Air France 447 May Have Stalled on Sensor Failure
Air France Flight 447’s flight recordings show the aircraft lost speed and stalled after its airspeed sensors failed while the two co-pilots were at the controls, two people with knowledge of the investigation said.
The chief pilot, Captain Marc Dubois, was not in the cockpit when the Airbus A330’s airspeed sensors malfunctioned, causing the autopilot to disengage over the Atlantic Ocean, said the people, who declined to be identified because the investigation is still confidential.
A low-speed stall occurs when an aircraft slows to the point where its wings suddenly lose lift, an incident pilots learn to overcome in basic training. 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 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 U.K. Royal Air Force pilot and safety editor at Flight International. Pulling out can be straightforward, “providing you realize you’re in one,” he said.
Making Progress
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 also declined to comment on the circumstances of the June 1, 2009, crash.
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 meters (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 (HO) airspeeds sensors, or Pitot tubes, occurred while the plane was cruising at about 35,000 feet, four hours after take-off 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.
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 Corp. (GR)
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.
According to a report by Der Spiegel Online, which could not be verified, the black boxes reveal that the Air France plane climbed sharply after the speed-sensor failure and Captain Dubois returned to the cockpit before the crash.
The BEA has said it plans to issue a preliminary factual statement May 27 on the findings of its initial black-box analysis, without identifying any of the accident’s causes. An interim report is due in mid-July.
To contact the reporters on this story: Laurence Frost in Paris at
[email protected]; Andrea Rothman in Paris at
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To contact the editors responsible for this story: Chad Thomas at
[email protected]; Benedikt Kammel at
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