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AF 447 Search to resume

Old 6th Sep 2010, 00:47
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bearfoil
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mm43 I believe the a/c was in Aternate Law almost immediately, and #II at that. RTLU is auto at reversion, and will not release more sweep until Flaps/slats aiui. It also is not possible to reacquire Normal Law until landing and re program. A complete failure of all tail components is entertained at impact. Consider the Crew Rest capsule. (treated below) If sufficiently left un snubbed by hydraulics, Rudder flutter could happen at almost any speed above the Stall. The definition of flutter would be strained at lower speeds, consider for now that the Rudder "vibrated" rapidly from max. aero pressure then back again.

JD-EE The "tail breaking just aft of the cabin's end, leaving intact the pressure vessel". The vessel is quite strong in resisting higher pressure inside. Failure would involve failing the longerons in tension, and the skin in shear combination tension. The aft bulkhead is a threat in reversal of pressure, as the vessel is not necessarily purposely considered in collapse. It is a stout "plug" if subjected to positive outside pressure, or a combination with aerodynamic and high outside pressure. It is difficult to consider the tail being thoroughly corrupted, and the Aft bulkhead remaining integral to the Fuse.

OE In the salt water long enough to muddy the fracture, a clean break is certainly possible, but perhaps not conclusively demonstrable. Follow me here. For the tip of the Arm to break in its intended fashion is to imply a specific stress path. This path is more indicative of vibrational or fatigue loss, rather than fracture, to wit: Vertical load imparts a tension on the Arm via a "pull" from the Hinge tower. this enters the Bolt, which must then push on the tip. Some dimensional leeway is assumed prior to fracture, yet again, the seal/resin, seat of the bolt on the Spar side appears ignorant of great stress. The Bolt would be the architect of tip fracture, but as I say, there doesn't appear to be any evidence of "movement". Hence the vibration or corrosion/fatigue model would apply. (subject to metallurgy and much closer inspection.) Your statement that you see evidence of lateral movement damage is what I claimed earlier, when criticizing the "Lateral rods".

HazelNuts39 I don't know the A400m, but notice a shift in thinking relative to the VS. There are 4 pair of Brackets, eight clevis pins. Take note of the "Eyes" at the bracket tops. Pair 1 and Pair 4 have much thicker eyes than the two center hold downs/brackets. .....447 impact: I think I see the exchange of energy now as a continuum, though certainly happening at rapid speed. I also think that the Horizontal velocity was kept alive until the nose dropped beneath the waves, making the Horizontal component more energetic than if a nose sub is not taken into account.

Crew Rest
I have looked at great length at the crew rest capsule. From a theory of tail, midsection, nose entry, I think I can hazard an opinion of what happened in the hold. The capsule appears to have an envelope of laminated skins of Aluminum. My guess would be two laminae, with a powerful adhesive joint to make a strong ratio of strength to weight. (The adhesive has the characteristic color of a phenolic resin, but that remains open.) The damage to this skin is more involved than simply being crushed between the Belly and the Cabin floor as the Fuselage flattened on to the surface of the Ocean. The Rest, if enclosed at impact, we may have three separate compression/decompression cycles. first, the Hold flattens out, reducing the volume of its structure, and pressurizes the rest capsule to some value higher than ambient Hold in Fall. The capsule may have held for a short time (even if not "pressurized").

As the Cabin floor comes crashing down on the hold and its contents, the capsule is overpressured, and expands (perhaps even explosively). The damage to the skin of the capsule is certainly rip/tear, but the damage also shows, via the delamination of the skin, that there was an explosion of some great force. Not at all a chemical or other type of explosion, but similar to a scuba tank or pressure cooker failure. Very energetic.

henra If horizontal speed was maintained, perhaps in a skimming reaction, the nose dropping into the water would create a substantially larger acceleration to the VS than previously entertained? Perhaps approaching the 66g?

bear

Last edited by bearfoil; 6th Sep 2010 at 01:09.
 
