The Sriwijaya Air 737 that crashed into the Java Sea last month had an imbalance in engine thrust due to misaligned throttle levers, that sent the plane into a roll and eventually a dive into the sea, according to a preliminary report on the incident.
Indonesian air safety investigation body, the KNKT, has released its preliminary report into Flight SJ 183, a Boeing 737-500, which crashed into the Java Sea just minutes after take-off from Jakarta on Saturday, 9 January 2021. All 63 people on board were killed in the accident.
According to the KNKT report, the plane climbed to 8,150 feet before the left engine throttle lever moved back, while the right lever stayed put.
“We don’t know if it’s broken or not, but it’s an anomaly because the left moved far back, the right did not as though it was stuck,” KNKT investigator Nurcayho Utomo said in a press conference.
Then, at 10,900 feet, the autopilot reportedly disengaged, which caused the plane to roll to the left by over 45 degrees, and start its dive, the report said.
It had been previously reported that the aircraft had pre-existing maintenance problems with its autothrottle system, which automatically controls the plane’s engine power.
However, the report states the autothrottle system was repaired by engineers four days before the crash.
Additionally, pilots can easily manually control the throttle meaning a malfunctioning autothrottle is not likely to be the single cause of such an accident.
Divers in Indonesia continue to perform underwater searches for the plane’s cockpit voice recorder, which would help investigators to better understand the cause of the crash, and the actions taken by the pilots before the crash.
Both pilots are said to have been very experienced, with the captain accruing over 17,900 flight hours over his career, and the first officer 5,100.
The KNKT stated that additional emergency training protocols have been rolled out throughout the Indonesian aviation industry, while the country’s engineers have been reminded to handle all defects per safety manuals.
An internal memo was sent to Sriwijaya staff to ensure that pilots write detailed maintenance reports to assist engineers in troubleshooting any issues found in the aircraft’s systems.
The investigation into the crash and its causes will continue, with a final report on the investigation due within one year of the crash, as per international standards.