TAM A320 crash at Congonhas, Brazil [Archive] - Page 9

bsieker

3rd Sep 2007, 00:30

When auto thrust is engaged on the A320, switch arm positions CLB, FLX, and TOGA are available as possible selector switch positions.

To be nitpicking, this is not strictly true. Above CL position, thrust lever position always directly selects thrust. (Above MCT with one engine out.) But I take your point.

In selector switch mode, lever position no longer equates to engine power thus the levers have no direct control over engine power, because they no longer function as throttles in any classic sense.

Even with A/THR engaged the thrust levers function as limiters (perhaps throttles, really), limiting the maximum thrust A/THR may set. Since this is rarely used, thrust levers may seem to be working more as a selector than a throttle during flight.

Perhaps not.

At least one A320 pilot (TyroPicard) said he did not think of them as mode selector switches, but rather thinks of selecting idle thrust when pulling them back at the flare. Others may feel different. I cannot judge that.

I also agree with him that most of the times you actually touch the thrust levers, they work as throttles. As long as they stay in CL and A/THR is active, they're not used, and not thought about much.

Typical thrust lever movements are: Using low thrust during taxi, setting medium power to stabilise engines, setting T/O thrust, reducing thrust at acceleration altitude, retarding to idle, selecting reverse idle, selecting max reverse, back to reverse idle, back to forward idle, low thrust for taxiing. (I also count 10, 12 if you count setting and reducing taxi thrust as two movements, more if you do it multiple times.)

In all cases in which you move the levers, thrust actually changes in the direction of lever movement. For all intents and purposes these are throttle levers.

Modes exist where the same gesture (control action) yields different results depending on system state at a time when your attention is not on system state.

Here's a problem with your reasoning:

Pulling the thrust levers to idle yields the same result, regardless of autothrust being engaged or not: it selects idle thrust. So by your own admission, this is modeless.

Bernd

Dani

3rd Sep 2007, 02:06

Flight Safety, I thank you very much for your post. Not because I agree with your analysis, but because you finally steer the discussing into the right direction: The human aspect of moving the TL - or not to move.

After going trough your post one thing stroke me most:

...the pilot leave ENG2 TL in the climb detent after pulling ENG1 TL back to idle 2 seconds after the "retard" call in the flare

I didn't know that, because I never laid the CVR beside the DFR. If this is really the case, then it is one reason more for the argument that they didn't really know how "to fly an Airbus".
Let me explain: On the line in every Airline I have been before there are Airbus pilots that wait for the "Retard" call to close the TL. It's not an exception. I guess it's around 80% of all Airbus pilots that went trought an Airbus procedure course, i.e. Toulouse or others. I also have been in Toulouse, so I know that Airbus says that you should go to idle BEFORE the retard call, since the call is only a reminder. Still, I make this observation on the line, that most of the pilots do it after. The result is often a great increase of flare and landing distance.

I always stand under the impression that pilots who do it this way are somewhat not pilots anymore but rather remote controled robots in an "executing mode", not acting like real pilots but listening to orders from the computer and then acting.

If you look at the FDR printout again, you see also very interesting facts in the last landing of the crew in Porto Alegre, executed by the captain in the right seat: Both TL go to Reverse! (although the Reverser was faulty already)

And when you look at the second last landing, in Congonhas (most probably done by the captain in the left seat again): Already there he reverses only one engine. When he does he doesn't retard both TL at the same time! He starts about half a second to retard TL1, then slows down, starts to retard TL2. But then TL 1 needs more than a second (!) more to go to idle than TL2. If you remember how quickly normally people retard engines on an Airbus (ever heard that clacking noise against the metal?), you clearly see that he had problems to fiddle around with these TLs. He most probably spent a lot of time and effort to carefully take one TL and then another because he wasn't really sure about what to do with them.

The fact that the TAM captain did it the same way twice lead me to believe that he was not ahead of his task. They didn't know what to do with that TL, and hence did the wrong thing. He was somehow in the above described "remote controlled" mode, not acting as a conventional pilot anymore.

We have to put more emphasis on conventional pilot training in Airbus aircraft. By using always this "Managed Mode", pilots become submissive to the machine, forgetting basic flying priciples and standard airmanship. We have to include the flare into the approach briefing (like a lot of airlines do): What type of Airbus we fly, what weight it has, where the wind is blowing from and what basic flare concept I will follow. Some mental preparation is needed. And it is needed before top of descent, not at the treshold.

Otherwise if pilots still neglect basic flying principles, I do not see any place for them in a cockpit - period.

Dani

marciovp

3rd Sep 2007, 03:44

Why did a 737 crew confuse a Cabin Altitude warning with a Configuration warning, both good questions that many on this thread are analyzing thoroughly

Three times, with three different crews, the same problem?

Please discuss the support for your statement that the pilots were well trained or could it be that is the real problem.

Good point. WIll not know for sure. Could it be that all three crews had pilots that were not well trained? Tam had the first officer that flew TAM since 1987 and landed safely in Porto Alegre. Of course the second officer had experience with Boeings 737 and 767 but he trained for six months in TAM before being a Comandant. Both had about 13000 hours flying time. In the other accidents I don´t know. But to make my answer short: yes there is a possibility that these six pilots or some of them were not well trained... I resist accepting this coincidence... but yes...it could be.

GMDS

3rd Sep 2007, 06:03

PBL:

I introduced Cat. e (rabble-rousing). BOAC tried to introduce another Cat. e. Now you want to try yet another Cat. e. What is this thing with the letter "e"? Could we maybe try "f"?

Sorry PBL, I didn't recall taht sequence. Not wanting to go for the "f", I'll settle for the g-spot then.............

ChristiaanJ:
It might seem that I long for the good old days, like grandpa, but there's more to it. I am a defender of proven designs, not against innovation, but only the ones that bring along improvement. A good example were the new tachymeters in the Auto industry. Citroën tried the digital display first in the early 80's, others followed and today almost all manufacturers went back to the original clock design. Why? They realised that the average Joe and Jane controlled speed better with the classic layout and less accidents were traced to misinterpretation. So, no improvement of a new design, no false pride of manufacturors but good analysis and the old one prevailed. It now seems that the fixed throttle design led to more confusion (just re-read the thread!!) than to any improvement, which might allow the assumption that logic and airmenship of the manufacturor could lead to a reversal to the proven moving throttle design.
Now why do I assume that this is not going to happen?

bsieker

3rd Sep 2007, 08:04

I didn't know that, because I never laid the CVR beside the DFR.

It has been done for you, on page 12 of the FDR graphs. They have the CVR ttranscript superimposed.

[Re. retarding thrust levers after "Retard" call.]
I guess it's around 80% of all Airbus pilots that went trought an Airbus procedure course, i.e. Toulouse or others.

That was my impression, having seen several cockpit videos of A320 landings. Not one is without the retard call, the usual number varies between 2 and 5 callouts.

So I assumed it was standard procedure to wait for the call. FCOM says:

. At about 20 feet:
- FLARE ..... PERFORM
- ATTITUDE .... MONITOR
- THRUST levers ..... IDLE
[...] "RETARD" callout is generated at 20 feet RA.

So wouldn't getting one or two calls be normal, when 20ft is both the normal flare altitude and the callout altitude?

(It usually goes like this: "fifty - forty - thrirty - twenty RETARD RETARD"), i. e. if you start flare at the "twenty" callout and then pull the levers back, you'd still get the RETARD call. It'd be nice to see at least one A320 landing video without the call :)

And when you look at the second last landing, [...] When he does he doesn't retard both TL at the same time! He starts about half a second to retard TL1,

The half-second difference is an artifact of the sampling rate (once per second, alternating between left and right lever).

Allowing for that, at the previous landing, he most likely pulled the thrust levers exactly together. And retarded them to idle quickly.

then slows down, starts to retard TL2. But then TL 1 needs more than a second (!) more to go to idle than TL2.

For all we know, TL2 may have been pulled back very quickly, at one sample it's at CL, the next sample it's at IDLE. no way of telling what exactly happened between the two samples.

But I agree, very strange that he didn't pull them to IDLE together.

If you remember how quickly normally people retard engines on an Airbus (ever heard that clacking noise against the metal?), you clearly see that he had problems to fiddle around with these TLs. He most probably spent a lot of time and effort to carefully take one TL and then another because he wasn't really sure about what to do with them.

Sounds like a possible explanation, and certainly deviation from trained procedures. "Most probably" I don't know.

Bernd

Dani

3rd Sep 2007, 09:25

Thanks Bernd for that insight information about recorders.

Where do you have your FCOM3 from? Mine says at 30 feet!

LANDING:

At approcimately 30 feet:

Flare ..................................................perform
Attitude...............................................monit or
Thrust levers........................................idle
The retard callout is generated at 20 ft.

Anyway, ANY landing on any aircraft starts at 50 ft. It doesn't mean that you start your flare or your idle there. But most definetly over the treshold ends an approach and starts the landing.

I'm always surprised that even very experienced heavy jet driver wait for very long to retard a trust lever (on any aircraft). It comes from the misconception that you have to keep V appr (Approach Speed) until touchdown. But this is not correct, on a perfect landing you land with slightly lower speed. But somehow they cannot accept that the speed drops below the speed bug.

This is very pronounced in people with turboprop background where they - depending on type - have bigger problems for a smoother landing with lower power settings and low tilted propellers.

btw, the "Retard" call always comes on, even when you have retarded already. Since I normally retard above 30 ft (depending on weights, winds aso), I can verify that on every flight. Sometimes you also get "wild" retard calls, like any other call, like uneven radio call outs. This is not always a sure hint.

Dani

DozyWannabe

3rd Sep 2007, 09:25

GMDS:
A good example were the new tachymeters in the Auto industry. Citroën tried the digital display first in the early 80's, others followed and today almost all manufacturers went back to the original clock design. Why? They realised that the average Joe and Jane controlled speed better with the classic layout and less accidents were traced to misinterpretation.
The problem with this, and a lot of other analogies comparing the car industry with aircraft manufacturers is that you end up with an apples-to-oranges comparison. There is a world of difference between a type of display that is technically fancier but turns out in practice to be harder to read than the traditional mechanical dial, and the throttle quadrant of a commercial airliner.

For a start, you have to look at the reasons for the change - the A320 was conceived as a completely modern machine, looking at what was possible with state-of-the-art technology to make the pilot's job easier and the aircraft more economical to operate and maintain. You can bet any amount that you like that AI weren't going to sink the millions required for a project of this magnitude without a significant amount of R&D on the engineering, customer and pilot's view of how this thing would work.

As I said before, modern technology meant that engine control no longer required a physical connection between levers and engines for throttle control - in fact statistically it behaved more reliably than the old arrangement, simply because digital control is not subject to physical entropy through wear and tear in the same manner. To backdrive the levers would require an artificial force-feedback system that would not only incur a weight penalty, but also compromise the simplicity of the system, incurring a maintenance cost penalty as well. At the time, none of the pilots involved in the project objected to the non-moving design that I've learned. Unless proven beyond a shadow of a doubt that non-moving throttles are dangerous - and I'm talking about more than hearsay and conjecture from a small but vocal group of pilots, a majority of whom haven't even flown the aircraft they're criticising.

In this case, I'm not even sure that moving throttles would have made a difference, as the evidence points to a lever that was deliberately left out of position. Even if the levers were of the moving type, the pilot may still not have selected the incorrectly positioned lever to idle, the only difference is in how far he would have had to move it to put it there. Of course, I think that Rananim is talking about the secondary levers that control reverse with the physical interlock. A very clever system, but again, one that goes against the design brief to keep it simpler from a maintenance perspective.

I can't answer ChristiaanJ's question regarding Concorde's system, because I don't know the designers involved on both projects, nor can I find any material about what informed their decision to go one way in the '60s and another way in the '80s.

As an aside, one thing I have noted during my time on here is the number of A320 sceptics who come from the other side of the pond. Would their objections be so vehement if it was Boeing, Douglas or Lockheed that designed and built a similar aircraft to the A320?

GMDS

3rd Sep 2007, 10:08

The problem with this, and a lot of other analogies comparing the car industry with aircraft manufacturers is that you end up with an apples-to-oranges comparison

It is in the nature of a analogie not to treat equal things, otherwise it would be a simple comparison. Analogies are used to clarify a idea or thesis. The setback is that people who don't want to understand will always bring up the apples and oranges.

As I said before, modern technology meant that engine control no longer required a physical connection between levers and engines for throttle control - in fact statistically it behaved more reliably than the old arrangement, simply because digital control is not subject to physical entropy through wear and tear in the same manner. To backdrive the levers would require an artificial force-feedback system that would not only incur a weight penalty, but also compromise the simplicity of the system, incurring a maintenance cost penalty as well.

A equally modern design (777) has just as little physical connection to the engine. But you pointed it out nicely: It must be the cost penalty that inhibited AI engineers to consider the backdrive depriving us of a (my interpretation) extremely useful feedback in case of screw up or confusion (as in this incident).

Just to comfort you: When I flew a MD product I was heavily involved in a fervent criticism/discussion about a lack of design/checklist. It has nothing to do with anti-AI feelings. I simply strive for the best pilot-machine interface available and strongly believe that the throttle design with feedback from autothrottle commands is safer than the one without.

Safe flights

GMDS

DozyWannabe

3rd Sep 2007, 10:37

A equally modern design (777) has just as little physical connection to the engine. But you pointed it out nicely: It must be the cost penalty that inhibited AI engineers to consider the backdrive depriving us of a (my interpretation) extremely useful feedback in case of screw up or confusion (as in this incident).

Hmm - your phraseology implies that it was monetary cost to Airbus I was referring to, when I was referring to cost in engineering terms, a very different meaning of the word. You should be aware that the anti-AI crowd make hay by ignoring that kind of distinction.

All the differences in implementation prove is that the engineers and pilots on the 777 project came to a different set of conclusions than their counterparts on the A320 project. No doubt both implementations have pluses and drawbacks.

ChristiaanJ

3rd Sep 2007, 10:44

GMDS et al,To backdrive the levers would require an artificial force-feedback system...
There seems to be a basic confusion here, that I've noticed in several other posts as well.
In "conventional" systems, throttle angle is NOT representative of actual engine thrust but of the commanded engine thrust. There is no feedback.

On Concorde (and I presume more recent aircraft as well), the autothrottle computer commands an electro-mechanical unit (inside the pedestal) which directly moves the thrust levers through clutches, rather than electrically signalling the ECU. There is no "artificial force-feedback system".

BTW, the autothrottle unit on Concorde weighed about 7 kg, so a similar unit for the A320 would have weighed about 4 kg. Hardly prohibitive.....

GMDS

3rd Sep 2007, 11:30

There seems to be a basic confusion here, that I've noticed in several other posts as well.
In "conventional" systems, throttle angle is NOT representative of actual engine thrust but of the commanded engine thrust. There is no feedback.

Come on ChristiaanJ, we're not as naive as that. Nobody requested a exact feedback of the actual thrust. The request, relating to this incident, would be more of a feedback of the intended command, i.e. "it wants to incresase thrust" as opposed to "it wants to retard thrust". This would have maybe triggered the poor pilot to close the second lever as well, because he would have FELT the lever moving forward as the autothrottle suddenly commanded more thrust, and not idle. In such critical moments, apparently the visual feedback from ECAM proved insufficient.

DozyWannabe

3rd Sep 2007, 11:45

ChristiaanJ:
BTW, the autothrottle unit on Concorde weighed about 7 kg, so a similar unit for the A320 would have weighed about 4 kg. Hardly prohibitive.....

True - so there must have been another factor that influenced that decision. The only way to get a definitive answer would be to ask anyone who worked on the A320 cockpit design team. Unfortunately my only contact with anyone involved extends only to software, so I can't help there.

GMDS: The throttle did *not* command more thrust until late in the roll, and then not a significant amount. The thrust remained constant (approach thrust) until the aircraft started decelerating.

GMDS

3rd Sep 2007, 12:01

GMDS: The throttle did *not* command more thrust until late in the roll, and then not a significant amount. The thrust remained constant (approach thrust) until the aircraft started decelerating.

I actually don't care WHEN it commanded more thrust: As a matter of fact it did.

I actually don't care HOW MUCH more thrust it commanded and for how long and how constantly: As matter of fact it did and a movement would most probably have been detected ....

Any twist or torsion of grammar or expressions does not avoid the tormenting thesis, that a throttle that would have moved, might just have helped picking up the glitch by the guys in this situation. All the "they should haves" or the "if they would haves" do not help here. Anyone might just screw up one day, maybe even Dani, and at that specific moment one would wish to have the best design to help mending fences.

DozyWannabe

3rd Sep 2007, 12:07

GMDS:
Anyone might just screw up one day, maybe even Dani, and at that specific moment one would wish to have the best design to help mending fences.
But "the best design" is itself subjective, unless you want to foot the bill for the HF research to prove it scientifically.

ChristiaanJ

3rd Sep 2007, 13:30

GMDS, Come on ChristiaanJ, we're not as naive as that. Nobody requested a exact feedback of the actual thrust. Not exactly, but several posts did equate TL position with actual thrust rather than commanded thrust, to the extent that in a reply somebody had to point out that the TL wouldn't budge even if the engine flamed out.

The request, relating to this incident, would be more of a feedback of the intended command, i.e. "it wants to increase thrust" as opposed to "it wants to retard thrust".My issue was with the word "feedback", since strictly speaking there is (or should be) none. The pilot positions the TL to set a thrust demand, the TL position is converted to an electrical signal and sent to the ECU (or FADEC or whatever), and the latter controls the fuel flow to meet this demand asap. At no time is there a feedback.

Having the autothrottle move the TLs mechanically actually simplifies the system slightly, since the command to the ECU always comes from only one source: the TL position sensors.

SyEng

3rd Sep 2007, 21:12

Some posters here have jumped to the conclusion that the PF left No.2 TL in the climb detent. That may very well be the case. However, all that can be inferred from the FDR trace is that the FDR continued to record TLA at CLB. I would guess that this is the signal from the EEC in control (1 of 2).

This is how the thrust lever mechanism works: the thrust lever moves a control rod which moves an input/output lever on the artificial feel unit (this provides friction to stop the TLs from wobbling about plus the detents and stops). The other end of the artificial feel unit input/output lever moves another rod which moves the input lever on the throttle control unit. The throttle control unit contains the RVDT resolvers which provide an anologue TLA signal to the ECUs. All of this lot is in the centre pedestal.

Each end of each control rod is located to its lever by a nut and bolt. Each nut is locked by a split pin. There are 4 such nut/bolt/split pin connections between thrust lever and throttle control unit.

Failure of either end connection on the artificial feel unit to throttle control unit rod would result in a normal-feeling TL but a frozen and valid TLA output from the throttle control unit. (Caveat: the TCU incorporates a "safety device" which drives the resolver out of range if the "driving device" fails. I believe this refers to the TCU internal driving device rather than a failure of drive into the TCU but my source runs out of detail here. Will attempt to investigate further.)

Failure of either end connection of the thrust lever to artificial feel unit rod would result in a floppy thrust lever ("look this" ? ) but a frozen and valid TLA output from the TCU.

In addition to the above there are the following possible failure modes:
- failure of the thrust control unit mountings
- failure of the artificial feel unit mountings
- unsignalled mechanical failure of the thrust control unit
- mechanical failure of the artificial feel unit

To my mind, the most likely of the above is a failure of one of the rod-end nut/bolt/split pin connections.

To those who have followed this post so far, firstly congratulations, and, here are some questions.

- Was there any recent maintenance work on the TL linkages?
- What physical evidence is there from the wreckage of the state of the TL mechanism?
- Might a proper spectoscopic analysis of the CVR recording show only one, or both TLs hitting the idle stop?
- Why is the design such that the primary connection is to the "secondary " feel unit function and the secondary connection is to the "primary" control function? Why not have the RVDTs on the TL pivot?

No doubt the official investigation will address all of the above in some detail.

Now, those of you who are not engineers/analytical types, don't get me wrong. The above is not my proposed "explanation" of this accident. It is very, very unlikely that the failure modes that I have identified here would occur. It is also very unlikely that an experienced pilot would neglect to retard the throttles in the flare. My point in posting this is simply that these failure modes need proper investigation. With the evidence available to the investigators it may be possible to rule them out.

ChristiaanJ

3rd Sep 2007, 21:30

SyEng,

We already have several reasons, HF mostly, why having left the TL#2 where it was (in view of the TR#2 being locked out) is not totally implausible.

A mechanical failure (or an electrical one) has also been postulated repeatedly.

Your post at least has the merit of describing the mechanical arrangement in more detail than I've sen before. Do you have any diagrams you can post? A picture always says more than a thousand words.

bubbers44

3rd Sep 2007, 21:35

SyENG, I have posted in a lot less technical detail what you just said that the pilot physically brought both TL's to idle but somehow the FDR and engines did not get the data because of a possible linkage failure downstream of the TL's but was blasted saying the pilots left the #2 throttle in climb and could not have retarded to idle. I agree with you that what they physically did with the #2 TL and what the computers sensed has not been verified at this point in the investigation.

SyEng

3rd Sep 2007, 21:38

ChristiaanJ

Yes I do have a picture. Anyone know how I post a .bmp on here?

EMIT

3rd Sep 2007, 21:45

As far as the unlikeliness of a pilot not pulling to idle, the T/L of the engine with the deactivated T/R: it has happened twice before CGH with accident consequences, and has happened even more times with only slight uneasiness for the pilots as a result, as, for instance, described by 4 Holer Poler on 23 or 24 august (page 22 or 24 of this thread).

As for the post which described how much design effort has been put into the development of the non-moving thrust lever system - effort is not yet a guarantee that it is right.
Look at the FCU (Flight Control Unit; in Boeing called MCP; for others, the glareshield panel). Airbus philosophy there is - push a knob for computer generated values (managed modes), pull same knob for pilot values (selected modes). Well, within that one panel they managed to make the function of the baroset knob just the other way round: push for pilot value (QNH), pull for standard altimeter setting!

Also, the vertical speed selector: in order to conform to the above stated philosophy, it could not be in the form of a "wheel", it works on the same principle as the heading selector. For a heading selector that is a natural control, turn left for a left turn, but for vertical speed there is no direction of the selector that is naturally connected to the aircraft reaction. Turn left for descent, turn right for climb is a learned trick that requires cognizant activity of the brain every time the control is used (not sure whether cognizant is a real word, hope though that the meaning is clear).

I know that these controls have nothing to do with the accident at hand, I have only used the examples to show the scientists and designers that wrong things can very well exist in an aircraft, even if it used succesfully for millions of hours.

BOAC

3rd Sep 2007, 21:45

SyEng
http://www.pprune.org/forums/showthread.php?t=246758

Rob21

3rd Sep 2007, 21:54

Does anyone know if, when "locking" one engine with reverse inop, maintenance has to alter something in the TL's pedestal?

When T/R is engaged on an engine with reverse inop, how the information to ECU (or Fadec) is canceled?

Again, thanks for your patience...

SyEng

3rd Sep 2007, 21:59

Thanks BOAC.

Try this:

http://i236.photobucket.com/albums/ff269/SyEng_01/A320ATA76Mech.jpg

SyEng

3rd Sep 2007, 22:17

Here's another one...

http://i236.photobucket.com/albums/ff269/SyEng_01/A320ATA76Mech2.jpg

ChristiaanJ

3rd Sep 2007, 22:25

And the pictures themselves:
http://i236.photobucket.com/albums/ff269/SyEng_01/A320ATA76Mech.jpg
http://i236.photobucket.com/albums/ff269/SyEng_01/A320ATA76Mech2.jpg

SyEng

3rd Sep 2007, 22:26

ChistiaanJ,

How do you do that then?

ChristiaanJ

3rd Sep 2007, 22:35

SyEng,

After copying the URL from photobucket:
Instead of just pasting the URL of the picture in the "Reply to Thread" window, as you did, click on the little http://www.pprune.org/forums/images/editor/insertimage.gif icon and paste the URL of the picture in the window that pops up.

TripleBravo

3rd Sep 2007, 23:17

bsieker wrote:
Is 1.19 EPR indeed 75% thrust?Yes (round about), the conversion table flew somewhere through the forum, I believe, and I saw it somewhere in the documentation, but forgot where precisely. The percentage is roughly referring to MCT, maximum continuous thrust. (Answer by heart, I stand corrected.)

Rananim,
wouldn't this be such a tragic topic, .... Seriously. One party is bashing Airbus that its planes are second guessing the pilot's orders (FBW and it's protections) and the other party is speaking about a "serious design error" when the airplane indeed does exactly what the pilot ordered it to do.

By the way, no, they had not been using everything they had in an instance. You forgot about the manual brakes.

Psychology (and thus human factors) is a very subtle and delicate area that I am glad that there are people who not accuse first and then try to find arguments other than "obvious". (Jeez!)

I pity those lost souls (being the very reason why I write here), but it takes more than just to rumble around in order to never let it happen again. We owe it them to not jump to prejudices, but to explore the causal chain as deep as possible. Sometimes that's a very long way, nothing for the impatient - and that's exactly how aviation reached its today's extraordinary safety standards.

Rananim wrote:
This plane didnt crash because the pilot forgot to retard the TL.Ah - if you didn't notice, engines are designed to push the bird in forward direction, even with just one operating. If you leave one of them at 75% - what do you think does this mean in terms of "causes"? Nothing? Well, ... (Jeeeez!)

---------------

bsieker wrote:
Really? I don't have the TAM FCOM, so I don't know. Do you?I do, but that doesn't help much. It is basically the A320 standard FCOM. The callouts "spoilers", "reverse green" and "decel" are mentioned like in FCOMs of other airlines. But that doesn't neccessarily mean that training and day by day airline operations adhere 100% to what's in there. (And not proceeding every comma like printed does not mean to fly unsafe, so this information might not be very helpful.)

BTW, I stumbled upon a note about the "decel" callout, it could clarify what is originally meant by definition (by the books, regarding a discussion earlier): "DECEL Callout means that the deceleration is felt by the crew, and confirmed by the speed trend on the PFD. It can also be confirmed by the DECEL light. If no positive deceleration, call NO DECEL."

PAXboy

4th Sep 2007, 00:39

Non-pilot speaking
SyEng Thank you for the detailed information on the physical layout of the TL linkages. In the earlier part of the thread (before #1000) someone gave the explanation of what the electronics are doing when the TLs are moved. It set out the duplicated system to try and catch physical failures.

Yet again I say - if there had been video cameras on the FD??

In the past, there have been proposals to mount one in the central console - just in front of the TLs - and one on the ceiling looking down and also seeing adjustment to ceiling mounted controls.

