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TAM A320 crash at Congonhas, Brazil

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TAM A320 crash at Congonhas, Brazil

Old 16th Aug 2007, 17:42
  #1741 (permalink)  
 
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Lemurian,
Boeing wont give you TR with TL's not idle.Only one TR needs to be activated to get GS if you've forgotten to arm them.Is that causing the confusion?

Bomarc sets an interesting challenge.
If I genuinely believed that it was pilot error(which I absolutely do not),I would have to accept against my best instincts that the failure to retard TL#2 was the last link in the chain that caused the crash.ie.the direct cause.Like Nigel on Draft,I would take the line that the plane is designed a certain way and that the pilot presumably knows this.Dispassionate and clinical but nevertheless it carries some weight.Instead of questioning the design,I would look at why he didnt shut down eng #2 and apply max manual braking OR look for a better warning to the pilot like THR ABOVE IDLE and the continuous chime or RETARD TWO instead of just RETARD.
These are the avenues I would want to see explored.
But I dont for two reasons:
i)The failure to retard TL was not an error;that implies irrevocability.It was an omission,a serious one under the circs.
ii)The last link in the chain that made the crash inevitable was the design error that enabled TR#1 with CLB thrust on #2.
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Old 16th Aug 2007, 18:56
  #1742 (permalink)  
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Originally Posted by Dani
The TLA engine 2 stays constant. In the CLB detent.
- yes - we know the 'reading' of the position on the FDR, but we do not know for sure the position, and the possibility (in my book the only other) would be that the signal of TL position was faulty. 'CLB' is where I understand it goes at clean-up and where it stays until it is retarded to idle. Likewise
All TL movements of the last 120 minutes of the flight.
- we know only the 'readings' of that position. The thrust changes are not relevant UNLESS the output of the TLA sensor is accurately feeding information to the engine control. If it was 'broken' (in the 'CLB' sense) then no amount of TL movement would show on the FDR.

Getting well out of my depth now, but I think I saw a hint earlier that a 'jam' of some other unit in the system was a possibile extra avenue to explore.

My personal (NB non-mod hat on) opinion is that the failure of what I understand to be 2 sensors is so unlikely as to be dismissed, so I go for human error and confusion.
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Old 16th Aug 2007, 19:03
  #1743 (permalink)  
 
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Well, BOAC, I'm not sure how much is or will be revealed about this all, but: as someone has explained, there's two independent readout systems, using different physical prinicples, for each thrust lever. The readings from those systems, which are themselves redundant, is fed into two different board systems (FADEC and FMS iirc?) so there's two data paths that technically will only have one linking point: the lever's bearing point on the frame. If data ca be obtained from both sources, I think we can be rather sure of the actual lever position, despite the fact that we might not have direct indication.

pj

as an aside:

this thread in itself is an interesting animal. It swings from being unbelievably frustrating for people read AB or B and go on a crusade against B or AB back to being very constructive and well educated. It's also probably one of the longest running threads I've ever been involved in...
An amazing amount of information has been amassed here, but also, I think there's an amazing amount of discrepancy in what should have been identical information.
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Old 16th Aug 2007, 19:04
  #1744 (permalink)  
 
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Rananim:
CLB thrust was not set on #2, it would have remained at approach speed (the last thrust setting before A/THR disconnect) throughout if I understand the logic correctly.

I'd say that one man's omission is another's error of omission and one man's design error is another's design feature. Both methodologies employed by the manufacturers have their advantages and drawbacks, it's in the nature of the beast.

At the end of the day, Airbus asked a group of pilots what they wanted in a modern FBW aircraft and Boeing asked a different group of pilots. Two different interfaces to the same basic system was the result.
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Old 16th Aug 2007, 19:16
  #1745 (permalink)  
 
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- yes - we know the 'reading' of the position on the FDR, but we do not know for sure the position, and the possibility (in my book the only other) would be that the signal of TL position was faulty.
Does anyone know which computer, or computers, actually sends the TLA signal to the FDR? Is it only one signal or several?

