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AF447 Thread No. 3

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AF447 Thread No. 3

Old 14th Jun 2011, 03:16
  #1981 (permalink)  
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… rather than having to dance between the stick, throttles and trim wheel with only two hands.
MAYDAY MAYDAY


The only way autotrim is activated is if the stick is fully deflected and held there past the elevator travel limit.
...
the autotrim will only move the THS in Alternate Law if the limit of elevator travel is reached and the pilot continues to demand pitch-up via the sidestick. It needs to be aggressive and maintained for a period of time. I did confirm this via PM with PJ2 …
How misinformed can you be, and I even cannot feel the slightest doubt in your voice.
Let me have a serious doubt PJ2 said anything like it, but he will confirm if he did …

DozyWannabe, you’re not a pilot and don’t pretend to be one, and nothing wrong with that, but PLEASE, maybe you should refrain talking as if you were the Experienced guy around.
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Old 14th Jun 2011, 06:58
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Deep stall

Machinbird

call it whatever you want. The fact is this plane was out of control from the top of the zoom until it hit bottom.
It did not respond to any of the inputs whether applied correctly or not.

I know of many instances where planes were unrecoverable.

Did a horrendous thunderstorm have anything to do with it?

I say absolutely.
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Old 14th Jun 2011, 07:36
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Rudder trim

Originally posted by DozyWannabe,
Why would you be using rudder in cruise?
How then, would you trim out a tendency to roll, if you were in Alternate Law at FL350?
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Old 14th Jun 2011, 09:55
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WRG

JD-EE:
Edit: I think we agree. I am in disagreement with A33Zab's assurance this is the problem.



Don't get me wrong, I didn't assured this is THE problem! On the contrary it's NOT.
I'm sure the abbr. 'WRG' statement is for WIRING. (NOT WARNING).
As I also said it's a Maintenance Class 2 message, presented to PFR at the start of maintenance phase and in 'Real Time" through ACARS.
No big deal usually.


The fact that this message is known in the system (detected by EFCS2 and confirmed by EFSC1) and rated as Maintenance Class 2 (no consequences for remainder of flight) should 'comfort' one.
EFCS knows this input is unreliable!
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Old 14th Jun 2011, 10:07
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ACARS abbreviations.

WND Wind (direction/velocity)
WOB Weather observation
WRN Warning
WXA Weather at
WXR Weather
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Old 14th Jun 2011, 10:10
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Originally Posted by CONF iture
How misinformed can you be, and I even cannot feel the slightest doubt in your voice.
Let me have a serious doubt PJ2 said anything like it, but he will confirm if he did …

DozyWannabe, you’re not a pilot and don’t pretend to be one, and nothing wrong with that, but PLEASE, maybe you should refrain talking as if you were the Experienced guy around.
Ahem...

Originally Posted by DozyWannabe
Speaking of which, I wanted to double-check something with you. Am I right in thinking that in ALT 2 (aka "NO PROT") with airspeed data gone, that the FCU (or A330 equivalent) autotrim will basically use the THS to meet pilot demands when the limits of the elevators are exceeded?
And the reply...

Originally Posted by PJ2
Regarding your question, yes, to put it simply, the THS will follow the sidestick orders in Alt 2 Law.

The elevators are short term pitch control, the THS long-term, providing the elevators with full authority throughout their range. The THS changes position as a result of inputs from the FCMC, (Fuel Control Monitoring Computer), LGCIU, (Landing Gear Control and Interface Unit), the SFCC, (Slat Flap Control Computer which input data to the in-command FMGEC, (in this case the #2, as #2 AFS was engaged). The FMGEC sums control command inputs including those from the sidesticks and the FCU (Flight Control Unit on the A330), and sends position orders to the FCPCs & FCSCs which in turn provide a "Delta QT" order for the THS, Delta Q for the elevators, and so on.

The AF 447 THS was simply doing as it was ordered within the limits of aircraft attitude in the FMGECs. The THS disengages under a number of important circumstances including an AoA of >30deg/< -10 but pilot authority is retained up to these limits and, most importantly.

This point has been completely missed by many (though not all, especially the old guys!), manual operation of the THS is a simple matter of rolling the trim wheel forward to return the setting from 13deg to 3 or whatever was needed until the system could re-engage.
So CONF, if you don't mind, maybe a little less of the emphatic declarative in your tone (and maybe, you know, one day accepting that Asseline was wrong and Jacquet *did* go mad trying to defend the indefensible) would be in order?

