Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

AF 447 Thread No. 6

Tech Log The very best in practical technical discussion on the web

AF 447 Thread No. 6

Old 30th Aug 2011, 18:20
  #621 (permalink)  
 
Join Date: Oct 2009
Location: berlin
Posts: 152
Likes: 0
Received 0 Likes on 0 Posts
mm43, your nice graphic.... what can be the reason of the escalate pitch- (and AoA-) change, frequency whith up and down within 5 sec ... (in the beginning of stall after 2:11:00.....)is it turbulenz from outside or is it a typical self-induced pitching movement of an A330 with higher AoA?

if one will learn to find a way out of stall..... one need to understand this.... and learn to use it....
grity is offline  
Old 30th Aug 2011, 19:00
  #622 (permalink)  
 
Join Date: Jun 2009
Location: NNW of Antipodes
Age: 81
Posts: 1,330
Received 0 Likes on 0 Posts
Originally posted by grity ...

.... or is it a typical self-induced pitching movement of an A330 with higher AoA?
Hello grity,

They were the test pilots taking an A330 into its first stall, and the period you have referred to is what I have called the 'PRE STALL'. I believe that pitching oscillation occurs as the wing starts to lose lift and the nose drops, then momentarily recovers lift and the nose pitches up. The fact that the elevator and THS were max NU may also have had a bearing on this oscillation.

IMO the pre stall buffet the BEA tried to define is not very clear, but the pitching oscillation in hindsight appears to be the very last clue.
mm43 is offline  
Old 30th Aug 2011, 19:51
  #623 (permalink)  
 
Join Date: Oct 2009
Location: berlin
Posts: 152
Likes: 0
Received 0 Likes on 0 Posts
mm43, ok but
the elevator is not at max NU in the "pre stall" it is just oscillating between -2 and -7 deg, there is also much SS with pull and push, but I am not shure if we can decide if the oscillation is caused by the elevator or by the move of the center of lift back and forth with the losing lift or all together with turbulence ...... it is realy not easy to discriminate cause and effect....
grity is offline  
Old 30th Aug 2011, 20:16
  #624 (permalink)  
 
Join Date: Jul 2009
Location: France - mostly
Age: 84
Posts: 1,682
Likes: 0
Received 0 Likes on 0 Posts
mm43;
Thanks for another great graphic! I'm wondering what you mean by 'pre stall'. At about 2:10:56 the "gee" starts to fall while AoA is increasing through nine degrees. Isn't that an indication of stall?
HazelNuts39 is offline  
Old 30th Aug 2011, 20:50
  #625 (permalink)  
 
Join Date: Jun 2009
Location: NNW of Antipodes
Age: 81
Posts: 1,330
Received 0 Likes on 0 Posts
grity;

Ok. The center of lift is moving, and the the cause of the pitching may be the 0.3g peak to peak shown in the Normal Acceleration trace. I suspect it will be a point of further discussion.

HN39;

Rather difficult to determine exactly what was going on. Your point is a good one, though it also seems with the synchronized oscillation of the pitch attitude and AoA angles that lift hadn't been lost.

What do you believe the Alpha Max was at 02:10:56?

I'm quite happy to change the indications on the graphic if a consensus can be reached.
mm43 is offline  
Old 30th Aug 2011, 21:43
  #626 (permalink)  
 
Join Date: Jul 2002
Location: UK
Posts: 3,093
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by HarryMann
I don't think you should polarise this so much
Harry, I'm not polarising anything - in fact I'm being neutral to a fault. You and others are saying that feedback and/or yokes would definitely have changed the situation, but I'm saying that isn't necessarily the case. I'm not saying it definitely isn't, or that feedback is purely a throwback. I'm saying there's not enough evidence to say that feedback would have made a difference.

Few, if any, are denying that PF was way below par from manual takeover to end of story... with general crew shortcomings becoming apparent.
I'm not even saying that! Everyone has bad days at the office, it's just that a bad day at the office for an airline pilot has an almost unique potential to become a bad day for everyone on their aircraft.

To say that lack of feedback may not have been an issue is not blaming the pilots, and to say that one necessarily implies the other is a strawman argument that is beneath a lot of the more reasonable people on here.

