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Old 8th Jun 2009, 22:06
  #721 (permalink)  
 
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I don't get it!

Now that we found the vertical fin, we are speculating about this part as the primary cause of the accident or the first part that fell off. What if we found a door first? Would we argue then that it was a door that fell out first and destroyed the plane?

The reason why they found the fin first is because it is one of the very few parts nearly completly made of composite materials and thus floats (better than the rest). On most accidents over water they find the fin first (remember the Armavia A320 near Sochi, Russia, May 3, 06). Nearly always intact.

Those fins depart from the fuselage (for whatever reason) and "fly" like a feather earthwards. That's why they don't get destroyed on impact.

Dani
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Old 8th Jun 2009, 22:07
  #722 (permalink)  
 
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The addition of photos to this thread sure does focus the attention of many and provides fodder for speculations way beyond the evidence at hand.

Consider always the #1 rule of observation

Occams Razor

e.g. the most likely explanation for the visual appearance of a piece of debris at a crash site is the impact with the ground.

the most likely explanation .....etc. of a field of debris away from a crash site is a cascading breakup.

The finding of an eureka cause in a single piece of debris is extremely remote.

To extrapolate that single photo to design and operational characteristics of the A330 is quite a stretch in my opinion.
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Old 8th Jun 2009, 22:28
  #723 (permalink)  
 
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ManaAdaSystem -
To me, turbulence is mostly about pitch and roll, not so much about yaw. For sure, on those occations when I have been hand flying in turbulence, the use of rudder has never been needed. Then again, I've never been in severe turbulence.
Exactly.....there's no need to apply any rudder. You basically hang on. I've been in extreme turbulence (that's right...more than 'severe'). However, it was in a DC-6. I was flying and all I could do was just try and keep it more or less straight, but level was the most important part. Didn't really care which direction it went. However, I do not think a jet transport of today's manufacture would have survived that encounter.
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Old 8th Jun 2009, 22:29
  #724 (permalink)  
 
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ACARS & Hydraulics?

My expertise is in aircraft engines (20+ years gas turbines) , but not airframes.
A question for those with real expertise with ACARS: Would it report any problems with the hydraulic systems? It would seem to be fairly safe to assume that all hydraulic lines leading to the rudder actuators would have been severed upon loss of the vertical stabilizer. Since ACARS did not mention anything related to hydraulics in its stream of error messages, would it then be reasonable to assume the stabilzer was still with the aircraft during that time? Or, is hydraulics simply not a system monitored by ACARS?
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Old 8th Jun 2009, 22:29
  #725 (permalink)  
 
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dani -- Thanks for that . It was needed.

lomapaseo -- Same comments as to dani above. (With the proviso that your reference to debris fields and cascading breakups is directly relevant to "ground impact" but significantly less so in this case of an ocean impact followed by a week of winds and currents.)
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Old 8th Jun 2009, 22:29
  #726 (permalink)  
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ManaAdaSystem;
Why would they be pumping the rudder to it's max during turbulence?
Where on earth are you getting that from?!

There is certainly no evidence nor even a suggestion that "pumping" the rudder was done. Stick to what is available.

(Why do I post here at all for heaven's sake?....).

Dani - there is NO suggestion nor should there be, as to how/when/why the vert stab came off. It is off and that is the only evidence we have before us. Your swatting at flies that don't exist.

lomapaseo;

I believe we agree here. There is no "eureka" suggested of course. I state my intent very clearly and warn that drawing conclusions cannot be done. I am trying to contribute to knowledge by examing "what is" and nothing more - we simply cannot do more without allowing imagination to take over from facts.


