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AF 447 Thread no. 4

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AF 447 Thread no. 4

Old 9th Jul 2011, 07:04
  #1061 (permalink)  
 
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Originally Posted by takata View Post
That was also my point from the last report. At any point before impact, did they really acknowledged that they were stalled? So far, it is leaked: NO.
If not, why this persistence in error? What really confused them?
My guess is that the PF confused them.

He didn't realise his sidestick input had caused the initial upset. During this time the PNF had his head down and the captain was in the bunk. Neither knew what he was doing, the reasonable assumption being that he was competent and not likely to make such a mistake.

Stall warning sounds, PNF head up asks what's going on, PF said 'Nothing I did' and this was accepted. Then total suspicion on aircraft which was throwing messages at them making it look like systems were in total meltdown. Invalid airspeeds assumed to be behind stall warning, aircraft descending rapidly, natural approach is to pull up.

Basically, the PF was believed instead of aircraft.
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Old 9th Jul 2011, 09:02
  #1062 (permalink)  
 
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@Takata:

Quote:
Originally Posted by A33Zab
NAV ADR DISAGREE needs 10s monitoring to trigger.
ACARS msg was received @02:12:51; CMC has 60s maximum to correlate
to any failure message ~02:11:51 - 10s monitoring = ~02:11:41.
I'm not that sure of your interpretation of this timming.
NAV ADR DISAGREE was time-stamped at 0212 during the ACARS sequence. As I understand it, this is a cockpit effect (WRN) and not a fault (FLR), then, I do not think that it needed a correlation window to open before being displayed and an ACARS triggered.
Consequently, as it takes 5-6 seconds for ACARS protocole and 10 seconds to trigger, I would rather time it at 0212:51 less 15-16 seconds -> 0212:35.
I agree this WRN will be displayed (after 10s monitoring) in RT on the EWD.
If you are right about the transmitting time, my theory - silenced STALLSTALL while AOA >35° (AOAsw = 10.8°); THS ANU stops at 13°; NAV ADR DISAGREE all at the same time - won't hold.

The only escape, I can think of, is that NAV ADR DISAGREE (ATA34) warning is transmitted by FCDC (ATA27) as detected by FCPC, thus being external and therefore requires CMC to search for correlated failures.
But I have to study the books again, if mentioned somewhere.

Everybody seems to interpret ADR DISAGREE solely in relation with airspeed issues. So far, I don't know if it was only airspeed related as both AOA or pitot probes measuring values outside of their valid envelope could have basically the same effect.
ex pitot probes, FCPC gets Speed and AOA ARINC input from ADR, no raw data from pitot probes. Of course speed is directly related to pitot probe data. But indeed one can't exclude AOA.

Thx for you comment, gives me something to do.....
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Old 9th Jul 2011, 09:21
  #1063 (permalink)  
 
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Originally Posted by takata
Everybody seems to interpret ADR DISAGREE solely in relation with airspeed issues. So far, I don't know if it was only airspeed related as both AOA or pitot probes measuring values outside of their valid envelope could have basically the same effect.
Agreed, and everybody seems to think of the pitots misreading at high AoA, forgetting that airspeed is derived from the difference between two pressures: pitot and static. Sometime ago someone posted a drawing showing the static ports on the bottom of the front fuselage. At these AoA's the misreading of the static pressures may be more important than that of the pitot pressures. EDIT:: Particularly when "The airplane was subject to roll oscillations that sometimes reached 40 degrees" (Thx to an anonymous reader of the thread).

Last edited by HazelNuts39; 9th Jul 2011 at 10:46. Reason: last sentence added
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Old 9th Jul 2011, 10:00
  #1064 (permalink)  
 
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@MM43

Very helpfull drawing with a view on all the angles involved.

But 13° ANU isn't equal to THS angle. A(NU) is for Aircraft nose up.

You can get the correct THS angle from this diagram, as being the guideline to paint the stripes on the fuselage.

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Old 9th Jul 2011, 11:40
  #1065 (permalink)  
 
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Hi A33Zab,

I agree - & that's exactly what mm43's diagram shows - with the stabiliser 13 degrees below the AC attitude.
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Old 9th Jul 2011, 12:03
  #1066 (permalink)  
 
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@A33Zab

Maybe the drawing hasn't been as helpful as I thought, but check the ANU position again. The 0° position is represented by the line marked Attitude and the 13° NU is 3° above the Horizon line. The Horizon to Attitude angle represents 16° pitch.

