According to the report, the first indication of trouble appeared three hours and 40 minutes into the flight, and 10 minutes after the captain had gone to the crew rest area for some sleep, a normal procedure for a long flight. Beforehand, he and the two co-pilots discussed the weather and noted they were nearing rough air. Flight attendants were cautioned.

Suddenly, the autopilot and auto-thrust functions of the plane disengaged. A stall warning sounded, twice.

“We’ve lost the speeds,” one co-pilot said, as the plane went to manual control at 37,500 feet. The report said the co-pilot tried “several times” to call the captain back, and that he arrived within less than a minute.

The report does not identify the pilots by name. But French news reports identified them shortly after the crash as Capt. Marc Dubois, 58, a veteran pilot who had flown nearly 11,000 hours and had extensive experience on Airbus A330 and A340 aircraft; David Robert, 37, a co-pilot with more than 6,500 hours of flight experience, 4,500 of them on A330s; and Pierre-Cédric Bonin, 32, the second co-pilot, with under 3,000 hours of experience.

Investigators confirmed separately that it was Mr. Bonin who was at the controls from the moment the plane ran into trouble.

The plane’s flight displays were showing inconsistent speed readings. Faulty airspeed indicators can mislead pilots into flying faster or slower than the plane can handle. In this case, investigators said, the plane abruptly lost speed.

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The pilot at the controls pulled up the nose of the aircraft. As the plane slowed, it began to ascend, reaching 38,000 feet. A third stall warning sounded, lasting for about a minute.

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Two minutes later, with the plane losing momentum and starting to roll left and right, and the captain back in the cockpit, the plane had fallen by about 3,000 feet. Its nose was pointing upward from the airstream at more than 40 degrees, though its angle from the horizon “did not exceed 15 degrees.”

The crew struggled to regain lift as the plane hurtled through 10,000 feet, its nose still up around 16 degrees from the horizon. According to the report, the engines continued to operate until the end and responded to crew commands.

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Two minutes before impact, the co-pilots said they had lost valid indications of airspeed.

Around the same time, the plane, which had veered slightly west of its original flight path, began to turn to the right, eventually reversing course and flying back toward the point at which it had lost contact with air traffic controllers.

In the flight’s final minute, it appears that the pilot at the controls ceded to the pilot in the second seat, perhaps the captain, saying, “Go ahead, you have the controls.” But the data indicate that the plane then received inputs from the control sticks of both seats simultaneously.

The data and voice recordings stopped at 11:14 p.m. local time for Rio de Janeiro.

It was not clear how aware the passengers were of the unfolding disaster; the aircraft’s rolling may have been more apparent than its plummet.

Robert Soulas, a victim’s father who was briefed with other relatives by investigators before the report was made public, said, “The plane was descending at a relatively constant speed, so we were told they may not have had the sensation of falling.”

The investigators’ report does not indicate that the crew communicated with the passengers during the last minutes.

Safety experts said they were stunned that the pilots had been unable to recover from the stall.

“It is mind-boggling that an aircraft can stay stalled for that long,” said William R. Voss, president of the Flight Safety Foundation in Alexandria , Va. “This was a perfectly flyable aircraft that was mishandled from 35,000 feet all the way down to the surface.”

Nonetheless, Mr. Voss, who has no involvement in the French investigation, said he was hesitant to blame the crew.

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“Those pilots did not plan to die that night,” he said. But their apparent focus on responding to the alarms and system failures, while failing to keep the plane at the proper attitude and power settings, suggests “there might be something either in their experience or their training that caused it to happen,” he said.

France’s main pilots’ union, Syndicat National des Pilotes de Ligne, did not directly address the description of the crew’s actions. In a statement, the union said the crew “found itself suddenly confronted with a situation that was extremely complex and puzzling, which they sought until the end to bring under control.” The report, the union added, “only describes part of the chain of events experienced by the crew.”

In a statement, Air France noted that the report’s “description of the facts” would replace “assumptions that have been made over the past two years,” and said the pilots “were committed to carrying out their task to the very end.” Airbus called the investigators’ report a “significant step towards the identification of the complete chain of events.”