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AF447 Thread No. 3

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AF447 Thread No. 3

Old 30th May 2011, 02:57
  #681 (permalink)  
 
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Originally Posted by Machinbird
From the BEA statement
Quote:

At 2 h 12 min 02, the PF said "I donít 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 enginesí N1ís were at 55%. Around fifteen seconds later, the PF made pitch-down inputs. In the following moments, the angle of attack decreased, the speeds became valid again and the stall warning sounded again.
Well, I should have read this report about 20 times now, in French and English and I certainly do remember it.
Now, this come at 0212:02 + 15 seconds... more than 2 minutes after the begining of manual flight. At this point, I would expect something like:
"The pilot made pitch-down imputs to the stops during 1-2 minute(s)" not "the PF made pitch-down imputs" (how many, how far, how long?).
I'm not sure that it is showing that the PF had fully realised the situation at this point (and I believe he did not).
Nonetheless, despite having a THS trim at +13 deg and being already in a full stall situation, it seems that those imputs are effective by reducing the AoA... hence, elevators were still effectives, don't you think?
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Old 30th May 2011, 03:27
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Lack of stall signal was the reason for the crash

My two cents...

.... once the plane stalled, why the pilot acted as he did:

The plane is losing height at 10912 ft/min. The pilot have to determine if the plane is:

1) Diving (then apply UP elevator)
2) Falling down in deep stall (then apply DOWN elevator)

The pilot knows the stall warning is the most important warning there it is.
...BUT... THERE IS NO STALL WARNING !!! ... so the pilot assumes the PITCH indicator that points to nose up attitude is WRONG!

He has two mutually exclusive indications:
1) PITCH UP
2) LACK OF STALL WARNING

The pilot choose to believe that if there is no stall warning, there is NO STALL, the pitch indicator has gone bad and the plane is in deep dive. Therefore he will PULL UP. No other crew member corrects him, because they all think the same. If any one believed they are in sustained stall for 2 minutes, they will be crying "STALL, PUSH DOWN" and not be mostly quet.

At one moment, the pilot pushes down the stick, the plane starts to recover and .... THE STALL WARNING COMES ON !!! So, the pilot is warned that his action CAUSES STALL. Being in confused state due to conflicting information, he goes back to pull from deep dive and all other pilots agree to the end...

Here is what BEA report says:


During the following seconds, all of the recorded speeds became invalid and the stall warning stopped.

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.

In my opinion, this is design problem that lead to the crash:

The fact is, during the 3 minutes descend while the plane was falling at 11000 fpm THE STALL WARNING WAS QUIET. If the stall warning was ON, the pilots would take the correct action to lower the trim, push down the stick and save the plane (if physically possible).

Here is the relevant text from BEA:

At 2 h 10 min 51 the stall warning was triggered again. The thrust levers were positioned in the TO/GA detent and the PF maintained nose-up inputs. The recorded angle of attack, of around 6 degrees at the triggering of the stall warning, continued to increase. The trimmable horizontal stabilizer (THS) passed from 3 to 13 degrees nose-up in about 1 minute and remained in the latter position until the end of the flight. Around fifteen seconds later, the speed displayed on the ISIS increased sharply towards 185 kt; it was then consistent with the other recorded speed. The PF continued to make nose-up inputs. The airplaneís altitude reached its maximum of about 38,000 ft, its pitch attitude and angle of attack being 16 degrees.

Note: The inconsistency between the speeds displayed on the left side and on the ISIS lasted a little less than one minute. At around 2 h 11 min 40 the Captain re-entered the cockpit. During the following seconds, all of the recorded speeds became invalid and the stall warning stopped.

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.

The altitude was then about 35,000 ft, the angle of attack exceeded 40 degrees and the vertical speed was about -10,000 ft/min. The airplaneís pitch attitude did not exceed 15 degrees and the enginesí N1ís were close to 100%. The airplane was subject to roll oscillations that sometimes reached 40 degrees. The PF made an input on the sidestick to the left and nose-up stops, which lasted about 30 seconds.

At 2 h 12 min 02, the PF said "I donít 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 enginesí N1ís were at 55%. Around fifteen seconds later, the PF made pitch-down inputs. In the following moments, the angle of attack decreased, the speeds became valid again and thestall warning sounded again. At 2 h 13 min 32, the PF said "weíre going to arrive at level one hundred". About fifteen seconds later, simultaneous inputs by both pilots on the sidesticks were recorded and the PF said "go ahead you have the controls".

The angle of attack, when it was valid, always remained above 35 degrees.
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Old 30th May 2011, 03:33
  #683 (permalink)  
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Originally Posted by Graybeard
Ok, Confiture, maybe you have a logical explanation why the GS reported was the exact same 107 kt as the vertical velocity. See post #552
I would also presume it is a coincidence, but ...

