- it is difficult for pilots to understand how MCAS works, and how to diagnose failures. They are not programmers or engineers. And MCAS doesn't provide any debugging information about its work anyway. And pilots don't have time to analyze it.

- it adds new points of failure

- sometimes there are situations when automatic systems shut down and pilots have to control everything manually. With MCAS, they would have more things to look after. Pilots who got used to flying with autopilot are usually not comfortable with manual flight, and systems like MCAS only make things more complicated for them. An example is a recent crash of SSJ100 in Moscow where experienced pilots failed to land a plane manually after autopilot has turned off.

So I think that plane designers should be very careful with adding more automatic controls. Especially if their purpose is only to save money at cost of making place less safer.

If I remember correctly, the behavior you promote as "fine" is forbidden by the regulators, and not accidentally.

Without the active MCAS the plane would have not been certified because the behavior of controls is then not inside of the prescribed limits.

If the plane must have natural behavior, then MCAS would not allow it to be certified because it's artificial control.

At high angle of attack, the MAX-8 is more unstable than pilots were trained to expect. And the MCAS has done an absolutely miserable job of fixing this. Worst case scenario bad: it caused the loss of two airplanes that, if the MCAS had never been added to the MAX-8, would have reached their destinations just fine.

Until the it flies predictably in every flight profile (including high AOA), it's demonstrably wrong to say "the aircraft flies fine." Maybe it will eventually "fly fine" but Boeing's got quite a bit of work to do first.

The specific design of MCAS and not adding any new procedures, was to lower the training requirements. Specifically, anyone certified on the old 737 was still certified on the max.

If they had improved the interface of MCAS and changed the procedure for runaway trim, it would have required more training. However, without MCAS or another remedy for the 'decreasing stick pressure at increasing pitch' problem, the plane would not have been allowed to fly at all.

The original one is https://news.ycombinator.com/item?id=19568158

and was written at night, so there's some loopy phrasing in there I never corrected. Let me unpack some of it to fit the context here.

The pressure applied on the stick itself does not change. Rather, the function of how much deflection you get out of the plane per unit force applied to the stick changes.

Design regulations state an airframe for which this curve at any point goes negative cannot be certified as a civil transport airplane.

That means, there should be no point in the flight envelope where the sensitivity of the controls drastically changes. It should be a predictable increase in force required to get more deflection, all the way to stall.

With the MAX without MCAS, this rule is broken at high AoA when the engine nacelles start making lift.

MCAS is meant to compensate for this necessary breakage by inducing some mistrim.

The effect of mistrim in that case is to cause the controls to require more force to induce those last few degrees of deflection, using the AoA sensor as the primary indicator as to whether the system should activate, in order to bring the curve into compliance.

The problem, as hinted by the response to my post in that thread, is that an honest to god stick-pusher would be more akin to the system you'd want for that. Adding the AoA sensor as a single point of failure is insane, due to the consequences should that sensor start spewing garbage data in normal flight.

Most of those are realizations I came to after stumbling across a Royal Aeronautics Society interview of D.P. Davies, a British test pilot for the ARB, the aircraft certification authority for the U.K., which I believe I linked in the comment.

At the time I wrote it I was in the midst of a deep dive into the more arcane aspects of control systems. I have some literature tucked away somewhere that I was referencing, bit I'd need to dig rather deep in my browsing history to recover all the context.

An interesting historical note: MCAS is similar to a system McDonnell Douglas implemented in MD-11's (LSAS, Longitudinal Stability Augmentation System) for the same reasons as Boeing eventually implemented MCAS: to be able to claim that the new aircraft flew just like the old MD-10.

Makes one wonder if someone brushed the dust off something that really shouldn't have been emulated again after the merger.

Pilots are trained extensively not to trust what motion feels like, and to use the horizon and instruments. An adjustment in stick pressure is not a notable new threat, they just need to be trained for the plane's behavior.

It seems that what you claim is "not a new threat" is actually forbidden by the regulations, because it was recognized to be a threat.

I'm not quite sure how that is related to beginner flight lessons. (?)

Most commercial planrs fly 3000 hours a year. There are about 400 787-Max planes built - that's a million flight hours per year already (if they weren't grounded...)