Air France Flight 447′s flight recordings show the aircraft slowed to a stall after its airspeed sensors failed while the two co-pilots were at the controls, two people with knowledge of the investigation said.
According to the sources, who declined to be identified, the confidential report revealed the chief pilot, Captain Marc Dubois, was not in the cockpit when the Airbus A330′s sensors malfunctioned, causing the autopilot to disengage over the Atlantic Ocean.
A low-speed stall occurs when an aircraft slows to the point where its wings suddenly lose lift, an incident pilots are trained to overcome. Flight 447′s last automated transmissions logged faulty readings from airspeed sensors that caused the autopilot to shut down in bad weather, minutes before the June 1, 2009, accident in which all 228 passengers and crew perished.
“To get out of a stall, you stick the nose down and wait for gravity to speed up the aircraft,” said David Learmount, a former UK Royal Air Force pilot and safety editor at Flight International. Pulling out of a stall can be straightforward, “providing you realise you’re in one,” he said.
Air France spokesman Jean-Charles Trehan said the company had no comment on the investigation’s early findings. France’s BEA air-accident investigation bureau, which also declined to comment, said it plans to issue a factual statement May 27 on its preliminary findings.
The cause of the crash is still unknown, but a report in German newspaper Der Spiegel suggests that a combination of human and technical errors may be to blame.
Nelson Marinho, who represents families of the Brazilian crash victims, said the group would wait for more information before commenting on the plane’s apparent stall.
“We’re rather concerned about this rush to blame the pilots,” Marinho said in an interview. “They are dead and cannot defend themselves.”
Investigators say they are making progress after maritime search and salvage experts retrieved the flight data and cockpit voice recorders this month from a depth of 3,900 metres (12,800 feet). Dubois was among the victims recovered from the sea surface in the weeks after the crash.
The failure of the Thales SA airspeed sensors, or Pitot tubes, occurred while the plane was cruising at about 35,000 feet, four hours after takeoff from Rio de Janeiro. At that stage in the Paris-bound flight, it is routine practice for the captain to take a rest break and leave the co-pilots at the controls, Air France has said.
The Airbus A330 has a small sleeping compartment where pilots can recline on long-haul flights.
“All members of the flight crew have the same technical skills and qualifications,” France’s SNPL pilot union said in a statement. It criticised what it described as “deliberately selective reports that cast suspicion on the crew.”
Airbus declined to comment beyond a BEA-approved May 16 telex, in which the company told airlines that preliminary black- box analysis yielded no additional recommendations. Two months after the crash, Airbus advised A330 and A340 operators to replace the Thales sensors with a model from Goodrich.
A stall is typically preceded by shaking and vibrating of the aircraft, and modern jets are equipped with a steering-stick shaker and audio warning to alert the pilot. Stall recovery requires pilots to coordinate the aircraft’s angle and power to the engines to avoid aggravating the situation.
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