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(CNN Business) —  

Boeing said Friday that it is addressing safety recommendations raised by Indonesian investigators about its 737 Max aircraft to ensure that a fatal crash “never happens again.”

The promise was part of Boeing’s lengthy response to the final report from Indonesia’s National Transportation Safety Committee into last year’s crash of a Lion Air flight. Investigators faulted the poor design of the Max and a lack of regulatory oversight from the US Federal Aviation Administration, along with errors by flight crews.

The agency plans to make the report public Friday, roughly a year after the 737 Max 8 plane crashed into the Java Sea. All 189 people on board died. Ahead of the report’s publication, investigators held a press conference in Jakarta.

A summary of the report blames the crash on faulty “assumptions” made during the design and certification of the 737 Max about how pilots would respond to malfunctions by the Maneuvering Characteristics Augmentation System (MCAS). CNN saw a presentation of the summary earlier this week. A press release detailing the report’s findings was also released Friday.

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 experienced issues on earlier flights and was replaced. 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.

Boeing has admitted this feature that should have been standard was instead enabled only for airlines that purchased an optional upgrade, and has said that it will fix the problem.

Problems not properly logged

Investigators also said that the crew on the flight before the one that crashed experienced problems, but deactivated the MCAS system and flew the plane to its destination. But that flight crew did not report all of the issues they experienced to the maintenance crew.

Investigators also concluded that issues with “flight crew communication” and “distractions” were contributing factors to the crash, according to the summary.

The 737 Max has been grounded since March after a 737 Max operated by Ethiopian Airlines crashed. That flight shared similarities with the fatal Lion Air flight. The two crashes killed 346 people.

Boeing (BA) on Friday said that it has been working to update its MCAS system in the wake of those crashes.

Going forward, Boeing said, its MCAS system will compare information from two AOA sensors on the plane before it activates, “adding a new layer of protection.” The redesign also means that a pilot experiencing an MCAS malfunction will be able to pull back on the control column and deactivate the system. Pilots on both the Lion Air and Ethiopian Airlines fatal flights struggled to override the planes’ automatic systems before crashing, according to preliminary reports.

Boeing also said it is “updating crew manuals and pilot training, designed to ensure every pilot has all of the information they need to fly the 737 MAX safely.”

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.” Decisions made by the agency and the aircraft makers have come under scrutiny in multiple investigations and reviews in the months since the planes crashed.

On Friday, the FAA said that its “first priority is always safety” and that the Indonesian committee’s accident report on Lion Air “is a sober reminder to us of the importance of that mission.”

And Lion Air called the crash an “unthinkable tragedy and one that the relatives and friends of those who were lost continue to mourn.”

“It is essential to determine the root cause and contributing factors to the accident and take immediate corrective actions to ensure that an accident like this one never happens again,” the airline said in a statement on Friday.

-— CNN’s Oren Liebermann contributed to this report.