Some investigative journalism indicates that this is not what happened. The FAA has different levels of redundancy and uptime requirements based on the outcome

Some investigative journalism indicates that this is not what happened. The FAA has different levels of redundancy and uptime requirements based on the outcome of system failure. A system categorized as “catastrophic” failing would lose the plane and all passengers, while “hazardous” might hurt some and kill a few, and so on. The FAA requires that catastrophic systems must have a backup, while hazardous can go without one if it’s reliable enough. Boeing classified the MCAS as “hazardous” only under certain flight characteristics, and they categorized it as a lower level than hazardous during level flight. This means that the crews designing the specification made the decision to depend upon only a single input, and it appears to have been built to spec[0]. It also appears that the FAA was experiencing internal pressure to delegate more certification authority to Boeing, with disastrous results. 0: https://www.seattletimes.com/business/boeing-aerospace/failed-certification-faa-missed-safety-issues-in-the-737-max-system-implicated-in-the-lion-air-crash/ https://www.seattletimes.com/business/boeing-aerospace/faile...