But really, you have to stop this black and white routine
Harry, can't you see that I'm the one trying to keep the shades of grey here by saying that the sidestick/passive feedback combo may not have (not didn't - *may not* have) played a causative role here.

All those 3 things did play some part (notwithstanding similar accidents in the past happening without them - that is a false negative), I believe.
That is your opinion, shared with some others - and as an opinion it is valid. My opinion (that it's a possibility, but equally that it could be a red herring), is also shared by some others and IMO equally valid. I'm not trying to argue here, I'm just trying to make sure that the parameters of debate remain open.

To start slamming a control column about like that (just think of the equivalent), would definitely have woken up the Captain upon entry, even if PNF had still stayed subdued (this accident will no doubt turn into a study case for at least pilot shock & stress behaviour as much as CRM itself).

There is almost no argument that Captain would not have responded to visually seeing a full aft stick in PFs hands - end of.
No doubt he would then have looked straight at the Trimwheel, and PFD
I disagree. See the posts on the Stony Point NWA 727 crash in the other thread. A three man crew *did* misdiagnose a stall as overspeed, *did* move the control column to its full extent, *did* stall the plane and *did* crash and die.

*You* may have picked it up in that situation, but there were and are trained pilots who aren't as good or as knowledgeable as you.
DozyWannabe is offline  
Old 30th Aug 2011, 21:59
  #627 (permalink)  
 
Join Date: Jan 2008
Location: Herts, UK
Posts: 748
Likes: 0
Received 0 Likes on 0 Posts
DW

Right, apologies then...

I wonder if yourself or anyone else could explain this to me:

I think I'm overspeeding, so I'm holding the stick back, I've tried a wedge load of thrust (oddly) and also now reduced it somewhat (more sensibly)

I'm also holding the stick almost fully to one side, then the other to keep the wings level, as they have a habit of rolling around in a rather airy fairy floppy fashion

Why in an overspeed situation, would this be happening, when the norm is a spiral dive (banked one way or the other and increasing) or just laterally diverging (again banked one way) ?
HarryMann is offline  
Old 30th Aug 2011, 22:35
  #628 (permalink)  
 
Join Date: Jul 2002
Location: UK
Posts: 3,093
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by HarryMann
Right, apologies then...
Don't mention it, and likewise, I'm sorry if I gave you the impression that I was being disrespectful at any point.

I think I'm overspeeding, so I'm holding the stick back, I've tried a wedge load of thrust (oddly) and also now reduced it somewhat (more sensibly)

I'm also holding the stick almost fully to one side, then the other to keep the wings level, as they have a habit of rolling around in a rather airy fairy floppy fashion

Why in an overspeed situation, would this be happening, when the norm is a spiral dive (banked one way or the other and increasing) or just laterally diverging (again banked one way) ?
I don't think the PF was ever completely convinced he was overspeeding, as I think he would have argued the toss with the PNF when the latter practically bit the PF's hand off when he reached for the speedbrake lever if he did. I suspect he didn't really know what was going on and was trying to throw out ideas (which is fairly common in a dynamic problem-solving environment). I also suspect that he was suffering encroaching tunnel vision from the outset and heard neither the "Alternate Law" callout from the PNF, nor the stall warning. As such, there's a little nagging suspicion in the back of my head that he was convinced that as long as he had TOGA selected, no amount of back stick could cause him to stall.

Another thing I'm not convinced of is that he was fighting a right-roll tendency that was entirely down to external forces. After the aircraft was stalled, yes the clues were all there, but at the apex of the climb and just prior he was still slamming the stick around. I wonder whether the initial right-roll was induced by an unfortunate combination of a pocket of turbulence at the same time A/P disengaged - and because of the magnitude of the inputs what we are actually seeing prior to the stall is PIO. While I'm not going to join the chorus of those saying that failure to release the raw FDR data is tantamount to wrongdoing, I do hope that with the final report will come some traces that are of a higher resolution in the time axis - especially around the time of A/P disconnect to the apogee. That way it should be possible to determine whether the PF stick inputs were excessive inputs to combat a serious roll issue or whether PIO had a part to play.

