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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

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.
        pedrocr 8y ago
        How does that change anything? If the instability is not aerodynamic and instead is runaway pitch up on power, how is that any different?
        mikeash 8y ago
        You keep insisting that we don’t know if this airplane is unstable. My point is that we do know. If you want to argue that some other aspect of it makes it equally dangerous, be my guest. I’m just correcting that one thing.
        pedrocr 8y ago
        >You keep insisting that we don’t know if this airplane is unstable. Because we don't. You've only corrected a strawman, that we know this plane isn't a fully aerodynamic unstable design like an F-16. No one thought that. I never even specifically said aerodynamically unstable, just that we don't know the level of instability MCAS is correcting for to know if it is unusual for an airliner design. From what I had read I had assumed it was actually a power-on issue and not aerodynamic. But as it turns out the issue is indeed apparently aerodynamic from the engine shape generating more lift at higher angle of attack and thus leading to pitch up. And no, we don't know. We the public at least. We don't know how big the flight envelope is where MCAS is needed or how much of an issue it would be if MCAS didn't exist. From public information we don't know if without MCAS the plane wouldn't enter an unrecoverable pitch up attitude in normal flying conditions. That's not knowing if the plane isn't inherently unstable.
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.

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.
      - pedrocr 8y ago
        How does that change anything? If the instability is not aerodynamic and instead is runaway pitch up on power, how is that any different?
        mikeash 8y ago
        You keep insisting that we don’t know if this airplane is unstable. My point is that we do know. If you want to argue that some other aspect of it makes it equally dangerous, be my guest. I’m just correcting that one thing.
        pedrocr 8y ago
        >You keep insisting that we don’t know if this airplane is unstable. Because we don't. You've only corrected a strawman, that we know this plane isn't a fully aerodynamic unstable design like an F-16. No one thought that. I never even specifically said aerodynamically unstable, just that we don't know the level of instability MCAS is correcting for to know if it is unusual for an airliner design. From what I had read I had assumed it was actually a power-on issue and not aerodynamic. But as it turns out the issue is indeed apparently aerodynamic from the engine shape generating more lift at higher angle of attack and thus leading to pitch up. And no, we don't know. We the public at least. We don't know how big the flight envelope is where MCAS is needed or how much of an issue it would be if MCAS didn't exist. From public information we don't know if without MCAS the plane wouldn't enter an unrecoverable pitch up attitude in normal flying conditions. That's not knowing if the plane isn't inherently unstable.

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.