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AF447 Thread No. 3

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AF447 Thread No. 3

Old 30th May 2011, 18:37
  #761 (permalink)  
 
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MurphyWasRight, sensor_validation's words led me to think "he" referred to the captain rather than PNF. But, I note further on in sensor_validation's remarks he says PNF was unhappy with what PF was doing, implying he was more alert than the PF.

I won't let you guys have it both ways.
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Old 30th May 2011, 18:40
  #762 (permalink)  
 
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LYKA:

NTSB studies show weather to be a factor in about 25 percent of all U.S. flying accidents between 1994 and 2003. Khatwa said initial and recurrent flight crew training should cover fundamental concepts in six areas of weather-radar operation: beam coverage, Earth-curvature effects, antenna stabilization, tilt and gain management, calibrated weather and range. System limitations, such as attenuation and the significance of green radar “echoes” at high altitude, also should be covered.

These recommendations arise from analysis of pilots’ difficulties and concerns uncovered while Honeywell was developing its RDR-4000 radar. Khatwa’s study included a human-factors evaluation of flight-crew radar use, a global survey to assess pilots’ fundamental understanding and perceptions of training, and analyses of weather radar-related incidents and accidents. He concluded pilots did not understand fundamental weather-radar concepts; typical equipment use precluded detection of severe weather; and dedicated training was not standard practice.
Not clear if this applies to all operators. How much training is typical in an airline environment? Given the importance of avoiding CBs, substantive formal training would seem to be warranted.

Has anyone developed a radar simulator? By comparison with a full flight simulator, it would appear be quite cheap and simple to develop one.
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Old 30th May 2011, 18:45
  #763 (permalink)  
 
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Originally Posted by FE Hoppy View Post
I'm not sure how you know that they found all airspeed information gone. There is no indication in the report that the airspeed information was false at any point. Only that for a minute the standby didn't agree with the PFD. I also don't see and indication of a "plethora of warnings".
Hi.

From 2 h 10 min 05 , the autopilot then auto-thrust disengaged and the PF said "I have the controls". The airplane began to roll to the right and the PF made a left nose-up input. The stall warning sounded twice in a row. The recorded parameters show a sharp fall from about 275 kt to 60 kt in the speed displayed on the left primary flight display (PFD), then a few moments later in the speed displayed on the integrated standby instrument system (ISIS).
...
Note 2: Autopilot and auto-thrust remained disengaged for the rest of the flight.
At 2 h 10 min 16, the PNF said "so, we’ve lost the speeds" then "alternate law […]".
All of this is consistent with loss of speed information to the computers (and the flight deck instruments) due to iced-up pitot tubes, and it would appear that the PNF correctly diagnosed this in a little over 10 seconds. The plethora of warnings came after whatever caused the pitch-up and stall condition.

Originally Posted by peplum View Post
40° AoA, read a such value and i guaranty the guy would have push all his weight on the stick ..
Then why didn't the Birgenair Captain in his 757 do just that in the same situation? This is where the psychological/human factors aspect comes in to play.

Originally Posted by bearfoil View Post
From three years ago, I have said pretty much the same thing, and after your last post I admitted to that very thing. The problem aisi, is the interface twixt a/c and PF's caress.
And the point I'm making is that the aircraft is, by design, doing exactly as the pilot commands. At this point there is no "interface" as such - the computers are simply doing everything they can to pass the pilot's commands along to the control surfaces.

Anyway - I *really must* leave it there!
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Old 30th May 2011, 18:54
  #764 (permalink)  
 
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DJ77:
With this in mind and noting that between 2 h 10 min 16 and 2 h 10 min 50 (citing the report) “The PF made nose-down control inputs”, I venture to submit that it is quite unclear what exactly caused the zoom climb to 37500 ft and this is a hint that BEA intends to closely examine this point.

