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AF 447 Thread No. 5

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AF 447 Thread No. 5

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Old 9th Jul 2011, 13:26
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AF 447 Thread No. 5

To make things a little easier to navigate, we'll include a number of links to various spots in the complete thread.

For no reason other than it's a tidy number, we'll try and contain each part thread to around 1000 posts from now given that it is obvious that the thread is going to end up being of epic proportion.

Thread part -

(a) #1 starts here and finishes here. Posts = 3890
(b) #2 starts here and finishes here. Posts = 2537
(c) #3 starts here and finishes here. Posts = 2071
(d) #4 starts here and finishes here. Posts = 1061


Links to the various BEA reports are given below with additional links to the spot in the complete thread where the particular BEA report was issued. If I have missed any of the useful papers, please PM me with the URL and I can include it.

(a) BEA site - French, English
- Report link page - French, English

(b) Interim Report (No, 1) Jul 2, 2009 - English

(b) Interim Report No. 2 Dec 17, 2009 - English
- Update Dec 17, 2009 - French, English

(c) Estimating the wreckage location Jun 30, 2010

(d) Wreckage search analysis Jan 20, 2011

(e) Briefing and associated update May 27, 2011
- Briefing - update French
- Briefing - update English
- Briefing - update German
- Briefing - update Portugese

(f) Third Interim Report July 2011 - French, English


Miscellaneous pertinent links -

(a) Airbus Operations Golden Rules
(b) ALPA FBW Primer
(c) C* and Civil Transports - Cranfield
(d) Longitudinal Flight Control Design - RAeS
(e) Longitudinal Stability: Effect of High Altitude and CG - Boeing
(f) pitot static system performance - USN (Pax River) FTM

Search hint: You can search PPRuNe threads with a filter in Google by using the following search string example -

ths af447 site:http://www.pprune.org/tech-log/

This will search for mentions of THS in the AF447 threads of tech log only.

Just change the THS in the string to whatever you want to look for. This allows one to search for any term or phrase of interest throughout the threads.

Adding the site:URL end part is the magic that restricts Google to only searching in Tech Log.

This filter technique is absolutely wonderful and can be used generically to find things of interest in PPRuNe - appears to work OK in the PPRuNe search function as well.
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Old 9th Jul 2011, 14:29
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Excellent work, thanks John - hope you wake up good looking
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Old 9th Jul 2011, 14:34
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John, first class moderator work, thank you. These threads are now a research tool as well as a "trace of the dialogue". The search tool created by a PPRuNe'r is especially appreciated.

(John, just getting up here on the west coast of N.A. (the 'beauty sleep' didn't work here...better luck!) and I would like to supply the following links to the first thread, (although the real first one (in R&N) got shut down almost immediately and is at http://www.pprune.org/rumours-news/3...0-missing.html. This first thread begins June 1, 2009 and ends on June 4 2009, is 952 posts long and ends at this posting, http://www.pprune.org/rumours-news/3...ml#post4974651.)

The "first" substantive thread, (really the second due the above), is 4598 posts long and was moved to Tech Log some time back and is here: http://www.pprune.org/tech-log/376433-af447.html. It begins June 4th 2009 and ends April 9th 2011.

The first post in that thread is at: http://www.pprune.org/tech-log/37643...ml#post4974708
Last post in that thread is at: http://www.pprune.org/tech-log/37643...ml#post6359812

For the archivists and historians among us! The thread contains some very prescient work.

Last edited by PJ2; 9th Jul 2011 at 15:10.
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Old 9th Jul 2011, 15:27
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Reply to Chris Scott, from thread #4:

Chris;
I donít think much would happen to the THS during the initial rotation from level flight, as it would have required little up-elevator to enter the climb. Once the 7000ft/min had been achieved, the trajectory would be maintained by the EFCS even with no back-stick. As the speed started to drop, more up-elevator would need to be introduced by the EFCS to maintain 1g, and it would then start to trim the THS a bit to retain full elevator authority. Once the aircraft got on to the back end of the drag curve, however, this process would proceed rapidly.
Your previous post on the THS on thread #4, here, explains the THS operation very well and this one connects that explanation with how the THS likely functioned with AF 447. I think its a reasonable explanation of what occurred to the THS and how, after the initial pitch-up.
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Old 9th Jul 2011, 17:10
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Missing ACARS explanations

Hi All!

