The families of victims in last year's Lion Air crash have been told by Indonesian investigators that poor regulatory oversight and the design of Boeing's 737 Max contributed to the fatal disaster.
Investigators on Wednesday provided victims' relatives with a summary of their final report on the crash, which killed 189 people. Details from the briefing for family members were shared with CNN by Anton Sahadi, a spokesperson for the relatives.
The report summary said that faulty "assumptions" were made during the design and certification of the 737 Max about how pilots would respond to malfunctions by the Maneuvering Characteristics Augmentation System (MCAS), according to the presentation seen by CNN.
MCAS lowers the nose of the plane when it receives information that the aircraft is flying too slowly or steeply, and at risk of stalling. The system was vulnerable because it relied on a single angle of attack (AOA) sensor, investigators said.
The AOA sensor on the doomed Lion Air plane had been miscalibrated during a repair, according to investigators. But the airline's maintenance crews and pilots couldn't identify the problem because one of the aircraft's safety features — the AOA Disagree alert — was not "correctly enabled during Boeing 737-8 (Max) development," they said.
Dian Andriani lost her 24-year-old son Muhammad Ravi Andrian in the crash. She told CNN that she's unhappy with the explanation given by investigators and that there wasn't much information she could clearly understand.
So far, Andriani said, what she does understand is that the plane wasn't safe to fly.
The popular 737 Max has been grounded since March as aviation regulators investigate the Lion Air disaster and a similar crash of a 737 Max operated by Ethiopian Airlines. The two crashes killed 346 people.
Boeing declined to comment on the Indonesian report.
"As the report hasn't been officially released by the investigative authorities, it is premature for us to comment on its contents," a company spokesperson said.
The twin disasters have thrown Boeing into crisis and forced it to take a $5 billion charge related to compensation for airlines. Kevin McAllister, CEO of the Boeing unit that builds passenger jets, left the company on Tuesday.
Last week, the company came under fire for failing to disclose that some employees had expressed concerns about MCAS during the plane's certification process.
Boeing has continued to build the 737 Max in order to try to meet a backlog of more than 4,000 orders for the plane that it has on the books. But it won't get most of the revenue from sales of the plane until delivery.
It's not clear when the plane will return to the skies: The US Federal Aviation Administration said last week that it's following a "thorough process, not a prescribed timeline, for returning the Boeing 737 Max to passenger service."
A spokesman for Indonesia's National Transportation Safety Commission said Wednesday that its final report will publish on Friday.
It has been sent to the US National Transportation Safety Board and other relevant parties, and those parties have replied with comments, the spokesman said.
Jamaluddin Masrur and Jo Shelley contributed to this report.