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AF 447 Thread no. 4

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AF 447 Thread no. 4

Old 19th Jun 2011, 18:54
  #201 (permalink)  
 
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Originally Posted by infrequentflyer789
The BEA text, and the "3D view" graphic, seems to me to indicate that stall warning was before the second nose-up input and ascent.
The occurrence of stall warning indicates that AoA was increasing through the threshold. The BEA text says it was six degree at threshold, and "continued to increase". What caused that increase, if not a nose-up input? BEA again: "About 15 seconds later, (...) the PF continued to make nose-up inputs".

Incidentally, you must have unbelievably sharp eyes if you can discern s/w in "3D view".

At M.68/215kCAS, FL375, AoA=4 degrees, the load factor is 0.8. It must be greater than one to increase vertical speed.

Last edited by Jetdriver; 19th Jun 2011 at 20:56.
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Old 19th Jun 2011, 20:48
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Originally Posted by Machinbird
Those that wish to add a large turbulence/updraft element to this loss of control seem to be putting unnecesary sauce on the stew. Occam's Razor applies.
Occam's Razor, yes and also simple physics.
The potential/kinetic energy transfert calculation shows that at 37500 ft TAS should be 413 kt @ Std + 10 assuming constant thrust and drag. The BEA reports CAS 215 kt (M 0.68) at this altitude which gives 399 kt TAS @Std + 10.
Factoring decreasing thrust with increasing altitude and a bit of extra drag due to manoeuvring should easily account for the 14 kt discrepancy.

In no way the a/c gained energy as would have been the case in an updraft.
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Old 19th Jun 2011, 21:22
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Originally Posted by HazelNuts39
The occurrence of stall warning indicates that AoA was increasing through the threshold. The BEA text says it was six degree at threshold, and "continued to increase". What caused that increase, if not a nose-up input? BEA again: "About 15 seconds later, (...) the PF continued to make nose-up inputs".
I was assuming that the nose-down inputs didn't completely stop the climb, therefore the a/c is still trading speed for height (albeit at a slower rate) and thus increasing AoA.

Incidentally, you must have unbelievably sharp eyes if you can discern s/w in "3D view".
Was going by the "5" marker which the text states as s/w point. Looks to be between the climbs - but I admit there's not many pixels in it.

I should have been clearer that my post was merely conjecture, and the info we have at this point form BEA doesn't give sufficient detail or clarity to confirm it.
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Old 19th Jun 2011, 21:42
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Originally Posted by infrequentflyer789
Was going by the "5" marker which the text states as s/w point.
Agreed, thanks for clarifying that. The next sentence says that at that point - "the PF maintained nose-up input", which I read as saying that the input commenced earlier.

Otherwise, I don't see how the airplane arrives 15 seconds later at FL380 with zero v/s.
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Old 20th Jun 2011, 05:00
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Originally Posted by DozyWannabe
That image looks a little... how should I say... "dramatic" for an accident report. It looks more like a sensationalistic press cutting to me - how are the BEA responsible for that (any more so than the investigators in other countries responsible for their press getting the wrong end of the stick)?
Problem, in their animation, BEA also 'forgot' to represent those 2 flights which adventured 'in the middle of the storm' … Are BEA and mass media so different …

Let me know what you think of the stuff I PM'ed you!
There is absolutely matter for constructive discussion on a dedicated thread to Habsheim.
You could be surprised I don’t actually disagree on everything you write …


Originally Posted by HN39
NAV ADR DISAGREE
That message, time stamped 2:12, was received at 2:12:51. At that point in time the airplane was already in a full stall, with all airspeeds probably misreading due to pressure errors at the pitots and at the static sources due to the high AoA. I wonder if that could tell us anything about the speed displayed on PFD2 prior to stall, but can't figure it out. Anyone?
If I get you right, you would see the NAV ADR DISAGREE as a consequence of the stall rather than due to the pitot probes icing.
PFD2 and ISIS speeds may have agree for a while …
BEA : How long is it "then a few moments later" ?
275kt at FL350 is not slow either – How far is it from Vmax ?
What was the reason for AP disconnect then ?
ALT LAW maybe came 'then a few moments later' … until then protections were still avail.
Also, if 2 speeds sharp fall to 60kt one after the other … don’t they agree again ?

Svarin, what’s your take on this ?

Full FDR data … anyone ?


