[ggreer]

The 737 max has multiple AoA sensors.

Having multiple sensors doesn't always help, as failures are correlated. For example, there was an Airbus A321 that had 2 of its 3 sensors get stuck in the same position due to icing.[1] The computer thought that the one working sensor was malfunctioning and disregarded it. It then engaged stall protection, dipping the nose and causing the plane to dive at 4,000ft per minute.

> The captain continued to hold “more than 50%” rearward stick in stable flight for a period, but with help from technicians on the ground, the crew was able to reconfigure the automation into the aircraft’s alternate control law, rather than its normal “direct” law. The action removed the alpha-protection checks and canceled the nose-down input. The aircraft then continued to its destination.

These failure modes tend to happen more with Airbus planes because their flight control systems default to overriding human input if the computer deems it unsafe. Boeing's flight computers will give more resistance in the controls, but they mostly won't prevent the pilot from doing what they want to do. The exceptions (such as auto-trim and stall prevention) can be disabled with by flipping a couple of switches.

1. https://aviationweek.com/commercial-aviation/german-investig...

[dmix]

True but 2/3 failing instead of 1/1 is still the better option. I’ve read the Max only used one sensor for the MCAS system.

But I’m not an expert on the subject so I’ll defer to the reports and more knowedgable people.

[ScottBurson]

I recall reading somewhere that while the 737Max has two AoA sensors, only one of them is connected to the MCAS.