AF 447 Thread No. 7
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Machinbird
I don't think we'll agree on this and to my mind it's because of a fundamental difference in the way we're looking at things. I am looking at the actions of the PF as those of a being capable of making independent decisions unaffected by external factors. Your approach seems to be more deterministic - the PF is subject to factors which force him to act the way he does. To a large extent he has no control over what he does.
Whilst both views have a measure of validity the (shall we say) free choice view is a far better and more realistic model for explaining things. The interesting paper you mention is problematic in that it reduces the human element to a 'cog in the machine' as it were but this is symptomatic of the whole PIO approach. It is logically flawed as a concept in that it assumes no choice of action. As I have mentioned, as a piece of research it is woolly and far too broad in its spread. Choices exist but how we exercise them depends on our training, professionalism or the culture we follow. But and this is the important thing - we always have the choice. This is the case with AF447 - the pilots had choices but ignored them.
Sorry for the philosophical digression but I felt it was relevant in this case.
I don't think we'll agree on this and to my mind it's because of a fundamental difference in the way we're looking at things. I am looking at the actions of the PF as those of a being capable of making independent decisions unaffected by external factors. Your approach seems to be more deterministic - the PF is subject to factors which force him to act the way he does. To a large extent he has no control over what he does.
Whilst both views have a measure of validity the (shall we say) free choice view is a far better and more realistic model for explaining things. The interesting paper you mention is problematic in that it reduces the human element to a 'cog in the machine' as it were but this is symptomatic of the whole PIO approach. It is logically flawed as a concept in that it assumes no choice of action. As I have mentioned, as a piece of research it is woolly and far too broad in its spread. Choices exist but how we exercise them depends on our training, professionalism or the culture we follow. But and this is the important thing - we always have the choice. This is the case with AF447 - the pilots had choices but ignored them.
Sorry for the philosophical digression but I felt it was relevant in this case.
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Originally Posted by OC
I don't think we'll agree on this and to my mind it's because of a fundamental difference in the way we're looking at things.
I am looking at the actions of the PF as those of a being capable of making independent decisions unaffected by external factors. Your approach seems to be more deterministic - the PF is subject to factors which force him to act the way he does. To a large extent he has no control over what he does.
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Machinbird + ChristiaanJ
The choice is to act or to delay your action. There is a belief that by acting quickly you can deal with the problem (and this is indeed the case in some situations) but more often than not it is better to pause and evaluate. This is frequently the case with DIO. One thinks of the supposed Prius issue which turned out to be driver induced. Drivers panicked and blamed the machine for their actions where taking their foot of the accelerator would have solved the problem.
With aircraft a pause with a light touch works wonders. Of course I agree that sometimes it isn't possible but most of the time it is. In the AF447 example there was ample time for the PF to pause and evaluate. He didn't and so ended up in a stall. But what we do have here is a training and possibly experience issue not an aircraft issue. The aircraft did what the PF told it to do. If the pilot had left things, the aircraft would have most likely stayed in a stable condition within its flight envelope. A properly disciplined and non-panicking pilot would have paused, evaluated and then followed the SOP for UAS. He would have worked in concert with his colleague to find a solution. PIO isn't the issue here (except as a mechanical process) but the pilot's conduct is (I am sorry to say). A look at the Korean Airlines Flight 8509 accident shows how a competent crew dealt with a roll issue due to an aircraft fault (I am referencing the first crew not the second). But in AF447 we cannot escape the issue of crew competence or rather the lack of it.
The choice is to act or to delay your action. There is a belief that by acting quickly you can deal with the problem (and this is indeed the case in some situations) but more often than not it is better to pause and evaluate. This is frequently the case with DIO. One thinks of the supposed Prius issue which turned out to be driver induced. Drivers panicked and blamed the machine for their actions where taking their foot of the accelerator would have solved the problem.
