May 27 (Bloomberg) -- Air France Flight 447 crashed in 2009 after the Airbus A330 lost speed and stalled before beginning a three-and-a-half minute plunge into the Atlantic Ocean that killed all 228 people on board, an investigation found.
The findings by the French BEA air-accident investigation bureau show the autopilot disengaged shortly after pilots alerted cabin crew of possible turbulence ahead. Data presented by BEA show the youngest of the three pilots, who was 32 and in control for most of the last minutes, angled the jet’s nose higher, a position the aircraft maintained until its impact.
The preliminary report sheds more light on the final minutes before the deadliest crash in Air France’s history, with pilots scrambling to avert disaster as the jet hurtled toward the ocean surface at a speed of 180 feet (55 meters) a second. The least experienced of the three pilots was managing the aircraft until less than one minute before recordings stopped, with the captain present though no longer in charge of the jet.
“The question is why the pilot kept giving nose-up inputs when the plane was in a stall,” said Paul Hayes, director of safety at Ascend Worldwide Ltd., a London-based aviation consultant company. “You should put the nose down to recover speed.”
Breakthrough Recovery
The search for clues achieved a breakthrough after the two flight recorders were recovered from 3,900 meters (12,800 feet) beneath the Atlantic and returned to Paris this month, two years after the jet disappeared into the night on June 1, 2009. All data and voice recordings from the two recorders were recovered in full, after being submerged for two years, the BEA said.
The report doesn’t mention if the pilots realized they were in a stall, or if Captain Marc Dubois, 58, ever attempted to regain control of the cockpit and relieve his junior crew. Dubois had been away from the cockpit when the autopilot disengaged, and his colleagues tried several times to call him back in the first minute of the unfolding drama, the BEA said.
A stall can occur when an aircraft slows to the point where its wings suddenly lose lift, an incident pilots are trained to overcome. Earlier transmissions from the jet had shown that airspeed sensors, or pitot tubes, made by Thales SA had failed, presenting pilots with a sharp drop in speed readings on their displays after they entered ice clouds.
Deteriorated Situation
The data and cockpit voice recording suggest the pilots never realized that the plane had entered a stall, BEA Chief Investigator Alain Bouillard said in an interview.
“They hear the stall alarm but show no signs of having recognized it,” he said. “At no point is the word ‘stall’ ever mentioned.”
Even as the plane plunged rapidly from 38,000 feet to 10,000 feet, “they make this observation without seeming to understand that they are in a stall,” Bouillard said.
By the time Captain Dubois had returned to the cockpit, “the situation had already deteriorated considerably,” Bouillard said.
The analysis shows that the pilot who took manual control after the auto-pilot shut down had favored climbing above the approaching stormy clouds but were prevented from doing so because it wasn’t cold enough for the jet to ascend to that level. The crew alerted flight attendants that they should “watch out” as the approaching zone would move the jet around.
Resting Pilot
With the flight captain resting and the two co-pilots at the controls, the auto-pilots disengaged four hours into the flight. The pilots acknowledged that the speed sensors had failed as they responded by pulling up the nose of the aircraft, voice and data recordings show. A stall warning sounded in the cockpit, the BEA said.
According to the BEA, the co-pilots continued to increase the angle of climb, rising rapidly from 35,000 feet to 37,500 feet. When a third stall warning sounded, they continued to pull back on the controls with the engines set to full thrust and rose to about 38,000 feet, where the plane entered a stall.
Less than two minutes after the autopilot went off-line, Dubois returned to the cockpit, and the conversation shows he was with his colleagues during the remainder of the flight. It’s routine for pilots to take a break away from the cockpit on long-haul flights, Air France has said.
Last-Minute Control
“The aircraft got well into the stall and pilots were acting as if they didn’t know that,” said David Learmount, a former combat pilot for the Royal Air Force and safety editor for Flight magazine. “The only way to recover is to put the nose down and get the speed back.”
Dubois had almost 11,000 hours of flight experience, compared with fewer than 3,000 hours for the youngest member of the cockpit. His body was found among debris and other victims floating on the ocean surface in the weeks after the crash.
The BEA’s report gave no indication about the tone in the cockpit, with only few reference to exchanges about who was in charge or the co-pilot saying early on “So, we’ve lost the speeds.” The third member of the crew, aged 37, was given control in the last minute before impact, receiving the order “Go ahead, you have the controls,” by his colleagues.
No further comments by pilots were published by the BEA for the last minute. The BEA said that the plane’s so-called angle of attack, which defines the angle between air flow and the longitudinal axis of the aircraft, always remained above 35 degrees during the descent.
‘Pull Up!’
“Why did the pilot fly the way he did? That’s the question of the day,” said Hans Weber, president of Tecop International Inc., an aviation consulting firm based in San Diego, who has given safety advice to the U.S. Federal Aviation Administration. “There was no indication they were flying through horrendous turbulence or weather.”
Air France said the crew made a detour to avoid bad weather, and that the pilots showed professionalism, according to an e-mailed statement by the French airline. Airbus said the report “constitutes a significant step towards the identification of the complete chain of events,” according to a release today. Airbus said last week that it had no additional recommendations to operators of the A330 aircraft.
With the plane’s nose still pointed up, the jet began falling at about 10,000 feet a minute, rolling heavily from left to right, the report found. Almost one minute into the stall, the pilots had reduced engine thrust and tried pushing down on the controls to lower the nose.
Close to Impact
Airspeed indications returned and the alarm sounded again as the stalled aircraft picked up some speed, though the plane continued falling until the first co-pilot commented that the aircraft was approaching an altitude of 10,000 feet.
The final recordings show the aircraft had fallen to a ground speed of about 123 miles per hour (198 kilometers), the BEA said. The collision warning, “Terrain! Terrain! Pull Up!” sounded at an altitude of about 1,500 feet, which at the plane’s speed of descent was “very close to impact,” Bouillard said.
The report concluded that the aircraft remained stalled during its descent, and that the engines were operational and responded to crew commands throughout. The preliminary findings from the black-box data have not yet established any conclusions about the accident’s causes or led to any recommendations, the investigator said. An interim report is due in mid-July.
“What we’re publishing today are technical observations, including actions by the crew, which don’t explain the accident,” BEA chief Jean-Paul Troadec told reporters. “Understanding this chain of events and the reasons behind the crew’s actions is a complex task that is just beginning.”
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