If this accident had been in the USA there might be strong calls for such a move but whether there is, will depend upon the report and if the investigators manage to discover everything to a good confidence and that will include the cause of the 'look this' question.

DownIn3Green

4th Sep 2007, 01:16

Got to love the "old" Boeings (i.e.-707, 727, 737, 747) where the pilots flew the airplane and not the "computer"....

Dani

4th Sep 2007, 03:51

If there had been a technical/mechanical problem then Airbus/TAM/CIAA would have at least done some checks on other Airbusses, issued technical recommendations and bulletins, instead they have revised the MEL and given advise to all Airbus pilots in the world to make sure to close the TL on landing (what a useless recommendation!). I'm pretty sure that in the investigation, the first they pulled after the recorders was the power quadrant.

I think we can easily rule out any other reason than the obvious one. The problem is that this thread has become so long, that the latest users don't know anymore what the first ones wrote, hence repeat arguments that have been falsified longtime ago. I think we can safely argue that the pilots left the TL in CLB detent, for yet unknown reason. This would cause an overrun in any aircraft, also in a mechanical Boeing. And if they did it intentionally (which most of us believe) there is also no moving TL of any help.

Back to the facts please...

Dani

GMDS

4th Sep 2007, 05:10

I think we can safely argue that the pilots left the TL in CLB detent, for yet unknown reason. This would cause an overrun in any aircraft, also in a mechanical Boeing. And if they did it intentionally (which most of us believe) there is also no moving TL of any help.

Back to the facts please...

Dani

- As far as I can remember mechanical Boeings had no such thing as a CLB detent.
- Furthermore: How on earth can you leave a moving TL on a digital Boeing in a non existent CLB detent?

I agree that you can leave thrust on in any design, mechanical or digital, moving or fixed. However the unintentional, computer commanded change of thrust is new only to the digital designs and can happen on AI, B and MD products. The difference here is, that only in the AI design this is not duplicated/feadback/visible/tactile, choose whatever you prefer, through the levers, but only on the middle screen in EPR/N1 values. Whereas on B and MD products you will have both.
There is my simple reflection: Beeing not the absolute perfect aviator, I definitely prefer having two reminders/back up's/warnings/etc., choose whatever you prefer, as to only one: A probabiltiy more of avoiding a incident, especially during these crucial moments like flare, liftoff etc.. If this would imply a huge cost, a almost impossible design reengineering, I might shut up. If it is only to avoid losing face or facing law suits (cost), tacitly knowing that it would only imply a small hardware change (you can leave the good logic and function), I will keep rubbing it under anyone's nose.
A Airbus would still be a Airbus, and a much more attractive one, if you would just leave it as it is, but add a moving throttle. It would help those like myself , who don't dislike the bird, only the dead TL, and it would in no way harm the more experts who also like the bird. It might even be construed in such a way that you can choose between fixed TL, moving TL and manual TL. :ok:

Dani

4th Sep 2007, 06:12

GMDS, wrong again! The trust didn't increase, it just remainded on the last set trust setting!

If you would have left a TL in a Boeing on the last existing approach trust setting it would have provided trust as much as the TAM A320 did. There is no difference in this case. In such a conventional cockpit, it would be even worse, because the TL position would only be a little above idle, thus more difficult to detect. But the problem was not that the TAM captain did not detect it (most prabably), but that he left it on CLB deliberatly.

Correct, the non-moving TL are not the ideal solution, but in this very case it has nothing to do with it. Because there wasn't ANY trust change!

You can argue a lot that AI's TL don't provide any tactile feedback, yet I have seen too many pilots fighting against the moving ones. The classical case of acting against an automatic, instead of concentrating on the FMAs and other flight modes. This possibility of overriding an automatic function is exactly the wrong instrument to train a pilot of good airmanship, i.e. first check the mode you're in then change the parameters.

AI's cockpit philosophy has helped a great deal because it really urges pilots to do the correct thing, not just anything. Still some people (mainly in less developed countries) try do go around such procedures and invent their own - to a catastrophic outcome from time to time.

I agree with you that the easiest man-machine interface would be to fly everything manual, only basic instruments and no help from the system. But it's still not safer.

Dani

bsieker

4th Sep 2007, 07:44

Thanks, TripleBravo,

Is 1.19 EPR indeed 75% thrust?
Yes (round about), the conversion table flew somewhere through the forum, I believe, and I saw it somewhere in the documentation, but forgot where precisely. The percentage is roughly referring to MCT, maximum continuous thrust. (Answer by heart, I stand corrected.)

So it is around 75% N1 (I have the graph printouts floating around on my desk somewhere), but I doubt that the relation between LP rotor rpm and actual force is linear. I suspect it to be polynomial of at least second order (most things fluid-dynamic are, and given that the relation between EPR and N1 is a fourth-order polynomial ...). I'm also sure it depends on airspeed, air pressure, air temperature, humidity, ...

So I don't think that 75% N1 is 75% of MCT thrust force (in its physical meaning, expressed in Newtons, or maybe pounds-force, if you're more at home with that).

I'm sure the experts will know, as it is crucial to know all the forces to determine if stopping would have been possible with ground spoilers, despite this thrust.

Bernd

BOAC

4th Sep 2007, 08:07

Dani - re-read the FDR please. No 2 thrust increased (as an A/T function to try to maintain set speed we are told) until the A/T dropped out, when it decreased again to level at (presumably) the EPR for the EITHER the T/L position or, if there had been some sort of sensor failure, the EPR for where the system THOUGHT the T/L was.

Assuming that the first scenario existed, the point being made was that if the T/L position was 'driven' for feedback AND the pilot had his hands on the T/Ls (which seems to be a point of question on this thread, and would have been difficult if they were 'split'), he would might have had the vital prompt to check its position.

I'm still waiting for an answer to whether the EPR on the reversed No 1 represents full reverse or idle?

bsieker

4th Sep 2007, 08:11

[...] but add a moving throttle [to the airbus flight controls].

This may also have been lost in the over-long thread, so I'll repeat that there are at least two arguments for static thrust levers, and against moving ones. And I will not be the judge whether or not these effects of the A320 design provide a more substantial (safety and convenience) advantage than the one ostensibly gained by adding movement.

- Alpha-Floor-Protection:
This feature sets TOGA thrust when exceeding a pre-defined angle of attack, to keep the aircraft from stalling (coupled with an enforced limit on the angle of attack that the pilot cannot exceed even at full backstick deflection.)

Pilots used to a moving-lever design desiring low-thrust would perhaps automatically reach for the thrust levers and pull them back if they quickly moved from a low setting to TOGA, denying them this form of flight envelope protection. Setting TOGA thrust without moving the levers gives the pilots one more second to think before cancelling utothrust, and thereby unlock TOGA thrust.

This argument may seem a bit far-fetched, but may happen more often than the scenario in this accident, which so far has occured at a rate of once per 17 million landings.

So I ask again if anyone knows about the number of times Alpha-Floor-Protection has been activated? Isn't this such an abnormal situation that it should be logged?

- Limiting thrust during Autothrust operation
The levers provide a simple and intuitive means to limit thrust on an engine producing excessive vibrations, while having maximum power available on the other engine.

Having "split" thrust levers is abnormal, so the ECAM will warn about it, but only in amber, meaning "this is not the normal way things are done, but it may be desired, so I won't make a big fuss about it, but simply tell you."

Mandating a change to the thrust lever system would have to prove that the gained advantage outweighs these (and probably other) advantages of the current design. This has not been shown.

Bernd

Dani

4th Sep 2007, 08:30

BOAC, thanks, I was wrong, you and GMDS are right. Still it is no argument for *his* argument since the same would haven to any other conventional aircraft with autothrottle: If you reduce only one TL and let the other keep the existing speed. Otherwise you couldn't survive any engine failure!

To my knowledge I assume that the EPR1 value is for full reverse.

Bernd, Alpha Floor protection is nothing Airbus has alone. Most airliners with autothrottle have it, too. It is also no argument for a non moving trust lever.

Dani

bsieker

4th Sep 2007, 08:34

Dani - re-read the FDR please. No 2 thrust increased (as an A/T function to try to maintain set speed we are told) out,

Correct.

until the A/T dropped when it decreased again to level at (presumably) the EPR for the EITHER the T/L position or, if there had been some sort of sensor failure, the EPR for where the system THOUGHT the T/L was.

Not quite. It was frozen at the setting it was at when autothrust disconnected, as is the specified behaviour for a so-called "involuntary disconnect".

The decrease in the graphs is more likely due to the fact that an increase in speed was achieved by the increased thrust, and so the feedback-control loop reduced thrust again.

During approach autothrust speed-mode, control is more complicated than during cruise flight, and takes into account both air- and ground speed. In the graphs we can see that the speed drops a bit after touchdown (18:48:24) and thrust increases, then speed increases slightly (18:48:32), after which thrust drops again, and then A/THR disconnects (18:48:29.5), freezing thrust.

Recorded thrust lever angle was CL detent (22 degrees or so), thrust associated with that would have been close to EPR 1.28 (see FDR graphs page 11, showing a take-off until shortly after thrust reduction.)

Thrust only changes to meet actual thrust lever position when A/THR is disconnected with the thumb-push-button on the side of the thrust levers (the standard way).

I'm still waiting for an answer to whether the EPR on the reversed No 1 represents full reverse or idle?

I'm also curious about that. Where exactly is EPR sensed? Maybe it gives an irrelevant reading with reverser doors deployed? An N1 reading might be helpful here.

It might even be construed in such a way that you can choose between fixed TL, moving TL and manual TL.

Terrible idea, as every HMI designer will tell you.

Bernd

bsieker

4th Sep 2007, 08:41

Bernd, Alpha Floor protection is nothing Airbus has alone. Most airliners with autothrottle have it, too. It is also no argument for a non moving trust lever.

Maybe. This wasn't actually my idea, it had been mentioned before in this thread.

Whether or not it is an argument really relies on whether TOGA-thrust at Alpha-Floor-Protection also moves the levers fully forward, and if so, on crew reaction to that.

(I can imagine that this sort of emergency function does not move the levers even on moving levers-systems; on Airbus, too, Alpha-Floor-Protection is abnormal in that it is the only case in which autothrust can be active outside its normal active range of thrust lever settings, and also the only situation in which thrust can be higher than lever setting.)

And I will also say that, as to my 2nd argument, if moving thrust levers could be shown to have a significant safety advantage (which has not been shown), then this convenience argument is less important.

Bernd

armchairpilot94116

4th Sep 2007, 08:59

Being very simplistic here, but perhaps Airbus should rethink their aircraft control logic and follow more the KISS principle in their basic design concept. Making their planes even easier to fly and more intuitive to the human brain . And making sure that those that pilot them are more then adequately trained.

Airbus has had more man/machine problems then the competition throughout the last few decades it would appear. Airbus aircraft have the final say , rather then the pilots in any pilot / plane confrontation. Unless you knew what the plane was designed to do and never ever forgot any part of it, you ARE in danger, because YOU wont be able to dictate what it does and wont be able to understand what it is doing.

GMDS

4th Sep 2007, 09:02

Bernd

And I will also say that, as to my 2nd argument, if moving thrust levers could be shown to have a significant safety advantage (which has not been shown), then this convenience argument is less important.

And just who would show that? If humble user-pilots try to reason as to why it might be so, they get a severe bashing. Furthermore they get their legitimacy questioned, because they are ... humble pilots only!! The manufacturor, authorities and airlines, all of them self proclaimed legitimate to "prove" or "disapprove" only, have no interest whatsoever to go ahead on this because it would: 1)cost, 2)show some of their ideas were wrong), 3)incite lawsuits, 4)sell less airplanes, 5)mean less "contributions" aso. A lost cause.
By the way: Has it been shown that a fixed throttle has a significant safety advantage?
Your argument about Alpha floor only withstands with the assumption that the pilot would interfere. Just as yours, Dani, that many pilots "fight" the moving AT.

Quote:
Originally Posted by GMDS
It might even be construed in such a way that you can choose between fixed TL, moving TL and manual TL.

Terrible idea, as every HMI designer will tell you.

I have to agree. Just as the idea of relying on HMI designers.
A "choice" for his subjects has always been a nightmare for any ruler .... (sarcasm out)

GMDS

PAXboy

4th Sep 2007, 11:06

Non-pilot speaking

A question I have long been waiting to be answered in this thread and, as it has not, now ask the question:

What is the operating procedure when a reverse is inop?
The equipment is physically isolated (by electrical, hydraulic or mechanical means) to that, even if you select REV, it will not happen but the engine will spool up as the TL is moved and provide forward thrust.
The equipment is Isolated (as above) but you are instructed NOT to select REV and NOT move the TL from idle, after closing thrust.
Some more sophisticated isolation that might involve ensuring that, even if you select REV and move the TL from idle - the engine will remain at idle and the REV equipment will not deploy. That is, some form of electronic - rather than physical - isolation is in place.In other words, must you remember not to lift the REV latch on the affected engine or, if you lift the latch, will it still be OK?

Is it better to be able to: close both TL's; select REV and move both (or 'all' if more than 2) TLs and not have to worry that one of the REVs is inop?

Rob21

4th Sep 2007, 11:09

I understand we have Airbus and Boeing pilots here.
Quick question: If a TL was to be "forgotten" during flare (one reverse inop), in which TL system this would be more likely to happen - moving or non moving TLs?

DozyWannabe

4th Sep 2007, 11:31

Rob, I suspect that you'll get both answers from each side.

Lemurian

4th Sep 2007, 12:40

Your argument about Alpha floor only withstands with the assumption that the pilot would interfere. Just as yours, Dani, that many pilots "fight" the moving AT.
Actually, they are more than assumptions. Please refer to the 744 incident in Tahiti, in which the handling pilot fought an automatic go-around, managed to land but then lost it when he couldn't bring all the reversers all together, leaving #1 to accelerate to full go-around forward thrust, while the other three were in full reverse thrust. Result was a visit to the coral reef.
The Air China A300 in Nagoya was in the same type of scenario. Only far worse.
A question that bugs me is why people do refuse to consider the human factor (s) in this type of accident and only concentrate on the M /non M argument ?

Dani,
Bernd, Alpha Floor protection is nothing Airbus has alone. Most airliners with autothrottle have it, too. It is also no argument for a non moving trust lever.

I do not know of any example outside the AI range of FBW planes and the Falcon 7X.

Regards.

armchairpilot94116

4th Sep 2007, 17:18

Yes the China Airlines A300-600 disaster in Nagoya is a very good example of the pilots unwittingly and unknowingly fighting with the aircraft's designed operating principles. And I am not clear why the power failed after the aircraft stalled, after which it fell to the ground.

That particular incident is worth VERY careful study.

http://www.rvs.uni-bielefeld.de/publications/Incidents/DOCS/Research/Rvs/Misc/Additional/Reports/taipei/taipei.html

http://www.rvs.uni-bielefeld.de/publications/compendium/incidents_and_accidents/nagoya_a300.html

EMIT

4th Sep 2007, 22:07

Bernd,

This accident at a rate of 1 per 17 million landings - no, the rate should be calculated versus the number of landings with one thrust reverser deactivated and the pilots using autothrust for the approach.
Rate would be closer to 1 per 17.000 landings then.

flyingnewbie10

5th Sep 2007, 01:15

Members of the Brazilian Chamber of Deputies had access today to the actual voice recording on the last 30 minutes of the PR-MBK.

I can't figure out what made one of the Congressmen say that after listening to the recordings and meeting with CENIPA personnel he got definitively convinced that the accident was not caused by HF.

Dani

5th Sep 2007, 03:25

I can't figure out what made one of the Congressmen say that ... the accident was not caused by HF.

I *can* figure out :E

Dani

5th Sep 2007, 03:45

Paxboy, on an Airbus you can never have trust increase on an engine with actual mechanical failure of a TR. The system is designed that if there's something wrong, there is no trust added. But in the actual case this was different because the TL remained in CLB so the pilots deliberately kept trust. Older aircraft where very different, as you might remember the latest NWA accident, where a MD-80 hit a A320 on ground with high speed (hydraulics failure, no reverser buckets, but full "revers" trust). .

In fact, in most cases there would be no harm if you would go to full revers even if the TR are u/s. Please check also the FDR from the previous landing, where the RHS pilot went into revers on both engines, and nothing happened. Airbus recommends not to go into revers if one is u/s, to cover all technical failures.

Studi, you have to leave the authority to the pilots. If you loose one engine during flare, or if you should get a reverser deployed in the air, you cannot automatically retard the other. Airbus is inspite of the advanced automatics always giving the last authority to the pilots. If they want trust, they get it. If you want trust, you leave the TL in CLB. A computer cannot read a human's mind! You have to change the mind of these pilots, not the automatics!

Lemurian, ANY airliner that I know add trust before they stall. Fokker 100 come to my mind, MD-11... I'm surprised that Boeing still doesn't do it. Maybe in the 787 finally... I'm so glad I'm not flying these oldtimers :eek:

Dani

flyingnewbie10

5th Sep 2007, 03:49

I * can * figure out

Ok Dani,

Maybe they just want to get some "extra" (as usual anywhere in this world) but I think it would be too risky.

Maybe there are some sounds out of the script...

Dani

5th Sep 2007, 07:56

Studi, I agree that these are situations where you shouldn't be in. In eighter case!
But sometimes you are! If it's your bad day, you have assymetrical trust, you have one reverser working and the other not.

1st case: you want to stop but do not have idle yet.
Why not block reverse until both levers are in IDLE
That's exactly what the system did! One TL was not in idle. Hence no braking. As long as a pilot wishes to have more than idle, the aircraft should not be brought to a stand still. The system design had completly anticipated the will of the pilot. Unfortunately that wasn't what the pilots wanted. Once again. A machine cannot read one's mind.

2nd case: you want to continue but have reverser
There is absolutely never ever the need for reverse on one engine and forward thrust on the other
Yes there is. Unintended reverser deployment. Mishandling of TL. Human error. Mechanical failure...
The system also anticipates this situation by adding the trust on the remaining engine.
Both cases are built in the system. It is fool proof. Believe me, those engineers spent a lot of time to go through all posibilities.
I don't know if Rananim is right about what he says about Boeing, but also if a Boeing doesn't give you reverse if you are not in idle, this doesn't help you in the TAM case. They never wanted to touch and go, never go around. They wanted to land, but "forgot" the TL. They could have never gone around, when they realized they were in big trouble.

There are a lot of people with doubts about AI technology here in this forum. I understand that, since they have never seen the system from close. Ignorance is the root of prejudice. But any aircraft in the world would have behaved in this TAM case like the A320. This is not an Airbus case, it is a HF case. The longer we ignore it, the longer we don't find the reason for the tragedy.

Dani

EMIT

5th Sep 2007, 08:23

Dani,

Already B-767/757 autothrottles have Alpha mode, which will not allow speed to go lower, if limit Angle of Attack is reached. This implies that TOGA thrust will be given, if that is what it takes to prevent further speed decay.

Just off the top of my head, difference between AI and B setup may be in the fact whether A/T has to be engaged or not, for this protection to work.
-------------------------------------------------

More or less the same goes for A/P modes - they will also respect speed limits, but do so when engaged. In B, if pilot manually puts the a/c on it's nose or back, the flight controls won't stop him. In A (FBW) a/c, the pilot is prevented, also in manual flight, from performing outlandish deeds by the flight control system.
-------------------------------------------------

This TOGA lock thing gives me another argument to illustrate the difference between moving and non-moving thrust levers.

To get out of TOGA lock in the A-320, you have to disengage A/T.
If you just pull back the thrust levers, nothing will happen. You would notice that nothing would happen, for instance, by looking at the engine instruments. Then you would have to consciously reason why the engine indications have not reduced to idle and then you would realize - oh, got to disconnect A/T.

In moving thrust lever setup, you may also have to disengage A/T to cancel ALPHA mode, but if you just pull levers to idle without disconnecting, the engines will go to idle and your hand will feel the A/T working against your hand, trying to move the levers forward again. In this way, you get what you want immediately, not only after the observation, reasoning, action cycle has been completed, and, the road towards realizing what you have forgotten may be more direct - from the hand that feels opposition directly to realization, without a knowledge based reasoning process.

EMIT.

bsieker

5th Sep 2007, 08:29

Lemurian, ANY airliner that I know add trust before they stall. Fokker 100 come to my mind, MD-11... I'm surprised that Boeing still doesn't do it. Maybe in the 787 finally... I'm so glad I'm not flying these oldtimers

They do add thrust, as does the B777. They also have stick-shakers, and increase the feedback-force on the column.

This is not the same as Airbus's "Alpha-Floor-Protection" on their FBW airliners.

I read up a bit on the FBW Boeing (there is a thread on PPrune under the Tech Logs about Flight Envelope Protection).

While that machine makes it difficult, with sufficient force on the yoke you can fly it outside the envelope and stall it.

An A320 (assuming Normal Law), will not let the pilot exceed a certain angle of attack ("Alpha-Max"), no matter how hard he pulls the stick back.
Before reaching Alpha-Max, (at "Alpha-Floor"), TOGA-thrust is set and locked, and has to be turned off explicitly.

Bernd

PBL

5th Sep 2007, 08:31

There is absolutely never ever the need for [XYZ] Never. So why give the pilots the possibility to do so?

studi, am I right that you are really new to this?

Let me try a short precis of how such systems need to be designed.

First, there are sensors which sense *some* of the system state (including *some* of the intentions of the operators). Then, on the basis of the sensor readings a designer has to decide
(a): what aircraft configuration makes most sense, and
(b) what the hazards are from hisher choice in (a).

Those hazards would be situations in which the aircraft configuration chosen in (a) mismatched the situation the aircraft really was in. And for all the hazards you can think of under (b), you then have to show:
(c) how the hazards can be mitigated.

You want to say there is never a situation in which one wants reverse on one engine and thrust on the other. That may be, but then a designer who is explicitly considering this undesirable situation would need to determine what is best to do. There seem to me two possibilities:
(i) the pilot wants to stop;
(ii) the pilot wants to go.
The hazards are equally obvious:
(x) if you inhibit thrust, the (most obvious) hazard is a situation in which the pilot wants to go;
(y) if you inhibit reverse, the (most obvious) hazard is a situation in which the pilot wants to stop.

How would one design a configuration to admit both these possibilities while mitigating the hazards? Answer: the designer must let the pilot choose in the given situation. Heshe can't choose in advance from hisher comfy desk.

PBL

EMIT

5th Sep 2007, 08:36

To STUDI.

People have repeatedly stated in this forum that B will not allow you to select reverse when *not all* thrust levers are at idle.

They have "proven" this with a quote from FCOM.

What those people have forgotten is, to quote from FCOM a few paragraphs earlier, where it says that *each engine has it's individual control on the flight deck* .
Now as far as I know, individual means - not in any way depending on the other one. Reading and understanding is a complicated activity!!

The thing is, finding out what is really meant in the books, would require playing around with those controls in a live aircraft. Now that is something that you don't do in practice, because, for instance you don't want a ground engineer to get wounded by your fiddling around during a ground stop.

Moreover, why would you ever want to know, if you just do as always, that is, pull alll thrust levers to idle when touching down?

bsieker

5th Sep 2007, 08:38

It is entirely possible to have reverse on one engine (= not flyable) and climb power on the other (= not landable, no spoilers), which is definitively a state which is never ever desirable.

Not sure how Boeing is doing it, but it's really obvious that you should always have at least one of the two options, braking or going around.

Please read about the accident described only two posts before yours. In a B747 three engines were in full reverse, one at Go-Around thrust. This is a general problem, not specific to Airbus.

Bernd

GMDS

5th Sep 2007, 08:42

Lemurian, ANY airliner that I know add trust before they stall. Fokker 100 come to my mind, MD-11... I'm surprised that Boeing still doesn't do it. Maybe in the 787 finally... I'm so glad I'm not flying these oldtimers :eek:

Dani

Just for your info: B777 FCOM 9.20.11:
The autothrottle can support stall protection if armed and not activated. If speed decreases to near stick shaker activation, the autothrottle automatically activates in the appropriate mode (SPD or THR REF) and advances thrust to maintain minimum maneuvering speed

This means, on or off (not disarmed though), the AT of this "oldtimer" will add thrust when approaching stall and stick shaker.
It's tricky pretending things about birds you haven't flown yourself.........

bsieker

5th Sep 2007, 09:19

This accident at a rate of 1 per 17 million landings - no, the rate should be calculated versus the number of landings with one thrust reverser deactivated and the pilots using autothrust for the approach.
Rate would be closer to 1 per 17.000 landings then.

Perhaps.

But when we're looking at the thrust lever design, we cannot separate TR-inop landings from those with all systems functional. One cannot have a different set of thrust levers installed, or a different way of operations when one (non-critical) system is unserviceable.

So the statement stands that the thrust control system (hardware, software and wetware) has worked as per design in 55 million landings, and failed in this particular way in 3 landings. Mandating a change to the system cannot only take special situations into account.

So the relatively high failure rate at handling the thrust levers with one reverser inop has to be addressed, but not by changing the thrust lever system. More consistent procedures, and better training will perhaps be more effective. (More about procedures and reversers inop shortly ...)

Bernd

Dani

5th Sep 2007, 09:57

GMDS, I find it amusing the least that you blame me to saying something wrong about Boeing, since I stated before that ANY aircraft with Autothrottle has some sort of alpha floor protection, then some very smart guys (forgive me that I believed them) told me that it's not so, then I give in because I don't really know every aircraft and accept their information. Now you blame me for repeating their opinion? I was defending your system, do you remember????

Dani

PBL

5th Sep 2007, 10:49

....... you blame me to saying something wrong about Boeing ....... then some very smart guys ...... told me that it's not so, then I give in because I don't really know every aircraft and accept their information. Now you blame me for repeating their opinion?

Yes, it does show the value of making sure one's information is correct *before* one posts it. :)

PBL

Lemurian

5th Sep 2007, 11:28

Wait a minute !
There is a bit more than a misunderstanding here. The discussion started when Dani wrote :
Alpha Floor protection is nothing Airbus has alone. Most airliners with autothrottle have it, too. It is also no argument for a non moving trust lever..
*Alpha floor* refers to a mode that's quite specific, involving not only a go-around thrust application but also the triggering of a pitch submode that will keep the AoA below the onset of stall.
I still stand by my previous statement :
I do not know of any example outside the AI range of FBW planes and the Falcon 7X.
That some airplanes - and I'll confess that there were more than I expected - have some sort of *thrust application * (how much / when /which mode ?) it doesn't give them the Alpha floor protection as we understand it in AI products.

GMDS

5th Sep 2007, 12:39

Now you blame me for repeating their opinion? I was defending your system, do you remember????

