> The reason for the MCAS hack was not any engineering wisdom but simply allowing them to build a completely different plane that they could claim was in fact t

> The reason for the MCAS hack was not any engineering wisdom but simply allowing them to build a completely different plane that they could claim was in fact the very same plane, and then sell it to airlines as such The idea that MCAS is some kind of 737 emulator intended to keep the plane under the 737’s certification, and that without MCAS it would have needed more thorough training, is a persistent myth on HN. The reality is that MCAS exists because without it the 737 MAX’s aerodynamics are uncertifiable no matter how much training pilots were given. During testing the MAX was discovered to have an inverted force curve on the stick approaching a stall — as the aircraft approaches stall angle, forces flip around and it becomes easier to pull the stick back (into the stall) than push it forward (out of the stall angle). This violates a fundamental airworthiness requirement — commercial aircraft cannot be certified as airworthy if the stick forces invert. MCAS “solves” this by commanding the stabilizers down when it thinks the airplane approaches stall — effectively using the stabilizer to put the forces on the stick that are “missing” due to the MAX’s aerodynamics, ensuring the force curve never inverts. MCAS isn’t really allowing the plane to pretend to be anything other than “a plane that doesn’t want to stall mid-air”. Desire to keep the MAX requiring minimal training for 737 pilots (probably) drove the concealment of MCAS mentions from the manual, but MCAS would need to exist even if the airframe had been totally recertified from the ground up.