Prior to the report's release, there was a lot of discussion about tail fuel and 39% MAC
There is something to be clarified here :
At takeoff the CG was pretty much forward around 23% which makes sense considering the heavy cargo load.
The estimation made by the BEA initially put the CG mainly aft around 37% at the time of the upset. But now the data tells it was at 29% only ...
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Old 30th May 2011, 04:05
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Originally Posted by CogSim
If only the 'knowledgeable' posted here, we'd all be the poorer for it
Absolutely, even if at time, like PJ2, I can feel a bit irritated by so many posts that may look as a waste, but to discard them of course you need to read first ... I have also no doubt I can irritate many myself.
Never mind, it is just question to let the storm go and already after 3 days things are cooling down, more constructive stuff can take place already.

Some even pretend the only 'knowledgeable' is the BEA, on which I fully disagree. In this time of INTERNET, full data should already be in the public domain, BEA itself would probably also gain something from it ...
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Old 30th May 2011, 04:06
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Takata
Nonetheless, despite having a THS trim at +13 deg and being already in a full stall situation, it seems that those imputs are effective by reducing the AoA... hence, elevators were still effectives, don't you think?
Absolutely yes, but they ran out of authority against that great big THS. If the THS had been set to a lower value at that point, it appears the aircraft would have continued rotating until its nose pointed down the velocity vector. We don't yet know how long the nose down input was held, do we? Only that it brought on the return of the stall warning.
The stall warning may have stopped the crew's nose down input, or maybe it didn't. Probably it was a matter of authority. BEA hasn't told us yet.
The crew was evidently trying everything they could think of, they just didn't think of the manual pitch trim because at some level they probably considered it irrelevant. That is what training needs to fix.
So how easy would it be to fly a right wing heavy A330 in Alt 2 law in your estimation? Could you keep from applying aft stick if flying with your right hand?
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Old 30th May 2011, 04:11
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THS inputs

Interesting post yesterday from Jcarlosgon

I was kindly allowed an extra exercise at FL350, about 170 tons, CG around 30%, about one year ago. Pull up from FL350, all 3 ADRs off, kept it at 15 degrees up till it stalled, ŗ la B707/27/37, A310, in gone years.

THS went full back, donít remember the figure, and sidestick was released, N1 at 85% (A/THR off). The nose came down to about -5 and went back up to +10. Rate of descent was between about 6K fpm and zero, or slight climb (sim is an A330 with PW engines, 85% is slightly above needed N1 for turbulence at M 0.80).


Not a Bus operator myself, what causes THS to move? Is it only pilot inputs from the trim button on the stick, or does the computer tell it to move?

Could it be that the pilot inadvertantly thumbed full nose up, while gripping the stick. I suspect that the audio of trim movement could well have been lost among other warnings sounds, and once trimmed full back, recovery would be almost impossible, unless trimmed back the other way.

Given all that was going on, white knuckles on the stick would not surprise me one little bit.

Last edited by beachbunny; 30th May 2011 at 05:49.
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Old 30th May 2011, 04:13
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OK, Conf iture, I went back and removed the MAC from the post. Thanks for the important clarification. 29% MAC is not near as serious as 39% when it comes to stall behavior and recovery.

I still think it is possible they dropped like a skydiver without a parachute.
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Old 30th May 2011, 04:25
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Cool

Hi,

Could it be that the pilot inadvertantly thumbed full nose up, while gripping the stick. I suspect that the audio of trim movement could well have been lost among other warnings sounds, and once trimmed full back, recovery would be almost impossible, unless trimmed back the other way.
Methink it's not "thumb trim button" on stick and methink movement of trim wheel is soundless.(that's not help but is how is that in Airbus)
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Old 30th May 2011, 04:33
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Not a Bus operator, what causes THS to move? Is it only pilot inputs from the trim button on the stick, or does the computer tell it to move?

Could it be that the pilot inadvertantly thumbed full nose up, while gripping the stick. I suspect that the audio of trim movement could well have been lost among other warnings sounds, and once trimmed full back, recovery would be almost impossible, unless trimmed back the other way.

Given all that was going on, white knuckles on the stick would not surprise me one little bit.
Beachbunny, it isn't what you think. The A330 is a Fly By Wire aircraft and is is designed to autotrim itself in pitch and roll. There is no trim button to accidentaly displace. If I remember PJ2's briefing correctly, the THS trim wheels move silently in response to automatic trim inputs. The THS trim is controlled by Prim computers, any one of the 3 can do it. If the Prim computers are inhibited in some way, or if certain protection features are activated, the trim doesn't move. To understand this takes familiarity with the flight control laws. You will have to break out the books, I'm afraid, to hope to understand what happened.
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Old 30th May 2011, 05:22
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Is it true that Airbus is "flight path stable", as opposed the FBW B777 which is like conventional aircraft "speed stable? This is an important distinction in that the B777 requires pilot input on the pitch trim to establish a speec, where a Airbus pilot sets a flight path he wants and uses auto-thrust or manual thrust to set or maintain an indicated airspeed. The two premises result in quite different handling characteristics.

Not a 'Bus pilot
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Old 30th May 2011, 06:01
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THS

Thanks for the reply, Machinbird.