Whether it was pilot induced or something else, this phase of the accident played a major role in establishing the confusion that followed.
The zoom climb and resulting loss of a/s and increase in AoA was the apparent cause of the stall, which the crew either didn't recognize or was unable to fly out of. So, after the loss of reliable a/s, it was essentially the proximate cause of the accident. And the report gives no real hints as to why the PF commanded nose-up. As the FDR didn't record the a/s displayed on the PF's display, it may, in the end, be unresolvable to a certainty.

Although it appears that this accident was a result of incorrect crew response to a UAS, that hardly absolves anyone else of responsibility. Airbus built a flight control system around critical flight data coming from instrumentation that proved, in the end, insufficiently redundant. Thales designed a pitot tube that, although meeting Airbus specs, proved far more prone to icing than did its competitors. AF did not appear to be sufficiently alarmed by previous instances of pitot icing to act to fix the problem with sufficient urgency. And, of course, the training provided to aircrews to deal with the situation proved inadequate.

Lots of blame to go around, based just on what's known so far. I do find it telling, though, that AF seems better at lining up the holes in the cheese than its competitors. That's not to say AF is unsafe; no major carrier is "unsafe" in comparison to competing modes of transport. But no other carrier has managed to have the first instance of hull loss in revenue service and/or loss of passenger life in four different aircraft types (Concorde, A320, A330, and A340.)

The French have managed superlative safety records in comparable high-tech enterprises (nuclear and high-speed rail in particular). AF appears an outlier in several ways.
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Old 30th May 2011, 18:58
  #765 (permalink)  
 
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Why no clarification of ACARS in BEA paper?

Hi!
I have been following these discussions on several forums for some years now.and learnt a lot. However, there are some unexplained, and unexpected, messages in the ACARS stream. Some of these seems to be ignored in the current discussion. Why? E.g. 2:11:55-.1/FLR/FR0906010210 27933406EFCS1 X2,EFCS2X,,,,,,FCPC2 (2CE2)/WRG:ADIRU1 BUS ADR1-2 TO FCPC2,HARD.
If WRG means wiring problems or signal problems it is a strange message from a healthy aircraft system.
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Old 30th May 2011, 19:10
  #766 (permalink)  
 
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From 2 h 10 min 05 , the autopilot then auto-thrust disengaged and the PF said "I have the controls". The airplane began to roll to the right and the PF made a left nose-up input. The stall warning sounded twice in a row. The recorded parameters show a sharp fall from about 275 kt to 60 kt in the speed displayed on the left primary flight display (PFD), then a few moments later in the speed displayed on the integrated standby instrument system (ISIS).
...
Note 2: Autopilot and auto-thrust remained disengaged for the rest of the flight.
At 2 h 10 min 16, the PNF said "so, we’ve lost the speeds" then "alternate law […]".
All of this is consistent with loss of speed information to the computers (and the flight deck instruments) due to iced-up pitot tubes, and it would appear that the PNF correctly diagnosed this in a little over 10 seconds. The plethora of warnings came after whatever caused the pitch-up and stall condition.
Wouldn't a "left nose up" command without any change in thrust cause airspeed to decrease?
For a stall warning to sound wouldn't the airspeed signal still need to be valid?
If with no increase in thrust and a nose up input after a stall warning sound along with a climb rate of up to 7000 ft/m cause the airspeed to rapidly fall?

I believe the correct position for the horse is in front of the cart not behind it.
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Old 30th May 2011, 19:15
  #767 (permalink)  
 
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JD-EE
MurphyWasRight, sensor_validation's words led me to think "he" referred to the captain rather than PNF. But, I note further on in sensor_validation's remarks he says PNF was unhappy with what PF was doing, implying he was more alert than the PF.
JD-EE and others.
Most of you may not recognize what sensor_validation is doing with his analysis, but if anyone is familiar with the communication analysis techniques of Sidney Dekker in (for example) "The Field Guide to Understanding Human Error" (a highly recommended read) they will recognize the process.

