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AF 447 Thread no. 4

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AF 447 Thread no. 4

Old 16th Jun 2011, 20:51
  #61 (permalink)  
 
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Until it is shown that the pilots knew they were in a stall, the limitations of the aircraft to generate the appropriate moments are irrelevant surely ? If they applied the appropriate inputs but the system, or some stability trap, frustrated them well fair enough but the evidence doesn't seem to currently point that way. First thing is to figure out what they knew and if they didn't get the correct appreciation, why not and how can it be avoided in future ?

And what was the late heading change about, can you do that in a stall ?

Last edited by Mr Optimistic; 16th Jun 2011 at 21:01.
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Old 16th Jun 2011, 21:01
  #62 (permalink)  
 
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Bear,

You can read the BEA Update as well as I.

There's no mention of any descent prior to the initial climb, and the THS seems to have been no more than 3degNU until 02:10:51 (at about FL375).

Don't think the rest of your hypothesis merits response, except the last paragraph. As far as that's concerned, I expressed a similar sentiment on May 27th.
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Old 16th Jun 2011, 21:12
  #63 (permalink)  
 
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As opposed to the direct admission of designing and building in a full stall
warning system ? Did they do that just for fun on their day off, being as it
wasn't in-spec ?
Iirc, that's a regulatory requirement, whereas stall recovery solutions are
not

I'm not being flip here and from fwics, whenever there is a known problem,
airbus do all the right things, issue advisories or press for regulatory
involvement. Development is a continuous process and no product is ever perfect.
The concern is, as you suggest, a mismatch between the goals of the manufacturers,
who have a passion, like most engineers, to build the best product, pursuit
of excellence etc and the end users, who are driven more by efficiency and the
need to minimise cost. In such a situation, there must be plenty of scope for
conflicts of interest at various points in the curve, hence the disjoint.

As you say, an interesting question. No doubt taxing the minds of many people
at present...
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Old 16th Jun 2011, 21:19
  #64 (permalink)  
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"There's no mention of any descent prior to the initial climb, and the THS seems to have been no more than 3degNU until 02:10:51 (at about FL375)."

I did not mention one either. I said the a/p had been trimming a descent OUT, With THS NU. And prior to a/p disconnect. At disconnect, if pilot became aware of the descent, and it was increasing, because the THS was no longer tracking it, his NU would make perfect sense. In additon, if robust, and additive to THS (~10degrees), the a/c would begin a breathtaking climb. No mention is made of the THS position of 3 at any particular time. Only that at some point it was the start of NU. During autopilot? After? We don't know

If PF also input right ROLL he may have over input, and began chasing his initial left roll.


..Until it is shown that the pilots knew they were in a stall..
Why would they know? They had two chirps that quit, and then a climb. At the Top of Climb, the STALLSTALL re entered, and quit.

THERE WAS NO FURTHER STALL WARNING.

WHY? BECAUSE SHE DID NOT STALL.

There was AoA of 4 degrees, and low speed. Who said it had to be 60 knots or less?

THERE WAS NO BREAK. Intead she slid down and back, LEAVING THE NOSE TO INCREASE ITS NOSE UP.

There was no nose drop to announce a STALL, merely (sic) a mush that had no end.

What about the PF's continuous stick back on the way down? Was he convinced he could CAUSE the a/c to STALL, and thence recover?

NOSE DOWN by now merely STALLED HS further, increasing the MUSH.

Stability Trap, Mr. O?

Last edited by bearfoil; 16th Jun 2011 at 21:34.
 
Old 16th Jun 2011, 21:32
  #65 (permalink)  
 
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We will soon be at FL100. Where was the desperation ?
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Old 16th Jun 2011, 21:35
  #66 (permalink)  
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The French are not Italian. They may have waited to a lower.
 
Old 16th Jun 2011, 21:36
  #67 (permalink)  
 
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Tail chute:
Probably a very bad idea. Aside from the complexity of certifying such a thing
(presumably a different design/size would be needed for each aircraft type),
the risk of inadvertent deployment causing it's own disaster would seem much
more likely than the incredibly rare situation where it might be of positive benefit.
It's way beyond my knowledge level, but it might be possible to find a solution
that just provided enough tail lift, while not presenting a danger in normal flight,
perhaps a release after use switch or time delay. The inadvertent deployment
issue could be solved via a two key, two man input with an on time requirement
of several seconds. Probably never happen though, but seems to me that something
needs to be done.

