A deluge of messages received before flight 447 plunged into the Atlantic suggest the Air France plane may have broken up in the air.
Flight 447 disappeared minutes after flying into an extremely dangerous band of storms Sunday night, but what exactly caused its electrical systems and cabin pressure to fail remains a mystery.
The "black box" cockpit recorders could be miles below the surface of the Atlantic Ocean. If they can't be recovered, investigators will have to focus on maintenance records and a burst of messages sent by the plane just before it disappeared.
French and Brazilian officials had already announced some details of these messages, but a more complete chronology was published Wednesday by Brazil's O Estado de S. Paulo newspaper, citing an unidentified Air France source.
The burst of automatic messages sent from the jetliner before it disappeared with 228 people on board suggests it probably broke apart in the skies and fell to the ocean in pieces.
The pilot sent a manual signal at 11pm local time saying he was flying through an area of "CBs" - black, electrically charged cumulonimbus clouds that come with violent winds and lightning.
Satellite data has shown that towering thunderheads were sending 160kph updraft winds into the jet's flight path just then.
Ten minutes later, a cascade of problems began: Automatic messages indicate the autopilot had disengaged, a key computer system had switched to alternative power, and controls needed to keep the plane stable had been damaged. An alarm sounded indicating the deterioration of flight systems.
Three minutes after that, more automatic messages reported the failure of systems to monitor air speed, altitude and direction. Control of the main flight computer and wing spoilers failed as well.
The last automatic message, at 11.14 pm, indicated loss of cabin pressure and complete electrical failure - catastrophic events in a plane that was likely already plunging toward the ocean.
"This clearly looks like the story of the airplane coming apart," an airline industry official said.
"We just don't know why it did, but that is what the investigation will show.
"That investigation is being done by France, Brazil's only responsibility is to find and pick up the pieces."
Bad weather has hampered recovery efforts as the first Navy ship arrived at the debris site of flight 447.
High seas and heavy winds have slowed the recovery effort and delayed the arrival of crucial deep-water submersibles to the mid-Atlantic site.
Search vessels from several nations pushed toward the floating debris, including a seven metre chunk of plane and a 20 kilometre long oil slick that Brazilian pilots spotted from the air.
Rescuers have still found no signs of life from the plane that was carrying 228 people from Rio de Janeiro to Paris.
A Brazilian navy spokeswoman said a patrol boat was close to one debris field after spending two days pushing through rough weather to reach the site, but had not yet retrieved any wreckage.
A Navy frigate was expected to arrive later in the day.
COMBINATION OF EVENTS
The fierce thunderstorms, turbulence, lightning or a catastrophic combination of events could have broken apart the plane, aviation experts have said.
And while the messages reported by the newspaper don't indicate why the aircraft went down, they strongly suggest it broke apart in the air.
The new debris was discovered about 90 kilometres south of where searchers a day earlier found an airplane seat, a fuel slick, an orange buoy and pieces of white debris.
The original debris was found roughly 640 kilometres northeast of the Fernando de Noronha islands off Brazil's northern coast, an area where the ocean floor drops as low as 7,000 metres below sea level.
Brazil was leading the search, while France took charge of the crash investigation, working with Air France, Airbus and meteorologists to determine what happened.
Brazilian divers were expected to arrive Thursday, but if the black boxes are at the bottom of the sea, their recovery will have to wait for the arrival early next week of a French research ship with remotely controlled submersibles that can explore as deeply as 6,000 metres.
The sturdy black boxes - voice and data recorders - are built to give off signals for at least 30 days, even underwater, and could keep their contents indefinitely.
But the head of France's accident investigation agency, Paul-Louis Arslanian, said in Paris that he is "not optimistic" about recovering the recorders - and that investigators should be prepared to continue the probe without them.
"It is not only deep, it is also mountainous," he said. "We might find ourselves blocked at some point by the lack of material elements."
A French AWACS radar plane and two other French military planes flew Wednesday over the area where debris was found to better narrow down the search zone.
A US Navy P-3C Orion surveillance plane - which can fly low over the ocean for 12 hours at a time - also joined the operation.
Arslanian said investigators didn't have enough information to determine whether the plane broke up in the air or upon impact with the sea, and that in the absence of black box data, they are studying maintenance and other records.
"For the moment, there is no sign that would lead us to believe that the aircraft had a problem before it took off," Arslanian said.
He said investigators did not know the exact time of the accident or whether the chief pilot was at the controls when the plane went down. Pilots on long-haul flights often take turns at the controls to remain alert.
If no survivors are found, it would be the deadliest crash in Air France's history, and the world's worst civil aviation disaster since the November 2001 crash of an American Airlines jetliner in New York City that killed 265 people.