That sounds real scary, if the pilot cannot control a primary control surface.
Surely there would have to be some way that it could be re-positioned during hand flying????
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Old 30th May 2011, 06:13
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That sounds real scary, if the pilot cannot control a primary control surface.
Surely there would have to be some way that it could be re-positioned during hand flying????
Mechanical trim can be used once the auto-trim is no longer available or the pilot overrides the auto-trim - however once in mechanical trim there is no reversion to auto-mode. That is a ground reset function.
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Old 30th May 2011, 06:24
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28 October 2009 - VH-EBA - Airbus A330-202

The only relation this incident has to AF447 is that the aircraft was an A332 and UAS was due to ice in the static port. A stall warning did not enter the equation, but similar warnings were generated. The crew followed the QRH and the graphic below shows the outcome.



The dip in altitude is not real, and for an explanation see the ATSB Report.

NB The graphic above is larger than that published in the report.

Last edited by mm43; 30th May 2011 at 06:45. Reason: reduced graphic size
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Old 30th May 2011, 06:39
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Abnormal Law Warnings or Messages?

Takata wrote that the plane would have kicked into Abnormal Law due to AoA and speeds:
From 0211:40, she would not be anymore in Alternate law as all speeds and AoAs were invalidated => abnormal law: THS is frozen at +13 deg and autotrim become inactive (like the RTLU was at 0210:05, remember? we told you that it was its last valid airspeed before ADRs faults).
Sorry in advance if this has been asked and answered before, but:
  • If/when the plane kicked into Abnormal Law, what warning or message would have been visible or audible to the pilots?
  • Why was the transition to Alternate Law indicated in one of the ACARS messages, but no message about any other change in Law?
Thanks
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Old 30th May 2011, 06:50
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Cool

Hi,

Dunno if this was already posted here ...
Interesting anyways (even as reminder)


http://aviationtroubleshooting.b l o g s p o t.com/2009/06/af447-unreliable-speed-by-joelle-barthe.html
Remove the spaces

Was in 2006
By Joelle Barthe
Flight Operations Engineer

6 Conclusion
An unreliable speed situatio may be difficult to identify, due to the multiple scenarios that can lead to it. Therefore, training is a key element: indeed the flight crew's ability to rapid detected the abnormal situation, and to correctely handle it, is cricial.
In case of any doubt, the pilot should apply the pitch/thrust memory items, and then refer to the QRH to safely fly the aircraft, and to positively determine the faulty source(s) before eliminating it (them).
In addition, to further assit the pilot in detecting the failure and safely fly the aircraft, Airbus has developed the BUSS, which provides a safe flying range indication.
Finaly, to reduze the probally of experiencing unreliable speed situations, on-ground actions, such as comprehensive maintenance and through pre-flight exterior inspection, should be stressed.

Last edited by jcjeant; 30th May 2011 at 07:15.
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Old 30th May 2011, 06:52
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falcor

Have a look at A340 / A330 Control: flight & laws
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Old 30th May 2011, 06:58
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IAS at 40 degrees AOA.

I don't think any pitot tube will produce a reliable output at extreme AOA's.
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Old 30th May 2011, 07:45
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Infrequentflyer789:

But on the C/L, buried in a postscript to a post a few pages back by Hyperveloce is this little bombshell:

Quote:
Originally Posted by Hyperveloce
PS) 5 days after the AF 447 crash, AF's safety direction released a note to all the navigating crews urging them not to apply this emergency maneuver in cruise phase: http://www.eurocockpit.com/docs/INFO_DIV_AIRBUS.pdf

Now, is that a "reminder to follow the procedures", or an urgent message that the previously advised procedures were wrong ???

If it is the latter, then AF found probable cause in training / SOPs only 5 days after the crash - who did they tell ?
That AF note says that, in the event of an Unreliable Airspeed Indication (plus a few other similar events):

- Above the safe altitude, whether in the climb or cruise, maintain the given pitch and thrust settings, then work the UAS Checklist without applying the UAS Emergency Procedure;

- Below the safe altitude, apply the UAS Emergency Procedure.

So the questions are, a) what was (in June 2009 when the note was issued) the USA Emergency Procedure, and b) does the new BEA note give any indication that the PF used it, even though he was in the cruise, and then in a climb?

We do know the a/c did not maintain given pitch and thrust; we do not know if the crew worked the checklist.
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Old 30th May 2011, 09:07
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mm43, re VH-EBA UAS:
UAS was due to ice in the static port
The report states that this short UAS event was due to pitot icing (impact pressure lost), not the static port.
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Old 30th May 2011, 09:28
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Abnormal Attitude Law

Hi,

Once the aircraft was in Abnormal Attitude Law (with IAS less that 60 kts or angle of attack >30degs) can anybody point me to an FCOM reference which indicates that "Use Manual Pitch Trim" would (not) be shown on the PFD (as in Direct Law)?

Thanks.

Last edited by rudderrudderrat; 30th May 2011 at 11:49. Reason: spelling
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