Dani

I didn't blame you, mate. I said "it's tricky".

GMDS

marciovp

5th Sep 2007, 13:53

The previous transcript of the voice recorder missed some time, perhaps the most dramatic one. The House of Representative Committee (CPI) heard the full tape recently, and after that they came to the conclusion that there was no HR in the disaster. They also learned that in the simulator the "retard" sign goes on until the TLs are in the right position while that in the TAM plane it stopped after repeating twice. From what they heard in the tape, there were dramatic moments with much despair and the pilots were very attentive to what they were doing. Finally they said that there was the noise of the TLs being placed on Idle. Here, in
portuguese-braziliam, the news:

http://si.knowtec.com/scripts-si/MostraNoticia?&idnoticia=741124&idcontato=47362&origem=secao&nomeCliente=DEMOCRATAS&data=2007-09-05

Ben_S

5th Sep 2007, 14:18

Not a pilot but the retard call not continuing has been discussed many times & is due to TAM not having the latest "software" on their planes.

DozyWannabe

5th Sep 2007, 14:20

Well that's settled, guess we can all go home now... ;)

Rananim

5th Sep 2007, 14:37

As I said before,the denial from the Airbus camp has always been entertaining..One of them even accused me of putting before the cart before the horse.How ironic then that this aircraft gives you TR before TL's are at idle.If ever there was case of putting the cart before the horse,this would be it.But with 200 people dead and 3 precursory incidents/accidents the time for facing the truth will come soon.

An interlock mechanism in the thrust lever assembly mechanically prevents simultaneous movement of the forward and reverse thrust levers.The reverse thrust levers can be raised only when the forward thrust levers are in the closed positionRaising the reverse thrust levers to the reverse idle detent locks the forward thrust levers in position.
B747-400 OPS MAN vol 1 72.10.18
Applies to all Boeing aircraft.I already quoted 777 FCOM and I dont need to quote 737 as I know the machine like the back of my hand.

Studi,
You have my respect for choosing reason over bias.Loyalty to the type you fly should never interfere with honest appraisal.I stand by that and know that no manufacturer is perfect.
Boeing too has faults.Of course it does.The 737 single rudder PCU broke the redundancy rules.The non-automatic retraction of speedbrakes with TOGA thrust remains controversial(they retract automatically on the rwy GA scenario but not in the EGPWS escape maneuver-to cover themselves,they proscribe specific pilot actions when carrying out such a manuever).The failure to truly update the 737 and replace master caution with EICAS was lazy and penny-pinching but they have experts who consider all the angles.

That's exactly what the system did! One TL was not in idle. Hence no braking. As long as a pilot wishes to have more than idle, the aircraft should not be brought to a stand still. The system design had completly anticipated the will of the pilot. Unfortunately that wasn't what the pilots wanted. Once again. A machine cannot read one's mind.

This quote from camp A stalwart Dani would be truly funny if we werent discussing such a serious subject.Even if you make allowances for the "English",it just makes me cringe when I read it.You cannot command something unwittingly.The pilot forgot to retard the TL.Thats not a command.If the computer accepts an illogical command,then it is as stupid as the pilot.Is it not?He says the will of the pilot was to land on a short wet rwy with app thrust on #2.Really?The computer understood this,accepted it and gave him the hybrid state.Thats nice.

Wait just a second..it gets funnier.
Quote:
There is absolutely never ever the need for reverse on one engine and forward thrust on the other

Yes there is. Unintended reverser deployment. Mishandling of TL. Human error. Mechanical failure...
The system also anticipates this situation by adding the trust on the remaining engine.
Both cases are built in the system. It is fool proof. Believe me, those engineers spent a lot of time to go through all posibilities.

Lets break this down closely.
Unintentional reverser deployment?Theres a need for this is there?Please tell me.If a reverser deploys in flight(as in lauda),then theres been a serious mechanical failure..and we certainly dont need or want that do we now?
Mishandling of TL and /or human error?.Theres a need for this?I'd like to know when.Theres a need for an interlock mechanism that prevents human error/mishandling of TL's becoming a smoking wreck at the end of the runway.
Mechanical failure?Theres a need for mechanical failure is there???????
The system is "foolproof"..the engineers went through all the possibilities.Did they now?Tell that to the families of the 200 dead.

He saves his piece de resistance for the end...
but also if a Boeing doesn't give you reverse if you are not in idle, this doesn't help you in the TAM case.
This reveals neatly his lack of understanding of the value of an interlock mechanism and how this TAM crash happened.NO RETARDATION=NO SPEED DECAY+NO CONFUSING HYBRID STATE=TOGA.The pilot is human and subject to survival instinct.If that intuitive argument doesnt convince you,consider that the pilots were experienced and must have mentally prepared for the TOGA option if retardation didnt proceed as per normal.How can you go for TOGA after TR activation?They were trapped.

bsieker

5th Sep 2007, 17:41

The reverse thrust levers can be raised only when the forward thrust levers are in the closed position

As EMIT pointed out, this is not unambiguous.It can relate to all thrust levers together, or each one individually. (And to reassure you, the B737-800 FCOM uses the same wording.)

It could be read as: On each thrust lever, the reverse lever can be raised only if the forward thrust lever is in the closed position.

And the paragraph a few pages earlier about each engine having its individual control suggests just that.

This is essentially no different from Airbus.

It could also mean, less ambiguous: The reverse thrust levers can only be pulled when all forward thrust levers are in the closed position., which is the reading you prefer.

But did you actually try it, to see which of these readings is correct?

I'm on shaky ground here, since I can only reverse-engineer the workings from the FCOM and various reports, so it would be nice to have some Boeing pilot test it in the simulator and report back.

The incident Lemurian mentioned (B747 overrun) indicates that there is no cross-engine mechanical interlock, otherwise the pilot either couldn't have gotten reverse if the one engine automatically went to Go-Around thrust, or the Engine could not have gone to Go-Around with at least one in Reverse.

Apparently there is only a per-engine interlock, which is not needed on Airbus, since Reverse and Forward thrust are commanded with the same lever. There is a latch that prevents accidentally going past IDLE in either direction.

Bernd

bsieker

5th Sep 2007, 18:05

Please refer to the 744 incident in Tahiti, in which the handling pilot fought an automatic go-around, managed to land but then lost it when he couldn't bring all the reversers all together, leaving #1 to accelerate to full go-around forward thrust, while the other three were in full reverse thrust. Result was a visit to the coral reef.

Interesting. I could only find the french report at the BEA web site. Is there an English translation available?

Bernd

bsieker

5th Sep 2007, 18:19

Lets break this down closely.
Unintentional reverser deployment?Theres a need for this is there?

That's not what he said. He said there may be a need for reverse on one angine and forward thrust on another, in case of uncommanded reverser deployment.

Wouldn't you agree to that?

The problem lies somewhere else. There may never be the need to have one thrust lever at CL and one at reverse. Which is different from having differential (or opposed) thrust on the engines.

But from what I can see, it is not clear that any manufacturer keeps you from setting the levers in such a way.

Bernd

FrequentSLF

5th Sep 2007, 19:08

No pilot here

In various posts is indicated the the braking effect of full reverse (both operative) will be at the best 6%, 3% with one operative. From other posts I also understood that once the pilot has engaged the TR he has commited to landing, and TOGA is no more an option.
Is it worth to drop the TOGA option to achieve at the best a 3% additional braking effect?

Andrea

PBL

5th Sep 2007, 19:37

Is it worth to drop the TOGA option to achieve at the best a 3% additional braking effect?

I am fairly sure it was pointed out some x-thousand posts ago that the proportion changes on a icy runway. Southwest went off the end of a snowy runway at Chicago Midway and killed a car passenger because deployment of reversers was significantly delayed over the assumed deployment time in their landing-distance calculation.

So they are good insurance for the weather. But these sliding-cowl 90+-degree thingies aren't as effective as good old clamshells, so I understand.

PBL

Lemurian

5th Sep 2007, 20:45

bsieker,
Is there an english translation available ?
I haven't found any, except some very basic info from *aviation safety Network*.
If you're really interested, I could volunteer a translation, but this is an excerpt of the report :
At 21:05 the aircraft touched down at a speed of 168 knots. Two seconds later no. 1 engine power increased to 107% N1.
Because of this the spoilers did not deploy and the automatic brake disarmed. Reverse thrust was used on all remaining engines. Because of difficulties due to thrust asymmetry, the no. 4 engine thrust reverser was cancelled. The aircraft overran the runway and ended up in a lagoon.

Oh dear ! Even bloody moving T/Ls can't save the day when your chips are down ! This musrt be the end of the world !

bsieker

5th Sep 2007, 21:03

If you're really interested, I could volunteer a translation, but this is an excerpt of the report

Yes, I found that, and I downloaded the French report from bea-fr.org.

Thanks for the offer, but I think my school French and an online dictionary will let me figure it out.

"système automatique de vol". What a beautiful language. :) (No sarcasm intended.)

Most important was the FDR graph, showing that N1 of no 1 engine went to "pleine poussée positive", and thrust reversers were deployed after that, which clearly shows: no inter-engine interlocks.

Bernd

ChristiaanJ

5th Sep 2007, 21:05

Lemurian,
Do you have a link for the French report?
Couldn't find it, but while looking found this one.
http://www.bea-fr.org/docspa/2000/tj-b001105/htm/tj-b001105.htm
Sorry, also in French.

flyingnewbie10

5th Sep 2007, 21:15

The previous transcript of the voice recorder missed some time, perhaps the most dramatic one. The House of Representative Committee (CPI) heard the full tape recently, and after that they came to the conclusion that there was no HR in the disaster. They also learned that in the simulator the "retard" sign goes on until the TLs are in the right position while that in the TAM plane it stopped after repeating twice. Finally they said that there was the noise of the TLs being placed on Idle.

Marcio,

Maybe the difference between the simulator and the PR-MBK retard warning is due to some update that the simulator complies with.

However I am very curious about the sound of (both ?) TLs being brought to idle... Maybe there is some analysis already being made with the CVR to confirm it or not.

An Audio Spectrum Analysis ?

SyEng

5th Sep 2007, 21:31

Dani,

Ref your response 1997 to my post 1982.

If there had been a technical/mechanical problem then Airbus/TAM/CIAA would have at least done some checks on other Airbusses, issued technical recommendations and bulletins...

Of course they would if the investigation establishes this as a causal factor.

I think we can easily rule out any other reason than the obvious one. ... I think we can safely argue that the pilots left the TL in CLB detent...

Well, I wouldn't bother applying for any jobs in accident investigation or safety/certification just yet if I were you. Here are a couple of rules:

- One can rule out possible failure modes on the basis of evidence only. Otherwise the best you can do is assign relative probabilities (based on past failures/fault trees/circumstantial evidence/engineering judgement etc..) to the different possibilites and maybe end up with a probable cause.

- If a failure mode has not yet occurred, this has no effect on the probability of its happening (a suprisingly common misconception).

My personal feeling from the evidence made public so far is that pilot error/HF is more likely than a linkage failure (based on previous incidents (not limited to Airbus)). The official inquiry must address the possible failures which I identified in post 1982. Hopefully adequate evidence has survived to give an unequivocal answer.

Human factors also apply to maintenance personnel. Split pins have a low (but non-zero) failure rate if they are correctly fitted. Their efficacy is much diminished if they are omitted.

Back to the facts please...

I couldn't agree more.

flyingnewbie10

5th Sep 2007, 21:41

I don't know if an Audio Spectrum Analysis of a CVR ever had so much importance as it apparently has now.

SyEng

5th Sep 2007, 21:53

I don't know if an Audio Spectrum Analysis of a CVR ever had so much importance as it apparently has now.

Neither do I, but it must surely form part of the official investigation. If the sound of TL retard was clear enough to transcribe by ear, then a proper audio analysis could be powerful evidence.

Are there any alternative CVR transcripts available following the latest political interference?

flyingnewbie10

5th Sep 2007, 22:07

Are there any alternative CVR transcripts available following the latest political interference?

I don't think so but at least we now know there is probably something being done to check all possibilities.

One thing I would like to figure out is the reason of that right TL deviation at idle stop (-3 degrees instead of zero) at chart 9 of the FDR, in a context of mechanical/electronical problem.

Lemurian

5th Sep 2007, 22:13

ChristiaanJ,
here is the link :
Rapport incident F-GITA (http://www.bea.aero/docspa/1993/f-ta930913/pdf/f-ta930913.pdf),
some 50 pages long.
Enjoy !

ChristiaanJ

5th Sep 2007, 22:48

Lemurian,
Thanks! I've saved the report.
"Enjoy" may not be quite the right word....
But I'll see if I can extract something relevant to the current subject (I'm bilingual English-French, so no language problem).

Lemurian

5th Sep 2007, 23:23

I took a quick look at the Camair CDG incident you gave us a link to, and I came across the comment made by the BEA saying that this overrun had some similarities with another two incidents, namely F-GITA at Faa and China Air B-165 at Kai Tak.
That one is also worth a careful read as, from the accident analysis,

they landed normally in difficult rain / windshear conditions
T/Ls retarded to *idle*, speedbrakes extended and autobrakes kicked in.
Somehow #1 T/L was pushed 8 degrees forward of idle, the other T/Ls in a lesser extent
this action on #1 T/L disconnected the autobrake and caused the speedbrakes to retract (with the corresponding lever movement on the pedestal)
The consequences of advancing the levers instead of selecting
reverse thrust were serious. Residual forward thrust
increased, wheel braking stopped and the speedbrakes were
retracted. Neither pilot noticed these very important
changes. They did not look at the speedbrake lever and they
may not have felt the effect of wheel brakes because brake
pressure was being phased in.
When eventually, reverse thrust was reapplied, the speedbrakes extended again
The airplane overrun the runway at a speed of some 30 knots.
No casualties.

Here is the link to that report :
China Air B-165 HKG (http://ebook.lib.hku.hk/HK/HKG/B35838838.pdf)
What I find quite interesting is that this report destroys all the blurb we've seen on this thread about the need for moving throttles (because of *tactile feed back*, *visibility* (knowing that 744 throttles are a damn sight bigger / taller than 320 T/Ls).
Finally, going back to the argument someone had with bsieker on occurrences'statistics, I'd say that, considering the number of sectors flown by a long -hauler, the statistics do not seem to be in favour of the M solution, do they ?
Of course I have a very simple mind
Best regards

HotDog

6th Sep 2007, 01:32

Not trying to blow my own trumpet as a flight engineer but had there been a flight engineer present, neither AF or Air China would have finished up in the drink. SOP on the classic 747s was for the flight engineer to hold the engineer's spur thrust levers against the stops after selection of reverse thrust which prevented any forward movement of the thrust levers.
http://i106.photobucket.com/albums/m246/adamtakach/Image0005.jpg
Sorry, I can't seem to be able to enlarge this image.

PBL

6th Sep 2007, 05:43

I don't know if an Audio Spectrum Analysis of a CVR ever had so much importance as it apparently has now.

TWA 800, Egyptair 990.

PBL

PBL

6th Sep 2007, 06:50

I have been thinking about some different ways to gain insight into this moving/non-moving thrust lever debate, as well as the somewhat lesser "leave the TOGA option" debate.

My intuition is that with sufficiently-trained operators, nothing decides the issue definitively. However, I am looking for general reasons why this may be so.

There is at least one such phenomenon for the "leave the TOGA option" debate. It is associated with the name of John Buridan, who was rector of the Sorbonne in 1328 and 1340, but apparently he never said it (see Anthony Kenny, Medieval Philosophy, A New History of Western Philosophy, Vol. 2, Oxford U.P. 2005, p96). If you take an ass and place it between two equally attractive bales of hay, it will be unable to decide between them and (so the theory goes) starve to death. The argument can obviously be generalised to two unequal bales of hay: there is a point in between them at which the ass will inevitably be undecided.

There is a theoretical formulation of this for (mathematical) metric spaces, due to Lamport and Palais, from the 1970's. There is, for every binary (generalise: discrete) decision function on a sufficiently continuous decision space a point of undefinition: where there is no defined decision. Lamport wrote this up in a more digestible version for non-mathematicians in a paper on the Buridan Problem in the 1980's. Both may be found on his WWW site.

The original application was to digital arbiters. Say, flip-flops, or even bits. Electrical current comes in, in a suitably continuous fashion, and you want the thing to go to 0 or 1. Can't always happen, say Lamport and Palais. Yes, but the chances of it not happening are vanishingly small, say "practical" people. Turns out not to be so. Turns out that chip producers have to do some work to figure out the "metastable behavior" (the new word for this indecision region) of certain HW to try to minimise the indecision behavior. Indeed, the phenomenon was discovered independently at about the same time by that eminently practical man Charles Molnar, who built the first desktop computer. Neither Lamport nor Molnar could get their papers published ("can't happen" said the referees. So much for the worth of peer review).

So, after all these words, Point 1: the "Buridan" indecision phenomenon is established. Now for its application.

For every discrete decision problem one constructs from continuous input, there will be an indecision region. It doesn't matter whether we are talking hardware, software or wetware. For every wonderful array of hinting devices, interlocks, moving/non-moving thrust levers, and so on, there is going to be a region in which one's decision criteria for continue the landing/go around don't yield a clear-cut decision.

If you change the technology, you just change the indecision region, you don't eliminate the phenomenon. If you push the decision somewhere else (say, 10 seconds before TD), you don't eliminate the phenomenon. If you wiggle the thrust levers, or leave them still, you don't eliminate.. etc.

Can I put this in one phrase? The "Buridan" indecision phenomenon persists through all technologies and designs.
One name? The Metastability Principle. One Mnemonic? Buridan's ass or yours!

This has a number of corollaries. One is to pull the teeth of the argument "yes, but if they had only had blue thrust levers instead of pink ones, this accident wouldn't have happened". Maybe true, but if you make the change you have just put the problem somewhere else, where some other flight will discover it which wouldn't have if you had left them pink.

There are more obviously larger areas of indecision. See the accident to a Tower Air B747 on RTO from JFK, December 20 1995,
https://www.flightsafety.org/ap/ap_mar97.pdf
http://www.ntsb.gov/Publictn/A_Acc2.htm
in which forward thrust was also applied during the RTO.

I am tempted, but too lazy this morning, to try to apply the Metastability Principle to the moving/non-moving thrust lever argument. I had some inkling from memory that there were examples of mismatched thrust levers on landing even on moving-lever airplanes, but I was simply too lazy to look them up or get on the phone to those who know (thank you, Lemurian!)

PBL

DingerX

6th Sep 2007, 08:06

Buridan was rector of the University of Paris, not the College de la Sorbonne (which was part of the University). In fact, Buridan taught at the College de Navarre.

Buridan's Ass applies specifically to beings without a rational soul. Humans are supposed to be able to reflect on the equal demand presented by the sensitive appetite to two equally attractive options, and determine that any decision is better than indecision.

atakacs

6th Sep 2007, 08:19

Buridan's Ass applies specifically to beings without a rational soul. Humans are supposed to be able to reflect on the equal demand presented by the sensitive appetite to two equally attractive options, and determine that any decision is better than indecision.

Never in my wildest dream would I have thought to read such a statement in this forum :)

PBL

6th Sep 2007, 09:38

Buridan was rector of the University of Paris, not the College de la Sorbonne (which was part of the University). In fact, Buridan taught at the College de Navarre.

Dinger's right. Gave me privately the low-down with references.

PBL

PBL

6th Sep 2007, 09:46

Rob21

6th Sep 2007, 13:44

The other day I was at the airport and bumped into some friends, airline pilots. We went for a coffee and an interesting "discussion" came up. At the "table" we could see two Boeing pilots, on their mid 50's, three Airbus pilots (one on his late 40's, the other two on their early 30's) and me (a mere helicopter pilot and a light twin airplane sunday driver). No academics there (sorry PBL).
The moving/non moving TLs issue came up, but didn't last long. The old timers said they don't mind if they move or not, as long as they do what they are supposed to - control thrust. One Airbus pilot (the older one) said he missed flying Boeings and the other two A pilots said they enjoy flying Airbuses very much, and they said non moving TLs makes more sense for them. One even said he would prefer big switches instead of TLs. Makes sense, he is from the computer games generation...
Of course, about this TAM accident, the TL was the most discussed thing. It was not a surprise to me when all three Arbus pilots mentioned problems with TLs, not only here in Brazil but also around the world. These problems were one of TLs not working at all. Two cases during taxi, one TL went dead (really dead, not "normal" dead...), one case reducing from TO power to CLB. I asked for more detail, they said they will e-mail me. When I get those, will post.
The Boeing pilots said that weard things happen with Bs too.

One interesting thing happened on that "round table" discussion, none of the pilots there were into discussing systems, A x B, etc... They all talked about maintenance, and Murphy's law was cited. All participants of that "coffee break" didn't rule out HF as probable cause, but since they know equipment fail all the time also (A or B), they are eager to see what investigators come up with. But not to put a blame, but to learn from it.

And the meeting ended with that old joke about future of aviation, when copilots will be replaced by a German shepherd dog...

Regards,
Rob

bubbers44

6th Sep 2007, 20:33

Rob21, After the German Shepherd bites you for touching something he doesn't think you should, he doesn't help with the situation you are in so I think we will have copilots for a very long time, hopefully.

donstim

6th Sep 2007, 20:34

Lemurian

6th Sep 2007, 22:26

HotDog
Not trying to blow my own trumpet as a flight engineer but had there been a flight engineer present, neither AF or Air China would have finished up in the drink. SOP on the classic 747s was for the flight engineer to hold the engineer's spur thrust levers against the stops after selection of reverse thrust which prevented any forward movement of the thrust levers.

Maybe, but one cannot generalise as in the Camair incident -a 742 -, the flight engineer participated in the confusion in the cockpit, with the consequences that we now know :
...the reason for the thrust increase of #1 engine remains difficult to explain...
That the F/E, by leaning over the pedestal in order to reach the speedbrake handle might have inadvertently displaced #1 throttle towards full forward thrust cannot be discarded...
A lack of coordination between the captain and the F/E, as well as an absence of cross monitoring with the F/O might have contributed in the irreversibility of the situation... (my translation)

In this instance, we see the often observed synchronised drops in performance of all the members of a crew in heavy stress situations.

marciovp

7th Sep 2007, 04:03

Interesting site from a talented Brazilain Jet Pilot. Mostly in Portuguese Brazilian, but some segments in English.

Interesting point he makes is that the right engine suddenly accelerated in a rapid pace before the front and the left wheels had touched the ground. This sudden acceleration reached its peak in 3-5 seconds raising the EPR of the right engine to 1,260.

He also has some considerations for the mechanics of the TLs and what could have gone wrong although not probrable.

Here:
http://aviationtroubleshooting.*************/

ironbutt57

7th Sep 2007, 04:12

As a neophyte 320 "pilot" followed the MEL procedure watched the "momentery" non ops rev engine accel as it takes a bit for it to "realize" the rev did not actually deploy then it returned to "idle" as per the "ops procedure"....all speculation aside...my experience was as per MEL "o" procedure....maybe theirs was not the case.....**** happens:ugh:

teropa

7th Sep 2007, 05:34

marciovp,

There is nothing peculiar about the acceleration of the other engine. It is only the autothrust trying to maintain the selected speed. As the other engine was put to IDLE, the remaining engine fights the sudden loss of energy, as the autothrottle still remained connected and tried to achieve the selected approach speed.

Tero

PBL

7th Sep 2007, 06:56

Southwest went off the end of a snowy runway at Chicago Midway and killed a car passenger because deployment of reversers was significantly delayed over the assumed deployment time in their landing-distance calculation.
There are many other factors that also contributed to that accident. Let's be careful in stating a single "cause," especially when the final accident report has not yet been published.

Let's also be careful in reading things into statements that aren't there. The word "because" does not imply "only".

It is ironic that the NTSB itself is the most influential remaining proponent of the "single cause" explanation.

PBL

PBL

7th Sep 2007, 10:50

bsieker has performed a Why-Because Analysis (WBA) of this accident from the information available so far. He has kindly made his interim WBA , including most importantly the Why-Because Graph (WBG) derived from the facts known so far, publically available. One may find it on the Compendium on Computer-Related Incidents with Commercial Aircraft, on the RVS WWW site at the University of Bielefeld:
http://www.rvs.uni-bielefeld.de/publications/compendium/incidents_and_accidents/TAM3054.html

This page also includes links to the CVR and FDR data, as well as this PPRuNe thread, since I judge the quality of technical discussion on the thread as sometimes very high, and some of it has obviously contributed to the analysis.

PBL

bsieker

7th Sep 2007, 12:41

PBL,

thanks for announcing my Why-Because-Analysis here and making it publicly available.

I'd like to thank my colleagues at Causalis Limited, Jan Sanders, Jörn Stuphorn and PBL, and the many contributors on this PPRuNe thread for their valuable input!

PBL's comments on the case on the web site are worth reading, as well as an introduction to WBA (http://www.rvs.uni-bielefeld.de/research/WBA/), which can also be found there.

I'm looking forward to hearing some comments on this analysis.

Bernd

marciovp

7th Sep 2007, 14:31

flyingnewbie10

7th Sep 2007, 15:17

Before the three wheels touched the ground?

Thanks

Marcio,

At the flare at least one of the TLs (the left one) was brought to idle.

At the same time the other one either was brought to idle but its TLA reading remained in CLB or remained also phisically at CLB.

In such a situation be the wheels on the ground or not the AutoThrust will rely in just one engine to keep assigned speed. Then the right engine will show a thrust increase.

I don't know whether this thrust increase should be limited by the right TLA reading or not in this case.

bsieker

7th Sep 2007, 15:19

TAM mechanics made a deposition at a CPI of the House, and said that they did work on the maintenance of the A320 that crashed fours days before. That they did have the part that was needed for the right reverser and that it would take three hours to replace it. But it had to be done at night and it would be noisy because the engine would have to work. So he consulted his supervisor who advised him to just lock the right reverser because according to Airbus the plane could fly ten days without it working.

This is probably not unusual, to make use of the liberty to reschedule maintenance, while still complying with limitations.

Also the technical guy from National Agency for Civil Aviation (ANAC) said that it was decided internally that planes to land in Congonhas had to have both reversers and that this direction was published in their site. He believed that this was to be followed but for some reason another director of ANAC said that this was not so and TAM said that they followed the Airbus directives, not ANAC. What a mess...

Interesting piece of information if it turns out to be true. Conflicting SOPs. Probably something for the lawyers to figure out which regulation would have been authoritative for TAM operations to CGH.

