8 ms·

In terms of project management, aviation software is one industry where the "three-legged stool" should always, always favor quality, so I'm more than happy to

In terms of project management, aviation software is one industry where the "three-legged stool" should always, always favor quality, so I'm more than happy to see Boeing take the extra time to get this right. Though the nose-pusher system's entire existence is due to the aerodynamic design of the entire MAX...which seems to be driven by the other 2 legs of the stool (i.e. budget and time).

sgc 8y ago
Airplanes are not gliders. There is no reason to not correct aerodynamics via powered systems since that is how virtually any airplane even flies, with the caveat being - as long as it is done well. In other words, I have no problem with the principle of their design choice, just its execution which lacked typical redundancy, and transparency to the industry.
- pron 8y ago
  Is there another unstable airliner in operation? Even if it's OK, at the very least flying one (with or without software controls) would seem to me to require a certification by the pilots, which, as I understand, is precisely what Boeing tried to avoid.
  - sgc 8y ago
    There are a number of unstable planes in service that work just fine. I don't see why it matters if they are airliners as long as instability does not translate to a higher safety risk, and I don't know if any other airliners are unstable or how unstable they might be. In this case the instability appears to have been far less significant than the faulty corrective mechanisms. I agree completely that Boeing was not transparent about how to use their plane and did not make it safe enough.
    - pedrocr 8y ago
      You are very certain of your conclusion while not knowing the answers to all the fundamental questions to make that conclusion. > I don't see why it matters if they are airliners as long as instability does not translate to a higher safety risk We don't know what the extra safety issue might be. > I don't know if any other airliners are unstable or how unstable they might be. We don't know if anyone has ever done this before, or how completely unusual it might be. > In this case the instability appears to have been far less significant than the faulty corrective mechanisms. And finally we don't even know the level of instability. The system was there possibly correcting for huge issues. After all the fleet is grounded instead of just disabling the system.
      - cjbprime 8y ago
        I've read that the extra lift generated by the nacelles doesn't actually result in aerodynamic instability -- the plane's not going to stall itself -- but results in reduced backpressure on the yoke in a way that fails airworthiness certifications for required amounts of pressure. (With the idea being that the pilots may induce a stall due to not needing to provide as much force on the yoke as they would expect to have to in order to do that.)
      - ethbro 8y ago
        > And finally we don't even know the level of instability It'd approach criminal liability if the FAA certified a plane they didn't know the level of instability of. This is why test flights are performed. As the other commenter mention, something that gets lost in this discussion is the fact that MCAS was there to make the control feel approximate other airframes. The same aero adjustments could be accomplished by the pilot, but regulations prohibit their being necessary. So, MCAS. We're talking 'stability that adheres to control forces required by regulation' rather than 'F-117 drop out of the sky' instability.
        pedrocr 8y ago
        > It'd approach criminal liability if the FAA certified a plane they didn't know the level of instability of. The question isn't if they didn't know, it's if this is an unusual level of instability for an airliner. >We're talking 'stability that adheres to control forces required by regulation' rather than 'F-117 drop out of the sky' instability. Hopefully yes, but we don't know how much instability there is. If you assume the answer there's no point having the discussion.
  - sandworm101 8y ago
    All high performance aircraft are, by definition, unstable. An airframe optimized for one flight regime will not be as suitable in another. An airliner like the 737 is optimized for cruise flight (30k feet, almost supersonic) and so isn't ideal during takeoff/landing. Making it good at both isn't an option. So we have systems to modify and adapt the cruise airframe for low-level flying such as this antistall system. The only really stable commercial aircraft are, perhaps, the bushplanes. They are not fast and not fuel efficient over any real distance.
    - davidw 8y ago
      I don't much care for planes, but I found this 'short take off and landing' contest pretty impressive: https://www.youtube.com/watch?v=2pw4OE7gM2M https://www.youtube.com/watch?v=2pw4OE7gM2M
    - hleszek 8y ago
      It might be possible in the future to have commercial aircrafts with an airframe changing depending of the flight regime. See https://m.phys.org/news/2019-04-mit-nasa-kind-airplane-wing.html https://m.phys.org/news/2019-04-mit-nasa-kind-airplane-wing....
      - sandworm101 8y ago
        Well, they do. That's what flaps are. They change the shape of the wing to better optimize for slow flight. Swing-wings work but are hideously heavy/expensive. We will never see an airframe able to morph into constantly ideal shapes like a birds do.
    - pedrocr 8y ago
      > All high performance aircraft are, by definition, unstable. This doesn't follow. Not even fighter jets were inherently unstable before modern control electronics. Using the electronics to make the flight characteristics better is not the same as the airframe being inherently unstable.
      - 8y ago
  - mhandley 8y ago
    The 737 Max is not actually unstable without MCAS. The requirement is for increasing angles of attack to require increasing back pressure on the yoke up until the edge of the flight envelope. The lift from the larger nacelles placed further forward is enough to violate this requirement at high angles of attack. It won't take itself to a stall unless you keep pulling, but it doesn't take extra back pressure to get it there either. Other airliners have had undesirable parts of the flight envelope. The 727 for example has a high T tail, and it's possible to get into a deep stall, which is not recoverable because at very high angles of attack the elevators are in the turbulent air behind the wings. In the UK, the CAA required 727s to be equipped with stick pushers to prevent them ever getting close to this regime. This was due to their experience with a BAC 111 that deep-stalled and crashed in 1963. I don't think the FAA ever required this though.
    - ams6110 8y ago
      DC-9;MD-[89]0;B717 have the same T-tail design, the deep stall was address by changes to the wing leading edge, not sure if they also have a stick pusher.
