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> 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

> 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.
- XCabbage 7y ago
  Can you cite sources for the factual claims you're making here, which contradict what's claimed by Wikipedia and many media sources I've read?
jayalpha 7y ago
"No it isn't. It is a stable design. To claim otherwise misunderstands the term." Well, then we just disagree on the term. "Because the 737 Max had been outfitted with larger new engines that could cause its nose to pitch dangerously skyward" (Source: https://www.nytimes.com/2019/03/14/opinion/business-economics/boeing-737-max.html https://www.nytimes.com/2019/03/14/opinion/business-economic... ) I don't call this a stable design. You can crash every airplane (e.g. "stall") but the plane should not enter an unsafe flying mode during normal flying behavior. No good engineer would have chosen that design. An airplane that can only be kept in the air with a computer must not be necessary unsafe. As far as I know the stealth bombers can only fly with massive computer help. But this must be a rational, conscious decision and the pilot must be aware of this. Not a quick fix to stick huge engines on a plane that was designed in the 60ies. I can put a Ferrari engine in a Mercedes from the 20ies. And I am sure it will drive. But the car, the brakes, everything is not made for this combination.
- WalterBright 7y ago
  > Well, then we just disagree on the term. When you're talking aeronautics, you should use the definition used by aeronautical engineers.
  - jayalpha 7y ago
    The author in the NYT is a pilot. "Unfortunately, in the case of the 737 Max, it seems that Boeing has built a plane with a fundamental aeronautical issue that it thought would be resolved by adding a new automated system. "
    - deleted 7y ago
      [deleted]
    - WalterBright 7y ago
      Mr. Wise is indeed a pilot, but not one for jetliners. Flying a high altitude jetliner is very different from flying a Cessna. Mr. Wise does not have a degree in aeronautical engineering, nor in engineering of any sort. http://jeffwise.net/about-the-author/ http://jeffwise.net/about-the-author/
FabHK 7y ago
The 737 Max would not pass certification requirements without MCAS. Agreed?
- PuffinBlue 7y ago
  Yes, I stated this already: https://news.ycombinator.com/item?id=21249017 https://news.ycombinator.com/item?id=21249017

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.

XCabbage 7y ago
Can you cite sources for the factual claims you're making here, which contradict what's claimed by Wikipedia and many media sources I've read?

jayalpha 7y ago

"No it isn't. It is a stable design. To claim otherwise misunderstands the term." Well, then we just disagree on the term. "Because the 737 Max had been outfitted with larger new engines that could cause its nose to pitch dangerously skyward" (Source: https://www.nytimes.com/2019/03/14/opinion/business-economics/boeing-737-max.html https://www.nytimes.com/2019/03/14/opinion/business-economic... ) I don't call this a stable design. You can crash every airplane (e.g. "stall") but the plane should not enter an unsafe flying mode during normal flying behavior. No good engineer would have chosen that design. An airplane that can only be kept in the air with a computer must not be necessary unsafe. As far as I know the stealth bombers can only fly with massive computer help. But this must be a rational, conscious decision and the pilot must be aware of this. Not a quick fix to stick huge engines on a plane that was designed in the 60ies. I can put a Ferrari engine in a Mercedes from the 20ies. And I am sure it will drive. But the car, the brakes, everything is not made for this combination.

WalterBright 7y ago
> Well, then we just disagree on the term. When you're talking aeronautics, you should use the definition used by aeronautical engineers.
- jayalpha 7y ago
  The author in the NYT is a pilot. "Unfortunately, in the case of the 737 Max, it seems that Boeing has built a plane with a fundamental aeronautical issue that it thought would be resolved by adding a new automated system. "
  - deleted 7y ago
    [deleted]
  - WalterBright 7y ago
    Mr. Wise is indeed a pilot, but not one for jetliners. Flying a high altitude jetliner is very different from flying a Cessna. Mr. Wise does not have a degree in aeronautical engineering, nor in engineering of any sort. http://jeffwise.net/about-the-author/ http://jeffwise.net/about-the-author/

FabHK 7y ago

The 737 Max would not pass certification requirements without MCAS. Agreed?

PuffinBlue 7y ago
Yes, I stated this already: https://news.ycombinator.com/item?id=21249017 https://news.ycombinator.com/item?id=21249017