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It's a bit more complicated than that even. The 737 was originally designed for a very different mission than it's being used for right now. If you find pictu

It's a bit more complicated than that even. The 737 was originally designed for a very different mission than it's being used for right now. If you find pictures of the original 737-200s they look very different from the MAX line of today. It was built in an era when it was assumed that 707 and soon after 747 class airliners would serve the hubs and then smaller 737s would serve the small regional airports. As such the 737 was designed with VERY low ground clearance such that it could offload without a ramp and generally be serviceable at these types of low infrastructure airports, hence the lack of wheel doors, the ovoid engine inlets and the generally low stance. Fast forward to today where airport infrastructure is much more developed and these small/medium size airliners are being pressed into front line service including intercontinental routes. The aircraft has changed drastically to accommodate these changes through the years, enough that it may be time for a clean sheet design. They've changed just about everything on the air-frame from the fuel load/cabin length/wing to the avionics to make this all work. Now, the other side of that coin is with systems. In theory this should be fine, but obviously isn't. It's hard to differentiate bandaids from regular systems and if either fails then safety is compromised. Obviously the amount of unnecessary systems should be minimized but as time goes on more systems WILL be added to gain the rewards of automation, which is a good thing. As such, we need to educate pilots on ALL of the systems, and rigorously test them before they enter service. Additionally, if you do as the pilots want and achieve very high aerodynamic stability through the air-frame instead of stability control systems (fly by wire essentially) it reduces the aerodynamic efficiency of the airliner, particularly with current conventional designs.