With aircraft a pause with a light touch works wonders. Of course I agree that sometimes it isn't possible but most of the time it is. In the AF447 example there was ample time for the PF to pause and evaluate. He didn't and so ended up in a stall. But what we do have here is a training and possibly experience issue not an aircraft issue. The aircraft did what the PF told it to do. If the pilot had left things, the aircraft would have most likely stayed in a stable condition within its flight envelope. A properly disciplined and non-panicking pilot would have paused, evaluated and then followed the SOP for UAS. He would have worked in concert with his colleague to find a solution. PIO isn't the issue here (except as a mechanical process) but the pilot's conduct is (I am sorry to say). A look at the Korean Airlines Flight 8509 accident shows how a competent crew dealt with a roll issue due to an aircraft fault (I am referencing the first crew not the second). But in AF447 we cannot escape the issue of crew competence or rather the lack of it.
Last edited by Old Carthusian; 21st Dec 2011 at 02:15.
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OC
I'm not entirely rejecting what you have just said, I prefer the firm&positive well considered method of operating flight controls, but I do have a lot of frightening incidents engraved on my eyeballs that are visible when I close my eyes.
Sometimes you have to act NOW, because there is no time to consider. How does one figure out which is which? I think the answer is experience and exposure.
I do not place AF447 in that category, however.
It seems that PF on that aircraft went to full respond mode when he was roused from his relaxed cruise state. The initial control movements are far too large-for what he was up against. Maybe the cavalry charge music had something to do with it?
I'm not entirely rejecting what you have just said, I prefer the firm&positive well considered method of operating flight controls, but I do have a lot of frightening incidents engraved on my eyeballs that are visible when I close my eyes.
Sometimes you have to act NOW, because there is no time to consider. How does one figure out which is which? I think the answer is experience and exposure.
I do not place AF447 in that category, however.
It seems that PF on that aircraft went to full respond mode when he was roused from his relaxed cruise state. The initial control movements are far too large-for what he was up against. Maybe the cavalry charge music had something to do with it?
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PIO:s
The SAAB company took a patent may years ago on a method to prevent PIO (after the 2 JAS 39 Gripen PIO accidents), but normally this seems to be simply done by rate-limiting in the software. I don't know which method is used in the A330:ies.
I have been wondering if any such PIO-preventing function, which ought to be in operation in normal law, is still operational in alt law 2.
PIO can apparently also occur if the hydraulic system is overloaded by extensive control surface movements, especially shortly after a reduction in N1.
Keep up the interesting and good parts of the discussion.
I have been wondering if any such PIO-preventing function, which ought to be in operation in normal law, is still operational in alt law 2.
PIO can apparently also occur if the hydraulic system is overloaded by extensive control surface movements, especially shortly after a reduction in N1.
Keep up the interesting and good parts of the discussion.
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Important information
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OC, I don't wish to belabor this point unduly, but you really do not understand the problem of what PIO is. If we were to completely accept your viewpoint, we would throw the work of several generations of aircraft handling specialists into the dumpster as an unnecessary complication.
The roll oscillation on AF447 which I suspect may have been PIO was a converging oscillation. There are other oscillations that diverge and are nothing to be trifled with.
Take a look at this video clip of the Sageburner accident and tell me how well your strategy of deciding to do nothing would have worked. This video is a pale imitation of the original phototheodolite film. On that film, the photointerpreters could clearly read out actual stabilator position and thus infer stick motions.
F-4 PIO - YouTube
The roll oscillation on AF447 which I suspect may have been PIO was a converging oscillation. There are other oscillations that diverge and are nothing to be trifled with.
Take a look at this video clip of the Sageburner accident and tell me how well your strategy of deciding to do nothing would have worked. This video is a pale imitation of the original phototheodolite film. On that film, the photointerpreters could clearly read out actual stabilator position and thus infer stick motions.
F-4 PIO - YouTube
Last edited by Machinbird; 22nd Dec 2011 at 02:52. Reason: playing with video display issues
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RR_NDB, I think we owe OC a vote of thanks for his reasoned challenge to my points.
