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AF 447 Thread No. 7

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AF 447 Thread No. 7

Old 17th Nov 2011, 00:30
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Originally Posted by CONF iture
Perpignan told a different story as the USE MAN PITCH TRIM FLAG was initially displayed but disappeared when the flight switched into Abnormal Attitudes Law.

Dani, what is that FCOM reference that could explain I was not able to get a forward autotrim ?
Did it disappear by law change or just get pushed out of view by other ecam messages ? Same effect, different reason. [I have vague recollection it was the latter, but could be wrong].

FCOM reference - section on abnormal attitude flight law. But you know that

The real issue is how you went into that law in sim, but DW didn't and 447 didn't.

Based on what I've read:
  • 447 stayed in Alt2 because triple ADR failure meant it wouldn't switch based on airdata conditions (and g-load conditions weren't breached).
  • Your sim went into abnormal law based on AOA following dual (not triple) ADR fail
  • DW sim again not triple ADR failure, but I'm not sure AOA got high enough to trigger abnormal law from what he's written.
Now, can anyone provide FCOM reference for the triple adr fail caveat on abnormal law entry conditions.... I don't think it's in there.

And yes, not having "use man pitch trim" displayed in abnormal law is not logical to me either. In fact, I'm not sure why abnormal law is there at all - can't see why not use direct law for this purpose (abnormal attitude recovery). What extra authority does abnormal law give over direct ?

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Old 17th Nov 2011, 00:34
  #322 (permalink)  
 
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Originally Posted by Clandestino
I still don't get it. You are trying to jump over towering cumulus by trading as much speed for altitude as possible - "green dot" is very technical term for minimum clean speed. You fail to clear TCU. You hit the updraft and lose downward pitch authority. And yet, you think it is normal aeroplane behaviour.

Congratulations on your coolness but I fail to understand source of it. Why would you think it is normal to loose downward pitch authority? Was it something in your training? Did you experience it many times? Why do you assume that what's valid for navigation system is also valid for flight controls system? Could you please explain how updraft can fool ELAC into robbing you of nosedown authority?

I have just passed 4000 hours mark on aeroplanes that would simply kill me if I ever stall them. Don't see anyone being too excited about it,
Green dot is not minimum clean speed. Green dot is L/D max. Considering this basic point, I fail to find it worth my time to further discuss this, or the AB with you.

Because you bring experience into the discussion, I've well more than three times the time you mention and have never NOT flown an aircraft that could simply kill me if I stalled them. But then again, I've intentionally stalled many a DC9 and am still here to tell the tale. Good day.
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Old 17th Nov 2011, 01:05
  #323 (permalink)  
 
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Originally Posted by IF789
I think the risks either way are going to be very very difficult to quantify which is why this is a tough call.
That is what the engineers get their pay for...making tough decisions on system design.

I don't design circuits for a living or write software, but I've done a fair amount of root cause analysis on defective equipment and have had pretty good exposure to same over the last 55 years. The following is a gut feeling hypothesis only so take it with a healthy dose of skepticism:

Once all 3 airspeeds become corrupted from high AOA, if any part of the primary or supporting calculations for operation of the trim rely on airspeed or its derivatives, then operation of the trim becomes compromised. Without looking at an actual complete logic diagram of how the system operates, this is difficult to analyze.. Something as mundane as a calculation of how much torque the hydraulic drive motors must generate to drive the THS (just for example) can have airspeed components in it that crash the whole logic chain for THS drive. Any reasonable software would then have error handling options for such an error. Generally the safest option would be to halt all automatic motion on error.

Now I could be seriously wrong here, but something stopped the THS from trimming nose up before it actually hit the end limits. If it was an error handling routine, it might stop nose down trim as well until some reliable airspeed information appeared. In this case you might effectively be in "Direct Law" without an indication, at least as far as THS trim goes. Elevator motion would then still be Alt2 though.

Last edited by Machinbird; 17th Nov 2011 at 04:20. Reason: Add clarification to error handling possibilities.
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Old 17th Nov 2011, 01:53
  #324 (permalink)  
 
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Machinbird,

without getting into the realism of your ideas - during their whole descent, they never even got to down elevator, so nothing weird is needed for the ths not to move...
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Old 17th Nov 2011, 02:57
  #325 (permalink)  
 
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Originally Posted by Zorin_75
Machinbird,
without getting into the realism of your ideas - during their whole descent, they never even got to down elevator, so nothing weird is needed for the ths not to move...
Yes, the elevator never made it past neutral, but that mayonaise stirring stick did for a large number of instances. So did the LH seat stick.

