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AF 447 Search to resume

Old 8th Apr 2011, 04:07
  #3181 (permalink)  
 
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I seem to remember that was dealt with by the BEA in Interim Report #2. From memory, the TCAS has an inbuilt function which checks that the static port pressure is valid and that the calculations that result fall within predetermined values. Should the TCAS detect erroneous values, it fails.
Altitude and its valid is transmitted on a data bus from the Air Data part of the ADIRU to the transponder. The transponder transmits own altitude on another data bus to the TCAS, and over the air to ATC and other aircraft.

Airspeed is not part of the TCAS calculation. TCAS uses only altitude difference, distance, and rate of closure.

If altitude data is flagged as failed, it does not cause a failure of the transponder or the TCAS. The transponder reverts to Mode A, and the TCAS annunciates OFF.

A TCAS Fail message means the TCAS has failed; it does not mean that it is turned off by an input fail or pilot selection.
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Old 8th Apr 2011, 04:23
  #3182 (permalink)  
 
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Originally posted by jcjeant ...
Is the distance between the wreckage and the vertical tail is logical with reference to wind speeds and current in this area?
It could be possible provided half the assumed current velocity is used. However as pointed out in the past, no one knows or knew at the time what the current was really doing. I am sure that attempts will be made to clarify where and how the V/S and all the other recovered debris made it to where they were found.

The position of the V/S in relation to the bodies found at the same time was reasonable, i.e. the leeway made by the V/S was greater than that of the bodies.

A standardized oceanic search and rescue protocol needs to be established to ensure in future that an initial aerial search doesn't make the same mistakes made with the AF447 accident.
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Old 8th Apr 2011, 04:38
  #3183 (permalink)  
 
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Originally posted by Graybeard ...
TCAS uses only altitude difference, distance, and rate of closure.
Not disputing any of that, other than in the case of this TCAS, it had a self checking routine that performed a "credibility" test.

From BEA Report #2:
This message indicates that the TCAS is inoperative. Without an associated fault message, it could be the consequence of an electrical power supply problem or of an external failure. Amongst the possible external failures, only one is compatible with the CFR received. This is a monitoring process internal to the TCAS which applies to the standard altitude parameter. The latter is received from the active transponder (it can thus be the altitude elaborated from ADR 1 or 2) and is submitted to a “credibility” test. In actual fact the TCAS elaborates an altitude prediction that it compares permanently with the altitude received. When these two parameters move too far apart, it stops operating and generates this ECAM message. Once the altitude becomes “credible” again, normal operation resumes and the message disappears.
We don't know if normal operation ever resumed. I doubt it.

Last edited by mm43; 8th Apr 2011 at 05:45.
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Old 8th Apr 2011, 05:49
  #3184 (permalink)  
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In post 3120 ( http://www.pprune.org/6355188-post3120.html )there was a detail of some weather overlaid the LKP and a question was asked to Tim Vasques about his interpretation of these colours.

Tim is too busy to follow the thread but his statement about the colours is as follows:

I haven't had time to research the incident since 2009, so I don't have anything to add. I saw your link and the question about colors. The colors shown indicate overall atmospheric radiance in the 10.7 micron infrared window. This would be a measure of cloud top temperature, with the reddest colors the coldest. This has a closer relation to updraft location than it does precipitation intensity, so I would be more prone to estimate turbulence from it than rain, though they will likely be closely associated in the tropics where the atmosphere is weakly sheared.

Tim


Tim produced a magnificent report about the weather conditions which were in place at the time of the accident
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Old 8th Apr 2011, 06:44
  #3185 (permalink)  
 
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TCAS FAULT message

BEA Interim Report No.2, 1.6.11.6 Consequences of a drop in the measured total pressure, explains that a sudden drop in measured total pressure entails a sudden drop (300 ft) in indicated altitude, due to the correction of the static pressure.

It would be of interest to know the tolerance of the “credibility” test of the monitoring process internal to the TCAS which applies to the standard altitude parameter. It shouldn't be too difficult for the BEA to get that from the TCAS manufacturer.

Regards,
HN39

Last edited by HazelNuts39; 8th Apr 2011 at 07:09.
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Old 8th Apr 2011, 08:46
  #3186 (permalink)  
 
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Colours on meteosat images

For the interested reader there is more information in BEA Report No.1 Appendix 1 and Report No.2 Appendix 3. The first reference has this Note:
See the MétéoFrance website
for details on the analysis of satellite images.

