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AF 447 Thread no. 4

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AF 447 Thread no. 4

Old 25th Jun 2011, 20:36
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Due to limited availability of class slots, I had to do my A330 ground school with a class start time of 2 AM. (This time is more suited for leaving a bar than being alert & receptive to technical instruction.)

However, reading some of the knowledgeable detailed technical discussions here, Im having flashbacks, not to the information presented, but to the difficulty in trying to understand what it actually meant at oh-dark-thirty in the wee hours.

Now occasionally in my head, in imaginary digitized voice, I'm sure I will hear all these computers "broadcasting, receiving, requesting, acknowledging, discussing, granting and permitting".

(Previously I never gave it a second thought with the SS firmly, i.e. lightly, in hand.)
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Old 25th Jun 2011, 22:55
  #382 (permalink)  
 
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Originally Posted by BOAC
[...]we appear to have a similar manouevre induced by the FCS and not the crew, resulting a (co-incidental) 'arrival' at FL380 after a 6000fpm zoom during which the IAS decayed below Vls. OK, I'm easily swayed by these things, but???????
[...]
I do not understand why the alpha reached 'alpha-prot' all on its own?
[...]
I am struggling to see, through my ignorant eyes, why this is not relevant to 447? I know, different type and 'history', but is there not an Occams Razor lurking here?
There is no indication so far the the 447 zoom climb was induced by the FCS, while there is knowledge of PF nose-up input prior to the climb. If invoking Occam, why would you add an FCS law change as cause of climb when there is already a known nose-up input from PF ?

In the other incident, my understanding would be alpha reached alpha prot due to severe turbulence causing fluctuations in speed etc., followed by (I think) crew reducing speed after momentary overspeed warning (hence next downward fluctuation in speed maybe takes alpha momentarily over alpha prot, and engages the law).

The other difference is that the other incident is in normal law, while 447 was in alternate, which doesn't have the alpha prot law.

[ Note: I know there are some posts on a theory that maybe 447 was still in normal law through one of the PRIMs, and therefore the climb oculd have been a protection doing the wrong thing - I think there is a fundamental flaw with that theory, which is that in normal law the FCS would never have allowed the a/c t exceed alpha max, which it clearly did. ]
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Old 26th Jun 2011, 00:10
  #383 (permalink)  
 
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Note: I know there are some posts on a theory that maybe 447 was still in normal law through one of the PRIMs, and therefore the climb oculd have been a protection doing the wrong thing - I think there is a fundamental flaw with that theory, which is that in normal law the FCS would never have allowed the a/c t exceed alpha max, which it clearly did
IF789: Right on w.r.t. this There are a number of problems with this 'hung on in Normal' theory - most significant of which is the lack of any comment within the BEA note of May 27th. I hardy can conceive of them (a) not reporting a disagreement of control law with that reported by the crew:

the PNF said "so, weve lost the speeds" then "alternate law []".
If this had been in error or something mislead the crew, then I firmly believe that would have been stated in the note. Otherwise the BEA have simply hung the crew out to dry to some extent. I realized that many folk have been attempting to "fit the foot to the shoe" and have been postulating theories that might work with the data we have, but Occam doesn't sit comfortably with any in my opinion.

The BEA data is maddeningly thin, but the shortest distant between two lines is most often the route traveled.
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Old 26th Jun 2011, 01:23
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Chronology of events @ 5 sec interval.

Updated here: LINK

Last edited by A33Zab; 3rd Jul 2011 at 04:05. Reason: Updated.
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Old 26th Jun 2011, 04:16
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I am probably guilty of inaccurate terminology here, apologies all - there is ample evidence that they flew into turbulent weather though.
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Old 26th Jun 2011, 05:35
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This was first brought to attention by takata in this post.

Airliners.net post with reordered ACARS message list. Since there is some discussion about the delay in NAV ADR DISAGREE, I thought I'd post it to help refocus.

Originally posted on Airliners.net

This is the list reordered...

0209 START
0210 34-11-15-0 FLR EFCS2
EFCS1, AFS - PROBE PITOT 1+2/2+3/1+3 (9DA)
9DA=HEATING ELEMENT PITOT 1 (6DA1/PHC1)
Heating Element Pitot 1 suspected failed.

