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AF 447 Thread No. 10

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AF 447 Thread No. 10

Old 23rd Aug 2012, 22:22
  #81 (permalink)  
PJ2
 
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roulishollandais;
The Pitot fault message was on the ACARS at 02:10... and was missing on the ECAM!
The pitot message was one of five fault messages (intended for Maintenance only - not presented to the crew). It is a Class I (of I, II, & III), Mtce Message and as such would require consultation with the MEL prior to the next departure. The pitot system itself did not fail in a way that was sensed by the FWC but due to blockage was providing erroneous data which was sensed by the EFCS2, (discussed in IRI, ppg 54, 55). The message is not an ECAM Level 1, 2 or 3 message and therefore would not have shown up on the ECAM because there was no "failure". If pitot heat itself had failed, a Level 2 message would be generated and it would show up as an amber message on the ECAM.

Whether this would have helped the PF comprehend what had happened cannot be stated. There seemed a predisposition to, and a determined focus on, certain actions in which the PM was unable to successfully intervene.

As to displaying an ECAM message with the abnormal, "Unreliable Airspeed" followed by suitable responses I cannot see that occuring within the current established ECAM philosophy. The reason is, I think, straightforward: The ECAM is a systems-abnormality page. It, and the Status Display page are intended to secure the aircraft systems for further flight within the limitations of the abnormality including performance additions or limitations where applicable. The ECAM system is not intended as a guide on how to fly the aircraft in certain abnormal circumstances - that is for the training regime to establish through the usual familiar ways.
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Old 24th Aug 2012, 01:04
  #82 (permalink)  
 
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Life is so much easier in a Boeing if UAS situation happens at altitude in cruise. Just keep the same attitude and power you had and get out the UAS check list. If the altimiter and VSI work you are even more golden. Not a real emergency at all. Just fly the airplane.
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Old 24th Aug 2012, 01:24
  #83 (permalink)  
 
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Originally Posted by HN39
It took about 5 - 6 degrees of NU elevator to stall the airplane. In direct law that would correspond to about 3 degrees (2.8 lbf) of sidestick, vs about 2 degrees (2.1 lbf) in alternate law. Do you really believe the PF would have felt the difference in his erratic movements of the sidestick?
But what is the THS setting already when the elevators reach 5 - 6 degrees NU for the airplane to stall at the 10 deg of AoA time 02 11 00 ?

You may as well disregard the following BEA comment on P187 :
However, positive longitudinal static stability on an aeroplane can be useful since it allows the pilot to have a sensory return (via the position of the stick) on the situation of his aeroplane in terms of speed in relation to its point of equilibrium (trim) at constant thrust. Specifically, the approach to stall on a classic aeroplane is always associated with a more or less pronounced nose-up input. This is not the case on the A330 in alternate law. The specific consequence is that in this control law the aeroplane, placed in a configuration where the thrust is not sufficient to maintain speed on the flight path, would end up by stalling without any inputs on the sidestick. It appears that this absence of positive static stability could have contributed to the PF not identifying the approach to stall.
Still, if the guy has direct law, he may as well bring the airplane to the stall, no question, but what do you make of the following ?

THS is still at 3 deg and the stall cannot be that developed so the indicated airspeed wonít go below the threshold to silence the stall warning that will still warn when the captain is back. Of course if that captain had the chance to naturally contemplate what kind of input is made by the PF on the flight control commands Ö that could enormously help him to positively evaluate whatís going on here.

What many here like to call 'graceful degradation' had nothing of graceful during that night.
That law that trim and that sidestick concept worked against that crew that night.
To that list of course I should have added that stall warning logic.


You did not comment ?
No one did ...
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Old 24th Aug 2012, 03:37
  #84 (permalink)  
 
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FBW interference with "natural" law

You did not comment ?
No one did ...
Well, I shall comment. I know that Doze will bring up operational requirements and such, but I maintain I can contribute to the discussion.

