TAM A320 crash at Congonhas, Brazil

[ChristiaanJ]

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]

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]

ChristiaanJ

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

[EMIT]

To SyEng and others

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]

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

[Rob21]

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]

Thanks BOAC.

Try this:

http://i236.photobucket.com/albums/f...0ATA76Mech.jpg

[SyEng]

Here's another one...


http://i236.photobucket.com/albums/f...ATA76Mech2.jpg

[ChristiaanJ]

And the pictures themselves:

[SyEng]

ChistiaanJ,

How do you do that then?

[ChristiaanJ]

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 icon and paste the URL of the picture in the window that pops up.

[TripleBravo]

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]

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]

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

[Dani]

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]

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.

[Dani]

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]

Thanks, TripleBravo,

Originally Posted by 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]

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]

Originally Posted by GMDS

[...] 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