4 ms·

I hate the fact that all discussion focuses on the software and ignores the airframe.

cmurf 7y ago
What's the problem with the airframe? What's the problem with the larger engine nacelle causing a different pitching moment? I've yet to read either of those violate any portion of FAR 25. There is still an open question whether the MAX should have or will have a separate type certificate from other 737's, thereby requiring pilots of a type rating to fly the MAX, thereby requiring full disclosure and training on all differences. Which pilots should have had anyway, even if it didn't require a new type rating.
- mrpippy 7y ago
  I wish I had a more authoritative source, but this matches my understanding: https://news.ycombinator.com/item?id=19512161 https://news.ycombinator.com/item?id=19512161 As a side note, it’s really unfortunate that we won’t get an NTSB-level (both in detail and widespread respect for the organization) report on what went wrong and how it happened. I’m not sure the Ethiopian and Indonesian authorities will really (be able to) dig into MCAS and all the details of its development as deeply as we’d like. I expect that some of the reporters covering this story will write books (Dominic Gates and Jon Ostrower in particular), and those will be the most authoritative accounts.
  - cmurf 7y ago
    The NTSB will issue a report. It's an American made airplane involved in an accident, so they are required to investigate. They just don't have primary jurisdiction over the investigation, per ICAO rules.
- tremon 7y ago
  What's the problem with the airframe? The #1 problem with the airframe is that it is not identical to the original 737 airframe. Therefore it shouldn't have been certified as a 737, and it should have required pilot training. Boeing has been using software to emulate a 737 airframe to avoid the pilot training costs. This approach itself is fraught with problems, and I hope the FAA puts a hard stop to these non-solutions.
  - magduf 7y ago
    I'd like to see the European and Chinese aviation authorities put a hard stop to these non-solutions if the FAA doesn't. At this point, I don't think the FAA is at all trustworthy; they've proven themselves untrustworthy with the way they handled the certification of this turkey and how they were literally the last aviation authority in the world to ground the plane.
  - cmurf 7y ago
    The 757 and 767 do not have identical airframes, they share a type certificate. The Airbus 320 and 340 do not have identical airframes, they share a type certificate. I think you do not understand type certification. The 737 MAX airframe is substantially more like a 737 NG airframe, than a 757 is to a 767. Etc. It sounds like you have a problem with how airplanes are type certified, not a problem with the airframe.
    - tremon 7y ago
      Rather, I have a problem with airplanes falling out of the sky because pilots don't understand what they're flying, and airplane manufacturers trying to obfuscate their machinery. The details of how and why are secondary to that.
      - cmurf 7y ago
        I think literally everyone has a problem with airplanes falling out of the sky. Anyone saying otherwise is perhaps a comedian. So I still have to insist you work harder to refine your complaint. The complaint is legitimate, but it's also ordinary. To contribute to the conversation you have to bring something a little bit more than just the ordinary. Indeed, it might very well be questionable that the 757 and 767 have the same type rating. But then, even though they have the same type rating they do still have difference training. Is iPad difference training really adequate? Who evaluated this? Were there contrary opinions?
- salawat 7y ago
