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AF 447 Thread No. 7

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AF 447 Thread No. 7

Old 8th Nov 2011, 16:42
  #21 (permalink)  
 
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Stick Force, Detent

The term 'detent' with SS controls keeps garabbing my attention.

So please excuse my ignorace of how the Buss's SS are rigged.
Reference point is the fly by wire stick on A-7 Corsair II aircraft.

The stick was mounted on a set of force bars with transducers.
Electronics package was set to ingnor stick forces under 4 pounds.

There was very little if any actual travel as I recall.
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Old 8th Nov 2011, 17:00
  #22 (permalink)  
 
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Originally Posted by grity View Post
well, I have to ask for pardon, for my mistranslation
That's OK - English isn't your first language. I made some quite embarrassing mistakes translating the initial French CVR transcript from Interim Report #3, so I can't be too hard on you.

Originally Posted by CONF iture View Post
It is more complex than that.
With full back stick, the PF managed to silent the STALL warning and to temporarily obtain a V/S between zero and -2500ft/min (it is not clear which V/S is recorded ...)
But he did have consistent stall warning for almost a minute, and a reliable V/S for just over a minute (if my reading of the traces is correct). The altimeter continued to unwind with the standby clearly visible from the right-hand seat, providing a secondary method of checking the aircraft's vertical trajectory.

Please don't think I'm criticising the PF, by the way - I'm just saying that those indications were there if he'd known where to look.

Of course both PNFs have no idea what are the inputs of the PF for that time.
Sometimes the simplest solutions can be obscured in a crisis situation - all they had to do was ask. The question is, why did they not think to do so?

@gleaf - The detents refer to the thrust lever settings, not the sidestick. The Airbus sidestick allows for a greater degree of travel than those generally fitted in fighters, however those comparing them to a computer joystick would really have to get their hands on one to understand that while the comparison works from a distance, they are obviously much stronger - chunkier and stiffly-sprung than that. They have to be to stand decades of constant operation.
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Old 8th Nov 2011, 17:09
  #23 (permalink)  
 
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IMO, the most important parts of the accident are being ignored, some through ignorance, and some through active effort.

My drum? Again, the intitial 10 seconds (manual), and the ten before.

The crew inherited a maneuvering aircraft, for one or the other of two basic reasons. The AirSpeed was unreliable, or the a/c autopilot was unable to keep up with turbulence. Either way, the a/c was therefore in or on the verge of Upset.

All the interesting blather about an aircraft's performance after the fact is not relevant, it is after the fact. Post Facto.

Actively unaddressed? A rerun WITHOUT TURBULENCE factored in? A lack of notation from BEA re: the "Zipper"?

The further the pendulum swings, the more blatant is this "unknown" zone.

The entire basis for the "conclusions?" Unrelated to the onset of Upset, imho.

Commanded or no, the climb qualifies as Upset. What initiated the Climb?

Crew, in response to instruments.

Ambulance Chasers? Fanatical Toadies? Nil/Nil. fmm.
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Old 8th Nov 2011, 17:17
  #24 (permalink)  
 
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Side stick

Salute gleaf!

You can find a good link and description of the 'bus sidestick by searching one of our earlier threads.

With no small amount of time in the SLUF, I can attest to the use of force transducers for the stick grip. Seems like breakout force was very low and the 4 pounds reference might have been when the physical stick began to move. For FCF's we would brace the stick with our knees and one hand, then exert force on the grip. With CONTROL AUG enabled, the control surfaces would move. Sure made formation flying a lot more precise.

That stick grip was used on the original Viper and worked the same way - no physical movement. Later jets, like from number 30 or so, had 1/8 inch of movement.

@DOZE

I take it that the increasing force per degrees of stick deflection was impressive?

back to our regularly scheduled discussion...
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Old 8th Nov 2011, 18:01
  #25 (permalink)  
 
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For the record, the turbulence encountered by AF447 was described as "MODERATE", which has a very specific meaning - namely :

MODERATE - Changes in altitude and/or attitude occur but the aircraft remains in positive control at all times. It usually causes variations in indicated airspeed. Occupants feel definite strains against seat belts or shoulder straps. Unsecured objects are dislodged. Food service and walking are difficult.
I'm sure that given the thousands of FBW Airbuses criss-crossing the globe on a daily basis for 23 years, most of them must have encountered "MODERATE" turbulence at one time or another. As yet there have been no reported incidents of such turbulence inducing an autopilot disconnect, but there have been several cases of disconnect relating to unreliable airspeed. Therefore it's quite reasonable to state that the most likely cause of disconnect was unreliable airspeed, and given the ACARS log and the DFDR records it becomes practically certain that unreliable airspeed was the reason.

As for ambulance-chasers, an example was the Aeroperu 757 crash, in which the initiating event was the inappropriate use by airport ground staff of silver duct tape to cover the static ports. The lawyers still elected to go after Boeing (who, true to the edicts of ambulance-chasing, had by far the deepest pockets), despite the manufacturer having done nothing materially wrong.