@rudderrudderrat - If the rudder was the only way to correct roll (and in this case we don't even know if the aircraft was having lateral stability issues or not - it's not in either the early interim report or the note), then there's a manual dial and switch on the centre console.

Last edited by DozyWannabe; 14th Jun 2011 at 10:40.
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Old 14th Jun 2011, 10:44
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A33Zab, post #1571

I have studied carefully what you posted. I decided to leave your own post in full and add my own commentary/questions in the middle. This is because your post addresses one set of problems and questions, whereas I am using the fascinating factual data you provided to address a different set of questions. Out of honesty I thought I would rather leave your post in full. The data I am using is set in bold, bolding is mine.

Went into the ADIRU today:

ADIRU computes AOAi from sensor resolver cos. and sin. and calculates
AOAc as function of AOAi, FLAPSLAT CONFIG and Sensor position(LH/RH)

If CAS < 60 Kts AOAi & AOAc are set to 0° and SSM (System Status Matrix) is set to NCD (No Computed Data),
this is also valid for TAS 0 Kts if CAS < 60

If CAS < 30 Kts it declares itself invalid and outputs 0 Kts and NCD.

These parameters are send to 8 similar ARINC output busses.
Bus 5-8 are reserved for the engines only. (Bus 7-8 are not used on A33).
Note: GE engine provides its own Air Data, A/C ADR is only used as backup.

PRIM 2 & 3 receives data by ADR's bus 2, FCPC 1 by ADR’s bus 3.
Therefore, failure between "ADR1-and-PRIM2-only", as in WRG:ADIRU1 BUS ADR1-2 TO FCPC2, means it is not a full bus fault, but rather a fault at either end of that line, either ADR1 or FCPC2.

Note: In Back-Up Speed Scale (BUSS) equipped A/C AOA is send via IR bus
Note: Couldn't find if a SSM NCD is taken in account by PRIM but most probably it will.

In the 1st BEA report the unreliable speed logic is explained.

The PRIMs trigger a monitoring process when one of the speeds decreases more than 30 Kts (in 1 sec.) compared to the median value.
This is what happens as a result of what triggered the PROBE-PITOT 1X2/2X3/1X3 message. Very likely high-altitude ice crystals clogging Pitot probes.

My main contention is that a latent software incompatibility between PRIM2 and ADR1 specific software versions revealed itself only under this specific set of circumstances, ie : the monitoring process of ADRs by PRIMs. In all other operating modes, they did cooperate smoothly.

This cannot be reported as a software fault by the system, because such things are not catered for in design, all perfectly logical because it is a high-reliability hard-wired system, not your average PC Operating System. Hence the WRG:ADIRU1 BUS ADR1-2 TO FCPC2 wiring message, which is not wiring at all but the only way the system could report incompatible message exchanging between ADR1 and FCPC2. A software fault.

The PRIM opens a monitoring window during which it operate in ALT 2 Law, the rudder deflection limit is frozen but associated message is inhibited.

At the end of the monitoring window, if the diff. is less than 50 Kts the PRIM returns to normal law.
Return to Normal law is therefore possible at this stage. PRIM2 lost ADR1. This likely happened during this process. Has PRIM2 returned to Normal Law as a result of acceptable difference between remaining two ADRs, unlike PRIM1 & 3 ?
Return to Normal Law would occur after 10 seconds have elapsed. This is important as will be shown.

If not it remain in ALT 2 LAW and at that time the F/CTL RUD TRV LIM FAULTmessage is shown.
This is what happened to PRIM1 which is master by default.

Outlier ADR is rejected and remaining control is on median value of the other 2 ADR’s
Is this what happens when PRIM2 loses connection with ADR1 ? Does it uses median value from ADR2 & ADR3 ?

(Stall warning is generated by highest AOA and not the median value)
This means actual AOA could be indeed 40° while not triggering ABNORMAL ATTITUDE LAW due to a median AOA value below <30° as already mentioned in the BEA ‘leak’.

