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AF 447 Thread No. 5

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AF 447 Thread No. 5

Old 18th Jul 2011, 13:01
  #441 (permalink)  
 
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Hi Dozy,
Originally Posted by DozyWanabe
As I said before regarding modern back-driven FBW controls a la B777, if you've got a triple-pitot failure and UAS scenario, how do you know that the computer is applying the correct column/yoke backdrive?
Maybe that this info is taken directly from its control surface feedback related to CG and trim position, rather than airspeed? (in Airbus, autotrim works without airspeed and it is based on FCMC/IR imputs)
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Old 18th Jul 2011, 13:04
  #442 (permalink)  
 
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Originally Posted by takata
Maybe that this info is taken directly from its control surface feedback related to CG and trim position, rather than airspeed?
Could well be, takata - but the point is we don't know, I'd suspect most B777 pilots don't know *exactly*, and the question is - would you bet your life?
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Old 18th Jul 2011, 13:05
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Hi DozyWannabe,

this is not like your computer or video game controller in that it exerts more counteracting force the further you deflect the stick.
That's strange - because yesterday it definitely felt like I have to exert more force the more I move it.

As I said before regarding modern back-driven FBW controls a la B777, if you've got a triple-pitot failure and UAS scenario, how do you know that the computer is applying the correct column/yoke backdrive?
I don't know, but if it defaulted to sensed zero air speed, then it would simply feel more twitchy. I would still be able to cope, just that I'd need to exert say half the force for the same effect.

whether you'd want to have to suddenly take over manual pitch trimming - in turbulence, at night, with no speed indications and the fuel transfer system causing the need for regular adjustments.
Do you bother to read any of my posts? That is exactly what a pilot wants to do. He wants manual control of his own pitch trim during UAS. Any fuel transfer cofg problem could be halted by turning off a couple of pumps until later.
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Old 18th Jul 2011, 13:47
  #444 (permalink)  
 
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Originally Posted by rudderrudderrat
That's strange - because yesterday it definitely felt like I have to exert more force the more I move it.
I'm pretty sure that's the same thing I'm saying, is it not?

Do you bother to read any of my posts? That is exactly what a pilot wants to do. He wants manual control of his own pitch trim during UAS. Any fuel transfer cofg problem could be halted by turning off a couple of pumps until later.
I'd say that reads more like what *you* want to happen. I'm sure you wouldn't claim to speak for all pilots any more than I could claim to speak for all engineers. Some pilots want different things is all - it'd be a boring world if we all wanted the same things given the options we have nowadays, wouldn't it?

Last edited by DozyWannabe; 18th Jul 2011 at 14:02.
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Old 18th Jul 2011, 13:55
  #445 (permalink)  
 
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Originally Posted by DozyWannabe
Could well be, takata - but the point is we don't know, I'd suspect most B777 pilots don't know *exactly*, and the question is - would you bet your life?
This is not really the question about making any bet.

I think that the constant comparison between A & B is fairly displaced and most pilots here have moved on on this subject. The fact is that it seems that there is some obvious differences when driving such aircraft, controls, autotrim and CG computing, being of course part of the equation.

Now, it isn't anymore about judgement but understanding. Airbus concept is not that bad but may certainly be improved: there is still quite a wide margin before considering it "near" perfect, whatever Boeing is doing on its own side.

Actually, some point of view developed here about Airbus a/c is based on a "conventional aircraft" with fanzy added systems, and some people are trying to figure out how much it is useful or could be useless/dangerous in certain cases. While in fact, the starting point for this design was not a "conventional" but a "protected aircraft" which may eventually lose some of its systems until the point that it will look very much like such a "conventional aircraft".

Then, it is in fact possible that in the middle of this reversion, you'll be left with an "hybrid" aircraft which is not what any kind of pilot (Airbus or others) is very likely used to. While an Airbus pilot, used to those systems, would preferably keep whatever is still working rather than to reverse to a fully "conventional a/c", another pilot would prefer to get it directly "conventional" because it is also what he is much more used to.

Nonetheless, one of the issue that I'm starting to understand, is that Airbus "protected" systems are now in use for about 25 years. Basically, all the documentation was at first aimed at those pilots converting to their systems from "conventional" a/c. Now, they also don't explain how it feels like to fly such "conventional a/c", but rather the opposite. In turn, there is not that much emphasis about how to do in "conventional" configuration, which was certainly ok at the time, because everybody knew to fly it like that.

Is it still the case today?
If you look at those two young F/O (less than 40), they obviously never flew anything else than Airbus (A320 and A330/40) after their basic training. Hence, what would be the point to say in FCOM: if you are in direct law, you are now flying a "conventional aircraft"... when they may have no idea about what it is really like?
Some questions I'm asking myself at this point.

