It's not known if the lack of the alert function played a role in the crashes of Lion Air and Ethiopian Airlines planes, which killed 346 people.
"Neither the angle-of-attack indicator nor the AOA Disagree alert are necessary for the safe operation of the airplane", Boeing said.
The alert lets pilots know if the one of the angles of attack is not working, while the disagree alert shows if the sensors contradict each other, CNN reported.
"In 2017, within several months after beginning 737 MAX deliveries, engineers at Boeing identified that the 737 MAX display system software did not correctly meet the AOA Disagree alert requirements", the aircraft manufacturer said in a statement.
Boeing said Sunday that the planes could be flown safely without the alert, but said it will be included in the 737 Max before the planes are flown again.
"When the MAX returns to service, all MAX production aircraft will have an activated and operable AOA Disagree alert and an optional angle of attack indicator", the company said.
The company's review board decided the setup was acceptable until the two alerts could be unlinked with the next planned software update for the plane's display system.
But the plane-maker didn't share its findings with airlines or the Federal Aviation Administration until after a Lion Air plane went down off the coast of Indonesia in October, according to a Boeing statement on Sunday as it provided additional details of an issue that first came to light last week.More news: Sri Lanka expels 200 Islamic clerics after Easter attacks
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It is not clear whether having the warning light would have prevented either the Lion Air crash or the March 10 crash of an Ethiopian Airlines Max near Addis Ababa.
Meanwhile, as part of a criminal probe into whether Boeing misled regulators or customers, investigators as recently as last week were asking questions about how the MAX jets gained approval for flight and about Boeing officials involved in the process.
The FAA put the bulk of blame on Boeing's shoulders, saying, "Boeing's timely or earlier communication with the operators would have helped to reduce or eliminate possible confusion". Boeing said the problem stemmed from software delivered to the company.
Ultimately, the company decided that the problem was not severe enough to merit action, and that it "did not adversely impact airplane safety or operation". That allowed the airline to activate the sensor-disagree warning lights on its 34 Max jets earlier this year, she said.
It believed the issue could be resolved in a later system update.
Boeing did not tell airlines or the FAA about this decision.
But the new jets were already being delivered, and USA regulators were not immediately told as Boeing did not believe the apparent mistake posed any risk.
Nevertheless, it did not reportedly provide some carriers and pilots with consistent explanations even after the first tragedy and became "more forthcoming" with airlines only after the second 737 MAX crashed in Ethiopia. Tajer said the American pilots were told in the meeting that on the flight deck of their 737 MAXs, the AOA disagree light would have lit up on the ground and so, because that's a "no-go item", the plane wouldn't even have taken off.