Being forced to defend a concept requires both parties to explore their thoughts carefully and to develop them to a greater degree than if there were no challenge.
PIO or APC or whatever you wish to call it is a very interesting topic, and produces many surprises. I am pleased that others find it interesting too.
In the case of AF447, the initial roll oscillation stands out as a very strange thing. It will be interesting to see what BEA makes of it.
Being forced to defend a concept requires both parties to explore their thoughts carefully and to develop them to a greater degree than if there were no challenge.
PIO or APC or whatever you wish to call it is a very interesting topic, and produces many surprises. I am pleased that others find it interesting too.
In the case of AF447, the initial roll oscillation stands out as a very strange thing. It will be interesting to see what BEA makes of it.
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I should have commented earlier. ...
I've read your recent posts with interest. Excellent work.
Thank you for bringing it forward, and thank you for your patience.
I mentioned this opinion before, that that the full set of technical elements involved in the AF447 (and other accidents), will be a reunion of those enumerated, and made public by BEA and those tacitly recognized and addressed by the manufacturer in improvements/enhancements coming with new versions.
Last edited by airtren; 22nd Dec 2011 at 03:22.
We're talking about a heavy, inertia laden aircraft at 265 knots, which is decelerating, with an initial max available roll rate in roll direct of less than 20-25 degrees per second (max rate is available at about 320+ KIAS clean, less on down). Rate-wise even at full SS deflection the thing is a slug.
NOT, as fighters go, an inherently pitch sensitive aircraft doing 900+ mph at 125' AGL with a malfunctioning pitch damper.
A330 IS a 'just let go'.
NOT, as fighters go, an inherently pitch sensitive aircraft doing 900+ mph at 125' AGL with a malfunctioning pitch damper.
A330 IS a 'just let go'.
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Machinbird
It has indeed been a fascinating discussion but I would still question the involvement of PIO in this case. The sageburner accident is indeed interesting but is it relevant? A high speed jet fighter going for a low altitude speed record? You are almost certainly more conversant with the design philosophy of the F4 than me but I would have thought that it was designed to be very responsive to control inputs - more so than a civilian airliner. Maybe for the pilot to have stopped the control inputs would have helped but once again I suspect you would be more knowledgeable on this point. However, PIO seems to be a phenomenon which affects small manoeuverable aircraft more than civil airliners (referencing the database in the Aristotel article). But even so with a small fast manoeuverable machine it is often better to 'let go and hold back'. I fully acknowledge your point that sometimes you have to act quickly but for most cases this would not be my approach.
OK465, I think, hits the nail on the head. The A330 is not a machine designed to be flung around. It is rather an aircraft designed to fly in a stable manner. Leaving the aircraft alone was the correct approach in this case - it would not have remained in its unstable state. A light touch on the controls if it threatened to roll too far but the roll amplitude was not excessive or too radical. PJ2 who commented on the incident in I believe the third thread of this subject advocated this approach and I would bow to his knowledge. I still find myself coming back to the crew behaviour in this accident. The complete lack of CRM cannot be disregarded and this is a more significant factor than any supposed PIO (and we must be honest we have no evidence of PIO in this accident - we have hypothesis but that is all). Remember in your experience in the simulator you were able to overcome PIO by use of your instruments (and I would assume a pause but do correct me if I am wrong). The PF in this case did not pause (a cavalry charge as you say) and does not seem to have had a scan and crucially to have ignored his copilot. This is the crux of the matter - a seeming panic reaction by both the flight crew.
It has indeed been a fascinating discussion but I would still question the involvement of PIO in this case. The sageburner accident is indeed interesting but is it relevant? A high speed jet fighter going for a low altitude speed record? You are almost certainly more conversant with the design philosophy of the F4 than me but I would have thought that it was designed to be very responsive to control inputs - more so than a civilian airliner. Maybe for the pilot to have stopped the control inputs would have helped but once again I suspect you would be more knowledgeable on this point. However, PIO seems to be a phenomenon which affects small manoeuverable aircraft more than civil airliners (referencing the database in the Aristotel article). But even so with a small fast manoeuverable machine it is often better to 'let go and hold back'. I fully acknowledge your point that sometimes you have to act quickly but for most cases this would not be my approach.
