_Phoenix_

Dozy, please revise the FDR graphics of XL888 and AF447. How is it possible that THS is maintained at max nose up position while AoA > AoAmax = stall warning on, for a prolong period of time? Obviously, this situation is not an accidental/false stall warning due gust.

Why the code doesn't implement a line:

If THS<-10 AND AoA>AoAmax Then MOVE(THS=0, rate X(AoA))

...otherwise “Say a prayer”

roulishollandais

I had to reread Bernard Ziegler-Rizzi's book in detail, about Gordon Corps. He is mentioned page 78 testing C* on the A300 via A/P , and page 80 and picture p.80 the first A320's flight.
Page 78:
"Le joystick vola d'abord sur Concorde, mais ne fut pas retenu sur un avion qui en était encore pour l'essentiel aux calculateurs analogiques. C'est aussi sur Concorde que fut inventée la loi de commande de vol appelée «C star», qui, seule, permettait d'utiliser un manche aux débattements limités. Elle consiste à piloter non pas une position de gouverne mais directement la trajectoire : sans ordre, l'avion reste aussi stable que vous lorsque vous êtes immobile sur vos pieds (à condition de ne pas avoir bu, bien sûr, mais les calculateurs ne boivent pas). Si vous tirez vous sautez, si vous poussez vous plongez. Il fut ensuite essayé sur un A300, à travers le pilote automatique, le copilote gardant un contrôle par le manche. «normal» à titre de sécurité. Ce fut l'excellent Gordon Corps qui mena une grande part de ces essais. Nous avions même dressé un rideau entre le pilote testeur à gauche et le pilote de sécurité qui, à droite, gardait la commande classique, pour que les réactions du volant n'influent pas le jugement. Devenu plus tard officier de sécurité sous la direction d'Yves Benoist, venu là exercer son étonnante connaissance de l'avion acquise au service de la réception, Gordon mourut en 1992 dans l'Himalaya à plus de quatre mille mètres, en se rendant à pied sur les traces d'un accident."

Page 80 with a picture (from left to right : Jürgen Hammer, Gordon Corps, Gérard Guyot, Pierre Baud, Bernard Ziegler, Jean-Marie Mathios -mécanicien navigant-).
"Pierre Baud était commandant de bord et il y avait deux copilotes, le regretté Gordon Corps, qui avait beaucoup participé à la définition et aux essais préliminaires sur l'A300, et votre serviteur, qui tenait à être à bord d'un avion qu'il avait porté sur don berceau. Jürgen Hammer, ingénieur navigant et pilote de motoplaneur, était de la fête, pour assister Gérard Guyot devant l'installation d'essais".

DozyWanabee, do you know who was sitting in the right seat and in the jump seat from the two copilots ?

About your last questions it seems that our interpretations are different. No problem.

DozyWannabe

Two reasons.

1. The code is not keyed in in that manner, as I said in the linked post - the logic paths are mapped graphically in the development software, and the actual code is generated by machine from pre-tested blocks of logic. These blocks are then further tested as a module, again in conjunction with the other modules and finally regression tested as a whole - a process that at the time could take several weeks per module, and could well end up being revised based on what the test pilots brought back from flight testing. The A320's systems took 6 years (plus a further 2 years beforehand on the A300 testbed) to develop for a reason!
   
2. (Perhaps more importantly) In Alternate Law (AF447), the computers defer to the input of the pilot - in this case the THS moved and stayed put because the PF was pretty much consistently pulling up. If he'd let go, then the "soft" protections would have started returning the THS towards the centre, and if the pilot had pushed forward for long enough, the THS would have moved forward significantly faster. In Direct/Abnormal Attitude Law (XL888), autotrim is off and all THS movement must be ordered by the pilot via the trim wheels.

Well, we're talking about the A300 test bed from what I can make out, not the A320.

But regardless, I'm sure BZ would have been present for the "photo-op" flights, as befitted his title. But the actual grunt work of doing the thousands of hours of flight testing, as well as refereeing the discussions between the engineering pilots and the aero/software engineers would have been done with GC in charge. Baud was chief test pilot, so of course he'd be in the LHS a lot of the time - and for the earlier test flights it would make sense to have GC in the RHS as monitoring pilot, as it was his job to evaluate the systems and how well they were working, so he could take reports back to the engineering teams and fine-tune them.

With respect, it's a little more complicated than that. It seems to me that you've come up with a conclusion based on your own beliefs (namely that FBW technology has eroded piloting skill), and are reading the graphs in such a way that fits that belief. What should be happening is that the data should be used to draw conclusions, not the other way round. The interpretation I presented (with regard to ageing airframes and older jets being sold to less safety-conscious markets) is not actually my interpretation, but those of many articles, papers and books I've read on the subject over the years - most of which I hope were written by people who had access to the supporting data needed to draw those conclusions.

