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AF 447 Search to resume

Old 9th Sep 2010, 03:18
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Also, there are new and old comments about bodies sinking and later surfacing due to gas build up. I expect that this scenario is limited to the common case of shallow water. Once something sinks in several thousand meters of water, it would take a LOT of gas to make it buoyant again,, due to the high ambient pressure.
Almost certainly yes. As the body sinks, the gas filled parts (ie lungs and gastrointestinal tract) will be compressed. The gas may or may not be expelled - doesn't really matter. But it must be compressed and the body will become more dense due to decreased volume (or if you prefer, less buoyant as it will displace less water).

Once this has happened (and there is no magic depth here - it is a continuum), then it is highly unlikely that subsequent gas build up will be sufficient to increase the volume of the body to that required to overall become less dense than water. There may well be gas production, but it will be exposed to the same ambient pressure and hence will not occupy much volume (or be able to displace much water).
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Old 9th Sep 2010, 04:51
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Silly question

If I were one of the Wright brothers watching this thread I suspect that I would not join the experts in posting speculation on whether passengers could or could not be released from a fastened seat belt by g forces of unknown magnitude. Instead, I might go to my bicycle workshop and fix a seat belt (if I had one) to the outside of a bicycle wheel with the buckle release lever outwards away from the center of the wheel. I migght then spin the wheel at gradually increasing speed until the centrifugal action eventually caused the release lever to rotate thereby releasing the buckle. From the rpm and the radius of the wheel I would then know the g force needed to release the buckle. In one hour I would have the answer.

From what I have read about the Wrights I suspect I might not even tell you result. In a week or two I might tell Octave Chanute in a letter. But I would certainly continue to follow this thread, but filter all the future expert contributions in the light of my knowledge of the g forces required.

I could do this experiment myself. I have a bicycle. Unfortunately I do not have a seat belt. Maybe somebody else does?

Last edited by PickyPerkins; 9th Sep 2010 at 13:25. Reason: typo
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Old 9th Sep 2010, 05:07
  #2163 (permalink)  
 
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Way back in the old threat it was pretty much settled that the bodies sank to an equilibrium level. Then as they bloated they rose if they managed to float out of loosely fastened seat belts. One person claimed that bodies, especially broken bodies, could work their way out of even fairly tight seat belts. He claimed sufficient fresh water experience, if I recall, to make that believable.
No disrespect intended here. Over this thread I have read a lot of your posts and learned a lot about radio and satellites etc. But there is some pretty poor science and plenty of vivid imagination on this thread.

There is no equilibrium level - once you sink you sink. All the way. It is a positive feedback process - progressive compression of gas filled compartments increases average density (or reduces buoyancy), which increases sink rate and so on and so on to the bottom.

This theory would suggest that the body and seat sank to such an equilibrium level (presumably the positive buoyancy of the body negating the negative buoyancy of the seat), and then gas formation created increased positive buoyancy which somehow caused the body to float free of the seat. Sounds like a late night horror movie.

There is some science here.

Bradley Stafford, "The Sinking and Rising of Drowned Bodies" (unpublished thesis, 1988).
"The human body weighs slightly more than fresh water. Consequently, when individuals become unconscious, they sink--regardless of fat level, which slightly increases buoyancy. Generally, a drowning victim will reach the bottom of a body of water in spite of the depth, unless it meets some obstruction on the way down. As the corpse descends further, the pressure of the water tends to compress gases in the abdominal wall and chest cavities. As a result, the body displaces less water as it sinks and, consequently, becomes less buoyant the further down it goes, until it reaches the bottom.

Almost without exception, a corpse lying on the bottom of a lake or river eventually will surface because of the gas formed in its tissues as a result of decay and the action of internal bacteria. This results in reduced specific gravity specific gravity, ratio of the weight of a given volume of a substance to the weight of an equal volume of some reference substance, or, equivalently, the ratio of the masses of equal volumes of the two substances.
..... Click the link for more information. of the body so that it rises. Witnesses to this event have described corpses breaking the surface of the water with force, like the popping of a cork.

