6 ms·

> First, the engine placement means it has a non-linear control force curve, so it needs some system to compensate for that. Hence MCAS. No. Boeing wanted it t

> First, the engine placement means it has a non-linear control force curve, so it needs some system to compensate for that. Hence MCAS. No. Boeing wanted it to share a type rating with the rest of the 737 family, hence MCAS. This plane would be perfectly safe to fly if it had no MCAS and required a new type rating. Consider the 767 which has a stronger pitch-up characteristic and operates just fine. This meme has been debunked several months ago but keeps getting repeated along with the more ignorant 'the plane is inherently unstable'. > The force required is extreme, weaker pilots may not be capable of trimming the aircraft. This is true in all planes. In certain conditions, aerodynamic loads exceed the pilot's or even the hydraulic system's ability to overcome. Pilots are trained for how to recover from these conditions and regain trim authority. > Canada stated that they would certify the MAX without MCAS and with required pilot training, if its performance characteristics were acceptable. Boeing has made no attempt (AFAICT) to try this, which raises suspicion that MCAS is in fact required for certification This claim contradicts your first claim, as the authority indicates they will accept the plane without MCAS. So clearly, MCAS is not critical to safe the operation of the plane in the eyes of this authority. Without MCAS the MAX loses the 737 type rating and becomes a commercial failure. Of course Boeing isn't going to even humour that avenue of action except as a last resort. Please stop spreading thoroughly debunked misinformation.