TP
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Old 16th Aug 2007, 19:31
  #1746 (permalink)  

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Lemurian,
Boeing wont give you TR with TL's not idle.Only one TR needs to be activated to get GS if you've forgotten to arm them.Is that causing the confusion?
You'll have to be a lot more precise than that peremptory affirmation of yours. I gave you the courtesy of copying the 777 FCOM, which specifically said that you could have one reverse deployed regardless of the other throttle position.
Therefore, as per my manual, your corollary is definitely wrong.
The last link in the chain that made the crash inevitable was the design error that enabled TR#1 with CLB thrust on #2.
I thought that all on this forum have understood that a throttle being in the CLB detent does not mean it's delivering climb thrust.
TyroPicard,
Lemurian
Quote:
with the very unusual dual autopilot configuration which one only uses for an autoland.
Not unusual at all.. it is Airbus SOP to engage both A/P for all ILS approaches.
Cheers, TP
.
Your comment proves again that there are out there some differences in opinions and/or SOPs.
In the company I work for and a few others, dual auto pilot appoach is only selected in view of an autoland. Otherwise, the A/P selected will be the one on the side of the handling pilot. That philosophy also applies for a control transfer.
Didn't know that choice and I would like to see the TAM procedure.
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Old 16th Aug 2007, 20:05
  #1747 (permalink)  
 
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Lemurian
I can only see AP1 status on the FDR ??????
TP
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Old 16th Aug 2007, 20:13
  #1748 (permalink)  
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.......and AP status missing on previous FDR landing traces - has someone been 'selective' or is this normal?
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Old 16th Aug 2007, 20:21
  #1749 (permalink)  

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TP, you are right, the A/P 2 status is missing.
On the CVR, though, Capt specifically announced "A/P 1 plus 2" (18:43:27).
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Old 16th Aug 2007, 20:54
  #1750 (permalink)  

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BOAC,

Have you still your non-Mod hat on ?
The problem is when what it thinks you want and what you actually want are not the same. We can go back to the beginnings of AB history and see the same problem - the Indian crash, the Strasbourg crash, Habsheim.
Why is it that these same three accidents are the only references to man-airplane interface ? After all, there have been a few other instances in the past 15 years (date of the Strasbourg accident) they have been argued about for years and they are not demonstrative. The Iberia 320 landing incident in Bilbao would have been a far better demonstration of your intent, for instance.

TyroPicard,
Page 2: From 18:48:20 to touchdown four seconds later I would expect to see increasing back stick in the flare.
Instead, on the graph Stick Long-L the stick goes to 4° back then neutral then 9° forward then neutral. Full deflection is 20° so 9° is a sizeable nose down input about one second before touchdown.
From first WOW there is dual stick input - RHS has a fairly steady 1 to 2° back stick for 6 seconds, during which LHS goes to 6° back to land the nosewheel. Not something you usually do.
Is the Stick Long - L graph representative of usual stick position in the flare?
TP, IMHO, the graphs are consistent with a landing with a very short flare and an entry into ground effect, well managed by the pilot. See the pitch trace which shows the -expected - nose up movement and the "landing" of the nose-wheel. The passage of the 50 ft point to the touch-down takes only three seconds and he landed slightly before passing abeam of the Glide shack.
If anything, the pilot knew how to maneuver that airplane.
What is a lot more worrying to me (as the RHS stick movements you mentioned are a lot weaker on this latest graph and can be due to the natural involuntary movements on the stick..) is that from T.S 18:48:28, the Capt has in all apparence left the side stick, and the action has been taken over by the F/O, without the CVR showing such transfer. (As an SFI, I would suspect that you would insist on the proper procedure for it )

Last edited by Lemurian; 16th Aug 2007 at 20:55. Reason: a mess of paragraphs !
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Old 16th Aug 2007, 21:06
  #1751 (permalink)  
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The Iberia 320 landing incident in Bilbao would have been a far better demonstration of your intent
- was that the training Captain that broke the a/c behind the cockpit? I never saw a report (but saw the result). I assumed it was just a very hard landing, and I was just picking some early ones.

PS A variety of hats available
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Old 16th Aug 2007, 21:38
  #1752 (permalink)  
 
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the natural involuntary movements on the stick..)
Not sure I like the sound of that - PNF is meant to guard the stick in case of incapacitation - not move it!
And if you are about to fall off the side of a hill at 94 kts. I think you can be forgiven for not handing over control correctly.
I did not intend to be critical of the PF handling - I merely tried to ask an expert if the trace was "normal" in terms of sidestick at the flare.
TP
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Old 16th Aug 2007, 23:06
  #1753 (permalink)  
 
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tyro:

you mention the lift arrow/fluff etc.

just wondering...would it have been more survivable to simply fall off the plateau or to fly off the plateau...or would it have been equally deadly?
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Old 16th Aug 2007, 23:49
  #1754 (permalink)  
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TP
Does anyone know which computer, or computers, actually sends the TLA signal to the FDR? Is it only one signal or several?
(non-pilot speaking) I do not know but I do recall that it was detailed in this thread. We saw diagrams of the duplicated system of monitoring the TL positions and, IIRC, an explanation of the input to the flight control systems. My guess is that these posts would have been around the #1,000 mark but a detailed search should find them. Of course, someone may well re-post them
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Old 17th Aug 2007, 00:36
  #1755 (permalink)  

