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AF 447 Thread No. 5

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AF 447 Thread No. 5

Old 15th Jul 2011, 19:27
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Hi HN39,
Originally Posted by HazelNuts39
Hmmm, may be the AB engineers cited in the ACA memo don't understand their aircraft, but they say explicitly on page 6: "Sur les PFD les vitesses VaPROT et VaMAX sont remplacÚs par Vsw".
Sorry, but it seems you are the one confused here.
What is quoted, with illustration, is only the manual, word for word, until the last sentence. Each part quoted is detailing a protection in NORMAL Law and what happen when mode switch to ALTERNATE (generic, as per the manual). Only the last sentence of each paragraphe is an addition which is explicitly telling what was the "real" condition in ACA case.
Read it again, it ends with "dans ce cas ... cette protection est perdue" (this protection is lost) for each of them, except for the load factor protection (no low/high speed stability after the rejection of all ADRs by the PRIMs).
Consequently, it is all taken from the manual and there is no need for one to refer to any hypotetical confusing Airbus engineers "quote".
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Old 15th Jul 2011, 20:19
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Hi Bearfoil,
Originally Posted by Bearfoil
Doesn't the Computer (FCS) take as much as TEN SECONDS to validate a LAW? In some situations, one imagines ten seconds may be an eternity, and in danger, delay is the Devil. (Unless it is appropriate, there's the rub).
Right. The EFCS will need 10 seconds to validate that ALTERNATE LAW 2 will be irreversably maintained at PRIMs level.
But then, what you don't understand is that EFCS logic is one thing that is different from Pilots information logic.

When you are flying this machine without system failure, you are protected by the system all the time. Most of the system single failures won't change the flight laws, they are completely transparent for the Pilot Flying as everything (protection) is maintained. They will trigger ECAMs for troubleshooting purpose.

As soon as a system failure is occuring that will change the EFCS flight law (generaly dual or triple faults), by following the EFCS logic, it will be translated into a degraded mode called "ALTERNATE" or "DIRECT", from the consideration of the flight controls on each axis.

But the Pilot Flying doesn't need to follow the same logic as EFCS : what he first needs to know is what protection remains available, or better, which one of the protection is removed. Remember that this is not linked with those LAW, sub-LAW modes, but to the specific nature of each failure => anything "NORMAL" that can be maintained is kept, anything affected is removed.

In fact, this information is displayed on his PFD where he can see what protection is working or not, it is all that will matter for him at this point. Any protection removed (flags or reconfiguration on each PFD) will mean something lost. following computer logic, a single protection lost is called "ALTERNATE" mode... you will know it immediately if any part of your PFD will get amber crosses or red flags instead of usual values.

Now, following computer logic, this translate also into ECAMs triggering and other warnings if an action is to be expected immediately. But most of this is not aimed at the PF (beside auto flight controls). This is for PNF troubleshooting and it doesn't really matter if an ECAM saying "ALTERNATE LAW (PROT LOST)" is delayed by 10 seconds or more.

The reason is that the PF is not taking this information from the ECAM console. It is taken on his PFD where he can see directly what is really affected. Then, it will be obvious for him as soon as ALT2 mode logic is triggered by EFCS in one second when CAS becomes monitored following a sharp variation: his PFD will be reconfigured without displaying any of those protection function nor those characteristic speeds. If he also get the red warning flashing on his PFD : "use manual Trim", he'll know immediately that DIRECT law (computer logic) was also triggered.

"ALTERNATE" by itself means nothing for the PF as to what is possible or not, being related to specific failures. His PFD would tell him everything needed (at least, it "should" tell him everything).

Last edited by takata; 15th Jul 2011 at 20:51.
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Old 15th Jul 2011, 21:08
  #343 (permalink)  
 
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Originally Posted by takata
Read it again,
I did. We're not discussing any protection, but the indication of Vsw on the PFD. But thanks anyway.
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Old 15th Jul 2011, 21:26
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Nope, it's a proprietary-systems-and-software-design thing. I don't
think they've even publicly released the tools they use, let alone
open-sourced the design and the software, and I'm almost certain that
no, B don't do it either.
No, that's not what i'm asking for. Things like inputs required for
transition between the various laws would not be proprietary and would
be expected to be available, as some of that is already in the fcom.
Just not the level of detail needed for analysis.

What i'm looking for might be covered by a technical training level
manual, but have only managed to find bits here and there for other a/c.

Found this title from a search, but not a download link, as yet :

A330 Technical Training Manual, Mechanics, Electrics and Avionics Course

As for the tools, some are known, but it would be a bit of a stretch to
expect sources to be available, let alone open source. Now that would be
proprietary ...
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Old 15th Jul 2011, 21:34
  #345 (permalink)  
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takata, merci.

