"attracteur etrange"
 

did you heard about the "attracteur etrange" (i do not know the name in english): see james gleick CHAOS. unstability has such a point that gums searched and found on.the a330. congratulations to gums, retiredF4 for the stall, and machinbird for the roll
Thanks

HN39 et al;

jc, the court case won't contribute to aviation safety.

It may make a few wallets fatter.

Slats,
It is completely incomprehensible why the captain, after he was summoned back to the cockpit by his crew, made no effort to take control. Indeed, for much of the time he seemed to be little more than a rather distracted observer.
Confiture,
We will never know what the captain was referring to when he uttered "prends ça!" Otelli writes that the BEA investigators thought he meant the Flight Path Vector (the "Bird") in the PFD.
Lyman,
So what if the C Chord seemed intermittent. Surely that alarm would be the least of the crew's worries. The way that plane was rocketing up and dropping back down, it's a wonder the C Chord generator didn't burn out.

Rock hound...

Yes, I would agree, I was curious about any failure in the a/c, not just what the pilots were doing with it. So you know the parameters of c chord burning out. Where can I find them? BEA are derelict in leaving so much information out. The general drill in a report is that data can be incorporated "by reference", leaving the reader to pore over it, after he locates it elsewhere.

Thanks

lonewolf_50
I think it may somehow contribute to safety .. simply by excluding some people by sentences ..
People or organizations that contribute to lower safety or not taken into account by their mismanagement
And I hope this will be those of the victims families
And it may also make a few wallets thin .....

Rockhound
I read nothing about that in the final report ...
The BEA report of course ... not the useless Otelli one :8

(Caveat - I have no specific FBW background)

I am a tad confused by some of the recent posts commenting on stability.

If the aircraft, in degraded modes, gets to the stage of having no computer protections, then it would appear to be unflyable for the typical pilot unless statically stable along with a dynamically stable SPO. If statically neutral or marginally unstable, still flyable if one knows what to do .. and then only for a short while until the fatigue levels take over any semblance of finesse.

However, I cannot imagine that it would have been certificated unless it were stable in the worst degraded mode ?

Has anyone any information regarding the matter ? Specifically,

(a) as modes degrade does the aircraft get to the point of having nil computer assistance ?

(b) if so, what are the stability characteristics ?

I am presuming that there is no flight test data relating the the AF447 extent of stalled flight ...

roulishollandais, "attracteur etrange" = strange attractor in English. More at :

Strange Attractors - Chaos & Fractals

If you are interested.

Hope that helps.

Yeah, JT, a good question.

Wiki has a fair explanation, but one of my original posts has a link to the Viper's design WRT static stability.

Longitudinal static stability - Wikipedia, the free encyclopedia

Have to look at my website files to get a link for our design.

Found the Code One articles on my website:

http://www.sluf.org/misc_pages/codeone_v1_n2.pdf

http://www.sluf.org/misc_pages/codeone_v1_n3.pdf

The deal with the 'bus is that what we all knew as "normal" was if you let go of the stick the plane would try to achieve the trimmed AoA ( not gee). So the cee gee was well forward of the center of aero pressure. This meant that when cruising along that the elevators were actually creating a force opposite of the main wing to keep the nose up. By moving the cee gee back and having HAL to help, you could have the elevators creating upwards lift and dramatically reduce "trim drag". In short, both the elevator and main wing were generating lift upwards.

From my A330 manuals, the thing never has an extreme aft cee gee as we had, but it does allow it to be further aft than most of the other jets. This helps for range due to reduced trim drag. Because HAL is helping, you don't feel like you are flying on the tip of a needle if you turn the AP off.

The 'bus direct law is one implementation I described. The electrons directly command control surface deflection via the actuators, just like the old days when our yokes/wheels/sticks moved a valve for the hydraulics. Because the plane has positive static stability, it is still flyable by mere mortals.

What bugs me is that the 'bus reversion sequence is not real clear as to the AoA bias on pitch. At first look, you think that you have some degree of AoA limits and actually command AoA. Then you read all the footnotes and find that some data failures do not provide the expected control response related to AoA. So the jet is still trying to achieve a gee, and the AoA can go to 40 degrees, as we now know can happen.

later from this old dinosaur...

Thanks for that .. I'll review later on today during a coffee break.

I don't have a problem if the box is still helping out sensibly as what is important is what the pilot is presented with in the worst certification degraded mode ...

However, some of the posts appear to be suggesting that the degradation can extend to nil box assistance and a statically unstable aeroplane.. that's my problem at the moment.

Either such

(a) isn't the case

(b) wasn't considered because the estimated MTBF suggested the probability of occurrence was up there with the other very small numbers .. ?

