Indonesian investigators on Wednesday said that a malfunctioning throttle may have caused the pilots of the Sriwijaya Air plane to lose control, leading to the aircraft crashing into the sea on January 9, reported AP. All 62 people on board had died in the crash.

In a preliminary report, the National Transportation Safety Committee investigators provided details of the pilots’ struggle to fly the plane as soon as it was airborne. The investigators, however, also said that they were struggling to understand why the plane nosedived into the Java sea minutes after taking off from Jakarta.

Nurcahyo Utomo, the lead investigator, said the left engine’s throttle lever had moved backward on its own while autopilot was engaged. This reduced the power output of the engine just before the aircraft plunged into the sea.

A family member of one of the deceased also spoke about the malfunctioning throttle, reported Bloomberg. The family members were given a briefing on Tuesday before the preliminary report was released.

“The NTSC [National Transportation Safety Committee] hasn’t reached any conclusion on the cause of the crash, but they did say that there was an uncommanded backward movement of the left throttle lever while the autopilot was in operation,” said Rafik Alaydrus, who lost his wife in the crash.

Utomo said the pilots in previous flights had reported problems with the automatic throttle system on the Boeing 737-500, a 26-year-old aircraft. The plane was out of service for nine months because of the cutbacks caused by the coronavirus pandemic. The regulators and the airline, however, had said that the plane had undergone inspections before commercial flight operations resumed in December.

The Boeing 737-500 crashed near Laki Island, about 12 km from the airport. The plane, which had departed for Pontianak in West Kalimantan, disappeared from the radar after taking off just after 2.30 pm.

Patchy safety record

The Boeing 737-500 is older than Boeing’s problem-plagued 737 MAX model. The older 737 models are widely flown and do not have the system implicated in the MAX safety crisis.

The incident came just after aircraft maker Boeing agreed to pay more than $2.5 billion (over Rs 18,350 crore) in fines and compensation after reaching a settlement with the United States Department of Justice for two plane crashes that killed 346 people and led to the grounding of its 737 MAX jetliner model.

In October 2018, 189 people were killed when a Lion Air Boeing 737 MAX jet crashed into the sea about 12 minutes after taking off from Jakarta on a routine one-hour flight.

The Jakarta-based Sriwijaya Air group flies largely within Indonesia and was founded in 2003. The airline has a good safety record till now, with no onboard casualties in four incidents recorded on the Aviation Safety Network database. Indonesia’s air safety record is, however, patchy.

In 2007, the European Union had banned all Indonesian airlines following a series of crashes and reports of deteriorating oversight and maintenance of planes. The restrictions were lifted in 2018. Further, the United States’ Federal Aviation Administration had between 2007 and 2016 lowered its Indonesia safety evaluation to Category 2, meaning that the regulatory system was inadequate.