I truly appreciate your response. In it alone, I have gained (finally!) an (basic) understanding of the "duality" of ProtLoss flight.

So, then, as things get challenging, the a/c keeps the Pilots informed, and the Pilots "adjust" as to the new parameters. Friends, then.

I'll keep reading, the last two or so pages have been most edifying. If Manual Trim is necessary, why would it be annunciated in two separate colors, AMBER, or RED?

bon chance
 
Old 15th Jul 2011, 21:38
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Originally Posted by HazelNuts39
I did. We're not discussing any protection, but the indication of Vsw on the PFD. But thanks anyway.
Agreed. But then, you should read this paragraphe as something informative about the system but unrelated to this specific case as the last sentence proves that it doesn't apply to it => you can't have Vsw displayed both with Speed Limit Red Flag.
About what I wrote previously, I've got also a conflicting note saying that a dual FMGC reset was attempted in flight in order to remove the Speed Limit Red Flag after UAS event (and having Vsw, Vmax indications back), but I don't know if it was successful. I'm still looking for more info about that anyway.
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Old 15th Jul 2011, 21:58
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Originally Posted by Bearfoil
If Manual Trim is necessary, why would it be annunciated in two separate colors, AMBER, or RED?
"Use Man Trim" doesn't mean that manual trim is "necessary" but that autotrim is not working in this flight law => direct.
At first it is displayed flashing during 5 seconds, and later stay normal on the display, about its color, I'm saying that from memory. If one read "Use manual trim ONLY", hence big trouble, EFCS is not working anymore (mechanical back up) and you are left with trim only as pitch control.
Amber is the color of the crosses on the PFD removing the bank, pitch, roll limits. Red is the color of the Speed limit Flag (meaning no speed limits, no speed protection).
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Old 15th Jul 2011, 22:06
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Sorry takata,

I am unclear which 'last sentence' you are referring to. I quoted from the section on "High Angle of Attack Protection", which ends with "Pour terminer, ... givrage des sondes PITOTS... entraine ... F/CTL ADR DISAGREE qui engendre ... ALTERNATE LAW 2 ... avec ... perte de ... LOW SPEED STABILITY."

Doesn't that 'prove' that this section deals with the consequences of ADR DISAGREE caused by PITOT icing?

Last edited by HazelNuts39; 15th Jul 2011 at 22:26. Reason: Last sentence added
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Old 15th Jul 2011, 22:19
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Originally Posted by HazelNuts39
I am unclear which 'last sentence' you are referring to. I quoted from the section on "High Angle of Attack Protection", which ends with "Pour terminer, ... givrage des sondes PITOTS... entraine ... F/CTL ADR DISAGREE qui engendre ... ALTERNATE LAW 2 ... avec ... perte de ... LOW SPEED STABILITY."
We'll finish by falling in agreement.
YES, I'm refering to this specific sentence. What it means is that everything above doesn't apply to ACA case : pitots fault => ADR Disagree => Low Speed Stability lost.
All the paragraphe above is quoting the FCOM's explanation of High AOA PROT in NORMAL, then its replacement by LOW SPEED STAB in ALTERNATE (hence Vsw displayed) and conclude that they had none of these protections because being in ALT2 with ADRs rejected.
Do we agree?
Originally Posted by HN39
Doesn't that 'prove' that this section deals with the consequences of ADR DISAGREE caused by PITOT icing?
Yes it does... by detailing that those High AOA/Low Speed Prot above explained... were lost due to this current PITOT fault!!!
French is not your primary language, is it?

Last edited by takata; 15th Jul 2011 at 22:34.
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Old 15th Jul 2011, 22:34
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Hi takata,

Thank you again for your patience with me. I'm quite happy to let the matter rest, simply because the available documentation apparently doesn't provide the answers we are looking for. I do not agree with "All the paragraphe above is quoting the FCOM's explanation" because the explanations contain a number of details that are specific to this incident.
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Old 15th Jul 2011, 22:45
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Originally Posted by HN39
I do not agree with "All the paragraphe above is quoting the FCOM's explanation" because the explanations contain a number of details that are specific to this incident.
Please, explain which part (words) of the paragraphe before the sentence "Pour terminer,..." is related to this specific incident?
I really can't see anything related to current flight and I'm struggling to understand what is confusing about this way of reviewing every system protection that were not available for ACA. My reading is 100% clear.
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Old 15th Jul 2011, 23:08
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takata.

one last, then I promise I'll leave you alone for awhile.