I have to say in general, that there is once again, great hazard in posting any suggestion or comment with reference to anything new coming in. At the slightest suggestion some ride off in all directions setting their hair on fire about all and unrelated sundry over new comments. Let's stick to what is known, which is extremely little. To give life to theories only serves interests which may not have the same goals in mind...
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Old 8th Jun 2009, 22:41
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PJ2,

I don't think ManaAdaSystem was suggesting that, I think it was a question, not a statement!
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Old 8th Jun 2009, 22:45
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Simply can not tell whether Stabiliser came off in flight or at impact from the pictures, however I suspect there is a good chance they may be able pin down a good estimate when it is carefully examined. The way everybody is amking announcements (though n ot always accurate) there is a good chance we'll hear what the likelyhood is when they get it back to land and examine it.

As a PPL and not anything to do with engineering either I was slightly astonished on learning of the standard set for stabiliser attachment after the AA chrash. I realise this is not just an Airbus thing too, and perhaps the engineering required to fix structure for high speeds would be just so out of order that travel limiting is the only reasonable option.

However looking at the type of attachment, rather like that fixing a keel on a high performance sailboat, one can not but be concerned at the moments and leverage involved and wonder why, if it is attached behind the after pressure bulkhead, they did not go for a lower leverage design with loads spread between the upper and lower fuselage construction.
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Old 8th Jun 2009, 22:46
  #729 (permalink)  
 
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The sheared vertical stablizer is for now unremarkable.

In normal cruise and climb, even through turbulence, the use of rudder is limited. On this particular aircraft, yaw control is augmented by the FBW system and yaw damper.

While the ACARS readout does show a degradation from Normal Law to Alternate Law, and the warning regarding the Rudder Travel Limiter (most likely from the ADIRU failures), there is no reason the PF would from that point forward have begun stomping on the rudder pedals willy nilly.

To suggest otherwise is irresponsible at this point in the investigation. Speculation is fine for a learning exercise, but let's refrain from pointing fingers at the crew when not even 1/1 millionth of the data & facts are at hand.
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Old 8th Jun 2009, 22:46
  #730 (permalink)  
 
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PJ2

People are speculating that the lack of rudder limiter had something to do with this accident. The lack of rudder limiter will not break the fin off, you would need to apply a lot of rudder (pumping is maybe not the best word) to do that, like in the AA case.

I just don't see why they would have to do that, that's all.

You're starting to sound like Rainboe.
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Old 8th Jun 2009, 22:53
  #731 (permalink)  
 
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there is NO suggestion nor should there be, as to how/when/why the vert stab came off. It is off and that is the only evidence we have before us.
With respect PJ2, I believe that some conclusions can be drawn from the failure of the VS / fuselage connection seen in the photographs.

A simple knowledge of mechanics tells us that a large sideways force was exerted on the VS at some unknown instant, generating a bending moment sufficient to fail either the bolts or the lugs (or a combination of both) holding it to the fuselage. It is not clear from the photographs whether the lugs or the bolts failed.

That sideways force could have happened towards the beginning of the sequence (as in the AA A300 accident), or at the point the VS hit the water, or any point in between. Time will tell.

The VS is a vertical cantilever. The VS failed at the point of greatest bending moment, occurring at the base of the cantilever (point of attachment to the fuselage).

From a simple analysis of the geometry of the complete VS / fuselage connection, there is no other plausible failure mechanism that explains the failure shown in the photograph.


Added - ChrisVJ, you posted while I was writing, I am very much in agreement with your thinking, particularly your last paragraph!

FBW
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Old 8th Jun 2009, 22:54
  #732 (permalink)  
 
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Or, is hydraulics simply not a system monitored by ACARS?
When ACARS tells you "probe-failure" it does not tell you, what probe fails. Thats how it works on most airplanes. My humble oppinion.
People are obviously having problems understanding acars. ACARS is a communications system that relays messages. It can be considered as an onboard fax machine and is completely independent of any onboard fault detection system. One of the more useful additional functions is to relay messages from the CFDS system. Therefore ACARS influences nothing. It doesn't decide which fault messages to send, it only sends those that are reported by another system.

So yes it will tell you which probe has failed and it will relay hydraulic, fuel, oxygen and any other message that CFDS has stored. It is also very useful when drivers start telling porkies about faults occuring on a home leg.

