AF 447 Thread No. 5

[glad rag]

Thank you for your posts #202 & 230.

I just love the way theories seem to gain momentum in the ether, only for them to be dashed by the cold FACTS.

[gums]

I welcome the "fresh blood" to the fray. Attaboy.

- Although the pitch moment chart I posted is for another aircraft, it illustrates two points ( one positive, one negative) that result in little or no pitch control authority for the existing HS/elevators/stabilators in either positive or negative direction.

My main point presenting that chart was to counter all the folks that think a deep stall is only a concern for the T-tail designs. I also wanted to show the c.g. of the Viper, and point out that under some instances the 'bus has a very aft c.g. The reduced trim drag of the main wing is reduced if we can fly with a more neutral longitudinal stability. Simple, really, as the HS doesn't have to induce a nose up moment, and can basically "float". The big savings are the reduced AoA of the main wing and associated reduced induced drag.

In my case, we had a great cruise drag reduction, but we also had the HS and the wing contributing to lift when in a turning fight. Yeah, I can just see the 'bus in a turning fight with a Sopwith Camel, heh heh. Except for the inital HS movement, our HS (stabilators) usually was "limiting" the nose up tendency. So when we got to the deep stall scenario, out HS were commanded full nose down. Turned out there was a small AoA/c.g. range that allowed the jet to settle into a classic deep stall.

- The gee and roll rate are two physical phenomena that pilots can sense instantly ( as opposed to the drone pilots at Creech AFB and other places). We tried pitch rate for the longitudinal axis, but seemed to most pilots that the gee was easier to sense and control. Rates are still involved to prevent overshoots of pitch commands and to "smooth things out" for the SLF's. No big deal.

'bus takes into account actual pitch attitude, so at a 30 deg climb angle you get a 0.87 gee command, not one gee. With a constant one gee command you would continue to pitch up once a few degrees greater than level. Because we weren't worried about the SLF's, we normally let the basic one gee trim setting alone and just manhandled the sucker. But many pilots would trim for zero gee and simply hold back pressure. Would be willing to bet that the Thunderbird slot pilot trims for slightly less than one gee, and prolly the wingies.

The Viper concept was that we flew around in something close to the 'bus "direct law", but we could never command actual physical movement of the control surfaces. Only exceptions were rolling down the runway and if we wound up in a deep stall with AoA above 30 degrees. Even then, we had no rudder control, as HAL cut us off, heh heh.

All of our "sub-laws" were due to things like gear down while airborne, special setting for carrying external ordnance and "standby gains" in case we lost air data. Interesting, that last feature, ya think?

- Our stick employed piezo-electric transducers - 4 of them for pitch and roll, Rudder pedals moved one half an inch and were linear voltage tranducers. After a few jets, we had 1/8 inch of movement and some springs or whatever could be felt. Initial jets had zero stick movement - all pressures.

As with every fighter built from the mid-fifties, there was no feedback from the control surface pressures. Some jets had bellows to provide a "stiff" stick at high speeds. Some had bobweights to help pulling too many gees too quickly. But zero actual physical feedback. The feedback was from your butt and inner ear.

[rudderrudderrat]

Hi Dozywannabe,

There has been no such thing as real "elevator feel" since the '60s, and Direct Law does not provide it.
You keep telling me that and I've tried to explain it to you before.
Would it help if I called it "sense of longitudinal speed stability"? The aircraft has it naturally by design concept.

Normal Law removes it, but adds Alpha Prot & Alpha Max.
Alternate Law removes it and has no such "protection" or "Limit".
Direct Law would restore it. Ask any conventional aircraft pilot - they would understand it.

[takata]

I repeat - there is NOTHING in the BEA report to tell you that the pilots caused the climb. A 'nose up' input of unspecified size or duration does NOT prove that and may well have been of short duration - you do not know.
Well, this is quite authoritatively expressed... but also quite illogical as for addressing the fact that any pilot nose-up imput (whatever duration and amplitude) could not have caused this aircraft to climb (at whatever rate, as this is likely proportional).
Considering this high speed profile, manual flight and elevators sensibility, what would be the illogical part about me mentioning that?

The BEA is providing this information about a pilot imput in the same direction as the trajectory followed by the aircraft, what would be the logic to affirm : the climb wasn't related to this imput?
Obviously, you are taking the possibility (that I'm also sharing) that this full climb rate could not have been fully achieved by pilot imput alone by translating it into "nothing in the BEA is telling us that the pilot caused the climb".

Hence, you are rhetorically jumping into the breach of us lacking the full detailed picture of this imput as making an illogical point by saying that there is absolutely no causality between a pilot imput nose up and a following climb.

For my part, I'm saying that whatever else could have been added to the climb rate (turbulences, initial pitch rate at AP off, whatever else you'll like more...), this single imput "nose-up" was certainly part of it because, of course, the system would have taken it as a commanded +x g maneuver order, translated it into pitch attitude increase and, once achieved, would maintain the trajectory in climb (1 g).
What we'll need to know is the value of "x", the resulting maneuver g-load, adding/substracting possible turbulence impact, as to verify if something else was not a factor of the climb rate achieved... which is certainly what the BEA would have to acertain before mentioning, as a fact, that climb was entirely due to pilot imput.
Saying otherwise (it was unrelated) seems fallacious.

As for your bit about "There is another way to change pitch attitude than pulling up on the sidestick as simply applying thrust could do the job if the amount is large enough." - you don't say? Now show me where the report tells you they increased thrust. You are making this up!
I'm just looking at the joined DFDR tracks of N1 % thrust and read that, when autothrust kicked off, N1 was already auto-throttled back at ~70%, then moved to 100% during the climb sequence.
You should know that thrust would freeze where it was (~70%) when autothrust disconnected; Hence, this increase was manually applied, even if not reported in the narative, which include an incoherence about "alpha-floor" kicking which is not available at such speed (inactive above Mach 0.53). This is based on AIB interpreted pilot confusion about "Alpha-lock" corrected by "Alpha-floor", while it certainly was "Thrust-lock" alarm (when ATHR disconnected).

Look by yourself if I'm making up this stuff:
http://takata1940.free.fr/Airprox340.jpg

Now to TC-JDN - have another look at the trace. The a/c began pitching while the engines were throttled back, the side stick did not move but the THS did.
The system will use every surface control and thrust to maintain 1g flight. Changes in THS trim were very limited during the whole sequence (much less than 0.5 deg), including a "zoom climb", "apogee", "descent"... while elevators moved in both sense with a much larger amplitude. Nonetheless, the system trimming THS seems to have not been "pitch up", but the other way as there is no such 5ND in the range of THS.

I note you come 'from Toulouse'
Right, I was there some time ago. I also note that you come from "Per Ardua ad Astraeu", but who cares?

[hetfield]

syseng68k (http://www.pprune.org/members/302789-syseng68k)

The voluminous fcom looks to me like a user guide,...No, it's just an insurance if something goes wrong......

[A33Zab]

Question: Why are two pots unused ?.

No more computers to connect. (5 in total)


Question: What is the function of the solenoid and does that lock
the stick at any point (zero ?) in it's travel ?.

The solenoid is activated by the A/P and add's a force threshold in neutral stick to prevent any unwanted switching to manual control, while keeping
the possibility to override the A/P if required.

simple schematic of xdcrs:

http://i474.photobucket.com/albums/rr101/Zab999/SSpitchInput.jpg

[DozyWannabe]

Normal Law removes it, but adds Alpha Prot & Alpha Max.
Alternate Law removes it and has no such "protection" or "Limit".
Direct Law would restore it. Ask any conventional aircraft pilot - they would understand it.

I've been asking a few people about it behind the scenes, but the answers I got back were too technical for me to comprehend easily (my brain has an annoying habit of shutting down when presented with algebra)... there's a pile of emails/PMs looking suspiciously at me as I type.

Let me see if I understand what you're getting at, and if I'm wrong please correct me. Prior to this I got the impression from your post that it related to the presence of autotrim - that is, when manually trimmed (with the THS at a fixed angle), the aircraft will tend to stabilise at a certain pitch angle and speed will remain more-or-less in the required ballpark. The presence of autotrim means that the THS is correcting itself based on sidestick input, and as such the trim angle is changing. In Normal Law, Alpha Prot and Alpha Max keep the trim settings within certain limits, but in Alt 2 those are not there, so there's nothing to stop the trim getting the aircraft into difficulty if the sidestick input is on the aggressive side.

Am I following you OK?

If I am, I think it's important to recognise that it takes a significant amount of input to cause the THS to get itself to such an extreme angle, and it's also important to recognise that autotrim has other benefits as well. It's pretty clear that Airbus FBW training at a basic level instructs pilots to be more careful with their sidestick inputs when law degradation has occurred. It's also worth bearing in mind that if you're in that situation and don't like what the trim is doing, all you have to do is set the manual trim as desired and avoid making large and consistent pitch inputs on the sidestick - this should cause the autotrim, when it kicks back in, to maintain a pitch angle at or near where you've just manually set it.

If I've read the "note" correctly, this isn't a case of a slight back-stick input in combination with (presumably corrective) roll input causing the THS to move to the 13deg nose-up angle in a matter of seconds, this is a case of the elevators causing the zoom climb in response to input, followed by the THS moving over the course of around a minute as repeated full or near-full backstick was held on the way down. From what I've read, THS movement from the autotrim is not particularly sensitive, nor is it likely to come into play with inadvertent sidestick deflection - the pilot *really* has to command it to be at that kind of angle for it to have got there, which is why the initial nose-down commands weren't enough to get the THS moving.

[rudderrudderrat]

Hi DozyWannabe,

You are getting closer.

It's also worth bearing in mind that if you're in that situation and don't like what the trim is doing, all you have to do is set the manual trim as desired and avoid making large and consistent pitch inputs on the sidestick
In Alternate Law, even with the stab trim wheel held stationary, longitudinal speed stability is not restored. The elevators will be held at a displaced position in order to satisfy the pitch stable law. (as in Loss of G & Y Hyds on A320, (or G & B I think on A330)). With UAS, the pilot would still not "feel" the aircraft getting slower and heavier in pitch.

[takata]

Hi Rudderrudderrat,

Normal Law removes it, but adds Alpha Prot & Alpha Max.
Alternate Law removes it and has no such "protection" or "Limit".
Direct Law would restore it. Ask any conventional aircraft pilot - they would understand it.
This is not entirely true.
In Normal Law (pitch), some feedback is artificialy maintained.
In Alternate Law (pitch), same, but there is less gain and feedback.
In Alternate Law (general), Valpha_prot is changed by Vstall_warning (g sensitive) There are still speed limits and speed protections available... but, of course, only if the system still have some valid airspeed sources.
In Direct Law (pitch), feedback is direct as you said (but artificial, as electric).
In Back up Law (no power for computers), pitch is changed using the mechanical THS trim.

[BOAC]

Quote:
Originally Posted by BOAC
As for your bit about "There is another way to change pitch attitude than pulling up on the sidestick as simply applying thrust could do the job if the amount is large enough." - you don't say? Now show me where the report tells you they increased thrust. You are making this up!

I'm just looking at the joined DFDR tracks of N1 % thrust and read that, when autothrust kicked off, N1 was already auto-throttled back at ~70%, then moved to 100% during the climb sequence.
You should know that thrust would freeze where it was (~70%) when autothrust disconnected; Hence, this increase was manually applied, even if not reported in the narative, which include an incoherence about "alpha-floor" kicking which is not available at such speed (inactive above Mach 0.53). This is based on AIB interpreted pilot confusion about "Alpha-lock" corrected by "Alpha-floor", while it certainly was "Thrust-lock" alarm (when ATHR disconnected).
- er - my bit refers to 447, not TC-JDN..............................:confused:

[takata]

- er - my bit refers to 447, not TC-JDN..............................http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/confused.gif
ergo. Indeed, mine (quoted) refers to TC-JDN, not to 447...:O
(looked clear to me when I wrote it... if not, sorry about my poor syntaxe!)

[Meikleour]

Bearfoil: The THS will move to satisfy long term trim solutions PROVIDED the `g` demand is not greater than -.5g ( namely -.6 to -1g ) or High Speed Protection is active. Once away from these constraints then it should resume movement if necessary.
HOWEVER manual movement of the THS is always available to the pilot and its authority is very large.

[DozyWannabe]

With UAS, the pilot would still not "feel" the aircraft getting slower and heavier in pitch.

Given that the sticks are not backdriven, they wouldn't feel it anyway, unless you're talking about in their bodies through the motion of the aircraft - in which case I'd say even if it could be felt, is it not preferable to use the ADI and thrust settings to make sure you're at a safe AoA?

[henra]

Otherwise, as I understand it, if the segment is "non-level", there is a good chance/probability that "inertia" and "control surfaces" as left after the disconnect, and lack of protections, can bring the "a/c" way out of being "level" - "up", or "down", or "left" or "right".


With regards to inertia, I agree.
Regarding Control surfaces I tend to disagree.
As I already stated the AP disconneting will not so much be the factor here.
The AP makes requests to the FCPC's like a human pilot would do.
In normal law the AP will ask for a roll or pitch demand and the FCPC will provide the 'implementation'.
Therefore Control Surface deflection will depend on FCPC and not directly on AP.
If they had still Normal Law after AP disconnect this would have assured wings level.
It is the reversion to Roll Direct Law that will dictate what the Control Surfaces will do.
As in Direct Law the position of the control surfaces is directly proportional to stick position it is reasonable to conclude that in the given scenario the ailerons would have moved to neutral after change to Alt2.

[takata]

Hi Henra,
The AP makes requests to the FCPC's like a human pilot would do.
In normal law the AP will ask for a roll or pitch demand and the FCPC will provide the 'implementation'.
Therefore Control Surface deflection will depend on FCPC and not on AP.
Very well explained.
To illustrate this point, the schematic of the control system, (note that AP box channel is treated like a Pilot imput channel):
http://takata1940.free.fr/flightcontrols.jpg

And the AIB annexe to the report quoted above on A330 behavior in full auto flight facing turbulences. (There is no THS track, but the FCPC would not have time to adjust it anyway, as such pitch corrections are mostly left to elevators and autothrust).
http://takata1940.free.fr/Airprox330.jpg

[henra]

Given that the sticks are not backdriven, they wouldn't feel it anyway, unless you're talking about in their bodies through the motion of the aircraft - in which case I'd say even if it could be felt, is it not preferable to use the ADI and thrust settings to make sure you're at a safe AoA?


Dozy,

Without judging what is better I would like to try and point out the difference:
With the THS at a given position there is a speed to which the aircraft will return by itself if you let go the yoke, even no matter what thrust you set.
If we assume that during cruise the trimmed speed is 270kts, and you command a Pitch Up, if you let go the yoke, the aircraft will lower the nose and finally settle again at 270kts, albeit at a slightly lower FL and after a couple of nice and accentuated phugoids.

You can only overcome this by constantly pulling the yoke or by deliberately changing the trim.

With any kind of Autotrim (be it AP or FBW) you do not have this constant point to which the AC will revert by itself. The Aircraft will follow a demanded flight path.
It needs clever logic (elaborated C*) in the FCS to deal with the fact that you could demand a flight path that could not be sustained by the AC.
This is done by blending over from 'g' demand to pitch demand. This makes sure the AC doesn't try to chase 1g at all costs.

Edit:
Caveat for any one who wants to bash Airbus Autotrim now: An AP mistrimming slowly and quietly and then disconnecting and handing back to the pilots can be equally bad or even worse as you cannot fix it just by applying ND on the Yoke, which would work on an AB as long as you have Autotrim.
It just has to be noted that trim is a very important aspect of flight in any aircraft and not clearly poinitng that out and training it is a clear mistake.

[rudderrudderrat]

Hi DozyWannabe,

I'm still not quite there am I?
unless you're talking about in their bodies through the motion of the aircraft Er .... No.
Given that the sticks are not backdriven - They don't have to be.

In Direct Law, the aircraft is stick free speed stable (just like a conventional aircraft). Provided I don't move the thrust or stab trim, it will continue on a trajectory at the same speed.

If I experienced UAS, all I have to do is leave it alone. If whilst attempting to hold the wings level, I inadvertently pulled back on the stick a little for a prolonged time, it would climb and slow down a little. If I relaxed on the stick, it would descend and regain speed again.

In order to get it to fly much slower, I'd have to pull back really hard or move the stab trim. That effect is what we call "elevator feel".

It is absent in ALt Law, and makes the pilot completely reliant on power and pitch. A human pilot, deprived of this sensory feed back, is reduced to an attitude clues processor - much like the autopilot that just gave up.

PS Please see JT's post #282, which explains it better.

[takata]

This is done by blending over from 'g' demand to pitch demand. This makes sure the AC doesn't try to chase 1g at all costs.
If the AC would try to chase 1g at any cost, disregarding pilots maneuver demand, it would make the aircraft unable to change its trajectory in any circumstance, as each maneuver is an excursion out of 1g flight. (this is the part I'm clearly unable to understand about THS Fantasy Law theories).

I'll bet that any test pilot would have noticed this Airbus design flaw... at first attempt to fly it!

[HazelNuts39]

This is done by blending over from 'g' demand to pitch demand. This makes sure the AC doesn't try to chase 1g at all costs. Thx Henra, I wasn't aware of that. In the case of AF447, when the pilot 'maintained nose-up inputs' after 2:10:51, and continued that '15 seconds later', reaching a pitch attitude of 16 degrees, and supposing he released the stick at that point, would the FCS then maintain 16 degrees pitch?

[mm43]

However, when in normal law, regardless of the pilot's input, the computers will prevent excessive maneuvers and exceedance of the safe envelope in pitch and roll axis.
However, as on conventional aircraft, the rudder has no such protection.The last sentence regarding the rudder is a prime example of the FCOM portraying something in the BASIC PRINCIPLE that turns out not to be true.

Just a few pages back I noted someone suggesting that "plenty of rudder" could have helped the situation, and it is worthwhile repeating that the rudder has two forms of protection, i.e.


Rudder Travel Limiter Unit (http://oi56.tinypic.com/ivvayo.jpg) (RTLU) which limits rudder travel between 35° at 150 KCAS and decreasing to 4° at 350 KCAS respectively,
Pedal Travel Limiter Unit (PTLU) which provides input dampening.

On latching of ALT2 LAW the rudder was limited for the remainder of the flight to +/- 7.9°.

[henra]

Thx Henra, I wasn't aware of that. In the case of AF447, when the pilot 'maintained nose-up inputs' after 2:10:51, and continued that '15 seconds later', reaching a pitch attitude of 16 degrees, and supposing he released the stick at that point, would the FCS then maintain 16 degrees pitch?

Not necessarily. I don't know the exact implementation of the C* law by Airbus. If it were a straightforward pitch rate law below a certain speed this would be the case but I'm sure it is not exactly implemented this way all the way to Stall speed.
Unfortunately I don't know how exactly they factor in AoA in the very low speed regime but it would not be too difficult to overlay AoA thresholds over a pitch rate law and I cannot see them not factoring this in.

Edit:
If someone has got access to a good sim the exact behaviour of the 'bus should be rather easy to find out. Put it in Alt2 in a constant climb at 5-10° NU pitch and wait what happens.
Take notes of Speed, AoA, Pitch, Trim while speed reduces close to the apogee.

[takata]

Hi mm43,
On latching of ALT2 LAW the rudder was limited for the remainder of the flight to +/- 7.9°.
It should be added to your sentence, "until the slats are extended"... but now, without valid airspeed, this is another question rising as there is also speed limitations to their extension.
Concerning the FCOM, this part is quite old, it could have been modified later. But you are certainly right that its litteral "meaning" is not exact (and curious in such a manual). They certainly meant something else like no rudder "active" protection is part of the flight envelope as for roll and pitch axis.

[busTRE]

mm43

I think you are being a bit harsh.

However, when in normal law, regardless of the pilot's input, the computers will prevent excessive maneuvers and exceedance of the safe envelope in pitch and roll axis.
However, as on conventional aircraft, the rudder has no such protection.

It is quite clear that they are referring to the type of the protection mentioned. The FCOM statement is absolutely accurate. The rudder has no protection that will prevent excessive maneuvres or envelope exceedance. The travel limiting system only limits the travel and so depending on conditions, excessive manuevres/envelope exceedance are indeed entirely possible.

[syseng68k]

PJ2, #232

These are not taught very thoroughly in initial ground schools at least
in my experience, and if one wasn't in the air force one's knowledge was
increased largely through one's own efforts.
A lack of completeness is to be expected in training, as it can only
ever be an overview in any complex professional discipline. However, it
is also a given that further study is expected and that this and
experience fill in the gaps over the years. Continuous education and the
learning of new techniques is what makes some types of work interesting
in it's own right. I doubt if training is being skimped in any way that
could affect safety, but perhaps the omission of certain aspects tends
to instill a false sense of security in terms of system capabilities,
especially at the edges. If the automation handles everything perfectly
99.999% of the time, is it really necessary to get into more than the
sops and regs demand, I guess is the received wisdom.

The frustrations of not knowing and not being able to find things out
easily have been endemic - while easy to fly and a joy to hand-fly,
"automation" has become as much a marketing tool as it has a way of
solving the problems of flight. The resistance to knowing more than the
"NTK". need-to-know, ground-school curriculum requires, comes first from
how expensive it is to train well, and next from a lack of knowledge in
those who must do the teaching, always of course, with wonderful
exceptions from those memorable instructors who's passion takes them,
and their students beyond NTK.
Passion is the right word, but passion is not always appreciated,
perhaps even denigrated in this modern age and beancounters don't
understand it at all. I've seen this in industry for years: The
difference between those who love their work and those for whom it's
just a gig. Anything that smells of instinct, intuition or creativity
might be seen as "unconventional", yet those are just the sort of
qualities that intelligent individuals need outlet for and that are also
needed to get out of unexpected situations.

This isn't "THE" problem, because clearly the aircraft and the design's
record is no worse in terms of fatal accident rates than conventional
types - in short, the airplane and the design work extremely well but
one should never be in a position to not understand and not anticipate
what his airplane is doing.
Safety has been improving over the years in any case, because of
advanced engineering techniques, more sophisticated design and
verification tools and improved infrastructure. The fact that fbw
techniques are used may not be a significant factor and imho, fbw can
only be for the good longterm. The problem is perhaps indirect, in the
culture that arises from it and it's promises.

Below is a nuts-and-bolts schematic of the pitch-basic loop. I hope it
is of some service in understanding the pitch control of the A330
Thanks for that. It just goes to show how complex the system is. I was
more interested in a state transition diagram / logic flow chart that
shows the input conditions, discreet and variable, required for
transition between the various laws. Gums posted a drawing for one of
his machines some time ago, but haven't been able to find it via forum
search. I don't see how anyone can analyse af447 without it, though I
bet the BEA have all this info and more...

[airtren]

Henra:
Thanks for your post, and to Takata's. The latter provides a good illustration of some of the elements I was referring to...

Glad to read you're in agreement on "inertia".

Two things regarding the disagreement on control surfaces, that may help bringing you in agreement:



1. You’ve quoted selectively from my paragraph, omitting the last sentence (marked in blue):


Otherwise, as I understand it, if the segment is "non-level", there is a good chance/probability that "inertia" and "control surfaces" as left after the disconnect, and lack of protections, can bring the "a/c" way out of being "level" - "up", or "down", or "left" or "right". The degree of how off from "level" depends also on the time interval between the "automation disconnect" and the taking of the controls by the pilot, as well as a correct control correction coming from the pilot.

That last sentence is important, as it has put an emphasis on the time window/interval between the AP & A/THR disconnect, and the time the Pilot is taking control and providing an input control/correction through the Stick - which is the time in which there is NO input (gap in input) to the F/CTL. The two are in the Takata's post's drawing, the two Input sources into the F/CTL Computer.



2. Your reference to Normal Law behavior is different from the case I refer to, and may indicate your missing of my reference to “lack of protections” (marked in blue) referenced as in pertinent protections, as a case in which the system is NOT in NORMAL LAW.



Note: Regarding the Takata's post text/excerpt of "...when in normal law, regardless of the pilot's (or AP) input, the computers will prevent excessive maneuvers and exceedance of the safe envelope in pitch and roll axis." I seem to be more conservative on the interpretation of the "prevent... exceedance of the safe envelope....", in regards to the extent of the creation of orders by the F/CTL Computers if no input is present from the AP or Stick..

That being said, during that time window mentioned above, and other than Normal Law, the control surfaces are left in a neutral/static position, and thus (a) they may be neutral, (b)they may reduce, or (c) they MAY AMPLIFY the effect of air flow change due to strong/heavy turbulence during, before, and after that window.

That effect may be NULL (a), may counter (b), or may compound (add to) (c) the “inertia” in getting the “a/c” way off the “level” flight.


Otherwise, as I understand it, if the segment is "non-level", there is a good chance/probability that "inertia" and "control surfaces" as left after the disconnect, and lack of protections, can bring the "a/c" way out of being "level" - "up", or "down", or "left" or "right".