If 2 ADR outputs are erroneous, but different, and the remaining ADR is correct OR all 3 are erroneous but different:

The AP and A/THR disconnects and if disagree last for more than 10s, the PRIMs trigger the NAV ADR DISAGREEmessage.
ALTERNATE 2 LAW become active and latched for remainder of the flight.
(AP and A/THR can be re-engaged if ADR output was only transient.)
In the case under discussion, NAV ADR DISAGREE was time-stamped by CMC at 02:12, acknowledged on the ground through ACARS at 02:12:51, which means the ECAM warning was generated between 02:11:58 and 02:12:46. Much later in the sequence. This also means that the ADRs monitoring process by the PRIMs from 02:10:05 to 02:10:16 did not generate this ADR DISAGREE immediately, which would have latched Alternate 2 law for all PRIMs. But this designed sequence did not evolve as expected.

What happened around 02:10:16, at the end of the initial monitoring process ?
No ADR DISAGREE yet. A Probe fault and a wiring fault, and PRIM2 in an undefined state, but quite possibly in Normal law.

BEA reports : "from 02:10:05 the autopilot then auto-thrust disengaged and the PF said "I have the controls" ("j'ai les commandes"). This marks the beginning of the monitoring process.
BEA reports : "The airplane began to roll to the right and the PF made a left nose-up input". BEA does not correlate this particular input with any significant change in attitude or flight path.

10 seconds elapsed.

BEA reports : "at 02:10:16 PNF says So we've lost the speeds, alternate law". This marks the end of the monitoring process.

BEA reports then "the airplane -attitude- increased progressively beyond 10 degrees and the plane started to climb".
This marks the beginning of the initial pitch-up event. I contend that it was undesired by PF :
BEA reports : "The PF made nose-down control inputs and alternately left and right roll inputs". Undesired climb.

I contend that this looks very much like an undesired overspeed protection acting on the basis of erroneous airspeed data.
FCOM notes that Overspeed Protection provides "positive static spiral stability" which means neutral stick roll-wise will actively return the aircraft to zero bank, instead of maintaining zero roll-rate.

This is a significant departure from the way the pilot usually flies this type of aircraft manually. I contend that this would at least partly explain the roll control difficulties faced by PF from 02:10:16 until the top of undesired climb, compounding his ability to identify a critical flight controls issue on the pitch axis.

Active PRIM could in this case reject the correct ADR data.
That's why crew need to perform the unreliable speed Indic/ADR check QRH procedure and isolate the ADR in error. (Thus it will not be used for faulty PRIM input & indication).

The PF slight but consistent nose up command is a +G request to the PRIMs, the A/C feedback by means of accelerometers however results in a -G.
PRIM deflects elevator and due to negative result drives the THS all the way ANU.

Unfortunate left unnoticed because any hand on the trim wheel had cancelled the PRIM THS orders.
This obvious "emergency exit" only works if the pilots are actually trained to use it against normal practice of Norm/Alt flight laws. The amber PFD indication USE MAN PITCH TRIM does not appear either in Normal nor in Alternate 1 or 2 laws. Only Direct Law provides it. Direct Law likely did not activate throughout the accident sequence.
Another manufacturer of FBW large civilian transport aircraft leaves speed trimming to pilot control. This helps keeping the habit of using manual pitch trim to assist elevator commands when the need is felt. On the other hand, with a full auto-trim which works perfectly 99.9999% of the time, this habit disappears.
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Old 14th Jun 2011, 11:07
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Thanks Lonewolf

Thanks for the response - I'll track down those threads in due course.
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Old 14th Jun 2011, 11:11
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@RR_NDB

And also i would like to known if Aluminum cable is used in 330/340 (being used in the 380).
Rest assured that the Alu & contacts developed and used by Airbus is light-years away from the white paste efforts I [we] started with on Canberras....

Alu also limited to non environmental zones.
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Old 14th Jun 2011, 11:37
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Svarin
FCOM notes that Overspeed Protection provides "positive static spiral stability" which means neutral stick roll-wise will actively return the aircraft to zero bank, instead of maintaining zero roll-rate.