0210 27-93-34-0 FLR EFCS1
EFCS2-FCPC2(2CE2) WRG:ADIRU1 BUS ADR1-2 TO FCPC2
No Data from ADIRU 1, ADR 1 & 2 no sending signal to FCPC2
No ADR Data from ADIRU 1 to PRIM2.

0210 27-90-45-5 WRN MXSTAT
EFCS1
ERROR NOTICED - Air Data Fluctuation/Inconsistency

0210 27-90-45-0 WRN MXSTAT
EFCS2
ERROR NOTICED - Air Data Fluctuation/Inconsistency

0210 22-10-00-0 WRN AUTO FLT
AP OFF
Autopilot Shut off for safety, result loss of 2 Valid Air Data Channels.
This prevents faulty Air Data from affecting autopilot into making the wrong actions.
Commence AP/FD FAULT ISOLATION PROCEDURE
System Filter & Check:
- DISAGREE AOA Sensor Data in FCPCs
- DISAGREE PITOT PROBE Data in FCPCs
- FAIL ADIRU 1 and 2
- FAIL ADIRU 1 and 3
- FAIL ADIRU 2 and 3
- FAIL ADIRUs

0210 22-62-01-0 WRN AUTO FLT
REAC W/S DET FAULT
Loss of 2 ADRs, autopilot cannot provide Windshear Protection.

0210 27-91-00-5 WRN F/CTL
ALTN LAW
2 ADR REJECTED, NAV DISAGREE NOT YET CONCLUDED - FAULT ISOLATION IN PROGRESS

0210 22-83-00-2 WRN FLAG
LEFT PFD LIMIT
Rejected ADR still feeding data to PFD
If there is valid ADR, it's not being selected for LEFT seat.

0210 22-83-01-2 WRN FLAG
RIGHT PFD SPD LIMIT
Rejected ADR still feeding data to PFD
If there is valid ADR, it's not being selected for RIGHT seat.

0210 22-30-02-5 WRN AUTO FLT
A/THR OFF
Autothrust Shut off for safety, result loss of 2 Valid Air Data Channels.
This prevents faulty Air Data from affecting Autothrust into making the wrong actions.

0210 34-43-00-5 WRN NAV
TCAS FAULT
Loss of ADR1 to Transponder 1 (if selected) or Loss of ADR2 to Transponder2 (if selected)
Loss of Mode C.
This is downstream of loss of ADR.

0210 22-83-00-1 WRN FLAG
LEFT PFD NO F/D
Automatic Flight System (AFS/FMGC) loss of 2 ADR sources.
Safety mechanism, prevents erroneous F/D for pilot to follow

0210 22-83-01-1 WRN FLAG
RIGHT PFD NO F/D
Automatic Flight System (AFS/FMGC) loss of 2 ADR sources.
Safety mechanism, prevents erroneous F/D for pilot to follow

0210 27-23-02-0 WRN F/CTL
RUD TRV LIM FAULT
Loss valid of ADR Data (require 2 ADRs) for FMGC/AFS
FMGC Flight Envelope Module locks in Rudder Travel for safety.

0211 34-12-34-0 FLR IR2
EFCS1X,IR1,IR3, ADIRU2 (1FP2)
ADIRU2(1FP2) - ADR2 self monitoring & PHC rejects own data
Loss of discrete data from ADR2 = PITOT 2, STATIC 2L, STATIC 2R, TAT 2, AOA 2.
NAV DISAGREE CONCLUSION DELAYED - ADDITIONAL FAILURES - RECOMMENCE FAULT ISOL

0211 34-12-00-0 FLR ISIS
ISIS (22FN-10FC) SPEED OR MACH FUNCTION
SUSPECT LOSS OF ADIRU1 AND/OR ADIRU3 FOR ISIS MACH
Suspect Loss of ADIRU3
NAV DISAGREE CONCLUSION DELAYED - ADDITIONAL FAILURES - RECOMMENCE FAULT ISOL

0211 34-12-00-1 WRN FLAG
LEFT PFD NO FPV

0211 34-12-01-1 WRN FLAG
RIGHT PFD NO FPV

0212 34-10-40-0 WRN NAV
ADR DISAGREE
NAV DISAGREE DISCOVERED - FAULT ISOLATION COMPLETED
Due to no further ADR faults occuring.

