3 ms·

It doesn't refuse to disable. People are mixing this up with overriding control inputs. It is still possible to take MCAS out if the control loop using stab tri

It doesn't refuse to disable. People are mixing this up with overriding control inputs. It is still possible to take MCAS out if the control loop using stab trim cutout. However when left active it does override pilot inputs. Think of it as the alpha authority that exists on airbuses. However if you follow proper stab trim runaway procedures you cutout stab trim taking MCAS out which restores pilot authority. Again this procedure should be second nature to 737 pilots of any submodel. In your example, if there were adaptive cruise control, I would turn off cruise control by hitting the button. Same options are present here. However it does mean that braking or acceleration would be overriden until that happens. But the real analogy is if all drivers had to be trained that you turn off cruise control in runaway. If you don't do that, well then you will crash and it's from system failure AND improper general procedure

im_down_w_otp 7y ago
The example analog I chose is actually a thing, and hitting the button does nothing. The problem is in the design. Despite the fact that it's possible to defeat the failure in some instances (assuming it hopefully doesn't manifest itself too close to the disaster envelope to start with), the failure case 1) never should have happened and 2) shouldn't require unintuitive remediation. It's bad design and bad functional-safety analysis. Neither of which fall to the fleet operator or system operator.
- CorvusCrypto 7y ago
  Yes I agree. And I'm pleading that everyone also recognise the other aspects of these.incidents such as improper basic procedure. It's all of the above. Edit: And remember at the end of the day, these airlines and pilots agreed to fly the plane. Even in the wake of the LionAir incident. At the end of the day, the pilots choose to fly and can say no if they aren't comfortable. And if the answer to this is that there is pressure from airlines to keep flying? We just found another major issue and danger in aviation Edit2: should clarify actually that I agree it's a bad design. Not about the procedures being "unintuitive". If the pilots think the corrective procedures are unintuitive they shouldn't fly any 737 since stab trim systems exist on all 737s and require the same corrective procedure in runaway stab trim.
  - cmurf 7y ago
    Are you a pilot? If so what are your qualifications? Have you read the ET302 preliminary report? In particular have you read page 25, section 2 "Initial findings" last bullet which I quote: The crew performed runaway stabilizer checklist and put the stab trim cutout switch to cutout position and confirmed that the manual trim operation was not working. How can you read that, and say multiple times in this thread "improper procedure"? On what basis? You have no idea how much mental discipline it's taking me, as a pilot, to refrain from ad hominem attack. Your arguments are that bad, they are that willfully contrary to the available facts.
    - CorvusCrypto 7y ago
      I get it. I understand everyone's frustration. In similar fashion I understand how unlikely it is a crew would have the mental capacity to deal with stick shakers, GPWS callouts, and still fix the problem and that is the tragedy here. However the report said they followed proper procedure but look at the data. 95% N1, turning auto trim on and off a few times, the last time causing the huge -2G bump. There also is not enough data to us yet to determine they did regain control of the plane before enabling electric trim again. I don't think in the case of runaway trim you are supposed to keep switching the cutoff and leave your plane above Vmo. Something doesn't add up according to the data imo.
      - cmurf 7y ago
        This is such a bullshit response. You don't answer any of my questions. You proceed to armchair pilot. You use terms you cannot completely understand from a big picture yet claim to come at this from a big picture perspective. That's so out of order. Do you know a power reduction causes a nose down moment and actually makes the problem worse? What does "turning auto trim on and off" mean? Are you referring to the you're toggle it the stab trim switches flipped between normal and cutoff? If the latter you are wrong, zero evidence that happened a few times. There was no -2 G vertical acceleration. What you are doing is in my view a mental disturbance. You are using terms as if you know what you're talking about. You don't. You are a bullshitter. Please stop.
cmurf 7y ago
In the case of ET302, you are ignoring mistrim at high airspeed being essentially impossible to retrim manually (by handcrank). If they followed the runaway trim procedure exactly, and did not re-enable autotrim, they would have died, they were mistrimmed, decending, and with increasing airspeed. How do you propose they get out of that without enabling autotrim, in order to have the electric trim motor help them retrim? In the case of LNI610, you are assuming MCAS upset and approach to mistrim looks anything like runaway trim. There's quite a lot of evidence that it doesn't look like that, but is rather insidious.

im_down_w_otp 7y ago

The example analog I chose is actually a thing, and hitting the button does nothing. The problem is in the design. Despite the fact that it's possible to defeat the failure in some instances (assuming it hopefully doesn't manifest itself too close to the disaster envelope to start with), the failure case 1) never should have happened and 2) shouldn't require unintuitive remediation. It's bad design and bad functional-safety analysis. Neither of which fall to the fleet operator or system operator.

CorvusCrypto 7y ago
Yes I agree. And I'm pleading that everyone also recognise the other aspects of these.incidents such as improper basic procedure. It's all of the above. Edit: And remember at the end of the day, these airlines and pilots agreed to fly the plane. Even in the wake of the LionAir incident. At the end of the day, the pilots choose to fly and can say no if they aren't comfortable. And if the answer to this is that there is pressure from airlines to keep flying? We just found another major issue and danger in aviation Edit2: should clarify actually that I agree it's a bad design. Not about the procedures being "unintuitive". If the pilots think the corrective procedures are unintuitive they shouldn't fly any 737 since stab trim systems exist on all 737s and require the same corrective procedure in runaway stab trim.
- cmurf 7y ago
  Are you a pilot? If so what are your qualifications? Have you read the ET302 preliminary report? In particular have you read page 25, section 2 "Initial findings" last bullet which I quote: The crew performed runaway stabilizer checklist and put the stab trim cutout switch to cutout position and confirmed that the manual trim operation was not working. How can you read that, and say multiple times in this thread "improper procedure"? On what basis? You have no idea how much mental discipline it's taking me, as a pilot, to refrain from ad hominem attack. Your arguments are that bad, they are that willfully contrary to the available facts.
  - CorvusCrypto 7y ago
    I get it. I understand everyone's frustration. In similar fashion I understand how unlikely it is a crew would have the mental capacity to deal with stick shakers, GPWS callouts, and still fix the problem and that is the tragedy here. However the report said they followed proper procedure but look at the data. 95% N1, turning auto trim on and off a few times, the last time causing the huge -2G bump. There also is not enough data to us yet to determine they did regain control of the plane before enabling electric trim again. I don't think in the case of runaway trim you are supposed to keep switching the cutoff and leave your plane above Vmo. Something doesn't add up according to the data imo.
    - cmurf 7y ago
      This is such a bullshit response. You don't answer any of my questions. You proceed to armchair pilot. You use terms you cannot completely understand from a big picture yet claim to come at this from a big picture perspective. That's so out of order. Do you know a power reduction causes a nose down moment and actually makes the problem worse? What does "turning auto trim on and off" mean? Are you referring to the you're toggle it the stab trim switches flipped between normal and cutoff? If the latter you are wrong, zero evidence that happened a few times. There was no -2 G vertical acceleration. What you are doing is in my view a mental disturbance. You are using terms as if you know what you're talking about. You don't. You are a bullshitter. Please stop.

cmurf 7y ago

In the case of ET302, you are ignoring mistrim at high airspeed being essentially impossible to retrim manually (by handcrank). If they followed the runaway trim procedure exactly, and did not re-enable autotrim, they would have died, they were mistrimmed, decending, and with increasing airspeed. How do you propose they get out of that without enabling autotrim, in order to have the electric trim motor help them retrim? In the case of LNI610, you are assuming MCAS upset and approach to mistrim looks anything like runaway trim. There's quite a lot of evidence that it doesn't look like that, but is rather insidious.