PARIS (AP) - Two co-pilots facing faulty instrument readings and a stall fought to regain control of an Air France flight before the plane slammed into the Atlantic in a 3 1/2 minute fall, killing all 228 people aboard, accident investigators said Friday.
A preliminary report into the crash of Flight 447 from Rio de Janeiro to Paris also revealed the captain was on a routine rest break when the trouble began on June 1, 2009 and he never retook the controls. The new information came from data gleaned from the Airbus 330's black boxes, which were recovered in early May.
But the report does not answer the key question: what caused the crash?
Asked whether faulty sensors, other mechanical issues or the crew's actions were responsible for the disaster, air accident investigation agency director Jean-Paul Troadec said: "It's a combination of all of this."
Friday's report by the French air accident investigation agency BEA was a factual description of the chain of events beginning with takeoff in Rio de Janeiro until recordings fell dead nearly four hours later.
Some families of victims who said they were given information in a meeting with the agency said it was possible their loved ones went to their deaths unaware of what was happening because there was apparently no contact between the cockpit and cabin crew in the 3 1/2 minutes.
"It seems they did not feel more movements and turbulence than you generally feel in storms," said Jean-Baptiste Audousset, president of a victims' solidarity association. "So, we think that until impact they did not realize the situation, which for the family is what they want to hear - they did not suffer."
The report revealed that the plane's captain, Marc Dubois, was out of the cockpit on a routine rest break when the problems began.
The data flight recorder and cockpit recorder were dredged from the ocean in April, along with some bodies, in the latest effort by investigators to explain the disaster. Both of the boxes were readable.
They show inconsistent speed readings, two co-pilots working methodically to right the plane manually and a resting captain returning to the cockpit amid what moments later became an irretrievably catastrophic situation. The data also showed that the plane went into an aerodynamic stall - - a loss of lift brought on by too little speed.
Investigators only provided partial quotes from the voice recorder in Friday's report.
The report confirmed that two sets of instruments on the plane were giving conflicting speed readings. On the voice recorder, one co-pilot is heard to say "so we've lost the speeds" about four minutes before the crash.
Experts have suggested external monitoring instruments iced over. Air France has now replaced the monitors, called Pitot tubes, on all its Airbus A330 and A340 aircraft
The plane was passing through ominous weather in mid-Atlantic, about three and a half hours after taking off, when the problems began.
More than eight minutes before the crash the co-pilot at the controls, one of three members of the flight crew, advised the cabin crew "you should watch out" for turbulence ahead. He said the plane could not climb out of the cloud layer where the turbulence was happening because it was not cold enough.
Turbulence caused the pilots to make a slight change of course, but was not excessive as the plane tried to negotiate a normal path - passing through a heavy layer of clouds.
Four minutes later, the plane's autopilot and auto-thrust shut off, the stall alarm sounded twice and the co-pilot at the controls, 32-year-old Pierre-Cedric Bonin, took over manual control. A second co-pilot, David Robert, 37, was also in the cockpit.
Pilots on long-haul flights often take turns resting to remain alert. Dubois returned to the cockpit about a minute and a half after the problems started but did not take back the controls.
Just over two minutes before the crash, Bonin is heard to say "I don't have any more indications." Robert says "We have no valid indications."
The interim report by accident investigation agency BEA did not analyze the data or cockpit conversations or assign blame. A full report on the crash is not due until next year.
Air France said in a statement that, based on the report, it appears "the initial problem was the failure of the speed probes which led to the disconnection of the autopilot" and loss of pilot protection systems.
The airline defended the captain, saying he "quickly interrupted his rest period to regain the cockpit."
Independent aviation analyst Chris Yates said the report appears "to raise more questions than it answers."
"It would seem to me, reading between the lines, that the cockpit crew weren't confident of the information that was being presented to them on the data displays. Maybe - and it's only a maybe - they took some action that led to the stall warning, and the plane stalling and then being unable to correct it."
The flight recorders were found along with bodies in early May in the latest in a series of meticulous searches using small submarines and robots to comb the ocean depths.
(Copyright 2011 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.)