AF447 Thread No. 3

[syseng68k]

With all due respect, I'd like to add that crimped connections, when done properly, are just as good (if not superior) as soldered connections in all respects, including resistance to corrosion. What's more important, crimped connections - again, using the right tool - are far more consistent, even when done by underpaid and ignorant personnel, which is often the case (hope that does not apply to Airbus).
Agreed. A crimped joint is effectively a cold welded gas tight joint and
without a skilled workforce, better than solder. Crimp tools do need to be
tested /calibrated to ensure that that the crimp pressure is not
too low (bad connection) or too high (embrittle the wire or even
partially shear through). Soldered joints can have a much greater
variability: "dry" if the joint is not heated enough and intermittent if
too little solder / flux or not properly wetted. Other problems with soldered
joints include embrittlement with temperature cycling and vibration.

A lot of early avionics, computer and mil kit was "wirewrapped", where
you get 16 or more cold welded joints as the wire is wrapped round a
square pin. Just about the most reliable board level interconnection
system ever devised and still used here occasionally for quick prototyping
work...

[Lonewolf_50]

Dozy:
At this point, BEA and Airbus know what was being displayed on at least one set of instruments, they know which versions of the software was installed on the aircraft's computers and they know what the timestamped ACARS messages were.

That's enough to gain a reasonable idea of what that particular aircraft did in terms of systems behaviour, over and above what control inputs were from the pilots.
Up until stall, yes.

How they determine validity of airmass data will be an interesting revelation, given spurious airmass data as contribution to the event.
This should be enough to run simulator tests with crews to gauge their responses to the situation that presented itself, in much the same manner as the Birgenair investigation did. The systems are not so complex that recreation of the incident is impossible.
Yes, except for the simulation of what happens once the aircraft stalls ... which goes back to "how do you train to get out of a stall once in?"

Up to that point, both stall prevention and error/trend detection processes and habits may be usefully analyzed.

There is a danger in making assumptions about what was on the PF's display set ... maybe BEA can figure out and publish more of that between now and when their final report comes out.

Also, crews put into the scenario ought to be unalerted, if you want to collect some data on the man-machine interface. <--- That appears to be a critical performance node that must be examined.

[RR_NDB]

A lot of early avionics, computer and mil kit was "wirewrapped" (http://www.pprune.org/tech-log/452836-af447-thread-no-3-a-101.html#post6513051)

We assembled a big System (SPC Telephone switching System) prototype using "wire wrap". Big dense boards presenting complex testability issues.

I am amazed they were used also in avionics. (you lost precious volume due pins lenght).

[DozyWannabe]

Lonewolf_50:

Absolutely correct on your last point (I said something similar before), though simulations are inherently limited by the fact that any crew in the sim will be expecting something to go wrong.

That said, the Birgenair sim tests almost universally ended with a crash into the sea, even with the most experienced and capable pilots at the controls. The combination of overspeed and stick-shaker warnings seemed to induce a psychological "freeze". Of course in this case there's no evidence of overspeed detection, warning or protection activation, but I'm fairly sure that the warnings would have been just as overwhelming even if not as disorientating due to their completely contradictory nature.

[bearfoil]

Doze

"Of course in this case there's no evidence of overspeed detection,"
I don't remember what the speed (Mach) ACARS record was about then. I thought it meant too much speed?

[DozyWannabe]

Hi bear,

None of the ACARS lists (raw and interpreted) that I can find give a MACH warning. Could you provide a link?

Thanks.

[Lonewolf_50]

bear/dozy:

If I may, we need to be careful and aware as we discuss this regarding the difference between what speed was through the airmass, and what speed was indicated, since an axiom in this case is that the sensed and processed airspeed was (for at least part of the event chain) unreliable, and not a reflection of the actual speed through the airmass.

This got me to thinking. Will BEA be able to compare inertial references to isolate when true airspeed was being detected before things went awry. You could backwards compute it from ground track for x minutes before the event. You would come up with wind and true airspeed then, and maybe get a better handle on (by using ground track compared to Airspeed during the event) a finer estimate of what the plane was doing despite what it was displaying ... airmass wise.

Hopeful.

[DozyWannabe]

LW_50, of course. I'm not concerned about what the actual speed was in terms of this discussion so much as what warnings and annunciations were presented to the pilots. They already knew their speed indications were unreliable, but I suspect things will become clearer once we know what aural warnings were sounding at the time.

Birgenair proved that insistent and contradictory warnings can overwhelm a crew, and procedures were developed in the wake of that incident to better cope with that situation. Were the crew able to recognise their situation and apply those procedures accordingly?

[bearfoil]

Doze

2:10:29 WRN/WN 090601 [2:10] 2288300206 FLAG ON CAPT PFD SPD LIMIT

[DozyWannabe]

Bear : According to this FCOM analysis:

http://www.keepandshare.com/doc/1319772/air-france-477-the-warning-messages-learning-by-fcom-august-19-2009-2-02-pm-1-7-meg?da=y

it refers only to the target speed displays:

- FLAG ON CAPT PFD SPD LIM and FLAG ON F/O PFD SPD LIM: characteristic speeds (green dot, VLS, ...) lost due
to loss of calculating function

This is not an indication of overspeed that I can see, nor would it trigger an overspeed warning.

[ChristiaanJ]

We assembled a big System (SPC Telephone switching System) prototype using "wire wrap". Big dense boards presenting complex testability issues.
I am amazed they were used also in avionics. (you lost precious volume due pins lenght).From my own experience, I think you'll find that in avionics "wire-wrap" was only used for the "mother-board" wiring, and not for the circuit boards themselves, so "volume loss" was not really an issue.

BTW, I think the whole "wiring" issue is a red herring.... I was hoping somebody with enough knowledge of the ACARS system would come forward with an exact definition of the "WRG" message label, but so far that hasn't happened (or did I miss that?)..

I would have expected faults such as a faulty SSM, or NCD, or parity errors, to have been flagged "BUS" rather than "WRG".

[bearfoil]

Thank you, Sir..

I'd be interested to find out if that indicates the warning Flag is unavailable, or that it is ON. Isn't ACARS just a sensing and recording (reporting) system? Kind of like a snitch? It doesn't compute, so how would it "know" that the PFD is bananas re: a/s? Is it told by the FMC what to report, or does it just record anomalous data? "Observe Only" kind of.

thanks for all,

Yesterday I jumped from the bridge down to the salon deck on my boat, rather hard. The GPU started up. Spooky.

[DozyWannabe]

@bear - I think the effective word is "lost" - i.e. FLAG ON is a notification to maintenance that the PFD SPD LIM has become unavailable. The PFD isn't "bananas", so much as it has lost some data that it would usually present.

[syseng68k]

RR NDB, 2003

We assembled a big System (SPC Telephone switching System) prototype
using "wire wrap". Big dense boards presenting complex testability
issues.
Wirewrap was used extensively in the old strowger exchanges and probably
electronic as well, though iirc, they used bigger pins and something
like 22swg wire, rather than the 0.025" pins and 30swg wire commonly
used in electronics. All the early Dec computers, pdp8, 11 etc and vax
used wirewrapped backplanes, because it has low capacitance, lends itself
to tape controlled machine wiring and makes it easy to reconfigure the
machine.

I did some work for a company in the early 80's who free issued an electric
w/w gun etc and a big box of pre stripped wires of various lengths. They
said keep it when the work was done and am still using the tools and wire
even now, from time to time.


I am amazed they were used also in avionics. (you lost precious volume
due pins length).
I don't have many examples, but have seen an early analog fuel
control "computer" that used wirewrapping between modules. Also, the sea
slug seeker head (really) that I saw at a show. The sea slug used
an X band'ish radar rx, painted externally. The analog electronics boards
were fitted into slots in a heavy ali extrusion, with each board having
wire wrap pins at each end. Pcbs at each end of the extrusion had associated
w/w pins that wirewrapped to the board pins, with the result that there were
no connectors in the system at all, other than a few 'D' series and sma for
the rf bits. Quite an impressive piece of kit, rf head and dc servos to
control the dish in azimuth and elevation. The sort of technology you don't
see very often, unless you work in that area, but interesting and it all
adds to the knowledge base.

