I'm not an airframe designer by any means but from the countless threads that I've read on this website about this subject (coming from people who seemed more knowledgable than me on the subject) it did seem like the plane was fundamentally unsound at a design level.
I strongly recommend not getting your 737-MAX facts from HN. Every time the topic comes up, the discussion continues to be riddled with inaccuracies, many of them strongly held beliefs.
The safety analysis was turbo hosed, the documentation was shat, they hid the issue from operators and regulators alike, and went out of the way to not make simulators.
They removed previous generation's safeties (the oh shit yank back hard electric trim switch override), and removed a level of granularity in terms of capability to isolate the flight computer from the trim motors (which they have to do because they can't certify the plane to carry passengers otherwise), they have electrical control and power circuits to the trim motors too close together, and not sufficiently protected from a thrown turbine blade.
The aerodynamics (without MCAS functional) fail to pass airworthyness requirements for passenger transport that have been in place since time immemorial, and critical structural components (pickle forks) are showing alarming degrees of premature failure given their design lifetime.
Explain to me how a plane that doesn't at all implement graceful degradation to a fundamentally safe configuration is not "fundamentally flawed". Explain to me how plane's assembled from components that are failing well before their designed lifetime (and yes, I understand MTBF) is not a sign fundamental flaws. Even with all the fixes they're doing, the design shows an astonishing lack of good engineering sense. You don't keep around an awkward, unpredictable, unergonomic tool built by someone who demonstrated a willful disregard for doing Generally Accepted Engineering Practices, and who have repeatedly been found to do stupid things like leaving tools or metal shavings to foul or clog up filters, damage gaskets/seals etc.. You bin it, and make/get one that won't kill 200 people a failure instead. I don't give a damn how expensive a mistake it was.
There are lines you don't cross. Supporting bad business is one of them. Bring on the Depression. Maybe it's time we all figured out what good business looks like all the way around again.
And no, all that isn't belief or mere opinion. It's fact laid bare for all to see. You can fly on them and risk your loved ones if you like. I know the mentalities that drive those types of boondoggle and I'll have none of it. Show me a massive culture revamp in Boeing first, then I'll consider it again.
However if the original 737 in the 60s had the design of the MAX, its pilots would be taught how to fly it without any MCAS software and it would fly just fine.
In reality, the force curves always deviate from the ideal, save in fly-by-wire designs. There are two different issues at play:
The first is a force curve that deviates so much that it becomes unintuitive or unmanageable to fly. This would not be acceptable, but I have not seen someone claim the 737 MAX would be characterized this way.
The second is whether the force curves of the older 737s matched the MAX closely enough. These pilots are expecting a certain behavior, and under single certification, could be going back and forth between these models often. Even small differences in handling between these could be jarring and lead to bad stick inputs.
This is a much more demanding requirement because of the context; in the first case, a pilot is making one transition to a new aircraft that they expect will be different from what they flew before. In the second, they are switching between aircraft often, perhaps after long stretches of becoming accustomed to one model or the other. They must then constantly be aware of these differences and continually adjust for them, a situation ripe for error.
My understanding is that the 737Max flies kinda like a 757 without MCAS. It's not a big deal.
It is hard to find reliable sources on this, I must say.
I base my conclusion for example on these excerpts from [1]:
> MCAS would trigger in narrow circumstances. It was designed “to address potentially unacceptable nose-up pitching moment at high angles of attack at high airspeeds,” Boeing told the FAA in a proprietary System Safety Assessment
(This doesn't specify whether it would be unacceptable for certification, or for certification under the same type certificate.)
> Engineers determined that on the MAX, the force the pilots feel in the control column as they execute this maneuver would not smoothly and continuously increase. Pilots who pull back forcefully on the column — sometimes called the stick — might suddenly feel a slackening of resistance. An FAA rule requires that the plane handle with smoothly changing stick forces.
(This seems to indicate that it would be unacceptable under the general FAA rule.)
[1] https://www.seattletimes.com/seattle-news/times-watchdog/the...
From my understanding, the MCAS system was built to offset these problematic default states that come with using an old body not compatible with the upgrades made. I also heard the weight of these new engines caused wings to develop stress cracks.
Not sure how it could be considered safe without a better designed MCAS system and addressing the other issues.
> It simply handles differently than pre-MAX 737s in certain scenarios
It handles differently than previous 737s due to airframe changes (namely engine position). MCAS was meant to "correct" this for the purpose of skipping re-certification. The airframe isn't fundamentally flawed, the process of certifying it this round was flawed. Which caused Boeing engineers to implement a flawed MCAS system.
See for example here:
https://aviation.stackexchange.com/questions/73132/did-boein...
(I agree, FWIW, that the plane would by flyable, easily in nearly all flight regimes, and carefully in some flight regimes, without MCAS. But that is not the issue at hand.)
Here is one example: https://www.reuters.com/article/us-boeing-737max/boeing-prop...
My understanding of that issue: The 737 is wired in such a way that was considered fine when it was designed. In 1998 an MC-11 crashed which resulted in revised design standards that would render the 737's wiring invalid, except the 737 was already a proven design by this point and consequently has been allowed to continue flying the way it is. The 737 MAX continues to use this wiring configuration, which was initially considered fine because the the 737 MAX "is a 737", a proven legacy design.
> Boeing did not forget how to design planes.
I certainly did not and would not suggest otherwise. It's possible I'm mistaken about the above, I'm certainly not an expert on FAA matters, but I earnestly don't think I'm wrong. If you still think I'm wrong, I'd appreciate a substantive correction.
Boeing failed to provide sufficient redundancy for the MCAS system and proper training to the air crews.
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.