The admission comes as Boeing and the FAA face tremendous scrutiny over whether design flaws could have contributed to the deaths of hundreds of people in Indonesia and Ethiopia, where two 737 Max jets crashed in recent months under similar circumstances.
The disclosure could also feed into a broader inquiry over whether the process for designing and certifying commercial jets in the United States is flawed. The 737 Max was grounded worldwide in mid-March after the second crash brought the death toll to 346.
The software, which connects the airplane’s external sensors to pilots’ cockpit displays, is designed to alert pilots when sensors on either side of the plane are reporting conflicting measurements for the plane’s “angle of attack," a measure of how the plane approaches oncoming wind. Boeing included the alert as an optional feature in the 737 Max to alert pilots to potential equipment failures.
In its statement, Boeing said the planes can be operated safely without the alert.
“Neither the angle of attack indicator nor the AOA Disagree alert are necessary for the safe operation of the airplane," the statement reads. "They provide supplemental information only, and have never been considered safety features on commercial jet transport airplanes.”
Boeing’s statement Sunday comes a week after the Wall Street Journal reported that the angle-of-attack disagree alert was inoperable when Southwest Airlines and other carriers started flying the planes.
“The disagree alert was not operable on all airplanes because the feature was not activated as intended,” Boeing said in a statement last Monday.
When it discovered the software problem in 2017, Boeing assigned a committee to review the issue, which ultimately determined the planes were safe to fly. But it wasn’t until November 2018, after the Indonesian plane crash, that the company informed regulators at the Federal Aviation Administration. It is unclear whether Boeing would have been required to do so under FAA regulations. The company said it followed its standard operating procedures.
Later that month an investigative report from Indonesian authorities found that those sensors had malfunctioned in the final moments of the flight, and that pilots had struggled to overcome an automatic anti-stalling feature that nudged the plane’s nose downward.
The FAA review board found the alert to be a “low-risk” safety issue which would not render the plane unsafe to fly. An FAA spokesman said Sunday, however, that "Boeing’s timely or earlier communication with the operators would have helped to reduce or eliminate possible confusion.”