December 4, 2022

A faulty automatic engine throttle system that was not properly monitored by pilots led to a fatal crash of a Sriwijaya 737-500 jet in January 2021, Indonesia’s aviation accident investigator KNKT said in a final report on Thursday.

The crash into the Java Sea after takeoff from Jakarta, which killed all 62 people on board, was Indonesia’s third major commercial plane crash in just over six years and highlighted its poor flight safety record.

Problems with the autothrottle system, which automatically controls engine power, had been reported 65 times in the 26-year-old jet’s maintenance logs since 2013 and were still unresolved prior to the accident, the agency said in its 202-page report.

A working autothrottle is not required for an aircraft to dispatch as pilots can manually control the throttles.

However, KNKT said that in this case they did not appear to have closely monitored the asymmetric thrust situation where the left engine throttle stick moved back to a speed of only 34% after takeoff while the right stick stayed in its original climb setting at about 92% . .

“There were several clues the pilots could have checked to identify the aircraft’s anomalies, such as engine parameters, thrust lever position and roll angle,” the agency said, adding that complacency and confirmation bias may have been a factor in the poor surveillance.

Sriwijaya did not immediately respond to a request for comment. Boeing, the maker of the 737-500 jet, declined to comment.

At about 10,700 feet, the autopilot disengaged and the aircraft rolled more than 45 degrees to the left and began its dive into the sea.

The first officer said “upset, upset” and “captain, captain” before the recording stopped, but the captain’s channel was not working, making it more difficult for investigators to analyze the events.

A disrupted situation involves an aircraft operating outside of normal flight parameters such as speed, angle, or altitude.

KNKT chief investigator Nurcahyo Utomo told reporters that there have been no regulations and guidelines for excitement prevention training by Indonesian airlines, ensuring a pilot’s ability to prevent undesirable situations from occurring, an important part of which is surveillance.

Sriwijaya has since conducted such training for its pilots, he said.

KNKT had addressed the lack of angry recovery training following the 2014 AirAsia Indonesia plane crash that killed all 162 people on board.

According to the final report, upset recovery training was then made mandatory in Indonesia in 2017, but Utomo said the aviation authority hadn’t updated the requirement after the UN aviation agency ICAO said in 2018 the course should also include upset prevention.

Indonesia is rolling out updated training on upset prevention and recovery, KNKT said in the report.