Boeing says a warning alert system that figures in the investigation of two catastrophic 737 MAX crashes didn’t work the way it was supposed to because of a software flaw that engineers identified a year before the accidents.
The revelation adds a new twist to the debate over the company’s safety practices.
In this case, the debate focuses on a feature known as the “AOA Disagree” alert, which is supposed to light up in the cockpit if there’s a mismatch in data coming from two angle-of-attack sensors on the plane. Investigators suggest that bad sensor data played a key role in October’s Lion Air crash in Indonesia, which killed all 189 people aboard the plane; and March’s Ethiopian Airlines crash, which killed 157.
Within days of the Ethiopian crash, all 737 MAX airplanes were grounded worldwide.
Boeing engineers knew about a problem with the “AOA Disagree” alert well before that. The alert was originally intended to be a standard feature on the 737 MAX and the previous generation of 737 planes, known as the 737 NG (for “Next Generation”). But in a statement issued on May 5, Boeing said that in 2017, several months after deliveries began, engineers became aware that the 737 MAX display system software didn’t meet the original requirements.