Last edited by takata; 18th Jul 2011 at 15:47.
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Old 18th Jul 2011, 13:58
  #446 (permalink)  
 
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Picky Perkins, a few thoughts from one of your posts.
We know that the training departments of the airlines had strenuously opposed any mention of the use of manual trim in training for upset recovery, even though the test pilots of both Boeing and Airbus had emphasized more than a decade ago that bringing the a/c into trim was in their opinion the first priority in a recovery ...if the crew had had upset recovery training (as distinct from training to recover from an approach to a stall) the use of manual trim would not have even been mentioned, and they may even had had warnings against its use (because of the danger of structural damage).
They followed their training, which in part told them to forget what they were told in primary training, particularly WRT stalls. They were never trained to use manual trim. It wasn’t even mentioned
.
FWIW: one of our posters (Mikelour) taught in the A330 sim. He has told us that there were/are some Unusual Attitude training scenarios where use of trim wheel was included. Is not Unusual Attitude related to Upset?
QUESTION: Being a French crew for a French airline and knowing that any deviation from training and SOP might be investigated by a French Court, might they have been inhibited from deviating from training and/or SOP in case they might be blamed for any subsequent damage?
Possible cultural factor. Whose gonna own up to that one? (Do I hear crickets chirping?)
When I say that some jets enter the stall gracefully, I don't mean you can't feel SOMETHING. But with the storms and such, and the "bus great aero, the buffet could have been masked. From a pilot perspective flying at conditions unheard of in the heavies, I learned when a buffet meant "close to stall", or "prolly in a stall", or whoa!!!
I had many students that could not "feel" the increase in buffet as I could. Bothered me, but some have "touch" and some don't.
This point appears worth repeating.

An AoA gauge might have been useful secondary scan instrument ... *ducks*

EDIT: I'd like to address a point in terminology.

Typically, an aircraft has primary flight controls and secondary flight controls. Aileron, rudder, or elevator, (primary) often have a trim surface (secondary) that allows you to influence the primary.
(Other secondary are: flaps, slats, spoilers, speed brakes ... which change air flow over a wing). (Thought: aren't spoilers sometimes in the role of primary flight control at high speeds and high altitudes?)

The relationship between the THS and the Elevator on this aircraft looks similar to how a trim surface on a conventional elevator (with fixed Horizontal Stab) influences elevator position.

THS is thus a primary flight control. Or is it? Initial control deflection of the stick moves the elevators (so the elevators are a primary flight control).

Does this make THS a secondary flight control?

Well, if one is controlling the nose with the trim wheel, THS becomes the primary flight control surface.

I may be trapping myself in archaic terminology here.

Can someone help me see this more clearly?

Last edited by Lonewolf_50; 18th Jul 2011 at 14:16.
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Old 18th Jul 2011, 14:31
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Cool

Hi,

If you look at those two young F/O (less than 40), they obviously never flew anything else than Airbus (A320 and A330/40) after their basic training. Hence, what would be the point to say in FCOM: if you are in direct law, you are now flying a "conventional aircraft"... when they may have no idea about what it is really like?
Some questions I'm asking myself at this point.
Woooaaa
The next question is...
Why Airbus bother to make available a "direct law" if the "new pilots generation" are not able to pilot the plane in that law ?
Is "direct law" can be crudely translated as "direct crash" ?
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Old 18th Jul 2011, 14:38
  #448 (permalink)  
 
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@Dozy:

UAS other than A. FBW airliner:

Unreliable Airspeed Indications.
Unreliable airspeed indications can result from blocking or
freezing of the pitot/static system or a severely damaged or missing
radome.
When the ram air inlet to the pitot head is blocked, pressure in the probe
is released through the drain holes and the airspeed slowly drops to zero.
If the ram air inlet and the probe drain holes are both blocked, pressure
trapped within the system reacts unpredictably.
The pressure may increase through expansion, decrease through
contraction, or remain constant.
In all cases, the airspeed indications would be abnormal.
This could mean increasing indicated airspeed in climb, decreasing
indicated airspeed in descent, or unpredictable indicated airspeed in
cruise.
Unreliable airspeed may cause noticeable effects in the normal speed
stability of the airplane since the normal pitch control law uses indicated
airspeed.
If the indicated airspeed falls below 50 knots, the flight control system
changes to the secondary mode, which does not depend on airspeed.
The autothrottle system also uses indicated airspeed and should be turned off.
If the flight crew is aware of the problem, flight without the benefit of
valid airspeed information can be safely conducted and should present
little difficulty.
Early recognition of erroneous airspeed indications requires familiarity with
the interrelationship of attitude, thrust setting, and airspeed.
A delay in recognition could result in loss of airplane control.
The flight crew should be familiar with the approximate pitch attitude for
each flight maneuver.
For example, climb performance is based on maintaining a particular
airspeed or Mach number.
This results in a specific body attitude that varies little with gross weight and altitude.
Any significant change from the body attitude required to maintain a
desired airspeed should alert the flight crew to a potential problem.
When the abnormal airspeed is recognized, immediately return the airplane
to the target attitude and thrust setting for the flight regime.
If continued flight without valid airspeed indications is necessary,
consult the Flight With Unreliable Airspeed/Turbulent Air Penetration table
in the Performance Inflight section of the QRH for the correct attitude,
thrust settings, and V/S for actual airplane gross weight and altitude.
Ground speed information is available from the FMC and on the instrument
displays.
These indications can be used as a crosscheck.
Many air traffic control radars can also measure ground speed.

