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AF447 Thread No. 3

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AF447 Thread No. 3

Old 10th Jun 2011, 03:26
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PJ2
By "do nothing", I didn't mean literally sit there, hands-off doing nothing
PJ2, Thanks for the clarification.

If they had been in Alt1 law, I would expect the aircraft to pretty much hold the attitude that it was in when the Autopilot dropped out. Control feel would then have been virtually the same as Normal Law. The PF could probably have almost taken a hands off approach to the situation without getting in too much trouble too quickly.

Since he was in Alt2 law, he had to fly the lateral channel and try to stay off the pitch channel unless a correction was necessary. This did not happen it seems.

Since the turnover briefing specifically included the discussion about the aircraft not being ready to climb higher, there are approximately two reasons the aircraft would be put in a climb.
  1. PF airspeed indication approaching Mmo or
  2. It was inadvertent.
The bulk of the PF's turn at the stick apparently involved nose up inputs by him, even after the the stall.

Conclusion: The climb was inadvertent.

What would cause an inadvertent climb?

If you rule out a malfunction of the pitch channel of the flight control system causing an inadvertent climb, (we will get back to this later.), then what appears to be left is a very serious lateral control problems taking the full attention of the PF.

The BEA note seems to indicate that the PF was making frequent large control inputs.

Large control inputs (high gain activity for the control theorists) are contrary to this Pilots training. Something scared the Bejesus out of him to get this type of behavior.
The only thing that makes sense is that he encountered lateral PIO (And PIO is definitely an aircraft problem). Another name for PIO is pilot in the loop oscillation.

Can we rule out a pitch channel malfunction? Probably not with the data we presently have. We will have to wait for BEA confirmation of more details.

Just my take on the situation. There are enough holes in this concept to drive a truck through right now. More information is needed.
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Old 10th Jun 2011, 03:59
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Is this comment up to date?

PJ2 ... where minimal loss of altitude has been not only stressed but is an actual IFR-ride failure if more than nnn feet are lost in the recovery!! .....
Is this statement up to date?

FAA SAFO 10012 July 6, 2010, says:
Purpose: To clarify the meaning of the approaches to stall evaluation criteria as it relates to "minimal loss of altitude" in the Airline Transport Pilot PTS. ......
.... Operators and Training Centers are encouraged to ensure that their training program and checking modules are written and administered to ensure the evaluation criteria for a recovery from a stall or approach to stall does not mandate a predetermined value for altitude loss. ......
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Old 10th Jun 2011, 04:57
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10 degrees Nose Down ?

I am concerned that the BEA makes absolutely no mention of the pitch during the 100 seconds or so following time 2:12:02 when things were getting in the right direction. If I read between the lines ... 10 deg ND is a possible figure.
Were they trapped ...
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Old 10th Jun 2011, 05:30
  #1724 (permalink)  
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PickyPerkins;
Is this comment up to date?
PJ2 ... where minimal loss of altitude has been not only stressed but is an actual IFR-ride failure if more than nnn feet are lost in the recovery!! .....
Is this statement up to date?
I can't say one way or another. It was the standard when I did any stall work for the initial ride when getting checked out on a new type. I recall that minimal altitude loss was required in the approach to stall and recovery. We never entered the stall. I am aware of SAFOs. Whether the SAFO has made it into training regimes and FAA standards is not known. I don't mean anything by that except we don't know if what the SAFO says has actually been incorporated into current stall training, standards and checking regimes.

Edit: I believe that the current Canadian Air Regulations, Section VII, Commercial Air Services, (equivalent to Pt 121 of the FARS I believe) and associated Standards for checking and training as well as related to the Pilot Proficiency Check ride, at this link, state in part, the following (my bolding):

Ex. 8 - Stall (Ex. 8 - Stall - Transport Canada)

Objectives

To teach:

recognition of the symptoms of an approaching stall
recognition of power-off stalls in both the landing and cruise configurations
positive and smooth recovery, while maintaining directional control, with a minimum loss of altitude

Date Modified: 2010-09-28
Commercial Pilot Flight Test Items - Ex. 12 Stall (Flight Test Items - Ex. 12 Stall - Transport Canada)

Please note: Sections that are highlighted in Yellow indicate new topic areas or important changes in criteria or policy.
Aim

To determine that the candidate can recognize the indications of the approach to a stall, enter a full stall and accomplish an effective recovery, without excessive loss of altitude.

Description

The candidate will be asked to perform one stall manoeuvre such as an approach to landing stall, cross-control stall, overshoot stall or a climbing or descending turn stall. The examiner will specify the aeroplane configuration for the stall scenario. Intentional stalls will be entered at an operationally safe altitude that allows recovery at or above 2,000 feet AGL, or the minimum height recommended by the manufacturer, whichever is higher.