Originally Posted by 'BEA note 2011 05 27
The recorded parameters show a sharp fall from about 275 kt to 60 kt in the speed displayed on the left primary flight display (PFD), then a few moments later in the speed displayed on the integrated standby instrument system (ISIS).
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Old 20th Jun 2011, 05:17
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Rudderrat & Retired F-4
From the BEA Note:
At 2 h 12 min 02, the PF said "I don’t have any more indications", and the PNF said "we have


no valid indications".
At that moment, the thrust levers were in the IDLE detent and the
engines’ N1’s were at 55%. Around fifteen seconds later, the PF made pitch-down inputs. In
the following moments, the angle of attack decreased, the speeds became valid again and the
stall warning sounded again.

This tells me that the crew performed an "experiment" that indicates they could have reduced angle of attack using the elevators.

Even if there was a notch in the wing pitching moment, it is likely that this aircraft could have developed enough nose down momentum to proceed past the notch. Particularly if, as the aircraft began to pitch down, they then began to roll nose down trim in using the manual trim. In effect, as the aircraft began to pitch nose down, they began to match (approximately) the rotation rate of the aircraft nose down with the THS rotation. Success would have been signaled by getting light in their seats and return of rapidly accelerating airspeed at approximately 45 degrees nose down attitude.

If you will think back to Gum's Viper deep stall recovery, the recovery technique was to pitch the aircraft up and then develop sufficient pitch momentum nose down to pass through the sticking spot. In effect (with all that NU THS), AF447 was starting from the stick back position already and just needed to start the ball rolling forward.

I am wondering whether as the aircraft began to rotate nose down, the crew began to get light in the seat as the aircraft began to fall faster. That also could have been a discouraging factor to continued nose down input.
Of course in my F-4, best acceleration occurred at zero g, but the AF447 crew was undoubtedly not accustomed to the concept.


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Old 20th Jun 2011, 06:36
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I am wondering whether as the aircraft began to rotate nose down, the crew began to get light in the seat as the aircraft began to fall faster. That also could have been a discouraging factor to continued nose down input.
and not everyone was in a seat or at least not strapped into one.
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Old 20th Jun 2011, 09:55
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Originally Posted by CONF iture
Problem, in their animation, BEA also 'forgot' to represent those 2 flights which adventured 'in the middle of the storm' … Are BEA and mass media so different …
The BEA aren't reporting on or scrutinising those flights, they're only working on AF447. I'm sure that the presence of those flights will be mentioned in the report if it turns out to be relevant. It's worth remembering that Delta 191 proved that it only takes a couple of minutes for weather conditions to change drastically - what might have been mild for those other flights may not have been for AF447.


There is absolutely matter for constructive discussion on a dedicated thread to Habsheim.
You could be surprised I don’t actually disagree on everything you write …
I don't think another public thread would be worth it - not only because there have been so many and the issue done to death, but because it almost always ends up in a bunfight. I'm happy to participate in PM discussions though.
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Old 20th Jun 2011, 13:23
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ADR DISAGREE and others

CONF iture asked :

Svarin, what’s your take on this ?
I will summarize very quickly here :

At the start of accident sequence, two apparently unrelated faults :
PROBE PITOT 1X2/2X3/1X3
WRG:ADIRU1 BUS ADR1-2 TO FCPC2

PROBE FLR is very likely due to icing of probes by high altitude ice crystals.
It triggers a specific 10 seconds ADR checking process by all three PRIMs.
Starts 02:10:05.

All three PRIMs work in Alternate 2 for 10 seconds.

WRG FLR affects PRIM2 by cutting it from ADR1 data. My take is this happens right at the start of above mentioned 10 seconds ADR checking process.

At the end of these 10 seconds, each PRIM will either confirm and latch Alternate 2 or revert to Normal law, based on differences between ADR values. This is the purpose of this 10 seconds checking. This happens at 02:10:15.

My take is PRIM2 reverted alone to Normal, while PRIM1 & PRIM3 latched Alternate 2. This is because PRIM2's set of ADR data, being different (only ADR2 & ADR3), would have allowed differences into the 50 kts range that triggers reversion to Normal law.

The sentence "the aircraft was in Alternate 2" makes no sense. The PRIMs compute flight laws, not "the aircraft". All three PRIMs are 99.9999% of the time in full agreement. Not this time.

NAV ADR DISAGREE is CMC stamped 02:12 and ACARS ground-received at 02:12:51, which means it happened on board between 02:11:58 and 02:12:43. Aircraft was downwards fast at that time. Therefore, the ADR DISAGREE condition was not in effect to latch Alternate 2 for all three PRIMs at the start of pitch-up sequence at 02:10:16.

