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AF447 Thread No. 3

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AF447 Thread No. 3

Old 5th Jun 2011, 19:20
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Fiklefinger may have a point here. With a blocked Pitot Tube & increase in altitude IAS increases, to the point of "indicated overspeed", even though the aircrafts actual speed may remain constant. Many years ago a B727 crashed as a result of a stall brought on by the the crew increasing pitch to reduce the false overspeed warning. They had departed with the Pitot Heaters switched off. In a conventional aircraft an overspeed is dealt with by thrust reduction (partially) or deployment of speed brakes. However 1 of the options the control laws have, in the result of an overspeed is pitch up. Maybe the cmptr did what the 727 crew did before. I understand recently a 330/340 entered an overspeed, due turbulence on the Atlantic run. The aircraft pitched up, with a "severe vertical separisation issue" on an aircraft coming the other way, even though the AB crew were pushing column full forward!! Remember, all these events occure under severe stress for the confused crew. This, IMHO is a design flaw in the aircraft.
Jumbo.
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Old 5th Jun 2011, 19:25
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@jumbojet

I don't know how many time I can say this - the computer did not "do" anything, because autoflight was inhibited by the detected erroneous speed indication. The issue you're referring to has been documented exhaustively on this forum, and is highly unlikely to be related, not least because thus far, no indications of an overspeed indication have been reported.
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Old 5th Jun 2011, 19:43
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Well thats what happens when you join a thread 70+ long half way through! Haveing said that though, why did it pitch up then? We all know, go above your max computed altitude at your peril! I would be very suprised if a pilot chose to climb above his/her max cruise level. Most pilots know the cost of this, even French pilots! Who knows whats in the brain of the ship & who knows it reaction to an unexpected indication, jiust ask MSN!!
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Old 5th Jun 2011, 19:47
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Re airbus can not stall

Quote:
Originally Posted by Smilin_Ed
Quote:
It seems that a number 1 priority is that AB recognise that their aircraft can stall....
BOAC:Fully agree!
infrequentflyer789
If they didn't think it could stall, why did they build in a stall warning and stick shaker ? Why did they document it ? Why did they publish info on stall recovery procedures ?

Airbus knows, and always has, that their aircraft can stall. Airbus state, and always have, that their aircraft can stall. So where does this "cannot stall" come from, who is saying it ? Are there really actual airbus pilots (as opposed to clueless journalists etc) who believe their a/c cannot stall ? If so, the training is way more broken than even the most extreem comments on this thread have suggested.
I can help out here. Some time ago (1998) the chief test pilot of airbus itself,
Captain William Wainwright, is saying:

"The end result of two years work is a training
package including a video and a CD-ROM,
giving an airplane upset recovery training aid.
This package is on free issue to all our
customers, to use as they wish. However, all
members of the joint industry group agreed that
the package is aimed at preventing loss of
control accidents on conventional aircraft. It is
not aimed at protected Fly-by-Wire aircraft.
There is no need for this type of continuation
training on protected aircraft, although a
general knowledge of the principles involved is
useful for every pilot
"

Source: Airplane
Upset Recovery Training Aid*


It was not the idea of airbus alone, however, on the boing page it looked somewhat different.

"Aerodynamic principles of large, swept-wing commercial jet airplanes are similar among all manufacturers. In the interest of safety, and the desire to acknowledge the commonality in recovery techniques, this article was written jointly by Airbus, Boeing Commercial Airplane Group, and Douglas Products Division. The article focuses on Airbus and Boeing airplanes that do not have electronic flight controls, commonly known as fly-by-wire. However, when a fly-by-wire airplane is in a degraded control law (mode), the recovery techniques are appropriate. Additionally, certain conditions can upset any airplane and the basic principles of recognition and recovery still apply regardless of the flight control architecture."

Source: Aerodynamic Principles of Large-Airplane UpsetsLoss of Control in Large Airplanes
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Old 5th Jun 2011, 20:14
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speeds and angles

I am sorry if this is redundant. I have been on and off here and have not had time to read every single message.