This thread has been most interesting to me. Especially on points where the opinions among "experts" differ.
I am still surprised by the fact that BEA gave no hints in the short list explaning where the various ACARS were coming from. One of the last was about faults in Prim 1 and Sec 1, which were earlier assumed to be either showing serious faults of caused by pilot shut-downs of these systems.
Very often it has been assumed in this thread that there was 5 computers involved on AF447, however each of the three ADIRUs also contain at least one each and perhaps also one in each of the Air Data Modules. I am making this conclusion from the australian report about sporadic AoA signals, where it is stated a software update for the ADIRU uncovered an old bug.
I am also thinking about a fixation of the pilots on a single phenomenon as part of the causes, somewhat similar to TMI-II operators failed behaviour.

Regards
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Old 9th Jul 2011, 18:08
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Sorry,
but I lost track.

Concerning the "zoom climb", could have A/P and/ or pilots received an "overspeed condition", which in turn traded speed to height, according relevant law?

Last edited by hetfield; 9th Jul 2011 at 18:30.
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Old 9th Jul 2011, 20:48
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John T,
Not sure a No.5 link is really the answer....

Unfortunately this is just a forum... without a way to index the various posts into categories like "THS", "Pitots", "Software", "SideStick", "FDR", etc. which would make them easier to "exploit".

Personally just looking forward to the next BEA report... and the way that will put the fox among the chickens, once again.
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Old 9th Jul 2011, 20:57
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Missing ACARS explanations?

Hi Diversification,

Originally Posted by Diversification
I am still surprised by the fact that BEA gave no hints in the short list explaning where the various ACARS were coming from.
Please, read again BEA interim reports 1 & 2 and specific ACARS chapters. Those reports, including the last note, are all completing each others and what could be explained with all informations on hand at the time each report was printed... was explained.
ACARS is designed for aircraft maintenance, not for aircrash investigations. Hence, some informations in ACARS sequence can not be acertained without access to other sources (CVR, DFDR, or by recovering avionics memories). Nonetheless, at this point, most is already explained or very narrowly conscripted.
What is much more disturbing on the subject is in fact this thread's noise/information ratio around some of the ACARS already explained from day 1 (see Bearfoil's posts still denying pitot and subsequent airspeed issues and consequences on flight systems!).

Originally Posted by Diversification
One of the last was about faults in Prim 1 and Sec 1, which were earlier assumed to be either showing serious faults of caused by pilot shut-downs of these systems.
PRIM 1 and SEC 1 ACARS are only ECAM messages (cockpit effects). There was no "fault" correlated with them that was sent by ACARS.
It could be due either to simple manual reset, or an auto-reset if some fault was detected, by its built-in test equipment (BITE); a single function affected may do that. There is no way to know more without looking into other system memories. If it was due to a manual reset, the CVR won't tell anything if nobody was talking about reseting the PRIM/SEC... The seriousness of this fault is quite improbable as there is 2 other PRIMs and another SEC.

Originally Posted by Diversification
Very often it has been assumed in this thread that there was 5 computers involved on AF447
There is effectively five Flight_Control_Computers": PRIM 1, 2, 3 + SEC 1 & 2. They very specific task is to manage pitch, roll, yaw, etc. depending on the various Flight Control Laws, which depend on other imputs (like Air Data, Inertial References, etc.)

