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AF 447 Search to resume

Old 8th Sep 2010, 09:03
  #2141 (permalink)  
 
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Silly question

There seem to be many questions about the fact that bodies found floating on the surface of the sea were not belted to seats, but that in contrast their spinal injuries are consistent with them having been in seats and belted at the time of impact, and subject to high vertical acceleration.

Ruminating on this I am tempted to ask a “silly question”, and simultaneously to take cover behind the notion that there ought to be no “silly questions”, particularly when the known facts and ideas do not add up neatly.

My “silly question” is rooted in the fact that all objects dropped on a surface bounce unless their properties are such as to be able to EXACTLY absorb all the kinetic energy of the falling object (which isn’t very often).

Pretty well everything bounces, not just tennis balls, etc. When you click a computer mouse button, the computer sees a long series of make and break events as the contact bounces, and special software exists in the computer to interpret this series as a single “make“ event.

Now for my “silly question”.

What happens when a passenger lap belt buckle is slammed down on a passenger’s lap with decelerations of say 20g-100g?

There is going to be some bounce.

The buckle as a unit is going to bounce upward, and the release lever may also impact the buckle body and bounce upward as well.

In either case, could the upward momentum of the release lever be enough to turn the release lever through 90+ degrees and thereby release the belt? The spring which normally holds the buckle closed is not very strong.

If one knew the weight of the release lever and the strength of the spring, it might be possible to calculate the accelerations needed to release the belt under “bounce” conditions.

Of course, if you have a seat belt and buckle available, like the one carried on every aircraft and used on every flight by flight attendants to demonstrate how to release the buckle, you could take it to the nearest “bouncy” surface and see how hard you have to slam it down in order to release the buckle.

I presume that no tests were required at the time that the seat design was approved since no 20g-100g forces were considered relevant.

The fact that most of the bodies were found with spinal injuries consistent with being subjected to high accelerations while being seated and belted, but that the bodies were recovered from the sea unbelted, strongly suggests to me there must be some common mechanism by which they became unbelted.

Taking cover ……….

Last edited by PickyPerkins; 9th Sep 2010 at 02:54. Reason: typo
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Old 8th Sep 2010, 10:52
  #2142 (permalink)  
 
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PickyPerkins wrote:-

There seem to be many questions about the fact that bodies found floating on the surface of the sea were not belted to seats, but that in contrast their spinal injuries are consistent with them having been in seats and belted at the time of impact, and subject to high vertical acceleration.
Are you sure they were belted in? I believe the consensus of opinion in this thread is that the bodies that were recovered were not belted in. Some may have been seated and others not. It is my opinion that there were "g" forces involved right from the commencement of loss of control that precluded unseated or non-belted persons from regaining their seats or securing a seat belt. Exactly how or when they received their injuries will never be known, but the FDR when recovered may shed some light on that issue.

We know that the vertical kinetic energy at impact was high. Exactly what it was can possibly be deduced from careful forensic analysis of the recovered debris. A photo in the BEA Interim Report No.2 shows the front edge of an overhead luggage compartment bent forward slightly. That in itself isn't very helpful in determining the horizontal kinetic energy as we don't know anything about what was in the locker, i.e. size, weight or distance it may have moved.

As Machinbird has already pointed out the mechanics of this breakup are complex. However, the BEA has placed some emphasis on the vertical descent rate and then said "nothing" about the horizontal component other than mentioning the aircraft impacted "en ligne de vol" with positive attitude and the tail yawing to port. I am sure the BEA has managed to put some numbers on both these vectors, but are astute enough not to muddy the waters should recovery of the DFDR and CVR reveal something else.

mm43
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Old 8th Sep 2010, 12:48
  #2143 (permalink)  
 
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I wonder what the vertical descent rate really was. I think we will do better to estimate velocity and calculate a probable acceleration rather than the other way round.

