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AF447 Thread No. 3

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AF447 Thread No. 3

Old 27th May 2011, 19:58
  #161 (permalink)  
 
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I guess I have difficulty understanding why the software would find 3.5 minutes of maximum nose-up for the THS perfectly acceptable while all other inputs were going to hell in a hand basket. Was the processor too busy with other interrupts to check the THS or was this combination of input anomalies not part of the decision tree?
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Old 27th May 2011, 20:00
  #162 (permalink)  
 
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@Rob21 - they've released this note as a counterweight to apparent press leaks. It's not even an interim report, just a collection of facts they've managed to prove so far. The reason there isn't more *right this second* is because that is literally all they have.

As was stated earlier, PJ2 was in the air - odds-on he'll be back sometime in the next 24-48 hours.
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Old 27th May 2011, 20:10
  #163 (permalink)  
 
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I guess I have difficulty understanding why the software would find 3.5 minutes of maximum nose-up for the THS perfectly acceptable while all other inputs were going to hell in a hand basket. Was the processor too busy with other interrupts to check the THS or was this combination of input anomalies not part of the decision tree?
So presumably you'd have preferred the software to decide this wasn't allowed and roll off the trim - despite the input from the pilot demanding nose up? You really can't have it both ways now, can you? On the one hand half the crowd here are screaming for the head(s) of the software programing team for removing so much 'authority' from the crew, and here we have a request for the software to "decide" that the crew demand was unhealthy - even if it *was* unhealthy, are you sure you want additional laws and protections? Given that the aircraft has an auto-trim system, it appears to have been operating as expected, given the commands from the crew?
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Old 27th May 2011, 20:11
  #164 (permalink)  
 
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Coming out of Quarantine

Presumably, this afternoon, you guys have been discussing the BEA "Update on Investigation". For what it's worth, I've been in voluntary quarantine since just before it came out. As soon as it appeared on the BEA website, I cut myself off completely from PPRuNe, all other media, and any contact with aviation-minded people; and that situation still pertains as I write. I deliberately progressed very slowly through the paper, taking notes and some very long stretch-breaks. There were a number of surprises. Since then, I've been mulling it over, and drafting this.

So what you are about (not/partially) to read are questions and comments arising from my own interpretation of the BEA account, uncoloured since its publication by the wisdom of third parties such as your good selves, and burdened by my limitations. No doubt, I'll have missed many points that, to you, are already "old hat". Nevertheless, here are my thoughts.

QUESTIONS & COMMENTS ARISING

(1) Why no R/H ASI parameter in DFDR? Would it be in QAR? The two recorded ASIs use pitots on the L/H side. (The PF was in R/H seat, presumably.)

(2) "From" 02:10:05, at what stage did the L/H (PNF's) ASI and ISIS ASI readings fall sharply from 275 to 60? After the two stall warnings, or before?

(3) Why did PF allow/encourage/command A/C to climb 3000ft and up to +16 pitch after receipt of stall warnings? One of the pilots had selected TOGA thrust, presumably in response to them.

(4) Why did/does the FBW system in Pitch-Alternate Law continue nose-up trimming of the THS past the stall-warning level of AoA?

(5) As the THS remained at 13 deg UP throughout the descent, is there any possibility that the THS motor stalled during down-elevator inputs? (The BEA "finding" is that "the inputs by the PF were mainly nose-up"[my emphasis of "mainly"].

(6) At about 02:11:04 (at the apogee of FL380), the L/H ASI and ISIS ASI showed 185kts. Was the R/H ASI showing a higher value possibly due to a blocked drain-hole PLUS the climb of 3000ft?

(7) Quote from BEA:
"At around 2 h 11 min 40 [6], 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."
[FONT=Verdana][SIZE=2]Why are the AoA values considered invalid below 60kts IAS when the A/C is not on the ground?
(Looks at this stage that: first the PF has mis-controlled the A/C into an inappropriate, steep climb, despite a stall warning; but now the systems are failing to inform him that he has stalled the A/C.)

(8) In the descent, why did neither pilot seem to recognise that the A/C was even in a stall, let alone a deep/super stall? Why was idle thrust selected?

(9) At 02:12:02, several thousand feet below FL350, does the PF's comment that he had no more indications indicate that his ASI reading had only just dropped to a value that he no longer believed? Is it remotely possible that, perhaps unlike the others, the drain hole of his pitot tube had blocked at the same time as the intake? During the initial climb, could he have thought that his ASI was still valid, and that he was trying to avoid an overspeed? [See (6) & (7), above.]

