Investigators probe whether automatic throttle malfunction caused Indonesian air crash

Nicola Smith
·3 min read
Funeral ceremony for Sriwijaya aircraft crew in Surabaya - Anadolu Agency
Funeral ceremony for Sriwijaya aircraft crew in Surabaya - Anadolu Agency

Investigators in Indonesia are probing whether a malfunctioning automatic throttle could have brought down the Sriwijaya Airlines flight that nosedived into the Java Sea on January 9.

A person familiar with the investigation told Bloomberg that the autothrottle was producing more thrust in one of the Boeing 737-500’s two engines than the other after the plane took off from Jakarta’s Soekarno-Hatta airport carrying 62 people.

Unequal thrust can cause a plane to roll onto its side and descend abruptly and autothrottle malfunctions have previously caused incidents on the 737 and led to the Tarom airlines crash in Romania in 1995, which killed 60 people.

The source said the device had been having problems on previous flights made by the aircraft.

Nurcahyo Utomo, the lead investigator at Indonesia’s National Transportation Safety Committee, confirmed that a malfunctioning throttle was “one of the factors that we are looking at, but I can’t say at this point that it’s a factor for the crash or there was a problem with it."

Earlier this month, officials investigating the tragedy were reported to be looking at a possible link to the 27-year-old plane’s prolonged grounding because of travel restrictions and reduced timetables during the Covid-19 pandemic.

A soldier and rescuer carry debris found in the waters near the crash site - Tatan Syuflana/AP
A soldier and rescuer carry debris found in the waters near the crash site - Tatan Syuflana/AP

“There’s a major problem starting to raise its head in terms of restoring these aircraft because while out of service for nine or 10 months, they need to be kept operating, otherwise they deteriorate,” said Hugh Ritchie, chief executive of Aviation Analysts International, an Australian air safety consulting firm.

The Indonesian plane did not fly between March 23 and Dec 19 last year, and was then used 132 times after it resumed operating, according to aviation data provider Flightradar24.

Indonesian officials have said that the plane passed safety inspection checks on December 2 – including for engine corrosion – and was declared airworthy on December 14.

Indonesian investigators and a team of engineers from Boeing are piecing together information from the aircraft’s flight data recorder that has been recovered from the underwater crash site, but rescuers are still trying to locate the memory module of the cockpit voice recorder, which was damaged on impact.

The part is important to ascertain how the pilots handled the autothrottle crisis if it is found to be the reason behind the crash.

Twin-engined jetliners are able to fly on a single engine so an autothrottle failure itself does not mean a plane will crash, although pilots must respond quickly to readjust the plane and can become disorientated in clouds.

Flight 182 abruptly nosedived more than 10,000 feet in about 15 seconds just minutes after take-off in heavy rain.

The Boeing 737-500 was carrying 50 passengers – including ten children - and 12 crew was en route to Pontianak in West Kalimantan province on Indonesia's Borneo island. At the time of the crash, local fishermen spoke of hearing a thunderous explosion.

When they reached the area, they discovered pieces of wreckage from the airliner. "The plane fell like lightning into the sea and exploded in the water," one fisherman told the BBC’s Indonesian service. "It was pretty close to us, the shards of a kind of plywood almost hit my ship."