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AF 447 Thread No. 7

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AF 447 Thread No. 7

Old 23rd Nov 2011, 13:31
  #461 (permalink)  
 
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Some of us have arrived at a conclusion, some of us have not.

That about sums it up.

"Dead men tell no tales"

I get the feeling that some of you would defend Jack the Ripper if he happened to use your favorite brand of butcher knife.

If the airplane consistently does what it is commanded to do, how do you explain "auto trim"? When does the pilot command trim?

Why does it wander around the selected speed? (for you Boeing , Embraer, Canadair, Douglas drivers - the bus will vary by ten or more knots below 10Kft when fully automated. It trims for flight path, not for speed)

For the open minded readers, I don't condem these actions as defective or bad; they just are what they are. Contrary to the spin (partisan positioning) you read here, the Airbus takes what you input, processes your input through its brain and outputs whatever it decides appropriate. The aircraft responds to the SS one way in normal law, and another in abnormal, and another in direct. Imagine, if you will, the steering wheel on your automobile randomly varying tire steering angle for a given steering wheel angle. Fun, huh?
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Old 23rd Nov 2011, 15:26
  #462 (permalink)  
 
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OK, I dont know how for certain, but post 456 suddenly became 457. I think DWs was inserted above. If not his, another was.

I suspect it is to do with our different computers (and maybe time zones) having different real times of posting, and the PPRuNe server sorts them into an order it recognises.

But what do I know?

Chris N.
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Old 23rd Nov 2011, 15:33
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Machinbird
Your post touches the issue of CRM as well as training very nicely. A proper division of responsibilities and teamwork come into play. These don't seem to have been present in this cockpit at all. The PF acted in a way that suggests he had no idea of what was happening and the PNF failed to take any action to correct this situation or to redefine the approach to the problem beyond saying "go down". At first the situation wasn't one where an intensive response was needed - sitting there, following the procedures would probably have solved it with AS returning after maybe a couple of minutes. Several threads back PJ2 suggested this very approach.
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Old 23rd Nov 2011, 16:01
  #464 (permalink)  
 
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From grity, PF input NURL at 2:10:08. The stick started at neutral. The a/c did not. It was NDRR. Did PF not re-index his stick to neutral? Did he carry on with NU 1/3 back as his neutral? It looks like it, the PITCH (stick) stays reasonably consistent whilst the roll was active.

Was he trying to maintain PITCH with a 1/3 back bias? That would explain the climb with no ND to arrest it. Did he climb, thinking he was 'maintaining'?
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Old 23rd Nov 2011, 17:00
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Cool

Hi,

DW
Quote:
Originally Posted by TTex600
If the airplane consistently does what it is commanded to do, how do you explain "auto trim"? When does the pilot command trim


To offload pressure on the primary flight surfaces, exactly the same as autotrim does. Autotrim is a way of solving the problem of not having the surfaces transmit the pressure through the primary flight controls - nothing more, nothing less.
"When does the pilot command trim ?"
You don't answer the question .. you just explain what is trim
With autotrim the pilot not command directly the trim
The position of the trim is a result of a combination of the elevators position and other factors
He have no power over the trim movements unless he switch to manual trim
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Old 23rd Nov 2011, 17:41
  #466 (permalink)  
 
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Originally Posted by OC
But the fact remains that there was a procedure availaible and a checklist to follow at the time. Maybe not clear but it did exist. It wasn't used and there seems to have been no attempt to troubleshoot the issue professionally. This is cultural as well as a gap in training.
My one reservation regarding the above is that knowing procedures and having checklists is not sufficient to do the job in some situations, e.g. the "night carrier landing equivalent type situation" or other similar hands on intensive task. Only recent training buildup is sufficient to allow these tasks to be accomplished..

In this case, the crew probably knew their (current) UAS procedure, but they never got that far. They were likely hung up by the PF's problems in roll over-control.

For those currently flying the 'Bus, would you action the ECAM procedures while the PF is still having difficulty with the actual flying part of his duties?

Last edited by Machinbird; 23rd Nov 2011 at 14:30. Reason: clarification
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Old 23rd Nov 2011, 18:01
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Establishing PITCH is an immediate concern, it cannot wait for ECAM, or conference with PNF.

TT. Do you get my question? Neither Pilot appeared to understand how in the weeds they actually were, from the very git. I believe the PF actually thought he had a reasonable NOSE, not one that was increasing its AoA. His lack of awareness not only seemed blase, it didn't get an instant "Hey!" from PM. Without attitude display, PF was blissfully thinking he had only the ROLL to mitigate? imo.