Again, remember you're clearly a pilot with some considerable technical and aeronautical knowledge under your belt. This is no slur on them, but a lot of guys on the line do not.
DozyWannabe is offline  
Old 30th Aug 2011, 22:35
  #629 (permalink)  
 
Join Date: Jun 2011
Location: Devonshire
Age: 96
Posts: 297
Likes: 0
Received 0 Likes on 0 Posts
PF may have had very much less hand flying at cruising level than either PNF or the Captain. And on this occasion it would have been sudden, not premeditated - and with a limited panel. (Only the PNF's instrument panel is recorded. it is assumed that the PF's panel would have been the same.)

When I asked how often pilots hand flew an A330, (let alone at cruising level, where some replies suggested that it requires more concentration) the responses were somewhere between "not if I can help it" to " my Company does not allow me to ..." ( Interesting to know the logic.)

All that I have seen of PF's gliding experience was that he had held a gliding licence some years ago. That could be quite irrelevant - or not.

Someone may know just how accurately Simulators reproduce an A330 's performance at cruising level. How easy is it to hand fly when some of your instruments failed, even before you have started ? Is the Simulator stable in rough air, or do you have to struggle to keep the wings level ? How often is this practiced ?

This kind of training was usual using a Link Trainer, fifty or more years ago, even in rather minor airlines.

One of the American trunk carriers in about 1950, was in the middle of a pay dispute with their pilots and nearly ordered their next batch of aircraft to be made without autopilots... "Make them work..." Somebody said. (They had bean counters, too !)
Linktrained is offline  
Old 30th Aug 2011, 22:52
  #630 (permalink)  
 
Join Date: Jun 2009
Location: California
Age: 54
Posts: 203
Likes: 0
Received 0 Likes on 0 Posts
Speedbrakes

Originally Posted by Dozy
I don't think the PF was ever completely convinced he was overspeeding, as I think he would have argued the toss with the PNF when the latter practically bit the PF's hand off when he reached for the speedbrake lever if he did.
Yes PF did take the extreme step of deploying the airbrake. Hence PF actions were consistent with him being convinced of overspeed at that point.

Originally Posted by Report #3, page 94.
2 h 12 min 04
-> 2 h 12 min 07 The airbrakes are controlled and deployed. I have the impression that we have some crazy speed no what do you think?

2 h 12 min 07 29,736 The angle of attack 2 is temporarily valid at 41°.The stall warning is triggered. No above all don’t extend (the) SV : “Stall, stall”

Last edited by xcitation; 30th Aug 2011 at 23:13.
xcitation is offline  
Old 30th Aug 2011, 23:01
  #631 (permalink)  
 
Join Date: Feb 2005
Location: Correr es mi destino por no llevar papel
Posts: 1,420
Received 0 Likes on 0 Posts
Originally Posted by gums
Still want folks to know that the human "body rates" can help for the first second when something unusual happens.
Absolutely! Feelings of acceleration or turning are not to be taken lightly. Without any doubt they have to be crosschecked against instruments to see whether they are in accordance with the aeroplane's maneuvers or they're just illusions.

Originally Posted by CONF iture"
Captain my great Captain, you may as well forget about any mechanical link for the AF447's rudder.
Because you say so? Because Airbus has radically redesigned rudder architecture on 330s since a couple of years ago? Because someone is unable to appreciate the difference between "controlled" and "operated" when discussing the flight controls as in "manually controlled and hydraulically operated"?

Originally Posted by Ian W
It could be said that the only reason that pilots are required is for when the automatics fail.
Of course it could be said but it would be a lie. There's no automatic decision making. There is no automatic take-off. More correct version would be: pilots must be able to manually fly the aeroplane out of any situation automatics put it into.
Originally Posted by Ian W
Several posts here have statements like: "The simulator does not perform like the real aircraft after a stall" or "the simulator cannot behave as the real aircraft does outside the normal flight envelope" and even "the simulator does not fly like the real aircraft in Alternate Law"

So the simulator is being used to train pilots in how to handle emergencies, upsets and LOC, despite actually not behaving like the real aircraft in emergencies, upsets and LOC?