With regards to inertia, I agree.
Regarding Control surfaces I tend to disagree.
As I already stated the AP disconneting will not so much be the factor here.
The AP makes requests to the FCPC's like a human pilot would do.
In normal law the AP will ask for a roll or pitch demand and the FCPC will provide the 'implementation'.
Therefore Control Surface deflection will depend on FCPC and not directly on AP.
If they had still Normal Law after AP disconnect this would have assured wings level.
It is the reversion to Roll Direct Law that will dictate what the Control Surfaces will do.
As in Direct Law the position of the control surfaces is directly proportional to stick position it is reasonable to conclude that in the given scenario the ailerons would have moved to neutral after change to Alt2.

[mm43]

Hi Takata,

Prior to the BEA Note, I had used the "until slats extension", but as you have suggested there were other issues in this descent.

busTRE,

I agree that I may be "pushing the boundaries" on this one, but Airbus had determined in their wisdom that the vertical stabilizer needed protection from rudder inputs, and the computers are programmed to provide that as per the graph. I accept that it is not directly "g" related but in all other respects is designed to protect the aircraft.

[takata]

That effect may be NULL (a), may counter (b), or may compound (add to) (c) the “inertia” in getting the “a/c” way off the “level” flight.
"Way off"... I'm not that sure (could be very few degrees on each axis)... Then a bit "off", certainly with light to moderately turbulent air (severe turbulence should have been notified by BEA). And that seems also the correct explanation (rather than fuel or CG issue) of this initial roll to the right at autopilot disconnection : rudder returned to neutral? (note = damping mode, no resistance to airflow) position, then possibly needed some correction and eventually retrimming.

As for AP/FD and ATHR corrective imputs preference during autoflight phase, it will also depend on Flight Director mode selected, that we don't know yet.
Diagram (not up to date) of the Flight Management Guidance and Envelope System (FMGS) :
http://takata1940.free.fr/FMGC.jpg

[takata]

Hi gums,

It is nice to read that you are still with us.
- Although the pitch moment chart I posted is for another aircraft, it illustrates two points ( one positive, one negative) that result in little or no pitch control authority for the existing HS/elevators/stabilators in either positive or negative direction.
I've got a question for you about pitch.
We know from BEA that AF447 had a MAC set at 29%, but also an optimum target that would be closer to 39% MAC, both being inside the safe certification limits. Now, people here tend to agree that, for an attempt to recover from a developed stall, having an aft CG would be a real issue.

Unless I'm mistaken, would not a further aft CG provide a better elevator authority (at least sensitivity)?
I seem to remember that moving the CG forward is a trade off for elevator sensitivity. Hence, in case of stall recovery, may be it is better to have more elevator control with a CG further aft, at least until the point that it is still inside the safe envelope.
What would you think preferable, in this case, 29% or 39% MAC?

[Turbine D]

takata,

Good question for Gums, it is what I was trying to understand when I posted this:

However, in the BEA Update, dated May 27, 2011, The weight of the aircraft was again reported at around 205 t, but the balance was changed to 29%, or in other words moved forward 8% or so. I thought the aft balance (37.3% - 37.8%) reduced drag and improved overall efficiency.
So my questions are: How did this happen? Why did this change happen? Does this have any effect on maintaining pitch either by the automatics or in a manual fly mode?

I just wasn't as clear as your post is.

[HarryMann]

Stepping in for gums (temporarily and with apologies):

Aft c.g.

Easier to stall
Easier to unstall (in theory) *

* Unfortunately though, a/c may well have departed - so you could be too late :eek:

Worth bearing in mind that the aft c.g. limit is not a completely black and white line, rather a grey area, especially with FBW and FCS messing with things. I guess that in the shorter term, everything is equiv to the old 'stick-fixed' stability, due to powered controls

: Aft c.g. (at or behind the neutral point) was encountered on heavily fuelled early mark PR Spits Usually just during the early initial climbout while rear fuel burnt off.. I think one or two were lost due to pitch osciallation and departures, fighters being pretty neutral anyway..

Occasionally NA P51s with certain types of arming & fuel loading got pretty close to neutral I believe, certainly overcontrol was responsible for pulling the wings off a few... albeit like as not in combat.

Would you call that stalling though? ;)

[HarryMann]

Reflecting on my miniscule PF time (c.f. PNF & SLF)

I do not think I would like being handed an aircraft in much turbulence of any kind, some way out of S&L wings level trim, with a FCS stick offering me (what I know as) neutral stability...
at night, when perhaps I'm not even too happy or in tune with > what has just occurred (perhaps a flight disturbance, small or large).

I do stand to be corrected that I have misread 12,543,298 posts :ugh: and that the a/c does not feel to me through the stick as one with neutral stability... but that is (within reasonable pitch rates and 'g' load) what the concensus seems to be.

=============

In other words, I suppose I'm asking.. was this a good choice for cruise flight? Indeed, was it considered just a fallback for 'occasional usage' and thus not too important.. the normal reason for moving away for a goodly degree of static stability is 1) maneouvrability (wrong type of a/c) 2) ease of control over longer periods (not usually applicable with auto-trim)

So...

[gums]

And yes, TK, I have been here recently.

Good points Harry, no problem with you jumping in.

As the c.g. moves back to the center of aero pressure, or so called neutral point, the jet has less tendency to revert to the 'trimmed" condition that existed when a disturbence upsets the flight path. In short, a very statically stable jet tries to get back to the trimmed state real quick. In non-FBW systems this is very apparent, as you have to "hold" control pressures to keep the beast from returning to its happy, trimmed state. This all goes out the window with most FBW implementations.

Flying with an aft c.g. is like balancing on the point of a needle. Lottsa work, and you better be good. So your inputs might, indeed. be very effective for a second or less. Then you overshoot your desired attitude or AoA or gee and you can get into the classic PIO or worse.

If you get the c.g. sufficiently rearward, the plane will flop end over end. Think about an arrow. See where the center of aero pressure is compared to the weight of the arrowhead and shaft. Ever see an arrow flip end over end? Didn't think so, heh heh.

One way to experience the real static stability of a FBW jet is to go to something like the "direct law", where all the electrons are doing is commanding a control surface movement. Then you make a small stick movement, relax pressure and see what the jet does.

I would take the forward c.g., and I have a feeling that the AF447 folks knew there was a possibility of some turbulence and didn't move a lotta gas rearward for the improved trim drag and such. If I got close to a stall I would have basic aero laws helping me as much as HAL's laws.

As a point ( short war story), our little jet had a negative static stability margin until about M 0.9 to 0.95. Like the 'bus, the "auto trim" tried to maintain our "hands off" gee command. Due to the negative static margin, our HS was actually providing "up" force. Hence, our first complete loss of the confusers at about M 0.6 or so resulted in the jet going nose down and between 10 and 20 negative gees on the pilot. He got to the bar that night with two super shiners and had bloodshot eyes for a week, heh heh. Next one was a fatality, and estimated 22 negative gees ( too low for a good ejection).

[PJ2]

Chris S, gums, Turbine D, takata, airtren, this paper may have been referenced before but if not it may be of interest in the present discussion, and also in the ongoing discussion regarding "Why the pitch-up?": "The Effect of High Altitude and Center of Gravity on Handling Characteristics of Swept-wing commercial airplanes (http://boeing.com/commercial/aeromagazine/aero_02/textonly/fo01txt.html)"

syseng68k;

Thank you for your response. Some of this has been discussed thoroughly before, but some has not - the following summary, part way through the Boeing paper referenced above, advances the point I was trying to make regarding training, knowledge of High Altitude flight and transport characteristics.

Believe me, these notions are not discussed in any groundschool I have ever had from start to retirement - "NTK" was, and is, taken seriously by cost-conscious beancounters, (as you say), but even in recurrent, none of this is discussed - it is assumed (self-study is fine, but materials the deal with the issues but which aren't academic papers, are scarce) - and in fact, accident reports and FOQA trends are never discussed either. Here's the relevent section, (my emphasis) - kindest regards, PJ2...
Summary
The use of wing sweep and stability augmentation on modern commercial airplanes makes them more fuel efficient. However, flight crews must understand the effects of CG and altitude on performance and handling qualities. For example, operating at an aft CG improves cruise performance, but moving the CG aft reduces static longitudinal and maneuvering stability. Many modern commercial airplanes employ some form of stability augmentation to compensate for relaxed stability. However, as long as the CG is in the allowable range, the handling qualities will be adequate with or without augmentation. An understanding of static and maneuvering longitudinal stability is an essential element of flight crew training.

[john_tullamarine]

Longitudinal Stability -

gums' last post highlighted the relationship of stick force/stability/CG. That is carried on in the Boeing paper cited by PJ2.

Casting the Boeing words a little differently, it is worth keeping in mind that longitudinal static stability is all about what stick forces the pilot "feels" when the aircraft is not on speed so far as trim speed is concerned.

At the trim speed the stick force should be at or very near zero.

If the aircraft slows down (for whatever reason) and the pilot desires to hold that lower speed, acceptable static stability requires that the pilot MUST hold on a PULL force of some measure. Furthermore, the further away from the trim speed, the HIGHER the pull required

If the aircraft speeds up etc we are looking at a PUSH force etc

As the CG moves aft the slope of this line (stick force against off trim speed delta) reduces and the aircraft gets progressively twitchier.

In an ideal world, the line would be straight and extend well away from trim speed. In reality sometimes the line does strange things and we need additional add ons (such as SAS) to adjust forces so that the pilot is fooled into believing that all is well. In small aircraft, this might be something as simple as a fancy spring arrangement bolted onto the elevator control circuit - typically seen in GA piston to turboprop conversions.

As CG moves aft we eventually get to a point where the static stability is unacceptable and we enter the region of static instability. The aircraft is still flyable (if you know what you are doing). The technique is tiring and stressful and consists of making an input, freezing the controls, assessing the response, making an input .. etc.. etc. A pilot in the know might manage to get the aircraft around the circuit for a landing .. but an extended flight recovery is a big ask. Hence the need for fancy electronic stuff to do the hard work.

Further CG aft movement eventually gets into a region of dynamic instability and the aircraft is beyond the ability of the human pilot altogether ...

Whatever the AF guys had in front of them in the cockpit, they had their hands well and truly full ... one way or the other .. not a situation any of us would wish on any pilot.

[takata]

Thank you (in chron. order) HarryMann, gums, PJ2 and John T. for providing some very usefull informations about longitudinal stability (or instability) related to CG position.

My question was also aimed at this aircraft pitch authority (or lack of it) once stalled at such an AOA : If, after a while, a recovery was attempted, the issue faced by the PF could be that he could lack the necessary pitch down authority in order to regain some lift.

If I understand correctly, assuming that the elevators were not fully stalled, an aircraft with an aft CG would have to be pitched down to a lower angle-of-attack but would also have a better pitch rate than with a more forward CG. On the other hand, more forward CG doesn't help for stall recovery but it's better for avoiding to enter the stall at the first place.
Then AF447 had a less than optimum lift cruise CG that did not prevent it from stalling without being (in theory) as much helpful for a recovery attempt.

[mm43]

Hi Takata,
If, after a while, a recovery was attempted, the issue faced by the PF could be that he could lack the necessary pitch down authority in order to regain some lift.I suspect that Airbus have already done some wind tunnel tests to prove what would happen, and the answer most likely was that sufficient THS and elevator authority was available with 29% CG.

The abnormal airflow and drag conditions during this high and increasing angle of attack appears to have had a stabilizing affect. ND on the elevator would have increased the surface area facing the airflow and provided the initial lever to pitch the nose down. Provided the THS followed along, the area and angle to the airflow would have been maintained and eventually all the airfoils would have slipped into an unstalled regime.

There is some evidence that this was tried and unfortunately stopped.

[Machinbird]

I think I have mentioned this before, but if an aircraft is pitching down after encountering a deep stall and has a significant pitch rate going while just getting into flying airspeed range, it is quite possible to overshoot the flying attitude and enter a negative g stall. If CG is aft & static stability is low, and with high enough pitch rate, you may not have enough control authority to stop the pitch down motion before stalling in the opposite direction.

Several military NATOPS manuals specifically address this point in stall and spin recovery.

Here is another situation where an AOA indicator gives you some warning before you actually float out of your seat that your AOA is approaching the normal range. Otherwise, when do you stop pushing the nose down?

[Old Engineer]

mm43 wrote:There is some evidence that this was tried and unfortunately stopped.

The reference is to the ND input by PF.

The question that must be asked is, did PF think that he could recover given enough altitude, but that at that point realize that the A/C would auger in before completing the recovery? Did PF then opt to return to the stable stall with vertical component just over 100 mph in the hope that some would survive?

Well, pasteboard cabinets survived. Suppose the PAX had been in rearward facing seats, and instructed to recline the seats? What more in the way of energy-absorbing collapsable support struts would have been required? After all, there are miles of support struts under those seats already, so that any airline can have any passenger density in any area of the cabin it may desire, cost and complexity be hanged for that.

Yes, I am aware that bearfoil said that someone was going to say this was a survivable crash, way back when. And I read the exellent helicopter post on this subject. But the PAX here were on top of many feet of crumple zone.

Would someone want to run a parabolic trajectory at 2.5g (normal to wing surface) recovery from a 45 degree descent, starting from the altitude at which PF abandoned the ND effort, and the assumed 1.414 times vertical speed of 100+ mph? This overlooks the time required to effect ND, of course, just for simplicity, as well as speed increase as the ND effort gradually takes effect, but would include the speed increase from starting on a 45 degree slope. Just a first cut to get a ballpark. Thanks, OE.

[takata]

Not sure if it is the right table but the CG should have been here:
http://takata1940.free.fr/cg.jpg

[BOAC]

As I have said before, once the crew found themselves with an 'unknown' ?60? degrees AOA at the top of the 'zoom', they were well outside any training environment we could contemplate. In terms of instantaneous manoeuvre, they would have needed to pitch around 50-60 degrees nose down to unstall - who outside an aeros/mil pilot would dream of putting the nose down 40 or more below?

If we, as pilots, are to expect 'cradle to grave' protection (with limited understanding of how it works) from our systems they have to PREVENT this position in the first place. IE

the system should either prevent or warn of excessive AOA
prevent or warn of excessive THS movement

in terms of the Mk1 FMCS (the pilot), he/she MUST be allowed to see a reliable attitude indication at the outset AND trained to maintain the correct one - before things go pear-shaped. Once IAS reaches the very low levels 447 saw, pitch attitude has little meaning in terms of performance

We still do not know whether 447's 'zoom climb' was initiated by the system. The AAIB appear to say TC-JDN's probably was due to the system dropping itself into alpha-prot. In both cases, it is probable that had crew reaction to the pitch changes been more effective and quicker, we would not be in this long thread. HOWEVER - this assumes that crews are aware of the pitfalls of the systems, do not lose attitude info AND retain some basic flying skills - and, of course - are 'permitted' by the FCS to make the necessary control inputs.

I regret to say (yet again) that either the fbw sytems AND/OR the training need to change. I watch in a state of disbelief as all our 'experts' jostle backwards and forwards, page after page, over this flow diagram or this servo circuit or this latching/voting logic and wonder how mr/miss average Mk1 FMCS is going to cope with it all in a failure state - in the very limited time available - when even the computers do not know what has happened. The same goes for 'relaxed' stability in the drive for economy. If the a/c is too statically unstable to allow the 'average' to fly it without the fbw systems, this also needs to be reviewed.

Several of us have re-iterated that had the crew been able to and had flown basic pitch/power at the outset, this would not have happened. We need to focus on the why. We should, in the short-term, forget all the millivolts etc. Someone knows. It is probably on the CVR.

[RetiredF4]

mm43
The abnormal airflow and drag conditions during this high and increasing angle of attack appears to have had a stabilizing affect. ND on the elevator would have increased the surface area facing the airflow and provided the initial lever to pitch the nose down. Provided the THS followed along, the area and angle to the airflow would have been maintained and eventually all the airfoils would have slipped into an unstalled regime.

There are other issues to be observed, and which could have favoured the establishing into this high AOA and prevented recovery.
As we know, airfoils produce lift also after CLmax is left behind, which means in the stall condition. We have two airfoils (wing and THS) and the complete fuselage producing lift at those stalled AOA areas. Prior to AF447 nobody would have believed that it would be possible to get such a big transport aircraft into an AOA above 35° and keep it there (disregard the protections, i mean just from the aerodynamic point of view). Everybody would have expected that there would be not enough THS / elevator authority to get it there and keep it there. This applies especially if the CG is that much forward like with AF447. So we have to ask ourself, are there factors in this post stall region which helped to stabilize AF447 in that high AOA besides the THS input?

As mentioned, both airfoils produce lift in stalled condition, and if the highly sophisticated main wing of AF447 produces more upward lift at a given stall AOA than the THS is able to counter with an upward lift (Full ND) as well, then we have a big problem to get the nose down. To get the nose moving down, the THS has to produce more upforce than the wings (we for sure have to take the leverage into the equation). Do we know, how the lift generating capabilities of those airfoils changed in this high AOA regions? No, we dont know. Do we know, how the lift will change, when we go f.e. from 50° AOA to 35° AOA by THS input (assuming it has enough authority at 50AOA)? No, we dont know.

Aditional lift producing parts would be the fuselage. Would the forward part produce more lift then the rear parts, or equal or less? We dont know. How would the lift change, when we change fuselage AOA from 50°AOA to 35° AOA? We dont know.

Travel of center of lift is another issue, we have not adressed yet. How far does center of lift move (aft or forward? In normal unstalled AOA conditions center of lift moves forward with increasing AOA?) with that high AOA? We dont know.

Maybe somebody has answers to those points, but its no use to disregard those issues when judging wether THS would be effective or not and only assume them to be a non issue.

Yes i know, We seem to have evidence that THS was effective. They did some nose down and AOA and speed changed....., but those changes might not be related to the ND input, or they might have not been effective enough (due to change of effectiveness in relation to different AOA), see my comment some posts before.


Edit: Center of lift = Center of pressure Cp

[HazelNuts39]

RetiredF4;

Please have a look at Figure6 (http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20050214373_2005208658.pdf), originally linked by
zumBeispiel (http://www.pprune.org/tech-log/449639-af-447-search-resume-part2-50.html#post6440142) and tell me what is so different about the A330?

[rudderrudderrat]

Hi PJ2,

Thanks for the link "The Effect of High Altitude and Center of Gravity on The Handling Characteristics of Swept-wing Commercial Airplanes"

"For a statically stable airplane the required column force, as speed varies from the trimmed condition, is less at an aft CG than it is at a forward CG. The minimum average gradient allowed by U.S. Federal Aviation Administration FAR Part 25 is one pound for each six knots."

Obviously AB FBW in ALT LAW does not meet that specification - and unfortunately the aircraft stalled. The known problem with the pitots should have been designed out much earlier.

[RetiredF4]

HazelNuts39

RetiredF4;
Please have a look at Figure6, originally linked by
zumBeispiel and tell me what is so different about the A330?

i dont know, but there should be data available which represent exactly the aircraft we are talking about and not any kind of airfoil to answer the question, how AF447 could get into this high AOA regime and how it could maintain it.

By the way, note the text associated with Figure 6 of your reference:

The pitch control remains effective throughout the angle of attack range but diminishes with increasing angle of attack, due initially to the immersion of the horizontal tail in the wing wake and ultimately due to flow separation on the horizontal tail itself at post- and deep-stall angles of attack. The maximum steady angle of attack with full nose-up elevator deflection is at α≈25˚, which is significantly higher than the stall region near α≈12˚ and this result indicates the potential for the airplane to enter upset conditions using normal pilot controls during un-accelerated flight.

There seem to be lot of differences, AF447 kept more then double the AOA on the way down.

[t54]

Assuming the PF could have got the nose down once he was falling, stalled at 100mph, what angle would he have had to go to?
I would guess that he would have gained even more downward velocity as the nose came down towards the wind (less drag). This would have meant the AOA increasing and him having to chase it.
Has anyone ever turned the nose of a big aircraft down to the 30 or 40 degrees?
How many seconds would it be before the wings came off?
Is stall recovery only possible in the very first moments, before the downward velocity gets too big?

[BOAC]

what angle would he have had to go to? - post #288?

[Owain Glyndwr]

As a ‘newbie’ here I have been reluctant to say too much in the presenc e of so much expertise, but I do think that I may be able to make a positive contribution towards understanding the aerodynamics – at least I hope so! I should preface any remarks by explaining that I was once an aerodynamicist, but anything I write is based on general principles and standard methods, not any particular knowledge of the A330, although I have of course used such data as is publically available. JT gave a lucid explanation of how the stability changes as CG is moved back, but before anyone goes off down one of those typical thread tangents about how the A330 with relaxed stability must be dangerous, it should be recognised that the CG where one arrives at static instability on the A330 is way back around 45~50% mac (it depends on Mach Number). Compare that with Takata’s CG envelope and you will see that it is nowhere near static instability even at the aft CG limit.
If I have understood correctly, the A330 in Normal, Alt and Alt2 laws operates under some form of C* control, and it is only in Direct law that this would come into consideration anyway. Also, AI would have had to show, for certification, that the aircraft was flyable in all states, including Direct law, without requiring exceptional piloting skill.
The requirements BTW, say that a pull must be required to obtain and maintain speeds below the specified trim speed and a push for speeds above that. The speed (in cruise) must return to within 7.5% of the original trim speed when the control force is slowly released but it is acceptable for the aeroplane, without control forces, to stabilise on speeds above or below the desired trim speeds if “exceptional attention on the part of the pilot is not required to return to and maintain the desired trim speed and altitude”. Not my words, not AI words; JAR words.
Retired F4 posed a lot of questions, most of which he answered by “We don’t know”. In this of course he is entirely correct, but that doesn’t stop us making sensible engineering estimates.
I suspect that most peoples’ mental image of a stall is a sudden loss of lift and a nose down pitching moment, typical of the straight, unswept wings on which they learned to fly (I am not a pilot BTW). However, a modern swept airliner wing does not stall like that.
The sweep, taper, camber and twist of a typical modern design will result in the maximum local lift coefficient occurring first at somewhere between half and two thirds semispan. This is generally a little way aft of the CG, so the first effect will be a gentle pitch up. What happens next will depend on how the wing is twisted. If the outer wing is more heavily loaded there will be a steadily increasing, but still relatively modest pitch up. When the inner (and forward of the CG) part of the wing stalls there will be a compensating pitch down. Throughout all of this process the wing lift coefficient is departing from the linear relationship with AoA that it had before stall, and eventually it will end up as a fully stalled wing with a more or less constant normal force coefficient. The actual ‘lift’ and ‘drag’ will then be the component of this normal force resolved into axes parallel and normal to the incoming airflow (i.e. to the FPA usually). When it gets to this point I think the centre of lift/pressure will be fairly close to the centre of area of the exposed wing. For the A330, this is about 70% mac. This means that when fully stalled the pitching moment from the wing will be a nose down value which does not vary much with AoA since the PM will be the normal force coefficient times the moment arm of this 70% to the CG at 29%, and the normal force coefficient will be nearly constant.
Net result of all this is that the actual process of stalling can be quite a gentle affair as Gums has suggested from time to time.
A couple of pages ago I posted an explanation of the mechanics of aerodynamic equilibrium in deep stall conditions, and nobody has yet said they think this was nonsense, so I am sticking with it. When you look at this, it is clear that the question to be asked is not will there be enough down elevator power to give a ND recovery moment, but rather will there be enough elevator power to get and hold 60 deg AoA. To recover all that would be necessary would be to remove the up elevator, although of course some down elevator wouldn’t hurt – so long as you don’t stall the THS.
OK, is forward or aft CG better/worse for stall/recovery?
The wing will stall at the same AoA regardless of CG position. With a forward CG the aerodynamic moment about the CG when approaching stall will be more ND because of the increased moment arm. So more up elevator will be required to approach and maintain a given AoA, the negative tail lift will oppose the wing and the overall lift coefficient will be lower with forward CG than aft and the aircraft will stall at a higher airspeed – but the same AoA!.
When the wing is stalled, for the reasons described above, the moment (a ND moment remember) will be nearly constant, so any variability in speed of recover will come from the elevator’s ability to provide ND pitch acceleration. This is going to be bigger with the moment arm from a forward CG, so my vote goes to forward CG as being more favourable.
Although it has been said that we cannot know what the post stall conditions are, we can calculate them for at least one point where we have ground speed, attitude, and descent rate; namely the point of impact. Taking the quoted values as ‘gospel’, one can calculate the airspeed as about 151 kts, the AoA as about 61 deg and the FPA as -45 deg. In addition it is believed that the engines were at Flight Idle at this time. For the sort of engine we are looking at this is as near zero net thrust as makes no difference. Assuming (OK, it is an assumption) that this was a stabilised state, then you can calculate what the lift and drag coefficients would have had to be to match – both lift and drag coefficients at about 1.07.
Hope this does eventually help and not spread more confusion!

[Owain Glyndwr]

[quote} There seem to be lot of differences, AF447 kept more then double the AOA on the way down. [/quote]

Not the least being that AF447 had the THS at -13 all the way down where this model was (probably) set to zero.

