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AF 447 Search to resume (part2)

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AF 447 Search to resume (part2)

Old 9th May 2011, 11:02
  #981 (permalink)  
 
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Originally Posted by jcjeant View Post
Hi,

I still feel very frustrated when I look at this map ...
It shows the very first search (aerial) and then those incurred by the BEA
The abyssal plain where you found the wreck was known (from a hydrographic point of view)
I always wondered why the BEA has not started his research in this area .. that was easy enough to explore .. compared with the rugged surroundings.
Over the means used during the aerial search (detection signal pingers) was not very efficient.
Pretty sure the BEA are frustrated too, however there were good reasons for what they did. The area around LKP, including the actual crash site, was searched in previous phases both aerial search for wreckage and undersea search for pingers (not aerial search for pingers - if that is what you meant). The third phase, which that map shows most clearly, was setup based on drift analysis of the wreckage - turned out to be wrong. Frustrating, yes, but understandable given the number of variables and the long delay in finding the floating wreckage.

As to why not look in the easy-to-search areas, the answer is that they had already been searched and no pingers detected. The assumption was that (at least one of) the pingers worked, so if sat on the abyssal plain, they would have been heard. In rugged terrain, pinger signal would be more likely to be blocked, so what do you do if you have not heard the pingers and the drift analysis points to a rugged area - search a different flat area because it's easier ?


The big questions (I think) are:

1 - did two independent pingers both fail (and if so why) or was the pinger search not done right

2 - how did the initial air & sea searches miss the floating wreckage despite apparently searching the right area
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Old 9th May 2011, 11:05
  #982 (permalink)  
 
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Swordfish41;

Thales and the French MOD's part in Phase 3 leaves a lot to be answered. I believe the shutters have come down on that episode, and the true reasons behind what went on will never be disclosed.

You might say that Thales got a little bit out of their depth when deciphering 37kHz pings in the noise. A hearing aid should have been on the shopping list.
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Old 9th May 2011, 11:18
  #983 (permalink)  
 
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Cool

Hi,

The assumption was that (at least one of) the pingers worked, so if sat on the abyssal plain, they would have been heard.
It's not that assumption you wait from professionals.
They know that pingers can fail ... or be destructed for any reasons
In a investigation you must be open at all options and exploit them
If you base an investigation on dogmas and faith .. it's the best way to fail.
So .. this assumption is even more frustrating for me.

Last edited by jcjeant; 9th May 2011 at 11:32.
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Old 9th May 2011, 11:27
  #984 (permalink)  
 
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jcjeant.
in the graphic of the crash and search phase areas that you posted, there is a seperate box to the south of the hemisphere that was intended to be covered in phase three. The square was searched because Thales reprocessed a sonar search carried out by the French Nuclear sub L'Emeraude, and believed that they could discern amongst the noise, signals from the pingers on the voice and data recorders. Because of this the methodical survey of the phase three area was interupted, and never completed. If it had been, the wreck would have been located. I understand that there was some disagreement amongst the search teams at the time about the wisdom of this diversion, but they were overruled.
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Old 9th May 2011, 11:32
  #985 (permalink)  
 
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Towed Pinger Locaters (TPLs)

Undoubtedly the BEA will be examining closely the reasons why the ULBs were not located.

In my mind, there are three reasons:-

The first is that there was only one functioning ULB as the ULB attached to the SSFDR was most likely struck and destroyed by collapsing frames/stringers during the initial impact sequence. Hence the reason it was not attached to the recorder.

Secondly, the SSCVR ULB finished up getting itself half buried and the effective output was attenuated by at least 3dB along with some localized acoustic absorption caused by silt. Overall, the radiated output was down by around 6dB as the polar ends are the least effective radiators.

Thirdly, the grid line that was being towed was north/south from 330'00"N to 300'00"N and there was the potential for the TPL to drift off line caused by the turn to head back north on the next grid line. If the towing vessel turned too early and gave insufficient time for the TPL to realign, then there was a potential for a nadir (shadow) to appear in the area covered by the tow. The fact that the tow (now deep at around 3,000m) may not have lined up until some time after passing through 300'00"N provided the opportunity for missed detection, coupled with the lower than optimal output by the remaining ULB.

The answer lies in the detail.
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Old 9th May 2011, 11:35
  #986 (permalink)  
 
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MM43
I too am sure that it will never be revisited, at least in public, although Thales themselves used to have an impressive undersea survey division. I suppose that coming to the final parts of the search area, without any results it was hard not to respond to new evidence, particularly given its source. That however is enough hindsight from me. I would just add that your explanation about the towed locator is why this technology provides far less certainty than AUV's.

