4 ms·

MCAS was only installed to cover up aerodynamic changes (not flaws) that would have required greater recertification and retraining of pilots. To save that expe

MCAS was only installed to cover up aerodynamic changes (not flaws) that would have required greater recertification and retraining of pilots. To save that expense, they covered it up with MCAS so they could say "See, it's just another 737!" which caused all the issues we know so much about.

andy_ppp 6y ago
So you’re saying without MCAS the plane flys just as safely but differently which would have required retraining. That’s interesting, thanks!
- geocrasher 6y ago
  Yes @andy_ppp that's what I'm saying :)
- cratermoon 6y ago
  No, the plane does not fly safely without MCAS. Without the MCAS there the aircraft has a tendency to pitch up, resulting in a stall situation.
  - redis_mlc 6y ago
    > Without the MCAS there the aircraft has a tendency to pitch up, resulting in a stall situation. That's not why MCAS was added. Airliners have certification requirements for "flying qualities" (smoothness) as a passenger and IFR platform. Without MCAS, the 787 MAX pitch-up in some cases exceeded the certification requirements, so MCAS was added to control the rate of pitch-up. Source: commercially-rated pilot.
  - geocrasher 6y ago
    LOTS of aircraft have a tendency to pitch up or down based on throttle. This isn't unique to the 737 MAX. A quick google on "thrust line pitch moment" gave me this: https://www.homebuiltairplanes.com/forums/threads/thrust-angle-for-pylon-mounted-pusher.26950/ https://www.homebuiltairplanes.com/forums/threads/thrust-ang... " I want to adjust the thrust angle from where it was (0° with respect to the chord line) to reduce the downward pitching moment when thrust is added (or more importantly the upward pitch moment when thrust is reduced)"
    - cratermoon 6y ago
      Not many passenger aircraft have a tendency to pitch up to the point of stalling, though.
      - geocrasher 6y ago
        Neither does the 737 MAX.
      - manigandham 6y ago
        It does not just pitch up randomly. It does pitch more than other 737s due to engine size and placement, but that's just the specific behavior of this plane. Stalls are not a serious problem, they're basically the first thing pilots learn to solve. And there are plenty of aircraft that are more challenging to fly. That's what training is for. The real issue is that pilots should have full understanding of the behaviors of the airframe instead of relying on software to change it. Especially when they don't have full understanding of the software either, and the system can both override manual inputs while being susceptible to faulty sensors.
        satellite2 6y ago
        > Stalls are not a serious problem They account for 25% of fatal accidents [1] [1] https://www.aopa.org/-/media/Files/AOPA/Home/Pilot-Resources/Safety-and-Proficiency/Accident-Analysis/Special-Reports/stall_spin.pdf https://www.aopa.org/-/media/Files/AOPA/Home/Pilot-Resources...
        jrockway 6y ago
        Seems like the vast majority of cases there are personal aircraft not piloted by ATPs. General aviation is what it is. Certainly there are airline pilots that don't recover from stalls successfully (Colgan Air Flight 3407's crew), but there are confounding factors like sleep deprivation. Personally, I worry a lot more about sleep deprivation than particular subsystems of jetliners. You can easily kill two airliners worth of people in a few seconds when you read back "hold short of runway 31R" and then just barel onto it because you're not alert.
  - manigandham 6y ago
    That's incorrect. All planes have a relationship with thrust and pitch based on multiple factors (size, weight, speed, wing configuration, altitude, etc). The aircraft was perfectly sound. The problem was software designed to alter the flight profile automatically to minimize the differences and new training required (and was allowed to override manual inputs). Any pilot with full training of this specific plane without MCAS would have no problem flying it. The planes didn't crash because they pitched up but because bad software mistakenly, and forcibly, pitched them down.
    - salawat 6y ago
