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AF 447 Thread No. 5

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AF 447 Thread No. 5

Old 5th Aug 2011, 09:40
  #1581 (permalink)  
 
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DozyWannabee, I note that takata's recent note about the plane aimed down when the PF requested NU and your comments about not seeing a conflict in that suggests another basic rule for "strange situations" such as the sudden drop to ALT 2 with no airspeed indication: Don't Play With The Throttles, Bunky.

The moment arm with the engines and their thrust do exactly the opposite of what you think you want. If you are thinking overspeed pull up. But don't drop the throttle. That will nose you down. If you are thinking stall, don't goose the throttle. That will tilt you up and slow you down. So don't play with the throttle.

But, for that matter, don't change anything except roll. Maintain pitch, don't touch the silly throttle, and keep the wings more or less level but fanaticism about it doesn't pay. Watch the altimeter. If it start changing rapidly aim the plane "slightly" to compensate. But don't play with the throttle except for VERY small nudges.
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Old 5th Aug 2011, 09:58
  #1582 (permalink)  
 
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Originally Posted by JD-EE
But, for that matter, don't change anything except roll. Maintain pitch, don't touch the silly throttle, and keep the wings more or less level
Roll control is problematic in the stall. When you're stalled, unstall first, then level the wings.
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Old 5th Aug 2011, 10:08
  #1583 (permalink)  
 
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HN39 - I am addressing what to do upon entering ALT 2 with no airspeed indication. Once in a stall first course on the table is admit you are stalled. Second course is nose down with an urgency depending on rate of drop of altitude. Third course is airspeed. Fourth course is a gradual pull up once airspeed is high enough. Fifth course is the dessert of moving back to planned course.

If no airspeed continues use AoA vane as a clue whether you are stalled or not. When it "agrees" with pitch you're good to pull up - gradually. No AoA report in the cockpit? Um, Er, Ah, Boss - you're gonna die?
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Old 5th Aug 2011, 10:58
  #1584 (permalink)  
 
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Thread drift

John has updated the very first post in this thread to include some essential links for all newbies here. Thx, great!

Can I also include some excellent weather analysis here: Air France 447 - AFR447 - A detailed meteorological analysis - Satellite and weather data by Tim Vasquez
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Old 5th Aug 2011, 11:32
  #1585 (permalink)  
 
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JD-EE;
Once in a stall first course on the table is admit you are stalled. Second course is nose down with an urgency depending on rate of drop of altitude. Third course is airspeed. Fourth course is a gradual pull up once airspeed is high enough. (...)
Agreed, almost. If you have AoA or next best, valid stall warning on/off as a substitute of it, I would put leveling the wings third. If you let yourself be guided by AoA, you don't really need to watch airspeed for recovery and can leave it to course five.
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Old 5th Aug 2011, 12:00
  #1586 (permalink)  
 
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van Horck, it would be nice if Tim Vasquez updated his graphics and analysis again, given the additional information in the Third Interim Report. e.g., the turbulence trace, and the sound of ice crystals.

The contrast between what the crew flying AF447 did at SALPU and ORARO and what the crew of AF 459 (35 minutes behind) did is striking. In essence, the crew of AF 447 thought they could ride near or at the top of the clouds, and never gave a second thought to the presence of Cbs, even though they were specifically cautioned about such.

For the lawyers seeking damages, their inattention and complacency is the equivalent of finding a vein of gold with the first dig of a shovel.

Reading between the lines, even the BEA seems at a loss to explain it. It will be interesting to see if the BEA can determine how many of the captain's and PF's rotations to South America occurred on flights through an active ITCZ.
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Old 5th Aug 2011, 12:10
  #1587 (permalink)  
 
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Questions: Selected Vertical Speed.

CONF iture:
Quote:
Originally Posted by takata
This graph is showing the VSS value after reseting to current flight level due to intermintent returns of flight directors (as they were never turned off).

No takata, we're not talking after but before !

What was the issue on the FDs before ... ?
Exact! and the spikes @ 02:10:16 'CLOSING of the CAS monitoring window & ADR rejections'?

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Old 5th Aug 2011, 12:42
  #1588 (permalink)  
 
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Hi Old Engineer,
Originally Posted by Old Engineer
I'm noting that this -5000 fpm appears to be without flight deck input, so I'd say the graph is saying something critical to us.
Before AP disconnecting (at 0210:05) the graph is showing a VSS of zero, not -5,000 ft. (one need to read the discontinuous green line) and the red line (real V/S) is not altered in any way by it. It is also showing a different active mode when autoflight is still ON.

The cyclical drops (regular pikes down to MIN value) is certainly due to this autoflight mode (hence normal). In fact, I did not comment on those regular pikes as nobody here knows how those values are sampled. The same channel may be used, when AP is ON, for recording another flight parameter at regular intervals. It looks for me to behave this way.

After FMGECs faults (at 0210:05), the mode change is obvious, next VSS value increase/decrease is now linked with FD resetings. But, before this point, the VSS values (including MIN) are not linked with FD as there is another graph for FDs showing nothing anormal before UAS.
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Old 5th Aug 2011, 12:42
  #1589 (permalink)  
 
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SaturnV

I've asked Tim, but he was too busy to come up with an update, he made the document then, to help us in the days when no plane had been found.

