8 ms·

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

by 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.
      - mikeash 8y ago
        Aerodynamically unstable aircraft cannot be flown purely by humans. They require a fly by wire system. The 737 is not fly by wire, thus we can pretty trivially conclude that the 737 is aerodynamically stable.
        pedrocr 8y ago
        That's pithy. MCAS is definitely fixing something.
        mikeash 8y ago
        Of course, but it’s not fixing aerodynamic instability.
        8y ago
  - sgc 8y ago
    "As long as" certainly does not translate to a judgment as to this particular plane's issues. It is a limit as to the type of instability I am fine with - ie safe - or at least not unsafe - instability. "I don't know" certainly does not translate to we don't know. Plenty of people know. That is FUD. The level of instability was absolutely known to the manufacturer and certifying agencies before delivery, and even before first flight. The reason why I said "appears to have been far less" is because the summaries of this instability I have read did not describe it as major, and even now, nobody is pointing to the instability as a significant issue. The issue is with how it has been dealt with. Until information comes to light contradicting the information known publicly so far, it is unreasonable for me to be afraid of something I have zero evidence is an issue when evidence to the contrary exists.
    - pedrocr 8y ago
      We are analyzing accidents that killed hundreds of people and most people are skeptical of Boeing and the FAA for the engineering and certification decisions they took. Saying "I don't know but surely better informed people were ok with this so it's fine" is well below most people's burden of proof. I'm not saying the plane is fatally flawed, I'm saying we don't know the fundamental things to have an opinion on that topic.
      - sgc 8y ago
        Since there is no evidence the problems you are bringing up are actually problems, even after a lot of information has been made public, I think it is more reasonable than not to presume the problem is where most everyone is looking for it. This does not seem to be a great mystery and a fix was already underway before the second accident. In the strict sense of the term, we the public will never know. The same people who built the plane will provide a fix, the same people who certified the plane will do so again, the same people who were flying them will do so again, and we will trust them or we won't. Some more people will have their eyes on it, but again, we still won't know. That is the way most science and technology works. Everyone has their small domain of expertise and must trust others in their own. Mistakes were made, and most mistakes look stupid/obvious on hindsight, but they don't negate the capacities of the parties involved. All car manufacturers have safety recalls extremely regularly and we don't make them out to be criminals, nor do we make the certifying agencies pariahs. I personally find it an exaggerated response to lose all trust in everyone involved - especially since new models of planes regularly have more accidents in their first few years of flight, because they are hard to make and they have bugs. It also seems unreasonable for me to criticize a manufacturer for taking economic/market concerns into account when historically even the largest manufacturers are on the verge of bankruptcy semi-regularly. Realistically, they must. At the same time this specific decision does not appear to have been the correct one, but I don't demonize them for making it and even at my most cynical, they obviously did not think people would be dying because of it.
  - throwanem 8y ago
    "Fly-by-wire" is a colloquialism for indirect, software-mediated control of an aircraft's control surfaces, whether to reduce pilot workload in some flight regimes, as with the 737 MAX 8, or to completely manage the aircraft's aerodynamics based on expressions of pilot intent made via cockpit control inputs, as with the last several generations of Airbus aircraft. Recent 737 models, including the MAX 8, make partial use of fly-by-wire systems, such as the MCAS that's elicited so many hot takes recently. Airbus aircraft, by comparison, make heavy use of fly-by-wire systems, and have for years. In terms of functionality, it's perhaps the single largest difference between their product line and Boeing's. On the other hand, the widebody 777 is the first Boeing product to go fully fly-by-wire, completely separating the pilots' control inputs from the aircraft's control surfaces in the way that all modern Airbus aircraft do. If fly-by-wire is the problem - if, as you seem to suspect, these systems exist to compensate for the inherent flaws of aircraft designs which otherwise would not be able to stay safely in the sky - then these Airbus models, and the 777, should have pretty rough safety records, shouldn't they? We should expect to see these other aircraft fail due to problems of the same sort as affected the 737 MAX 8's MCAS, right? Luckily, we don't actually need to expect anything in this case, because we have good information on the frequency, severity, and causes of airliner accidents more or less all over the world. Indeed, that information is so good, and so available, that it's a major scandal, and a fecund ground for conspiracy theories, in the rare case where it's not available, as with Malaysia Airlines flight 370. Thanks to that information, we know that the safest airliner on the planet, by flying hours, is the Airbus A340, which has not yet had a fatal accident. Second is the Boeing 777, which has seen only 541 fatalities in its almost quarter century of revenue service - and that's counting the 298 souls aboard MH 17, shot down five years ago over Ukraine. Both of these aircraft are about 25 years old. Both have full fly-by-wire control systems. And both are, by any measure, among the safest commercial airliners in the world. If fly-by-wire were intended to cover up for the deficiencies in basic aerodynamic design you seem to lump into the term "instability", is this the safety record you'd expect to see?
    - pedrocr 8y ago
      You're having a completely different discussion unrelated to what I wrote. Fly-by-wire doesn't imply an inherently unstable airframe.
  - bluGill 8y ago
    Disabling the system is a possibility, but then they have to train all pilots to fly the plane without that system. Of course there is no training program in place, it would only take a few months to design it, then a few more to get the program certified as enough, then a few more months to teach the trainers how to teach it, then teach the pilots... It is much faster to fix the system once and for all.
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.

