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AF 447 Thread No. 5

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AF 447 Thread No. 5

Old 31st Jul 2011, 21:41
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"....it would be like entering an arse-kicking contest with a monstrous entity that has a thousand legs - and no arse"

DW, thanks for that. Saved for future use.
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Old 31st Jul 2011, 21:41
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Back to impersonal matters

There has been a lot of debate on whether the aircraft could have been recovered from the stall and if so how much height would have been needed. I think what has been missing is not so much a question whether it could have been brought back inside the flight envelope but a recognition that it was actually held in the stall by pilot action and that the first stage of recovery would have been simply to remove the up elevator by relaxing on the sidestick. This would not have been sufficient by itself, but would have removed any doubts about the efficacy of down elevator, application of which would have further reduced the AoA and brought the THS back towards 3 deg NU rather than 13 deg.
I hope what follows is not too confusing, but the graph, which is taken from the AIAA/NASA/Boeing report on upset recovery is as near as Gums is going to get to pitching moment curves for the A330. Looking at the model test geometry it is difficult to see anything that would make these curves substantially different from the A330. Even so, treat them as qualitative not quantitative.
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On the zero elevator line you can see the typical mild pitch up near the stall that I mentioned in an earlier posting.
For the tail geometries typical of modern civil designs, the relative pitching power of THS and elevator would be about 1deg THS equivalent to 1.5 deg elevator. So for a THS set at -13 deg we can read these curves at about 20 deg up elevator to get a feel for things. This would take us up to a trimmed AoA (Cm = 0) of just over 20 deg. However, if you add 30 deg up elevator, you would end up at just over 40 deg AoA, which is pretty similar to AF447 in the same state. So to get to the high AoAs we see from the DFDR data, it looks like you have to be holding full back stick as well as having the THS at -13 deg.
If you now return the stick to neutral at this elevated AoA you get a substantial nose down pitching moment which will take the aircraft back towards sanity. But it will not take it the whole way – just back to the AoA set by the THS angle.
To get back inside the flight envelope you MUST apply some down elevator, which will give another substantial recovery pitching moment but also will, with the A330 logic, start to return the THS back to its cruise setting of -3 deg.
To get an idea how much height loss is involved, you can approximate by a simple energy height trade and a pull-up. Simple geometry says that this latter is surprisingly small. Obviously it depends on the steepness of the descent, the airspeed and the amount of ‘g’ one can pull. This last item also depends on the airspeed. It isn’t any good accelerating to Vs1g because there is no spare lift for the pull-up. To get a reasonable ‘g’, say a 0.5g increment, you need to accelerate to 1.23Vs. Starting from a 20 deg dive the pull-up with that ‘g’ will take about 500 ft altitude.
Starting from 100 kts CAS at 34000 ft and accelerating to say 240 kts CAS at about 28000 ft you need to accelerate from around 300 ft/sec TAS to about 650 ft/sec TAS, which equates to a height loss of just over 5000 ft. Add the 500 ft for a pull-up and in round figures you should be able to recover in 6000 ft altitude.
On that analysis the aircraft WAS recoverable from the stall, but it would have required a definite and sustained nose down elevator application that never materialised – in fact, despite Bear’s latest remarks, DOWN elevator was never applied, just a relaxation of the up elevator

As I said, treat this as a qualitative explanation of what the aerodynamics are likely to have been. Looks quite reasonable to me though
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Old 31st Jul 2011, 21:45
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Pilots

Quote 3holelover
"Two kinds of pilot" I thought. "Old" and "New". "Old" could fly almost anything with wings, but not a newer, glass and computer machine. "New" could fly the computer generation "smart" birds, but probably not an old DC3.

I'm still mulling over those distinctions, but it has occurred to me more recently that this particular airplane needed both kinds of pilot, and the two "New" types that were in the seats just had none of the abilities of that "Old" type. I simply cannot fathom any of the type "Old" failing to recognize a stall. ... at any point during a 35000ft descent.

These poor blighters were more computer programmers than pilots. They needed an old geezer.... and when their best shot at that re-entered the cockpit, he'd missed the beginning of it all, and in any case his AF training had probably left a whole quilt of cobwebs on any "Old" pilot within him.


