CONF iture;
I believe it is worth questioning WHAT in the Airbus thrust management conception makes that a crew is more prone to demonstrate this kind of ''temporary insanity'' ?
I think the question you ask is a very good one.
Restated, the question being asked is: "What is different about the A320-type thrust management/thrust lever system that would/could cause a change ('more prone to') in pilot behaviour?"
I would like to explore this question. The main assumption I make is, when the airplane is flown within its certification boundaries and when in manual flight (
the obvious 'default' condition should pilot confusion arise), aircraft control is entirely ordinary and traditional and should not be second-guessed or out-thought.
I think the question is one of erroneous perception that the Airbus autothrust system is 'more complex' than other aircraft and doesn't work like "traditional" aircraft and that this mistake in understanding leads crews to either subtlely second-guess or sub-conciously out-think what is, when disconnected, an ordinary thrust control system. I think this error in understanding extends to thrust-lever handling when reversers are MEL'd and locked out.
When disconnected, there are no technical reasons for thinking/believing that the autothrust system is somehow different than other systems such that pilot behaviours should be somehow modified, so the matter is one of perception and understanding, not one of additional or obscure technical complexity.
When under manual control, there is no more complexity in the A320 thrust control system than is to be found on any other manufacturer's system. The A320's thrust levers work in entirely traditional ways when under manual control but I think that many pilots mistakenly believe otherwise even when disconnected; they believe that automation is 'always there, mediating pilot input', making the assumption that because the system control is not as transparent as other aircraft that it 'may' be interfering with or modifying pilot input.
The question of
difference references, by comparison, more "traditional" throttle/thrust lever arrangements. The main physical difference which has been pointed out is that the A320 thrust levers "do not move", (are not back-driven). The implied expectation and therefore problem for pilots is that moving levers indicate what the autothrust system is doing while non-moving levers do not.
The counter-example is, however, with some exceptions on an auto-coupled approach, (CATII, etc) in later generations of DC8/B707, non-moving thrust levers were standard on first and second generation transports, with no incidents caused thereby.
So why is the A320's autothrust system the focus of so much disagreement?
There is no disagreement that the A320 concept is, when under fully-automated flight, more complex than what we have seen as 'solutions' from other manufacturers. It takes longer to understand the airplane and 'wear it' such that it is second-nature. Usually that time period is at least one year if not more.
And as always is the case, if training is parsimonious or provided through processes which are poorly designed or poorly informed about the A320 automation systems, the results will reflect lack of comprehension and where that is permitted to occur, the resulting vacuum will be filled with mythologies, misperceptions and genuinely mistaken understanding of the airplane and its complexities. It necessarily goes without saying that despite such complexities the fatal accident record of the type is not an outlier and is instead about the same as equivalent types of other manufacturers.
But, except at the boundaries of certified flight, the airplane and the autothrust system are entirely ordinary and traditional when under manual pilot control. That is a fact, not a perception; the A320/A330/A340 series are as ordinary to fly as a DC8 or B727, etc.
Given this fact but given also the fact that there remain disagreements and even complaints, it makes sense to ask your question then, Why?, if the airplane flies 'ordinarily' like any other transport when manually-flown.
Why would an experienced crew leave one thrust lever (of the engine on which the reverser was locked out), in the CLB position and retard just the other thrust lever? Why, when the system behaves in a completely ordinary manner would not both thrust levers be retarded just as every other transport aircraft requires?
I think the answer may at least partially be found in the theory above - that pilots somehow assume that the system is 'different' and require different handling. I think this is the case because there is the notion that, because of the '
perceived veil of automation', they don't know what will happen if they treat it 'ordinarily', and thus assumptions and therefore behaviour, changes.
Edit;
As I re-read all this, I would like to make my intentions clear that I am focussing on natural misperceptions which may emerge due to a perceived 'mystique' about the type. I am neither focussing on 'blame' (of pilots for not understanding the airplane) nor inabilities of crews to fly the airplane.
I am trying to flesh out an answer to an important, perennial and relevant question which is partially human-factors, partially-design driven but mostly based upon the fundamental need, despite the "marketing of automation to airline managements" and the notion that the airplane "flies itself", of a clear and robust pilot-training and checking regime.
I think the accident record shows that this is already largely the case but mythologies, misapprehensions and which cause mistakes in handling have not gone away and I am trying to conceive of a different approach as to why.
This all acknowledged, we have the example of the THY B737 at AMS as a counter-example that even simple systems with moving thrust levers do not resolve the automation issues raised in this discussion.
PJ2