Secondary and Direct Mode Pitch Control
Airplane pitch control is different in the secondary and direct flight control
modes.
The control columns now command a proportional elevator deflection
instead of a maneuver command.
Secondary and direct modes do not provide automatic pitch compensation for:
• thrust changes
• gear configuration changes
• turbulence
• flap and speedbrake
configuration changes
• turns to 30° bank angle.
In secondary and direct modes, the elevator variable feel system provides
two feel force levels instead of a continuous variation with airspeed.
The force levels change with flap position.
With the flaps up, the feel forces provide maneuver force levels that
discourage overcontrol in the pitch axis at high speeds.
With flaps extended (flaps 1 or greater), the feel forces decrease to
provide force levels appropriate for approach and landing.
In the secondary and direct modes, both the primary pitch trim switches
and the alternate pitch trim levers move the stabilizer directly.
There is no trim reference speed.

Last edited by A33Zab; 18th Jul 2011 at 14:53.
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Old 18th Jul 2011, 14:53
  #449 (permalink)  
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Your post is food for thought! Cautions about attitude, (assiete), continued flight w/UAS, etc, very compelling.

Could you comment on the inclusion of "damaged or missing" radome?

Long ago, it seemed to me at least possible that the radome could have been damaged by hail, or lost due overspeed. This could tie in with the suspicious lapses in Radar (Wx) uses and deviation questions. Likewise, a damage to one or more Pitots if impacted by debris?
 
Old 18th Jul 2011, 15:22
  #450 (permalink)  
 
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bear, upon what data are you basing your idea of overspeed loss => lost radome? At the speeds flown, lost radome likely causes non-trivial drag, likely a radar fault, and hence an ACARS message well before the upset event.

I don't see there being any data presented to date that supports this hypothesis. Indeed, what little we have from CVR is that pilots had noticed something ahead and made a small course change based on that info. So, if radar was not working, that would most likely have come up in conversation.
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Old 18th Jul 2011, 15:33
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Originally Posted by jcjeant
Why Airbus bother to make available a "direct law" if the "new pilots generation" are not able to pilot the plane in that law ?
Is "direct law" can be crudely translated as "direct crash" ?
My point was to underline what seems (for me) to be lacking in pilot's basic documentation about flying their aircraft. I don't think that such knowledge of "conventional aircraft" may still be considered today as being part of the background of that many pilots than it was in the past. Much more informations would be needed in this flight manual about how the aircraft would behave in manual control during reversion phases mostly without any protection.

If your point was to make fun of mine, this is completely zero added value, like one said. Obviously, any pilot needs surely to be trained from A to Z in order to ensure his full ability to fly whatever aircraft. Hence, I think that this manual is not reflecting very well this basic requirement, considering some parts of its flight domain, for the reasons explained above.
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Old 18th Jul 2011, 15:54
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Hi takata,

There is a beautiful aircraft waiting to come out once the Normal & Alt Laws have been removed.

From FCTM
Direct Law
In most triple failure cases, direct law triggers.
When this occurs:
• Elevator deflection is proportional to stick deflection. Maximum deflection depends on the configuration and on the CG
• Aileron and spoiler deflections are proportional to stick deflection, but vary with the aircraft configuration
• Pitch trim is commanded manually
Handling characteristics are natural, of high-quality aircraft, almost independent of the configuration and of the CG. Therefore, the aircraft obviously has no protections, no automatic pitch trim, but overspeed or stall warnings.

OPERATIONAL RECOMMENDATION:
The PF must avoid performing large thrust changes, or sudden speedbrake movements, particularly if the center of gravity is aft. If the speedbrakes are out, and the aircraft has been re-trimmed, the PF must gently retract the speedbrakes, to give time to retrim, and thereby avoid a large, nose-down trim change.
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Old 18th Jul 2011, 15:56
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I think my approach is one that is misunderstood by some. I haven't proposed any kind of conclusions, I am making an effort to keep my mind open to possibilities that indeed may have naught to do with 447. In an effort to understand UAS, overspeed, RadarWx, etc. I am adding to my own personal backgound, and if at a later time, a conclusive presentation is made (it will be, we hope!), then a broader understanding offers a firmer foundation for finality.