SUMMARY OF KNOWN ENERGY ASPECTS (from BEA text and diagram)

02:08:07 02:10:05 (~15nm)
FL350 (about 37000ft amsl). Average GS ~450kts.

[FONT=Verdana]02:10:05 02:10:51 (~5.4nm)
FL350, then climbing steeply. Average GS ~420kts.

02:10:51 02:11:40 (~4.3nm)
Climbing to apogee of FL380 (about 40000ft amsl), then descending steeply through FL350, all with TOGA thrust. Average GS ~320kts.

02:11:40 02:14:28 (Tear-drop track-distance unknown)
Descent from (passing) FL350 (about 37000ft amsl) to sea-level, Thrust reduced from TOGA to ~IDLE by 02:12:02.

Footnote
During the couple of hours I spent reading this short report (including going back and forth), making notes, and referring to system diagrams, I made several unnecessary errors with my printer. Some sheets had to be discarded and fresh attempts made. The flight crew had less than three minutes to diagnose the problem, take action, and recover from any mistakes.
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Old 27th May 2011, 20:12
  #165 (permalink)  
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Quote:
At around 2 h 11 min 40 <snip>
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 airplane’s pitch attitude did not exceed 15 degrees and the engines’ N1’s 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 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%. 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.
At 2 h 13 min 32, the PF said "we’re 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 initial altitude (FL350) and 2 minutes @ 10K/min gets you close to FL100

************************************************************ **

(My new bold) Between 2h13m32s and eor, 2h14m38s, the a/c descended ~two miles.

Just before, with ND, the AoA lessened, the pitots stopped blanking, and an a/s was presented. Still at Stall, the vertical speed was 107 knots, square with horizontal, also 107 knots. This is an AoD of 45 degrees, with full power seemingly available. So at FL100, and these numbers......If this is true, they did not "miss" by much, a recovery...?
 
Old 27th May 2011, 20:13
  #166 (permalink)  
 
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Originally Posted by Rob21 View Post
Henra, I am talking about pitch, not only roll.
As far as I know, an attitude indicator indicates (or should) pitch and roll.
Hmmm, maybe I misinterpreted your post. If that is the case, I do apologise.
I understood your post pointing to a non-functioning of attitude indication.
And that is where I get a bit sick and tired reading it time and again, although there is not the slightest indication that IR and thereby attitude information was lost.

And the description of the attitude during descent aboslutely points in the same direction. The attitude was always rather level. In all axis btw.
Ok there was a 40° bank at one point which the pilots tried to correct immediately. This confirms they had suitable attitude information.

Aircraft in IMC where Attitude information is lost arrive in a totally different way.
Absolutely totally different....

My feeling is the thing was seemingly somehow under control, seemingly missing only one piece in the puzzle, the trajectory.
I'm afraid these poor guys never really figured out their effective flight path and speed through the air. Being lost in warnings, seemingly benign attitude and physical sensations and strange instrument indications.
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Old 27th May 2011, 20:17
  #167 (permalink)  
 
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Hello all PPRuNers, I have been following this thread with great interest since tragic loss of AF447 two years ago (and other PPRuNe threads also ). I am not a pilot nor I do have any connection to aviation industry whatsoever, except great passion for airplanes and flying but only as SLF. I must thank to you all as over time I did learn a lot from you and I am very grateful for that.

As I read BEA I was puzzled by THS being in almost full up position for about 3,5 minutes and not changing its position although PF made pitch-down input. Unfortunately report doesn't mention for how long pitch-down input lasted. I took my copy of A330 FCOM (not current one) and found out, please correct if I am wrong, that flight control law could have changed from ALT 2 to Abnormal attitude as angle of attack was greater than 30 deg causing no auto trim available until angle of attack decreases below 30 deg, which according to BEA report did not happen.

Is there any indication in the cockpit when this happens?
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Old 27th May 2011, 20:18
  #168 (permalink)  
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1- AoA at 6 degrees and increasing + STALL warning
How is it possible the THS was still trimming up ?
What's wrong here ?

2- As both recorded IAS became consistent again, did the FDs reappear ?

3- BEA, give us all but not that so little !
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Old 27th May 2011, 20:19
  #169 (permalink)  
 
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Chris:

(4) Why did/does the FBW system in Pitch-Alternate Law continue nose-up trimming of the THS past the stall-warning level of AoA?
I believe Pitch Attitude protections are lost in Alt1 law and I remember a note about stall protections being 'override-able' in Alt law.

See: A340 - A330 Control: Flight & Laws
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Old 27th May 2011, 20:21
  #170 (permalink)  
 
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About fifteen seconds later, simultaneous inputs by both pilots on the sidesticks were recorded and the PF said "go ahead you have the controls".

