4 ms·

The aircraft flies fine in most flight profiles, yes. At high angle of attack, the MAX-8 is more unstable than pilots were trained to expect. And the MCAS has

The aircraft flies fine in most flight profiles, yes. At high angle of attack, the MAX-8 is more unstable than pilots were trained to expect. And the MCAS has done an absolutely miserable job of fixing this. Worst case scenario bad: it caused the loss of two airplanes that, if the MCAS had never been added to the MAX-8, would have reached their destinations just fine. Until the it flies predictably in every flight profile (including high AOA), it's demonstrably wrong to say "the aircraft flies fine." Maybe it will eventually "fly fine" but Boeing's got quite a bit of work to do first.

_ph_ 7y ago
Alternatively just train the pilots on the behavior in the domain where MCAS would activate. MCAS main purpose is to lower the training requirements.
- rocqua 7y ago
  Not quite if I am to believe other HN comments. The thing MCAS compensates for is that, in certain cases, as you pitch up more, the pressure on the stick decreases. This feels to pilots like leveling out, which is dangerous. MCAS was designed to counter this. The specific design of MCAS and not adding any new procedures, was to lower the training requirements. Specifically, anyone certified on the old 737 was still certified on the max. If they had improved the interface of MCAS and changed the procedure for runaway trim, it would have required more training. However, without MCAS or another remedy for the 'decreasing stick pressure at increasing pitch' problem, the plane would not have been allowed to fly at all.
  - Dylan16807 7y ago
    > This feels to pilots like leveling out, which is dangerous. MCAS was designed to counter this. Pilots are trained extensively not to trust what motion feels like, and to use the horizon and instruments. An adjustment in stick pressure is not a notable new threat, they just need to be trained for the plane's behavior.
    - bronson 7y ago
      That’s the whole point: the MCAS was supposed to be cheaper/easier for the airlines than new training.
      - mveety 7y ago
        You wouldn’t be retrained to ignore cues from your senses and trust your instruments. That training happens when you’re young and getting your IFR ticket.
        bronson 7y ago
        I'm just pointing out that "they just need to be trained for the plane's behavior" isn't on the table for the MAX-8. The contracts said it would have the same type rating, and therefore the MCAS, for better or for worse. I'm not quite sure how that is related to beginner flight lessons. (?)
    - acqq 7y ago
      > An adjustment in stick pressure is not a notable new threat, they just need to be trained for the plane's behavior. It seems that what you claim is "not a new threat" is actually forbidden by the regulations, because it was recognized to be a threat.
  - salawat 7y ago
    To clarify, since this seems to be a slight misreading of one of my comments. The original one is https://news.ycombinator.com/item?id=19568158 https://news.ycombinator.com/item?id=19568158 and was written at night, so there's some loopy phrasing in there I never corrected. Let me unpack some of it to fit the context here. The pressure applied on the stick itself does not change. Rather, the function of how much deflection you get out of the plane per unit force applied to the stick changes. Design regulations state an airframe for which this curve at any point goes negative cannot be certified as a civil transport airplane. That means, there should be no point in the flight envelope where the sensitivity of the controls drastically changes. It should be a predictable increase in force required to get more deflection, all the way to stall. With the MAX without MCAS, this rule is broken at high AoA when the engine nacelles start making lift. MCAS is meant to compensate for this necessary breakage by inducing some mistrim. The effect of mistrim in that case is to cause the controls to require more force to induce those last few degrees of deflection, using the AoA sensor as the primary indicator as to whether the system should activate, in order to bring the curve into compliance. The problem, as hinted by the response to my post in that thread, is that an honest to god stick-pusher would be more akin to the system you'd want for that. Adding the AoA sensor as a single point of failure is insane, due to the consequences should that sensor start spewing garbage data in normal flight. Most of those are realizations I came to after stumbling across a Royal Aeronautics Society interview of D.P. Davies, a British test pilot for the ARB, the aircraft certification authority for the U.K., which I believe I linked in the comment. At the time I wrote it I was in the midst of a deep dive into the more arcane aspects of control systems. I have some literature tucked away somewhere that I was referencing, bit I'd need to dig rather deep in my browsing history to recover all the context. An interesting historical note: MCAS is similar to a system McDonnell Douglas implemented in MD-11's (LSAS, Longitudinal Stability Augmentation System) for the same reasons as Boeing eventually implemented MCAS: to be able to claim that the new aircraft flew just like the old MD-10. Makes one wonder if someone brushed the dust off something that really shouldn't have been emulated again after the merger.
- codedokode 7y ago
  There are already lot of things that pilots have to keep in mind and look after. Learning how MCAS changes the behaviour of the plane makes everything more complicated.
thucydidesofusa 7y ago
The MAX will fly predictably, just perhaps in a way that's ultimately different from the NG 737s, maybe it will mean that pilots will need a check out flight instead of a iPad tutorial. Maybe it means there will be a new type certification, who knows. All planes with rear engines and t-tails have unforgiving parts to the flight profile, we still fly MD-80s and Boeing 717s and all those regional jets. The Max isn't ideal, but Boeing has a chance of getting ahead of this issue and not junking the product line or existing planes.