You couldn't do that kind of useless rapid motion with the old irreversible hydraulic driven- cable controlled flight controls of yesteryear. The actuators generally had to move to follow up the input command. Until the cylinder followed up, you only had the limited motion.of the control valve travel available.

With a stick flailing around like that, you would have to mentally integrate your motion relative to the center detent to properly evaluate what the net effect of your control motions was. Are we sure that FBW is the better control system??
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Old 17th Nov 2011, 03:59
  #326 (permalink)  
 
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The aircraft "knows" nothing. It relies on appropriate air data and "intelligent" pilot inputs to perform within its design boundaries.

AF447 did all it was designed to do, and when the "intelligent being" making the command inputs wanted NU, the aircraft complied.

What bothers me is the "intelligent" part of this equation was missing.

I doubt if any of the pilots on this thread would want the aircraft designers to put the "intelligent" part into the automation so that the aircraft "knows" best.

The degradation of control laws is indicated on ECAM as well as on PFD.

On ECAM
in ALTN : CAM EW/DFLT CTL ALTN LAW (PROT LOST)
MAX SPEED 305/.82

in DIRECT : CAM EW/DFLT CTL DIRECT LAW (PROT LOST)
MAX SPEED 305/.80
USE MAN PITCH TRIM

On PFD
The flight control status awareness of the crew is enhanced on the PFD.
Indeed the availability of PROTECTIONS is outlined by specific symbols = (green), and by the specific formatting of the low speed information on speed scale, in normal law.
When protections are lost, amber crosses X are displayed instead of the green protection symbols =.
When automatic pitch trim is no longer available, this is indicated as USE MAN PITCH TRIM amber message below the FMA.
Auto trim is always available except when indicated to the contrary as detailed above.

As I have posited previously, the PF effectively spent 4 minutes battling with a compromised yaw damper that contributed to the roll and at no time was the SS left in the longitudinal neutral position. Without regurgitating the stuff long since posted (many times), if you simply don't know, the result will be equally simple.

Last edited by mm43; 17th Nov 2011 at 17:41.
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Old 17th Nov 2011, 10:50
  #327 (permalink)  
 
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Originally Posted by ALphaZuluRomeo
See the point? That's about "graceful degradation" if I understand the concept correctly.
Quite so. Concept is giving as much protection as realistically possible. With all air data gone but with reliable inertial reference, everything goes out the window except the load protection.

Originally Posted by CONFiture
BEA pretends Altn Law was the active Law all the way
BEA is Bureau d'Enquêtes et d'Analyses pour la sécurité de l'aviation civile. It is the French authority responsible for safety investigations into accidents or incidents in civil aviation. It doesn't pretend. It states so, accepting the full responsibility for its words. Where is the problem with that? You have good arguments it was otherwise? Let's see them!

Originally Posted by Lyman
P/P is always the Drill?
It is. It wasn't applied here. No evidence so far supports the hypothesis that A330 flight controls systems prevented the application.

Originally Posted by airtren
if there was no "trimmed stabilizer" on a plane, the pilot did NO trimming at all
Nope. Even with fixed stab, elevator is trimmed for zero force, usually via tabs. I can't recall ever seeing aeroplane without pitch trim.

Originally Posted by airtren
We have the STALL condition being announced loudly - and after so much analysis, very clear in its meaning to us - and throughout the duration of that announcement, we have an "automation" decision/action of employing the "autotrim" to max NU, which obviously if it did anything, it helped the STALL.
Trim was applied IAW control demand. Demand came mainly from right hand sidestick. "Stirring mayonnaise" and "it went forward a few times" are incomplete, therefore inaccurate and possibly misleading description of SS movement. SS traces are available in interim 3.

Originally Posted by infrequentflyer789
Now, can anyone provide FCOM reference for the triple adr fail caveat on abnormal law entry conditions.... I don't think it's in there.
It isn't explicitly written, however FCOM reference is consistent with BEA explanation - since all air data were rejected neither speed<60 kt nor AoA>30° triggering condition could be met.

Originally Posted by infrequentflyer789
What extra authority does abnormal law give over direct ?
None. It just retains G protection.

Originally Posted by TTex600
Green dot is not minimum clean speed. Green dot is L/D max. Considering this basic point, I fail to find it worth my time to further discuss this, or the AB with you.

Because you bring experience into the discussion, I've well more than three times the time you mention and have never NOT flown an aircraft that could simply kill me if I stalled them. But then again, I've intentionally stalled many a DC9 and am still here to tell the tale. Good day.

I am sorry you feel it this way but it really is not about contest between you and me. If it were so, I'd rather go down the PM path, in the unlikely event of finding debate worth pursuing further. As this is Profesional Pilots Rumour Network, open anonymous forum, I believe that details behind your temporary loss of control would be interesting to many a reader here. So what if your company allows regular operation below green dot while my does not? Is my wrong assumption that no Airbus operator would, reason enough to withdraw and retain all the information for yourself?