It comes down to the control law implementation and then the natural stability of the jet.

Ours was negative static stability until about 0.95 mach. So the FBW system kept the pointy end forward. This is not the case with the 'bus. The thing has positive static stability unless the fuel transfer system goes awry. But HAL tries to provide a neutral speed stability ( no regard for AoA) and also corrects the basic gee command for pitch attitude. So the BEA comment is correct, with the exception that it should mention that the 'bus has inherent longitudinal static stability. In other words, go to "direct" law and the thing flies like most planes we have all flown ( not the Viper, which would be impossible without HAL).

Without some sort of stick pressure corresponding to the commanded gee as the jet slows down, then it becomes unclear as to what is happening. FOR THE ONE THOUSANDTH TIME....AoA is very important. AoA is what keeps the plane flying. So our primitive FBW system ( for the benefit of Doze, heh heh) had a neat AoA limit that kept you from stalling unless......... If you climbed at a steep attitude and reduced power, you could reach a speed where those air molecules and full nose down horizontal tail positions were not sufficient to prevent entering the stall. A true "deep stall", it was, due to our cee gee and pitch moment at 40 degrees AoA or so. Does this scenario sound familiar?

I disagree with the BEA terminology with respect to stability. The basic aero of the 'bus is fine. It's the FBW interference that makes the jet seem like it has neutral speed stability and static longitudinal stability. Go to "direct law" and you have what all planes have had since Wilbur and Orville flew the first one. Could be "touchy", but the sucker would try to achieve the trimmed AoA, and AoA is what planes use to provide those liftie doofers.

I do not recommend that the 'bus go from full laws to "direct law" willy nilly. But seems to me that a few practice sessions in the real jet in "direct law" would provide a lotta confidence to the crews and also show them the inherent characteristics of the jet.
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Old 24th Aug 2012, 07:02
  #85 (permalink)  
 
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Originally Posted by CONF iture
But what is the THS setting already when the elevators reach 5 - 6 degrees NU for the airplane to stall at the 10 deg of AoA time 02 11 00 ?
The airplane stalled at the 10 deg of AoA time 02 10 57. The THS was then at -3.5 degrees. Elevator 5 - 6 degrees should be read as equivalent elevator angle for THS = 3 degrees.

BEA quote: However, positive longitudinal static stability on an aeroplane can be useful since it allows the pilot to have a sensory return (via the position of the stick) on the situation of his aeroplane in terms of speed in relation to its point of equilibrium (trim) at constant thrust. Specifically, the approach to stall on a classic aeroplane is always associated with a more or less pronounced nose-up input. This is not the case on the A330 in alternate law. The specific consequence is that in this control law the aeroplane, placed in a configuration where the thrust is not sufficient to maintain speed on the flight path, would end up by stalling without any inputs on the sidestick. It appears that this absence of positive static stability could have contributed to the PF not identifying the approach to stall. (End of quote)

The BEA comment is correct, of course. But in the circumstances of AF447 it is mostly theory. It applies if you approach the stall slowly, in still air at low altitude gently manipulating the stick so that you can feel the stickforce increasing the closer you get to the stall. The subtle change in stickforce characteristics hardly matters to a stressed pilot who jerks the stick backwards to increase pitch from 6 to 12 degrees in a couple of seconds. I quantified the difference in terms of stick angle and force.

Still, if the guy has direct law, he may as well bring the airplane to the stall, no question, but what do you make of the following ?

THS is still at 3 deg and the stall cannot be that developed so the indicated airspeed wonít go below the threshold to silence the stall warning that will still warn when the captain is back. Of course if that captain had the chance to naturally contemplate what kind of input is made by the PF on the flight control commands Ö that could enormously help him to positively evaluate whatís going on here.
I agree with the first sentence, and wrote essentially the same in one of my recent posts. Regarding the captain, the stall warning is loud enough to be heard through a closed cockpit door. The captain must have heard it when he entered the cockpit.

