Investigators in the Lion Air crash in October off the coast of Indonesia and the Ethiopia Airlines disaster in March have zeroed in on the planes’ anti-stall system, called the Maneuvering Characteristics Augmentation System (MCAS).
Last year, inspectors with the Federal Aviation Administration discovered Boeing de-activated a signal designed to advise the cockpit crew of a malfunctioning of the MCAS system, the source said.
The inspectors were in charge of monitoring Southwest Airlines, the biggest user of 737 Max planes, with a fleet of 34 of them at the time, added the source.
Before the Lion Air crash, which killed all 189 people on board, “the (signals) were depicted as operable by Boeing on all MAX aircraft” regardless of whether the cockpit crew thought they had them turned on or off, said a Southwest spokeswoman.