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AF 447 Search to resume (part2)

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AF 447 Search to resume (part2)

Old 29th Apr 2011, 19:06
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Thanks Machaca, superb illustrations yet again.

PJ2, looking at the BEA APU picture, is it possible that the exhaust cone has deformed under impact? difficult, very difficult to say due to the debris around it.
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Old 29th Apr 2011, 19:16
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@deSitter

No question it's the APU, obvious really. The airplane is torn all to hell. I don't see how this is possible without a high speed impact
.

Don't underestimate hydraulic damage, particularly if the object is impacting in excess of 70M/s. Take a look at the bulkhead damage for US Airways Flight 1549.

http://www.ntsb.gov/Dockets/Aviation...026/418716.pdf
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Old 29th Apr 2011, 20:43
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Machaca - excellent work!

BJ-ENG;
Don't underestimate hydraulic damage, particularly if the object is impacting in excess of 70M/s.
I agree.

Hatches in the bottom of the aft fuselage and tailcone structure provide a naturally-weak entry point for tremendous upward-directed hydraulic forces; - Forces which, throughout the length of the fuselage would "peel back" skin from their frames & ribs, weakening the entire supporting structure and providing essentially unimpeded exits for that which was recovered days later, all this occurring in the first few milliseconds.

I would have thought that the results of such high impact forces between water and an essentially-frangible hollow tube with heavy, specifically-located structures such as engines, landing gear, wing-boxes, spars and APU, would have been obvious but perhaps I am mistaken and that the violence of such a collision is being under-estimated.

For a notion of airframe fragmentation after a high-forward-speed impact one need examine just two examples: - the Turkish DC10 high-speed impact at Ermenonville, France, (450kts IIRC), and the SR111 MD11 impact (300kts) with the sea as another.

deSitter;
Here, not only what was recovered on the surface several days later, but what we thus far are permitted to see, if only dimly through remarkable photography of the site, is not "fragmented".

An entire wing section, (starboard) exists, with gear still attached; cabin structure is recognizable. When an entire galley unit, F/A seats, hundreds of parts of cabin material, doctor's kit, defibrilation kit, remain, the impact is not high-speed as seen in the two (of many) examples above.

In fact I posted links to the China Airlines A300 accident at Nagoya for this reason, and another poster cited the Afrikiyah A330 at Tripoli - both on hard surfaces. There is fragmenation, but not the kind one expects or sees in a high-speed impact.

I think it is reasonable to conclude at least, that this was not a high-forward-speed impact. I think an engineer's view of both structure and impact forces must be taken seriously at least until further evidence may lead us away from such an understanding.
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Old 29th Apr 2011, 22:18
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Given that the BEA state that the memory module is not present under the DFDR chassis, they must presumably have had the submersible round the other side at some point to check. Any smoothness of the seabed just there could easily be due to the submersible's thrusters when it was round the back. Really, there are far simpler explanations here than any conspiracy theory.
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Old 29th Apr 2011, 22:57
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I see three possibilities for the DFDR memory module after breaking away on water impact:
  • Unencumbered free fall
  • Entanglement in another component
  • Being covered by another object once on the bottom.
We don't yet know if small dense objects would bury themselves in the bottom on final impact. That depends on the composition of the ground. However it seems that other dense objects have not dug themselves in deeply.

I expect a complete visual search of the area will be the next step in the hope that the memory module is not covered or entangled by a larger piece.

Lifting components from the tailcone may be especially problematic as there is a possibility that the memory module could fall out; so, it would first be necessary to place each component over a net to catch bits that might fall out during the hoist. You want to close the scuppers before releasing the net on deck as it would not do for a certain cylindrical object to roll away back into the deep
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Old 29th Apr 2011, 23:30
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There have been distractions in nearby London today...

Catching up, I notice that the BEA now makes reference to the CVR memory module also being missing, though I don't recall any mention of its chassis, which someone earlier said is mounted on the forward side of the aft pressure bulkhead, the other side of it from the DFDR?

Looking at Machacha's images, am reminded how far aft the APU is of the tailplane. My initial thought that the DFDR memory module might lie close to the heavy APU fails immediately, as the aft pressure bulkhead is presumably forward of the forward tailplane spar. (Does anyone have a cutaway to hand, and is that correct?)

