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AF 447 Thread No. 7

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AF 447 Thread No. 7

Old 15th Nov 2011, 08:13
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Originally Posted by Old Carthusian
AirTren
This is not what I say at all - what the statement says is that some people PROCESS audio signals quicker than they process visual signals. You could say that their hearing functions at a higher rate then their vision if you wanted to simplify. The processing and interpretation of the signal are the significant factors not the receipt or transmission of the signal. Some people will even respond to an audio signal whilst they may overlook a visual cue. In fact visual cues are often missed - a simple example, think of the times you've missed someone waving at you but responded when they spoke to you.
Please read carefully - re-read - what I wrote, as I explained my interpretation of what you wrote.

I don't think we refer to the same people, which is commercial airline pilots, which need to meet certain medical requirements.

I had the luck from an early age to be in contact with airplane flying professionals, and know since I can remember their visual and word perception abilities.

I never experienced the example of your post.

Last edited by airtren; 15th Nov 2011 at 14:57.
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Old 15th Nov 2011, 08:31
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AirTren
I would say it might be thought a trifle dishonest to edit your comments and then claim that they were your original thoughts.
Be that as it may - I am not referring to visual impairment or otherwise. I am referring to how perception and interpretation work which varies from person to person. It is not a fixed process and it is perfectly possible for people to respond in different ways to different sources of stimulus. Comprehension does not always come immediately and this is the point that needs to be remembered.
A sound is a sound signal - if you wish to transform it into a visual signal you can do but it is conscious. If you don't it stays a sound signal. One does not listen to music and transform the signals into visual stimulae unless one wants to.
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Old 15th Nov 2011, 08:57
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A number of additions, to fill in the holes:


A system in software is called a “software system” . Once the marketing and requirements phases are completed, a software system gets defined as a product by a product definition and architecture group. A Software System Architecture Specification and a Functional Specification are developed, which provide a full map of all the functional blocks of the software system, the major algorithms, and their interactions, inputs data flow, and output data flow, as well as how map of its functions, respectively how they are controlled, managed, monitored, etc... A major element part of these specifications can be the type of real, or virtual hardware platforms on which the software will run. Designing the software for each functional block may be assigned to smaller groups. Functional Block Software Architecture Specifications may be developed, along with Block Functional Specifications. Algorithms are further specified in minutia details, It is followed by a Software Development Specifications, which defines the software mechanisms to be employed for implementing the algorithms and desired functionality in software. In parallel, there is a Quality and Test Plan Specification as one, or as two different documents, each defining the steps and tools to achieve the quality and testing targets. The software development – writing the programs - is done based on the latter, with unit testing done in multiple stages, from unit to system testing. Important to note that the Functional Specifications are the basis of the User Documentation development, which end up carrying most of the information of those specs..






For an airplane, the process is many times more complex, as the process multiplies, and there are so many specific technologies involved besides software. The requirements are external and internal – yes, company internal groups, from research, to manufacturing participate at defining a new product. An airplane system definition and architecture specifications is very complex, containing a a map of the various functional blocks of the airplane, etc… It is further divided into subsystem definition and architecture specifications.




For the airplane command and control subsystem, there is an subsystem architecture specification that goes into the details of the subsystem, defining the algorithms,





For larger airplane manufactures is not unusual to have the product specification done in paralele with the product simulation. Super-computers, and special programming languages, and compilers are used for modeling, and simulation of the functional blocks of the airplane, so that software can be run and the functioning of the functional blocks can be tested, and verified, through modeling, and simulation, long before any hardware piece has been physically ready for such a thing. It’s amazing, mind boggling….





The modeling and simulation during product development can be done even just for software systems, if the software systems are very large, and if the hardware platforms are developed in parallel, or not available immediately.






This is believe it or not... a very brief summary....