Why is "USE MANUAL TRIM ONLY" (I have no quote function, so if I misquote you, please understand). "Big Trouble". ? Why is this TRIM only for Pitch control?

iF EFCS is inop, and mechanical back up only, are you saying the elevators are inop also? Pitch must be managed by Trim Wheel alone?

If that is telling of my ignorance, so be it, but shouldn't an a/c in trouble have elevators? Not a slow, massive Tailplane alone?
 
Old 15th Jul 2011, 23:27
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Originally Posted by Bearfoil
Why is "USE MANUAL TRIM ONLY" (I have no quote function, so if I misquote you, please understand). "Big Trouble". ? Why is this TRIM only for Pitch control?
iF EFCS is inop, and mechanical back up only, are you saying the elevators are inop also? Pitch must be managed by Trim Wheel alone?
When "USE MANUAL TRIM ONLY" appears on the PFD, you are effectively in big trouble as, either you have lost both elevators (L+R) or EFCS is not powered anymore (see basic schematic posted above about flight controls). They could be other failures but I'm just pointing that in order to illustrate that what is related to critical F/C faults should be displayed on the PFD directly to the PF without the need to wait further for PNF ECAM troubleshooting sequence.
Beside, the correct wording is USE MAN PITCH TRIM, displayed in amber, while MAN PITCH TRIM ONLY, is displayed in red. See below:

Last edited by takata; 15th Jul 2011 at 23:47. Reason: added illustration
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Old 15th Jul 2011, 23:27
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Originally Posted by bearfoil
iF EFCS is inop, and mechanical back up only, are you saying the elevators are inop also? Pitch must be managed by Trim Wheel alone?
That's about the size of it, pitch trim and rudder become your primary controls.

If that is telling of my ignorance, so be it, but shouldn't an a/c in trouble have elevators? Not a slow, massive Tailplane alone?
Think of this mode as the equivalent of total hydraulic failure on a previous generation jet (like, say, a DC-10). In the previous generation jet you'd have had no control other than thrust, but in this case you have thrust, pitch trim and rudder. I haven't heard of this mode coming into play outside of simulator training (thankfully, like total hydraulic failure it is expected to be an extremely rare occurrence), but it is indeed what you've got.
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Old 16th Jul 2011, 00:16
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Originally Posted by DozyWannabe
Think of this mode as the equivalent of total hydraulic failure on a previous generation jet (like, say, a DC-10). In the previous generation jet you'd have had no control other than thrust, but in this case you have thrust, pitch trim and rudder.
Don't you think Airbus trim and rudder need hydraulic too ... !?
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Old 16th Jul 2011, 00:17
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No, read what I'm saying - the *equivalent* of total hydraulic failure, only in this case it's the electronics that have failed. I'm well aware that the control surfaces are hydraulically actuated.
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Old 16th Jul 2011, 00:18
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I haven't heard of this mode coming into play outside of simulator training (thankfully, like total hydraulic failure it is expected to be an extremely rare occurrence), but it is indeed what you've got.
And just to be crystal clear (and not that ANYONE has said this or even hinted it) this is NOT the control mode that AF447 found itself in. Just in case any casual observer or passerby should get the wrong impression.
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Old 16th Jul 2011, 00:57
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Flag on capt (f/o) pfd

HazelNuts39,
Check 01.31.40 about Flags on PFD.
(Still not up to date infos):





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Old 16th Jul 2011, 01:10
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Dozy

I get that. But hydraulics haven't failed. They have been disabled (by design? A lack of alternate actuation?). With APU, Alternators and or Battery or even RAT, and hydraulics, why throw away the standard, (elevators), to struggle along like Al Haynes had to? (just a metaphor, I suggest it is not the same thing, exactly).

Rare or no, why not go for non-existent?

I sense a high level of agreement on the potential for THS TRIM WHEEL as the ignored resource, here. THS is large, powerful, and slow moving, not my first choice in Turbulent air, where TRIM (traditional) is not a primary resource in a conventional a/c recovery?

Powerful TRIM TABS as a default no/fail?

aside. Please don't think I am suggesting bellcranks, tensioned cables, and bellows to replace ECFS.

Last edited by bearfoil; 16th Jul 2011 at 01:22.
 
Old 16th Jul 2011, 01:21
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Bear,
Take it easy. This (mechanical) back-up law may be ultimately useful in case of electrical reconfiguration when the power switch from one source to another (something very transient, to begin with). As you say in about every post, the THS is powerful, and all FBW aircraft are fully certified to be flown with THS trim instead of elevator pitch control.
Design is based on FBW (electrical control), whatever you can say about that won't change this fact. Anyway, they have provided a mechanical back-up, just in case, in a very remote situation, it may be needed at one point for the pilot to use it.
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