In some cases, the body may remain immersed. Extremely deep, cold water conditions (e.g., natural glacier lakes, deep impoundments) may prevent a corpse from ever becoming buoyant enough to overcome the immense water pressure.
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Old 9th Sep 2010, 05:20
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Hi,

Thank you slats11
So we can discard a lot of posts out this thread
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Old 9th Sep 2010, 06:47
  #2165 (permalink)  
 
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If I were one of the Wright brothers watching this thread I suspect that I would not join the experts in posting speculation on whether passengers could or could not be released from a fastened seat belt by g forces of unknown magnitude. Instead, I might go to my bicycle workshop and fix a seat belt (if I had one) to the outside of a bicycle wheel with the buckle release lever outwards away from the center of the wheel. I migght then spin the wheel at gradually increasing speed until the centrifugal action eventually caused the release lever to rotate thereby releasing the buckle. From the rpm and the radius of the wheel I would then know the g force needed to release the buckle. In one hour I would have the answer.
You could do this. And if so I would be interested to learn the answer. Until then, here is my guess (and it is just a guess). The buckle flap won't simply fly open, at least not until you reach some fantastic rpm. The flap is not that massive and won't be very susceptible to this centrifugal force. Depending on design, it may not be at all susceptible. But it won't be susceptible enough for this to happen at the sort of force we are talking about. What you could measure would be increased tension along the belt as the circle (ie the loop of belt and buckle) sought to enlarge - but this tension is what the belt is designed to oppose.

I realize that some QF72 pax claimed their belts failed. And just maybe they did get caught on something. But I also know that Qantas routinely advises pax to wear belts even in smooth cruise. And so any pax seeking damages would have thought that they better have been wearing a fastened belt.
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Old 9th Sep 2010, 08:24
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RE seatbelts, bodies, etc:

I've tried to choose my words carefully, as descriptions regarding this subject can be distressing. If you may be offended by such things, please don't read this post.
  • The range of g-force presumed at impact (by most) for this occurrence is greater than the force the seats are manufactured and certified for (which can generally be described as "16G" but is a little more complicated than that seemingly simple figure).
  • In failures of this (presumed and postulated) type of impact (high vertical component, low forward component) there can be some fairly common failure characteristics. One of these -- which I have seen myself many times -- includes the failure or separation of the seat to seat-back attachments. So the two portions become separate pieces, or if still joined, it is a broken and "floppy" join, in which case the seats are often found in an open or "reclined" postion. In either case, even without stuctural compression or failure of the seat mounting itself -- the "legs" so to speak -- it is sometimes very easy for a body to be released (by recovery personnel) or to slide out if in water, without unfastening what was once a snug belt.
  • IMHO the notion that many of the recovered bodies were "unseated" at impact is in clear contradiction to the described injury patterns. For someone not seated, the predominant injuries would certainly not be the pelvic and spinal patterns described. One can't have it both ways. If the BEA injury summaries and comments are correct, then the "forty some odd" people exhibiting those traits were seated.
I don't mind engaging in further discussion of these points via PM but, due to the inherently nasty nature of getting more specific, I'm not prepared to do so on an open forum.

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Old 9th Sep 2010, 08:58
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Inadvertent unbuckling of seat belts

Gentlemen,

I need to emphasize here that the only way I can consider unvoluntary unbuckling due to minor or moderate accelerations is the way described and tested by the ATSB during the inquiry into the QF72 incident : that the buckle gets snagged under the armrest in the right position for the release to catch the armrest and open the buckle.

