Boeing was aware of a faulty system that inactivated a cockpit alert function in its 737 Max jets for months before the deadly Lion Air crash but failed to disclose the issue to airlines and regulators until after the accident, according to a statement the company put out Sunday.
The aerospace manufacturer maintains that the issue “did not adversely impact airplane safety or operation.” While it’s not known if the lack of a functioning alert light—known as the “angle of attack disagree alert”—played a role in the Lion Air and later Ethiopian Airlines crashes that killed a combined 346 people, the statement raises further questions about how transparent the company has been in dealing with the 737 Max jets.
Preliminary investigations for both accidents suggest faulty data from a malfunctioning angle of attack, or AOA, sensor, sent the signal to the plane’s anti-stall software that the plane was pointed at a dangerously high angle, putting it at risk of stalling. The software, known as MCAS, reacted by pitching the nose downward. The pilots struggled and failed to regain control of the plane.
Boeing had become aware shortly after rolling out the new 737s in 2017 that the AOA disagree alert, which might have warned pilots that the AOA sensors were sending inaccurate information, did not work unless the airlines also bought a separate optional feature called an AOA indicator. The jets have two AOA sensors, and the optional indicator would trigger the alert if the two sensors were sending contradictory information, indicating one or both of them was faulty. When Boeing began delivering the jets in 2017, the company included the cockpit warning light as a standard feature, but when a few months later it determined it only worked in jets that also contained the optional indicator, as the New York Times put it, “a safety feature that Boeing thought was standard was actually a premium add-on.” Only 20 percent of customers had purchased the indicator, according to the Times. Lion Air and Ethiopian Airlines were among those that chose not to buy it.
But Boeing insisted—and still insists—that the 737 Max jets were safe to fly even without the disagree light, given the other gauges present to measure the plane’s position, speed, and performance. And Boeing told the Times that the disagree light would not have warned pilots of sensor disagreement until the jets were 400 feet above the ground, meaning it would not have alerted the Lion Air pilots to a faulty sensor until after takeoff. (According to the Times, conflicting information over this was another source of frustration for pilots. A spokesman for pilots for American Airlines, which had purchased the optional indicator, told the Times they were given extra confidence to fly the 737 Max jets because Boeing told them the alert would function while still on the ground.)
Boeing notified the Federal Aviation Administration of the nonfunctioning warning lights after the Lion crash in October 2018. An FAA spokesman said the agency then determined that the issue presented only a low safety risk but still chastised the company for the delayed notification. “Boeing’s timely or earlier communication with [airlines] would have helped to reduce or eliminate possible confusion,” the spokesman told the Associated Press.
Airlines were then informed of the need for the add-on for the alert to work. Southwest Airlines told the AP that after Boeing notified it of the issue, Southwest added the optional feature.
The Justice Department is conducting a criminal investigation into whether Boeing misled regulators about features on the plane, including the MCAS software, which relied on only one of the two AOA sensors. Boeing is also facing a number of lawsuits from the families of the passengers and an investigation by the Transportation Department’s inspector general.
Boeing is working on an update to make the anti-stall system less powerful and reliant on both sensors, according to the Times. It will also update the disagree alert to make them independent of the AOA indicators, which will also be installed in all 737 Max jets before they are allowed to fly again.
Correction, May 7, 2019: The photo in this post originally showed an Alaska Airlines 737 jet that was not one of the new Max aircraft. The photo has been replaced with one showing Max 737 jets.