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TAM A320 crash at Congonhas, Brazil

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TAM A320 crash at Congonhas, Brazil

Old 31st Aug 2007, 09:40
  #1961 (permalink)  
 
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EMIT,

very insightful, and some interesting facts. Thanks a lot.

The deepest root cause of this accident may well be, the extremely slow acceleration of the engines from idle.
I do not quite follow you there. In a very deep causal analysis this may turn out to be a causal factor, but I rather think that the links between the engine properties via FADEC control laws via the changed MEL procedures via confusion to neglecting to retard a thrust lever are too weak to stand the Counterfactual Test.

1. (fact) The A-320's IAE engines accelerate very slowly from idle.
Do the CFM engines accelerate significantly faster? I thought slow spin-up was inherent in all gas turbines. (Evident also in the tubo lag in turbocharged piston engines.)

Slow spin-up from idle was a causal factor in the Habsheim accident.

All the discussion so far has been about points 8 and 9. Very interesting by themselves, but only scratching the surface.
There has been quite some discussion that the changed MEL procedures (points 5 and 6) might have added to the confusion, although the reason for the changes in the procedures were unknown.

In the discussion about point 8, I want to state clearly, but at this moment I have no time to elaborate on it further - the autothrust system with non-moving thrust levers is well thought out and logical, but it is NOT NATURAL!
Perhaps not, but then again, what is natural in controlling complex machines? As I pointed out, though, the operation of the levers may be considered natural: accelerate: push, cruise: leave alone, stop: pull.

Incidentally, same as with moving levers.

Bernd
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Old 31st Aug 2007, 10:19
  #1962 (permalink)  
 
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Answer to BSIEKER's question.

Spool up of jet engines.

Yes, all engines spool up somewhat slowly.
On every take-off, we initially set the thrust levers to about 1.05 EPR. When the engines actually produce that thrust, we advance the thrust levers to take-off thrust. This procedure is there to prevent uneven engine acceleration (meaning, left and right not accelerating at the same time), which would cause directional control problems.
In terms of RPM, idle on the ground is roughly 25% N-1, 1.05 EPR is roughly 50% N-1.
The comparison that I can make is with the B-767 mounted P&W 4060: more than twice the thrust output, so roughly more than twice the spinning mass, yet half the spool up time from idle to 1.05 EPR.

I don't know how fast the CFM's react.
I don't know whether with the CFM's idle is also increased already on pulling the thrust lever into the reverse range (even if reverser itself is deactivated).

I do know that following the Lauda crash in 1991, we (767 fleet worldwide) have flown around one or two years with both thrust reversers deactivated. Explicit operating advice was to keep pulling the reverse thrust levers to the interlock stop on each landing, to stay in the habit. Compare this with the specific Airbus instruction to *not* pull thrust levers into reverse range when both reversers are deactivated.

Now for something completely different, is there a way to paste text into a post? Sometimes it is easier to write while you are offline, but so far I have been unable to transfer such text into a post. This limits my opportunity to post useful (longer) replies for lack of time at the appropriate moment.
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Old 31st Aug 2007, 12:03
  #1963 (permalink)  
 
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is there any transcript from the black box ?

how is the investigation so far?
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Old 31st Aug 2007, 12:26
  #1964 (permalink)  
 
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Having flown both CFM and IAE A320 versions myself, I know what you mean with slow spooling up. This is in fact the case on capturing an altitude or a speed. I doubt that it is the case in go-around or any other critical flight phases. Airbus has certified both aircraft and they deliver more or less the same performance.

The myth also stems from the fact that the IAEs need much longer engine start time, hence pilots see the slowness every day several times.

There is nothing to add to this TAM accident. There hasn't been any spool up because there hasn't been any spool DOWN! The TL remained in approach thrust, that's why they overrun that runway. Hasn't this been noticed yet?

And hellas! We have reached 100 pages of this thread. Let's be grateful and hope for another 100. Champagne!

Dani
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Old 31st Aug 2007, 12:32
  #1965 (permalink)  
 
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Spool up.