[Lonewolf_50]

Owain: wow.

Here is a summary of what I gleaned from your post. Please let me know what I have misunderstood.

Once stalled at altitude, and with CG as estimated, (be it 29% or 37%) the center of lift of the wings will provide a self-correcting nose down pitching moment proportional to such lift as the wing is still creating.

Per the FBD I just sketched on my napkin, the arm that the force acts through is of the length somewhere between 70-29 to 70-37, (as outer boundaries). Based on where the THS is, I'd guess its relative number for arm calculation is about 96 or 97. (Am I close?) as compared to the center of pressure on the wing. (@takata: thanks for the posted CoG chart).

Thought: IF THS and elevator (as a lift producing system) have lost control authority or were stalled, THEN there would initially be no force from the back end, or a very small force, countering the "self correcting" pitch down moment of the stalled wing.

Thought number 1:

As the nose attitude gets closer to level, wouldn't the C of P start to move forward from 70 towards a smaller value, and gradually reduce the length of the arm, and thus the moment, of the correcting tendency?

Thought number 2:

THS is an airfoil, so even if stalled, it produces some amount of lift and thus provides, through that longer arm, some counter to the correcting tendency of the wing whether or not it is stalled.

Your line of thought presents me with the provisional conclusion that the THS was not stalled, since the nose stayed up (per the BEA report) and didn't (as far as we know) oscillate up and down as it might if the THS were stalled.

What you described is a "natural" pitching down movement (??) of the stalled wing, which seems to have been countered by the longer arm being acted on by lift from an unstalled tail/THS.

Am I close?

If that's about right, it leaves me with a non trivial concern:

if the nose stayed up due an input or command other than pilot control inputs, the nose being held up by (THS lift) x (arm) prevented stall recovery for about 30 thousand feet worth of travel down to the surface.

As Retired F4 points out, "We don't know." In this case, ignorance is surely not bliss. :(

The above sort of reasserts a fairly obvious point: an ounce of stall prevention avoids about 200 tons of attempted cure. :{

From PJ2's linked article on high altitude handling:

3 Maneuvering Stability
An additional effect is that for a given attitude change, the change in rate of climb is proportional to the true airspeed. Thus, for an attitude change for 500 ft per minute (fpm) at 290 knots indicated air speed (kias) at sea level, the same change in attitude at 290 kias (490 knots true air speed) at 35,000 ft would be almost 900 fpm. This characteristic is essentially true for small attitude changes, such as the kind used to hold altitude. It is also why smooth and small control inputs are required at high altitude, particularly when disconnecting the autopilot.

[t54]

BOAC
As I have said before, once the crew found themselves with an 'unknown' ?60? degrees AOA at the top of the 'zoom', they were well outside any training environment we could contemplate.The AOA wouldn't have been high at the top of the zoom. It would have increased to its terminal, large value as the plane gained downward velocity, creating an upward component for the wind, so to speak.
I'm thinking they had a chance if they'd been able to act quickly, but once they were falling fast the dip needed for the nose might have been more than they were prepared to contemplate - or would have resulted in greater forces than the airframe could withstand.

[Yiorgos]

#1 - Amen to Owain's post.

#2 - Some of the contributrors here may benefit from being reminded that lift & drag are defined as the aerodynamic forces perpendicular & along, respectfully, to the free airsteam, NOT the airframe.

As far as the THS is concerned, with the airplane 'falling' @ ~60deg AOA (e.g) drag would contribute more pitch down moment than lift.

[gums]

Excellent presentation by Owain, just peachy.

I also wonder about recovery possibilities if the THS was moved to the opposite position/angle from that which existed all the way down to the ocean. Pitch moments would change, and it's possible that the nose would come down

When you look at this, it is clear that the question to be asked is not will there be enough down elevator power to give a ND recovery moment, but rather will there be enough elevator power to get and hold 60 deg AoA. To recover all that would be necessary would be to remove the up elevator, although of course some down elevator wouldn’t hurt – so long as you don’t stall the THS.

In other words, as with the Viper, at extreme AoA, you still have nose up authority, but not down. We had the equivalent of the THS all the time - no elevators at the rear of the stabilators. All but delta designs of the lites use the all-moving stabilzer. Because we had a lotta lift from the fuselage and the strakes, our aero c.p. was quite a ways forward of the airliner designs. So we could get to a fairly stable condition, stalled, but still with nose up authority.

I would add that as the speed rapidly slowed and the jet entered the abnormal AoA regime that there could be a brief time where downwash could "help" increase the nose up moment, like the classic T-tail deep stalls. In other words, without doing anything the AoA would continue to increase, driving the main wing further into the stall until equilibrium was reached.

Lastly, I do not believe that an extreme nose down pitch attitude would be required to recover. As 'bird suggests, this is where an AoA indication could really help. We aren't talking about 100 knots of extra speed, as it looks like we already had 150 knots or so of effective forward speed. Get to 200 + knots and start pulling back to level flight. And BTW, I always thought the gee requirements for the heavies was 3 gees, plus a standard addition until structural failure. The 2.5 gee number surprised me.

[HarryMann]

As far as the THS is concerned, with the airplane 'falling' @ ~60deg AOA (e.g) drag would contribute more pitch down moment than lift.Yes and when in a highly separated flow regime (fully stalled foils), extreme AoA, we may typically dispense with the assumption we are flying, per se, and often revert to just summing the Resultant Force vectors rather than thinking in terms of Cl, Cd and Cm, associated with the fairly linear ranges of the lift curve slope and pitching moment slope (Cd just about remains a mashup of a parabola and drag dropout buckets at high Mach)

[Lonewolf_50]

#2 - Some of the contributrors here may benefit from being reminded that lift & drag are defined as the aerodynamic forces perpendicular & along, respectfully, to the free airsteam, NOT the airframe.

As far as the THS is concerned, with the airplane 'falling' @ ~60deg AOA (e.g) drag would contribute more pitch down moment than lift.

Yiorogos, it seems that if the THS isn't stalled, not important.

If it is, then doesn't that drag force act "up" (a component of the vector, anyway) in a nose pitch down moment, when acting through the arm based on where the CG resides?

I am still left with the picture from my little FBD here that you have forces acting normal to the axis of the aircraft (vector components of vectors acting along the axis you point out) which tend to pitch the nose down, the only component acting against that being the body drag vrom CoG forward to the nose. There's more surface area aft of CG, based on my sketch. Am I missing something here?

Harry, we aren't at a high Mach number if we are stalled, are we?

[Owain Glyndwr]

Here is a summary of what I gleaned from your post. Please let me know what I have misunderstood.

Once stalled at altitude, and with CG as estimated, (be it 29% or 37%) the center of lift of the wings will provide a self-correcting nose down pitching moment proportional to such lift as the wing is still creating.

Yes that is right

Per the FBD I just sketched on my napkin, the arm that the force acts through is of the length somewhere between 70-29 to 70-37, (as outer boundaries). Based on where the THS is, I'd guess its relative number for arm calculation is about 96 or 97. (Am I close?) as compared to the center of pressure on the wing. (@takata: thanks for the posted CoG chart).

I may have misunderstood your numbers, but no, The CG and CoP numbers are % of mean aerodynamic chord, which is about 7.3m. The tail arm, from 37% mac back to the usual reference point of 25% tail mac is just under 29m, so the relative number for calculation is around 400.

Thought: IF THS and elevator (as a lift producing system) have lost control authority or were stalled, THEN there would initially be no force from the back end, or a very small force, countering the "self correcting" pitch down moment of the stalled wing.

Not sure what you mean by lost control authority, but if THS and elevator were stalled there would still be a substantial force at the back end, either up or down depending on which way the THS stalled, but it could only be decreased from whatever value it had before the stall.

Thought number 1:

As the nose attitude gets closer to level, wouldn't the C of P start to move forward from 70 towards a smaller value, and gradually reduce the length of the arm, and thus the moment, of the correcting tendency?

Yes it would, but of course the aeroplane would be moving back towards the unstalled state and the tail would still be giving substantial ND moments, which greatly outweigh the wing contribution.

Thought number 2:

THS is an airfoil, so even if stalled, it produces some amount of lift and thus provides, through that longer arm, some counter to the correcting tendency of the wing whether or not it is stalled.

Yes, as noted earlier

Your line of thought presents me with the provisional conclusion that the THS was not stalled, since the nose stayed up (per the BEA report) and didn't (as far as we know) oscillate up and down as it might if the THS were stalled.

Yes again.

What you described is a "natural" pitching down movement (??) of the stalled wing, which seems to have been countered by the longer arm being acted on by lift from an unstalled tail/THS.

Am I close?

Yes

If that's about right, it leaves me with a non trivial concern:

if the nose stayed up due an input or command other than pilot control inputs, the nose being held up by (THS lift) x (arm) prevented stall recovery for about 30 thousand feet worth of travel down to the surface.

That implies an input or command other than pilot control inputs. As I said in that earlier posting, without significant and continued up elevator application, even with the THS at -13 deg, you won't get any nose up pitch from the back end above about 26 deg AoA. Well maybe I didn't actually SAY that, but it is implicit in my argument. 26 deg is more than enough to stall the aeroplane of course, but AF447 has been linked to much larger values of AoA that, IMHO, can only be achieved with up elevator. I will leave it to others to argue whence came that up elevator.


The above sort of reasserts a fairly obvious point: an ounce of stall prevention avoids about 200 tons of attempted cure. http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/boohoo.gif

Who could deny that!

[Lonewolf_50]

Owain:

I went back to sketch, and yes, I should have been looking more like 300 or more. Came back to your post, thanks for the 400. :ok:

By lost control authority I meant 'move your flight control X amount' (by telling the Flght Control computers to move it as far as it will go) and get less response than what will change your pitch, or get no change.
Go to full deflection (or largest allowed command) and get less change than needed, or none.
That to me is loss of control authority. I may be using the term in a non standard way.

Part of what was in the back of my mind as I typed that was that each knot lost costs you lift/force as the square of the velocity lost, roughly. I move the stick and expect a response, don't get one, so keep moving the stick more to try and get it to respond at all ... mind goes back to the old slow flight demonstrations, and how "sloppy" the control responses are compared to cruise flight.

Rudder travel limits are a built in control authority limit. (To avoid damage to tail). That's an intentional limit to control authority. What I was thinking about was inadvertent loss of control authority in the pitch channel due to loads/forces being insufficient for the amount of force needed to change pitch.

Also in the back of my mind as I wrote that is a loss of control authority problem in helicopter tail rotors, where you put controls to full deflection but are unable to overcome the torque due to limitations on control surface travel (or tail rotor blade stall). In that case, your authority over your nose, (yaw) is lost, since it goes one way while you are trying to get it to go the other way, or just stop it from moving.
As I said in that earlier posting, without significant and continued up elevator application, even with the THS at -13 deg, you won't get any nose up pitch from the back end above about 26 deg AoA. Well maybe I didn't actually SAY that, but it is implicit in my argument. 26 deg is more than enough to stall the aeroplane of course, but AF447 has been linked to much larger values of AoA that, IMHO, can only be achieved with up elevator. I will leave it to others to argue whence came that up elevator.
Thanks for the clarification. :)

[Owain Glyndwr]

And BTW, I always thought the gee requirements for the heavies was 3 gees, plus a standard addition until structural failure. The 2.5 gee number surprised me.

Gums,

The actual requirement is a complicated formula that depends on MTOW, but pretty well all civil airliners this equates to 2.5g as a 'limit' load with a factor of 1.5 to be applied for ultimate (breaking) load. i.e. 3.75*MTOW is the design condition. At less than MTOW of course one could pull more.

[EMIT]

Gums

G limit in the heavy industry:

minus 1 till plus 2.5 in clean configuration

0 (zero) till plus 2.0 with high lift devices in anything but UP.

Of course, like Owain states, Ultimate (breaking) load is 1.5 times limit load.

[henra]

2. Your reference to Normal Law behavior is different from the case I refer to, and may indicate your missing of my reference to “lack of protections” (marked in blue) referenced as in pertinent protections, as a case in which the system is NOT in NORMAL LAW.




I know.
The point I was trying to make was that it was the Flight Law that was determining the position of the control surfaces and not the AP.
Therefore my reference to Normal Law to make this difference a bit clearer.

In this case after AP disconnect the system would have soon/immediately/at the same time switched to Roll Direct Law and thus very likely to control surfcaes neutral.
Control surfaces neutral means just that. It doesn't mean the aircraft will try to level the wings. But it means the ailerons will not actively contribute to further roll after change to Roll Direct Law (AP doesn't enter into the equation at all), only inertia and/or other forces will.

[takata]

Hi Owain,
I do think that I may be able to make a positive contribution towards understanding the aerodynamics
You did Sir! great posts, and please, don't stop making many other positive contributions like that...:D

[takata]

More relevant infos (still not up to date):
About the Characteristic speeds:
http://takata1940.free.fr/Speed0
http://takata1940.free.fr/Speed1.jpg

About Thrust settings in Adverse Weather:
http://takata1940.free.fr/thrust0.jpg
http://takata1940.free.fr/thrust1.jpg

[takata]

About the lost infos due to Unreliable Airspeed.
The characteristic speed function (see above) computed by the FE (Flight Envelope part of the FMGC) is lost, meaning that Speed limits, computed by the PRIMs (FCPC), are also lost, including Valpha_prot (Normal) and VSw (Alternate).

Two other functions, displayed by the Primary Flight Display (PFD) were also lost (flagged, see ACARS): Both Flight Director (FD) and Flight Path Vector (FPV) were flagged. This is very bad as the FPV would also provide a visual form of AOA via the Flight Path Angle:
http://takata1940.free.fr/fdfpv.jpg

[HazelNuts39]

Speed limits are lost, including Valpha_prot (Normal) and VSw (Alternate).Maybe I'm misreading that sentence, or else I would like to clarify that Vsw is shown on the PFD in Alternate Law, it is not shown in Normal Law. Perhaps it's just a typo, and the intended speed is Valpha_max.

[takata]

Hi HN,

Thank you for pointing that for clarification. This is what I meant by specifying the Law related to each. VAlpha_prot (Normal) is replaced by VStall_warning (VSw) in Alternate... But, it should never be displayed on the PFD if the change of Law is due to an UAS event. Instead, there is a flag -SPEED LIMIT- meaning that the limits (high an low) are lost.

[HazelNuts39]

Thanks Takata,

can you please provide a reference?

[DJ77]

Hi Gums,
I think that perhaps on the graph of the pitching moment of the Viper the points where the stabilator starts stalling may be detectable. Do you know its max deflections? was it a symetric airfoil?

[takata]

can you please provide a reference?
Sure I could... but let me think about where to find it first!
My notes are:
"Apparition du SPD LIM RED FLAG sur l'échelle des vitesses des PFD.
Les parties FLIGHT ENVELOPPE des deux FMGEC sont INOP.
Perte des informations:
- VLS, S, F, GREEN DOT, Vtrend, Vmax, VFEnext, Vsw"
I noted it from Air Caraïbes report, should be also in BEA #1 or #2, but it is of course somewhere else in the FCOM as I did read it more than once.

[Turbine D]

PJ2,

Thanks for the paper you posted on CG. It answered my question/questions.

I also want to say to all the posters in the past day on this and related subjects,
It has been most educational to me, thanks:ok:

[syseng68k]

A33Zab, #254

Thanks again for the illustration. From that, I assume from that pitch
and roll are shown yellow and blue gear train and that primary computer
pots are red, green and blue, while secondaries are red and blue only.

If this is correct, there is in fact no redundancy at hardware level in
terms of (ideal?) multiple pots per axis, per computer. For this configuration,
redundancy can only be done in software, between computers, using
messaging. I guess it makes sense. It reduces the overall number of
pots, still provides the required redundancy, but potentially introduces
a far more complex set of failure modes...

[takata]

HazelNuts39,
Concerning "SPD LIM RED FLAG", note that I'm also refering to those ACARS in the sequence:
2:10:29 -.1/WRN/0210 228300 2 06 > FLAG ON CAPT PFD SPD LIMIT
2:10:41 -.1/WRN/0210 228301 2 06 > FLAG ON F/O PFD SPD LIMIT
Those two FLAGS, despite the lag in recieving time, will be displayed on the PFD (and all characteristic speeds removed) as soon AP OFF + ALT2 switch (immediately or up to 10 seconds after AP OFF).

In fact, out of 15 ACARS time stamped 0210:
- 10 are Real Time ECAM/FLAGS
- 1 is a Real Time Position Report (kicking between those two SPD LIMIT flags above)
- 2 are System Maintenance Advisory (not displayed in flight)
- 2 are the related Faults to the above sequence which are delayed by the opening of the 1 min correlation window.

Now, if all of them kicked at the exact same time (0210:05, but it is not the case), they will be queued and it will take for the SATCOM nearly the same ammount of time up to the last fault recieved at 0211:55. The difference is only a small lag of 8-10 seconds between two FLAGs that were displayed at the same time in F/O, and CAPT PFDs... hence, this small lag is due to satellite's bandwith rather than system lag.
The processing time was nearly constant at 6 seconds +/- 1 second per ACARS, consequently, only one more message could have been sent during the same time window (01'50'') without such little lag.

[grity]

RetiredF4 Do we know, how the lift generating capabilities of those airfoils changed in this high AOA regions?with very high AoA the effect of the profile with his flow is becoming smaler, the center of lift and Cd and Cl approaches the forces of a flat panel with the same AoA.... with an AoA of 90 deg every different foil ends with an center of lift near 50% and an Cd near 1....

[syseng68k]

PJ2, #281

Thanks for the reply and the reference. What was interesting was the
comment about access to tech detail information and it's scarcity. At
the risk of repetition, if I were flying these machines, I would want to
study the detail. A deeper understanding of the machine can only improve
pilot skills, in the same way that knowing what goes on under the hood
of a car helps to appreciate the limitations and to get the best from
it.

Perhaps the (secrecy ?) is a european thing and wonder if boeing provide
more free access to such information.

Anyway, this is probably a bit off topic for tech log :)...

[HazelNuts39]

takata;

I think I basically agree with what you wrote. I just wasn't aware of it and thanks for patiently clarifying this point. However, I'm left with a few grey areas which may be relevant for what the pilots of AF447 saw.

The text you copied from the Air Caraibes memo appears on page 5 in the context of the protection named "CAS MONITORING" which in the BEA reports is the initiating event at 2:10:05 of the whole 2:10 sequence and results in the PROBE PITOT fault message after closing the one-minute correlation window.

Page 7 of the ACA memo shows pictures of the PFD speed scale in Normal and Alternate law in the context of an ADR DISAGREE message with Vsw in the Alternate Law 2 case.

While it may be unimportant whether or not a calculated Vsw is indicated on the speed scale when IAS has dropped to 60 kt or less, the intriguing question for me is whether it would be shown in the intermediate period when one or more of the indicated speeds had become valid again. EDIT:: Why should Vsw not be shown along the speed scale showing a 'valid' speed, first on PFD1, later on ISIS, and at an unknown time on PFD2?

[DozyWannabe]

Perhaps the (secrecy ?) is a european thing and wonder if boeing provide more free access to such information.

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.

Bear in mind that in Redmond - a few miles away from Boeing HQ - lives the second-biggest PITA for proprietary software there has ever been!

[HarryMann]

Harry, we aren't at a high Mach number if we are stalled, are we?Can't see where I suggested we were at high mach no:)

Yes, we can easily be stalled at High Mach, just as in incompressible flow (that's what the lower cruise buffet boundary and coffin corner is about, no?)

What do you mean by high Mach ? > M 0.5? transonic? or supersonic?

[takata]

The text you copied from the Air Caraibes memo appears on page 5 in the context of the protection named "CAS MONITORING" which in the BEA reports is the initiating event at 2:10:05 of the whole 2:10 sequence and results in the PROBE PITOT fault message after closing the one-minute correlation window.
Right. There is two independant functions for monitoring the speed for essential systems which should be the first to detect probe errors (beside plenty of other systems self monitoring their own recieved imputs, just in case).

a) ADR monitoring at Auto Flight System (AFS) level (-> FMGC). This should also be the first one to react as the threshold is set at 0.45 seconds for a variation of 20 KT.

b) ADR monitoring at Electronic Flight Control System (EFCS) level (-> FCPC/PRIM) which is "CAS Monitoring" you refered to. Here, the threshold is a variation of 30 KT during 1.0 second. It is also responsible for changing immediately the Flight LAW to ALT2 when a variation is detected. Hence, it takes 1 second to change the flight law, but it's at first temporary. After this point, the last valid value (before change) is retained and a comparison is made with the current value 10 seconds later: if the difference is > 50 KT, ALTERNATE 2 is confirmed, whithout the possibility to revert to NORMAL until post flight reset.



Page 7 of the ACA memo shows pictures of the PFD speed scale in Normal and Alternate law in the context of an ADR DISAGREE message with Vsw in the Alternate Law 2 case.
This illustration is taken from the FCOM and is generic for ALTERNATE if airspeed is not unreliable. In case of UAS, What you will have instead is the red flag "SPD LIM" (see report previous page) without Vmax, VSL nor VSW and... It will last for the remainder of the flight like ALT2! (read me well: even if the airspeed come back to normal after a while, this is lost as it is displayed only when ALTERNATE low/high speed protections could work, which would not be the case after an UAS. Even if coherent, speed will always be considered spurious by the system). That is also the reason why some long haul flights turned back and landed after an UAS event which was not transient (lasted more than 10 seconds).


While it may be unimportant whether or not a calculated Vsw is indicated on the speed scale when IAS has dropped to 60 kt or less, the intriguing question for me is whether it would be shown in the intermediate period when one or more of the indicated speeds had become valid again. EDIT:: Why should Vsw not be shown along the speed scale showing a 'valid' speed, first on PFD1, later on ISIS, and at an unknown time on PFD2?
Quite simply, it is an EFCS function that compute all the characteristic speeds from data comming from the FE part of FMGC and ALL ADRs. This function become inoperative as soon as more than 1 ADR is rejected by the FCPC. After this point, it will consider both FMGC (1 & 2) as inop regardless if the data will be later coherent again. Hence, the display of probe data (speed) on each PFD or ISIS is directly available for the crew but it is unrelated with the function computing the characteristic speeds which is lost. Those data displayed are not what the system could use as it will need two "valid" sources, at any time, for safe operation.

[gums]

For DJ77, et al:

- The stabilators, or horizontal stabilizers/elevators, moved +/- 21 degrees.
- They had a symmetrical airfoil, and...
- They were interchangeable from one side to the other
- They moved independently in order to help with roll, especially when supersonic

[Lonewolf_50]

Harry:
You were talking about a highly separated flow regime. That's (in the context of this case) the low speed regime stall. The case under discussion isn't, as far as I understand, a high speed (and thus high mach for this airplane) stall example.
Yes and when in a highly separated flow regime (fully stalled foils), extreme AoA, we may typically dispense with the assumption we are flying, per se, and often revert to just summing the Resultant Force vectors rather than thinking in terms of Cl, Cd and Cm, associated with the fairly linear ranges of the lift curve slope and pitching moment slope (Cd just about remains a mashup of a parabola and drag dropout buckets at high Mach)
I wasn't sure what to make of your reference to high mach, honestly.
That's why I asked. I think, on reading your post again, you were comparing shapes of Cd curves at different ends of the spectrum ... as a general reference? :confused:
What do you mean by high Mach ? > M 0.5? transonic? or supersonic?
In the context of this class of airfoil (large transport) let's say transonic or approaching supersonic (limits of airfoil before the high speed buffet, coffin corner, etc.) would seem to me "high mach" as the airfoil isn't shaped for operations in supersonic flight. (I confess, it's been over thirty years since I studied compressible flow, and things like Prandtl Meyer flow, so it doesn't recall well from memory.)

I don't think we'd get anywhere discussing this airfoil under conditions at Mach 2, for example. :cool:

[HarryMann]

Ah yes, thanks (Cd just about remains a mashup of a parabola and drag dropout buckets at high Mach)

Just covering as you say either end of the spectrum, though drag buckets due to a cruise Cl laminar regime also can have a Mach element (be a function of).

[Lonewolf_50]

Just covering as you say either end of the spectrum, though drag buckets due to a cruise Cl laminar regime also can have a Mach element (be a function of).
Just out of curiosity, is this a boundary layer phenomenon? (BL is an area I wasn't all that strong in when studying fluid mechanics. )

[HarryMann]

Yes, very much so...

I find there is always a lot of confusion between separated flow, turbulent flow and laminar flow. The later two are boundary layer states, the former (whilst to some extent the result of boundary layer effects) is a total flow phenomena.
Saying the flow is turbulent does not mean its separated, indeed a turblent boundary layer has a greater facility to resist negative pressure gradients (behind a body) and remain attached.. .nor laminar meaning low darg and attached (indeed again, laminar flows easily separate , the classic being a 'laminar separation bublle' at the l.e. of a thin foil at high alpha; draggy too (pressure drag)... whilst the laminar layer itself has low (frictional) drag.
So it isn't difficult to spot a lay commentator when it comes to aerodynamics, or certainly flow discussions ;)

[HazelNuts39]

Just out of curiosity, is this a boundary layer phenomenon? Stall always involves the boundary layer. It wouldn't occur in friction-less flow, but there wouldn't be any lift either. To comment on the Mach involved - I noted a while back that alpha-max is defined by low-speed stall at more or less constant AoA up to M=0,275, and is defined by Mach-related buffet above that M. In AF447 stall occurred at about M=0,6 (2:11:06, 185 kCAS at FL375).