The current approach of only using simulators for training pilots to fly simulators does not seem extremely logical. I am sure that the accountants love it.
What a slippery slope! Simulators don't simulate the areas that we know nothing about because no flight testing was done (or required to be done) in them. They have to very realistically simulate stall behaviour but to check what the transport aeroplane would do if someone stubbornly insisted in pulling into stall would be asking far too much from the test pilots. Statement that simulator doesn't realistically simulate aeroplane's behaviour within normal flight envelope or different control laws is also untrue and that leaves your idea that we train in simulators just to fly simulators completely baseless.

It's not just accountants that love using simulators for training. Pilots, insurers and anyone living under the training zone appreciate it too. Face it: you want to go far, high, fast and with plenty of payload. There's no way in our Newtonian world to make an aeroplane that would do all that and still have the stall behaviour of Cessna 172. People get killed by stalling 172s, anyway.

Originally Posted by Ian W
(...) it is because the human brain has a limited number of cognitive channels and they can only handle ONE input at a time.
That's the best explanation of someone's inability to chew gum and simultaneously tie his laces I've heard in a long time. Attention distribution, proper scanning and avoiding the fixation are basic pilot's survival tools, taught and checked from day one at the controls. If you suck at them, tough luck, you can not be a pilot. What AF447 crew did was the sign of the severe incapacitation, not usual and ordinary human behaviour.

Originally Posted by Ian W
The reason that 'steam gauges with needles' seem to be easier to read is that they are a spatial cognitive load and form patterns that can be recognized without much cognitive effort.
(...)
I should have made it plainer in my wording.
When the verbal cognitive channels are overloaded you can add more to them and all you do is make the effect worse. However, the analogue gauges do not require any verbal cognitive analysis so that channel is unloaded. So you can see a VSI needle move hard down and understand what it means even if the verbal cognitive channel is in overload - numbers changing though won't work as that requires a level of verbal analysis.
Speed and altitude tapes might be digitally driven but their presentation is analogue! There might be a digital readout added but there's no need to read it while performing normal instrument scan. Patterns on modern EFIS can be recognized without much cognitive effort and you might be surprised that Airbus EFIS does include VSI needle.

I have never heard about real life pilot that had problems switching from round dials to tapes (me included). I have came across those who made painless transition from sidestick and tapes to round dials and yoke, so when reading complaints about modern aeroplanes' cockpits, I am left with the distinct what-the-heck-are-they-talking-about feeling.


Originally Posted by Ian W
One of the aspects I expect the BEA Human Factors investigators to look at is the cognitive workload that the ECAM and failure messages put on the pilots.
It is very basic task sharing: one pilots flies, the other takes care of ECAM. It was very similar before ECAM, since we started putting two guys up front. One would fly, the other would execute the checklist. Eastern learnt the hard way what happens when everyone goes troubleshooting and no one is minding the store. So Crossair.

Originally Posted by Ian W
Perhaps every potential emergency scenario should be subject to what is called a 'cognitive walk-through' that actually assesses the cognitive loads and identifies likely overloads.
And then what? Prohibit by decree emergencies that overload the crew? There were thirty two cases of UAS on A330/340 fleet before AF447. Question is what made the AF447 crew overloaded and not other 32.

Originally Posted by Ian W
Older pilots may well have followed a rather older but repeatedly successful dictum - disregarding all the cacophony - aviate (i.e. pitch and power), navigate, then communicate.
New pilots too - not following that old dicta is guaranteed to shorten your operational life even on modern jets with all the electronic bells and whistles. You are very unfairly pitting the ideal pilot of yesterday against the single modern crew which tragically underperformed.
Clandestino is offline  
Old 30th Aug 2011, 23:06
  #632 (permalink)  
 
Join Date: Jan 2005
Location: France
Posts: 2,315
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by Linktrained
Someone may know just how accurately Simulators reproduce an A330 's performance at cruising level. How easy is it to hand fly when some of your instruments failed, even before you have started ? Is the Simulator stable in rough air, or do you have to struggle to keep the wings level ? How often is this practiced ?
That question has been asked before (I've asked it) and so far I've not seen a clear answer. The consensus (from NASA reports etc.) seems to be that even FFS systems just extrapolate from the limits of the flight envelope. To what extent those extrapolations are 'real' is still an open question.

