Design flaws in Boeing Co.’s 737 Max, a failure to share vital information with pilots and airline maintenance stumbles contributed to last year’s crash of Lion Air Flight 610, which killed 189 people, investigators have concluded.

In a nine-point presentation to victims’ families prior to the Friday release of a formal crash report, the Indonesian National Transportation Safety Committee criticized the jet’s certification, saying that a now infamous flight-control mechanism was approved based on incorrect assumptions. The Maneuvering Characteristics Augmentation System has been implicated separately in the crash of an Ethiopian Airlines 737 Max in March that claimed 157 lives.

“Only after the tragedy in Ethiopia, they concluded that it’s Boeing’s fault. Why didn’t they say it in the first place?” said Evi Samsul Komar, whose 24-year-old son died in the Oct. 29 Lion Air crash. “We never been contacted by Boeing,” he said after the briefing in Jakarta.

Read: Pilot’s Mother Calls for More Training as Boeing Blamed in Crash

Indonesian investigators are due to publish their final report on the crash at 2 p.m. local time Friday. The findings come as regulators worldwide assess the fate of what was Boeing’s best-selling plane, which has been grounded globally since March 13, costing the company over $8 billion. The head of its jetliner division stepped down Tuesday after less than three years in the job.

Investigators examine engine parts from Lion Air flight JT 610, Nov. 2018.

The 737 Max’s MCAS feature, which automatically pushes the plane’s nose downward to make an aerodynamic stall less likely, has long been in focus in investigations into the two crashes. In its slide show Wednesday, the NTSC said the system was too reliant on a single angle-of-attack sensor, making it vulnerable if that sensor malfunctioned and transmitted erroneous readings.

The government agency said a lack of guidance around MCAS -- it wasn’t mentioned in pilot manuals or in training -- made it harder for crews to respond to its automated attempts to dive.

In spite of concluding that both Boeing and the U.S. Federal Aviation Administration approved the design without recognizing its hazards, the NTSC found that the plane’s certification was done according to existing guidelines. Those certification standards failed to anticipate how the failure would affect flight crews, it concluded.

The report also focused on maintenance at the rapidly growing airline. A replacement angle-of-attack sensor, installed on the doomed Lion Air plane the day before the crash, wasn’t properly calibrated during the repair, and the error hadn’t been detected.

As a result of that poorly executed repair, the identical failure on the plane occurred the night before the accident on a flight from Denpasar to Jakarta. The flight crew, with the help of another pilot riding on the cockpit jumpseat, were able to disable MCAS and continued to their destination.

However, the crew on that earlier flight failed to fully document the failure and their need to override the so-called trim system, which was being driven by MCAS. As a result, investigators concluded, mechanics in Jakarta failed to fix the underlying problem and the failure occurred again the next morning on the flight that crashed.

“I’m not satisfied with the briefing and the explanation but this is the result,” said Komar, who was accompanied by his wife and broke down in tears while speaking to reporters.

Lion Air and the country’s civil aviation authority recently objected to findings in a draft of the final report on the grounds that they received too much of the blame, people familiar with the matter said last month. One of the people said at the time that 25 of 41 lapses were directed toward the airline.

Representatives of Boeing and the FAA wrote in emails that it was premature to comment on the report as it hasn’t been officially released. Lion Air didn’t immediately respond to calls seeking comments.

What Indonesia Investigators Told Families of Lion Air Crash Victims Incorrect assumptions were made about how pilots would response to malfunctions while designing the 737 Max and getting it certified

MCAS relied on one sensor based on false assumptions

MCAS was vulnerable to errors as it relied only on a single angle-of-attack sensor

Pilots found it more difficult when the MCAS activated without command, as they were not trained on the system

A key alert wasn’t correctly enabled during the 737 Max’s development

The angle-of-attack sensor installed on the crashed plane wasn’t calibrated correctly during an earlier repair

The improper calibration of the sensor wasn’t detected

Previous instances of warnings of an immediate stall weren’t documented in flight and maintenance logs. The lack of information prevented maintenance crew and accident crew from taking appropriate action

Multiple alerts, MCAS activation, air-traffic-control communication and manual flying were not managed well Source: NTSC slides shown to family victims

“There were many different deficiencies and failures that were involved in this accident,” said Jeffrey Guzzetti, the former chief of accident investigations at the FAA.

The long laundry list of failures outlined in the briefing for families, from design shortfalls to pilot actions, were “lining up perfectly to conspire against this flight,” Guzzetti said.

Recently published messages between two senior Boeing test pilots showed they had misgivings about the MCAS on 737 Max jets during its certification in 2016, with one describing its handling performance as egregious. That pilot’s lawyer has said it was the result of a faulty simulator and didn’t indicate concerns with the plane’s safety.

The FAA, which has faced criticism for approving the feature and giving Boeing too much authority to oversee itself, said Friday that it was concerned by comments in the messages between the two pilots and chastised Boeing for not sharing the information sooner. Boeing said it told regulators it had expanded the role of the flight-control software.

“As we have suspected since the very beginning, the accident was caused by these two institutions, Boeing and FAA,” said Latief Nurbana, whose 24-year-old son died in the Lion Air crash. “FAA shares the blame as the certification process was not conducted thoroughly.”

Problems with the three-month-old Lion Air jet’s sensors had been reported on four previous flights, including one made from Bali the day before the crash. In that instance, an off-duty pilot traveling in the cockpit identified the problem and told the crew how to disable the malfunctioning control system.

However, the pilots didn’t report key issues with the flight after they landed.

A different crew was on board the following day. Flight 610 took off from Jakarta at 6:20 a.m. on the Monday Oct. 29, heading to the tourist destination of Pangkal Pinang, off Sumatra’s east coast. Minutes later, it plunged into the sea after the pilots were unable to regain control in a battle with the controls to keep the aircraft from repeatedly diving.

It was Indonesia’s deadliest airline crash since 1997 and reignited worries about its aviation safety record. The nation’s airlines, including Lion Air, were banned from flying to the European Union and the U.S. for almost a decade until 2016 because of safety concerns.

Boeing was hit with a lawsuit earlier this month demanding records that will allegedly show if mismanagement is to blame for safety issues leading to the grounding of the 737 Max fleet. Chief Executive Officer Dennis Muilenburg is due to face questions from lawmakers in Washington next week.

Boeing shares rose after the company reported earnings Wednesday in New York. Boeing said that while the price tag for the Max’s grounding climbed to $9.2 billion in the third quarter, production of the Max will increase 36% to 57 jets a month by late next year. The company also said it remained confident that the beleaguered plane would be cleared to fly this year.

— With assistance by Kyunghee Park, Dave Merrill, and Alan Levin