Dani, I don't mean to imply that spool up played a role in this acident as a physical quantity.
I was wondering whether it stands at the basis of the choice to increase idle already at entering reverse range, rather than at open state of the reverse sleeve. That choice prompted .... the sequence of points in my previous post.
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Old 31st Aug 2007, 13:46
  #1966 (permalink)  
 
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Is there a possible credible scenario with one TL at reverse, the other at cl, brake pedals pressed, where one does not want to stop?
Yes, there is.

1) If you can have a TL inadvertently in CLB position at touchdown, you can also have a TL inadvertently in REV during other flight phases, where this is not desired (e. g. climb or go around).

2) Usage of rudders can imply inadvertant activation of brake sensors by deflection of the pedals with the toes.

=> This can lead to the scenario that there was something wrong with your TL (being in REV while still on your approach path), you want to abort and sort this out while airborne, because of asymmetric thrust you have to use rudder - and you're almost automatically falling from the sky, because the spoilers are deploying, because your toes applied a bit too much of a pressure.

When somebody argues this scenario to be not likely - so was leaving the TL at CLB position during landing roll!

Again though, the more complex you make the logic tree, the higher chance you have of an error manifesting.
Absolutely. What's more, it makes it even harder for the crew to understand in complex situations and therefore reducing the chance of successful troubleshooting in time.

This is another indication that the TAM's captain mindset was somewhat in "another aircraft".
These were my thoughts also some weeks ago. It gave me a new thinking about transitions from other aircraft families.

Once again, as we saw in this thread, the non-deployed ground spoilers did not have such a big effect on the landing roll distance that it would have turned things much. Therefore I am not sure if it helps a lot when we consider the spoiler's logic to be changed. I would rather concentrate on what might have caused the crew to leave the thrust lever where it was. Wordings in paperwork like MEL and training awareness seems to be a good starting point as well as tactible feedback to the crew like moving levers (thrust or spoilers). For sure the most effective spoilers cannot override an engine running at some 75% thrust (which was more than the approach thrust, by the way).
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Old 31st Aug 2007, 14:13
  #1967 (permalink)  

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bsieker, EMIT,Dani

There has been quite some discussion that the changed MEL procedures (points 5 and 6) might have added to the confusion, although the reason for the changes in the procedures were unknown.
I know for a fact that there have been many occurences of both reversers selection in cases of a MELed T/R, and there have been inquiries from the airlines to AI about a change in the procedure.
So it is an airline originated change. Will try and confirm it.
I don't know how fast the CFM's react.
I don't know whether with the CFM's idle is also increased already on pulling the thrust lever into the reverse range (even if reverser itself is deactivated).
The CFM 56s of the latter series is faster than the -A series. If, as I suspect Dani flies the old 'Bus -A series equipped 100s - along with the newer IAE engine-equipped fleet and doesn't see a difference, the IAE engine is indeed slower to accelerate. (btw, the Habsheim 320 had the A1 engines ).
The requirement for stabilising the engines at 50% N1 /1.05 EPR is for getting all the flow control ancillaries at a stable state (the VBVs come to mind).
The slight increase of N1 /EPR reverser idle is quite general on the 'Bus fleet and as it has never bothered me, I would suspect it wasn't anything new to me from my previous types. Need to see that , too !
I know what you mean with slow spooling up. This is in fact the case on capturing an altitude or a speed. I doubt that it is the case in go-around or any other critical flight phases.
The slow spool-up in cruise /speed has to do with the AI speed stability algorythm which prioritises fuel consumption / pax comfort over instantaneous speed-keeping accuracy. B has another philosophy.

EMIT's theory has some merit, but I think it could be applied somewhere else : a confusion about inop T/R and inop engine.
If I may present it this way, I would take an analogy I've seen / experienced countless of times in the sim :
Any crew would successfully perform a single engine go-around without any major problems.
Now, if some time during the approach the SFI / TRE tells the crew that they won't land but they would have to overshoot, the go-around performance would drastically drop : forgotten items, call outs, under-par rotation...etc...
Could that phenomenon of confusion on an over-rehearsed procedure have applied to this accident ?