I am sure the velocity was substantial, but I'm having trouble envisaging 90-100 m/sec (post 2067, mm43). 1 km every 10 seconds? From cruise to sea-level in approx 100 seconds? The thing should have been slowing down if anything in the thicker atmosphere. That's faster then the terminal velocity for a dense object such as a skydiver. For an aerodynamic air-filled structure? Am I missing something here?

Assume 100m/sec. Assume cabin contents (including pax) decellerated to zero over maybe 10 m (combination of the hole in the water and collapse of the cabin floor into the hold). That is an average decelleration of 500m/sec/sec. Does the galley look like it took a force like this? I am not an engineer so am happy to be corrected. But it just doesn't look right to me.

The compression fractures of the spinal column associated with the fractures of the pelvis, observed on passengers seated throughout the cabin, are compatible with the effect, on a seated person, of high acceleration whose component in the axis of the spinal column is oriented upwards through the pelvis.
I am also wondering about the wording here. Does this really mean that they believe that the passengers recovered had to have been seated at impact. Does the bit "throughout the cabin" refer to seat allocation - are they implying that this force was applied to all the passengers (and hence the cabin was still in one piece) rather than the passengers were actually seating. And it is difficult to know what the injuries were and were not compatible with when we don't know the injuries. Maybe I am over-reading this, but the wording is a bit odd.
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Old 8th Sep 2010, 13:12
  #2144 (permalink)  
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A330 is large, and has local differential accelerations. Schiphol 737 collapsed onto the tail, then the mid section, then the (accelerated) nose. The Ocean was roiled as well, swell and wave action could have "littered" the impact point. It is even possible here that the nose section separated before contact with the surface. "Throughout the Cabin" is an expression that asks more questions than it settles (En Ligne de Vol?) If Pitch excursions were rapid (likely) unseated passengers would have been tossed about sufficient to cause dramatic and fatal injuries well before impact.

I return to the obvious. The use of language, the selective parsing of evidence and cause and effect; the reports strike a pose, yet one that can be withdrawn pending the finding of "new evidence". The Rest Capsule was collapsed and utterly destroyed, it was under the cabin floor, the galley was above it. Again, it is a large airplane, and local accelerations are not a surprise at all. "Intact at impact", It frankly is not beyond the pale to entertain a loss of hull integrity well before the impact with the Ocean. It is a long discussion, and because the Reports serve to dissuade a discussion, one that is unlikely to be considered. It is at all costs necessary to avoid any speculation that this wreck bears any resemblance to AA587.

mm43 Was the Tail yawing to port? Or was the a/c Yawing to port, the tail to starboard?

bear

Last edited by bearfoil; 8th Sep 2010 at 13:23.
 
Old 8th Sep 2010, 15:14
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belted pax

Originally Posted by mm43
I believe the consensus of opinion in this thread is that the bodies that were recovered were not belted in.
Does anyone remember this recent post?

Originally Posted by JD-EE
In post:
http://www.pprune.org/5892859-post1986.html
bearfoil: ...
I thought you were around in the old group when it was explained that water action can ease bodies out of their seats even when fully belted in. Somebody with experience in this regard explained it well.
JD-EE:
Can you find the post that you referred to above? Working free of the seat in 6 days seems quite probable if the seat back is also broken and free to "recline". I don't know the condition of any seats that were found.
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Old 8th Sep 2010, 16:12
  #2146 (permalink)  
 
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Unbuckling at impact ?

Gentlemen,

in the QF72 incident, the ATSB report does indeed give an explanation of how a buckled-up passenger could come unbuckled as they suffer vertical accelerations.

It is so that some belts have their buckles located at the leftmost side of one's belly when seated and buckled-up. As a large number of injured passengers on incident flight QF72 did wear their belts and the buckle simply caught and snagged below the left armrest at the moment they experienced a -0.8g pitch excursion. This snagging caused the buckle to open, and subsequently the unfortunate passengers were thrown to the cabin ceiling and injured.

I am quite ready to envision that the recovered bodies of those unfortunate passengers in flight AFR447 were forcibly removed from their seats, likely at impact, through a similar scenario.

