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AF447

Old 7th Jul 2009, 15:47
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re: AstraMike #3183 - sink or float

There is one view that at the time a body enters the water it either sinks or floats subject to such factors as the amount of fat content, and clothing which will trap air. Cold water tends to inhibit resurfacing, and if sufficient deep is reached no amount of decomposition gas will overcome external water pressure (Schafer 1978)

Advances in forensic taphonomy By Haglund, and. Sorg

- BJ
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Old 7th Jul 2009, 16:05
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It does not always take a while for a body to come to the surface and float. When the Aegis shot down Iran Air in the Persian Gulf, some of the bodies floated on the surface immediately.

As for current drift, here is the plot of the last body recovered and wreckage recovered on that day (June 17).



Here is the surface current for a five day period centered on June 17, 2009, using NOAA/NASA satellite observations (OSCAR) to generate the chart.



To me, there looks to be a pretty fair correlation between the surface currents and the plot for recovery of the objects and body. I'll leave the calculation of Reynolds numbers for a human body half-floating on the surface to others.

The 45 day meteorology for the closest buoy (0N, 35W) can be found here:
http://www.ndbc.noaa.gov/data/realtime2/31001.drift
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Old 7th Jul 2009, 16:06
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As Air France has very bad safety statistics (4 aircrafts destroyed and 341 deaths in the past 10 years), I would like to study the report of the 1989's Dryden crash which seems to present some similarities on structural causes.

Does somebody have this report or a large summary of it ?

Thanks much...
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Old 7th Jul 2009, 16:07
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AstraMike:

The mentioned Russian aircraft that crashed following a “flat spin” entered at altitude, in turbulence, had a Second Officer who was a qualified aerobatics pilot - not that it helped.
I thought I read that the 2nd Officer was a former national champion at aerobatics, which strengthens your point about how hard it is to recover. I cannot personally imagine any passenger liner recovering from a fully developed flat spin (maybe a fighter with thrust vectoring might be able to do it, I don't know).
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Old 7th Jul 2009, 16:25
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ELT

Here in Brazil, small a/c engaged in air-taxi/corporate operations MUST have at least one ELT, and operated by a G-Switch.

You can have as many manually operated ELTs you want, but at least one should have the G-Switch.

If this is true on much smaller a/c (including helicopters), I want to believe A300s also has one.

Supposing this is true, why not a beep was heard? ELTs transmit on 121.5, the freq. everybody is "listening" to, specially when crossing the "big lagoon"...
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Old 7th Jul 2009, 16:33
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Philemon:
I don't fully understand where you're coming from. Any airline can have a run of bad luck. Pan Am's safety record form the '60s to the '80s could be considered very dodgy by your standards - hell, they lost 341 in a single incident!

Lest we forget, in the case of one of the AF hull-losses everyone got off safely. Trying to compare the Dryden crash, presumably to point a finger at AF for allowing commercial pressures to override safety when in fact the incidents are nothing alike, just smacks of a desire to smear.
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Old 7th Jul 2009, 16:41
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ELT

Rob21
Supposing this is true, why not a beep was heard? ELTs transmit on 121.5, the freq. everybody is "listening" to, specially when crossing the "big lagoon"...
Or were the ELTs the new 406 MHz models???

Verbal maydays would be on 121.5 or 243.0, guys listen there. The one ELT found wasn't armed and the others drowned after some time.

Last edited by ttcse; 7th Jul 2009 at 17:00.
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Old 7th Jul 2009, 16:43
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AstraMike, your ‘aerodynamics lesson’ {post 3197} showed how a modern large aircraft might enter a spin, but not with any relationship to the A330, nor why you focus on a flat spin in preference over a more common type. Similarly, where stall precedes a spin, you provide little supporting evidence, unless you agree with some of the previous ideas – then why ‘pick and choose’ evidence to suit your case.
Also the choice of spin mode appears back driven from the scant evidence of the wreckage, for which the conditions in many other scenarios might account for the damage.

If an aircraft has a tendency to drop a wing during a stall then the resultant downward attitude/motion could just as likely provide the necessary increase in airspeed to un-stall the wings – thence a spiral dive and not a spin.
All that the current evidence points too is the loss of airspeed information, procedural flight on standby horizon and power setting, and in atmospheric, procedural, and WAT conditions conducive to low speed loss of control (stall).

Noting some interesting observations on trim operation, how the loss of airspeed procedure might be adhered to in the absence of stall identification, and generalities about crew training performance, there are still many unknowns.
Should we expect the airspeed display to be regained as the aircraft descended clear of icing conditions?
If there was a loss of control and instruments were recovered, why wasn’t stable control wasn’t regained?