This is a significant departure from the way the pilot usually flies this type of aircraft manually. I contend that this would at least partly explain the roll control difficulties faced by PF from 02:10:16 until the top of undesired climb, compounding his ability to identify a critical flight controls issue on the pitch axis.
That only applies in Normal Law - in ALT 2 the roll control is direct - so no positive spiral stability. That is why the a/c rolled on AP disconnect instead of maintaining zero roll-rate.
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Old 14th Jun 2011, 11:57
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Autotrim

Quote from DozyWannabe (Jun13/2255z):
"The only way autotrim is activated is if the stick is fully deflected and held there past the elevator travel limit. It's there to give the pilot more authority when the chips are down."

Like CONF_iture, I think you are misunderstanding the role of autotrim and, in your latest post (Jun14/1010z) you also seem to be misinterpreting the following piece you quote from PJ2:
"...to put it simply, the THS will follow the sidestick orders in Alt 2 Law.
The elevators are short term pitch control, the THS long-term, providing the elevators with full authority throughout their range."

The role of the autotrim is to enable the elevators to return to neutral as soon as possible after a change of pitch or of pitch-trim has been executed. The latter may have been ordered by PRIM or SEC (for example, to maintain 1G with a decreasing airspeed). In the case that you are discussing, it is by sidestick movement.

Even if the PF moves the stick back a small amount, he is ordering a pitch-up. The elevators deflect slightly up. This reduces the available pitch-up capability slightly, so the autotrim adjusts the THS slightly in the nose-up-trim sense, allowing the elevators to neutralise again. As PJ2 says, "The elevators are short term pitch control, the THS long-term, providing the elevators with full authority throughout their range."

But even with no sidestick displacement, this FBW system would provide up-elevator as the aeroplane slowed down: initially to maintain the 1G-trajectory that the pilot's inaction would have in effect commanded. Again, the "short-term" up-elevator would be backed up by "long-term" THS.

Hope this makes sense.

Last edited by Jetdriver; 14th Jun 2011 at 14:09.
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Old 14th Jun 2011, 12:04
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Dozy:
Warmest regards, but what PJ2 stated (which you quoted) and what Conf cited you as saying (he quoting you) aren't the same thing. I think his concern is ...
"The only way autotrim is activated is if the stick is fully deflected and held there past the elevator travel limit. It's there to give the pilot more authority when the chips are down."

Ah, I note Chris Scott has responded, I'll not comment other than to say "the way you paraphrased that isn't how I understood PJ2's point."

Regarding this:
rather than having to dance between the stick, throttles and trim wheel with only two hands
You might be surprised to learn that novice student pilots do this every day in cable operated aircraft (I did in the T-28 ages ago, with prop lever and throttle and mixture on the throttle quadrant, just above the trim wheel for the elevator, and Naval flight students still do this in the T-34 with just throttle above the trim wheel) and don't seem to be overloaded. It isn't that hard, particularly at altitude. Now, in a high task environment ... depends on what you train to do and what your habits are.
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Old 14th Jun 2011, 12:29
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@Chris Scott, Lonewolf_50,

Thanks for taking the time to clarify my paraphrasing, though I think that the spirit of what I'm saying (that you don't get 13 degrees of THS nose-up trim unless you do something pretty drastic to the controls, and even then you can disable autotrim with the wheel) isn't that far off - I'm trying to translate the tech-speak into as near layman's terms as possible.

LW_50, I think we've discussed handling trim, stick and throttles in our PMs. I'm not insinuating that pilots can't or shouldn't juggle the three controls, but I wonder whether it's not something of an improvement to be able to do it with two (one less thing to concentrate on in a high-stress, high-workload environment).

Still, I note that now we're getting into theories involving computer "glitches" that rapidly oscillate between Normal and Alt Law and cause the computer to trigger overspeed protection, despite there being no evidence of an overspeed warning in the material we have so far...

Seeing as how I've been accused of trying to blame the pilot, being "in love" with the automatics and having "blind faith" in technology by CONF, bearfoil and others over the course of this thread - when none of these things are true - I can't help but feel a little irritated by that. The only reason I'm posting what I am is because the reflexive knee-jerk attempt to blame the aircraft and systems is unfounded (as is any attempt to blame the pilot) until we have all the facts, and for that we have no choice but to wait for the next report, be that final or interim.

Last edited by DozyWannabe; 14th Jun 2011 at 12:40.
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Old 14th Jun 2011, 12:52
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Lonewolf 50,
Sorry to steal your thunder.

