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Qantas 744 Depressurisation

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Qantas 744 Depressurisation

Old 27th Jul 2008, 15:33
  #481 (permalink)  
 
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bcgallacher

Early 747 had the passenger O2 bottles horizontal in the roof of the forward cargo area opposite the door - later 747 have the bottles mounted vertically in the right sidewall of the cargo area aft of the crew bottle stowage .
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Old 27th Jul 2008, 15:34
  #482 (permalink)  
 
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The words "hit", "nail" and "head" come to mind...

"...the system, which also by its very failure, possibly caused the decompression which the system was there to protect against!"

Nicely put!

Last edited by pappabagge; 27th Jul 2008 at 15:35. Reason: spellin, innit?
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Old 27th Jul 2008, 15:36
  #483 (permalink)  
 
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What were the FA doing?

From the passenger video from post #154, it appears that the FA were handing out trays and serving drinks rather than clearing up - see about 40 seconds in for a tray being handed to seat D or E. There is also a shot that seems to show a coffee pot being wielded.

This was all happening after the "plunge", as the seat-back display shows altitude 10002 feet and ground speed 348 miles per hour. Another video in the same set shows the seat C passenger still with a tray and altitude going down through abot 9500 feet.

With the order of an hour to go to Manilla and things more or less stable, it seems reasonable that the cabin crew should maintain normal service. That would give everyone less time to worry!
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Old 27th Jul 2008, 15:53
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No other visible external damage?

With all this talk of oxygen bottles making the hole, incl. the Frames/Stringers/Skin/Cargo, etc. that did exit the hole....

I am amazed, especially noting the location of the damage that no other part of the aircraft was hit by the debris....

Is this luck or are there reasons why this would not occur?

I'd happily accept luck!

Well done to the crew, and glad everyone made it down safe.
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Old 27th Jul 2008, 15:56
  #485 (permalink)  
 
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Last thoughts

On the very few occasions since I started flying (TAROM, Bucharest 1958) when I have been frightened, I too have had inappropriate thoughts, although these have seldom concerned the whereabouts of my passport. In the current case can I just say, without being excoriated by Rainboe, that this incident has simply served to increase my trust in the 747 as one of the safest machines ever to grace our skies.
Almost unbreakable. I for one will miss them sadly when they are gone. And I remember with particular gratitude being whisked out of a riotous Jakarta not so long ago on a Qantas SP. Great plane, great crew.
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Old 27th Jul 2008, 15:56
  #486 (permalink)  
 
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Finally, yes, a rocketing gas tank would need to accelerate for a few metres to knock a hole in a seam, but that folded-up bit of fuselage is interesting nevertheless.
If we are to believe the report of the first 'clunk' (20 mins ex-LHR), is it not possible that was the alleged bottle dislodging ? After which it could have rolled around down there sustaining increasing damage until it finally let go from an undetermined position; conceivably the necessary 'several metres' from impacting the skin.

Speculation. So sue me.
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Old 27th Jul 2008, 16:18
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Speculation. So sue me.
My lawyer will be contacting you shortly

You seem to pre-suppose that there is lots of room down there to move arround in and get it up to speed
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Old 27th Jul 2008, 17:06
  #488 (permalink)  
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You seem to pre-suppose that there is lots of room down there to move arround in and get it up to speed
There seems to be a lot of pre-supposition that an oxygen bottle exploded, when the only fact we have is that one is merely missing.

Gas tank explosions are exceedingly rare and as far as I can recall we've never had one explode in the air. The very few occasions where bottles have failed were during in-situ ground charging (which is possibly the reason why we don't do that any more.) Anyone who watched the Mythbusters going about their hilarious business would know not only how difficult it is to break the neck off a gas bottle, but how slowly it accelerates when you do succeed. Impressive it may be, but a rocket it isn't. The bottles in an aircraft are securely clamped into place in any case. When the mythbusters tried busting a bottle as in the Jaws movie, their stunt required several attempts with a 30.30 carbine to get the bottle to burst - with a dead square-on hit to the long edge. Most hits either bounced off or simply punched a bullet sized hole through which the gas escaped with a loud hiss. Gas bottles are tough.

The final point is that an oxygen bottle explosion is extremely violent. An oxygen cylinder explosion, apart from being sufficient to blow a hole in the fuselage, would certainly have blown out the cabin floor (which is simply a lightweight honeycomb sandwich) above the area. We don't see such damage.

If the investigation shows that the fuselage rupture was indeed due to an oxygen bottle exploding, then we have a very serious problem. The bottle is missing - what was its failure mode? Without knowing that we don't know how to prevent a repetition.

Last edited by Blacksheep; 27th Jul 2008 at 17:36.
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Old 27th Jul 2008, 17:25
  #489 (permalink)  
 
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Bottle débris

I thought the investigators found bottle débris? I swear I read that on this thread. I can't seem to find it now. I think I've got a headache coming on...
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Old 27th Jul 2008, 17:34
  #490 (permalink)  
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It was alleged, but we don't see any in the photograph, despite that wall of luggage stuffing up the hole. One would expect at least some shrapnel stuck in the baggage.
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Old 27th Jul 2008, 18:01
  #491 (permalink)  
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If we are to believe the report of the first 'clunk' (20 mins ex-LHR), is it not possible that was the alleged bottle dislodging ? After which it could have rolled around down there sustaining increasing damage until it finally let go from an undetermined position; conceivably the necessary 'several metres' from impacting the skin.
Stopover in Hong Kong.
Would cargo hold door be opened?
(I assume that baggage not for/from Hong Kong would remain in situ, therefore any derangement of the oxygen cylinders wouldn't therefore be noticed?)
Is the area where the hole appeared part of the cargo hold? (I understand that it might be 'curtained-off')

There appeared to be a hole in the cabin floor (I think I saw a picture). Is this directly above the structural hole? Could this be explained by 'suction' from the evacuation of the cabin air through the breach in the structure? There was talk of papers etc flying around the cabin.
OTOH, any upward rupture of the cabin floor would indicate an 'explosion' of some sort (I'm not suggesting a chemical detonation, merely rapid expansion of a gas, as occurs when a child's balloon bursts).