Last edited by airtren; 15th Nov 2011 at 16:52.
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Old 15th Nov 2011, 09:31
  #264 (permalink)  
 
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Originally Posted by Old Carthusian
AirTren
I would say it might be thought a trifle dishonest to edit your comments and then claim that they were your original thoughts.
The text posted originally before it should have, so as it was not what I intended, I performed an editing right away, which took a couple of minutes. I saw your post only after finishing the edit, and it seems you probably caught my original post, while I was editing it.

While I am sorry for this to be confusing to you, I think you're exaggerated in your accusation which is gratuitous, particularly when I've spend extensive time to understand what you're saying, and trying to respond, so that could have a decent dialog.
Be that as it may - I am not referring to visual impairment or otherwise. I am referring to how perception and interpretation work which varies from person to person. It is not a fixed process and it is perfectly possible for people to respond in different ways to different sources of stimulus. Comprehension does not always come immediately and this is the point that needs to be remembered.
A sound is a sound signal - if you wish to transform it into a visual signal you can do but it is conscious. If you don't it stays a sound signal. One does not listen to music and transform the signals into visual stimulae unless one wants to.
People that are accepted as pilots are within well defined health requirements range. That does not mean that those that don't meet the requirements are impaired.

I am afraid our communication is not working well, as it seems to me that somehow you're not reading or getting the meaning of what I am writing, as your replies seem to be such a radical deviation from what I wrote. ..

The visual perception of a change of a "control" position which is so simple, and done within the normal training, and cockpit routine, does not require any sophisticated comprehension, nor does it expose any peculiarity with one's visual perception. Such "visual perception" is plentily demonstrated by its use on a large number of airplanes world wide.
.

Last edited by airtren; 15th Nov 2011 at 10:12.
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Old 15th Nov 2011, 09:59
  #265 (permalink)  
 
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Progress, then. You take note of ISIS' accuracy by stating "because the Captain makes reference to it". Slight praise, and poor foundation. It was the duffward descent of the panel that caused the crash, do you not agree? Just as PF lost his PITCH sense when he first articulated the stick, the flight went South from that point. Are you conversant with the length of time the a/c was responding to its own problems with the incorrect speeds prior a/p loss?

For the record, I'd like to suggest a different perspective on the AirBus operation re: Pilotage. A pilot trains to fly, as a platform is built to be programmed. Once qualified to pilot a commercial a/c, he is typed.

Just like typing is necessary to program a platform, so is typing necessary to meld Human/Bus. Perhaps other a/c as well. My suggestion is this. The Airbus is NOT just a conventional aircraft, and for different reasons, it was not intended to be similar.

The deadly enemy of airborne pilotage is Surprise. People spend years and small fortunes to learn the craft, most of which is directed at "staying ahead" of the airframe. Each of the UAS incidents, and this accident, are extreme condemnation of the Airbus busted approach at mitigating a known fault. Without belaboring this conclusion, suffice to say there is ample proof.

Not a single one of the UAS problems recorded inspires confidence in the platform. A generic foundation for criticism is the aircraft's tout. All aircraft will bite. This one has had a generation of marketing, and 'training', attempting to diminish the harsher side of the platform's performance.
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Old 15th Nov 2011, 10:22
  #266 (permalink)  
 
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AirTren
Certainly I accept your explanation and am sorry if I imputed too much to the changes.
My point is not about the type of people, qualifications or standards they have to meet. My point is about how people comprehend signals via various stimulae. It varies and we cannot be too dogmatic or assume that everyone will respond in the same way to the same stimulus. We cannot even assume that someone will respond the same way to an identical stimulus all the time. This affects all sectors of society and all professions. Aviation history is replete with accidents caused by pilots missing visual and/or aural cues. Even an otherwise excellent pilot may miss a cue on that one vital occasion and precipitate an accident. This however is drifting off the subject somewhat.
Perception, interpretation and comprehension play a far more important part than the nature of the visual or aural stimulus. If you set up a frame of reference you enhance the chances of a correct understanding of the situation. Sometimes direct is not the best.