This kind of training was usual using a Link Trainer, fifty or more years ago, even in rather minor airlines.
Let's be honest.... A Link Trainer (and yes, I've "flown" one) did not yet really attempt to fully simulate the flight characteristics of a specific aircraft type, neither would it have been capable of doing so.
ChristiaanJ is offline  
Old 30th Aug 2011, 23:14
  #633 (permalink)  
 
Join Date: Jul 2002
Location: UK
Posts: 3,093
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by xcitation
Yes PF did take the extreme step of deploying the airbrake. Hence PF actions were consistent with him being convinced of overspeed at that point.
Agreed, but he doesn't seem convinced enough to press the point with the PNF when he chews him out for it and shuts down that avenue. The PNF's immediate following action is to defer to the Captain.
DozyWannabe is offline  
Old 30th Aug 2011, 23:29
  #634 (permalink)  
 
Join Date: Jun 2009
Location: California
Age: 54
Posts: 203
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by Ian W
Older pilots may well have followed a rather older but repeatedly successful dictum - disregarding all the cacophony - aviate (i.e. pitch and power), navigate, then communicate.
New pilots too - not following that old dicta is guaranteed to shorten your operational life even on modern jets with all the electronic bells and whistles. You are very unfairly pitting the ideal pilot of yesterday against the single modern crew which tragically underperformed.
PF/PNF did fly pitch and power but it was for the low altitude UAS as they had practiced in the sim, Rio departure, 3 months prior to the incident. The key difference being the high 15 deg pitch at low altitude UAS compared with 5 deg pitch high altitude (now revised 2.5 degree). No high altitude UAS was trained for in the sim. Therefore it would appear they both applied the nearest training they had in the abscence of specific training.
xcitation is offline  
Old 30th Aug 2011, 23:33
  #635 (permalink)  
 
Join Date: Jun 2009
Location: I am where I am and that's all where I am.
Posts: 660
Likes: 0
Received 0 Likes on 0 Posts
Olr Carthusian

Most likely their training did fail them, very badly and fatally. In addition the displays lead to confusion. And data that might have resolved that confusion was either not presented to them at all (AoA) or was presented on a display that was not a part of their usual instrument scan - pure inertially derived speed, attitude, and so forth.

The primary cause of the whole chain of events was PF pulling NU on the stick when he should have very carefully stabilized roll without touching pitch. After that he seems to have become fixated on the concept of the plane going too fast rather than that it was actually stalled. He had no experience in training or real life with the situation into which he was thrust. And communications between crew members never cleared up the situation. Contributions by PNF were ignored. PNF tried to take over. PF grabbed back control and the plane and its freight died.

  1. Communications were inadequate to absent.
  2. Cockpit Resource Management was sloppy.
  3. Data was inadequate.
  4. Training was inadequate.

That set of inadequacies teamed up as a perfect storm of inadequacies to send AF447 and its passengers to the bottom of the ocean.

I say inadequacies rather than other words because on the whole all three factors are sufficient that the vast majority of flights take place uneventfully. And I suspect fixing even one of the problems might have saved AF447. All four should probably be fixed for best results. (Fix 4 and both 1 and 2 should end up repaired in the process. Fixing 3 is a major change to get it right. But they should be able to at least show an icon if a plane in a stall to get the message across through a non-verbal channel as well as the verbal warnings.)
JD-EE is offline  
Old 30th Aug 2011, 23:37
  #636 (permalink)  
 
Join Date: Feb 2001
Location: UK
Posts: 647
Likes: 0
Received 0 Likes on 0 Posts
There have been several references in these threads to the PF’s previous gliding experience, most recently post #625 by Linktrained, and also several suggesting that gliding training would be good for all pilots.

I cannot claim any knowledge of CAT flying, but I do know something about glider flying and gliding training, and also something about gliding accidents and what surviving pilots have said on occasion.