Last edited by HazelNuts39; 24th Aug 2012 at 09:38. Reason: THS changed to 3.5 degrees based on final report fig. 63
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Old 24th Aug 2012, 08:10
  #86 (permalink)  
 
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I agree with the first sentence, and wrote essentially the same in one of my recent posts. Regarding the captain, the stall warning is loud enough to be heard through a closed cockpit door. The captain must have heard it when he entered the cockpit.
CVR transcript
2 h 11 min 41,8

I have the
impression (we
have) the speed
SV : stall
2 h 11 min 42,4 SV : stall
2 h 11 min 42,5

Er what are you
(doing)?


Noise of cockpit
door opening

2 h 11 min 43,0
Whatís happening? I
donít know I donít
know whatís
happening

cricket
2 h 11 min 44,5 SV : stall
2 h 11 min 45,5
Weíre losing control
of the aeroplane
there
The captain heard the stall warning ... an if he was in the rest station (who is just side the flight deck) he will have heard ( trough the wall ) this ( loud ) warning from about a minute ..
Of course .. as I'm certain .. he was not in the rest station .. unfortunately ( bad luck again ... )
In fact .. nobody know where he was ... not Robert who bell him and ask frantically for the captain return ... nor the BEA ....
And it's not Bonin preoccupation ... he have the hands full and more ....
Maybe shame for him but the best was that Robert make a general call "the captain is requested urgently in the cockpit" ...

Last edited by jcjeant; 24th Aug 2012 at 08:22.
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Old 24th Aug 2012, 09:00
  #87 (permalink)  
 
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Originally Posted by bubbers44
Life is so much easier in a Boeing if UAS situation happens at altitude in cruise. Just keep the same attitude and power you had and get out the UAS check list. If the altimiter and VSI work you are even more golden. Not a real emergency at all. Just fly the airplane.
Wouldn't that also work in other types, including the FBW Airbuses?
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Old 24th Aug 2012, 13:08
  #88 (permalink)  
 
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Originally Posted by DL-EDI View Post
Wouldn't that also work in other types, including the FBW Airbuses?
Indeed. Several Airbus (and non-Airbus) guys advanced the fact that if the crew had left the controls alone for a few seconds at the point of autopilot disconnect, power and trim settings would in all likelihood have been maintained.
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Old 24th Aug 2012, 13:34
  #89 (permalink)  
 
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Originally Posted by gums
I do not recommend that the 'bus go from full laws to "direct law" willy nilly. But seems to me that a few practice sessions in the real jet in "direct law" would provide a lotta confidence to the crews and also show them the inherent characteristics of the jet.
Your experience makes you the most knowledgeable man here around on FBW and flight control laws.

Do not lose of sight that direct law is already practiced for every single early part of takeoff and every late part of landing by an Airbus pilot.
Direct law is also active after a number of malfunctions, which are encountered during usual training.
Direct law has been practiced during the initial training when only one Flight Control Computer was left ON to demonstrate how the Airbus behaves as a 'conventional aircraft'.
Also some exercises as LOST OF ELEV and MANUAL BACKUP go further that direct law as the main way to control pitch and overall performance is done through the THS ONLY (stick useless for pitch control).

Just to mention that direct law is not that wild thing.


But what Iím more interested here is how direct law would have simplified the all situation of AF447.
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Old 24th Aug 2012, 13:37
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Originally Posted by HN39
I agree with the first sentence, and wrote essentially the same in one of my recent posts. Regarding the captain, the stall warning is loud enough to be heard through a closed cockpit door. The captain must have heard it when he entered the cockpit.
You know better than that HN. You told me the other day I was maybe 'evading' the issue, it was not justified and as soon I could properly get what your point was, we were able together to bring the subject further.

