To be clear, I think MCAS was a massive engineering failure for Boeing, I'm just pointing out why I think they didn't automatically say "hey, we've got two sens

To be clear, I think MCAS was a massive engineering failure for Boeing, I'm just pointing out why I think they didn't automatically say "hey, we've got two sensors, lets compare the readings before we act on it". However, for the autopilot example, I don't think you are quite right. Typically there are multiple autopilots (2 or 3 is quite common), and each is driven by a different set of flight data. In some scenarios multiple autopilots are engaged at same time, for example during CATIII auto-landings but as far as I'm aware that is the exception rather than the rule. It's true that the autopilot may disconnect if there is a warning like 'IAS Disagree', I suspect this is driven by a separate monitoring process though, rather than being an integral part of the system.