Technical faults that led an ill-prepared crew to lose control sent an Air France airliner plunging into the Atlantic in 2009, killing all 228 people aboard, French accident investigators said on Thursday.
The final report by France's BEA authority comes after an almost two-year search of the seabed for the Rio to Paris flight's black boxes and amid a bitter row between Airbus and Air France over who should bear ultimate responsibility.
It made 25 new safety recommendations on top of the 16 called for in a July 2011 report, blaming the Airbus A330's ergonomics as well as inappropriate actions by the pilots who were under great stress.
The BEA said that the drama began with the malfunctioning of speed sensors known as Pitots, manufactured by French company Thales, which have since been replaced on Airbus planes.
"The crew was in a state of almost total loss of control of the situation," the probe's chief, Alain Bouillard, told journalists.
The BEA report stressed the importance of "pilots' training so that they have a better knowledge of the plane's systems in the event of an unusual situation."
"The pilots stuck to what they do usually... When you lose awareness of the situation you hang on to what you're used to doing," said Bouillard.
Relatives of those who died were invited to BEA offices outside Paris where they were informed of the report's conclusions ahead of its public release.
Many of them were unhappy with what they learned.
"I get the impression that they're always talking about human error which I don't believe in at all," said Keiko Marinho, who heads a Brazilian victims' relatives association and lost a sister in the accident.
But John Clemens, who lost a brother in the crash, said he was "satisfied with the conclusions."
"There's a lot more information than before," he said. "The authorities have worked well and made a lot of safety recommendations."
The Airbus A330 vanished at night and during a storm on June 1, 2009. It took days before debris was located in the remote equatorial area of the Atlantic Ocean, and far longer until the wreckage was recovered.
$40-million search for black boxes
The black boxes were finally located by robot submarines after a search spanning 23 months and costing about $40-million.
The report said the pilots had failed to react correctly when the Airbus stalled and lost altitude after its speed sensors froze up and failed.
As the two co-pilots struggled to understand the situation, the captain, who had left the cockpit to take a rest, returned but did not retake control of the plane.
Investigators had difficulty explaining why the crew did not respond to the stall alarm, saying this could have been down to not understanding the alarm's sound or that it was too discreet.
"If the BEA thought that this accident was only down to the crew, we would not have made recommendations about the systems, the training, etc. Which means that this accident could no doubt have happened to other crews," said BEA head Jean-Paul Troadec.
Air France has insisted the pilots were not to blame, saying the stall alarm had malfunctioned. The airline said in a statement that the crew had remained "engaged in flying up to the last moment."
"The BEA report shows the crew acting according to the information supplied by the instruments and onboard systems, and the plane's behaviour as observable from inside the cockpit," Air France said.
It said the crew's readings of the instruments, alarms, aerodynamic sounds and aircraft vibrations "did not allow them to apply the appropriate actions."
Charges of manslaughter to follow?
French magistrates are investigating both Air France and Airbus for alleged manslaughter in connection with the crash.
Airbus said in a statement after the report was released that it would take all necessary safety measures "to contribute to this collective effort towards optimising air safety."
A separate judicial report - due to be presented to victims' families next Tuesday - has concluded that both pilot error and malfunctioning speed sensors were responsible, a source has told AFP.
The source said the 356-page judicial report had found that while the Pitots froze up and failed, the "captain had failed in his duties" and "prevented the co-pilot from reacting".