Thats why the information is useful and relevant. However it has a few drawbacks too. One good example is AP off. AP off will be reported but you cannot tell if it was a manual disconnect or an automatic one. Although in this case considering the amount of failures it would be reasonable to assume it was automatic but we don't know that.

Any warning that appears on the ECAM system will be stored in CFDS and if the acars option is in use that warning will be sent back to base.
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Old 8th Jun 2009, 22:55
  #733 (permalink)  
 
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SteamCat---SOSUS isn't completely gone. Used for civilian monitoring (whale farts, NOAA's VENTS program in the North Pacific). Don't know if it's continuously monitored.
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Old 8th Jun 2009, 22:58
  #734 (permalink)  
 
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what we have learned from these posts

avoid bad wx

really know what to do with wx radar

be ready for just about anything, including loss of computer assisted flying, loss of airspeed and changes in flight control limits.

always be ready.
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Old 8th Jun 2009, 22:58
  #735 (permalink)  
 
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PJ2 -- Deep breaths . . .

I didn't get the impression that either dani's post or lomapaseo's were referring directly to you or your posts. In dani's case he wasn't at all swatting at flies; he was making (what I thought at least) was an accurate and appropriate comment re some of the speculation of the past day. It seems to me that Lompaseo was doing the same thing.

Grizzled
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Old 8th Jun 2009, 22:58
  #736 (permalink)  
 
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It's clearly very unlikely that the VS/rudder assembly broke off during an impact of a complete or nearly complete plane - there would be all manner of debris riding along with the same currents, evidence of hydraulic fluid on the water surface etc. etc.

-drl
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Old 8th Jun 2009, 23:00
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vapilot

On this particular aircraft, yaw control is augmented by the FBW system and yaw damper.
Would the yaw damper remain operational following the air data disagreements?

IOW -- would it auto-disengage along with the AP and the downgrade to Alternate Law?
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Old 8th Jun 2009, 23:05
  #738 (permalink)  
 
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Thanks!

Thanks for the clarification -ACARS doesn't directly monitor systems - it just relays data from other monitoring systems. You also answered the main question I was asking - hydraulic system problems would be reported to and relayed by ACARS if they occur.

Thanks!
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Old 8th Jun 2009, 23:07
  #739 (permalink)  
 
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I didn't get the impression that either dani's post or lomapaseo's were referring directly to you or your posts. In dani's case he wasn't at all swatting at flies; he was making (what I thought at least) was an accurate and appropriate comment re some of the speculation of the past day.
Grizzled, Dani seemed to be pretty explicitly stating that he believed that the VS had separated in flight:
Those fins depart from the fuselage (for whatever reason) and "fly" like a feather earthwards. That's why they don't get destroyed on impact.
I think that was part of what PJ2 was getting at.

FBW
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Old 8th Jun 2009, 23:08
  #740 (permalink)  
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FBW;
A simple knowledge of mechanics tells us that a large sideways force was exerted on the VS at some unknown instant, generating a bending moment sufficient to fail either the bolts or the lugs (or a combination of both) holding it to the fuselage. It is not clear from the photographs whether the lugs or the bolts failed.
Yes, I think so and agree. That was the only reason I wanted to work a bit on the photos of the VS - to see if that one area in the photo was sufficient to show the lug structure or not. I think it does but it's just indefinite enough to cast a bit of doubt so I posted it to see what others thought.

Re Dani's comment,
I think that was part of what PJ2 was getting at.
Exactly, and from ManAdaSystems regarding "pumping of the rudder":
I just don't see why they would have to do that, that's all.
Like Rainboe...we'll leave online personalities out of this, thanks. I was blunt perhaps, for which I apologize, but really, you simply don't know that any such crew action took place.

grizzled - thanks. I post only to deal with "what is" because I think it is important to be very careful where conlusions, even one's that seem reasonable, go. Until today, there has not been anything new, ergo, no reason to post.

Last edited by PJ2; 8th Jun 2009 at 23:28.
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