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AF 447 Thread No. 5

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AF 447 Thread No. 5

Old 12th Jul 2011, 16:56
  #161 (permalink)  
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PJ - having never handled a side-stick I have no idea what a 'normal' manual input would be to maintain level flight, but 3-4 cm seems excessive to me, and certainly 6" on a Boeing yoke would raise my eyebrows as PNF. Would you expect that as a 'corrective' input?

I disagree on the 200t being immaterial - you speak of momentum - yes, 200t of it to get moving upwards. It does not matter what the steady state S&L match is, you still have to start the elephant moving upwards from his seat!

The more times I read the interim, the more unlikely the whole scenario becomes - at some indeterminate time after 2:10:16 a climb begins. The next 'fix' we have is at :51 with a stall warning AFTER the climb has been 'killed', so we assume that around 30 seconds or less of 7000fpm happened (probably about right for the height gain) during which NOSE_DOWN inputs are the only ones mentioned. So, the a/c must have pitched fairly rapidly to climb pitch to do what it did (and equally 'fallen out' or bunted over equally rapidly at the top) and can we assume then that it was pitching nose-down in response to the elevator input for several seconds?. Do we have any idea of the 'g' required for this pitch up into the climb? I see 1.75g quoted as an over-speed FCS 'increase' in applied PF input. Are we close?
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Old 12th Jul 2011, 16:59
  #162 (permalink)  
 
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JD-EE:

I "think" what I meant was that a ND input would still come out NU and an NU input would also be an NU input. Whether they reversed as gums has said can happen, I don't know. I don't THINK the charts showed a full reversal even to the level that ND was more NU than an NU input. All I remember is that it looked like both resulted in NU type motion.
Then stop THINKING and read.

Look, the damn text from BEA states that pitch authority was STILL working well in the descent:

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.
The only real information we have is in the ?BEA note, so stop making up fantasy land la-la imaginary stuff. I don't understand the need or necessity to be doing this.

Seriously, making up cr@p doesn't make it real.

The aircraft RESPONDED to ND with ND. In the stall. OK....?

Sorry for the hard language, but this is becoming increasingly frustrating.

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Old 12th Jul 2011, 17:06
  #163 (permalink)  
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BOAC

Would the Pitchup to that roc be easier to entertain if the a/c had begun the rotation in NU (but level) flight to begin with? Were the PF's inputs in any way additive to an existing state? We do not know what the attitude was at 2:10:16. Or is BEA's "Ten Degrees" a clue? For me, the dynamic nature of this twenty second picture is difficult to grasp. It will help immensely, I trust, when BEA releases all the Data.
 
Old 12th Jul 2011, 17:12
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We need the conversation record !

So long as the BEA refuses to deliver the contents of the CVR, we will only lead us astray in trying to understand what has happened.

Il is urgent that the BEA make public the whoole raw CVR and DFDR .

Aviation safety is a requirement for an modern aviation.

Transparency is essential to improve flight safety.

Thank you for supporting my request.
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Old 12th Jul 2011, 17:21
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Look, the damn text from BEA states that pitch authority was STILL working well in the descent
There's ample evidence in reports linked to in the previous thread to support the facts reported so far by the BEA that nose-down pitch control would remain effective even when the mainplane/tailplane were stalled. Why some people persist in believing that stalled == totally ineffective is a mystery.
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Old 12th Jul 2011, 18:02
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Hi HeavyMetallist,

Why some people persist in believing that stalled == totally ineffective is a mystery.
Please could you explain the forces acting on the tail during the stall for me?

Normally, the elevator and stab produce a down force at the tail. (to balance the nose down couple with the c of G being forward of the Centre of Lift).
During the stall, with an angle of attack of about 45 degs on the elevator and Stab, the forces on the tail must have been upwards. If not - then I don't understand why.

Please explain how holding full back side stick kept the attitude at around 15 degs until impact.
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Old 12th Jul 2011, 18:04
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Originally Posted by roulishollandais
So long as the BEA refuses to deliver the contents of the CVR, we will only lead us astray in trying to understand what has happened.

Il is urgent that the BEA make public the whoole raw CVR and DFDR.
Why should they? No other accident investigator has this demand made of them. Are you another of Norbert's disciples?
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Old 12th Jul 2011, 18:17
  #168 (permalink)  
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Both of you are wrong, imho.

Any data gathered in an investigation into commercial carriage that involves Death or substantial commercial Loss must be made available to those involved, and to those who are affected, either directly or indirectly.

Some discretion with personal grief must be allowed for, when it is not directly appurtenant to the accident.

Commercial Carriage (Travel) is a CONTRACT. A CONTRACT that disallows disclosure of material bearing on the CONTRACT is not a legal CONTRACT.

