A confused cockpit crew without proper training to head off high-altitude disaster flew toward it, instead, with wrong-headed maneuvers, no task-sharing and perhaps unaware their flight was about to end in the Atlantic Ocean.
Screeching stall alarms and incoherent speed readings from faulty sensors, bad weather in a darkened sky and growing stress make up the chaotic cockpit scenario in the final moments of the Air France flight from Rio de Janeiro to Paris on June 1, 2009. All 228 people aboard the plane were killed.
Friday's third report by France's accident investigation agency, or BEA, lays out almost second-by-second technical data on the flight's deadly trajectory but cannot answer the ultimate question _ whether pilot error, equipment failure or other still unknown factors caused the crash.
The BEA's findings raised worrisome questions about the reactions of the cockpit crew _ two co-pilots _ as the A330 went into an aerodynamic stall and their ability to fly the A330 manually as the autopilot disengaged. The report expressed broader concern about the state of training of today's pilots flying high-tech planes when confronted with a high-altitude crisis.
BEA officials said they are bringing together a bevy of experts, from psychologists to physiologists, to try to reconstitute the scene from the crews' point of view _ the human factor which could include potential disorientation. Those findings would be included in the final report expected early next year.
Many of the crews' actions "seem contrary to logic and we're seeking rational explanations," chief BEA investigator Alain Bouillard told a news conference, adding that the cockpit crew even seemed unaware the plane had gone into an aerodynamic stall.
"We understood how the accident came about," Bouillard said. "Now we must learn why it came about."
Friday's 117-page report, based on a full reading and analysis of the flight and data recorders dredged from the ocean depths, recommends mandatory training for all pilots to help them fly planes manually and recover from a high-altitude stall.
With the captain of Flight AF447 on a rest break, the report also expressed concern over "non-optimal task sharing" between the two co-pilots. Among the BEA's 10 recommendations, it wants authorities to further define criteria for appointing a relief captain to ensure better synergy among relief crews.
When the captain of the Air France flight returned in the midst of the crisis, "neither of the two co-pilots gave a precise accounting of the problems encountered nor of actions undertaken, except that they had lost control of the plane and that they had tried everything," the report said.
The captain had "implicitly" appointed the younger co-pilot as his relief before taking his regulation nap.
Experts caution against laying blame on the pilots _ all experienced and qualified to fly the aircraft.
"The information they're getting from the brain of the airplane, the thing that they've been trained to trust, is sending them all off on tangents," said John Goglia, a former U.S. National Transportation Safety Board member and an expert on airline safety.
"They've got bells and whistles going off, they've got a face full of lights," Goglia said. And yet, "the pilots had an awful lot of information denied to them to help them deal with the situation" because of malfunctioning computers.
The crew had less than 4.5 minutes to act to correct an aircraft that was sounding alarms and giving sometimes false readings. However, BEA chief Jean-Paul Troadic said that, at the start at least, "the situation was salvageable."
The chilling scenario as described by the voice and data recorders began at 2 hours, 10 minutes and 5 seconds into the overnight flight, when the autopilot and auto-thrust disengaged and a stall warning sounded twice in a row. The recordings end at 2 hours, 14 minutes and 28 seconds.
The co-pilot designated by the captain quickly took over manual controls of the aircraft, and nosed the plane upward _ the opposite of what was needed to give the plane lift.
A basic maneuver for stall recovery, which pilots are taught at the outset of their flight training, is to push the yoke forward and apply full throttle to lower the nose of the plane and build up speed. But he nosed up throughout much of the impending disaster and the plane reached a maximum height of 38,000 feet.
The report confirms that external speed sensors obstructed by ice crystals produced irregular speed readings on the plane. Since the accident, Air France has replaced the speed monitors on all its Airbus A330 and A340 aircraft.
The BEA's report noted that Airbus warned pilots in 2008 that incorrect speed readings from the Pitot tubes could cause erroneous stall warnings. But Bouillard, the chief investigator, maintained that the pilots should "always respect a stall warning."
Passengers, finishing dinner or napping, were never advised of the plane's plight.
"From what we've been told, nobody realized what was going on. On that level, for my mental and moral comfort I am very pleased to hear this, when you know you had two people on board who were dear to you," said Corinne Soulas, whose 24-year-old daughter Caroline and son-in-law were aboard the flight.
The alarms _ computer-generated voices screeching "stall ... stall ... stall" sounded numerous times, and once for a full 54 seconds.
Incomprehension and growing tension ensued.
At an alarm sound, the co-pilot not flying said at one point "What's that about?" Curiously, the crew made no reference in cockpit exchanges to the warnings, the report said.
As described by the BEA report, several calls were made to the captain. The pilot not flying expressed concern several times at the captain's absence, a concern that "probably raised the stress level of (that) pilot as he faces a situation he doesn't understand."
The flying pilot twice said he had lost control of the plane. Then, 27 seconds later the pilot not flying takes control but the designated pilot retakes control "almost immediately without any announcement."
A minute and a half later, the captain arrived, but with no pertinent information from the co-pilots and a lack of information from the control panel he appears not fully aware of the situation _ and did not ask questions to better understand.
The report said that "multiple stops and reactivation (of the alarm) probably added to the confusion and disturbed his diagnosis of the situation."
There has been a silent tug-of-war between Air France and Airbus, the plane's constructor, over the crash.
Both were charged last March with involuntary homicide following the accident.
In a statement, Air France said there was currently no reason to question the crew's technical skills. The airline said the report showed that a series of unlikely failures led to the stall and crash.
Angela Charlton in Paris, Slobodan Lekic in Brussels, Joan Lowy in Washington and Masha MacPherson at Le Bourget contributed to this report.