6 ms·

0. They added software hack (keeping their cert) to use engines on a aircraft not desinged for them.

mlyle 7y ago
I strongly disagree with this one being a real link in the chain. OK, we put bigger engines on. The 737 is kinda already sporty and easy to get the nose too high on departure. Now it's a little worse with bigger engines. This is part and parcel for what happens when you stretch planes, adapt new engines, etc; there are minor, associated design changes you need to make to improve handling, etc. Software is a reasonable way to do it. The criticality of this was badly misunderstood and mis-characterized.
- jakeogh 7y ago
  Regarding the engines, indeed none of them would have crashed without MCAS.
  - mlyle 7y ago
    Sure, but 737's have crashed before from crews getting the nose too high on departure, so... arguably the entire 737 fleet would benefit from a "proper" MCAS. The people who built MCAS thought they were taming a 737 handling weakness that was worsened by the new engines. Again-- a normal kind of thing to have to work on when stretching jets.
    - jakeogh 7y ago
      Not stalling on takeoff is pilot 101. If an aircraft is prone to it I personally do not want layers of software hiding the issue. It's practically a law of nature that software is full of bugs.
      - mlyle 7y ago
        Better avoid Airbus, then, because there's a massive control law between the pilots and the actuators to create a "do what I mean" interface with envelope protection and all kinds of characteristics tamed. https://www.skybrary.aero/index.php/Flight_Control_Laws#Normal_Law https://www.skybrary.aero/index.php/Flight_Control_Laws#Norm... Boeing has mostly avoided that. MCAS is kind of an unusual form of control augmentation as far as Boeing is concerned.
        jakeogh 7y ago
        Thanks. I couldnt agree more. It would make sense if the bar was higher for adding control software than training pilots. To me it seems like the type cert problem was backwards.
        mlyle 7y ago
        In fairness, we've added a whole lot of automation since 1970, and most people think that increased automation has been a key factor in why aviation is so much safer overall. (Along with crew resource management). Automation definitely has directly killed people, though, too.
      - losvedir 7y ago
        > Not stalling on takeoff is pilot 101 So is trimming the stabilizer. Boeing was proven wrong by the two crashes but it's not a priori obvious that pilots wouldn't know to manually trim the stabilizer and then pull the cutout after MCAS kept kicking in.
        mlyle 7y ago
        Yah. If I'm holding massive backpressure on the yoke, my thumb is on the trim switch to ease that up.
        mantap 7y ago
        They were following Boeing's advice! Boeing said if MCAS misbehaves then pull the cutout. They did that but then they couldn't move the manual trim wheel because of the forces on the stabilizer. So they reenabled the electric trim, at which point MCAS jumped in again and everybody died.
        mlyle 7y ago
        They couldn't move the manual trim wheel because the plane had been allowed to overspeed. It was climbing at Vmo; they could have pulled back the power to not let the plane overspeed, rather than exceeding Vmo. Hopefully at Vmo they could move the trim wheel, but if not, they could wait until they had a few thousand feet more height, aerodynamically unloaded and trimmed. > So they reenabled the electric trim, at which point MCAS jumped in again and everybody died. They re-enabled the electric trim, and touched the electric trim switch a couple of times but left the plane far out of trim. I can't figure this out-- there's even an indicator that makes it obvious you're out of trim. Why re-enable electric trim and not really use it? Then after a timeout after they pushed the trim switch, MCAS jumped in again and everyone died.
        salawat 7y ago
        That's what you would do, you weren't there though, they were. Confronting a system whose implementation details were not well known, already two potential memory item checklists into the flight to the ground. It's easy now to point the finger and say "Airmanship" when you know the innards of the damn thing. They had one airworthyness directive, and maybe a grand total of five paragraphs in the entire manual, plus a memory item checklist that didn't accurately reflect the detail of an MCAS failure. An MCAS failure is not continuous uncommanded trim. It's discrete pulses, I appreciate the detail and effort, and you certainly speak as an experienced member of the industry; but pushing this off to the pilot's when there is so much that had to happen before the plane left the factory for them to be in that position is a bit much. There is whistleblower testimony that the decision to not implement a multi-sensor MCAS was intentional to avoid the financial consequences of having to have pilots put in simulator time. You can't sit here and say the pilots weren't good enough when the manufacturer went out of their way to make sure they could skulk a plane by regulators with the least amount of training humanly possible, safety be damned. To do so is not just mad, it's unconscionable. It's the very thing of insanity. A Catch-22 if I've ever heard one.