Last edited by Jetdriver; 10th May 2011 at 03:52.
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Old 9th May 2011, 11:43
  #987 (permalink)  
 
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Heterodyning ULBs

ULB Spec.
Operating Frequency: 37.5 kHz 1 kHz
Operating Depth: Surface to 20,000 feet
Pulse Length: Not less than 9 milliseconds
Pulse Repetition Rate: Not less than 0.9 pulse per second.
With two ULBs close to one another, and transmitting, is there not a chance that heterodyning will affect the already very weak signals? Two RF transmitters would certainly be affected - so why not 37Khz?
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Old 9th May 2011, 12:17
  #988 (permalink)  
 
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Originally Posted by jcjeant View Post
Hi,

It's not that assumption you wait from professionals.
What do you want then ? Guesswork ?

Some assumptions have to be made or you have an unfeasibly large search area. ACARS can fail too - and that is our only source of LKP. Suppose the a/c lost all power and glided from LKP - it could have been many miles from all the search areas.

The assumptions were (to me) reasonable at every stage, the area searched in phase 1&2 included the crash site - and failed to find the wreckage, but not because of looking in the wrong place.

Phase 3 was specifically targeted based on drift analysis of the floating wreckage.

Phase 4 went back with no assumptions except that the crash was in the vicinity of LKP (ie. no power loss and glide etc.), and no assumption that earlier searches were correct.


They know that pingers can fail ... or be destructed for any reasons
In theory yes, but historically they almost always work, and there are two independent that would have to fail. It was a reasonable assumption for the first two phases, after that it was not assumed.
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Old 9th May 2011, 12:29
  #989 (permalink)  
 
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Cool

Hi,

Suppose the a/c lost all power and glided from LKP
I don't agree with this supposition ... if you read the ACARS ..
BEA read also the ACARS ... and maybe more we don't know about.
I can't suppose a glide from them.

unfeasibly large search area
The aera phase 1 the very first research .. (with ASSUMPTION of working pingers) was not a large one !

phase 1&2 included the crash site
And phase 4 included the crash site.
The difference is they used appropriate tools for this search and they assumed (this time) that the pingers were no more working !
At the first search .. they have two doors to open ....
One with the pingers in the room .. the other with no pingers ...
They opened only one door .

Last edited by jcjeant; 9th May 2011 at 12:44.
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Old 9th May 2011, 12:58
  #990 (permalink)  
 
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@Chris Scott ; HN39

Although that a violent pitch-up to FL 400+, (or "zoom-boom scenario" like takata it humorously called) was not direkt against one of the ACARS is very surprisingly for my myself, because I just searched the fastest way to reduce the horizontal speed, nothing else

but even the violent pitch-up itself need high aerodynamicel lift and will generate lots of g, how fast can we generate this climb without a wing-brake? 10 sec...15 sec...?

Last edited by grity; 9th May 2011 at 13:12.
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Old 9th May 2011, 12:59
  #991 (permalink)  
 
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jcjeant;

With some help from takata for the last ACARS message (cabin v/s), the airplane could have started its final 130 nm glide from FL350 at 2:15:14.

grity;
the violent pitch-up itself need high aerodynamicel lift and will generate lots of g
The zoom-climb doesn't have to be violent nor involve 'lots of' g. But what caused it?
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Old 9th May 2011, 13:25
  #992 (permalink)  
 
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mm43,
the SSCVR ULB finished up getting itself half buried
Do you know that for a fact ?

One thing that surprised me was the statement that the pingers could only be detected by TPLs at a bit more than 1700m. Important variables necessary to asses the valididy of this statement are missing: I couldn't find acurate specifications for the TPLs on the net. Another essential variable was the noise intensity spectrum level around the pingers frequency. In this frequency band I think that rainshowers and, to a lesser degree the sea state play a major role. But rainshowers randomness may make detection rely on luck.
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Old 9th May 2011, 14:39
  #993 (permalink)  
 
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Pitching Moment vs AoA

Possibly re-regoing over old ground here but Figure 6 from the following NASA report stands out to me ... (thanks to BJ-ENG for posting the link)
http://ntrs.nasa.gov/archive/nasa/ca...2005208658.pdf

So, from the wind tunnel data for this generic-ish twin engined commercial aircraft, we have a family of curves showing the relationship between pitching moment and AoA for elevator angles from -30 deg to +20 deg, all at a zero HS angle and CG mid.

How about we then factor in a typical HS cruise trim angle and aft CG and consider what sort of AoA value might start becoming a nasty place to be?

From page 4 (Section B) of the same document:

1. Static Pitch Stability
Aerodynamic pitching moment characteristics from the
wind tunnel tests are shown in Fig. 6. This figure shows the
variation in static pitch stability and elevator control
effectiveness over the angle of attack range. The
configuration is statically stable at low angles of attack as
indicated by the negative local slope of pitching moment
coefficient with angle of attack. However, in the stall region


(
α10-14), the stability is reduced generally due to
combined effects of outboard wing stall and downwash
interactions with the horizontal tail. The pitch control
remains effective throughout the angle of attack range but
diminishes with increasing angle of attack, due initially to
the immersion of the horizontal tail in the wing wake and
ultimately due to flow separation on the horizontal tail itself
at post- and deep-stall angles of attack. The maximum
steady angle of attack with full nose-up elevator deflection
is at

α25, which is significantly higher than the stall
region near

α12 and this result indicates the potential for
the airplane to enter upset conditions using normal pilot
controls during un-accelerated flight.

