4 ms·

737MAX: Trim Cutout can be difficult to recover

13 points by themgt 8y ago

dboreham 8y ago
My thoughts as someone with not much aerospace engineering knowledge: FFS why on earth should it be so hard to just keep an airframe in controlled flight under benign weather and mechanical conditions?? Isn't this the equivalent of expecting my Mom to know to reboot her car's engine management computer in order to be able to steer away from an oncoming brick wall? I guess I find it astonishing that this kind of mid flight debugging is even considered viable as an approach by the industry. Are they inspired by Armstrong's manual override feats on the Apollo 11 landing descent?
- cjbprime 8y ago
  In theory, nothing here is obscure. Trim is a control that airplanes have that cars don't. It's a very basic control, it's right there on the control column. A mechanical or computer failure could cause the plane to mistrim itself, so one of the most basic emergency responses that every airliner pilot knows is how to disable the auto-trim and fix it manually. MCAS is a new way for mistrim to happen, but there were already many others before. It sounds like the main issue is that Boeing didn't predict that MCAS would mistrim at such low altitude that you don't have time to disable the trim motor and perform the recovery before the ground intervenes.
  - miketery 8y ago
    > nothing here is obscure Boeing chose to have the indicators that show the trim is on as a separate add on, not as a default feature (i.e. an indicator showing the trim is enabled). This is beyond unsafe, and unethical by all measures. For a car it would be like having cruise control turn on automatically and accelerating (without telling you), and worse yet, when you brake to try to control your speed, it doesn't disable or do anything (pulling on the steering column did nothing). To disable you need to do something totally different (which is unnatural for a human). I hope this error is costly to Boeing, and that the FAA learns from this experience. This should have never been certified.
    - cjbprime 8y ago
      > Boeing chose to have the indicators that show the trim is on as a separate add on, not as a default feature (i.e. an indicator showing the trim is enabled). This is nonsense. The optional light was just an AoA disagree sensor. It doesn't provide any information about trim.

13 points by themgt 8y ago

My thoughts as someone with not much aerospace engineering knowledge: FFS why on earth should it be so hard to just keep an airframe in controlled flight under benign weather and mechanical conditions?? Isn't this the equivalent of expecting my Mom to know to reboot her car's engine management computer in order to be able to steer away from an oncoming brick wall? I guess I find it astonishing that this kind of mid flight debugging is even considered viable as an approach by the industry. Are they inspired by Armstrong's manual override feats on the Apollo 11 landing descent?

cjbprime 8y ago
In theory, nothing here is obscure. Trim is a control that airplanes have that cars don't. It's a very basic control, it's right there on the control column. A mechanical or computer failure could cause the plane to mistrim itself, so one of the most basic emergency responses that every airliner pilot knows is how to disable the auto-trim and fix it manually. MCAS is a new way for mistrim to happen, but there were already many others before. It sounds like the main issue is that Boeing didn't predict that MCAS would mistrim at such low altitude that you don't have time to disable the trim motor and perform the recovery before the ground intervenes.
- miketery 8y ago
  > nothing here is obscure Boeing chose to have the indicators that show the trim is on as a separate add on, not as a default feature (i.e. an indicator showing the trim is enabled). This is beyond unsafe, and unethical by all measures. For a car it would be like having cruise control turn on automatically and accelerating (without telling you), and worse yet, when you brake to try to control your speed, it doesn't disable or do anything (pulling on the steering column did nothing). To disable you need to do something totally different (which is unnatural for a human). I hope this error is costly to Boeing, and that the FAA learns from this experience. This should have never been certified.
  - cjbprime 8y ago
    > Boeing chose to have the indicators that show the trim is on as a separate add on, not as a default feature (i.e. an indicator showing the trim is enabled). This is nonsense. The optional light was just an AoA disagree sensor. It doesn't provide any information about trim.