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.
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 on 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.
“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.
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.
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.