The National Transportation Safety Committee (KNKT) has found that errors in the design of the Boeing 737 MAX 8 jet as well as a lack of information on how to deal with failures in one of the aircraft’s control systems were among several factors causing a deadly crash of Lion Air flight JT610 last year.

The downed aircraft, a brand-new Boeing 737 MAX 8, crashed into the Java Sea on Oct. 29, 2018 shortly after taking off for a flight from Jakarta to Pangkalpinang, Bangka Belitung Islands. All 189 passengers and crew members on board, including three minors, were killed in the accident.

In a presentation for the families of the victims, the committee said the crashed aircraft’s Maneuvering Characteristics Augmentation System (MCAS) was approved based on incorrect assumptions. 

The system adjusts the aircraft by bringing its nose down when it detects that the plane is in imminent danger of entering an aerodynamic stall, based on data collected from the airspeed, altitude and angle of attack sensors.

“During the design and certification of the Boeing 737 MAX 8, assumptions were made about pilot response to malfunctions which, even though consistent with current industry guidelines, turned out to be incorrect,” the committee told families of the victims on Wednesday.

“The absence of guidance on the MCAS or more detailed use of trim in the flight manuals and in pilot training have made it more difficult for flight crews to properly respond to uncommanded MCAS,” the KNKT went on to say.

It added that the indicator of the error was not correctly developed during the development of the aircraft. As a result, the error could not be documented by the flight crew who later could not tell maintenance staff to identify the miscalibrated sensor.

The KNKT is expected to release its final investigation report on the Lion Air JT610 crash to the public on Friday.

The MCAS is suspected to have played a role in two deadly accidents involving Boeing 737 MAX 8 aircraft. Apart from the Lion Air crash, Ethiopian Airlines flight ET302 crashed after taking off from Addis Ababa on its way to Nairobi in March. The crash claimed the lives of all 149 people on board.

United States-based aircraft manufacturer Boeing stated several months after the second accident it had updated the anti-stall software and pilot training to ensure the jetliner’s flight safety.

The two incidents led to the grounding of Boeing’s latest jet worldwide. In Indonesia, two airliners operating the aircraft — Lion Air and Garuda Indonesia — have not operated their Boeing 737 MAX series jets for months.

Families of the victims, however, were not satisfied with the KNKT’s final report, saying it did not provide them clear and detailed answers about what actually happened.

“It seems like during their presentation, they only blamed the pilot of the previous flight for not documenting the error experienced by the aircraft. I don’t believe that explanation,” Anton Sahadi, 30, told journalists after a meeting with the KNKT on Wednesday. “We are Indonesian citizens. We deserve to know what happened!”

The KNKT in March confirmed the presence of an off-duty pilot on board Lion Air flight JT043 from Denpasar to Jakarta on Oct. 28, 2018, whose actions have been cited in media reports as having saved more than 100 lives.

The flight experienced problems but landed safely in Jakarta. The next day the same aircraft on flight JT610 from Jakarta to Pangkal Pinang crashed into the Java Sea.

The dissatisfaction was echoed by 52-year-old Epi Samsul Komar, a parent of Muhammad Rafi Andrian who was among the killed passengers. He called the KNKT’s explanation “too technical and not understandable.”

“Moreover, Boeing representatives have yet to contact us. They should also be blamed for the accident,” he said.

Boeing on Tuesday replaced the chief of its commercial plane division, the most significant executive departure since the 737 MAX grounding plunged the company into crisis seven months ago, AFP reported.

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