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AF 447 Thread No. 5

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AF 447 Thread No. 5

Old 17th Jul 2011, 14:25
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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......
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Old 17th Jul 2011, 14:38
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Hi Confiture,
Originally Posted by CONF iture
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.
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Old 17th Jul 2011, 14:52
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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.
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Old 17th Jul 2011, 15:02
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Originally Posted by CONF iture
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.
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Old 17th Jul 2011, 15:07
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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 !)
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Old 17th Jul 2011, 15:36
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Fuel + CG

More fuel AFT:








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Old 17th Jul 2011, 16:34
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Stall Protection

Hi HarryMann,
Originally Posted by HarryMann
Originally Posted by grity
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.




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.

Last edited by takata; 17th Jul 2011 at 16:45.
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Old 17th Jul 2011, 17:05
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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?
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Old 17th Jul 2011, 17:16
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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!).

Last edited by bearfoil; 17th Jul 2011 at 18:05.
 
Old 17th Jul 2011, 17:50
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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.
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Old 17th Jul 2011, 18:06
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Kind of like the way 'bearfoil' posts?
 
Old 17th Jul 2011, 21:07
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(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.
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Old 17th Jul 2011, 21:10
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Originally Posted by 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.
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.)
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Old 17th Jul 2011, 22:01
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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.
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Old 17th Jul 2011, 22:04
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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:




























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Old 17th Jul 2011, 22:15
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Law Reconfiguration.

Part 2:





























End.
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Old 17th Jul 2011, 23:04
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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.
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Old 17th Jul 2011, 23:14
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Originally Posted by gonebutnotforgotten
It can't be the errant overspeed protection that caused the Turkish A340 skywards leap in 2000
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.
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Old 17th Jul 2011, 23:21
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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".
 
Old 17th Jul 2011, 23:28
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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.
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