Nose refusing to go down when commanded so is definitively not normal behaviour of FBW Airbus, especially as with low speed you were far from high speed protection and I really doubt you hit G protection at -1. There must have been something else.

As for hours, they were not intended to illustrate my experience but that aeroplanes that are very likely to enter really unrecoverable stall are flying around in hundreds every day and no one makes a fuss about it. Every aeroplane equipped with stick-pusher is such. Now you mention DC-9, it's good example of T-tail without pusher (Super80's hydraulic elevator ram is not true pusher as it is not activated automatically) implying that T-tailed configuration is not automatically predestined to suffer from deep stall. BTW, there is no direct link between yoke and flight controls on DC9.
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Old 17th Nov 2011, 11:45
  #328 (permalink)  
 
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Clandestino the DC9 series has cables directly connected to the control surfaces. IIRC, specifically the control tabs. The tab directly drives the ailerons and elevators. Transport category jets don't get any more direct controlled than the DirectCable9. Any other other point is purely semantics.
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Old 17th Nov 2011, 13:18
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Originally Posted by Clandestino
There must have been something else.
Probably turbulence: Transition from updraft to downdraft could very well create sufficient reduction of "gee" to satisfy the "gee" demanded by a moderate nose-down SS input, without immediately dropping the nose.
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Old 17th Nov 2011, 13:27
  #330 (permalink)  
 
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Originally Posted by mm43
Auto trim is always available except when indicated to the contrary as detailed above.
It should be the logical way, but Airbus thought otherwise as demonstrated in Perpignan.

I doubt if any of the pilots on this thread would want the aircraft designers to put the "intelligent" part into the automation so that the aircraft "knows" best.
I agree - Actually we would need less of that "intelligence" especially when some data are conflicting. After a discrepancy between AoA data + discrepancy between IAS we do not want automation to stay on the way - Autotrim is NOT welcome.

If I had to keep only one single item, I would say that autotrim has been the killer.
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Old 17th Nov 2011, 13:42
  #331 (permalink)  
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Originally Posted by HN39
Probably turbulence: Transition from updraft to downdraft could very well create sufficient reduction of "gee" to satisfy the "gee" demanded by a moderate nose-down SS input, without immediately dropping the nose.
- the more we think we discover the worse it gets!

Pilot: I want the nose to go down

***: No! (Dave) I can achieve your demand for a change in vertical acceleration in another, far more clever way ( could even be nose up?)

Pilot: But I only wanted the nose to go down.

For heaven's sake - are you serious? Where have we gone wrong? (Answers on a postcard, please). When I move a control I expect a proportionate response in the desired direction.
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Old 17th Nov 2011, 13:44
  #332 (permalink)  
 
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IF789,
USE MAN PITCH TRIM is a message that appears in the PFD.
It appears as well in the ECAM as a reminder but at a later stage on the STATUS page once all ECAM actions have cleared.

For the Abnormal Attitude Laws I must admit I am not convinced by the BEA statement on page 40 :
The flight control law switched from normal to alternate at about 2 h 10 min 05. The alternate law adopted was alternate 2B and it did not change again subsequently. Due to the rejection of the three ADR by the flight control computers (PRIM), the abnormal attitudes law could only have been triggered for criteria relating to inertial parameters, but these conditions were never met.
AoA data were inertial parameters as described on the traces and they met the conditions ...

Also, as Machinbird reminded, what stopped the trim to reach the limit ?
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Old 17th Nov 2011, 14:28
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BOAC,

Perhaps you should re-read TTex600's description of the incident in his posts #169 (p. 9) and #205 (p. 11).
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Old 17th Nov 2011, 14:34
  #334 (permalink)  
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It was you I quoted!
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Old 17th Nov 2011, 15:05
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If I had to keep only one single item, I would say that autotrim has been the killer
Because they were trying to get the nose down for four minutes but autotrim didn't let them?
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Old 17th Nov 2011, 15:11
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Sorry if this is going back a few pages. I'm still trying to catch up, but had to comment on this:

NARVAL wrote:

I think that we should keep in mind the very scant knowledge and training of the pilots at the time in the aerodynamics, stall recovery techniques, stall recognition…It was NEVER thought at the time that those planes could fly beyond the « approach to stall ». It was never thought either that the plane could « fly » with 40 degrees AOA and only 8 or 10 degrees of nose up.
And there was I, a very humble SLF, and happy to be abused with that name by all you god-like pilots, because I was under the impression that the reason I trusted my life to the people at the pointy-end was because they were like me, shared my fascination with things aeronautical, and had both the interest in and the knowledge of just what it is that keeps them up there amongst the clouds; that they actually understood something about the "little arrows" (underneath the wing) and the big ones (on top), and the significance of getting these the wrong way round.

