It's been revealed that Boeing knew about its 737 MAX safety problems before the fatal Lion Air and Ethiopian Airlines crashes, but did not disclose the issue to aviation authorities.
The aircraft manufacturer didn't tell US regulators for more than a year that an alarm system designed to alert pilots to possiblly incorrect data was available as an optional extra on the new 737 model, as opposted to being installed as standard.
In both fatal crashes, the nose of the aircraft appears to have continuiusly pointed down shortly after take-off, regardless of pilot actions. Sensors designed to inform the crew of the flight angle are believed to have provided false data, triggering the flawed software onboard to point the nose down.
In a statement released on Tuesday morning (NZ time), Boeing said it only discovered once deliveries of the 737 MAX had begun in 2017 that the so-called AOA Disagree alert was optional, instead of standard as it had intended.
However, Boeing insists this data was not critical to safety.
A Federal Aviation Administration (FAA) official told Reuters on Sunday that Boeing waited 13 months before informing the agency in November 2018.
By becoming optional, the alert had been treated in the same way as a separate indicator showing raw AOA data, which is seldom used by commercial pilots and had been an add-on for years.
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Boeing said a safety board review convened after a fatal Lion Air crash in Indonesia last October corroborated its prior conclusion that the alert was not necessary for the safe operation of commercial aircraft and could safely be tackled in a future system update.
The FAA backed that assessment but criticised Boeing for being slow to disclose the problem.
Boeing briefed the FAA on the display issue in November, after the Lion Air accident, and a special panel deemed it to be "low risk," an FAA spokesman said.
"However, Boeing's timely or earlier communication with the operators would have helped to reduce or eliminate possible confusion," they added.
Sunday's statement marked the first time since the two fatal accidents that Boeing explicitly acknowledged doing something inadvertently in the development of the 737 MAX, albeit on an issue that it contends has no impact on safety.
The 737 MAX was grounded worldwide over safety concerns following the Ethiopian crash in March, killing 157 people.
When the jet returns to service, all new aircraft will have a working AOA Disagree alert as a standard feature and a no-charge optional indicator showing the underlying data, Boeing said.
Airlines with grounded 737 MAX jets will be able to activate the AOA Disagree function directly.
Federal prosecutors, the Transportation Department inspector general's office and a blue-ribbon panel are also looking into the 737 MAX's certification.