Is it a fair assumption that the APU-containing tailcone, being aft of the tailplane, would have sheared off on impact? I think PJ2 proposed something on the lines that the tailplane deceleration on impact would be great, causing the fuselage to fail forward and aft of it?

Quote from the BEA today:
"The forward and aft parts of the airplane are broken apart and mixed up, which means that a time-consuming systematic search is required."
Sounds a nightmare, but they must have known that once the thousands of photos from Phase 4 had been perused.

Do we know the medium used for the QAR cassette? Is it a "magneto-optical disk" and, if so, is that about as accident-proof as a DVD disk?

By the way, we owe young HeathrowAirport a response to his/her idea that the module memoire might float.

Excuse these somewhat rambling jottings.
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Old 29th Apr 2011, 23:55
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By the way, we owe young HeathrowAirport a response to his/her idea that the module memoire might float.
I don't think it can float. Part of the thermal protection system involves a significant mass of metal which acts as thermal inertia for the memory modules. This is inside of the shielding layer of insulation. Then the whole thing is wrapped in a steel canister to protect it against the crash environment. With all that metal, the memory modules should sink like a stone.
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Old 30th Apr 2011, 00:23
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Machinbird;

"Like a stone...", yes, IIRC, the entire SSFDR weighs around 15lbs, and the CSMU is heavily-clad with steel, thermal layers, etc, etc and isn't going to float. It is certified for 30days @ 6000m so hopefully longer at 3900m. Even if compromised, the chips may be in data-retrievable condition.

Chris;

Congratulations on London's "distraction" - a bit of good news among the huge dregs of the other kind.

Re the QAR, it is mounted in the main Equipment rack below the cockpit floor. There are many variations on such an installation. Someone can correct the information if they know for sure, but it is possibly either a 256Mb or more likely a 512Mb PCMCIA card. Given the current impression we have of the nature of the impact and the location of the equipment rack, the survival of the QAR intact is questionable but always worth finding/retrieving as are any cards/memory units from the MCDUs, etc.

Here is a simple diagram of a representative aft fuselage and tail cone structure:


Last edited by PJ2; 30th Apr 2011 at 00:42.
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Old 30th Apr 2011, 00:24
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Originally posted By HeathrowAirport ..

Obviously the CSMU is shaped in such away that it can stay afloat?
Specifications I have seen for the complete SSFDR don't break down the chassis, CSMU and ULB weights. Anyway as it is a mass/volume issue, I suspect that the weight/effective volume of the crash / fire / depth resistant outer steel container will probably exceed 1.025 and floating is not an issue. The attached ULB will probably seal its fate.

If that is not the case, there is a serious design problem.

Last edited by mm43; 30th Apr 2011 at 01:38.
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Old 30th Apr 2011, 00:36
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Black Box Locations

Just musing here. The A330 FDR is outside the pressure vessel, while on the 747 jurassic and other US planes that come to mind, both are inside. Seems from distant memory that the FDR on the BAe-146 was outside. Is there a technical basis for the difference, or just cultural?

I remember early CVR on which the pinger was an afterthought. The pinger was attached to the front of the chassis, not the hard module.

Judging by density and location, I would expect to find the FDR module nearer the APU than anything else.
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Old 30th Apr 2011, 01:38
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When describing reasons for structural damage in an airplane crash. I would first describe the overall speed vector (forward speed combined with downward speed) Then describe the pitch angle (steep versus flat). Then describe the impacting surface (hard vs soft) soft being mostly high water content.

Most of the transport category catastrophic crashes involve moderate forward speed moderate downward speed and moderate pitch into hard surfaces.

Some unique combinations have occured where water has been contacted in mostly flat trajectory and low forward speed. Such as breakup in the air and dropping pieces to the water (TWA800). While other events like Valujet in the swamp were steep impact at high speed into water.

If hard ground is contacted then numerous point contacts are made producing many tears and holes which coalesce into multiple pieces (typical of the majority).

