A fault with the rudder control system was a major factor in the AirAsia plane crash last December in which 162 people died, Indonesian investigators have said.


In their final report into the crash, Indonesia's official national transportation safety committee also said that crew action in response to the fault caused the jet to lose control.


Repeated problems with the rudder system led to the pilots disengaging the autopilot in stormy weather in an attempt to fix the situation. Investigators said the soldering on the Rudder Travel Limiter system '" which helps control the rudder's movement -- was cracked, leading it to send repeated warning systems to the pilots.


When they received the fourth warning, the pilots pulled circuit-breakers on part of the aircraft's control system in a bid to reset the system. This turned off the autopilot, and the plane then started to roll, the report said.


"Subsequent flight crew action resulted in inability to control the aircraft,' said the report. The plane went into a "prolonged stall condition that was beyond the capability of the crew to recover', it said. It added the flight data recorders did not indicate the weather had affected the aircraft.


The cracked solder joint had malfunctioned repeatedly, including four times during the flight, and 23 times the previous year. The Airbus A320 aircraft crashed less than halfway into a two-hour flight from the Indonesian city of Surabaya to Singapore on 28 December last year.