As far as I can tell from what we know to date, the crew were not aware they
were in a stall (you'd have assumed someone would have used the words "we're
in a stall" and that the BEA would have reported such in the note) and as such
it seems unlikely they would have "punched the button" to deploy such a thing.
I don't think they did. The pf saw the alt unwinding towards zero, didn't
believe the air speed and kept pulling up to get out of what he thought was a
dive. The fact that UAS is a known problem coupled with the fact that the pf
didn't believe that the a/c could stall, all his training telling him this,
made him disbelieve what were probably quite accurate asi readings.

The question is: How does engineering solve this problem ?...
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Old 16th Jun 2011, 21:36
  #68 (permalink)  
 
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Not A Stall????

There was no nose drop to announce a STALL, merely (sic) a mush that had no end.
Bear, is that "mush" not a stall?
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Old 16th Jun 2011, 21:45
  #69 (permalink)  
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Until it is shown that the pilots knew they were in a stall. Mr.O

Bear, is that "mush" not a stall? ...
Of course, an unannounced one. What does she do at 60 knots and 48 AoA?

How do the pilots know? BEA report one STALLSTALL, then PF NU, and no STALLSTALL? They were not properly introduced I'm saying. By now, without a NOSE DROP, THS has no authority, it is Stalled further if ND is input, and if effective, the Nose goes UP, NOT DOWN.

Was the stubborn NU on the way down an attempt to get her to BREAK?

Or was he getting most of his "Nose Down" from pulling back? IOW, full back dropped the nose (it would), and pushing caused the Nose to rise. (also true). The Horizontal Stabilizer in this extreme aspect would behave like a spoileron, or spoilerator, getting authority from drag only, not aero.


wadda ya think

Last edited by bearfoil; 16th Jun 2011 at 22:07.
 
Old 16th Jun 2011, 21:54
  #70 (permalink)  
 
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But didn't the speeds become valid again, implying the nose came down as commanded ? Then renewed stall warning and maybe an instictive undoing of the last input as it 'caused' the warning ? I know the US commuter aircraft accident had the pilot pulling back but he could have been confused with a super stall, a known possibility in that case. In anything but an experimental regime, would anyone pull back when in a known stall ?
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Old 16th Jun 2011, 22:00
  #71 (permalink)  
 
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Bearfoil;
From BEA update ...
The airplane began to roll to the right and the PF made a left nose-up input. The stall warning sounded twice in a row.
That statement appears to be quite straight forward, and gives a clear impression that at the time of the AP/ATHR disconnect the aircraft was in level flight at FL350. The status of the airspeed data is then described, and absolutely no mention (other than the UAS reference) of other untoward environmental conditions is made. Likewise, if the THS actuator was proceeding on direction of the PRIMs to apply another +10 to the CRZ +3 trim, don't you think they would have mentioned it?

Don't you think it would be overly disingenuous of the BEA then to leave out of their update those obvious factors that you so keenly believe they have?

Of course my naive assumptions may be proved wrong, but until they are, I will continue to believe in the integrity of the investigation.
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Old 16th Jun 2011, 22:01
  #72 (permalink)  
 
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Drogue Chutes

Many aircraft, B-47, B-52, and F-4 come to mind, had no extensive problems with uncommanded deployment but they had specific reasons for having them installed. For the F-4, with the introduction of fatter tires than required for carrier ops, the reason diminished, but the chute was still there and I was glad to have it on a wet, mid-length runway one night.

Tactical aircraft, where their normal employment requires flight near the boundaries of control effectiveness, are fitted with spin-chutes for tests near those boundaries, but there is no justification for that kind of testing in transport category aircraft.

Spin-chutes didn't always work as desired. A colleague of mine took an F-4 out for stall investigations and got into a spin. He deployed the spin chute but it came off completely and did no good. They had to punch out.