I probably should have bid onto the A320 when I had the opportunity rather than staying on the FLUF.

Actually, if you go by the anti-bus crowd around here, the modes degrade as you add FC computers. :}

With only one secondary FCC (of possible 5 total FC computers) available to connect SS/rudder inputs to the flight control surfaces you have a 727.

With either no computers, or no electrical power, you have mechanical control, thru hydraulic actuators, of the THS using the trim wheel, and the rudder using the pedals. Though set up to provide control while resetting computers, as others have said, you can actually land the aircraft, if necessary, in this condition. Complete electrical failure, you've got no choice but to land it this way. Challenging and satisfying. :)

It is never divergent around any axis, regardless of the level of computer assistance or lack of.

The wonderful world of FBW.

Thanks, Okie, you nailed it.

There might be more dependence upon electrons than you suggest, but the aero characteristics of the 'bus seem really good to this old fart.

I am not anti-bus. I am bitching about all the reversion sequences and such, which seem very confusing to me. I want something to hang my hat on, and if various sensors are FUBAR, and HAL doesn't use them, I still want to know what I am playing with. I also have a problem with the THS still in operation once outta Normal law. Another thread topic.

I joined the fray here to show that some knew about unexpected aero problems over 30 years ago that the cosmic FBW systems could not fathom. It's why I detest the term "protections". Although our system had different mission requirements than the 'bus, it was the first one fielded with a fully FBW system and had several hundred jets flying within two or three years. We initial cadre were afraid that the newbies would forget how to fly a "real" jet. And I can't help but see that fear realized in the AF447 disaster.

@ JT,

From what I have read about the A330/340, IMHO, both possess static and dynamic stability to the point that in the worst situations, the aircraft is flyable. If it were not, I don't see how it could of been certified in the first place. I think the Airbus folks, designers, engineers, aerodynamicists and software folks thought of virtually everything to enable this, complicated as it may seem or be.

The worst two cases would be Direct Law and/or complete loss of electrical power.

Direct Law - In pitch direct law, elevator deflection is proportional to stick deflection and, in all configurations, max elevator deflection is a function of CG. This should be a transitory phase prior to PRIM reset and re-acquisition of Alternate Law. There is NO automatic trim meaning you have to use manual pitch trim. The yaw damper still provides yaw damping but gives minimal turn co-ordination. So protections of g, pitch attitude (manual pitch trim is required), high alpha, high speed, bank, MLA, turbulence, low energy and AP are all lost. But, the aircraft is flyable with care.
Should a complete electrical failure occur, mechanical pitch control is through the THS using the trim wheel. There should be caution here as if the CG is back there is a pitch up bias, if the CG is forward there is a pitch down bias. Manually operating the trim wheel requires gentle and smooth movement as the THS is a large aerodynamic surface. Mechanical lateral control is the secondary effect of rudder pedal inputs. The BYDU provides Dutch roll damping.
An example of an event which would put you in Direct Law would be a double engine failure, which at high altitude cruise, would probably mean that you will need to descend in a controlled manner to a lower altitude to initiate engine restarts.

I would say a good example of a unstable large aircraft without FBW computer controls would be the B2 USAF bomber. If the computers quit, IMHO, the aircraft would not be hand flyable.

Just some thoughts and opinions from a non-pilot, engineering type.

Hi Turbine D & JT,
Direct Law would occur only after putting the Landing Gear down. Up until then, you'd be in Alternate Law.

The aircraft is only statically neutral with the aid of the FBW computers. In Direct Law (stick deflection proportional to control surface deflection) they are (beautifully) dynamically stable.

OK thanks again :)
As I said earlier, I'm not that fond of maths. Would you be so kind as to "translate" what impact will a different 'a' value have (in AF447 scenario, and/or in general)?

Yep, read that too. A/P issues deflection orders directly, sidesticks issue manoeuver demands which are translated into deflection orders by the flight controls computers/laws.

Regards.

Hi AZR,
I've only ever flown in ALT LAW in full motion simulators which do not simulate realistic g loads. (constant 1 g felt in turns & TCAS events with smart pull or push etc. The pitch attitude of the box changes to simulate horizontal accelerations; and the box moves up and down within the travel length of the jacks to simulate turbulence).

There is no perceptible difference in pitch control when flying in ALT LAW v Normal Law. Roll control is however noticeably different - if feels like a conventional aircraft.

