JAKARTA • Mechanical and design issues contributed to the crash of a Lion Air 737 Max jet last October, Indonesian investigators told victims' families yesterday, ahead of the release of a final report.
Contributing factors to the crash of the new Boeing jet, which killed all 189 on board, included incorrect assumptions on how an anti-stall device called the Manoeuvring Characteristics Augmentation System (MCAS) functioned and how pilots would react, the families were told during a presentation.
It also showed that a lack of documentation about how systems would behave in a crash scenario, including the activation of a "stick shaker" device that warned pilots of a dangerous loss of lift, was another contributing factor.
"Deficiencies" in the flight crew's communication and manual control of the aircraft contributed to the crash, as did alerts and distractions in the cockpit.
The deficiencies had been "identified during training", the presentation noted, without elaborating.
Reliance on a single angle-of-attack sensor made the MCAS more vulnerable to failure, while the sensor on the plane that crashed had been miscalibrated during an earlier repair.
The final report will be released tomorrow.
Some relatives of the victims at the briefing in Jakarta expressed disappointment that direct responsibility was not assigned.
"Why isn't the airline heavily sanctioned?" asked Mr Anton Sahadi, 30, whose relatives Riyan Aryandi and Muhammad Rafi Andrian were killed in the crash.
"This isn't about one or two lives, it's about 189 lives."
The civil investigators' role is not to assign blame but to draw lessons that will make flying safer. Separate court actions will address who is legally responsible for the crash.
A Boeing spokesman said: "As the report hasn't been officially released... it is premature for us to comment on its contents."
The 737 Max has been grounded worldwide since a second deadly crash in Ethiopia in March.
Planemaker Boeing is under growing pressure to explain what it knew about the 737 Max's problems before it entered service.
Boeing has already said it would redesign the MCAS anti-stall system so that it will rely on more than a single sensor.
The company last month settled the first claims stemming from the Lion Air crash, a US plaintiffs' lawyer said. Three other sources said the families of those killed will receive at least US$1.2 million (S$1.64 million) each.
Boeing faces nearly 100 lawsuits over the Ethiopian Airlines crash on March 10, which killed all 157 people on board the flight from Addis Ababa to Nairobi.