Mansfield, #42,
Your points about the AoA vane are well made. However for the complete picture it would be necessary to compare vane failure ‘rates’ between NG and MAX. Short of that, 3 failures so early in a new aircraft’s life is suspicious, but not beyond probability.
Whilst the weight of evidence points towards the vane, we should not forget wiring.
As for crew procedures, the use of the trim runaway drill was a hasty response to an accident. With hindsight it appears very inadequate, e.g. use of autopilot, which is very important for trim runaway, but less so for MCAS.
We should not blame crews for not following any checklist, for as much as the industry overly depends on crews being able to manage ‘all’ abnormal situations, so too that they will follow procedures - a grossly misused assumption.
For the human factors (cognitive) aspects, because we cannot know what the crew perceived and deduced, all that should be concluded is that a crew acted as they saw the situation at that time, with all of the confusing inputs, alerts and distractions, which now ‘we’ cannot comprehend - thats our limitation not the crew’s.
There is growing weight of argument that with trim already offset, then neither electric or wheel will be effective - speed dependant, note the ‘equivalent safety case’.
A simplified overview of the situation / dilemma (with hindsight) - from alf above.
With incorrect MACAS operation using yoke trim before selecting trim cutout would loose the battle with MCAS 10 to 5 against (misleading procedure - ‘can be used’).
Using manual trim wheel after trim cutout, then the (one) pilot might be unable to restore trim to give an acceptable stick force for the other pilot, as speed and trim ineffectiveness increase.
Thus there is a finely balanced point where cutout is used and aircraft trim can be recovered, or after cutout it is unlikely that the aircraft can be controlled. The first Lion flight was the ‘right’ side of the line - three crew, the second Lion flight understandably not so.
Others have argued a range of scenarios for switching and trim operation re fdr; we don’t know, we might only deduce. The important aspect for aircraft control is what the tail did, not that a switch was operated.
Re crews’ recording technical issues; this could be influenced by the widely used electronic log and self test - are there manufacturer’s recommendations re this (or sales pitch); compare with other operators.
I would not oppose your final suspicions, but suggest that they might better be phrased as a worldwide industry issue, and less interpretable as applying to particular operators.