Last edited by HazelNuts39; 8th Apr 2011 at 09:04. Reason: corrected link
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Old 8th Apr 2011, 12:35
  #3187 (permalink)  
 
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Hello ZeeDoktor (re posts #3174 and #3144),

Am wondering if you read my post as carefully as I read yours. I am pleased you have now acknowledged that sideways displacement of the sidestick gives a rate of roll, not an attitude (angle of bank). You seem also to have accepted that the white cross (that you call "caret") is not present in flight. (By the way, it is used - on the ground only - to give both pilots an indication of the position of the duty sidestick, and the resultant stick-to-surface deflections.)

We don't normally deal with the absolute basics of Airbus FBW philosophy on this thread, but to avoid misinformation this paragraph of yours had to be challenged:
"The A3XX sidestick (control) philosophy is not rate but attitude based, i.e. you move the sidestick to the side (and with it a caret on the PFD), and the bus will keep the attitude you demand by pointing that caret. So, for example, you move the caret in the right hand side of the PFD and the bus will maintain an attitude to follow that caret."

That was completely misleading, as I think you now realise. So, in your new post, you now write:
"While you initially give a rate based on stick displacement, the airplane then holds the commanded attitude (with centered controls!)."

That statement is correct. Good. But you continue:
"It hence does NOT behave like an airplane we all learnt to fly on, also the only airplanes we ever had any *real* upset recovery training in."

Also true, and I never said otherwise. Returning to your original post, your next paragraph reads:
"When in direct law [...], it'll start behaving like an airplane you learnt to fly on... and you're in effect flying a rate based control system..."

It is true to say that Direct Law is rather "like an airplane you learnt to fly on" (stick-to-control surface). But that is not "a rate-based control system", as I pointed out in my PS. So actually, the problem for Airbus FBW pilots is the transition from the rate-based Normal (or Alternate) Law, with which they have become accustomed in routine situations, to the (roughly speaking) stick-to-surface Direct Law. I don't think we yet know if the pilots ever had to handle that transition on this flight.

You now say: "...one should never implement systems which behave differently from what one learnt initially." While I have some sympathy with that point of view, I think in the real world it is a tall order when manufacturers are constantly striving to improve performance and efficiency.
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Old 8th Apr 2011, 13:16
  #3188 (permalink)  
 
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Possible behaviour of a MLG leg if still retracted at impact

Quote from mm43:
I thought I had proposed a similar look at the relative forces involved in post #3106, but may be it got overlooked, because I believe that Chris Scott came up with a similar scheme a little later in post #3143.

It was also post #3134, actually, but you evidently got their first. You were just too subtle and succinct, I guess!

JD-EE, I think we agree about the initial sequence. CliveL has written an excellent post, as did PJ2, and they both seem to be on similar lines. It's what happens once the bogie/truck has fully emerged from the bay that is less clear.

Yesterday evening, exchanging PMs with HN39, he included the following : "I doubt that the difference in breaking force exerted at the two ends, integrated over the milliseconds time interval that it operates, against the moment of inertia of the gear in pivoting, would be sufficient to pivot the gear over 90 degrees to its 'down' position."

Taking account of what he had said, I offered him this: "I think the bogie/truck would barely decelerate initially, crashing through the flimsy door. But, as you say, it would soon be pivoting outwards (we have seen its pivot has survived). Also, by this time it would encounter the drag of the water. So I share your doubt that it would swing all the way into the fully extended position it looks to be in now. I should be very surprised if it had been in the extended position at the end of the flight, so further extension by gravity seems the most likely explanation."

Chris

Last edited by Chris Scott; 8th Apr 2011 at 16:29. Reason: Title amended; Para 3 extended.
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Old 8th Apr 2011, 14:21
  #3189 (permalink)  
 
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BEA Announces Ship for Phase 5

Just posted to:

Sea Search Operations, phase 4

Information, 8 April 2011
The ship Ile de Sein belonging to the company Alcatel-Lucent Submarine Networks (ASN), equipped with a ROV from Phoenix International Inc., is planned to undertake the fifth phase of maritime operations. This mission will be directed by the BEA and financed by the French State.
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Old 8th Apr 2011, 15:01
  #3190 (permalink)  
 
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Ile de Sein is currently off the west coast of Africa heading north, probably to pick up equipment from Phoenix.