There is nothing peculiar about the acceleration of the other engine. It is only the autothrust trying to maintain the selected speed. As the other engine was put to IDLE, the remaining engine fights the sudden loss of energy, as the autothrottle still remained connected and tried to achieve the selected approach speed.

This is our interpretation, too.

Before the three wheels touched the ground?

The increase in thrust on engine #2 starts immediately after thrust lever #1 is retarded to idle, around MLG touchdown, as far as one can tell at the limited sample rate of the FDR. It reaches its peak around NW touchdown, and slightly after reverse thrust was selected on engine #1.

Bernd

flyingnewbie10

7th Sep 2007, 15:26

In the case of the TAM 3054, it seems that A/THR thrust assignment to the right engine wasn't limited by the right TLA reading.

Also the technical guy from National Agency for Civil Aviation (ANAC) said that it was decided internally that planes to land in Congonhas had to have both reversers and that this direction was published in their site. He believed that this was to be followed but for some reason another director of ANAC said that this was not so and TAM said that they followed the Airbus directives, not ANAC. What a mess...

Marcio,

Does it have an identifier (portaria, resolucao, etc) and number ?

bsieker

7th Sep 2007, 15:34

In the case of the TAM 3054, it seems that A/THR thrust assignment to the right engine wasn't limited by the right TLA reading.

Well, the right engine thrust would be limited to the right engine TLA reading (thus, to CLIMB power), I suppose you meant limited by the left TLA.

Some paragraphs in the FCOM, where the thrust-limiting function of the thrust lever position with autothrust active is described in the singular form, confirm that these limits are independent.

Bernd

flyingnewbie10

7th Sep 2007, 15:40

Well, the right engine thrust would be limited to the right engine TLA reading (thus, to CLIMB power), I suppose you meant limited by the left TLA.

The right engine thrust was apparently limited to climb power after or just before A/THR desengagement.

But before A/THR desengagement the right engine thrust was (apparently) above climb power when the left TL was brought to idle.

Dani

7th Sep 2007, 15:45

Please, don't start it all over again!

It is absolutely per design of an A320 (as of any aircraft with autothrottle) that the aircraft wants to maintain it's ordered speed, even when there is one engine not providing any forward trust anymore.

Imagine the same aircraft in another scenario: aircraft shortly before landing, pilots see that they cannot stop it, so they order a Go Around and shuffle in some power. Unfortunately, one engine quits, or even worse, it goes to revers (a very feared case which has happened a few times, although never on a A320). So they are hanging barely in the air, 20 ft above the runway, the end rapidly approaching. You can be happy that the other engine is providing trust, i.e. the ordered speed, and both pilots prey that it will be enough to get away from the ground.

You have to learn that a machine doesn't know the intention of a pilot nor does it know the outcome of the case. It's just there, designed to work under every thinkable circumstance.

Likewise it has to be repeated that all data given in the published data recorder are completly consistent and logical with each other. There is hardly any other convincing theory other than that the system itself worked completly as it was designed. There most probably (I know that some are attacking me for early conclusions) was never any technical problem on this aircraft (except the unservicable reverser 2), and that all went down the drain with one single action, the TL 2 being in CLB detent.

I understand that our Brazilian friends try to find also other channels of information. Lots of them are in a hectic manner to produce "evidence" and strong action so it can never happen again. This is understandable. Still I believe rather a set of data of a FDR than an commision of a parliament or an "enhanced audio tape". Bear in mind that the FDR data has been "issued" by the Brazilian Air Authority. There might be the case of falsifying it, but as previous said, the data is perfectly consistent and logical.

Dani

DozyWannabe

7th Sep 2007, 15:47

Not quite, flyingnewbie10,
The TL was in the CLIMB detent, which is at the top end of the A/THR active zone of travel. SPEED mode kept that engine's thrust at approach thrust, not climb. If the engines were at climb thrust the aircraft would likely have sailed straight over the runway.

If I understand this right:
While A/THR was still connected, the thrust of the right engine crept up to balance the reduction in thrust from the left, which is normal for SPEED mode. When the A/THR disconnected, the actual engine thrust remained where it was at disconnect and did not change until impact.

flyingnewbie10

7th Sep 2007, 15:55

The TL was in the CLIMB detent, which is at the top end of the A/THR active zone of travel. SPEED mode kept that engine's thrust at approach thrust, not climb. If the engines were at climb thrust the aircraft would likely have sailed straight over the runway.

Let me correct myself.

First someone said here that the TLA reading limits A/THR maximum thrust for each engine even in speed mode

After the left Tl was brought to idle and then to reverse, you can see in the graphs a considerable EPR increase in the right engine. It leaves approach thrust and surpasses climb EPR (apparently).

Then EPR in the right engine starts to reduce again until it gets fixed at (I suppose) CLB power.

It looks like that in a first moment the A/THR is somehow trying to compensate reverse thrust in the left engine, surpassing CLB thrust in the right one.

Maybe this "anomalous" thrust in the right engine is just derived from a momentaneous difference between ACTUAL EPR and TARGET EPR.

flyingnewbie10

7th Sep 2007, 16:06

Still I believe rather a set of data of a FDR than an commision of a parliament or an "enhanced audio tape"

My apologies but an Audio Spectrum Analysis of the CVR could show whether both TLs were brought to idle or not.

The pedestals have stops that probably make some noise when the TLs pass by them. This noise could be isolated in the analysis.

DozyWannabe

7th Sep 2007, 16:13

And the Eng2 increase in thrust is notable, but it doesn't reach anything like climb thrust, If I'm reading that chart right.

My apologies but an Audio Spectrum Analysis of the CVR could show whether both TLs were brought to idle or not.
I don't think such evidence would be admissible in court though.

Is it such a terrible thing to admit that the likeliest explanation is that the pilots made a mistake?

J.

bsieker

7th Sep 2007, 16:14

After the left Tl was brought to idle and then to reverse, you can see in the graphs a considerable EPR increase in the right engine. It leaves approach thrust and surpasses climb EPR (apparently).

No.

It never exceeds climb power. It cannot with autothrust. (except Alpha-Floor, and one-engine-out, in which case the A/THR limit is MCT) .

Then EPR in the right engine starts to reduce again until it gets fixed at (I suppose) CLB power.

No.

It is frozen at the power last commanded by autothrust. Ca. EPR 1.18

It looks like that in a first moment the A/THR is somehow trying to compensate reverse thrust in the left engine, surpassing CLB thrust in the right one.

No.

Please compare the EPR values with the ones from the one Take-off that is also provided in the EPR graphs. (p11).

FLEX power is set for take-off, in this case delivering around EPR 1.35, at thrust reduction levers are brought to CL, activating autothrust, and setting (still in climb) CLIMB power, which in this case is around EPR 1.28.

During this landing, EPR never exceeded EPR 1.26, well below CLIMB power.

This has been discussed before, but glad to be of help, again :)

Bernd

flyingnewbie10

7th Sep 2007, 16:15

I don't think such evidence would be admissible in court though.

In Court ?

(By the way: Yes, it would)

flyingnewbie10

7th Sep 2007, 16:18

No. It is frozen at the power last commanded by autothrust. Ca. EPR 1.18

It was probably discussed before but you will have to admit it is hard to get all those details systematically ordered just from reading a lot of posts. A periodic and constant summary would help :)

From what you said above I can suppose that the right engine thrust remained locked.

Is that it ?

bsieker

7th Sep 2007, 16:27

From what you said above I can suppose that the right engine thrust remained locked.

Is that it ?

Yes, after the autothrust disconnect, at 18:48:29 (cf. p. 3, FDR graphs).

In case of an "involuntary disconnect" of autothrust, i. e. any mode of disconnect other than bringing both levers to idle or pressing the pushbutton on the lever side, thrust remains locked. Until the levers are moved.

Bernd

donstim

7th Sep 2007, 16:28

Quote:
Originally Posted by donstim
Quote:
Originally Posted by PBL
Southwest went off the end of a snowy runway at Chicago Midway and killed a car passenger because deployment of reversers was significantly delayed over the assumed deployment time in their landing-distance calculation.

There are many other factors that also contributed to that accident. Let's be careful in stating a single "cause," especially when the final accident report has not yet been published.

Let's also be careful in reading things into statements that aren't there. The word "because" does not imply "only".

I realize that English may not be your native language, but when "because" is used the way you used it (with a single cause and effect), it does indeed imply "only."

PBL

7th Sep 2007, 16:32

I realize that English may not be your native language, but when "because" is used the way you used it (with a single cause and effect), it does indeed imply "only."

Two posts, two wrong assumptions, perfect score.
I am sorry you didn't understand what I meant, but now that you do, could we possibly drop the subject?

[I just tried to send you a private message with the reason why your claim that use of "because" implies enumerating all causes is false. But you don't receive private messages. What a shame. I'm not going to belabor the thread with it.]

PBL

DozyWannabe

7th Sep 2007, 16:38

(By the way: Yes, it would)
Presumably with expert witnesses from all interested parties. I very much doubt that it would be conclusively proved one way or the other. This isn't CSI.

Why are you continually trying to push the 'Innocent pilots let down by faulty aircraft' angle? What do you have to gain?

flyingnewbie10

7th Sep 2007, 16:40

Yes after the autothrust disconnect, at 18:48:29, cf. p. 3, FDR graphs). In case of an "involuntary disconnect" of autothrust, i. e. any mode of disconnect other than bringing both levers to idle or pressing the pushbutton on the lever side, thrust remains locked. Until the levers are moved.

Thanks.

First let me just make a summary:

No controversy about A/THR behaviour. It worked as expected in any case in which one of the TLA readings remained in climb.

The right engine thrust never surpassed climb power as expected. It remained locked at ca. 1.18 EPR. after A/THR desengaged therefore below CLB power.

From here we have four possibilities:

1 - The right TL wasn´t physically brought to idle and remained "untouched" until the very end;

2 - The right TL was brought to idle but the TLA reading remained at CLB. The right TL remained "untouched" ever since. The crew didn't figure out right engine EPR was above idle;

3 - The right TL was brought to idle but the TLA reading remained at CLB. The crew tried to put the right engine thrust back to idle moving the right TL but the thrust remained locked;

4 - The right TL was physically locked, meaning that the FP couldn't phisically move it even when he tried to do so.

flyingnewbie10

7th Sep 2007, 16:43

Why are you continually trying to push the 'Innocent pilots let down by faulty aircraft' angle? What do you have to gain?

Nothing... (ps: the fault could be originated by a bad maintenance and not by a design error)

Now back to you...Why do you resist that much to consider other explanations for the accident ?

Dani

7th Sep 2007, 16:50

Why do you resist that much to consider other explanations for the accident ?

...because he's thinking logically and you are not!

flyingnewbie10

7th Sep 2007, 17:00

...because he's thinking logically and you are not!

Your logic is very different from that of accident investigators for sure.

Let me review some facts:

1 - The crew followed the right procedure in the previous landing (maybe they changed seats in Congonhas what could explain the FP "forgetting" the TL at climb);

2 - There is an (apparently) anomalous right TLA reading at idle stop in the previous landing in Porto Alegre;

3 - An Audio Spectrum Analysis could show whether both or a single TL was pulled to idle;

4 - There isn't a sufficiently detailed explanation of the A320's TCU mechanism and its software interface to rule out a mechanical/electronical failure yet.

Do yout think it is logical in a context of an accident investigation to rule out the possibilitly of a mechanical/electronical failure from the beginning ?

bsieker

7th Sep 2007, 17:01

First let me just make a summary:

[...]

I invite you (and everyone else) to also take a look at our analysis, which tries hard not to be judgmental, and leave open all possibilities as to why TL #2 was recorded at CL detent on the FDR graphs (the theory about the flight crew actually leaving it there is included, as it is believed by many to be the most likely explanation, but is clearly marked as an assumption).

Here's the article in our compendium (http://www.rvs.uni-bielefeld.de/publications/compendium/incidents_and_accidents/TAM3054.html), here's the actual PDF file of the analysis (http://www.rvs.uni-bielefeld.de/publications/compendium/incidents_and_accidents/TAM3054-WBG.pdf).

I recommend PBL's introductory article, as it contains a lot or explanatory remarks on the Why-Because Graph. To those unfamiliar with the Why-Because-Analysis I also highly recommend the the Why-Because-Analysis (http://www.rvs.uni-bielefeld.de/research/WBA/) web pages.

Your comments will be appreciated.

Bernd

flyingnewbie10

7th Sep 2007, 17:06

Here's the article in our compendium (http://www.rvs.uni-bielefeld.de/publications/compendium/incidents_and_accidents/TAM3054.html), and here is an introduction to the analysis technique we use, called the Why-Because-Analysis (http://www.rvs.uni-bielefeld.de/research/WBA/).

I will read it carefully.

PBL

7th Sep 2007, 17:13

Come on, guys! Let's at least give newbie credit for knowing something about law and courts; it is his profession.

All kinds of analysis, including analysing the sounds on a recording and what they might meant, are admissible in evidence. Usually, it requires the analyst turning up in court and verifying that the piece of evidence is, indeed, hisher analysis and explaining hisher conclusions. And it requires that the piece of evidence (the analysis) satisfy the rules of evidence, which suffice to ensure for example that the presented analysis is indeed of the CVR of the actual accident being discussed and not of some other accident, or a simulation, and so on.

Whether the court believes anything of what is said is, of course, entirely another matter.

Newbie wants to leave open the possibility that the signal recorded on the FDR and interpreted by the FADECs may have had some other cause than that the thrust lever was left voluntarily near the CL detent. That is his privilege. Let us please recognise that, at this stage, nobody has the evidence to contradict him.

PBL

BOAC

7th Sep 2007, 18:13

By no means my first go at this question and so far only one 'interested party'.

I am puzzled by the low (recorded) EPR on the number 1 engine in reverse in the final landing at CGH. If I were landing on a limiting (and possibly) slippery runway with 1 (or 2 reversers) I would be using full reverse until my stop was assured. This to me would give me a clue to the (sadly) missing mindset/briefing for the landing.

I wonder if some kind EPR driven 320 pilot could (at a suitably calm moment, of course:)) note the EPR for idle reverse and another time for full reverse? Please either post here or PM me with the results if you would be so kind.

DozyWannabe

7th Sep 2007, 20:13

PBL:
Newbie wants to leave open the possibility that the signal recorded on the FDR and interpreted by the FADECs may have had some other cause than that the thrust lever was left voluntarily near the CL detent. That is his privilege. Let us please recognise that, at this stage, nobody has the evidence to contradict him.
Absolutely.

Flyingnewbie10, I apologise if I've come across as combative - I just want to make sure that we're not going back over old ground.

EMIT

7th Sep 2007, 20:36

To BOAC,

EPR at full reverse seems to be approximately 1.05.
Number seems not very high, but EPR measurement is apparently not very realistic in the disturbed flow situation during reverse application.
EPR at idle, either forward or reverse would be about 1.00

The 1.05 I have gathered from QAR data readouts of a couple of my own landings.

A better indication of engine output during reverse would be N1, but to tell you the truth, I have never checked those numbers. I just hear the noise and feel the deceleration, and look out in front to judge whether deceleration satisfies me.

The thrust lever angle for full reverse is (-)22.5 degrees, perhaps you can deduce that number from the FDR readout.

EMIT.

(added line about full reverse TLA).

SyEng

7th Sep 2007, 20:37

FlyingNewbie10, PBL,

I agree, but some might interpret PBL's latest as damning FN with faint praise.

Let me try to say this again in the hope of getting through to some who seem uncomfortable with contemplating any possible explanation except blaming the pilots, without recourse to any logical process, mentioning no names (Dani).

From the FDR evidence in the public domain one can infer only the following concerning the TLs:

"The FDR recorded a valid commanded No.2 TLA of CLB throughout the landing roll."

My best guess is that the FDR TLA commanded signal comes from the EEC in command of the subject engine. Dual FADEC has 2 EECs (engine electronic control) per engine.

Two (a subset of all) possible reasons for this occurring are:

(1) The pilots left No.2 TL at CLB

(2) No.2 TL was brought to idle but the thrust control unit (TCU) continued to provide a valid TLA commanded = CLB signal.

From anecdotes on this thread, reason (1) appears to have contributed to several previous incidents. It is possible (some are of the opinion that it is overwhelmingly likely) that this happened in this case.

It is not acceptable to state that (2) did not happen at Congonhas unless you have the evidence to prove it. There are several failure modes that could produce this effect (see my post 1981).

EMIT

7th Sep 2007, 20:52

To SYENG,

Good post about what can be taken as fact and what is deduction.

Having said that, I trust the investigators enough to leave the microscopic testing of wreckage parts to them, and to trust their impartiality in the final report.

Next point is, as a pilot, I think that the most valuable point to ponder is, the question how or why did the PF leave the T/L #2 in CLB detent?

EMIT.

bsieker

7th Sep 2007, 21:15

It leaves approach thrust and surpasses climb EPR (apparently).

I think I see another reason for your misunderstanding here.

There is no such thing as "approach thrust" as a fixed value, which can be "left".

Unlike "maximum climb thrust" ("CLIMB", the highest thrust used after thrust reduction on a normal flight), "maximum continuous thrust" ("MCT", the highest thrust used during single-engine operation after thrust reduction) and "maximum take-off-thrust ("TOGA"), which are more or less constant.

Approach thrust is whatever is necessary to maintain approach speed.

Obviously, with both engines operating that is a lot less than if a single engine has to achieve that, so consequently EPR rises.

As you can see, during the approach, the EPR value fluctuated between 1.1 and 1.06.

Bernd

SyEng

7th Sep 2007, 21:31

EMIT,

As I've said before, my feeling (and that's not worth anything, really) is that it is more likely (but not overwhelmingly) that the TL was left in the climb detent than there was a mechanical disconnection between the TLs and the TCU.

It is humbling to witness the infallibility which pilots seem to attribute to those who design and those who maintain the systems of mechanical, electrical and electronic linkages which you never see, but rely on for the lives of yourselves and your trusting passengers.

The formal enquiry needs to rule out a linkage failure (based on evidence) if it is to safely conclude that the TL was left at CLB. Even if it doesn't, Airbus would be as well to re-visit the ATA76 FMEA.

I've had enough of re-iterating the same old points and I concede that I'll never get through to those who have already made their minds up, so I'll shut up now.

flyingnewbie10

7th Sep 2007, 21:41

Bsieker,

I will dare to post a preliminary comment about your why-because graph. My apologies If I say any nonsense:

1 - Factor 11 (assumption) could well be the one you pointed out (F/C did not expect autobrake not to operate) to explain F/C not commencing "Loss of Braking" procedure immediatelly. But if "Loss of Braking" implies using full manual braking (is it ?) I suppose it could also be explained by the fact that the crew at least thought that the runway was slippery and did not start using braking immediatelly to avoid an hydroplanning as the speed was still high;

2 - Is there a way to have a more detailed description of factor 18 (Thrust Lock after A/THR disconnected) just to contemplate the fact that it worked exactly as designed and the "locked" thrust was within the range of the right TLA reading ?;

3 - Does the graph accept multiple assumptions ? Could Factors 36 and 42 have parallel hypothesis ?

exeng

7th Sep 2007, 21:52

I suppose it could also be explained by the fact that the crew at least thought that the runway was slippery and did not start using full braking power immediatelly to avoid an hydroplanning

Just to say in respect of this one suggestion (because I will not comment on the crash or it's causes until the final report is out):

Hydroplaning (or aquaplaning) will occur regardless of brake application - it is a function of tyre pressure, speed and depth of water. The relevant point is that if the criteria for aquaplaning are present then the application of brakes will be very ineffective; the application of braking does not in itself cause aquaplaning.

Regards
Exeng

flyingnewbie10

7th Sep 2007, 21:53

I've had enough of re-iterating the same old points and I concede that I'll never get through to those who have already made their minds up, so I'll shut up now.

SysEng,

Please remember that not everybody here has made his mind up :)

This is just a guess (probably flawed)

I saw the picture you posted about the TL mechanism and I tried to figure out how a "broken" or "loose" link between the pushrods, artificial feel unit and TLA sensor box could eventually yield that wrong TLA reading at the right TL idle stop.

Maybe the artificial feel unit and the TLA sensor box pushrod link was somehow loose (The last pushrod from top to bottom being "below" his correct position) thus marking a "negative" TLA reading.

But this would not explain the correct TLA reading for the other TL positions (CLIMB, etc).

EMIT

7th Sep 2007, 22:05

SYENG,

Although I have trust in engineers, I know that things can and will break or go wrong. Just 2 weeks ago I had a case of a blocked pitot tube, but because we (my copilot and I) played the game the way it should be played, we didn't make any headlines like e.g. Birgenair in POP.

I think it is not a case of being levelheaded if the pilots on this forum are more inclined to view this affair from the human factors side, which is their daily bread and butter, while leaving the detailed analysis of the wreckage to the technical experts.

good night now.

ChristiaanJ

7th Sep 2007, 22:22

SyEng,I've had enough of re-iterating the same old points and I concede that I'll never get through to those who have already made their minds up, so I'll shut up now.We must be a very small minority having been through all the 2100 posts so far. So yes, the same old points have been re-iterated, but let's try and give a hand to the late-comers. They also want to learn.

EMIT,Next point is, as a pilot, I think that the most valuable point to ponder is, the question how or why did the PF leave the T/L #2 in CLB detent?If you start looking back through the earlier posts, you will find mostly two answers.

1) Somehow, somewhere, landing on a short slippery runway, with one TR locked out, with none-to-clear SOPs about how to handle TL and TR in that case, with a vague memory of having to leave the TL concerned in idle, not reverse idle, etc. etc. the PF did not move the #2 TL but left it in CLB detent.
The ensuing chaos was not something the average human mind could sort out in the 90 seconds remaining.
Some of the posts on that subject are really worth reading.

2) The pilot pulled both TLs to idle, but there was a mechanical or electrical failure, so the engine controls still saw "CLB detent".

Personally, I've seen so many well-reasoned posts on the subject, that I tend towards 1). "Pilot error"? Yes. But that "pilot error" was only the end of a long chain of "causal factors", that should be addressed.

2) ? As an engineer, I find it improbable at just that moment. But, again as an engineer, I will not discard that answer until there is evidence to the contrary.

marciovp

7th Sep 2007, 22:22

Things get a little complicated. A Federal Judge had issued an order to close Congonhas Airport. Then ANAC (National Agency Civil Aviation) published in their website the "Instrução Normativa IS-121-189" stating that for an airplane to land in Congonhas both reversers should be on and working. Gilberto Schittini who elaborated the IS said today that it was in force. This was shown to the judge who after reading it allowed Congonhas do open. Then a director from ANAC Denise (she asked to leave) said that the IS was not enforced and was published in the site of ANAC by mistake. That it was just an internal discussion not to be promulgated as valid. Not so, said Gilberto Schittini, saying that he cried when he realized that if TAM followed his IS-121-189 the disaster would not happen. TAM said that it followed the Airbus directives not ANAC´s...

Here is the news (portuguese-brazilian):
http://si.knowtec.com/scripts-si/MostraNoticia?&idnoticia=741491&idcontato=47362&origem=secao&nomeCliente=DEMOCRATAS&data=2007-09-07

In case you all want to know, I am not a lawyer and I have no agenda. I just love aviation. I am a psychiatrist/psychoanalyst who used to fly Piper Tripacers and Cherokees (ah, also a Cessna 150). In my work with patients I prepare them to "fly solo" in this world...

Lemurian

8th Sep 2007, 02:57

bsieker,
There are a few points that seem to be absent in the graph :

Between 11 and 12, there is no *No Decel* call out, whether it is in the SOPs or not, that call, in the airlines where it is SOP is a trigger for manual brake application,
Looking at the rudder displacement print-out, it appears that there was some rather drastic application of rudder pedal, hence the assumption that, combined with 26 -*persistent significant forward thrust*- and 28 -*lower friction coefficient* -, there was some directional control difficulties which would have participated in 25 -*lower than expected wheel brake deceleration*-, or even 20 -*wheel brake application is delayed*-.
I think that the "flatness" of the captain's 'stick inputs cannot be discarded, especially when we observe that quite early the F/O flight controls seem to be very active and that he is the one going aggressively with the braking.There is, from the FDR a glaring takeover by the F/O.
(I'm going to hate myself for this but it looks as if F/C suffered some incapacitation of some sort , whether mental -approach / landing /weather stress combined with a rapidly deteriorating situation -, psychological - bowing to the F/O' apparently strong personality - or plain physical ).

Sorry, I'd have preffered someone to pick on my earlier hints but nobody seemed interested.
Need to rest now.
Regards.

Dani

8th Sep 2007, 04:23

Thank you to the two Engineers (SyEng and ChristiaanJ) for repeating the technical reasoning. I'm sad that SyEng won't take part anymore because he showed the way of thinking with much more patience than I could.

For our Brazilian friends, who joined us later, two more points have to be added:

1. Technical failure:

If there was a broken TL or any associated system there would have been a failure/warning produced by the FWC/ECAM. The system is so heavily electronified that several sensors watch each other, and if one sensor fails you also get a warning. This has been explained before but I couldn't find it anymore. I'm aware that we don't possess the FDR data from the ECAM but it can be assumed with high certainty that if there had been such failures, the Brazilian authorities would be the first to publish it, and Airbus would have also given out bulletins to their operators, maintenance personal and pilots.

2. Human aspect:

If there would have been a failure in the TL, its associated system, in the EEC, the FADEC, the trust revers system or any other relevant system, the pilots would have reacted differently. In case their intention was to stop (as they were) and a TL failure occurs, they would cut a trusting engine, i.e. put Master Switch 2 to off.
If their intention was not to cut engine 2, go around, they would have to put both TL to TOGA, would have gone around and problem would also be solved. Remember that with only minimal higher speed than they had at the end of the runway, they could have attempted a GA.

These two aspects lead most of us to believe that we can falsify the other reasons just brought up again by our Brazilian friends and the Brazilian Parliament committee.

[Sorry for my convinced way of arguing now and in all my previous posts. It doesn't mean that I have evidence but that I follow the most likely causes and put them together. If I use the words certainty and likelihood, it doesn't imply that I have the absolute solution.]

Can we finally agree with that and come back to a more needed discussion about what to do to avoid further accidents like these?

Dani

bubbers44

8th Sep 2007, 06:58

Dani, On a short slick runway as soon as you touch down you will be in reverse thrust and the go around option is not recommended. A system failure, broken linkage is not something that can be easily detected by electronic detection so probably doesn't exist. If they brought both TL's to idle but the computer only sensed #1 at idle because of a linkage failure or electronic failure they would have little time to sort out the problem and shut down the #2 engine while sliding down the runway with no brakes because for some reason they didn't use manual brakes. Without ground spoilers and auto brakes they were in a desperate situation but if they didn't push on the brake pedals why would they shut down an engine to help their situation? 11 seconds is a very long time to not try to save yourself by simply pushing on the brake pedals. Only when manual braking is applied would the thought of shutting down an out of control engine enter your mind.

bsieker

8th Sep 2007, 08:23

I will dare to post a preliminary comment about your why-because graph. My apologies If I say any nonsense:

Thank you very much for your comments.

