Originally Posted by
Ian W
As stated by SystemsNerd, the human cognition has limitations and foibles that many people are unaware of. One of these is the limited number of 'cognitive channels' also known as multiple resource theory. (see papers by Christopher Wickens and Erik Hollnagel) Simply you cannot read this posting and recite a something you have learned like NNC memory items at the same time - both use verbal cognition - if you are reading and someone says something you may hear them but you will not understand what they said and you will stop reading and ask them to repeat what they said. If you have to read, talk and listen at the same time you can only really do one at a time (we have all had to read a paragraph again as we stopped understanding what we were reading and listened instead).
So if you are running through memory items of an NNC - and you read the EICAS you may miss NNC items or not understand the EICAS - if the PM is shouting at you it may just be noise - if there is sufficient noise that channel stops completely and you do not even hear/comprehend the PM or that cavalry charge.
Mixed into this is the effect of the level of stress/alertness. This is normally referred to as an 'inverted U'.
from MindTools.com
So when you are bored with low stress your performance is actually poor, A little pressure / stress and your performance is ideal, but too much high stress and your performance will drop off rapidly.
Putting all that into an aviation perspective, A well trained pilot with experience of things going pear shaped and operating under pressure will not feel so much stress and concentrate on one item at a time and a lot of what will be done will be (what is called here ) muscle memory - innate training like stamping on a brake or steering a bike to stay balanced - or trimming an aircraft - it requires no thought as it is second nature. This is the importance of training - with not so much training it is easy to get into the overstressed very low performance state and 'get behind the aircraft'. The more inputs you are given the higher the stress and the less you are able to process and the normal human reaction to that is what is known as attentional or cognitive tunneling - a concentration on one aspect of what is happening that you _do_ think you can control and a total disregard of anything else. Everyone is different in this regard and the only way to avoid getting into the wrong side of the U is training, repeated training to get that muscle memory. Unfortunately, there is always a beancounter standing in the way of that.
I would like to see a stick shaker attached to a judges chair and then watch him make some complicated judgement with all that racket and distraction going on, but he won't die if he gets it wrong.
Where the MCAS trim runaway becomes difficult to deal with is it's transient nature, kind of like a partial engine failure in a single, oh, the engine has died, ok look for a landing area, good, got that, oh it's going again, so I'll turn a 180 and try to head back to the strip, oh no, it's failed again, now where was that grassy field, but if it was a straight out constant trim runaway, it would most likely have been caught sooner as there was training for that scenario.