Sensor_validation gets a big attaboy for those initial efforts.
There is a lot that can be learned from this type of analysis process.
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Old 30th May 2011, 19:25
  #768 (permalink)  
 
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Originally posted by Diversification ...
... there are some unexplained, and unexpected, messages in the ACARS stream. Some of these seem to be ignored in the current discussion. Why? E.g. 2:11:55-.1/FLR/FR0906010210 27933406EFCS1 X2,EFCS2X,,,,,,FCPC2 (2CE2)/WRG:ADIRU1 BUS ADR1-2 TO FCPC2,HARD.
What we are up against here, is that the BEA has provided a brief description of what happened, but not why. In that context the ACARS message you have mentioned is a "maintenance" message that is indicating a fault that occurred at 0210. It may be indicating something that is complicit in what was happening, or a by product. Svarin has spent some time trying to analyse what it was trying to tell us, but until the BEA have completed their investigation, the relationship to this accident and the above ACARS message will remain a mystery.

Having said that, I did mention it a few pages back in relation to what caused the initial upset.
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Old 30th May 2011, 19:26
  #769 (permalink)  
 
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JD-EE:
MurphyWasRight, sensor_validation's words led me to think "he" referred to the captain rather than PNF. But, I note further on in sensor_validation's remarks he says PNF was unhappy with what PF was doing, implying he was more alert than the PF.

I won't let you guys have it both ways.
The only "fact" is that the PNF (recently asleep) was calling the Captain, whether he was seriously unhappy or just following protocol for any unusual situation is not mentioned in the report.

I would suspect it well could be both, however the point remains that he may not have been at the top of his game when things went wrong and thus less likely to be able and or willing to offer suggestions or intervene.

If I understand correctly he could have taken control at any point but did not utill much later.

----

As to Captain taking over the controls, not likely since his body was found, hence not strapped in.
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Old 30th May 2011, 19:28
  #770 (permalink)  
 
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DozyWannabe, all that's correct about loss of airspeed. However, I am an engineer and apparently so are the BEA people. They specifically noted the RHS is not recorded. So they never directly said all airspeed was lost. They could not sit down and directly prove it without "circumstantial evidence".
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Old 30th May 2011, 19:30
  #771 (permalink)  
 
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Originally Posted by FE Hoppy View Post
Wouldn't a "left nose up" command without any change in thrust cause airspeed to decrease?
Yes, but not by that much. We're not told how much deflection went into the "left nose up" input, nor are we told how long it was held.

For a stall warning to sound wouldn't the airspeed signal still need to be valid?
No, it's as much a function of AoA as anything (while the A330 doesn't have a specific indicator, it *does* have a vane sensor). Stall *protection* requires valid airspeed (which is why the degradation to Alt 2 law).

If with no increase in thrust and a nose up input after a stall warning sound along with a climb rate of up to 7000 ft/m cause the airspeed to rapidly fall?
Not by that much and not that quickly.

I believe the correct position for the horse is in front of the cart not behind it.
I believe that the BEA and Airbus considered the ACARS messages they received consistent with pitot icing. Is your supposition that this was not the case, and if so, what do you suppose it was?

JD-EE - see above.

(Damn, caught posting *again*!)
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Old 30th May 2011, 19:33
  #772 (permalink)  
 
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Originally posted by JD-EE ...
They could not sit down and directly prove it without "circumstantial evidence".
They were dealing with the FDR and CVR, and it may well be that data will be available from the QAR. I doubt if we will know that until the next Interim Report.
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Old 30th May 2011, 19:38
  #773 (permalink)  
 
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MurphyWasRight - it looked like sensor_validation was drawing conclusions or making inferences beyond the bare facts that I didn't think were particularly valid for the very procedural and ritualized aspects of being in a cockpit - or even being a waiter going on break briefing his replacement.
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Old 30th May 2011, 19:48
  #774 (permalink)  
 
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Dozy
In Alternate Law 2 the pilots have complete control over all aspects of the aircraft, though you're commanding pitch and roll rate unlike in Direct Law which commands deflection. In short - the pilot is in charge and the computers are specifically programmed to do whatever the pilot asks.
I think you are missing a big aspect of the crew's control problem that night.