Last edited by Old Carthusian; 15th Nov 2011 at 10:46.
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Old 15th Nov 2011, 11:50
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Maybe this message is not exactly « technical » enough for the Tech log, but I think that training and experience, after all, are the key to explaining the difficulties met by the crew. So I hope you will show patience…
When I first started thinking, feeling wise, with all the time I needed and all the documents I could find, I thought…they were surprised, they were disoriented, the crew did not work as a crew, maybe they could have done better. But time passed, I learned surprising things on the plane, on its systems, on its protections, although I flew for years on the A320 family (from 318 to 321) and I was not especially lazy or complacent.
And in very recent times, I have talked to friends, captains who fly on the 330 or 340, and who are very serious and trustworthy. They told me that they learnt from that accident a lot of things they certainly did not know at the time. Things their training had not prepared them for. Facts that are well known to test pilots or military fighter pilots, but which you have no way to learn in a career where you start at nearly zero experience on the A320 and end on the A380.
For example, when in an unusual position, a stall, a spin, you move the controls to a position that you think useful…or that the airplane manufacturer recommends,and you wait. You wait for long seconds, until the new position of the flight controls gives a result. Then, eventually, you wait some more…Many airline pilots have never practised that, and have no knowledge of it. My friends certainly did not.And I will not hold it against them, I had the good luck to be a military pilot first, flying some strange airborne objects of all kinds, but that does not make me better (in fact I was a very average IFR pilot)…only that different experience was useful at times.
The stall warning ? None of my friends knew that it stops at low speed, by a mysterious agreement with the DGAC, when the certification rules say that it should only stop when the angle of attack becomes normal again.
The trim protection in low speed mode, in alternate law…forget it, nobody knew anything about it (the fact that it is speed and not angle of attack that inhibits the trim from running too far aft…alas there were no speeds available).
The decision to apply TOGA thrust (made on the second stall alarm) was perfecly applying the first step of the Stall procedure at the time. It happens that now, that is forbidden at altitude and the procedure has completely changed.
Knowledge of the aerodynamics of the stall on the A330…none at the time, and, even now, very cloudy (experts are now considering a pitch-up into the deep stall never encountered in flight testing).
The A330 was modified after the crash (those at air France anyway) to have a « dual Input « alarm when both pilots act on the sticks at the same time. It did not have that alarm on the night of the accident.
I think that we should keep in mind the very scant knowledge and training of the pilots at the time in the aerodynamics, stall recovery techniques, stall recognition…It was NEVER thought at the time that those planes could fly beyond the « approach to stall ». It was never thought either that the plane could « fly » with 40 degrees AOA and only 8 or 10 degrees of nose up.
So, of course the crew might have done better, but they certainly were not seriously prepared for what happened. May they rest in peace.
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Old 15th Nov 2011, 12:05
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Excellent post NARVAL! EXCELLENT
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Old 15th Nov 2011, 12:06
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NARVAL

Maybe this message is not exactly « technical » enough for the Tech log, but I think that training and experience, after all, are the key to explaining the difficulties met by the crew. So I hope you will show patience…
Wise words from a wise pilot.....

thank you sir!

franzl
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Old 15th Nov 2011, 12:24
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dual input

Narval,

I beg to differ on your comment regarding the lack of dual input alarm on AF 447 that night.
If you go back to the CVR transcript in the #3 report, you'll find that the synthetic voice stated "DUAL INPUT" on five occurences : 2:13:23, 2:13:41, 2:13:43, 2:13:45 and 2:13:47.
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Old 15th Nov 2011, 12:25
  #271 (permalink)  
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Narval - may I join the commendation of that post - perfectly placed in Tech Log in my judgement.