Within days of this accident, I was focused on the attitude of the a/c at a/p loss, until it became increasingly ignored in favor of what I thought was extraneous interest by the thread in general. What goes around comes around, and here we are with A33Zab's post of "Other than fbw UAS procedure."

We are back at the several seconds around the loss of the autopilot.

I believe what is technically considered "Upset" (not at all what many think it is....) happened seconds (or more) prior to a/p dropout. The LOC, (again by definition) 'happened' at "I have the controls".........

I do not need to be correct. I have no airframe bias. I am a pilot. I am with the crew, until such time as anyone can conclusively prove to me that PE was the procuring cause of this tragic accident.

Was it "in there"? Who among the pilot community would have an expectation of flawless competency in such conditions?

I have no "need" to be understood. On the contrary, I crave to understand.........
 
Old 18th Jul 2011, 16:14
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Originally Posted by Rudderrudderrat
There is a beautiful aircraft waiting to come out once the Normal & Alt Laws have been removed.
I think that any pilot who is flying it will tell you that it is certainly also a beautifull aircraft to fly in Normal law, which is what they are doing 99.99% of the time. The problem that need to be addressed, I think, lies somewhere else:
When there is such a non-commanded law reversal, it is either in the sim (where, most of the time, always the same scenarios are played), either in very critical conditions. It will be then, for anyone, quite hard to appreciate how much "beautifully" it is flying without either airspeed, inertial reference, hydraulics, electrics...
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Old 18th Jul 2011, 16:22
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well said. Do you have any thoughts on the speedbrakes v. Trim and "nose down" trim change? Also, could one of the right side spoilers have failed to stow completely, causing that annoying (and persistent) "roll" to starboard? If so, would the rolling aspect of the climb and descent be possibly related?
 
Old 18th Jul 2011, 16:33
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Originally Posted by Bearfoil
well said. Do you have any thoughts on the speedbrakes v. Trim and "nose down" trim change? Also, could one of the right side spoilers have failed to stow completely, causing that annoying "roll" to starboard? If so, would the rolling aspect of the climb and descent be possibly related?
I know that you are SO very "open-minded". But have you got ANY information that she could have been in direct law, at any point before crashing, not even mentioning before this UAS declared?
Bearfoil, nothing unusual happened before 0210:05, take it as a fact or consider, with your usual very open-mind, that the BEA is lying the entire world.
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Old 18th Jul 2011, 16:55
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I do NOT believe BEA are lying. I do NOT have sufficient evidence to pour concrete around my opinions, as some have. I do have an open mind. I will embrace the truth when (!) it appears.

You are the one who knows, evidently, sufficient data to reject all speculation that isn't conformed.

For what it is worth, You have opened up greatly in the last two weeks, and offered valuable information in every way, some even that is neutral re: Airbus.

I try to eliminate the personal from this thread. If you are correct, and my prose is mostly zero-value-added, you should try ignoring it, or resisting the urge to respond to it with snark. If it is just so much dead weight, you might want to avoid worrying about someone else's bandwidth?
 
Old 18th Jul 2011, 17:12
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Originally Posted by Bearfoil
I try to eliminate the personal from this thread. If you are correct, and my prose is mostly zero-value-added, you should try ignoring it, or resisting the urge to respond to it with snark. If it is just so much dead weight, you might want to avoid worrying about someone else's bandwidth?
Fair enough.
My urge comes from your own typical urge at bouncing up after any word taken out of its context.
Did you even noticed that Rudderrudderrat was quoting something related to Direct law, or not? Hence, the first question to address, with an open mind, should have been: was she in this mode? If one bother to answer it, his fast composed theory would spin and crash many times faster than AF447.
Nothing personnal otherwise.
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Old 18th Jul 2011, 17:16
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Originally Posted by rudderrudderrat
There is a beautiful aircraft waiting to come out once the Normal & Alt Laws have been removed.
In your opinion. I personally don't understand this conservative streak in a minority of pilots. Why so negative about something which was designed to help you do your jobs and move the art of aviation forward? Why such a burning need to move no further forward than the 1970s?

(Just to add, I'm not being facetious here - heaven knows I'd rather be hacking away at low level code on the machines I grew up on on a day to day basis than doing the corporate stuff that puts a roof over my head, and I know what it is to feel that one's career path has been commoditised by the endless march of big business - but IMO it's not fair to blame the technology for that)

Last edited by DozyWannabe; 18th Jul 2011 at 17:51.
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Old 18th Jul 2011, 17:20
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mais oui.

My Bad. Lately I type faster than I think, I am sorry. But is there any value in considering that the trimming the A/P was doing had some importance on the PF's choice to manuever quickly instead of "waiting"?

Do you have a thought re: the first manuever? It happened, it had a reason, and no, no one can read the PF's mind. Qu' est-ce que c'est?

thanks
 

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