May 6 (UPI) -- Boeing acknowledged that it knew for a year that a key alert indicator on the 737 Max 8 connected with two recent crashes was only operable in 20 percent of the aircraft but did not inform anyone until after October's Lion Air accident.
The alert only worked on Max aircraft for which customers bought an added optional feature, Boeing said in a statement Sunday. Engineers initially believed the alert was standard in all 737 Max aircraft.
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. While investigators have not determined if the lack of the alert function played a role in the Lion Air crash and the Ethiopian Airlines crash that followed, the disagree alert could have told pilots that a sensor was malfunctioning.
Investigators believe that incorrect data from an "angle of attack" sensor triggered the aircraft's anti-stall software, known as MCAS, causing the nose of the planes to pitch down as the pilots struggled for control.
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Boeing engineers knew in 2017 that the 737 Max display system software did not correctly meet the AOA disagree alert requirements but concluded "the existing functionality was acceptable until the alert and the indicator could be de-linked in the next planned display system software update."
Boeing said that senior company leadership was not involved in the review of the aircraft and first became aware of this issue in the aftermath of the Lion Air accident.
"When the discrepancy between the requirements and the software was identified, Boeing followed its standard process for determining the appropriate resolution of such issues," the company said it its statement.
"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," the statement continued.
The Federal Aviation Administration said Sunday that even if Boeing believed the issue was "low risk," "timely earlier communication with the operators would have helped to reduce or eliminate possible confusion."
Dennis Tajer, a spokesman for the union representing American Airlines pilots, told the New York Times that Boeing's statement suggests that it did not fully understand all the features of its own airplane.
"You better start knowing things about the airplane you're building and selling because my life and the passengers that I carry safely across the globe depend on it," Tajer said.