by pron 8y ago

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.
    - mikeash 8y ago
      Aerodynamically unstable aircraft cannot be flown purely by humans. They require a fly by wire system. The 737 is not fly by wire, thus we can pretty trivially conclude that the 737 is aerodynamically stable.
      - pedrocr 8y ago
        That's pithy. MCAS is definitely fixing something.
        mikeash 8y ago
        Of course, but it’s not fixing aerodynamic instability.
        8y ago
- sgc 8y ago
  "As long as" certainly does not translate to a judgment as to this particular plane's issues. It is a limit as to the type of instability I am fine with - ie safe - or at least not unsafe - instability. "I don't know" certainly does not translate to we don't know. Plenty of people know. That is FUD. The level of instability was absolutely known to the manufacturer and certifying agencies before delivery, and even before first flight. The reason why I said "appears to have been far less" is because the summaries of this instability I have read did not describe it as major, and even now, nobody is pointing to the instability as a significant issue. The issue is with how it has been dealt with. Until information comes to light contradicting the information known publicly so far, it is unreasonable for me to be afraid of something I have zero evidence is an issue when evidence to the contrary exists.
  - pedrocr 8y ago
    We are analyzing accidents that killed hundreds of people and most people are skeptical of Boeing and the FAA for the engineering and certification decisions they took. Saying "I don't know but surely better informed people were ok with this so it's fine" is well below most people's burden of proof. I'm not saying the plane is fatally flawed, I'm saying we don't know the fundamental things to have an opinion on that topic.
    - sgc 8y ago
      Since there is no evidence the problems you are bringing up are actually problems, even after a lot of information has been made public, I think it is more reasonable than not to presume the problem is where most everyone is looking for it. This does not seem to be a great mystery and a fix was already underway before the second accident. In the strict sense of the term, we the public will never know. The same people who built the plane will provide a fix, the same people who certified the plane will do so again, the same people who were flying them will do so again, and we will trust them or we won't. Some more people will have their eyes on it, but again, we still won't know. That is the way most science and technology works. Everyone has their small domain of expertise and must trust others in their own. Mistakes were made, and most mistakes look stupid/obvious on hindsight, but they don't negate the capacities of the parties involved. All car manufacturers have safety recalls extremely regularly and we don't make them out to be criminals, nor do we make the certifying agencies pariahs. I personally find it an exaggerated response to lose all trust in everyone involved - especially since new models of planes regularly have more accidents in their first few years of flight, because they are hard to make and they have bugs. It also seems unreasonable for me to criticize a manufacturer for taking economic/market concerns into account when historically even the largest manufacturers are on the verge of bankruptcy semi-regularly. Realistically, they must. At the same time this specific decision does not appear to have been the correct one, but I don't demonize them for making it and even at my most cynical, they obviously did not think people would be dying because of it.
- throwanem 8y ago
  "Fly-by-wire" is a colloquialism for indirect, software-mediated control of an aircraft's control surfaces, whether to reduce pilot workload in some flight regimes, as with the 737 MAX 8, or to completely manage the aircraft's aerodynamics based on expressions of pilot intent made via cockpit control inputs, as with the last several generations of Airbus aircraft. Recent 737 models, including the MAX 8, make partial use of fly-by-wire systems, such as the MCAS that's elicited so many hot takes recently. Airbus aircraft, by comparison, make heavy use of fly-by-wire systems, and have for years. In terms of functionality, it's perhaps the single largest difference between their product line and Boeing's. On the other hand, the widebody 777 is the first Boeing product to go fully fly-by-wire, completely separating the pilots' control inputs from the aircraft's control surfaces in the way that all modern Airbus aircraft do. If fly-by-wire is the problem - if, as you seem to suspect, these systems exist to compensate for the inherent flaws of aircraft designs which otherwise would not be able to stay safely in the sky - then these Airbus models, and the 777, should have pretty rough safety records, shouldn't they? We should expect to see these other aircraft fail due to problems of the same sort as affected the 737 MAX 8's MCAS, right? Luckily, we don't actually need to expect anything in this case, because we have good information on the frequency, severity, and causes of airliner accidents more or less all over the world. Indeed, that information is so good, and so available, that it's a major scandal, and a fecund ground for conspiracy theories, in the rare case where it's not available, as with Malaysia Airlines flight 370. Thanks to that information, we know that the safest airliner on the planet, by flying hours, is the Airbus A340, which has not yet had a fatal accident. Second is the Boeing 777, which has seen only 541 fatalities in its almost quarter century of revenue service - and that's counting the 298 souls aboard MH 17, shot down five years ago over Ukraine. Both of these aircraft are about 25 years old. Both have full fly-by-wire control systems. And both are, by any measure, among the safest commercial airliners in the world. If fly-by-wire were intended to cover up for the deficiencies in basic aerodynamic design you seem to lump into the term "instability", is this the safety record you'd expect to see?
  - pedrocr 8y ago
    You're having a completely different discussion unrelated to what I wrote. Fly-by-wire doesn't imply an inherently unstable airframe.
- bluGill 8y ago
  Disabling the system is a possibility, but then they have to train all pilots to fly the plane without that system. Of course there is no training program in place, it would only take a few months to design it, then a few more to get the program certified as enough, then a few more months to teach the trainers how to teach it, then teach the pilots... It is much faster to fix the system once and for all.

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.