Thoughts ?
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Old 8th Sep 2010, 17:37
  #2147 (permalink)  
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The lap belt is engineered to resist forward 40g (air.) It is not intended to keep the passenger centered or from some "unusual" situation. A five point harness would be better for that. Up and forward resistance is designed for. The seat should withstand 40g also, but not in sideways (lateral) or "up". Beyond 40g is considered unnecessary, it is the rare human body that can survive that load anyway. The buckle itself is designed to resist opening in most aspects, for obvious reasons. The consideration is that the device works. If proven to have failed, it would require a determination such as you report, an exception. If as HazleNuts39 posits, the VS encountered a 66g load at impact, this opens up an area where the fuselage contents could have been so exposed. Old Engineer proposes earlier disruptive damage at the VS, again, it is logical to assume similar loading within the Fuselage.

With limited reporting of injuries and limited conclusions therefrom, little is known by the public relative to the passengers and the actual mechanism of impact/entry.

edit to add the most salient conclusion. The BEA imply "seated throughout the cabin". Fine, but that would eliminate a prior belt malfunction. Instead it would speak to the survivability of the wreck, and belted passengers proven via injury assessment. It also requires a subsequent belt release, as no chairs survived to be recovered. Does not add up. The Pelvis can fail in any number of ways, as can compression of the Spine be caused in different body aspects to acceleration. The conclusion lacks a foundation at least, if it exists, it is not presented.

Last edited by bearfoil; 8th Sep 2010 at 18:30.
 
Old 8th Sep 2010, 18:20
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Svarin,

I believe it's unlikely very many pax left their seats due to "inadvertant seatbelt release."

However, the QF72 Nov. 2009 2nd Interim ATSB TRANSPORT SAFETY REPORT does state that "At least 60 of the 303 passengers were seated without their seatbelts fastened..." That's about twenty percent unfastened during a Singapore to Perth cruise. Could we expect similar proportions for an AF447 Rio to Paris cruise? With quite a few unsold seats on AF447, how many PAX may have been stretched out across two or more unassigned seats for sleep, and were at best but loosly belted?

More from the QF72 report:

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).
GB
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Old 8th Sep 2010, 21:26
  #2149 (permalink)  
 
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slats11 wrote:-

I wonder what the vertical descent rate really was. I think we will do better to estimate velocity and calculate a probable acceleration rather than the other way round.
I posted something similar a few pages back -
  • On 22 October 1963 a BAC 1-11 G-ASHG entered a deep stall during a prototype test flight. The aircraft descended from FL180 to the ground over Cricklade, Wiltshire in 80 seconds - 13,500 fpm [133 knots]. Horizontal velocity at impact was effectively nil, as the aircraft belly-flopped and burned in-situ.
Post #2067 was a rehash of an earlier post and had both the vertical and horizontal velocity components doubled. I'm not happy with those velocities and believe that 75KT and 13,500 fpm is probably closer to the mark.

There has been speculation in this thread that AF447 stalled a number of times during its descent, which could explain the nominal FL350 to terra oceania time of 5 minutes. This assumption of a stall(s) has developed as a result of discussion around a "Pollution Spot" located at 2°43.5'N 30°30.5'W by satellite radar imaging some 30 hours after the LKP time.

Bearfoil
From BEA Interim Report #1:-
  • The tail fin was damaged during its recovery and transport but the photographs available made it possible to identify the damage that was not the result of the accident. The middle and rear fasteners with the related fragments of the fuselage hoop frames were present in the fin base. The distortions of the frames showed that they broke during a forward motion with a slight twisting component towards the left.
  • Observations of the tail fin and on the parts from the passenger (galley, toilet door, crew rest module) showed that the airplane had likely struck the surface of the water in a straight line, with a high rate [of] vertical acceleration.
Underline is mine.

mm43

Last edited by mm43; 8th Sep 2010 at 21:43.
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Old 8th Sep 2010, 21:55
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slats11, consider that at least on some planes the seat bottom cushions are designed for flotation. 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.

