fuel systems, etc. Typically something like this I would expect multiple AOA vanes/sensors, with a signal comparator to say, “hey, one is out of whack, check against other indications - airspeed, pitch, etc. - to determine the good one”. This is basically how we deal with air data.

Boeing builds in tons of “protections” into many of the systems on all of their jets now that work with the autopilot off. For example, with the autopilot off and I try or bank the plane over ~30°, the force required is noticeably more. If I attempt a steeper turn, at a certain point, the plane will try to pushback. Another is low or slow speed protection. In certain slow speed conditions (depends on configuration, flaps, etc.) the throttles can advance on their own, with the auto throttles on or off. It’s a low speed protection.

I believe the 737 Max already has 2 AOA vanes, but only uses data from one for the MCAS system. Picture is of the B777 AOA Vane. There is another in the starboard side.

BTW - I typically find AOA to be much more reliable than airspeed. For example, from an erroneous input on my part, on the ground, before even leaving the gate, the airplane computers may think the plane is lighter than it actually is and then computes take off and landing data accordingly. If I’m flying an approach and the nose attitide seems high (which would be the case if I’m flying slower than required for the heavier actual weight), a quick reference to an AOA gauge in my HUD would be my fix. Most planes have no AOA indication as a cross referenc though.

This scenario may seem far fetched, but it happened to an MD11 crew of ours. Multiple weight and balance changes during preflight. Last one came late and unexpected. In a hurry, crew rushed and entered a weight -100K less than they actually were. Making it worse, going into Denver, a high altitude airport. They flew it to the runway barely above stall buffet. If they had referenced the AOA in the HUD, they would have seen higher than normal AOA - which is generally correct for all weights/configurations. Fatigue was an issue as well.
[Post edited by B777Fr8Dog at 03/18/2019 11:55AM]