It is reassuring to see you say that, as I had hoped, pilots of these systems have learn much from this accident. I do hope that these lessons (plus those to be learnt by the manufacturer, trainers and operators) will mean that something useful, even if hideously costly, has come out of this accident.
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Old 15th Nov 2011, 13:06
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Knowledge of the aerodynamics of the stall on the A330…none at the time, and, even now, very cloudy (experts are now considering a pitch-up into the deep stall never encountered in flight testing).
Narval, I agree with all you are saying (except that they didn't have dual input indications), but transport aircraft are never exposed to any of these flying condition, certainly not deadly ones like deep stall and aerobatics. If the certification authority required this, they would also have to consider other highly unusual maneuvers, like rolls (yes, certain designer tested it out...), inverted flight, spirals aso. This is no aerobatics aeroplane or fighter, and it has a rather limited flight envelope.

If the next crash ends up in inverted flight, are we asking certification for this condition?

As you say, emphasize has to be put on training, that crews are never going close to these flight conditions. If they are, give them the tools to get out of it.

btw everyone who ever did basic aerobatic training knows the "let the stick in its position" procedure (which is only valid for stall and spins, not for all attitudes). Me thinks we should teach some cadets more aerobatics...

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Old 15th Nov 2011, 14:25
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Acro, no. STALL recovery, no.

A full and complete brief on UAS, stabilization at a/p loss, and some esprit de corps, de minimus.

RADAR, lack of comms prox, a sane approach to fault recognition and mitigation, prioritization, Command process, a rethink of controls placement, benchmark and minimum instrumentation, and recurrent training on impaired panel, dual input block/annunc., BUSS refit immediately, AHI alt., sterile cockpit in ITCZ transit, ad infinitum.

Narval. You are a wise and important oasis of thought, many thanks.
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Old 15th Nov 2011, 14:34
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Originally Posted by CONF iture
airtren, would you be kind enough to let me know how you proceed to be able to present the data in a different order.
Please see your PM inbox.
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Old 15th Nov 2011, 15:00
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Exactly! Some time ago someone (A33Zab, IIRC) explained that the stall warning stops because the ADR outputs AoA=0 when airspeed is <60 kCAS.
Ok thanks HN39, I think that is the post ?
Still, I don't get it as the AoA never reduced to 0 deg when speed was below 60kt and the warning stopped.

The way you write it (voluntary or not ?) as a binary system could make more sense to me :
  • ADR outputs AoA=0 if CAS below 60 : meaning no AoA data therefore no possible stall warning
  • ADR outputs AoA=1 if CAS above 60 : meaning AoA data therefore possibility for stall warning

It is also the way I understand it in the report :
When the measured speeds are below 60 kt, the measured angle of attack values are considered invalid and are not taken into account by the systems.

For the zero deg ... ?
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Old 15th Nov 2011, 15:31
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Originally Posted by CONF iture
For the zero deg ... ?
I think he means the AoA output of the ADR is zero literally, meaning no output rather than zero degrees - the data is discarded.

[EDIT : Thanks to HN39, he's found the post that clarified it. The AoA output is zeroed and the Sign/Status Matrix set to Non-Computable Data. Interested parties can get an overview here:

ARINC 429 - Wikipedia, the free encyclopedia

(Even I had trouble with some of the acronyms... )

]

Last edited by DozyWannabe; 15th Nov 2011 at 17:16.
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Old 15th Nov 2011, 15:38
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Dozy (re: #201)
I'm aware that some terms used are not the proper ones, but being on an aviation forum I felt OK to use them as intended by other posters. Besides, english is not my mothertongue.
So, about logical/algorythm errors: let's look at them from the end-user point of view, i.e. the flight crews in the present situation. To be honnest, I don't think the "clients" (pilots) do care if the problem is :
- a hole in the specifications
- a implementation bug
- another type of bug
- an hardware failure
They see the outcome, which is that from a pilot's point of view, the system is illogical.

