The Paris-bound Airbus A330-203 stalled and crashed into the Atlantic Ocean during a thunderstorm early on June 1, 2009, more than two hours after it took off from Rio de Janeiro.
All of the 216 passengers, including Guelph, Ont., native Brad Clemes, and 12 crew members died. It was the worst accident in Air France's history.
The report says a co-pilot pulled the nose of the aircraft up, even though it was already in a stall, because of faulty data from flight sensors.
The crew never understood they had lost control of the aircraft, said Alain Bouillard, chief investigator at the French civil aviation safety authority, Bureau d'Enquêtes et d'Analyses.
"The crew never understood that they were stalling," he said.
In response, Air France said the pilots on the flight "acted in line with the information provided by the cockpit instruments and systems. … The reading of the various data did not enable them to apply the appropriate action."
The BEA is recommending better pilot training and stricter plane certification rules as part of its report. Airbus said in a statement that it is working to improve the flight sensors.
Investigators had released three interim reports since the crash, but had not drawn a conclusion on what caused the crash.
Its third report, released in July 2011, said the crew did not appear to know the plane was in a stall moments before it crashed. A stall warning sounded numerous times, and once for a full 54 seconds, but the crew made no reference to it in cockpit exchanges before the jet crashed, according to the BEA.
There was no evidence of task-sharing during the crisis by the two co-pilots in the cockpit at the time, according to the BEA's 2011 findings. The captain was on a rest break when the warnings began.
The BEA says it's unclear why the co-pilot at the controls, flying manually, maintained a nose-up input — contrary to the usual procedure to come out of an aerodynamic stall. Normally, the nose should be pointed slightly downward to regain lift in such a stall, which is often caused because the plane is travelling too slowly.
The crew also did not inform passengers that there was anything wrong before the jet plunged into the sea.
The same report also said external speed sensors, called pitot tubes, were obstructed by ice crystals, producing irregular speed readings on the plane.
Air France replaced the speed monitors on all its Airbus A330 and A340 aircraft following the crash.
A separate judicial report, which is due to be presented to the victims' families next week, has concluded that pilot error and malfunctioning speed sensors played a role in the crash, according to Agence France-Presse.
Plane plunged for 3½ minutes
The investigation into the accident was helped after the plane's flight data and cockpit voice recorder were recovered from the ocean in May 2011, following a long and costly search operation.
The passenger jet last made contact with air traffic controllers at 1:35 a.m. on June 1, 2009, approximately 600 kilometres from the northeastern coast of Brazil, according to the BEA's third interim report.
The captain took a scheduled break around 2 a.m., leaving the plane in the hands of two co-pilots.
Ten minutes later, the pitot tubes became obstructed causing speed indicators to become unreliable and several automatic flight systems disconnected. The captain re-entered the cockpit shortly thereafter but the plane's stall continued.
The plane plunged for a total 3½ minutes before slamming into the Atlantic Ocean at 2:14 a.m.
According to the BEA, many of the passengers may have been asleep or nodding off as the plane fell and likely didn't realize what was happening.Suggest a correction