Apologies for the drift :8 ...

[bearfoil]

Doze I get your description. I also appreciate your great patience. I am not getting the 'language' used in ACARS. "FLAG ON". If that means it is recorded, wouldn't the MX know that? It sounds like "A Warning that is displayed on PFD has been recorded." Is that so that it can be read by Mx more eassily? As in "Speed Limit" .functionality' is lost? Or is all this just bunk airspeed data at the Peetos?

Thanks, you are a gold mine.

[RR_NDB]

Hi, syseng68k

used wirewrapped backplanes, because it has low capacitance (http://www.pprune.org/tech-log/452836-af447-thread-no-3-a-101.html#post6513366)

Being "hardware oriented" it seems they had a lot of stray capacitance and inductance with no ground plane, therefore "non controlled impedance. Just basing in my RF intuition. :8. At this time i characterized back panel daughter boards connectors using TDR reflectometers. Very interesting results. :8

Back to main program :)

Like, ChristiaanJ put:

2:11:55 FLR/FR0906010210 27933406EFCS1 X2,EFCS2X,,,,,,FCPC2 (2CE2) /WRG:ADIRU1 BUS ADR1-2 TO FCPC2,HARD

What kind of Failure is this?

[daved123]

syseng68k, you can add DEC pdp9 in the mid sixties to that list. Can't remember the wire gauge tho, and we did occasionally re-jig the wiring.

[rgbrock1]

daved128

DEC's PDP-9, the first system I worked on, used 30-gauge wire. (The wire-wrapped backplanes did anyway.)

[DozyWannabe]

It sounds like "A Warning that is displayed on PFD has been recorded." Is that so that it can be read by Mx more eassily? As in "Speed Limit" .functionality' is lost? Or is all this just bunk airspeed data at the Peetos?

Thanks, you are a gold mine.

No problem.

Now, I'm pretty sure that MX will have a lookup table to cross-reference what those brief text statements actually mean. If you read the PDF I linked, you'll find all the FCOM references to those ACARS messages and what they mean. In the case of the message you're talking about, the "green dot" display on the PFD which gives the manouvering speed and the VLs (minimum selectable airspeed) has disappeared because the airspeed information has dropped out. In this case SPD LIM means that those limiting speeds are not displayed.

If I've done my homework right, an ACARS overspeed message would be similar to the ECAM messages and would clearly be identified as OVER SPEED.

@RR_NDB:

These are the ACARS messages that are effectively maintenance-only:

2:11:49 - .1/FLR/FR0906010210 34111506 EFCS2 1,EFCS1,AFS,,,,,PROBE-PITOT 1X2 / 2X3 / 1X3 (9DA),HARD
2:11:55 - .1/FLR/FR0906010210 27933406 EFCS1 X2,EFCS2X,,,,,,FCPC2 (2CE2) /WRG:ADIRU1 BUS ADR1-2 TO
FCPC2,HARD

They're listed in the same PDF. FCOM information is given, but if I understand it correctly, the first message refers to pitot data failure, and the second refers to the same data discrepancy in the computer system itself (ChristiaanJ : note the presence in the full message of BUS, implying data transmission rather than physical wiring problem).

[daved123]

Remember adding in a - gasp - 64K ferrite core store as an upgrade.

[henra]

I would invite you to make a case for any of the other involved people making the release with precisely the data given and no other data. It looks like the data benefits AirBus, is neutral to or damages Air France, and smears the pilots' reputations. It might have been the French government. Blaming the pilots gets them off a financial hook to some degree. Who else benefits?

JD-EE

Honestly I don't know the motivation behind it.
It could simply be that they wanted to give some upfront information to the public as the interest in the causes of this accident were disproportionally high. Much higher than in any previous accident that I'm aware of.
In other accidents of comparable public interest (e.g. Concorde) a general picture about the reason transpired pretty early. So there was no need for the investigating agencies to leak anything, it was clear from the videos what roughly happened.
This case was different. It was pretty much a complete mystery for almost 2 years so the impatience for a 'rough picture' was extremely high and couldn't be satisfied by information available in the public domain.
(For that matter the first information about a bomb explosion in the Lockerbie crash was also published quite early, before the preliminiary report IIRC)

On the other hand it could indeed be that Airbus had an interest in getting information which indicates that the Aircraft was not the main culprit to the public and asked them a favor. I would not rule that out completely although I don't know what their real motivation was.

My only comment to this is that also in the second case I assume BEA would only do them this favor if they are sure that the final result will not deviate too much fron this preliminary picture.

Common guys and girls, they are Accident Investigators. This kind of people tend to do it with a passion. Otherwise you would look for a job where you earn easy money without having to deal with melted metal and burnt corpses, going through thousands of meticulous details on a regular basis.

[henra]

How would you recover from a deep stall in a twin-turbofan conventional tailplane aircraft? Do you create a lot of asymmetrical thrust to either create a big side-slip and possibly large bank angle, or even roll over if absolutely necessary? If there's nothing for the aero-surfaces to bite on what do you do?

I seriously hope you are not flying any of those!
A twin engine propeller aircraft with a conventional tail will almost 100% sure not stay in an unrecoverable deep stall.
What will be unrecoverable in almost all twins is a spin !
Therefore you DO NOT WANT TO CREATE ASYMMETRY IN A TWIN DURING A STALL !!!! It will kill you almost 100% sure !

[syseng68k]

Being "hardware oriented" it seems they had a lot of stray capacitance
and inductance with no ground plane, therefore "non controlled
impedance. Just basing in my RF intuition.
I guess it wouldn't be too well controlled, but the ttl bus drivers of the
day seemed to match wirewrap backplanes fairly well. The waveforms looked good
on a scope anyway, fwir, but bus speeds were only in the low Mhz at the time.


At this time i characterized back panel daughter boards connectors using TDR
reflectometers. Very interesting results.
That does sound interesting, though I assume that you matched the tdr source
Z with the connecter characteristics ?. Sounds like an order of magnitude or
two faster than unibus or qbus, and signals through the connector would be
significant. I still have a tdr plugin for tek 7000 series scope, though haven't
used it for a long time. 1970's technology and it can detect a 0.25" or less
piece of hardline or sma T no problem. 30pS risetime and not bad for what was
a design using 60's technology. Tek were very, very good at that time and way
ahead of the curve.

Am droning on a bit again, but, to bring back on topic, found a very interesting
discussion on tech log re aircraft testing and stall:

http://www.pprune.org/tech-log/173167-can-airliners-recover-stall.html

Definately worth a read, imho, but prepare to be disturbed :eek: ...

[infrequentflyer789]

Am droning on a bit again, but, to bring back on topic, found a very interesting
discussion on tech log re aircraft testing and stall:

http://www.pprune.org/tech-log/173167-can-airliners-recover-stall.html

Definately worth a read, imho, but prepare to be disturbed :eek: ...

Nice one, fascinating old thread. This post http://www.pprune.org/tech-log/173167-can-airliners-recover-stall.html#post1878088 is particularly notable:


also did a lot of recoveries from the stall warning, NEVER to the fully developed stall. On one occasion, the student got such a fright as the overly assertive stall warning triggered, that he applied full BACK stick, precipitating the full stall. On that day, my own full stall exposure paid big dividends. It can, and does, happen.

Hopefully, one day, pilots will receive simulator training in recognition of and recovery from the full stall. Until that day, the title of this forum should perhaps have been amended from "Can airliners recover from a stall?" to "Can airline pilots recover from a stall?"
One particularly prescient poster, or an industry doomed to repeat history until it learns from it ?