That has me wondering "where are the cushions that should have floated?"
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Old 8th Sep 2010, 22:08
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slats11, something else besides acceleration is worth considering, the rate of change of acceleration or "jerk". That is what whips the head around on thrill rides, for example. A person can set muscles and adapt to some levels of acceleration. But if it's that same acceleration limit and rates of onset well below a second the sudden change in acceleration is acting on a rag doll. Jerk is why railroads use transition curves on mainlines to minimize the onset rate of the curve's radial acceleration.

Then consider that the seats are not in any way designed to support the body safely in a sudden onset vertical acceleration the broken pelvis becomes believable modulo just how it broke. It's a strong structure. But it's not all THAT strong.

Meanwhile the back is to some degree supported by the seat back so pressure would tend to remain more or less straight down the backbone, particularly with a sudden stop from a mostly downwards and slightly forwards motion.

So I'd but invest too much in pelvis broken and backs not totally wiped out. The accident investigators have seen this sort of injury before and probably have a pretty good idea what causes it.
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Old 8th Sep 2010, 22:16
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FF, bodies sink. Then after they start to putrify the gases produced provide floation. So they come back to the surface. The colder the water the longer time they stay under water. Then after they've been on the surface awhile they sink again.

This is supported by there being no visible bodies until several days had passed.

So presuming the VS and the bodies were subjected to the same drift currents is a mugs game.
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Old 8th Sep 2010, 22:16
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That has me wondering "where are the cushions that should have floated?"
I wonder why much more debris was not spotted, or recovered. It appears that the airplane sunk very rapidly, simular perhaps to Air Florida at MIA, leaving very little on the surface. So little, that first responders could not locate the airplane, despite very reliable electronic information and vectors.

As to belted or not, I believe at the onset of LOC that whereever an unbelted pax was if thrown from his seat, is where he remained until impact, be it on the ceiling or on the floor. I doubt full information regarding injuries has not been forthcoming, which begs the question can what has been released be relied upon to base conclusions.

Getting into September - awaiting BEA info on a continuation of the search?
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Old 8th Sep 2010, 22:38
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Auvee, Google to the rescue. For some reason at least one of thee mssages seems to be suppressed by moderators. But it can be found from the Google Cache. Ah it's on the preceding page now unsuppressed. So that will allow reading forwards and back with some context. The poster's ID is Kulwin Park.
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Old 9th Sep 2010, 01:18
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Its a little hard to know for sure how the seat belts will cope with these sort of excessive forces. They are designed to serve their purpose - to reduce injuries in a survivable crash, not to restrain bodies exposed to forces far greater. But I doubt that there were a lot of belt failures.

A high proportion of unrestrained pax midflight is common. But probably not if there was a gradual increase in turbulence. Moderate turbulence will wake people up, and pax will be advised to put their belts on. In my limited experience of turbulence, most pax are pretty nervous and quick to comply.

No Mayday. No life jackets. Lots of possible explanations. But a common explanation (and one explanation that fits is more likely than lots of different explanations) is sudden and catastrophic loss of control. This situation would also be expected to result in lots of unrestrained passengers - which I believe is what we have here.

The seat cushions when removed from the seat do provide limited flotation. I think they are a legal option on non-overwater flights???? But I doubt that a row of seats with bodies attached would float. I would imagine this would sink fairly quickly. Something that can easily be tested however. Certainly there were not many seats recovered, and there were plenty of empty seats on that flight. A floating seat would be a much easier target to spot than a semi-submerged body, so I suspect they sank. Very limited positive buoyancy of some bodies will not keep the seats afloat.