Old 6th Sep 2010, 04:20
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Bearfoil wrote:-

mm43 I believe the a/c was in Aternate Law almost immediately, and #II at that. RTLU is auto at reversion, and will not release more sweep until Flaps/slats aiui. It also is not possible to reacquire Normal Law until landing and re program.
Yes, I fully understand the RTLU lock at Normal to Alternate Law and the slats extension to clear the RTLU locked position.

What I am seeking is clarification that RTLU WRN message will be generated at Law change. It seems like more information overload (e.g. Wind Shear Fault WRN at FL350!) and in that respect I suspect that a rudder pedal depressed and held created the reason for it.
A complete failure of all tail components is entertained at impact.
I agree with that.
If sufficiently left un snubbed by hydraulics, Rudder flutter could happen at almost any speed above the Stall. The definition of flutter would be strained at lower speeds, consider for now that the Rudder "vibrated" rapidly from max. aero pressure then back again.
That part I do not agree with. Let me put it this way.
  1. I don't believe the rudder was damaged at altitude.
  2. Damage occurred during the impact phase.
  3. The horizontal velocity component was relatively low.
  4. Departure of the V/S and Rudder was due to a complex combination of forces -
  • Aerodynamic to terra oceania.
  • Reactive buoyancy moments.
For instance the rudder's bottom damage is possibly a combination of the tail-cone/APU exhaust pipe being deflected into it and the rudder slamming hard-over to port as the hydraulics let go. There is absolutely (IMO) no signs of trailing edge "flutter" damage to be seen.

Initial bottom up compression through the aft frames compounded by the V/S downward thrust weakened the No.2/3 clevis mounts sufficiently for them to be torn out as the V/S rotated forward. Likewise, the No.1 mounts suffered a similar fate, but the lug mounts were ripped from the V/S as it rotated forward and to port. This indicates to me that longitudinal continuity still existed between the empennage and the fuselage forward of the aft pressure bulhead (frame 80) as this detachment took place.

No high speed impact damage with water is evident to the V/S composites as was noted on the Outer Spoiler.

NOTE: (IMO) I'm not so sure the horizontal impact velocity was even 100 knots. Recovered items, e.g. galley, toilets etc.. don't indicate that sort of speed. This was no "skipping stone" impact. The aircraft dug a watery hole and rapidly came to a complete stop, though then subject to the reciprocal buoyancy moments that completed the cycle of damage.

mm43

Last edited by mm43; 6th Sep 2010 at 10:59.
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Old 6th Sep 2010, 07:31
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''High vertical speed''

Hello!

Would be possible from the structural analyze of recovered parts to have a fair estimation of energy/speed (particularly vertical speed) at impact - a generally accepted value or a range , and then to make scenarios regarding pre-impact evolution of aircraft?
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Old 6th Sep 2010, 11:04
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A400M cargo door

Originally Posted by bearfoil
HazelNuts39 I don't know the A400m, but notice a shift in thinking relative to the VS. There are 4 pair of Brackets, eight clevis pins.
The A400M carries outsize loads such as helicopters, heavy engineering equipment and armoured vehicles that are too large or too heavy for current tactical airlifters. It is powered by four turbo-propeller engines, has a straight shoulder-mounted wing and a T-tail. The rear fuselage is a big hole covered by a load-carrying ramp that allows large vehicles to be driven into the hold. I really think you should click on the link and scroll two screens down to see a view of the cut-open fuselage, and the need for 'a shift in thinking' will be immediately apparent.

regards,
HN39

Last edited by HazelNuts39; 6th Sep 2010 at 21:55.
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Old 6th Sep 2010, 19:48
  #2125 (permalink)  
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mm43 You pose an interesting question. I consider ACARS a system status report/Log, intended for the a/c base. RTLU WRN. falls within that milieu, it can be assumed (can it?) not to be a pilot alert. Of the more salient data in the ACARS log, TCAS and RTLU seemed initially to be more alarming than a/p drop. Their direct relationship to the crash may escape one, but they tell a tale.

