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1) Like most people, I’m far from qualified to give aeronautical engineering advice, but as fly-by-wire technology gets more advanced, won’t this be the norm?

1) Like most people, I’m far from qualified to give aeronautical engineering advice, but as fly-by-wire technology gets more advanced, won’t this be the norm? ie: Airframes that are difficult to fly might always be more efficient, so have a computer do the hard part. 2) This part seems like the real damning misdesign: Boeing offered the single angle-of-attack sensor as standard equipment, and charged extra for a second along with a “disagree” indicator that would allow 737 MAX pilots to “cross-check” a faulty sensor. Citing those decisions, another observer noted: “Who would design a system with a single point of failure?”

wetpaws 8y ago
>Who would design a system with a single point of failure? I guess we now have an answer to this question.
kalleboo 8y ago
Re: 1, today I learned about this: > https://en.wikipedia.org/wiki/Relaxed_stability#Unstable_aircraft https://en.wikipedia.org/wiki/Relaxed_stability#Unstable_air... > Relaxed stability designs are not limited to military jets. The McDonnell Douglas MD-11 has a relaxed stability design which was implemented to save fuel. To ensure stability for safe flight, an LSAS (Longitudinal Stability Augmentation System) was introduced to compensate for the MD-11's rather short horizontal stabilizer and ensure that the aircraft would remain stable. However, there have been incidents in which the MD-11's relaxed stability caused an "inflight upset." > Updates to the software package made the airplane's handling characteristics in manual flight similar to those of the DC-10, despite a smaller tailplane to reduce drag and increase fuel efficiency. Maybe this isn't as new of a development as we think.
- inferiorhuman 8y ago
  Maybe this isn't as new of a development as we think. Considering that McDonnell Douglas management is running Boeing these days…
kalleboo 8y ago
> “Who would design a system with a single point of failure?” According to the original design, the MCAS was only supposed to adjust trim to a level that was easily overridden by the pilot essentially just pushing on the stick/adjusting the trim. If it had been implemented this way, sensor failure would not have been catastrophic and hence doesn't require redundancy. At some point this was either changed or implemented incorrectly so that MCAS had much more authority.
- kuzehanka 8y ago
  It was changed. Flight testing showed that much larger trim was required for MCAS to function, and that was implemented. The failure was not reassessing the risks after that.
  - russdill 8y ago
    Echos of the Hyatt Regency walkway collapse.
  - kalleboo 8y ago
    That's pretty damning. I would have assumed Boeing of all people had a comprehensive change management system to automatically trigger a re-assessment in these cases.
- heisenbit 8y ago
  They underestimated the aerodynamic instability and then decided just to give this auxiliary system total control. What possibly could go wrong? They should have gone back to the drawing board, putting of the launch and figuring out how to lift the airplane a bit higher. May have required them to lower the 737 prices for a while to stay competitive against the 320neo and may have cost them a fortune. Feedback loops with high gain (strong engine pulling up, powerful MCAS pushing down) are difficult to control. Minor failures have out-sized impact. Adding rules to constrain the system introduces new operating modes all of them having the potential to confuse the pilots. And in this system the pilots are close to ground and have very little time to act.
mehrdadn 8y ago
> “Who would design a system with a single point of failure?” Relevant: https://news.ycombinator.com/item?id=19158562 https://news.ycombinator.com/item?id=19158562
inferiorhuman 8y ago
Boeing offered the single angle-of-attack sensor as standard equipment, and charged extra for a second along with a “disagree” indicator that would allow 737 MAX pilots to “cross-check” a faulty sensor. Unfortunately for the author that's not an accurate representation of reality. I'm a bit surprised as I thought that EETimes was a credible news source.

wetpaws 8y ago

>Who would design a system with a single point of failure? I guess we now have an answer to this question.

kalleboo 8y ago

Re: 1, today I learned about this: > https://en.wikipedia.org/wiki/Relaxed_stability#Unstable_aircraft https://en.wikipedia.org/wiki/Relaxed_stability#Unstable_air... > Relaxed stability designs are not limited to military jets. The McDonnell Douglas MD-11 has a relaxed stability design which was implemented to save fuel. To ensure stability for safe flight, an LSAS (Longitudinal Stability Augmentation System) was introduced to compensate for the MD-11's rather short horizontal stabilizer and ensure that the aircraft would remain stable. However, there have been incidents in which the MD-11's relaxed stability caused an "inflight upset." > Updates to the software package made the airplane's handling characteristics in manual flight similar to those of the DC-10, despite a smaller tailplane to reduce drag and increase fuel efficiency. Maybe this isn't as new of a development as we think.

inferiorhuman 8y ago
Maybe this isn't as new of a development as we think. Considering that McDonnell Douglas management is running Boeing these days…

kalleboo 8y ago

> “Who would design a system with a single point of failure?” According to the original design, the MCAS was only supposed to adjust trim to a level that was easily overridden by the pilot essentially just pushing on the stick/adjusting the trim. If it had been implemented this way, sensor failure would not have been catastrophic and hence doesn't require redundancy. At some point this was either changed or implemented incorrectly so that MCAS had much more authority.

kuzehanka 8y ago
It was changed. Flight testing showed that much larger trim was required for MCAS to function, and that was implemented. The failure was not reassessing the risks after that.
- russdill 8y ago
  Echos of the Hyatt Regency walkway collapse.
- kalleboo 8y ago
  That's pretty damning. I would have assumed Boeing of all people had a comprehensive change management system to automatically trigger a re-assessment in these cases.
heisenbit 8y ago
They underestimated the aerodynamic instability and then decided just to give this auxiliary system total control. What possibly could go wrong? They should have gone back to the drawing board, putting of the launch and figuring out how to lift the airplane a bit higher. May have required them to lower the 737 prices for a while to stay competitive against the 320neo and may have cost them a fortune. Feedback loops with high gain (strong engine pulling up, powerful MCAS pushing down) are difficult to control. Minor failures have out-sized impact. Adding rules to constrain the system introduces new operating modes all of them having the potential to confuse the pilots. And in this system the pilots are close to ground and have very little time to act.

mehrdadn 8y ago

> “Who would design a system with a single point of failure?” Relevant: https://news.ycombinator.com/item?id=19158562 https://news.ycombinator.com/item?id=19158562

inferiorhuman 8y ago

Boeing offered the single angle-of-attack sensor as standard equipment, and charged extra for a second along with a “disagree” indicator that would allow 737 MAX pilots to “cross-check” a faulty sensor. Unfortunately for the author that's not an accurate representation of reality. I'm a bit surprised as I thought that EETimes was a credible news source.