JAKARTA, Indonesia -- A rudder control system problem that had occurred nearly two dozen times in the previous 12 months coupled with the pilots' response led to last year's crash of an AirAsia plane in Indonesia that killed all 162 people on board, investigators said Tuesday.
In releasing their report, the country's National Transportation Safety Committee said an analysis of Flight 8501's data recorder showed the rudder control system had sent repeated warnings to the pilots during the Dec. 28 flight from the Indonesian city of Surabaya to Singapore.
Aircraft maintenance records for the Airbus A320 showed that similar problems with the rudder system had occurred 23 times during the year prior to the crash, including nine times in December. The investigators said the fault was caused by cracked soldering on an electronic card.
Investigator Nurcahyo Utomo said the malfunction by itself should not have been dangerous. But after the fourth time an alarm went off during the flight, a crew member apparently went outside of handbook recommendations and removed a circuit breaker to try to reset the system, he said.
The autopilot then 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. It then began climbing rapidly before stalling and plummeting into the Java Sea.
Utomo said the voice recorder showed the pilot said "pull down," but in fact the plane was ascending.
"It seemed that there was a miscommunication between the pilot and co-pilot after the fourth fault," he said.
The same warnings had occurred three days before the crash with the same pilot, who witnessed a technician on the ground addressing the problem by removing the circuit breaker and then replacing it, according to Utomo and the investigation report. The data recorder showed the circuit breaker was apparently removed during the flight, they said.
Ruth Simatupang, a former Indonesian aviation investigator who was not involved with the report, questioned how the rudder system problems could have continued without any proper action by AirAsia or the government.
"It should be a big question for the airline," she said, adding that if the plane had been properly maintained, the problem would have been flagged and repaired. "With the 23 faults, there should have been a strong warning about the plane issued by the Transportation Ministry."
The last contact the pilots had with air traffic control indicated they were entering stormy weather. They asked to climb from 32,000 feet (9,753 meters) to 38,000 feet (11,582 meters) to avoid threatening clouds, but were denied permission because of heavy air traffic. Four minutes later, the plane dropped off the radar. No distress signal was issued, and investigators said weather conditions did not play a role in the crash.
Only 106 bodies were recovered from the sea due to rough conditions and poor underwater visibility that hampered divers' efforts. Most of those on board were Indonesians headed to Singapore ahead of the New Year holiday.
"There is much to be learned here for AirAsia, the manufacturer and the aviation industry," tweeted Tony Fernandes, chief executive of the Malaysia-based budget carrier. "We will not leave any stone unturned to make sure the industry learns from this tragic incident."
AirAsia Indonesia said in a statement that more pilot training and a new system that provides real-time monitoring of aircraft warning messages have been initiated as a result of the crash. The airline gave no direct reply when asked why the faulty rudder system was never fixed.
Indonesia's aviation industry has been plagued with problems stemming largely from the explosion of travelers and new airlines in the archipelago of 250 million people. Pilot shortages, shoddy maintenance and poor oversight have all been blamed following a string of deadly accidents in recent years.
The AirAsia crash came at the end of a particularly tragic year for air travel in Southeast Asia, including the mysterious disappearance of Malaysia Airlines Flight 370 in March 2014 with 239 people aboard, and the downing of Malaysia Airlines Flight 17 four months later over Ukraine, which killed all 298 passengers and crew.