The Air France Airbus A330 that crashed into the South Atlantic last month is thought to have hit the sea belly first with a high rate of acceleration, but did not break up in mid-air, say investigators.
Speaking after the issuing of an interim report into the AF447 accident on 2 July, Alain Bouillard of France's BEA investigation agency said: "As of today we are far from having any real idea of the causes of this accident."
But he says that bottom-to-top deformation of structural components recovered from the water showed the aircraft appears to have struck the ocean surface with "a sharp vertical" acceleration. He added: "The aircraft was not destroyed while it was in flight and the aircraft seems to have hit the water on the bottom of the fuselage."
All 228 passengers and crew on board the A330-200 were killed in the 1 June crash, which happened during a flight between Rio de Janeiro and Paris.
Bouillard says the A330's maintenance complied with requirements, there were no reports of technical problems from the crew, and there was no distress call - either to air traffic control or other aircraft - at the time of the loss.
Efforts to locate the flight recorders have so far been fruitless, and with the sonic transmitters only required to operate for 30 days, the current search effort was due to be abandoned on 10 July. A second phase, using different techniques, will start after 14 July.
"We refuse to believe that we will not find them," says Bouillard.
Meanwhile, the investigation has so far been unable to determine the composition of the flightcrew on duty at the time of the crash. The crew had been reinforced with a third pilot to meet flight-duty time regulations, and the aircraft's configuration included a crew rest area.
The aircraft's captain is among 51 victims recovered, but investigators have not established whether he was in the cockpit at the time of the accident. "From the current state of the information gathered, it is not possible to determine the composition of the flightcrew on duty at the time of the event," says the BEA.
The rest station on Air France A330-200s includes two beds and is behind the cockpit. While the reinforcing crew stays in the cockpit for departure and arrival, during the cruise each member of the crew must be able to rest for at least 1h 30min continuously.
Under Air France procedures the captain determines the allocation of tasks before any prolonged absence from the cockpit, identifying the pilot who will replace him. He also specifies the conditions that would necessitate his return to the flightdeck.