[acqq]

> MCAS was put in place to allow the MAX to be type certified w/ other 737's

But the expected behavior which MCAS was to provide was not something invented only for "other 737's." Whichever plane would behave as the MAX behaves without MCAS turned on would also be rejected from certification.

Only Boeing being silent about MCAS is the effect of the goal of "avoiding re-certification."

> We don't know

I can't agree to that. Based on the above, I think it is obvious that we do know: 737 MAX without any MCAS-like help is dangerous to fly according to the security expectations which weren't specially invented for 737 MAX.

[lmm]

> But the expected behavior which MCAS was to provide was not something invented only for "other 737's." Whichever plane would behave as the MAX behaves without MCAS turned on would also be rejected from certification.

No, it would have been a perfectly certifiable plane with a particular set of handling characteristics (including 777-like pitch-up). It just wouldn't be a 737, and would require its own type certificate. No-one's suggesting that large turbofan aircraft with pitch-up behaviour are inherently unsafe when flown by pilots appropriately trained and certified for them - otherwise the 777 would be grounded.

[acqq]

> No-one's suggesting that large turbofan aircraft with pitch-up behaviour are inherently unsafe

It is as long it keeps 737 MAX body and engines and doesn’t have something like MCAS I.e. Inherently unsafe under conditions under which MCAS was supposed to turn on when properly functioning.

The certification requirements are the result of the clear safety goals not something invented “just so.”

[salawat]

MCAS was a type certificate hack.

The poster you're responding to is right; there isn't anything wrong with the behavior given the right training.

It's just that the investment in that training, and extra certification hoops to jump through would have made WhateveroModelNumberus MAX a non-starter.

It had to be a 737 to work at all.

[acqq]

> there isn't anything wrong with the behavior given the right training.

The behaviour without MCAS on 737 MAX is that minimal movements of pilot’s controls effectively activate what would be considered “amplification” of nose up movement, resulting in an uncontrollable plane and sure crash.

It’s definitely not something that pilots or passengers should be exposed to: being punished for approaching more dangerous position by plane forcing a deadly outcome.

Training pilots to not to move even minimally the controls in the “wrong” direction is maybe technically possible but in practice still totally wrong: It’s comparable to what Boeing told everybody before Ethiopian crash, and their attempts to blame the pilots. In reality, the pilots had almost no chance to rescue themselves and the plane.

In engineering the “positive feedback loops” (amplification of control inputs) are bad the “negative feedback loops” (correction of the input) are good.

The functioning MCAS provides a correction. The plane without MCAS amplification. Badly functioning MCAS also amplification and crash. That's why the wrong behavior was regulated, and that's why it had to be fulfilled for the certification. It’s that easy.

To convince me that 737 MAX without the "properly functioning MCAS" isn't inherently dangerous under higher angles of attack you'd have to provide some explicit proofs.

[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.

[caconym_]

> To convince me that 737 MAX without the "properly functioning MCAS" isn't inherently dangerous under higher angles of attack you'd have to provide some explicit proofs.

I am legitimately curious, do you have any explicit proofs of the converse, that (as you say) "the behaviour without MCAS on 737 MAX is that minimal movements of pilot’s controls effectively activate what would be considered “amplification” of nose up movement, resulting in an uncontrollable plane and sure crash"?

The standard should be that a an unimpaired pilot properly trained in flying the aircraft will normally (practically) be in no danger of a "sure crash".

[acqq]

> The standard should be that a an unimpaired pilot properly trained in flying the aircraft will normally (practically) be in no danger of a "sure crash".

Exactly. And under that assumptions 737 MAX with no MCAS was never certified. Boeing didn't even want to admit that MCAS even exists to avoid even showing the flight characteristic of the plane "without MCAS." It's on Boeing to prove "737 MAX without MCAS" is safe, and up to now they did all they could to avoid that, and I expect they'll do more of that unless there is a pressure outside of both Boeing and FAA.