Bodies themselves vary. Some float, some sink - depending mainly on fat content, whether the lungs filled with water or not, and clothing worn. A person dying at impact is more likely to float than a person who survived impact and subsequently drowned with water filled lungs. Sometimes a sunken body will refloat - but not always. Gas does form in the gastrointestinal tract, and this will create some positive buoyancy. But this gas formation is variable. Sometimes the body will belch (sorry) and this buoyancy will then be lost. The pressure of the gas will simply overcome the passive resistance of the esophageal sphincter. Sometimes the gas will be retained. It is actually a very fine balance - not surprising given we are mostly water, and the denser and less dense components pretty much cancel out. Try it swimming sometime - a few hundred ml more or less in your lungs affects whether you sink or float. Same with SCUBA - it doesn't take much extra weight belt or gas in your chamber to alter your buoyancy.

I can see wave action dislodging a body from a seat on the surface. Not after it has suck however - the seat and body will drift as one with the subsurface current.

On 22 October 1963 a BAC 1-11 G-ASHG entered a deep stall during a prototype test flight. The aircraft descended from FL180 to the ground over Cricklade, Wiltshire in 80 seconds - 13,500 fpm [133 knots]. Horizontal velocity at impact was effectively nil, as the aircraft belly-flopped and burned in-situ.
Thats 70m/sec. So if deformation allowed decelleration of cabin contents over 10 or so metres, figure a force around 25G. That sounds more likely than figures of 100G. Clearly still non-survivable, but perhaps more consistent with what we are seeing.
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Old 9th Sep 2010, 01:36
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... and we could also postulate that most of those found might have been in one section, that happened to experience less ultimate 'G' than others.
Except that they appeared reasonably spread throughout the cabin.

What was most important, the section they were in (or visiting at the time), or the fact they weren't in their seats?
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Old 9th Sep 2010, 01:54
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Meanwhile the back is to some degree supported by the seat back so pressure would tend to remain more or less straight down the backbone, particularly with a sudden stop from a mostly downwards and slightly forwards motion.
I think the body would have flexed forward with impact - assuming it wasn't already as per brace position. There was some forwards movement which stopped with impact. I know we have been talking about lowish forward vectors, but it would still represent a reasonably high speed car crash. Plus the top half of the body had to go somewhere when the bottom half stopped. It had a lot of momentum, the body can't simply telescope downwards into itself, and the muscles would not be sufficiently powerful to stop this forward flexion.
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Old 9th Sep 2010, 01:55
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JD-EE, thanks for the link to the old thread. However, on reading Kulwin Park's post, he does not really say anything about bodies slipping out of seat belts. I now consider this a somewhat doubtful possibility, except where accompanied by seat or belt failure.

--

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. Something that is very slightly negative can reach equilibrium in mid-water (water density increases slightly with depth), but that is hard to arrange on purpose, and not likely to happen by coincidence.
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Old 9th Sep 2010, 02:10
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Hello. Just a couple notes. None of the victims drowned. This does not preclude wet lungs, but the chances are the lungs remained empty. Salt Water will elevate a typical body, it is denser than fresh. The Surface may have had a degree of aeration, from wave, swell action, and also the disturbance of the a/c impact. These considerations are not emphatic, but must be utilized.

Harry Mann

Neither the section nor the unseated part. If unseated, they remained unseated and unbelted, yet BEA claim "Seated injuries". "Vertical compression...etc." This is not consistent with logic. Those seated were simply not recovered, and those recovered were not seated, hence no "Seated injuries."

The "Removal from Seat belt"? Probably a reference to something altogether different, wave action in the removal of clothing. Postulates that pax may have been ejected from a holed hull at altitude brought out someone who remembered Comet, and the Mediterranean crash where unclothed passengers were recovered.
 
Old 9th Sep 2010, 02:13
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This is supported by there being no visible bodies until several days had passed.
I am not suggesting the bodies didn't sink. There was also no confirmed sightings of any parts before June 5, with a body being sighted before the VS so I guess one can also follow this logic and find support for the notion that the VS didn’t surface till after the first body. Or perhaps it merely confirms that if you look in the wrong place you don't find anything.
My original analysis was merely to suggest IMO that there is a high probability that the impact point was related to the slick. The last comment was answering the query re the VS drift.
FF
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