At 02:10:16, the pitch-up sequence and "zoom-climb" happened with (according to my research and "flimsy theory") PRIM1 & PRIM3 in Alternate 2 and PRIM2 in Normal.
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Old 20th Jun 2011, 14:08
  #210 (permalink)  
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Svarin - that is interesting. Excuse the non-AB brain here, but what are you are saying in terms of the Air Data presented to the crew at the outset? I'm afraid 'Prim 1 and 3 in Alt2 and 1 in normal' needs some translation for me. With 1 in 'normal' and the other two in 'Alt2' what would be the governing control law? Would the ASI's L and R now show a disagreement? Would they be 'invalidated'. Would the standby ASI be affected? What other baro/ADC sourced info is useable? IE Would the altimeters/VSI show the extreme climb?

Lastly, can you comment on what effect (if any) a low airspeed in the system might have on autotrim?

Apologies for all the questions, but your post is vastly more important than tailplane camber!
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Old 20th Jun 2011, 14:11
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Where I'm not so sure if I understand it correctly is the thing with the Sine.
I will give it a try based on how I understood your approach:
Henra, thank you for post 125, I crossed up where to use the axis of aircraft (external coord system) and the wing chord. It appears that I became a flesh version of one of RetiredF4's confusers.

I had experienced glorious moments . . and I now realize that it was all very beautiful. But I shall never again fly through a thunderstorm . ... unless the Fatherland should demand it. "
Source : Manfred von Richthofen's letters to his family
Hmm, an early definition of "Operational Necessity," and a consideration not consistent with operating commercial transport aircraft. OKC< thanks for the bon mot, The Red Baron has provided us with many such.
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Old 20th Jun 2011, 14:32
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BOAC asked :
Air Data presented to the crew at the outset? [...]
Would the ASI's L and R now show a disagreement? [...]
Would the standby ASI be affected?
BOAC, your questions are all related to what the crew is being provided as indications on their instrument panel. What I am dealing with is computerized flight controls.

ASIs were affected. But there is no way I could discern exactly how and when. Inside my own subset of research in this, however, ADR data (provided to Flight Controls Computers -> the PRIMs) was affected. In Normal law, PRIMs could effect ultimate authority on flight control surfaces. There are 3 of them. What happens when PRIMs are in disagreement ? Now that is a question...

FDR might reveal some of these parameters. It is however unfortunate that ADR2 data and associated RHS airspeed was not recorded on FDR...
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Old 20th Jun 2011, 15:00
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Governing control law ?

BOAC asked :

With 1 in 'normal' and the other two in 'Alt2' what would be the governing control law?
A simplified approach to this problem is to examine which computer governs which flight control surface, and examine carefully how the different flight laws work, and how they interfere with pilot actions. Reality would tend to be even more complex.

Occam's try on these hypotheses is the triggering of an undesired normal law (full authority) overspeed protection by PRIM2 only which uses erroneous airspeed data after having unexpectedly returned to Normal law. This protection reacts to speed only, and simply adds a nose-up order, with authority superior to that of pilot sidestick. Alarms and warning triggers to the crew are a big unknown in this situation...

This situation I described is absolutely not what should happen on a FBW aircraft. Flight Controls Computers are not supposed to disagree at every turn. They are almost always in full agreement to the 0.0000001% precision.

I have determined, however, that in this particular instance, they were likely not in agreement. After such an unprecedented problem, all bets are off.

This is not fundamentally different from the unexpected rudder hardover in a 737, or the unexpected loss of all hydraulics on a DC-10 or 747, or whatever... These happen extemely rarely and are always specific to a certain design. No design is perfect, even this one.

Designs always contain certain trade-offs, carry certain basic assumptions, and try to cater for the unexpected in the best way possible. The more complex they are, however, the more prone to human-like error they become.

James Reason is always quoted for his Swiss-cheese model, but he could also be quoted for this : "intelligence and error are both sides of the same coin".

Last edited by Jetdriver; 20th Jun 2011 at 15:18.
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Old 20th Jun 2011, 15:05
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Dozy, the BEA seems to have had extensive conversations with the crews of the other three flights (Lufthansa, Iberia, and AF459).