The ATSB tested this, and manual forces were enough to open the buckle. No need for dozens of Gs here.
Potential for inadvertent seatbelt release : Six passengers reported to the ATSB that they were seated with their seatbelt fastened at the time of the first upset, but that the seatbelt became unfastened and did not restrain them in their seats. Three of those passengers advised that they had their seatbelts tightly fastened, and three advised that they had their seatbelts loosely fastened. None of the six passengers could provide details of how their seatbelts released. As advised in the first Interim Factual Report, the investigation identified a scenario whereby seatbelts could inadvertently release. For this to occur, the seatbelt had to be loosely fastened and the buckle had to be positioned in a vertical orientation underneath the right armrest prior to an upward force being applied. The lift-latch could then catch on the armrest and the buckle release. The ATSB has conducted further examinations of this inadvertent release scenario on one of the operator’s A330 aircraft. Those examinations found that, for this scenario to occur on those aircraft, the seatbelt had to be adjusted so that there was at least 25 cm of slack in the belt (comparing the length of a firmly-fastened seatbelt with one that was loosely fastened to the minimum extent necessary to enable the inadvertent release scenario to occur). The certification requirements for aircraft seatbelts required that the possibility for inadvertent release of seatbelts is minimised. However, design and testing requirements for seats and seatbelts are based on the principle that seatbelts are ‘properly worn’.

Last edited by Svarin; 9th Sep 2010 at 09:00. Reason: manual formatting of quoted text
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Old 9th Sep 2010, 11:15
  #2168 (permalink)  
 
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HarryMann, might the bodies recovered possibly be those who were standing around the lavatory doors when the foo hit the fan? Suppose they had no way to stagger "safely" back to their seats. That sounds like a lot of people up and around at that hour. But....
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Old 9th Sep 2010, 11:34
  #2169 (permalink)  
 
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auvee, the reference I could find with Google for that issue is about clothing working its way off due to wave action. Here is another one. Somewhere in that rather large region I thought somebody had remarked about the limp bodies working their way out of the seat belts, too. If the seats broke from the floor there would be little to impede a loosely belted body from sliding downwards and out with the probably damaged spine providing the flexibility needed.

Of course, I could be conflating clothing being stripped off with seats being stripped off. Finding the correct Google search terms is difficult.
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Old 9th Sep 2010, 11:38
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PickyPerkins, in the usual seat belt position the lever is going to be mashed down tighter by the G forces rather than opened. It'd have to bounce to open the lever.
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Old 9th Sep 2010, 13:15
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Silly question

PickyPerkins, in the usual seat belt position the lever is going to be mashed down tighter by the G forces rather than opened. It'd have to bounce to open the lever.
Yes, I completely agree. Look at my original post:
http://www.pprune.org/5921178-post2140.html

I am talking about g forces following (after) a bounce of a belt buckle on a passenger's lap..

Last edited by PickyPerkins; 9th Sep 2010 at 13:26. Reason: typo
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Old 9th Sep 2010, 13:36
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IMHO, this stuff about seat belts and broken bodies sliding out is all conjecture and probably irrelevant.

What is relevant is that the seats sink - occupied or not. The seat cushion alone can float. But the seat as a whole sinks. And even if subsurface currents cause the bodies to slide out (and I guess this is conceivable), by that time the body too has sunk. And will stay sunk.

So this scenario can really only happen if the bodies slide out quickly due to wave action in the initial period when the seat is on the surface ie before it gets waterlogged and starts to sink. Look I guess its probably possible. But I can't help thinking that unrestrained pax are the more likely explanation. Especially when we take into account the lack of Mayday and the absence of life jackets.

We don't know exactly what injuries the bodies displayed. We have vague and likely incomplete information about a proportion of the bodies. But we don't know the full picture. I do understand the honorable desire to spare relatives the details. But the fact is we can't make too many conclusions on the results released..

People who die jumping off buildings routinely experience pelvic fractures and spinal fractures. You don't have to be strapped into a seat.
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Old 9th Sep 2010, 18:20
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slats...