Sometimes i`m going really mad here.Although my english is good enough for the daily talk, i`m not really able to explain the psychlogical aspects i see in this crash like i could do it in german ; and that drives me crazy.
I´m no pilot etc. so why is he posting in the tech log,some may ask ,among all these profs and not in rumours % news ?
I can tell you. I`m feeling well here,because all in all it`s a serious discussion.
and no, i`m not here because there is a need for me to lift up my selfconfidence among the gods of flying and others.
So i can`t say much about the tech.aspects,but i comprehend what is said.
Thank you for your patience with me and sometimes recognizing my posts !

Back to business.

I´ve read a few hundred accident invest.reports and there was always a chapter about the prof.career of the pilots and what they were doing in the 48-24 hours before the flight and their behaviour with colleagues in duty.
This i miss here. so why ? Bad talking about gone people not allowed.The others were also mostly dead.
So why it is missing here,quite unusual.

Law degradation
 

When discussing the different laws and its effect to the flight control system it is imho important to know and accept, that there are different Alt Laws available . In the last few post those differences didn´t get any attention (see my last post).

ALt Law 2B differs substantially from the other alt Laws, as all protections except load factor protection is lost. The biggest difference being, that in this Alt2b law the FCS works along the Nz law with no high speed stability (VMO2) or low speed stability protection (Vc prot) present.

Here the details of those protections in ALt Law (not in Alt2B):

Both those limited protections had not been available.

When discussing the the stability and control issues as well as the stall entry of AF447 that point makes quite a difference. It´s the cause, that a SS in neutral on the way up to the apogee would have changed nothing, as the Nz-Law would have been active all the way into the stall. It may also be the reason, that in Dozys experiment in the A320 simulator a permanent stick force was required to maintain the pitch into the stall, or that the THS trim stopped, as VCprot worked against it or that PJ2 couldn´t achieve the same pitch as AF447 did in his simulation.

It might also make the difference between some of the other UAS flightpath excursions gone well.

If i would have to grade the handling in the different laws from a theoretical standpoint, it would be kinda

- Normal Law (artificial neutral stability with full protections)
- Alternate LAw except ALT 2b (artificial neutral stability with limited protections)
- Abnormal law (artificial neutral stability with limited protections without autotrim)
- Direct Law (natural positive stability)
- Alternate Law 2b (artificial neutral stability without protections except g-load protection)

But again, i didn´t fly that aircraft, but i doubt that all pilots are familiar with the consequences of all the different laws, as graceful as they may be (gums i´m with you on that one).

Edit:
It would be interesing to know, if the law Alt2b changed intermittently when the speeds came back on line or the above limited protections reactivated itermittently.

Again my understanding, and I may be wrong. With stick free the Nz law tends to maintain essentially the current trajectory at approximately 1 g (nz=0). If that trajectory is such that the airplane decelerates, it will have to pitch up to maintain approximately 1 g at decreasing airspeed. The pitch rate q depends on the rate of deceleration dV/dt. It will not quite maintain 1g but it will settle for nz = - q/a, i.e. an incremental load factor that is slightly negative, depending on the value of 'a'.

P.S.
For example, at FL350, M.6, 205t and decelerating at 2 kCAS/second, the pitch rate maintaining 1g is 0.27 degrees/second.

The answer at your question is in the BEA meeting with the press (the day they released the final report)
One journalist asked same question as yours..
Answer BEA:
They made researches about what made the crew in Rio
They find nothing interesting or related to the crash ..... so nothing of value to put in the final report ......

Lyman,
What I said about the C chord generator burning out was tongue-in-cheek. I know nothing about how it functions. As I said, does it really matter?
JCJ,
Regarding the meaning of the captain's "prends ça", Otelli wrote that it is difficult to know what he was referring to but the BEA investigators favoured the idea that it was the FPV.
Why do you call Otelli's book "useless"? Not only does it contain the entire CVR transcript but the transcript is an improvement on the bare-bones version released by the BEA in that the reader gains an impression of the tone of voice used (exclamation, question, etc.). Also, Otelli has filled in some of the blanks in the BEA release (whether that's accurate or not is another matter, of course). Finally, Otelli has keyed the CVR to the FDR and thus provides background to at least some of the crew's statements and actions.
Clearly the key to the tragedy of AF447 is the CVR transcipt. For those of us who possessed a copy of Otelli's book (published in late 2011), the release of the BEA final report was very much an anti-climax.

jcjeant and philip2412:

Gruess di'.

In the final BEA report it is written that the investigation was not able to ascertain what the 3 pilots were doing for the 72 hours they were in Rio. PF did have his wife on board AF447 and she spent his layover time with him in Rio.

What else the three crew members did was not able to be determined.

Hi Rockhound...

Tongue likewise in cheek in my question...