ILE DE SEIN - 9247039 - Vessel's Details and Current Position

Of perhaps more interest is this from the BEA:

The team on board the Alucia will complete vehicle operations on Friday. The vessel will leave the search area on Saturday 9 April and should reach the port of Suape (Brazil) on the morning of Tuesday 12 April.
This suggests either:
a.) WHOI is pausing its mapping and photography, and will resume after photos are interpreted, or when the Ile de Sein is enroute to the location;

b.) WHOI has photographed the recorders, or where they are likely to be, and thus there is no need for further photography at this time.
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Old 8th Apr 2011, 15:08
  #3191 (permalink)  
 
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Thanks

What a thorough description of the sonar imaging process and the creation of the images themselves. Thanks auv-ee.

When I first saw the sidescan image, I thought, "where are the remaining tail surfaces?" But, based on what you said, and my experience with radar, I'm not convinced that one should expect to see any tailplane segments in that image. It's tough enough to make out the wings.

I guess we'll have to wait for the Ile de Sein to learn any more, although I'd feel a little more comfortable if BEA would release some more images from the Woods Hole team.
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Old 8th Apr 2011, 15:09
  #3192 (permalink)  
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Machaca - Pursuant to your excellent photos, I think it important to explain why some here are curious about inflight loss of VS. The two lug pairs and supports are from the front (1,2) of the attach, and show fracture due to rollover of the VS itself (side to side). The front lug has pulled with it the hoop structure attendant to the Aft Pressure bulkhead. The bulkhead is CFRP, and responsible for the integrity of the pressure vessel. If the VS separated at the outset of the loss of control, cabin pressure would be lost, and since the disc is not designed for rupture, it is reasonable to assume that some contents of the cabin may have spilled at altitude. This would describe some of the reports of flail and rupture to soft tissue evident in the victims. Of note also are the failure signatures of the rivets holding the lug bracket to the hoops. There is no longitudinal deflection of the hoop forward, which would be evident if the VS had rolled off the fuselage forward. In fact, the fractures suggest more than one episode of stress leading to complete failure. The composite Fin tabs have fractured in sideways aspect, and show no separation one from the other, a condition that would be expected had the single jolt theory of BEA occurred. A similar failure occurred on a 747 in Japan, leading to loss of the a/c due flight w/o Vertical Stabilizer.

Know that this is but a theory, and bears no malice toward aircraft or investigation, simply a recognition of upset leading to structure failure and loss.
 
Old 8th Apr 2011, 16:05
  #3193 (permalink)  
 
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bearfoil,

I fear you need to go back to BEA's Report No.2, and to the extensive discussions we have had earlier on this thread. The V/S has three pairs of attachments. The front pair stayed with the pressure bulkhead. What you are looking at in Machaca's first photo is a side view of the middle and rear attachments.
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Old 8th Apr 2011, 16:20
  #3194 (permalink)  
 
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Originally Posted by Machinbird
Originally Posted by Takata
No-one can so far explain why switching at 0210 to ALT2, due to unreliable airspeed, would cause an immediate upset as none of the similar events ever caused one! After being switched to manual control, any manual imput could cause one in relation with other unknown factors (workload, weather, technical, etc.)
Perhaps this is stated backwards.
"Why would an upset cause unreliable airspeed indications??", might be a better question.
The answer is in the link below and subsequent discussion.
AF 447 Search to resume

Note: With the discovery of the wreckage virtually under its 2010 position, the case for an immediate loss of control becomes stronger. The key question becomes how can it happen?
Well, sure, this question maybe stated backwards as, in my opinion, it can't be totaly ruled-out so far. Nonetheless, the A330 operational records should speak by itself as the probability for an "upset" happening some time before 0210, while flying in automatic (protected) mode at cruise level (A/P and A/THR ON) is clearly very very close to zero if related to her systems behavior.

One should remember that the only "system glitch" recorded after more than 15 years of operational duty accross a fleet of several hundred long haul aircraft was QF72. One will also note that this aircraft used a different (faulty?) hardware and would remember that this issue was not an "upset" properly: in fact, even if this situation could have caused some serious harm to the passengers, it did not cause an "upset" as the aircraft did not departed from its safe flight envelope (which doesn't mean that this problem was not dangerous for the aircraft safety).

Now, that the weather alone would put suddendly this aircraft close to an "upset" attitude, while flying in automatic mode at Mach 0.82, would certainly disconnect everything the same way. Then, if this was followed immediately by the freezing of all the probes, this would be quite a serious situation for the crew to manage. In this case, this would mean that they were not aware of the weather situation as they were not flying in "turbulence penetration mode", having their A/THR still ON up to this point. This would also be contrary to the right AF procedure and any cautious weather management at this dangerous spot.

