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As I see it there are several critical flaws in the MAX. First, the engine placement means it has a non-linear control force curve, so it needs some system to

As I see it there are several critical flaws in the MAX. First, the engine placement means it has a non-linear control force curve, so it needs some system to compensate for that. Hence MCAS. This is because the landing gear can't be lengthened without expanding the gear bays, which would void the type certificate AFAICT. Second, the larger size of the plane means that a single pilot cannot be guaranteed to be able to use the manual trim wheels in all flight modes. The force required is extreme, weaker pilots may not be capable of trimming the aircraft. This can't be fixed without changing the trim wheel size (which requires a new cockpit layout) and/or the horizontal stabilizer, both of which would void the type certificate. Third, critical flight control systems need to be triple-redundant, and there are only two AOA sensors. Since the plane cannot be certified without MCAS (point 1) and MCAS can command a catastrophic failure (see two craters) it should be a triple-redundant system. A new AOA sensor would void the type certificate. 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, which would make it a Fly-By-Wire system (and subject to appropriate regulations, requiring hardware changes) and not just a stability augmentation system. Essentially Canada called Boeing's bluff. It's not the software that's the (only) issue. If it were, the plane would be flying by now.

iscrewyou 7y ago
With all those changes listed, you are basically saying that if it was a different plane, the software would not be a problem (which in turn is an issue because we don’t really know that would be true or not since Boeing seems to have institutional problems). The issue is that the plane was changed only enough to avoid a cert issue but to keep the plane flyable, software had to be implemented to keep the pilots and the plane in check. So, the plane needs to be either redesigned or it won’t certify. You are correct in that Canada called Boeing’s bluff. But the software is the issue or the plane would not be flying anyways because it wouldn’t certify.
devit 7y ago
Can't one add mechanical gears so that the trim wheel requires less force to turn but needs to be turned more, without any other visible changes?
- jdsully 7y ago
  If there weren’t already 500 of them manufactured that would be feasible. Assuming it could still be adjusted fast enough (which I don’t know).
- dboreham 7y ago
  It would presumably be easier to just not have the rogue computer pulling on the control surface the other way? The trim wheel seems like a last ditch mechanism to deal with a malfunctioning hydraulic control system but that's not the problem with the MAX, rather the hydraulics are working fine but being told to do the wrong thing.
dralley 7y ago
>A new AOA sensor would void the type certificate. Why would a new (third) AOA sensor void the type certificate?
- cjbprime 7y ago
  (It would probably require training on what to do when the system becomes inoperable, at least.)
dredmorbius 7y ago
As the 737 MAX saga unfolds, I've been wondering just why options to modify the landing gear (say: telescoping legs, or placement, or both), is such anathema. Clearly, moving engine pods alone is not without its risks.
- kayfox 7y ago
  Ground handling equipment for most of the 737 operators is designed around the low clearance. So if they were to make it sit higher, operators would have to remove a significant amount of equipment. Also the 737-10 does sit higher: https://www.geekwire.com/2018/boeing-737-max-10-landing-gear/ https://www.geekwire.com/2018/boeing-737-max-10-landing-gear...
  - inferiorhuman 7y ago
    Also the 737-10 does sit higher: https://www.geekwire.com/2018/boeing-737-max-10-landing-gear/ https://www.geekwire.com/2018/boeing-737-max-10-landing-gear... Watch the video from your link. The landing gear only extend on rotation. When it's on the ground the 737 MAX 10 sits at the same height as every other 737 MAX. https://www.youtube.com/watch?v=F4IGl4OizM4 https://www.youtube.com/watch?v=F4IGl4OizM4
- AWildC182 7y ago
  Laziness. This is absolutely a "fuck it, we'll fix it in software" problem. I don't think it would necessarily invalidate the type certificate to change the legs but Boeing has gotten away with doing the bare minimum of structural changes necessary to keep the 737 relevant. Adding fuselage tube sections is far easier than reworking the complex gear systems and moving everything out of the way to make the bays longer (737 has an equipment bay around the nose gear, mains have systems routed around them) so they will do just about anything to avoid that.
  - mattmaroon 7y ago
    It's not laziness, it's cost to cost-sensitive customers who have a viable alternative with Airbus A320 Neo. Boeing actually initially set out to make an entirely new plane. The airliners instead wanted a re-engined 737 to keep type certification so that they didn't have to retrain pilots and could keep new equipment purchases to a minimum. It's not that Boeing would have been unwilling to build an entirely new plane, their CEO announced that as the plan in 2011, it's that operators would rather they didn't.
missosoup 7y ago
> 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.

