Only after the deadly Indonesian Lion Air crash in October did Boeing come forward about a warning light problem it had been aware of for more than a year before the tragedy, the company admitted Sunday. It was created to warn pilots about the kind of sensor malfunction that occurred in the crash in Indonesia and another five months later in Ethiopia.
In 2017, Boeing discovered an error with the angle of attack (AOA) Disagree alert, which notifies pilots of discrepancies with the sensors that track the lift of a plane's nose. The faulty sensors activate an anti-stall software that sent both planes into a nose-dive.
The software linked the AOA disagree alert to a separate indicator, which was not standard and had to be purchased as an add-on feature, Boeing wrote.
The alert only worked on Max aircraft for which customers bought an added optional feature, Boeing said in a statement Sunday. "At that time, Boeing informed the FAA that Boeing engineers had identified the software issue in 2017 and had determined per Boeing's standard process that the issue did not adversely impact airplane safety or operation", the statement further read.
Boeing said a Safety Review Board convened after a fatal Lion Air crash in Indonesia last October corroborated its prior conclusion that the alert was not necessary for the safe operation of commercial aircraft and could safely be tackled in a future system update. Boeing's entire 737 MAX fleet has been grounded since shortly after the Ethiopian Airlines crash in March, while investigators study the incidents and engineers work on solutions. But the new disclosure raises questions about how forthright the company has been about issues with the planes.
The FAA statement then adds: "However, Boeing's timely or earlier communication with the operators would have have helped to reduce or eliminate possible confusion".
The two AOA sensors on the Lion Air jet disagreed by a large margin, about 20 degrees, throughout the flight and even while the jet taxied on the ground before takeoff when both readings should have been zero.
Neither the Lion Air aircraft nor the Ethiopian Airlines jet had the feature.
Boeing didn't tell airlines or the FAA about this decision.
It said it had meant to deal with the problem in a later software update.
It believed the issue could be resolved in a later system update.
Boeing briefed the FAA on the display issue in November, after the Lion Air accident, and a special panel deemed it to be "low risk", an FAA spokesman said, according to Reuters.
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.
Boeing is also developing a software upgrade and training changes to the MCAS system that must be approved by global regulators before the jets can fly again.
"The Boeing design requirements for the 737 MAX included the AOA Disagree alert as a standard, standalone feature, in keeping with Boeing's fundamental design philosophy of retaining commonality with the 737NG".