Witholding pertinent material of any description that bears on the ability to perform, is a species of FRAUD. I purchase a Ticket (Contract) and I am not aware of the dangers inherent therein, by design, violates the DUTY of CARE implicit therein. This can be waived, by me, a right that is alienable, (removed). Disclosure is the foundation on which the contract reposes. Secrecy is for subjects, not citizens.
 
Old 12th Jul 2011, 18:24
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GarageYears
Look, the damn text from BEA states that pitch authority was STILL working well in the descent
BEA
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
HeavyMetallist
There's ample evidence in reports linked to in the previous thread to support the facts reported so far by the BEA that nose-down pitch control would remain effective even when the mainplane/tailplane were stalled. Why some people persist in believing that stalled == totally ineffective is a mystery.
To say the truth, we dont know or at least nobody can know from the BEA stuff. I f BEA was sure at the moment of the statement that the reduction of the AOA and the validation of the speeds was a direct outcome of the former ND input, the wording could be clearer like

----Around fifteen seconds later, the PF made pitch-down inputs, the angle of attack decreased, the speeds became valid again and the stall warning sounded again.------- my wording

The wording " in the following moments" needs also to be noted as non standard expression to describe an event, which based on an preceeding one and was immidiately following. I see hesitation and time delay in this expression like saying ------- that was happening,, but we dontīt know yet how it is connected----. Why is no time mentioned, it would be available on the second.

The amount of reduction of angle of attack was not mentioned, but we know that it was not below 35°, as BEA stated that AOA never was better than 35AOA until impact. The triggering of the stall warning therefore has to be caused by the speed increase to above 60kts, if i remember the numbers correctly. But the speed was subjected to erroneous indications before, at the beginning ice (at least most of us agree on that) and later on due to disturbed airflow due to high AOA, yawing and banking and maybe even WX input. In the descent the ship might have entered the bad WX zone again, which could cause speed changes as well. AOA did decrease, BEA does not say how much, it might only have been some few degrees. It might have been caused by other movement of the aircraft, like rolling from much bank through the zero bank to the other side. There also AOA would decrease and later increase again.

And we have three pilots in the pointy end, who for sure contributed to the tragic outcome somehow, but wouldnīt they have made the conclusion that their ND input was successfull und therefore should have been maintained? They deliberately made ND input and reduced power out of TOGA, so we can assume that 3 pairs of eyes tried to see an improvement of the situation. Instead they gave up on it and tried something else? Why? Did they not recognize the AOA change and the increase in speed or did they not relate it to there former ND input? Maybe they discontinued their ND input and at that time the aircraft responded due to outside factors.

I dont know, i think it is to early and founded on meager information, on just one sentence with uncommon wording (or is that my language barrier) to say ND was effective and the crew just didnīt notice it.

Lots of options and possibilities, and sure, one of them is also that there was a ND input and it had an effect, which the crew did not recognize.

Last edited by RetiredF4; 12th Jul 2011 at 19:25.
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Old 12th Jul 2011, 18:34
  #170 (permalink)  
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The AoA could have been decreasing due to the mass itself, not its controls. At the top of a ballistic climb, the nose comes down naturally, with controls or without. Drag. Sharp end has less. What is left of energy.
 
Old 12th Jul 2011, 18:43
  #171 (permalink)  
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Hello BOAC;
Would you expect that as a 'corrective' input?
No, I would not - my reaction would be the same as your own, for sure. But that doesn't mean it didn't happen. But even a smaller SS deflection is going to have quite an effect - I suspect that the two stall warning "blips" occurred as a result of momentarily exceeding the Stall AoA threshold.
I disagree on the 200t being immaterial - you speak of momentum - yes, 200t of it to get moving upwards. It does not matter what the steady state S&L match is, you still have to start the elephant moving upwards from his seat!
My thought was, relatively speaking, the airplane is, in terms of available lift against weight, able to respond to small control inputs and climb very rapidly. It doesn't take more than a couple of seconds to start the change pitch, and my guess is it took less than 10" to get to >10deg from a nominal 2.8deg[/I]), given the amount of excess energy (in forward momentum) available (and spent) in the trade for altitude.
The more times I read the interim, the more unlikely the whole scenario becomes -

. . . .

I see 1.75g quoted as an over-speed FCS 'increase' in applied PF input. Are we close?
On your first comment, yes, agree. We need the data. Hopefully it will come soon, and with as much completeness as possible. One your second re gee, I suspect fairly gentle...1.3g's, perhaps, for the pitch-up?