From EMIT :
is there a way to paste text into a post? Sometimes it is easier to write while you are offline, but so far I have been unable to transfer such text into a post. This limits my opportunity to post useful (longer) replies for lack of time at the appropriate moment.
My method is to type my text in WORD, then copy/paste. Works fine for me.


Cheers !
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Old 31st Aug 2007, 15:58
  #1968 (permalink)  
 
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BBB,

Thanks a lot for your input. Very good to have differing opinions here. We need to consider all things.

[scenario with one TL in reverse, brake pedal inputs, but not wanting to stop ...]

Originally Posted by TripleBravo
Yes, there is.

1) If you can have a TL inadvertently in CLB position at touchdown, you can also have a TL inadvertently in REV during other flight phases, where this is not desired (e. g. climb or go around).
Yes it had crossed my mind, that, although the scenario would be considered extremely unlikely, so was the scenario we seem to have in this accident. Yet it did occur.

2) Usage of rudders can imply inadvertant activation of brake sensors by deflection of the pedals with the toes.
I was aware of this one. I'm curious about it. If the FDR graphs really show degrees of brake pedal deflection, it has a stop at 80 degrees, which seems a lot. I don't think that inadvertent brake-pedal inputs would be anywhere near that range, even in flight phases where larger rudder inputs may be needed, e. g. cross-wind go-around with turbulence and asymmetric thrust, etc ...

So to make additions to GS logic that will actually be useful, we have to be very careful not to make things worse instead.

Data mining through quick access recorder data will be useful, to see what maximum magnitude "parasitic" brake inputs while using the rudder can have. Try to find out if there might be bigger inputs still for reasons yet unidentified (slippery pedals, inappropriate footwear, ...), and add a sufficient safety margin. And see if that is still well below the normal brake pedal input used for braking during landing and rejected take-off.

Am I right in assuming that the desired mode of operation is to move the rudder bar with the heels, and the brake pedals with the toes?

=> This can lead to the scenario that there was something wrong with your TL (being in REV while still on your approach path), you want to abort and sort this out while airborne, because of asymmetric thrust you have to use rudder - and you're almost automatically falling from the sky, because the spoilers are deploying, because your toes applied a bit too much of a pressure.

When somebody argues this scenario to be not likely - so was leaving the TL at CLB position during landing roll!
And this scenario is indeed very rare, and would probably have been considered "unthinkable" by most type-rated pilots prior to the well-known occurences.

Absolutely. What's more, it makes it even harder for the crew to understand in complex situations and therefore reducing the chance of successful troubleshooting in time.
Worth considering. But any addition here is to reduce the need by the pilot to analyse the logic, and rather to offer him one more way out of a pinch which he will resort to without thinking: firm manual braking.

Without needing to know that this is one of the possible GS deployment conditions. The thrust lever position, in an emergency, may not be the obvious way to look for to stop the aircraft (although maybe it should).

Brakes are.

Once again, as we saw in this thread, the non-deployed ground spoilers did not have such a big effect on the landing roll distance that it would have turned things much. Therefore I am not sure if it helps a lot when we consider the spoiler's logic to be changed. I would rather concentrate on what might have caused the crew to leave the thrust lever where it was. Wordings in paperwork like MEL and training awareness seems to be a good starting point as well as tactible feedback to the crew like moving levers (thrust or spoilers).
We witness that brakes even without ground spoilers did reach about 1.3m/s^2, And since GS have a three-fold effect ---(1) increasing normal force, thus friction force, thus deceleration, (2) avoiding hydroplaning, thus increasing friction coefficient, thus friction force, thus deceleration, and (3) increasing aerodynamic drag, thus deceleration, especially at high speeds--- its effect may have been considerable, and while not preventing the overrun, may have reduced it to a much slower one. We'll never know exactly.