      - raverbashing 8y ago
        From a quick look at both planes it might be that going into deep stall in the 727 might be easier because the AOA needed is smaller, but that's just my quick guess (For those who don't know, a Deep Stall happens when the horizontal stabilizer gets in the "air shadow" of the wings, hence you can't get airflow there to move the plane) Some interesting discussion on t-tails and deep stalls http://www.rbogash.com/Safety/deep_stall.html http://www.rbogash.com/Safety/deep_stall.html
    - acqq 8y ago
      > It won't take itself to a stall unless you keep pulling, but it doesn't take extra back pressure to get it there either. It won't "take itself" but possibly just a very light pull would stall the plane in some situations, and that is the very safety problem which Boeing tried to solve with MCAS, while keeping silent on its existence, because the plane is behaving differently than the one for which the pilots trained. Which is the opposite of how the plane was advertised and sold. So any time when the MCAS is off the plane behaves differently than the one for which the pilots trained, therefore "just keep it turned off" was also not an option. And we don't know how "light" is light, it can really be the case that it's even dangerously light.
- d1zzy 8y ago
  > Airplanes are not gliders. Actually... Wasn't there a famous case where the pilots managed to save a plane without engines by just gliding to an airport? Would such a thing even work on the MAX design? Ah yes, here it is: https://en.wikipedia.org/wiki/Air_Transat_Flight_236 https://en.wikipedia.org/wiki/Air_Transat_Flight_236
  - txcwpalpha 8y ago
    > Would such a thing even work on the MAX design? Yes, because the problem with the MAX is that the engines provide an off-center-of-gravity thrust. If the engines weren't running, the MAX would glide just like any other 737. There is also the case of the Gimli Glider [1], and any commercial airliner is certainly capable of "gliding" for at least some time, but I think the GP was adhering more to the actual definition of "glider" [2], which is an aircraft that can fly entirely without power from any engines at all. 1: https://en.wikipedia.org/wiki/Gimli_Glider https://en.wikipedia.org/wiki/Gimli_Glider 2: https://en.wikipedia.org/wiki/Glider_(aircraft) https://en.wikipedia.org/wiki/Glider_(aircraft)
    - ams6110 8y ago
      All jet airliners with engines under the wings have an "off-center-of-gravity" thrust. They all want to pitch up when thrust is applied. The MAX, with the engines higher and more forward, actually has less of an issue with this. The issue with the MAX is that the large engine nacelles forward of the wing can produce their own aerodynamic lift at high angles of attack. This is what MCAS compensates for.
  - cal5k 8y ago
    Why would it not? You still have to be able to fly the thing in case of a dual engine failure. MCAS has one function: give the MAX 8 flight characteristics that are similar enough to previous versions to not require significant training. In fact, it's only when the engines are actually working that you'd need this... they're more powerful and further forward, meaning that at high thrust the aircraft will have more of a tendency to pitch up.
- cmurf 8y ago
  Transport category aircraft have a vast number of aerodynamic behaviors written in regulations, FAR 25. Approach to stall, stall, and stall recovery are described behaviors they must exhibit (FAR 25.201 - 25.207). Longitudinal static stability and dynamic stability are also defined (FAR 25.171 - 25.181). There is no such thing as certifying an aerodynamically unstable transport category aircraft. An open question I haven't yet been able to determine is to what degree software is an acceptable mediator to compel such behaviors. But I'm very skeptical that it's acceptable at all, let alone by something that can be intentionally disabled with two switches as a troubleshooting/override, and then also not require any difference training for the new behavior that ensues. Whether MCAS exists strictly for FAR 25 airworthiness, or to avoid a different type rating for the pilot under FAR 61.31 from any other 737, it's questionable how you get around either of those things once it's disabled on purpose as a emergency/troubleshooting technique. Which is worse upon setting STAB TRIM to cutoff? That the airplane isn't legally airworthy? Or that the pilot isn't legally type rated? Or even possibly both? And was either the case with the previous 737 models? Definitely not.
aunty_helen 8y ago
>Though the nose-pusher system's entire existence is due to the aerodynamic design of the entire MAX...which seems to be driven by the other 2 legs of the stool (i.e. budget and time). Sorry, but this isn't a credible comment. Modern engines run bigger slower fans to reduce fuel consumption and noise. Bigger engines don't fit under the wing. The engine fitment issue has been around since the 737 went from JT8D -> CFM56, hence the punched in the jaw look of most current non MAX 737s. New generation, bigger engines, same form factor. Sure they could've redesigned the half of the plane but then it's not really a 737.
- bunderbunder 8y ago
  > Sure they could've redesigned the half of the plane but then it's not really a 737. That is exactly the budget and time bit - lots of time and money for Boeing spent designing a new airframe, then the "not really a 737" part means lots more time and money spent by Boeing getting it certified, and lots of time and money for their customers in getting their pilots trained for the new plane.
- dan678 8y ago
  Isn't that the point? They attempted to save time and money by not designing a new aircraft (as they originally planned) and found a way to mount the new larger engines that necessitated the MCAS system. In addition, the solution they sold did not, by design, utilize both AoA sensors and did not advise pilots if the sensor disagree unless an additional package was purchased. Furthermore, all of this was in effort to sell an aircraft that would not need significant pilot re-training, resulting in pilots not being familiar enough with the failure mode that resulted in many deaths.
  - aunty_helen 8y ago
    'Additionally, former Boeing CFO James Bell said during the company's second quarter 2011 earnings call, the research and development cost to Boeing to re-engine would be 10%-15% of the cost of a new airplane, which was at the time widely estimated by aerospace analysts to be $10-$12 billion' A factor of 10 cost difference 'if they had only done x' isn't realistic. Completely agree with your additional point though, the competition was the A320neo and the us vs them economics look better if you don't have to pay pilots to sit in a simulator and re cert. https://www.flightglobal.com/news/articles/boeing-disputes-737-max-development-cost-report-367504/ https://www.flightglobal.com/news/articles/boeing-disputes-7...