- x0x0 7y ago
  You seem quite knowledgeable. You disagree with the statement that roughly the urge to avoid recertifying pilots caused Boeing to not mention MCAS even in manuals, leading directly to these deaths? Because from my pov, Boeing introduced a new failure mode (MCAS failure leading to intermittent forcing of the nose down) without any warning to the pilots. Now maybe the pilots' standard training should have compensated, and there are obviously maintenance or training deficiencies, but Boeing also knew good and well they were selling planes to pilots with these existing training deficiencies. And should have designed a plane to be operated by real world pilots. Very curious for your thoughts; thank you!
  - mlyle 7y ago
    I disagree that deciding to stretch the 737 is fundamentally bad engineering. Yes, it realistically requires some control augmentation (and maybe earlier 737's should really have had something like MCAS, too). Yes, bigger engines and heavier 737's have the problem worse, but it isn't unreasonable to fix this with systems. I think there were failures across the board. The fundamental analysis of MCAS was flawed: it was much less reliable than was thought, and failures of it provided a much more difficult situation for pilots than anticipated. I suspect the analysis boiled down to "MCAS provides a little defense against getting the nose excessively high on departure; it shouldn't be necessary so no big deal if it fails. And the worst failure we can think of is like stabilator trim runaway, which everyone knows how to deal with." This was compounded by the fact that many developing countries do not require pilots to demonstrate they can deal with runaway trim as part of a checkride and recurring training. Not disclosing information about the system made the problem even worse-- and this is harder to attribute purely to being part of bad initial analysis. I do not understand some of the aircrew actions, even in retrospect. If I am fighting pulling the yoke back-- I am going to have my finger on the trim switch to try and get rid of those control forces, even before I am thinking about the problem. This would have inhibited MCAS and retrimmed the plane. I think that Boeing assumed that this would happen. I am lazy and would rather not have to tug the yoke so I use trim a lot. :P
    - x0x0 7y ago
      Just for clarity, I have no qualms about stretching the plane. It's building in a new control system and not telling the pilots about it that seems crazy to me. Thanks so much for your thoughts!

I strongly disagree with this one being a real link in the chain. OK, we put bigger engines on. The 737 is kinda already sporty and easy to get the nose too high on departure. Now it's a little worse with bigger engines. This is part and parcel for what happens when you stretch planes, adapt new engines, etc; there are minor, associated design changes you need to make to improve handling, etc. Software is a reasonable way to do it. The criticality of this was badly misunderstood and mis-characterized.

jakeogh 7y ago
Regarding the engines, indeed none of them would have crashed without MCAS.
- mlyle 7y ago
  Sure, but 737's have crashed before from crews getting the nose too high on departure, so... arguably the entire 737 fleet would benefit from a "proper" MCAS. The people who built MCAS thought they were taming a 737 handling weakness that was worsened by the new engines. Again-- a normal kind of thing to have to work on when stretching jets.
  - jakeogh 7y ago
    Not stalling on takeoff is pilot 101. If an aircraft is prone to it I personally do not want layers of software hiding the issue. It's practically a law of nature that software is full of bugs.
    - mlyle 7y ago
      Better avoid Airbus, then, because there's a massive control law between the pilots and the actuators to create a "do what I mean" interface with envelope protection and all kinds of characteristics tamed. https://www.skybrary.aero/index.php/Flight_Control_Laws#Normal_Law https://www.skybrary.aero/index.php/Flight_Control_Laws#Norm... Boeing has mostly avoided that. MCAS is kind of an unusual form of control augmentation as far as Boeing is concerned.
      - jakeogh 7y ago
        Thanks. I couldnt agree more. It would make sense if the bar was higher for adding control software than training pilots. To me it seems like the type cert problem was backwards.
        mlyle 7y ago
        In fairness, we've added a whole lot of automation since 1970, and most people think that increased automation has been a key factor in why aviation is so much safer overall. (Along with crew resource management). Automation definitely has directly killed people, though, too.
    - losvedir 7y ago
      > Not stalling on takeoff is pilot 101 So is trimming the stabilizer. Boeing was proven wrong by the two crashes but it's not a priori obvious that pilots wouldn't know to manually trim the stabilizer and then pull the cutout after MCAS kept kicking in.