RetiredF4

Dozy, where do you have that (colored part) conclusion from? From year long discussions on several AF447 threads I remember, that the FBW system in ALT 2b, which was the mode AF 447 defaulted to, still strives for flight path stability in the pitch axis and thus in the absence of most all protections in the mentioned flight LAW would try to maintain the selected flightpath (which was most of the time an unhealthy climb) despite the unavailability of the required speed, although when the stick would have been released to neutral position. Remember, in normal LAW you change the flight path to a specific climb rate or bank angle, release the stick to neutral and the FBW logic would maintain this bank angle or climb rate until the pilot intervenes by a new command or the protections cut in. The same happens in ALT2b, except that there are no suitable protections active.

Your description would fit the pitch direct mode, (because it it would not have trimmed nose up anyway) which never latched.

DozyWannabe

Hullo F,

Yes, you're right about "striv[ing] for flight path stability in the pitch axis", but from http://www.airbusdriver.net/airbus_fltlaws.htm:

This low-speed stability function operates in both major modes of Alternate Law as I understand it. The important points with regard to AF447 (bolded) are 1 and 2 - namely that the mode will bring the nose down when low speed is detected (as would most probably have been the case when the pitot tubes shed the ice), and that because this is a "soft" protection in a degraded control law (and therefore the possibility exists that the human pilot may know something the degraded systems don't), the mode can be overridden by sidestick input. Because the THS trims to follow the nose-down input, it should have come forward if the PF let go of the stick and allowed the protection mode to operate.

I'm pretty sure I mentioned the existence of "soft" protections in the original mega-thread...

Disregard the following EDIT section, people, it appears that if Alt2B was latched, Low Speed Stability never returned...

[EDIT: Taking a look at the DFDR traces, the speeds came back online from approx. 02:10:38 until approx. 02:11:45 - at which point the airflow generated by the stall starts fouling the pitot tubes. The latter point is around the same time the THS hits the NU stop. The THS starts its roll NU at approx. 02:10:55, which leaves a window of about 40-45 seconds in which the low-speed stability function could have arrested and/or reversed the THS movement before the stall rendered the air data unusable again. Furthermore, releasing the stick between 02:10:38 and 02:10:55 presents a 17 second window in which the THS roll could have been avoided entirely. ]

DozyWannabe

@Winnerhofer:

Doesn't need to cover sub-modes, Low Speed Stability is available in all modes of Alternate Law.

Yes the A330 series is architected differently (PRIMs and SEC[ondarie]s replace ELACs, SEC[spoiler/elevator]s and FACs in the A320 series), but the overall logical setup in this case is more-or-less the same.

Sorry I couldn't find a better source at short notice but:

A330 Systems Parameters flashcards | Quizlet

See also:
http://tinyurl.com/mbjpdtj
http://www.skybrary.aero/index.php/Flight_Control_Laws

etc.

RetiredF4

Come on Dozy,
you can do better than that.

From FCOM A 330/340

AF447 Final report:
There was no low speed stability function available in Alt 2b. A neutral stick would not have led to a reduction in trim. With the kind of tripple ADR failure Direct Law should have latched and thus disabling autotrim, but this did not happen as all three ADR's were rejected simultaneously.
But i'm not going to go through this again after all these years.

DozyWannabe

Are "longitudinal static stability" and "low speed stability" one and the same thing then? It may be, and you may be right, but I'm not 100% sure.

The wording is a little vague - it does not state what happens when the three ADRs come back online. I was pretty sure that it would bring the soft protections back, but I could be wrong.

[EDIT : This link : http://webcache.googleusercontent.co...&ct=clnk&gl=uk

seems to suggest that Low Speed Stability is lost in the event of double or triple ADR failure, but I'm having trouble finding material confirming what happens when the ADRs come back online. I'm *guessing* that "longitudinal static stability" in the context of the FCTM is referring to the requirements of restoring High AoA Protection mode (and thus Normal Law), but I admit it'd definitely be handy to know for sure. ]

[EDIT 2 :
(I must say that the Final Report seems to drop some useful background info from the 3rd Interim, and the wording regarding Alt 2B is a bit sketchy in places - though if it is correct in that 2B denotes loss of low speed stability, and that the law never changed from 2B, then you're right - and it was missing, my apologies.)
]

_Phoenix_

How much is long enough?

see FDR at 2:12:32 to 2:12:42. Bonin pitched down +4 deg but elevator never passed -15 deg. Commonsense says that 10 sec. is more that enough for a crew in distress.