And now I learn that it comes as a complete surprise to experienced 'pilots' that the flow of air over an aerofoil doesn't always produce LIFT, and that even though the nose is pointing up, you might be going down. Furthermore, I've learnt that the 'pilots' responsible for the safety of the SLF at the back of 447 hadn't actually been trained in what to do if the auntonomics dropped out and left them in control. Which makes me wonder why they were there. You could make more money by using the seats for more passengers.

Somebody please re-assure me that I'm wrong; that what NARVAL wrote, and what was so warmly applauded by quite a few 'pilots' on this forum, does not represent the average level of expertise of commercial pilots, that most of them do actually understand what keeps them in the air, because otherwise I'm sticking to sailing!
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Old 17th Nov 2011, 15:14
  #337 (permalink)  
 
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It is a matter of some consequence...."Flight Law changed at approximately 2:10:05...." per BEA.

This is a word that invites doubt, and conjecture. It is an inappropriate statement, and not consistent with accepted levels of research. Alone, the phrase is amateurish, and there is no further refinement.

What prompted the statement? How was it derived? What is the Data referenced to prompt this speculation?

The only data I can find re: the LAW degradation is by the pilot, PNF.

"We have lost the speeds, ALTERNATE LAW."

Which ALTERNATE LAW? It remains unreported by the crew, or referenced by BEA per DFDR. The comment was made sixteen seconds later, after loss of A/P and A/THR.

Of some importance would be the record of airspeed loss, rate and value.

I continue to doubt ICE. A sudden loss of all three ADRs means simultaneous blockage. This is preposterous. A more probable problem would be turbulence, by way of windshear, or blanking of probes similar to a WS alert. OR AoA excursion WITH ROLL.

Clandestino: The fact remains, PF input a PITCH motive, and this defines PITCH, as in PITCH/POWER. It is most definitely possible his stick at two seconds after loss a/p was a preface to P/P. No?

idle bystander. You misunderstand. It is only remotely likely that these pilots were unqualified. By law, they were. This accident is not understood, and do NOT form conclusions as to safety from what you read here. There are perhaps a half dozen events that happened in the correct sequence that downed this a/c. Not that they happened at all, but that the sequence itself occurred. Incredibly remote. You may not believe, but knowing what I know now about 447, I would board with comfort this same flight, pursuant only to the fact that this crew also knew what happened.

The Devil has surprised us all. He saves up for generations to ennable such a catastrophe.
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Old 17th Nov 2011, 15:25
  #338 (permalink)  
 
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Lyman
It is a matter of some consequence...."Flight Law changed at approximately 2:10:05...." per BEA.

This is a word that invites doubt, and conjecture. It is an inappropriate statement, and not consistent with accepted levels of research. Alone, the phrase is amateurish, and there is no further refinement.

What prompted the statement? How was it derived? What is the Data referenced to prompt this speculation?
Though I am not inclined to blindly trust the reports that come from a French organization (because of France's huge investment in AI), I'm waiting for the final report before I'd judge that items are missing.

And, I don't understand your term, "inappropriate statement." Isn't that event documented be ACARS?

Last edited by Organfreak; 17th Nov 2011 at 16:38. Reason: correction
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Old 17th Nov 2011, 15:30
  #339 (permalink)  
 
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In which we find that OF is not finished yet

Lyman
It is only remotely likely that these pilots were unqualified. By law, they were.
Then the legal definition of 'qualified' was sorely lacking and needs revision, as has already been officially acknowledged. Agree that there are many questions and factors, though.

The Russian pilot who let his son 'steer' that A300 was 'qualified' too, and yet everybody died.
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Old 17th Nov 2011, 16:02
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Originally Posted by Lyman
It is a matter of some consequence...."Flight Law changed at approximately 2:10:05...." per BEA.
(...)
What prompted the statement? How was it derived? What is the Data referenced to prompt this speculation?
The DFDR includes two discrete parameters: Control normal law in pitch engaged/not engaged, and Altenate law engaged/not engaged (see page 107 of Interim #3). There is also an ACARS message to that effect.

Of some importance would be the record of airspeed loss, rate and value.
Airspeeds 1 and 3 are recorded and shown in Interim #3.

A more probable problem would be (...) AoA excursion WITH ROLL.
The FCPC's use the mean of AoA1 and AoA2 to eliminate effects of roll and sideslip.
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