I'm not sure the distinction should be between old and new but rather those with a passion for the work they do and those for whom it is a job; alas the reality is often the latter in all walks of life but where lives are at risk such as in aviation or medicine I think we would all prefer to be in the hands of those for whom it is a true vocation and are passionate about it.

Whilst it seems clear that there was a serious lack of training, even I, who am not a pilot, would hope that understanding, avoiding and dealing with a stall were first principles of flying.

I do understand the issues are both complex and emotive and have followed the thread since the accident, personally I am horrified at the apparent lack of training and concerned about the recruitment criteria.
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Old 31st Jul 2011, 22:01
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It's all about psychology, not technology.

The PF couldn't fly the plane without computer help but he thought (hoped) he could (Dunning-Kruger effect, alias "innocence of youth").
The PNF didn't want to offend him and damage the PF's self-esteem, especially as the PF's wife was in the back.
The PF wanted to get above the turbulence, anyway.
The captain would have marked him down (promotion prospects?) if he'd disturbed him for nothing.
The normal-law disconnection represented an OPPORTUNITY for the PF!

Result -
total disaster - reminiscent of crashes before anybody knew anything about how wings work. The PF didn't know anything (worthwhile) about how the most important machine on the aeroplane (the wings) work. Not surprising, really, when this simple device is shrouded in pseudo-mystery by mathematical nonsense spouted from so many sources.
Perhaps he had never swapped yarns with old-timers over a beer or two. Perhaps he had never heard of "coffin corner". Perhaps he thought that when you said "Up!" the plane always went up, When you said "Down!" the plane always went down. Just like on the computer.
But if you enter a skid, due to too vigorous actions...what then.....
Turn into the skid, of course - if you can do it in time.

What OUGHT to have happened was that the PF said immediately "I'm totally out of my depth here. For God's sake, you take over. I'll get the captain".
"Ce situation est trop difficile pour moi. Prennez-vous les controles, tout de suite. Je vais reculer le capitaine." (apologies for the French)

But that would NOT have gained him any Brownie points. The guy was between a rock and a hard place.
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Old 31st Jul 2011, 22:25
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Ozone concentrations as a function of altitude:



^^^^ B and C reflect stratospheric air intruding into the upper troposphere.

AF 447 at FL 350 is 15000 feet below the tropopause boundary. The overshooting top of the Cb near their track is between 52000 and 56000 feet.



^^^ An overshooting top.
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Old 31st Jul 2011, 22:27
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For those struggling with interpreting some of the BEA's FDR traces, the following shows the longitudinal data from prior to AP/ATHR disconnect through to shortly after the aircraft entered the stalling regime.

A few English words have been added, and the AP and ATHR disconnects plus the Stall Warnings are also marked.


Last edited by mm43; 4th Aug 2011 at 21:32. Reason: changed graphic - correct ATHR disconnect time
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Old 31st Jul 2011, 22:35
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Some pages back I had asked abut the effect of thrust from under-slung engines. I was informed that an increase in thrust tended to pitch the aircraft's nose up.
Would I be correct, then, in assuming that reducing thrust to Flight Idle would therefore tend to lower the nose ?
This should help to get the aircraft's wings unstalled sooner. Power could be resumed gently, to reconvert a not too bad glider ( see Sully) to a powered aeroplane again.
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Old 31st Jul 2011, 22:36
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Buying a satnav for your car doesn't justify no longer being able to read a road atlas, just in case, if we are talking analogies.
But I know a youngster or two today that refuse to have a map in the car (for when their satnav gets them lost)

I can only conclude they don't want to show their ignorance to their girlfriends by holding it the wrong way up and takinga left turn when it should be right
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Old 31st Jul 2011, 22:36
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Re T54

With due respect, that seems an unreasonable assessment of the PF.
He was a qualified glider pilot, so he had a practical basis for how the aerodynamics work.
He went from a happy situation where the Captain gives him the responsibility in a dark and stormy passage to a nightmare where the instruments play false, including the stall warnings, while the plane bucks and rolls and plunges, despite his best efforts.
With no visual cues and the stall warning turning off when he went slow, while turning back on when he went faster, his despairing comment that 'I don't understand' is entirely reasonable.
There is lots to improve in the training, which clearly should bear the blame, rather than the PF, who was just one of the victims.