Performance Criteria

Assessment will be based on the candidate’s ability to:

complete appropriate safety precautions before entering a stall;

establish the configuration and power as specified by the examiner;

transition smoothly to a flight condition that will induce a stall;

recognize the onset of the stall by identifying the first aerodynamic buffeting or decay of control effectiveness;

stall the aeroplane;

maintain directional control;

promptly and effectively recover using control applications in the correct sequence;

avoid a secondary stall and excessive altitude loss;

if applicable, retract flaps as recommended by the manufacturer and retract landing gear after a positive rate of climb is established; and

return to the altitude, heading and airspeed specified by the examiner

Date Modified: 2010-05-20
(e) Manoeuvres

(i) At least one steep turn in each direction with a bank angle of 45° and a change in heading of at least 180° but not more than 360°;

(ii) Approaches to stalls

For the purpose of this manoeuvre the required approach to a stall is reached when there is a perceptible buffet or other response to the initial stall entry.

The following approaches to the stall are required during initial and upgrade PPC's:

(A) one in the take-off configuration, except where a zero-flap take-off configuration is normally used in that model and type of aeroplane;

(B) one in a clean configuration; and

(C) one in a landing configuration.

One of the approaches to stall shall be performed while in a turn with a bank angle of between 15° and 30°.

(iii) Steep turns and approach to stalls are not required when the PPC is conducted using either a LOFT scenario, a scripted PPC or a fly-by wire aeroplane; and
(amended 2000/12/01; no previous version)

(A) for an initial PPC on aeroplane type, steep turns and approach to stalls have been satisfactorily demonstrated during initial training;

(B) for a semi-annual or an annual PPC:

(I) steep turns and approach to stalls that are required in the applicable annual training syllabus have been satisfactorily demonstrated during this training; or

(II) steep turns and approach to stalls are not required in the applicable annual training syllabus.

Date Modified: 2011-05-31
Apparently, things haven't changed here, but we need to take care regarding any conclusions. Again we have no data from this accident, but we do have a history of loss of control through stalling. We can't ride off in all directions under full sail but the trend is disturbing and requires timely, specific study in my view.

Edit: As a last entry on this Picky, this document, COMMERCIAL AND BUSINESS AVIATION ADVISORY CIRCULAR No. 0247, 2005.08.24 seems to follow along the same lines as the SAFO document you have cited. So this is at the level of an Advisory Circular at present.

Last edited by Jetdriver; 10th Jun 2011 at 11:43.
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Old 10th Jun 2011, 07:06
  #1725 (permalink)  
 
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Machinbird wrote:

The BEA note seems to indicate that the PF was making frequent large control inputs.

Large control inputs (high gain activity for the control theorists) are contrary to this Pilots training. Something scared the Bejesus out of him to get this type of behavior.
The only thing that makes sense is that he encountered lateral PIO (And PIO is definitely an aircraft problem). Another name for PIO is pilot in the loop oscillation.
I believe machinbird may have hit on something. This is an area that may eventually provide an explanation and enlightenment for what some people currently see as inexplicable behaviour by the PF. And, though Machinbird's scenario (PIO) is quite possible, it certainly isn't the only possible scenario that involves lateral control issues once the aircraft was in Alt2.
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Old 10th Jun 2011, 07:40
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It puzzles me why the plane dropped to Alt 2 with no roll protection when the original problem was reportedly in pitch. Seems like there was an unimaginative lack of WHAT IFs in the design.

Pitch controls airspeed.
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Old 10th Jun 2011, 07:42
  #1727 (permalink)  
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grizz;

Yes, there are alternate scenarios for sure. If weather, especially if it includes airframe icing, (rare at that altitude, rarer at -40C, but not impossible as we know), was present, perhaps an immediate, momentary climb was the only (emergency) quick escape. Although unusual, even a very slightly-roughened leading edge would be far more sensitive to any AoA increase than a completely clean wing. Escape makes complete sense if such conditions obtained. The comments prior to the AP disconnect didn't indicate an immediate issue but we're going to learn more soon, I hope.
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Old 10th Jun 2011, 11:03
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Altimeter Data Available?
Have not seen much mention if any of whether altimeter data was available. It appears to me from looking at the releases that it should have been there, and would have been unreeling downward and would have been part of the instrument cross-check. Anyone knowledgeable on the -330 want to comment on this?


This is a pretty important piece of information, but no comments on this post???

Last edited by Lazerdog; 10th Jun 2011 at 11:27.
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Old 10th Jun 2011, 12:44
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Nothing to suggest altitude data wouldn't be there, in fact there's nothing to suggest any instrument malfunction other than airspeed.

I'm also still not convinced by the "fighting roll tendency" theory either, in fact my position remains that we don't know what was going on past a few discrete facts and that any further speculation will be just that.