[Lonewolf_50]

Harry/HN:

Thanks to you both, some of it's coming back to me. I am thinking that I am wrong to posit that the stall wasn't at "high mach," given the numbers HN kindly reviewed. The conversion of CAS to IAS at high altitude reminds me of how fast the plane was traveling at stall entry ~ M0.6. I can see where one can say that it was a stall at a relatively high Mach number ... depends on frame of reference for what "high" or "low" means.

(HN, I am aware that stall involves boundary layer effects, what had me curious was the Harry's pointing out the mach elements within drag ... I suspect that was once taught to me but it wasn't in long term memory).

[CONF iture]

Low Speed Stability is lost in Alternate (2) Law.
Not always true :

http://i45.servimg.com/u/f45/11/75/17/84/fcom_110.gif (http://www.servimg.com/image_preview.php?i=106&u=11751784)


Won't going to Direct Law remove the nose down demand that it just tried to apply? It says in Direct Law all protections are inoperative.
That must be part of the complexity of the system, laws, protections, stability ... In the mean time, can we presume that if under Low Speed Stability in ALT2, autotrim does not operate ?

Caveat for any one who wants to bash Airbus Autotrim now: An AP mistrimming slowly and quietly and then disconnecting and handing back to the pilots can be equally bad or even worse as you cannot fix it just by applying ND on the Yoke, which would work on an AB as long as you have Autotrim.
If no autotrim never under manual flying, at least a pilot knows trim is under his watch always - No ambiguity.

[bearfoil]

henra, CONFiture.

henra's comment ( "a/p mistrimming, disconnecting and handing back", etc.), was one of the very first progenitors of passionate disagreement here on thread. I said, (roughly) that getting the a/c back under these 'unproven as yet conditions' would be like having a wet enchilada dumped in one's lap. Distracting, uncomfortable and in immediate need of a clean up.

THS as TRIM versus THS as CONTROL? How can one be separated from the other? It seems an incestuous combination of duties, and ripe to provide confusion.

As CONFiture has said, "One way or the Other". SA should be natural, intuitive, and rapidly moving. Stopping to think just to get a handle on the moment seems a dangerous waste of time.

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).

[HazelNuts39]

takata,
This illustration is taken from the FCOM and is generic for ALTERNATE if airspeed is not unreliable. In case of UAS, What you will have instead is the red flag "SPD LIM" (see report previous page) without Vmax, VSL nor VSW and... It will last for the remainder of the flight like ALT2! 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 remplacés par Vsw".

[A33Zab]

Thanks again for the illustration. From that, I assume from that pitch
and roll are shown yellow and blue gear train and that primary computer
pots are red, green and blue, while secondaries are red and blue only.

If this is correct, there is in fact no redundancy at hardware level in
terms of (ideal?) multiple pots per axis, per computer. For this configuration,
redundancy can only be done in software, between computers, using
messaging. I guess it makes sense. It reduces the overall number of
pots, still provides the required redundancy, but potentially introduces
a far more complex set of failure modes...


In fact there is another (identical) set of xdcrs for the roll channel.

De redundacy is: 2 potmeters for each Flight Computer (2x roll & 2x pitch)
If 1 input rod becomes disconnected, both potmeterclusters are driven by the other crank & geartrain by means of the shearpin.
If 1 input rod/geartrain is jammend, the shearpin will break and allows free operation of the other set of potmeters.

[gums]

I suggest we interested parties crank up a thread in the Tech Forum specifically devoted to FBW systems - philosophy, real engineering crapola, human factors, experience from several folks here when things went awry, and of course lessons-learned from AF447 and other FBW airline types.

I can't moderate, but can help.

I only suggest this as I was around when we saw the first fully-FBW system fielded in significant numbers - a charter member, if you will. My engineering background is so-so, not half as good as some here, but "adequate". I also worked with the high-tech avionics in operational jets earlier than many here due to my military experience, and most of that time I was solo.

I recall a question from a U.S. Senator at a hearing with our new Sec Def ( McNamara) who was fascinated with high-tech and other aspects of military equipment designs. He asked the Secretary, "Just what experience, if any, do you have in these matters?"

[CogSim]

I apologize if this has already been posted.

For safety critical system design folks:

Spaceflight Now | STS-135 Shuttle Report | Astronauts restart computer; Obama to call Atlantis today (http://spaceflightnow.com/shuttle/sts135/110715fd8/index.html)

From the article: (bolding mine)

"Well, it [flight computer] actually failed last night, I think it was about an hour and a half after we fell asleep the alarm went off," Ferguson told CBS Radio in an orbital interview. "I think we all looked at each other, had that bright-eyed, sort of bushy-tailed look, and raced up to the flight deck. The folks on the ground did a nice job helping us get through that. We brought up another GPC to help out with the functions (GPC-)4 was performing. We got it, hopefully, back up and running this morning so it's hanging in there and we're confident it's going to work for entry for us."

[infrequentflyer789]

That must be part of the complexity of the system, laws, protections, stability ... In the mean time, can we presume that if under Low Speed Stability in ALT2, autotrim does not operate ?


I don't think that is correct - I think autotrim is always active outside of direct law (or manual backup) except in abnormal attitude law. Abnormal attitude law could, I guess, co-incide with low speed stability activation, but would not automatically follow from it.


If no autotrim never under manual flying, at least a pilot knows trim is under his watch always - No ambiguity.It's a good theory, but there are incidents (more than one 737 I can think of) where it hasn't held up in practice. In situations where the automatics dump the plane back in the pilots' lap unexpectedly (perhaps trimmed up to the limit) it can only add to the workload.

Also, I think autotrim is effecitively requried for C* control law, so without it you are looking at direct law, and no protections/limits whenever A/P is out. Not sure that is going to be an improvement.

You could reduce the number of laws/transitions to simplify things - as others have suggested. Go straight to direct law, and hence manual trim, when things start to go wrong. I'm ambivalent on that - I can see from a design & engineering point of view that the current laws are a nice graceful degradation, which should make things easier.... however, all the different laws, sub-laws, caveats and footnotes add up to a lot of combinations to learn and fit in training on. It's arguably little use having intermediate graceful degradation modes if pilots are never trained on them.

Be careful what you wish for though - there are reasons why non-normal laws get latched, and the A/P doesn't handle direct law, so you could be looking at hand-flying a long way when stuff goes wrong. On the other hand, maybe if the previous UASs had been a bit more of an "event" the **** pitots might have got fixed sooner (like when AB suggested it, or earlier).

[takata]

Hi HN39,
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 remplacés 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".

[takata]

Hi 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).

[HazelNuts39]

Read it again,I did. We're not discussing any protection, but the indication of Vsw on the PFD. But thanks anyway.

[syseng68k]

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 :E:

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:suspect: ...

[bearfoil]

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

[takata]

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.

[takata]

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).

[HazelNuts39]

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?

[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."
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?
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?

[HazelNuts39]

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.

[takata]

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.

[bearfoil]

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?

[takata]

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:http://takata1940.free.fr/reconf.jpg

[DozyWannabe]

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.

[CONF iture]

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 ... !?

[DozyWannabe]

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.

[GarageYears]

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.

[takata]

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

http://takata1940.free.fr/flagon0.jpg

http://takata1940.free.fr/flagon2.jpg
http://takata1940.free.fr/flagon3.jpg
http://takata1940.free.fr/flagon4.jpg

[bearfoil]

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. :eek:

[takata]

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.

[takata]

THS is large, powerful, and slow moving
I don't think it is that "slow moving". I remember a figure from 1°/sec. up to 3°/sec in elecrical control, like for rudder trim, but I don't know where it is buried nor how much is the rate in manual control. Also, in this mode (back up), it could have a much higher rate than the one needed for precision trimming.

And again, I'm feeling now like the one having feed the (sleeping) Troll. You deliberatly use whatever is provided to make many assumptions based on nothing but your self ignorance. Your first assumption should be to give some credit to the engineers who designed those aircraft. You can be sure that there was a lot of thinking put in every design choice even if you don't quite understand the end result. Hence, study them in depth and, after that, come back with some constructive critisism about something you'll have really studied.

[bearfoil]

Hi takata. No problem. In 447's case, it was not THS authority that was desired, it was the desire (seemingly unaddressed, or ignored) to defeat it, to zero it. The Elevators were fine, yes? GY points out DIRECT LAW was not in. If TRIMMING can get the a/c into trouble, (fbw, or not :D), it should have a Zero channel, no?

This is what I need to know. It is said the THS follows the Pilot's ss input.
This isn't emergency; on the way up, it was doing NORMAL LAW stuff? Given the dire nature of the a/c assiete at top of climb, How could the lack of Power to the THS be the reason it stayed at ~13 NU? It appears at this point, that the climb was a problem (!), independent of conjecture re: the accident, With a need for STALL recovery, and the THS limit of 2degrees ND, no matter the reason, how did she abandon the THS so NU?

This is a big question for Pilotless flight, notwithstanding whatever 447' PF did or did not do?

Thanks again for your pics, and wow. (words of wisdom)

edit re: upper post. Manual Trim was required, isn't that .65 degree per "hand sweep"? Also, in active dynamic flight , (UA recovery), power and rate are not desired coupled together? Q/N, (Quick and Nasty?) Cruise flight wants those tender touch, Yes?

[takata]

Hi takata. No problem. In 447's case, it was not THS authority that was desired, it was the desire (seemingly unaddressed, or ignored) to defeat it, to zero it. The Elevators were fine, yes?
Of course yes.
What we are talking about is that the aircraft seems to have done, so far, nothing wrong by itself. The THS was trimmed here and left here. The obvious reason is that there was no real attempt to pitch down with elevators. Hence THS remained where it has been ordered to be and helped to maintain this aircraft nose-up, certainly added to further NU elevators imputs by pilots...

Then, everything is pointing at the pilots not understanding the situation at all: that they were stalled, and that they will crash without pitching down the aircraft. Consequently, what happened to them? What caused them to believe something else happened and lead them to make those imputs?
Maybe the full transcript will tell us more about that. What was their strategy? We can't recognise any procedure applied from their acts alone, be it UAS, stall recovery... or whatever else.

[bearfoil]

I must agree. The only hesitancy I have is I am nonplussed the crew would apparently leave out the THS in the recovery attempt.

And also that I remain convinced the actual problem began perhaps many seconds prior to a/p loss, and became critical alomost immediately. Alas, further data from BEA will be most welcome.

[PickyPerkins]

takata
Originally Posted by Bearfoil
…. In 447's case, it was not THS authority that was desired, it was the desire (seemingly unaddressed, or ignored) to defeat it, to zero it. ….


bearfoil
… The only hesitancy I have is I am nonplussed the crew would apparently leave out the THS in the recovery attempt. …

As a distant observer listening to all you experts being puzzled by the non-use of manual trim, I am in turn puzzled by your puzzlement.

We know that the training departments of the airlines had strenuously opposed any mention of the use of manual trim in training for upset recovery, even though the test pilots of both Boeing and Airbus had emphasized more than a decade ago that bringing the a/c into trim was in their opinion the first priority in a recovery.

So I assume (I don’t know) that if the crew had had upset recovery training (as distinct from training to recover from an approach to a stall) the use of manual trim would not have even been mentioned, and they may even had had warnings against its use (because of the danger of structural damage).

So why are you puzzled by the non-use of trim? They followed their training, which in part told them to forget what they were told in primary training, particularly WRT stalls. They were never trained to use manual trim. It wasn’t even mentioned.

QUESTION: Being a French crew for a French airline and knowing that any deviation from training and SOP might be investigated by a French Court, might they have been inhibited from deviating from training and/or SOP in case they might be blamed for any subsequent damage?

The crew were probably unaware of the characteristics of a deep stall and had never experienced one. One of Gums’ early posts mentioned a deep stall as being “just like cruise flight”. So while on this subject, how many of you experts are happy with the recent upset recovery screed which lists as one of the indications of a stall as “Buffeting”? While this is true, there is still no mention of the possibility of a buffetless stable stall. Are you all happy with this omission?

An unrelated QUESTION (my apologies if this was already been answered 2,000+ posts back):
From where did the BEA get their 107 kts ground speed on impact with the sea?

[takata]

Hi PickyPerkings,
As a distant observer listening to all you experts being puzzled by the non-use of manual trim, I am in turn puzzled by your puzzlement.
Hopefully, you did not quoted me (it was Bearfoil's) as I'm neither an "expert", neither puzzled about the non-use of manual trim!!!
Nonetheless, you seem to be the one highly suffering from tunnel vision about a "manual" THS non-existant issue (related to AF447).
Quite simply, if you don't pitch down, autotrim won't certainly trim nose down, no? Then, why would you pitch up your nose and manually trim down your THS? Where would be the logic and what is the real issue?
Ask yourself!
Then maybe you'll understand why either "manual" nor "autotrim" are a NON issue from what is published so far from the investigation.

After this point, your comments seems a bit moot.

[bearfoil]

Not an expert. Also, far away. For me, TRIM is a verb. It implies through common usage the implementation of a small aerodynamic device to position a control surface in the airstream such that no continued force is necessary to keep it in place. It relieves the operator of a consistent and irritating need for pressure to be applied to the controls. As such it implies an adjustment in control pressure so that an attitude may be extended for a length of time. As used in large and flyable Horizontal surfaces, it takes on a somewhat different meaning. Rather than freezing a small device in place to relieve the pressure needed to maintain an attitude, THS essentially moves the whole kit and changes the "Angle of Incidence" of the Wings themselves.

So a THS is not strictly speaking a transitory attempt to relieve Pressure on the Controls, it changes the aspect of the airframe itself. It is in essence the 'Elevator'. It makes 'permanent' a flight attitude commanded by the FCS. It 'follows' elevator input, giving them a great deal more authority in Pitch.

So see, I am not an expert, as my clumsy explanation proves.

[takata]

They were never trained to use manual trim. It wasn’t even mentioned.
(Sorry for the typos above about your name)
Did you find any detailed informations about this crew training?
Just have a look at the the two or three pages above and you'll see that manual trim use is a mandatory training as for being able to fly this aircraft in particular flight control modes. Did they ever had the real oportunity to experience it? Who know, but I really doubt it. Nonetheless, they were all certified pilots for flying this aircraft in all configurations.

As for the manual, there was a very short part about stall at cruise :
The aural stall warning may also sound at high altitude, where it warms that the aircraft is approaching the angle of attack for the onset of buffet. To recover, the pilot must relax the back pressure on the sidestick and reduce bank angle, if necessary. When the stall warning stops, the pilot can increase back pressure again, if necessary, tu return to the planned trajectory.
So, how would you interpret "relax back pressure on the sidestick"?
Would not one use the trim wheel?
From where did the BEA get their 107 kts ground speed on impact with the sea?
Don't they have retrieved the DFDR? It should have recorded the acceleration at impact (assuming all those accelerometers). Hence, a basic function will give the ground speed at impact, if not provided directly by the GPS.
PS: onset of buffet... buffet may be expected close to stall speed, but gums was also certainly talking about a completely developped stall, where 1 g stall is fully achieved, that may be quiet in such a large and basically very stable aircraft.

[Machinbird]

So, how would you interpret "relax back pressure on the sidestick"?
Would not one use the trim wheel?If you are getting a stall warning, it is because you are maneuvering (applying g).

Relax back pressure means do not pull so hard on the stick-period.

Using the trim wheel would have you trimming into a stall. Not a good idea.

[takata]

Hi Machinbird,
If you are getting a stall warning, it is because you are maneuvering (applying g). Relax back pressure means do not pull so hard on the stick-period.
What you say makes perfect sense. I interpreted that for cruise level flight while being trimmed a bit too high. Stall warning could trigger in turbulence (basically the same effect as maneuvering). It's certainly due to tunnel AF447 thinking about its first stall warning that I'm trying to explain. I don't know also how the EFCS would render this trim feedback with neutral sidestick (hence it was stupid).
Using the trim wheel would have you trimming into a stall. Not a good idea
I was certainly thinking about opting for the other way!

[HazelNuts39]

The modern commercial heavies have really great aero characteristics that can make a stall insidious. And the stall is not like the Airbus manuals depict on the lift versus AoA curve. There is no sharp break in the curve at "x" AoA. It's a very gentle curve and one can fly at fairly extreme AoA's without the sharp pitch excursion we all saw when checking out in a Chipmunk or Cessna or T-28 or......Gums' point is illustrated in this graph: cLalphaM06.gif (https://docs.google.com/leaf?id=0B0CqniOzW0rjMTVlZGNiMDEtYzA3NC00MTkwLWI1ODEtZWZlODE xMDk2NzBm&hl=en_GB)

It should be noted that only the blue data points are 'fact'. The extrapolation of the trend line beyond the last datapoint should be treated as a 'guess'.
PS: onset of buffet... buffet may be expected close to stall speed, but gums was also certainly talking about a completely developped stall, where 1 g stall is fully achieved, that may be quiet in such a large and basically very stable aircraft. You will note in the graph that there is a substantial margin between the onset of buffet (alpha-max) and the 1 g stall. BEA says in its interim report no.2 that the stall is identified by 'vibrations' which is french for buffet, and I think they mean heavy buffet.

[rudderrudderrat]

Hi takata,
What we are talking about is that the aircraft seems to have done, so far, nothing wrong by itself.
I agree it seems to have performed as designed.

One has to wonder at the wisdom of starting with an aircraft concept which is naturally longitudinally speed stable, and design ALT LAW handling characteristics which allow the aircraft to be flown (with UAS), to stalling Alpha and beyond in a trimmed condition.

[DJ77]

- The stabilators, or horizontal stabilizers/elevators, moved +/- 21 degrees.
- They had a symmetrical airfoil, and...
- They were interchangeable from one side to the other
- They moved independently in order to help with roll, especially when supersonic

gums, many thanks for the data.
I am aware that the Viper has a delta wing and strakes that generate powerful vortices at high AoA. The stabilators also form a delta-shaped plan (but without the strakes). Such wings tend to “stall” rather smoothly AFAIK, meaning there is no sharp drop in lift as AoA increases past Clmax AoA, thanks in part to vortex lift.

I tried to understand why the stabilators efficiency (measured as the distance between the neutral and full deflections curves of pitch moment vs AoA) starts decreasing at a lower AoA for ND than for NU deflection. I surmised this had to do with the downwash of the wing and since the stab airfoils are symmetric it is possible to evaluate the downwash and stabilators local Clmax AoA. This gives 21 deg and 15 deg respectively. I was puzzled by a 21 deg downwash angle until I remembered that the FCS adapts the wing curvature at high AoA, drooping slats and flaperons.

Of course, we miss pitch moment curves for the A330 to understand what ND or NU inputs could do. Owain Glyndwr posted a very interesting explanation but I am not convinced the THS was not stalled at 60 deg AoA. We know that the elevator was still working from BEA’s note but perhaps this was due to the elevator presenting a larger frontal area to the airflow in ND position than in NU. The effect of a stalled THS would be a positive slope of the Cm curve in the stalled area, meaning a decreasing downward moment with increasing AoA.

Another point where I doubt Owain’s conclusions is the estimation that, at high AoA, the mean aerodynamic center will move longitudinally to the wing center of area, hence behind the CG. Looking at the Viper curves that move apparently occurs at about 60 deg AoA when the curves turn south. Owain considered the wing only whilst he should consider the wing/body assembly. Adding the fuselage will generally move the mean aerodynamic center forward so I think it is unclear whether the wing/body adds up to or opposes the ND moment of the tail at high AoA.

The stall was very probably recoverable but imho it would take much more time and obstinate ND input to recover than the crew expected.

[HarryMann]

Yes DJ77, I wonder whether this 'lack of persistence' with ND inputs, was because no time in training (since ab initio) seems to have been allocated to 'stall recovery' - whereas 'stall avoidance' seems to have taken the allocated 'stall' training time... Without this recovery emphasis, few other than long time (old hands) would have any appreciation of what it takes to rotate such a beast back to a sensible AoA + time to accelerate back to a sensible speed.


One has to wonder at the wisdom of starting with an aircraft concept which is naturally longitudinally speed stable, and design ALT LAW handling characteristics which allow the aircraft to be flown (with UAS), to stalling Alpha and beyond in a trimmed condition.

That's I think what I was trying to get at a few posts back... I just wish I had the wisdom to chose those words - nicely put rrr :D

[bearfoil]

DJ77

Have you addressed the THS' AoA as an independent entity from the a/c?

What was 447's trimmed state nearing the top of climb? I ask because at cruise, the Tail would be loaded and would want some (minor?) value of a/cND to create its lift (which is subtracted from its cruise duty AoA?)

Assuming an input of steady ND, (after the initial NURL), would there be any chance of the Tailplane Stalling and dropping the tail before the Mainplane Stalled? Given slow speed and gentle (?) entry, would lack of buffet and a rapid NU cause alarm in the cockpit? Would the a/c have assumed a very high NU communicating an alarming (seat of the pants) reaction from PF to input max ND? Did the a/c "recover" (actually not a recovery, but a predictable "fall" off). This would set the stage for the PF's return to NU inputs for the duration? For that matter, What was 447's trimmed state at Handoff? One way to enter a remarkable climb is to experience a lack of effectiveness from the tailPlane? The initial SW, the PF NU, the roc, things went South quickly.

If of no value, disregard.........

[DozyWannabe]

One has to wonder at the wisdom of starting with an aircraft concept which is naturally longitudinally speed stable, and design ALT LAW handling characteristics which allow the aircraft to be flown (with UAS), to stalling Alpha and beyond in a trimmed condition.

To be fair, it would appear from the evidence we have to hand so far that it requires actions that would be pretty counter-intuitive from a trained pilot's perspective to do so though.

[rudderrudderrat]

Hi DozyWannabe,

I don’t think that’s a fair comment.

From PJ2’s post #282 "The Effect of High Altitude and Center of Gravity on Handling Characteristics of Swept-wing commercial airplanes" -
“For a statically stable airplane the required column force, as speed varies from the trimmed condition, is less at an aft CG than it is at a forward CG.The minimum average gradient allowed by U.S. Federal Aviation Administration FAR Part 25 is one pound for each six knots.”

If at FL 350 with UAS, the PF had pulled back with several pounds of force on the controls, and then manually selected several degrees of nose up stab trim – then I would agree with you and call that counter-intuitive.

I suspect that all he did was inadvertently pull back on the stick with a few ounces of force for a prolonged period of time (maybe the next report will clarify). The stall recovery action with the application of TOGA power was the start of the next chain of errors. (N.B, his action was i.a.w. the guidance in FCOM at the time – the new stall warning recovery procedure has removed that action because of the nose up couple it causes)

[DJ77]

Bear,
Have you addressed the THS' AoA as an independent entity from the a/c?
AoA_tail = AoA_wing/body - downwash angle - THS trim angle.

What was 447's trimmed state nearing the top of climb?

No BEA info but close to 3 deg NU I think.

... would there be any chance of the Tailplane Stalling and dropping the tail before the Mainplane Stalled?

No.
As most people here, I cannot understand the PF insisting on NU inputs especially after the zoom climb. To me, it's akin to pilot incapacitation.

[Owain Glyndwr]

Of course, we miss pitch moment curves for the A330 to understand what ND or NU inputs could do. Owain Glyndwr posted a very interesting explanation but I am not convinced the THS was not stalled at 60 deg AoA. We know that the elevator was still working from BEA’s note but perhaps this was due to the elevator presenting a larger frontal area to the airflow in ND position than in NU. The effect of a stalled THS would be a positive slope of the Cm curve in the stalled area, meaning a decreasing downward moment with increasing AoA.My point was that to maintain 60 deg AoA you need a lot of UP elevator, which takes the THS away from stall. Gums curves and the curves in that NASA report on civil aircraft upset recovery (cited in thread #4 IIRC) show that the THS can stall if DOWN elevator is applied at that sort of AoA but there is no sign of stall with up elevator in either case. To hold 60 deg AoA you need a DOWNLOAD on the THS. What you describe is a stall with a POSITIVE THS load. What I meant was that ND moment can be obtained by reducing the up elevator just as well as applying down elevator - just a different starting point.

Another point where I doubt Owain’s conclusions is the estimation that, at high AoA, the mean aerodynamic center will move longitudinally to the wing center of area, hence behind the CG. Looking at the Viper curves that move apparently occurs at about 60 deg AoA when the curves turn southAs you note, the Viper is a delta wing, and the centre of pressure will be greatly affected by the strong LE vortices a la Concorde. Quite different flow patterns to a high aspect ratio swept wing.