sgc 8y ago

Airplanes are not gliders. There is no reason to not correct aerodynamics via powered systems since that is how virtually any airplane even flies, with the caveat being - as long as it is done well. In other words, I have no problem with the principle of their design choice, just its execution which lacked typical redundancy, and transparency to the industry.

pron 8y ago
Is there another unstable airliner in operation? Even if it's OK, at the very least flying one (with or without software controls) would seem to me to require a certification by the pilots, which, as I understand, is precisely what Boeing tried to avoid.
- sgc 8y ago
  There are a number of unstable planes in service that work just fine. I don't see why it matters if they are airliners as long as instability does not translate to a higher safety risk, and I don't know if any other airliners are unstable or how unstable they might be. In this case the instability appears to have been far less significant than the faulty corrective mechanisms. I agree completely that Boeing was not transparent about how to use their plane and did not make it safe enough.
  - pedrocr 8y ago
    You are very certain of your conclusion while not knowing the answers to all the fundamental questions to make that conclusion. > I don't see why it matters if they are airliners as long as instability does not translate to a higher safety risk We don't know what the extra safety issue might be. > I don't know if any other airliners are unstable or how unstable they might be. We don't know if anyone has ever done this before, or how completely unusual it might be. > In this case the instability appears to have been far less significant than the faulty corrective mechanisms. And finally we don't even know the level of instability. The system was there possibly correcting for huge issues. After all the fleet is grounded instead of just disabling the system.
    - cjbprime 8y ago
      I've read that the extra lift generated by the nacelles doesn't actually result in aerodynamic instability -- the plane's not going to stall itself -- but results in reduced backpressure on the yoke in a way that fails airworthiness certifications for required amounts of pressure. (With the idea being that the pilots may induce a stall due to not needing to provide as much force on the yoke as they would expect to have to in order to do that.)
    - ethbro 8y ago
      > And finally we don't even know the level of instability It'd approach criminal liability if the FAA certified a plane they didn't know the level of instability of. This is why test flights are performed. As the other commenter mention, something that gets lost in this discussion is the fact that MCAS was there to make the control feel approximate other airframes. The same aero adjustments could be accomplished by the pilot, but regulations prohibit their being necessary. So, MCAS. We're talking 'stability that adheres to control forces required by regulation' rather than 'F-117 drop out of the sky' instability.
      - pedrocr 8y ago
        > It'd approach criminal liability if the FAA certified a plane they didn't know the level of instability of. The question isn't if they didn't know, it's if this is an unusual level of instability for an airliner. >We're talking 'stability that adheres to control forces required by regulation' rather than 'F-117 drop out of the sky' instability. Hopefully yes, but we don't know how much instability there is. If you assume the answer there's no point having the discussion.
- sandworm101 8y ago
  All high performance aircraft are, by definition, unstable. An airframe optimized for one flight regime will not be as suitable in another. An airliner like the 737 is optimized for cruise flight (30k feet, almost supersonic) and so isn't ideal during takeoff/landing. Making it good at both isn't an option. So we have systems to modify and adapt the cruise airframe for low-level flying such as this antistall system. The only really stable commercial aircraft are, perhaps, the bushplanes. They are not fast and not fuel efficient over any real distance.
  - davidw 8y ago
    I don't much care for planes, but I found this 'short take off and landing' contest pretty impressive: https://www.youtube.com/watch?v=2pw4OE7gM2M https://www.youtube.com/watch?v=2pw4OE7gM2M
  - hleszek 8y ago
    It might be possible in the future to have commercial aircrafts with an airframe changing depending of the flight regime. See https://m.phys.org/news/2019-04-mit-nasa-kind-airplane-wing.html https://m.phys.org/news/2019-04-mit-nasa-kind-airplane-wing....
    - sandworm101 8y ago
      Well, they do. That's what flaps are. They change the shape of the wing to better optimize for slow flight. Swing-wings work but are hideously heavy/expensive. We will never see an airframe able to morph into constantly ideal shapes like a birds do.
  - pedrocr 8y ago
    > All high performance aircraft are, by definition, unstable. This doesn't follow. Not even fighter jets were inherently unstable before modern control electronics. Using the electronics to make the flight characteristics better is not the same as the airframe being inherently unstable.
    - 8y ago
- mhandley 8y ago