[jcjeant]

Hi,

Originally Posted by JD-EE http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/buttons/viewpost.gif (http://www.pprune.org/tech-log/452836-af447-thread-no-3-a-post6511813.html#post6511813)
I would invite you to make a case for any of the other involved people making the release with precisely the data given and no other data. It looks like the data benefits AirBus, is neutral to or damages Air France, and smears the pilots' reputations. It might have been the French government. Blaming the pilots gets them off a financial hook to some degree. Who else benefits?
A letter from the prime minister of Françe (F.Fillon)26 May 2011
« L’enquête technique, qui suppose l’étude et la comparaison de très nombreux éléments, ne fait que commencer. Le BEA a fait savoir officiellement et clairement qu’à ce stade de l’enquête aucune conclusion sur les causes de la catastrophe ne peut encore être tirée. Il a indiqué qu’il publierait le vendredi 27 mai une note d’information sur les premières constatations résultant de l’exploitation des enregistreurs de volMultiupload.com - upload your files to multiple file hosting sites! (http://www.multiupload.com/EUNSMG7ELZ)

« Soyez dans ce contexte assuré de ma pleine détermination à faire en sorte que la parole officielle de l’Etat, que relaient les Ministres compétents et le Représentant Spécial que j’ai souhaité nommer auprès des familles et des proches des victimes, demeure claire, rigoureuse et cohérente. »And after you have the Mariani statement !

Le cabinet du secrétaire d'Etat aux Transports, Thierry Mariani, l'affirme : "La responsabilité dans l'accident du Rio-Paris, en juin 2009, revient à 5 % à l'avion et à 95 % à l'équipage. Les experts ne comprennent pas pourquoi les pilotes ont redressé l'avion alors qu'il fallait piquer pour lui redonner de la portance, leurs réactions sont incompréhensiblesRio-Paris : à qui la faute ? - L'EXPRESS (http://www.lexpress.fr/actualite/indiscrets/rio-paris-a-qui-la-faute_1000516.html)

Fillon ????
à faire en sorte que la parole officielle de l’Etat, que relaient les Ministres compétents et le Représentant Spécial que j’ai souhaité nommer auprès des familles et des proches des victimes, demeure claire, rigoureuse et cohérente.

Indeed :(
remains clear, rigorous and consistent.

Note:
I let you the translation task ....

[RR_NDB]

syseng68k,

A little bit more off topic just to answer you: My motivation at that time in this issue was very high for several important reasons. Most of other engineers were "bit minded" and i realized they were designing complex circuitry with no analog background specially in areas like EMI, RFI, etc. I started my career dealing with RF (NDB´s, HF vacuum tube transmitters from PAA, etc) and i was concerned on signal degradation in their digital design of the SPC switching exchange, a very fascinating challenge for all of us. I went to the lab and dive "doing the necessary" to characterize the backplanes, connectors, etc. Was a memorizing experience. I found details (using the Tek TDR) and geometric "why´s" of "N" type connector being better than a BNC or PL259/SO239. I bring to the lab, war surplus components, from Collins radio gear, etc. from old birds. After the lab days (and nights :)) i was able to tell them what was better in their connections, etc.

Well, thanks for the link. For one addicted with K.I.S.S. design rules you can imagine how i feel with the complex (sometimes with K.I.C.S. behavior :} ) "Advanced Systems". Probably from "trauma" after working with "testability",:)

Regards and glad to hear from series 7000 and the fantastic plugins. At this time i had all HP, Tek (and few other companies) model numbers in my mind. Better than their salesmen had, just because i was using all the equipt´s (and they were just selling):)

I made all possible Z matching and a lot of combinations to leave the lab able to answer any question:cool:

[DozyWannabe]

I would invite you to make a case for any of the other involved people making the release with precisely the data given and no other data. It looks like the data benefits AirBus, is neutral to or damages Air France, and smears the pilots' reputations. It might have been the French government. Blaming the pilots gets them off a financial hook to some degree. Who else benefits?

Any chance of avoiding the conspiracy theories here? There's barely a country in the western world that produces civil airliners that hasn't learned the hard way about political/business meddling with safety concerns. We had it in the '50s when BOAC was allowed to continue Comet services despite the metal fatigue problem being neither discovered nor fixed. The Yanks had it in the '70s with the infamous "Midnight Gentlemen's Agreement" between the head of McDonnell-Douglas and the FAA. And finally our Gallic cousins had a similar controversy in the '80s over the Habsheim accident (though I suspect the remaining controversy over that one has a very different motivation than that put forward by the Airbus-bashers, not that I could ever prove it).

In every case, the system was embarrassed in public and forced to play by the rules in future. The BEA are no different - when the Air Inter A320 crashed on Mont St. Odile they made sure that they brought the NTSB in as an impartial party. IMO they've learned their lesson - give them a chance.

[Chris Scott]

bearfoil, quote:
"I had always thought the purpose of Aft Trim Tank, or even "geographic" changes to enhance aft trim were intended to add Drag, "Lift" to the tail such that the AoA of the wing could be reduced, and lower Fuel Burn. It is a slight Overall reduction in Drag, but on long haul can save buckets of dough. Was I laboring under a misconception?"
Don't think so, although you don't want to "add drag", and the tailplane never produces positive lift on a public-transport aircraft. (Note I said TAILplane: the HS on a Rutan canard does.) Less negative lift from the HS is the objective, enabling less lift from the wing, and less drag from both. As I was trying to say to DW, I know of no evidence to suggest that the cruise THS setting on AF447 was anything other than routine prior to the UAS event.

bearfoil, quote:
"So now we know the Airbus does use PITCH to control SPEED ? And does it do this with Autotrim (PITCH) with the Throttles in "manual" (A/THR disconnect)."
Presume you mean pitch TRIM? Aerodynamically, Airbuses are conventional aeroplanes with elevators mounted on a trimable horizontal stabiliser – very like a B767, but with FBW controls. When the AP is disengaged, autotrim is still available. It acts a bit like the CWS (control-wheel steering) on a DC10, for example. Like any such aeroplane, 1G flight with a reducing airspeed (and constant thrust) can only be maintained by up-elevator and/or trimming in the nose-up sense. If not, the nose drops and the aircraft starts to follow a curved trajectory at less than 1G. When this results in a steep enough descent, the speed starts to rise.
The Airbus FBW, on the other hand, maintains 1G without any sidestick displacement until – in the case of Pitch-Alternate Law – the wing runs out of lift. (In Normal Law, as witness Habsheim, the nose is lowered to prevent a stall – even with full back-stick.)

bearfoil, quote:
"Could the a/c ever have autotrim without Autothrottle?"
Most of my hand flying on the A320 was without A/THR. Never had to use manual pitch-trim except for training purposes.

DozyWannabe, quote:
"With autoflight out, the only thing that the autotrim could respond to (if the system was indeed behaving as designed) was pilot input."
Non monsieur! I respectfully suggest that you read (http://www.pprune.org/tech-log/452836-af447-thread-no-3-a-100.html#post6512770) what I carefully explained to you at Jun14/1157z, particularly the last paragraph, as well as my note to Bear herewith.

Err, by the way, agree with your comments re the BEA.

[DozyWannabe]

Hi Chris,

I did read it - what I mean by "the only thing the autotrim could respond to was pilot input" was that the autoflight system was out, ergo if the systems were functioning properly the aircraft was only doing as it was commanded by the sidestick inputs. In Alt 2 the protections are also effectively out, meaning that the computers - by design - are unable to counteract any inputs made by the pilot or make any adjustments to maintain airspeed, because that information is gone. Unless you're saying that it's possible for the FBW system to command up elevator with commeasurate THS trim to maintain G-loading in this scenario I don't see how we're disagreeing.

