The pilot in charge of the doomed Air Asia jet that crashed into the sea was out of his seat when the plane went down, according to sources close to the investigation.
Details emerging of tragic flight QZ8501 suggest the captain was carrying out an "unorthodox procedure" when the plane's inexperienced co-pilot apparently lost control - and by the time he returned to his seat it was too late.
The Airbus A320 plunged into the Java Sea while en route from Surabaya, Indonesia, to Singapore on December 28, killing all 162 people on board.
A source close to the investigation said the jet, which had been flown by the same pilot just days before the crash, had been suffering maintenance faults on a key flight controller for over a week.
It was reported this week that problems with the Flight Augmentation Computer (FAC), and the way the pilots reacted to them, were at the heart of the crash investigation.
Investigators believe that, after trying to reset the device, the pilots pulled a circuit-breaker to cut its power.
Sources say it was the Indonesian captain Iriyanto who took this step, rather than his less experienced French co-pilot Remy Plesel, who was left flying the plane manually in delicate high altitude conditions.
The decision to cut off the FAC has surprised people following the investigation who said the usual procedure would be to press a button on the overhead panel.
"You can reset the FAC, but to cut all power to it is very unusual," said one A320 pilot, who declined to be identified. "You don't pull the circuit breaker unless it was an absolute emergency. I don't know if there was one in this case, but it is very unusual."
Aviation experts said the move was significant because the captain would have had to rise from his seat to reach the circuit breakers, which are located on a wall panel immediately behind the co-pilot.
Shortly after the pilot stood up, the junior pilot pulled the plane into a sharp climb, from which investigators said it then stalled or lost lift.
"It appears he (the co-pilot) was surprised or startled by this," said a person familiar with the investigation, referring to the pilot's decision to cut power to the affected computer.
The captain eventually resumed control, but he was unable to rescue the stricken aircraft.
Trajectory data also suggests it may have been difficult for someone to move around the cockpit in what was by then an upward tilting and unstable aircraft.
"The co-pilot pulled the plane up, and by the time the captain regained the controls it was too late," a source close to the investigation said.
AirAsia said it would not comment while the matter was under investigation by the National Transportation Safety Committee (NTSC) of Indonesia.
Tatang Kurniadi, chief of Indonesia's NTSC, told Reuters there had been no delay in the captain resuming control but declined further comment.
Airbus also declined to comment.
Meanwhile, lawyers for the family of the French co-pilot say they have filed a lawsuit against AirAsia in Paris for “endangering the lives of others” by flying the route without official authorisation.
Investigators have said the accident was not related to the permit issue.
AirAsia did not immediately respond to requests for comment on the lawsuit.
People familiar with the investigation have also warned against making assumptions on the accident's cause, which needs more analysis.
Safety experts say air crashes are most often caused by a chain of events, each of which is necessary but not sufficient to explain the underlying causes of the accident.
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