The investigators said the fault was caused by cracked soldering on an electronic circuit board. Investigator Nurcahyo Utomo said the problem by itself should not have been dangerous. But after the fourth time an alarm went off during the flight, a crew member apparently went against recommendations and removed a circuit breaker to try to reset the system, he said.
The autopilot became disengaged, and the aircraft began to roll, but no movement was detected on the plane’s manual control stick for nine seconds, he said.
“Subsequent flight crew action resulted in inability to control the aircraft … causing the aircraft to depart from the normal flight envelope and enter a prolonged stall condition that was beyond the capability of the flight crew to recover,” the committee said in a statement.
The aircraft then began climbing rapidly before stalling and plummeting into the Java Sea. The plane reached an altitude of 38,000 feet before falling, at a maximum speed of 20,000 feet per minute. There were “about five minutes” from the time it stalled to the moment of impact.
Utomo said the voice recorder showed that whenever the plane ascended, “the captain said ‘pull down’ ... To go down, the captain has to say ‘push,’ while to go up, the captain has to say ‘pull,’ in reference to moving the side stick handle … It seemed that there was a miscommunication between the pilot and co-pilot after the fourth fault.”
The investigators said bad weather conditions did not play a role in the accident and no distress signal was received.
Lawyers for the victims’ families, the airline and its manufacturer are likely to debate whether the problem with the rudder system was a maintenance or design issue. Some relatives have begun action against the airline and Airbus.
Indonesia AirAsia said it has upgraded pilot training and enhanced safety standards since the crash.
“There is much to be learned here for AirAsia, the manufacturer and the aviation industry,” AirAsia founder Tony Fernandez tweeted.
In Europe, Airbus declined immediate comment.