As you said : "In the case [DW is] discussing, it is by sidestick input". That's all I was saying.

[Chris Scott]

DozyWanabee, quote:
"Unless you're saying that it's possible for the FBW system to command up elevator with commensurate THS trim to maintain G-loading in this scenario I don't see how we're disagreeing."

That is indeed what I'm saying. If this recent understanding of mine is correct, it may be relevant to AF447, even though the BEA indicates that the PF was making pitch inputs. I don't think the loss of IAS data would necessarily alter the FBW logic in this regard. You may note that I've added a rider to my previous post.

[CONF iture]

I had always thought the purpose of Aft Trim Tank, or even "geographic" changes to enhance aft trim were intended to add Drag, "Lift" to the tail such that the AoA of the wing could be reduced, and lower Fuel Burn.
As a complement to what Chris Scott wrote, here are some FCOM and FCTM references :

http://i25.servimg.com/u/f25/11/75/17/84/af447_15.png (http://www.servimg.com/image_preview.php?i=89&u=11751784)

http://i25.servimg.com/u/f25/11/75/17/84/af447_16.png (http://www.servimg.com/image_preview.php?i=90&u=11751784)

http://i25.servimg.com/u/f25/11/75/17/84/af447_17.png (http://www.servimg.com/image_preview.php?i=91&u=11751784)

Do we Know what the THS setting was in the cruise prior to the UAS event?
The idea of the trim tank is to enable the THS to be fairly neutral.
At 29%, the CG was pretty far from the ideal 38%, but how much NU THS does it represent … As an estimate, I would go for anything between 2 and 3 degrees but I’m really not sure ... it would be something to look at the next opportunity, unless the BEA is ready to 'leak' it.

[CONF iture]

The only way autotrim is activated is if the stick is fully deflected and held there past the elevator travel limit.

the autotrim will only move the THS in Alternate Law if the limit of elevator travel is reached and the pilot continues to demand pitch-up via the sidestick. It needs to be aggressive and maintained for a period of time.
As anticipated, PJ2 never wrote anything like it.
As you don’t seem to realize what’s the function of a trim, if you have a chance, go in a flying club and see by yourself if you are able to apply a full deflection before you feel the urgency to trim.
Chris Scott and Lonewolf_50 are more diplomat than I am, but what you wrote simply don’t make sense.

What about this one :
If that hypothetical pilot (either PF or PNF) doesn't like what they see, they can disable autotrim by moving that wheel, which will engage mechanically-driven manual trim for the duration of the flight
Trim wheel has priority over the electrical control but does it 'disable autotrim for the duration of the flight' ?
Now, you won’t mind if I ask to back up that one …


A33Zab and Svarin, you make fascinating reading, Please, carry on !

[Lazerdog]

As they were descending in the the stall through 10,000 feet, the THS was trimmed up automatically. Would full forward side-stick have caused immediate stall recovery, or would the PF have to wait until the THS auto-trim caught up with nose-down trim? (How long would that take if so?) I think the THS trim has pretty high authority over side-stick elevator inputs in the whole anhederal trim scheme. Time delays would add an odd factor to the kinesthetic aspects of stall recovery. Comments?

[Chris Scott]

Quote from Lazerdog:
"As they were descending in the the stall through 10,000 feet, the THS was trimmed up automatically."
All of us are occasionally running into problems of ambiguity, due to the inherent limitations of written language. That's why the FBW design engineers have to avoid it. I'm sure you don't mean to imply that the autotrim was still changing the THS trim position as AF447 was passing 10,000ft?

The BEA Update is not entirely free of ambiguity, but it states:
"At 2h 10 min 51, the stall warning was triggered again. [...] The... [THS] passed from 3 to 13 degrees nose-up in about 1 minute and remained in the latter position until the end of the flight."

Read it yourself and draw your own conclusions, but my inference is that the 13degNU was reached at around the apogee (38,000ft) or soon after.

Lazerdog, quote:
"Would full forward side-stick have caused immediate stall recovery, or would the PF have to wait until the THS auto-trim caught up with nose-down trim?"
Short answer is: don't know. But I think we can expect that the AoA would have started to reduce immediately. Unless the THS motor stalled, which would be unlikely at such a low airspeed (low loading), the THS would have started moving immediately. I don't know its maximum rate. What do you mean by "anhedral trim scheme"? What does "kinesthetic" mean in this context?

The BEA Update indicates that the aircraft passed 10,000ft at or after 02:13:32. The rate of descent seems to have been in excess of 10,000ft/min. The process of stall recovery would have increased the ROD initially...

[FE Hoppy]

At 2 h 12 min 02, the PF said "I don’t have any more indications", and the PNF said "we have no valid indications". At that moment, the thrust levers were in the IDLE detent and the engines’ N1’s were at 55%. Around fifteen seconds later, the PF made pitch-down inputs. In the following moments, the angle of attack decreased, the speeds became valid again and the stall warning sounded again.

They had some pitch authority but didn't use it until very late and it's not stated for how long.

[Lazerdog]

Chris,

Thanks for your comments. Regarding your questions...

What do you mean by "anhedral trim scheme"?

This is the design of the aircraft enabling proper forces (moments) from the tail plane to cause to wings AOA to change and stabilize at a given angle of attack, dependent on many factors including CG, airspeed, and Center of Lift. Anhederal trim is not an often-used term, but it is important in the design of all aircraft.

What does "kinesthetic" mean in this context?

In this context, it is the effectiveness of the aircraft giving the pilot a "seat-of-the-pants" feeling of control authority. Some aircraft (for instance) have immediate pitch change upon application of stick, while others have a lumbering feeling or are heavy on the controls. Adding a time delay means that the pilot needs to learn to wait, and without any stall recovery experience, that automatic kinesthetic experience in not available.

[RetiredF4]

Lazerdog, quote:
"Would full forward side-stick have caused immediate stall recovery, or would the PF have to wait until the THS auto-trim caught up with nose-down trim?"

hris Scott
Short answer is: don't know. But I think we can expect that the AoA would have started to reduce immediately. Unless the THS motor stalled, which would be unlikely at such a low airspeed (low loading), the THS would have started moving immediately.

Again the question on what ground this believe on THS authority is founded.
The aircraft was in a stall with an AOA of around 60°. If this AOA applies to the aircraft cell, it applies as well to the two airfoils of the aircraft, the wings and the THS with minor offsets.

What AOA did the THS have during the fall from FL380? Aircraft AOA of 60° minus the 13.5° noseup trim of the THS, which gives us a THS AOA of 46.5, right? (I disregard the effect of curvature of the THS, dont know how that changes my assumption).
What kind of airfoil is working at that AOA and with what kind of outcome? If we trim the THS to full ND as necessary for recovery, the THS AOA even increases to 63.5° AOA plus the profile change due to elevator deflection.

See that nice picture in post 1817 from mm43 (http://www.pprune.org/tech-log/452836-af447-thread-no-3-a-91.html#post6507819). Just move the depicted angels to the THS!

What kind of miracle airfoil is there on the THS of the Bus? To bring the nose down its not enough to produce drag at the tail, you need a functioning (unstalled) airfoil producing lift (in this case downward ).

Remember also, the liftvector of an airfoil points basically perpendicular to its chordline, not to the relative wind. So even if the THS produced any measurable amount of lift, the main part of it would not have pointed in the desired direction.

IMHO Elevator ND or trimming the THS down, after this high AOA of 60° was established, only increased the drag of the tailplane but had no permanent effect to get the nose down to the horizon and to increase the speed as necessary.

Whereas stick NU decreased the AOA on the THS below 46.5° , reducing drag and causing some feedback to the crew (noseup input brings the nose somewhat up, but nosedown input doesn´t change anything). That would also explain the noseup input in the final moments.

I might well be wrong, just tell me where!