A working theory is that A/P disconnect and Law reversion signalled the initial response of ACARS to upset, not the beginning of a trail of fails, but the deluge of data needing to be sent to Mx. As has been noted many times, A330 Autopilot has a responsibility to maintain control up to its manouvering limits. I submit that the limit was reached as a result of upset, not at its beginnings.

TCAS depends on a/s, Rudder on Law. I don't think the pitots and statics crapped out as a result of simultaneous icing, but instead did not crap out at all, their individual reports may have been consistent with airflow in unusual attitudes. Simultaneous failure (icing) would it seems to me be dependent on a consistent airflow, and temp.; At least one to facilitate a sudden icing of all sensors.

Given a simultaneous icing, there would also be no discrepant readings, right? They would be wrong, but each reasonably to be expected wrong in unison (at the same rate). If ice was not simultaneous, TCAS is expected up front in the cascade of warnings. Law change follows a/p autonomous quit, but AL II? I do not know this.

I am not persuaded that RTLU WRN wasn't a malfunctioning limit, not the acquisition of reverted and mechanical limits. Again, if the RTLU was operating correctly, why would ACARS "WRN" maintenance? Even had the 16 degree lock been working, If god forbid any Rudder was input, the potential for airframe damage at this speed is clear. I think there was substantial tail failure at altitude, a beginning at least of tailplane and VS complete loss. The THS was full of 10,593 pounds of fuel, and the Rudder had 16 degrees of sweep available. If upset occurred prior to a/p loss, it is more likely damage occurred in flight, than not, but certainly as a precursor to water impact. Thoughts?

edit: This before even broaching a Windshear WRN at or about upset!! Caveat! ACARS makes for a lousy FDR.

edit: It is unlikely the a/c did NOT bury her snout. the mass is concentrated well forward of the tail, no? This would all but stop her forward momentum.

bear

Last edited by bearfoil; 6th Sep 2010 at 20:02.
 
Old 6th Sep 2010, 23:35
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Bearfoil

On further reflection and re-analysis of the BEA Interim Report No.2, I am now persuaded that 0210 cockpit effect messages were displayed solely as a result of the conflict between the ADIRUs which meant that data required for their updating was no longer valid or available. The modified graphic from Interim Report No.2 reproduced below tends to support that.



Which means that with ADM/ADIRU inputs from the 3 x pitots in disagreement, [F/CTL RUD TRV LIM FAULT] that the RTLU no longer had valid input and on reversion to Alternate Law was now locked. The Reactive Wind Shear fault [AUTO FLT REAC W/S DET FAULT] was displayed for a similar reason and would no longer be available at around 2,500 feet. In fact all the Cockpit Effect Messages timed at 0210 were all related to the same cause and advised of appropriate changes as they had no valid inputs.

Some of these messages do look like "information overload", but when considering that they could happen at any stage of the flight profile, it was deemed safer to display them rather than applying a filter.

So in summary the message displayed needs to be considered in the context of what triggered it, and I have now convinced myself that the RTLU WRN was not as a result of crew action.

EDIT:: The TCAS fault has been identified [by me] in the graphic, and is directly related to the other 0210 Cockpit Effect Messages.

mm43

Last edited by mm43; 7th Sep 2010 at 21:52. Reason: replaced graphic
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Old 7th Sep 2010, 03:01
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Pitch on impact

mm43. With reference to your pic in post 2067 http://www.pprune.org/5902693-post2067.html if AF447 comes in at a much higher pitch it is easier to get the water into the tail cone to bend the frames backwards (after failing underside skin, and perhaps the pressurising bulkhead) and pop off the VS due to water pressure, bending frames, as well as the vertical loads from the tail cone impact. Also the water pressure on the hull due to impact is always virtually perpendicular to the ‘cylinder’ so a high pitch and relatively high ‘forward’ speed stills gives the damage impression of landing with high ‘vertical speed’ with a ‘low’ forward speed . In this case there is also a short 'horizontal' deceleration as the horizontal stabilisers hit the water and the tail cone skin is torn and water penetrates the cone.. This provides the ‘forward damage of the A/C internals’, tears off the tail cone (trim tank sinks here) and allows the rest of the plane to go a relatively long way to form the ‘incoming’ leg of the slick albeit after loosing a large amount of forward velocity due to this tail cone failure.
Nothing new here, just interested in why the pitch on impact is not considered to be much higher.