If high foward speed is involved then the oblong fuselage gets splintered as the ribs split at junction points and many small pieces are formed. (makes little difference if it was water or hard since its mostly a point contact on the nose view.

If flat impact is involved with water, hydraulics occur across broad surfaces uniformly buckling the skin against mostly intact ribs until local fractures of the ribs finally give way and the skin is either missing in this area or partially sheared away by the water. It would not be uncommon to expect an oblong fuselage structure to still be smooth and round at the top while the bottom half has completely given way from the hydraulic loads and buckling.

The easiest part to read these kind of evidences would be the inlets to the engines themselves as they often tell the complete story of forward speed, downward speed, pitch and roll.
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Old 30th Apr 2011, 01:51
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PJ2
The BEA 2nd Interim Report states that AF447 had a Honeywell SSFDR 980-4700-42. Information on this recorder may be easily found on the web using standard search techniques. It may help with a few details. The link can't be posted because it is commercial material. The SSFDR weighs about 13 lbs and is mounted between frames 84 & 85 very close to the bottom of the airframe.
Thanks for the information on the recorder. Given that it is solid state, flash memory based, I would be pretty optimistic about being able to recover data if they find it.

I'm not certain how corrosion sensitive the circuit card and supporting electronics are. There could conceivably be corrosion of traces on the circuit board, power supply components, etc. However the individual chips are pretty unlikely to be damaged. They could be removed from the board and read out separately. Even if the leads / contacts on the chip packages are broken, there are still ways to work around it.

So here's to hoping they find it.
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Old 30th Apr 2011, 01:58
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The DFDR seems to sit on a shelf attached to the pressure bulkhead. No part of that shelf appears with the chassis on the bottom.

We also see that the platform that joins the chassis to the memory module has a slight bend up relative to its position when mounted. It may be worth asking how that bend got there. Possibly the lower skin was pushed up by the water, perhaps bending at the bulkhead so that the first hit on the DFDR would be on the portion farthest from the bulkhead. Alternatively an access panel came loose and was pushed by the water against the DFDR housing. That bend in the DFDR platform may have been what popped the memory module loose in the milliseconds before the chassis parted company with its shelf. How the memory module ricocheted inside the remainder of the tailcone is open, but I would not be surprised if it lodged into some component before the entire tailcone came apart. Some of us can remember the complex path a certain oxygen bottle took on its way out of a 747.

It might be worth checking the recovered tailcone parts under the fin for memory module sized dings or red paint smears. Worst case scenario is that it lodged there for an extended period before coming loose miles away from the wreck.
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Old 30th Apr 2011, 02:07
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RR NDB;
The oscillator frequency changes near a metallic object.

Not just ferrous! And the memory type inside is insensitive to magnetic field.
Lets be careful with the word "metal". Not all metals are ferri/ferromagnetic, and looking at the properties of brass and aluminium/aluminum should be enough to demonstrate. An old trick when working on tuned circuits using threaded ferrite cores in the coils was to test them by not attempting to screw the often breakable ferrite core, but instead used a simple yet not destructive way of checking.

The method used a standard poly/plastic tuning tool with a small rod of iron on one end and brass on the other. Inserting the brass end raised the frequency and inserting the iron end lowered the frequency.

In the case of the CSMU we are looking for a lump of steel, and the frequency of a tuned detection loop will lower ("dip") once the inductive field is intersected by the lump of steel. Your bold red correction of what I originally stated, is IMO not warranted. Yes, I knew the memory was "flash" from the Honeywell specs, but I didn't set out to put the original poster "down".
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Old 30th Apr 2011, 03:20
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hydraulic forces

So are you guys saying, the over-pressure wave from compressing the inflated balloon of the aircraft is what shatters it into manifold pieces? But that does not explain how pylons become separated from wings, and the engines themselves be torn apart.
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Old 30th Apr 2011, 03:36
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My understanding is that hydraulics are not immediate. Whether nose first or belly on, there is a hole created whether the surface is Dirt or water. Water doesn't get hydraulic until some of the energy of impact dissipates, and the displaced water has some place to go, since water is basically incompressible when contained. The 447 is a very large essentially hollow cylinder with concentrations of mass where necessary. There are two volumes inside the tube, cargo and cabin. She hit flat, so the cargo hold pressurized quickly to a high value (for a not so very long time, however).