zanmat0 8y ago
>if you do as the pilots want and achieve very high aerodynamic stability through the air-frame instead of stability control systems (fly by wire essentially) it reduces the aerodynamic efficiency of the airliner It's crazy to me that that would be an acceptable compromise.
- AWildC182 8y ago
  How so? When I say stability control, we're not generally talking about unstable or "relaxed stability" airframes where the system failing would cause a pitching moment to accelerate rather than converge and the aircraft would tumble and disintegrate. From an efficiency and handling standpoint, this would be ideal, but it's only used in tactical military aircraft where the crew can bail if there's a problem. In most cases, we're talking about preventing stall in a swept wing aircraft. Swept wings are necessary to cruise efficiently beyond ~300mph at high altitude so they have to stay obviously, however they have VERY poor stall characteristics. As such, we have to do some things to prevent the aircraft from stalling such as playing with trim, using a stick pusher, etc.
  - mehrdadn 8y ago
    > Swept wings are necessary to cruise efficiently beyond ~300mph at high altitude Layman here, but 737, 747, etc. don't have swept wings, right? So they all cruise inefficiently... but are in fact stable... which is the opposite of what you wrote earlier? Sorry, I'm just really confused.
    - dragonwriter 8y ago
      > Layman here, but 737, 747, etc. don't have swept wings, right? They do, in fact, have swept wings.
    - stickfigure 8y ago
      You're picturing a fighter jet or something with severely swept wings. Do an image search - 737s, 747s, et al do indeed have gently swept back wings. They don't stick straight out at 90 degrees like aircraft from the piston era.
      - mehrdadn 8y ago
        Ohh I see, okay thanks.
        tpowell 8y ago
- anovikov 8y ago
  Obviously stability has to be achieved through fly by wire tech. Doing it through natural aerodynamic stability is a waste of resources of insane proportions as such airframes induce more drag and burn more fuel. If this sounds too scary for people in a forum of software developers it only puts a shame on our profession, from ourselves.
  - joe_the_user 8y ago
    No one knows better than software engineers how difficult it is to make inherently reliable software and how much complexity can add to the difficulty of making reliable software. That said, the cost of not using latest fuel efficient airplane would indeed be huge and the actual reliability of modern aircraft is very high and has been increasing over the years in which fuel efficiency also increased. Sometimes, human can hit on a formula that produces objects that satisfy all the given parameters more fully rather than compromising on any of the requirement. But it's quite plausible that these formulas cannot be milked forever - thus the "Max" may be the point where tradeoffs stop working.
    - cco 8y ago
      Could you clarify your assertion that it would be massively more expensive? A quick look at the numbers suggests that a 737 MAX 8 is about 10% more efficient on fuel burn compared to a 737 300. That is not "massive" in my book and I'm more than happy to pay a little bit more per ticket if it means a higher safety margin. Did you mean something older and less efficient than a 737 300?
  - edoloughlin 8y ago
    such airframes induce more drag and burn more fuel As a curious bystander, I assumed using fly by wire tech to achieve stability would involve using control surfaces, which increase drag by their nature. How would an airframe that's naturally stable and doesn't require control inputs burn more fuel?
    - AWildC182 8y ago
- namirez 8y ago
  Fly-by-wire means the control surface actuators are connected to cockpit controls electronically rather than with hydraulic lines or metal cables; it's not necessarily related to stability and control augmentation system. With regard to the other point, I don't think anyone is advocating for very high aerodynamic stability. That would be a B52 carrying nuclear weapons. It was designed to be extremely stable and forgiving. That being said, you don't want to rely solely on stability augmentation for trimming an airliner. It reminds me of Air Canada flight 143, the pilots lost both engines and power. yet they were able to land the plane safely on an abandoned airport. I'm not sure if that would be possible with a 737 Max.
  - sandworm101 8y ago
    Yes it would. There are backup systems to keep things working even with both engines dry (ram air turbine etc). In fact, if you really want to stretch our a glide, all those automated systems are probably a good things. They will keep the aircraft more perfectly trimmed for a glide than the pilots ever could by hand. https://en.wikipedia.org/wiki/Ram_air_turbine https://en.wikipedia.org/wiki/Ram_air_turbine
    - cududa 8y ago
      Yeah as long as the sensors actually work
    - StreamBright 8y ago
      And in case of the electrical system being down how do you control the flight when you have fly by wire controls?
      - zrobotics 8y ago
        If the electrical failure is severe enough to lose control authority, it seems just as likely that a hydraulic system would have failed. These planes are just too large to operate the controls mechanically, so in practice there is just as much to fail in a hydraulic system as electrical control, since both require power.
pasta 8y ago
Trump tweeted that planes have become too complicated and that the old and simple form is much better. His tweet sounds dumb but there is some truth in it. As you say, planes and procedures have become very complicated. And I think there are only two options: making planes simple again which make them less efficient or let computers fly the plane and make the interface simple(r). If you look at the rockets of SpaceX then you can say they are the extreme form of fly by wire and very instable when it comes to aerodynamics. But computers can land them within centimeters when they fall out of space. So maybe that will be the future. Planes that are very efficient instable flying 'rockets' that are controlled by computers.
- erokar 8y ago
  > His tweet sounds dumb but there is some truth in it. There really isn't. Automation is part of what has made flying safer over the years. Also, compare the cockpit of an Airbus with e.g. an old B737, the 300 series for instance. The Airbus cockpit is much simpler, in the sense that there are less gauges and knobs for the pilots to be concerned about. Automation has, over all, made things simpler and safer.
  - theoh 8y ago
    Citation needed, please. The most convincing popular article I've read on this topic is https://www.vanityfair.com/news/business/2014/10/air-france-flight-447-crash https://www.vanityfair.com/news/business/2014/10/air-france-... It's far from clear-cut that the way automation is happening is advisable, however conservative it might appear to be, and I'm sure you'd agree that there are many confounding variables that make it difficult to say just what is responsible for the trajectory of aircraft safety. There's not much of a control group of advanced modern aircraft which omit automated features.
  - deleted 8y ago
    [deleted]
StreamBright 8y ago
Are you saying that the lack of proper response to changed requirements is the primary source of 737MAX's issues?
- AWildC182 8y ago
  Maybe? Let me leave you with one other tidbit though. Beyond the requirements, airframe changes, and added electrical stuff, to fly the 737s you need a type rating and that rating is basically an education on all systems and procedures for the airframe. Boeing worked hard to make all aircraft from the 200 through the MAX fall under one type rating so if you get certified to fly an old low bypass 200, you can hop out, walk across the tarmac to a MAX and take off with another load of passengers. Obviously almost nobody runs the 200 anymore but the later aircraft are all still operated in some capacity and having one rating to rule them all makes it cheaper for small operators with mixed fleets to afford the training costs. In doing this, Boeing had to make the basic "UI" for the aircraft all the same, regardless of model. I'm not typed in the 737 but from what I've heard, it's resulted in a lot of user flow and documentation idiosyncrasies, particularly in the MAX lineup which could be part of the issue here. All that said, the trim motor disconnectors have been in the same place for most of the aircraft's history I'm told and hitting them would have likely prevented the Lion Air accident.
fnordprefect 8y ago
> the ovoid engine inlets The original design of the 737 did not have ovoid inlets. You can see regular circular nacelle inlets on the 737-100: https://secure.boeingimages.com/archive/Boeing-737-100-2JRSXLJHF87M.html https://secure.boeingimages.com/archive/Boeing-737-100-2JRSX... and on the 737-200 here: https://secure.boeingimages.com/Assets/V2/jrZYYwCXohU1rDmk4e2ZmPQKtlJfz26Fzwne5SfMNed5FYacKbauoFJ@zQ9jERvMC.kTM3RzuLZwYZUsHemcbfrLYYqyixr8DL3R46X5OvHwwekj9nKAPc@1UHDPQ1.l/b02a@W0kvLkwoMRT/PU3kQnbgHvQzWk6V/BI24872.jpg https://secure.boeingimages.com/Assets/V2/jrZYYwCXohU1rDmk4e... The ovoid inlet design was introduced with the 737-300, when the engine was changed to the CFM56.
- AWildC182 8y ago
  The ovoid engines were a result of high bypass engines being added on the 300. The low bypass turbines on the older models was much smaller. These were then removed on the max because the engine was mounted higher and further forward on a low profile pylon.

