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Throttle again noted as possible Sriwijaya crash cause

written by Hannah Dowling | February 11, 2021
A Sriwijaya Air 737-500, PK-CLC, crashed into the Java Sea shortly after take off from Jarkarta on 9 January 2021.

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 182, 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.

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“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.

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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.

9 Comments

  • Jeff

    says:

    For goodness sake if an auto system is malfunctioning disconnect it! Let’s get away from the Aeroplane controlling the Pilot iso the Pilot flying the aeroplane!

    • Matt

      says:

      Not completely disagreeing with the sentiment of your point, but your proposed solution is assuming that the crew noticed the auto throttle abnormality. Perhaps the autopilot was doing a good job of masking the asymmetry…until it suddenly wasn’t?

    • Chris Malone

      says:

      Pilot error ,Pilot training lacking

  • Kevin

    says:

    Unlike an Airbus, the thrust levers on the 737 move as the thrust level changes or is commanded to do so. Sit in the pilots seat. It is very hard to miss a t/l moving back towards idle with associated loss of thrust. Fix: push the T/L forward, if it comes back, disconnect the autothrottle and manage the thrust on both engines manually. The A/P will auto disconnect if it cannot control the roll . That is part of its function.

  • Ron Cook

    says:

    My concern is over the maintenance. It would not be the first time proper maintenance wasn’t done but it was signed off. Sometimes the fault can’t be reproduced. Sometime fake parts or faulty parts are used as replacements. Pressure from management on maintenance and QA prevents a proper assessment and repair more often than airlines will acknowledge.

  • Mike

    says:

    The way the Boeing Autothrottle system works even if you are in a smoke filled cockpit you can detect asymmetry between the Thrust Levers-they each have their own servo so there is a tactile split. Even if the A/T malfunctioned and one thrust lever was full forward and the other full aft the aircraft would be completely controllable by anyone with basic flying ability given they were already at altitude. If a malfunctioning A/T system lead to LOCI at the altitude they were at neither crew member belonged in any type of cockpit.

  • Mr John E Brett

    says:

    It sounds horribly familiar to a very similar accident to another Indonesian B737 that was deliberately crashed into the ocean by the Captain, after locking the FO out of the cockpit because he was demoted to an ordinary line pilot for some strange reason!!? 😳🤔😪

  • Td

    says:

    Once that nose is pointing down at the ocean at the rate of descent suggested even if the engines were at low power or shut down the airspace that would be carved out in a properly controlled recovery without overstressing would be enormous. The final report will certainly be interesting.

  • I have worked in that part of the world. You would not get me to fly on any of their aeroplanes.

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