see http://www.icas.org/ICAS_ARCHIVE/ICA...PAPERS/605.PDF

***quote
When the airplane enters a stall, the load factor and the pitch rate feedback responses tend to fall off, due to lift loss and nose-down pitching moment. Consequently, the elevator is more and more driven nose-up, due to integration of the increasingly large C error, in particular, if a nose-up stick input is maintained. Operation of the automatic stabilizer trim function will exacerbate this condition to the point where both the elevator and the horizontal stabilizer can end up on the nose-up stop, unless the pilot reverses his stick input early enough to overpower the adverse C feedback error and drive the elevator to a nose-down position.

these characteristics may have played a role in the two accidents, making recovery from any full blown stall for a C or CU based FBW design difficult, even for experienced test pilot

The pilot’s awareness of the horizontal stabilizer position is of crucial importance to flight safety, especially when the automatic stabilizer function is suddenly lost in flight conditions close to the edge of the envelope***

Therefore, the options are:
- more and more recurrent training for pilots, make them supermen
- redesign of the trim wheels for more visual awareness, maybe color spectrum from up to down pitch, with blinking amber for MAN Pitch mode or extreme positions

However, I still believe that the implementation of the line of code posted previously is a feasible option for the issue.
Sometimes, the cowboy style is the best option.

roulishollandais

I'm writing from my experience not from what I'm reading here and there without having to prove the facts, writing black when they know it is white, shouting up if the publisher requests to shut up, and not present at the Court to testify, or rewriting again and again the wrong buzz like about the failures of the both Ste Odile approach charts.
I'm amazed to see these new refs after years of threads and official investigations.

RetiredF4

DW,
We discussed the matter in great detail 2 years ago,

http://www.pprune.org/tech-log/48977...ml#post7303835

and my post there still holds.

http://www.pprune.org/7303835-post578.html

jcjeant

I still believe that simplicity is the solution
Full automatic when all is well
Full manual when something goes wrong (my aircraft)
All Intermediate laws are a labyrinth in which pilots often get lost
But of course why make it simple when you can complicate all !
Of course it was certainly gratifying for Airbus programmers and technicians to show their technological know-how ......

DozyWannabe

@RetiredF4:

Looks like that post came in the middle of one of my self-imposed "sanity breaks", and I must have skimmed over it when I came back. Apologies for missing it, as I said.

@_Phoenix_:

If you look, the "Low Speed Stability" basically does what your proposed "line of code" suggests, except it pitches the aircraft down rather than moving the THS directly (which makes sense given that the autotrim follows pitch commands). Now, as RF4 states, it appears that Alternate 2B loses all but the load factor protections due to the rejection of all three ADRs (a double failure will keep High Speed Stability) - looking at the Flight Law table I linked to earlier, it does not seem to preclude the stability protections from returning after a time, it may just be that there was not enough time in which the airspeed data came back to do so in this case.

This seemed odd to me at first, but having thought about it for a bit I'm guessing that the design team considered an inappropriate automatic pitch down in the event of all 3 ADRs agreeing on bad data more of a risk than eliminating the low speed stability protection entirely. Again, this makes sense if you bear in mind that they'd assume the pilots to be making appropriate inputs, and not consistently pitching the aircraft up into and beyond the stall regime.

@jcj - The pilots didn't get "lost" in the modes, they simply never properly assessed the situation or came up with a solution. For whatever reason, the PF seemed to have become fixated on pulling the nose up - going as far as to hit the sidestick priority button several times (and thus shutting out the PNF), and at the same time told neither the PNF nor the Captain what he was doing and why.

The only time flight laws ever came up on the CVR was the PNF's call of "Alternate Law" at the start of the sequence.

A33Zab

Quote:

Terminology
ADR = Airbus
ADIRU = Boeing

Airbus & Boeing = ADIRS (Air Data Inertial Reference System)

Airbus ADIRS = 3x ADIRU
Boeing ADIRS = 1 x Dual Channel ADIRU + 1x Dual Channel SAARU

DozyWannabe

@A33Zab - right.

@Winnerhofer - ADR in this instance refers to the Air Data reference module of the combined ADIRU unit (I in this case referring to the Inertial reference module).

Sorry - didn't see this earlier. I don't think there's that much new here in terms of data, just a bit more background info. To be honest, a lot of what's here was probably in the older threads as well, but I don't think many people are nuts enough to want to wade through thousands of posts in their entirety.

