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Boeing admitted Sunday it knew there was an issue with a warning system in its 737 Max plane well before the Lion Air crash in late 2018 that left 189 people dead. Yet it didn’t share that information until after the tragedy.

The company said it discovered in 2017 that a warning system it thought was standard only worked in aircraft outfitted with an optional indicator. The warning light was supposed to show when there was a disagreement about the direction the plane was pointed, indicating there might be an issue with the angle of attack (AOA) sensors.

In both recent high-profile crashes involving the 737 Max — Lion Air Flight 610 and Ethiopian Airlines Flight 302, which killed 157 people in March — preliminary investigations appear to show there was an issue with the angle of attack sensors, which triggered anti-stall software that led to nosedives that took the aircraft down.

It’s not known if the lack of a disagree alert system contributed to the catastrophic crashes.

In its statement, Boeing said the disagree alert was not necessary to fly the plane safely.

“When the discrepancy between the requirements and the software was identified, Boeing followed its standard process for determining the appropriate resolution of such issues. That review, which involved multiple company subject matter experts, determined that the absence of the AOA Disagree alert did not adversely impact airplane safety or operation. Accordingly, the review concluded, the existing functionality was acceptable until the alert and the indicator could be delinked in the next planned display system software update.”

Boeing didn’t share the problem

Boeing said its senior leadership and the Federal Aviation Administration weren’t aware of the issue until after the Oct. 29 Lion Air crash. The New York Times reported that just 20 percent of the 737 Max planes had the optional indicator that would have allowed the disagree alert system to function properly, which means the majority of Max planes flew without the system Boeing thought was standard.

The issue with the warning system was only shared with airlines and pilots after the Lion Air crash. The FAA said Sunday that the problem was deemed low -risk, but added: “Boeing’s timely or earlier communication with the operators would have helped to reduce or eliminate possible confusion.”

Boeing also said in its statement that a Safety Review Board was convened in December 2018, and it agreed the lack of the disagree alert system did not present a safety issue.

Pilot fears

The Ethiopian Airlines Flight 302 crash in March left passengers and pilots wary. A number of countries grounded the plane shortly thereafter, but the U.S. dragged its feet for three days until President Donald Trump issued an emergency order grounding the plane in the United States.

The Max planes have now been out of commission worldwide for more than a month, and Boeing has been trying to get a handle on the issues with its best-selling plane ever. A congressional hearing on the status of the 737 Max is scheduled for May 15 and representatives from Boeing are expected to be summoned.

As far as the disagree alert system goes, the company said in the statement that it will update the Max’s software so the warning is a standalone system.

The company is also working on an update to make the anti-stall software less powerful, with the goal of getting the 737 Max back in service by late summer, The New York Times reported.