      What the poster was more likely referring to was the uncertifiable behavior that would occur without MCAS during a wind-up turm or during descent whereby stick control forces would slacken on the way to stall instead of requiring steadily increasing pressure on the control column to bring the plane to a stall due to extra lift from the forward nacelles. While technically a pilot could deal with it, aircraft that demonstrate said behavior cannot be certified as civil transport aircraft without appropriate mitigations.
      - cratermoon 6y ago
        It seems to me that the folks here arguing that the 737 Max is safe have a definition of "safe" that would satisfy a military test pilot. I'm sure that even without MCAS a top-notch pilot could fly the Max without incident, but when it comes to passenger aircraft safety, the bar is considerably higher.
    - avereveard 6y ago
      Both incorrect. The stability system to correct pitch to avoid training is only one side of the story. The other side is there wasn't a linear relationship between pitch, aoa and stick forces, and that would not have passed the faa certification.
cratermoon 6y ago
No, they are legit flaws. https://www.business-standard.com/article/international/boeing-hid-design-flaws-in-737-max-from-pilots-regulators-us-panel-120091602119_1.html https://www.business-standard.com/article/international/boei...
- waiseristy 6y ago
  So I actually went and found this fabled 245-page report : https://transportation.house.gov/imo/media/doc/2020.09.15%20FINAL%20737%20MAX%20Report%20for%20Public%20Release.pdf https://transportation.house.gov/imo/media/doc/2020.09.15%20... And this, I think, is where the whole faulty/flawed thing gets introduced : > Faulty Design and Performance Assumptions. > Boeing made fundamentally faulty assumptions about critical technologies on the 737 MAX, most notably with MCAS. Based on these faulty assumptions, Boeing permitted MCAS—software designed to automatically[...] It also expected that pilots, who were largely unaware that the system existed, would be able to mitigate any potential malfunction. Boeing also failed to classify MCAS as a safety-critical system, which would have attracted greater FAA scrutiny during the certification process.[...] So, I would agree that Boeing's design flaw here was not alerting the pilot with a huge red warning light (and being cheeky about re-certification). But I don't think that this report goes so far as to say that the airframe was flawed and therefore necessitated MCAS.
- geocrasher 6y ago
  I respectfully disagree. A news article calling them flaws does not make them a flaw. Here's the issue: At lower speeds such as you'd see during a landing approach, the throttle setting of the 737 Max directly affects its pitch. If the pilot were to suddenly reduce throttle, the nose would pitch up. This is due to the engine's more forward position. The forward position of the engines was done so that they wouldn't have to re-engineer half the plane to fit the larger engines. High bypass turbo fans are big, and they couldn't maintain ground clearance without either moving the engines up higher or making the landing gear longer. To move the engines higher they had to move them forward. So they did. The new behavior of the aircraft required retraining and making sure pilots knew how the throttle and pitch were related. Mind you, a lot of aircraft have such relationships, so this is not in itself a flaw. The real flaw came when they decided to replace training with software, and then conveniently forgot to tell anybody about the robo-pilot that they put in the cockpit. THAT was the failure. The airplane itself, even without MCAS at all, would be a bit more of a handful to fly, but nothing terrible. With a properly functioning MCAS, and proper training about how to disable it in case of a problem, the issue is solved. And that's what the FAA believed happened when they recertified the 737 MAX to fly again. But by now the reputation has been tarnished so badly that we're hearing news about unrelated failures because it happened on a 737 MAX. So you can see the real failure isn't aerodynamic, its pretty much everything else. If I got any details wrong, I apologize. I'm flying by the seat of my pants on this layman's analysis after a long day.
airhead969 6y ago
It's a feature, not a bug.