FF
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Old 7th Sep 2010, 03:27
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FluidFlow

Like your illustration!

The BEA observed -
  • The aircraft was probably intact on impact.
  • The aircraft struck the surface of the water with a positive attitude, a low bank and a high rate of descent.
  • There was no depressurisation.
They also mentioned that there was a left-right symmetry of compression damage throughout the length of the aircraft. For that reason, I feel that their description of "positive attitude" didn't imply anything dramatic, and I opted for +5 degrees. Also, if the airframe had ruptured abaft the main wing with a high forward velocity, the chances of the symmetrical bottom up compression damage to the forward section would be remote. I believe that a "cartwheel" type of breakup would then have occurred.

As usual, I could be wrong, and your suggestion is well worth a look.

mm43
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Old 7th Sep 2010, 09:04
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Another way to look at things


Consider this side view of an A330 Tail as taken from the Second BEA Interim report. Imagine that the aircraft is impacting on its belly with approximately 100 knots of forward speed and 100 knots of vertical velocity.
The following breakup scenario is speculative but I'm offering it to illustrate the complex way energy can be transmitted to the structure when you look at very small time intervals.

As the belly of the aircraft begins to make contact with the surface, the relatively stiff wing center section decelerates very rapidly because its area of contact expands rapidly and it vertically decelerates the aircraft fuselage section above it, causing the fuselage to bend downward both ahead of and behind the wing. As the wing begins to submerge, its forward velocity is braked as well and this deceleration causes the wing to pitch downward from the mass of the fuselage section above the wing. This pitch down reverses the bending moment on the forward fuselage ahead of the wing and tears through the crown of the aft fuselage behind the wing.
Now lets consider what is happening to the aft fuselage.
The aft fuselage is now weakly coupled to the center section, probably mostly by the floor and some of the belly skin. The cargo compartment has largely crushed upward absorbing some of the vertical kinetic energy. The aft pressure bulkhead has no such cushion below it, and as it contacts the surface, it trasmits considerable force up to the forward pair of rudder attach lugs. The VS begins to tilt aft and fail aft of the forward lugs as the fuselage begins to shear aft of the pressure bulkhead. About this time, the THS makes contact with the surface and initially vertically decelerates the aft two sets of lugs to which it is still attached by virtue of Frame 91 structure and then begins to horizontally decelerate the bottom of the broken segment aft of the rear pressure bulkhead as the THS submerges and is torn from its mountings. The aft motion imparted by the THS as it detaches gives the remainder of the tail a sharp rotation which throws the VS in a forward direction. The structure torn off by the THS tears off the bottom of the rudder at an upward angle in its departure from the aircraft.
The above sequence is just a scenario. It should meet most of the findings of the BEA investigators regarding AF447, but I have no doubt it also overlooks critical data and needs additional detail.
The inexorable crushing and tearing apart of an aircraft as it meets a virtually immovable object (the ocean surface) can be quite complex when you start to look at happenings in the milli-second time frame.
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Old 7th Sep 2010, 10:39
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What was meant by BEA in talking about low forward speed and high vertical descent rate? When I first read it, I took it to mean low forward speed compared with the normal cruise, and high vertical descent rates compare with the normal approach descent rate.

I certainly did not take it that the vertical descent rate could be as high or higher than the forward speed on impact.

Could the relatively undamaged state of the internal rack/cupboard be consistent with a vertical descent at hundred knots? Is the damage to the recovered bodies in any way indicative of such a relatively high descent rate?

Chris N
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Old 7th Sep 2010, 14:52
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Descent rate

Is the damage to the recovered bodies in any way indicative of such a relatively high descent rate?
From p. 32 of the English version of the Interem Report No. 2:

---- START QUOTE ---
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.
---- END QUOTE ---
(my italics)

Sounds to me like high vertical acceleration in all parts of the cabin.