  The 737 Max is not actually unstable without MCAS. The requirement is for increasing angles of attack to require increasing back pressure on the yoke up until the edge of the flight envelope. The lift from the larger nacelles placed further forward is enough to violate this requirement at high angles of attack. It won't take itself to a stall unless you keep pulling, but it doesn't take extra back pressure to get it there either. Other airliners have had undesirable parts of the flight envelope. The 727 for example has a high T tail, and it's possible to get into a deep stall, which is not recoverable because at very high angles of attack the elevators are in the turbulent air behind the wings. In the UK, the CAA required 727s to be equipped with stick pushers to prevent them ever getting close to this regime. This was due to their experience with a BAC 111 that deep-stalled and crashed in 1963. I don't think the FAA ever required this though.
  - ams6110 8y ago
    DC-9;MD-[89]0;B717 have the same T-tail design, the deep stall was address by changes to the wing leading edge, not sure if they also have a stick pusher.
    - raverbashing 8y ago
      From a quick look at both planes it might be that going into deep stall in the 727 might be easier because the AOA needed is smaller, but that's just my quick guess (For those who don't know, a Deep Stall happens when the horizontal stabilizer gets in the "air shadow" of the wings, hence you can't get airflow there to move the plane) Some interesting discussion on t-tails and deep stalls http://www.rbogash.com/Safety/deep_stall.html http://www.rbogash.com/Safety/deep_stall.html
  - acqq 8y ago
    > It won't take itself to a stall unless you keep pulling, but it doesn't take extra back pressure to get it there either. It won't "take itself" but possibly just a very light pull would stall the plane in some situations, and that is the very safety problem which Boeing tried to solve with MCAS, while keeping silent on its existence, because the plane is behaving differently than the one for which the pilots trained. Which is the opposite of how the plane was advertised and sold. So any time when the MCAS is off the plane behaves differently than the one for which the pilots trained, therefore "just keep it turned off" was also not an option. And we don't know how "light" is light, it can really be the case that it's even dangerously light.
d1zzy 8y ago
> Airplanes are not gliders. Actually... Wasn't there a famous case where the pilots managed to save a plane without engines by just gliding to an airport? Would such a thing even work on the MAX design? Ah yes, here it is: https://en.wikipedia.org/wiki/Air_Transat_Flight_236 https://en.wikipedia.org/wiki/Air_Transat_Flight_236
- txcwpalpha 8y ago
  > Would such a thing even work on the MAX design? Yes, because the problem with the MAX is that the engines provide an off-center-of-gravity thrust. If the engines weren't running, the MAX would glide just like any other 737. There is also the case of the Gimli Glider [1], and any commercial airliner is certainly capable of "gliding" for at least some time, but I think the GP was adhering more to the actual definition of "glider" [2], which is an aircraft that can fly entirely without power from any engines at all. 1: https://en.wikipedia.org/wiki/Gimli_Glider https://en.wikipedia.org/wiki/Gimli_Glider 2: https://en.wikipedia.org/wiki/Glider_(aircraft) https://en.wikipedia.org/wiki/Glider_(aircraft)
  - ams6110 8y ago
    All jet airliners with engines under the wings have an "off-center-of-gravity" thrust. They all want to pitch up when thrust is applied. The MAX, with the engines higher and more forward, actually has less of an issue with this. The issue with the MAX is that the large engine nacelles forward of the wing can produce their own aerodynamic lift at high angles of attack. This is what MCAS compensates for.
- cal5k 8y ago
  Why would it not? You still have to be able to fly the thing in case of a dual engine failure. MCAS has one function: give the MAX 8 flight characteristics that are similar enough to previous versions to not require significant training. In fact, it's only when the engines are actually working that you'd need this... they're more powerful and further forward, meaning that at high thrust the aircraft will have more of a tendency to pitch up.
cmurf 8y ago
Transport category aircraft have a vast number of aerodynamic behaviors written in regulations, FAR 25. Approach to stall, stall, and stall recovery are described behaviors they must exhibit (FAR 25.201 - 25.207). Longitudinal static stability and dynamic stability are also defined (FAR 25.171 - 25.181). There is no such thing as certifying an aerodynamically unstable transport category aircraft. An open question I haven't yet been able to determine is to what degree software is an acceptable mediator to compel such behaviors. But I'm very skeptical that it's acceptable at all, let alone by something that can be intentionally disabled with two switches as a troubleshooting/override, and then also not require any difference training for the new behavior that ensues. Whether MCAS exists strictly for FAR 25 airworthiness, or to avoid a different type rating for the pilot under FAR 61.31 from any other 737, it's questionable how you get around either of those things once it's disabled on purpose as a emergency/troubleshooting technique. Which is worse upon setting STAB TRIM to cutoff? That the airplane isn't legally airworthy? Or that the pilot isn't legally type rated? Or even possibly both? And was either the case with the previous 737 models? Definitely not.