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TyroPicard

t sure I like the sound of that - PNF is meant to guard the stick in case of incapacitation - not move it!
Very true, but look at the RHS stick inputs. They match almost to perfection the lat/long accelerations...until the real take-over.
Let's say, he was guarding it very closely.
Your remark poses another problem : the quality of that crew in terms of CRM : One training captain flying wth an F/O who was very recently a commander -with an instructor rating to boot- still fresh from another type of airplane.
What are your comments on
  • the authority gradient in the cockpit
  • the manner of the Captains on communicating his action project (T/R one side only...)
  • the general adherence to procedure -Quite a few call-outs were missed, there has never been,on the document we were provided , speed readings, commands ( we still don't know whether they were on managed or commanded final speed )...
  • etc...
I've seen crews in an emergency and my first remark would be that they naturally grab the procedure, with its technical lingo...I have this gnawing feeling that there was a lot more to this approach than we know for the captain and upon touch-down he just let go the pressure. A sigh as a response to a malfunction -no spoiler deploy !- which could change the parameters of the landing on wet, which has been very much in his mind before is not natural.
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Old 17th Aug 2007, 00:41
  #1756 (permalink)  

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BOAC

Yes. A partial report is on A.S.N.
Very good reading and the only case of an afore seen limit to the FBW. Granted that the conditions were dire.
Brought quite a change.
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Old 17th Aug 2007, 02:18
  #1757 (permalink)  
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About the pilots

From what I read, the pilot who was in charge had been with TAM (AB) since 1988, was single, lived with his family and was close to retiring. The co-pilot had been recently promoted to Comandant after being with TAM since January 2007 training for 6 months with the AB. In 2001 he worked for GOL (Boeing 737) from September to December. GOL did not inform why he left. We don´t know what he did in terms of flying from 2001 to 2007. Previous to 2001 he flew about 20 years for Transbrasil
(Boeings, including 767 to and from the US). A colleague of his at Transbrasil wrote a very good paper on him saying how he was a nice person, competent and healthy in the 20 years they worked for the same company. I am not sure if this helps but remember that one of my ifs was that one of the pilots only recently had been trained to fly the A-320.

I also find it interesting that after the crash TAM is now anouncing that it will not allow its planes do land on wet runways with one reverser locked up. And that they will buy (US$5000.00) the new software with better warning for pilots when facing the situation that seemed to have developped in this disaster.
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Old 17th Aug 2007, 03:56
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"It's time to do the flare? Don't worry, engine thrust will come to idle. Forget the TLs..."

Autothrust does not reduce thrust in the flare, as a matter of fact, if left engaged, it will fly you down the rwy at approach speed. Believe me, it has been done.
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Old 17th Aug 2007, 04:09
  #1759 (permalink)  
 
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SoaringTheSkies

You have clearly articulated what I have been thinking, but unable to get into the keyboard. I have felt all along that the crux of the issue was a user interface issue. Your description really clarifies that point.
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Old 17th Aug 2007, 04:37
  #1760 (permalink)  
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I don't know whether others have a similar impression to mine, that the discussion seems to be spinning its wheels now. Part of it may just be length - 1,800 messages is a lot to go through to see what was noted already and what was not.

But I must say I am not finding the discussion here of ergonomics and cognitive psychology of much help in furthering my partial understanding of this accident. I understand that stories of the sort "they would have seen this, and then they would likely have been thinking this, and then ...." are of use in seeing how one might oneself react in similar situations, but they are of limited use in explaining the accident, or in figuring out how we may change things to avoid a repeat, since there are lots of such, differing, stories and we have no way of deciding between them.

I find others of the ergononic arguments equally unpersuasive. For example, STS provides us with a Boolean expression equivalent to the condition for spoilers to be deployed, and asks us if we imagine we can understand it quickly, but fails to argue why we must judge *this* formulation rather than some other. Lemurian correctly points out that there are other, equivalent, expressions that are cognitively more straightforward to understand.
Others try to identify some "gotcha" in the spoiler operation, and fail to persuade the Airbus pilots amongst us of their point. There are two acid tests of a gotcha: either the operators agree with you, or it recurs regularly in operations. Well, the operators don't agree; what about regular recurrence? As far as we can tell something similar has happened once, maybe twice before (and we won't be able to decide that, because the one report was so sparse). Bit thin on that criterion too, it seems.