So it is my turn to question : Are you evading the points of discussion ?
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Old 24th Aug 2012, 15:18
  #91 (permalink)  
 
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So it is my turn to question : Are you evading the points of discussion ?
I don't think that I am evading any point of substance. I do have the feeling that, having clarified the facts, our discussion has reached the point were remaining differences are matters of opinion. Regarding matters of opinion, I am always reminding myself that I am an engineer participating in a pilot's forum. If there is a technical point to discuss, please be more specific.

Last edited by HazelNuts39; 24th Aug 2012 at 15:23. Reason: wording (italics)
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Old 24th Aug 2012, 18:49
  #92 (permalink)  
 
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Originally Posted by HazelNuts39
The BEA comment is correct, of course. But in the circumstances of AF447 it is mostly theory. It applies if you approach the stall slowly, in still air at low altitude gently manipulating the stick so that you can feel the stickforce increasing the closer you get to the stall. The subtle change in stickforce characteristics hardly matters to a stressed pilot who jerks the stick backwards to increase pitch from 6 to 12 degrees in a couple of seconds. I quantified the difference in terms of stick angle and force.
I'm probably in over my head here, maybe you guys are talking about some deeper issue, but....

I never tried to stall a transport category jet above 17500ft, so I must speculate, but I think you over rate the "subtleness" of stick force characteristics. I'll leave it up to the more research minded among us to find the regulatory standard, but if memory serves there is a minimum value of stick force per knot of deviation from trimmed speed. For the simple minded pilots out there, including me, that means that it takes an ever increasing amount of stick force to fly further and further away from trimmed speed. If the aircraft is trimmed for M80/260KIAS, and the pilot slows down, he must exert an not insignificant amount of force on the stick in order to maintain his new speed. Assuming of course that the aircraft does NOT trim automatically.

I think the BEA wording that you quoted is correct, and it is correct all of the time. It matters not whether you enter the stall from low and steady, or from high and unstable (flight path), either scenario in a "classic aeroplane" (BEA words) requires increased stick force to move and hold the airplane in the slower, approaching stall, situation.

The Bus, offering ZERO control feedback, denies its pilot, completely denies its pilot, this time tested tactile clue to airspeed.

The point I want to make is simple, in our scenario but in a "classic aeroplane" the pull necessary to stall the airplane would not have been "insignificant". In our scenario in the accident airplane, the pull force necessary to induce a stall was apparently "insignificant".
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Old 24th Aug 2012, 18:57
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Originally Posted by CONF_iture

Direct law has been practiced during the initial training when only one Flight Control Computer was left ON to demonstrate how the Airbus behaves as a 'conventional aircraft'.
Also some exercises as LOST OF ELEV and MANUAL BACKUP go further that direct law as the main way to control pitch and overall performance is done through the THS ONLY (stick useless for pitch control).
Maybe your sim instructor know tricks mine does not, but an Airbus MIA A320 Simulator with only one ELAC/SEC/FAC on handles like a truck with malfunctioning power steering and broken dampers.

The only way my instructor could force Dir Law left us with no roll control spoilers, slow ailerons, and resulted in an extremely unresponsive airplane.

Direct Law, in the manner some desire, would offer full control of all control surfaces, as its name implies, directly.

Last edited by TTex600; 24th Aug 2012 at 19:16.
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Old 24th Aug 2012, 19:56
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TTex says...

"The point I want to make is simple, in our scenario but in a "classic aeroplane" the pull necessary to stall the airplane would not have been "insignificant". In our scenario in the accident airplane, the pull force necessary to induce a stall was apparently "insignificant"."

The pull force to induce STALL was certainly insignificant, and may I also add, 'irrelevant'. The aircraft wanted a gee, and found it, since at post STALL "free fall" it had it. at terminal velocity, the THS appeared content with one gee.....

The pilot input was never exactly in command. To be in command, one needs data, and shy of its full quiver, (notwithstanding the hue and cry re: instruments, which are not known, never will be...) PF had a STALL warn he was ignoring, feel that was not there, and a load of confusion that appeared in the form of FD.