aunty_helen 8y ago

>Though the nose-pusher system's entire existence is due to the aerodynamic design of the entire MAX...which seems to be driven by the other 2 legs of the stool (i.e. budget and time). Sorry, but this isn't a credible comment. Modern engines run bigger slower fans to reduce fuel consumption and noise. Bigger engines don't fit under the wing. The engine fitment issue has been around since the 737 went from JT8D -> CFM56, hence the punched in the jaw look of most current non MAX 737s. New generation, bigger engines, same form factor. Sure they could've redesigned the half of the plane but then it's not really a 737.

bunderbunder 8y ago
> Sure they could've redesigned the half of the plane but then it's not really a 737. That is exactly the budget and time bit - lots of time and money for Boeing spent designing a new airframe, then the "not really a 737" part means lots more time and money spent by Boeing getting it certified, and lots of time and money for their customers in getting their pilots trained for the new plane.
dan678 8y ago
Isn't that the point? They attempted to save time and money by not designing a new aircraft (as they originally planned) and found a way to mount the new larger engines that necessitated the MCAS system. In addition, the solution they sold did not, by design, utilize both AoA sensors and did not advise pilots if the sensor disagree unless an additional package was purchased. Furthermore, all of this was in effort to sell an aircraft that would not need significant pilot re-training, resulting in pilots not being familiar enough with the failure mode that resulted in many deaths.
- aunty_helen 8y ago
  'Additionally, former Boeing CFO James Bell said during the company's second quarter 2011 earnings call, the research and development cost to Boeing to re-engine would be 10%-15% of the cost of a new airplane, which was at the time widely estimated by aerospace analysts to be $10-$12 billion' A factor of 10 cost difference 'if they had only done x' isn't realistic. Completely agree with your additional point though, the competition was the A320neo and the us vs them economics look better if you don't have to pay pilots to sit in a simulator and re cert. https://www.flightglobal.com/news/articles/boeing-disputes-737-max-development-cost-report-367504/ https://www.flightglobal.com/news/articles/boeing-disputes-7...