      - mlyle 7y ago
        Yah. If I'm holding massive backpressure on the yoke, my thumb is on the trim switch to ease that up.
      - mantap 7y ago
        They were following Boeing's advice! Boeing said if MCAS misbehaves then pull the cutout. They did that but then they couldn't move the manual trim wheel because of the forces on the stabilizer. So they reenabled the electric trim, at which point MCAS jumped in again and everybody died.
        mlyle 7y ago
        They couldn't move the manual trim wheel because the plane had been allowed to overspeed. It was climbing at Vmo; they could have pulled back the power to not let the plane overspeed, rather than exceeding Vmo. Hopefully at Vmo they could move the trim wheel, but if not, they could wait until they had a few thousand feet more height, aerodynamically unloaded and trimmed. > So they reenabled the electric trim, at which point MCAS jumped in again and everybody died. They re-enabled the electric trim, and touched the electric trim switch a couple of times but left the plane far out of trim. I can't figure this out-- there's even an indicator that makes it obvious you're out of trim. Why re-enable electric trim and not really use it? Then after a timeout after they pushed the trim switch, MCAS jumped in again and everyone died.
        salawat 7y ago
        That's what you would do, you weren't there though, they were. Confronting a system whose implementation details were not well known, already two potential memory item checklists into the flight to the ground. It's easy now to point the finger and say "Airmanship" when you know the innards of the damn thing. They had one airworthyness directive, and maybe a grand total of five paragraphs in the entire manual, plus a memory item checklist that didn't accurately reflect the detail of an MCAS failure. An MCAS failure is not continuous uncommanded trim. It's discrete pulses, I appreciate the detail and effort, and you certainly speak as an experienced member of the industry; but pushing this off to the pilot's when there is so much that had to happen before the plane left the factory for them to be in that position is a bit much. There is whistleblower testimony that the decision to not implement a multi-sensor MCAS was intentional to avoid the financial consequences of having to have pilots put in simulator time. You can't sit here and say the pilots weren't good enough when the manufacturer went out of their way to make sure they could skulk a plane by regulators with the least amount of training humanly possible, safety be damned. To do so is not just mad, it's unconscionable. It's the very thing of insanity. A Catch-22 if I've ever heard one.
x0x0 7y ago
You seem quite knowledgeable. You disagree with the statement that roughly the urge to avoid recertifying pilots caused Boeing to not mention MCAS even in manuals, leading directly to these deaths? Because from my pov, Boeing introduced a new failure mode (MCAS failure leading to intermittent forcing of the nose down) without any warning to the pilots. Now maybe the pilots' standard training should have compensated, and there are obviously maintenance or training deficiencies, but Boeing also knew good and well they were selling planes to pilots with these existing training deficiencies. And should have designed a plane to be operated by real world pilots. Very curious for your thoughts; thank you!
- mlyle 7y ago
  I disagree that deciding to stretch the 737 is fundamentally bad engineering. Yes, it realistically requires some control augmentation (and maybe earlier 737's should really have had something like MCAS, too). Yes, bigger engines and heavier 737's have the problem worse, but it isn't unreasonable to fix this with systems. I think there were failures across the board. The fundamental analysis of MCAS was flawed: it was much less reliable than was thought, and failures of it provided a much more difficult situation for pilots than anticipated. I suspect the analysis boiled down to "MCAS provides a little defense against getting the nose excessively high on departure; it shouldn't be necessary so no big deal if it fails. And the worst failure we can think of is like stabilator trim runaway, which everyone knows how to deal with." This was compounded by the fact that many developing countries do not require pilots to demonstrate they can deal with runaway trim as part of a checkride and recurring training. Not disclosing information about the system made the problem even worse-- and this is harder to attribute purely to being part of bad initial analysis. I do not understand some of the aircrew actions, even in retrospect. If I am fighting pulling the yoke back-- I am going to have my finger on the trim switch to try and get rid of those control forces, even before I am thinking about the problem. This would have inhibited MCAS and retrimmed the plane. I think that Boeing assumed that this would happen. I am lazy and would rather not have to tug the yoke so I use trim a lot. :P
  - x0x0 7y ago
    Just for clarity, I have no qualms about stretching the plane. It's building in a new control system and not telling the pilots about it that seems crazy to me. Thanks so much for your thoughts!