jiggawatts 7y ago
While I see your point, there's a rub. If you're right and he's wrong, then MCAS is a non-critical system (augmentation, not fly-by-wire) and would require a mere software fix, which ought to have been completed by now. Why hasn't it?
- missosoup 7y ago
  MCAS is a critical system if it's present in its current form, and may very well require more than just a software fix (3rd alpha vane perhaps). At this point not a lot is publicly known about what Boeing is doing to remediate the issue and I don't want to engage in speculation. But their ultimate fallback plan if all else fails, will be to remove MCAS and have this thing get its own type rating and dedicated pilots.
- salawat 7y ago
  It hasn't because the Flight Computer represents a single point of failure in a system with a catastrophic consequence of failure. This is not allowed. If it's even possible in theory but unlikely, it doesn't matter, it has to be redesigned. That redesign alone is likely enough to violate the little or no training required that was the original intent of the resign. https://www.seattletimes.com/business/boeing-aerospace/newly-stringent-faa-tests-spur-a-fundamental-software-redesign-of-737-max-flight-controls/ https://www.seattletimes.com/business/boeing-aerospace/newly... Note, these weren't "newly stringent" as if they've never been done before now. Worst case scenario bit flips by cosmic rays are textbook test cases in aerospace projects. That they weren't considered before then is a marked demonstration of lack of due-diligence or follow-through in enumerating the fault-tree.
FabHK 7y ago
> This plane would be perfectly safe to fly if it had no MCAS and required a new type rating. GP didn't claim otherwise. GP claimed: >> [...] so it needs some system to compensate for that. And it does need that system - whether for safety is debatable, but it needs it for certification (not within the 737 family certification, but for certification full stop), because the FAA requires basically a linear control force curve. >> weaker pilots may not be capable of trimming the aircraft. > This is true in all planes. Source? I'd assume, in fact, that in most planes that is not the case - superhuman strength is not required to trim. > This claim contradicts your first claim, as the authority indicates they will accept the plane without MCAS. So clearly, MCAS is not critical to safe the operation of the plane in the eyes of this authority. No, it doesn't. There are three possibilities: 1. Without MACS, the plane is safe and certifiable, but not similar enough to be certified with the 737 family. 2. Without MACS, the plane is reasonably safe, but not certifiable under the specific FAA rule requiring linear control forces (though possibly under more lenient, eg Canadian rules). 3. Without MACS, the plane is not safe and not certifiable. I think 2 is the case. 1 has been debunked, and you argue that 3 is false, too.
- bicubic 7y ago
  You claim 1 is debunked but you’re replying to a quote from GP indicating Canada will accept the plane as per 1? If you can back up the claim that 1 is debunked with a credible source, I suggest shorting Boeing stock because it means the 737 max is a complete failure, the line will likely be killed as it won’t be able to compete with the Neo, and stock price going to plummet through the floor.
  - FabHK 7y ago
    No, Canada would accept the plane as per 2.
    - bicubic 7y ago
      Source for any of this? The notion of Canada accepting the plane on looser conditions than FAA is laughable.
clon 7y ago
> This meme has been debunked several months ago but keeps getting repeated along with the more ignorant 'the plane is inherently unstable'. Yet, there has been no information released, at least publicly, as to the bare airframe flight characteristics (bare as in sans MCAS). The reasons for the initial inclusion of the MCAS seems like it may have been related to the augmentation of the "touch and feel" of the flight controls, but we simply do not know at this point what were the reasons for the increase of it's operating envelope and authority. > Please stop spreading thoroughly debunked misinformation. If you have a source for the debunking, I would appreciate if you could share it. In the meantime, our best bet is to hope for one of the other CAA-s to conduct said bare airframe tests. I suspect that one must also consider that the Boeing's PR department is busy coloring the narrative in a favourable way. Source: https://www.faa.gov/news/media/attachments/Final_JATR_Submittal_to_FAA_Oct_2019.pdf https://www.faa.gov/news/media/attachments/Final_JATR_Submit... Recommendation R3.4: The FAA should review the natural (bare airframe) stalling characteristics of the B737 MAX to determine if unsafe characteristics exist. If unsafe characteristics exist, the design of the speed trim system (STS)/MCAS/elevator feel shift (EFS) should be reviewed for acceptability. Observation O3.4-A: The original implementation of MCAS was driven primarily by its ability to provide the B737 MAX with FAA-compliant flight characteristics at high speed. An unaugmented design would have been at risk of not meeting 14 CFR part 25 maneuvering characteristics requirements due to aerodynamics. Observation O3.4-B: Extension of MCAS to the low-speed and 1g environment during the flight program was due to unacceptable stall characteristics with STS only. The possibility of a pitch-up tendency during approach to stall was identified for the flaps-up configuration prior to the implementation of MCAS. Finding F3.4-A: The acceptability of the natural stalling characteristics of the aircraft should form the basis for the design and certification of augmentation functions such as EFS and STS (including MCAS) that are used in support of meeting 14 CFR part 25, subpart B requirements. In short, Boeing designed a full-authority flight envelope protection system, just like Airbus has. Except for the fact that Airbus uses a full triplex system (3 ADIRU-s with their own set of sensors), while Boeing went with a single source of data, treating the wetware on the seat as the pseudo duplex channel ("you are the backup", while neglecting to inform them of their role, or their potential physical inability to accomplish this, nor provide accurate force feedback in sims). Now they are trying to sell us a duplex/pseudo-triplex model with the consolation that while the beast still has half a brain (pun intended), it is at least more tame. All this while simply neglecting to tell us, the pilots and the flying public, exactly why it was needed in the first place. See O3.4-B above. Disclaimer: pilot.
dbcurtis 7y ago
> Without MCAS the MAX loses the 737 type rating and becomes a commercial failure. Does it fail? I will grant you this: 1) A significant number of people would refuse to fly it. 2) Pilots would need to be trained to the new type. 3) There would have to be more simulators constructed to handle the training load, and the airlines would likely force Boeing to bay for that. OTOH: All the 737 ground equipment and gates and so forth will work perfectly fine. It seems to me that with suitable discounts, it would sell through. Not an easy sale, certainly. Does the 737MAX really become an economic loser?
- cjbprime 7y ago
  Good point. The airlines would certainly be less happy, but it's unclear that they'd be unhappy enough to make the plane unprofitable. I guess the question is whether it would make them all buy the A320neo instead.
cjbprime 7y ago
> Pilots are trained for how to recover from these conditions and regain trim authority. I agree with all of your corrections except this one. I've read that this yo-yo or rollercoaster maneuver was described in old 737 manuals decades ago, but then removed. It's not in the current manuals and I haven't heard anyone else claim that it was ever trained for by airline pilots, either back then or now. I get the impression that Boeing decided some decades ago that needing to retrim without the motor and at extreme airspeeds and aerodynamic load was so unlikely that they didn't need to prepare pilots for it. This would probably be true if they hadn't introduced a system that makes the stabilizer try to kill you, and then tied the off switch for that system to the off switch for the trim assist motor. (A reason to be pedantic on this point is that it's important to know whether the lack of having performed this maneuver can be reasonably described as a pilot error.. although in the MAX cases there probably wasn't enough altitude to perform it anyway at the speeds involved.)
mopsi 7y ago
> This plane would be perfectly safe to fly if it had no MCAS and required a new type rating. It does not qualify for a new one. The crew alerting system (EICAS) does not meet modern standards. https://www.seattletimes.com/business/boeing-aerospace/boeing-pushed-faa-to-arelax-737-max-certification-requirements-for-crew-alerts/ https://www.seattletimes.com/business/boeing-aerospace/boein...