1 - Factor 11 (assumption) could well be the one you pointed out (F/C did not expect autobrake not to operate) to explain F/C not commencing "Loss of Braking" procedure immediatelly. But if "Loss of Braking" implies using full manual braking (is it ?)

As much as you deem necessary. Since it is often an emergency situation, I would guess that it usually implies full braking. (On less than optimal surface conditions brake performance will be limited by anti-skid anyway.)

I suppose it could also be explained by the fact that the crew at least thought that the runway was slippery and did not start using braking immediatelly to avoid an hydroplanning as the speed was still high;

I don't think so. As someone has pointed out, hydroplaning is independent of braking, it happens even with spinning wheels. (In driver-training one common exercise is to accelerate in (low) standing water and experience the onset of loss of control (steering) that happens at hydroplaning. Don't try this on public roads!) For all we know anti-skid was operative, so would prevent wheel-locking. (I have to admit I don't know if or how well it works during hydroplaning.)

The strongest argument, though, is that they had selected autobrake MED, which would commence braking 2s after MLG touchdown, even though they perhaps suspected the runway to be slippery and maybe anticipated some degree of hydroplaning.

I don't think it makes any sense to delay braking because one anticipates hydroplaning.

2 - Is there a way to have a more detailed description of factor 18 (Thrust Lock after A/THR disconnected) just to contemplate the fact that it worked exactly as designed and the "locked" thrust was within the range of the right TLA reading ?;

Since it worked as designed, I don't think there is a need for that. I may add an annotation that the locked thrust was well below the maximum allowed by A/THR operation.

3 - Does the graph accept multiple assumptions ? Could Factors 36 and 42 have parallel hypothesis ?

Not normally. The usualy way to deal with differing possible explanations for one event is to create a set of subgraphs for the event in question.

I have included the one (of many) hypothesis that I consider the most likely. Others may disagree, which is why I have marked the nodes as assumptions.

Both (6) and (36) have alternative explanations, and, of course, (42) also requires an explanation. Be it crew action, or a mechanical problem impeding free movement of the levers. After the final report is released, this may be amended.

The stopping rule in WBA, i. e. when to leave nodes as leaves, is variable and depends on the intended scope, the available information, and other factors. I have decided in this case that I have too little information to decide why (42) might have been the case.

Bernd

Jorge_Vilarrubi

8th Sep 2007, 08:37

bubbers44 said:
"If they brought both TL's to idle but the computer only sensed #1 at idle because of a linkage failure or electronic failure they would have little time to sort out the problem and shut down the #2 engine"

If there is a hardware failure in the TLs linkage and the computer senses Eng. #2 at CLB, let's suppose the pilots become aware of the failure and shut eng#2 down, would this action lead to Spoilers Deployment?

I apologize for my total ignorance on flying machines, I'm just a computer experienced guy.

Jorge.

bsieker

8th Sep 2007, 08:48

If there would have been a failure in the TL, its associated system, in the EEC, the FADEC, the trust revers system or any other relevant system, the pilots would have reacted differently. In case their intention was to stop (as they were) and a TL failure occurs, they would cut a trusting engine, i.e. put Master Switch 2 to off.

In case of a detected problem with the thrust levers, the engine would have been put to idle anyway, if on the ground or if in flight with slats extended, and if not during take-off/go-around (iirc FLEX or TOGA will be maintained in case of TL fault, since these settings are only used if very high thrust is crucial ...)

I'm not arguing that I believe there was an undetected fault, I also think that possibility is very remote, but my intention with making my analysis public is to have a common ground, which all can agree to, and go on from there, without having to explain everything over again.

These two aspects lead most of us to believe that we can falsify the other reasons just brought up again by our Brazilian friends and the Brazilian Parliament committee.

I mostly agree with you, but falsify is too strong a word, that would require positive evidence, that nothing was wrong mechanically, which we do not have yet.

Can we finally agree with that and come back to a more needed discussion about what to do to avoid further accidents like these?

It may be a good starting point if we could agree to the Why-Because-Graph, or if someone does not agree, modify it such that all interested parties agree that this is what we know, and other aspects are some of the most likely hypotheses.

I hope that this will give a clear overview, and eliminate a lot of questions and repetitive back-and forth on this thread.

Bernd

bsieker

8th Sep 2007, 09:04

Lemurian,

thanks a lot for your feedback.

Between 11 and 12, there is no *No Decel* call out, whether it is in the SOPs or not, that call, in the airlines where it is SOP is a trigger for manual brake application,

There are some guidelines on the incorporation of so-called "un-events" in a Why-Because Graph. It requires that the missed event is prescribed in regulations/laws, is a standard operating procedure, or at least common practice. it is not clear that this was the case in TAM operations. I may add it as an assumption, though, togehter with the missing "DECEL" light, in the same way as the missing Spoilers-indication.

Looking at the rudder displacement print-out, it appears that there was some rather drastic application of rudder pedal, hence the assumption that, combined with 26 -*persistent significant forward thrust*- and 28 -*lower friction coefficient* -, there was some directional control difficulties which would have participated in 25 -*lower than expected wheel brake deceleration*-, or even 20 -*wheel brake application is delayed*-.

Very interesting point.

Directional stability issues caused by asymmetric thrust are not in the graph, but may have played a role in brake application delay. Maybe I should add this as assumptions, together with a node about thrust asymmetry (having 26 (modified to read "... on engine #2") and 39 (or an effect of 39: "Reverse thrust on engine #1") as causal factors.)

I think that the "flatness" of the captain's 'stick inputs cannot be discarded, especially when we observe that quite early the F/O flight controls seem to be very active and that he is the one going aggressively with the braking.There is, from the FDR a glaring takeover by the F/O.

Yes, but this is most likely not a causal factor in this accident, although very interesting to note in itself, and will be subject of investigation into training procedures, etc. at TAM.

I think we cannot say who made the brake pedal inputs, and L and R here does not refer to the Captain's and F/O's pedals, but left MLG and right MLG brakes.

Sorry, I'd have preffered someone to pick on my earlier hints but nobody seemed interested.

I'm sorry, I must have missed that. Which post are you referring to?

Bernd

Dani

8th Sep 2007, 10:21

Originally posted byBsieker:
In case of a detected problem with the thrust levers, the engine would have been put to idle anyway
Bernd, I agree with you completly. I just mentioned this very unlikely cause for our Brazilian friends, who still believe that there is a great likelyhood in the scenario of the pilots fighting with TL 2. If there had been a problem in TL 2, they mostly likely wouldn't have left it in CLB. And if it had been stuck in CLB they would have simply switched it off. There was enough time.

The same I have to answer to bubber44. I do not think that GA would have been a very good solution after TR 1 on, but I add it to the scenario to show the unlikeliness. I was critizised for saying "you are not thinking logically". Our engineers repeated all technical backgrounds, I added the procedural aspects from a pilot's point of view. So we have brought up all scenarios and can assume all theirs probabilities.

Ergo there is only one reasonable answer what happened, and this is: They left it in CLB - initially most probably intentionally.

slip and turn

8th Sep 2007, 10:32

Bernd
Your continued work is I am sure extremely well regarded and much appreciated. It is very heartening to see esteemed members and indeed a broad spectrum of the PPRuNE community responding to excellent chairmanship, summation and guidance from PBL and yourself.

One point about hydroplaning/aquaplaning, if I may - I am not up with the discussion enough to understand the full significance of it now, but I hesitate to accept that the "function of the square of tyre pressure only" theory was as well known/accepted in practice as it has become with recent hindsight.

I learned the 9 x version in ATPL theory I think, but it wasn't dwelled upon in class or study notes. You really have to be a good physicist to fully understand why it is so I think. So, at least in ATPL theory, this 'phenomena' was almost treated as just one of those interesting things worth an extra mark or two. The only consequence of failing to 'know' was the loss of a mark or two. As a piece of theory, it certainly didn't receive the same attention as the speed of sound being a function of temperature only, for example.

As I said, I am however no expert, so I don't know if type-rated pilots are expected to be much more aware of consequences of the theory than I was.

So I wonder if it might still be fair to say that any hesitation in braking was a natural reaction to the knowledge couplet of a reported slippery runway and any 'feeling' after touchdown that indeed it was so.

Certainly until reading the thread, and despite being taught enough about the tyre pressure angle to answer a simple exam question correctly, I would have been one who was tempted to stay off the brakes at higher speeds in the (false) assumption that I was improving my chances of a controlled stop by allowing the one reverser to do the lion's share of the initial deceleration work first. It's moot if the brakes aren't effective anyway of course, but might explain any hesitation.

My apologies if this is too simplistic to be useful.

bsieker

8th Sep 2007, 11:14

S&T,

thank you for your kind words.

(I don't know about chairmanship and guidance, I only try to figure out facts, and enjoy much of the very contentful discussion in this thread. We also found it useful to provide a concise summation of the known (and some speculated) facts and causal relationships in this accident with the help of a WB-Graph.)

So I wonder if it might still be fair to say that any hesitation in braking was a natural reaction to the knowledge couplet of a reported slippery runway and any 'feeling' after touchdown that indeed it was so.

I think the most important fact why we can dispel this theory, is that the pilots selected autobrake MED, which would have started applying brake pressure two seconds after being triggered.

If they had envisaged careful or delayed braking to avoid hydroplaning and/or its consequences (brake asymmetry comes to mind), they would have opted for manual braking from the start.

Bernd

Rob21

8th Sep 2007, 12:17

Please, correct me if I'm wrong.

1- From the "spoiler nada" call to manual brakes application five seconds went by, not ten. Why apply manual brakes before the spoiler status call?

2- The pilots "cycled" the ground spoilers armed switch almost at the same time they started applying manual brakes. This is probably because they knew braking would not be effective with no ground spoilers.

3- Autobrakes at medium is the correct (or recommended) selection for slippery runway (I learned this here).

Lemurian

8th Sep 2007, 12:32

Bernd,
Looking at the FDR print-out, between time tags 18:48:30 and :47, there are two very definite instances of a combination of

an application of right *almost* full rudder
an application of *almost* full right brake pedal application
a release of left pedal brake

The pilot was perfectly capable of maintaining max braking on both pedals outside these instances, and others that are less obvious,considering the *apparent 1°/second sampling rate.
The only conclusion is that these instances indicate attempts -successful - at using differential braking for directional control, which seems to confirm the slipperiness of the runway (I still haven't given-up on the presence of aquaplaning ).
Directional stability issues caused by asymmetric thrust are not in the graph,
It seems that the general application of right rudder is another indication.
There is, from the FDR a glaring takeover by the F/O.
Yes, but this is most likely not a causal factor in this accident, although very interesting to note in itself, and will be subject of investigation into training procedures, etc. at TAM.

Can't it be also a factor in the delayed application of pedal brakes ? The time tags for stick inputs and braking seemed to indicate that possibility.
we cannot say who made the brake pedal inputs, and L and R here does not refer to the Captain's and F/O's pedals, but left MLG and right MLG brakes.

Yes. I've had this idea about F/O taking over so strongly and for so long that I overlooked this fact. Thanks, and apologies .
I'm sorry, I must have missed that. Which post are you referring to?
I started as early as the 10th of august : See posts 1410, 1508, 1525.
Have to go now, but I submit this document to your perusal and study, as it covers most of the oPs and H/F sides of this discussion in depth. It is really worth a read.
Getting to grips with ALAR (http://www.smartcockpit.com/pdf/flightops/aerodynamics/0019/)

Regards.

Roland

P.S I understand that prevention is different ! But good SOPs should be universal.

bsieker

8th Sep 2007, 13:05

There is, from the FDR a glaring takeover by the F/O.

Yes, but this is most likely not a causal factor in this accident, although very interesting to note in itself, and will be subject of investigation into training procedures, etc. at TAM.

Can't it be also a factor in the delayed application of pedal brakes ? The time tags for stick inputs and braking seemed to indicate that possibility.

We have too few facts about the mode of this Takeover. In the CVR transcript there is no "I have control" or similar callout, which, particularly in a side-stick cockpit, must be called out in one form or another during a transfer of control.

So it is almost impossible to say what, if any, effect this may have had on delaying braking. So it is not included in the graph. But I think I'll give it some more thought. Thanks for pointing me to it again.

The only conclusion is that these instances indicate attempts -successful - at using differential braking for directional control, which seems to confirm the slipperiness of the runway (I still haven't given-up on the presence of aquaplaning ).

At 100+ knots the rudder would still have significant influence on directional control, I assume?

We still consider aquaplaning a possibility (so it is in the graph), but again, this has yet neither been confirmed nor denied. A comparison of wheel speed (if recorded), actual (A/S-limited) brake pressure and possibly other factors will tell.

I started as early as the 10th of august : See posts 1410, 1508, 1525.

Oh, yes, I remember, about the stick-control take-over. But, now as then, I cannot comment on that, other than that I find it interesting to see a complete takeover without callout.

Would be interesting to know if the priority-takeover pushbutton was pressed, and, if so, if the deactivated stick's inputs are still recorded, or suppressed even on the FDR?

Have to go now, but I submit this document to your perusal and study, as it covers most of the oPs and H/F sides of this discussion in depth. It is really worth a read.

Getting to grips with ALAR

Thanks a lot for this, it looks indeed very interesting.

Bernd

Flight Safety

8th Sep 2007, 15:53

What follows is a timeline analysis of the few seconds before and after touchdown, that might explain how a failure to retard ENG2 TL may have occurred, by failure to recognize thrust lever mode (or state) change from a switch function to a throttle function for ENG2 TL (left in the CLB detent), as I've discussed in previous posts. There have been several good theories discussed as to why ENG2 TL was left in the CLB detent, and I thought it prudent to attempt to "apply" the theory I've put forward to the actual CVR and FDR data. I also think theories that there was an electrical or sensor fault in detecting ENG2 TLA cannot be discounted at this point either. Hopefully we'll know the actual causes once the investigation is complete.

I assume from reading the CVR transcript that HOT-1 is PF and HOT-2 is PNF.

18:43:04 - HOT-1 (PF) remember, we have only one reverse.
18:43:06 - HOT-2 (PNF) yes...only the left.

Verbal reminder for both pilots that they only have one reverser discussed about 5 minutes 20 seconds before touchdown. Auto Thrust is activated and remains activated until after touchdown. Everything seems normal until close to touchdown, so I'm picking it up at the RA twenty callout.

18:48:21.0 - FWC twenty.
18:48:21.6 - FWC retard
18:48:22 - FDR - beginning of ENG1 TL movement to idle
18:48:23 – FDR – beginning of ENG2 increase in power
18:48:23.0 - FWC retard
18:48:23 - FDR - L-MLG WOW
18:48:24 - FDR - R-MLG WOW
18:48:24.5 - CAM [sound of thrust lever movement]
18:48:24.9 - CAM [sound of increasing engine noise]
18:48:25.5 - GPWS retard
18:48:26 - FDR - beginning of ENG1 TL movement to reverse
18:48:26.3 - CAM [sound similar to touchdown]
18:48:26 (between 26 and 27) - FDR - NG WOW
18:48:26.7 - HOT-2 (PNF) reverse number one only
18:48:27 - FDR - ENG1 TL in reverse

If I understand the A320 correctly, the retard callout should occur at RA twenty (it's RA thirty for the A340). According to the FDR data the movement of the ENG1 thrust lever begins about 1 second after the retard callout begins, around 18:48:22. Perhaps this movement didn't make a sound loud enough to be picked up by the CAM until 18:48:24. From the FDR data, this movement is the ENG1 TL being moved to idle, which is reached around 18:48:24.

It seems strange to me that the sound of increased engine noise at 18:48:24.9, which corresponded with a rise in engine power of ENG2 from the FDR, does not seem to get the attention of the pilots, as they make no comment about it, nor do they seem to take any action regarding it, because increasing engine power in the flare just prior to touchdown is pretty abnormal, unless your attempting a go-around from the flare. I think the pilots should have both heard and felt the increase in engine power.

The engine noise increase (as picked up by the CAM) occurred about the same time as the ENG1 TL reached the idle position. The FDR data shows the engine power started to increase about a second before the CAM picked it up, during the thrust lever movement to idle. The ENG2 power increase makes sense in light of the fact that the Auto Thrust System was still engaged at this point and a decrease in power on one engine would cause an increase in power of the other engine to maintain airspeed. Some have commented about the spike in power of ENG2 to EPR 1.24 or 1.25 at around 18:48:27 before settling to EPR 1.19 This looks like simple overshoot to me, common in many automatic systems.

Since according to the CVR and FDR, the pilots made no comment and took no action regarding the increasing engine power (which I think they would have heard and felt), I wonder if they were expecting it?

One possibility to explain why they might have been expecting it could be they got "creative" with the thrust levers (outside of Airbus procedures to retard both TLs) by trying to deploy ENG1 TR as soon as possible after touchdown. Both their actions taken and the comment made at 18:48:26.7, strongly suggest that getting ENG1 TR out as soon as possible was the goal of the PNF. Could he (PNF) have thought that the Auto Thrust System was still engaged when he started to move ENG1 TL back to idle (just above touchdown), thus leaving the ENG2 TL in the CLB detent on purpose so the ATS would continue to maintain airspeed (which the ATS did until ATS disconnect after touchdown)? Perhaps he didn't want to unsettle the flare just prior to touchdown, in order to get a good touchdown in the prevailing conditions, while still deploying the TR as soon as possible.

Another possibility is that the sound and vibrations of engine power increasing could have been associated with Reverse Thrust on ENG1 in the pilot's mind, as insidious as this scenario sounds.

18:48:29 (between 29 and 30) – FDR – Auto Thrust System disconnects
18:48:29.5 – HOT-2 (PNF) spoilers nothing
18:48:30.8 – HOT-1 (PF) aaiii [sigh]

The timeline at 18:48:29 and 18:48:30 re-enforces my belief that the pilots missed the state change from the thrust levers changing their mode (or state) from being selector switches to throttle levers. The state change happened at about the same time that the PNF called out “spoilers nothing”. This callout would have been shocking to the pilots, as both of these very experienced pilots would know in an instant what no ground spoilers meant in the prevailing conditions. The “sigh” from the PF suggests immediate recognition of those consequences.

This shocking and immediate turn of events could easily take the mind away from recognizing any state change in the working of the thrust levers, or recognition that the ATS has just disconnected and thus the ENG2 TL HAD to be pulled back to idle to activate the ground spoilers and auto brakes. If the increased engine power noise from ENG2 was associated with the TR from ENG1, how insidious this would have been, as it would sound and feel close to normal for thrust reverse.

I still argue that one habituated reason to leave an A320 thrust lever in the CLB detent is because it “lives” in that detent (as a selector switch) most of the time while an A320 is operating. It is also THE most common position to leave the thrust lever in when the Auto Thrust System is operating. On an all moving throttle lever system, the thrust levers don’t “live” in any particular position in the quadrant, and are thus habitually always thought of as throttles.

Dani

8th Sep 2007, 16:21

Very good theory.

I must add that pilots don't "feel" trust but rather hear noises and feel accelerations. So for me it's obvious that they heard the noise of spooling up and assumend that it was the reverser. What they felt was the missing deceleration. That's why they concentrated immediately to the available means of breaking, i.e. spoilers, reversers and breakes (auto and manual). In this order, since it is to be checked according SOP.

My theory goes this way: The captain had a plan in his head: I must go assymetric, 1 in revers, 2 in idle. He knew that there would be an assymetric power constellation on his pedestral. In time stress of the flare towards the short and slippery (?) runway he got it wrong: instead of 1 in revers 2 in idle, he did 1 in revers, 2 in clb. Which is just one little mistake for the hand, but one huge error that killed them.

I think in real life I would go both in reversers, although AI doesn't recommends it, but you avoid such assymetric manipulations. It's been proven by the junior captain one sector before. I do the same in OEI cases as soon as the failed engine is secured and stopped. AI is generally biased towards "double protection" (e.g. switching of a transponder on gnd altough it's connected to WOW, or putting out the nose light altough its off if gear is retracted, aso). This is also one of these cases. Makes technically sense. But is a possible cause for errors for some pilots not completly sure about SOPs.

Dani

bsieker

8th Sep 2007, 20:42

Could he (PNF) have thought that the Auto Thrust System was still engaged when he started to move ENG1 TL back to idle (just above touchdown), thus leaving the ENG2 TL in the CLB detent on purpose so the ATS would continue to maintain airspeed (which the ATS did until ATS disconnect after touchdown)? Perhaps he didn't want to unsettle the flare just prior to touchdown, in order to get a good touchdown in the prevailing conditions, while still deploying the TR as soon as possible.

The flare is supposed to be performed at idle thrust.

Reducing thrust doesn't "unsettle" the flare, it is an integral part of performing it.

Having higher positive thrust instead will cause the aircraft to float longer, and touch down later, faster and lighter. None of this could have been desirable here.

Bernd

bomarc

9th Sep 2007, 02:54

there is one small advantage to having had some thrust at flare...the engines will be slightly more quick to spool up once reverse thrust is selected.

SIDSTAR

9th Sep 2007, 07:35

Outstanding discussion, especially from ELAC, Bernd, ChristiaanJ, Flight Safety et al. I'm sure we have all learned a huge amount about both the accident itself and the workings of the A320 (auto) thrust system. The whole 100+ pages should be compulsory reading for all Airbus pilots. Danny, the whole reason for having Pprune in the first place is eloquently proved by the contributions of the above gentlemen - thank you all.
If one discounts the possibility of a fault in the thrust/thrust lever system (I'm not discounting the possibility but it is a long shot), then the investigation must centre on the "WHYs."
Why did the PF leave the lever in the climb detent?
Why was his mind set in that direction?
What was it about the system that had him thinking in that way?
Why did Airbus design it that way?
Having flown both Airbus and Boeing types in the past 5 years including the 320, I am convinced that the non-moving thrust levers are not a good idea. Someone asked a long way back why it is that Airbus designed the system this way. I seem to remember that one of their sales brochures mentioned that it was simpler (no back-drive mechanism to go wrong), thus lighter and of course cheaper but I cannot find the reference now.
Having also watched many pilots new to this system, operate the aircraft very poorly in both sim and aircraft, with little or no idea of what actual thrust the system was giving them, I am convinced that the design is inherently faulty. The essential cues of a moving lever are missing from the pilot's sensory system particularly in the most critical areas - approach and landing.
I've lost count of the number of times I've covered the EPR/N1 gauges and asked the other pilot what his power setting was, only to discover he had absolutely no idea. The system sucks you into believing that it will always look after you.
The tactile, aural and visual cues given by the thrust lever position cannot be over-emphasised, in my opinion. Having read the whole thread from day one, I find it very difficult to believe that this is not seriously implicated in whatever thinking led to the No 2 being most probably left in the CLB position. This is not anti-Airbus - one has to remember merely the ridiculous config/cabin altitude warning horn on the 737 to see that bad design affects both manufacturers - but it surely is an area that must be looked at in a critical manner after a number of such incidents/accidents. If not, I fear we will be discussing a similar accident in a few years time. The confusion that reigned on the TAM flight deck after touchdown should not be possible on any modern airliner. Unfortunately, such mode/situational confusion is common on many types. Professional pilots and the travelling public deserve better. Airbus and Boeing please do not forget the fallible humans at the front end and design man/machine interfaces that take full account of our human frailties. Your machines are technically excellent in most areas and rarely fail catastrophically. Can the same be said for the humans?
SID
ps It is also worth bearing in mind that Airbus and Boeing are not above using forums such as this for their own purposes, especially after an accident such as this. Major corporations don't have morals or scruples - only 'interests'.

Dream Land

9th Sep 2007, 07:45

On a short slick runway as soon as you touch down you will be in reverse thrust and the go around option is not recommended by Bubbers Please don't put everyone in this category, this would not be my technique, I choose to keep my options open. :=

bsieker

9th Sep 2007, 08:39

SIDSTAR,

very well put. I do not necessarily agree, but since I don't fly the machines I will not pass judgment.

Having also watched many pilots new to this system, operate the aircraft very poorly in both sim and aircraft, (my emphasis)

Couldn't that be a key point? Lack of type-training?

The systems of different aircraft are fundamentally different in this respect (as well as the sidestick vs. conventional yoke respect, the sidestick also having been implicated in at least one accident I am aware of ... )

Even if it is possible that the static lever design has influenced this accident, the case for changing it is a far more compex one. We have seen accidents with similar (though ultimately less fatal) consequences which were in part caused by the back-driving mechanism of the B747-400 thrust levers.

While it is true that no part of a flight deck design can be allowed to be above criticism, a single (or even three) accident cannot be viewed individually to make a case for a fundamental design change. Looking at the balance of moving/non-moving levers in all situations, the score does not look so clear any more.

Add to that Buridan's Ass ("metastability", "undecidability", call it what you will, eloquently introduced here by PBL), and we have to wonder if changing the design here will not simply move the problem to another region.

Bernd

BOAC

9th Sep 2007, 08:48

Couldn't that be a key point? Lack of type-training?
- I agree - well back I was talking about the training mind-set not keeping up with 'technology'. Basically though, in this case, I'm sure that reminding pilots to close the T/Ls on landing (unbelievable:eek:) will go along way to preventing a recurrence. The training side/AB may also need to consider a drill for a failed T/L sensor along the lines of the 'failed braking' drill.

PBL

9th Sep 2007, 09:48

It is also worth bearing in mind that Airbus and Boeing are not above using forums such as this for their own purposes ...

SID,

it is maybe worth inquiring what such purposes would be, and how they could hope to achieve them in this forum.

If anyone helps establish The Truth, then more power to them, whatever the motivation. And if someone wants to spread falsehoods, it's hard for me to see how they would make it past the barrage of criticism.

PBL (NOT affiliated with any big company's marketing department :) )

GMDS

9th Sep 2007, 09:50

BOAC

The training side/AB may also need to consider a drill for a failed T/L sensor along the lines of the 'failed braking' drill.