People who die jumping off buildings routinely experience pelvic fractures and spinal fractures. You don't have to be strapped into a seat.
With respect,

Of course you don't have to be strapped into a seat to experience pelvic and / or spinal fractures. I didn't say that, and neither did the BEA. That sort of simplification is exactly why so many of us don't wish to get into debates on fora like this one.

BEA made that satement based on the specific character of those injuries and in conjunction with other injuries. All as examined and reviewed by medical / accident / pathology experts. I am certainly no apologist for the BEA (I've written and spoken on many occasions concerning some of their weaknesses) but they would not have made the relevant statements unless satisfied as to the accuracy and validity of the data. Otherwise, at this point, it would simply not have been mentioned.

As I already offered, I'm available to discuss this more adequately "offline".

No more from me on this thread on this aspect of the AF447 disaster.

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Old 9th Sep 2010, 21:50
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Fair enough Griz. I understand where you are coming from. I am not trying to argue how the injuries occurred - I obviously can't know. However I am trying to point out that we can't conclude anything on the basis of the information released into the public domain.

With the now very unlikely recovery of the recorders, after endless speculation about what the ACARS messages may or may not mean, and after 15 months of continuous debating various hypotheses, we are left with the conclusion that no one will ever no for sure what happened to AF447. And so we have to accept that in 2009, a modern aircraft can simply cease to exist - along with 228 people.

To me, the human factors analysis is the most helpful lead. Why did no one get a life jacket? Is there a reason why we have so many bodies and so little else? And what do the injuries suggest is most likely to have happened?

In pathology there is an old saying:.
Mortui Vivos Docent -The Dead teach the Living


Without wishing to offend anyone here, I suspect there are lessons to be learned. I just hope they have been.
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Old 10th Sep 2010, 02:02
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In medicine at large........

Internists know much, and do little.

Surgeons know little and do the most.

Pathologists know everything and do everything...........too late.
bear
 
Old 10th Sep 2010, 02:07
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slats11
With the now very unlikely recovery of the recorders, after endless speculation about what the ACARS messages may or may not mean, and after 15 months of continuous debating various hypotheses, we are left with the conclusion that no one will ever no for sure what happened to AF447. And so we have to accept that in 2009, a modern aircraft can simply cease to exist - along with 228 people.
Well, the BEA can confidently sit down and write their final report. Wont be much to add to what they have already written.

I for one do not think that will be happening, and suspect your statement may get a "shark bite" or two in it before "la fin" is stamped on a report by the BEA.

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Old 10th Sep 2010, 02:11
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mm43

I believe you, and pray you are correct.
 
Old 10th Sep 2010, 10:18
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Slats11
Please answer a simple question - how do the people get their life vests out when they are strapped into their seats in heavy turbulence? Even if they were in the seat back pouches why would they unless the plane was known to be about to ditch?

PickyPerkins
Have you ever tried to bounce a water balloon? Human bodies are large water balloons covering bones that break. What bounce do you expect? 1/2 a g or 20g or what?
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Old 11th Sep 2010, 18:35
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slats...

I certainly share your obvious frustration over the fact that in 2009 / 2010 we are in a position where a major aircraft accident occurs and we may not be able to gather the information as to "what really happened". My gut tells me there are some genuine surprises in this instance and we need to learn what happened in order to prevent whatever it was from happening again.

One area I have a bit more optimism than you (and I may of course be wrong!) is regarding the eventual location of the FDR andCVR.

Cheers,
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Old 11th Sep 2010, 23:38
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36g

There was a fair amount of discussion centred around arm '36g'. Can't say I followed it or why a piece should be rated according to a maximum inertial load as opposed to x N/mm^2. Sadly, the pathology may well provide the most clear evidence of forces. Can anyone tell me the rated strength of a fastened seat belt and how that relates to the strength of the seat fixing, and remind me of which recovered articles allowed the 'line of flight' BEA conclusion (ie is it in any doubt with respect to the whole airframe ?). Thanks.
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