SEATTLE — A lawsuit filed Thursday in Seattle against Boeing alleges that a malfunctioning autothrottle system on an older 737 led to the crash of Sriwijaya Air Flight SJ182 in Indonesia on Jan. 9, killing all 62 people on board.

The suit, filed in King County Superior Court on behalf of 16 families of crash victims, cites a list of previous incidents involving malfunctions of the 737 autothrottle system, arguing that this history suggests the system should have been redesigned.

"Specifically, the automatic throttle can stick and thereby cause significant differences in power between engines, resulting in a loss of control of the aircraft," the lawsuit states. The plaintiffs further allege that "Boeing did not provide adequate warnings and instructions about how to respond to a failure in the automatic throttle."

Because this was a 737-500 jet, built in 1994, its autothrottle system does not comply with later safety regulations.

A separate problem with the autothrottle may have contributed to the crash of Ethiopian Airlines ET302, the 737 MAX that crashed in March 2019, killing 157 people.

"We're seeking justice in the United States for Indonesian citizens as our judicial system works for everyone," said Lara Herrmann of Seattle's Herrmann Law Group, which filed the suit, asking for unspecified damages.

Boeing in a statement extended sympathy to the families and loved ones of those who died in the crash but added that "it would be inappropriate to comment while our technical experts continue to assist with the investigation, or on any pending litigation."

Automated systems didn't meet latest safety standards

This specific 737 had been parked for nine months last year due to the COVID-19 pandemic air travel downturn. The Indonesian aviation regulators issued a new certificate of airworthiness in mid-December 2020 that allowed it to return to service.

According to the preliminary report into the crash by the Indonesian National Transportation Safety Committee ("KNKT"), maintenance logs show that pilots repeatedly reported issues with the autothrottle in the days before the fatal flight and technicians attempted to rectify the problem by cleaning switches and connectors.

One of the safety regulations introduced after the older 737 planes were certified requires that a jet's automated systems be designed to give pilots a smooth transition if for any reason they disengage and revert to manual flight.

If automated systems disengage, the jet must not abruptly shift its behavior in such a way as to require unusual pilot skill or strength to maintain control.

In the Sriwijaya crash, after an autothrottle malfunction causing unequal thrust between the two engines had been ongoing for some time, the automated systems eventually disengaged. The plane immediately rolled to an angle of 45 degrees and the pilots lost control, according to the preliminary report.

Joe Jacobsen, a former FAA safety engineer who publicly criticized the FAA's certification of the 737 MAX just before he retired last month, said in an interview Thursday that this suggests the jet's autopilot system was "handling the fault, until it let go," after which the plane abruptly rolled.

Up until that point, he said, the autopilot would have been compensating for the unequal thrust between the engines by moving the rudder and trailing edges on the wings (ailerons) to prevent the plane from yawing or rolling to one side.

"Basically what the system does is it masks the fault until such time as it lets go ... all the way up until it finally runs out of authority and then it releases, and puts the airplane into a bad situation," Jacobsen said. "That's not allowed anymore, but it was in the old certification basis of the 737-500."

While at the FAA, Jacobsen pushed for more than a decade without success to have just one of the higher safety standards on automated systems retroactively applied to older 737s.

Speaking to The Seattle Times in February, Jacobsen described an autothrottle problem that contributed to the ET302 crash and mentioned then his concern about the Sriwijaya crash.

He was not involved in the investigation into the Sriwijaya crash nor in the lawsuit filed Thursday.

Report describes loss of control

The preliminary report into the crash states that when the plane reached 8,150 feet, the left engine throttle lever moved back, reducing thrust in that engine, while the right thrust lever stayed in its position.

This suggests the right autothrottle system was stuck, the lawsuit states.

As the plane continued to climb through 10,000 feet, "the thrust lever of the left engine continued decreasing. The thrust lever of the right engine remained," the KNKT report states.

However, at an altitude of 10,900 feet, the autopilot and the autothrottle disengaged. At that point, "the aircraft rolled to the left to more than 45°," the report states.

The pilots lost control and the jet dived into the Java Sea.

In addition to concern with the autothrottle design, the lawsuit separately alleges that corrosion in an engine valve during the extended period when the jet was grounded may have contributed to the reduced thrust in the right engine.

"Boeing did not provide adequate warnings and instructions about ... the dangers of parking an aircraft for an extended period," the lawsuit states.

The lawsuit cites four prior incidents, including two fatal accidents, in which an autothrottle failure played a contributing role.

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