Back to "my" four points:
Point 1] (non-inhibition of the nose-up autotrim when stall warning is active)
You said: "I can foresee a couple of situations off the top of my head where that could be more dangerous than letting the trim run."
Well, I cannot. Could you elaborate, please? I did the reasonning with: "Would a pilot (provided he's aware & not mental) trim up when the aircraft is (near) stalled?" I could not see a single reason/circonstances where the answer is "yes".
About complexity: Yes, such a feature would add one more logical test. It's not a big deal in my opinion. And, more important, it doesn't seem a big deal to Airbus either because the NU autotrim is inhibited in Normal Law when the pseudo equivalent of the S/W (namely: the AoA protection) is active (ref: FCOM A330). If they can implement it in Normal Law, the complexity argument is IMO moot in Alternate Law.

Point 2] (inhibition of the stall warning under 60kt IAS)
I would like to know if such an inhibition is present on other aircrafts, too. I'm afraid a lot more aircrafts than "just" the A330 do more or less the same, indeed.
Latching the S/W state with no AoA valid measure: Why not, but I'm not sure about the risks of a false positive, here.
Other way is perhaps to inform the crew (how: to be thought) that currently "AoA measure is invalid. Consequence: S/W inop". That far more simple to implement, and avoids the need to "assume" what the S/W state should be.

Point 3] (V/S switching source from air data to inertial (and back))
Yes, I'm sure the V/S source switched. There is such a parameter in the FDR traces : "VERTICAL SPEED SELECTED FROM ADR (1=ADR 0=IR)"
The V/S recorded (and I assume, displayed during the flight) is "erratic" when ADR is the source, but "stable" when IR is the source.
When the PF said "J’ai un problème c’est que j’ai plus de vario là" (02:11:58) that's ~10-15 seconds after the switch to ADR source, and the beginning of the erratic values...
Note that at the same time as the V/S first swith to ADR source & display erratic values, other parameters go erratic too: CAS, AoA, FPA... and the S/W stops. So I agree that the V/S go erratic at the same time the stall is well established.

Point 4] (non-inhibition of the F/Ds when an UAS situation is detected)
I've perhaps written to quickly about that one. If the F/Ds indeed are inhibited, that's good. The logic hole I saw there is that while A/P and A/THR are dropped (i.e. the crew must re-engage them manually if they want them back), the F/Ds seem to just go flagged, but come back "from themseleves" when the conditions seem back to good: Would it not be better to let the crew manually re-engage the F/Ds, having assessed the which data are good and which are not?

----------------

jcjeant (re: #202)
One cannot hope a 100% reliable sensor. One can (must) work to go as near as possible to the 100%, but must know he cannot obtain it.
My position is one cannot advocate for dropping automation until a perfect sensor is available, unless the goal is to drop automation itself without saying it.
On the other hand, yes there seem to be problems with the certification criteria regarding the probes. If proved, then the industry should work on that. But by no mean calling to a "stop" until perfection is reached will be of some help IMO

----------------

Originally Posted by NARVAL
The A330 was modified after the crash (those at air France anyway) to have a « dual Input « alarm when both pilots act on the sticks at the same time. It did not have that alarm on the night of the accident.
I don't know what/who is your source on that, but based on the CVR transcript from AF447, it's wrong.

I'm not aware that TOGA is now forbidden at altitude?
I'm aware, on the other hand, that the stall (old) procedure which was good only to an approach to stall condition is now reworked so that it's good in a stalled condition too, implying the "lower AoA" rule, most important/first action.
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Old 15th Nov 2011, 15:38
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NARVAL,
I like your post too.
For the DUAL INPUT, obviously F-GZCP was equipped.
Maybe other A330/340s in the AF fleet were not.
Where I work, some airplanes are not modified, I was ignoring this, don't know if they will be either.
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Old 15th Nov 2011, 15:39
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Originally Posted by Dani
If the next crash ends up in inverted flight, are we asking certification for this condition?
Let us hope you are not being prescient. This could easily result from a number of scenarios. I would be a shame if protections got in the way of an attempt to roll to the nearest horizon. This relates to any FBW aircraft.

Narval gets a big . He has stated very compactly the state of general airline pilot knowledge in the period leading up to AF447.

