[salawat]

727 had about the same issue. Interactions with high lift devices would cause major problems on approach to stall.

The FAA certified it anyway. The U.K. gave it conditional certification contingent on the addition of a stick-pusher to be able to operate in U.K. airspace. See the Royal Aeronautics Society D.P. Davies Interview, specifically the 727 one.

There was quite a bit of controversy amongst test pilots at even granting the certification, seeing it as setting a precedent that would lead to a slippery slope that would culminate in less and less airworthy designs.

Nevertheless, the certification authorities accepted the argument that as long as instabilities could be countered by technological means, it would be acceptable.

Let me clarify though, that without MCAS, a responsible pilot would definitely be constrained to a much thinner envelope, but within that thinner envelope, the plane can fly just fine.

The deployment of flaps, also takes the plane out of a regime where MCAS is a factor.

So both legal, and practical precedent for it exists. Given additional training of course.

[acqq]

> The U.K. gave it conditional certification contingent on the addition of a stick-pusher to be able to operate in U.K. airspace.

Boeing 727 was clearly from another times: "As of July 2018, a total of 44 Boeing 727s were in commercial service" "Many airlines replaced their 727s with either the 737-800 or the Airbus A320."

> both legal, and practical precedent for it exists.

Does it? The devil is in the details. Speaking as an engineer, both the measurements of the ranges in which the changes happen and the characteristics of the responses to controls still matter. I wouldn't be surprised that it's still 737 MAX that would be "a precedent" with worse characteristics when the stall is possible (and without proper MCAS-like help) than those measured in 727.

It's the conditions under which the problems occur and the response diagrams that the regulators are supposed to verify, not the binary "has or hasn't" a problem near the stall. I'm quite sure that the technology at the time of 727 introduction was already more than capable of producing the relevant diagrams, so they can be compared. Thanks for specifying your arguments in the answer.

[salawat]

No problem! I'm as eager to get to the bottom of things as anyone, so I'm trying to be a careful steward of as much context as I can to keep discussions productive, and to rephrase in as many different ways as possible to increase visibility and reasonability to anyone who can help contribute more context.

>It's the conditions under which the problems occur and the response diagrams that the regulators are supposed to verify, not the binary "has or hasn't" a problem near the

Ah, I hadn't run into this tidbit before! Can you elaborate on it? I'd love to get some more detailed information if only to facilitate my own deep diving. I've been repeating the 727 simimilarity, and if there's any footwork I can do to make that more accurate, I'd be thrilled to run with it.

I do know Boeing was generally considered notorious amongst test pilots for knowing exactly how their designs would fly, so I can't imagine that those diagrams can't be found somewhere.

[acqq]

> Can you elaborate on it? I'd love to get some more detailed information if only to facilitate my own deep diving.

To appreciate non-binariness of the problem, just try to find the pictures of different flight envelopes under different flight conditions for different planes and compare them. The wrongness in claiming that every plane can be qualified with just "has x" or "hasn't" is then more than obvious.

Then imagine that you'd actually need the response diagrams -- some valid measurement of how the plane reacts to the controls. That is the actual point of problem: exactly how the curves look like, where are which limits between "fine" and "deadly" and how dangerous is which kind of movement or non-movement of which control.

Then consider that Boeing even after the first crash claimed that "everything's fine" in their "additional instructions" which were followed by the Ethiopian air pilots but that then the plane responses were such that the pilots were practically helpless: the plane "didn't listen." That's what's happening with the positive feedbacks, and that is what "nose up" behavior is -- but the answer is not "yes-no" but where and how much in every point.

The helplessness (or not) of the pilots (i.e. how much of their force produces how much of the outcome under which conditions) is also something that can be plainly measured and drawn.

