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Old 4th Aug 2007, 22:43
  #1133 (permalink)  
SoaringTheSkies
 
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You seem intent on believing what you want to believe regardless of the facts.
it might be a little thin skinned, but I think this comment was unneccessary.

On *most* conventionally designed aircraft you have to pull the thrust levers to idle when you flare, there is no such thing as autothrust in a very large percentage of airplanes. Well, at least that's the way it's worked on the B727 and pretty much every other non-FBW aircraft I've ever flown.
Of course, but that's not the type of aircraft we're talking about here. If I do fly by steel wire or pushrod, I'm 100% in the loop. It's that way with all flying I've ever done, being a non ATPL.

Even on most conventional aircraft with autothrust, such as the B757, this is usually disconnected at the time the pilot disconnects the autopilot leaving the thrust levers under manual control. If you don't pull them back yourself when you land they produce whatever thrust the lever demands.
They do, and they do that all the while. It would be fairly difficult to get an airplane to land with one or both engines producing a substantial thrust, right? So with fully manual thrust control, it would be an art to bring the plane down at approach speed, flare it and get the wheels spinning. Chances are, if you would really forget manual throttles in the approach, that you would just float along the runway.

Funnily enough this was never pointed out to me in training as a design flaw.
There's nothing like a fine measure of polemic, hmm?

The difference you seem to be getting at is between the Airbus and certain recent Boeings which are landed manually with autothrust active. The Boeing TLs move whereas the Airbus ones do not. There are arguements for either system when looked at holistically, but the Airbus system is not one iota more complicated or different in philosophy in this particular respect than a B757, B727 or a DC-3 for that matter.
They are different in one simple way:
the way they leave the TL when autothrust disconnects.

You want idle thrust, pull the levers to idle. Simple.
Absolutely.

But for some reason, this has not happened here.

I've said earlier that good system design means to avoid error, tolerate error or at least fail gracefully.
It's just my feeling that a system that leaves the TLs in a position that is directly reflecting the thrust setting at AT disconnect does avoid the possibility of the error at hand completely. Not pulling back a TL is just a non issue (even though I agree with you, it's still an error). The system of non-moving TLs however seem first to create the possibility for this error. Question is from there, how well does it tolerate the error and how gracefully does it fail.

Don't get me wrong, I don't want to bash Airbus, why should I?
But at the same time, I think that there's evidence that there was more than one incident where this system has been mishandled, thus I think it's only fair that it is questioned.

Also, I would be (really) interested in what the rationale behind that design decision was. When introducing a whole new paradigm, someone surely must have had a good reason for it.

pj
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