.... basically we will then end up with many more drills the pilots have to recall instantly, under all circumstances, without any doubt about which one to apply, by switching off or on any failing lever, switch, pushbutton, without warnings as the system cannot know it failed, the pilot however has to recognise instantly .......................... to back up failing automatics, programs, designs, you name it.
That's the ultimate perversion to why automation has been brought in! We wanted help in the cockpit and end up beeing a watchdog for brilliant ideas of engineers, not so brilliantly implemented and not adapted to our human skills.
I pledge for the other way. Take out the ambiguous stuff, even if it brings us back a technologie or two, and REDESIGN AUTOMATION where it proved to confuse us. Take the average Joe and Jane to determine this, not the specialists who guide us through the wonders of engineering on pprune.
As has been said, it is not only a AI phenomenon.

PBL

9th Sep 2007, 09:54

The training side/AB may also need to consider a drill for a failed T/L sensor along the lines of the 'failed braking' drill

How could you detect it? As opposed to, say, a failed EPR gauge/sensor/data computation? Without lots of time and opportunity?

If the FMEA is done right, I would imagine a failed TLA sensor arrangement is a 10^(-9) item, isn't it?

I pledge for the other way. Take out the ambiguous stuff, even if it brings us back a technologie or two, and REDESIGN AUTOMATION where it proved to confuse us. Take the average Joe and Jane to determine this, not the specialists who guide us through the wonders of engineering on pprune.

Well, that is Billings's Human-Centered Automation concept (HCA). Used extensively, as far as I know, by both major producers as well as by most major avionics firms.

It's not as simple as lookit n fixit. If it were, we wouldn't be having this discussion.

PBL

BOAC

9th Sep 2007, 11:28

basically we will then end up with many more drills the pilots have to recall instantly - from my limited understanding of the way the beast works, it seems that a failure of the sensors would be very difficult to detect and therefore IF it is a possibility inside the 'automation' it needs to be thought of.

Let's suppose it happened at CGH.

a) Were the crew aware of the possibility? - I suggest not

b) would they have known instantly what action was required? - ditto

c) are there any SIGNIFICANT clues, preferably visual (or STRONG audio) to tell crew it has happened? - ditto?

I support GMDS's 'Joe and Jane' approach.

bsieker

9th Sep 2007, 11:56

- from my limited understanding of the way the beast works, it seems that a failure of the sensors would be very difficult to detect and therefore IF it is a possibility inside the 'automation' it needs to be thought of.

Due to its redundancy a sensor failure would be easy to detect. And there are two different failure modes documented in the FCOM that have an associated ECAM (Airbus equivalent of Boeing's EICAS) procedure:

THR LEVER FAULT: no reliable reading
THR LEVER DISAGREE: different readings from both sensors.

The handling is only slightly different, but TOGA/FLEX thrust during take-off/go-around will be maintained. In other situations, IDLE, MCT, or thrust according/limited to the higher reading in case of "disagree" will be set, according to various circumstances (speed, flight phase, slat position, TLA at failure ...).

Standard procedure is to set the lever of the affected engine to IDLE, and, if possible, keep autothrust on.

There may be some mechanical failures (namely failure of the pushrod between artificial-feel unit and throttle control unit, which incorporates the sensors) that are hard to detect, but since these are mechanical parts, making them highly reliable is well-understood, and barring maintenance problems a failure seems unlikely.

Then again, a failure of the slat-track downstop on B737NG was also considered very unlikely, ...

(See this thread (http://www.pprune.org/forums/showthread.php?t=288717) for reference.)

Bernd

BOAC

9th Sep 2007, 14:14

according to various circumstances - do you know how it would have 'reverted' in this case, bearing in mind it could have failed at any time from clean up out of previous to landing at CGH and the pilots would not know until....?

FullWings

9th Sep 2007, 14:40

I've read through this whole discussion and it's been extremely interesting. What no-one seems to have adequately answered is why a system's logic should allow the selection (not unwanted deployment through failure) of reverse thrust on one engine with significant commanded forward thrust on the other. I've spent some time thinking about it and cannot see a situation where this wouldn't lead to severe/terminal handling difficulties, both on the ground and in the air.

Just to re-iterate: I can see that for a non-normal situation like uncommanded T/R deployment in the air, you might want to have the ability to add thrust on the other engine. What I can't envisage is the need to select reverse on one having selected >idle forward thrust on the other - to my mind this just shouldn't be an available option as it will always be a bad one... :uhoh: Comments?

PAXboy

9th Sep 2007, 15:31

SIDSTARIt is also worth bearing in mind that Airbus and Boeing are not above using forums such as this for their own purposes ...The world moves by cøck-up, not by conspiracy. If a manufacturer wanted to influence matters in a malign way, they have all the money and advisors and politicians that they need. :rolleyes:

bsieker

9th Sep 2007, 15:44

Quote:
[setting of thrust at thrust lever angle sensor failure] according to various circumstances

- do you know how it would have 'reverted' in this case, bearing in mind it could have failed at any time from clean up out of previous to landing at CGH and the pilots would not know until....?

I'll give it a try. Here we go.

. THR LEVER DISAGREE (this warning is inhibited between touchdown and 80kts, i. e. for entire "roll-out" in this accident):

- Before slats extension, TLA at or below MCT during failure:
-- with A/THR ON
===> A/THR active, limited to higher TLA reading, but max MCT.
-- with A/THR OFF
===> Thrust set to higher TLA reading, limited to MCT.

- After slats extension, TLA at or below MCT during failure:
===> IDLE.

- on the ground
===> IDLE, reverse is available.

. THR LEVER FAULT (this warning is not inhibited during approach and landing):

- Before slats extension, TLA at or below MCT during failure:
-- with A/THR ON
===> A/THR active, limited to MCT
-- with A/THR OFF
===> MCT

- After slats extension, TLA at or below MCT during failure:
===> IDLE

on the ground
===> IDLE, reverse is not available, deployed reverser will be restowed.

I hope I got it all right.

Bernd

BOAC

9th Sep 2007, 16:12

Thanks Bernd - so are you saying that unless the 'pushrod' failed at touchdown there would have been a recorded indication (somewhere?) of a disagreement between the two position sensors on the No 2 T/L? Where would the disagree signal be recorded?

So, as I read you, ?in the absence of such?, it really focusses on pilot mis-positioning of the lever - or an unlikely failure of the 'pushrod' as the T/L No2 was closed.

bsieker

9th Sep 2007, 16:45

Thanks Bernd - so are you saying that unless the 'pushrod' failed at touchdown there would have been a recorded indication (somewhere?) of a disagreement between the two position sensors on the No 2 T/L? Where would the disagree signal be recorded?

I'm sorry, I have to pass on that one. I know from other FDR graphs I have seen that it is recorded which ECAM pages are displayed, but I don't know about warnings and failures.

Since Autothrust remained active, either failure described above would not have made a difference until Autothrust-disconnect. But a deteced failure, as described above, would have put the affected engine to IDLE after Autothrust disconnect, which did not happen.

So, as I read you, ?in the absence of such?, it really focusses on pilot mis-positioning of the lever - or an unlikely failure of the 'pushrod' as the T/L No2 was closed.

A pushrod or link failure might have occured at any time after thrust reduction ...

This is speculative, but I guess that even after the fire, the experts (the real ones conducting the hands-on-work of the investigation) will be able to tell if and in which way the thrust lever mechanics may have failed.

If there had been an indication of such a failure, there would have been an all-operators telex and/or service bulletin and/or an emergency AD, as has been the case in the China Airlines fire in Okinawa.

That there wasn't is a strong indication that there was nothing wrong mechanically with the throttle system.

... Leaving only an undetected electronics failure. Very remote, but we never said it was absolutely impossible.

Bernd

PAXboy

9th Sep 2007, 20:52

With the resurgent interest in the TLs and their possible failure. I checked back to see where the electronic explanation was given. There are more posts, as well as the diagrams of the physical layout but this is about the electronic layout. To the outsider (me) who spent 25 years in IT, this looks like they have covered the eventuality of mechanical failure and ensured that it can be picked up by electronic means, which are themselves heavily duplicated.

TyroPicard #884There are two Angle sensors on each Thrust Lever. If the two sensors disagree about the TLA, on the ground, but not at TOGA or FLX/MCT (i.e. take-off thrust setting), the FADEC selects Idle thrust irrespective of thrust lever position. An ECAM warning occurs and as part of the drill the pilot backs this up by selecting idle.
If neither sensor produces a valid signal, on the ground, the FADEC selects Idle thrust. An ECAM etc......
TripleBravo #1474The position information is transmitted by 6 cables per sensor, which allow to cross-check for cable breaks and potentiometer breakups for each sensor. These analog signals are fed into one channel of FADEC (A), the other 6 from the second sensor are treated completely separate in channel B. The arbitration between the two FADEC channels takes place after input check and evaluation of the signals. Each channel is capable to control the engine on its own if the other fails. They are independent, also physically, which means that every chip is only responsible for one of the two channels.

Once again, this is no cheapo hardware like just one microcontroller doing all the math, so there is no need for such constructions like IRQs.

The engineering is well aware of the importance of treating these things right. Also the test departments are very creative inventing scenarios the engineering departments might have overlooked, kind of competition. Trust me, I have worked in that business, although not especially on thrust levers and engines.vapilot2004 #1510
Airbus thrust lever description
The mechanical thrust controls for the A320 consists of three main parts:
The Levers,artificial feel units and control units.

This setup is common for most FADEC equipped aircraft with the only difference between Airbus A320/330/340 and others is the addition of a servo motor to back drive the throttle levers in autothrust mode.

Each thrust lever is connected by a pushrod to the input of an artificial feel unit. This unit provides friction and the detents throughout the motion of the thrust levers.

The artificial feel unit's output shaft is connected to the thrust control unit via a second pushrod. Within each thrust control unit are 6 potentiometers and 2 thrust angle resolvers.

The pots provide thrust lever position to the flight control system while the resolvers are dedicated to the engine thrust control.

A resolver is a sort of rotary transformer that outputs sine & cosine waves corresponding the the thrust lever angle. The mechanical ratio of the thrust lever angle and the resolver angle is 1:1.9. For every degree of movement of the levers, there is a 1.9 degree movement indicated by the resolver. Resolver units are more accurate and reliable in translating angular position data than potentiometers and is the reason for their use here.

Each thrust control unit has two resolvers - one for each EEC channel. A disagreement of more than 15' (1/4 degree) causes the EEC to go into resolver failure mode.

Each EEC also checks the resolver output for upper and lower limits. For the IAE engines the limits are from -41 to 88 degrees. Any value outside of these limits will cause the FADEC system to transfer engine thrust control to the alternate EEC.

Outside of a jammed feel unit or thrust control unit, a failure of the A320 manual thrust control system seems unlikely.

bubbers44

9th Sep 2007, 23:16

Quote:
On a short slick runway as soon as you touch down you will be in reverse thrust and the go around option is not recommended by Bubbers

Please don't put everyone in this category, this would not be my technique, I choose to keep my options open.

Options open means you want to be able to go around without coming out of reverse first which can easily be done but is not recommended by sop. How far with your procedure of landing on a short slick runway do you travel before you select reverse thrust? How much does that extend your landing distance? Most airplanes, you know the ground spoilers will work so if you fly that airplane you can always get ground spoilers so there isn't any reason to wait for ground spoilers to deploy before commiting to a landing. If you fly an airplane that you don't know if you can get ground spoilers I see your point.

marciovp

10th Sep 2007, 03:03

From a talented Brazilian Jet Pilot (http://aviationtroubleshooting.*************/

Sábado, 1 de Setembro de 2007

TAM 3054 - Aceleração BRUSCA antes do pouso (http://aviationtroubleshooting.*************/2007/09/tam-3054-acelerao-brusca-antes-do-pouso.html)

http://bp1.blogger.com/_uaAGqzcfNRI/RtmWFH1i_1I/AAAAAAAAAHk/VMQevFMvHTU/s400/A320TAM3054graficosTimeline2.jpg (http://bp1.blogger.com/_uaAGqzcfNRI/RtmWFH1i_1I/AAAAAAAAAHk/VMQevFMvHTU/s1600-h/A320TAM3054graficosTimeline2.jpg)
A aceleração do motor DIREITO, cujo reversor estava 'pinado', começou ANTES das rodas do Trem-de-pouso DIREITO e NARIZ terem tocado o solo.

The acceleration of the RIGHT motor, where the reverser was locked out, started BEFORE the RIGHT and NOSE wheels touched the ground.

Na imagem acima apresenta o detalhamento na linha do tempo sobre o fato da aceleração ter se iniciado num momento inconveniente.

In the above graphic one can see the details of the libe of time about the fact that the acceleration having started at an incovenient moment,

Não foi uma aceleração típica de correção de potência dos motores e sim uma BRUSCA aceleração que atingiu o pico em 3.5 segundos subindo a EPR do motor DIREITO para 1,260.

It was not a typical acceleration for the correction of the potency of the motors, instead it was a sudden acceleration that reached the peak in 3.5 seconds raising the EPR of the RIGHT motor to 1,260.

Esta observação já foi postada neste Blog, mas alguns internautas não entenderam.

I already posted this observation in this Blog but some internauts did not understand.

É injustificável um sistema de automatização acelerar vertiginosamente a potência de um dos motores, ANTES da aeronave estar com as 3 (três) rodas do Trem-de-pouso no solo, a menos que uma arremetida tenha sido executada.

One can´t justify a system of automatization accelerating dramatically the potency of one of the motors, BEFORE the airplane have the three
(3) wheels on the ground, unless a go around has been executed.

Observe no gráfico que o terceiro alerta, RETARD, aconteceu quando as rodas principais, Esquerda e Direita, do Trem-de-pouso já estavam no solo, porém a roda do NARIZ ainda estava no ar.

Observe in record that the thirs alarm, Retard, happened when the LEFT and RIGHT wheels where on the ground but the NOSE wheel was yet on the air.

O anúncio RETARD foi silenciado devido ter sido selecionado o reversor ESQUERDO na posição angular de -2.5 graus (menos dois decimal cinco).

The warning RETARD became silent because the LEFT reverser was selected in the angulkar position -2.5 degrees (less two decimal five)

Sorry for the translation. My impression is that George Rocha, this talented Jet pilot feels that the software did not work very well because even eith the LEFT motor reversed and the pilot aplying brakes, it still behaved as if the plane wanted to go around (I am just trying without knowing for sure if this is his thinking. I am not a jet pilot, much less a
Airbus or Boeing pro pilot. I just love aviation and my experiences have been with small planes. Just trying to help).

PBL

10th Sep 2007, 03:38

A aceleração do motor DIREITO, cujo reversor estava 'pinado', começou ANTES das rodas do Trem-de-pouso DIREITO e NARIZ terem tocado o solo.
The acceleration of the RIGHT motor, where the reverser was locked out, started BEFORE the RIGHT and NOSE wheels touched the ground.

This is incorrect. He is forgetting about parameter sampling rates on the FDR transcript.

EPR is sampled on the #1 roughly on the full-second boundary; #2 EPR is sampled slightly before the 1/2-second boundary. WoW LMLG occurs between 18:48:23 and :24; WoW RMLG between 18:48:24 and :25. The first *slight* divergence between EPRs occurs between the #1 sample at 18:48:24 and the #2 sample at 18:48:24+.

I would incline more towards the conclusion that WoW RMLG occurred just past the 18:48:24 second boundary, and the EPRs started to diverge after that.

PBL

Dream Land

10th Sep 2007, 04:15

How far with your procedure of landing on a short slick runway do you travel before you select reverse thrust? by bubbers44 On this type of runway and severe winter conditions I will wait until I feel deceleration before T/R operation.

RWA

10th Sep 2007, 05:16

I’ve followed this thread from the beginning with great interest, and learned a lot from it. But (being only a GA and glider pilot, and retired at that) I’ve only just plucked up courage to mention something that I’ve been wondering about, which so far doesn’t appear to have been discussed.

Most people will have seen this video of a (highly-competent, ‘textbook’) A320 landing at Madeira. It’s unusually informative because the camera guy, instead of just filming straight ahead during the touchdown, filmed the pilot’s hand retarding the throttle levers and then applying reverse thrust.

http://www.youtube.com/watch?v=3OtcaFkpUpk

It shows that the pilot’s grip on the handles looks slightly odd – only the forefinger is actually hooked over the levers, the thumb and middle finger are gripping the sides of the levers. I researched this a bit and found that there are in fact red buttons on the outside of each lever, which trigger ‘autothrust disconnect.’ That is presumably the reason for the odd grip, so that the pilot could disconnect the autothrust before flaring – even though he would have been planning to pull the levers back to ‘idle’ in any case.

From information earlier in the thread, we all know that, with the A320 setup, autothrust disconnect does not automatically reduce engine thrust to ‘idle.’ If the throttles are above ‘idle’ the thrust merely ‘defaults’ to the last recorded thrust setting (which in this case was presumably the power required to maintain landing speed on final approach). So, as I see it, even if the wheels are down, the ONLY way to reduce thrust on a given engine to ‘idle,’ and keep it there, is to retard the lever all the way to the ‘idle’ stop?

Is it even barely possibly that the pilot at CGH didn’t know this, or didn’t recall the point under the pressures of landing on a short wet runway with only one operating reverser? And therefore, in his own mind, used the buttons to order ‘autothrust disconnect’ and then interpreted that as ‘finished with engines,’ and concentrated only on making sure that he got hold of the correct lever for the operating reverser and moved it into ‘max. reverse’ as soon as possible?

Thought I’d ask the question, anyway. If I’m talking rubbish, don’t hesitate to say so and I’ll shut up.

SIDSTAR

10th Sep 2007, 05:28

Bernd,

As I am not either an expert in accident investigation or aircraft design I bow to your expertise and that of many others on this thread in such matters. However, following this latest accident, I would expect the investigators to recommend Airbus to objectively examine the benefits of the system to see if it can be improved without transferring the problem elsewhere or creating a totally new problem, which I acknowledge is always a possibility. An example of such recommendations would be the UK AAIB's recommendation regarding the ECAM procedure after the BA 320 lost its displays at night.

I was just making the point that I've seen pilots become totally unaware of their thrust setting at almost all phases of flight and this is certainly not helped by the non-moving levers. I agree, better training is part of the answer but the type rating courses that I've seen do not really allow for much of this basic training in the simulator due to the huge number of system failures that must be at least touched on during 7 or 8 sim sessions. While this could be demonstrated in the simulator, the real place where it needs to be emphasised over and over again is in the line training phase. However, even with the point ingrained in a pilot's psyche during line training, operating the system day in day out without any problems can instill a sense of complacency. As professional pilots we all have a duty to try to be aware of such dangers.

I just feel so sorry for these two pilots who clearly were thrown out of their normal "comfort zone" on this landing. The confusion in their minds must have been appalling and it appears that hey did react within a reasonable timeframe when they realised that they weren't decelerating. Unfortunately it was too late on this occasion.

There but for the grace of God go you or I!

bsieker

10th Sep 2007, 08:02

marciovp,

As PBL has already pointed out, making observations about event timing at a precision higher than the sampling rate is impossible, maybe we should hold a short course "Reading Time-Discrete Data Plots". Drawing a linear interpolation between the points implies a continuity in the data that's not there.

I'm also not sure what point George Rochas is trying to make.

There are some points to consider about autothrust operation:

- Thrust in engine #1 was reduced
- Slightly before the dramatic increase around 18:48:26, there is a notable drop in longitudinal acceleration at 18:48:24.2, corresponding to a recorded drop in speed around the same time
- Autothrust is especially responsive to speed variations during approach, trying to compensate quickly even for small deviations, since approaches are usually flown rather close to minimum speed. This submode of operation is known as "approach autothrust", in this mode, precise speed-keeping has priority over comfort considerations, safely to keep the speed above stall speed.

Taking this into account, the reaction of the engines is perfectly normal.

Even with two engines operating, sudden thrust increases shortly before touchdown are not unusual, especially in gusty conditions. Again I recommend watching some landing videos, youtube has a wide selection.

My impression is that George Rocha, this talented Jet pilot feels that the software did not work very well because even eith the LEFT motor reversed and the pilot aplying brakes, it still behaved as if the plane wanted to go around

Yes, this has been widely discussed here, almost from the beginning. The problem still being that the aircraft cannot read the pilot's mind so has to follow control inputs, because there is no obvious Right Thing to do.

And the aircraft was not behaving as if it was tryng to go around; going around requires a whole different region of thrust, closer to sustained EPR 1.4, and not a peak at 1.26, and then settling at 1.18.

Bernd

peterperfect

10th Sep 2007, 08:26

Does anyone know if the runway re-grooving at Congonhas has been completed ? I last saw a projected date of 8th Sep. Any updates ? Thanks.
pp

Dream Land

10th Sep 2007, 10:04

Is it even barely possibly that the pilot at CGH didn’t know this, or didn’t recall the point under the pressures of landing on a short wet runway with only one operating reverser? And therefore, in his own mind, used the buttons to order ‘autothrust disconnect’ and then interpreted that as ‘finished with engines,’ and concentrated only on making sure that he got hold of the correct lever for the operating reverser and moved it into ‘max. reverse’ as soon as possible? by RWA
My guess is no, not a dumb question, you seem to be very educated on the system, I doubt if a person can make it to the left seat without being more familiar with the A/TH system.

FlightDetent

10th Sep 2007, 10:30

So, as I see it, even if the wheels are down, the ONLY way to reduce thrust on a given engine to ‘idle,’ and keep it there, is to retard the lever all the way to the ‘idle’ stop?
Exactly. In fact, by reatarding TL to "idle", you will initially reduce the "dead-band" between TL position and actual thrust setting, then limit the autothrust commanded N1 setting to TL position and when at idle the autothrust will disconnect. Unless you do so, A/THR will attempt to maintain speed indefinitely. KILL-THE-THRUST is normal operation at every single landing. There is no way any A320 pilot could attempt and succeed landing other way around.
Is it even barely possibly that the pilot at CGH didn’t know this, or didn’t recall the point under the pressures of landing on a short wet runway with only one operating reverser? And therefore, in his own mind, used the buttons to order ‘autothrust disconnect’ and then interpreted that as ‘finished with engines,’ and concentrated only on making sure that he got hold of the correct lever for the operating reverser and moved it into ‘max. reverse’ as soon as possible?
The buttons are not used and not needed in normal operations - this landing was a normal operation, albeit demanding and with little room for error. You do not need buttons to disconnect A/THR for landing, you do not need them to disconnect A/THR to salvage a too high flare, you do not need them when little extra thrust is required. You do not need them for go around thrust. The system is a complicated piece of engineering because it is designed to be operationally VERY simple.

The way you finish with the engines, is you put them in idle. The grip witnessed on the video makes a lot more sense on different autothrust designs. n.b: technically speaking. I am nowhere near being authorized for Madeira landings - definitely no secondguessing here.

If metal gets bent and people hurt, there are lesson to be learned. Personally I feel lost in here, there's nothing to grasp, I cannot come up with anyting to change that would really had made a difference. :suspect:

bsieker

10th Sep 2007, 11:40

http://www.youtube.com/watch?v=3OtcaFkpUpk

It shows that the pilot’s grip on the handles looks slightly odd – only the forefinger is actually hooked over the levers, the thumb and middle finger are gripping the sides of the levers.

The grip in this video looks like the pilot keeps ready for go-around, by keeping the thumb and middle finder behind the levers to be able to push them quickly and decisively all the way forward. Note that contrary to some general SOPs for landing, he does not select reverse at touchdown, but waits for the spoilers call instead.

Some pilots here have remarked that this is also their preferred way on short runways, because, although this carries a small LDR penalty, it keeps open the GA option in case something goes wrong.

I researched this a bit and found that there are in fact red buttons on the outside of each lever, which trigger ‘autothrust disconnect.’ That is presumably the reason for the odd grip, so that the pilot could disconnect the autothrust before flaring – even though he would have been planning to pull the levers back to ‘idle’ in any case.

You only need one button, most comfortably I guess pressed with the thumb. It is a bad idea to disconnect autothrust explicitly before pulling the levers to idle on landing, because thrust would then rise to meet the lever position. After pulling the levers to idle autothrust disconnects, but can be re-activated, but in either case, thrust would be limitied to the lever position, i. e. idle.

From information earlier in the thread, we all know that, with the A320 setup, autothrust disconnect does not automatically reduce engine thrust to ‘idle.’ If the throttles are above ‘idle’ the thrust merely ‘defaults’ to the last recorded thrust setting (which in this case was presumably the power required to maintain landing speed on final approach).

Careful here. There are four distinct ways autothrust can disconnect:

1/ by pulling the levers (both) to idle. This is the normal way during landing. Thrust is reduced to and stays at idle.
2/ by pressing the so-called "instinctive disconnect" pushbutton at the thrust lever side. Thrust rises to meet the lever position. Standard procedure when using this method is to first move the levers to match the actual thrust setting, but it is not technically necessasry.
3/ by pressing the A/THR pushbutton on the glareshield. Thrust is locked until the levers are moved, after which thrust meets lever position.
4/ by an internal failure condition. Thrust is locked until the levers are moved, after which thrust meets lever position.

(4/) was the most likely way in this accident.

So, as I see it, even if the wheels are down, the ONLY way to reduce thrust on a given engine to ‘idle,’ and keep it there, is to retard the lever all the way to the ‘idle’ stop?

Yes, the above notwithstanding.

Is it even barely possibly that the pilot at CGH didn’t know this, or didn’t recall the point under the pressures of landing on a short wet runway with only one operating reverser? And therefore, in his own mind, used the buttons to order ‘autothrust disconnect’

No. In that case, thrust would have risen to the lever position (maximum climb power, around EPR 1.28). And A/THR disconnection would have been recorded in the FDR graphs. Neither is there.

Bernd

PAXboy

10th Sep 2007, 11:46

SIDSTARI would expect the investigators to recommend Airbus to objectively examine the benefits of the system to see if it can be improved without transferring the problem elsewhere or creating a totally new problem, which I acknowledge is always a possibility.Unfortunately, even rigorous testing may not test the combination of events that causes an incident. So, you might change something in the equipment configuration and test it for six months and declare it safe. Perhaps five years later, you will discover that a new set of circumstances has occurred and they met the new weakness in the system that you made.

However, you could change nothing and the exact same fault might be repeated in five years. That is the nature of the business of aviation.

alemaobaiano

10th Sep 2007, 14:38

Does anyone know if the runway re-grooving at Congonhas has been completed ? I last saw a projected date of 8th Sep. Any updates ? Thanks.

The work has been completed but as of Friday the authorisation to reopen the runway had not been received. This is probably related to the ongoing legal battle over documents submitted to the courts by a director of ANAC during the "closed when it rains" situation some months ago. Everybody wants this to be legal and above board this time around with no disputes over who said what.

ab

marciovp

10th Sep 2007, 14:47

Does anyone know if the runway re-grooving at Congonhas has been completed ? I last saw a projected date of 8th Sep. Any updates ? Thanks.
pp

Yes, from what I read, the job has been done. They are now thinking about the soft cement on 150 meters at the end of the runway (I guess on the sides?...). And some are talking about the steel horizontal net...

