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......

Hi Confiture,
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.

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.

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.

Fuel transfer
 

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 !)

Fuel + CG
 

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

Stall Protection
 

Hi HarryMann,
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.

Q for Pilots:
 

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?

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!).

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.

Kind of like the way 'bearfoil' posts?

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.

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.)

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.

Law Reconfiguration.
 

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/r...ab999/Dia1.jpg

http://i474.photobucket.com/albums/r...ab999/Dia2.jpg

http://i474.photobucket.com/albums/r...ab999/Dia3.jpg

http://i474.photobucket.com/albums/r...ab999/Dia4.jpg

http://i474.photobucket.com/albums/r...ab999/Dia5.jpg

http://i474.photobucket.com/albums/r...ab999/Dia6.jpg

http://i474.photobucket.com/albums/r...ab999/Dia7.jpg

http://i474.photobucket.com/albums/r...ab999/Dia8.jpg

http://i474.photobucket.com/albums/r...ab999/Dia9.jpg

http://i474.photobucket.com/albums/r...b999/Dia10.jpg

http://i474.photobucket.com/albums/r...b999/Dia11.jpg

http://i474.photobucket.com/albums/r...b999/Dia12.jpg

http://i474.photobucket.com/albums/r...b999/Dia13.jpg

http://i474.photobucket.com/albums/r...b999/Dia14.jpg

http://i474.photobucket.com/albums/r...b999/Dia15.jpg

Law Reconfiguration.
 

Part 2:

http://i474.photobucket.com/albums/r...b999/Dia16.jpg

http://i474.photobucket.com/albums/r...b999/Dia17.jpg

http://i474.photobucket.com/albums/r...b999/Dia18.jpg

http://i474.photobucket.com/albums/r...b999/Dia19.jpg

http://i474.photobucket.com/albums/r...b999/Dia20.jpg

http://i474.photobucket.com/albums/r...b999/Dia21.jpg

http://i474.photobucket.com/albums/r...b999/Dia22.jpg

http://i474.photobucket.com/albums/r...b999/Dia23.jpg

http://i474.photobucket.com/albums/r...b999/Dia24.jpg

http://i474.photobucket.com/albums/r...b999/Dia25.jpg

http://i474.photobucket.com/albums/r...b999/Dia26.jpg

http://i474.photobucket.com/albums/r...b999/Dia27.jpg

http://i474.photobucket.com/albums/r...b999/Dia28.jpg

http://i474.photobucket.com/albums/r...b999/Dia29.jpg

End.

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.

According 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.

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".

Hi Grity,
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.

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.

link

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

(afaik)

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.

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?

http://www.pprune.org/tech-log/45687...ml#post6573663

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

FBW Thread
 

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

Hi Bearfoil,
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.

Hi takata,

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.

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.

Hi Rudderrudderrat,
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.

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.

Hi takata,

Thanks for the reply.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.

- heavens! What have we come to? Is it too much to ask of an AB pilot - I mean, like FLY an aeroplane, man??:ugh:

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.

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.

Hi gonebutnotforgotten,
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.

Hi Graybeard,
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.

CG-travel
 

Found this reference some time ago about CG travel due to fuel
Getting to grips with weight and balance

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.

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?

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.

Hi Franz,
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.