Edit: added aft CG

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Old 9th May 2011, 14:54
  #994 (permalink)  
 
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Originally Posted by DJ77
mm43,
Quote:
"the SSCVR ULB finished up getting itself half buried"

Do you know that for a fact ?

One thing that surprised me was the statement that the pingers could only be detected by TPLs at a bit more than 1700m. Important variables necessary to asses the valididy of this statement are missing: I couldn't find acurate specifications for the TPLs on the net. Another essential variable was the noise intensity spectrum level around the pingers frequency. In this frequency band I think that rainshowers and, to a lesser degree the sea state play a major role. But rainshowers randomness may make detection rely on luck.
I think that mm43 is referring to the photo that BEA published of the CVR, showing the pinger half-buried. I am less sure than mm43 about the configuration of the transducer in the pinger case, and what the effect on the sound level would be of the way the pinger landed on the bottom.

I gave an approximate estimation of the the pinger detection range in this post:

http://www.pprune.org/5683946-post951.html

Rain would have some influence at 37kHz. I don't know if it was raining when they searched the now-known debris area. According to the classic text by Robert Urich, there is a 20db difference between the minimum and maximum ambient noise in the deep ocean, between calm and 30knts wind (sea state 0 and 6). I expect that rain is added to that, but light rain does not add much, as near as I can tell. I assumed about sea state 2-3 in my calculation.
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Old 9th May 2011, 15:38
  #995 (permalink)  
 
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Zoom climb initiation

HN39

It seemed to me some time ago that the 340 scenario was a prospective candidate to initiate this - and still is the leading possibility IMO. There has been a number of excellent discussions related to it over the last couple of days that have pointed to possible inconsistencies - that were subsequently potentially addressed by others i.e. ACARS, etc. Is this zoom then deep stall scenario within the capabilities of accurate modeling in a simulator?
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Old 9th May 2011, 15:55
  #996 (permalink)  

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Is this zoom then deep stall scenario within the capabilities of accurate modeling in a simulator?
As my old boss used to say: 'It's surprising what you can find out by flying the sim'.
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Old 9th May 2011, 16:00
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Is this zoom then deep stall scenario within the capabilities of accurate modeling in a simulator?
Unfortunately no. The airframe makers do not test into the region that AF447 apparently found itself, and thus do not collect data for this region of "flight". Any such simulator runs would be purely speculative.

Such testing is inherently dangerous and real flight data sufficient for a simulator is unlikely to be available even for a stray event. Best hope is that Airbus collects data in a wind tunnel and compares it with CFD models (CFD=Computational Fluid Dynamics) to see if the results are rational.
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Old 9th May 2011, 16:24
  #998 (permalink)  
 
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Originally Posted by oldengmkr
Is this zoom then deep stall scenario within the capabilities of accurate modeling in a simulator?
Only up to the point where the manoeuvre gets outside the simulator's envelope of valid data, and that does not include the deep stall, at least not in the simulators intended for training of airline pilots.

Last edited by HazelNuts39; 9th May 2011 at 16:36.
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Old 9th May 2011, 16:38
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May 9 update from BEA

Information, 9 May 2011

The French Navy patrol boat La Capricieuse reached the search vessel the Ile de Sein on Saturday 7 May during the morning. It is currently sailing towards the port of Cayenne with the flight recorders, under judicial seal, on board. Also on board are the Investigator-in-Charge, an investigator from CENIPA, the Brazilian equivalent of the BEA, and an Officer of the French judicial police.



The patrol should reach Cayenne by the morning of Wednesday 11 May. The flight recorders will then be transported to the BEA by plane.


Recovery of airplane parts has continued over the past few days, with one engine and the avionics bay, containing onboard computers, having been raised.
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Old 9th May 2011, 16:53
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Simulation during control program development

Mahcinbird, HN39

I would hope that simulator programs would extend into regions beyond normal airframe testing limits - based on wind tunnel test data. One can expect aircraft to, on rare occasion, inadvertently experience excursions into extreme realms even with highly trained crews and state of the art instrumentation focused on avoiding it - as nature is always capable of surprising us. Take for instance the temperature fluctuations encountered by the A340 and implications for exceeding mach limit. One would expect such an event could be anticipated during control design but it probably would not be the subject of airframe testing. Thus it seems appropriate to do simulator modeling (during design) - to test the control design for the response to such an event. Perhaps that range of information is only available to A300 Engineering in their simulator.
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