As a matter of interest, the drawing was originally posted in the AF447 Wreckage Found thread and thoroughly dissected over there! In fact the biggest concern expressed in that thread was the original THS camber which favoured the top and has since been changed.
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Old 9th Jul 2011, 12:05
  #1067 (permalink)  
 
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@HN39:

HN39,

Normally roll is of no influence because average is used between LH and RH static ports, however with such large roll oscillations and AOA angle?



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Old 9th Jul 2011, 12:34
  #1068 (permalink)  
 
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Hi A33Zab,
Originally Posted by A33Zab
The only escape, I can think of, is that NAV ADR DISAGREE (ATA34) warning is transmitted by FCDC (ATA27) as detected by FCPC, thus being external and therefore requires CMC to search for correlated failures.
But I have to study the books again, if mentioned somewhere.
Basically, you don't need to look at that for ECAM messages: external/internal detection is also related to fault message classification and correlation, while ECAM messages would be sent in realtime, as displayed on the Engine Warning Display (E/WD). In any ACARS sequence, they would be ahead of the subsequent related system faults (if any).

The main problem in addressing the timming of an ACARS sequence is that maintenance in-flight report (CFR) is different from post flight reports (PFR) so as to identify the correlation between the related faults and cockpit effect messages (ECAM or flag/advisory):
Unlike the CFR, the PFR presents correlations between the fault and cockpit effect messages. The relative positions of the messages in a CFR and in the corresponding PFR may therefore be different.
Now, it seems clear to me if I look at BEA explanations in the first interim report (p. 25-27)

All the messages are timed to the nearest minute. The timing of an ECAM message consists of the time of its acquisition by the CMC, and that of a fault message is the time at which the correlation window opened. It is therefore possible in a CFR to find an ECAM message preceding a fault message that is nevertheless timed one minute before it.

In order to transmit the messages by ACARS, the CMC sends them to the ATSU.
* ECAM messages are transmitted in real time as soon as they are acquired.
* Flag or advisory messages are transmitted as soon as they have been confirmed.(1)
* Fault messages are transmitted as soon as the corresponding correlation window is closed.
________________
(1) The CMC acquires certain ECAM messages from the FWC, in the order that the latter transmits them. This is not necessarily the order in which those messages were displayed on the Engine Warning Display (E/WD). Up to one hundred messages can be acquired in one second. The messages indicating a flag or an advisory are received from the DMCs and must be confirmed for between 2.4 and 3 seconds in order to be acquired. They are timed once this confirmation has been made.

Last edited by takata; 9th Jul 2011 at 13:02.
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Old 9th Jul 2011, 13:47
  #1069 (permalink)  
 
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Use of Sidestick (continued)

Quote from Linktrained:
From the threads that I have read inly a few mm of movement would cause the THS to try to compensate by increasing from the initial cruising figure of 3 or 4 NU.

I don’t think much would happen to the THS during the initial rotation from level flight, as it would have required little up-elevator to enter the climb. Once the 7000ft/min had been achieved, the trajectory would be maintained by the EFCS even with no back-stick. As the speed started to drop, more up-elevator would need to be introduced by the EFCS to maintain 1g, and it would then start to trim the THS a bit to retain full elevator authority. Once the aircraft got on to the back end of the drag curve, however, this process would proceed rapidly.

In fact the PF arrested most of the climb at FL375, by “nose down control inputs...”, so some down-elevator may have been used briefly by the EFCS at this point. This partial recovery was to be short-lived, as the PF seems to have reacted to a stall warning by selecting TOGA (causing a pitch-up) and resuming “nose-up inputs”. Resuming the climb at that point, on the wrong side of the drag curve, was when the EFCS had to start using up-elevator and nose-up trim (THS) in earnest, in order to try and maintain the trajectory it thought the PF wanted.

Quote:
It has also been suggested that the PF may have inadvertently gripped the SS with his fingers gently, (more strongly than with his whole hand ?). C

Rather the reverse, in my opinion. In Normal and Alternate laws, the best way to avoid over-controlling with the sidestick is to make brief inputs, in between which you do not touch the stick. The exceptions are rotation on take-off, and the landing flare. The inputs are best made with fingers and thumb only. If you keep the stick permanently in the palm of your hand, as some do, it’s difficult not to move it accidentally − particularly in turbulence.

But this aircraft was degraded to ALT 2 law: a combination of Direct law for roll (stick-to-aileron/spoiler) and Alternate law for pitch, the latter without any high-AoA protection.
In trying to cope with the roll-control problems described (but not yet explained) by the BEA, it is almost inevitable that the PF was making continuous roll inputs, and probably had the stick in the palm of his hand. This would have made accurate pitch control difficult.
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Old 9th Jul 2011, 13:58
  #1070 (permalink)  
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Time for thread #5.
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