The 'bent back inwards' edge of that failed skin (front of 'hole'

from:- http://media.aftenposten.no/archive/...___816172a.jpg ) suggests that there was a larger piece attached immediately post-'failure' that was subsequently blown backwards by the airstream before (eventually) being w*nked off (bending backwards and forwards as you would to 'break' a piece of metal by fatigue failure), leaving an inwards bending edge.

Last edited by G-CPTN; 27th Jul 2008 at 18:44.
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Old 27th Jul 2008, 18:12
  #492 (permalink)  
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Just to clear up some points. The B747 does not use individual seat row oxygen generators. There are Passenger and Crew oxygen bottles in separate systems, feeding ring mains- the passenger one goes right around the aeroplane, the crew one just to the Flight Deck. There is no interchange of supply, and the crew one cannot be fed from the passenger system. The passenger system in a full aeroplane may only have a capacity for about 25 minutes, the flight deck crew system considerably longer, but it is a smaller bottle which supplies up to five people. There are no easily to hand alternative supplies on the flight deck. If your ring main system did not work, you would be unable to get to another supply. As for indications that the pilot supply is supplying oxygen satisfactorily, on each pilot's oxygen supply panel where he gets his mask, there is a yellow cross shaped device that changes size as he takes oxygen each breath giving a visual indication that oxygen is flowing. With the commotion of what is going on in the background, I have never known anybody check this in an emergency. Sticking ones head in the forward hold, there is no sighting of oxygen bottles at the rear. I assume access would be through the rear face of the hold somewhere. I have no idea what it looks like or how the bottles are mounted, but they are all fitted with stopcocks and overpressure venting systems, and feed into a common main, therefore they must have NRVs and PRVs individually.
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Old 27th Jul 2008, 18:35
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I thought the investigators found bottle débris? I swear I read that on this thread. I can't seem to find it now. I think I've got a headache coming on...
I hope that you don't beleive everything that you read on here

About the only thing that you can trust is that relased by the official investigators which in this case is the Australian ATSB. You also have to treat with caution even words like "they are looking very closely at...." being paraphased by news media.

and for gosh sakes this forum is just a discussion forum with many "what ifs" and "probably was" to fill in the blanks in our minds.

at the minimum it at least shows that we care about the subject
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Old 27th Jul 2008, 18:44
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Vertiginous, see #354 re the initial Bottle Debris quote from the NY Times:

One person close to the investigation, who was not permitted to speak to the media while the inquiry was under way, said Saturday that “some kind of explosion” might have occurred, because the floor above the cargo hold had been pushed up. Two oxygen bottles that supply the pilots are stored in that area.

Australian investigators, who got their first look inside the plane Saturday, discovered shards of an oxygen bottle throughout the cargo hold and in the floor above, which sits below the cabin, this person said. Officials cautioned that it was too soon to know if the oxygen canister had caused the damage, but theorized that it might have played a role, this person said.
...it is just an anonymous source though. So take it for what it is....

Last edited by lissyfish; 27th Jul 2008 at 18:58. Reason: typo
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Old 27th Jul 2008, 18:46
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747 front cargo hold

Here is a good picture of the forward cargo hold, in this case from a Virgin 747-4Q8. You can see the cargo door in the foreground. I presume the oxygen bottles are behind the vertical sidewalls furher aft. Those familiar with the 747, feel free to comment.

Photos: Boeing 747-4Q8 Aircraft Pictures | Airliners.net

Last edited by snowfalcon2; 27th Jul 2008 at 18:52. Reason: typo
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Old 27th Jul 2008, 19:20
  #496 (permalink)  
 
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what is the little door

Excuse my ignorance in advance - but nobody mentioned the little door hanging open only a bit towards aft of the whole...?
(interested SLF, no pilot or engineer)

Last edited by grimmrad; 27th Jul 2008 at 19:30. Reason: disclaimer
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Old 27th Jul 2008, 19:23
  #497 (permalink)  
 
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Old 27th Jul 2008, 19:46
  #498 (permalink)  
 
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Snowfalcon2

The photo you reference (thanks!) leads me to believe the bit of cloth with the letters STA in the incident photos is a portion of the beige nomex/pbi fire curtains with the station label affixed to it.
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Old 27th Jul 2008, 19:58
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I know it's not exactly an O2 bottle, but for those of you not well versed in either physics or comprehension of explosive forces, here is a short video of a well understood substance when it decides it wants to leave the bottle:

YouTube - Dangerous Cole

I am sure you can use a little imagination to understand the possible cause of the hole!
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Old 27th Jul 2008, 20:11
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What about an oxygen leak from one of the cylinders/pipes?If the leaking oxygen came in contact with grease/oil or anti-corrosive compound would this cause an explosion?
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