[Graybeard]

With the engines at flight idle, what propels the plane forward? A fully stalled wing does not provide any forward planing. Therefore, I maintain their trajectory was near vertical, and not recoverable by movement of the controls.

[RR_NDB]

Hi,

Therefore, I maintain their trajectory was near vertical, and not recoverable by movement of the controls.

Question:

Suppose an APU turbine with afterburner; Suppose it´s nozzle pointed 45° down.

How many pounds of thrust you typically need to "restore pitch" in order to start flying again in this class of a/c? To "restore a decent AoA"

A drag chute is unthinkable in an airliner. An special APU may save?

Just a theoretical question!

[badgerh]

Infreq:
Having read the article "Can airliners recover from a stall" (http://www.pprune.org/tech-log/173167-can-airliners-recover-stall.html#post1878088) I was astonished to read this extract, also from the same poster who has clearly been there, done it and got a cupboard full of tee shirts:

"Normal 'full back stick' stall testing is done with idle thrust, and stabiliser trim trimmed for Vs+10, and a controlled deceleration at 1Kt/sec until stall occurs. 747FOCAL's and my definition of a 'wind up' stall may differ, but for deliberate efforts to enter the deep stall, large UP stabiliser trim was used with large thrust settings to gain high pitch attitudes just pre-stall, and then chopping the thrust and rapidly applying full UP elevator. Disneyland offers no more exciting ride."

The actions described in the last sentence to induce a deep stall seem to be taken close to verbatim from the recent BEA report. Frightening :{

[Lonewolf_50]

Lazerdog: As they were descending in the the stall through 10,000 feet, the THS was trimmed up automatically."
Chris: All of us are occasionally running into problems of ambiguity, due to the inherent limitations of written language. That's why the FBW design engineers have to avoid it. I'm sure you don't mean to imply that the autotrim was still changing the THS trim position as AF447 was passing 10,000ft?
Lazerdog: "Would full forward side-stick have caused immediate stall recovery, or would the PF have to wait until the THS auto-trim caught up with nose-down trim?"
Chris -- Short answer is: don't know. But I think we can expect that the AoA would have started to reduce immediately. Unless the THS motor stalled, which would be unlikely at such a low airspeed (low loading), the THS would have started moving immediately. I don't know its maximum rate.

Chris, I think some of the ambiguity that has people concerned is that even with the THS being ~13 deg at apogee, other info from BEA based on FDR describes pilot nose down inputs at various times during the event, with apparently little or no influence on the THS position. (Ah, I see RetiredF4 has made an analysys that makes some sense to me).

Concern -- were control surfaces unable to respond (??).

Concern -- without creating an error message, (which a stalled THS motor would generate??) did properly operating functions (alt law speed stability, which you addressed earlier) or Abnormal Attitude law (at present conclusion is that it wasn't active) provide trim commands in opposition, or as a "correction," to the nose down commands? I would think it wouldn't, but if Airspeed sensing is out the window, what is speed stability using as a reference to direct an assist toward "better" nose pitch?

Since pilot can override the speed stability functions, Lazerdog's kinesthetic comments IIRC don't come into play with side stick forces, but can factor in to "seat of the pants."

(In unusual attitudes, in night instrument conditions, descending in stall, the "seat of the pants" fast becomes a false reference ...)
Idea: pilot is putting in nose down input, stability is either over helping (doubtful, as pilot overrides) or sensing speed at the other extreme, so that as soon as pilot input stops, it helpfully moves THS in the wrong direction. That (if the THS isn't stalled) might be felt as turbulence, or not at all if there is already turbulent air as the environment.

But that idea may be nonsense.

There are still nose down commands from the sidestick of unknown duration. RetiredF4's post finally puts a finger on something I was trying to ask: were they at some point futile? :confused:

Or, were the pilots reverting to back stick inputs to get the aircraft to respond at all. (Seen something similar to that in spin training with a pilot mentally behind the aircraft ... ) RetiredF4's post explores that nicely.

The skeletal nature of the reported timeline (needs a bit more meat on the bone, hopefully to come in time) leaves the question of "why didn't nose down commands (such as they were) change the THS position from the reported ~13 deg from apogee to the surface?"

If I am saying roughly what you are saying, my apologies for the repetition.

Back to one of our other posters, who described a while back how long it took for the nose to respond in stall recovery ... per lazerdog's kinesthetic comments. I will add to that thought the sense of tempopral distortion that frequently arises during disorienting events.

I've experienced it myself, and it ain't pretty.

By temporal distortion I mean a sense of it all happening in slow motion, where the sense of time passage is lost. This can influence actions and thoughts. Sample:

"I pushed the stick, nothing happened, I need to do something else" so another control input is made.

The decision/act cycle (or the OODA loop) happens in compressed time scales (fractions of a second) as compared to normal flying of a passenger jet, where smooth and deliberate is the normal pacing. (OT: That smooth and deliberate approach is much appreciated by the passengers, I can assure you! :ok: )

[Graybeard]

From the above, it seems fuel transfer to the tail is automatic once in cruise. There is no mention in the BEA info that fuel was manually transferred forward, so how did the CG get to 29% in latest BEA note, from 37% in initial reporting?

37% CG would be a big difference from 29% in manual pitch control. It's real easy to over control with aft CG.

[syseng68k]

Inrequentflyer, 789

One particularly prescient poster, or an industry doomed to repeat history until it learns from it ?
Another quote from Collinson:

"The high integrity, full authority FBW can provide the automatic
stabilisation required to enable a civil aircraft to be designed
with reduced stability margins under certain loading configurations
and flight conditions. This enables a lighter aircraft to be produced
with an increased performance and payload capability compared with a
conventional design".

Weasel words. Saying that stability can be traded against cost and
performance, but are current designs going too far in this respect ?.

Note: "reduced stability requirements". This implies that when
the systems gives up, the aircraft will be more difficult to control
manually, than a non fbw aircraft. I think someone already mentioned
elsewhere that the a/c would be very sensitive to control inputs. Just
what's needed when confronted with an emergency situation with ambiguous
or unreliable data from the flight control systems and a crew with no
training or experience of such conditions.

On balance, correct me if wrong, once AF447 stalled, only a test pilot
with a lot of experience would have had any chance of recovery...

[GarageYears]

Suppose an APU turbine with afterburner; Suppose it´s nozzle pointed 45° down.

How many pounds of thrust you typically need to "restore pitch" in order to start flying again in this class of a/c? To "restore a decent AoA"

A drag chute is unthinkable in an airliner. An special APU may save?

I suppose the lack of additional information leads to idle minds wandering off into "la-la land"... the idea of something as dangerous as an afterburner equipped APU with a nozzle at 45 degrees down, well, let's just say I have horrible visions of aircraft tumbling end-over-end due to inadvertent engagement. Assuming such a monstrosity were fitted (and at what cost), how often would this find any application and how well might it function?

Personally, I suspect the great cost of the extra training such a dangerous devices would require, would be far better spent on upset training, either by putting regular line-pilots into a glider or acrobatic aircraft for 4+ hours a year (pick a number), or funding enhanced simulator development to include the extended stall regimes (and before the masses jump down my throat read this -> http://www.idt-engineering.com/image/ICATEE_Master_Plan_25JUL09.pdf ).

[Graybeard]

Just yesterday I talked with a retired aero engineer who had worked on the design of the MD-11 THS. He said its small size was predicated on the assurance (from Honeywell) that the LSAS, Longitudinal Stability Augmentation System, would meet 10 <-9 probability of No Undetected Failure. It didn't, of course, and many MD-11 crashes have been related.

Could the A330 be operating on similar assumptions?

[DozyWannabe]

As anticipated, PJ2 never wrote anything like it.

I oversimplified the description, but it seemed pretty clear to me that with autoflight off, the only thing that can move the THS is pilot input, PJ2 agreed with that.

