Originally Posted by Austrian Simon
KISS in combination with human psychology means, that the system should only assume the last command given by the human as valid, and disregard any conflicting earlier commands.
Now where does that come from?
I share PBL's sentiment.
If you want to voice your opinion, to which you are entitled, it is a good idea first to get the facts straight. I'll point out
some of the numerous factual errors in your post. There are others.
In this particular accident the last commands given to the systems were by autothrust: engines to idle,
Wrong.
and by the humans: left hand engine to idle and into reverse. Hence, the right hand engine had no reason to spool up
A command was given to the left engine. What does that have to do with the right engine?
Giving a pilot something other than what he has commanded is hardly "keeping it simple".
Now, assume, the airplane is in the flare, and autothrottles brings the engines back to (nearly) idle. At 20 feet the human retards only one thrust lever (TL#1).
Wrong. Autothrust maintains approach speed. Except in the case of Autoland, Autothrust does not know about reducing thrust to idle in the flare. (Even in autoland (A/THR in RETARD mode), levers must be retarded to idle, only difference being the timing of the RETARD! callout (20ft manual, 10 ft autoland).
What was the last command given by the human? Correct - go to idle (on the left engine), we are going to land.
Wrong. Only one engine to idle could also be done to avoid excessive vibrations, among other things.
As a result, autothrottle disconnects.
Wrong. Autothrust remainded active.
So far, so good - and so far that's what happened in this accident (as seen by the computers and the FDR recordings).
Wrong again. Go back and read the FDR graphs yourself and look for the moment of A/THR disconnection (hint: you need to read more than one page).
So, in this conflict, why did autothrust disengage then?
Take a look at my Why-Because-Analysis to see why, how and when A/THR disconnected.
Hence, the engine should not spool up as it did in this accident, but remain at whatever power setting it was producing at the time of autothrottle disengagement.
It did.
When it spooled up, A/THR was still active.
This solution would be equivalent to the moving thrust levers in other plane types, too. As the autothrust system on those types would move those throttles to idle during the flare,
Would it? How many types have you flown? In all aircraft you put the levers to idle in the flare. Moving or non-moving.
What happens, if the pilot forgets both levers in the CLB detent? During the flare autothrust would command both engines to idle.
No. It would maintain approach speed and float the aircraft along the length of the runway.
As a result, spoilers and brakes would arm
Spoilers and Autobrakes are armed by the flight crew, they don't arm themselves.
Have I overlooked something, that would not be covered in such a scenario?
Too much to mention. Start with the points above, which show some lack of understanding of the A320 systems.
Bernd