@Graybeard : I think any air data malfunction -> instant Alt 2 because in that situation none of the protections can function reliably.
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Old 10th Jun 2011, 12:52
  #1730 (permalink)  
 
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JD, I don't think training a 15 sec wait for a stall warning at altitude is a good idea. I used to teach stalls and spins, albeit in small trainers not in large transport aircraft. To sloppily quote Mr Davies --" if you have a choice between being stalled and something else, choose something else."

The first indication of stall warning ought to clue the pilot to decrease AoA, even if slightly, and cross check immediately what to do next. If the stall warning is determined to be spurious later, then recover, reestablish flight condition, and press on.

Do nothing for 15 seconds? 15 seconds is enough time for a stall to turn into something worse. Depends on flight contitions and configuration.
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Old 10th Jun 2011, 13:03
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Originally Posted by Machinbird
Since the turnover briefing specifically included the discussion about the aircraft not being ready to climb higher, there are approximately two reasons the aircraft would be put in a climb.
  1. PF airspeed indication approaching Mmo or
  2. It was inadvertent.
I would perhaps also add "they lost attitude indications and thought they were diving" (somatogravic illusion etc.)

I think it is low probability, but PF displays aren't in the flight data, and there is the line in the BEA release:
PF said "I don’t have any more indications", and the PNF said "we have no valid indications".
As well as the comment itself, I find it interesting that the BEA chose to include it in this early release. We have what is surely just secleted excerpts of the CVR transcript at this point, so why did they include this line ? Do they already believe it is significant ?

Did the pilots lose attitude info, or did they distrust attitude info, or ? Climb might therefore possibly have been deliberate ? [ I know the climb happens before this comment, but the comment could be on a failure (or not) that happened earlier ].

Large control inputs (high gain activity for the control theorists) are contrary to this Pilots training. Something scared the Bejesus out of him to get this type of behavior.
The only thing that makes sense is that he encountered lateral PIO (And PIO is definitely an aircraft problem). Another name for PIO is pilot in the loop oscillation.
Entirely possible, and I've been wondering about it too.

Inspired by Gums' great posts on the Viper FBW (further back than my small knowledge of it, and fascinating history) I did some digging for info on that, and one thing that came up was this paper on PIO: http://www.nasa.gov/centers/dryden/p...ain_H-2031.pdf - looks like just putting the g-forces on the pilot's arm into the loop can get you interesting results in certain conditions. I doubt that is what happened here, but it gives an insight into the complexity of the overall model and what it can throw up. [ Note: for the anti-FBW brigade - PIO is not a consequence of FBW, and modelling the overall control system for direct cable control would be at least as complicated, and likely much more so ].
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Old 10th Jun 2011, 13:22
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TurbineD: We know that speed was deteriorating rapidly after the nose up side stick command, but perhaps the pilots didn't know this.
Turbine: I'll go out on a limb here, and assert that pilots, when they put nose up, know they'll slow down. (Particularly if they don't touch the power lever).
The exceptions I can think of are:
-Space shuttle pilots on lift off
-A fighter pilot whose aircraft has a greater than 1:1 thrust to weight accelerating in Afterburner nose high.
infrequentflyer789
Did the pilots lose attitude info, or did they distrust attitude info, or ? Climb might therefore possibly have been deliberate ? [ I know the climb happens before this comment, but the comment could be on a failure (or not) that happened earlier ].
Some pages ago,
PF "I don’t have any more indications",
PNF said "we have no valid indications"
was discussed and it is an open question what that meant, though some think it was related to previous comments on airspeed indications.

No evidence has been presented to suggest the attitude indications weren't working.

ChristiaanJ made a point a few pages back, on why the pilots would, or would not, be talking much during a high workload condition.

Pilots tend to act (aviate) and then talk(commnicate), particularly a PF. Afte all, it's something we all had drilled into our heads.
ANC (not the political party ...)
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Old 10th Jun 2011, 13:57
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"Hysteresis" x Early warning

So, if possible*, would be useful to have early warning indications of UAS, conditions leading to Stall, etc.

* Technically speaking even the UAS condition seems be detectable "before" the Systems (Pitot scanning, etc.) process it. Freezing, etc. (most events) very probably are not instantaneous and could trigger an Early warning (of this very important parameter to "advanced planes").

Improving "Fault tolerance" and "Graceful Degradation" in order to give the crew "better chances" to timely understand and precisely act, very fast, ASAP.

A sudden law switching together "non reliable indications" clearly is not compatible to the "advanced planes" design philosophy of "Fault tolerance" and "Graceful Degradation".

Not to mention the ABSURD reliance on IDENTICAL (and statistically unreliable) AS sensors. This is not redundancy at all (in most situations).

Clearly IMHO creating instead "highly complex scenarios", even for an "advanced plane" designer.