andy_ppp 6y ago

So you’re saying without MCAS the plane flys just as safely but differently which would have required retraining. That’s interesting, thanks!

geocrasher 6y ago
Yes @andy_ppp that's what I'm saying :)
cratermoon 6y ago
No, the plane does not fly safely without MCAS. Without the MCAS there the aircraft has a tendency to pitch up, resulting in a stall situation.
- redis_mlc 6y ago
  > Without the MCAS there the aircraft has a tendency to pitch up, resulting in a stall situation. That's not why MCAS was added. Airliners have certification requirements for "flying qualities" (smoothness) as a passenger and IFR platform. Without MCAS, the 787 MAX pitch-up in some cases exceeded the certification requirements, so MCAS was added to control the rate of pitch-up. Source: commercially-rated pilot.
- geocrasher 6y ago
  LOTS of aircraft have a tendency to pitch up or down based on throttle. This isn't unique to the 737 MAX. A quick google on "thrust line pitch moment" gave me this: https://www.homebuiltairplanes.com/forums/threads/thrust-angle-for-pylon-mounted-pusher.26950/ https://www.homebuiltairplanes.com/forums/threads/thrust-ang... " I want to adjust the thrust angle from where it was (0° with respect to the chord line) to reduce the downward pitching moment when thrust is added (or more importantly the upward pitch moment when thrust is reduced)"
  - cratermoon 6y ago
    Not many passenger aircraft have a tendency to pitch up to the point of stalling, though.
    - geocrasher 6y ago
      Neither does the 737 MAX.
    - manigandham 6y ago
      It does not just pitch up randomly. It does pitch more than other 737s due to engine size and placement, but that's just the specific behavior of this plane. Stalls are not a serious problem, they're basically the first thing pilots learn to solve. And there are plenty of aircraft that are more challenging to fly. That's what training is for. The real issue is that pilots should have full understanding of the behaviors of the airframe instead of relying on software to change it. Especially when they don't have full understanding of the software either, and the system can both override manual inputs while being susceptible to faulty sensors.
      - satellite2 6y ago
        > Stalls are not a serious problem They account for 25% of fatal accidents [1] [1] https://www.aopa.org/-/media/Files/AOPA/Home/Pilot-Resources/Safety-and-Proficiency/Accident-Analysis/Special-Reports/stall_spin.pdf https://www.aopa.org/-/media/Files/AOPA/Home/Pilot-Resources...
        jrockway 6y ago
        Seems like the vast majority of cases there are personal aircraft not piloted by ATPs. General aviation is what it is. Certainly there are airline pilots that don't recover from stalls successfully (Colgan Air Flight 3407's crew), but there are confounding factors like sleep deprivation. Personally, I worry a lot more about sleep deprivation than particular subsystems of jetliners. You can easily kill two airliners worth of people in a few seconds when you read back "hold short of runway 31R" and then just barel onto it because you're not alert.
- manigandham 6y ago
  That's incorrect. All planes have a relationship with thrust and pitch based on multiple factors (size, weight, speed, wing configuration, altitude, etc). The aircraft was perfectly sound. The problem was software designed to alter the flight profile automatically to minimize the differences and new training required (and was allowed to override manual inputs). Any pilot with full training of this specific plane without MCAS would have no problem flying it. The planes didn't crash because they pitched up but because bad software mistakenly, and forcibly, pitched them down.
  - salawat 6y ago
    What the poster was more likely referring to was the uncertifiable behavior that would occur without MCAS during a wind-up turm or during descent whereby stick control forces would slacken on the way to stall instead of requiring steadily increasing pressure on the control column to bring the plane to a stall due to extra lift from the forward nacelles. While technically a pilot could deal with it, aircraft that demonstrate said behavior cannot be certified as civil transport aircraft without appropriate mitigations.
    - cratermoon 6y ago
      It seems to me that the folks here arguing that the 737 Max is safe have a definition of "safe" that would satisfy a military test pilot. I'm sure that even without MCAS a top-notch pilot could fly the Max without incident, but when it comes to passenger aircraft safety, the bar is considerably higher.
  - avereveard 6y ago
    Both incorrect. The stability system to correct pitch to avoid training is only one side of the story. The other side is there wasn't a linear relationship between pitch, aoa and stick forces, and that would not have passed the faa certification.

cratermoon 6y ago

No, they are legit flaws. https://www.business-standard.com/article/international/boeing-hid-design-flaws-in-737-max-from-pilots-regulators-us-panel-120091602119_1.html https://www.business-standard.com/article/international/boei...

waiseristy 6y ago
So I actually went and found this fabled 245-page report : https://transportation.house.gov/imo/media/doc/2020.09.15%20FINAL%20737%20MAX%20Report%20for%20Public%20Release.pdf https://transportation.house.gov/imo/media/doc/2020.09.15%20... And this, I think, is where the whole faulty/flawed thing gets introduced : > Faulty Design and Performance Assumptions. > Boeing made fundamentally faulty assumptions about critical technologies on the 737 MAX, most notably with MCAS. Based on these faulty assumptions, Boeing permitted MCAS—software designed to automatically[...] It also expected that pilots, who were largely unaware that the system existed, would be able to mitigate any potential malfunction. Boeing also failed to classify MCAS as a safety-critical system, which would have attracted greater FAA scrutiny during the certification process.[...] So, I would agree that Boeing's design flaw here was not alerting the pilot with a huge red warning light (and being cheeky about re-certification). But I don't think that this report goes so far as to say that the airframe was flawed and therefore necessitated MCAS.
geocrasher 6y ago
I respectfully disagree. A news article calling them flaws does not make them a flaw. Here's the issue: At lower speeds such as you'd see during a landing approach, the throttle setting of the 737 Max directly affects its pitch. If the pilot were to suddenly reduce throttle, the nose would pitch up. This is due to the engine's more forward position. The forward position of the engines was done so that they wouldn't have to re-engineer half the plane to fit the larger engines. High bypass turbo fans are big, and they couldn't maintain ground clearance without either moving the engines up higher or making the landing gear longer. To move the engines higher they had to move them forward. So they did. The new behavior of the aircraft required retraining and making sure pilots knew how the throttle and pitch were related. Mind you, a lot of aircraft have such relationships, so this is not in itself a flaw. The real flaw came when they decided to replace training with software, and then conveniently forgot to tell anybody about the robo-pilot that they put in the cockpit. THAT was the failure. The airplane itself, even without MCAS at all, would be a bit more of a handful to fly, but nothing terrible. With a properly functioning MCAS, and proper training about how to disable it in case of a problem, the issue is solved. And that's what the FAA believed happened when they recertified the 737 MAX to fly again. But by now the reputation has been tarnished so badly that we're hearing news about unrelated failures because it happened on a 737 MAX. So you can see the real failure isn't aerodynamic, its pretty much everything else. If I got any details wrong, I apologize. I'm flying by the seat of my pants on this layman's analysis after a long day.

airhead969 6y ago

It's a feature, not a bug.