As you don’t seem to realize what’s the function of a trim, if you have a chance, go in a flying club and see by yourself if you are able to apply a full deflection before you feel the urgency to trim.
Chris Scott and Lonewolf_50 are more diplomat than I am, but what you wrote simply don’t make sense.

No need to be insulting, I know what the function of aircraft trim is. In normal circumstances that's what it's used for. Under Alt law, the autotrim is designed to follow the pilot's sidestick commands. This gives the pilot regular trim control through the sidestick, but has the additional side-effect of effectively giving them full pitch authority with little or no interference from the computers.

Chris has been kind enough to state that his "G" theory is just that - a theory. I'll try and track down some information over the next couple of days to confirm or refute that theory - I've also sent some PMs to people who might know.

If you want to get personal, I could say that at least I'm not trying to defend a man guilty of the manslaughter of three people who to this day is still arrogantly unrepentant about not taking responsibility for those deaths.

Trim wheel has priority over the electrical control but does it 'disable autotrim for the duration of the flight' ?
Now, you won’t mind if I ask to back up that one …

A330 Flight Deck and Systems Briefing (http://www.scribd.com/doc/30183769/A330-Flight-Deck-and-Systems-Briefing)

Page 5.13

The control wheels are used in case of major failure (Direct Law or mechanical back-up) and have priority over any other command

The implication is that manual trim will have priority and can be used for the duration of the flight if the pilots are not happy with what autotrim is doing. Svarin claimed in an earlier thread that some airlines train pilots to avoid use of the wheel for that reason (which IMO is a dreadfully myopic practise).

[JD-EE]

JD-EE
Quote:
Originally Posted by JD-EE http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/buttons/viewpost.gif (http://www.pprune.org/tech-log/452836-af447-thread-no-3-a-post6509851.html#post6509851)
Kinetic energy is 1/2 mV^2. Potential energy is mgh. So the mass washes out of the equation. So a 3000' climb would give "gh" = 1/2 v^2 = 96000 ft^2/s^2 equals about a 438 '/s velocity change or about 300 MPH.

I am probably being a bit thick, but does this relate to the aircraft in question and if so, are you saying the aircraft lost 300mph in its climb?
Roughly speaking - I cheated on the math somewhat. Rudderrat posted the more correct equation from which mass drops out. I presumed a drop to zero velocity which is a cheat. It gives the general idea, though. A plane drops a staggering amount in the 3000' climb with no additional power input through the energy tradeoff.

Since we're working on the difference between the squares of two velocities it does vary. I'm not sure of the actual velocity of the plane to apply this to the AF447 case. (Too lazy to look up speed of sound at 37000'.) If the plane's physical speed was around 300MPH it'd have been dead stopped. If it started at 475 MPH the drop is probably around 120 MPH.

Again, the key takeaway is that the mass isn't part of the equation until you worry about flying bricks vs flying pillows of equal size and shape.

[GarageYears]

Trim wheel has priority over the electrical control but does it 'disable autotrim for the duration of the flight' ?
Now, you won’t mind if I ask to back up that one …

But you don't!

Using the TRIM WHEEL does NOT disable autotrim for the duration of the flight.

What it does is override the instantaneous demand and allows the direct pilot input to take effect. The computers continue to track the trim state.

[DozyWannabe]

@GY - Unless I'm mistaken, they track it, but they don't change it.

[JD-EE]

icehart says, "(hope that does not apply to Airbus)".

Sadly, it does. Solder pot connections don't work very well over time. Crimps work very well over time.

To see why solder pots (not wires wrapped around terminal lugs or the like) fail find a 6" or so length of 1/16" or solder. Secure it around a heavy spoon by one end of the solder. Secure the other end of the solder to a door knob or the like. Let it percolate a few days. Odds favor the spoon waking you up at night as it clatters to the floor when the stretched solder breaks. The weight of the spoon will stretch it. (You may have to adjust the size of the spoon so it doesn't visibly stretch as soon as the weight of the spoon is on it.)

With old bar solder you simply clamped one end of the bar to the table top with the other end hanging over. It would become Dali-esque over time. The 1/8" solder I had at one time would stretch itself and break with only its own weight on a 3' length given some time.

The magic of the crimp is the tight mechanical connection that actually cold welds the two objects, wire and connector pin, together. Wire wrapped around terminals for a secure mechanical joint also performs well because of the good mechanical joint. Solder pot connections have no mechanical strength to speak of. So over time the connection can break if there is any stress on it.

[rudderrudderrat]

FCOM 1.27.30 ALt LAW
"In flight, the alternate law pitch mode follows a load-factor demand law much as the normal law pitch mode does, but it has less built-in protection (reduced protections)."
Originally Posted by DozyWannabe
I oversimplified the description, but it seemed pretty clear to me that with autoflight off, the only thing that can move the THS is pilot input,

I don't think so.
With stick free, the aircraft will attempt to fly 1G (either level or climbing etc.) and if the speed is reduced the stab will be auto trimmed to more nose up aircraft attitude.
(Modified Attitude stable flight law rather than Speed stable flight law.)

[Lonewolf_50]

From GB's link:
Loss of control following an upset is the largest single cause of airline crashes and fatalities.

Stick shakers and pushers are warnings of last resort, and pilot attitudes or experience may lead to such indications being ignored or wrongly attributed, resulting in no or incorrect actions.
Training issue, which appears to be what the paper intended to address.
Pre-stall indicators do not provide sufficiently timely or accurate cues to alert the crew to a developing situation. More flexible types of indicators, which can be integrated into primary cockpit displays, have been developed which provide dynamic information on the aircraft’s attitude and velocity with respect to its normal flight envelope. These could provide the cues needed to alert pilots to developing situations, and to provide guidance on aircraft handling and performance during recovery manoeuvres.
I wonder how many pilots disagree with that bolded part? This bit looks toward tools, rather than training ... but training (personal bias here) is the higher payoff target. You get another tool, you just added to your training requirement. :cool:

[DozyWannabe]

I wouldn't take this as read, but here's an interesting post from someone purporting to be a former A330 pilot on another forum. (emphasis mine)

Ok, as the aircraft decelerates from say, 250 knots to 210 knots from a level flight with no bank, the aircraft starts with a given pitch of x, and a 1G corrected for pitch. As the aircraft decelerates, the full deflection of the sidestick (which should normally give you a load factor of +2.5G) will not be able to provide you such G load. So, as the speed decreases, the command is no longer neutral stick=1G, but it become neutral stick=0 pitch rate. This means that you start having a ever so slight change in V/S. It is almost not noticeable, and as a matter of fact, most pilots new to Airbus may not even notice that they are slowly correcting the pitch to maintain level flight (they just actually do it without noticing because it is intuitive for a pilot to do this as an aircraft decelerates in level flight, and in the airbus this corrections are very minute compared to a conventional aircraft). Yes, techinally you wouldn't be maintaining exactly 1G, as an increase in V/S (decent) would translate to a change from 1G to something less than 1G (almost negligible in my humble opinion). Sorry for the confusion. The bottom line is the aircraft will switch from G-factor command with the sidestick deflection to pitch-rate command with the sidestick deflection as speed reduces.

There's some other interesting stuff there, link below.

Air France 447 - On topic only! - Page 60 - JetPhotos.Net Forums - The Friendly Way to Fly (http://forums.jetphotos.net/showthread.php?t=49818&page=60)

[HazelNuts39]

As they were descending in the the stall through 10,000 feet, the THS was trimmed up automatically. Would full forward side-stick have caused immediate stall recovery, or would the PF have to wait until the THS auto-trim caught up with nose-down trim? (How long would that take if so?) I don’t think that stall recovery could have been immediate. With the aircraft “deep” into the stall (AoA >40 degrees ?) it must be pitched down over a considerable arc: 10, 20 or 30 degrees, would that take 5, 10, or 15 seconds? I don’t know, but I believe one should think in terms of those delays.

