A French airliner plunged out of control for four minutes before crashing into the Atlantic in 2009, investigators said, in a report raising questions about how crew handled a “stall alarm” blaring out in the cabin.
Information gleaned from black boxes recovered almost two years after the disaster killed 228 people, confirmed that speed readings in the Airbus cockpit had gone haywire, believed to be linked to the icing of speed sensors outside the jet.
As Air France pilots fought for control, the doomed A330 dropped 11,582m, rolling left to right, its -engines flat out, but its wings unable to grab enough air to keep flying.
The plane crashed on June 1, 2009, en route from Rio de Janeiro to Paris. The black boxes stopped recording at 2:14am GMT.
France’s BEA crash investigation agency said in a detailed chronology of the crash that commands from the controls of the 32-year-old junior pilot on board had pulled the nose up as the aircraft became unstable and generated an audible stall warning.
Aviation industry sources said that this action went against the normal procedure which calls for the nose to be lowered in response to an alert that the plane was about to lose lift or, in technical parlance, “stall.”
This type of aerodynamic stall is nothing to do with a stall in the engines, both of which kept working as crew requested.
“A stall is the moment at which a plane stops flying and starts falling,” said David Learmount, operations and safety editor at the British aviation publication Flight International.
A top aircraft industry safety consultant said the standard guidance in the Airbus pilot manual called in this event for the pilot to lower the nose by pushing the control stick forward.
“The BEA is now going to have to analyze and get to the 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.
French investigators said the emergency began with the autopilot disengaging itself two and a half hours into the flight and the junior pilot, who had been in control at take-off, picked up manually and saying: “I have control.”
The autopilot appears to have responded to a loss of reliable airspeed information. This was accompanied moments later by the disembodied voice of a recorded “stall” alert.
It is what happened next that is likely to fuel most theories on what preceded the crash, but Air France and its main pilots union insisted faulty speed probes were the root cause.
In a passage likely to attract particular scrutiny, the BEA said the pilot “maintained” the nose-up command despite fresh stall warnings 46 seconds into the four minute emergency.
“The inputs made by the pilot flying were mainly nose-up,” the report added.
The Airbus jet climbed 914m to 11,582m despite the crew having decided earlier against a climb, and then began a dramatic descent, with the youngest pilot handing control to the second most senior pilot a minute before impact.
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 the black boxes.
By the time the 58-year-old returned, just over a minute into the emergency, the aircraft was in serious trouble: plunging at 3,050m a minute with its nose pointing up 15 degrees and at too high an angle to the air to recapture lift.