Owain considered the wing only whilst he should consider the wing/body assembly. Adding the fuselage will generally move the mean aerodynamic center forward so I think it is unclear whether the wing/body adds up to or opposes the ND moment of the tail at high AoA.Not that naive DJ - I did consider the wing body assembly - see my post of 12th July- and the net effect is the way I described it.

[A33Zab]

I’ve got these figures of THS rate.

The THS itself (the ballscrew) is driven by 2 hydraulic (B & Y) motors.

Max. Operating Load and Max. Speed (2 motors)

18940 daN (42578.81 lbf) ----- 0.4°/s
16950 daN (38105.11 lbf) ----- 1.0°/s
6770 daN (15219.56 lbf) ---- 1.2°/s

Limit load (both compression as tension) is 32500 daN (73062.9 lbf).
I assume this limit load is mentioned as being the limit for the Hydr.
motors to drive the THS.

Half speed for 1 motor (1 hydr. B or Y system failure) operation.

The rate for the BEA mentioned 1 minute to go from 3 to 13 ANU was 10°/60 = 0.16°/s.


For going back to the 3° ANU position:
The hinges are on the trailing edge and therefore the aerodynamic
load on the drive spindle is in the AND direction it would take 12 sec. to travel from 13° back to 3° ANU.

The manual trim wheel THS displacement is ~0,65° a stroke, if one need
1s to complete the stroke and 1s to re-grab the wheel, the rate will be 0,325°/s.

--

For the PFD messages "MAN PITCH TRIM ONLY":


ELEVATORS NORMAL OPERATION
Each elevator servocontrol is connected to two computers (one FCPC
and one FCSC).
In the normal configuration, the inboard servocontrol is in active mode
while the outboard is in damping mode.
FCPC 1 having the servo-loop control priority:
- sets its dedicated servocontrol in active mode and ensures the servoloop
control,
- commands the damping mode on the adjacent servocontrol (one solenoid
valve (S) energized).
For the elevator servolooping computation the computers need to acquire:
- the elevator surface position,
- the elevator servocontrol piston position.
This information is sent by servocontrol transducers (XDCRs) units and
the surface position transducer (RVDT).
In the event of large deflection demands, the two servo-controls can
become active to avoid the saturation of one servocontrol.

ELEVATORS ABNORMAL OPERATIONS

HYDRAULIC OR ELECTRICAL FAILURE
If a servocontrol being in active mode is either not hydraulically powered
or not electrically controlled anymore,
the faulty servocontrol falls in damping mode and the adjacent one
becomes active according the servoloop reconfiguration.
If both servocontrols of one elevator are depressurized (e.g. Hydraulic failure)
both servocontrols are in damping mode which prevents fluttering.
When P1, P2, S1 and S2 are no longer able to control their dedicated
servocontrol (ie: inputs missing, electrical failure, etc...), the servocontrols
fall in re-centering mode.
The elevator becomes a 'fixed' part of the THS. (=MAN PITCH TRIM ONLY)

When autotrim in not available (e.g. Direct Law, Flare Law in case RA is
unavailable or NAV IR DISAGREE the PFD message "USE MAN PITCH TRIM" is shown.

[adrianrf]

after your very thoughtful and helpful posts, I'm nevertheless still unclear about the bottom line as you see it.
"to maintain 60 deg AoA you need a lot of UP elevator, which takes the THS away from stall"...
..."ND moment can be obtained by reducing the up elevator just as well as applying down - just a different starting point".
do you consider, on an aerodynamic basis, that the A330 is actually likely to be recoverable from even a ~60-degree AoA magnitude of stall upset, given some other set of control inputs [i.e. besides maintaining max NU on the SS until altitude is exhausted]?

[DJ77]

What you describe is a stall with a POSITIVE THS load.
Right, with the elevator in full up position almost masked to the airflow and counterbalanced by an assumed nose up wing/body moment. If the elevator goes down, the THS + elevator frontal area increases about 30% and could overcome the wing/body moment.

I did consider the wing body assembly
Sorry then, I thought you did not based this sentence in your post #295: “When it gets to this point I think the centre of lift/pressure will be fairly close to the centre of area of the exposed wing. For the A330, this is about 70% mac”.

[Owain Glyndwr]

I'm nevertheless still unclear about the bottom line as you see it.

Maybe because I was careful not to give a bottom line http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/wink2.gif

do you consider, on an aerodynamic basis, that the A330 is actually likely to be recoverable from even a ~60-degree AoA magnitude of stall upset, given some other set of control inputs [i.e. besides maintaining max NU on the SS until altitude is exhausted]?

Certainly not from the altitude at which they seem to have arrived at that AoA!

If they had had enough altitude then maybe yes, but they would have to have done it carefully. We know, or at least we think we know, that they were at something more like 40 deg AoA for a lot of the descent, so by my reckoning they could have got back that far just by relaxing on the stick. The problem with a more aggressive recovery from 60 deg is that if they tried to apply any significant nose down elevator when at that AoA they might have stalled the THS as DJ77 suggests. This would have screwed things up mightily.

If they had first got back to 40 deg, or indeed if they had started recovery from 40 deg or thereabouts in the first place then, again as DJ77 says, the THS AoA would be body AoA minus downwash minus THS setting - say about 40-20-13 = 7 deg. There wouldn't be any problem applying down elevator from that sort of AoA, so they should have been able to pitch the nose down far enough to get out of stalled conditions, accelerate a bit and initiate a pull up. Trouble is, that process would eat up several tens of thousands of feet in altitude, so unless they recognised the situation and started recovery early they were always going to be in danger of not being able to recover before they hit the sea.

[Owain Glyndwr]

Right, with the elevator in full up position almost masked to the airflow and counterbalanced by an assumed nose up wing/body moment. If the elevator goes down, the THS + elevator frontal area increases about 30% and could overcome the wing/body moment.

Yes in principle, but I must admit that my remarks are biased by the curves for a 'typical twin engined aircraft' as shown in that NASA upset recovery report (plus some intuition) which seems to me to indicate that nose down capability would be strictly limited at this level of body AoA because of the risk of stalling the tail with down elevator applied (the nonlinearity of the published Cm~alpha curves in the NASA report shows this).

[quote] Sorry, I thought you did not based this sentence in your post #295: “When it gets to this point I think the centre of lift/pressure will be fairly close to the centre of area of the exposed wing. For the A330, this is about 70% mac”.['quote]

Sorry in turn; I didn't make it clear that this referred only to the wing contribution to PM.

[grity]

DJ77 Another point where I doubt Owain’s conclusions is the estimation that, at high AoA, the mean aerodynamic center will move longitudinally to the wing center of area, hence behind the CG.in which height lays the CG over the wing (over the aerodynamic center) ? for the stability intresting is the horizontal distance, but with an pitch >15 deg the CG begins also to move back if it is high over the wing

[Smilin_Ed]

Dozy:
To be fair, it would appear from the evidence we have to hand so far that it requires actions that would be pretty counter-intuitive from a trained pilot's perspective to do so though.

Not at all. In fact, just the opposite. A properly trained pilot would know intuitively that he must reduce AoA to get out of a stall and to do that, he must push forward on the stick and trim nose-down if necessary to get the needed nose-down moment. That is why I've been saying for a couple of threads now that the autotrim should drop out with the autopilot so that he doesn't find himself with too much nose up trim. Autotrim with the autopilot engaged is what you need to ensure that when the autopilot is disengaged you don't get big attitude excursions. When hand-flying, trim should be a deliberate act by the pilot. I agree with the opinion stated by someone else here, there was a lack of situational awareness which allowed the trim to go to full NU unnoticed. I think these guys were blindsided due to inadequate training. This is a pilot's opinion.

Originally Posted by rudderrudderrat
One has to wonder at the wisdom of starting with an aircraft concept which is naturally longitudinally speed stable, and design ALT LAW handling characteristics which allow the aircraft to be flown (with UAS), to stalling Alpha and beyond in a trimmed condition.


Rudderradderrat says it all.

[DJ77]

Hi Grity,

I don't think the height of the CG plays a significant role at any attitude.

[gums]

First - A33'a tidbit scares the hell outta me.

the servocontrolsfall in re-centering mode.
The elevator becomes a 'fixed' part of the THS. (=MAN PITCH TRIM ONLY)

Deja vu one more time. Exactly what the Viper did if the confusers all failed ( in our case, it was total power loss to them, and the FCS folks were afraid the things would melt. We voted to keep them running if the main power supply had an overvoltage - let the suckers melt). Otherwise, the stabilators went to a neutral setting, and this meant 10 to 20 negative gees within a second!! Ask Wolfman, who survived one of those incidents back in 1981.

I do not fault the crew for training, or lack thereof. This was one in a thousand or more of "loss of pitot system" incidents. When I say that some jets enter the stall gracefully, I don't mean you can't feel SOMETHING. But with the storms and such, and the "bus great aero, the buffet could have been masked. Until the final report is out, I can't believe the pilots held back stick for 3 minutes. Shoot, just let go and watch for 30 seconds, then DO SOMETHING DIFFERENT. The OODA loop. From a pilot perspective flying at conditions unheard of in the heavies, I learned when a buffet meant "close to stall", or "prolly in a stall", or whoa!!! I had many students that could not "feel" the increase in buffet as I could. Bothered me, but some have "touch" and some don't.

Until I see a pitch moment chart of the 'bus with various THS angles of incidence, I shall continue to believe that a sustained nose down input could have helped at the outset. Once into a deep stall, all bets are off. The c.p. moves a lot, and as with the Viper, maybe a max up command could result in an attitude change, then put in max down and "rock" the thing outta the stall. DON'T TRY THIS AT HOME!

[rudderrudderrat]

This CAA document (http://www.caa.co.uk/docs/33/012010.pdf) may explain the PF's actions on receipt of the stall warning and his subsequent nose up inputs.

"STALL RECOVERY TECHNIQUE

1 Recent observations by CAA Training Inspectors have raised concerns that some instructors (both SFIs and TRIs) have been teaching inappropriate stall recovery techniques. It would appear that these instructors have been encouraging their trainees to maintain altitude during recovery from an approach to a stall. The technique that has been advised is to apply maximum power and allow the aircraft to accelerate out of this high alpha stall-warning regime. There is no mention of any requirement to reduce the angle of attack – indeed one trainee was briefed that “he may need to increase back pressure in order to maintain altitude”.

2 It could be argued that with all stall warning devices working correctly on an uncontaminated wing, such a recovery technique may well allow the aircraft to accelerate out of danger with no height loss at the lower to medium altitudes. The concern is that should a crew be faced with anything other than this idealised set of circumstances, they may apply this technique indiscriminately with potentially disastrous consequences.

3 The standard stall recovery technique should therefore always emphasise the requirement to reduce the angle of attack so as to ensure the prompt return of the wing to full controllability. The reduction in angle of attack (and consequential height loss) will be minimal when the approach to the stall is recognised early, and the correct recovery action is initiated without delay.

NOTE: Any manufacturer’s recommended stall recovery techniques must always be followed, and will take precedence over the technique described above should there be any conflicting advice."

Jan 2010

[Smilin_Ed]

gums:
Shoot, just let go and watch for 30 seconds, then DO SOMETHING DIFFERENT.

Someone please correct me if I'm wrong but, as I understand it, letting go with this airplane wouldn't be enough because the THS would have trimmed in the new attitude and you would continue at that attitude rather than go back to the previously trimmed speed. You would also have to get your nose back to the original position.

[takata]

Hi Gums,
First - A33'a tidbit scares the hell outta me.
MAN PITCH TRIM ONLY is a mechanical backup mode provided in case one lose its electrical elevator control (total electrical failure), which is displayed on PFDs, and A33Zab gave few more details about it.

But you certainly do understand that AF447, an no point during this event, ever came close to this situation, right?
In unlikely case that pitch trim was switched to manual mode (direct law, abnormal attitude,...), this backup would NOT be triggered. It is only in case of complete failure of electrical elevator control, and this never happened to AF447.

[CONF iture]

Also, I think autotrim is effecitively requried for C* control law, so without it you are looking at direct law, and no protections/limits whenever A/P is out. Not sure that is going to be an improvement.
The question has to be : What is an improvement ?
If the B or others were crashing at a far greater rate than the A, I would say that the protections were absolutely justified and needed ... but is it the case ?

No, read what I'm saying
It is actually what I do and don't see any justification for such phrasing :
"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."
unless you consider that electronics will prevent the Airbus to suffer from total hydraulic failure ... ?

[rudderrudderrat]

Hi Smilin Ed,

as I understand it, letting go with this airplane wouldn't be enough because the THS would have trimmed in the new attitude and you would continue at that attitude rather than go back to the previously trimmed speed.
Correct.
AB ALT LAW is a very peculiar manual flight mode. It has a mixture of Roll Direct (conventional aileron behaviour) and auto-trimmed pitch stable mode.
They require different ways to fly them satisfactorily. The ailerons would require constant adjustment, but the pitch only needs a nudge and then let go (else the input gets continuously integrated).

I don't understand why it was deemed necessary to design such an awkward combination.

[takata]

I have found the document I was talking about few pages ago about the CG.
Airbus A330 Instructor Support - Normal Operations (DEC 2000)
________________________
SOME CONSIDERATIONS ABOUT THE CG
The location of the CG has significant influence on Performance, on Loading flexibility, on structure and on handling characteristics when in Direct Law.
All those factors contribute to define the CG envelope.


- Performance considerations
The weight and lift forces do create a pitching moment which is counteracted by the THS setting.
When the CG is located forward, the resulting pitching down moment is counteracted by a large THS nose
down setting which induces a lift decrease and a drag increase.

http://takata1940.free.fr/cgfig1.jpg

At Take-Off and landing, it affects:
* The Stall speeds: typically on A330/A340, the stall speed increases by 1.5 kts when CG varies from 26% to full forward CG. This affects Take-Off and landing speeds thus associated distances.

* The rotation maneuver: it is “heavier”, thus longer at forward CG. This affects the Take-Off distance. For example, on an A340 at 250 t, the TOD increases from 3,165 m to 3,241 m, when CG varies from 26% to full forward CG, which represents a 2.42% TOD increase (T/O, FLAP3, PACK: OFF, ISA, ALT 0).

* The climb performance itself: for example, if a climb gradient of 5% is required (e.g. due to obstacles) in the previous Take-Off conditions, the MTOW is reduced from 257.6 t down to 256.2 t when CG varies from 26% to full forward CG.

This is why on A320 and A340 Take-Off Performance charts are provided at forward CG (which, in most cases, is penalizing) and at 26%; these last charts may be used provided the actual aircraft CG is at least 28%.


In cruise, an AFT CG minimizes the THS induced drag, thus improves fuel consumption. For example, the fuel increase on a 1,000 nm cruise segment is as follows, considering a heavy aircraft in high altitude and CG 20% or 35%:
http://takata1940.free.fr/cgfig2.jpg

- Handling Characteristics considerations
On Fly By Wire aircraft, in Direct Law, the handling characteristics of the aircraft are affected by the location of the CG as a mechanically controlled aircraft:


Stability Issue
- Aerodynamic Centre or Neutral Point
The aircraft is considered as stable, if in case of a perturbation or gust, the aircraft tends to react back towards its previous status. The aerodynamic centre, also called neutral point, is the location where an increase (or decrease) of lift is applied when the aircraft angle of attack varies.

http://takata1940.free.fr/cgfig3.jpg

Maneuvering criteria – Maneuver point.
Depending upon the CG location, a given deflection of the elevator causes a more or less sharp aircraft maneuver. In other words, the CG has a direct influence on the maneuverability of the aircraft. If a very small deflection of the elevator causes “a lot of g”, the efficiency of the elevator is very high; the aircraft is considered as very touchy to maneuver.

The maneuver point is the location of the CG for which the efficiency of the elevator is infinite. The CG must obviously be forward of the maneuver point by a lot. This lot is defined by a maneuverability criteria which states that “at least 1° of elevator deflection is required to pull 1g load factor”. This condition defines the AFT CG limit maneuverwise.

But the CG must not be too far forward: indeed, the maximum elevator deflection must allow to pull at least the maximum acceptable load factor (e.g. 2.5 g). This condition defines a FWD CG limit maneuverwise.

http://takata1940.free.fr/cgfig4.jpg

Ground handling characteristics
Essentially at high GW (thus at Take-Off), the CG is limited AFT so as to ensure enough Nose Gear adherence to allow an efficient aircraft steering on the ground.


Take-Off rotation characteristics
The CG must be limited so as to allow:
- enough maneuverability during rotation -> FWD CG limit.
- enough margin versus potential tailstrike -> AFT CG limit.

Obviously the the THS is preset nose up in case of forward CG or nose down in case of AFT CG, in order to get homogeneous aircraft rotation. But certification maneuvers require to demonstrate “abuse cases” such as taking-off with FWD CG limit while THS is set nose down.


THS stall potential
- in approach with flaps extended, there is a nose down moment counteracted by a THS nose up setting. The more CG is forward, the more THS nose up setting is required. This may lead to a THS stall, more particularly in cases of push over where the pilot pushes hard on the stick when he notices a significant speed decrease. This limits the FWD CG in approach.

- in Go-Around or Alpha Floor, the thrust increase to TOGA, more particularly at low speeds, induces a significant pitch up moment which increases when CG is more AFT. The elevator efficiency must allow to counteract this pitch up moment, even at very low speed. This limits the AFT CG in Go-Around and Alpha Floor.


Structural Considerations
The CG cannot be too much forward due to Nose Gear structural limits; it cannot be too much AFT due to wing and main landing gear strut limit.


Loading Considerations
All the previous criterias allow to determine limits which, for example, would favor AFT CG configurations for obvious performance efficiency. However, the CG envelope must also take into account loading flexibility constraints.

Passenger movement
The CG envelope must also allow passenger to move in the cabin. This is the reason why once the Take-Off CG envelope has been determined, as well as the landing one (which is less constraining), then the inflight envelope is defined usually providing at least a 2% margin with the previous envelopes.

http://takata1940.free.fr/cgfig5.jpg

1) Performance / loading compromise at Take-Off and Landing
2) Nose gear strength structural limit
3) Main gear strength structural limit
4) Alpha Floor limit
5) Nose gear adherence limit
6) Alpha Floor limit (landing)

The inflight limit is deduced from the Take-Off / Landing envelope by adding a typical 2% margin, provided all handling characteristics criteria are fullfilled.

http://takata1940.free.fr/cg.jpg

[Linktrained]

Takata #393

Thank you for the information.

In an earlier post I had mentioned that when hand flying a York as F/O in the 1950s, that when the Captain went back to the toilet, I was able to fly 1 or 2 kts faster and when he returned the speed reverted. He had altered the C of G slightly.
In Autumn 1970 I asked "our" Boeing rep. what was the optimum C. of G. for a 707. I had a telex the following day saying that aft loading would save 1/2 % fuel.
( Perhaps not really measureable on a flight. But a year... ? For a fleet...? And that was with cheap fuel, too, £20/tonne.)
Boeing's Airliner of January 1974 put the figures at 0.5% per 4% of aft shift of M.A.C. on 707, 727 and 737, but 0.2% for the 747.
The last type of aircraft that I had flown ( also made by a B.) with a full load of SLF (usually), baggage was normally loaded 2/3 forward and 1/3 aft. With hindsight it ought to have been the other way round.
Another manufacturer,( yet a different B.) refused to give any information. ( It may have been a coincidence that the airline ordered more aircraft from the B. who wanted the airline to make a profit.)

No fuel trim tanks were fitted.

[grity]

DJ77 I don't think the height of the CG plays a significant role at any attitude. ok, it is not realy significant with pitch 15 deg, but also for the calculation for the pich-up moment for the engins (toga...) you need the different in height between the engins and CG...

[takata]

Hi Linktrained,
Perhaps not really measureable on a flight. But a year... ? For a fleet..
If one takes Airbus average FH per a/c and figures (above) for its fleet, Mach .82 at cruise :

A340 = 5,000 FH/year => ~ 2400 (1000 NM)*380 kg = 912 tonnes saved per a/c.
-> 912*367 (a/c operational) => 334,704 tonnes of fuel.

A330 = 3,000 FH/year => ~ 1425 (1000 NM)*220 kg = 313 tonnes saved per a/c.
-> 313*791 (a/c operational) => 247,583 tonnes of fuel.

Total = 582,287 tonnes saved per year for the fleet.
Quite a few bucks then at today prices.

[HarryMann]

ok, it is not realy significant with pitch 15 deg, but also for the calculation for the pich-up moment for the engins (toga...) you need the different in height between the engins and CG... Well, there could be some debate here.. its often said you only need to do the sums about a (any) fixed point (usually the c.g) and resolve them all out as a single force vector together with a moment (torque)

However, instantaneously, the engine thrust moment will rotationally accelerate around the c.g. but in resolved steady state flight the nett lift and drag centres are where the thrust will be opposed from. So only in accelerated conditions will the c.g. be the obvious force resolution centre.

Agree?

[CONF iture]

takata,
Your Airbus cg post is great reading.
That aft fuel transfer for fuel economy is a great concept, but your figures are a bit on the optimized side. MEL mentions only 1% penalty if trim tank is disabled (no aft xfer)
Nevertheless, one A330 at 6000 kg/H for 3000 FH/year is still 180 tonnes saved.

[Linktrained]

Takata

Thank you for working it out... It was beyond both my Jeppeson and my Dalton. Both of them overheated.
Each aircraft might have a Working Life of ( x ) Years, too.

[grity]

HarryMann full agree, but if the pich up starts with a change in trust, (like in the A340 event....) than it is an accelerated condition, and the bird moves around the Cg

and for a recovery it is a question how much pich-up moment you can take away if you lower the trust to idle, (this is also an accelerated condition...)

but shure in case of af447, if you not longer try to lower the pitch you will not think about the pitch up moment of the engines....


my smal feeling is that the PF wrongly intrusted in one of the lost protections (AoA) and thought it will be ok to hold the stick back, it might be that he had learnd this (wrongly-) skill......

[takata]

Hi Confiture,
That aft fuel transfer for fuel economy is a great concept, but your figures are a bit on the optimized side. MEL mentions only 1% penalty if trim tank is disabled (no aft xfer). Nevertheless, one A330 at 6000 kg/H for 3000 FH/year is still 180 tonnes saved.
You are certainly right about that. The figure I quoted (and used for calcul) is the difference between MAC 20% and 35%. While, if I understand yours, it would certainly be for a lower difference in flight.
Nonetheless, what I posted above should also answer Rudderrudderrat's question about the design. It seems better to have in this case a pitch Alternate rather than direct, certainly because autotrim (inop in direct law) will permanently deal with fuel transfers (the pitch law is mostly based on CG computation by fuel computers). It will also damper pitch sensitivity if CG is aft, while roll axis should be trimmed by rudder and the aircraft is supposed to fly in straight line hands off.

[HarryMann]

my smal feeling is that the PF wrongly intrusted in one of the lost protections (AoA) and thought it will be ok to hold the stick back, it might be that he had learnd this (wrongly-) skill......It might and would be awful to contemplate if so... there must be others.
The corollary if true, is that even with protections, it must surely be acknowledged as still the wrong thing to do.. what is wrong with S&L or a slight easing of ND.

Is there likelihood of pilot(s) having a great fear of Mach buffet and overspeed do you think, indeed a greater fear? But long term holding of stick back, does surely, must, come from some sort of conditioned training or ingrained understanding of the safest thing to do... as well as indicating a rather 'fact learning' approach to flying rather than a raw law comprehension of basics.


.. and of course, this conjecture only applies if the evidence persists in concluding that there is no other explanation for this phantastic phugoid phlight than a very unfortunate and hasty response to an a/p disconnect at night in some turbulence.

[henra]

If no autotrim never under manual flying, at least a pilot knows trim is under his watch always - No ambiguity.

Yes but in reality manual flying at cruise in bad Wx will almost always be the result of an AP handing back a potentially already mistrimmed AC after it reached its limits, read rather after the fact not before.
And this is not only true for FBW AC. Any AP will do.

[Linktrained]

CONFiture

How much of an aircraft's flying is done with the Trim Tank "inoperative"?
Is it a Return to Base item, or does it need a Major Check, somewhere, to be fitted into a schedule before it can be rectified ?
Of course " It depends...!")
That used to be called " an Engineers' Hour.." ( IE , never less than...!)
Not having it available, costs money. (Ask your bean counter !)

[takata]

More fuel AFT:
http://takata1940.free.fr/fcms0.jpg
http://takata1940.free.fr/fcms1.jpg
http://takata1940.free.fr/fcms2.jpg
http://takata1940.free.fr/fcms3.jpg
http://takata1940.free.fr/fcms4.jpg
http://takata1940.free.fr/fcms5.jpg
http://takata1940.free.fr/fcms6.jpg
http://takata1940.free.fr/fcms7.jpg
http://takata1940.free.fr/fcms8.jpg

[takata]

Hi HarryMann,
my smal feeling is that the PF wrongly intrusted in one of the lost protections (AoA) and thought it will be ok to hold the stick back, it might be that he had learnd this (wrongly-) skill......
It might and would be awful to contemplate if so... there must be others.
The corollary if true, is that even with protections, it must surely be acknowledged as still the wrong thing to do.. what is wrong with S&L or a slight easing of ND.
The feeling that the PF wrongly intrusted in High-Alpha-Protection (Normal Law) was also my first impression. But now, I don't share it anymore. Basically, he was not aware at all that he was stalling... I believe that he was confused by something else. Even if one looks at this procedure in Normal law, this doesn't fit unless one would really fly at Alpha-Max... but without Alpha-prot, Alpha-Max displayed on the speed scale (and SPEED LIMITS were lost on his PFD from the beginning).