There are some pertinent ergonomical observations that don't seem to have surfaced yet. People have been talking about the braking systems and the (complex or not-complex) trigger logic, as well as evoking principles of cognitive simplicity (or complexity). But no one has yet observed that, when landing with autobrake armed, braking is cognitive simplicity itself. Your braking is concentrated in one control: your thrust levers. Pull them back, you brake; don't pull them back, you don't brake. And if this doesn't work (you don't get the "decel" light), you stomp on the pedals. It couldn't be simpler, could it?

If one is being honest about trying to figure out the ergonomics of the situation, one must take this simplicity into account when weighing up, say, whether to encourage people to grab for the spoiler handle if things aren't going right (by giving it a supplementary function on rollout which it currently does not have). My inclination would be to maintain the simplicity, and not give people lots of other options to think about in the time-constrained, critical phase of touchdown and rollout.

But what happens when this setup doesn't work? Short, slippery runway, maybe? Well, can we figure out what is "short" and what is "slippery"?

Sort-of-maybe. We can have a go at guessing parameters of "short"ness (say, length of runway needed to perform all SOP actions) "slippery"-ness (say, using rate of deceleration). For example, we can try to figure out if the TAM aircraft would have stopped had manual braking been applied ASAP. A ball-park guess would proceed along the following lines. Take the demonstrated acceleration on application of brakes, which I estimate to be about -1.26 m/s/s, and figure out how long it takes to stop from a touchdown speed of 70 m/s. (Remember calculus? Integrate a = -1.26 with respect to time to get v = -1.26.t + v0, put in v= 0 and v0 = 70 to get t, integrate again s = -1/2.(1.26) t^2 + v0.t, put in v0 = 70 again and the value of t you have just calculated).

This gives me something just over 1940 m, so the answer is probably no, it is unlikely they would have stopped. (Please don't forget this is ball-park - a good analyst will wiggle the input numbers some to see how much the answer changes, and will also not forget that constant acceleration is an approximation, but a pretty attractive one remembering the lengths to which ELAC had to go to try to estimate braking performance taking more parameters into account.)
So then one might ask at what speed they might have gone off the end. Here is how one might do that. One guesses where touchdown would have occurred (displacement from the threshold), subtract from LDA, put that distance for s in the quadratic equation above, use the Quadratic Formula to solve for t, and substitute this value of t back in the formula for v to solve for v. Say we use an s of 1600 m, meaning with an LDA of about 1880 m we are saying they touched down at about 280 m beyond threshold. Turns out to give about 30 m/s or 60 kts.

We can wonder what might have happened then if the aircraft had belly-flopped onto the road, remembering Kegworth and how many people survived that, but I think the game of "what if" gives out here, given that they still had quantities of fuel.

I think the more pertinent conclusions lie in asking how such calculations might affect operations. Acceleration of -1.26 m/s/s is degraded braking, certainly (autobrake LO has a target of -1.7 m/s/s [Edit: I changed "MED" here to "LO" after my mistake was pointed out by TripleBravo]). How often does one get that kind of degraded acceleration? Under what conditions? Never? Once in how often? Once in too-often? And at distributed airports? Or just one or two? Some data-mining in the FOQA readouts could maybe give guidance. So, for example, you find that at airport XYZ it has happened M times in N units of operation. So now you look at the LDA at XYZ, do the ball-park calculation as above to figure out how much room you need (and don't forget that couple of seconds for a leisurely application of braking after WoW) and maybe alter your ops accordingly. Maybe quite a few operators are now doing exactly these sorts of calculations.

Which, incidentally, they would not be able to do if we couldn't estimate the mean braking effectiveness but had to wait (a year? more?) for the official report. (PJ2 reminded me privately of a short note I wrote in the Risks Forum on this over a decade ago http://catless.ncl.ac.uk/Risks/18.44.html#subj4.1)

BTW, for those who haven't noticed it, there is a major difference between the Warsaw overrun accident and this one. At Warsaw, there was nothing the pilots could do to get the braking they needed. To my mind, that is why there was a deep discussion about, and a change in, the braking logic. As far as we know so far, that isn't the case in the Congonhas accident, or in its putative analogies.)

I am also somewhat sceptical, as others here (such as Lemurian) about adding warnings, such as that suggested in the Taipei-Sungshan report. Given that there is one braking control in this configuration, namely the thrust levers, and given that pilots have not responded to a *very specific* suggestion to activate it ("Retard"), one may wonder what would lead one to think that they would then respond more appropriately to a *general* warning (CRC, red master warning light), or whether the general hullabaloo would not be more likely to distract them further from the task at hand.

PBL

Last edited by PBL; 18th Aug 2007 at 07:56.
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