A faulty component was a “major factor” when an AirAsia plane crashed into the Java Sea, killing 162 people last December, Indonesian officials say.
The first major report into the crash found that actions by the crew in response to the malfunction also contributed to the disaster.
The Airbus A320-200, going from Surabaya to Singapore, was 40 minutes into the flight when contact was lost.
The report is the result of a year-long investigation.
Officials pinpointed the fault to the plane’s rudder control system.
The pilots responded to four warning alerts by resetting the system, which caused the autopilot to disengage, and they lost control of the aircraft.
The plane’s wreckage was found days after the crash at the bottom of the Java Sea near Borneo. Only 106 bodies have been retrieved so far.
Most of the passengers were Indonesian.
Analysis: Karishma Vaswani, BBC News, Singapore
Families of the 162 people on board AirAsia flight QZ8501 have been waiting anxiously for the results of this investigation.
Indonesian investigators didn’t release their preliminary findings earlier this year, saying they were under no legal obligation to do so.
Covering the crash at the time, the working theory was that pilot error must have been a major contributor, or that bad weather was a factor.
But this report shows that it was actually the response of the crew to a chronically faulty component on the plane that caused the plane to crash and that bad weather had nothing to do with it.
AirAsia will now have many questions to answer about why the aircraft was not better maintained and why its pilots were not better prepared to handle these problems.