I don't have the corresponding (complex) pictures of Boeing 737 MAX flying without the MCAS. And I don't think they are available at the moment. But that is the point. Who are those who claim that they know it's safe and what is the basis of their claim? We have already plain demonstration that Boeing openly lied with their "everything's fine" claims -- I can't imagine that nobody inside of a company that is supposed to sell the planes orders of which measure hundreds of billions of dollars has such pictures.

But who can say simple "it's safe" when to be able to really claim it somebody has to evaluate these complex aspects demonstrated by the diagrams and not just construct a simple "yes-or-no-is-it-kinda-same-as-this-other-thing" question?

Reducing that whole topic to such kind of argument "well 727 was bad too" is obviously misleading. The way I still see it is: had it been it actually safe to fly it without a functioning MCAS, there would be no "regulatory requirement" to put it there at all. The "requirement" was an actual "it's not safe without it." But the way that "requirement" looked like was also not "yes no" but "see this diagrams -- the plane should approximately behave so and not the opposite of that." And the opposite is the characteristic of the positive feedback loops. MCAS was there to polish one resulting from the design driven by the marketing goal, not by physics.

Imagine when you would move the steering wheel to make a slight turn and when the car would "listen to you" under e.g. 30 mph but respond in turning you much out of the road when the speed is higher. "Well you should be trained not to try to turn the wheel when over 35 mph" "Really?" "Yes you see that other old car also responded kinda like this one, yes that old one couldn't have killed you so easily, yes, this one will, but don't worry that's actually the same, trust me, because I'm the one making and selling you this new car." "..." That's not how the sameness is compared.

[salawat]

I get where you are coming from. And understand it isn't binary. I was hoping you knew what what the name of the various diagrams you asserted were being evaluated were.

I understand there are different levels of problematic behavoor, because something that causes a 3 degree uncommanded pitch over say 10 seconds is a sight less severe than one that does the same over 3 seconds.

I'm still not seeing anything that's significantly changing my mental model of this problem. Physically, legally and pragmatically speaking.

-The plane remains statically stable within the majority of the flight envelope.

-Dynamic stability still isn't quite there, but can be handled with more conservative maneuvering.

-Critical information was deemphasized in the certification process, or changed after the fact

-the promised deliverable did not achieve it's stated goals without excessive "compliance engineering"

The plane is absolutely dangerous to an uninformed pilot; but aerodynamically, within a constrained flight envelope, it's fine. I don't personally feel it should be airworthy, as I agree with many test pilot's from back in the 60's. It just encourages the use of less airworthy designs with less problematic behavior, because a computer can smooth out the curve, and yet as a programmer myself,I believe a passenger plane should not be reliant on that level of hack necessarily.

As it is, I'm not even highly confident that if there were something wrong with the software update, that the FAA would even catch it in it's current incarnation.

But without language naming the graphs you're talking about, or need to see to be convinced of safety, a FOIA would honestly be fruitless.

Thanks for the contributing though. I'll see if I can find the paperwork.

[acqq]

If you consider FOIA then it could be, for example:

- of the logs of the measurements of the test flights flown on the 737 MAX prototypes with the new engines but without the MCAS, if the test flights are flown to establish the flight envelope, especially of the correlation to the pilot's input and the plane's response.

- of the calculations or of the physical models of the said response to the pilots input, on the plane without the MCAS. Such parameters and models are indeed used e.g. in the flight simulators.

- Note that even if there were planed deliveries of hundreds of billions (!) worth of 737 MAX planes, up to recently only four (!) flight simulators for 737 MAX were delivered. I don't know if it's possible to even fly them without assuming MCAS "always working perfectly."

I'm not directly in that field to be able to give you a "local" jargon though. My view is a result of just reading those newspaper articles which provided enough engineering details (and a few forums) and I do remember seeing some complex enough related graphs for which I''m sure they couldn't be invented by a journalist, but surely not a "definitive plainly obvious proof". But there is indeed a lot still kept hidden from the public, and I'm sure there are more technical details that are significantly worse than we are ready to imagine.