Maybe someone with medical knowledge could comment on how much acceleration had to be involved?

Last edited by PickyPerkins; 7th Sep 2010 at 17:05. Reason: spelling
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Old 7th Sep 2010, 15:43
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Hard to give anything more than a semi-quantitative answer to this.

Compression fractures of the lumbar spine are relatively frequent in pilots ejecting from fighter jets. Typical forces involved here are in the order of 12 - 14G. The bony pelvis would be expected to withstand these forces. Note however that:
a) we are talking about young adult males (20-30's) where bone strength is at a peak
b) these pilots are wearing a harness
c) the seats are engineered to deliver this vertical acceleration as safely as possible.

Very different in a commercial airliner - heterogeneous population, lap belts only, in seats not designed for this vertical acceleration. So you certainly would start seeing some compression fractures at much lower forces.

If you were talking about a fall and landing in the sitting position, it would take a fall from at least a couple of metres onto hard ground or concrete to cause vertebral fractures plus pelvic disruption in a young adult male (and obviously a significantly higher fall if landing on legs as decelleration will be more gradual). An elderly person can suffer the same injuries with a fall from the standing position.

Not sure that this helps much however. Without knowing over what distance the vertical speed was reduced to zero, you can't really estimate vertical velocity even if you can take a good guess at the peak acceleration.
v squared = 2as, so you need a good estimate of s and a in order to even guess v.

Also, it is almost certain that a was NOT constant - injury pattern (sort of) correlates with peak a rather than average a.

Last edited by slats11; 7th Sep 2010 at 16:05. Reason: typo
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Old 8th Sep 2010, 03:49
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I certainly did not take it that the vertical descent rate could be as high or higher than the forward speed on impact.
Nor I, assuming (like you) that the statements were comparative (to a normal descent), just enhanced values of vertical and typical or somewhat less than normal horz component...

One really cannot read too much into such subjective statements.

===

With the VS separation analysis now proceeding to this high level (of credence), it seems on balance then, that the airframe was substantially intact at impact - and that the exact break-up sequence on impact can never be fully simulated/modelled. Any impact angle and velocity that results in a separated VS, with similar support structure damage, is acceptable... there may be more than one set that fits the bounding conditions!

What matters, next... review the VS drift again making the assumption it originated at the crash site. Can that correlate with the estimated backtracked position of the slick?
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Old 8th Sep 2010, 04:05
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I do certainly agree. A reasonable starting point (visualization) might be the impact of the 737NG at Schipol. A forward velocity insufficient for aerodynamic flight, and a vertical rate in excess of merely standard rates. 2-3,000fpm? The fuselage broke into three parts, a rather common result A result probably unlike 447's might be Afriqiyah.

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Old 8th Sep 2010, 04:13
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From BEA Interim report #2
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.
Fractures of the pelvis combined with compression fractures of the spine point to much higher levels of vertical acceleration than experienced in an ejection seat. Yes, airline seating is sub-optimum to support the human body and probably contributed to pelvic fractures. There are other injuries one would expect to see associated with very high g levels. See this student research paper for a general idea of the g levels associated with lethal levels of acceleration: Acceleration That Would Kill a Human
In actuality, fatal human g levels in the vertical axis are lower than with fore and aft acceleration for reasons related to the content of the next to last sentence.

Last edited by Machinbird; 8th Sep 2010 at 04:33. Reason: To correct a sentence reference
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Old 8th Sep 2010, 04:23
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Two thing that have always struck me odd about this are the number of bodies that were found, and the absence of life-jackets.

Seat belts don't fail - they will carry you to the bottom. Those bodies that were found were therefore presumably not restrained and were able to float free of the disrupted cabin as it sank. There were more unrestrained people than you would expect in moderate turbulence with "all passengers and crew returned to their seat with seat belts fastened". There were almost certainly more unrestrained people than bodies found - some bodies were simply never found or sank over the following days.