I will mail him and ask him again I promise, but he is a busy man......


Update 14:50 Amsterdam time I've emailed Tim and will come back on this if relevant

Last edited by vanHorck; 5th Aug 2011 at 12:50. Reason: further info
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Old 5th Aug 2011, 12:45
  #1590 (permalink)  
 
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Gums and JD-EE

Asymeteric Thrust

Other old(er) Dinosaurs than Gums might recall that the HP42's top two engines needed careful handling on the ground. The tail wheel could lift, unexpectedly.

JD-EE reminds us that asymetric thrust is not only what we practice when one engine is shut down. TWO (or more) Underslung engines have a pitch effect.

( Would that be equal to 4 units of NU trim ? I have no way of telling as my armchair is uncalibrated. I am sure that the answer is "...It depends...")

Takata noticed a small improvement in the recovery from the stall when the power was reduced, all too briefly - and then, sadly, it was restored.

What would I have done as PF ? I have not had the luxury of time to think, to change my mind from climbing with full thrust, to pitching nose down. Closing down BOTH engines to flight idle might be the right thing to do - but would FEEL very wrong. Descending at night through a Cb without any clear Airspeed...I know that my Penetration speed should be between 240 and 260 kts, but how can I tell... I must try to keep my wings fairly level if I can...

Perhaps.... it is as well that my armchair does not feel overloaded, too!
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Old 5th Aug 2011, 12:51
  #1591 (permalink)  
 
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This is where I believe the Air France way of doing things is fundamentally flawed. Most other airlines have a distinct chain of command, Captain > Senior First Officer > Junior First Officer. In this case the older, more experienced first officer should have been "In Charge" while the Captain was resting. [This would not prevent the Junior FO controlling the flight and making tactical decisions but may have encouraged the Senior FO to be more assertive when things were not going so well.]

This may have resulted in a better outcome !
maybe, maybe not.

AF pilot unions have always refused the "distinct chain of command, Captain > Senior First Officer > Junior First Officer" as this would mean less trained/less qualified (read : less paid) "junior F/O".

The underlying idea being : total qualification of the crew is better with one captain and two fully qualified F/O's.

Now, of course, the two F/O's being "equal" means CRM problems can arise as we see here.
Obviously the PNF had a, slightly, better understanding of the mess, but at no time he ordered "my plane" (at the time, F/O's did not get any LHS-flying training).

One last comment, the older/more experienced F/O is not always the best choice for PIC.
Never flown with aging, not very concerned F/O's ?
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Old 5th Aug 2011, 13:09
  #1592 (permalink)  
 
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vanHorck, thank you, and thank Tim as well for all his past effort.

The assessment that I would be most interested in is whether the loud noise that can be heard on the CVR of ice crystals hitting the plane indicates they had penetrated the Cb itself, or if not, how close would one need to be to a Cb to get that amount of ice crystals.

I don't recall that the BEA gave sufficient data to correlate the time when the sound of ice crystals can be heard on the CVR and the PNF turns on the anti-ice.
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Old 5th Aug 2011, 13:10
  #1593 (permalink)  
 
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Hi A33Zab,
Originally Posted by A33Zab
Exact! and the spikes @ 02:10:16 'CLOSING of the CAS monitoring window & ADR rejections'?
Well, not sure. In fact, I'd say that at around 0210:16, speeds could have been coherent again for a very short time and FDs were back, disapearing almost immediately. In between, a new set VSS was sampled, taking the actual value from the real V/S at this exact point.
CAS monitoring doesn't alter the VSS parameter (see 0210:05-0210:15 and subsequent values staying where they were while V/S increased or decreased). Its value freezes to the current V/S when FDs kicks off.
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Old 5th Aug 2011, 13:20
  #1594 (permalink)  
 
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AF pilot unions have always refused the "distinct chain of command, Captain > Senior First Officer > Junior First Officer" as this would mean less trained/less qualified (read : less paid) "junior F/O".
What about Captain / Senior First Officer / First Officer ?

Surely this means a special training for LHS qualification including ground school, sim training, line training with checkout as Senior First Officer.

And yes, pay is inbetween First Officers (not called Junior..) and Captains.

I don't see something wrong with that.
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Old 5th Aug 2011, 13:26
  #1595 (permalink)  
 
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Hi Confiture,
Originally Posted by CONF iture
No takata, we're not talking after but before !
What was the issue on the FDs before ... ?
Thank you for attracting my attention on this point. It seemed normal to me and no, BEA would not comment something "normal" without good reasons to do so.

Nonetheless, the fact that FDs were not turned off attracted also their attention in order to find what kind of indications could the bars have displayed on PFDs. There is a discussion on it and they are trying to reconstruct everything displayed for analysis. So, I don't think that there is any sort of conspiracy about that, don't you agree?