I must confess I don't share your cynicism regarding all reporting (those written by those that know aviation, anyway). Sure, some of the books I read got things wrong, and the way I've found that out over the years has been to do even more reading - many people on here have helped with that as well. That said, I think some of the errors in those books were either genuine mistakes, or simply that they were writing about events that had not yet been thoroughly analysed. In today's world of self-publishing, there are certainly likely to be more published works that present an agenda rather than simple reportage, but you can generally spot those when comparing other works on the subject. Hell, M. Asseline's book is probably one of the most agenda-driven works in modern aviation history!

Regarding the approach charts, I think there are several reasons why that aspect became a footnote - firstly that the FCU input mechanism was a glaring issue that needed to be fixed, and that took up many column inches at the time, secondly that all the SNPL hoopla about Airbus FBW was being pushed hard at the time, and also because if I recall correctly, the flight was being vectored by radar from the ground, and given the high workload in the flight deck regarding changing approach procedure it is unlikely that they based their flightpath on the charts. Significantly I believe the radar controller actually vectored them incorrectly (turned them onto finals a little too early), so they were laterally adrift of the localiser as well as descending too rapidly.

jcjeant

From memory ... all the FBW Airbus accidents or incidents held in one of the alternates laws .. not in normal law
For all those accidents incidents it is commented "pilots error"
The price paid was victims
Memory again .. the only time alternate law saves lives is the crash of the Hudson

DozyWannabe

Sorry, I'm not sure what you're describing, are you referring to just the FBW Airbus accidents that were outside of Normal Law ore are you saying that all FBW Airbus accidents happened outside of Normal Law? (if so, they didn't)

In any case, please give us a couple of examples, because I know the investigative agencies don't tend to use "pilot error" anymore in their reports - in fact in the case of BEA investigations, they're not allowed to attribute responsibility at all.

If you're referring to how the press report these things, then that's just down to lazy journalism.

Alternate Law doesn't save or take lives, it's just a reconfiguration mode for degraded systems, similar to what the Flight Engineer used to do in the days of 3-crew cockpits.

roulishollandais

@DozyWanabee
Many things to say about wrong books, reports, analysis, SteOdile, aso.
We need some cynism to keep the eyes open and the mind clear when we see people dying for nothing.

Just one word about Ste Odile flight's ATC , as I would not like that the reader of our thread would get misinformed again : The flight of Ste Odile was NOT RADAR VECTORED. After the trial there is no more doubt about that for anybody. The approach was a VORTAC /VOR-DME approach. The controller did a immediately corrected mistake and showed as not being considered by anybody as connected to the crash (sense of turn, the BEA had to note the fact and noted it, ask question, but nothing followed).

During the trial we discovered that military police searched the Controller immediately without he was asked anything to help to find the plane still missing.
The military lawyer of the controller said me they didn't want to attack Air France for the wrong chart (probably because the IAC was wrong too on that military airfield open to civilian planes).

"Une injustice faite à un seul est une menace faite à tous" - Montesquieu

DozyWannabe

Healthy scepticism is a good thing, but cynicism not so much in my opinion.

OK, we're off-topic here, so I don't want to get too much into the subject, but from what I understand (based on what I've read and the portions of the report I've translated), the controller offered radar vectors to the ANDLO beacon (from which the VOR-DME approach could be made), but turned them slightly too early, and then used non-standard language when asked to confirm their position. This is in everything I've ever read on the subject.

Right, and you can thank the SNPL and M. Asseline for that, because the gendarmerie were absolutely determined that there would be no margin for error this time.

So let me get this straight - you're asking me to disregard pretty much everything I've read on the subject on the basis of your word that a military lawyer told you something.

Forgive me if I'm a little sceptical...

roulishollandais

@DozyWanabee
Today the trial and appeal are completed. You should find the Final Judgment somewhere. It is public. I myself have attended the both trials of Colmar. A point was even discussed on "judicial truth" and "scientific truth" but not the "journalistic truth"! The trial and judgment have addressed all of these things with bright and talented lawyers whose names are now well known.

I understand your scepticism : that is the way it happened . I thought the military Lawyer would talk from the Air France approach chart for defense, ans days passing I finally asked him when ... His answer was "We don't want attack Air France". I was amazed how he would defend the military Controller : He did that perfectly, answering to all the questions of the Court and other Lawyers, but not more and finally said that Military had to decide too. (Me Soulez-Lariviere defended Mr Frantzen (SGAC) in a similar way with administration).

These Lawyers did their job very well.... As did the Airbus Lawyers team and the Court who has been able to find a way of Justice threw that big garbage of things written or hidden.
Victims were less happy and let me add that they took a wrong way :
1. Creating an association of victims after a crash cannot be used in French Law to get damage (we don't have Class Action)
2. Trying to manipulate the Court "to get more money" (from Airbus) was a very very bad idea.
Not only they didn't show a criminal act from the five persons, but they missed a better damage...