The first interim report had this to say about AF459's use of radar. (AF459 was 35 minutes behind at 350)
After flying through a turbulent zone in the head of a cumulus congestus formation at the level of NATAL, without having detected this zone on the radar, he selected gain in MAX mode. At about 2 h 00, he observed a first echo that differed significantly depending on whether the radar’s gain was in CAL or MAX mode. The TILT was set between -1° and 1.5° ....the screen, which was set to a scale of 160 NM. The echoes were yellow and red when the radar was set with gain on the MAX position and green and yellow when the gain was on the CAL position
Lufthansa (20 minutes ahead at 325, (FL based on AMDAR trace))
The crew reported that it flew at the upper limit of the cloud layer and then in the clouds in the region of ORARO. In this zone they saw green echoes on the radar on their path, which they avoided by changing their route
Iberia (12 minutes behind at 370), the BEA report does not mention their use of radar.
These conditions were particularly severe 70 NM to 30 NM before the TASIL waypoint. They moved away from the route by about 30 NM to the east to avoid cumulonimbus formations with a significant vertical development, and then returned to the airway in clear skies close to the
TASIL waypoint.
As for AF459, same model airplane, presumably same radar system, similar flight crew training, and also had presumably received a similar message from dispatch re: satellite observation of Cbs vicinity ORARO-TASIL. (AF459 departed approximately same time as AF447, but from further south.) Did the captain of AF459 take a rest at the typical time? Did AF459 change comm frequency away from ATLANTICO immediately after a SELCAL check? Comparisons of behavior between the two crews could be quite enlightening.

Even in the absence of a full CVR, inferences can start to be drawn regarding the situational awareness of the AF447 flight crew, before and during.

In its brief note, the BEA did not mention any crew conversation about the radar setting. If they had changed the mode and discussed it, would not the BEA have mentioned such? The BEA does note that the flight crew notified the cabin crew that they would be going through an area of turbulence, but no indication of any specific instructions to the cabin crew to be seated, stop service, etc. The BEA does not note any attempt by the crew to communicate with ATLANTICO or DAKAR about its circumstances, even though it had looped in its heading. (If IB6024 had not deviated, it would be only eight minutes behind at the climactic point.)

My own feeling is that if there was exculpatory conversation on the CVR, the BEA would have referenced such in its brief note.
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Old 20th Jun 2011, 15:14
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ATSB's 1st Interim Report on the QF32 pitch-down accident describes the role division between the PRIMs:
Review of PRIM monitoring functions
The aircraft’s flight control system included three flight control primary computers (FCPCs, commonly known as PRIMs) and two flight control secondary computers (FCSCs, commonly known as SECs). One PRIM functioned as the master while the other two PRIMs could take over as master if a fault in the current master was detected. The master PRIM processed and sent control surface deflection orders to other computers, which executed them using servo-controls. The two other PRIMs continuously computed control orders and monitored control surface deflections but those orders were not actioned.
Each PRIM consisted of two independent parts, a Command (COM) part and a Monitor (MON) part. The MON part monitored the performance of the COM part and the position of the control surfaces. If there was a discrepancy between COM and MON, then the PRIM would ‘fault’ itself. The fault could be for only a part of the PRIM (for example, pitch channel) or for the whole PRIM. A PRIM could not generate a fault for the whole PRIM unless it was the master. The PRIM Fault parameter recorded by the FDR was active only for a fault of the whole PRIM and not for a partial fault (for example, a pitch channel fault). However, partial faults were recorded by the PFR.
For elevator control, the active servo-controller in normal operation was PRIM 1. The servo-controller priority order was PRIM 1, PRIM 2, SEC 1 and SEC2. If PRIM 1 could not perform this function, then the servo-control function reverted to PRIM 2 and so on.

Table 4 provides a sequence of events for the PRIMs and is based on a review of the FDR and PFR data by the aircraft manufacturer and investigation team.

Table 4: PRIM sequence of events
(table deleted, does not reproduce in PPRuNe - HN39)

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 20th Jun 2011, 15:56
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CONF iture asked :Svarin, what’s your take on this ?

I will summarize very quickly here :

At the start of accident sequence, two apparently unrelated faults
PROBE PITOT 1X2/2X3/1X3
WRG:ADIRU1 BUS ADR1-2 TO FCPC2

PROBE FLR is very likely due to icing of probes by high altitude ice crystals.
It triggers a specific 10 seconds ADR checking process by all three PRIMs.Starts 02:10:05.

All three PRIMs work in Alternate 2 for 10 seconds.

WRG FLR affects PRIM2 by cutting it from ADR1 data. My take is this happens right at the start of above mentioned 10 seconds ADR checking process.

At the end of these 10 seconds, each PRIM will either confirm and latch Alternate 2 [B]or revert to Normal law, based on differences between ADR values. This is the purpose of this 10 seconds checking. This happens at 02:10:15.

My take is PRIM2 reverted alone to Normal, while PRIM1 & PRIM3 latched Alternate 2. This is because PRIM2's set of ADR data, being different (only ADR2 & ADR3), would have allowed differences into the 50 kts range that triggers reversion to Normal law.

The sentence "the aircraft was in Alternate 2" makes no sense. The PRIMs compute flight laws, not "the aircraft". All three PRIMs are 99.9999% of the time in full agreement. Not this time.