Was just about to add a PS to my post: I venture to say that Airbus FBW aircraft in Pitch-Normal and Pitch-Alternate laws lack the speed-stability of a Chipmunk, B747 or, for that matter, the A310.

Regarding the argument about whether the PF would be better off with a reversion straight to Direct Law, I'm ambivolent. Once I was on the A320 (14 years), I never re-trained to a conventionally-controlled jet, although I did a bit of Chipmunk flying. However, many of our A320 copilots went off to get their commands on B757/767, or to the B747 for long-haul experience. Many found it difficult to adapt to doing their own pitch-trim, particularly if the A320 had been their first jet type.

Speaking generally, the need to pitch-trim, and maybe rudder-trim, while using sidestick and throttles doesn't seem any more difficult than one's first instrument rating exam on a light-twin during which you're also expected to produce immaculate R/T calls. (Ah, the nostalgia...)

DozyWanabee,
It now seems clear that unlike a pilot (see Smilin_Ed Jun13/2321z) Pitch-Alternate continues trimming regardless of the speed or AoA. Having accepted that, the fact that the THS reached 12deg nose-up trim at the apogee does not surprise me, although I have no figures to confirm the assertion. You might be surprised how much nose-up trim is applied for a normal approach to land, even when flapless. (Again, I can't supply any figures.)

Last edited by Jetdriver; 14th Jun 2011 at 14:09.
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Old 14th Jun 2011, 13:00
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Dozy:

To add a point on task loading regarding flight controls and power.

In a multi-place cockpit, where there are four hands , depending on how you train and use CRM, you can in difficult scenarios split the tasks up so that the PF applies his hand (sidestick) feet( rudders) and other hand (trim wheel), while the PNF handles power adjustments ... and they talk to each other while this goes on.

I won't make a generalized statement beyond that, since the opinions on that, and variations on how one breaks down task management is both organizationally and "culturally" influenced.

Chris: better you than me, as I think you understand it better than I.
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Old 14th Jun 2011, 13:01
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@Chris Scott - For landing, sure. But in high-altitude cruise? There's absolutely no way that could be considered a normal or wise setting, surely?

@Lonewolf_50 - Yes, I'm aware that normally there are four hands on a two-person flight deck, but if you go back to the point I made originally, I put forward the hypothesis that two-handed operation would be an improvement in the case of a pilot incapacitation scenario, when the number of available hands is reduced to two.
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Old 14th Jun 2011, 13:37
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DW,
Do we Know what the THS setting was in the cruise prior to the UAS event? The idea of the trim tank is to enable the THS to be fairly neutral. As far as I know, the THS was thus until the steep climb with rapidly-decaying (actual) IAS. Unless I'm missing something, there's no mystery in it. The FBW was doing its best within its terms of reference to comply with PF commands. The natural tendency of the nose to drop as the speed decayed was counteracted by increasing nose-up trim, provided by the THS in autotrim right up to the stall and beyond.

By the way, I've made a small clarification to my previous post.

Last edited by Jetdriver; 14th Jun 2011 at 14:09.
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Old 14th Jun 2011, 14:05
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Hi Chris

I asked that a while ago, and reading your question, I think I may be misinformed. I had always thought the purpose of Aft Trim Tank, or even "geographic" changes to enhance aft trim were intended to add Drag, "Lift" to the tail such that the AoA of the wing could be reduced, and lower Fuel Burn. It is a slight Overall reduction in Drag, but on long haul can save buckets of dough. Was I laboring under a misconception?

I suppose it could be viewed similarly, as the reduction in AoA of the HS reduces Drag also? I see you added to your post, so I will ask another question in reference to your ad.


"...The natural tendency of the nose to drop as the speed decayed was counteracted by increasing nose-up trim, provided by the THS in autotrim right up to the stall and beyond...".

So now we know the Airbus does use PITCH to control SPEED ? And does it do this with Autotrim (PITCH) with the Throttles in "manual" (A/THR disconnect). Could the a/c ever have autotrim without Autothrottle?

Last edited by bearfoil; 14th Jun 2011 at 14:16. Reason: additional question
 
Old 14th Jun 2011, 14:08
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Increasing complexity investigation task

Svarin,

You asked: These faults are unrelated : wiring + icing. How can this be ?

