The 737 Max does fly differently, the MCAS and AoA checks to offset the engine "pitch up" due to more powerful engines was to get around a regulation/certification [1].

> The LEAP engine nacelles are larger and had to be mounted slightly higher and further forward from the previous NG CFM56-7 engines to give the necessary ground clearance. This new location and larger size of nacelle cause the vortex flow off the nacelle body to produce lift at high AoA. As the nacelle is ahead of the C of G, this lift causes a slight pitch-up effect (ie a reducing stick force) which could lead the pilot to inadvertently pull the yoke further aft than intended bringing the aircraft closer towards the stall. This abnormal nose-up pitching is not allowable under 14CFR §25.203(a) "Stall characteristics". Several aerodynamic solutions were introduced such as revising the leading edge stall strip and modifying the leading edge vortilons but they were insufficient to pass regulation. MCAS was therefore introduced to give an automatic nose down stabilizer input during elevated AoA when flaps are up.

The regulation that they had to make to fit within the 14CFR §25.203(a) regulation/rule was first tried by physical designs but ultimately settled on a sensor/software solution that constantly polls every 9 seconds to check the nose pitch/attitude and adjust, if it goes to0 far MCAS is triggered and pulls the nose down. Since there was a faulty sensor, this caused the nose dive catastrophic failures.

The 14CFR §25.203(a) regulation (a) is [2]:

>It must be possible to produce and to correct roll and yaw by unreversed use of the aileron and rudder controls, up to the time the airplane is stalled. No abnormal nose-up pitching may occur. The longitudinal control force must be positive up to and throughout the stall. In addition, it must be possible to promptly prevent stalling and to recover from a stall by normal use of the controls.

Since the change had to do with "No abnormal nose-up pitching may occur" in that rule, then the plane definitely flies differently as the cause of the MCAS and sensor flow is to constantly check for a nose pitch up that it corrects, if too far, enable MCAS to bring the nose down. This plane flies differently definitely and a bit opposite in that other planes will pitch down, it pitches up due to engine power of the larger more fuel efficient LEAP engines.

Ultimately the root of the problem was cost cutting which led to retro-fitting the 737NG to the 737 Max 7-10 to fit within cost/training/testing/regulations and in the end that was the problem that caused the end result of a software/sensor single point of failure which has squandered trust in Boeing engineering, management and safety as well as the 737 brand. Most people don't know the 737 Max is essentially an entire new plane. How the FAA let Boeing get away with this will be a focus as time goes on.

As a software engineer, the 737 Max looks like a legacy system hack that they tried to version 2 with it rather than make a new plane and incur all the training/testing/certifications of a new plane.

Boeing other planes don't have these issues, the 767 is has only had a couple issues beyond terrorism and those were related to pilots and fuel [3]. Two crashes of two new Boeing 737 Maxs within months of release and service is not a good trust enabling product.

[1] http://www.b737.org.uk/mcas.htm

[2] https://www.law.cornell.edu/cfr/text/14/25.203

[3] https://en.wikipedia.org/wiki/Category:Accidents_and_inciden...