As someone here, or in another thread, pointed out, you don't fly transport aircraft near the edges of the maneuverability envelope. Teaching the pilots how to recognize how far the airplane can be flown before they get into some kind of controlability problem should be enough. This seems to be an area that may not have been given enough emphasis in training, given the circumstances of AF447.
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Old 16th Jun 2011, 22:18
  #73 (permalink)  
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mm43

No. it doesn't. The opposite is true.

Bearfoil;
From BEA update ...
The airplane began to roll to the right and the PF made a left nose-up input. The stall warning sounded twice in a row.
That statement appears to be quite straight forward, and gives a clear impression that at the time of the AP/ATHR disconnect the aircraft was in level flight at FL350.
It tells me that the a/c was descending, and rolling off to the right. The PF tells me that, BEA needn't repeat it. If the a/c was not in s/l, but was being kept trimmed by an a/p that released the controls, this means that the PF couldn't just "sit there", he needed to continue to trim. My assumption would be that if continuous, this turbulence may have ended up being "too much" for the a/p parameters, and its loss might be due to inability to maintain trim. This inability, whether from uas and commanded, or turbulence and self commanded might just be the wheels coming off re: UPSET.
 
Old 16th Jun 2011, 22:31
  #74 (permalink)  
 
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Bear;

Strange that that propensity to develop the starboard roll was evident all the way to the deck. Was it not fuel imbalance that the A/P was keeping trimmed, or do you think that it had another aerodynamic cause? Rudder, elevator trim or something else?
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Old 16th Jun 2011, 22:41
  #75 (permalink)  
 
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Chris Scott, 54
No, you are right. In case you haven't seen it before, here is my opinion:

LH A320 Rough Landing @ Hamburg
Have limited flying experience, but remember the words of the instructor:
"Be gentle with the aircraft, small inputs have a big effect". Or a little
more crudely: Make love to the aircraft, don't rape it. Strange, but you
get the best out of a well sorted and tuned car using the same technique.

Easy to say sitting at home in an armchair, but who can say what the
reaction would be on a cold dark night, with no visual cues and lost faith
in the machine's integrity...
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Old 16th Jun 2011, 22:53
  #76 (permalink)  
 
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Sometimes I wonder if we're all reading the same report...

Originally Posted by bearfoil View Post
Ten degrees nose UP? That tells us nothing about the AoA, or the position of the THS. Was it already at 13.2? Did pilot cease his initial NU and begin his repeated ND inputs? The 7000fpm suggests the climb was (initially) very rapid, and there is no reason to think the THS was not "UP" having corrected for a chronic descent?
I doubt THS could get to 13 nose up in normal law without triggering protections. Unless AoA was busted (as at Perpignan) - but there is no indication given of that.

Even if it did, how didi it then get back down to 3deg (during climb and nose-up inputs) in order to rise from 3 to 13deg later in the time line ?

BEA clearly state pitch increased progressively at start of climb, 7000fpm was the rate reached at the end of the first climb, at the point PF started nose-down inputs.

Turbulence? There is nothing in this sequence (sic) to base a conclusion of PF
chronic NU. BEA say ".......A INPUT....."
and indeed they don't specify a duration, however the next mention of inputs is nose down after the (first) climb.

During that first climb PF gets stall warning. At 37500ft he gets stall warning again and "maintains" NU input in response. If the response to the SW is consistent, then the conclusion is chronic PF NU.

If the descent was transient, and chronic, why shouldn't the THS react with 13 degrees nose up?
What descent ? You either mean transient or chronic, or, with respect, you don't know what you mean. It can't be both. If it was transient, there would be insufficient time for THS to move, if it was chronic (and significant rate), there would be a noticeable altitude loss before a/p drops out.

Why did the Pilots not MAN TRIM ND? First of all, they were trained not to, and secondly, How were they to know the THS was at 13.2 degrees NU or at the limit.
So they were trained not only not to touch the trim wheel, but also that if they concentrated hard enough, it would actually disappear ?