zanmat0 8y ago

>if you do as the pilots want and achieve very high aerodynamic stability through the air-frame instead of stability control systems (fly by wire essentially) it reduces the aerodynamic efficiency of the airliner It's crazy to me that that would be an acceptable compromise.

AWildC182 8y ago
How so? When I say stability control, we're not generally talking about unstable or "relaxed stability" airframes where the system failing would cause a pitching moment to accelerate rather than converge and the aircraft would tumble and disintegrate. From an efficiency and handling standpoint, this would be ideal, but it's only used in tactical military aircraft where the crew can bail if there's a problem. In most cases, we're talking about preventing stall in a swept wing aircraft. Swept wings are necessary to cruise efficiently beyond ~300mph at high altitude so they have to stay obviously, however they have VERY poor stall characteristics. As such, we have to do some things to prevent the aircraft from stalling such as playing with trim, using a stick pusher, etc.
- mehrdadn 8y ago
  > Swept wings are necessary to cruise efficiently beyond ~300mph at high altitude Layman here, but 737, 747, etc. don't have swept wings, right? So they all cruise inefficiently... but are in fact stable... which is the opposite of what you wrote earlier? Sorry, I'm just really confused.
  - dragonwriter 8y ago
    > Layman here, but 737, 747, etc. don't have swept wings, right? They do, in fact, have swept wings.
  - stickfigure 8y ago
    You're picturing a fighter jet or something with severely swept wings. Do an image search - 737s, 747s, et al do indeed have gently swept back wings. They don't stick straight out at 90 degrees like aircraft from the piston era.
    - mehrdadn 8y ago
      Ohh I see, okay thanks.
      - tpowell 8y ago
anovikov 8y ago
Obviously stability has to be achieved through fly by wire tech. Doing it through natural aerodynamic stability is a waste of resources of insane proportions as such airframes induce more drag and burn more fuel. If this sounds too scary for people in a forum of software developers it only puts a shame on our profession, from ourselves.
- joe_the_user 8y ago
  No one knows better than software engineers how difficult it is to make inherently reliable software and how much complexity can add to the difficulty of making reliable software. That said, the cost of not using latest fuel efficient airplane would indeed be huge and the actual reliability of modern aircraft is very high and has been increasing over the years in which fuel efficiency also increased. Sometimes, human can hit on a formula that produces objects that satisfy all the given parameters more fully rather than compromising on any of the requirement. But it's quite plausible that these formulas cannot be milked forever - thus the "Max" may be the point where tradeoffs stop working.
  - cco 8y ago
    Could you clarify your assertion that it would be massively more expensive? A quick look at the numbers suggests that a 737 MAX 8 is about 10% more efficient on fuel burn compared to a 737 300. That is not "massive" in my book and I'm more than happy to pay a little bit more per ticket if it means a higher safety margin. Did you mean something older and less efficient than a 737 300?
- edoloughlin 8y ago
  such airframes induce more drag and burn more fuel As a curious bystander, I assumed using fly by wire tech to achieve stability would involve using control surfaces, which increase drag by their nature. How would an airframe that's naturally stable and doesn't require control inputs burn more fuel?
  - AWildC182 8y ago
namirez 8y ago
Fly-by-wire means the control surface actuators are connected to cockpit controls electronically rather than with hydraulic lines or metal cables; it's not necessarily related to stability and control augmentation system. With regard to the other point, I don't think anyone is advocating for very high aerodynamic stability. That would be a B52 carrying nuclear weapons. It was designed to be extremely stable and forgiving. That being said, you don't want to rely solely on stability augmentation for trimming an airliner. It reminds me of Air Canada flight 143, the pilots lost both engines and power. yet they were able to land the plane safely on an abandoned airport. I'm not sure if that would be possible with a 737 Max.
- sandworm101 8y ago
  Yes it would. There are backup systems to keep things working even with both engines dry (ram air turbine etc). In fact, if you really want to stretch our a glide, all those automated systems are probably a good things. They will keep the aircraft more perfectly trimmed for a glide than the pilots ever could by hand. https://en.wikipedia.org/wiki/Ram_air_turbine https://en.wikipedia.org/wiki/Ram_air_turbine
  - cududa 8y ago
    Yeah as long as the sensors actually work
  - StreamBright 8y ago
    And in case of the electrical system being down how do you control the flight when you have fly by wire controls?
    - zrobotics 8y ago
      If the electrical failure is severe enough to lose control authority, it seems just as likely that a hydraulic system would have failed. These planes are just too large to operate the controls mechanically, so in practice there is just as much to fail in a hydraulic system as electrical control, since both require power.