0213 27-90-02-5 WRN F/CTL
PRIM1 FAULT

0213 27-90-04-0 WRN F/CTL
SEC1 FAULT

0213 22-83-34-9 FLR AFS
FMGEC1(1CA1)

0214 34-10-36-0 WRN MXSTAT
ADR2
RESULT OF 32-12-34-0

0214 21-31-00-2 WRN ADVSRY
CABIN VERTICAL SPEED
LOSS OF ADR DATA

------------
Be warned, the above is still incomplete. More cross checking is needed. The failures here aren't simply upstream faults leading to downstream failures, but there are some "same level" data feed, and "upstream" data feeds... and I do not guarantee the above is correct.
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Old 26th Jun 2011, 05:48
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Cool

Hi,

I want also brought to attention .. this ...

In the BEA note (27 May 2011)

The chronology of events is not rigorous: A 2h10min51sec it is said that a couple of seconds later, the speeds become consistent. So, 2h11min06sec speeds are consistent. It is said, small on the next line (foot note), that the inconsistency between the speeds lasted less than one minute. So let's say 59 seconds. This therefore means that the inconsistency between the speeds appeared earlier than 2h10min07sec. So before 2h10min07sec speeds were consistent. So why 2h10min05sec to the autopilot and auto-thrust and disengage the OP says "I have control"? The autopilot had disengaged while he speeds were consistent?

This BEA note can't be a serious one to elaborate any scenarios from it
Only the FDR can be a valable source for a scenario .. instead of some truncated dialogues between pilots and fantasy timing ..
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Old 26th Jun 2011, 06:47
  #388 (permalink)  
 
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So before 2h10min07sec speeds were consistent. So why 2h10min05sec to the autopilot and auto-thrust and disengage the OP says "I have control"? The autopilot had disengaged while he speeds were consistent?

This BEA note can't be a serious one to elaborate any scenarios from it
Disagree, suggest you read the report closely again.

The aircraft, and it's systems (AP etc.) work from 3 airspeed sources. The FDR only records 2 of those. So prior the 2:10:07 any observations / system anomalies would be down to the 3rd (unrecorded) speed source.
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Old 26th Jun 2011, 07:16
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How an aircraft aerodynamically moves though the airmass is essentially an engineering problem which is very well understood. Computers solve these engineering problems very well, better than humans, and it is clear that automation of the nature used by Airbus has saved many lives. Computers, as well as pilots, require sensors to fly and if the aircraft sensors are working it makes sense for the aircraft to fly the aircraft instead of the pilots. When all aircraft systems are working, it also makes sense for the aircraft to override all 'flying' actions that the pilots make which the equations for flight deem to be dangerous. i.e. Normal Law.

When the aircraft sensors fail, as they appear to have done here, it is essential that the aircraft hands over control of the flying of the plane to the pilots. This appears to have been done properly. As the aircraft had degraded sensor information it removed any protections that rely on this sensor information. This is also a correct action to take, aircraft in ALT 2, no AoA protections in place.

It then appears that the pilots mismanaged the further flying of the aircraft. Unusual, but the evidence we have so far points strongly in this direction. The reported sidestick position invalidates all the other improbable theories proposed so far.

On the descent, it appears that the input from the aircraft sensors became valid again. This is entirely to be expected if the initial problem was icing. The aircraft would presumably have known that all it's sensors were now working. However it was latched into ALT 2, AoA protections are not in place, and so it could do nothing about the stall.

If once the aircraft had validated the sensor data, it could have legitimately reverted to normal law, it could then have applied AoA protections and all on board saved.

So why is this not programmed to happen?
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Old 26th Jun 2011, 08:03
  #390 (permalink)  
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OC - if it helps with your 'terminology' the ITCZ IS an area of 'turbulent weather' which pretty much circles the globe, commonly with CB activity but generally always with 'bumps'. It may help you to Google ITCZ and see? As such, dozens if not hundreds of aircraft penetrate this 'zone' every day and nearly always experience 'turbulent weather'. Sometimes light or moderate, occasionally severe. It may be that 447 did fly into a CB - we do not yet know, but I do not see any evidence of it so far. Very few of them experience the loss of pitot systems which appear to have triggered this event so until we can establish that an 'active' CB was penetrated by them it is not really relevant.