Tim Vasquez' weather analysis was good but it pictured an aircraft position which was wrong as he took the projected "0215" position as reference alongside a wrong 0210 position.

concerning the wreckage position, I still doubt the 5 minutes "flat spin theory" direct from FL350 at a rate of 7,000 ft/mn while she was still powered all along her "free fall" (as no dual flameout occured). But who Knows?
The "deep stall theory", from the same level, will certainly imply a quite different aiframe (with T tail) and much more distance covered from LKP. The crash time (based on ACARS sendings) was estimated by the BEA between 0214:26 and 0215:14.

But, of course, it may have happened later in time, if she was not powered anymore after this point, as nothing, so far, can rule-out also this possibility.

We'll see what is found in the deep sea.
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Old 8th Apr 2011, 16:34
  #3195 (permalink)  
 
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bearfoil:
I think it important to explain why some here are curious about inflight loss of VS

That curiosity is sadly mistaken.

There is no way to explain the damage seen on the VS/lugs/hoops by any manuoevers and forces while airborne.
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Old 8th Apr 2011, 17:10
  #3196 (permalink)  
 
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This accident really remains a mystery.

I have to say I (along with some others) was strongly in favour of a search close to LKP. The really strange thing about it is now that they found it close to LKP I'm somehow at a loss as to why it is so close to LKP ?!

It would be really interesting to know where it is exactly, but if it is closer than 5nm from LKP, even a 'simple' spin scenario rather wouldn't do it.

From the Pulkovo crash we have a pretty good idea how long it can take from FL400 down to SL in a flat spin.
Looking at the Wing Loading of AF447 being ~580kg/m^2 compared to ~400kg/m^2 for the Pulkovo Tu154 we can assume that the vertical velocity /Rate of Descent in a flat spin should be a bit higher.
So the time for spinning from Fl400 all the way down should be below 200s, maybe rather 180s. (back then I roughly calculated terminal velocity of the A330 @210t as being in the order of magnitude of 140kts which seems reasonable with the ~120kts of the TU154 at Pulkovo))
Now let's assume the overall event took between 4,5 to 5 minutes. that would mean 90s - 120s before entry into the spin. if we decelerate from 480kts to 350kts the plane would travel between 10 and 15 minutes in that time span before entry into the spin. And even then there is still momentum to continue forward travel for some distance.

Looking at these assumptions I tend to assume there was some kind of course reversal, maybe unvoluntarily due to e.g. a massive wing drop ending up in opposite direction after recovery, maybe followed by a second upset this time losing it for good.
Unfortunately it really takes some creativity to get the plane to a point that close to LKP after a 5 minute struggle. Occam's razor seems to be off for vacation.

The other possibility would be that the speed was shed much quicker initially. With a full pull-up manouver it should be possible to decellerate to 350kts in maybe 30s. That would cover ~5nm. But then the remaining time of 4 - 4,5 minutes would require some form of recovery before the final plunge. All this w/o effectively traveling any distance.

None of the scenarios is really convincing. However, somehow it must have happened ????!
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Old 8th Apr 2011, 17:19
  #3197 (permalink)  
 
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@bearfoil, this is a view from the bottom to the VS, it is nearly impossible to generate a nearly left/right symetricle break line like this in the air, every force to the VS in the air will generate a breake to the left or right and must end in a very asymmetric break line

a very nice front view to the gear of F-GZCP is this:
Photos: Airbus A330-203 Aircraft Pictures | Airliners.net
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Old 8th Apr 2011, 21:15
  #3198 (permalink)  
 
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"Ile de Sein"

Originally Posted by Mr Optimistic
But does it matter if the gear was down. Surely the question is about what sequence of events took the a/c from level cruise to initial upset.
In some way, I guess it may give a hint about a stall recovery attempted but the crew, then a possible type of upset causing this crash.

All in all, what will certainly bring to us much more information are the ship from Alcatel-Lucent embarking the ROV from Phoenix International.
Here it is: L'Île de Sein, câblier (460 ft x 77 ft) , displacing 8,000 tons, built in 2002 by Hyundai Mipo Dockyard (South Korea) - her sister ships are: L'Île de Bréhat (at first named by BEA) & L'Île de Ré.
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Old 8th Apr 2011, 21:24
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Mr Optimistic
"But does it matter if the gear was down. Surely the question is about what sequence of events took the a/c from level cruise to initial upset."

Well said my good man. We have had about 3/4 pages dedicated to landing gears. Next we will have posts concerning the toilet ACARS.

Takata, I have to say I read your posts with great enthusiasm, as you are so convincing in your statements, even if you might be wrong sometimes. You could convince me planet Earth was flat.
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Old 8th Apr 2011, 22:15
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The earth is NOT flat?
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