If I find the time, I will try to translate the Judicial report which is very instructive about how other AF crews (21 interviewed) reacted to previous UAS events.

Have a look at this High-AOA procedure. Everything is clearly pointing at reducing alpha to get out of it, even in NORMAL LAW, with a fully protected envelope and speed working fine. Note also what autotrim is doing when the protection is working.

http://takata1940.free.fr/stall0.jpg


I really think that it's pretty hard to conclude that he was doing something about this stall situation. First, the PF ignored deliberately the first warning and there is absolutely no mention of TOGA, neither thrust at this point but only a pitch-up, certainly inducing this initial climb. At the second stall warning, TOGA was applied but the pitch up was decupled. Hence the conclusion really lies elsewhere and I've got another bad feeling about what could have really happened.

[3holelover]

This question I address to the pilots among you:

Assume you're in IMC cruise, at night, and expecting some turbulence... Your instruments start "acting up", your AP drops, your ECAM/EICAS starts showing a cascade of failures, your PFD is showing various flags and missing data, and what data is displayed looks wrong to you..... among the various messages are intermittent stall warnings, but your airspeed has already been notably erroneous or absent...

.... you start to feel light in your seat. ... you soon see altitude displays that appear as if you are indeed falling fast. ... ... ... If you were still experiencing something less than 1g, would you believe your aircraft is diving, or stalled?

[bearfoil]

The last part of your post is exactly the "feeling" of the STALL. Best not to feel anything when IMC. Look, and think, imo.

OTOH, a dive does feel the same. It is the result of a well designed a/c Stalling, they want to start flying again. So, are you saying he tried to 'recover' the Stall too quickly? Because that would not be a 'wrong' action.

It is spookily in line with 'recovery' from 'approach' to STALL, as trained prior to 447's demise. "Lose minimal altitude". If STALL was Captain Renslow's nemesis, his altitude would be appropriate for losing little altitiude. He was 900agl at STALL.

IF 447 PF pulled a Renslow, there is evidence for establishing a "New Procedure". (wait, they already did!).

[Mr Optimistic]

Is it me being old fashioned, but the airbus schematics seem to flatter to deceive - there is so much less information in them than first meets the eye.

[bearfoil]

Kind of like the way 'bearfoil' posts?

[gonebutnotforgotten]

(Takata) I really think that it's pretty hard to conclude that he was doing something about this stall situation. First, the PF ignored deliberately the first warning and there is absolutely no mention of TOGA, neither thrust at this point but only a pitch-up, certainly inducing this initial climb. At the second stall warning, TOGA was applied but the pitch up was decupled. Hence the conclusion really lies elsewhere and I've got another bad feeling about what could have really happened.

I'm not entirely sure what your bad feeling is, but I agree, the simplest explanation of PF's continued Back Stick/nose up demand after reaching apogee is that the aircraft was going down, and the usual way to stop it is to ask for it to go up. There is no evidence that anyone realised the aircraft was stalled, not least because for a lot of the time there was no stall warning for the reasons supplied by the BEA. Whether the aircraft was recoverable in the end from the extreme AoA conditon is debatable. None of us, and I suspect not even Airbus knows what the pitching moments are at extreme angles, nor do we know whether in the end nose down stick with consequent eventual change in THS angle to airplane nose down/THS nose up actually makes things worse (both actions increase the THS incidence), though there are hints from the BEA that it doesn't.

If there are learning points from the accident, they won't be how to extricate oneself from 60 deg Aoa, but how to avoid getting there in the first place. I am still baffled by the cause of the initial pitch up. A month ago on the preceding thread I asked for a good explanation or a comment on my own hunch that it was a reaction to the initial decrease in indicated altitude after the start of the UAS event (due to the loss of appropriate Mach number correction). No one took me up on the challenge then, though HN39 took me to task for suggesting that the pull up was very robust, saying that even 0.2g would produce 7000 fpm in 18 secs; true, but 0.2 g is not exactly gentle controlling, it would normally only be exceeded by a TCAS RA (ideally 0.25g) or a GPW, and I don't believe I ever experienced such hamfisted inputs in my 35 years up front. So the question is still unanswered. It can't be the errant overspeed protection that caused the Turkish A340 skywards leap in 2000 because AF447 was not in normal law, Alt 2 doesn't offer overspeed protection (I understand), and anyway no one thinks the speed increased during the UAS event. So, suggestions pelase. Only by understanding what was going on in PF's mind from the beginning can we hope to prevent it happening again.

[ChristiaanJ]

Is it me being old fashioned, but the airbus schematics seem to flatter to deceive - there is so much less information in them than first meets the eye.Schematics come in "layers".

Most of the ones that you have seen here are the outer "explanatory" layer.
Each little rectangle has its own internal schematic (block diagram), and each of those has another few layers, before you actually get down to circuit diagrams (in analogue systems) or logic diagrams and software code (in digital systems).

Unless you're a design or maintenance engineer, those last few layers would contain no information that you could make any sense of....

So... no, Mr Optimistic, you're not old-fashioned, but schematics need a lot of background knowledge to interpret correctly. (Been there, done that, haven't got the T-shirt, but drawn a lot of diagrams, from basic circuit diagrams to block diagrams. Mostly for my own use and for the colleagues that were working on the same system.)

[bubbers44]

I'm a three hole lover too but looking at our attitude indicators and reacting accordingly rather than going by seat of pants feeling saved us one day in a jet at high altitude. It is hard to do in that situation but you have to scan your instruments and decide which ones you believe in that situation to stay alive.

I hope the final report comes out soon because we all know the full report is available whenever they wish to release it.

[A33Zab]

Found an 'very' old A330 Flight Law re-configuration PPT on the www.
It gives a good picture of the laws reconfiguration (despite the 'cartoonesk' illustrations)
some, but NOT all, situations were valid for AF447!

Part 1:
http://i474.photobucket.com/albums/rr101/Zab999/Dia1.jpg

http://i474.photobucket.com/albums/rr101/Zab999/Dia2.jpg

http://i474.photobucket.com/albums/rr101/Zab999/Dia3.jpg

http://i474.photobucket.com/albums/rr101/Zab999/Dia4.jpg

http://i474.photobucket.com/albums/rr101/Zab999/Dia5.jpg

http://i474.photobucket.com/albums/rr101/Zab999/Dia6.jpg

http://i474.photobucket.com/albums/rr101/Zab999/Dia7.jpg

http://i474.photobucket.com/albums/rr101/Zab999/Dia8.jpg

http://i474.photobucket.com/albums/rr101/Zab999/Dia9.jpg

http://i474.photobucket.com/albums/rr101/Zab999/Dia10.jpg

http://i474.photobucket.com/albums/rr101/Zab999/Dia11.jpg

http://i474.photobucket.com/albums/rr101/Zab999/Dia12.jpg

http://i474.photobucket.com/albums/rr101/Zab999/Dia13.jpg

http://i474.photobucket.com/albums/rr101/Zab999/Dia14.jpg

http://i474.photobucket.com/albums/rr101/Zab999/Dia15.jpg

[A33Zab]

Part 2:

http://i474.photobucket.com/albums/rr101/Zab999/Dia16.jpg

http://i474.photobucket.com/albums/rr101/Zab999/Dia17.jpg

http://i474.photobucket.com/albums/rr101/Zab999/Dia18.jpg

http://i474.photobucket.com/albums/rr101/Zab999/Dia19.jpg

http://i474.photobucket.com/albums/rr101/Zab999/Dia20.jpg

http://i474.photobucket.com/albums/rr101/Zab999/Dia21.jpg

http://i474.photobucket.com/albums/rr101/Zab999/Dia22.jpg

http://i474.photobucket.com/albums/rr101/Zab999/Dia23.jpg

http://i474.photobucket.com/albums/rr101/Zab999/Dia24.jpg

http://i474.photobucket.com/albums/rr101/Zab999/Dia25.jpg

http://i474.photobucket.com/albums/rr101/Zab999/Dia26.jpg

http://i474.photobucket.com/albums/rr101/Zab999/Dia27.jpg

http://i474.photobucket.com/albums/rr101/Zab999/Dia28.jpg

http://i474.photobucket.com/albums/rr101/Zab999/Dia29.jpg

End.

[Machinbird]

I hope the final report comes out soon because we all know the full report is available whenever they wish to release it.
Until all the 'i' s are dotted and all the 'T' s crossed, the report will not be available, otherwise some of our clever sharp eyed folks will discredit it. Every statement of fact will be checked for accuracy.
Only then will the report be released. That is just the way it is in our modern world, and even then, it will only be an interim report.

[HazelNuts39]

It can't be the errant overspeed protection that caused the Turkish A340 skywards leap in 2000According to the AAIB report there was indeed a short overspeed condition but overspeed protection was never active. The zoom climb was due to the AoA exceeding alpha-prot due to turbulence, and the Nz law then changed to an AoA law, which maintains alpha-prot until the sidestick is moved forward.

[bearfoil]

Machinbird.

Before being granted an advanced degree in one's field of study, the final hurdle is what is called "Defense". It is ruthless, performed by peers, mentors, and invited scholars. They are harsh, eagle eyed, and sceptical, though likely known (perhaps even 'friends') to the "wannabe".

After it is over, one frequently hears the following:

"Do NOT expect applause for doing what is expected of you".

[DJ77]

Hi Grity,
ok, it is not realy significant with pitch 15 deg, but also for the calculation for the pich-up moment for the engins (toga...) you need the different in height between the engins and CG...

In the context of calculations of moments relative to the CG, the longitudinal components of aero forces and the "vertical" distance (i.e. the distance measured along the yaw axis) between the CG and the wing mean chord are both low and the resulting moment is generally negligible. In any case, the moment coefficients depend mainly on AoA, not on attitude.

You are right about the moments due to engine thrust.

[Linktrained]

3holelover #407

To add to your concerns as PF... When did you last hand fly, using a SS at cruising level ?

An earlier entry from a Captain said that he had asked a number of F.O.s to look him in the eye whilst cruising and tell him what the aircraft's pitch was. He said that he got some surprising answers.

Someone else said that AB did offer an "ordinary", standby A/H, (not taken up by AF).

60 years ago Handley Page provided their Hermes 4,( which had a lot of then new(ish) and by the standards of the day advanced, electric instruments) with a standby basic, battery-powered Turn and Slip, which was fitted forward of the Captain's left knee. This may have been at the request of the original purchaser.

[bearfoil]

link

It is offered on the A330, and AF took a pass. It is mounted upper left, Captain's side.

(afaik)

[bubbers44]

Soon, hopefully, we will see if it might have helped them. Depends on what their training and experience was. It might not have helped them with their experience.

[bearfoil]

bubbers44

You were here in the very first thread. Do you remember the action about the AH deselect on 447? It was a big knock on Air France, (as was the pass on BUSS) and my memory is that The FD's were gone, and the PF had no Pitch. Do you remember it the same way? The upshot was, if the PF had a horizon, his SA would have been nails, and no crash.

What I recall is that the Pilots were commanded to fly PITCH and POWER, but were helpless w/o instruments to pin that down. Am I misremembering?

[john_tullamarine]

http://www.pprune.org/tech-log/456874-af-447-thread-no-5-a-17.html#post6573663

gums, by all means do start up a specific thread to discuss FBW things. JT

[andianjul]

...and if you do, can you put a link here as I'd love to follow it, thanks. -A

[takata]

Hi Bearfoil,
You were here in the very first thread. Do you remember the action about the AH deselect on 447? It was a big knock on Air France, (as was the pass on BUSS) and my memory is that The FD's were gone, and the PF had no Pitch. Do you remember it the same way? The upshot was, if the PF had a horizon, his SA would have been nails, and no crash.
What I recall is that the Pilots were commanded to fly PITCH and POWER, but were helpless w/o instruments to pin that down. Am I misremembering?
I don't really follow you. What do you meant here?
1. There is no link between FD (Flight Director) and Artificial Horizon. A/H was displayed during this night on Captain and F/O's PFD (Primary Flight Display) just fine... they absolutely never lost it - there is not a single fault detected in the IR part of ADIRUs that may translate into the loss of those displays!... but also, they had a third A/H source on their large Standby Instrument (ISIS).
2. ISIS (Integrated Standby Instrument System) is an option for A330 that can replace the standard unreadable standby indicators. Hence, for AF, it was a "plus", not a "less".
.3. AF choice to not take this BUSS option is understandable as its draw backs are pretty clear (disconnection of all ADRs) and its readability not very good. It may be very useful if one loss its speed during the final descent or climb phase, but it was not designed to replace those ADRs at cruise in the middle of the South Atlantic.

[rudderrudderrat]

Hi takata,

It seems better to have in this case a pitch Alternate rather than direct, certainly because autotrim (inop in direct law) will permanently deal with fuel transfers (the pitch law is mostly based on CG computation by fuel computers). It will also damper pitch sensitivity if CG is aft, while roll axis should be trimmed by rudder and the aircraft is supposed to fly in straight line hands off.
Is the reason that AB FBW don't have the option for the pilots to deliberately select Direct Law (unlike B777) because the allowed CofG can be so far aft and the subsequent handling characteristics?

I agree that rudder should be used to trim out any roll tendency - maybe if the aircraft had been perfectly in trim at the time of AP disconnect, then the PF could have just left the controls centred and continued at FL 350.

[gonebutnotforgotten]

HN39,

Agreed, I should have just said that whatever 'protection' was responsible for the Turkish zoom climb event, it couldn't apply to AF447 if, as we are told, none of the protections other than g were active in ALT 2. The brief description given by the BEA suggest that it was indeed PF who commanded the climb, which just makes it all the more important to figure out what persuaded him this was a good plan, or prevented him from stopping it.

[takata]

Hi Rudderrudderrat,
Is the reason that AB FBW don't have the option for the pilots to deliberately select Direct Law (unlike B777) because the allowed CofG can be so far aft and the subsequent handling characteristics?
CG set at max envelope aft should not be an issue for handling in direct law if one is carefull about not over controlling (elevators are really powerfull at high altitude). In any circumstance, with full aft CG, (beside some related FCMC faults) Airbus state that no forward fuel transfer is needed (turbulences, whatever...). Nonetheless, direct pitch is loosing autotrim and, during normal operation at cruise, there is a constant displacement of the CG due to fuel transfers (by +/- 0.5%) . Hence in direct law, one would have to retrim constantly in pitch or disable the fuel transfer function.

I agree that rudder should be used to trim out any roll tendency - maybe if the aircraft had been perfectly in trim at the time of AP disconnect, then the PF could have just left the controls centred and continued at FL 350.
Right. They had just completed a virage before AP disconnected. It's then possible that ailerons were still adjusting in autoflight when AP kicked off and PF had to correct this roll tendency. It certainly played its part as the attention of the PF was then attracted by this correction of the roll rate rather than keeping his pitch in range. As the roll axis was direct, it was much more sensitive than previously and he certainly over-controlled for some time. This could also happen if pitch would be translated directly into direct law, especially at this altitude where the aircraft was flying.

[rudderrudderrat]

Hi takata,

Thanks for the reply. As the roll axis was direct, it was much more sensitive than previously and he certainly over-controlled for some time.
In ALT LAW, if pitch remains attitude stable, what's the reason for having roll direct? Why can it not be designed to be roll attitude stable, (but still with no protections)?

[takata]

In ALT LAW, if pitch remains attitude stable, what's the reason for having roll direct? Why can it not be designed to be roll attitude stable, (but still with no protections)?
Good question. For sure, there is a reason linked to the change of flight law that would limit an EFCS function, but I don't know which one precisely. What you are loosing is the ability to maintain a bank angle, hence, you are left with a limited coordination in turn, and a different feeling in control.

[BOAC]

Nonetheless, direct pitch is loosing autotrim and, during normal operation at cruise, there is a constant displacement of the CG due to fuel transfers (by +/- 0.5%). Hence in direct law, one would have to retrim constantly in pitch or disable the fuel transfer function. - heavens! What have we come to? Is it too much to ask of an AB pilot - I mean, like FLY an aeroplane, man??:ugh:

[Graybeard]

I hope BEA explains how the cg moved from the automatic 38% MAC, as shown above, and in the initial report, to 29% (or was it 23?) in its latest report.

[rudderrudderrat]

Hi BOAC,

If AB pilots had conventional control columns, I'm sure they would cope. I think the problem lies with the side sticks. They are good at telling the the computer what attitude you'd like, but they are hopelessly lacking in tactile feed back.

The only feel is the centring spring in the box, they lack the conventional back driven clues. The control forces required is measured in ounces rather than pounds. It would be like driving your car with the steering wheel replaced by a joy stick. Ok in a straight, but would feel horrible at speed through tight bends.

takata is correct, I think they would be far too sensitive for manual direct law flight at altitude.
Edit - unless the "sensitivity" could be manually selected by the pilots.

[takata]

Hi gonebutnotforgotten,
A month ago on the preceding thread I asked for a good explanation or a comment on my own hunch that it was a reaction to the initial decrease in indicated altitude after the start of the UAS event (due to the loss of appropriate Mach number correction). No one took me up on the challenge then, though HN39 took me to task for suggesting that the pull up was very robust, saying that even 0.2g would produce 7000 fpm in 18 secs; true, but 0.2 g is not exactly gentle controlling, it would normally only be exceeded by a TCAS RA (ideally 0.25g) or a GPW, and I don't believe I ever experienced such hamfisted inputs in my 35 years up front. So the question is still unanswered.
Your point that a sharp altitude decrease on PF display seems to me a fairly possible explanation of his initial imputs, including his roll correction. It will depend on what displayed information he was looking at... then, to which one he first (over)reacted.

Everything in the fault sequence analysis makes me think that the PF display was the first affected. The PROBE fault recorded imply that the 3 probes readings were different as well as out of range with previous median values. Hence, no single ADR could be rejected but the three altogether. We are also told of the recorded sequence implying PNF speed decrease followed by ISIS: the first value then to drop should have been the one on the PF display.

There is also an indirect proof of an altitude drop and range: the following reported TCAS fault by ACARS. AFS/FMGES (autoflight system) ADR altitude monitoring fault treshold is set at 400 ft instead of 3,000 ft at EFCS level (flight control monitoring). Hence, TCAS should have faulted because of that. So, could it be that uncorrected static pressure was dropping to the point of displaying an over 400 ft of instantaneous altitude change, Mach going down from 0.81 to about 0.18? Could it be that static pressure was also affected by icing?

If this was the first information taken by the PF in addition to the roll at AP disconnection, he could have effectively feared that some kind of spiral dive could follow. Likely, his pitch rate wasn't his first concern, then without speed, after ignoring the first stall warnings as spurious, he might have lacked the correct info necessary to understand how much energy was lost during the climb with an altitude under reading, then he also would be spatially disoriented. There was also no mention of thrust change during this climb and this would rather fit with a PF trying to slow down than one fearing of stalling.

Nonetheless, I don't think that the climb took as much as 18 seconds to be engaged. BEA prose is somewhat hard to follow. It is hard to deduce the correct chronology of the flight events that may be different from what is induced by their description. Language is ambiguous enough as to make one believe that some events were following each other, as it is written, while basically, they could have occured almost at the same time.
Anyway, we'll check that in next report.

[takata]

Hi Graybeard,
I hope BEA explains how the cg moved from the automatic 38% MAC, as shown above, and in the initial report, to 29% (or was it 23?) in its latest report.
They say 29%. Either a typo, either it means that the aircraft was loaded with a heavy nose, hence, target CG could not be moved aft, even with a fully loaded THS.

[RetiredF4]

takata
CG set at max envelope aft should not be an issue for handling in direct law if one is carefull about not over controlling (elevators are really powerfull at high altitude). In any circumstance, with full aft CG, (beside some related FCMC faults) Airbus state that no forward fuel transfer is needed (turbulences, whatever...). Nonetheless, direct pitch is loosing autotrim and, during normal operation at cruise, there is a constant displacement of the CG due to fuel transfers (by +/- 0.5%) . Hence in direct law, one would have to retrim constantly in pitch or disable the fuel transfer function.

Greybeard
I hope BEA explains how the cg moved from the automatic 38% MAC, as shown above, and in the initial report, to 29% (or was it 23?) in its latest report.


Found this reference some time ago about CG travel due to fuel
Getting to grips with weight and balance (http://www.smartcockpit.com/data/pdfs/flightops/aerodynamics/Getting_To_Grips_With_Weight_and_Balance.pdf)

A330 /340 starrts at page 49, inflight CG-travel page 59.

The mentioned CG from BEA makes me wonder as well, it´s that far forward form desired target CG

Aft target cg would be around 39% MAC (see page 60 of above reference) and how it is influenced by the trim-tank shows page 63.

CG target:
In flight, the FCMC controls the position of the center of gravity. It calculates the CG position and compares it to a target value, which depends on the aircraft weight. According to this calculated CG position compared to the target, the FCMC determines the fuel quantity that needs to be transferred aft or forward.

The FCMC determines the fuel quantities to be transferred to maintain the aircraft CG in a control band limited by the CG target position and CG target position +/- 0.5%. Takata, are those the 0.5% you mentioned as fuel transfer cg shift?

[DozyWannabe]

If AB pilots had conventional control columns, I'm sure they would cope. I think the problem lies with the side sticks. They are good at telling the the computer what attitude you'd like, but they are hopelessly lacking in tactile feed back.

The only feel is the centring spring in the box, they lack the conventional back driven clues. The control forces required is measured in ounces rather than pounds. It would be like driving your car with the steering wheel replaced by a joy stick. Ok in a straight, but would feel horrible at speed through tight bends.

If what you're suggesting is that the sidestick response goes from balanced and gradual to "squirrelly" with law degradation, that is apparently not the case, and if I recall correctly it was PJ2 who gave the lie to that particular idea. He said the difference can be noticed, but is not that great that it would either cause trouble or could not be corrected for very quickly. I'm told the spring response is actually quite dynamic - this is not like your computer or video game controller in that it exerts more counteracting force the further you deflect the stick.

As I said before regarding modern back-driven FBW controls a la B777, if you've got a triple-pitot failure and UAS scenario, how do you know that the computer is applying the correct column/yoke backdrive?

As for BOAC's question, I don't think takata's point is a case of Airbus pilots not being able to fly an aircraft so much as it is the question of whether you'd want to have to suddenly take over manual pitch trimming - in turbulence, at night, with no speed indications and the fuel transfer system causing the need for regular adjustments.

[takata]

Hi Franz,
The FCMC determines the fuel quantities to be transferred to maintain the aircraft CG in a control band limited by the CG target position and CG target position +/- 0.5%. Takata, are those the 0.5% you mentioned as fuel transfer cg shift?
Yes. I also posted above the informations and tables (not up to date) concerning the A332. CG is constantly moving forward, aft by this margin at cruise, providing fuel transfer is taking place. If the THS tank is full, but target CG can't be achieved (possible AF447 case), then no such transfer is taking place until later during the flight.

[takata]

Hi Dozy,
As I said before regarding modern back-driven FBW controls a la B777, if you've got a triple-pitot failure and UAS scenario, how do you know that the computer is applying the correct column/yoke backdrive?
Maybe that this info is taken directly from its control surface feedback related to CG and trim position, rather than airspeed? (in Airbus, autotrim works without airspeed and it is based on FCMC/IR imputs)

[DozyWannabe]

Maybe that this info is taken directly from its control surface feedback related to CG and trim position, rather than airspeed?

Could well be, takata - but the point is we don't know, I'd suspect most B777 pilots don't know *exactly*, and the question is - would you bet your life?

[rudderrudderrat]

Hi DozyWannabe,

this is not like your computer or video game controller in that it exerts more counteracting force the further you deflect the stick.
That's strange - because yesterday it definitely felt like I have to exert more force the more I move it.

As I said before regarding modern back-driven FBW controls a la B777, if you've got a triple-pitot failure and UAS scenario, how do you know that the computer is applying the correct column/yoke backdrive?I don't know, but if it defaulted to sensed zero air speed, then it would simply feel more twitchy. I would still be able to cope, just that I'd need to exert say half the force for the same effect.

whether you'd want to have to suddenly take over manual pitch trimming - in turbulence, at night, with no speed indications and the fuel transfer system causing the need for regular adjustments.
Do you bother to read any of my posts? That is exactly what a pilot wants to do. He wants manual control of his own pitch trim during UAS. Any fuel transfer cofg problem could be halted by turning off a couple of pumps until later.

[DozyWannabe]

That's strange - because yesterday it definitely felt like I have to exert more force the more I move it.

I'm pretty sure that's the same thing I'm saying, is it not?