Perhaps the graphs posted earlier would help to answer questions about AoA and pitch.
The green line in Figure (https://docs.google.com/leaf?id=0B0CqniOzW0rjM2Q3NTE3YTItOTI2MC00YWY1LWJhM2YtNDI3Yzk 4ZTMzNTMx&hl=en_GB) 1 shows the total energy (expressed as the equivalent FL) at five instants at which the BEA update provided altitude and airspeed. Total energy is the sum of:
Potential energy = m*g*h, and
Kinetic energy = 0.5*m*TAS^2,
where m=mass, g=acceleration of gravity, and h=height.
The red line shows the vertical acceleration assumed to calculate the actual FL (shown in blue), by integrating vertical acceleration to obtain vertical speed, and integrating that again.

Figure 2 (https://docs.google.com/leaf?id=0B0CqniOzW0rjYjlmMDk5MWYtOGUzMy00MmUzLThmOGUtNjMwYWF lOTVkNmEx&hl=en_GB&authkey=CL_l_eQN) shows the vertical speed and altitude, and also the airspeed calculated from the kinetic energy, i.e. from the difference between altitude and total energy FL shown in figure 1.

Figure 3 (https://docs.google.com/leaf?id=0B0CqniOzW0rjZGZiMjlmZDQtOTIxYy00MDgzLTk4NDgtY2E1YzN jYzcxNzZm&hl=en_GB&authkey=CIrjtuEJ) shows the air-based flight path angle calculated from TAS and vertical speed, and the AoA that corresponds to the lift force that would produce the vertical acceleration at the calculated CAS. The pitch angle is then the sum of FPA and AoA. The two red nearly parallel lines show the alpha-max for the Mach-number at each instant (full line), and the stall warning threshold (dotted line).

How does one recover from a stall without reliable airspeed and without AoA display?

AP and A/THR disconnected when one or more pitots iced up at 2h10min05 at FL350 and M=0.8. Less than one minute later the airplane’s climb peaked at FL380. The airplane stalled some seconds earlier, and the PF apparently made only a half-hearted attempt to prevent that. His pitch-down input reduced the pitch to about 7 degrees up, and the v/s from 7000 to 700 fpm. Maybe if he had stopped the rate of climb, and reduced pitch to below 5 degrees, that would have been enough to prevent stalling. Given the inadequate control commands in that first minute it is perhaps unlikely that, even if the PF had been aware that the was in a fully developed stall, he would have made the more agressive commands that were needed for recovery from “deep” into the stall.

The inconsistency between speeds 1 and 3 lasted less than one minute in this case, but in one documented cases of UAS as much as 3 minutes and twenty seconds. So I asked myself: how does one recover from a stall without reliable airspeed and without AoA? I would think that the proper action would be a determined nose-down push, maintained until the stall warning stops, and then trying to maintain an AoA on the edge of s/w, gently allowing the nose to raise until s/w occurs, then a small nose-down correction to silence it, etc., until back in approximately level flight at a reasonable pitch attitude.
EDIT:: Can anyone be expected to do that succesfully without being trained for that eventuality?

[HeavyMetallist]

@RetiredF4: Your analysis of the likelihood of recovering from a fully developed stall is based on some flawed assumptions, principally that a stalled aerofoil has "stopped working". Lift coefficient doesn't just fall to zero after the stall AoA is reached, it falls gradually (and may even have a second peak that's not that far off the stall value). At 60 deg AoA you may still have a lift coefficient half the primary stall value, so a stalled HS can still be generating a lot of lift. In addition the wing pitching moment (nose down) typically increases significantly with AoA post-stall. In principle a conventional design is still recoverable, given reasonable lateral control and enough height.

[MurphyWasRight]

I am probably being a bit thick, but does this relate to the aircraft in question and if so, are you saying the aircraft lost 300mph in its climb?


JD-EE:
Roughly speaking - I cheated on the math somewhat. Rudderrat posted the more correct equation from which mass drops out. I presumed a drop to zero velocity which is a cheat. It gives the general idea, though. A plane drops a staggering amount in the 3000' climb with no additional power input through the energy tradeoff.


For those having a hard time beleiving a massive (true) speed drop from the climb consider a cart on a roller coaster going fast at the bottom of the first drop, as it reaches the top of the next hill it's velocity drops to close to 0 then accelerates again as it goes down.

The a roller coaster cart has no thrust and less friction/drag losses than an airplane however the principle is the same: trade speed for altitude.

Note, ignoring drag no energy is "lost" just converted from kinetic to potential, at the top of climb most of it is still available to convert to speed if the nose is pointed down.

[bearfoil]

syseng68k

You mention a very important part of the puzzle. At the critical time of a/p drop, the PF had a sensorial challenge. I believe he read the panel and made corrections consistent with his overall and immediate assessment. If the a/c is in ROLL Direct, but with Trimming Pitch, his ability with the ailerons will need to be immediately adjusted to inputs with Elevator.

The pic supplied by Machaca of the engineer on the ladder working on the RCU shows the massive HS and its actuator jack screw. A/C operate in three planes, and when one starts reacting substantially differently when it still needs to be used in co-ordination with the others can cause that focus you note.

you say:

"...Note: "reduced stability requirements". This implies that when
the systems gives up, the aircraft will be more difficult to control
manually, than a non fbw aircraft. I think someone already mentioned
elsewhere that the a/c would be very sensitive to control inputs..."

How often did the pilots train to the discrepancy in "touch" to Roll compared with Pitch? How necessary was the Rudder, if at all, to settle the Yaw produced by Roll excursion? I believe firmly the accident began at loss of a/p, and the corrections input by PF. It is very easy to entertain getting a bit behind, which makes it not difficult to question whether they caught up, and if not, perhaps the a/c and Pilots started down different paths? In a general way, I think this will be the fulcrum of the findings.

Reading the A320 thread (Unreliable Air Speed Flaw), there simply seems to be an uncomfortable lack of understanding between crew and a/c in off normal regimes.

Lonewolf Re: Boyd. Coram makes mention of very high drag in ACM, in his biography, which has an excellent Index.

Are you sure aircrews should study OODA? With patience and calm being part of the Air Bus check list, how will you fold AGILITY into the Loop?

[Neptunus Rex]

Graybeard

Automatic fuel transfer normally starts at FL 255 in the climb and FL 245 in the descent. The CG position is monitored continously and fuel transferred to give optimum CG for best fuel economy.

However, you don't get something for nothing. At 205 tonnes, compared with 29%, a CG of 37% will give a reduced Buffet Margin of more than Mach 0.02.

Fuel can be transferred forward at any time by the pilots using a switch on the fuel panel.

[RR_NDB]

GY,

I suppose the lack of additional information leads to idle minds wandering off into "la-la land" May be this is happening with other people


I am just asking the required thrust (and if this could "save").

I agree in general with the other comments you made.

I just would like to known if a typical APU class turbine could fit the thrust requirements (augmented) or if we would need much bigger ones for the task.
It´s just a "quantitative" question.

[HazelNuts39]

At 205 tonnes, compared with 29%, a CG of 37% will give a reduced Buffet Margin of more than Mach 0.02.You sure? I thought it was the other way round.

[JD-EE]

RR_NDB

Digital signals had no problems with wire wrap connections in the 60s and 70s. That was one of the ways Burroughs built some of their mainframes in that era. I bet the RF was basically contained on one card and brought down to a rather low frequency or to sampled data before it was shoved out onto the wire wraps. OR the cards were connected via SMA for the RF connections.

I saw a lot of that in the bad old days. (And if wrapped just a tad tight vibration was unkind to the wire wraps because of the inherent nicks in the wires on the square edges of the posts.)