But granted, training awareness is paramount.Early onset of manual braking combined with ground spoilers would have done the trick. I'm not sure the MEL wording was a problem, but it has to be chosen carefully. And MEL procedures should be subject to the same rigorous risk analysis as other procedures.


For sure the most effective spoilers cannot override an engine running at some 75% thrust (which was more than the approach thrust, by the way).
Is 1.19 EPR indeed 75% thrust? (i. e. 75% force? And what is 100%? CLIMB or TOGA?)

But you are right, and I stand corrected, it is significantly more than the thrust during final approach, which was between 1.05 and 1.1 EPR.


---

Originally Posted by Lemurian
The slow spool-up in cruise /speed has to do with the AI speed stability algorythm which prioritises fuel consumption / pax comfort over instantaneous speed-keeping accuracy. B has another philosophy.
If I recall correctly, A320 also has "Soft altitude" mode, allowing deviations from the flight level by up to 50ft, in order to reduce thrust changes and save fuel.

During approach, thrust variations are quicker, in "approach autothrust".

Bernd
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Old 31st Aug 2007, 16:12
  #1969 (permalink)  
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TripleBravo requotes this from earlier, I am sorry that I cannot recall who originally said this:
This is another indication that the TAM's captain mindset was somewhat in "another aircraft".
All that I have read states that the PF was a training captain on the 320. It would seem reasonable to guess that he was not mistaken?
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Old 31st Aug 2007, 23:36
  #1970 (permalink)  
 
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Rananim:
KISS.
But it could be just as easily argued that it doesn't get much simpler than "Levers forward for acceleration and managed speed, back to slow down, all the way back to stop."
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Old 31st Aug 2007, 23:42
  #1971 (permalink)  

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Rananim

You *forgot* to add (d) the Boeing cheerleaders who can't understand anything positive about an Airbus product to your list, in all fairness.
Of course we know very well nothing happens to Boeings. Pity that only suicidal fools fly them, hey ?
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Old 31st Aug 2007, 23:50
  #1972 (permalink)  
 
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Lemurian, I understand where you're coming from, but *please* let's not get into that again. I think that most of us on here know each other's preferences (or indifference) in that area by now.
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Old 1st Sep 2007, 09:21
  #1973 (permalink)  
 
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Originally Posted by marciovp
If this is the third accident with A320s where the pilots landing with one reverser locked up left the two TLs in opposite positions (forward and reverse), should we simply say that it was a human error?
Originally Posted by preta
marcio vp
you are forgeting the Phoenix/USA accident.
This one was different, in that both thrust levers were retarded to idle during the flare, and reverse was selected on both engines. Only after that, the thrust lever of the engine with the inop reverser was moved forward, first to CL (at which time ground spoilers would also retract), and then to TOGA, where it stayed for 11 seconds, before being pulled back to idle again.

No fatalities.


Bernd
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Old 1st Sep 2007, 09:53
  #1974 (permalink)  
 
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Originally Posted by marciovp
So, we are talking about four accidents and eight well trained and experienced pilots.

Don´t you think I have a good question?
I don't think it's a very useful question. And I'll tell you why ...

Originally Posted by Rananim
I would say thats an excellent question but many here choose not to face it and instead look the other way.Seems we have 3 camps:
a)the AB pilots who naturally dont want to see the design error
b)the resident "experts" who just love discussing the man-machine interface
c)simple folk who think its a bad idea to have reverse unless and until BOTH TL's are at IDLE.
This is an extreme oversimplification, and unfair categorisation of people.
Do you really believe (1) that Airbus pilots would not like to have the safest plane possible, and are not the most qualified to judge the interface, and (2) that "simple folk" should design aircraft human/machine interfaces? Heaven forbid!

Those who talk of the MEL and THR ABV IDLE/RETARD/continuous chime see the trees but not the woods.There can be no better or clearer warning to a pilot that TL's are not at IDLE than the denial of TR.
I don't agree.