In an effort to investigate the difference between the data at point 6, 2:11:40 (35,000 ft, 10,000 fpm down, AoA > 40 and pitch angle 15) and impact, 2:14:28 (0 ft, 10,912 fpm down, groundspeed 107 kt, and pitch angle 16.2) I measured the ground distance along the flight path from point 6 to impact. (I did this on the assumption that the BEA graphics are computer-generated from GPS data and are therefore precise.) It is about 7.37 nm. The elapsed time is 2.8 minutes. The average rate of descent is 12,500 fpm and the average groundspeed is 158 kt. The average true airspeed is 201 knots, the average glide path angle is 38 degrees. Assuming that the pitch angle does not deviate much from 15-16 degrees, the average angle of attack is 53-54 degrees.

Since these numbers do not match those at either the starting point or the impact point, there must have been considerable variation in between, and in particular a higher rate of descent.

While I have argued (and written) against the "deep stall" theory, which unfortunately remained untested by the crew, I am having a hard time understanding how this airplane managed to maintain this high an angle of attack for this long a time without departing into a spin. Can anyone point me to wind tunnel or flight test work relevant to transport aircraft of this configuration at extreme angles of attack? The Langley stuff I've found is all about spinning. I'm going to telephone them tomorrow.
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Old 5th Jun 2011, 20:20
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Abnormal Attitude Law

A33Zab
If certain values are exceeded abnormal attitude law is triggered.
  1. Pitch (50 degrees up, 30 degrees down)
  2. Bank (125 degrees)
  3. AOA (>30 degrees, < -10 degrees)
  4. Speed (>440 kt, < 60 kt)
  5. Mach (0.96, 0.1).
The above has been the accepted list of "triggers" for this event, and looking at the list you would assume that either of the 5 noted conditions would be the "trigger". It now appears, if the BEA press release via Flight Global is to be believed, that if the ADR's have all disagreed, the only "trigger" depends on an Inertial upset whereby items #1 and/or #2 above are the only means of entering Abnormal Attitude Law.
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Old 5th Jun 2011, 20:35
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Garrison
I am having a hard time understanding how this airplane managed to maintain this high an angle of attack for this long a time without departing into a spin.
Go back to post #1396 by grity, where you will find some interesting basic concepts. Also have a look at a post by PickyPerkins
at #1394.

Last edited by mm43; 5th Jun 2011 at 22:36. Reason: error in PP handle
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Old 5th Jun 2011, 21:19
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Perhaps the BEA will release the weight and balance numbers for AF 459 on June 1. AF 459, an A-330-203, departed Sao Paolo for CDG, and after ORARO requested, as part of its deviation, a climb from 350 to 370 and was authorized such by ATLANTICO.
___________________________
With respect to the outside air temperature at 350, I believe Vasquez as does the BEA relies on the AMDAR measurements from EU 0046, thought to be the LH preceding AF 447 by about 20 minutes. The 744 is stated as being at 10660 meters, FL 325, and the outside air temperature was -40.6C. I believe Meteo France calculated the temperature at the top of the MCC that AF 447 encountered as -64C at 2h 07. I think the outside air temperature at 350 or 380 was likely lower than -40.6C.
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Old 5th Jun 2011, 21:42
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Turbine D

I am sorry if the term "icing" confused the situation, it was a word Tim Vasquez used in his report I quoted from and I didn't change it. I believe icing is when supercooled water encounters a surface and then freezes. In the case of AF447, this was not the case. There was no supercooled water involved to the best of the weather expert's knowledge.

What I was attempting to say was the aircraft passed through a cloud or clouds containing ice crystals which, when coming into contact with wetted heated surfaces, can stick and buildup. I am very aware this phenomenon can and does cause problems with turbofan engines to varying degrees depending on a particular engine design. As Boeing studies have indicated, the ice buildup can both adversely affecting engine airfoil aerodynamics (power loss) and in severe cases, damaged compressor blading (ice shedding) or even cause combustor flame outs (water extinguishes the flame).

From what has been said so far by the BEA, the GE CF6-80E engines were not affected and performed in a normal manner. However, I am not so sure the pitot tubes did, they could have indeed clogged which lead to the erroneous speed sensing and eventually the AP/AT disconnect.

Indeed there is considerable testing done during the initial development and certification testing of new turbofan engines to determine effects of ice ingestion, large and small particles and shedding characteristics. I have seen it done in person on several occasions.

As Boeing points out, it is best to avoid areas of storms where ice crystals are present as the volume tends to be unknown and onboard weather radar may not detect the presence of ice crystals at all.

I stand to be corrected on any of the above.
I don't understand the need for semantics in this discussion at the level of interest at this point in the investigation.