Early on, I noticed the crew rest capsule appeared to be a lamination of two sheets of aluminum with an adhesive layer of Phenolic resin. The separation of the aluminum sheets appeared to have signature of gas compression/release, acting as a miniature pressure chamber, a la the hold and cabin. Where BJ-ENG noticed a floor former on the seabed, I noticed what looked like a casting for some machinery structure, in other words, cargo.

I think that an a/c is made of millions of parts, and when undergoing such an impact as 447 has, these fastenings one to the other are virtually (essentially??) irrelevant, save some very strong assemblies, Gear, Engines, Wing box, etc.

So what happens is the a/c comes completely apart due to chaotic and multiple stressors, for several quantifiable reasons, reasons beyond my ability to understand, to be sure. The theory that the cabin could briefly have acted as a gigantic "airbag" is seductive, though the fuselage is probably the weakest structure on the airplane. I can see how some contents could have escaped obliteration, though placed in proximity with other parts that were destroyed.

I think the cause of the accident is somewhere in the simple understanding of systems weaknesses, and probably some quirks of fate that ganged up on our 447.
 
Old 30th Apr 2011, 04:21
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hydraulic forces
So are you guys saying, the over-pressure wave from compressing the inflated balloon of the aircraft is what shatters it into manifold pieces? But that does not explain how pylons become separated from wings, and the engines themselves be torn apart.
-drl
Let me jump into this for a second. For the AF447 impact, Imagine the skin of the belly was made of aluminum foil instead of ~1mm aluminum alloy. (The hydraulic force from below is so overpowering that the actual skin is little better than foil). The stringers and formers are immediately behind this thin surface. As the aircraft impacts, a considerable amount of this "foil" in the belly of the aircraft simply ruptures from the overload and folds back over its supporting structure. The internal pressure upon the remaining structure above could act to distort some structure above until major ruptures from fuselage bending allow the pressure to escape, but moments later the hammer of a surge of water from below will do the bulk of the damage. Mixed into this surge of water from below is the wreckage of the belly of the aircraft being thrown into the structure above and causing localized damage.

So hydraulic pressure tears up the belly skin, and fuselage bending + flying wreckage from below continues the destruction and tears up the things in the top of the aircraft. This is a macroscopic view.
On a local level within the aircraft, Whatever was below greatly influenced the damage pattern above.
The FDR may well have been thrown up into THS structure with the initial hydraulic induced debris flow.
I really suspect that the THS structure was then pushed up and aft out of the aircraft, throwing the aft part of the VS upward and forward and taking a bite out of the rudder bottom as it passed by.
Although this was a violent destruction compared to an automobile accident, it bears none of the hallmarks of a really high speed impact wherein very little of the aircraft is recognizable and the average piece size is hand sized or smaller.
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Old 30th Apr 2011, 04:48
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Machinbird;

I like your description. Just like a ship with light scantlings; the hull plating clearly outlines the frames and stringers where the ship has been pitching into heavy seas. Multiply that force by many times and it is easy to see how the skin would rupture.
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Old 30th Apr 2011, 06:29
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I would have thought that the results of such high impact forces between water and an essentially-frangible hollow tube with heavy, specifically-located structures such as engines, landing gear, wing-boxes, spars and APU, would have been obvious but perhaps I am mistaken and that the violence of such a collision is being under-estimated.
PJ2,

Agreed. Keep in mind that if we assume the initial impact was on the tail of the plane, a secondary violent impact could have thrown everything forward towards the nose, dispersing debris and large objects, and creating jarring destruction.

One question. With so many pieces of the plane found, will they at some point begin to build a reconstruction jig?
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Old 30th Apr 2011, 07:20
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razoray...

One question. With so many pieces of the plane found, will they at some point begin to build a reconstruction jig?
The answer is yes IF BEA feels it necessary to solve the causal puzzle. If, on the other hand, the recorders and other evidence yield enough information to reach firm conclusions as to cause(s) without such a reconstruction, then it won't be done.
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