pasta 8y ago

Trump tweeted that planes have become too complicated and that the old and simple form is much better. His tweet sounds dumb but there is some truth in it. As you say, planes and procedures have become very complicated. And I think there are only two options: making planes simple again which make them less efficient or let computers fly the plane and make the interface simple(r). If you look at the rockets of SpaceX then you can say they are the extreme form of fly by wire and very instable when it comes to aerodynamics. But computers can land them within centimeters when they fall out of space. So maybe that will be the future. Planes that are very efficient instable flying 'rockets' that are controlled by computers.

erokar 8y ago
> His tweet sounds dumb but there is some truth in it. There really isn't. Automation is part of what has made flying safer over the years. Also, compare the cockpit of an Airbus with e.g. an old B737, the 300 series for instance. The Airbus cockpit is much simpler, in the sense that there are less gauges and knobs for the pilots to be concerned about. Automation has, over all, made things simpler and safer.
- theoh 8y ago
  Citation needed, please. The most convincing popular article I've read on this topic is https://www.vanityfair.com/news/business/2014/10/air-france-flight-447-crash https://www.vanityfair.com/news/business/2014/10/air-france-... It's far from clear-cut that the way automation is happening is advisable, however conservative it might appear to be, and I'm sure you'd agree that there are many confounding variables that make it difficult to say just what is responsible for the trajectory of aircraft safety. There's not much of a control group of advanced modern aircraft which omit automated features.
- deleted 8y ago
  [deleted]

StreamBright 8y ago

Are you saying that the lack of proper response to changed requirements is the primary source of 737MAX's issues?

AWildC182 8y ago
Maybe? Let me leave you with one other tidbit though. Beyond the requirements, airframe changes, and added electrical stuff, to fly the 737s you need a type rating and that rating is basically an education on all systems and procedures for the airframe. Boeing worked hard to make all aircraft from the 200 through the MAX fall under one type rating so if you get certified to fly an old low bypass 200, you can hop out, walk across the tarmac to a MAX and take off with another load of passengers. Obviously almost nobody runs the 200 anymore but the later aircraft are all still operated in some capacity and having one rating to rule them all makes it cheaper for small operators with mixed fleets to afford the training costs. In doing this, Boeing had to make the basic "UI" for the aircraft all the same, regardless of model. I'm not typed in the 737 but from what I've heard, it's resulted in a lot of user flow and documentation idiosyncrasies, particularly in the MAX lineup which could be part of the issue here. All that said, the trim motor disconnectors have been in the same place for most of the aircraft's history I'm told and hitting them would have likely prevented the Lion Air accident.

fnordprefect 8y ago

> the ovoid engine inlets The original design of the 737 did not have ovoid inlets. You can see regular circular nacelle inlets on the 737-100: https://secure.boeingimages.com/archive/Boeing-737-100-2JRSXLJHF87M.html https://secure.boeingimages.com/archive/Boeing-737-100-2JRSX... and on the 737-200 here: https://secure.boeingimages.com/Assets/V2/jrZYYwCXohU1rDmk4e2ZmPQKtlJfz26Fzwne5SfMNed5FYacKbauoFJ@zQ9jERvMC.kTM3RzuLZwYZUsHemcbfrLYYqyixr8DL3R46X5OvHwwekj9nKAPc@1UHDPQ1.l/b02a@W0kvLkwoMRT/PU3kQnbgHvQzWk6V/BI24872.jpg https://secure.boeingimages.com/Assets/V2/jrZYYwCXohU1rDmk4e... The ovoid inlet design was introduced with the 737-300, when the engine was changed to the CFM56.

AWildC182 8y ago
The ovoid engines were a result of high bypass engines being added on the 300. The low bypass turbines on the older models was much smaller. These were then removed on the max because the engine was mounted higher and further forward on a low profile pylon.