Ask HN: Boeing 737 Max MCAS' Purpose
Boeing rated MCAS as "hazardous" (http://www.tc.faa.gov/its/worldpac/techrpt/ar11-28.pdf, page 32, section 4 and https://www.seattletimes.com/business/boeing-aerospace/failed-certification-faa-missed-safety-issues-in-the-737-max-system-implicated-in-the-lion-air-crash/).
Reasoning based on the assumed competency of the pilots, reacting in only a few seconds by following the "Runaway Trim" checklist (https://www.wsj.com/articles/the-four-second-catastrophe-how-boeing-doomed-the-737-max-11565966629) they expected the usual pilots of a narrow-body plane to have quite a bit of training and experience, despite narrow-body, short-to-medium range planes are mostly piloted by not-so-experienced pilots.
MCAS was implemented as a system which depends on just one (known as to be unreliable) sensor (https://www.bloomberg.com/news/articles/2019-04-11/sensors-linked-to-737-crashes-vulnerable-to-failure-data-show, https://www.satcom.guru/2018/12/angle-of-attack-failure-modes.html).
This leads to the facts:
* For certification, pilots need to have the same feeling as the 737NG / 737 classic in certain unusual flight conditions only
* The used (one) sensor has a comparatively high failure rate
* With or without MCAS, being outside of the unusual flight condition, the plane feels as a 737 classic/737NG does
So, considering this, from my point of view, a risk supposedly most pilots could handle (different handling characteristics) was traded with a risk at least 2 pilots couldn't handle.
How did Boeing come to the conclusion this is acceptable? Do you have any theories, aside from adhering to grandfathering rules set by most international FAA equivalents?