Even before the Lion Air and Ethiopian Airlines crashes claimed 346 lives,
Boeing flight tests had revealed problems similar to those encountered by pilots on the ill-fated 737 MAX flights.
Company officials learned that its MCAS anti-stall system -- which is at the center of both accidents -- activated within minutes of takeoff, repeatedly pushing the nose of the aircraft down even when the plane was operating in normal conditions at lower speed.
This discovery, recounted to AFP by two former Boeing engineers who spoke on the condition of anonymity, suggested that mastering the MCAS was important for safely flying the MAX.