iscrewyou 7y ago

With all those changes listed, you are basically saying that if it was a different plane, the software would not be a problem (which in turn is an issue because we don’t really know that would be true or not since Boeing seems to have institutional problems). The issue is that the plane was changed only enough to avoid a cert issue but to keep the plane flyable, software had to be implemented to keep the pilots and the plane in check. So, the plane needs to be either redesigned or it won’t certify. You are correct in that Canada called Boeing’s bluff. But the software is the issue or the plane would not be flying anyways because it wouldn’t certify.

devit 7y ago

Can't one add mechanical gears so that the trim wheel requires less force to turn but needs to be turned more, without any other visible changes?

jdsully 7y ago
If there weren’t already 500 of them manufactured that would be feasible. Assuming it could still be adjusted fast enough (which I don’t know).
dboreham 7y ago
It would presumably be easier to just not have the rogue computer pulling on the control surface the other way? The trim wheel seems like a last ditch mechanism to deal with a malfunctioning hydraulic control system but that's not the problem with the MAX, rather the hydraulics are working fine but being told to do the wrong thing.

dralley 7y ago

>A new AOA sensor would void the type certificate. Why would a new (third) AOA sensor void the type certificate?

cjbprime 7y ago
(It would probably require training on what to do when the system becomes inoperable, at least.)

dredmorbius 7y ago

As the 737 MAX saga unfolds, I've been wondering just why options to modify the landing gear (say: telescoping legs, or placement, or both), is such anathema. Clearly, moving engine pods alone is not without its risks.

kayfox 7y ago
Ground handling equipment for most of the 737 operators is designed around the low clearance. So if they were to make it sit higher, operators would have to remove a significant amount of equipment. Also the 737-10 does sit higher: https://www.geekwire.com/2018/boeing-737-max-10-landing-gear/ https://www.geekwire.com/2018/boeing-737-max-10-landing-gear...
- inferiorhuman 7y ago
  Also the 737-10 does sit higher: https://www.geekwire.com/2018/boeing-737-max-10-landing-gear/ https://www.geekwire.com/2018/boeing-737-max-10-landing-gear... Watch the video from your link. The landing gear only extend on rotation. When it's on the ground the 737 MAX 10 sits at the same height as every other 737 MAX. https://www.youtube.com/watch?v=F4IGl4OizM4 https://www.youtube.com/watch?v=F4IGl4OizM4
AWildC182 7y ago
Laziness. This is absolutely a "fuck it, we'll fix it in software" problem. I don't think it would necessarily invalidate the type certificate to change the legs but Boeing has gotten away with doing the bare minimum of structural changes necessary to keep the 737 relevant. Adding fuselage tube sections is far easier than reworking the complex gear systems and moving everything out of the way to make the bays longer (737 has an equipment bay around the nose gear, mains have systems routed around them) so they will do just about anything to avoid that.
- mattmaroon 7y ago
  It's not laziness, it's cost to cost-sensitive customers who have a viable alternative with Airbus A320 Neo. Boeing actually initially set out to make an entirely new plane. The airliners instead wanted a re-engined 737 to keep type certification so that they didn't have to retrain pilots and could keep new equipment purchases to a minimum. It's not that Boeing would have been unwilling to build an entirely new plane, their CEO announced that as the plan in 2011, it's that operators would rather they didn't.

missosoup 7y ago

> 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.