Boeing test pilots and engineers have determined in simulations of the Lion Air crash an unrecoverable dive leading to a crash would have occurred if the MCAS was not shut down within 40s of an AoA data error.
Basically an undisclosed system, which was put in place to save airlines the cost of retraining pilots, had a single point of failure which can kill an untrained flight crew in under a minute. A trained flight crew would have no problems disabling the system. Saving training costs for the airlines cost 300+ people their lives.
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In testing performed in a simulator, Boeing test pilots recreated the conditions aboard Lion Air Flight 610 when it went down in the Java Sea in October, killing 189 people. The tests showed that the crew of the 737 MAX 8 would have only had 40 seconds to respond to the Maneuvering Characteristics Augmentation System’s (MCAS’s) attempts to correct a stall that wasn’t happening before the aircraft went into an unrecoverable dive, according to a report by The New York Times.
While the test pilots were able to correct the issue with the flip of three switches, their training on the systems far exceeded that of the Lion Air crew—and that of the similarly doomed Ethiopian Airlines Flight 302, which crashed earlier this month. The Lion Air crew was heard on cockpit voice recorders checking flight manuals in an attempt to diagnose what was going on moments before they died.
One of the controls—the electric stabilizer trim thumbswitch on the pilot’s control yoke—could temporarily reset MCAS’ control over stabilizers. The Lion Air pilots hit this switch more than 24 times, buying them some time—but MCAS’ stall prevention software kicked in afterwards each time because of faulty data coming from the aircraft’s primary angle of attack sensor.
Completely disabling MCAS’ control over the aircraft’s stabilizers would be the only way to overcome that sensor failure in the current software version. That requires throwing two additional switches on the console and turning a trim wheel on the console manually to re-establish manual control.
The Lion Air crew would have had to accomplish this while dealing with a host of alerts, including differences in other sensor data between the pilot and co-pilot positions that made it unclear what the aircraft’s altitude was. As a result, the crew continued to fight MCAS’ attempts to push the nose down until the end.
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https://arstechnica.com/information-...vent-disaster/