Doomed Sriwijaya Air plane had problem with throttle control system: Indonesia transport safety commission

JAKARTA : The Indonesian passenger aircraft that plunged into the Java Sea shortly after take-off last month, killing all 62 people aboard, had a problem with its throttle control system, preliminary investigations by the country’s National Transport Safety Commission (KNKT) showed.

“The left throttle lever was trimming back (the engine output), while the right throttle remained normal… The plane’s auto throttle system was not active,” Captain Nurcahyo Utomo, head of air safety investigation at the KNKT, told a virtual press briefing on Wednesday (Feb 10).

Capt Nurcahyo ruled out weather as a factor in the crash.

Bloomberg News, quoting a person familiar with the investigation, reported last month that the plane had problems with the automatic throttle on previous flights. It said investigators were looking at the device as a reason for the pilots losing control of the aircraft. Unequal thrust can cause a plane to roll onto its side and descend abruptly.

Indonesia's KNKT investigators inspect the debris of Sriwijaya Air flight SJ 182 plane recovered from the crash site on Jan 13, 2021.
Indonesia’s KNKT investigators inspect the debris of Sriwijaya Air flight SJ 182 plane recovered from the crash site on Jan 13, 2021.PHOTO: EPA-EFE

The 27-year-old Boeing 737-500 belonging to Sriwijaya Air took off on Jan 9 in the afternoon from Indonesia’s main gateway Soekarno-Hatta International Airport on the outskirts of Jakarta, en route to Pontianak, the provincial capital of West Kalimantan. It disappeared from radar four minutes after take-off.

On Jan 11, Capt Nurcahyo told The Straits Times the plane likely broke apart when it hit the water, noting that debris would have been scattered across a larger area if the aircraft had broken apart in mid-air.

Based on field data, the wreckage was found in an area between 300m and 400m in length and 100m in width.

The final piece of data received from the aircraft was when it reached 76m from the surface of the Java Sea.

Earlier, the head of KNKT, Mr Soerjanto Tjahjono, disclosed that the data at 76m indicated the aircraft system was functional. This, he said, apparently indicated that the engine was still operating before the plane hit the water.

Capt Nurcahyo said efforts were still underway to retrieve the memory unit of the aircraft’s cockpit voice recorder (CVR), which would further help the investigation. So far, only the flight data recorder has been found.

The CVR would help investigators determine why the flight parameters were changed. 

“Divers are being deployed again to a number of spots (on the seabed) where the CVR is suspected to be located, buried under the thick mud,” Capt Nurcahyo said.

He said the CVR would yield key information, including what was discussed between the pilots and what happened in the cockpit during the flight. 

“If we don’t find the CVR, it would affect our investigation significantly,” Capt Nurcahyo said. 

Indonesia has seen two other major plane disasters in recent years – a Lion Air crash in October 2018, which claimed 189 lives; and another in 2014 when 162 people were killed after an an AirAsia jetliner went down in the Java Sea.

By : Wahyudi Soeriaatmadja – THE STRAITS TIMES

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