To me this suggests that the interval between normal mild turbulence (with people still walking around the cabin or seated without belts) and sudden loss of control (which incapacitated people such that they could not get to any empty seat) was very short. And that control was never regained.

Also the life-jackets. Hard to believe that no one had a jacket on if there was any semblance of control on the way down. The crew would have told people to put jackets on, and some would have - some likely would have even in the absence of any instruction. They would have all known that it was the middle of the night in the middle of an ocean. Again, maybe the loss of control was so serious and so sudden that no one had an opportunity to put on a jacket over the following minutes. Hard to imagine, but it is difficult to support any other conclusion. I have seen speculation that it was an attempted ditching, or they were recovering control and lost visual reference and ran out of space. If either of these were true, I think we would have seen some jackets.
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Old 8th Sep 2010, 04:35
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Fractures of the pelvis combined with compression fractures of the spine point to much higher levels of vertical acceleration than experienced in an ejection seat.
Correct. Maybe I was not sufficiently clear in my earlier post.

Ejection seats will sometimes cause lumbar vertebral crush fractures but certainly not a fractured pelvis. Not in a young adult male anyway.

At even lower G levels than an ejection seat, you might find a few fractures among a couple of hundred heterogeneous people on a passenger aircraft. However the very high prevalence of these injuries among the recovered bodies here does suggest much higher forces than this.
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Old 8th Sep 2010, 05:09
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slats11

Your conclusions relative to seated/belted, and lack of jackets are well founded. The upset, by this logic, was sudden and led to a chaotic "g" environment from the outset. I too believe the "seated passengers" stretches credulity, it is too "pat". Any pax belted in at the onset of upset would have remained so, unable to release their lapbelt, even if they were alive to do so. I believe no belted pax were recovered here. The pelvic saddle is subject to disarticulation as any joint system is, but the Sacrum, Femur processes, and Ilia are the strongest part of the skeletal structure. I venture to say that any human frame left to bounce about the fuselage would have injuries consistent with flail, impact, and soft tissue ablation in the extreme. BEA have isolated these "Pelvic" trauma as though the victims recovered suffered only this, no other. A crepitous spinal column is virtually impossible without accompanying severe trauma, here, left w/o description. Of those recovered, "42" had remarkable "trauma while seated". The others were not described, their injuries were not as extensive? Unbelted pax were recovered, yet 42 of the 53 were "seated". No, I think. No one regained his/her seat after upset, let alone rode this a/c down unbelted and in their chairs, to suffer "vertical impact". This wants more explanation, with the evidence assembled, I should think.

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Old 8th Sep 2010, 05:28
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VS drift

What matters, next... review the VS drift again making the assumption it originated at the crash site. Can that correlate with the estimated backtracked position of the slick?
Cant do exactly that due to lack of info. But the VS was sighted 4.1Nm south and recovered 5.3 Nm south of the ‘body drift centreline’ with respect to time. It was sighted 9.2Nm west and recovered 14.2Nm west of the ideal body centreline (noting there was a large fanning out by this stage). It does show the VS moving west relatively quickly (4.95hrs and 5.1 Nm or 1 knot different to a body) so appears to suggest that there is a reasonable (? or perhaps statistically irrelevant) probability that the VS did not enter the water west of the impact site. (The assumption here is that they were both at the slick 30 hrs after the crash which is also unlikely to be exactly correct – cant to the maths otherwise).
IMO this implies the VS was still attached until impact or very close to impact but the maths is not strong re this point and perhaps not even relevant. The bending of the frames below the VS mounts is likely stronger evidence the VS fell off due to its foundations being damaged by water pressure than this drift ‘evidence’.
FF

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Old 8th Sep 2010, 06:00
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Thats my take on it Bear. Sudden and complete LOC.

Those strapped in were incapacitated, died at or before impact, and are still strapped in. Those not restrained could not get to a seat, nor don a jacket and suffered major injuries either before or at impact. That many non-restrained (at least as many as bodies recovered) suggests passengers were not advised to strap in.

This scenario also explains why no Mayday. It was that sudden and that bad.
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