Again, at the outset, the a/c attitude was quite different from stick position.

Is this an awareness issue on the BUS?
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Old 23rd Nov 2011, 19:55
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Machinbird, If one goes "by the book", the PF orders "ECAM Actions" or "Stop ECAM Actions" as necessary. In other words, the PF should be in command of the situation. I would not expect the PM to proceed with ECAM actions outside of my command. At the very least, the PM should query the PF for guidance before beginning ECAM actions.

In reality, I suspect that some PM's might begin the actions if they perceive the PF to be overloaded and they believe the ECAM actions beneficial to resolving the issue. If I believed the PF, in my case that would be the First Officer, to be in difficulty flying the airplane, I would take over. I believe that my First Officers would likely do the same if they believed I was having the same difficulties. They would likely wait slightly longer before taking over from the Captain, but they would take over.

Last edited by TTex600; 23rd Nov 2011 at 20:06.
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Old 23rd Nov 2011, 20:06
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Lyman, I get what you are saying, No I don't think this is an issue in the Bus. At least not any more so than any other EFIS/"tape for speed and altitude" aircraft. The initial upset could have happened in any airplane that uses computer generated flight instruments. If I remember correctly ( I don't live and breath this accident and don't have the time to look back at the BEA rpts), the A/P gave up and gave the airplane back to the pilots while the aircraft was still stable. I have followed your thoughts and don't have any idea if you are correct. Hopefully we will learn all the facts when the final reports are issued.
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Old 23rd Nov 2011, 20:24
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Dozy. You misunderstand. PF never allowed the Stick to visit its neutral point after taking control. It was aft the entire time of grity's pictorial. My assumption is that he 'established a neutral point', in his mind only, and hence disregarded the aft stick he consistently input.

See how the PITCH trace stays aft of neutral? PF may have been 1/3 of the way back at odds with the stick. (Actually at odds with the attitiude,).

NR. I can't imagine that he had an attitude display. How could he have, and keep asking for more NU?
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Old 23rd Nov 2011, 20:32
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Originally Posted by Neptunus Rex
My post in reply to #465 has goe into 459!!! So here goes again;
Please note that posts can be deleted, in which case, I believe the post count and posts numbers past the deleted one(s) get updated.
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Old 23rd Nov 2011, 21:17
  #472 (permalink)  
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Post number is not critical and can alter but post order should be appropriate to DTG. Clearly something is not working quite right at the moment.

I've passed the information back up the totem pole so we can presume that the computer folk will have a looksee at the problem for us over the next few days.

(Following on from my previous post, this one is now logged with the correct DTG and is posted in the correct order - definitely quaint).
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Old 23rd Nov 2011, 21:48
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From the 'Las Vegas Slot Machine Technique & Aviation & Other Technology' weekly for today:

Time Travel research & testing at a well known Nevada military site have been temporarily suspended due to unanticipated effects on the world's most renown aviation forum, PPRuNe. Expect updates on the 10 o'clock news, if it actually comes on at 10 o'clock.
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Old 23rd Nov 2011, 22:21
  #474 (permalink)  
 
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Originally Posted by Lyman
NR. I can't imagine that he had an attitude display. How could he have, and keep asking for more NU?
What did PNF have when he referred repeatedly to "go back down" and "According to the three youre going up so go back down" ? From the phrasing (and maybe need to go back to the original French) would it be attitude, vs or something other ?

BEA state "Reading the three instruments (the two PFDs and the ISIS), the PNF noticed that the airplane was climbing and asked the PF several times to descend." - how the heck they know which instruments PNF was reading I'm not sure, but maybe the assumption is that there was no other possible source to infer "climbing". If so, then logical conclusion is that no source for that information was unavailable...


And yet, like you, I've always wondered if attitude info was in some way lost. Post after post on here has said no way would you pull the nose over 10deg up in cruise, so it seems the only way to explain PF actions... but then not PNF comments. The HF report is going to be very interesting I think - there is much in that domain that just seems to make no sense.
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Old 24th Nov 2011, 00:25
  #475 (permalink)  
 
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infrequent flyer 789.

The a/c was NOSE DOWN at handoff. It was also climbing at 1000fpm. So, yeah, VS. Robust UPDRAFT. I don't pretend to know what each pilot saw, but it seems that one was using ATT the other VS. At least at first. Then, perhaps each one, feeling 'burned' by one or the other of the instrument readings, switched horses.

