helped by the rich data sources that we have; we may be able to move a little more rapidly," he explained.
"But we would anticipate taking as a much as 12 months to complete the analysis that would end up with a probable cause determination, as well as recommendations… in order not to have an incident like this again."
Virgin Galactic issued a statement in which it committed to full and open co-operation with the NTSB over the course of the investigation.
The company also stated its desire to continue with its space venture.
"While this has been a tragic setback, we are moving forward and will do so deliberately and with determination," the statement said.
"We are continuing to build the second SpaceShipTwo (serial number two), which is currently about 65% complete and we will continue to advance our mission over the coming weeks and months.
"With the guidance of the NTSB and the assurance of a safe path forward, we intend to move ahead with our testing program and have not lost sight of our mission to make space accessible for all."