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> marketing an inherently unstable aircraft The 737 Max is not an inherently unstable aircraft and to say so grossly misunderstands the term and what MCAS was

• acqq 7y ago
  > Design changes had forced the addition of this system in order to retain the same type rating because those design changes caused the aircraft to handle differently to previous generations. It's not "just to retain the same type rating" that the MCAS worked as it worked. The MCAS, as it was implemented in the planes which crashed had to be implemented for the plane to pass the certification requirements which exist because of the safety. The plane is with its geometry inherently unsafe without some clever devices correcting the "inherent" behavior. Anybody who claims it's not "unstable" does misdirection of clinging to the technicalities of wording of the specific claim (as the plane can be technically-speaking "stable", if nothing unexpected happens, while still being the death trap under non-average conditions, and that's what happened here), as there are more elephants in the room remaining, to be specific: - The regulation exists to provide safety. - Boeing 737 MAX is unsafe to fly without some additional hardware and software which does the compensation. Nobody can sell or certify the Boeing 737 MAX as it is designed without adding some hardware and software that would do something similar to MCAS. "Just turning off MCAS" permanently or "just removing it" makes the plane non certifiable safety-wise, not only losing its "type rating." - MCAS design (its power) wasn't decided only once and implemented. The set of events was that only during the test flights the additional problems with the safety of the plane's response to the commands were detected, and the MCAS revisions added more power to MCAS (and less to the pilots) through the time. The result was that the MCAS which exists on all the planes sold (and the planes crashed) is not the MCAS from the initial specifications or claimed by Boeing after the crashes, as they still quoted the original characteristics. - The goal of Boeing of "keeping the same type rating" is the motivation why they decided to lie about what they implemented and why they actively reduced the safety of the plane to the point of plane actively being the death trap. - Specifically, Boeing misused the trust it had: through the years Boeing was allowed to do more and more of the certification work for their own planes. - Not to mention disastrous public claims there's nothing wrong with their planes even after the two crashes, a lot of information already public and most of the world already having grounded the planes. - Not only Boeing lied about what they did to the FAA and the rest of the world, even after the first crash happened, but while making the plane the engineering decisions have been made more than once just with the goal of preserving the false promises made by the Boeing managers as they have sold the planes: that's why there was the change in the behavior of the switches where there were separate switches before but they changed two switches to behave identically, only to actively hide what the new MCAS was doing. That's why the system was made glaringly non-redundant: adding redundancy would make it obvious that the system was (and it actually was) critical. In short, it's not misinformation that 737 MAX was a death trap made as such under the guidance of Boeing's managers. There are many levels of evilness Boeing managed to achieve in designing the plane and responding to the existing crashes. Some managers should be prosecuted for what they did. If that doesn't happen, the laws should be changed to allow that kind of responsibility the next time, or there will be even more victims.
  • PuffinBlue 7y ago
    > The plane is with its geometry inherently unsafe without some clever devices correcting the "inherent" behavior. No it isn't. It is a stable design. To claim otherwise misunderstands the term. The 737 can be flown just fine without MCAS turned on as it has absolutely nothing to do with making the aircraft stable. Many people seem to want to shit on Boeing for making an 'unstable' aircraft. They simply did not make an unstable aircraft. They made an inherently stable aircraft that handled a little bit differently and then to save money (in order to prevent the need for a new type rating and pilot retraining) they used MCAS to make it handle like previous generations. To repeat, the 737 Max flies just fine without MCAS (indeed previous flights of one of the downed aircraft pulled the stabiliser cut out switches and flew just fine) and MCAS was about handling, keeping the same type rating and saving money.
