LE BOURGET, FRANCE — A combination of faulty sensors and mistakes by inadequately trained pilots caused an Air France jet to plunge into the Atlantic Ocean in 2009, killing all 228 people aboard in the airline’s deadliest ever crash, French investigators said Thursday.
Investigators are urging better instruction for pilots on flying manually at high altitudes and stricter plane certification rules as a result of a three-year investigation into what happened to Flight 447.
Airbus, manufacturer of the A330 plane, said in a statement that it is working to improve speed sensors known as pilot tubes and making other efforts to avoid future such accidents.
Air France stressed the equipment troubles and insisted the pilots “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.”
But the Bureau for Investigations and Analysis’ findings raised broader concerns about training for pilots flying high-tech planes when confronted with a high-altitude crisis.
The report also could have legal implications: A separate French judicial investigation is still under way, and Air France and Airbus have been handed preliminary manslaughter charges.
The investigators noted a combination of “human and technical factors” behind the crash. The plane flying from Rio de Janeiro to Paris slammed into the sea during a nighttime thunderstorm on June 1, 2009.
Ice crystals that blocked the pilot tubes were the “unleashing event” that set off the plane’s troubles, chief investigator Alain Bouillard said. The plane’s autopilot shut off, and the co-pilots had to fly manually while a succession of alarms were going off. The captain was on a rest break.
In one fatal decision, one of the co-pilots nosed the Airbus A330 upward during a stall – instead of downward, as he should have – because of false data from sensors about the plane’s position. Mr. Bouillard said that was an “important element” of the cause of the crash.
The two pilots at the controls never understood that the plane was in a stall, he said, adding that only a well-experienced crew with a clear understanding of the situation could have stabilized the plane in those conditions.
“In this case, the crew was in a state of near-total loss of control,” Mr. Bouillard said.
Central to the accident is the fact that when the automation failed, the pilots were presented with conflicting information that was obviously incorrect, said William Voss, president of the Flight Safety Foundation in Alexandria, Va. But they were unable to look through this and understand what the aircraft was actually doing.
“Pilots a generation ago would have done that and understand what was going on, but [the AF447 pilots] were so conditioned to rely on the automation that they were unable to do this,” he said.
“This is a problem not just limited to Air France or Airbus,” Mr. Voss said. “It’s a problem we’re seeing around the world because pilots are being conditioned to treat automated processed data as truth, and not compare it with the raw information that lies underneath.”