_ph_ 7y ago

Alternatively just train the pilots on the behavior in the domain where MCAS would activate. MCAS main purpose is to lower the training requirements.

rocqua 7y ago
Not quite if I am to believe other HN comments. The thing MCAS compensates for is that, in certain cases, as you pitch up more, the pressure on the stick decreases. This feels to pilots like leveling out, which is dangerous. MCAS was designed to counter this. The specific design of MCAS and not adding any new procedures, was to lower the training requirements. Specifically, anyone certified on the old 737 was still certified on the max. If they had improved the interface of MCAS and changed the procedure for runaway trim, it would have required more training. However, without MCAS or another remedy for the 'decreasing stick pressure at increasing pitch' problem, the plane would not have been allowed to fly at all.
- Dylan16807 7y ago
  > This feels to pilots like leveling out, which is dangerous. MCAS was designed to counter this. Pilots are trained extensively not to trust what motion feels like, and to use the horizon and instruments. An adjustment in stick pressure is not a notable new threat, they just need to be trained for the plane's behavior.
  - bronson 7y ago
    That’s the whole point: the MCAS was supposed to be cheaper/easier for the airlines than new training.
    - mveety 7y ago
      You wouldn’t be retrained to ignore cues from your senses and trust your instruments. That training happens when you’re young and getting your IFR ticket.
      - bronson 7y ago
        I'm just pointing out that "they just need to be trained for the plane's behavior" isn't on the table for the MAX-8. The contracts said it would have the same type rating, and therefore the MCAS, for better or for worse. I'm not quite sure how that is related to beginner flight lessons. (?)
  - acqq 7y ago
    > An adjustment in stick pressure is not a notable new threat, they just need to be trained for the plane's behavior. It seems that what you claim is "not a new threat" is actually forbidden by the regulations, because it was recognized to be a threat.
- salawat 7y ago
  To clarify, since this seems to be a slight misreading of one of my comments. The original one is https://news.ycombinator.com/item?id=19568158 https://news.ycombinator.com/item?id=19568158 and was written at night, so there's some loopy phrasing in there I never corrected. Let me unpack some of it to fit the context here. The pressure applied on the stick itself does not change. Rather, the function of how much deflection you get out of the plane per unit force applied to the stick changes. Design regulations state an airframe for which this curve at any point goes negative cannot be certified as a civil transport airplane. That means, there should be no point in the flight envelope where the sensitivity of the controls drastically changes. It should be a predictable increase in force required to get more deflection, all the way to stall. With the MAX without MCAS, this rule is broken at high AoA when the engine nacelles start making lift. MCAS is meant to compensate for this necessary breakage by inducing some mistrim. The effect of mistrim in that case is to cause the controls to require more force to induce those last few degrees of deflection, using the AoA sensor as the primary indicator as to whether the system should activate, in order to bring the curve into compliance. The problem, as hinted by the response to my post in that thread, is that an honest to god stick-pusher would be more akin to the system you'd want for that. Adding the AoA sensor as a single point of failure is insane, due to the consequences should that sensor start spewing garbage data in normal flight. Most of those are realizations I came to after stumbling across a Royal Aeronautics Society interview of D.P. Davies, a British test pilot for the ARB, the aircraft certification authority for the U.K., which I believe I linked in the comment. At the time I wrote it I was in the midst of a deep dive into the more arcane aspects of control systems. I have some literature tucked away somewhere that I was referencing, bit I'd need to dig rather deep in my browsing history to recover all the context. An interesting historical note: MCAS is similar to a system McDonnell Douglas implemented in MD-11's (LSAS, Longitudinal Stability Augmentation System) for the same reasons as Boeing eventually implemented MCAS: to be able to claim that the new aircraft flew just like the old MD-10. Makes one wonder if someone brushed the dust off something that really shouldn't have been emulated again after the merger.
codedokode 7y ago
There are already lot of things that pilots have to keep in mind and look after. Learning how MCAS changes the behaviour of the plane makes everything more complicated.

thucydidesofusa 7y ago

The MAX will fly predictably, just perhaps in a way that's ultimately different from the NG 737s, maybe it will mean that pilots will need a check out flight instead of a iPad tutorial. Maybe it means there will be a new type certification, who knows. All planes with rear engines and t-tails have unforgiving parts to the flight profile, we still fly MD-80s and Boeing 717s and all those regional jets. The Max isn't ideal, but Boeing has a chance of getting ahead of this issue and not junking the product line or existing planes.