The best post came from woodvale.How pilots tunnel their vision in a bad situation.Repetitive chimes and/or EICAS annunciations can get filtered out.However,something fundamental like the physical inability to engage TR will find a way through that tunnel vision.It has to.You wont stop without TR.It either leads the pilot by active-recall to retard the forgotten TL or at the very least enables the abort scenario.
Yes, I agree he made a good point. A CRC may indeed not be the optimal way of warning. I like the "Retard TWO!" modified FWC callout better, but that, too, may not be the best way.

You are asserting that not getting reverse thrust "has to" get through tunnel vision, and give the flicght crew the correct clues, without giving any persuasive reason. "It has to" is not a reason. And "You wont (sic!) stop without TR" is flat wrong. There even are jet airliners that don't have TR at all.

Reverse thrust has an even smaller contribution to stopping performance than ground spoilers (I imagine an aircraft with inop spoilers would not be dispatched), so not getting reverse thrust despite selecting it is not going to help much in alerting the pilots to the real reason of their problems. Pilots may simply assume a failed reverser. (Thrust reversers are not the most critical systems, and thus are not required to be among the most reliable, as evident by not even being required to operate the aircraft).

Unless they also know the logic for not giving them reverse even if they asked for it. (Additional confusion. Another logic to learn by heart?)

Bernd
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Old 1st Sep 2007, 10:05
  #1975 (permalink)  
 
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I would say thats an excellent question but many here choose not to face it and instead look the other way.Seems we have 3 camps:
a)the AB pilots who naturally dont want to see the design error
b)the resident "experts" who just love discussing the man-machine interface
c)simple folk who think its a bad idea to have reverse unless and until BOTH TL's are at IDLE.

I dont say the tech jargon from camp (b)(if I could only understand what the hell they're saying)and the denial from camp(a) hasnt been interesting.It has.
rananim,

As is beginning to seem usual and repetitive in your posts, you appear to have placed the cart before the horse. Or, perhaps it's the placement of the cranium relative to another beast of burden? Whichever.

You, and any others who are under the illusion that operating an aircraft makes one an apologist for its design need to wake up and recognize some important facts. No serious professional here wishes to see the propogation of inferior designs. We have to work with them and consequently we have a vested interest in seeing that they are is good as they possibly can be. If any design is found to have a significant weakness that compromises safe operation we will want it fixed.

Where I, and I suspect other "Camp A" pilots as well other technically knowledgeable contributors part ways with you is in the process of analysis. Your approach as laid out in post #1715 has been:

Its not an AB/Boeing thing I can assure you although I do admit that I have deep-seated mistrust of the AB design.I quite understand though that as long as a pilot forgets everything hes been taught and learns the new concept,everything should be just fine....
You choose to start with a conclusion, that the design is flawed, and work it back to an attribution of cause. That, however, is not how analysis works, and it is fortunate that at least a few people here recognize that.

One particular difference that informs the posts from contributors who have flown the aircraft is simply that. They have flown the aircraft and have experience with its strengths and weaknesses and are capable of putting what we know of this accident into context with those experiences.

Another particular difference is the tendency to not make assumptions beyond their scope of knowledge. You, on the other hand, have chosen to conclude that the accident was induced by design without having the benefit of being able to assess the full set of environmental, design, corporate, training and individual human elements that may be involved. It seems you would prefer to jump to your sole conclusion in ignorance of these factors instead of investigating them fully and impartially in search of a complete set of causal factors.

So far as I've seen, those from your camp A (who are neither in denial nor "not wanting to see)" have tried to explain the aircraft's systems processes and operating procedures as they understand them to those who, like yourself, don't. They have not been busy advocating a specific conclusion for the simple reason that they know there is a great deal of information that is not publicly available, and most of that which is is in a raw state and has yet to be rigorously analyzed.

ELAC
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Old 1st Sep 2007, 10:07
  #1976 (permalink)  
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Dozy,

I understand also, and support, your wish to keep the discussion contentful.

