Investigators have traced additional ACARS messages from the ill-fated Air France Airbus A330 back to the aircraft's anemometric systems, but have yet to understand the final few minutes of the flight.
Ten of the 24 automated messages transmitted in the final five minutes of communication have been attributed to an inconsistency of speed measurements, while another 11 can also be linked to anemometric problems.
France's Bureau d'Enquetes et d'Analyses has been able to understand several messages which it had been unexplained in its preliminary report into the loss of flight AF447 over the South Atlantic on 1 June.
These include messages centred on invalid or inconsistent air data references, as well as the inoperability of the collision-avoidance system - a situation which could be triggered by electrical problems or a failed altitude credibility check.
While several of the messages refer to the loss of individual functions, such as the flight director and characteristic speed markers, the BEA says that none of the messages indicates a loss of displays or attitude information.
Investigators have discovered that at least one additional message - a follow-up to a maintenance status transmission - should have been sent by the aircraft, but was never received. The BEA has yet to determine the reason.
"At this stage, in the absence of any data from the flight recorders, the main parts of the aircraft, and any witness testimony on the flight, the precise circumstances of the accident, and therefore its causes, have still not been determined," it states.
One of the messages indicates that the aircraft's cabin altitude underwent changes in excess of 1,800ft/min for five seconds, although the BEA has not confirmed the direction of this change.
But investigators state that there was no in-flight depressurisation, adding that oxygen masks had not been deployed in the cabin.
Evidence gathered from the crash site has also revealed other aspects of the accident which have yet to be fully understood.
All of the life-jackets retrieved were still packed in their containers. Examination of the cabin crew seats - three of the 11 fitted have been found - shows that none of them had been occupied on impact, but the location of the cabin crew at the time remains unclear. The inquiry has also still to determine the location of the captain.
No distress message from the flight was received by any aircraft or air traffic control centre.
From the damage sustained by the aircraft investigators have concluded that its nose was pitched up when it struck the water heavily, but that its wings were only slightly banked and its flaps were retracted. Damage to the vertical fin, adds the BEA, is "not consistent" with an in-flight failure from lateral forces.
Source: Air Transport Intelligence news