People insist he had a Pitch cue, possibly so.... The CVR has the answers, probably in the "deemed irrelevant" category.... Captain heard the STALL warn plus cricket, he said nothing? My ass.....
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Old 24th Aug 2012, 22:05
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Originally Posted by bubbers44

Life is so much easier in a Boeing if UAS situation happens at altitude in cruise. Just keep the same attitude and power you had and get out the UAS check list. If the altimiter and VSI work you are even more golden. Not a real emergency at all. Just fly the airplane.

Wouldn't that also work in other types, including the FBW Airbuses?
Yes it would but my neighbor Airbus captain said he might have done the same thing. What does AB training teach these people?
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Old 24th Aug 2012, 23:05
  #96 (permalink)  
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bubbers44;

Your neighbour Airbus pilot likely has access to the Airbus-produced Flight Crew Training Manual. The FCTM has very clear guidance on how to handle the UAS abnormal and/or ADR failures.

The following, from an FCTM in early 2007, is the essential part of the response:

PART 1: MEMORY ITEMS
If the safe conduct of the flight is affected, the flight crew applies the memory items. They allow "safe flight conditions" to be rapidly established in all flight phases (takeoff, climb, cruise) and aircraft configurations (weight and slats/flaps).The memory items apply more particularly when a failure appears just after takeoff. Once the target pitch attitude and thrust values have been stabilized, as soon as above safe altitude, the flight crew will enter the 2nd part of the QRH procedure, to level off the aircraft and perform trouble shooting. This should not be delayed, since using the memory item parameters for a prolonged period may lead to speed limit exceedance.


PART 2: TROUBLE SHOOTING AND ISOLATION
If the wrong speed or altitude information does not affect the safe conduct of the flight, the crew will not apply the memory items, and will directly enter the part2 of the QRH procedure.


Airbus also produced the following in September, 2006:

http://www.iag-inc.com/premium/Airbu...ableSpeeds.pdf
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Old 25th Aug 2012, 00:08
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Hi PJ2,

Thanks for the link to ppt.
Can you please explain why both the QRH and ECAM in slides 19 & 20 say to turn the FDs OFF, (that action was not accomplished in AF744) yet the diagram clearly shows the FDs ON and with no pitch guidance annunciated.

Last edited by rudderrudderrat; 25th Aug 2012 at 00:09.
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Old 25th Aug 2012, 00:49
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Where has basic training gone? Has automation made them robots? I hope not but in this case it did.
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Old 25th Aug 2012, 01:36
  #99 (permalink)  
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Can you please explain why both the QRH and ECAM in slides 19 & 20 say to turn the FDs OFF, (that action was not accomplished in AF744) yet the diagram clearly shows the FDs ON and with no pitch guidance annunciated.
Nice catch!

No, I can't explain it but the indication is inconsistent - there is no "1FD2" or "--FD2" or "1FD--" in the FMA displayed yet as you've observed, the FD is "ON", (shown in the HDG-V/S mode vice FPV symbol and FP director).

It's not the first time I've seen oddities and inconsistencies in training materials though, and this one appears to be in development - who knows what its history is. The qualifying condition "Safe conduct of the flight affected?" is shown, "Defined during training" so there's obviously other training associated and a narrative that goes along with this one.
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Old 25th Aug 2012, 03:19
  #100 (permalink)  
 
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BUSS requires the 3 ADR's be physically deselected.

It's basically a recover (land) the aircraft and optimized for the approach mode.

Does the ISIS not have ILS capability with an ISIS FD?

...would this be similar and account for the limited FMA annunciations?

LOC* & GS arm are what's displayed...

Interesting.....and weird

edit: I would have sworn lateral and vertical are reversed on the FMA, but beer can create a feeling of more knowledge than one actually possesses.

Last edited by OK465; 25th Aug 2012 at 14:38. Reason: added italics in the clearer light of day
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