Sriwijaya Crash – Autothrottle A Likely Suspect?

By Spyros Georgilidakis | January 22, 2021

Indonesia’s investigators are looking at the possible role the autothrottle system may have had, in the Sriwijaya 737-500’s crash.

Just yesterday, Basarnas (Search & Rescue) announced that their role in the accident was ending. The search for human remains ended. So from this point on, the Indonesian Air Accident Investigation authorities (KNKT) take over. However, KNKT have had the Flight Data Recorder (FDR) in their hands for 9 days by this time. And they already have a lead on how the Sriwijaya crash unfolded, and a suspect, in the autothrottle system.

Sriwijaya Crash – Autothrottle An Early Suspect?

The KNKT were able to download the information of the FDR successfully. And early reports suggest that the autothrottle system is a point of interest in the Sriwijaya crash. The Indonesian aviation authority has ordered users of Boeing 737 ‘Classics’ (-300, -400 and -500 models) to make “inspections”. Neither the airlines nor the KNKT have made public the exact nature of these inspections.


Previous Autothrottle Incident – Relevant to Crash?

A few days before the crash, another Sriwijaya crew reported issues with the autothrottle system. However it appears that this issue was not written up properly. KNKT investigator Nyrcayho Utomo confirmed this yesterday to Reuters:

There was a report of malfunction on the autothrottle a couple of days before to the technician in the maintenance log, but we do not know what kind of problem. If we find the CVR (cockpit voice recorder) we can hear the discussion between the pilots, what they talked about and we will know what is the problem.

Sriwijaya Crash – Autothrottle An Early Suspect?

Malfunctioning autothrottles are not unheard of. But they shouldn’t lead to a loss of control or crash, as in Sriwijaya’s case. Typically, if the system is malfunctioning, pilots will turn it off and continue flight by controlling the throttles manually. This is what the previous crew did, when they had problems with the system two days earlier.

According to Wall Street Journal, the crew flying the day of the accident did something different. On the day of the crash, the Sriwijaya crew did not turn off the autothrottle system. WSJ’s sources suggest the issue was affecting one engine. So the crew appeared to be trying to work around the problem.


Distraction Or Cause?

What is not clear if the autothrottle problem was a distraction for the Sriwijaya crew, that lead to the crash. Or if perhaps it had a more direct role, causing asymmetric thrust that overpowered the crew or the autopilot. These are questions that KNKT investigators hope to answer with information from the cockpit voice recorder (CVR).

With the search for human remains officially over, now efforts are focusing on finding that CVR. The FDR has shown investigators what the autothrottle and the pilots were doing, leading up to the Sriwijaya crash. But they now need to understand how and why the event evolved in the way it did. Also, investigators believe that the aircraft was intact and both engines producing power, at the time of the crash.

Haryo Satmiko, the Deputy Head of Indonesia’s KNKT, did confirm that they are looking into an autothrottle problem, as part of the Sriwijaya crash investigation. But more detail on the matter will come from a preliminary report. KNKT expects to be able to release it within 30 days from the crash. This is what ICAO standards call for.

Hopefully, that preliminary report will have the CVR data, to draw more information on the matter. But finding the CVR could take more time. This is because its pinger/locator separated from the recorder itself.

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