Is it important? Yes, and no. To a technical person, whose specialty is ergonomics, perception, sensories, etc. But to you? Perhaps not. The take away from the report is that it is minimalistic. In its brevity, BEA allows popular comment and perception to remain in the discussion, rather than exhausting all reasonable questions. An exquisitely important CVR artifact, the comments re: ambient temp in cockpit could have several causes, where is this addressed in the report. Where is the elimination of possibilities, and in the elimination, the establishment of a probable cause? The cause is allowed to be dictated by PPRuNe, evidently, incompetent pilotage....

If as you think the transcript is the key to the accident of AF447 ... I'm certainly not going to consider the writings of Otelli but instead .. will consider the BEA transcript
In addition to his writings about the transcript is not accurate .. thus we have seen in the transcripts appearing in the final report
We have many "Otelli" in this forum (or at least able to write a book like Otelli) .. they can write it .. this will not change a ounce about what happened and what is engraved in stone in the BEA final report ...
The only place where the final report can be .. (maybe) challenged .. is the judicial court ...
And be sure that Otelli will not spoke a word there

@Lyman
 

I'm sorry, sir, but....
Whaddaya, NUTZ????

:yuk:

about time...
 

Don't know if someone else posted this link, but seems relevant.

Airbus reviews instrument logic in aftermath of AF447

What I don't understand is why the flight directors don't just display last attitude or maybe a benign pitch attitude when the air data goes to la-la land.

Then there's all the audio warnings and AoA issue.

Decent article, IMHO.

@Gums,
Thank you for the three ref.
About FD, I can find no correlation between the pilot action and the parts of FD displayed. Does anybody ?
The problem was C* as you pointed it with retiredF4, and now the BEA final report. Thanks !

@ChisN,
Thank you for the strange attractor (of course !) it is such one effectively, but not for the famous Lorenz system but A330 ! (to compute!) It is an important concept for stability of non linear dynamic systems.

from post #392, clandestino, (a few days ago)

(my bold)

It appears the 'magic' agree number is ANY two ADR's <20 knots difference, no matter how 'off the wall' the actual values are as long as they meet other engagement criteria. [Of interest, this can be the two PFD displayed values OR one of the displayed and the other not selected ADR value (i.e. the other displayed PFD >20 knots difference with both 'agreeable' ones).]

This appears to also be the point at which the FD's return.

Pardon if this figure has been provided before in other threads, I may be late for dinner here, but does anyone have a reference for confirmation of this value, if in fact it is correct? A33Zab?

@A33Zab: With ALT2(B?) 'latched', the SPD LIM flags displayed and no characteristic speeds displayed (including no VLS), and no FMGEC VLS (dashes), the A/P pb latching appears to depend only on 2 ADR's within 20 knots, not FMGEC VLS. The A/P pb apparently latches with the 2 values in 'agreement' below actual VLS. Is there a reference somewhere? Once again, apologies if it has already been provided previously.

@RF4: The report states that ALT2B was 'latched' so I would assume there were never any intermittently available speed stability functions, but I erroneously thought the same of the A/P pushbutton. :}

If the FD was intermittently on and off, working and not working, I may have a better guess at the answer to my old question regarding the PF: what was he seeing?

If what I guess is close to right, then I begin to understand another factor in his confusion and frustration, particularly if his habitual instrument scan relied heavily on the "bird."

Mind you, this is guessing. Maybe a puzzle piece that fits better than others, maybe not.

Perhaps, Lonewolf, the PF did not comprehend what he was seeing. He probably never saw things on that flight deck that night, before in his entire career.

This possibility, together with sensory overload, preoccupation with weather, ignoring of various "bells and whistles", the so called startle effect, his losing focus on the task at hand (fly the damn plane), little communication with the PNF, piss-poor CRM (including the Captain), total lack of situational awareness and a host of other issues and is it any wonder he was pulling back the entire time? To this non aviator it would seem the guy was scared !!!!less and had no idea what the hell was going on around him.

When the !!!! hits the fan, as I learned several moons ago, it's fight or flight. He went the latter path. He didn't choose it though. It overwhelmed him.

rgbrock1. You have spent a paragraph focused on PF and what he felt, how he may have felt it, and what he may have seen and done. That is perfectly ok. There is a lot of it, and a lot of repetitive opinions on feelings, startle, fatigue, experience, what they did prior to launch, ad nauseous, again ok.

"What is that smell?". "it's hot.." "Yes it is gotten hot in here..."

"Ozone"....". (end of). Re: the increase in cabin temp? Nothin'......

STALLSTALLcricket... What is that? ( no answer, no answer, no answer)

BEA "probably his reaction to STALL WARN" fine, case closed, end of...