I really believe that BEA investigators are trying their best as to verify everything, but it takes time, as you know as well, to investigate every single bit of data. You should drop off this attitude of conspiracy as it won't help families or pilots to continue this way by discrediting them constantly.
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Old 5th Aug 2011, 13:26
  #1596 (permalink)  
 
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Is it possible that the F/O who was PNF in the left seat was also reluctant to take control because of a lack of dexterity with the LHS sidestick? As a F/O, primarily sitting in the right seat, his experience and dexterity would with using his right hand. Indeed, I have heard mentioned elsewhere that when two F/Os are on the flight deck, the PF is always supposed to be the one in the right seat.
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Old 5th Aug 2011, 13:36
  #1597 (permalink)  
 
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Hi SeenItAll,
Originally Posted by SeenItAll"
Is it possible that the F/O who was PNF in the left seat was also reluctant to take control because of a lack of dexterity with the LHS sidestick?
Very probable, added to the fact that he wasn't sure of his own understanding of events. Very sad in fact as he seems to be always on the verge of doing the right thing.
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Old 5th Aug 2011, 13:53
  #1598 (permalink)  
 
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Certainly this is material for reflection, and better understanding of the moments before, and when all of it started.....

Here is a set of graphs, that may help visualize certain parameters at the moments before the AP disconnect, and passing from Normal Law to Alternate Law - this is the moment of the AP and A/THR disconnects.

A red vertical line marks the moment of the Normal to Alternate Law change.

I notice a Pitch Nose Down, right before the Law change.
I can also see now, that the slight Altitude loss (if the BEA graph is accurate) was right after the Law change. At the time of the previous post, I thought it is before the Law change

One can visualize the increased degree of turbulence based on the areas marked on the 3 graphs of acceleration right before the Law change. There is an increase in up-down-left-right-forward-backward motion. The Vertical Speed around that time also show and increase, and decrease - reflecting the Vertical Acceleration changes.





Very important point. So...

AP disconnects
a/c at 0 deg pitch => will descend
pilot stick back 3/4 causing nose up pitch 11 deg.
climb rate goes up.
after 4 seconds first stall warning
after 15 seconds altitude has not changed (downdraft/reduced thrust?)

So PF was correct to stick back but he over does it.
Stall alarm sounds, he eases off on the stick pushes it fwd briefly, alarm stops.
Then he resumes stick back to maintain altitude.
Now the THS starts helping PF to pitch nose up.
Now he is gaining altitude with help from THS.

Report #3, Page 111, Longitudinal parameters

Notice the insidious influence the auto THS (cyan) has on elevator position. At some points he is stick forwards (red line, 02:12:17) yet elevators stay around -30 deg (purple). Clearly this would add to the confusion of inputs.

Last edited by airtren; 5th Aug 2011 at 16:06.
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Old 5th Aug 2011, 14:01
  #1599 (permalink)  
 
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SaturnV, “… how close would one need to be to a Cb to get that amount of ice crystals.” # 1584.
Some research and flight tests suggest that significant amounts of ice crystals can be found up to 10-15 nm from a Cb (measured from the edge of the red zone).
From experience around and in Cbs with ice crystals, it is most unlikely IMHO that AF 447 entered a Cb core, although the aircraft may have passed through or over the tops of smaller cells.
Ice crystals can be heard – a sort of swishing sound; this is often accompanied with a very wet windscreen (screen heating), which adds to the confusion. Furthermore the ice crystal cloud is very tenuous and might not even be classified as IMC in some circumstances.
Louder, harsher noises come from hard hail often found in the same situations, particularly over the core; this can be heard clearly and might on occasions sound like rain.

The best advice is to stay well clear of Cbs, the avoidance distance (from the edge of the red zone) being proportional to the size of the core. I have encountered signs of outflow cloud up to 60nm in one Caribbean cell and 100nm from a huge cell in Africa; basically any anvil cloud can have a high concentration of crystals.

Just because modern aircraft have high tech radars which automatically detect the severity of ‘this, that and everything else’, and in multicolour, does not imply that technology understands the effect of the conditions on a particular aircraft type, or on a on a type thought not to be susceptible, but now operating with different performance parameters, e.g. engine power, TAT.
Ice crystals caught the industry napping several years ago with engine problems – the engine design had changed, not the weather. At the time there were signs of blocked ‘tubes’ and overpowered heaters (TAT) but no connection was made with pitots.
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Old 5th Aug 2011, 14:13
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Originally Posted by airtren
A red vertical line is the moment of the Normal to Alternate Law change.
I notice a Pitch Nose Down, right before the Law change.
I can also see now, that the slight Altitude loss was right after the Law change.
Removing, at this point, the "turbulence" effect (the good clue to see its effect is to look at simulated longitudinal axis analysis tables provided), nonetheless you are right about the up/down caused.

Anyway, change of law is due to unreliable airspeed.
The pitch down (at longer term) moment is also due to the reduction of thrust at 0209:58 (Mach 0.80 selected), decrease is about 15% in few seconds.
Altitude is "indicated altitude", as well as speeds, and UAS is causing a loss of "indicated" altitude (but ISIS is barely not affected, about 100 ft). It is obvious when you compare pitch vs V/S curves and altitude altogether: the former increased but altitude indicated change is delayed by 10-15 seconds.
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