Originally Posted by Diversification
however each of the three ADIRUs also contain at least one each and perhaps also one in each of the Air Data Modules.
Most avionic part of the system may be considered as a "computer". But they are very dedicated "computers" performing some straitforward tasks: ie. An ADM (Air Data Module) task is to digitalise the pneumatic source of a sensor for an ADR unit ; the ADR (Air Data Reference) role is simply to compute the various functions derived from those sensors (Speed, Mach, AoA, barometric altitude) for other "computers" like the FMGC, FADEC, PRIM, SEC, FWC...

Originally Posted by Diversification
I am making this conclusion from the australian report about sporadic AoA signals, where it is stated a software update for the ADIRU uncovered an old bug.
I have read the same report and the conclusion was that no "bug" was found on this ADIRU. Nonetheless, something went wrong, twice, with the same unit, but they did not found what it was. AoA spikes filtering was suspected but they could not reproduce it into the lab. Hence, what could have caused it? Was it internal or external? In fact, nobody knows.

Last edited by takata; 9th Jul 2011 at 21:20.
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Old 9th Jul 2011, 21:24
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At 2 h 10 min 51.......Around fifteen seconds later...........altitude reached its maximum of about 38,000 ft, its pitch attitude and angle of attack being 16 degrees

The recordings stopped at 2 h 14 min 28.

The last recorded values were a pitch attitude of 16.2 degrees nose-up.

So from 10:51 +0:15=11:05 to 14:28, ie 3 minutes +, all the efforts of the crew seem to have had no net effect on NU, but the heading changed. Is this plausible ?
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Old 9th Jul 2011, 21:54
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Missing ACARS explanations

Diversification;

Just to add another observation to takata's post - at 2h13min the aircraft was descending through FL175, deeply stalled, making uncontrollable roll oscillations left/right.

A similar temporary 'computing' condition may have occurred during the uncommanded pitch-down of QF72 - from the ATSB interim report on QF72:
In summary, the PRIM PITCH FAULTs and PRIM 3 FAULTs that occurred during the flight were consistent with the system design. They were consequences of the pitch-down events and not the initiators of those events.
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Old 9th Jul 2011, 22:14
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Originally Posted by Mr Optimistic
So from 10:51 +0:15=11:05 to 14:28, ie 3 minutes +, all the efforts of the crew seem to have had no net effect on NU, but the heading changed. Is this plausible ?
Based on the released information on the crew actions, it is entirely plausible. The great mystery is why the crew did not take decisive action to unstall the airplane. According to BEA's "3d" depiction of the flight path, the heading changed after point 6, when the airplane descended through FL350 at around 2:11:40. No further information on the heading change is available in the Update. I think the explanation must be sought in the difficulty of controlling the bank angle in a deep stall.
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Old 9th Jul 2011, 22:52
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Yes, I understand. But I struggle with it. The clearest interpretaion is that the crew sat for 3 minutes asking for NU and the a/c held its stalled attitude more or less constant through the descent for all those minutes. There are some who may wish to argue that the crew in fact wanted ND but the 'system' frustrated their attempt, but I see no evidence for that intent or that obstruction. Could it be that they just gave up ?

Edit: perhaps as an SLF I should wind my neck in, as they say, but the upshot is the a/c was stalled - clearly and obviously to the a/c systems- but it failed to convey that one vital piece of information to the crew despite all its cleverness and left them guessing for 3 minutes of descent in the turbulent darkness.
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Old 9th Jul 2011, 23:14
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without a way to index the various posts into categories like "THS", "Pitots", "Software", "SideStick", "FDR", etc. which would make them easier to "exploit".

I have yet to figure out an easy way to do this. However, the filtered search query will do just this for a given term - not quite as convenient but achieves the aim.
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Old 9th Jul 2011, 23:20
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Mr. O

Clearly, BEA believe that what they have witheld holds no danger in current A330 flights, or there would be mitigation; it would be difficult to hide any substantive change to the control system or airframe.

They allowed Airbus to make a statement, and one believes its accuracy, for it will harm the builder greatly if they are found to tell lies. BEA have no duty to "correct" public speculation, for they are comfortable that the information they provided is sound, and no corporate or gvernmental harm lurks.