Bearfoil;
Re S&L flight, I am partially inferring from reading in the BEA Reports and partly drawing from experience. At 02:08:07 the PNF suggest going, "a little left." There was no hint of any changes in altitude and I suspect and infer but do not know, that whatever turbulence that may have been encountered was light, possibly slightly more with no material effect upon altitude or pitch attitude. At 02:10:05 the event began, with an AP/AT disconnect and moments later the ECAM messages were displayed, (we infer from the existence of the ACARS messages - I doubt if the the ECAM messages were recorded). There are no strong reasons to consider that the aircraft was not in stable, level flight and that the pitch up left (departed) FL350 in a climb. Remember, the altitude parameters were available and valid until, (as I know some have suggested), both roll and AoA will likely have affected altitude readings somewhat). There are no suggestions in the BEA Update of any change in altitude (downwards) which the PF was reacting against. That would have been material to the update and it was not said.

My sense of it is we will see stable, level flight in the data when it comes out. If the A330's sidesticks are the same as the A320's, the fore-and-aft movement is +/-20°, the lateral movement +/- 25°. I think we will see a five-to-seven degree, (out of a maximum deflection of 20 degrees), aft movement of the sidestick followed a neutralizing of the SS, then a strong (perhaps 10deg) forward ND movement and at 02:10:51 likely a 15-20deg aft movement of the stick, continuing for some time. I think the next ND movement will be mild, less than 10deg ND where the speed begins to pick up.

Please bear in mind that I am not "predicting" values so much as conveying a sense, from experience in the airplane, of what these movements may have been. I'm not interested in "getting it right" but I think there is some legitimacy in providing a sense, a "metric" so to speak, from experience, of what is likely and what is not likely in these various notions. It is not a matter of being right or wrong because very soon we will know. As with others, this is being assessed with the available data and so, as with all extrapolations, must be viewed with great caution.

Regarding pitch up, you are correct in stating that SOPs generally require a reduction in pitch attitude, (and TOGA thrust), if a stall warning occurs. The pitch-up may be explained in a few ways. One scenario is already discussed, (UAS drill response), the other is a "startle" reaction which would not be a sustained back-SS. Other than those scenarios which we either know about or have discussed, I can't explain the pitch-up or the back-SS in the descent.

Last edited by PJ2; 12th Jul 2011 at 20:10. Reason: Corrections due to incorrect use of physics terms - with thanks.
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Old 12th Jul 2011, 18:56
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@ bearfoil. As far as I am aware your contract of carriage is between you and the airline. So far as I am aware the regulatory body responsible for investigating a crash is not party to that contract. Perhaps you have discovered something in the contract of carriage that the rest of us have missed? If so, please feel free to share.
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Old 12th Jul 2011, 19:03
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Bearfoil, did you ever actually read the BEA report or are you just randomly making stuff up?
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Old 12th Jul 2011, 20:20
  #174 (permalink)  
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In US Law and NZ, I warrant, (both based on Queen's Bench), A contract must be a legally binding agreement. It is enforceable at Court, once juris and standing are established, (not difficult). So yes, it is founded in the Law, and the Law is a Lady, one who must not be teased.

At Court, the Judge is the Law, and he may issue a subpoena to those he deems may have pertinent information. These beneficiaries of his invitation do not have the luxury to deny, save for declaring a personal and biased interest, founded in their rights at Court. At which time they are subject to indictment as accessories to defraud the Court. In America, any individual, any one, may request a document be divulged. Save for Government security, this request must be honored. To avoid delivery of the document constitutes a felony subject to punishment by the Law.

amica populi, the other side of the coin.
 
Old 12th Jul 2011, 20:36
  #175 (permalink)  
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Of course I read it. More than once. I give it the credence it deserves, which is not very much.

Here's why:

In the Note, (I assume you are referring to this last missive to the masses), They State the PF says "I have the controls". They state then, The pilot input a NoseUp Roll left command. Fine, so far, except........


Was the pilot himself responsible for the Nose Down Roll Right he was chasing with the SS? It does not say, so we have two possibilities.

To wit: The aircraft was ND, descending, Rolling right prior to the Pilot Flying adding his stick?

As above, in 'carpe baton', did he instill a nudge down, a nudge right?

Worse yet, they go on such that the esteemed group here present vomits
such...............

"When I was in kneepants, Stall meant Nose Down....FOOL"

"He held backstick instead of ND? What a moron!" ETC.

The best here were convinced the PF SINGLE NURL was actually back pressure up to, and over the top.

So, BEA either unwittingly and/or innocently, advantaged the Manufacturer in an ongoing investigation. Or, with curious timing as to said manufacturer's Day at the FAIR........they allowed themselves to be manipulated into writing a laughable document that erodes their credibility in their mission quest.

BEA deserves neither abject guessing nor unquestioning allegiance, EH?