Last edited by etudiant; 31st Jul 2011 at 22:37. Reason: Add a reference to T54 comment
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Old 31st Jul 2011, 23:01
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Cool

Hi,

Level100
So what exactely do you think is of any significance here for the genesis of the accident?
Cheers
I send you a PM .. more easy for understand what I mean (en français of course)

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Old 31st Jul 2011, 23:21
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That initial climb (again), and some other questions

The 3rd Rapport d'etape adds a lot of detail, and clarifies a lot of what was previously just speculation, and it still tells me that the most interesting part of the event was that extraordinary climb from FL350. Not only did it put the aircraft in a hopeless energy state from which a stall was inevitable, but it also tells us a lot about the instrument flying skills of the PF. In fact it is so bizarre that I am still looking for an 'AHAH' moment that reveals just what it was he was trying to do and how he was doing it. I don't buy the argument that because he had previously thought about climbing out of the turbulence, this was now his way of doing it; no one in their right mind would have done it at that rate, nor deliberately pitched to 10 deg nose up at that level. Nor do I believe that these pitch inputs were inadvertent side effects of lateral inputs - at one point he was achieving 1.6g, and even if some of that was due to turbulence (and there isn't much sign that it was really particularly rough in the 20 sec or so before disconnect), there is still a lot to explain away. The stick force needed to do that isn't zero, some one posted the calibration some time back and I think you need around 5kg pull to do that, hardly inadvertent.

So what was he reacting to? I suggested a month ago that when the speed and Mach became invalid the altitude corrections would have been wrong causing a sudden change in indicated altitude, as happened in the Air Caraibes incident. In that case the change was -300ft, not a huge amount but just possibly enough to prompt the PF to want to pull up. the current BEA report's graphs don't show any such jump, though, intriguingly, the table on pages 92/93 shows that at the start at 2:10:05 the altitude (on the left PFD?) was 35 024ft, while 4 seconds later at 2:10:09 it is shown as 34 664ft, so I guess there was a jump. Nothing other than a complete disregard of attitude explains PF's later insistence 'Okay, okay okay je redescends', and similar phrases, when he plainly achieved no such thing. It seems the BEA are wondering whether reappearances of the FD bars might have had an influence, but if they did, this merely shows how the poor fellow seemed unable to 'look through the bars' to see and assess the underlying attitude. There may be good explanations for this behaviour, but I am struggling to find them. On the face of it, the question for Air France is whether this skill level is typical (in which case they have a humongous training problem to resolve) or unique to this co-pilot (in which case checking and evaluation needs attention).

One other puzzle, why (as had been noted) does the AP disconnect occur a few secs before the indicated speed loss?

I note Owen Glyndwr's Cm - alpha curves, which suggest that return to normal flight should have been possible. but is it enough just to correct the pitching moment? Don't you have to pitch down to within a few degrees of the actual flight path angle, which in this case, once the full stall (I also don't like calling it a deep stall because that's different) is developed, would mean pushing the nose down about 45 deg? I can't see them having the insight to do that
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Old 31st Jul 2011, 23:23
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Originally Posted by jcjeant
I send you a PM .. more easy for understand what I mean (en français of course)
Would you be able to give us poor old Anglophones a quick summary? I don't like all this secrecy and dancing around the point...
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Old 31st Jul 2011, 23:34
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Hi Owain,
Very interesting post, but what about engine thrust maintaining high pitch up with barely no airspeed?
Originally Posted by Owain Glyndwr
So to get to the high AoAs we see from the DFDR data, it looks like you have to be holding full back stick as well as having the THS at -13 deg.
I noticed, from the tracks, that the first nose-down attitude recorded during the stall sequence was achieved between 0211:45 and 0212:00.

During the sequence, the PF was maintaining full elevators deflection (-30°) and, in addition, the THS was reaching -13°. He was also maintaining a full left stick order, but the aircraft rotated to the right in high bank. When it started, the airspeed was for the first time recorded under 30 kt (sensed).

Nonetheless, the pitch came down from about 16°NU to 12°ND!
Vertical Speed increased from -10,000 to above -15,000 ft/mn.

The only other parameter changing (beside the right turn) was that N1 was reduced, at the start of this sequence. N1 decreased in 20 seconds from about 105% (CLB) to IDLE (about 55-60%).