Please no wild speculations about locked in spins – first show that this aircraft type could, or would experience a stall, an incipient spin, then a ‘spin’, and then why ‘flat’’.
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Old 7th Jul 2009, 17:02
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ELT

ttcse,

This is strange, ELTs for extended overwater operations can be manually operated, but should actuate upon contact with water.

Unless this ELT found was completely dry, then I can understand why it didn't actuate. Switched to off position, ELTs will transmit when wet. This is a requirement, I believe.

I can be wrong, though...
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Old 7th Jul 2009, 17:03
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AstraMike - Re your # 3179 - "Flat Spin"

Thank you; excellent post.

It seems to me we are pretty close to saying much the same thing, certainly there are many big ifs involved at this stage and maybe always will be. My point was and is to take what seems to be judged as “known” or believed by competent authority and see if it fits anything known in the world of aerodynamics. If there is a fit, and it seems to me that there might be, surely it is interesting and should lead one to wonder about less sure assumptions.
[Emphasis by S1]

The idea is to suggest a solution that allows the evidence to fit, not manipulate the evidence to fit a solution.
That was precisely my intent. Obviously I do not know if a "flat spin" occured. I suggested the hypothesis only because the BEA opined that the aircraft struck the ocean in a level flight attitude with a near vertical trajectory. If that did happen a "flat spin" seemed (to me) to be the only thing that could make it so. It goes without saying that a flat spin or any other type of spin - did not cause the upset but is only a possible aftermath that might fit the evidence of a touch down on the belly.

Your description of a flat spin is quite on the mark. The one place we might differ is on what would keep the aircraft in a sustained flat spin. I do not think that possible unless there is a failure of some kind in the tail section or the separation of engines from their mounts, or both. Otherwise, I believe, the "flat spin" would change to a normal spin or a spiral.

The stated impact evidence in the BEA report appears to preclude a normal spin or a spiral.
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Old 7th Jul 2009, 17:10
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Ligne de vol

My personal understanding is that, at impact, the fuselage was parallel to the ocean surface.
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Old 7th Jul 2009, 17:23
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ELT

Rob21
ELTs will transmit when wet.
But when submerged, the radio signal would be significantly attenuated. At some minor depth unhearable by other airliners. ( And again xmitting on 121.5 or 406?? )

Off & still triggered by being wet? I could be wrong but I believe it needs to be set to the 'armed' setting. Off is off.


AstraMike, many long posts so I'm starting to skip but your #3179 was a good read.

Last edited by ttcse; 7th Jul 2009 at 17:39.
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Old 7th Jul 2009, 17:29
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Ligne de Vol

"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 vertical acceleration".


"Les observations effectuées sur la dérive et sur les éléments de la cabine
passagers (office, porte de toilettes, module de repos PNC) font apparaître que l’avion a vraisemblablement heurté la surface de l’eau en ligne de vol, une forte accélération verticale"


To me, it means that the plane's trajectory was rectilinear both in the horizontal (en ligne de vol) and vertical planes, with a velocity vector close to the vertical. It would also imply that the plane was not banking or not spinning at the impact.
Jeff

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Old 7th Jul 2009, 17:39
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Hyperveloce:

I agree about the unlikelihood of a flat spin because if it was a spin, we would expect a strong sideways force on the VS, while BEA stated that it failed forward and only slightly to the left. This implies horizontal deceleration as well, along the line of flight.
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Old 7th Jul 2009, 17:41
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To me, it means that the plane's trajectory was rectilinear both in the horizontal (en ligne de vol) and vertical planes, with a velocity vector close to the vertical. It would also imply that the plane was not spinning at the impact.
To determine if the aircraft was spinning, IMHO, you should look in which attitude was before impact, the BEA statement does not clarify that.
A spinning object when impacting ground is horizontal and has a velocity vector close to the vertical. Unless you know the horizontal vector before impact you cannot establish if was spinning or not.
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Old 7th Jul 2009, 17:43
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une forte accélération verticale"
It seems rather sloppy text even in french. Surely it should say velocity or speed, since I don't see how it can be deduced whether or not the aircraft was accelerating at the time of impact.
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Old 7th Jul 2009, 17:53
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Why is it out of the realm of possibility that there could have been an uncontrolled fire on board AF447? I see no one entertaining this possibility.
Along the lines of SwissAir 111. An uncontrolled fire on board would certainly bring any aircraft down. Or am I way off base here?
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Old 7th Jul 2009, 17:53
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body drift

AstraMike:
I thought it was well established that it took a while, days in fact, depending on surrounding temperature, before a human body would float. Equally, the conditions below the surface are different than those on the surface.
Therefore you cannot base constant drift assumptions on the bodies, until they surface
Hi,
This is what most people think but, having being involved in several sea rescue operations in the past, I can tell you that it isn't true (or partially wrong) from direct experience. Sorry for the following details.

Like any objects in water, there is three cases: sink, float or stall.

