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The automated-flight-control feature on the 737 Max, which is called a Maneuvering Characteristics Augmentation System (MCAS), was designed to prevent a high-speed stall. It works by tilting part of the horizontal stabilizer in the tail of the plane, and investigators at the Ethiopian crash site have found physical evidence that this part of the plane was, indeed, configured to dive.
Radar data has indicated that both planes jerked up and down in erratic fashion after takeoff. The captain of the Ethiopian Airlines flight reported a “flight control” problem to the air-traffic control tower. Data from the black box of the Lion Air plane showed that its pilots repeatedly pulled back on the control yoke to try to disengage the MCAS and level the flight path of the plane. “The pilots fought continuously until the end of the flight,” an official from the Indonesian National Transportation Safety Committee said in November, after the plane’s black box was recovered.
This is all frightening enough, and it raises serious questions about why Boeing didn’t tell airlines and pilots much more about the MCAS—in particular, how to disengage it in an emergency—before the 737 Max was put into service, in 2017. Boeing has delivered three hundred and seventy-six of these planes to airlines around the world. Practically all of them have now been grounded out of safety concerns.
Boeing has promised a software fix to address some of the potential problems created by the MCAS. That’s too little, too late, of course, and it doesn’t address the even larger issue of how the 737 Max was allowed to fly in the first place.