If the aircraft is right wing heavy, the aircraft will only fly straight with continuing left stick. How easy is it to separate the roll chanel from the pitch channel in this case? This aircraft was flying in Direct Law in roll.

Think about what this means to the lateral trim situation.!!!
NO Lateral Trim.
NO tendency to return to wings level. You must fly the roll angle full time.
Yes you have enough roll authority to level the wings.
You cannot let go of the stick-It will roll.
Do you see how a guy settling into this situation might apply nose up at the same time???

If not, do this experiment:
Place right arm on table in front of you. Point thumb up.
Put a stick in hand. Tilt stick to left.
With opposite hand, resist the attempt to tilt stick. Do you accidentally tilt stick toward you?? If not, apply more force until you have to cup stick in hand instead of with finger tips.
Get the idea?
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Old 30th May 2011, 19:53
  #775 (permalink)  
 
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Quoth DozyWannabe:
Quote:
If with no increase in thrust and a nose up input after a stall warning sound along with a climb rate of up to 7000 ft/m cause the airspeed to rapidly fall?
Not by that much and not that quickly.
OK, let's look at energy. Potential energy is mass times gravitational force times height, mgh. Kinetic energy is 1/2 the mass times the speed squared.

So we should be able to calculate speed lost from the height gained. "m" or mass is the same in both equations. So we can leave it out. The change in potential energy was m * 32 feet per second times 1500 feet. The change in kinetic energy must equal this. So 1/2 m dV^2 (delta-V squared) is 32*1500. Or dV^2 = 32*1500 or about 219 feet per second which is about 130 knots REAL speed. That needs to be converted to a change in kCAS and I'm not sure of that conversion. But it puts the plane's velocity change within the ballpark of what was shown.

Thanks for tweaking me into doing the rather simple math. They note no change in thrust took place. PF may have expected, for whatever reason, CLB thrust to be asserted. This might be because he moved the stick before the stall warning was played.
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Old 30th May 2011, 20:00
  #776 (permalink)  
 
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The initial storm climb

Although not an airline pilot, I have read every post on this thread. There are a couple of things as yet unexplained:
1) there seems to be an assumption that the first (2) stall warnings (just after 2h 10m 05) were spurious, possibly related to the IAS error. Firstly, there is nothing in the BEA statement to suggest they were spurious; and secondly, as the stall warner is fed from the AOA indicators and not the pitots, the IAS error would surely not cause a stall warning
2) the "storm climb" at 7000fpm for 2500 feet is not explained. The PF made "a left nose-up input" not, as he is later stated to be making, "sustained" nose-up input. And there is nothing in the text to suggest that he pitched the aircraft up to the extent needed to climb at this rate on cruise power settings - surely that would have required 20-30 degree pitch angles that would surely have been mentioned? There is also a mention of nose-down inputs in this phase

On the other hand, a big updraft would both lift the aircraft without big pitch-up, and cause the AOA to increase, perhaps setting off the stall warner?

Where this leaves the explanation of the crash I don't know, but we do not yet seem to have satisfactorily explained this first 45 seconds.
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Old 30th May 2011, 20:03
  #777 (permalink)  
 
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Machinbird . . .

Excellent example with the stick! That clarified much of the difficulty I was having in understanding the continual trim up. That, combined with the sudden mixed rules of operation in different stick axes . . . in a crisis . . . what a recipe for disaster.
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Old 30th May 2011, 20:04
  #778 (permalink)  
 
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Back in post #260 I made some assumptions about the THS and the AoA. The basic post is repeated below with a small addendum and should be self explanatory.
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% the angle of attack decreased, the speeds became valid again and the
stall warning sounded again.
My interpretation is that the aircraft was in a well established stall (deep stall?) and passing through FL250 with RoD about 10,000 feet/min, and even though both engines N1's were 55%, the pitch-down inputs decreased the AoA and the airspeed data became valid. However, that IAS was low and the stall warning activated again but ceased with further pitch-up commands as the data again became invalid.