To me, some of the scariest comments on these threads have been on training practices. Was PFs only training for stall warning "pull up" (to minimize alt loss) ? That is all it would take.
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Old 16th Jun 2011, 23:11
  #77 (permalink)  
 
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Originally Posted by MurphyWasRight View Post
The point though is that like the UAS the O ring erosion was a known issue that was swept under the rug with "nothing bad has happened" etc.
I wouldn't call a worldwide Service Bulletin mandating the replacement of all Thales AA pitot tubes on Airbus A330/340 aircraft a case of sweeping the issue under the rug, would you?

As far as the Space Shuttle Challenger incident goes, the reason the Thiokol managers overrode their engineers (under intense pressure from NASA, don't forget) was because they were competing for the renewal of their contract to supply the SRB assemblies, and they feared that exposing a weakness in their product to the customer during the competitive phase would work against them. A similar thing happened with the DC-10 cargo door debacle - Convair (the supplier of the fuselage assemblies, including the cargo doors) knew of the problems and had encountered them in testing, but upper management at Convair downplayed the risk to McDonnell-Douglas, fearing that their supply contract might be endangered.

In this case, Airbus, Air France and Thales all have some stake in them owned by the French State, so it's unlikely that such contractual shenanigans would be a problem. The one time that politics may have been played (Habsheim), it backfired on all parties in a bad way.

Despite the Challenger disaster, Morton Thiokol retained their supply contract to build STS SRB units, presumably in part because when one makes such a major mistake in public, efforts to avoid any such thing happening again will be redoubled. I'd be very surprised if the same isn't true of the BEA (as I said earlier, note their bringing in of the NTSB as an independent observer in the Air Inter accident). The Airbus FBW technology is proven and flies people around the world safely every day - there's nothing to hide anymore.
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Old 16th Jun 2011, 23:32
  #78 (permalink)  
 
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The question is: How does engineering solve this problem ?...
Build BETTER training devices that provide extended flight and upset envelope training. I have posted several time about the RAeS ICATEE working group. Real aerodynamicists can model beyond flight data realistically (plus support such s/w models with wind-tunnel data). Please take a look RAeS Flight Simulation Group - Introduction to the ICATEE This group has been studying this issue for 2 years and can make a significant contribution to all extended envelope training situations.
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Old 16th Jun 2011, 23:37
  #79 (permalink)  
 
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Originally Posted by infrequentflyer789 View Post
To me, some of the scariest comments on these threads have been on training practices. Was PFs only training for stall warning "pull up" (to minimize alt loss) ? That is all it would take.
The training practices may need some new scenarii but none of the past Pitot incidents (with the same pattern) analyzed in the BEA interim report n2 showed such a crew reaction (maintained NU inputs), some of them did not identify the "unreliable IAS" situation, some of them chose not to react to the stall alarms, some of them put their A/C in descent, etc... the persistent NU inputs of the PF are one thing, but there are two pilots (and 3 a bit later) in the cockpit: the PNF did not stop this critical high altitude sequence (pitch & AoA skyrocket)(the BEA says he has been trying several times to get the CPT back to the cockpit), and the CPT did not recover it (even if there was ND inputs which reduced the AoA).
The recent BEA note is so coarse, there are huge gaps in the chronology, we have been given a limited set of new facts, and it raises so many questions. Hopefully in one month, the BEA will have fully released its findings, and we will have all the time plots of all the flight parameters (and automation states), crew inputs, a more detailed review of the CVR content, of the procedures implemented (or not), maybe a numerical simulation of the stall,... many new facts, and maybe unanswered questions. Note that AF and Airbus have not been waiting for the BEA findings to alter the stall procedure or prohibit the emergency maneuver (memory items CLB/5) in cruise phase.

Last edited by Hyperveloce; 16th Jun 2011 at 23:49.
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Old 16th Jun 2011, 23:41
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what was the THS' deflection at a/p drop? BEA don't say. A/P will hang in until 13 degrees Pitch UP before it quits.
According to BEA, the THS passed from 3 to 13 degrees nose-up in about 1 minute at 2:10:51, 46 seconds after a/p disconnect. Even applying the least plausible interpretation to the report, that it was already arriving at 13 deg at 2:10:51, THS would just have started moving when the a/p disengaged.

When there are such large holes in what we know at this point, I don't really understand why it is necessary to make up stuff that even contradicts the few facts we do have?
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