Guarulhos main runway is being repaved... it will take a while so the pilots are using the secondary runway (shorter).

It seems, so far, that the Air Force will remain with Air Traffic Controll (people and equipments). The federal government has released moneys
for the Armed Forces (including the Air Force).

Slowly things seem to be improving, thanks God.

Yes, this has been widely discussed here, almost from the beginning. The problem still being that the aircraft cannot read the pilot's mind so has to follow control inputs, because there is no obvious Right Thing to do.

But with the pilot doing a reverse and trying to brake the plane could there be a doubt on what he wanted to do? Couldn´t the software be programed for this situation?...

bsieker

10th Sep 2007, 16:06

But with the pilot doing a reverse and trying to brake the plane could there be a doubt on what he wanted to do? Couldn´t the software be programed for this situation?...

I believe it could, to a point. Firm braking being the key factor here. Some data mining needs to be done to establish what would unambiguously constitute braking instead of "parasitic" brake pedal deflections while making rudder inputs.

I will shortly publish an extension to the ground spoiler-extension logic, taking braking into account, while allowing for one above-idle thrust lever reading.

Great care must be taken, because ground spoiler deployment in the wrong moment can be just as disastrous as lack of ground spoilers when they are needed.

I expect it to be controversial, and hope for a constructive and fruitful discussion.

Watch PBL's web site for news.

Bernd

Dani

10th Sep 2007, 16:34

I guess it could, but it contradicts completly the Airbus design philosophy. In spite of being highly electronically based, Airbus aircraft never do something themselves! You might be surprised.

Example: If you have an engine failure, the software could easily do everything for your, Rudder deflected, MCT set, Master off, ...

Boeing in 777 for example does automatic rudder compensation in case of OEI (if I'm right). Saab does automatic APU start. MD-11 is extensively automated when it comes to switchings in the hydraulic and pneumatics (to replace the FE from DC-10).

Airbus' intention is, if you take the pilot out of the loop, he doesn't know what's happening anymore. That's why you have to brake yourself. And you can revers one engine and go on TOGA on the other. The system is completly pilot-oriented.

Dani

EMIT

10th Sep 2007, 16:58

A couple of pages ago there was some question/discussion about the apparent take-over of control during the landing roll.

If both pilots had given simulteneous inputs on the sidesticks, there would have been a "DUAL INPUT" callout.

If one had pressed the take-over pushbutton on a sidestick, there would have been a "PRIORITY LEFT" callout (or RIGHT, for that matter).

If CM2 did give control inputs while CM1 was busy with braking and cycling speedbrake lever, I think this would be a fairly natural tendency with death looming about 15 seconds away. Forgetting an SOP call ditto.

bsieker

10th Sep 2007, 17:25

EMIT,

good point about the "PRIORITY RIGHT" automatic callout. I had forgotten about that.

It does not appear in the WARNINGS AND CAUTIONS section, so do you have any idea in which flight phases (if any) it might be inhibited? Or which other aural signals might have priority?

(We found out analysing another accident, that the "DUAL INPUT" warning, even though FCOM says it is not inhibited in any flight phase, has a lower priority to the EGPWS "pull up" call-out, and was thus inhibited.)

Bernd

SIDSTAR

10th Sep 2007, 17:50

Dani,

Just to clarify the AI position: Airbus changed the method of dealing with a locked out reverser last year but gave no reason for the change. Perhaps it was linked to the previous incidents? The revision to the MEL clearly now shows that on landing with a locked out reverser, you pull reverse on both engines even though this will result in an increase (small they say) in forward thrust on the engine with the locked out reverser.

EMIT

10th Sep 2007, 19:05

Bernd,

Off the top of my head, those calls are never inhibited (if you mean inhibition based on flight phase), but indeed they may be overruled by calls of even higher priority like (GPWS) PULL UP.

EMIT.

gpvictor

10th Sep 2007, 20:46

I'm not a pilot (my domain is psychology), but I like aviation. I care also for my safety, so I stay informed: in fact, I were in Brasil when the crash occurred, and it was quite impressive.
I wonder why Airbus did maintain a somewhat complicated landing procedure with one locked reverse (first both to idle, then only one to reverse) that the two TAM's pilots followed, probably in a wrong way. Sidstar says that they changed it on the MEL, but, after two crashes (Philippines and Taiwan) with similar dynamics (and probably some other occurrences where the pilots discovered quickly the error), a change in the software i.o. to unify all landing procedures, with or w/out reverse, should be implemented. When you are relying more on perceptions than on logic (and it occurs), the image of two asimmetric levers can be misleading.
And I would ask to the pilots flying on A320 if a warning when the engines of the plane are pushing one in the opposite direction of the other could be useful

EMIT

10th Sep 2007, 21:37

SIDSTAR,

MEL changes are never accompanied by "reasons why". Even stronger, since MEL is a book, or a file on our LPC laptop, that we only have available on board (not as "at home documentation" like FCOM and QRH), we as pilots see the MEL only when we have a dispatch deficiency on the aircraft.

Whether or not the procedure for de-activated reverser was changed, was probably not known by the pilots. The procedure as it was at their time, of course must have been viewed by them.

Strange thing to realize is that, in case of a reverser failure happening during the flight, e.g. in case of hydraulic system failure on G and/or Y system, ECAM and QRH will only state REV 1(/2) INOP. You will receive no guidance on what to do with the thrust levers! (I mean whether to pull into reverse range or to leave in idle). Remember that in such a case, MEL is not applicable, so you are not required to consult it.

Couple this with perhaps very good FCOM knowledge (about the increase in fwd thrust when T/L is moved into reverse range) or experience from SIM sessions where this phenomenon may have made the difference between stopping on, or just beyond the end of, the (simulator) runway, and there may be the ground for wanting to leave the "offending" thrust lever in idle, rather than taking it along into reverse range as the latest AI MEL instructions tell you to do.

EMIT.

RWA

11th Sep 2007, 03:24

I doubt if a person can make it to the left seat without being more familiar with the A/TH system.

KILL-THE-THRUST is normal operation at every single landing. There is no way any A320 pilot could attempt and succeed landing other way around.

Quite agree, Dream Land, Detent. But I'm trying to 'think outside the box'; it's let's say 80% certain, on the FDR evidence, that a highly-experienced pilot made a mistake. The only reasons I can think of for that are 'overload' (too much else to think about) or a less than full understanding of the interacting systems.

Careful here. There are four distinct ways autothrust can disconnect:

That's what's 'bearing in on me' - four different methods, but only ONE (TLs to 'idle') that actually does what you want. Does anyone know why the systems got that complicated - in particular, why the red 'instinctive disconnect' buttons are provided at all, when in fact (as I understand it) they don't kill the power but merely 'freeze' the thrust where the autothrust had left it?

My 'starting point' (from the rare occasions when I was let loose on anything expensive enough to have an autothrottle) is that in those days you disconnected the A/T quite early in the approach. Thanks to moving throttle levers you knew exactly what the remaining power setting was.

I've learned, from chatting to pilots, that the technique nowadays is to leave the A/T on much longer, almost into the flare; but the whole idea of that 'bothers' me somehow. Since flaring inevitably involves a slight but progressive reduction in airspeed, aren't you just about asking for the engines to give you a 'kick in the pants' at the very moment when you least need it, unless you get the timing of the 'retard' exactly right?

The grip in this video looks like the pilot keeps ready for go-around, by keeping the thumb and middle finder behind the levers to be able to push them quickly and decisively all the way forward.

Have cordially to disagree on that point, bieseker. As far as I know, all he'd need if he wanted to apply full power would be the heel of his palm behind the levers. Unless all these 'systems' are even weirder than I've gathered to date. :)

peterperfect

11th Sep 2007, 06:56

alemaobaiano,
Thanks for the update on the runway re-grooving situation. pp

bsieker

11th Sep 2007, 08:25

That's what's 'bearing in on me' - four different methods, but only ONE (TLs to 'idle') that actually does what you want.

This is rather looking at it backwards. At the flare your aim is not to disconnect autothrust, but to cut engine power. So the most natural thing is to move the levers to idle. That autothrust also disconnects is "merely a courtesy detail."

Does anyone know why the systems got that complicated - in particular, why the red 'instinctive disconnect' buttons are provided at all, when in fact (as I understand it) they don't kill the power but merely 'freeze' the thrust where the autothrust had left it?

One does not turn off autothrust to kill power, but to have manual thrust control.

The red buttons don't freeze thrust. They adjust thrust to match the lever position and are used if you want manual thrust control in the IDLE-to-CLIMB range. Adjust the levers to meet actual thrust, push the button, you have it. (or just push the button and be prepared for a sudden change in thrust. As the FCOM puts in in other places, this is probably "discouraged if passenger comfort is a priority.)

(N. B. Disconnecting A/THR with the illuminated pushbutton on the FCU, which does freeze thrust, is non-standard.)

Have cordially to disagree on that point, bieseker. As far as I know, all he'd need if he wanted to apply full power would be the heel of his palm behind the levers. Unless all these 'systems' are even weirder than I've gathered to date.

Well, that was just a blind guess anyway. It looks like a position I would find most comfortable and safe when anticipating to push as quickly as possible. I use similar grips on the gearshift-lever of my car sometimes, which others also find strange-looking, but I happen to feel comfortable with.

The fingers reach a bit farther than the heel of the hand, so you'd have to move your arm/body a bit less.

You'll notice that he uses the same grip to get from reverse back to forward idle (going a bit past and pushing firmly back to idle stop, as other pilots said is normal.)

Bernd

DozyWannabe

11th Sep 2007, 08:26

SIDSTAR:
Just to clarify the AI position: Airbus changed the method of dealing with a locked out reverser last year but gave no reason for the change. Perhaps it was linked to the previous incidents?

In all likelihood, if the human factors reports on those incidents suggested that some pilots had a tendency to filter the information "both to idle, then one reverse" in such a way that only one lever was pulled back in some circumstances, then I expect it was down to that.

PBL

11th Sep 2007, 10:04

I wonder why Airbus did maintain a somewhat complicated landing procedure with one locked reverse ......... a change in the software i.o. to unify all landing procedures, with or w/out reverse, should be implemented.

gpvictor,

you are likely new to this thread. This, and a number of related issues, have been extensively discussed already. I know this doesn't necessarily help much, given 2000+ posts, but it would explain why many will not rush to answer you.

PBL

FlightDetent

12th Sep 2007, 10:38

SIDSTAR:
Just to clarify the AI position: Airbus changed the method of dealing with a locked out reverser last year but gave no reason for the change. Perhaps it was linked to the previous incidents?In all likelihood, if the human factors reports on those incidents suggested that some pilots had a tendency to filter the information "both to idle, then one reverse" in such a way that only one lever was pulled back in some circumstances, then I expect it was down to that.

I believe it is related to the Irkutsk S7 accident where most probably fingertrouble led to increasing thrust on one engine when reverse was being deselected on the other.

RWA

12th Sep 2007, 14:25

You'll notice that he uses the same grip to get from reverse back to forward idle (going a bit past and pushing firmly back to idle stop, as other pilots said is normal.)

Quite correct, bsieker - maybe, as you imply, it's just that particular pilot's 'patent' grip. Possibly he uses it to make sure he keeps the movement of both handles exactly even, rather than the 'twist of the wrist' that most pilots use. But looking at the video again, another point occurred to me that I don't think has previously been discussed; the question of the reverser latches.

As far as I know the A320 is unique among Boeing/Airbus designs in having the same levers do duty both as throttles and reverser levers. Boeing have completely-separate reverser levers, other Airbus marques have reverser levers built in to the top of the main throttle levers; but these are also separate. As far as I know, in all the separate lever types, the reverser levers won't move at all unless both (or all four) throttles are at idle.

With the A320 approach, there also has to be a safety-catch arrangement preventing the accidental movement of one or both of the 'dual-purpose' levers into the reverse position in the wrong circumstances. On researching this I found that this takes the form of safety-latches in front of, and at the base of, each lever; which have to be lifted before the levers can be moved into the 'reverse thrust' section of the throttle quadrant.

Looking again at the Madeira video oner can clearly see that that pilot, in order to lift the latches, had to reach quite far over the handles, with his fingers extended and his wrist possibly resting on the top of the handles.

Seems to me that this arrangement (unique to the A320, as far as I know) could, in a situation where the pilot was intent on selecting reverse on one engine only, materially increase the risk of the OTHER handle being accidentally knocked, if not right up to the CLB detent, at least out of the 'Idle' detent?

Hunitng round for a picture of the A320 throttle setup I chanced on this article. It does indeed provide a picture of the console (from which you can see how far 'over' the throttle handles the reverser-latches are) but i discover that it also provides quite a lot of analysis of the Congonhas accident and also discusses several other 'one-reverser-inop.' accidents, all but one involving A320s, in which the same 'misplaced lever on inop. side' cause was found to have been to blame.

http://www.airaccidentdigest.com/0807_story3.php

marciovp

12th Sep 2007, 21:31

The last issue of Aeromagazine is out. www.aeromagazine.com.br (http://www.aeromagazine.com.br)

It mentions the TAM accident two times.

1. One saying that AB sent a note (AIT 4) with considerations about Flight 3054 from TAM saying that there were nothing abnormal about the plane. But now some information in the AIT 4 are being contested by pilots and security especialists. AB states that "manual actions for plain breaking started 11 seconds after touchdown". However analysis of FDR show that the pilots applied maximum breaking only 5 seconds after touching down. In the final text of the AIT 4 they say that " the data of the recordings DFDR and CVR don´t show evidence of malfunction in the airplane". But sources cinnected to the investigation said that the information only refers to the state of the black boxes of the airplane and not to all systems.

2.The TLs. There is a enigma of the TLs of autothrust. According to FDR the right motor had the reverser blocked and presented a peak of potency seconds before touch down and after that deccelerates a little but remained accelerating while the reverser of the left motor was applied. However the TL of the right motor was not in the Climb position and instead was half the way betwenn Idle and Climb (22.5 degrees). The suspition problems with the software were at work became more important after the pilot Marco Aurelio Incerti from TAM who piloted the plane on the day of the accident said that he did not follow the recommendation of AB for landing with one reverse locked out. He said that when he landed he went into reverse with motor 1 and he left the TL on motor 2 on Idle. CENIPA os also investigating a voice in the cockpit that was not in the transcript saying that the "TL doesn´t move, it is jammed".

bsieker

12th Sep 2007, 21:52

On Reverse Levers

(Boeing uses reverse levers on top of the normal thrust levers, at least in the B737NG, as does Airbus in the A340, from what I can see.)

As far as I know, in all the separate lever types, the reverser levers won't move at all unless both (or all four) throttles are at idle.

This has been falsified, at least for the B747-400, by the Tahiti overrun, which has been mentioned in this thread.

The FDR graphs clearly show engine #1 "escaping" to around 106% N1 (probably at or near go-around thrust), and afterwards the other three engines being put into reverse. So there is no cross-lever interlock, despite what some people here seem to have inferred from the FCOM.

Seems to me that this arrangement (unique to the A320, as far as I know) could, in a situation where the pilot was intent on selecting reverse on one engine only, materially increase the risk of the OTHER handle being accidentally knocked, if not right up to the CLB detent, at least out of the 'Idle' detent?

Perhaps. But this is speculative.

It is also irrelevant.

The FDR graphs show that the #2 thrust lever was not "knocked up" after being pulled down, but stayed untouched, in the CL detent (if we take FDR reading to be the actual TL position).

Bernd

bsieker

12th Sep 2007, 22:03

marciovp, thanks for the translation,

However the TL of the right motor was not in the Climb position and instead was half the way betwenn Idle and Climb (22.5 degrees).

Another one of those "experts" at work here.

According to the FDR graphs, the #2 thrust lever was left at the position where it had been, and at the same angle where #1 thrust lever also was, until that was retarded. This is crystal clear in the graphs.

22.5 degrees is halfway of the total forward TL movement. But not halfway to CL, but halfway to TOGA. And at that position happens to be the CL detent.

Bernd

atakacs

12th Sep 2007, 22:40

CENIPA os also investigating a voice in the cockpit that was not in the transcript saying that the "TL doesn´t move, it is jammed".

They must be kidding ! :eek:

flyingnewbie10

13th Sep 2007, 00:33

CENIPA was also investigating a voice in the cockpit that was not in the transcript saying that the "TL doesn´t move, it is jammed".

Despite being myself someone who is asking for some investigation on the possibility of an electronical/mechanical failure I have to admit that the article has a lot of misinformation (autothrust levers ?).

Maybe someone really said something about a jammed TL but the source does not seem to be that credible.

Lemurian

13th Sep 2007, 00:53

Back again into the fray ! (Some have to fly for a living, you know !)
Referring to my #20954 post :
The only conclusion is that these instances indicate attempts -successful - at using differential braking for directional control, which seems to confirm the slipperiness of the runway (I still haven't given-up on the presence of aquaplaning ).
At 100+ knots the rudder would still have significant influence on directional control, I assume?
But that's exactly the point, Bernd : They shouldn't have needed differential braking for directional control. Unfortunately, due to the tools I have here, I cannot really cerrelate with any acceptable accuracy the lateral acceleration with the brakes and rudder inputs. I think we could dismiss the accidental brake application on rudder pedal movement as the then pilot flying was quite able to do so on most of the brake pressure graph.
Seems to me that this arrangement (unique to the A320, as far as I know) could, in a situation where the pilot was intent on selecting reverse on one engine only, materially increase the risk of the OTHER handle being accidentally knocked, if not right up to the CLB detent, at least out of the 'Idle' detent?
That's what I call clutching at straws :The design is such that the hand just goes over the T/Ls handfles -I'm not very big,but I manage quite easily to keep the ball of my thumb on the top of the throttles, reaching with two fingers only for the latches ; in this way my hand is in the ideal position for pulling the T/Ls into the reverse range.
Why wasn't this set-up kept for the twin-engined A330 ? Just for commonality with the A340. That airplane having four throttles makes the latch solution impractically ackward, unless one has six fingers.
Had you read the Camair incident mentioned four pages earlier, you would have found that the risk of moving accidentally the throttles was achieved by that particular 747 crew.
marciovp,
Thanks for your translations and your honesty in letting us know about the technical knowledge of Airbus systems by bloggers and journalists in your country. Rest assured that they exist also in every country I know. So please stop citing articles on subjects we dealt with on this thread a few hundred posts ago. Please ?

marciovp

13th Sep 2007, 03:51

Thanks for your translations and your honesty in letting us know about the technical knowledge of Airbus systems by bloggers and journalists in your country. Rest assured that they exist also in every country I know. So please stop citing articles on subjects we dealt with on this thread a few hundred posts ago. Please ?

OK Lemurian, I thought it would be of some interest to bring to this thread what appears in Brazil press and especialized magazines (Aero). If this is not being helpful or of some interest, of course ,I will oblige and try to stop waisting the time of people here. Many regards.

flyingnewbie10

13th Sep 2007, 04:33

So please stop citing articles on subjects we dealt with on this thread a few hundred posts ago. Please ?C'est le Roi des Lemurians qui est arrivé...
Et Il ne peut pas etre conteste...
Donc S'il vous plait,
Arretez de l'importuner, MarcosVP :)

(Apologies. French from elementary school...)

Dani

13th Sep 2007, 04:45

AI is not the only manufactor using TL as revers levers. All turboprops I know come into my mind (and don't tell me that on turboprops the reverser is less essential than in a medium jet). These levers in between the TL are very common. I remember that there were always pilots having problem with it, but to try first, you have to pull both into idle, which the TAM pilot obviously never tried.

Dani

flyingnewbie10

13th Sep 2007, 05:05

you have to pull both into idle, which the TAM pilot obviously never tried.

Obviously you admit you could make the same mistake in a similar situation.

RWA

13th Sep 2007, 05:56

This has been falsified, at least for the B747-400, by the Tahiti overrun, which has been mentioned in this thread.

Since, as far as I can make out, that was a no-injuries 'incident' back in 1993, bieseker, I'm not surprised that I can't google up any sort of comprehensive report on it. Were there any identified 'causes' of it that are relevant to the CGH crash?

Perhaps. But this is speculative.

I thought we were all speculating? :) I hope I've made my own position clear. There isn't much difference between any of us as to WHAT happened; the 80% probability is that a pilot with over 10,000 hours made a dumb mistake, failed to bring a throttle lever back to 'idle' before landing. Contrary to the drill that is drummed into everyone who has ever flown anything before they're even allowed to solo.

I'm much more concerned with the question of WHY he made such a huge mistake. Only if the 'why' is established ('beyond reasonable doubt,' anyway) can the authorities and the manufacturer take steps to prevent the same thing happening again. It's certainly not enough just to 'prove' that it was pilot error; especially since there have been several recent exactly-similar 'errors' involving highly-experienced pilots landing A320s with one reverser inoperative, and few if any recent ones with other marques?

That's what I call clutching at straws

Wasn't aware that I was in danger of drowning, Lemurian? :)

The design is such that the hand just goes over the T/Ls handfles -I'm not very big,but I manage quite easily to keep the ball of my thumb on the top of the throttles, reaching with two fingers only for the latches ; in this way my hand is in the ideal position for pulling the T/Ls into the reverse range.

Thanks for the first-hand information. Have you ever had to operate the levers as laid down in the previous MEL, 'one to idle, one to full reverse'? Or opted to, or been asked to, practise the drill on a simulator? If so, how did you get on? Any snags or difficulties?

sky9

13th Sep 2007, 06:56

Many years ago we had a spate of cabin staff opening the doors with the slides armed. The initial management response was to put out a notice saying that the next cabin staff to do it would be fired.
It was pointed out to the management that one slide activation could be an error, a regular occurrence would indicate that the procedure was wrong.
The procedure was changed and no more slides were deployed.
Now about the 320 thrust levers ......

IFixPlanes

13th Sep 2007, 07:05

Now about the 320 thrust levers ......
If the Crew follow the SOP the TL is in idle.
IMHO no change required

bsieker

13th Sep 2007, 08:03

I thought we were all speculating?

Of course we are.

I'm much more concerned with the question of WHY he made such a huge mistake. Only if the 'why' is established ('beyond reasonable doubt,' anyway) can the authorities and the manufacturer take steps to prevent the same thing happening again. It's certainly not enough just to 'prove' that it was pilot error; especially since there have been several recent exactly-similar 'errors' involving highly-experienced pilots landing A320s with one reverser inoperative, and few if any recent ones with other marques?

I agree.

But since the persons directly involved in the handling of the thrust levers in this accident cannot be asked any more, I don't think we will ever reach the "beyond reasonable doubt"-state. So a "reasonably credible explanation" will have to do. And if there is more than one, perhaps more than one thing should be fixed. Accident investigation reports usually contain many recommendations, which may or may not be made mandatory by the authorities.

The reason I dismissed this particular speculation was not that it was speculative, but that it was obviously not what happened here. TL#2 reading was and stayed in CL undisturbed.

Bernd

PBL

13th Sep 2007, 08:05

However analysis of FDR show that the pilots applied maximum breaking only 5 seconds after touching down.

This is complete rubbish.

However the TL of the right motor was not in the Climb position and instead was half the way betwenn Idle and Climb (22.5 degrees).

Also complete rubbish, as bsieker has pointed out.

The suspition problems with the software were at work became more important after the pilot Marco Aurelio Incerti from TAM who piloted the plane on the day of the accident said that he did not follow the recommendation of AB for landing with one reverse locked out. He said that when he landed he went into reverse with motor 1 and he left the TL on motor 2 on Idle.

And even here they manage to screw it up. What have different procedures for handling REV INOP have to do with software?

David Evans did raise a point in his article on the crash, cited by RWA, which I have not yet seen on this thread. David pointed out that the apparently different ways of handling thrust reduction with REV INOP on the two flights previous to the crash demonstrates a training issue at TAM.

In contrast to others, I appreciate marciovp citing a specialist magazine in Brazil which is publishing nonsense. For those concerned with propagating correct information and analyses, it is good to know what is "out there". But it is not as if we are entirely without our own. People who think that the only cause (read "causal factor") was the pilot failing to reduce thrust to idle might do well to read the first few inches of column space of David's article, in which he discusses the runway situation at Congonhas.

PBL

Lemurian

13th Sep 2007, 10:45

RWA
Have you ever had to operate the levers as laid down in the previous MEL, 'one to idle, one to full reverse'? Or opted to, or been asked to, practise the drill on a simulator? If so, how did you get on? Any snags or difficulties?
Yes, I have, both on the sim and in real line operations. There is no problem at all, both on reverse selection and on directional control, even on a wet runway.(Mind you, never in the short / slippery surface that was CGH runway at the time of the accident ).
As a matter of fact, flying for an airline that completes some 1100 /1200 landings per day on the 320 family, I have never heard of any such mis-manipulation of the T/Ls.
flyingnewbie
C'est le Roi des Lemurians qui est arrivé...
Et Il ne peut pas etre conteste...
Donc S'il vous plait,
Arrete de l'importuner, MarcosVP
Your french is pretty good. just add a *z* to "arrete" to get the polite form of verb address and it would be perfect.
Regarding marciovp's citations, and here I disagree with PBL, it is not a matter of contestation, it's the fact that obviously this accident has a lot of political implications which are polluting both the families' privacy and right to mourn their losses serenely and this thread which should remain as objective as possible.
I was -and still am - rather concerned about the publication of the CVR transcript, although it has been quite severely edited as the last moments of the crew -therefore of all the people inside this airplane- became fodder for the public's - often ghoulish - curiosity and scrutiny.

Rob21

13th Sep 2007, 11:43

PBL,

The pilot did apply manual brakes five seconds after the "no spoilers" call.

Why do it (apply manual brakes) before the call?

IMO, the delay to apply manual brakes was not 10 or 11 seconds, as stated for almost 2160 posts by "experts".

PBL

13th Sep 2007, 12:02

The pilot did apply manual brakes five seconds after the "no spoilers" call.

The first recorded significant application of both brakes is at
18:48:35, ten seconds after recorded WoW on both mains.
Maximum braking is recorded at 18:48:36

Why do it (apply manual brakes) before the call?

Because you want to stop as fast as possible, rather than waiting a number of seconds for the autobrakes to kick in.

IMO, the delay to apply manual brakes was not 10 or 11 seconds, as stated for almost 2160 posts by "experts".

I doubt you have read the posts in this thread discussing this issue. And if you don't think those discussants were experts, exactly who do you think is an expert?