Without AoA information, neither pilot had any idea in what part of the stall regime they were, and seemed to react as if a return of the SW was indicating Vmo, hence the continuing pitch-up command. So failure at this time to persist with the pitch-down command effectively left them doomed, as even then with the time taken for the THS to readjust (if it was going to**) and for the wings to start flying, meant that the chance of reducing the RoD to zero before FL0 was marginal.

It strikes me that no-one on the flight deck realized that the AoA data was only valid when IAS was greater than 60KTS. Even though they went looking for the FPV, it seems it was only after the SW stopped at 2:11:40 plus a few seconds, and therefore to no avail - see ACARS FPV messages timed 0212z. Their final chance to grab the FPV page was missed shortly after 2:12:02 when the stall warning sounded again - meaning valid airspeed!

** The THS question?? As IAS had gone below 60KTS, the aircraft was no longer in Alternative 2 Law, but was now in Abnormal Law which means that the THS must be manually trimmed. Even so, in the description given above, I believe that with the low airspeed the elevator was still capable of making an attitude change, provided it received a nose-down command.

Last edited by Jetdriver; 30th May 2011 at 21:33.
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Old 30th May 2011, 20:07
  #779 (permalink)  
 
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Note: When the measured speeds are below 60 kt, the measured angle of attack values are considered invalid and are not taken into account by the systems. When they are below 30 kt, the speed values themselves are considered invalid.
This note from the report links the vane angle signals to the validity of the airspeed.

Later when the nose is lowered and airspeed increases back to above 60kts the stall warning sounds again. The pilot responds by pulling and the warning stops as the airspeed drops below the lower limit.

So while we cannot say what caused the airspeed to drop we do know that it happened after the nose up command and after the stall warning.

We also know that the pitch attitude increased to 10° and the aircraft began to climb.

We also know that after the first mention of nose down input the VS dropped from 7000f/m to 700f/m and the airspeed increased sharply to 215kts by which time the aircraft had climbed 2500ft

The first mention of thrust increase is after this initial climb after a further stall warning.

If I bunt at the top of a zoom climb but fail to increase thrust will this cause a stall warning as the g reloads after the bunt?

I'm not discounting anything but I'm not adding information that isn't described in the record of events described in the report.
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Old 30th May 2011, 20:23
  #780 (permalink)  
 
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Originally Posted by Machinbird View Post
If the aircraft is right wing heavy, the aircraft will only fly straight with continuing left stick. How easy is it to separate the roll chanel from the pitch channel in this case? This aircraft was flying in Direct Law in roll.

Think about what this means to the lateral trim situation.!!!
NO Lateral Trim.
NO tendency to return to wings level. You must fly the roll angle full time.
Yes you have enough roll authority to level the wings.
You cannot let go of the stick-It will roll.
Do you see how a guy settling into this situation might apply nose up at the same time???

If not, do this experiment:
Place right arm on table in front of you. Point thumb up.
Put a stick in hand. Tilt stick to left.
With opposite hand, resist the attempt to tilt stick. Do you accidentally tilt stick toward you?? If not, apply more force until you have to cup stick in hand instead of with finger tips.
Get the idea?
All fair points.

Firstly, was the aircraft right-wing heavy?

Secondly, I can see how it would be a handful, but the force we're talking about here is not an accidental tweak in the wrong direction. To get the THS up to 13 degrees requires full back pressure for several seconds. This is the problem that is not going to be solved until at least an interim report is out, and anything we suggest is ultimately pointless.

Thirdly, I couldn't get your experiment to work - would the fact that I am left-handed be a problem there?
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