Indonesia's aviation accident investigator concluded on Thursday, Nov. 9, that a malfunctioning automated engine throttle system that pilots did not adequately monitor caused the tragic crash of a Sriwijaya Air 737-500 plane in January 2021.
On January 9, 2021, only a few minutes after takeoff, Flight 182 made an emergency landing in the waters of the Java Sea about 3,000 meters off the coast of Jakarta.
There were 62 passengers aboard, and all of them were killed. On the aircraft were two pilots, four flight attendants, and 56 passengers, Bloomberg reported.
Mechanical Issues
As detailed by The Straits Times, the National Transportation Safety Committee of Indonesia (KNKT) identified several reasons that led to the accident, beginning with mechanical problems.
According to a press statement issued by KNKT, an issue occurred with the autothrottle system of the twin-engine airliner, which resulted in the aircraft veering off course.
The autothrottle system automatically controls the power output of the engine. Based on the government agency's 202-page assessment, problems with the system had been recorded 65 times in the plane's maintenance records since 2013 but had not been fixed at the time of the disaster. The jet is 26 years old.
Because pilots can regulate the thrust levers manually, it is not necessary for an airplane to have a functional autothrottle for it to be dispatched.
However, KNKT stated that in this particular instance, they did not appear to have carefully monitored the asymmetrical thrust situation, which involved the left engine throttle lever moving back to as low as 34% speed after takeoff while the right engine throttle lever remained in its original climb setting at approximately 92%.
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Pilot Complacency
The agency also stated that there were various signals provided, which the pilots could have verified to detect aircraft abnormalities. These indications included engine parameters, the position of the thrust levers, and the roll angle.
The primary investigator, Nurcahyo Utomo, said at a briefing that "complacency and confirmation bias led to limited monitoring" by the pilots, who failed to instantly remedy the issue despite having enough opportunity to do so.
On the reports, the autopilot became disconnected at around 10,700 feet (3,260 meters). At that point, the aircraft rolled to the left at an angle of more than 45 degrees and began its descent into the water.
Before the recording ended, the first officer stated "upset, upset" and "captain, captain," but the captain's channel was not functioning, which made it more challenging for authorities to analyze what had happened.
When an aircraft operates outside of the typical flight parameters - such as speed, angle, or altitude - this is referred to as an upset scenario.
Conclusion
Utomo told reporters that Indonesian airlines lacked norms and procedures on upset prevention training, which includes monitoring.
He stated there was nothing wrong with the machine's design or mechanics. If they'd observed it, "the pilots could have fixed it."
He added Sriwijaya has subsequently trained its pilots.
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Written by Trisha Kae Andrada