Last edited by Jetdriver; 10th Jun 2011 at 18:15.
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Old 10th Jun 2011, 14:07
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For RR

So, if possible*, would be useful to have early warning indications of UAS, conditions leading to Stall, etc.
RR, "early warning indications of UAS" doesn't make sense to me. UAS is a symptom of a problem. There is in play a very simple and effective tool that under discrete situations is prone to temporary malfunction.

Conditions leading to stall are typically warned by the stall warning device. The warning usually goes off before a stall.
* Technically speaking even the UAS condition seems be detectable "before" the Systems (Pitot scanning, etc.) process it. Freezing, etc. (most events) very probably are not instantaneous and could trigger an Early warning (of this very important parameter to "advanced planes").
UAS isn't just a symptom of freezing (pitot heat is pretty standard equipment).
Improving "Fault tolerance" and "Graceful Degradation" in order to give the crew "better chances" to timely understand and precisely act, very fast, ASAP.
Disagree with your assertion on what does, or doesn't, need to be acted up on "very fast." I find your assumption of ASAP out of synch with how malfunctions are dealt with. Dealing with a malfunction is a deliberate process which typically precludes there being an emergency.

"Not to mention the ABSURD reliance on IDENTICAL (and statistically unreliable) AS sensors. This is not redundancy at all (in most situations)."
RR, it appears that the statistical reliability is at odds with your assertion. What is of concern is the known failure modes, and how to mitigate them.
1. Some manufacturers seem to have gotten farther along than others.
2. The regulatory bodies still have some work to do on that score.

I'd like to point out that pilots are trained to fly in a variety of degraded modes, because no matter how much you spend, things break.

Points on "graceful failure" not disgareed.
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Old 10th Jun 2011, 15:09
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The failures seemed remarkably graceful

Until somebody pulled back on the stick

And held it there

And even then the aircraft, which was essentially flying in the blind, tried to help out as much as it could.

STALL STALL STALL

Just typing it makes we want to push my laptop off my desk
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Old 10th Jun 2011, 15:16
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Extract from the ATSB report on A330 VH-EBA incident (28 October 2009) – Flight Guidance system description:

“Each flight director automatically re-engaged when its associated FMGEC detected that at least two ADR values were again valid and consistent.”
Note: ATSB always uses the past tense.

If this is correct, according to the BEA update on AF447, the FDs could have been available from 02:11:06 (when the IAS was restored on the ISIS) to a few seconds after 02:11:40 (when all speeds became invalid).

In what mode would the FDs “re-engage”?

Did you ever observe FD hypnosis?

For those interested, there is a hint about HS / Elevator relative efficiency in the A330 FCOM3 under F/CTL STAB CTL FAULT emergency C/L:

“If trim is locked above 8 degrees UP, pitch down authority may be insufficient for speed above 180 knots”
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Old 10th Jun 2011, 15:33
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Originally Posted by Lazerdog #1729
Altimeter Data Available?
Have not seen much mention if any of whether altimeter data was available.
The BEA note provided altitude information which means that altimeter data was recorded just as the (failing) airspeed was recorded. So at least one of the altimeters was functioning correctly and though they don't say, I would think all of them were functioning.

infrequentflyer789;
I would perhaps also add "they lost attitude indications and thought they were diving" (somatogravic illusion etc.)
Understand the somatogravic illusion possibility but we have no indications in the ACARS of a loss of the IRSs so attitude information would likely have been available.
I think it is low probability, but PF displays aren't in the flight data, and there is the line in the BEA release: PF said "I don’t have any more indications", and the PNF said "we have no valid indications".
The BEA note doesn't indicate that the "PF displays aren't in the flight data", it states that the #2 CAS parameter isn't recorded which is quite different. At this point I don't think we should put too much stock in the plural of the word "indication". We'll know by the end of July I think.
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Old 10th Jun 2011, 15:38
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PJ2 wrote:

Understand the somatogravic illusion possibility but they had altitude information
If they had altitude information, and the PF watched it quickly unraveling, could that then not explain his constant back pressure on the stick?
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Old 10th Jun 2011, 15:43
  #1739 (permalink)  
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rgbrock1;
If they had altitude information, and the PF watched it quickly unraveling, could that then not explain his constant back pressure on the stick?
Well, perhaps, but then what does that say?
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Old 10th Jun 2011, 15:53
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Originally Posted by DJ77
If this is correct, according to the BEA update on AF447, the FDs could have been available from 02:11:06 (when the IAS was restored on the ISIS) to a few seconds after 02:11:40 (when all speeds became invalid).
Maybe even before, when speed displayed on the left side increased sharply to 215kt. Airplane was at 37500ft with a recorded AoA around around 4 degrees.
What would have shown the FDs (or FPVs) at that time ?




Good catch DJ77
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