  The problem with the airframe is that the shape of the nacelles, and their forward position create extra lifting surface in front of the center of gravity at high AoA. What this results in, is a non-compliant stick force response curve at high AoA. This violates FAA regulations which state that the stick force required to bring a plane to a stall must consistently increase all the way to the stall. No sickening or decreases in apparent required stick force are certifiable as airworthy for Civil Transport Aircraft. This was explained in a recent Seattle Times Article. I also posted it here as a theory back in March abouts. [1]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... [2]https://news.ycombinator.com/item?id=19568158 https://news.ycombinator.com/item?id=19568158 [3]relevant FAR 25.173, see stick force requirements MCAS was designed to artificially induce a mistrim which has the end result of smoothing out that force curve. Initially it was only for high-speed, high-G, but was eventually loosened to accommodate the same behavior happening at a low speed low G part of the flight envelope. This is a hack in the truest sense of the word, because you'll notice the regs indicate the plane having to be within a certain point of appropriate trim; except in those flight regimes, the trim is artificially massaged from what the pilot set it to, to what MCAS thinks it should be, which is determined by the input of only a single AoA sensor. In short, the airframe is aerodynamically flawed in some of the most fundamental ways known to the aviation community. It can work; given a correct MCAS system. There was no excuse, however, to hide this from both regulators and pilots. Hope that explains things.
  - cmurf 7y ago
    I appreciate the response but it does not help at all one bit, it's a rehash of everything I've already read. In all of these 737 MAX discussions I'm one of the first to have brought up FAR 25.173(c) (although that whole section is relevant). I do not see how software augmentation can be permitted to compensate for a deviation from FAR 26.173. That section is titled: Static longitudinal stability. Software augmentation cannot cause an airplane that lacks positive static stability to have positive static stability. You have to understand that what you're proposing represents such a magnificent perversion of FARs, if true, that it is not conceivable to me that this is not a big f'n deal in the aviation community. It would be the elephant in the room, that somehow Boeing and the FAA permitted an airplane that in fact does not have certifiable positive static stability in one or more axis, to have been certified because of a software routine; let alone a software routine with no redundancy and is easily disabled in flight with no documentation on the consequences. Let me put another fine point on it: I do not care if there are 50 AoA sensors and 100 independent computers on this airplane to compensate for a FAR 25.173 deficiency (or pick any of the other axis for that matter). You cannot use a goddamn computer to make an airplane statically stable when aerodynamically it is not statically stable. At least not without changing the FARs. As they are written, transport category airplanes must comply with FAR 25, and I see nothing in FAR 25 that permits computers papering over aerodynamic requirements.
afterburner 7y ago
The aerodynamic/stability effects of moving the engine position is a complicated topic, and I haven't seen a really good thorough explanation of it yet that really goes into the gritty details. There's so many rules of thumb and generalizations in the vast majority of peoples' understanding of aircraft stability and forces, even for pilots or engineers in the field.
spaceandshit 7y ago
This is HN, where a majority of the readers are in the software/tech industry.

