AF447 Thread No. 3
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?
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.
Last edited by henra; 14th Jun 2011 at 20:52. Reason: corrected worst typo's
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?
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 !
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.
and inductance with no ground plane, therefore "non controlled
impedance. Just basing in my RF intuition.
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.
reflectometers. Very interesting results.
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/17316...ver-stall.html
Definately worth a read, imho, but prepare to be disturbed
...
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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/17316...ver-stall.html
Definately worth a read, imho, but prepare to be disturbed ...
discussion on tech log re aircraft testing and stall:
http://www.pprune.org/tech-log/17316...ver-stall.html
Definately worth a read, imho, but prepare to be disturbed
...
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?"
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?"
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Hi,
A letter from the prime minister of Françe (F.Fillon)26 May 2011
Multiupload.com - upload your files to multiple file hosting sites!
And after you have the Mariani statement !
Rio-Paris : à qui la faute ? - L'EXPRESS
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 ....
Originally Posted by JD-EE 
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?
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?
« 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 vol
« 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. »
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 incompréhensibles
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 ....
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Tek(tronix) TDR and edge connectors characterization
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
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
Last edited by RR_NDB; 15th Jun 2011 at 02:58.
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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?
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.
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 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.
"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 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.
Last edited by Jetdriver; 15th Jun 2011 at 01:13.
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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.
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.
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.
"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.
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Originally Posted by bearfoil
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.
Originally Posted by Chris Scott
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.
The idea of the trim tank is to enable the THS to be fairly neutral.
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Originally Posted by DozyWannabe
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.
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 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 :
Originally Posted by DozyWannabe
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
Now, you won’t mind if I ask to back up that one …
A33Zab and Svarin, you make fascinating reading, Please, carry on !
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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?
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...
"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...
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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.
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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.
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.
THS the stall
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?"
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. 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!
"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.
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.
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. 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!
Last edited by RetiredF4; 15th Jun 2011 at 13:13.
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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.
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Augmented special (APU) turbine
Hi,
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!
Therefore, I maintain their trajectory was near vertical, and not recoverable by movement of the controls.
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!
Last edited by Jetdriver; 15th Jun 2011 at 18:52.
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Infreq:
Having read the article "Can airliners recover from a stall" 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:
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 
Having read the article "Can airliners recover from a stall" 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."