Same. My understanding is that adding larger engines, and moving them forward on the wing, make the the airframe unable to fly at level altitude without software automatically adjusting the pitch.
This is flown to test the stick force as a function of load factor. Now, it is a certification requirement that the stick force increases basically linearly with the load factor ("The stick force curve must have a stable slope" [3]), and that was not given - the stick slacked.
This is what MCAS was designed to address.
From what I gather, a 737 MAX without MCAS would not be certifiable, but safely flyable, possibly with some surprising, but manageable behaviour under very rare circumstances: namely, flying at a high angle of attack with high speed would require you to release some stick force instead of having to pull hard to keep the nose up.
Having said that, the whole saga has revealed so many problems at Boeing and the FAA that I am reluctant to fly the 737 MAX and 787 myself.
https://www.seattletimes.com/seattle-news/times-watchdog/the...
https://www.scribd.com/document/53095046/NASA-Information-Su...
How do you suppose they might do that without completely redesigning the plane? I don't think type recertification is why they kept the landing gear the same length.
Plus Southwest basically won’t buy anything but 737s, so maintaining that type rating was critical to selling the new plane to one of their biggest customers.
Boeing had initially proposed a clean sheet redesign of the 737, but the market for that aircraft is very sensitive to training and operation costs.
Not really. Without MCAS, the plane would not have been certifiable. (So, MCAS does make it more similar to the regular 737 in that it is certifiable, but that was not the only reason.)
As I understand it, the 737 MAX was the first commercial airframe ever approved by the FAA with this sudden inflection point in behavior when approaching a stall. (There's a term for it, something like "positive rate characteristic", but I forget. Perhaps someone who knows it will mention it here.) Seeing how well that worked out, one hopes it'll also be the last such airframe approved.
Virtually all aircraft will do that, including the original 737. Different aircraft do this at different points; provided the pilot is trained for the aircraft, it's not a fundamental problem.
The problem for the MAX is they wanted pilots to be able to treat it like an airplane it wasn't.
But evidently the stick shaker isn't enough, because the 737 MAX also has MCAS, which operates to actively deflect the nose back down as the aircraft approaches stall. That shouldn't be necessary. That's the thing that other airframes, including prior marks of the 737, do not do. In those airframes, you don't need to push the nose down to get away from a stall. You only need to stop pulling the nose up. MCAS exists to try to replicate this behavior in the 737 MAX, but that MCAS needs to exist for that purpose is enough to demonstrate that the 737 MAX does not behave that way by default.
I agree that the falsely shared type certification, and the consequent lack of training on the MAX's type-unique and dangerous stall behavior without MCAS, is a problem. Where we disagree is that I don't consider acceptable a design that exhibits that behavior at all in the absence of an active control system that can fail or be turned off. Neither do the relevant regulations for certification - I linked them above; they make no mention of an exception for an airframe with something equivalent to MCAS - and neither, historically, has the FAA. Not, at least, until the 737 MAX was itself type-certified, and the way that process played out is itself highly suggestive of significant corruption, in the form of regulatory capture if nothing else.
edit: And, having checked the Wikipedia page for the system, I find myself surprised that that is in fact a lie Boeing has told.
They may as well go ahead and try to rebrand the damned thing, I guess. On top of everything else they've done, I can't see how it would make their problems any worse...
also edit: Via Wikipedia, 14 CFR 25.203: "No abnormal nose-up pitching may occur. The longitudinal [pitch] control force must be positive up to and throughout the stall." This is the characteristic the MAX lacks due to the engine placement. If you want to add an active system to correct for that, the AoA sensor is what you use to drive it, since that's what tells you the difference between the direction of airflow and the angle of the wing. That's how you know you're approaching a stall, and need to add a negative pitching moment. But if that sensor jams, which being a mechanical device it can do, and you don't have input from another sensor so you can see the disagreement, you risk spurious activation of the system when it isn't needed, potentially forcing the aircraft out of level flight.
I get that it's in Boeing's interest to claim MCAS isn't an anti-stall system. Why would they say anything else? To do so would implicitly admit not only that they built an aircraft that would fail dangerously in a common situation, but also that the FAA let them get away with selling it and selling it as type-identical with prior versions lacking the fail-dangerous characteristic. Neither admission would serve their interests.
But, equally, why should we take them at their word on this, or indeed anything? It's pretty clear that their corporate interests have ceased to align with ours as potential airline passengers. It's generous unto foolishness, in light of that, to give them the benefit of any doubt whatsoever.
What Boeing did was hide the change in flight characteristics caused by the new engines using software, so pilots didn't need to retrain, and they borked the implementation.