Air France pilots made a series of errors on the Rio to Paris flight that crashed in 2009 killing 228 people, partly due to a lack of training, investigators said Friday.
Pilots failed to react correctly when the Airbus jet lost altitude after its speed sensors froze up and failed, and lacked training to deal with the sensors' failure, said French aviation authority BEA.
The pilots "did not formally identify the loss of altitude" despite an alarm ringing for nearly a minute, it said in a report.
Air France immediately defended its pilots, however, saying the altitude-loss alert system had malfunctioned, in a statement released at the same time as the BEA report on Friday.
The BEA's report said the pilots failed to notice that the plane had lost altitude after its speed sensors, known as Pitots, malfunctioned during the overnight flight on June 1, 2009.
Air France replaced the Pitots, manufactured by French company Thales, on its Airbus planes with a newer model after the crash.
Both Air France and Airbus are being investigated for alleged manslaughter in connection with the crash.
It was the third formal report from years of investigations into how the Airbus plane on flight AF447 crashed en route from Rio de Janeiro to Paris on June 1, 2009, killing all on board.
The Inquiry and Analysis Bureau (BEA) took nearly two years to locate the wreck of the crash and its "black box" flight recorders and retrieve many of the victims' bodies.
Officials insisted earlier that the BEA's findings would not amount to an official attribution of blame for the disaster that has implicated pilots, the airline and plane and equipment makers.
"The BEA establishes the facts and makes recommendations based on those facts," Environment and Transport Minister Nathalie Kosciusko-Morizet said on RTL radio Friday. "As to who is responsible, that is up to the courts."
Victims' families alleged that the involvement of big French corporations such as Airbus and Air France risked influencing the affair.
"The economic stakes take precedence over the search for the truth," said Robert Soulas, leader of a victims' relatives' association.
Rescue workers recovered 50 bodies in the days immediately after the crash and this year retrieved a further 104, which were returned to France last month. More than 70 could not be recovered.