Do you bother to read any of my posts? That is exactly what a pilot wants to do. He wants manual control of his own pitch trim during UAS. Any fuel transfer cofg problem could be halted by turning off a couple of pumps until later.

I'd say that reads more like what *you* want to happen. I'm sure you wouldn't claim to speak for all pilots any more than I could claim to speak for all engineers. Some pilots want different things is all - it'd be a boring world if we all wanted the same things given the options we have nowadays, wouldn't it?

[takata]

Could well be, takata - but the point is we don't know, I'd suspect most B777 pilots don't know *exactly*, and the question is - would you bet your life?
This is not really the question about making any bet.

I think that the constant comparison between A & B is fairly displaced and most pilots here have moved on on this subject. The fact is that it seems that there is some obvious differences when driving such aircraft, controls, autotrim and CG computing, being of course part of the equation.

Now, it isn't anymore about judgement but understanding. Airbus concept is not that bad but may certainly be improved: there is still quite a wide margin before considering it "near" perfect, whatever Boeing is doing on its own side.

Actually, some point of view developed here about Airbus a/c is based on a "conventional aircraft" with fanzy added systems, and some people are trying to figure out how much it is useful or could be useless/dangerous in certain cases. While in fact, the starting point for this design was not a "conventional" but a "protected aircraft" which may eventually lose some of its systems until the point that it will look very much like such a "conventional aircraft".

Then, it is in fact possible that in the middle of this reversion, you'll be left with an "hybrid" aircraft which is not what any kind of pilot (Airbus or others) is very likely used to. While an Airbus pilot, used to those systems, would preferably keep whatever is still working rather than to reverse to a fully "conventional a/c", another pilot would prefer to get it directly "conventional" because it is also what he is much more used to.

Nonetheless, one of the issue that I'm starting to understand, is that Airbus "protected" systems are now in use for about 25 years. Basically, all the documentation was at first aimed at those pilots converting to their systems from "conventional" a/c. Now, they also don't explain how it feels like to fly such "conventional a/c", but rather the opposite. In turn, there is not that much emphasis about how to do in "conventional" configuration, which was certainly ok at the time, because everybody knew to fly it like that.

Is it still the case today?
If you look at those two young F/O (less than 40), they obviously never flew anything else than Airbus (A320 and A330/40) after their basic training. Hence, what would be the point to say in FCOM: if you are in direct law, you are now flying a "conventional aircraft"... when they may have no idea about what it is really like?
Some questions I'm asking myself at this point.

[Lonewolf_50]

Picky Perkins, a few thoughts from one of your posts.
We know that the training departments of the airlines had strenuously opposed any mention of the use of manual trim in training for upset recovery, even though the test pilots of both Boeing and Airbus had emphasized more than a decade ago that bringing the a/c into trim was in their opinion the first priority in a recovery ...if the crew had had upset recovery training (as distinct from training to recover from an approach to a stall) the use of manual trim would not have even been mentioned, and they may even had had warnings against its use (because of the danger of structural damage).
They followed their training, which in part told them to forget what they were told in primary training, particularly WRT stalls. They were never trained to use manual trim. It wasn’t even mentioned.
FWIW: one of our posters (Mikelour) taught in the A330 sim. He has told us that there were/are some Unusual Attitude training scenarios where use of trim wheel was included. Is not Unusual Attitude related to Upset? :confused:
QUESTION: Being a French crew for a French airline and knowing that any deviation from training and SOP might be investigated by a French Court, might they have been inhibited from deviating from training and/or SOP in case they might be blamed for any subsequent damage?
Possible cultural factor. Whose gonna own up to that one? (Do I hear crickets chirping?)
When I say that some jets enter the stall gracefully, I don't mean you can't feel SOMETHING. But with the storms and such, and the "bus great aero, the buffet could have been masked. From a pilot perspective flying at conditions unheard of in the heavies, I learned when a buffet meant "close to stall", or "prolly in a stall", or whoa!!!
I had many students that could not "feel" the increase in buffet as I could. Bothered me, but some have "touch" and some don't.

This point appears worth repeating.

An AoA gauge might have been useful secondary scan instrument ... *ducks*

EDIT: I'd like to address a point in terminology.

Typically, an aircraft has primary flight controls and secondary flight controls. Aileron, rudder, or elevator, (primary) often have a trim surface (secondary) that allows you to influence the primary.
(Other secondary are: flaps, slats, spoilers, speed brakes ... which change air flow over a wing). (Thought: aren't spoilers sometimes in the role of primary flight control at high speeds and high altitudes?)

The relationship between the THS and the Elevator on this aircraft looks similar to how a trim surface on a conventional elevator (with fixed Horizontal Stab) influences elevator position.

THS is thus a primary flight control. Or is it? Initial control deflection of the stick moves the elevators (so the elevators are a primary flight control).

Does this make THS a secondary flight control?

Well, if one is controlling the nose with the trim wheel, THS becomes the primary flight control surface.

I may be trapping myself in archaic terminology here.

Can someone help me see this more clearly?

[jcjeant]

Hi,

If you look at those two young F/O (less than 40), they obviously never flew anything else than Airbus (A320 and A330/40) after their basic training. Hence, what would be the point to say in FCOM: if you are in direct law, you are now flying a "conventional aircraft"... when they may have no idea about what it is really like?
Some questions I'm asking myself at this point.

Woooaaa
The next question is...
Why Airbus bother to make available a "direct law" if the "new pilots generation" are not able to pilot the plane in that law ?
Is "direct law" can be crudely translated as "direct crash" ?

[A33Zab]

UAS other than A. FBW airliner:

Unreliable Airspeed Indications.
Unreliable airspeed indications can result from blocking or
freezing of the pitot/static system or a severely damaged or missing
radome.
When the ram air inlet to the pitot head is blocked, pressure in the probe
is released through the drain holes and the airspeed slowly drops to zero.
If the ram air inlet and the probe drain holes are both blocked, pressure
trapped within the system reacts unpredictably.
The pressure may increase through expansion, decrease through
contraction, or remain constant.
In all cases, the airspeed indications would be abnormal.
This could mean increasing indicated airspeed in climb, decreasing
indicated airspeed in descent, or unpredictable indicated airspeed in
cruise.
Unreliable airspeed may cause noticeable effects in the normal speed
stability of the airplane since the normal pitch control law uses indicated
airspeed.
If the indicated airspeed falls below 50 knots, the flight control system
changes to the secondary mode, which does not depend on airspeed.
The autothrottle system also uses indicated airspeed and should be turned off.
If the flight crew is aware of the problem, flight without the benefit of
valid airspeed information can be safely conducted and should present
little difficulty.
Early recognition of erroneous airspeed indications requires familiarity with
the interrelationship of attitude, thrust setting, and airspeed.
A delay in recognition could result in loss of airplane control.
The flight crew should be familiar with the approximate pitch attitude for
each flight maneuver.
For example, climb performance is based on maintaining a particular
airspeed or Mach number.
This results in a specific body attitude that varies little with gross weight and altitude.
Any significant change from the body attitude required to maintain a
desired airspeed should alert the flight crew to a potential problem.
When the abnormal airspeed is recognized, immediately return the airplane
to the target attitude and thrust setting for the flight regime.
If continued flight without valid airspeed indications is necessary,
consult the Flight With Unreliable Airspeed/Turbulent Air Penetration table
in the Performance Inflight section of the QRH for the correct attitude,
thrust settings, and V/S for actual airplane gross weight and altitude.
Ground speed information is available from the FMC and on the instrument
displays.
These indications can be used as a crosscheck.
Many air traffic control radars can also measure ground speed.

Secondary and Direct Mode Pitch Control
Airplane pitch control is different in the secondary and direct flight control
modes.
The control columns now command a proportional elevator deflection
instead of a maneuver command.
Secondary and direct modes do not provide automatic pitch compensation for:

• thrust changes
• gear configuration changes
• turbulence
• flap and speedbrake
configuration changes
• turns to 30° bank angle.

In secondary and direct modes, the elevator variable feel system provides
two feel force levels instead of a continuous variation with airspeed.
The force levels change with flap position.
With the flaps up, the feel forces provide maneuver force levels that
discourage overcontrol in the pitch axis at high speeds.
With flaps extended (flaps 1 or greater), the feel forces decrease to
provide force levels appropriate for approach and landing.
In the secondary and direct modes, both the primary pitch trim switches
and the alternate pitch trim levers move the stabilizer directly.
There is no trim reference speed.

[bearfoil]

Your post is food for thought! Cautions about attitude, (assiete), continued flight w/UAS, etc, very compelling.

Could you comment on the inclusion of "damaged or missing" radome?

Long ago, it seemed to me at least possible that the radome could have been damaged by hail, or lost due overspeed. This could tie in with the suspicious lapses in Radar (Wx) uses and deviation questions. Likewise, a damage to one or more Pitots if impacted by debris?

[Lonewolf_50]

bear, upon what data are you basing your idea of overspeed loss => lost radome? At the speeds flown, lost radome likely causes non-trivial drag, likely a radar fault, and hence an ACARS message well before the upset event.

I don't see there being any data presented to date that supports this hypothesis. Indeed, what little we have from CVR is that pilots had noticed something ahead and made a small course change based on that info. So, if radar was not working, that would most likely have come up in conversation.

[takata]

Why Airbus bother to make available a "direct law" if the "new pilots generation" are not able to pilot the plane in that law ?
Is "direct law" can be crudely translated as "direct crash" ?
My point was to underline what seems (for me) to be lacking in pilot's basic documentation about flying their aircraft. I don't think that such knowledge of "conventional aircraft" may still be considered today as being part of the background of that many pilots than it was in the past. Much more informations would be needed in this flight manual about how the aircraft would behave in manual control during reversion phases mostly without any protection.

If your point was to make fun of mine, this is completely zero added value, like one said. Obviously, any pilot needs surely to be trained from A to Z in order to ensure his full ability to fly whatever aircraft. Hence, I think that this manual is not reflecting very well this basic requirement, considering some parts of its flight domain, for the reasons explained above.

[rudderrudderrat]

Hi takata,

There is a beautiful aircraft waiting to come out once the Normal & Alt Laws have been removed.

From FCTM
Direct Law
In most triple failure cases, direct law triggers.
When this occurs:
• Elevator deflection is proportional to stick deflection. Maximum deflection depends on the configuration and on the CG
• Aileron and spoiler deflections are proportional to stick deflection, but vary with the aircraft configuration
• Pitch trim is commanded manually
Handling characteristics are natural, of high-quality aircraft, almost independent of the configuration and of the CG. Therefore, the aircraft obviously has no protections, no automatic pitch trim, but overspeed or stall warnings.

OPERATIONAL RECOMMENDATION:
The PF must avoid performing large thrust changes, or sudden speedbrake movements, particularly if the center of gravity is aft. If the speedbrakes are out, and the aircraft has been re-trimmed, the PF must gently retract the speedbrakes, to give time to retrim, and thereby avoid a large, nose-down trim change.

[bearfoil]

lonewolf

I think my approach is one that is misunderstood by some. I haven't proposed any kind of conclusions, I am making an effort to keep my mind open to possibilities that indeed may have naught to do with 447. In an effort to understand UAS, overspeed, RadarWx, etc. I am adding to my own personal backgound, and if at a later time, a conclusive presentation is made (it will be, we hope!), then a broader understanding offers a firmer foundation for finality.

Within days of this accident, I was focused on the attitude of the a/c at a/p loss, until it became increasingly ignored in favor of what I thought was extraneous interest by the thread in general. What goes around comes around, and here we are with A33Zab's post of "Other than fbw UAS procedure."

We are back at the several seconds around the loss of the autopilot.

I believe what is technically considered "Upset" (not at all what many think it is....) happened seconds (or more) prior to a/p dropout. The LOC, (again by definition) 'happened' at "I have the controls".........

I do not need to be correct. I have no airframe bias. I am a pilot. I am with the crew, until such time as anyone can conclusively prove to me that PE was the procuring cause of this tragic accident.

Was it "in there"? Who among the pilot community would have an expectation of flawless competency in such conditions?

I have no "need" to be understood. On the contrary, I crave to understand.........

[takata]

There is a beautiful aircraft waiting to come out once the Normal & Alt Laws have been removed.
I think that any pilot who is flying it will tell you that it is certainly also a beautifull aircraft to fly in Normal law, which is what they are doing 99.99% of the time. The problem that need to be addressed, I think, lies somewhere else:
When there is such a non-commanded law reversal, it is either in the sim (where, most of the time, always the same scenarios are played), either in very critical conditions. It will be then, for anyone, quite hard to appreciate how much "beautifully" it is flying without either airspeed, inertial reference, hydraulics, electrics...

[bearfoil]

rudderrat

well said. Do you have any thoughts on the speedbrakes v. Trim and "nose down" trim change? Also, could one of the right side spoilers have failed to stow completely, causing that annoying (and persistent) "roll" to starboard? If so, would the rolling aspect of the climb and descent be possibly related?

[takata]

well said. Do you have any thoughts on the speedbrakes v. Trim and "nose down" trim change? Also, could one of the right side spoilers have failed to stow completely, causing that annoying "roll" to starboard? If so, would the rolling aspect of the climb and descent be possibly related?
I know that you are SO very "open-minded". But have you got ANY information that she could have been in direct law, at any point before crashing, not even mentioning before this UAS declared?
Bearfoil, nothing unusual happened before 0210:05, take it as a fact or consider, with your usual very open-mind, that the BEA is lying the entire world.

[bearfoil]

I do NOT believe BEA are lying. I do NOT have sufficient evidence to pour concrete around my opinions, as some have. I do have an open mind. I will embrace the truth when (!) it appears.

You are the one who knows, evidently, sufficient data to reject all speculation that isn't conformed.

For what it is worth, You have opened up greatly in the last two weeks, and offered valuable information in every way, some even that is neutral re: Airbus.

I try to eliminate the personal from this thread. If you are correct, and my prose is mostly zero-value-added, you should try ignoring it, or resisting the urge to respond to it with snark. If it is just so much dead weight, you might want to avoid worrying about someone else's bandwidth?

[takata]

I try to eliminate the personal from this thread. If you are correct, and my prose is mostly zero-value-added, you should try ignoring it, or resisting the urge to respond to it with snark. If it is just so much dead weight, you might want to avoid worrying about someone else's bandwidth?
Fair enough.
My urge comes from your own typical urge at bouncing up after any word taken out of its context.
Did you even noticed that Rudderrudderrat was quoting something related to Direct law, or not? Hence, the first question to address, with an open mind, should have been: was she in this mode? If one bother to answer it, his fast composed theory would spin and crash many times faster than AF447.
Nothing personnal otherwise.

[DozyWannabe]

There is a beautiful aircraft waiting to come out once the Normal & Alt Laws have been removed.

In your opinion. I personally don't understand this conservative streak in a minority of pilots. Why so negative about something which was designed to help you do your jobs and move the art of aviation forward? Why such a burning need to move no further forward than the 1970s?

(Just to add, I'm not being facetious here - heaven knows I'd rather be hacking away at low level code on the machines I grew up on on a day to day basis than doing the corporate stuff that puts a roof over my head, and I know what it is to feel that one's career path has been commoditised by the endless march of big business - but IMO it's not fair to blame the technology for that)

[bearfoil]

mais oui.

My Bad. Lately I type faster than I think, I am sorry. But is there any value in considering that the trimming the A/P was doing had some importance on the PF's choice to manuever quickly instead of "waiting"?

Do you have a thought re: the first manuever? It happened, it had a reason, and no, no one can read the PF's mind. Qu' est-ce que c'est?

thanks

[hetfield]

Why so negative about something which was designed to help you do your jobs and move the art of aviation forward?

Because it MAY have been a contribution for this accident and other incidents?

[rudderrudderrat]

Hi DW,
Why so negative about something which was designed to help you do your jobs and move the art of aviation forward? Why such a burning need to move no further forward than the 1970s?
You misunderstand me.
Normal Law is brilliant, the aircraft is wrapped in cotton wool.
Direct Law is beautiful "Handling characteristics are natural, of high-quality aircraft, almost independent of the configuration and of the CG."
Alternate Law is a confusing mixture of both - without "protections" and without the natural longitudinal speed stability the aircraft has naturally.

In the 70s, when I flew L1011s we had CATIII NO DH auto land capability, Autopilot CWS (like hand flying in Normal Law), autothrust Alpha Floor protection (Like VLS).
When the auto pilot was out, she handled beautifully with manual pitch trim.

What forward progress do you think we've made?

[A33Zab]

What forward progress do you think we've made?


Nothing against L-1011, way ahead of it's time but:

Incidents and accidents

As of August 2008, the L-1011 was involved in 56 incidents, including 11 hull-loss accidents (out of 250) with 534 fatalities.

As of June 2011, the Airbus A330/A340 had been involved in thirteen major incidents, including six confirmed hull loss accidents (out of 1140) and two hijackings, for a total of 338 fatalities.

[DozyWannabe]

Not to mention that the thing's lighter, requires one less donk and one less full-time crew member (which makes it more economical to run). Don't get me wrong, the L-1011 was a fantastic airliner and still has to be matched in some aspects today, but in economic terms it was flawed and sales suffered badly at the hands of the DC-10, which turned out to be another more seriously-flawed gem.

[foster23]

Thanks for a very easy explanation of all the laws. :ok:

[jcjeant]

Hi,

Not to mention that the thing's lighter, requires one less donk and one less full-time crew member (which makes it more economical to run)In my opinion it is the heart of the problem
A plane (was) should be a means of transport which allows to go quickly from one point to another and is relatively expensive for passengers and must be of an acceptable return for its owners (airlines)
A plane must now be a means of transport which allows to go from one point to another (but now the emphasis is no more on speed ! ) and to be inexpensive for passengers and who must have a return to report the maximum possible for its owners (now mainly banks and shareholders)
This is also the other side of progress
Progress is being made in terms of economy and efficiency ..

[rudderrudderrat]

Hi A33Zab & DozyWannabe,

It depends how you manipulate statistical data. You have to compare apples with apples.

The link below lists fatal events with aircraft type where “A fatal event is defined as 'an event in which one passenger was fatally injured solely due to the operation of an aircraft.' The number of fatalities in each fatal accident is irrelevant in the statistics presented below.”
AirDisaster.Com: Statistics (http://www.airdisaster.com/statistics/)

According to this analysis, B727, B737, B757, and B767 are all ranked as having fewer fatal events per flight than 320 series.

The L1011 is ranked as having fewer fatal events per flight than DC-10, DC-11 or B747.

[DozyWannabe]

AirDisaster.Com: Statistics (http://www.airdisaster.com/statistics/)

The problem with the AirDisaster stats is that Chris Kilroy is a known Boeing partisan, and revealed some very negative opinions of Europeans and the French in particular in 2001.

Besides that, those figures don't take into account the longevity of each airframe, and the fact that a lot of accidents in new types will occur in the first 5 years of service. Once an aircraft has plugged the line for a while, its "quirks" are known by the piloting communities and they cease to be as much of an issue. It would only be fair to either compare the first decade of service of each, or discount the first 5 years as a statistical anomaly and take the stats from there. Either way it skews the stats in favour of aircraft that have been around for longer.

[rudderrudderrat]

Hi DozyWannabe,

Page 20 on this Boeing Document is up to 2010. (I can't find an Airbus Document yet)

http://www.boeing.com/news/techissues/pdf/statsum.pdf

Once I've analysed the data a bit more - I'll be able to reply better.

Edit. From Page 20:

Hull loss rate per million departures
rate = with fatalities accident rate / Hull loss accident rate total
B737-600/-700/-800/-900 rate = 0.18/0.30
A320/321/319/318 rate = 0.20/0.33
B737-300/-400/-500 rate = 0.28/0.52

B757 rate = 0.24/0.24
B767 rate = 0.13/0.38
B777 rate = 0/0.18
A330 rate = 0.46/0.46

A340 rate = 0/0.87
B747-400 rate = 0.31/0.62

I can't detect that much difference between B or AB - they are very similar.

[henra]

According to this analysis, B727, B737, B757, and B767 are all ranked as having fewer fatal events per flight than 320 series.



If someone tries to tell me that the 727 has a better accident statistic than a modern Airliner, that is exactly the second where I throw the paper away instantly.

FWIW the 747 has a much much worse statistic than the 320 or 737 (especially if you include the older versions).
What do you make of that ???

edit:

I can't detect that much difference between B or AB - they are very similar.


Agreed. However the data is only really meaningfull for the 737 and A320 from a statistical perspective.

With the A330/340 and 777 the absolute number of occurences and flight cycles (Not flight hours in this statistic) is too small so that one occurence more or less makes a difference between excellent and not so good. Best example is Concorde from 'safest' to 'unsafest' airliner after one single crash.
When you have got >20-30 Hull losses the statistic starts to become more meaningful.

[RetiredF4]

Could some expert explain the following part of the
FCOM (http://www.smartcockpit.com/pdf/plane/airbus/A330/systems/0010/) page

FlightControls Normal Law, 1.27.20 P2 Seq. 001 Rev03

Pitch Control / light mode

Automatic trim is frozen in the following cases
- ....
- ....
- load factor lower than 0,5gs
- .....

Would that not inhibit the trim to move ND when unloading enough (provided elevator authority is big enough)?

further down:


When angle of attack protection is active, THS is limited between setting of entry in protection and 2° ND(f.e. further NU trim cannot be applied)
Similarily, whe the load factor is higher than 1.3 g or when the bank angle gets outside 35°, the THS is limited between the actual setting and 2° ND

Shouldn´t that have prevented or hindered the THS to move to 13°ANU?

Im familiar, that the described paragraphs relates to normal law. Are those vital features lost in ALT LAW?


A few pages down another one causing headache:
Flight controls Reconfiguration Control LAWS
Alternate LAw Alt 1
Protections
Low speed stability

At low speed, a ND demand is introduced in reference to IAS, instead of angle of attack, and Alternate law changes to direct law. It is available whatever the slats/ flaps configuration, and it is active from about 5 kts up to about 10 kts above the stall warning speed , depending on the aircrafts weight and slats/ flaps configuration.
A gentle progressive ND signal is introduced which tends to keep the speed from falling below these values. The pilot can override this demand.
Bank angle compensation is provided.
...........

As IAS was incorrect from beginning and leading to AP /Athr disconnect, and later dropped to 60 kts, could this mode have been activated on behalf of the wrong IAS? How would the ND input by the system differ on behalf of an incorrect IAS (systems gets slow IAS, but actual AS is considerable amount higher, would the ND input be more pronounced then with real lower IAS?
Could this have tricked the PF to counter the system ND input (if this protection was active and the ND input was commanded by the system) by NU SS input and contributed to the high pitch result, when PF NU input overrode the ND input of the Low speed stability protection? Which was then possible, because pitch attitude protection is lost in ALt law?

And what is meant by the term "bank angle compensation is provided"?

I still dont get the whole picture of those law changes and the asociated protection changes or protections lost.

So please be patient, if my questions look uneducated or if the questions have been answered already. And it has nothing to do with A vs. B.

[A33Zab]

I can't detect that much difference between B or AB - they are very similar.


Conclusion: FBW is as worse as NON-FBW?

I can detect a difference, why did they separate A330 with A340?
They are identical A/C apart from amount of engines.

[WilyB]

It depends how you manipulate statistical data. You have to compare apples with apples.

The link below...

... shows statistics valid through December 31, 2004.

[WilyB]

a return to report the maximum possible for its owners (now mainly banks and shareholders)


JC, shareholders are, by definition, owners. Now that we established this, shareholders might be banks, yourself, or your retirement plan. Whatever the case, Airlines are historically a risky investment most of the time.

[john_tullamarine]

Could you comment on the inclusion of "damaged or missing" radome?

I don't think I saw any comment on this question.

Pitot static performance is dual input - pitot and static.

Apart from blockage pitot performance generally is pretty robust and doesn't give too much in the way of problems.

Static performance, on the other hand, is a bit of a prima donna.

- in the certification phase development of PEC data is a major part of the flight testing program.

- we even go to the trouble of using trailing drogue (cone) static sources (http://www.flickr.com/photos/65483667@N00/4495205541/) to get out of the aircraft's interfering flow fields

- modifications forward of the static source can be a nightmare for PEC effects. I recall one tale about a B52 program where a mod up forward made a BIG difference to IAS during the takeoff - fortunately, the TP had a feeling in the water during the first takeoff and rejected.

- in routine operations, the easiest way to get a massive airflow disturbance which will always cause an effect on the PEC is to have the radome disintegrate ...

For those who like some arithmetic and lots of fancy mathematical symbols, you might like to read reports like this one (http://www.aviation.org.uk/docs/flighttest.navair.navy.milunrestricted-FTM108/c2.pdf). (Everything you wanted to know about pitot statics but were afraid to ask ...)

