The sensor's role in engaging MCAS will put more scrutiny on whether Boeing was too reliant on a single device to trigger an important change in the jetliner's trajectory.
Normally,aircraft manufacturers use multiple data points to guide a plane's automated systems. Regulators,lawmakers and federal investigators are reviewing whether Boeing cut corners as it raced to get the 737 MAX to market to counter Airbus SE's A320neo aircraft.
Evidence from the flight-data recorder of the Ethiopian 737 MAX 8 showed that the missing sensor was malfunctioning and that a device known as a"stick-shaker"-- which makes a loud nose and rattles a pilot's control column to warn of an impending aerodynamic stall -- had been activated on the same side of the aircraft. It could be heard on the cockpit voice recorder,the person said.
The details about the sensor,which haven't previously been reported,indicate a scenario similar to the one on the final flight of a Lion Air jet that crashed on October 29 off the coast of Indonesia.
The pilots were battling an automated feature called the Maneuvering Characteristics Augmentation System,MCAS for short,and weren't able to shut if off as the jet plunged into the Java Sea. That accident claimed 189 lives,while the Ethiopian crash killed 157.