7 ms·

It's absolutely not unsound at any level. It simply handles differently than pre-MAX 737s in certain scenarios, which would have required pilot re-certification

It's absolutely not unsound at any level. It simply handles differently than pre-MAX 737s in certain scenarios, which would have required pilot re-certification if not for the flawed MCAS software.

catalogia 6y ago
From what I understand it would not get certified today if it were introduced as a new airplane completely unrelated to any others, for a variety of obscure reasons. 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.
- jaywalk 6y ago
  You understand incorrectly. The 737 MAX would have no trouble being certified as a new type without MCAS. Boeing did not forget how to design planes.
  - genoapol 6y ago
    Without MCAS wouldn't the plane be unbalanced due to engine placement issues and excess weight? 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.
    - dan_quixote 6y ago
      You seem to be conflating ideas. jaywalk said it best with: > 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.
      - FabHK 6y ago
        I believe this to be a myth. MCAS is not "just" so that it feels like the old 737. Without MCAS, it would not be certifiable. See for example here: https://aviation.stackexchange.com/questions/73132/did-boeing-need-mcas-because-the-737-max-didn-t-meet-faa-longitudinal-stability https://aviation.stackexchange.com/questions/73132/did-boein...
        bcrl 6y ago
        That statement is incorrect. It would be perfectly certifiable with additional pilot training. The killer feature was the theory that MCAS would allow airlines to get away without additional training. Practice proved to be quite different, as is so often the case.
        FabHK 6y ago
        Do you have an authoritative reference for that, stating unambiguously that the plane without MCAS would fulfil all the regulatory requirements for manoeuvring stability in terms of stick force curve slope, for example during a wind-up turn? (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.)
  - FabHK 6y ago
    My understanding is that it would not have been certifiable under part 25.175, requiring a control stick force curve with stable slope across a wide variety of flight regimes. https://www.law.cornell.edu/cfr/text/14/25.175 https://www.law.cornell.edu/cfr/text/14/25.175
    - Obi_Juan_Kenobi 6y ago
      The force curve precluded single-certification without MCAS, but I haven't seen any claim that it would not be certified at all. 'Stable' is the critical term, and is loosely defined. 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.
      - FabHK 6y ago
        Insightful clarification. 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-inside-story-of-mcas-how-boeings-737-max-system-gained-power-and-lost-safeguards/ https://www.seattletimes.com/seattle-news/times-watchdog/the...
  - catalogia 6y ago
    I've read there are various details of the airplane unrelated to aerodynamics that are considered fine in a legacy design but would need to be revised if the 737 MAX were to be certified from scratch. Here is one example: https://www.reuters.com/article/us-boeing-737max/boeing-proposal-to-avoid-max-wiring-shift-does-not-win-u-s-support-idUSKBN20W018 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.
CamperBob2 6y ago
Using a single AoA sensor to drive a safety-critical system -- a largely-undocumented one at that -- wasn't "unsound?"
- CamperBob2 6y ago
  If I have this wrong, btw, I'm more than open to correction. Downvoting without commenting doesn't say "You're wrong," it says, "You're right, but ptthhthhhth."
- jaywalk 6y ago
  I was referring to the airframe itself. The plane is perfectly capable of flying without MCAS, it just doesn't handle the same as pre-MAX 737s.
salawat 6y ago
It was unsound in terms of having single points of failure in the flight computer. When a cosmic ray bit flip can send you into the ground, you cannot carry passengers. 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.
- foldr 6y ago
  You're missing OP's point. MCAS was flawed, but the plane would have been fine if they hadn't added MCAS. It would just have required pilot retraining (which Boeing desperately wanted to avoid). I have never seen a reliable source for the claim that the handling characteristics without MCAS would fail to meet airworthiness requirements.

It's absolutely not unsound at any level. It simply handles differently than pre-MAX 737s in certain scenarios, which would have required pilot re-certification if not for the flawed MCAS software.

catalogia 6y ago

From what I understand it would not get certified today if it were introduced as a new airplane completely unrelated to any others, for a variety of obscure reasons. 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.

jaywalk 6y ago
You understand incorrectly. The 737 MAX would have no trouble being certified as a new type without MCAS. Boeing did not forget how to design planes.
- genoapol 6y ago
  Without MCAS wouldn't the plane be unbalanced due to engine placement issues and excess weight? 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.
  - dan_quixote 6y ago
    You seem to be conflating ideas. jaywalk said it best with: > 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.
    - FabHK 6y ago
      I believe this to be a myth. MCAS is not "just" so that it feels like the old 737. Without MCAS, it would not be certifiable. See for example here: https://aviation.stackexchange.com/questions/73132/did-boeing-need-mcas-because-the-737-max-didn-t-meet-faa-longitudinal-stability https://aviation.stackexchange.com/questions/73132/did-boein...
      - bcrl 6y ago
        That statement is incorrect. It would be perfectly certifiable with additional pilot training. The killer feature was the theory that MCAS would allow airlines to get away without additional training. Practice proved to be quite different, as is so often the case.
        FabHK 6y ago
        Do you have an authoritative reference for that, stating unambiguously that the plane without MCAS would fulfil all the regulatory requirements for manoeuvring stability in terms of stick force curve slope, for example during a wind-up turn? (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.)
- FabHK 6y ago
  My understanding is that it would not have been certifiable under part 25.175, requiring a control stick force curve with stable slope across a wide variety of flight regimes. https://www.law.cornell.edu/cfr/text/14/25.175 https://www.law.cornell.edu/cfr/text/14/25.175
  - Obi_Juan_Kenobi 6y ago
    The force curve precluded single-certification without MCAS, but I haven't seen any claim that it would not be certified at all. 'Stable' is the critical term, and is loosely defined. 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.
    - FabHK 6y ago
      Insightful clarification. 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-inside-story-of-mcas-how-boeings-737-max-system-gained-power-and-lost-safeguards/ https://www.seattletimes.com/seattle-news/times-watchdog/the...
- catalogia 6y ago
  I've read there are various details of the airplane unrelated to aerodynamics that are considered fine in a legacy design but would need to be revised if the 737 MAX were to be certified from scratch. Here is one example: https://www.reuters.com/article/us-boeing-737max/boeing-proposal-to-avoid-max-wiring-shift-does-not-win-u-s-support-idUSKBN20W018 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.

CamperBob2 6y ago

Using a single AoA sensor to drive a safety-critical system -- a largely-undocumented one at that -- wasn't "unsound?"

CamperBob2 6y ago
If I have this wrong, btw, I'm more than open to correction. Downvoting without commenting doesn't say "You're wrong," it says, "You're right, but ptthhthhhth."
jaywalk 6y ago
I was referring to the airframe itself. The plane is perfectly capable of flying without MCAS, it just doesn't handle the same as pre-MAX 737s.

salawat 6y ago

It was unsound in terms of having single points of failure in the flight computer. When a cosmic ray bit flip can send you into the ground, you cannot carry passengers. 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.

foldr 6y ago
You're missing OP's point. MCAS was flawed, but the plane would have been fine if they hadn't added MCAS. It would just have required pilot retraining (which Boeing desperately wanted to avoid). I have never seen a reliable source for the claim that the handling characteristics without MCAS would fail to meet airworthiness requirements.