@gums - Yes, the build quality of the sim was very impressive in general. There's a reason why the top-drawer *home* sim component sidestick costs approximately $3,500 (thus the real deal I experienced likely costs more) and home computer controllers cost 1/100th of that.

Last edited by DozyWannabe; 8th Nov 2011 at 18:17.
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Old 8th Nov 2011, 18:20
  #26 (permalink)  
 
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Otelli Book

Good Morning, Ppruners,

I have eaten all of my prunes this morning, and feel quite regular!
Has anyone found a source for the Otelli book, in English, for sale in the U.S.?

I personally feel that Otelli is out-of-line in drawing any conclusions at all at this juncture, and he comes off as an ambulance-chaser, but that doesn't mean I wouldn't be interested in reading the book.

All I can find is the French version, for $50!

Thanks for any feedback.
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Old 8th Nov 2011, 20:29
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From one who "makes" those noises...

DW, does the sim produce a lot of noise when “stalled” and held in the stall with high RoD?

(It was reported in an earlier thread that somebody who had heard the CVR said that the air rush noise in the AF447 cockpit was very loud, and may have added to the PF confusion by reinforcing any belief he might have had that their problem was overspeed, as that too would have been noisy; and the pilots had probably never heard either noise before in the aircraft, and may not have heard both in the sims.)
As noted previously, I am one of "those" engineers responsible for developing the sound models used to generate the sounds in simulators (many, many types now). There would be no vertical speed component contributing to the noise signature in the sim, unless the company producing that sim extrapolated way outside of the available sound data supplied with the aircraft data package. The key driver for aeronoise is CAS modulated by Mach factor.
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Old 8th Nov 2011, 21:12
  #28 (permalink)  
 
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Sometimes the simplest solutions can be obscured in a crisis situation - all they had to do was ask. The question is, why did they not think to do so?
James R.Chiles
The most dangerous time is when the operators don’t know what they don’t know
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Old 8th Nov 2011, 21:38
  #29 (permalink)  
 
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Interesting discussion. Congratulations to Dozy for his field research. I do not doubt any second that what he experienced was very close to what did the crew of AF447.

Still this is no proof that he (and me, and BEA and some other pro Airbus people) are right about the accident. You still could argue that the simulator did not simulate what the real aircraft experienced in her dire situation. That the simulation of the case is just an interpolation of known aircraft situations. That the AF447 was so far away from known that they experienced something completly else.

The only thing that Dozy proofed is what we (Airbus people) already knew: stick movement were consistent with aircraft movements, Airbusses are pretty easy to handle and stall recognition, recovery and UAS situation are possible to handle.

But I'm sure he is right. And that an A330 is behaving very similar if not easier than a A320.
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Old 9th Nov 2011, 01:06
  #30 (permalink)  
 
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Originally Posted by DozyWannabe
Sometimes the simplest solutions can be obscured in a crisis situation - all they had to do was ask. The question is, why did they not think to do so?
The simplest solution has a name : Fully visible control columns - they tell without talking.

What do you wanna ask ?

What can you reply ?
"I am full left - half back - a third left - full back - neutral - a touch forward - mainly right - full forward - back left .........................."
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Old 9th Nov 2011, 05:56
  #31 (permalink)  
 
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It is highly unlikely that control columns would have made any difference. Go and read the accident report on the Airborne Express DC8 stall crash which involved control columns - they didn't make any difference to the outcome. Absorb that report and remember it before you post - the control column is another red herring. A proper and comprehensive instrument scan and properly executed CRM are what would have helped. The fact that (as Dozy identified) no one asked is highly significant and indicates a serious breakdown in communication at a vital time, just when communication should be clear and frequent.
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Old 9th Nov 2011, 13:18
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Originally Posted by Old Carthusian
The fact that (as Dozy identified) no one asked is highly significant and indicates a serious breakdown in communication at a vital time, just when communication should be clear and frequent.
The fact that a PM would need to ask the PF what are his inputs on flight control commands is highly significant how the concept of the sidesticks by Airbus is poor.

Read and absorb my previous comment regarding the DC8 event and remember it before you post.


Sidestick is a sure way to waste valuable information in a multi crew operation.

Dozy never replied - Where such statement is erroneous Old Carthusian ?
Please comment.
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Old 9th Nov 2011, 13:24
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Stability in the stall

There were a few comments earlier that AF447's long stall had been very stable, with a high AoA, although with a fairly steady bank. When flying as a SLF when I have been able to see a wing tip through a rear cabin window across the aisle during Take-off, at what I would guess was Vr, the wing tip lifts aerodynamically, thus increasing the static dihedral. With the very high AoA AF447 had, might not this aeroelastic effect have tended to keep the aircraft stable, awaiting some other control input ?

The aircraft that I flew, attempted to have more rigid wings. (The biplanes even had Flying wires and Landing wires between the wing struts !) And later, I would be unable to see the wing tips on Take-off, even had it been safe to do so. With more rigid wings I would guess that we got a rougher ride in any turbulence for a given TAS.