jiggawatts 7y ago

While I see your point, there's a rub. If you're right and he's wrong, then MCAS is a non-critical system (augmentation, not fly-by-wire) and would require a mere software fix, which ought to have been completed by now. Why hasn't it?

missosoup 7y ago
MCAS is a critical system if it's present in its current form, and may very well require more than just a software fix (3rd alpha vane perhaps). At this point not a lot is publicly known about what Boeing is doing to remediate the issue and I don't want to engage in speculation. But their ultimate fallback plan if all else fails, will be to remove MCAS and have this thing get its own type rating and dedicated pilots.
salawat 7y ago
It hasn't because the Flight Computer represents a single point of failure in a system with a catastrophic consequence of failure. This is not allowed. If it's even possible in theory but unlikely, it doesn't matter, it has to be redesigned. That redesign alone is likely enough to violate the little or no training required that was the original intent of the resign. https://www.seattletimes.com/business/boeing-aerospace/newly-stringent-faa-tests-spur-a-fundamental-software-redesign-of-737-max-flight-controls/ https://www.seattletimes.com/business/boeing-aerospace/newly... Note, these weren't "newly stringent" as if they've never been done before now. Worst case scenario bit flips by cosmic rays are textbook test cases in aerospace projects. That they weren't considered before then is a marked demonstration of lack of due-diligence or follow-through in enumerating the fault-tree.

FabHK 7y ago

> This plane would be perfectly safe to fly if it had no MCAS and required a new type rating. GP didn't claim otherwise. GP claimed: >> [...] so it needs some system to compensate for that. And it does need that system - whether for safety is debatable, but it needs it for certification (not within the 737 family certification, but for certification full stop), because the FAA requires basically a linear control force curve. >> weaker pilots may not be capable of trimming the aircraft. > This is true in all planes. Source? I'd assume, in fact, that in most planes that is not the case - superhuman strength is not required to trim. > This claim contradicts your first claim, as the authority indicates they will accept the plane without MCAS. So clearly, MCAS is not critical to safe the operation of the plane in the eyes of this authority. No, it doesn't. There are three possibilities: 1. Without MACS, the plane is safe and certifiable, but not similar enough to be certified with the 737 family. 2. Without MACS, the plane is reasonably safe, but not certifiable under the specific FAA rule requiring linear control forces (though possibly under more lenient, eg Canadian rules). 3. Without MACS, the plane is not safe and not certifiable. I think 2 is the case. 1 has been debunked, and you argue that 3 is false, too.

bicubic 7y ago
You claim 1 is debunked but you’re replying to a quote from GP indicating Canada will accept the plane as per 1? If you can back up the claim that 1 is debunked with a credible source, I suggest shorting Boeing stock because it means the 737 max is a complete failure, the line will likely be killed as it won’t be able to compete with the Neo, and stock price going to plummet through the floor.
- FabHK 7y ago
  No, Canada would accept the plane as per 2.
  - bicubic 7y ago
    Source for any of this? The notion of Canada accepting the plane on looser conditions than FAA is laughable.