OK465, I think, hits the nail on the head. The A330 is not a machine designed to be flung around. It is rather an aircraft designed to fly in a stable manner. Leaving the aircraft alone was the correct approach in this case - it would not have remained in its unstable state. A light touch on the controls if it threatened to roll too far but the roll amplitude was not excessive or too radical. PJ2 who commented on the incident in I believe the third thread of this subject advocated this approach and I would bow to his knowledge. I still find myself coming back to the crew behaviour in this accident. The complete lack of CRM cannot be disregarded and this is a more significant factor than any supposed PIO (and we must be honest we have no evidence of PIO in this accident - we have hypothesis but that is all). Remember in your experience in the simulator you were able to overcome PIO by use of your instruments (and I would assume a pause but do correct me if I am wrong). The PF in this case did not pause (a cavalry charge as you say) and does not seem to have had a scan and crucially to have ignored his copilot. This is the crux of the matter - a seeming panic reaction by both the flight crew.
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Address OC comments
Originally Posted by OK465
We're talking about a heavy, inertia laden aircraft at 265 knots, which is decelerating, with an initial max available roll rate in roll direct of less than 20-25 degrees per second (max rate is available at about 320+ KIAS clean, less on down). Rate-wise even at full SS deflection the thing is a slug.
At altitude, roll damping is lower. Did PF understand he was in roll direct? Did he have appropriate training in flying in a roll direct law? Even sluggish aircraft can be overcontrolled or oscillate, they just do it slower, but they still oscillate.
Whether fighter or transport, 900 knots or 300, these things are aircraft and aircraft oscillate if not properly controlled. For an aircraft the size, mass, and control power of AF447, the roll oscillation it encountered was surprisingly quick, but the roll did not reach significant angles until after the stall. This may have deterred PNF from intervening.
The difference between divergent and convergent PIO is the amount of damping available. If the oscillation is building energy, bad things are going to happen as they did in the Sageburner accident. At some oscillation frequencies, pilots cannot effectively intervene.
OC, we are in full agreement that PF came on too strong when he took control. The problem appears to be that his initial mistake was not easily reversed.
The one surprising thing I learned reading the Sageburner file was that the aircraft was headed for an 8 g peak when the pilot released the stick in an attempt to break the oscillation. The aircraft had been trimmed in the alignment turn, and the additional nose up stabilator motion caused the aircraft to breakup somewhere around 15 g.
FWIW, On my roll PIO experience in the visual simulator, the only pause was the minor delay in visually locking on to the attitude indicator.
Last edited by Machinbird; 22nd Dec 2011 at 04:42.
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OC:
How about this, then? A bigass Boeing:
PIO jet airplane landing - YouTube
...However, PIO seems to be a phenomenon which affects small manoeuverable aircraft more than civil airliners (referencing the database in the Aristotel article).
PIO jet airplane landing - YouTube
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Feedback Systems complexity
Feedback Systems are inherently complex. When you introduce human inputs specially of high amplitude the results can be dangerous.
Anyway when you don' t know for sure all the "inputs" the PF "received" it's risky to conclude.
We are talking of a complex scenario with a crew (PF/PNF) lacking the training for the situation.
I love the KISS approach but for this analysis we must consider everything plausible and PF was reacting to stabilize.
Unfortunately due CRM, "tunnel effect", difficulties due "auto THS", use of SS or just panic then the entire crew failed to timely act properly or even "understand".
I understand MB comments on oscillation as a possible complex factor. OTOH in general i agree with many points OC put.
PS
I tend to respect too much all kind of oscillations or "transients" leading to dangerous situations or crashes, mostly the ones affected by human beings inside the feedback loop introducing extra "inputs".