[Lonewolf_50]

HazelNuts39, is the pitch angle trace in figure 3 from the FDR released info (so far)? How confident are you of pitch angle to timeline synchronization for your graph?

[RR_NDB]

JD,

I saw a lot of that in the bad old days:=

In the good old days :) the wire wrap indeed was a very good approach.

About wiring issues, are you familiar with Kapton issue?:}:E

This is IMO the real monstrosity.

[Lonewolf_50]

Bear, the A in OODA is Act, not Agility.

For those unfamiliar, OODA is Observe, Orient, Decide, Act

You then go back to Observe, hence the loop. Your loop is a continuous process until the point where what you observe makes you decide to stop acting. At that point, in theory, you are at equilibrium, or have achieved the desired state of whatever it is you are doing, or trying to do.
Are you sure aircrews should study OODA? With patience and calm being part of the Air Bus check list, how will you fold AGILITY into the Loop?
bear, FFS, OODA describes what pilots DO when they fly.

Your instrument scan and your control inputs on a hand flown ILS or VOR in crap weather is a perfect application of OODA in flying. You have desirerd performance parameters (airspeed, altitude, position, course, heading, track, descent rate, glide slope, etc) and you make constant small corrections until you have iced the heding, power, nose attitude, trim, etc, to achieve the desired glide slope on course, on speed, needles centered, until MDA or DH and you Observe the runway, decide to land, or To Go Around. (Or you decide to cheat down a few feet to take a peak below mins and maybe it all ends in tears ... :{ )

OODA came from a pilot, Boyd. No surprise, since it is what pilots do. He gave it a name. He applied it to dogfights, a similar process to the above: run through the OODA loop faster than your opponent (get inside his decision cycle) until you get into that sweet spot for Fox 2, and shoot.

[RR_NDB]

JD,

icehart says, "(hope that does not apply to Airbus)". Sadly, it does.

Where? Cabling? System Interconnections? Are you concerned with a/c aging?

Did you see how they soldered WWII internal radio wiring gear, against a/c vibration? For example, the soldering of BC348´s, ART13, etc. Practically zero chances to fail. (Despite nearby dynamotors, etc,)

[forget]

What with private conversations on wiring it's becoming harder to remember just what this thread is really about. :suspect:

[sensor_validation]

@HazelNuts39 (http://www.pprune.org/members/305001-hazelnuts39) re http://www.pprune.org/tech-log/452836-af447-thread-no-3-a-103.html#post6515113

Is it possible to deduce from your great graphs at what point the zoom climb becomes 'ballistic'? Strikes me that a some point before the apogee airspeed and pitch wouldn't be be able to generate enough lift for level flight - and the only way out would have been a carefully managed pitch down and controlled descent past the apogee. Was FL375 @ M0.68 sustainable? Guess need to make assumptions about engine thrust and response time if not already full.. At what point on your graphs was/should the stall warning be triggered?

It was never clear to me exactly how the A340 airprox zoom climb was successfully recovered - pilot or AoA protection avoiding the stall warning using full thrust and pitch down?

[syseng68k]

Did you see how they soldered WWII internal radio wiring gear, against
a/c vibration? For example, the soldering of BC348´s, ART13, etc.
Practically zero chances to fail. (Despite nearby dynamotors, etc,)

More radio :8. I too had a mispent youth, starting around age 11 building s/w
valve radios and well remember command sets, hro, R1155 etc. The soldering
procedure was different than that for bucket style connectors though. Wires
and parts were first fed through a hole in the tag or valveholder, before
being wrapped round the tag at least once to make a good mechanical joint before
soldering. Such soldered joints are very reliable, especially when done by a
dedicated (as they were then) and skilled workforce who took pride in doing
the job right. The inspectors even dabbed paint spot on every joint in those
days in some cases, unheard of now. The wire was often cotton covered,
cable harnessed and tied down, all of which absorb vibration quite well.
Larger components, such as caps, chokes and power resistors etc, were nearly
always screwed down to the chassis before wiring. The command sets in particular,
were beautifully lightweight engineered, with mica sealed components and
invar plates used in the tuning capacitor for stability.

In the states in 1977, flew in a DC3 between cities at one point and could
not believe it when I went up front and saw a rack full of command receivers
and associated transmitters etc, in an alcove just behind the crew. All the
black crackle paint and smell of hot valves and motors took me back several
decades :)...

[Chris Scott]

RetiredF4,
Thanks for your interesting post (http://www.pprune.org/tech-log/452836-af447-thread-no-3-a-102.html#post6514873), and for drawing my attention to the recent contributions of mm43, A337ab, and PJ2. Must admit that, since reading completely the deluge of about 50 pages of posts in the first four days – much of it rubbish – I've only been reading bits here and there until I happened to spot a significant typo in Smilin_Ed's pertinent post yesterday. (My own response (http://www.pprune.org/tech-log/452836-af447-thread-no-3-a-9.html#post6477446) to the BEA Update on May27/2011z had provoked no PPRuNe feedback.)

You make a strong case for the possibility that the deep stall from about FL350 in the descent (AoA +40) might have been sans-issue (even disregarding the height required for any recovery). gums and others have talked about the pitching-moment problem on the previous thread, and I guess that's the essence of your proposal. Like a THS movement in the nose-down sense, down elevator would itself increase the already positive AoA of the THS, whose aerofoil was producing lift in the opposite direction to that for which it was designed. Can we assume that an increase in its AoA from +40 would decrease the vertical component of its lift? Probably.

On the other hand, at the FL380 apogee (pitch and wing-AoA +16), the THS AoA would have been "only" +3 (already producing lift in the wrong direction). At that stage, therefore, there was still a possibility of pitching the nose down with forward stick. My expectation that, with full forward stick, "the AoA would have started to reduce immediately" seems to be justified up to that point – and perhaps a few seconds longer.
An irony of the BEA Update is the way they are confident enough to state AoA data for moments in time when the FBW system had probably ruled the data invalid on the basis of (false) low-airspeed indications.

One possible explanation for the PF's apparent reluctance to try and pitch down before the deep stall is, as I suggested on May27, that his (unrecorded) ASI might have been over-reading. Later, about 20 seconds after passing the cruise altitude (FL350) in the descent, he said "I don't have any more indications."

At that stage in the descent, with wing AoA not quoted, but probably over +40, the BEA reports that "the PF made pitch-down inputs. In the following moments, the AoA decreased..." Was that merely coincidence?

[ChristiaanJ]

RR_NDB....I bet the RF was basically contained on one card I remember nifty bits of thin coax that could be wire-wrapped, and that kept the "RF" (bus and clock frequencies) more or less where they belonged.

[MurphyWasRight]

Quote:
Originally Posted by JD-EE http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/buttons/viewpost.gif (http://www.pprune.org/tech-log/452836-af447-thread-no-3-a-104.html#post6515161)
RR_NDB....I bet the RF was basically contained on one card


I remember nifty bits of thin coax that could be wire-wrapped, and that kept the "RF" (bus and clock frequencies) more or less where they belonged.



Also common for higher frequency/critical nets was the use of twisted pair with one side wrapped to nearby ground pin. This worked fairly well up to 30Mhz or so.
I did manage to get a 66Mhz clock line to behave by slipping a tiny ferrite core over the driver pin before connecting the wire but that was definatly at the limits.

Another reason wire wrap worked fairly well was that the boards had solid ground and power planes that provided good decoupling and return paths. A common "newby" mistake was to carefully lay all the wires in neat XY rows, this resulted in really bad crosstalk, the best bet was to use direct routing and avoid parrallel runs.

As I recall the original Cray super computers used WW twisted pairs for a lot of interconnect, all of carefully specified lengths so signals would line up as desired.


Thread No 4 continues Here. (http://www.pprune.org/tech-log/454653-af-447-thread-no-4-a.html)