Failure to fix throttle led to plane crash in Indonesia

JAKARTA, Indonesia — Indonesian aviation investigators concluded Thursday that a nearly decade-long failure to properly fix a faulty auto-throttle, pilots’ overreliance on the aircraft’s automation system aircraft and inadequate training contributed to a Boeing 737-500 crash last year that killed 62 people.

National Transport Safety Committee investigators said in their final report that Sriwijaya Air’s jet maintenance record showed the problem with the auto-throttle had been reported by pilots 65 times since 2013 and was still unresolved. unresolved when the 26-year-old plane plunged into the Java Sea. after taking off from Jakarta on January 9, 2021.

Lead investigator Nurcahyo Utomo told a press conference that the pilots’ last conversation with air traffic control was about 4 minutes after takeoff, when they responded to an instruction to climb to 13 000 feet. The plane’s flight data recorder showed it reached an altitude of 10,900 feet and then began to decline, Utomo said.

He said the plane required less engine thrust as it approached its target altitude, but the auto-throttle was unable to reduce power to the right engine due to friction in the system. mechanical.

The auto throttle attempted to compensate by further reducing power to the left engine, reducing its output to 34%. Power from the right engine remained at its climb setting, about 92%, which resulted in highly uneven thrust, according to the report.

The pilot struggled to get the plane up, but “was unable to recover from the situation”, and the plane rolled onto its left side, according to the report.

A minute later, the flight data recorder showed that the auto-throttle had been disengaged when the aircraft nosed over. The recorder stopped recording a few seconds later.

Auto throttle can be used by pilots to automatically adjust speed, reducing their workload and engine wear. The auto-throttle movements are linked to 13 other aircraft components, according to the report.

Many of the issues leading up to the accident were revealed in a preliminary report released by Indonesian authorities last year. The final report released Thursday provided new details on the pilots’ response.

Utomo said inadequate training “contributed to the pilot’s inability to prevent and recover from the condition.”

The pilots’ overreliance on the aircraft’s automation system may have resulted in inadequate cockpit monitoring, so the flight deviation was not immediately noticed, the report said.

Utomo said the voice data recorder only operated on one audio channel, and another channel that was supposed to record all voices in the cockpit was filled with an unknown hum that prevented investigators from fully analyzing the coordination between the two pilots.

The report concluded that repeated attempts to repair the auto throttle over the years failed because they failed to properly address the mechanical problem.

Investigators worked with Boeing and engine maker General Electric to review information from the flight data recorder. A team from the National Transportation Safety Board and the US Federal Aviation Administration also joined the investigation.

The plane had been out of service for nearly nine months due to flight curtailments caused by the coronavirus pandemic. Regulators and the airline said they underwent inspections before resuming commercial flights in December 2020.

The disaster rekindled safety concerns in Indonesia’s aviation industry, which grew rapidly after the country’s economy opened up after the fall of dictator Suharto in the late 1990s. banned Indonesian airlines from operating there in 2007, but lifted the measure in 2016, citing improvements in compliance with international aviation standards. The European Union lifted a similar ban in 2018.

Sriwijaya Air, an Indonesian national airline founded in 2003, has had only minor security incidents in the past, although a farmer was killed in 2008 when a plane ran off the runway while landing due to a hydraulic problem.

In 2018, an Indonesian Lion Air Boeing 737 MAX 8 crashed, killing 189 people. An automated flight control system played a role in this accident, but the Sriwijaya Air jet did not have this system on board.