A little excerpt from NY Times:
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Between Two Boeing Crashes, Days of Silence and Mistrust
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April 2 2019
When a new Boeing 737 Max 8 plunged into the waters off Indonesia last October, a terrifying mystery confronted the aviation industry: What could have caused Lion Air Flight 610, flown by experienced pilots in good weather, to fall out of the sky just 12 minutes after takeoff?
But it took the second, equally terrifying crash of an identical aircraft under similar conditions five months later, in Ethiopia, to reveal the climate of mistrust that has plagued inquiries into what caused the first disaster....
...In November, Haryo Satmiko, the deputy chief of Indonesia's National Transportation Safety Committee, known as KNKT, recounted confusing conversations he was having with Boeing employees who had arrived in Jakarta. Mr. Haryo said he brought up whether inaccurate data readings could have prompted Flight 610's sudden descent.
What Mr. Haryo was describing, though he did not know it at the time, was a malfunction of MCAS, which automatically forces the plane's nose down if data indicates that the jet is angled too sharply upward and might stall.
Nurcahyo Utomo, the head of the safety group's air-accident subcommittee, said he first learned of the term MCAS from news reports....
...Days after Flight 610 crashed, Polana Pramesti, the head of Indonesia's civil aviation authority, waited for visiting Boeing and F.A.A. officials to talk to her. As head of Indonesia's version of the F.A.A., she wanted advice on whether to ground Max 8 jets in Indonesia. But the Americans, who did spend time with transportation safety committee officials, never came to her, she said.
The official in her office in charge of airworthiness and aircraft operation, Avirianto, who like many Indonesians goes by one name, fired off messages to the F.A.A. asking for an explanation of MCAS, which at the time was only vaguely understood, even by aviation experts, because Boeing had failed to put information about it in the plane's manual.
Although he conducted four teleconferences with F.A.A. officials, Mr. Avirianto said he was never given a clear explanation of how MCAS worked or whether it was safe. "They kept saying they were still analyzing, evaluating," he said. "We never received any guidance because there were never any clear answers for us.",,,
...Ms. Polana also sent a letter to Boeing in November, asking for guarantees about the Max. But Boeing was not forthcoming, either, she said. "Of course, we were worried," Ms. Polana said. "We wanted reassurance that the Boeing 737 Max 8s in Indonesia are airworthy."
Boeing and the F.A.A. have come under scrutiny since the Lion Air crash. The United States Department of Transportation is examining the F.A.A.'s certification of the Max model, amid revelations that Boeing employees may have facilitated that process.
Only after the Ethiopian Airlines crash, Ms. Polana said, did the F.A.A. and Boeing become more responsive. On March 22, she had her inaugural teleconference with F.A.A. officials -- the first time Indonesian officials received a precise explanation of how MCAS worked and how Boeing was planning to fix it, they said...
...After the crash, the replaced angle of attack sensor was shipped to Minnesota, home of Rosemount Aerospace, the Boeing subcontractor that made it, Mr. Nurcahyo said. He and other Indonesian investigators went to Minneapolis in December. The sensor, he said, was deemed defective...
...For Lion Air Flight 610, even after the vane was changed, the Max 8 continued to malfunction, producing an array of errant data. Some aviation experts believe the variety of airspeed problems points not to a defective sensor but a more fundamental problem with the processor that collects the data displayed in the cockpit.
"I don't think it's a vane failure. It makes no sense," said Bjorn Fehrm, an aeronautical engineer. "It's more like a computer failure or a component failure, a system failure."
The air data inertial reference unit is the processor that helps collect data from the probes and vanes on the plane. A malfunction in that system could be consistent with data inaccuracies that triggered MCAS, aviation experts said.
Mr. Nurcahyo acknowledged that Indonesian investigators were looking into the possibility of an issue with the air data inertial reference unit...
Source:
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https://www.nytimes.com/2019/04/02/w...-lion-air.html