PBL

Rob21

13th Sep 2007, 13:06

PBL,
Maybe I got it wrong, but until the "spoiler nada" call, the landing was "normal".
So why apply manual brakes (@ 140 kts) before that call? With no spoilers you won't have effective braking anyway... I agree with you that pilots want to stop as soon as possible, but brakes alone do almost nothing @ 140 kts with no spoilers. Am I wrong?
You shouldn't "feel" some decel (from reverse thrust) before applying manual brakes?
Note that the TAM's pilots cycled the spoiler armed switch almost at the same time they went to manual brakes.
And last, the nose wheel shouldn't be on the ground before applying manual brakes?

Lemurian

13th Sep 2007, 14:04

The FCOM and some manufacturers publications give some guidance to the landing and go-around techniques. The following are general rules, applicable to all types of aircraft.

A stabilised approach, in configuration, speed and flight path.
A firm touch-down as close as possible to the touch-down zone.
A prompt selection of thrust reversers.
A monitoring of the availability of speedbrakes
A timely and modulated brake application ensuring a controlled speed before runway exit.

The main problem lies with the built-in priorities in the deceleration devices : The speedbrakes' failure to extend means the unavailability of automatic wheel brakes which should trigger a pilot takeover on *manual* use of the brake pedals and the deployment of a thrust reverser discourages an attempt for a go-around and we find ourselves in a *cul-de-sac* where the apparent only option is to stick to the landing and try to stop before the end of the runway.

CONTINUE THE LANDING
The procedure requires a good crew's grasp of the aircraft systems and SOPs, in terms of adherence to general call-outs and systems abnormality management, the *triggers* for emergency memory items...etc... In this instance, the addition of a *No Deceleration* to the correct *No Spoilers* announcement by the co-pilot could have speeded-up the pedal brake application. The study of the dynamics of the accident show that the exit speed would have been vastly reduced. IMHO, a change in the SOPs is required.
ABORT the LANDING
I am here on a very shaky ground as both manufacturers expressly discourage an attempt to go-around after reverser election.
The reasons are :
1/-The risk of an engine compressor stall
2/-The risk of the reverser not stowing properly in its locked position
3/-The risk of major thust assymetry as both will accelerate at different speeds
4/-The risk of not meeting the required climb gradient with a late rotation on the runway compounded with an important flaps drag.
Thinking in general terms, any attempt to touch-and-go has to cater for all the above points but in reality, everything boils down to *Get the engine{s} out of reverse and allow it (them) to stabilise in forward thrust with the reversers stowed* before a go-around thrust application.
That delay will also be used for retracting the flaps to a lesser setting (which is a normal requirement for an overshoot anyway).

Looking now at the different times required :
- 3 seconds to cancel reverse thrust
- 2 seconds for stabilisation into forward idle
- 5 seconds for acceleration to CLB thrust, during which directional problems will be the most important as the engine left in CL will reach GA sooner.
- 3 seconds to reach GA thrust.
Total time : 13 seconds. Considering the landing speed of the CGH A320 - 140 kt or 72 m/s - it represents a ground roll of some 936 meters beyond the touch-down zone.. Of course, we have to consider that the aircraft might have achieved airborne speed before the end of these long 13 seconds as the deceleration was basically nil.
Any attempt to rush that procedure means impending catastrophe and, as far as I know, only TRIs who have practised touch-and-goes during initial base training seem capable of pulling it off successfully.
Should our training be changed to include *rejected Landing*?
A few articles for your perusal :
AI rejected landing (http://www.smartcockpit.com/pdf/flightops/flyingtechnique/0026/)
BAC wet runway guide (http://www.smartcockpit.com/pdf/flightops/aerodynamics/0044/)

bsieker

13th Sep 2007, 14:20

And last, the nose wheel shouldn't be on the ground before applying manual brakes?

Should be for comfort, but does not have to be.

[...]
. Braking may be commenced before nosewheel is down, if required for performance reasons; but when comfort is the priority, it should be delayed until the nosewheel has touched down.
[...]

Bernd

flyingnewbie10

13th Sep 2007, 14:43

Your french is pretty good. just add a *z* to "arrete" to get the polite form of verb address and it would be perfect.Fixed.

Let me help you to keep as objective and exact as possible. Going back to the discussion about manual brake application:

1 - The information in the Article was really wrong when it stated that brakes were applied 5 seconds after touchdown. Something I think that is not controversial.

2 - Rob21 asks why manual brake should be applied before the spoiler (state) call. I think the question wasn't objectivelly answered as yet.
And I aggre with him though I am not an expert. At 140knts (almost 260 km/h) why would one apply manual brake at touchdown in a (supposedly) slippery runway to face the risk of stopping in the depths of Jabaquara (a district nearby) ?

RatherBeFlying

13th Sep 2007, 14:59

the deployment of a thrust reverser discourages an attempt for a go-around and we find ourselves in a *cul-de-sac* where the apparent only option is to stick to the landing and try to stop before the end of the runwayThis doctrine came about as a result of the Cranbrook accident where a 737 cancelled reverse and attempted a go-around upon seeing a snowplow on the runway. Back in the air one of the engines fell back into reverse and the affected throttle snapped back to idle with such force that it broke the captain's thumb:(

Some hundreds of posts ago, I suggested waiting for spoiler confirmation before selecting reverse to preserve the option of a rejected landing since as we have seen, an announcement of "spoilers nada" on a critical runway after reverser deployment is not much more than an announcement that we will be going off the end.

Using Lemurian's 72m/s at 140 kt. and his 5 seconds to cancel reverse and stabilise in forward idle, we would be using 360 m less runway.
To that we would have to add a few seconds of waiting for spoilers, which may result in recalculation of landing distances on contaminated runways where spoiler usage is factored in.

flyingnewbie10

13th Sep 2007, 15:26

Anyway,

This accident will demand a lot of work from investigators.

A detailed knowledge of the A320 Thrust Control System, TLA reading, hardware/software interfaces, etc. I think that at the present status either a HF or electronical/mechanical problem have the same probability.

Maybe the CVR shows something but I am not too confident on that.

If the Thrust Levers at least had some independent sensors at the TL track this investigation might not be that difficult. A TL motion could be detected independently of a change in the TCU TLA reading.

marciovp

13th Sep 2007, 15:49

Regarding marciovp's citations, and here I disagree with PBL, it is not a matter of contestation, it's the fact that obviously this accident has a lot of political implications which are polluting both the families' privacy and right to mourn their losses serenely and this thread which should remain as objective as possible.

Of course I respect your views but I decided to allow myself the right to disagree in a proper way. You know that air disasters have many dimensions and this one is not different than the others. Even if indeed the "objective" cause was the TLs giving opposite commands because the pilots did not pull the right engine to Idle, still there are questions to be asked. Let me mention a few, some of them very "subjective" that, in my views, could be addressed:

1. Why the plane was loaded with more fuel than needed?
2. Why the plane was carrying more people than it was certified for? (It was certified for 162 seats and had 174 seats).
3. Why did this plane landed with a locked out reverser in a short, wet, slippery runaway?
4. Why didn´t AB make it mandatory for all A320s to have the new software that keep advising the pilots of one TL not being in Idle or Rev.
5. Why this particular plane has had now three similar accidents by six pilots making the same mistakes?
6. Why ANAC made a rule that planes should not land in Congonhas with one reverser locked out and then withdrew it?...
7. Why Congonhas runway was liberated in a rainy day without grooving?
And so on.

If our aim is to learn the better we can about the factors that may have made this disaster possible in order to prevent further ones, isn´t this a way to respect and protect many crews, passengers and families in the future?...

It seems to me that it is of interest to know not only what CENIPA is investigating but also about information coming from any agency that is investigating the disaster.

PBL

13th Sep 2007, 17:39

Maybe I got it wrong, but until the "spoiler nada" call, the landing was "normal".

The landing was anything but normal throughout. They had significant forward thrust on #2 engine during and after the flare.

With no spoilers you won't have effective braking anyway......... brakes alone do almost nothing @ 140 kts with no spoilers. Am I wrong?

Yes, you are very wrong.

For example, it appears that with one engine producing significant forward thrust on a wet "slippery" runway one can obtain braking without ground spoilers at the rate of over 1.2 m/s/s. Imagine what you could do on a dry runway with both engines at idle!

You shouldn't "feel" some decel (from reverse thrust) before applying manual brakes?

You can apply manual braking whenever you think it necessary, say at WoW both MLG.

Please, Rob21, go back and read the extensive discussion on this thread about the braking and the braking performance. I don't have the time to repeat it all over again, and I doubt that others will feel much differently.

PBL

Rob21

13th Sep 2007, 20:33

PBL,

Yes, maybe I'll go back and read again posts about this braking issue.

But as for now, I don't agree when you say that during flare engine #2 had significant forward thrust. It had the expected thrust. It was only when engine #1 had reverse engaged that EPRs "split" (by FDR). And this was after the flare and after touchdown. Untill then, yes, things were "normal".

So maybe I should refrase my question on when the pilot was expected to apply manual brakes. Autobrake was selected to med, as recommended for slippery runways. Autobraking starts with ground spoiler deployment.
Why not start manual braking also with spoiler deployment?

If you brake with no ground spoilers on a wet runway, the risk of aquaplaning isn't higher?
It makes more sense to me that only without lift on the wings you can think on stopping fast.

I now know that manual brakes can be applied before nosewheel touchdown. But this is a correct procedure on a wet runway?

Are you sure I am wrong assuming pilots wait for spoiler status call before applying manual brakes, when landing on a wet and slippery runway?

bsieker

13th Sep 2007, 21:25

Autobrake was selected to med, as recommended for slippery runways. Autobraking starts with ground spoiler deployment.
Why not start manual braking also with spoiler deployment?

Why should manual braking depend on ground spoilers? If you planned to depend on ground spoilers, use autobrake.

If you brake with no ground spoilers on a wet runway, the risk of aquaplaning isn't higher?

Higher compared to what?

The risk of aquaplaning isn't higher when braking than when not braking.

The risk of aquaplaning is higher without ground spoilers than with ground spoilers.

It makes more sense to me that only without lift on the wings you can think on stopping fast.

There is nothing gained by delaying braking. If and when ground spoilers deploy, all the better, you will get optimal braking conditions. But until then you can, as we have seen, brake with perhaps 1.2m/s/s, instead of nearly nothing if you don't brake. Every little bit helps.

Bernd

flyingnewbie10

13th Sep 2007, 22:31

For example, it appears that with one engine producing significant forward thrust on a wet "slippery" runway one can obtain braking without ground spoilers at the rate of over 1.2 m/s/s.

PBL,

Technical sources, please. With actual experiments preferably.
(Maybe one can get a much higher braking rate this way by just skidding out of the runway and hitting something around...:})

Soga

13th Sep 2007, 23:06

The data which follow have been approved for release by the Brazilian
investigation authorities.
>
> It is confirmed that the aircraft was dispatched with the Engine 2 thrust
reverser inoperative as
> authorized by the MEL.
>
> It is confirmed that the associated operational procedure of TAM MEL was
updated according to
> current MMEL page 02-78 p1 SEQ 001 REV 29 which reminds the crew to select
both thrust
> levers to idle before touchdown and requires to select both reversers at
touchdown
>
> The following is the sequence of events according to the recorders:
>
> Final Approach phase:
> - The aircraft was approaching runway 35L.
> - The last wind information given to the crew by the ATC was
330°/8kts.
> - The runway condition given to the crew by the ATC was wet and
slippery.
> - Landing configuration was established with Slats/Flaps fully
extended, gear down, ground
> spoilers armed, autobrake selected to MED.
> - Approach speed was 145 kts
> - The final approach was performed with Autopilot OFF -
disconnected at about 370 feet
> (radio-altitude), Flight Directors ON, Auto-Thrust (ATHR) ON.
> - The CM1 was the Pilot Flying.
> - The crew approach briefing included a reminder that only the left
engine thrust reverser
> was available.
>
> Flare and touch-down:
> - During the flare, the "RETARD" call-out has been normally
triggered
> - The "RETARD" call-out has been triggered 3 times, ending at the
selection of the engine
> 1 reverser.
> - Before touchdown, the engine 1 throttle was retarded to idle.
> - The engine 2 throttle is recorded in the Climb position and
remained in this position to the
> end of recording.
> - Preliminary trajectory computation indicates that the aircraft
landed in the touch-down
> zone.
>
> Landing roll
> - Just after touch-down, idle reverse was selected on engine 1,
followed within 2 seconds
> by the selection of max reverse which was kept to the end of
recording.
> - Following reverser 1 selection, the ATHR disconnected as per
design and remained
> disconnected to the end of recording.
> - With the engine 2 throttle being in the Climb position: 1/ the
engine 2 EPR remained at a
> value of approximately 1.2 corresponding to the EPR at the time of
ATHR disconnection;
> and 2/ the ground spoilers did not deploy and the autobrake was
not activated.
> - Maximum manual braking actions began 11 seconds after touch-down.
> - Rudder inputs and differential braking have been applied during
the landing roll.
> - The aircraft overran the runway at approximately 100 kts.
>
> DFDR and CVR data show no evidence of aircraft malfunction.
>
> At this stage of the investigation, and as already indicated in the
previous AIT n°3, Airbus remind
> all operators to strictly comply with the following procedures:
>
> A- During the flare at thrust reduction select ALL thrust levers to IDLE.
>
> B- For the use of the thrust reversers when landing with one Engine
Reverser inhibited refer to :
>
> - For A318/A319/A320/A321 MMEL 02-78 Page 1 Rev 29
> - For A310 MMEL 02-78 Page 1 Rev 17
> - For A300-600 MMEL 02-78 Page 1 Rev 15
> - For A330 MMEL 02-78 Page 1 Rev 17
> - For A340 200/300/500/600 MMEL 02-78 Page 1 Rev 19

broadreach

13th Sep 2007, 23:36

Local TV news announcing that CGH main runway is to be shortened by 300m to accomodate 150m overrun patches at either end. I haven't seen details yet but presume these are of the crushable concrete variety already discussed here.

First impression is that this a knee-jerk reaction under strong political pressure to show "we're doing something". Now that we have some Brazilian pilots on the thread, their opinions would be interesting.

Lemurian

14th Sep 2007, 00:45

marciovp'
1. Why the plane was loaded with more fuel than needed?
2. Why the plane was carrying more people than it was certified for? (It was certified for 162 seats and had 174 seats).
3. Why did this plane landed with a locked out reverser in a short, wet, slippery runaway?
4. Why didn´t AB make it mandatory for all A320s to have the new software that keep advising the pilots of one TL not being in Idle or Rev.
5. Why this particular plane has had now three similar accidents by six pilots making the same mistakes?
6. Why ANAC made a rule that planes should not land in Congonhas with one reverser locked out and then withdrew it?...
7. Why Congonhas runway was liberated in a rainy day without grooving?
And so on.

Some of these questions have been answered before on this very thread :

1. They were tankering, apparently in order either to save on fuel costs because jet a is more expensive at CGH or saving on turn-around time, or both. Normal practice on all airlines. Whether it was reasonable or not is not for me to say. What I know is that performance-wise, there were no objections.

2. Careful, here. According to FAR 25.807, the seating capacity for such an aircraft, equipped with 4 Type I and 4 Type III exits is 179 seats, crew members excluded. Therefore, the number of seats was correct for the configuration.

3. You pose a question on TAM procedures and policy that I'm not in a position to discuss. Once again, they had the performance to land on a wet runway such as CGH 31. On the other hand, was the *slipperiness* taken into account ? In all probability, no but a definition of slippery in terms of friction. braking action...seems to be lacking on that airline FCOM.
If you are interested, you could have a very careful look at this BAC powerpoint presentation on

Landing on slippery runways (http://www.smartcockpit.com/pdf/flightops/flyingtechnique/0018/)

4.Airbus Industrie -AI- has absolutely no control on mandatory procedures. The certifying authorities do, and that will be the local DGCA services or their equivalent. What I know is that the implementation of this new warning was not well received by a great number of customers' technical services as inducing even more confusion than the old software. They went instead into more training on similar situations.

5.That's also a training question or a question of training. Depends how one looks at it. To concentrate on a perceived aircraft system fault amounts to putting the blame for a flat note on the piano instead of the pianist. I have shown, along with Christiaanj that very comparable events happened on 747s without anyone yelling for a change on its throttle system. Can't have it both ways.

6. and
7. Both belong to Brazilian politics that I am not ready to discuss. Let the politicians deal with them after the report has been published.

Another question you could have asked - based on the FDR - is about the preflight preparation for a landing at CGH. As the previously recorded times of landing and takeoff from the previous station are just about 31 minutes apart, including taxying in and out, was all consideration due to the reported poor braking taken into account ?

Or -second question- what destination was on the flight plan. Was it really CGH ? Was it GRU (as the initial conversation with the flight attendant suggests ) ? The implications are not equivalent, are they ?

Technical sources, please. With actual experiments preferably.
PBL is referring to the deceleration achieved by this aircraft taken from the FDR print-out. A very *poor* braking indeed.
Regards.
Lemurian

Rob21

14th Sep 2007, 01:19

Maybe this is an attempt to force heavy A/C to operate in/out of Guarulhos (Cumbica) and Viracopos (Campinas).

Better start to train those tractor drivers on how to pull airplanes out of the gravel, because companies will continue to "push" the envelope and land at Congonhas.

Airline companies should bring back the Electras, they can operate on the "new" CGH 300m shorter with no problem.

flyingnewbie10

14th Sep 2007, 01:23

PBL is referring to the deceleration achieved by this aircraft taken from the FDR print-out. A very *poor* braking indeed.That's what I thought.
However if (if) he was based on the FDR the information might not be accurate as we still don't know how slippery the runway was.

What we know is that the crew thought that the runway was slippery. And this could explain their hesitation to apply manual braking before spoiler extension if after all such hesitation showed up to be expected from a crew in the same situation.

marciovp

14th Sep 2007, 02:07

Careful, here. According to FAR 25.807, the seating capacity for such an aircraft, equipped with 4 Type I and 4 Type III exits is 179 seats, crew members excluded. Therefore, the number of seats was correct for the configuration

Thanks for your answer and dialog Lemurian. I acknowldege that you know a lot more about this airplane and aviation than I do. For me it is a privilege to be here. What I said is that ANAC (National Agency of Civil Aviation) certified that plane to fly with 162 seats. Also if there was some plans for the A320 to land at Congonhas in a raining slippery night efforts should be made to make the plane as light as possible, no?

Insofar as Congonhas, just saw the Minister of Defense. Yes they will use 150 meters at each end of the runway as escape zone with soft cement. The Minister said that one consequence of this change is that only lighter airplanes will be using the airport (not clear which ones are those) with the shorter runway (I believe 1940 meters minus 300= 1640 meters). The big planes that lad there? Boeing 737 (400 to 800), A320, Fokker 100...

Yes, it is true it seems. Besides having a shorter main runway, the auxiliaru runway also will go to 1250 meters, with escapes of 120 meters in both ends.

This decision was made by the Minister of Defense and the Air Force. Congonhas no longer will be a hub and 737s and A320s will not land there unless they manage to have less weight with fewer seats and lessa cargo, the note said.

PBL

14th Sep 2007, 05:06

But as for now, I don't agree when you say that during flare engine #2 had significant forward thrust.

I regard an EPR of nearly 1.1, and then rising, as showing significant forward thrust.

PBL

bsieker

14th Sep 2007, 07:50

PBL is referring to the deceleration achieved by this aircraft taken from the FDR print-out. A very *poor* braking indeed.

Poor, but still more than nothing.

That's what I thought.
However if (if) he was based on the FDR the information might not be accurate as we still don't know how slippery the runway was.

The figure PBL quoted was observed deceleration, i. e. the deceleration that was actually achieved in this landing (derived from the ground speed plot, and supported by the longitudinal acceleration pliot).

This is independent of how it was achieved, and under what conditions.

What is, is.

What we know is that the crew thought that the runway was slippery. And this could explain their hesitation to apply manual braking before spoiler extension if after all such hesitation showed up to be expected from a crew in the same situation.

If you expect poor braking action, you must brake as soon as possible to get the most out of the available distance. Not delay it.

Also if there was some plans for the A320 to land at Congonhas in a raining slippery night efforts should be made to make the plane as light as possible, no?

No. Taking all parameters into account one arrives at a maximum landing weight for a given configuration/airport/runway condition/... Either from tables or (I guess) the LPC ("Less Paper in the Cockpit") computers.

One can go up to that weight. One does not have to take into account every possible adverse situation, like keeping the thrust on and lack of ground spoilers during roll-out.

Bernd

slip and turn

14th Sep 2007, 08:22

Not directly associated with landing weights but then again heavier might help up to a point when slippery if what follows is true ... I was somewhat informally taught by ex military that in potential hydroplaning conditions a "heavy even if a bit uncomfortable" arrival was SOP because it was doubly useful to cause the tyres to break through the surface water & initiate spin-up & traction, and to get positive WoW at earliest opportunity.

Certainly from basic mechanics I would assume that if there is any missing friction force on touchdown, then there is also a missing WoW vector component. I couldn't put a magnitude on it.

I imagine some of this is formalised in type training?

HotDog

14th Sep 2007, 08:43

Definitely correct. Our company training emphasised landing in conditions of possible aquaplaning. A firm touchdown is necessary to bang through the water, get the weight onto the wheels by pushing fwd on the stick , select full spoilers and max reverse immediately followed by braking action when the aircraft is firmly on three points.

TyroPicard

14th Sep 2007, 09:14

Some thoughts following this from Rob21
So maybe I should refrase my question on when the pilot was expected to apply manual brakes. Autobrake was selected to med, as recommended for slippery runways. Autobraking starts with ground spoiler deployment.
Why not start manual braking also with spoiler deployment?
Three braking strategies for this approach ...
1. Autobrake OFF, apply manual braking as required.
2. Autobrake MED, no manual braking - monitor Autobrake effectiveness and apply manual braking if necessary.
3. Autobrake MED, but apply manual braking as required - if for some reason you forget to brake the a/c does it for you.
Without access to the approach briefing, we cannot tell which of 2 or 3 was planned. Even with access we may still be in the dark.
Had it been my landing, I would have used strategy 2. Had I judged that full manual braking was required from mainwheel touchdown I would have diverted - risk assessment. Therefore I think it likely that this crew thought this landing was normal - but a shade demanding, because of the evidence of a "duck-under" and selection of G/S warning OFF.

Regarding waiting for the Ground Spoilers call... nowhere in my Airbus FCOM/FCTM is this mentioned as a procedure or recommendation, and I cannot recall any training (in two airlines) where this was mentioned. I assume the reason is that in the absence of ECAM warning or other known problem, they will always work when conditions are met. If you know all/some are INOP then you choose a runway of appropriate length.
One of the potential problems is.. if NOT armed the Ground Spoilers extend on Reverse selection as a back-up.. so if you wait for the call before selecting Reverse you might wait a long time...
Thanks to Soga for re-posting the Brazilian release..
The crew approach briefing included a reminder that only the left engine thrust reverser was available.
What we do NOT know is what T/L handling MEL procedure they briefed, if any. I think it important to brief what will happen, what indications you expect. It appears from the FDR that crews used different procedures at different airports.....
Cheers, TP

Rob21

14th Sep 2007, 11:15

PBL,
You forgot to "quote" my whole phrase. What you said, and I did not agree, was that engine #2 had "significant forward thrust" during flare, therefore the situation was not "normal". My full statement was that during the flare, engine #2 had the "expected" forward thrust, and EPR "split" occurred after reverse on engine #1 was selected. And only then problems began, when ATHR was disengaged.

TyroPicard,
Thanks for clarifying my thoughts on this braking issue.
I believe that when the pilot went to the ground spoilers arm switch it was a desperate attempt to have G/S, and he knew he would not be able to stop. If he had had a manual G/S "deployment device", I'm sure he would have used it, instead of clycling the G/S arm switch.
I know, on A320 the "manual G/S deployment device" is TLs at idle. But at that point, TL was or "forgotten" or inop.
Too bad...

bsieker

14th Sep 2007, 12:00

Rob21, please read the thread.

Best to search for the things about which you wish to make claims, before posting unverified stuff about them.

[...] EPR "split" occurred after reverse on engine #1 was selected. And only then problems began, when ATHR was disengaged.

- When exactly problems began is hard to say, some might say all was well until they hit the building, but possibly at diverging thrust, particularly at the sharp increase in forward thrust on engine #2, around 18:48:24, coinciding with selection of reverse thrust on engine #1.

- Autothrust remained active until 18:48:29, around 5 seconds later, and until after EPR of engine #2 had decreased again.

- Autothrust wasn't disengaged, but automatically disconnected due to an internal failure condition. Please review previous posts by Lemurian and myself, the Taipei-Sungshan-Overrun report, p148, and my Why-Because-Graph (http://www.rvs.uni-bielefeld.de/publications/compendium/incidents_and_accidents/TAM3054-WBG.pdf) on the matter. Be sure to read the introductory words by PBL (http://www.rvs.uni-bielefeld.de/publications/compendium/incidents_and_accidents/TAM3054.html) on the analysis.

Bernd

Rob21

14th Sep 2007, 12:41

bsieker,
Please, also read the thread!!
My reply was to PBL, in an answer to his statment that things were NOT normal during flare. I disagree, things were not normal for us, but for the pilots nothing "abnormal" was happening. Only after touchdown and reverse on engine #1 was selected "things" went bad (for the pilots).
For some of us, maybe "things" started to go bad even before takeoff in Porto Alegre.
But thanks for your effort on trying to educate me.

flyingnewbie10

14th Sep 2007, 12:53

The figure PBL quoted was observed deceleration, i. e. the deceleration that was actually achieved in this landing (derived from the ground speed plot, and supported by the longitudinal acceleration pliot).

This is independent of how it was achieved, and under what conditions.

What is, is.

What was: The plane had a given deceleration
What we don't know whether it was or not as yet: The runway was (very) slippery

PBL stated that one can get a given deceleration in a slippery runway. I supposed he was basing his statement on the TAM's PR-MBK FDR.

Then I finished by stating that his statement might not be accurate not because the plane didn't decelerate at that given rate (What was) but because we don't know in what extent that runway was slippery (what we don't know whether it was or not).

If you expect poor braking action, you must brake as soon as possible to get the most out of the available distance. Not delay it.

No controversy about that when you don't have a (very) slippery runway (or don't think you have).

However, I found this article

http://www.jet-jobs.com/articles/hydropln.html

which I am not certain whether it is accurate or not. It deals with a "Minimum Hydroplanning Speed" i.e., a threshold above which you should not apply braking when facing a slippery runway.

Again, I don't know whether the article is accurate or not.