I really don't have any corrections to make either. However, AFAIK the ice crystals at high altitude do not adhere to blading (unlike low idle conditions at low altitudes in freezing rain).

I would add that some engines have been affected by the effects of probe blockage which affected the FADEC control on stall recovery which of course affects power.

AFAIK, no conclusions have yet been drawn by the BEA regarding the presence of water droplets or ice crystals on any of the systems in AF447.

However, for those that intend to pursue a loss of speed signal to the aircraft computers in their causal factors I do understand their presumptions that the aircraft might have been in a position to accumulate ice blockages in the Pitots. Why and how doesn't strike me as important right now in the early investigation. And in the final analysis, if Pitot systems were somehow affected by ice of any kind, even that is less important then to understand why the subsquent downstream layers of swiss cheese got eaten up.

Of course an upgrade of pitot systems is probably still warranted based entirely on past history.
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Old 5th Jun 2011, 22:27
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Originally Posted by RetiredF4

[...]
It is
not aimed at protected Fly-by-Wire aircraft.
There is no need for this type of continuation
training on protected aircraft, although a
general knowledge of the principles involved is
useful for every pilot
"

It was not the idea of airbus alone, however, on the boing page it looked somewhat different.
[...]
"The article focuses on Airbus and Boeing airplanes that do not have electronic flight controls, commonly known as fly-by-wire. However, when a fly-by-wire airplane is in a degraded control law (mode), the recovery techniques are appropriate. Additionally, certain conditions can upset any airplane and the basic principles of recognition and recovery still apply regardless of the flight control architecture."
There may be less difference than you think, and may be down to semantics and/or translation. Your first bolded statement was unanimously agreed by A & B reps (and test pilots). The second, from boeing, does not actually contradict it, and effectively says the same as Airbus do elsewhere. An Airbus in Alternate or Direct laws is a non-protected FBW aircraft, therefore, as the Boeing quote says, the same recognition and recovery applies.

Alternate Law
[...]
The handling characteristics within the normal flight envelope, are identical in
pitch with normal law.
Outside the normal flight envelope, the PF must take appropriate preventive
actions to avoid losing control, and/or avoid high speed excursions. These
actions are the same as those that would be applied in any case where non
protected aircraft
That's from Airbus FCTM (admittedly an old copy downloaded from somewhere or other). Says effectively same as boeing, accounting for it probably being translated from French.

To me though, the real proof is still in the engineering - those that designed and built the buses put a stall warning system in, and I'm absolutely sure they didn't do it because it looked pretty or to get the weight up to the design spec.
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Old 5th Jun 2011, 22:28
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PickyPerkins wrote..

Several people have noted the 61 AoA of the mainplane and the 45 angle of decent, and agreed that the mainplane was therefore fully stalled.

With a nose-up up-trim of 13 the HS had an AoA of about 48 and was therefore also fully stalled, also with an angle of decent of 45.
and any nose down input increases the HS depth of stall.

Is the C0G so far aft (for efficiency) that it doesn't help with recovery? If so does that leave the engines as only means of recovery?
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Old 5th Jun 2011, 22:33
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Originally Posted by lomapaseo
... AFAIK the ice crystals at high altitude do not adhere to blading (unlike low idle conditions at low altitudes in freezing rain).

I would add that some engines have been affected by the effects of probe blockage which affected the FADEC control on stall recovery which of course affects power.
A good reference on this, which has been posted here before :-
http://airs-icing.org/AIRS_II/AIAARe...06-206-739.pdf


...Of course an upgrade of pitot systems is probably still warranted based entirely on past history.
Err yes, but the Thales AA probe in use was known to be deficient on this type of aircraft before this event, (ref Air Caraibes for example), and the replacement Thales BA probe not as good as the best Goodrich probe - hence the ADs around the world in September 2009.

But the now preferred Goodrich probe also failed in the Guam October 2009 incident, and if you read the report and the recommendations

Unreliable airspeed indication - 710 km south of Guam, 28 October 2009, VH-EBA, Airbus A330 202

your comment probably still applies!