Never the twain to meet. Frankly, in the longer term, the PNF had the better guess. It is clear from the absolute gitgo that the pilots were not flying the aircraft as most experts on this thread would have. But they were not up to the standard evident here, alas.

The ship was climbing 1000fpm. What does that say about the Zipper? With the turbulence ("fortes"), I still am not convinced ICE was the culprit re: speeds.
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Old 24th Nov 2011, 02:37
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Cool

Hi,

The ship was climbing 1000fpm. What does that say about the Zipper? With the turbulence ("fortes"), I still am not convinced ICE was the culprit re: speeds.
You can maybe never know .. as it's no alarm for pitot tube problems (like clogged by ice or other substance) on the A330
So it can be a real pitot tube problem or " turbulence ("fortes") "
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Old 24th Nov 2011, 03:30
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I suspect the probable outcome will be described as "super-cooled" icing.

It appears from an article in news.com.au published a few hours ago that the lowest temperature that pure H2O will remain as a liquid has been extended from -41/-42C to -48C.

This would cover the AF447 situation where the nominal OAT was -43C and an updraft containing super-cooled droplets could have created an "ice-block" on the pitots and possibly other surfaces within a second.

The initial pitch down and roll to right at A/P disconnect may have had as its origins, the same cause.
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Old 24th Nov 2011, 04:51
  #478 (permalink)  
 
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Originally Posted by TTex600
The aircraft responds to the SS one way in normal law, and another in abnormal, and another in direct. Imagine, if you will, the steering wheel on your automobile randomly varying tire steering angle for a given steering wheel angle. Fun, huh?
[Car analogies - the staple diet of internet discussion boards, how did we manage so long without one ?]

Not so much random as predicatable change in feel. Not disimilar to power-steering failure... which happens. Most of us will never see it and never (these days) drive without power steering or remember what it was like.

However, in this case there was no change in control law in pitch axis - which was where it all went wrong - but a change in roll law may have pre-occupied the pilot and lead to failure to manage pitch. More like failing to steer the car right while worrying about accelerator or brake failure. Those do happen, and probably more often than steering fail. Many modern cars can go into a "limp home" mode for all sorts of failures (MAF sensor, DPF...) which is exactly the same principle as the degraded control laws. Fun ? Probably not, but not considered dangerous enough that drivers are given any training (or sometimes any information) in advance of it.

In the aircraft case, at least there is the sim to train and prepare for it. Except someone apparently decided it wasn't necessary to train the AF crew...


While we're on cars, it maybe worth comparing this case with the Prius accelerator issue. Initially blamed on the design/manufacture (type) and the computer control (fbw) going wrong. Turns out that in the end it's down to an age-old human-factors issue of not figuring out that something on the floor is stuck under the pedal. Yes, an element of bad design - floor-mat - but mostly HF issue that's happened before on other types. Just that the new computer control (and maybe the foreign mfr.) is a convenient initial scapegoat - one that some will still believe in even after all the investigation and reports are done and point a different way.

Also contributing is automation dependency - changes to reduce driver workload. Where a whole nation of drivers can't co-ordinate more than one foot, or take a hand off the wheel to change gear (because it's got a phone in it) - resulting in the removal of the mechanically connected clutch & pedal. Which, on those rare occaisions where your car decides to accelerate away uncommanded, is actually a really really important safety backup. [feel free to draw different conclusions on the a/c equivalent for that one].
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Old 24th Nov 2011, 08:44
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Lyman,

Look on page 42 (IR#3, en). At 02:10:05 the vertical speed was zero, the next 5 seconds it was descending 400 fpm max, and at 02:10:10 the V/S became positive, i.e. it started to climb.

Moderators: This was posted around 19:00 GMT, in reply to Lyman's #483, posted 24 Nov 2011, 18:42 GMT.

Last edited by HazelNuts39; 24th Nov 2011 at 18:47. Reason: Message to moderators
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Old 24th Nov 2011, 10:41
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Originally Posted by Organfreak
Yi-yi-yi-yikes!!!
It certainly appears that the mayonnaise is well-blended.
The important thing to note is that in the videos the stick is quickly "blipped" in a given direction and allowed to return to neutral. What we see in the AF447 traces are inputs that are large, sustained and held for noticably longer.
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