For Saturn, I have never been to FL500 in the ITCZ so I cannot answer your question but I would expect (and not be particularly surprised by) the activity on an active ITCZ to easily produce water vapour up to FL560. It may be useful to try and look at other Sat weather images of the zone on other days. I believe it is generally accepted that the tropopause can be at FL560+ in the tropics so it should not be a surprise.
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Old 26th Jun 2011, 08:28
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Cool

Hi,

Quote:
So before 2h10min07sec speeds were consistent. So why 2h10min05sec to the autopilot and auto-thrust and disengage the OP says "I have control"? The autopilot had disengaged while he speeds were consistent?

This BEA note can't be a serious one to elaborate any scenarios from it
Disagree, suggest you read the report closely again.

The aircraft, and it's systems (AP etc.) work from 3 airspeed sources. The FDR only records 2 of those. So prior the 2:10:07 any observations / system anomalies would be down to the 3rd (unrecorded) speed source.
It's no matter of airspeed sources or what is recorded or not .. it's simply matter of timing described by BEA.
The numbers are there black on white .. no need of "what if" or or complicated scenarios
Make the maths ... it's simple arithmetic ... and something is wrong ..
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Old 26th Jun 2011, 09:11
  #392 (permalink)  

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0210 22-30-02-5 WRN AUTO FLT
A/THR OFF
Autothrust Shut off for safety, result loss of 2 Valid Air Data Channels.
This prevents faulty Air Data from affecting Autothrust into making the wrong actions.
Because of the Airbus A/T design, the thrust would have gone to full power. A fundamental design flaw, imho, and one that will never be admitted to by Airbus. I hated the T/L not moving design of the Airbus. It works fine when all is going smoothly. But in the failure case, and non standard configuration case it causes more trouble than it is worth. It is so difficult to work out what it is or is not doing under high workload situations. Very often all you have to go on is the "cyan arc." a tiny blue trend line. Miss that and chaos can ensue.

With all the warnings and the chaos on the flight deck, it is doubtful if the FO hd the spare capacity to even notice the AT going to full power. That would have instantly de-stabilised the aircraft. Making a bad situation far worse.
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Old 26th Jun 2011, 09:25
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TCAS Fail

Thanks, Cogsim:
0210 34-43-00-5 WRN NAV
TCAS FAULT
Loss of ADR1 to Transponder 1 (if selected) or Loss of ADR2 to Transponder2 (if selected)
Loss of Mode C.
This is downstream of loss of ADR.
Loss of Mode C results in TCAS Off, not TCAS Fail.

I can only conclude the BEA reporting is inaccurate.
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Old 26th Jun 2011, 09:46
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Hi
Originally Posted by PA 18 151
If once the aircraft had validated the sensor data, it could have legitimately reverted to normal law, it could then have applied AoA protections and all on board saved.

So why is this not programmed to happen?
I think you misinterpreted what "valid speed" means. When the BEA writes "The speeds became valid again", it means the speeds were no longer below 60kt (for AoA stall warning) or below 30kt (for speed itself).
A valid speed (system speaking) is not by definition a correct speed (i.e. real).
The system cannot know if the sensed speed, after the pitot failure/icing, is back to correct values. In fact in some cases, speeds may be valid (above 60kt), consistent (3 equal values, or at last 2 equal values, the third being voted out) but not correct.
It's only the discrepency in speeds (from 3 sensors) that make the system decide "We got a problem". Unless you can confirm the correct speed by other means, it's safer IMO that the system let the crew decide. That needs the crew to be trained for such situations, and the SOP to be OK.

For the system to be able to decide, by itself, that the speeds are back to correct values, it would need to compare the ADR speeds with other sources. Perhaps the INU/GPS may be a source, here, in combination with the altitude (pression), the temperature and the wind speed/direction. If you have all of them, I suppose it's just maths (which a computer can do, and quickly).
The wind speed will be a problem, to me. How do you know it ?
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Old 26th Jun 2011, 09:55
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CogSim;

It should be noted that both referenced posts are dated 30 june 2009, i.e. before BEA published its first Interim Report. I believe BEA's reports are based on more authoritative information than these posters (with all due respect) had at their disposal at that time.
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Old 26th Jun 2011, 09:59
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Originally Posted by AlphaZuluRomeo
Hi

I think you misinterpreted what "valid speed" means. When the BEA writes "The speeds became valid again", it means the speeds were no longer below 60kt (for AoA stall warning) or below 30kt (for speed itself).
Thanks for reply. I should have quoted the report, I was referring to the reported fact that the speeds became consistent during the descent (as to be expected once the icing conditions had been left behind if the initial problem was pitot icing, which appears likely)

"Around fifteen seconds later, the speed displayed on the ISIS increased sharply towards 185 kt; it was then consistent with the other recorded speed."