PF had "a very high speed" feeling, released SPEED BRAKE, applied CLB again (105°) and 15 seconds later, the aircraft attitude was nose up again without having gathered that much speed (below 100 kt).
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Old 31st Jul 2011, 23:43
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Cool

Hi,

Would you be able to give us poor old Anglophones a quick summary? I don't like all this secrecy and dancing around the point...
Well I have posted before in english .. and it's crystal clear.
Seem's a french man don't understand .. so "par courtoisie" I send him a PM in french
It's not secrecy
I exercise my right to just send a PM to another member
I do not see where there is a problem or some secrets ...
Is there an atmosphere of paranoia on this board ?
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Old 31st Jul 2011, 23:55
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Not a problem - could you provide a link to where you explained your position?

Not paranoia at all, just slightly confused.

[EDIT : Got it :

Originally Posted by jcjeant
Hi,

takata whrote
So .. when read all this .. my feeling is:
The pilots were rated on type ... but nevertheless were not qualified for the situation of AF447 was
They had not knowledge of basic flying skills
They don't know how the Airbus systems work
So we can conclude that:
The formation and training of those pilots is very low
So Air France bear all the responsibility for this accident by not providing adequate training to their pilots or not detecting by exams (simulator) that those pilots were not qualified for fly a Airbus A330
At least and even if this above is not entirely true .. Air France stay bear the responsibility of this accident as the contract between Air France and their passengers was to transport them from A to B and they failed....
Are my feelings good ?

I take it your position remains the same?]
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Old 1st Aug 2011, 00:09
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Bear, continuous left and right controls and pitch up control tells me he was probably not aviating properly. Most of us believe if he had held pitch and power we wouldn't be talking about this now.

The wild pull up to a nonflyable attitude put it in a deep stall, then they had no clue how to recover from a deep stall so spent several minutes with full nose up SS before impact with the Atlantic.

My students in a J3 cub with three hours knew you couldn't get out of a stall by holding the stick back.
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Old 1st Aug 2011, 00:09
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Excuse my intrusion.

As a lifelong dedicated enthusiast (much reading), beside the facts stated, surely one will feel the "fall" (rate of descent, albeit relatively level, in one's belly.)

Was on a 738 in 2007. Felt my guts responding upon descent. Last off and chatted with pilots. Asked about descent and was told it was rapid so as to make up time for the late departure.

Losing altitude at that rate must certainly induce a bodily reaction, which would then inform the brain.

Maybe, under turbulent conditions, one does not pick it up.
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Old 1st Aug 2011, 00:27
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....So IF PF had not "felt very high speed..." and could have left his power off for a bit longer (30 seconds, say ?)... Who knows ...
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Old 1st Aug 2011, 00:32
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Mike X, no you wouldn't. You could be falling at 20,000 fpm and not know it, you only pick up accelerations - and never believe your senses blind - that's what the instruments are for, and attitude was there...

==============

Originally Posted by takata
During the sequence, the PF was maintaining full elevators deflection (-30°) and, in addition, the THS was reaching -13°. He was also maintaining a full left stick order, but the aircraft rotated to the right in high bank. When it started, the airspeed was for the first time recorded under 30 kt (sensed).
Of course, when fully stalled, the roll control via ailerons, and even spoilerons, would be weak at best, and possibly even have some reversal effects. The wallowing in roll and lack of definite corrective lateral stick control, should have been a big signal that he was heavily stalled. A glance at the Attitude, at the Trimwheel and...

..but not even once, was the question asked of PNF, even colloquially, 'Hey! D'ya think we're stalled' - or 'Please check, are there indications that we may be stalled' - and all this despite the Stall Warnings.

As with the Buffalo accident, one does wonder whether recent briefings or reading material were foremost in the pilot's minds - that is, tail icing with the former and false stall warnings with UAS in this case, there is a psychology there perhaps, last meaningful imprint takes precedence.

Originally Posted by takata
Nonetheless, the pitch came down from about 16°NU to 12°ND!
Vertical Speed increased from -10,000 to above -15,000 ft/mn.
The Airbus was displaying some natural stability tendences maybe, whilst rocking in roll, it was from time to time, dipping its nose... nodding. Either that, or this coincided with PF releasing some of that NU, NU stick pressure. Commensurate, an increase in vertical speed would be expected.
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Old 1st Aug 2011, 00:37
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As has been stated so many times before, pitch and power, the basics. Bearfoil's interesting point re waiting to see how the aircraft reacts after auto dropout is worth considering.
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