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My understanding is that the recovery scenario wasn’t supposed to be complicated at all, because in the event of a MCAS failure, it would always manifest as a r

by Cacti 8y ago

My understanding is that the recovery scenario wasn’t supposed to be complicated at all, because in the event of a MCAS failure, it would always manifest as a runaway trim scenario, and that pilots are trained heavily on recognizing as correcting for that scenario, and that by following the standard runaway trim solution/checklist/process that this would necessarily involve disabling MCAS whether the pilots were aware of it or not. So the question is, did they, and if so did this fail, and if not, why didn’t they? Is this actually a direct problem with MCAS or is it closer to an issue of basic pilot training that only happened to involve MCAS? I suspect as the investigations unfold that our understanding of the accidents is only going to get more complex and nuanced.

ncallaway 8y ago
One significant problem as I understand it was the assumption that a failing MCAS would present as runaway stabilizer trim. When, in actuality, it may not have looked much like runaway stabilizer trim to the pilots. My understanding is in a runaway stabilizer trim situation the trim wheel (a medium sized wheel near the pilot and co-pilots knees) spins continuously and makes a loud clacking noise as part of the spinning. This makes runaway stabilizer trim easy to identify. The wheel is spinning (for no identifiable reason) and making noise. The MCAS failure, however applies trim discretely with intervals of 10-20s. This means it might be very hard to spot the adjustments to the trim wheel if you glance down briefly. A pilot might notice the control column is heavy, glance down to see if it's runaway trim see the wheel not moving, rule out that scenario and move on to other diagnostic steps.
- AceyMan 8y ago
  NB. It seems this moment news is breaking that the Ethiopia pilots indeed followed the checklist — yet they still lost the airplane. This is getting worse for Boeing at every turn.
  - Cacti 8y ago
    Well, it sounds like they turned off the autopilot but then turned it back on, which is not part of the checklist. It’s not clear from the reporting exactly what happened and I would hesitate to jump to conclusions. Accidents like this are almost always hugely complicated and are the result of many things going wrong in a specific order at a specific time, rather than a single factor. In fact we don’t even know what the cause of the crash was, and we won’t actually know for several months—there have been a number of crashes where everyone “knew” what the cause was early on, only for it later to come to light that is was something completely unrelated.

by Cacti 8y ago

ncallaway 8y ago

One significant problem as I understand it was the assumption that a failing MCAS would present as runaway stabilizer trim. When, in actuality, it may not have looked much like runaway stabilizer trim to the pilots. My understanding is in a runaway stabilizer trim situation the trim wheel (a medium sized wheel near the pilot and co-pilots knees) spins continuously and makes a loud clacking noise as part of the spinning. This makes runaway stabilizer trim easy to identify. The wheel is spinning (for no identifiable reason) and making noise. The MCAS failure, however applies trim discretely with intervals of 10-20s. This means it might be very hard to spot the adjustments to the trim wheel if you glance down briefly. A pilot might notice the control column is heavy, glance down to see if it's runaway trim see the wheel not moving, rule out that scenario and move on to other diagnostic steps.

AceyMan 8y ago
NB. It seems this moment news is breaking that the Ethiopia pilots indeed followed the checklist — yet they still lost the airplane. This is getting worse for Boeing at every turn.
- Cacti 8y ago
  Well, it sounds like they turned off the autopilot but then turned it back on, which is not part of the checklist. It’s not clear from the reporting exactly what happened and I would hesitate to jump to conclusions. Accidents like this are almost always hugely complicated and are the result of many things going wrong in a specific order at a specific time, rather than a single factor. In fact we don’t even know what the cause of the crash was, and we won’t actually know for several months—there have been a number of crashes where everyone “knew” what the cause was early on, only for it later to come to light that is was something completely unrelated.