[Linktrained]

WileyB

Eddie Richenbacher stressed "Reliability" of air transport back in the 1930s. His backers understood that this had to include the then new technologies, Radio Range etc. Others understood that any mishap, and that included off- schedule operation, costs money and ultimately insurance premiums would rise.
"Safety is no Accident"
Newer aircraft became larger, faster, and more productive, and must be kept working to repay their initial cost. And they became more efficient. Staff need suitable training, to get the best from the Capital - it is an investment. Reliability encourages profitability.
( Just think of re-equipping AF with Constellations to do its present work. In 1970 I replaced the fleets of one airline with 400 Yorks, which would not have been subject to Night Jet bans ! )

[CONF iture]

ISIS is an option for A330 that can replace the standard unreadable standby indicators.
ISIS is not especially larger than the standard standby indicator, and the standard standby indicator is not more 'unreadable' than the ISIS.

How much of an aircraft's flying is done with the Trim Tank "inoperative"?
Pretty rare, but I can still remember flying under MEL an entire week or so without it due to a defective trim tank isolation valve.

I hope BEA explains how the cg moved from the automatic 38% MAC, as shown above, and in the initial report, to 29% (or was it 23?) in its latest report.
Never the MAC could have been to 38% after only 3 hours something in the flight, not with the initial very much forward 23% CG at takeoff time. My own estimate would have put it around 32% at the time of the event, but the BEA now mentions 29% ...

As for BOAC's question, I don't think takata's point is a case of Airbus pilots not being able to fly an aircraft so much as it is the question of whether you'd want to have to suddenly take over manual pitch trimming - in turbulence, at night, with no speed indications and the fuel transfer system causing the need for regular adjustments.
If now to have to trim an airplane overloads a pilot, so, something is very wrong with the airbus philosophy. How will cope a pilot the day he has to do it when the system pushes him to lose that practice. Let the pilot trim, it is just more pleasure and SA in the mean time.

Could it be that static pressure was also affected by icing?
Icing maybe or just the unusual 'AoA' for those static probes induced unreliable readings for altitude and/or Vertical Speed ...

Something big is missing in the story : I can't believe 3 guys would have maintained NU inputs for 3 minutes with 3 A/H showing blue blue blue and 3 altimeters going down like crazy. BTW, what did say the captain ? Nothing ... ?

BEA, just publish the data, and if we don't deserve them, the victim's families surely do. Why can't they get them ... ?

[Graybeard]

Originally Posted by Graybeard
I hope BEA explains how the cg moved from the automatic 38% MAC, as shown above, and in the initial report, to 29% (or was it 23?) in its latest report.

Conf Iture: Never the MAC could have been to 38% after only 3 hours something in the flight, not with the initial very much forward 23% CG at takeoff time. My own estimate would have put it around 32% at the time of the event, but the BEA now mentions 29% ...

How come BEA didn't know the takeoff cg was 23% at time of first report? Why didn't they do your math?

As long as BEA is being vague and inspiring wild guesses: what is the chance that the takeoff cg was really 30%, and not 23%? You can see where that would lead..

Is cg calculated based only on pre-takeoff W&B, or is it computed constantly from AOA, IAS, ALT and trim?

[grity]

for me cg seems calculated based only on pre-takeoff W&B.... and fuel consumption....

who made the load- and fuel-weight datainput normaly?
there can also be a data entery error, captain again needs best skills to control this



@ john tullamarine can you explain the different places of the pitots between A+B, can this have an influence of the reliability (ice)

[A33Zab]

Quote:
Originally Posted by Linktrained
How much of an aircraft's flying is done with the Trim Tank "inoperative"?

Pretty rare, but I can still remember flying under MEL an entire week or so without it due to a defective trim tank isolation valve.


Happen to have deactivated a THS tank a few months ago, due to access panel leakage.
Repair interval Cat C (10 days), empty TT; manual closing and deactivating TT isolation & TT inlet valve to prevent fuel entering TT but to keep trim pipe with fuel for APU ops.
Crew selects TT Tank Feed switch to ISOL, 1% fuel to be increased due CG control not available.
Indeed very rare, it was the first time in our company.

@GB:
Is cg calculated based only on pre-takeoff W&B, or is it computed constantly from AOA, IAS, ALT and trim?



Flight preparation:

GROSS WEIGHT INSERTION (INIT B page) :
- ZFCG/ZFW --------------------- INSERT
- BLOCK FUEL--------------------- INSERT
Block fuel may be automatically computed by the FMGC, using the FLIGHT PLANNING function.

CAUTION:
Part of characteristic speeds, displayed on the PFD (green dot, F, S, VLS), are computed from
the ZFW and ZFCG entered by the crew on the MCDU. In addition, the pitch trim will be
automatically set to the takeoff position, according to the entered ZFWCG.
Therefore, this data must be carefully checked (Captain's responsibility).


The flight crew should insert the weights after completing all other insertions. This is to avoid cycles
of prediction computations at each change in flight plan, constraints, etc...
If ZFCG and ZFW are not available, it is acceptable to enter the expected values in order to obtain
predictions. Similarly, the flight crew may enter the expected fuel on board, if refueling has not been completed at that time.
If ZFCG, ZFW, and BLOCK FUEL are inserted, the FM will provide all predictions, as well as the EXTRA fuel, if any.



In Flight:

The FMGC uses the weight and center of gravity from the FCMC (Fuel Computer) when available.
The GW and CG computed by the FE part are used:
– as back-up in case of dual FCMC failure.
– to trigger the aft CG caution and warning signals (independently of the FCMC).
FE Weight computation (back up)
– When the aircraft is below 14625 feet and 255 knots :
GW = f(α, CAS, N1/EPR actual, CG from FE part, altitude)
– When the aircraft is above 14625 feet or 255 knots :
GW = TOGW − WFU
TOGW: takeoff gross weight
WFU: weight fuel used acquired from FADECs.
FE Center of gravity computation (back up/aft cg computation)
The CG is computed from the position of the horizontal stabilizer and is
function of the N1/EPR, Vc, ALT, MACH and GW from FE part.

[takata]

Hi Franz,

Automatic trim is frozen in the following cases
- load factor lower than 0,5gs
Would that not inhibit the trim to move ND when unloading enough (provided elevator authority is big enough)?

Yes, it will be limited to the duration of threshold excess, when load factor will be lower than 0.5gs, IF, at any time, they applied that much ND, which doesn't seem to be the case either.


"When angle of attack protection is active"
Shouldn´t that have prevented or hindered the THS to move to 13°ANU?
Im familiar, that the described paragraphs relates to normal law. Are those vital features lost in ALT LAW?

Yes they are lost. This protection, like any other active protection, was lost from the start of the event when EFCS is directly set in Alt 2.
UAS is very nasty, only g-load protection (which is passive) will remain and protect the airframe from g-load exceedances.


could this mode ["Low speed stability"] have been activated on behalf of the wrong IAS?...And what is meant by the term "bank angle compensation is provided"?
No, same as above, it doesn't work with UAS in Alt 2. There was no more "Stall_Speed" to refer to for the system to make it working.
"Bank angle compensation", should mean that the system will try to bring back the wings level or prevent any increase of bank angle while reducing NU attitude.


I still dont get the whole picture of those law changes and the asociated protection changes or protections lost.

It's not easy to grasp it at the first reading.
When going to Alternate law mode, the five active Normal law protections are lost. But, depending on the kind of fault causing Alternate law switch, two protections may be replaced by Alternate ones (Low Speed and High Speed).
In our AF447 case, with a triple ADR fault, those protections are lost as well, and it seems very bad as they could have prevented this crash.

[takata]

Hi CONFiture,
ISIS is not especially larger than the standard standby indicator, and the standard standby indicator is not more 'unreadable' than the ISIS.
You are right, but ISIS includes more functions than default standby. About ISIS access, flying the aircraft from the RHS would make it harder for the PF to check ISIS, which is closer, in the central console, from Captain's seat.

Icing maybe or just the unusual 'AoA' for those static probes induced unreliable readings for altitude and/or Vertical Speed ...
AoA wasn't an issue when speed issues started. I was talking about the first PF reaction inducing the initial climb that could be related to his focus on roll and initial sharp altitude drop. I agree that it doesn't explain why he continued NU orders when, 40-50 seconds later, the aircraft stalled. But disorientation and instrument disbelief could cause the later orders.


Something big is missing in the story : I can't believe 3 guys would have maintained NU inputs for 3 minutes with 3 A/H showing blue blue blue and 3 altimeters going down like crazy. BTW, what did say the captain ? Nothing ... ? BEA, just publish the data, and if we don't deserve them, the victim's families surely do. Why can't they get them ... ?
It is quite hard to understand.
But, we never faced the same stress and situation as, with hindsight, we are fully aware of many things they may have never acknowledged during this event. Captain's return could have bring some confusion with him. Did they agreed about the situation? Was the PNF nose-down in ECAMs reading while the PF pursued stubornly his false impression of what really happened?

I still believe that a BEA hastily release of raw data would have caused more harm than good. Many things really need to be checked and cross-checked before reporting them to the public. Without expert analysis, it may be very harmful to everybody. Any inquiry needs time, patience and in depth processing in order to avoid mistakes and wrong conclusions.

I would like to know everything, straight away, but not before everything is well sorted out and seriously verified. I'm pretty sure that there will be no final report this summer, as some believe, only an interim one.
We'll see.

[LandIT]

From takata

Everything in the fault sequence analysis makes me think that the PF display was the first affected. The PROBE fault recorded imply that the 3 probes readings were different as well as out of range with previous median values. Hence, no single ADR could be rejected but the three altogether. We are also told of the recorded sequence implying PNF speed decrease followed by ISIS: the first value then to drop should have been the one on the PF display.

There is also an indirect proof of an altitude drop and range: the following reported TCAS fault by ACARS. AFS/FMGES (autoflight system) ADR altitude monitoring fault treshold is set at 400 ft instead of 3,000 ft at EFCS level (flight control monitoring). Hence, TCAS should have faulted because of that. So, could it be that uncorrected static pressure was dropping to the point of displaying an over 400 ft of instantaneous altitude change, Mach going down from 0.81 to about 0.18? Could it be that static pressure was also affected by icing?

If this was the first information taken by the PF in addition to the roll at AP disconnection, he could have effectively feared that some kind of spiral dive could follow. Likely, his pitch rate wasn't his first concern, then without speed, after ignoring the first stall warnings as spurious, he might have lacked the correct info necessary to understand how much energy was lost during the climb with an altitude under reading, then he also would be spatially disoriented. There was also no mention of thrust change during this climb and this would rather fit with a PF trying to slow down than one fearing of stalling.


FWIW after following this and other thread for many months and wanting to believe the PF reacted to indications (not terrified rabbit pulling up), takata's theory is what I believe happened. That in my view is saying a lot after all the posts and credits takata with a conclusion that has taken so many months of analysing, questioning and thinking.

My worry now is the PF (RHS) instrument datas were not recorded and the BEA may have difficulty concluding about why the PF inputs were as recorded. But I fundamentally believe the PF was reacting to what he saw on instruments (outside was "black", no horizon). I do however think he failed to integrate his feelings from the seat, i.e. G forces over time (which probably began before AP disconnect with subtle descent). I can excuse him from that in the urgency of the situation, but am still trying to understand ~30 sec of 7000fpm climb.

My hope is that the A330 will become even safer (it probably already is due to modified UAS procedures promulgated). Surely we must find a more resiliant way to measure airspeed than those pitot's. But if takata is right, we must find a better way to reliably measure altitude at all times as well.

[john_tullamarine]

can you explain the different places of the pitots between A+B, can this have an influence of the reliability (ice)

I have little (approximately nil) knowledge of AB pitot statics and only those Boeings which I have flown. Generically, I suspect that you will find both marques are similar with multiple pitots around cockpit FS and statics a little further aft (to stay in a shallow boundary layer region without too much local flow acceleration).

Ice problems are probably a bit too specialised for my general comments to be of much use.

[bearfoil]

Thales have (had) issues. All a/c operations have 'issues'. Transport does not function in a vacuum. A/C are certifiably up to the challenge, but they do not fly in a laboratory, with scrupilously maintained parameters.

To be safe, maintenance must be relentless. Pitot probes gobble up whatever atmosphere they are in, they have no choice. Salt air, grit, moisture, pollution, it is the fact of life. Thales had drain corrosion problems (from memory, original thread, and subject to flame). So in a bad way, the probes developed a less than reliably redundant read? Maybe.

From takata and his point re: three way adr rejection due discrepant reads, a slight hesitancy may be allowed re: ICE.

IMO, ICE would present as other than an instantaneous three way discrepancy. It seems more reasonable to entertain airflow changes. imo.

I have read only LandIT's repost of takata's post. It is a feast, and his best yet, imho. Injecting TCAS ACARS for altitude suggests perhaps looking at W/S for airflow disturbances?

I am relieved and fully support any writing that gives an objective basis for speculation. Of course the crew were qualified; where in the world did the initial objectivity of this forum go?

LandIT. I spot an idea in your post. "He did not incorporate his feelings from his seat".

Should He? That way lies danger. He was in the panel, making the best sense of what he saw, I would guarantee it. It was in flying by the book that did them in....... Interpreting "G", especially over time, isn't that potentially a conflict with the a/c?

I think takata is spot on. PF was likely F/O, from the RHS. Not relief pilot?

[syseng68k]

Chris

DozyWannabe, #466


Besides that, those figures don't take into account the longevity of
each airframe, and the fact that a lot of accidents in new types will
occur in the first 5 years of service. Once an aircraft has plugged the
line for a while, its "quirks" are known by the piloting communities and
they cease to be as much of an issue. It would only be fair to either
compare the first decade of service of each, or discount the first 5
years as a statistical anomaly and take the stats from there. Either way
it skews the stats in favour of aircraft that have been around for
longer.
I don't quite see the connection there. It's almost as though you are
implying that you shouldn't fly in any new a/c until it's at least 5
years old, to get all the bugs shaken out, which seems like a spurious
argument.

While you may need to wait a few years before upgrading to any new
version of windows, (I'm still using W2k on one development machine, but
for other reasons), a/c are not quite the same thing. Of course,
statistics can show anything you like, but the answer to that is to take
samples from > 1 data source, especially where a given data source is
suspected to be biased or unreliable.

I doubt if there is meaningfull difference in the figures anyway, as accident
rates, in terms of flight hours are down in the noise...

[Lonewolf_50]

for John T:

If ice is the trigger for a fault in the function of static ports, what sort of evidence does that leave behind? Your posts leave me an uneasy feeling that a possible fault that left no evidence was involved for a part of the upset event.

If that is the case, it has remained hidden. Sufficient function was retained or regained to leave coherent altitude data for most of the event.

[bearfoil]

hi Lonewolf.

Give me a steer, here. My take on the accident involves mostly the idea that the initial event happened rather quickly, and was unrecoverable almost as fast.

Aren't 'Upset' and "Loss of Control" two separate regimes? My understanding is that Upset need define one set of criteria, and LOC another.

Upset I think, includes control excursions that are quite recoverable, similar and quite consistent with loss of a/p. Not boring, but not life threatening either. A Loss of Control exists when command of the a/c is lost?

So, for whatever reason, what caused 3ADR reject and ALTERNATE LAW2 satisfies 'Upset'? The zoom climb, at least for now, defines LOC?

Early in #4 thread, I think, the criteria for Jet upset (regardless of airframe type) were posted here. Not so for LOC, but LOC is pretty simply "Loss of Command" (mechanical or Pilot induced?)

[BOAC]

Whatever barometric anomalies you introduce into the theories, you still have to explain why two competent pilots allowed or caused the pitch attitude to change so dramatically without an apparent word said between them? Here's hoping BEA tell us something useful at the end of the month. Otherwise I'm afraid it just does not 'compute'.

[bearfoil]

Never having been there before, neither aircraft nor Pilot 'knew' what they were "doing".

At least Orville and Wilbur expected the unexpected.

[speedbirdconcorde]

Lets all keep in mind when discussing pilot action....we have had 2 YEARS to review, analyse, review, discuss...analyse...... they had minutes....NOT a situation any one of us would ever want to be in...

Eagerly awaiting the next installment from BEA...

[Lonewolf_50]

hi Lonewolf. Give me a steer, here. My take on the accident involves mostly the idea that the initial event happened rather quickly, and was unrecoverable almost as fast.
"Quickly" is a relative term. Depending upon how responsive your aircraft is, quick time horizon will very.

At some point in a three thousand foot climb, which took about half of a minute, remedy to the pitch problem seems to have not worked, whatever was tried.

For me, thirty seconds is a long time if what I am dealing with is simple attitude flying, but as I have stated time and again, I am at a loss concerning what the PF was seeing (and for that matter, what he wasn't seeing) from the event's onset to its conclusion.
Aren't 'Upset' and "Loss of Control" two separate regimes? My understanding is that Upset need define one set of criteria, and LOC another.
I would use "upset" to describe those unusual attitudes and conditions that precede stall, or other out of control flight, and classify only stall and beyond states as "loss of control."
Caveat: if you have a control channel that doesn't work, you may be, by default, in a loss of control state. If you have spoilers or slats going wild (there was a bold face for that in the A-4 NATOPS that I can vaguely recall) you may be in OCF until you get the asymmetry fixed.
Upset I think, includes control excursions that are quite recoverable, similar and quite consistent with loss of a/p. Not boring, but not life threatening either. A Loss of Control exists when command of the a/c is lost?
You can call a trim runaway a loss of control, unless you are able to overcome it and regain control. Had that happen in a helicopter once, it was an adrenalin rush, but it was recoverable.

Bear, I am not sure I'd phrase the distinction as you did.

Over the past two years, a number of pilots who have flown big transports into stalls (usually on purpose with that one degree per second entry method) have told us how the stall recovery went. What seems to be true, (other than the deep stall problem of the T tail aircraft) is that recovery is often viable when partial control over some or all flight surfaces is exercised in a particular way, likewise power adjustments, to affect a change in airflow and restore lift, and thence control.

(Aside: If you want an interesting loss of control story, take a read on the Vortex Ring State flight test done by two test pilots for the V-22 Osprey as they investigated one of the V-22 mishaps that involved VRS).

So, for whatever reason, what caused 3ADR reject and ALTERNATE LAW2 satisfies 'Upset'? The zoom climb, at least for now, defines LOC?
I don't see it that way. I don't think zoom climb is LOC, it looks to me more of an upset. Once stalled, you could argue LOC. I'll let those who are more current in state of the art terms correct me on that, as necessary.
Early in #4 thread, I think, the criteria for Jet upset (regardless of airframe type) were posted here. Not so for LOC, but LOC is pretty simply "Loss of Command" (mechanical or Pilot induced?)
A stall due to windshear is neither mechincally induced, nor pilot induced, so maybe a third category is needed. Or a fourth. ;)

[PJ2]

takata;
still believe that a BEA hastily release of raw data would have caused more harm than good. Many things really need to be checked and cross-checked before reporting them to the public. Without expert analysis, it may be very harmful to everybody. Any inquiry needs time, patience and in depth processing in order to avoid mistakes and wrong conclusions.
Having done for some time now the work of interpreting flight data in flight data analysis programs I fully concur with your views.

The release of "raw" data is simply never done.

I made the observation long before anything was released after the recorders were found, that the data would not, (and may not) be able to provide us with the full picture of what happened and why.

There is no "magic" in the flight data or the CVR. It is without question, an interpretive process requiring thorough training and long experience. How someone may imagine themselves as capable of doing better alone, is a puzzle.

The release of the traces, (which is a very long way from "raw data"), is sometimes done as part of the report, supporting the text and investigative work. Asking for or even demanding "the raw data" is the clearest indication of how little someone understands the flight data and accident investigation processes.

The impression that "the raw data" will give final, conclusive answers and "we will finally know what happened", is a misconception of the flight data and investigative process. A release of "the traces" without a thorough interpretation would indeed be a serious mistake and could even delay an understanding of what really happened.

While there are a few here whose capabilities have clearly been demonstrated and whose interpretations would benefit from being able to work with "the traces", the investigative process does not work that way and those capable of the work would know and understand that. The vast majority of us are not the "check-and-balance on the BEA" some may imagine themselves to be. When the report and the data are both available, there will be time enough for those who can do the engineering and flight safety work to verify, and critique where warranted.

[ChristiaanJ]

Thanks, PJ2.
Count me in your camp....

[bearfoil]

believe it or don't, me too.

When the Reaper enters the room, many present begin to whistle. Human beings function (and desire to) in states that can be managed, and understood. If understanding is not available, we trust others to supply some manner of acceptance by proxy. Lacking any understanding or management, we choose denial.

This is true, and even perhaps more so, for those who believe knowledge is perfection, and there is an answer for everything. There is not, and fear is therefore inescapable, and natural.

It is possible that this Airbus and these Pilots performed perfectly, and the consequence was unavoidable. Life has risks, and to the extent that we honor that, it is incredibly exciting.

I think this thread is back to still water. The BEA report will never satisfy everybody. It satisfies me, and I haven't even seen it yet.

[ChristiaanJ]

.... without an apparent word said between them?How do you know that?
All we have at the moment is an interim 'cherry-picked' extract from the initial data from the recorders (FDR and CVR) , as described in text format by the BEA, and then translated into another language (English), with all the usual pitfalls of those processes....

Yes, we're all frustrated by the limited amount of 'hard' data we have.

Yet, the BEA report seems to have satisfied the 'meedia', which now have switched to 'DSK', 'Murdoch', the 'Red-haired Witch of Wapping' and other more juicy bits.

If I was working for the BEA (and no, I'm not) I'd heave a sigh of relief. To do serious hard reliable work, it does help not having the media, etc., breathing down your neck. Even if getting a full interim report out by the end of July might have seriously :mad: up my holiday.

[jcjeant]

Hi,

Yet, the BEA report seems to have satisfied the 'meedia', which now have switched to 'DSK', 'Murdoch', the 'Red-haired Witch of Wapping' and other more juicy bits.

Are you sure ?
Seem's not all meedia

France/Monde | L’AF447 ou le droit de savoir (http://www.ledauphine.com/isere-sud/2011/07/15/l-af447-ou-le-droit-de-savoir)

[Lonewolf_50]

Yet, the BEA report seems to have satisfied the 'meedia', which now have switched to 'DSK', 'Murdoch', the 'Red-haired Witch of Wapping' and other more juicy bits.
Thanks for that, I had a momentary visual of The Sun running coverage, page 3 perhaps, of Red Haired Witch's juicy bits, and nearly poked my eyes out with a pencil. (Yes, I still know how to use one! )

The media pressure has got to be a process obstacle for BEA.

Been in a few (thankfully) scenarios in my life where the Media took and interest ... it's not much fun.

[DozyWannabe]

I don't quite see the connection there. It's almost as though you are implying that you shouldn't fly in any new a/c until it's at least 5 years old, to get all the bugs shaken out, which seems like a spurious argument.

Not at all - it's just statistically more likely that there will be a marginally higher risk of an incident or accident in the first years of a new airframe's life. The chances of being in an accident when boarding a new type are still incredibly unlikely.

But the facts bear this out - the 727 had a series of very nasty accidents in the first few years of service due to a combination of pilots getting to grips with the tail-heavy aspect of the design in combination with the powerful flaps causing a much higher bleeding-off of airspeed on approach than they had hitherto been used to. Both the Comet and the DC-10 revealed serious design flaws in their first few years of service (and the L-1011 revealed a minor one, regarding the weight -on-column required to disengage the automatics). The 737 proved that it wasn't as longitudinally stable as the 727 (unlike the 727 you couldn't rescue a fast approach by throwing the gear out early) and the A320 had some mode-confusion issues in her early days (of which Habsheim was *not* an example).

Those are just some examples, but I think it's a pretty good rule of thumb. It's a testament to the improving quality of aeronautical engineering over the years that the number of these incidents has gone down dramatically (the 757's record was unblemished until the mid-'90s and the 777 has suffered only a single hull-loss, as has the A340 in service).

While you may need to wait a few years before upgrading to any new
version of windows, (I'm still using W2k on one development machine, but
for other reasons), a/c are not quite the same thing.

Believe me - that's not the comparison I'm making! For a start, home and business OS "teething problems" usually *are* down to flaws in the design and implementation rather than the users getting used to how they operate. This isn't relevant to an aviation discussion though. :)

I doubt if there is meaningfull difference in the figures anyway, as accident rates, in terms of flight hours are down in the noise...

Funnily enough, it was A33Zab who brought up the safety record, not me...

[mm43]

I'm sure the "Red Haired Witch of Wapping" is not featuring in the BEA's analysis of the demise of AF447, and likewise the same lady wouldn't have found anything of salacious media interest worth publishing in her former rag(s).

On the other hand, Le Dauphine's latest article - L’AF447 ou le droit de savoir (http://www.ledauphine.com/isere-sud/2011/07/15/l-af447-ou-le-droit-de-savoir) (AF447 - The right to Know) - is clearly pointing the finger at "crew competence" or lack of it, and to the dubious credibility of Air France.
The exponential demand for pilots by companies in emerging countries means that more than ever the need for competent men in charge must be faced.Protect the integrity of Airbus Industries and make Air France and its employees the "sacrificial lamb" is my read on this Irène Perrin article.

Numerous issues are raised, including simulator training and management, but nowhere in the article does the word "securitie" in the safety sense get a mention.

jcjeant - Thanks for the link.