What's the problem with the airframe? What's the problem with the larger engine nacelle causing a different pitching moment? I've yet to read either of those violate any portion of FAR 25. There is still an open question whether the MAX should have or will have a separate type certificate from other 737's, thereby requiring pilots of a type rating to fly the MAX, thereby requiring full disclosure and training on all differences. Which pilots should have had anyway, even if it didn't require a new type rating.

mrpippy 7y ago
I wish I had a more authoritative source, but this matches my understanding: https://news.ycombinator.com/item?id=19512161 https://news.ycombinator.com/item?id=19512161 As a side note, it’s really unfortunate that we won’t get an NTSB-level (both in detail and widespread respect for the organization) report on what went wrong and how it happened. I’m not sure the Ethiopian and Indonesian authorities will really (be able to) dig into MCAS and all the details of its development as deeply as we’d like. I expect that some of the reporters covering this story will write books (Dominic Gates and Jon Ostrower in particular), and those will be the most authoritative accounts.
- cmurf 7y ago
  The NTSB will issue a report. It's an American made airplane involved in an accident, so they are required to investigate. They just don't have primary jurisdiction over the investigation, per ICAO rules.
tremon 7y ago
What's the problem with the airframe? The #1 problem with the airframe is that it is not identical to the original 737 airframe. Therefore it shouldn't have been certified as a 737, and it should have required pilot training. Boeing has been using software to emulate a 737 airframe to avoid the pilot training costs. This approach itself is fraught with problems, and I hope the FAA puts a hard stop to these non-solutions.
- magduf 7y ago
  I'd like to see the European and Chinese aviation authorities put a hard stop to these non-solutions if the FAA doesn't. At this point, I don't think the FAA is at all trustworthy; they've proven themselves untrustworthy with the way they handled the certification of this turkey and how they were literally the last aviation authority in the world to ground the plane.
- cmurf 7y ago
  The 757 and 767 do not have identical airframes, they share a type certificate. The Airbus 320 and 340 do not have identical airframes, they share a type certificate. I think you do not understand type certification. The 737 MAX airframe is substantially more like a 737 NG airframe, than a 757 is to a 767. Etc. It sounds like you have a problem with how airplanes are type certified, not a problem with the airframe.
  - tremon 7y ago
    Rather, I have a problem with airplanes falling out of the sky because pilots don't understand what they're flying, and airplane manufacturers trying to obfuscate their machinery. The details of how and why are secondary to that.
    - cmurf 7y ago
      I think literally everyone has a problem with airplanes falling out of the sky. Anyone saying otherwise is perhaps a comedian. So I still have to insist you work harder to refine your complaint. The complaint is legitimate, but it's also ordinary. To contribute to the conversation you have to bring something a little bit more than just the ordinary. Indeed, it might very well be questionable that the 757 and 767 have the same type rating. But then, even though they have the same type rating they do still have difference training. Is iPad difference training really adequate? Who evaluated this? Were there contrary opinions?
salawat 7y ago
The problem with the airframe is that the shape of the nacelles, and their forward position create extra lifting surface in front of the center of gravity at high AoA. What this results in, is a non-compliant stick force response curve at high AoA. This violates FAA regulations which state that the stick force required to bring a plane to a stall must consistently increase all the way to the stall. No sickening or decreases in apparent required stick force are certifiable as airworthy for Civil Transport Aircraft. This was explained in a recent Seattle Times Article. I also posted it here as a theory back in March abouts. [1]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... [2]https://news.ycombinator.com/item?id=19568158 https://news.ycombinator.com/item?id=19568158 [3]relevant FAR 25.173, see stick force requirements MCAS was designed to artificially induce a mistrim which has the end result of smoothing out that force curve. Initially it was only for high-speed, high-G, but was eventually loosened to accommodate the same behavior happening at a low speed low G part of the flight envelope. This is a hack in the truest sense of the word, because you'll notice the regs indicate the plane having to be within a certain point of appropriate trim; except in those flight regimes, the trim is artificially massaged from what the pilot set it to, to what MCAS thinks it should be, which is determined by the input of only a single AoA sensor. In short, the airframe is aerodynamically flawed in some of the most fundamental ways known to the aviation community. It can work; given a correct MCAS system. There was no excuse, however, to hide this from both regulators and pilots. Hope that explains things.
- cmurf 7y ago
  I appreciate the response but it does not help at all one bit, it's a rehash of everything I've already read. In all of these 737 MAX discussions I'm one of the first to have brought up FAR 25.173(c) (although that whole section is relevant). I do not see how software augmentation can be permitted to compensate for a deviation from FAR 26.173. That section is titled: Static longitudinal stability. Software augmentation cannot cause an airplane that lacks positive static stability to have positive static stability. You have to understand that what you're proposing represents such a magnificent perversion of FARs, if true, that it is not conceivable to me that this is not a big f'n deal in the aviation community. It would be the elephant in the room, that somehow Boeing and the FAA permitted an airplane that in fact does not have certifiable positive static stability in one or more axis, to have been certified because of a software routine; let alone a software routine with no redundancy and is easily disabled in flight with no documentation on the consequences. Let me put another fine point on it: I do not care if there are 50 AoA sensors and 100 independent computers on this airplane to compensate for a FAR 25.173 deficiency (or pick any of the other axis for that matter). You cannot use a goddamn computer to make an airplane statically stable when aerodynamically it is not statically stable. At least not without changing the FARs. As they are written, transport category airplanes must comply with FAR 25, and I see nothing in FAR 25 that permits computers papering over aerodynamic requirements.

afterburner 7y ago

The aerodynamic/stability effects of moving the engine position is a complicated topic, and I haven't seen a really good thorough explanation of it yet that really goes into the gritty details. There's so many rules of thumb and generalizations in the vast majority of peoples' understanding of aircraft stability and forces, even for pilots or engineers in the field.

spaceandshit 7y ago

This is HN, where a majority of the readers are in the software/tech industry.