( This "wing-tip-lift" is not unique to A or B, it is just that I have seen it there, on both, as an SLF .)

Last edited by Linktrained; 9th Nov 2011 at 14:27. Reason: the aisle
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Old 9th Nov 2011, 16:00
  #34 (permalink)  
 
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Lateral stability in a stall

My experience at and beyond stall AOA in swept wing jets (trying to hold the nose up in a low speed scissors) was that centering the stick laterally and using gentle rudder inputs had the best effect in keeping the wings level. But even then the wings rocked a lot and it needed bigger and bigger rudder inputs to pick the low wing up.

I'm wondering if all those spoilers on the A330 wing more than counterbalance the adverse effect of the ailerons and make it practical to reverse the roll using the stick, particularly once well past the stall AOA? Or is it just the rudder effects from the BYDU and pedal inputs that rolled AF447 back the other way.
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Old 9th Nov 2011, 16:15
  #35 (permalink)  
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Originally Posted by MBird
I'm wondering if all those spoilers on the A330 wing more than counterbalance the adverse effect of the ailerons and make it practical to reverse the roll using the stick, particularly once well past the stall AOA? Or is it just the rudder effects from the BYDU and pedal inputs that rolled AF447 back the other way.
- I'm pretty convinced you are right. The apparent 'restorative' effect of aileron on 447 in a fully stalled condition has puzzled me for a long time and goes against 'conventional wisdom'. I now believe that the commonality of large spoiler deflections with aileron means we may have to re-write the book on the effect of roll control at the stall..
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Old 9th Nov 2011, 16:51
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Hi BOAC,

I now believe that the commonality of large spoiler deflections with aileron means we may have to re-write the book on the effect of roll control at the stall..
I don't think so.

On page 96:
At 2.12.45. "The copilot sidestick is to the left in stop position. The roll angle changes from 12° right to 41° right in 3 seconds then fluctuates between about 20° and 40° right (period of 10 seconds)
"Hey you’re in … get the wings horizontal Get the wings horizontal"
"That’s what I’m trying to do"
"Get the wings horizontal"
At 2.12.59:
"I’m at the limit … with the roll"
"The rudder bar"

It strikes me that the roll control worked the wrong way during the stall (which agrees with current wisdom). The Captain ordered the use of the rudder bar, which then picked up the wing.

I agree with Linktrained and think it was simply the massive side slip which they had with 40 degs of bank (due no radius of turn) and the dihedral effect which caused it to stabilise.

Last edited by Jetdriver; 9th Nov 2011 at 22:37.
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Old 9th Nov 2011, 18:28
  #37 (permalink)  
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Quite possible.

Can someone remind me please? We know that fore and aft SS demands are 'processed' by HAL according to some 'law', be it 'g'/attitude or whatever . What does HAL think a pilot wants when the SS moves over in whichever *** 'law' the beast was in at the time? Roll Rate/bank angle/acceleration in roll?? IE When PF moved the stick to the left, what did HAL think he wanted - and gave him?
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Old 9th Nov 2011, 18:48
  #38 (permalink)  
 
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Roll control is direct law, stick position -> surface position.
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Old 9th Nov 2011, 19:47
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SS commands and actual control surface movements

Salute!

Beg pardon, but roll commands do not command a 1 for 1 deflection of either the spoilers or ailerons in Alt1 or Alt 2, only in "direct law". That's what my copy of the FCOM shows.

The commands except in "direct" are roll rates, and the "gains" are set by various inputs and other control surface settings. So no direct deflection of surfaces according SS deflection.

This is a fairly standard implementation for FBW jets. The rudder will move to help rolling and minimize adverse yaw. In the Viper, HAL would command the rudder to very large deflections when rolling at max rates and slow speed.

At high AoA's, I go with 'bird. Use rudder and not aileron for roll. Spoilers can reduce adverse yaw and such, but my understanding is that the outboard spoilers on the 'bus are inhibited once gear up. So the inboard spoliers may not have helped as much as rudder.

The CVR shows the PNF mentioning the "rudder bar" when PF had full SS deflection for roll and the jet was not responding. Here again, knowing you were stalled or approaching a stall might have changed the PF stick inputs. However, in view of most PF stick inputs and PF's possible lack of experience flying at extreme AoA , then I can see a bit of the rationale for roll inputs, but not pitch.

Sent by an old FBW pioneer.
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Old 9th Nov 2011, 19:56
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OK - seconds out - round 2

Zorin Roll control is direct law, stick position -> surface position.

Gums roll commands do not command a 1 for 1 deflection of either the spoilers or ailerons in Alt1 or Alt 2, only in "direct law". That's what my copy of the FCOM shows. The commands except in "direct" are roll rates, and the "gains" are set by various inputs and other control surface settings. So no direct deflection of surfaces according SS deflection.

Which FCOM/understanding is correct? It could be important in a confused cockpit. Not a lot of time to open an FCOM volume? Let's get it right?

Ding Ding Ding.

Oh yes- a round is 3 minutes I think - about the time from 38,000 to sea level at a high rate of descent .
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