Why would he relinquish control ? Is there some dialogue we are missing ?
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Old 27th May 2011, 20:25
  #171 (permalink)  
 
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(9) At 02:12:02, several thousand feet below FL350, does the PF's comment that he had no more indications indicate that his ASI reading had only just dropped to a value that he no longer believed? Is it remotely possible that, perhaps unlike the others, the drain hole of his pitot tube had blocked at the same time as the intake? During the initial climb, could he have thought that his ASI was still valid, and that he was trying to avoid an overspeed? [See (6) & (7), above.]
02:10:16
PNF "...we've lost the speeds" "...alternate law"
No acknowledgement from PF.

02:12:02
PF "I don't have any more indications"
PNF "We have no valid indications"
First sign of PF identifying problem with indications.
PNF acknowledges.
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Old 27th May 2011, 20:28
  #172 (permalink)  
 
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Let's step back.

Surely the point in having more than one crew member is so that the PNF can say either:
1- What the fxxx are you doing or;
2- What the fxxx is IT doing depending on whether your are requesting the right or wrong inputs and getting the right or wrong responses from the system.

So, in the Bus, can the PNF or jump seat occupant see what the PFcommanded with the stick? If not, do not expect them to be able to call you on it.

Could someone who flies this confirm the simple question
"Can you tell what the other is doing?"

Frankly I am impressed with the self restraint of a PNF who waited 27k feet before deciding to put hands on. I stop being a team player way before that
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Old 27th May 2011, 20:29
  #173 (permalink)  
 
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That's a very calm sounding FD considering what's going on. The report of the CPT 'shouting' sounds more like it. Think the FD communications may be a bit too dramatic to release without other context and explanation.
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Old 27th May 2011, 20:29
  #174 (permalink)  
 
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GarageYears; Perhaps you misunderstood my question. I was inquiring whether maximum nose-up for 3.5 minutes was considered acceptable by the software and whether or not the PF should have been made aware of that fact (although he probably had more than enough software output to handle). The pilot should be making the final decision but when a computer puts a flight control in an extreme position for a considerable time (not directly by his command) it might be helpful for him to know what he's fighting.
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Old 27th May 2011, 20:34
  #175 (permalink)  
 
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The data from the DFDR will undoubtedly find its way to a sim in the future. What might the outcome had been if the PF had not touched the sidestick at all and allowed the a/c to ride out the uas. Presumably in that night, the movement of the trim wheel and subsequent lack of movement back would not have been a high priority.
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Old 27th May 2011, 20:35
  #176 (permalink)  
 
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Mr. Optimistic...

Is there some dialogue we are missing ?
The answer is yes. Lots. Without any doubt.
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Old 27th May 2011, 20:37
  #177 (permalink)  
 
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KMD - Do you know of any aircraft in which a computer will override the pilots trim command input in that manner? The computer did not put the flight control in an extreme position, the pilot put the THS there through the continued application of nose up stick. The auto-trim did exactly what it was designed to do and which any Airbus pilot would be expecting.
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Old 27th May 2011, 20:37
  #178 (permalink)  
 
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That's a very calm sounding FD considering what's going on. The report of the CPT 'shouting' sounds more like it. Think the FD communications may be a bit too dramatic to release without other context and explanation.
That begs the question what were the criteria used in the editing process. Clearly they must believe whatever was released presents the event without too much distortion.
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Old 27th May 2011, 20:37
  #179 (permalink)  
 
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kmd:

Yes, I guess I was a little spicy there - apologies for barking! I understand where you're coming from now - I suppose the question is "how does the crew know AT ALL where the THS is pointing?". And as a supplemental to that, should there be some (obvious) indication when the THS falls outside of some nominally "normal" range? Presumably 13 degrees up is not a common demand....?
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Old 27th May 2011, 20:39
  #180 (permalink)  
 
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Originally Posted by Mr Optimistic View Post
About fifteen seconds later, simultaneous inputs by both pilots on the sidesticks were recorded and the PF said "go ahead you have the controls".

Why would he relinquish control ? Is there some dialogue we are missing ?
The thought that occurs to me - and take it as it is, a wild-arsed guess - is whether the Captain managed to regain his seat at that point. We know there were some large rolls on the way down, but whether that would have presented a major obstacle to him doing so either because of excess deck angle or G is unknown at this point.

It also rather scotches the idea that the PF was unaware of any control inputs made on the other side, because whatever he saw, whether it was the occupant of the LHS moving the stick or the "DUAL INPUT" warning, he was immediately aware that the stick was being moved and relinquished control via the switch at the base of the LHS sidestick, just as protocol states.
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