    • acqq 7y ago
      > the 737 Max flies just fine without MCAS No. Without the MCAS (but implemented correctly with the redundance etc) it behaves dangerously wrong in some ranges of its flight envelope: it effectively amplifies the small changes in the pilots control to the catastrophic results. Also see that the final MCAS was delivered non-redundant and also modified to turn itself on under more than one condition and also to exert much more power in overriding pilot than in the initial design. What you're claiming is a retelling of an initial belief about the MCAS as it was introduced, not about the MCAS as it was actually sold and as it was present in all the planes. The claim wasn't true then and isn't true now. Edit: What I'm talking about is documented here: https://www.seattletimes.com/seattle-news/times-watchdog/the-inside-story-of-mcas-how-boeings-737-max-system-gained-power-and-lost-safeguards/ https://www.seattletimes.com/seattle-news/times-watchdog/the... "This original version of MCAS, according to two people familiar with the details, was activated only if two distinct sensors indicated such an extreme maneuver: a high angle of attack and a high G-force." "About a third of the way through flight testing in 2016, as first reported by The Seattle Times in March, Boeing made substantial changes to MCAS. The flight-test pilots had found another problem: The same lack of smooth stick forces was also occurring in certain low-speed flight conditions. To cover that issue too, engineers decided to expand the scope and power of MCAS. Because at low speed a control surface must be deflected more to have the same effect, engineers increased the power of the system at low speed from 0.6 degrees of stabilizer nose-down deflection to 2.5 degrees each time it was activated. On the stabilizer, maximum nose down is about 4.7 degrees away from level flight. So with the new increased authority to move the stabilizer, just a couple of iterations of the system could push it to that maximum. Because there are no excessive G-forces at low speed, the engineers removed the G-force factor as a trigger. But that meant MCAS was now activated by a single angle-of-attack sensor." "While the changes were dramatic, Boeing did not submit documentation of the revised system safety assessment to the FAA." The "low-speed flight conditions" is effectively what was discovered only in 2016, what was changed in the implementation of the MCAS only then and what was not documented and what eventually caused the crash of both planes. And they had to add it for safety, not for "type rating." And it seems PuffinBlue is either not aware of that part of the story or intentionally ignores these findings in the comments, sticking to the the first part of the story, the MCAS as it was initially planned, not as it was actually implemented. The "type rating" motivation was why they lied about what they did. But the intention of the MCAS changes were to make it safer to fly, not to fit the type rating.
• hpaavola 7y ago
  > the 737 Max is an inherently stable aircraft without MCAS. Ok, but 737 MAX wihout MCAS is not the aircraft in question. 737 MAX is the aricraft and it comes with MCAS. And that is unstable, right?
  • PuffinBlue 7y ago
    No. In no way is the aircraft unstable with or without MCAS activated. Delete 'unstable' from the discussion. It's is a completely incorrect term to be using. MCAS - Movement Characteristics Augmentation System is a system to give the 737 Max the same handling characteristics as previous generation 737. The use of larger engines on the 737 Max and the short undercarriage meant that the engines had to sit further forward on the wing. This caused a vary very small difference in handling characteristics but was enough to cause the aircraft to need a new type rating as it didn't handle in the exact same way as previous generations. MCAS was born to make adjustments to the horizontal stabiliser in order to make the aircraft feel the same as before so pilots wouldn't need retraining and the aircraft could keep the same type rating. Absolutely no part of the 737 Max is unstable and no part of MCAS has anything to do with stability. This information is widely verifiable for anyone taking the time to look.
    • onethought 7y ago
      So if it is stable. Then it crashed because of pilot error? (No retraining required. These pilots never crashed a non MCAS plane, and MCAS was actively moving the plane towards the ground). <--- How do you conclude this plane is stable?
      • _ph_ 7y ago
        No, it crashed because MCAS malfunctioned and drove it into the ground.
        • jacobush 7y ago
          AND it must always be said in the same, the pilots were not trained in what to do. (Because not training pilots is cheaper than training them.)
• onethought 7y ago
  Yet four highly trained pilots plowed this "inherently stable aircraft" into the ground. "keeping the same type rating" lead to creating an "inherently unstable aircraft". As shown by the fact that over 100,000 hours of accumulated training didn't help. Saying the "737 Max is an inherently stable aircraft without MCAS" is like saying its stable if it never leaves the ground. It has (well had) MCAS by default. Minimising the size of this mistake is what is detrimental to the discussion. Boeing should go out of business. They are responsible for hundreds of deaths. If this were a person, this wouldn't even be a discussion. But corporations some how get a free pass on man-slaughter.
  • scrollaway 7y ago
    PuffinBlue's problem seems to be one of terminology and I'd agree with them. "Unstable" is not a good term for what you're trying to describe. It's like if I started to describe your app's database as "unstable" because your website's down due to cloudflare configuration. (With that said it's all just petty semantics; we all understand what the post is trying to convey)
    • PuffinBlue 7y ago
      > With that said it's all just petty semantics Ordinarily I would agree with you, but this issue of stability is clouding the truly detestable course of action Boeing took. Boeing was trying to save money. They wanted to keep the same type rating, so they added MCAS to an inherently stable and flyable aircraft for purposes of retaining the same type rating. The system they added included optional safety measures that airlines had to pay more to install [0]. Boeing new that MCAS would be safer with these features and charged more for them! The true outrage here should be directed at this underlying cause and the erroneous discussion over stability should be put by the wayside. [0] https://www.theguardian.com/business/2019/mar/21/doomed-boeing-737-air-max-planes-ethiopia-indonesia-crashes-lacked-two-optional-safety-features-report https://www.theguardian.com/business/2019/mar/21/doomed-boei...
