PARIS — Confronted with faulty instrument readings and alarms going off in the cockpit, pilots struggled to control an Air France jetliner as it went into an aerodynamic stall, rolled and finally plunged 38,000 feet into the Atlantic Ocean in just 3½ minutes.
But the passengers on that doomed Rio de Janeiro-to-Paris flight were probably asleep or nodding off and didn't realize what was going on as the aircraft fell nose-up toward the sea, the director of the French accident investigating bureau said after releasing preliminary black-box data on the June 1, 2009, disaster.
All 228 people aboard the Airbus A330 died.
The brief, highly technical report by the Bureau of Investigations and Analyses, or BEA, contains only selective remarks from the cockpit recorder, offers no analysis and assigns no blame. It also does not answer the key question: What caused the crash?
Several experts familiar with the report said the co-pilot at the controls, at 32 the youngest of the three-man cockpit crew, Cedric Bonin, may have responded incorrectly to the emergency by pointing the nose upward, perhaps because he was confused by the incorrect readings.
The plane's external speed sensors, called Pitot tubes, have long been considered a likely culprit in the disaster, with experts suggesting they may have been iced over. And the BEA investigators found that two sets of instruments on the plane gave different speed readings, with the discrepancies lasting less than a minute.
An official at Airbus said the aircraft's nose should have been pointed slightly downward to enable the plane to regain lift after it had gone into an aerodynamic stall.
Other aviation experts concurred. In an aerodynamic stall, a plane most often loses lift because it is traveling too slowly, and begins to fall out of the sky. Pointing the nose downward enables the aircraft to pick up speed, gain lift and pull out of the stall.
Pulling the nose up is "an inappropriate way to respond" to an aerodynamic stall, said Paul Hayes, director of air safety for aviation consulting firm Ascend Worldwide Ltd. "He either misidentified what was happening or became confused."
He cautioned that Friday's report was brief and that it was still unclear how the series of events started.
The captain of the jet was in the cockpit, though not at the controls as the crew struggled to recover from the stall that occurred as the plane entered a zone of moderate turbulence over the mid-Atlantic, according to the initial report.
Just 10 minutes before, the plane's captain, Marc Dubois, had gone to the crew rest area for some sleep — a normal procedure for such a long-distance flight, Air France has said. Before retiring, he and the two co-pilots discussed the weather conditions and noted that they were entering an area of rough air.
"We are still trying to interpret this information in order to have a better understanding of what happened," said BEA director Jean-Paul Troadec. "That work has just begun."
"Our role is not to assess blame, merely to determine the facts," he added.
The timeline published Friday was based on an initial synthesis of roughly 1,300 pieces of data from the plane's computers and recordings of the final two hours of cockpit conversations.
The information was contained on the plane's so-called black boxes, which were retrieved earlier this month from the ocean floor. The information was seen by investigators as a major breakthrough in the investigation, which has been stalled for nearly two years.
"The pilots never panicked," Troadec said on RTL radio, adding that they maintained professionalism throughout.
The passengers, he suggested, probably fell to their deaths without knowing they were doomed.
Dinner had been served and "you can imagine that most passengers were already asleep or nodding off," Troadec said. He said the cabin crew never contacted the cockpit to see what might be wrong.
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.
"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."
At least one expert disagreed with the theory of a soft descent.
Data from the flight recorders shows the plane was falling almost 11,000 feet per minute (124 mph, or 200 kilometers per hour), its nose slightly tilted upward.
"Eleven-thousand feet a minute is a huge rate of descent," said Ronan Hubert, who runs the Aircraft Crashes Record Office in Geneva. "I would say some of the people on board would have lost consciousness."
Troadec said the agency planned to publish a more comprehensive report by the end of July, which will aim to provide a detailed interpretation of the accident.
Information from the New York Times was used in this report.