Has this strangest of dual failures ever been foreseen ?
How can one expect the design to operate as advertised in this likely un-designed for situation ?
Does anyone have reliable information as to the exact state of PRIM2 operation after this combination of faults ?
How can anyone be certain that PRIM2 did indeed latch Alternate 2 Law ?
How can one be sure it did compute identical to PRIM1 & PRIM3 when it is obvious its state is different ?
What happens if PRIMs differ in their assessment of the outlier ADR ?
What happens if, after their 10 seconds ADR cross-checking "window", PRIMs end up in different states, deciding on different flight laws ?
Has anyone considered what could happen to PRIM2 if it lost datalink with ADR1 at the very moment when the PRIMs tried to eliminate the outlier ADR ?
The accident investigation of "hardware based" a/c involves dealing with facts "recorded' in wreckage, site evidences, recorders (if available), forensic analysis of victims, etc.

The answer of your (above) questions depends "working" with resources and data we don´t have.

In this case, with a highly complex a/c, with a chain of events triggered by analog parameters (individually recorded?), the info on RH not recorded, and an intriguing coincidence (icing+wiring issue), unfortunately i can only reply with more questions:

1) The recorded data (FDR) could be sufficient to simulate and understand what could happened (with same config´s, software versions, etc)
2) Could BEA operate properly, considering only Airbus SAS has all (most) expertise to understand all (most) issues involving it´s complex product and probable behavior under such circonstances?
3) Are recorded parameters (FDR) enough to analyze and understand all important facts (possible intermitent failures, glitches, etc.)

What concerns me is:

The crew actions and responses are fully recorded and can be used to identify responsabilities.

The "System" working could be analyzed and understood (simulating similar inputs, etc) based in available recorded data? There are other recorded data that could be used in the BEA investigation?

Or we may enter (due the complexity of the a/c System) in a situation to never understand completely what happened at that critical moments (7,000 fpm climb, NU inputs, etc)?

In summary: The recorded data (FDR) is sufficient to fully characterize System responsibilities in this specific case?

My question is because i don´t know if available recorded data could be sufficient to fully analyze the working of a complex "finite states machine" (with this responsibility in Airbus SAS planes design)

And, are current FDR compatible to "advanced planes" using Systems with increasing responsibility? Current FDR are capable to allow a full understanding of what really happens in the Systems? And at what level?

Last edited by RR_NDB; 14th Jun 2011 at 14:16. Reason: typo
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Old 14th Jun 2011, 14:13
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@Chris Scott

I think we're more-or-less on the same page, though it looks like I oversimplified my description of autotrim function in Alt 2 to make my point, if so - my bad.

Now, for the duration of this thread I've been trying to keep speculation to a minimum in the hope that others would do the same. To be clear, as an engineer I have no desire to defend a systems design or implementation that is seriously broken, likewise as someone who has had a love of aviation since primary school and a commeasurate respect for pilots I have no interest in blaming them. However to make a call we need more evidence, and the amount of pontificating that's been going on regarding what the computers might have done based on nothing more than anti-Airbus prejudice has been as frequent as it has been sadly predictable.

So, to make things clear:

- With autoflight out, the only thing that the autotrim could respond to (if the system was indeed behaving as designed) was pilot input
- If a hypothetical pilot is unsure of what the autotrim system is doing, he or she can check the position of the THS on the wheel indicator inboard of their seat
- If that hypothetical pilot (either PF or PNF) doesn't like what they see, they can disable autotrim by moving that wheel, which will engage mechanically-driven manual trim for the duration of the flight

How relevant these factors are to this incident is as yet unknown, because the BEA are still sifting through the data and working on the report. Trying to blame either the aircraft and it's systems or the pilot at this juncture is as pointless as it is frustrating, so why are people doing it?

@RR_NDB

At this point, BEA and Airbus know what was being displayed on at least one set of instruments, they know which versions of the software was installed on the aircraft's computers and they know what the timestamped ACARS messages were. That's enough to gain a reasonable idea of what that particular aircraft did in terms of systems behaviour, over and above what control inputs were from the pilots. This should be enough to run simulator tests with crews to gauge their responses to the situation that presented itself, in much the same manner as the Birgenair investigation did. The systems are not so complex that recreation of the incident is impossible.

Last edited by DozyWannabe; 14th Jun 2011 at 14:24.
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