They deserve nothing, perhaps except for Airbus' debt of gratitude. A case of Guinness, then? Bus Badges for all? Favored seating at the Oktoberfest?

A Half Truth is a Whole Lie.
 
Old 12th Jul 2011, 20:40
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Please could you explain the forces acting on the tail during the stall for me?

Normally, the elevator and stab produce a down force at the tail. (to balance the nose down couple with the c of G being forward of the Centre of Lift).
During the stall, with an angle of attack of about 45 degs on the elevator and Stab, the forces on the tail must have been upwards. If not - then I don't understand why.

Please explain how holding full back side stick kept the attitude at around 15 degs until impact.
Since you ask ....

First thing is that MM43's excellent graphic of THS flow (Thread 4 #1042) is missing one important parameter. A lifting wing, even a stalled wing, produces downwash at the tail. A ballpark range for this would be between 0.4 and 0.5 times body AoA. So at 60 deg AoA as in the graphic, the THS AoA would have been around 17 or 18 deg. With zero elevator this would have been on the point of stalling - but it would have been stalling with UPWARDS lift.

That means that without any elevator the THS would have been giving a substantial ND moment. The centre of lift of a fully stalled wing is probably fairly close to the centre of area, which on the A330 is slightly aft of the CG given for AF447. So both of these are ND. What could hold the nose up then?

The forward fuselage has roughly the same moment arm about the CG as the THS, but nobody would pretend that it has the same aerodynamic lift efficiency, so that cannot balance the THS ND moment. Thrust? sure, but do the sums and you will find that the NU moment even with both at TOP won't come anywhere near what is needed.

What's left? Up elevator! Enough of it to make the THS plus elevator force downwards and give enough NU moment to balance the AoA at (in this case) 60 deg. Up elevator would also take the THS away from upwards stall.

For lower AoAs the THS would be even further from upwards stall.

Full back sidestick put the aircraft at 60 deg AoA - the FPA was 45 deg downwards, so the pitch was 15 deg. OK?
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Old 12th Jul 2011, 20:47
  #177 (permalink)  
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I think FPA of 45 degrees was a construct, here, to allow for ease of computing the velocity through air.

In the sense of the word Stall at the tail (upwards), you do mean that when the Tail Stalls the Nose goes down right?

bear

There is no STALLSTALL for Tailplane afaik.
 
Old 12th Jul 2011, 20:50
  #178 (permalink)  
 
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FPA of 45 degrees is what you get from the BEA stated impact conditions with zero surface wind.

No, if the tail stalls when giving upwards lift the loss of that lift would give a nose up pitch increment.

Last edited by Owain Glyndwr; 12th Jul 2011 at 20:51. Reason: addition of FPA
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Old 12th Jul 2011, 20:57
  #179 (permalink)  
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Upwards lift at the tail creates downforce on the fuselage, and prevents the Nose from falling to make a big hole.

"Upwards" to the tail is the opposite of UP to the wing. Its camber is on the bottom surface, no?
 
Old 12th Jul 2011, 21:03
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THS and deep stall characteristics

Owain seems to have a decent description of some of the factor involving the THS and its effects upon all the moment arms.

I refer all to my graph of the Viper pitch moments ( will find the post later, as on slow landline connect now). Granted, we flew at a very aft c.g. compared to the 'bus. But the fact that the jet could settle into a fairly benign condition at 50 deg AoA with no violent pitch changes and a very good directional condition ( no spin), and only small roll change was a surprise to all of us.



Our HAL cut out all pilot pitch inputs via the stick once AoA was above 30 deg or so. HAL also took over rudder to help prevent a spin. In short, once in the deep stall we were observers. But we still had NU capability if we could only gain direct control of the HS. So they gave us the "manual pitch override" doofer. It only worked if AoA was above 30 deg, but it allowed us to "rock" the jet outta the deep stall.

Show us the pitch moment graph!!!! And I realize that BA did not get a 'bus into a deep stall to get the data. But it would seem to me that they could calculate all the moments and control surface effects.

I have a feeling that the THS could have helped the pilots if they had manually moved the doofer to the nose down angle. I don't have the control logic for the THS, but looks to me from reading all the manuals that it simply moves the HS to minimize deflections of the elevator. A neat idea, and doesn't need AoA or airspeed or ..... So a constant pitch input could result in moving the HS to the limits, especially if speed was slow.

On a personal note, and being a pilot, I feel sorry that the crew was presented a condition that just didn't "compute". I think that if any had seen films of the Viper deep stall that they would have tried something after about a minute, anything, do something different fer chrissakes. Would love to find film of our deep stall, and you would be surprised how easily the jet settled into the stall.

Last edited by gums; 12th Jul 2011 at 21:22. Reason: added graphic
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