Paris: Pilots wrestled with the controls of an Air France airliner for more than four minutes before it plunged into the Atlantic with its nose up, killing all 228 people on board, French investigators said on Friday.
Aviation industry sources told Reuters pilots appeared to have acted contrary to normal procedures in raising, rather than lowering, its nose in response to an alert that the the plane was about to lose lift or, in technical parlance, 'stall'.
But they said information from black boxes hauled up from the Atlantic floor earlier this month was still incomplete.
The 2009 emergency began with a stall warning two and a half hours into the Rio-Paris flight and nine minutes after the captain had left the cockpit for a rest period.
Shortly before, a junior pilot had told flight attendants to prepare for a "little bit of turbulence"
The Airbus A330 jet climbed to 38,000 feet and then began a dramatic three and a half minute descent, rolling from left to right, with the youngest of three pilots handing control to the second most senior pilot one minute before the crash.
The timeline was described in a note by France's BEA crash investigation authority, which said it was too early to give the causes of the crash ahead of a fuller report in the summer.
"These are so far just observations, not an understanding of the events," BEA director Jean-Paul Troadec told reporters.
The captain returned after "several attempts" to call him back to the cockpit but was not at the controls in the final moments, according to information gleaned from black boxes.
By the time the 58-year-old returned, just over a minute into the emergency, the aircraft was plunging at 10,000 feet a minute with its nose pointing up 15 degrees and at too high an angle compared to the onrushing air to provide lift.
The BEA said the reading of the black boxes suggested the crew were not able to determine how fast the plane was flying.
That echoes earlier findings which suggest the pitot tubes or speed sensors on the plane may have become iced up.
The airline said in a statement that the crew had demonstrated a "totally professional attitude". France's pilots union declined to comment.
"It's very emotional to see the unrolling minute by minute or second by second at some points of what happened," said John Clemes, vice president of the families' support group.
"You automatically think of your family member and how they were living through this. It's the events that caused the deaths of 228 people so it's traumatic and moving.
France's BEA crash investigation agency said pilots pulled the nose up at crucial moments as the aircraft became unstable and the aircraft generated an audible stall warning.
"The inputs made by the pilot flying were mainly nose-up," the BEA said in a timeline based on initial examination of the cockpit voice and data recorders.
A top aircraft industry safety consultant said the standard guidance in the Airbus pilot manual called for the pilot to push the control stick forward to force the plane's nose down in the event of a stall, which can lead to a loss of control.
"The BEA is now going to have to analyse and get to bottom of how crew handled this event," said Paul Hayes, safety director at Ascend Aviation, a UK-based aviation consultancy.
"The big question in my mind is why did the pilot flying (the aircraft) appear to continue to pull the nose up," he said.
"I must stress we are commenting and speculating on peliminary factual information, which will need analysing."
The BEA report was strictly factual and did not allocate any blame or cause of the crash on June 1, 2009.
"These are so far just observations, not an understanding of the events," BEA director Jean-Paul Troadec told reporters.
In a passage likely to attract scrutiny, the BEA said the pilot "maintained nose-up inputs" when a fresh stall warning went off 46 seconds after the autopilot disengaged itself.
The BEA declined to say whether this was the correct action to take and the information given so far does not give a complete picture of the information displayed to the crew.
But the response contrasts with the latest advice to pilots contained in an Airbus training seminar in October last year, according to a document obtained by Reuters.
In large red capital letters, the document says that in the event of a stall warning, pilots should "APPLY NOSE DOWN PITCH CONTROL TO REDUCE AOA (ANGLE OF ATTACK)".
Two aviation industry sources said the drill in force at the time of the accident was to apply full thrust and reduce the pitch attitude of the aircraft, which means lowering the nose.
Later guidance calls for pilots to push the nose down and adjust thrust as necessary, they said, asking not to be named.
The crew's response will be added to what is already known about probable icing of the aircraft's speed sensors, which Air France identified as the most likely cause of the crash.
Airbus said the report upheld earlier evidence which was based on automated maintenance messages relayed from the plane.
An aerodynamic stall is a loss of lift due to a high angle of attack, or angle between the plane and airflow. Pushing the control stick forward and lowering the nose adjusts for this.
It does not refer to a stall of the engines, which the BEA said had operated and responded throughout to crew actions.
The BEA dampened speculation that the jet may have been engulfed by a freak equatorial storm.
Pilots had decided without apparent stress to alter course slightly to avoid turbulence shortly beforehand. But the junior pilot told flight attendants to prepare for a "little bit of turbulence"
"In two minutes we should enter an area where it'll move about more than at the moment; you should watch out," he told cabin staff. "I'll call you back as soon as we're out of it."
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