Remember me the "butterfly region" . I feel "butterflies" in stomach when imagining what can happen.
In general, "laissez faire" is safer, i agree. But in some cases you must act decisively.
Which ones? How to manage in "degrading modes" not perfectly timely understood.
Acting decisively avoided me two serious car crashes. And subsequently i had to stabilize the vehicle. And was very difficult and requiring extremely dangerous maneuvers. Full of adrenaline in the end.
May be applying precise and ABSOLUTELY NECESSARY inputs, proportional to the surprise in the beginning.
When confused, better to wait and see.
This remembers me about people*:
(*) A friend told me about people entering the Army.
Anyway when you don' t know for sure all the "inputs" the PF "received" it's risky to conclude.
We are talking of a complex scenario with a crew (PF/PNF) lacking the training for the situation.
I love the KISS approach but for this analysis we must consider everything plausible and PF was reacting to stabilize.
Unfortunately due CRM, "tunnel effect", difficulties due "auto THS", use of SS or just panic then the entire crew failed to timely act properly or even "understand".
I understand MB comments on oscillation as a possible complex factor. OTOH in general i agree with many points OC put.
PS
I tend to respect too much all kind of oscillations or "transients" leading to dangerous situations or crashes, mostly the ones affected by human beings inside the feedback loop introducing extra "inputs".
Remember me the "butterfly region" . I feel "butterflies" in stomach when imagining what can happen.
In general, "laissez faire" is safer, i agree. But in some cases you must act decisively.
Which ones? How to manage in "degrading modes" not perfectly timely understood.
Acting decisively avoided me two serious car crashes. And subsequently i had to stabilize the vehicle. And was very difficult and requiring extremely dangerous maneuvers. Full of adrenaline in the end.
May be applying precise and ABSOLUTELY NECESSARY inputs, proportional to the surprise in the beginning.
When confused, better to wait and see.
This remembers me about people*:
- Intelligent and active, no problem
- Intelligent and passive, no problem.
- Dumb and passive, no problem.
- Dumb and active, extremely dangerous...
(*) A friend told me about people entering the Army.
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Organfreak
..However, PIO seems to be a phenomenon which affects small manoeuverable aircraft MORE than civil airliners (referencing the database in the Aristotel article).
Machinbird
I do believe the PF understood he was in ALT2 - after all he calls "I have the controls" (which I interpret as an acknowledgment of the switch) but if he didn't that was also an indication of poor flight deck management and serious training deficiencies.
I think we are all in agreement that sometimes you must act and act quickly. Getting that right depends on your experience and training and here I think the latter let the flight crew down. I am afraid the PF's behaviour fits RR NDBs fourth category.
..However, PIO seems to be a phenomenon which affects small manoeuverable aircraft MORE than civil airliners (referencing the database in the Aristotel article).
Machinbird
I do believe the PF understood he was in ALT2 - after all he calls "I have the controls" (which I interpret as an acknowledgment of the switch) but if he didn't that was also an indication of poor flight deck management and serious training deficiencies.
I think we are all in agreement that sometimes you must act and act quickly. Getting that right depends on your experience and training and here I think the latter let the flight crew down. I am afraid the PF's behaviour fits RR NDBs fourth category.
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Approx 16s later the PNF announces "Alternate Law protections" but I've never seen any indications of acknowledgement from the PF, nor whether he really understood what that means about the available protections - which seems to fit with your second point above. However other things like cognitive overload were also well-argued in the past.
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I am afraid the PF's behaviour fits RR NDBs fourth category.
We have the advantage on them of knowing how their efforts turned out.
They were humans like us and did not intend to have their efforts turn out badly. We make mistakes, we have training issues, and poor performance issues. The same weaknesses applied to them. We are only in the early phases of learning what they were up against. Hopefully BEA will be able to put this whole puzzle together.
If we are to be critical, let us be critical of their performance, not their persons.
There is still a lot we do not know.
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