It was inconsistent speeds that caused the aircraft to depart normal law and hand control to the pilots. If the speeds later became consistent there should be, IMO, logic that at least contemplates a return to normal law. 185kts is well above the lower limit where the aircraft ignores the speeds as being out of range.

Had the aircraft returned to normal law, applied AoA protection, it almost certainly would have recovered in the 30,000ft available.

Apart from that I cannot, with the information available, fault the aircraft at all.

Why is ALT 2 latched?
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Old 26th Jun 2011, 10:13
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Originally Posted by PA 18 151
It was inconsistent speeds that caused the aircraft to depart normal law and hand control to the pilots.
IIRC it was not an inconsistency between the three ADR speeds, but a sudden drop in one of them, the "polled" value that the PRIMs were using and considered the most accurate of the three. That anomaly was confirmed at the end of the monitoring period.
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Old 26th Jun 2011, 10:18
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PA 18 151 : My mistake on the "valid" speed.
I agree with you, in AF447's case, a return to normal law may have helped, or even have saved the plane.
But I stand still : how can the system decide the speeds are corrects ? It would be a guess. And I think that, in other scenarii, such a guess would be wrong and lead to incorrect actions by the system.
That's why I suggested a comparison between the ADR speeds and other sources. The ADR redudancy is not enough, as 3 (identical) probes can be faulted by an identical phenomenon at ~ the same time : icing, ash cloud...

I suppose that's why ALT2 is latched. The point is, as you said : If the aircraft system doesn't know, let's give control to the crew.
The aircraft system cannot know, cannot be 100% sure (using only the ADRs) that the speeds are back to correct values "just" because the speeds have rised, and/or are consistent again. The crew is better IMO to assume that, based on other sources (pitch, power, feel, visual clues...)

For the record : Agreed with the rest of your posts
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Old 26th Jun 2011, 10:38
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Originally Posted by HazelNuts39
IIRC it was not an inconsistency between the three ADR speeds, but a sudden drop in one of them, the "polled" value that the PRIMs were using and considered the most accurate of the three. That anomaly was confirmed at the end of the monitoring period.
Hi Hazelnuts,

Yes, it used polled value, explained by BEA (Interim Report 2) my italics:
Like the FMGECs, the PRIMs consolidate the parameters that they use by means of monitoring mechanisms. Concerning the airspeed, it is the voted value that is used. In normal operation, this is the median value. When one of the three speeds deviates too much from the other two, it is automatically rejected by the PRIMs and the polled value then becomes the average of the two remaining values. But if the difference between these two remaining values becomes too great the PRIMs reject them and the control law switches to alternate 2.
So my reading is:
1) No single value is more imporant than the other in normal operations
2) When one becomes inconsistent with the other two it is rejected
3) When the other two become inconsistent with each other the law goes to ALT 2

It is inconsistent speeds that causes the plane to reject them

Consistent AND valid = Correct

The speeds later became Consistent AND Valid therefore they should have been considered correct. i.e. Normal Law conditions = AoA protections = aircraft breaks the stall.

AlphaZuluRomeo:

Consistent AND valid = Correct

Well, yes it's a good assumption to make that the crew will act correctly once the plane hands over control. Is this what the designers assumed too? Perhaps another flaw in system design?

Normal Law would almost certainly have saved the day. I submit that from the evidence we have, for over two minutes and 30000 ft AFTER the initial problem, that normal law conditions existed. Unfortunately in the interim, ALT 2 had been latched, and the aircraft was unable to break the stall the pilots had caused and failed to recover from.
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Old 26th Jun 2011, 11:21
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Originally Posted by A33Zab
Pls. comment, correct or update as required.
Very nice timeline, hope we get that level of presentation in the BEA reports (though just fdr traces would be ok).

Haven't gong through it all, but it looks right per the information we have to date. One comment - initially there was a PF left + nose-up input which seems to be missing.
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