clon 7y ago

> This meme has been debunked several months ago but keeps getting repeated along with the more ignorant 'the plane is inherently unstable'. Yet, there has been no information released, at least publicly, as to the bare airframe flight characteristics (bare as in sans MCAS). The reasons for the initial inclusion of the MCAS seems like it may have been related to the augmentation of the "touch and feel" of the flight controls, but we simply do not know at this point what were the reasons for the increase of it's operating envelope and authority. > Please stop spreading thoroughly debunked misinformation. If you have a source for the debunking, I would appreciate if you could share it. In the meantime, our best bet is to hope for one of the other CAA-s to conduct said bare airframe tests. I suspect that one must also consider that the Boeing's PR department is busy coloring the narrative in a favourable way. Source: https://www.faa.gov/news/media/attachments/Final_JATR_Submittal_to_FAA_Oct_2019.pdf https://www.faa.gov/news/media/attachments/Final_JATR_Submit... Recommendation R3.4: The FAA should review the natural (bare airframe) stalling characteristics of the B737 MAX to determine if unsafe characteristics exist. If unsafe characteristics exist, the design of the speed trim system (STS)/MCAS/elevator feel shift (EFS) should be reviewed for acceptability. Observation O3.4-A: The original implementation of MCAS was driven primarily by its ability to provide the B737 MAX with FAA-compliant flight characteristics at high speed. An unaugmented design would have been at risk of not meeting 14 CFR part 25 maneuvering characteristics requirements due to aerodynamics. Observation O3.4-B: Extension of MCAS to the low-speed and 1g environment during the flight program was due to unacceptable stall characteristics with STS only. The possibility of a pitch-up tendency during approach to stall was identified for the flaps-up configuration prior to the implementation of MCAS. Finding F3.4-A: The acceptability of the natural stalling characteristics of the aircraft should form the basis for the design and certification of augmentation functions such as EFS and STS (including MCAS) that are used in support of meeting 14 CFR part 25, subpart B requirements. In short, Boeing designed a full-authority flight envelope protection system, just like Airbus has. Except for the fact that Airbus uses a full triplex system (3 ADIRU-s with their own set of sensors), while Boeing went with a single source of data, treating the wetware on the seat as the pseudo duplex channel ("you are the backup", while neglecting to inform them of their role, or their potential physical inability to accomplish this, nor provide accurate force feedback in sims). Now they are trying to sell us a duplex/pseudo-triplex model with the consolation that while the beast still has half a brain (pun intended), it is at least more tame. All this while simply neglecting to tell us, the pilots and the flying public, exactly why it was needed in the first place. See O3.4-B above. Disclaimer: pilot.

dbcurtis 7y ago

> Without MCAS the MAX loses the 737 type rating and becomes a commercial failure. Does it fail? I will grant you this: 1) A significant number of people would refuse to fly it. 2) Pilots would need to be trained to the new type. 3) There would have to be more simulators constructed to handle the training load, and the airlines would likely force Boeing to bay for that. OTOH: All the 737 ground equipment and gates and so forth will work perfectly fine. It seems to me that with suitable discounts, it would sell through. Not an easy sale, certainly. Does the 737MAX really become an economic loser?

cjbprime 7y ago
Good point. The airlines would certainly be less happy, but it's unclear that they'd be unhappy enough to make the plane unprofitable. I guess the question is whether it would make them all buy the A320neo instead.

cjbprime 7y ago

> Pilots are trained for how to recover from these conditions and regain trim authority. I agree with all of your corrections except this one. I've read that this yo-yo or rollercoaster maneuver was described in old 737 manuals decades ago, but then removed. It's not in the current manuals and I haven't heard anyone else claim that it was ever trained for by airline pilots, either back then or now. I get the impression that Boeing decided some decades ago that needing to retrim without the motor and at extreme airspeeds and aerodynamic load was so unlikely that they didn't need to prepare pilots for it. This would probably be true if they hadn't introduced a system that makes the stabilizer try to kill you, and then tied the off switch for that system to the off switch for the trim assist motor. (A reason to be pedantic on this point is that it's important to know whether the lack of having performed this maneuver can be reasonably described as a pilot error.. although in the MAX cases there probably wasn't enough altitude to perform it anyway at the speeds involved.)

mopsi 7y ago

> This plane would be perfectly safe to fly if it had no MCAS and required a new type rating. It does not qualify for a new one. The crew alerting system (EICAS) does not meet modern standards. https://www.seattletimes.com/business/boeing-aerospace/boeing-pushed-faa-to-arelax-737-max-certification-requirements-for-crew-alerts/ https://www.seattletimes.com/business/boeing-aerospace/boein...