Transport category aircraft have a vast number of aerodynamic behaviors written in regulations, FAR 25. Approach to stall, stall, and stall recovery are describ

Transport category aircraft have a vast number of aerodynamic behaviors written in regulations, FAR 25. Approach to stall, stall, and stall recovery are described behaviors they must exhibit (FAR 25.201 - 25.207). Longitudinal static stability and dynamic stability are also defined (FAR 25.171 - 25.181). There is no such thing as certifying an aerodynamically unstable transport category aircraft. An open question I haven't yet been able to determine is to what degree software is an acceptable mediator to compel such behaviors. But I'm very skeptical that it's acceptable at all, let alone by something that can be intentionally disabled with two switches as a troubleshooting/override, and then also not require any difference training for the new behavior that ensues. Whether MCAS exists strictly for FAR 25 airworthiness, or to avoid a different type rating for the pilot under FAR 61.31 from any other 737, it's questionable how you get around either of those things once it's disabled on purpose as a emergency/troubleshooting technique. Which is worse upon setting STAB TRIM to cutoff? That the airplane isn't legally airworthy? Or that the pilot isn't legally type rated? Or even possibly both? And was either the case with the previous 737 models? Definitely not.