But there was a question of fact. Rananim said (ignoring his mode of expression for the moment which others have well addressed above), that there were three classes of people in this discussion, and listed them. Well, was he right? Do his three classes cover (with some measure of interpretation) the major classes of participants?

Lemurian pointed out that he, quite obviously, missed a class, and said which one it was.

I think that is legit. Rananim was, objectively, wrong, and Lemurian corrected him.

Here are the classes without emotive words:

a) rated Airbus pilots who do not find the interface confusing
b) technical experts who are interested in analysing the interface
c) others who may not be pilots who are contributing to the analysis from intuitive principles
d) rated Boeing pilots who are wary of the thrust-lever interface on Airbus machines

I'm in class b. So are bsieker and TripleBravo, I believe. ELAC, Lemurian, PJ2, TyroPicard are in classes a and b. Dani is in class a. I think BOAC is in class d but I can't tell if he is in b as well. I don't know where Rananim (probably class e: rabble-rousing )

There are also some people who don't fit these categories. But so far, I have only read of one type-rated contributor who found the interface confusing, and he has long dropped out of discussion.

PBL

Last edited by PBL; 1st Sep 2007 at 10:22.
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Old 1st Sep 2007, 10:39
  #1977 (permalink)  
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Just a touch of over-simplification!

I would not presume to be in b), and neither am I in d) inasmuch as I am not WARY of it - I just have no experience of it, which places me in group e) - trying to understand how it interfaces with and confuses pilots and why this accident occurred plus what needs to be addressed by manufacturers and training. You also need, sadly I think, to include the pilots from CGH in e)?
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Old 1st Sep 2007, 11:12
  #1978 (permalink)  
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Originally Posted by BOAC
Just a touch of over-simplification!
By which I take it you mean spoonfuls. Yes, indeed (Disclaimer: I only proposed one of these categories. The others came from a Cat e contributor)

Originally Posted by PBL
(probably class e: rabble-rousing )
Originally Posted by BOAC
which places me in group e) - trying to understand how it interfaces with and confuses pilots and why this accident occurred
That's not exactly what I meant by "rabble-rousing"

I think most contributors are trying to understand why this accident occurred, and any category in which most people fit is not a useful classifying device, so I wouldn't highlight it.

There are also some who are prepared to delve deeper than others. Some say "didn't retard the thrust lever" and don't want to go deeper. Others want to know about braking behavior and performance, even with significant thrust on #2. I don't think that part of the discussion is concluded yet, because no one has drawn lessons for improved landing decision making. Yet others want to know about the entire set of braking scenarios (RTOs as well as landings, with partial kit INOP). Indeed I believe bsieker, who in the background of this discussion is doing the equivalent of a sophisticated FMEA with the state machines reverse-engineered from the FCOM, has identified some questionable states which we could profitably discuss when he is finished.

PBL
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Old 1st Sep 2007, 12:08
  #1979 (permalink)  
 
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Thanks for your very comprehensive post, PBL, for the first time short and precise, bravo!

Although you put me correctly in class A (I'm not confused with AI man-machine interface), it's rather obvious that other AI-pilots are.

[offtopic]Please excuse that I write AI because this is the more official abbreviation for Airbus Industries, compared to AB=Air Berlin[/offtopic].

It is a simple fact that at least 3 crews ever messed up something very badly. I have argued this way already before.
I have to repeat that it's pretty clear that this error of "forgetting" a TL is not a case of amnesia or any other pathologic reason but because they really *though* that they were acting correctly.
There must be a reason why you don't touch a broken TL/TR. I still haven't found out where and when and why. On a short runway and in an Airbus, that's fatal. But in other cases there must be a reason.

This is what we have to find out and why. This will then be the terminal cause of this accident.


Dani
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Old 1st Sep 2007, 12:45
  #1980 (permalink)  
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I don't see why you can not pull a reverser lever into reverse position if that reverser has been deactivated by maintenance? Not familiar with the bus or two engine airplanes as such, but I presume the affected thrust lever has to be at idle before you can select reverse thrust, activated or not.
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