The lawsuit alleges Boeing introduced angle of attack correction software that made planes inherently vulnerable to faulty sensor readings, and pilots were never informed about its functionality.

The US-based plane maker Boeing was hit with a class-action lawsuit filed Friday, seeking millions of dollars in damages in favor of over 400 pilots trained to fly the 737 MAX, ABC News report says.

The original plaintiff, known only as “Pilot X,” claims Boeing engaged in an “unprecedented cover-up of the known design flaws, which predictably resulted in the crashes of two MAX aircraft and subsequent grounding of all MAX aircraft worldwide.”

The plaintiff in the lawsuit claims that the Boeing 737 MAX has an “inherently dangerous aerodynamic handling defect.” They state that Boeing retrofitted newer, larger engines onto an older airframe, and the new engine’s size and shape caused the aircraft to pitch up during flight, posing a risk of crash due to aerodynamic stall.

In order to mitigate the problem, Boeing introduced a software system called the Maneuvering Characteristics Augmentation System (MCAS), which automatically tilted the nose down if it determined the pitch – aka Angle of Attack (AOA) – was wrong.

The software made the plane vulnerable to faulty or mismatched readings from the two AOA sensors installed on each aircraft. Pilots could only find out about faulty readings if their planes had optional AOA displays installed. All planes were supposed to have an AOA mismatch alarm light, but, due to a design flaw, the light only worked on planes with optional displays onboard.

In March, CBC reported that the MCAS was mentioned in the plane’s operating manual only once: in the glossary, explaining the MCAS acronym. Boeing did not deny the omission.

The lawsuit is scheduled for a hearing in Chicago court in 21 October.

Two of the aircraft, belonging to Lion Air and Ethiopian Airlines, crashed in 29 October 2018 and 10 March 2019, respectively, killing 346 people total. The crashes led to the worldwide grounding of the 737 MAX.