D.P. Davies was spot on in describing how treacherous it is to experience a stall in a near level flight attitude.

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Old 15th Nov 2011, 16:29
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Originally Posted by AlphaZuluRomeo
I'm aware that some terms used are not the proper ones, but being on an aviation forum I felt OK to use them as intended by other posters. Besides, english is not my mothertongue.
Not a problem - it wasn't intended as a criticism of you or your writing, it was just a case of getting the terminology straightened out.

So, about logical/algorythm errors:
...
They see the outcome, which is that from a pilot's point of view, the system is illogical.
Absolutely - I'm all about the information-sharing though, for two reasons. Firstly, to a software guy, seeing minor inaccuracies like that would be a bit like you guys reading "The plane crashed because the pilot pulled on the wing flaps that make it climb or descend" in the papers - the difference is that in your case it's well-meaning, but it still gives me a nervous tic when I see it, so sorry about that. Secondly, we know journos trawl these pages, and the last thing we need is a headline like "PILOTS SAY COMPUTER ERROR AT HEART OF FATAL AIRBUS PLUNGE", or similar silliness.


Well, I cannot. Could you elaborate, please? I did the reasonning with: "Would a pilot (provided he's aware & not mental) trim up when the aircraft is (near) stalled?" I could not see a single reason/circonstances where the answer is "yes".
The problem (as you state below regarding another point, and as I think I said in my original reply) is with false positives. If a sensor jam or genuine technical error causes the stall warning to sound when the aircraft is neither at or near the stall, that solution would prevent the pilot from trimming up when he wanted or needed to. You're then faced with the option of holding attitude with the primary controls and thrust (which would be fatiguing) - or if the limit applied to autotrim only, forcing pilots who are not used to trimming manually to do so at altitude with an abnormal situation on their hands.

I don't know why the A320 sim limits the nose-up trim and the A330 didn't in this case. Someone suggested that the limit might be airspeed-dependent, but the TRE had failed both ADCs. It's a question to ask Airbus, for sure.

About complexity: Yes, such a feature would add one more logical test.
See airtren's post - it's a lot more involved than that, going right back to the specification and trying to define potential knock-on effects of the change.

it doesn't seem a big deal to Airbus either because the NU autotrim is inhibited in Normal Law when the pseudo equivalent of the S/W (namely: the AoA protection) is active (ref: FCOM A330). If they can implement it in Normal Law, the complexity argument is IMO moot in Alternate Law.
The protections are a separate subsystem entirely from the annunciation/warning subsystem. There is no overarching logic connecting them, which makes implementing such a change considerably harder. I can see where you're coming from, I just think that a hard limit on autotrim under certain flight control circumstances would make more sense.

Other way is perhaps to inform the crew (how: to be thought) that currently "AoA measure is invalid. Consequence: S/W inop". That far more simple to implement, and avoids the need to "assume" what the S/W state should be.
With an eager and switched-on crew, sure that'd work. But this crew in the wee hours appeared not to notice a Stall Warning that was blaring in their ears for nearly a minute. By the time the AoA values became invalid, the situation was pretty grim - what chance they'd notice the warning you suggest?

Yes, I'm sure the V/S source switched. There is such a parameter in the FDR traces : "VERTICAL SPEED SELECTED FROM ADR (1=ADR 0=IR)"
Thanks, it's been a while since I read it in depth (thought I've gone back to specific traces briefly since.


The logic hole I saw there is that while A/P and A/THR are dropped (i.e. the crew must re-engage them manually if they want them back), the F/Ds seem to just go flagged, but come back "from themseleves" when the conditions seem back to good: Would it not be better to let the crew manually re-engage the F/Ds, having assessed the which data are good and which are not?
I think that design decision is a compromise - i.e. after an abnormal situation like that, would the crew notice that FDs were available and switch them back on again? I think the idea there was that they'd bring the FD back once the data was good, it would then be up to the crew to either use, disregard or disable them.

Food for thought - thanks!
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