JAKARTA, Indonesia — Design flaws in an automated feature on Boeing’s 737 Max, attached to a sensor that had likely been poorly repaired, plus regulatory lapses and false assumptions about pilots’ responses to new systems, combined to cause last year’s fatal Lion Air crash, Indonesian investigators said Friday.

Shortly after Flight 610 left Jakarta on Oct. 29, the sensor began sending bad information to the jet’s computer, triggering the automated feature and driving down the plane’s nose, according to the investigators’ report. The pilots — who knew nothing about the feature, which was new to the Max — struggled to respond, grappling with controls that felt as though they weighed 100 pounds.

The plane plunged into the Java Sea, killing all eight crew members and 181 passengers on board.

The new report underscores a link between the crash and the new feature, known as the Maneuvering Characteristics Augmentation System, or MCAS, that emerged soon after the October 2018 disaster.

The feature was designed to account for changes in the latest model of the 737, a more fuel-efficient version of Boeing’s most popular jet with larger engines, to make it feel like its predecessors, avoiding costly simulator training for pilots, the investigation concluded.

Similar problems were blamed for the crash of an Ethio­pian Airlines flight in March that killed 157 people. The Max has been grounded worldwide since shortly after that crash.

Since then, Boeing’s decision to adopt the feature and the Federal Aviation Administration’s role in certifying the plane have come under intense scrutiny from the Justice Department, congressional investigators and lawyers representing the families of dozens of those who died. The new report’s findings line up with those of other official reviews of the crash and the design of the Max.

Officials from Indonesia’s transportation safety regulator said a total of nine factors worked together to doom the Lion Air jet. 

“These items were connected to each other. If one of them was not occurring on that day, the accident may not have happened,” said Nurcahyo Utomo, an investigator at the National Transportation Safety Committee.

Those factors included incorrect assumptions by Boeing about how pilots would respond to the MCAS.

The report also highlighted a lack of training for pilots in the new system, a lack of documentation about problems on previous Lion Air flights involving the same plane and ineffective coordination between flight crews. Investigators concluded that the plane should have been grounded after an earlier problem.

The report traces the origins of the crash back years, to the design of the Max and MCAS and its journey through the FAA approval process. It also reveals how a repair job in the United States on the critical sensor likely caused it to generate faulty data after being installed on the Lion Air jet.

The details of the backstory of the external sensor point to the role of a maintenance firm in Florida and oversight by U.S. regulators.

A dirty angle-of-attack sensor was sent to a Miramar-based company, Xtra Aerospace, for maintenance in 2017. It was then sent back and installed on the left side of the Lion Air plane the day before it crashed, the report said.

Angle-of-attack sensors are supposed to give pilots, and airplane systems, reliable information to help understand how the aircraft’s nose is pointed in relation to oncoming wind.

But shortly after takeoff, the newly installed left sensor showed a reading that was different, by 21 degrees, from the one on the right. Investigators say that inaccurate reading caused the MCAS to mistakenly fire repeatedly.

The “sensor was most likely improperly calibrated at Xtra Aerospace,” the Indonesian crash report said, noting that tests have been performed for the FAA and National Transportation Safety Board indicate that certain actions during the calibration process “could potentially introduce a bias” in parts of the sensor.

The report said Xtra should have had a written procedure regarding the part of the process that may have gone wrong. The lack of such a written procedure was not detected by a relevant FAA office, the report said, and “this indicates inadequacy of FAA oversight.”

The FAA said it issued an order revoking Xtra Aerospace’s repair station certificate Friday, saying the company had “failed to comply with requirements to repair only aircraft parts on its list of parts acceptable to the FAA that it was capable of repairing.” The FAA said it began investigating the company in November 2018, shortly after the Indonesia crash.

A representative of Xtra Aerospace had no comment on the allegation it may have improperly calibrated the sensor. A company statement said, “the FAA’s enforcement action is separate” from the Indonesian investigation “and is not an indication that Xtra was responsible for the accident.”

Safety is “central to all we do,” the statement said, adding that the company expresses “our deep sadness and sympathy” to the families of the victims.

The Lion Air flight was captained by 31-year-old Bhavye Suneja, a native of India who had logged 6,000 flight hours. He said he was suffering from the flu the day of the crash, according to a description of his recorded cockpit conversations included in the report.