      • reactor4 7y ago
• m12k 7y ago
  According to this article https://spectrum.ieee.org/aerospace/aviation/how-the-boeing-737-max-disaster-looks-to-a-software-developer https://spectrum.ieee.org/aerospace/aviation/how-the-boeing-... the engines had become so big that they had to be moved in front of the wings instead of under them, which in turn causes the plane to pitch up when the engines apply power (which was not the case with previous 737s). Whether this can be called 'unstable' or not seems to be a matter of definition. Sure it's not unstable the same way that something that completely randomly pitches up or down is. But if you got to drive a car that veers to the left at high speeds and to the right at low speeds, and needs a computer to compensate (oh, and this computer compensates based on sensor readings that may be faulty, so you might need to disable the computer's compensation and compensate yourself), would you perhaps call that unstable compared to a normal car? Doesn't seem unreasonable to me. It's unstable in the sense that controls that are normally independent are not.
  • _ph_ 7y ago
    All aircrafts with engines below the wings have the pitch up tendency at high angles of attack. The only problem with that is, that it is required that the stick force the pilot needs to apply need to increase with high angles of attack. Therefore, most airplanes have some way of augmenting the stick forces in those domains.
    • bret6 7y ago
      Using those Positive, Neutral, and Negative stability terms from PuffinBlue's comment, is the problem that we want positive stability, but the MAX without MCAS exhibits negative stability at a certain part of its flight envelope? That is, if the pilot is holding the airplane with a constant amount of force and the airplane is climbing at a certain angle, some turbulence or other disturbance could cause the nose to pitch up, and then continue pitching up?
      • sokoloff 7y ago
        No. The Max exhibits positive pitch stability in all flight regimes. What it fails to do is have sufficiently linearly increasing stick forces (required by certification) at high pitch. It’s still aerodynamically stable (not neutral or divergent).
• yk 7y ago
  Frankly, that makes matter worse. A steering system that stabilizes and unstable aircraft would be needed and it would be a tragedy if it fails. An system that just changes the behavior from stable to stable in the same way as the previous generation so that there is no need to retrain pilots, is just a cost cutting measure.
  • PuffinBlue 7y ago
    Yes, I totally agree. You have correctly identified the true source of much 'professional' outrage at what Boeing has done here. The MCAS system was, at its core, about saving money. Boeing thought it could retain the same type rating with an automated system that would make the aircraft fly the same. It is an almost unforgivable and detestable course of action.
    • mcguire 7y ago
      Is a "cost cutting measure" really a bad thing? Most employers, consumers and the aviation industry would regard saving money as a good thing. The way Boeing went about it is foolish, short-sighted, exceptionally dangerous, and very poor engineering.
      • bradstewart 7y ago
        Exactly. MCAS was a "cost cutting measure" implemented without consideration for anything else--including safety. SpaceX's (almost) entire existence is centered on a cost cutting measure: reusing rockets. But they didn't approach it in a way that killed a bunch of people.
        • mcguire 7y ago
          Yet. SpaceX hasn't killed a bunch of people yet. If you look at the history of flight, the biggest periods of progress killed people left and right. I'm not sure space can't go forward without doing the same.
      • dredmorbius 7y ago
• nemetroid 7y ago
  This is misleading. Yes, the aircraft is most likely stable. But without MCAS, the 737 MAX would likely NOT meet certification requirements (at all, not just 737 type requirements) with regard to handling, specifically FAR 25.173 point C. https://leehamnews.com/2019/02/15/bjorns-corner-pitch-stability-part-10-wrap-up/ https://leehamnews.com/2019/02/15/bjorns-corner-pitch-stabil... https://seekingalpha.com/article/4286602-boeing-737-max-misconceptions-engineers-view https://seekingalpha.com/article/4286602-boeing-737-max-misc... > If test pilots from the OEM and subsequently from the FAA/EASA consider the feel in pitch for a part of the envelope above a certain rating, the aircraft will not pass Certification. It needs augmentation for this part of the flight envelope. > The aircraft OEM is asked to propose fixes to the pitch characteristics of the aircraft so it can be judged acceptable for use by a minimum standard (Re. training and proficiency) pilot. This was the reason behind the MCAS pitch argumentation for the 737 MAX.