No answer to cabin calls, none... No problem? end of......

Constant and vigorous speculation on the pilots, mostly about things that will never be known,,,,, Mechanical issues? Not so much...

Because the physical evidence recovered does not correlate with mechanical or electrical problems (aside from the pitot tubes), and no amount of wishing will make it so.

Remember, just because it's not in the final report doesn't mean it wasn't investigated.

I ask again - what makes it so tough for you to believe?

Ref this post.

The aircraft is only statically neutral with the aid of the FBW computers. In Direct Law (stick deflection proportional to control surface deflection) they are (beautifully) dynamically stable.

This is the bit with which I'm having difficulty although my reading of the various links (and thanks to those who PMd/emailed other suggestions) may answer my questions ..

Neutral static stability infers a more aft CG than "normal". The box then can give the pilot an impression of stability (and, at the end of the day, it is this impression that is required). If, now, the box departs controlled operation .. the aircraft CG is still where it was (until it can be moved) and the pilot potentially now is stuck with neutral static stability .. OK if you recognise it and know what to do .. but, otherwise, a recipe for rapid disaster ...

@OK465;If you can follow the logic schematic posted by A33Zab, you will note there are a number of variables that must meet specified values before the p/b can be effectual.

The latching of ALT 2B was a result of diverging ADR speeds. ADR2 was nominated the "median" value and when speeds hadn't returned to within 50KTS of the median in 10 secs, law reversion to ALT 2B occurred and remained for the rest of the flight.

A33Zab has previously pointed out that the FD may be engaged on the ground in V/S mode, and on AF447 the A/P was inhibited due to CAS < VLS from 02:10:08.

AP Engage is inhibited:
if abs(φ) > 40°,
or θ < -10°, or θ > +22°,
or CAS < VLS,
or CAS >(VMO/MMO or VLE/VFE)

In respect of the FD Bars, they do appear to have been available when 2 ADRs (also 2 IRs) agreed within 20 KTS. The same agreement is also a provision of A/P engagement, plus FMGEC, FCPC (also no breakout by SS or pedals), plus the φ, θ and CAS conditions being met per the schematic.

John, I agree, neutral stability means the CG is at it's aft limit area to save fuel but it needs a computer to keep it stable. A pilot would have a hard time to keep it at a constant altitude. I guess a good pilot could still fly it by hand but it would be difficult. They would probably with no autopilot transfer fuel forward to make it easier to fly.

neutral stability means the CG is at it's aft limit area to save fuel but it needs a computer to keep it stable

Not quite right. For a conventional aircraft (and I presume this is what the Airbus becomes in the event that ALL computers roll over and die), the aft CG limit may (amongst other requirements) be limited to give an acceptable positive static stability .. neutral stability would be a fail and require either a further constraint of the aft limit or another flight test engineering fix.

It follows that, if the CG is sufficiently far aft to result in neutral stability, then it wouldn't be certificatable or, perhaps, the probability of box failure demonstrated at certification is sufficiently low to be acceptable.

However, this latter consideration may be tied in with the present mishap - inextricably. Are we not all concerned with the possibility that this crash may have been involved with events so out of left field (but only because of presumptions regarding training and competence standards) that the original certification program may not have considered them at all ?

I don't know what the certification story was for the Airbus FBW machines but would sure be interested to find out ..

A pilot would have a hard time to keep it at a constant altitude

True, but that's only a part of the problem. The typical pilot, faced with a sudden deterioration in the stability he/she feels/sees is more likely to rip the wings/tail off while trying to figure out what might be going on ..

a good pilot could still fly it by hand but it would be difficult

More a case of needing to recognise the problem and then be aware of/trained in the changed techniques required to fly the aeroplane. TPs cover this during their training course and there are documented cases of the occasional TP having to drag a statically unstable aircraft around the patch to get it back onto the ground .. but for Captain Average Joe Pilot .. the story, in all probability, is going to have an unhappy ending.

We did the fuel transfer thing to the aft tank in the 70's in a Lear jet. You get level at FL410, set power for .82 mach, transfer fuel aft and bring back the power to maintain speed as speed increases, FREE SPEED.

Aft CG as everybody knows means the horizontal stabilizer doesn't have to push down as much because of the forward fuel.

.. but, I suggest, with the aft tank loaded .. the aeroplane was still statically stable (ie still had an acceptable stick force gradient) for certification ?

John, that is why I said the area of the aft CG limit, not at it. All aircraft have to be certified to meet requirements.

Confused a tad by your comment. Presumably, with aft tank loaded you still were within the aft CG AFM limit ? At the published aft limit, one would still expect to see acceptable LSS.