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Didn't the crew save the airplane because there was a third person there to help manually trim as the force required was too much for two people alone, whilst a

Didn't the crew save the airplane because there was a third person there to help manually trim as the force required was too much for two people alone, whilst also having to pull back on the yoke with massive force? That means it was dumb luck (a third person being there) and not due to following procedures if those procedures are nearly impossible to follow, or require superhuman strength.

sokoloff 7y ago
No; the third crew member on prior Lion Air flight (043) is the one who diagnosed the issue as runaway trim and cued the flight crew to execute that checklist. I've read nothing to suggest that they participated physically in the response (despite having read quite a bit on the topic). The excessive force on the trim required in the Ethiopian Air case was a consequence of the crew leaving the engines at high power, the trim having run farther nose down, and the elevator being held nose up, resulting in loading the horizontal stabilizer thus making the trim difficult to move. (Though I'm critical of their decision to restore and leave power to the trim system without commanding aircraft-nose-up after correctly diagnosing runaway trim, I don't really fault them for leaving excessive power in. That's a reasonable response to the initial indications and by the later time they realized it was a trim issue, they were pretty well loaded up struggling with the airplane that was well out of trim, so undoing their thrust command [which would typically result in a descent that they didn't want/couldn't afford] probably isn't reasonable to expect.)
- chopin 7y ago
  One should however mention that the failing sensor gave an "unreliable airspeed" warning. The checklist for that requires a designated power setting as well as a designated pitch for which the airspeed is known for the altitude. Afaik the pilots executed that checklist at least for the power setting part before moving to the stab trim runaway memory item. The failing AoA sensor triggered several checklists to work on. From an armchair perspective a checklist for AoA sensor failure would have been required for the flight to end safely (maybe with "cutoff stab trim" on the list).
  - salawat 7y ago
    This would have been complicating in Boeing's attempt to get the plane certified without simulator training, as it would have raised inconvenient questions as to why a previously non-safety-critical sensor suddenly needed a checklist, which would have kicked off a chain of very difficult and expensive to remediate questions upon a more in-depth, impartial design review.

sokoloff 7y ago

No; the third crew member on prior Lion Air flight (043) is the one who diagnosed the issue as runaway trim and cued the flight crew to execute that checklist. I've read nothing to suggest that they participated physically in the response (despite having read quite a bit on the topic). The excessive force on the trim required in the Ethiopian Air case was a consequence of the crew leaving the engines at high power, the trim having run farther nose down, and the elevator being held nose up, resulting in loading the horizontal stabilizer thus making the trim difficult to move. (Though I'm critical of their decision to restore and leave power to the trim system without commanding aircraft-nose-up after correctly diagnosing runaway trim, I don't really fault them for leaving excessive power in. That's a reasonable response to the initial indications and by the later time they realized it was a trim issue, they were pretty well loaded up struggling with the airplane that was well out of trim, so undoing their thrust command [which would typically result in a descent that they didn't want/couldn't afford] probably isn't reasonable to expect.)

chopin 7y ago
One should however mention that the failing sensor gave an "unreliable airspeed" warning. The checklist for that requires a designated power setting as well as a designated pitch for which the airspeed is known for the altitude. Afaik the pilots executed that checklist at least for the power setting part before moving to the stab trim runaway memory item. The failing AoA sensor triggered several checklists to work on. From an armchair perspective a checklist for AoA sensor failure would have been required for the flight to end safely (maybe with "cutoff stab trim" on the list).
- salawat 7y ago
  This would have been complicating in Boeing's attempt to get the plane certified without simulator training, as it would have raised inconvenient questions as to why a previously non-safety-critical sensor suddenly needed a checklist, which would have kicked off a chain of very difficult and expensive to remediate questions upon a more in-depth, impartial design review.