It is not entirely wise to label what they have done as damage control. Typically, history teaches us that bad news is less disruptive if it is released slowly, and the public has the time both to soften, and go on to other things, (forget).

From the timetable itself, the a/c was in Alternate Law as she climbed. This provides no protection for Roll limiting, but includes AoA protection and direct control for both roll and pitch, aiui.

Right along with doubts about the climb whilst the PF is represented as commanding it, one must suitably indict the a/c for trimming for maximum Pitch UP. What was he THINKING.......

What was she DOING? Certification is mainly a mystery to me; I trust the system to certify a/c to be safe and reliable.

One understands the need for emphatic NU at TO and landing, but in the arena 447 found herself, why doesn't the THS have a LAW LOCK on it similar to the RTLU?

Your question is not so mysterious to me, The PF held back stick because he thought it the correct play. At 10k, his pard thought otherwise, and overrode the PF. "Your Airplane".

The Fourth ACT awaits us later this month?


EDIT. For Mr. O. The a/c systems did NOT know the a/c was stalled, no one did, Why would it protect itself from goofy feet (RTL), and let the Powered slab in back demolish everyone?

Trim is for comfort, when I learned how to use it. Giving any control surface the power to doom the a/c is so............unlike AirBus.

"She did everything asked of her....." Reminds me of what they said post Perpignan.......
 
Old 9th Jul 2011, 23:23
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Bear, all I can say is that they have my blessing: they were intelligent, trained and wanted to get home.
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Old 9th Jul 2011, 23:27
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It is so reassuring to hear you say that, it is in short supply here.

best wishes.
 
Old 9th Jul 2011, 23:31
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Yes, but my sympathy can't help them. If they did the wrong thing I would be reluctant to hold it to their account with so much software, and so many 'protections', standing guard over them.
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Old 9th Jul 2011, 23:45
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"Protections".

The nugget at the core of the Grand discussion. Keep in mind the Protections are to protect the a/c.

Loss of Autopilot in this fbw a/c is not an everyday or mundane thing. It should not be dangerous, and likely was not in this case.

From even the few scraps we were thrown with BEA's note, the first inputs by PF post a/p drop seem innocent enough. They morphed into ever more serious states of flight in very few seconds.

The AB flies "different" out of automatic, not fundamentally, though, and as I see it, the challenge is mounting the horse in full stride with gentle hands. Would this accident have happened if THS "TRIM" was disabled? Doesn't a certified a/c have to demonstrate recovery without trim? What in the World is so much control authority doing in STALL recovery? So much authority that the a/c cannot recover......it says so in the FCOM!!

Simplistically, why does this a/c have anything in addition to NORMAL LAW except bowing out gracefully to let the boys and girls fly it?

Such a needy, dependent, and conflicted aircraft is this one. Has a hard time "Letting Go". Or was it those who programmed her who can't give it up. Control Freaks?
 
Old 9th Jul 2011, 23:56
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Static (from last page of thread 4)

HN39:
Agreed, and everybody seems to think of the pitots misreading at high AoA, forgetting that airspeed is derived from the difference between two pressures: pitot and static. Sometime ago someone posted a drawing showing the static ports on the bottom of the front fuselage. At these AoA's the misreading of the static pressures may be more important than that of the pitot pressures. EDIT:: Particularly when "The airplane was subject to roll oscillations that sometimes reached 40 degrees" (Thx to an anonymous reader of the thread).
Thanks also to A337 for the refresher pix of the static ports.

The A330 has an apparent up to 300 ft static port correction at low airspeeds. This is not unusual, but at a greater AOA than stall warning, the static pressure is sure to increase to the point the static ports nearly become pitot ports.

Rather than, "What's it doing now?", the more I read the more I question, Why did they design it that way?"
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Old 9th Jul 2011, 23:58
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Well there is the question as to why the crew commanded a climb when 'pitch and power' was what was needed, unless you contend this wasn't wanted. UAS alone shouldn't have caused this loss.
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