It is based on the differential between object and sea water specific gravity. In clear water, the tendency for the large majority of humans (+90%) is to sink, because their specific gravity is higher than clear water (0.97) but in standard sea water (1.027), it is the contrary and the majority of human (+70%) is naturaly buoyant. Some will have an equal gravity and stall close to the surface but 100% submerged for some time. The buoyancy of most human is very close to 0, say 0.01 meaning that only 1% of the body will surface and it will be almost invisible at some distance.

Now, when one sink, he will go to the bottom and, if deep enough, he will never re-surface because of high pressure compressing the human body added to higher density of deep and cold water. In tropical seas, the high temperature of water means lower density and a higher sink rate.

Plenty of factors will affect people buoyancy (like age, gender, physical condition, etc.) but the most important one, considering disasters at sea, will be the clothing which may affect buoyancy one way or the other. Victims will usually float face down, with a very small part of their back immerged during several days, then they will start to turn belly up after some time, depending of the sea temperature.

In conclusion, it is nearly impossible to predict how many people will surface immediately following a disaster and it is very common to miss some of them until they reach some very remote coastal areas, sometime after drifting for months over several thousand of milles.

S~
Olivier
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Old 7th Jul 2009, 17:56
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Comms...

Originally Posted by takata
What to do now?
1. aviate: avoiding stall?
2. navigate: where we go?
.. Cap Verde: ahead but too far
.. Brazil (Fernando Noronha) turn needed without colliding an active cell
3. communicate: Mayday? we'll see later, hands full now
and...

Originally Posted by OleOle
I see the logic in your conclusion, but how long would it take to glide down from FL350 over a distance of ~100 nm ? (15-20 min?). I think the closer they would get to the surface the higher their priority to communicate would become. Taking into acount that in this scenario they would have had sufficent time (and a crew of three) one would expect distress calls to be made on 121.5 and to be picked up by nearby a/c.
Before completely ruling out the possibility that the aircraft may have glided or attempted a controlled descent/diversion and ultimately compromised ditching, is it worth considering again that the report mentions the swapped RMP1 at Rio?

I dont mean to introduce any extra area of unecessary speculation, but can we rule out takata's scenario purely on the basis of assumed certainty that comms were fully operational on the A/C? - whether post upset or for that matter during the whole flight?

Is it possible that all the radio calls leading up to the incident were made using RMP2 up until the initial point of the scenario developing; and that thereafter the person operating RMP1 subsequently took charge of putting some emergency calls in, possibly on several occasions? With a rapidly developing situation and the knowledge that they were in the midlde-of-VHF-nowhere... can we rule out the possibiility that even in a controlled emergency descent, the crew may have overlooked a function check / repeat calls on RMP2, feeling that calls had been made as per procedure?
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Old 7th Jul 2009, 17:58
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NARVAL;

Lowering the gear would certainly place the aircraft in Direct Law but to what end? The thesis is, the pilot has "more control" to push/pull the aircraft out of an abnormal attitude - the "kind of control" we find on more "accessible" designs such as those that don't have control laws to "interfere" with what the pilot would do with the controls. I submit that such thinking is faulty and not supportable in fact.

I understand the long-posited argument that when circumstances are so dire that access to all possible control (direct law) with the attendant possibly of a) high-speed-stalling of the aircraft or b) breaking the aircraft, is preferable to the certainty of a crash. But this argument presumes that there is more performance available from the aircraft, under the 'g'-loads and/or attitudes/speeds contemplated, than the control laws are permitting access to. In the absence of clear cases to the contrary, the question then becomes, is there a very slight hint of romanticism in assuming that "the airplane ain't read the manual" and that the pilots would, in all cases, be better off with immediate and full authority over all flight controls, setting aside the engineering data regarding structural and aerodynamics issues?

The argument then takes both forks in the automation road: Design software and hardware that will prevent such excursions in all cases, thereby removing the pilot altogether, or hand full authority over the aircraft in all cases, thereby placing recovery of the aircraft in the pilots' hands. Control laws in fbw aircraft occupy the design-space in between these two forks in the road.

I can't think of a single accident where this kind of reversion (instant access to Direct law via the "big red button" notion) would have made a difference in the survival of the aircraft, bearing in mind that such laws may already be exercising that very fine balance between loss of control (high-speed stall through pulling 'g') and breaking the airframe and that the aircraft has no more to give, (Perpignan case?) On the contrary, we have at least one clear example where Airbus and 777-type laws would have saved the aircraft, (AMS B737).

At the same time I recognize the complexities of the issue and would not hold out such a view if it could be demonstrated otherwise but if that were the case, (and perhaps this lies in "greatest hope" territory), likely Airbus and probably Boeing would be far ahead of any of us in responding with a different view of computerized flight and its reversion laws.
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