Boeing 737 MAX winglet. Photo: Boeing
In 2017, Boeing learned that the angle-of-attack (AOA) disagree alert — a standard feature on all 737 MAX aircraft — didn't work on the majority of the planes. The company determined that the alert was not necessary for safe operation, so it did not inform operators or the FAA.
In a Sunday statement, Boeing explained that its engineers found that the AOA disagree alert was incorrectly set as linked to the AOA indicator, an optional feature purchased by only about one-fifth of 737 MAX buyers. As such, the remaining 80 percent of operators, including both the doomed Lion Air flight 610 and Ethiopian Airlines flight 302, were without the alert.
Multiple Boeing subject matter experts determined "the existing functionality was acceptable until the alert and the indicator could be delinked in the next planned display system software update," Boeing's statement said. "Senior company leadership was not involved in the review and first became aware of this issue in the aftermath of the Lion Air accident."
Boeing did "discuss the status of the AOA disagree alert with the FAA" after the Lion Air crash, the manufacturer said, and the November 2018 airworthiness directive clarified that the alert was not available to operators without the premium AOA indicator option. The company said that a Boeing-convened safety review board affirmed in December that the absence of the AOA disagree alert from flight displays would not have presented a safety issue.
The FAA confirmed the discussion and that it deemed the issue "low risk" at the time. "However, Boeing’s timely or earlier communication with the operators would have helped to reduce or eliminate possible confusion," the agency said.
As part of the updates to the 737 MAX, Boeing said that before its best-selling plane returns to service, the AOA disagree alert will be corrected to be a standalone feature available to all operators and separate from the optional AOA indicator.