NAV ADR DISAGREE is CMC stamped 02:12 and ACARS ground-received at 02:12:51, which means it happened on board between 02:11:58 and 02:12:43. Aircraft was downwards fast at that time. Therefore, the ADR DISAGREE condition was not in effect to latch Alternate 2 for all three PRIMs at the start of pitch-up sequence at 02:10:16.

At 02:10:16, the pitch-up sequence and "zoom-climb" happened with (according to my research and "flimsy theory") PRIM1 & PRIM3 in Alternate 2 and PRIM2 in Normal.
If so, this would be a serious system flaw and therefore I disagree.

There’s only 1 PRIM in control and that will be the one which can deliver the highest possible law and in the sequence PRIM 1, 2 & 3

If PRIM 2, in your view, is in control and able to deliver NORMAL LAW this means that PRIM 1 was not able to compute NORMAL LAW protections and doesn’t say anything about the ability of PRIM 3. If PRIM 2 is in control in ALTERNATE LAW this means PRIM 1 and PRIM 3 could not deliver NORMAL LAW and PRIM 1 was also unable to deliver ALTERNATE LAW.

I’m sure if PRIM 2 was in (NORMAL or ALTERNATE) control this had already been mentioned in the BEA update.

ALTERNATE 2 mode is latched, so once it is declared (at the time message F/CTL ALTERNATE LAW appeared on ECAM and PF called it out) there can only be a reset on ground with all hydraulic systems depressurized.

In my view, at that time PRIM 1 was in control, PRIM 2 and 3 couldn’t compute NORMAL LAW either.
Due to the PITOT problem they had all the same ADR information.

PRIM 1 declared ALTERNATE 2 LAW and no PRIM can revert to a higher law anymore even if ADR becomes normal thereafter.
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Old 20th Jun 2011, 16:45
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savrin:

How do you fit your analysis with this from the BEA note?

At 2 h 10 min 16, the PNF said "so, we’ve lost the speeds" then "alternate law […]".
You state:

My take is PRIM2 reverted alone to Normal, while PRIM1 & PRIM3 latched Alternate 2. This is because PRIM2's set of ADR data, being different (only ADR2 & ADR3), would have allowed differences into the 50 kts range that triggers reversion to Normal law.

<snip>

At 02:10:16, the pitch-up sequence and "zoom-climb" happened with (according to my research and "flimsy theory") PRIM1 & PRIM3 in Alternate 2 and PRIM2 in Normal. 20th Jun 2011 05:55
Unfortunately, based on the voice comment above, I seriously doubt the control law in effect was Normal during the "zoom-climb" event, unless you are saying that the PF controls were in Normal, while PNF was seeing Alternate (but my understanding is that this is not possible).
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Old 20th Jun 2011, 17:05
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GY

As the system is supposed to work (based on what I understand of it) that seems to be the case, but what has Svarin concerned seems to be the system not working as advertised ... which would lead the cockpit crew into some confusion regarding "what instruments are right?" and "what is it doing now?" In that state of confusion, attention to flying can easily be diverted, and diverted attention is one of the few hypotneses available to explain an inadvertent 3000 foot climb. <-------- That makes little sense.

(Pitch and power chorus in three, two, one ... )

If there's a bug, how to you find it? How much time and effort, and what initial conditions are necessary, to replicate it?

And, cui bono? (Small bit of tinfoil on me head for the following)

What incentive does AB have to pursue a very low probability bug with only circumstantial, and possibly second or third order, evidence? From a practical point of view, how do you determing the initial conditions (internal to the system) to try and trigger it? With a certain amount of information missing ... it may not be doable.
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Old 20th Jun 2011, 17:25
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Originally Posted by Lonewolf_50
With a certain amount of information missing ... it may not be doable.
Please....
Don't confuse what we are trying to deduce here, from just an initial 'text' description of the 'events' from the BEA note, with the work being done by the BEA, with (one expects) AB support.
THEY have the traces, the full FDR and CVR records, and the full documentation of the FCS.
I'm sure they're going through some of the same discussions, but with a far greater amount of information at hand.

I've seen no mention of the QAR having been recovered. It might have provided even more info.
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Old 20th Jun 2011, 17:42
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Understood, ChristiaanJ, and I'm not trying to get too far ahead of the problem.

The problem with electrical ghost faults is the damnable time one has in replicating them. I've had gripes and write-ups that repeatedly got signed off as "could not replicate on deck" which sometimes, because they could not be replicated, were very difficult to trouble shoot.

That is also true for spurious signals and strange behavior in computer driven equipment in aircraft. Sometimes, the only maintenance action was to reboot the damned thing.

If the QAR is available, that raises the odds for successful analysis, but it is no guarantee.
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