Last edited by sensor_validation; 5th Jun 2011 at 22:54.
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Old 5th Jun 2011, 22:54
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Originally Posted by infrequentflyer789
Airbus knows, and always has, that their aircraft can stall. Airbus state, and always have, that their aircraft can stall. So where does this "cannot stall" come from, who is saying it ?
If you're told to pull with no fear isn't it because we protect you ?
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Old 5th Jun 2011, 23:06
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simultaneous multiple pitot icing

DJ77, we'll never know for sure if this accident was caused by simultaneous multiple pitot icing or not. The RHS readings were not recorded. (And, of note, the RHS was flying the plane.) I bet Air France is a little concerned about that lack and may become more so when the next report (months off?) comes out.
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Old 5th Jun 2011, 23:16
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Rush To Judgement

bearfoil, I agree with the kick some butt sentiment in a limited way. If there is a suitably guilty, proven in court, butt to kick I figure the court should administer a suitable kicking in the suitable place - although it might be more effective if the kickee were rotated 180 degrees.

Now that I've established my blood-thirsty creds I also note I did say "court". There is not sufficient knowledge for a court to act. You may think so; but, I notice you are very wrong very often. (Have you finally given up on the VS came off?)

Can we leave off the blood thirsty, please? If you have something new to contribute or if you see a discrepancy between a posting here and information we have available directly from BEA, then chime in. Otherwise you are being somewhat inurbane and outright boorish with your demands for butt kicking.

Just sayin'.
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Old 5th Jun 2011, 23:27
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Turbine D, stand up and take a bow.

If faulty design of pitot probes are "at fault" here perhaps the radar manufacturers are also at fault for not building a radar that can detect the ice crystals by running at one of the H2O molecule's resonances. There may be conflicting frequency allocations involved. But that can be dealt with for safety, I suspect.

Regarding the probe, it appears nobody has been able to reproduce this in the lab. They cannot develop the conditions postulated to create the problem because they are so outlandish. So should they be blamed for that? Should retribution be extracted from them for that?

Please God, can we use this accident as a way to improve system safety and not enrich trial lawyers to extract "retribution?" Kick a butt is there is one clear butt to kick. Otherwise move to the real problem, making it safer.
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Old 5th Jun 2011, 23:38
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The BEA report notes that the RHS airspeed is not recorded on FDR. So even though we know that the LHS and ISIS speeds matched again shortly after 2:11 we cannot be sure that the RHS airspeed also matched the other two. From this, many here have concluded that the PF may have working off incorrect IAS.

Of course, it's entirely possible that the RHS airspeed also matched the others. If the problems with two of the Pitots resloved themselves, why would the third not have as well?

More to the point, even if the RHS airspeed continued to differ from the others, would it continue to be displayed? Would the computer not substitute one of the other measured airspeeds for the one that it has decided is invalid? Or if it keeps displaying the invalid airspeed, would it not flag it as suspect?
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Old 6th Jun 2011, 00:41
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The BEA report notes that the RHS airspeed is not recorded on FDR. So even though we know that the LHS and ISIS speeds matched again shortly after 2:11 we cannot be sure that the RHS airspeed also matched the other two. From this, many here have concluded that the PF may have working off incorrect IAS.

Of course, it's entirely possible that the RHS airspeed also matched the others. If the problems with two of the Pitots resloved themselves, why would the third not have as well?

More to the point, even if the RHS airspeed continued to differ from the others, would it continue to be displayed? Would the computer not substitute one of the other measured airspeeds for the one that it has decided is invalid? Or if it keeps displaying the invalid airspeed, would it not flag it as suspect?
Lets think about it a different way. It has leaked that the aircraft never achieved the abnormal attitudel law. For this to happen, It would seem that there was no synchronization of two airspeeds to form a "consensus" after the initial switch to ALT2 law.
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Old 6th Jun 2011, 00:43
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lomapaseo,

AFAIK the ice crystals at high altitude do not adhere to blading (unlike low idle conditions at low altitudes in freezing rain).
Take a look at this presentation by Boeing and tell me what you think.

http://icingalliance.org/meetings/RI...ersion_nss.pdf
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Old 6th Jun 2011, 01:01
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Originally Posted by spagiola
More to the point, even if the RHS airspeed continued to differ from the others, would it continue to be displayed? Would the computer not substitute one of the other measured airspeeds for the one that it has decided is invalid? Or if it keeps displaying the invalid airspeed, would it not flag it as suspect?
There would be a IAS DISCREPANCY ECAM MSG and it would be to the crew, after cross checking the different IAS, to select the suitable ADR as air data source.

What I'm very curious at is, what were showing the FD Crossed Bars (or Flight Path Director if FPV was already selected) as soon as both recorded speeds were again consistent ?

Is it possible the NU inputs were suggested by the FD ...
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