  • PuffinBlue 7y ago
    I addressed this in another comment more fully as the discussion evolved away from the use of the terms stable Vs unstable.
    • nemetroid 7y ago
      In a different comment, you wrote: > The 737 can be flown just fine without MCAS turned on as it has absolutely nothing to do with making the aircraft stable. which suggests that MCAS would not have been necessary for certification, if the MAX was being certified as a completely new aircraft type.
      • FabHK 7y ago
        An aircraft might be stable and able to be flown just fine, yet not pass certification requirements.
  • ppod 7y ago
    As noted above, stable has a precise definition in this context, and in that context the Max is stable.
• SomeOldThrow 7y ago
  > MCAS existed to make an inherently stable aircraft handle in the same was as previous 737 generations. I understand this is the attempt, but my understanding is that this is fundamentally impossible and the aircrafts fundamentally handle differently. This is the basis of the allegations of fraud.
• Xelbair 7y ago
  Didn't 737 MAX edge towards stalling when you increased the speed due to oversized engines? Isn't that violating one of most basic rules of aviation?
  • briandear 7y ago
    If an airplane, even one like a Cessna, is trimmed for straight and level, if you add full power without retrimming, you can definitely stall the airplane. Power-on stalls are a thing, in fact responding to them correctly is a fundamental training task taught in the earliest days of flight training. If I take a Cessna Turbo 206 in the landing configuration and apply full power with no other input, you can stall or even spin the airplane. Critical factors include the position of the center of gravity. The point is that you might be misunderstanding one of the critical rules of aviation — a stall is independent of speed or power, but entirely dependent on the exceeding the critical angle of attack. A stall can occur at any speed and any power setting.
    • matheusmoreira 7y ago
      > a stall is independent of speed or power, but entirely dependent on the exceeding the critical angle of attack. Air France Flight 447 is a perfect example of this. They pulled back on the stick so much the AoA reached 40 degrees. The wings lost lift and the aircraft fell like a rock tail-first despite the engines running at full throttle. "But I've been at maximum nose-up for a while!" https://en.wikipedia.org/wiki/Air_France_Flight_447 https://en.wikipedia.org/wiki/Air_France_Flight_447
  • privateSFacct 7y ago
    "violating one of most basic rules of aviation" This really illustrated how poor the articles about this have been. the 737 MAX was not violating the "most basic rules of aviation". We keep hearing the design is unstable. But no one can tell us where in the flight envelope it is unstable.
• FabHK 7y ago
  From what I gather, you're half correct: 1. Yes, the 737 Max is stable in the conventional aerodynamic sense. 2. No, MCAS was not introduced only to make it handle like the previous 737 generation. Without MCAS, the 737 Max would not fulfil certification criteria related to stick forces at high angle of attack. (I've never figured out whether the 737 Max stick force is sub linear, but monotonically increasing at high AoA, or decreasing.)
• salawat 7y ago
  You're confusing aerodynamicist's idea of stability with the regulatory idea of stability. I.e. You're in the wrong namespace. To be said to be stable, and certifiable as a Civil Transport Aircraft, an airframe must pass all relevant prescriptive tests as specified in the FAR's. FAR 25.173(c) is not demonstrated without MCAS, and therefore in regulatory parlance, not necessarily aerodynamic parlance, the aircraft is unstable by virtue of failing to demonstrate longitudinal stability as specifically prescribed in the FARs. The fact that MCAS was added to minimize the risk of losing grandfathered type cert, and the terrible engineering that went into it is just icing on the cake. The specific behavioral failure occurs during a wind-up turn. If you look up the procedure for the test, one of the independent variables is trim setting. That you have to adjust the trim (an input variable) during the maneuver in order to pass the test (preservation of control stick force response curve characteristics) kind of invalidates the entire endeavor. Never mind that the mechanism you leveraged to pass that corner case can doom the plane in case of false positive activation. So yes. It may be aerodynamically stable in 98% of the operating envelope, but in order to eke out that last 2 percent, caution was thrown to the winds, and implemented a kludge that was never safely integrated. Note I'm not arguing against the point you're trying to make. Just pointing out where the confusion in terms is likely arising in translation from technical to layman. The layman only cares that the regulatory definition is hit, as the regulation is the compromise point between aviation and everyone else's interest in not having craters.