He was joined by a first officer with 5,000 hours of experience who used only the single name Harvino. On the recording Harvino said he had been roused at 4 a.m. that day to take a flight that wasn’t part of his normal schedule.

Soon after takeoff, as the plane took in the faulty sensor data, MCAS began to kick in.

But as it did, the two men struggled to determine what was happening, according to the report. They began running through a checklist as the cockpit recorder captured the sound of pages being riffled through.

They struggled in part because Boeing had decided to remove references to MCAS from the plane’s manual and pilots weren’t trained on how it worked, which the investigators wrote, “resulted in it being more difficult for the flight crew to diagnose the problem and find the corrective procedure to solve it.”

The investigation also concluded that the crews’ efforts were hampered by the lack of a warning message that would show when the plane’s two angle-of-attack sensors disagreed. That message was a standard feature of older 737s and was supposed to be on the Max, but was mistakenly only included as part of an optional upgrade.

Boeing caught the problem only after it had begun delivering the Max to its customers in 2017, but decided it could wait to fix it until late 2020.

The Indonesian investigators said their report was not aimed at pinpointing culpability, but at ensuring passenger safety and preventing a similar crash. The report cannot be used for liability or compensation issues in court.

But Vini Wulandari, Harvino’s sister, said the investigation reinforced her family’s belief that her brother was not to blame for the crash, and she demanded that Boeing take more responsibility for the loss of life.

“From the beginning, I’m sure that Harvino was innocent because he had done everything according to procedure,” Vini said in an interview Friday. Her family is among those suing Boeing.

“Someone must be held responsible for what has happened,” she added.

Austin Bartlett, a Chicago attorney representing the families of 60 of the crash victims, said the report “lends credibility to the plaintiffs’ theory of the case that this was fundamentally a defectively designed aircraft.”

The report calls for improved oversight by the FAA more broadly, and changes at Boeing as well as Lion Air.

The airline is Indonesia’s largest budget carrier, operating in a fast-growing industry across an archipelago where air travel is a necessity. In a statement, the company said it was essential to take “immediate corrective actions to ensure that an accident like this one never happens again.”

Ahead of Friday’s release of the crash investigation report, a review by the NTSB found that Boeing underestimated the risk posed by MCAS and made faulty assumptions about how pilots would respond to a barrage of alerts in the cockpit if something went wrong.

And an international group of aviation regulators and U.S. experts concluded that Boeing shared information with the FAA in a fragmented way, resulting in insufficient scrutiny of the new feature.

The protracted grounding of the Max has battered Boeing’s finances and its stock price. This week, the company reported that its revenue fell to $20 billion in the third quarter, down 21 percent from a year earlier. Profits were down 51 percent to $1.17 billion.

The company also announced the resignation this week of Kevin McAllister, head of the Boeing division that made the Max.

The company’s fortunes rest on it winning approval from aviation regulators in the United States and abroad for the Max to resume flights.

Boeing reiterated Friday upon the report’s release that the crashes prompted the company to make changes to the 737 Max. The fixes included changing how the angle-of-attack sensors feed information to the cockpit and improving crew manuals and pilot training. 

“These software changes will prevent the flight control conditions that occurred in this accident from ever happening again,” the company said in a statement. 

The changes are being reviewed by aviation authorities. FAA officials say they have several more weeks’ work to do, and airlines have said they are keeping the Max off their schedules into January and February.

Boeing’s chief executive Dennis Muilenburg, who was stripped of his role as chairman of the company’s board this month, is scheduled to testify about the Max before Senate and House committees next week. Lawmakers are weighing whether there ought to be changes to an FAA program that turns over to industry much of the responsibility for certifying that safety standards are being met.

Rep. Peter A. DeFazio (D-Ore.), the chairman of the House Transportation and Infrastructure committee, said he was considering legislation to ensure unsafe airliners aren’t given the green light.

“It’s clear that reforms will be needed to ensure that future safety-critical systems don’t create single points of failure that bring down new commercial aircraft designs,” DeFazio said in a statement. “I will continue to use every tool at my disposal to get to the bottom of the failures in the system that led to not one, but two tragic crashes.”

Correction: This story was updated to correct the spelling of Boeing chief executive Dennis Muilenburg’s last name.

Mahtani reported from Hong Kong and Duncan and Laris reported from Washington.