For the record, not all glider pilots take to their training as ideally one should. One pilot I talked to, who crashed following a cable break and spun, luckily surviving, told me he knew the tail had fallen off so that there was nothing he could do. (IMHO, like PF in AF447, he became fixated on a problem he didn’t have, and never diagnosed what he was actually dealing with.) When the nose went down, he “knew” that trying to raise it by pulling back on the stick would not work, because of his “missing tail”, but he tried anyway. When it did not succeed, and he saw the ground spinning round (his words – still did not connect it with a spin), he let go and the glider recovered from the spin itself. Hence his survival, in spite of failing to recognise what he should have been trained to understand.

Good basic training in flying, including stall and spin awareness, is no doubt an ideal that would stand any pilot of fixed wing aircraft in good stead. Unfortunately, there are some pilots who do not learn it well enough. To paraphrase Dozy, I am not saying that this was or was not the case with PF; only that his prior gliding experience (How long ago? How extensive? How good was he?) is not necessarily a useful piece of information.
chrisN is offline  
Old 30th Aug 2011, 23:43
  #637 (permalink)  
 
Join Date: Jun 2009
Location: I am where I am and that's all where I am.
Posts: 660
Likes: 0
Received 0 Likes on 0 Posts
HarryMann said, "No problem, miniature lightweight LED ribbons/tapes are now being used in many applications, the batteries being small enough to be encompassed within the string I should think... go on, give it a go"

Why not get a small little LED flashlight and shine it at the window when you want to see the string. It should reflect back quite nicely. Shine the light mostly upwards at the string to avoid direct flashlight reflections into your eyes.

Now, what kind of chewing gum will you use to affix the front edge of the string to the window? I suspect common transparent tape would not do to well, nor would common duct tape. Umpty degrees below zero is not compatible with most adhesives I know that won't become a permanent part of the window.
JD-EE is offline  
Old 30th Aug 2011, 23:46
  #638 (permalink)  
 
Join Date: Jul 2002
Location: UK
Posts: 3,093
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by HarryMann
No, there are plenty of other reasons for not doing that... one being that the aircraft simply 'could not be put in that situation'
Harry, I don't mean to nag like an old fishwife, but what is your source for that assertion, and if you do have one, how old is it?

Airbus themselves have been perfectly willing to accept the possibility of their FBW aircraft being "stall-capable" in degraded control laws, and have been quite open about it since at least the mid-'90s.
DozyWannabe is offline  
Old 30th Aug 2011, 23:50
  #639 (permalink)  
 
Join Date: Jan 2008
Location: Herts, UK
Posts: 748
Likes: 0
Received 0 Likes on 0 Posts
Let us be clear...

EASA Airbus knows closely what a very high AoA A330 behaves like, did and does... assertions that a decent simulation of beyond the stall behaviour, couldn't be made... Pah!

Wouldn't but not couldn't... lateral and directional might have had to be a bit of a fudge, but plenty of high AoA data exists even there. CFD tunnels as well as work in many different (real) tunnels exists and a pretty reasonable model could have been built well beyond the stall, very accurate longitudinally including simulated buffet and no doubt predicted nodding or other type specific behaviour.

No, there are plenty of other reasons for not doing that... one being that the aircraft simply 'could not be put in that situation'
Another? Airlines wouldn't be interested in it...(read, pay for the extended sim or the time in it)
HarryMann is offline  
Old 31st Aug 2011, 00:04
  #640 (permalink)  
 
Join Date: Jun 2009
Location: I am where I am and that's all where I am.
Posts: 660
Likes: 0
Received 0 Likes on 0 Posts
Be honest, I just did a Google search for an image host after noticing I couldn't just attach a photo file here. Found that one (postimage.org) first and admit, know nothing about them...all my fault and my apologies to any offended.
Just a general note - spammers and malware authors are getting depressingly good at manipulating Google results. So sometimes the first one or even two results can lead to bad sites. Doing a quick check with the Linux "whois" tool shows that postimage.com seems to be the real site. Postimage.org has a hidden registration. That is as often as not an indication of something questionable being hosted at the site. If you play with "http://www.dnsstuff.com/" over time you can develop some intuition about "good" vs "bad" sites.
JD-EE is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.