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AF 447 Thread No. 7

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AF 447 Thread No. 7

Old 12th Dec 2011, 11:08
  #621 (permalink)  
 
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We'd need someone more qualified to confirm, but moderate turbulence by any definition should not be enough to take out autopilot/autothrust and I don't think it did in this case.

The climb was caused by the human and not the computer, depite Lyman's ever more bizarre protestations.

@hillberg - we're not going into the force-feedback loop again if we can help it - suffice to say there are as many valid reasons for dropping it as there are for keeping it, so it becomes a matter of personal preference.
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Old 12th Dec 2011, 13:16
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DW
@hillberg - we're not going into the force-feedback loop again if we can help it - suffice to say there are as many valid reasons for dropping it as there are for keeping it, so it becomes a matter of personal preference.
I do not think whether it's a matter of preference by anyone
This is something that can affect (in some cases) the (safe) conduct of flight
In fact .. there are currently two systems (the yoke and the sidestick) with or without feedback
There are questions about these two systems concerning the conduct of the flight and one of the two will prove better than the other
It's to weigh the advantages and disadvantages of each and make the best choice for flight safety
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Old 12th Dec 2011, 13:17
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Originally Posted by HazelNuts39
According to FCOM 1.31.40 p.15 description of indications on PFD:
The displayed vertical speed information is normally based on both inertial and barometric data.
Hi HazelNuts39,

How come there is a trace about that in the FDR, the choice being:
V/S from AirData
or
V/S from Inertial

(i.e. no choice "V/S from both sources").

Thanks
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Old 12th Dec 2011, 13:54
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Vertical speed is derived from the IRs with the barometric input providing a damping function. If the IR becomes invalid the V/S indication changes to pure barometric. This is indicated by an amber box around the digital V/S display.

I seem to remember the intertial V/S being considered invalid above a certain value. 10 000 ft/min is what springs to mind.
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Old 12th Dec 2011, 13:57
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@AZR

Inertial V/S data actually seems to be a hybrid signal (IR & Barometric),
as posted earlier by Takata in august 2011:

http://www.pprune.org/tech-log/45687...ml#post6624383
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Old 12th Dec 2011, 14:09
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Dozy Wannabe

1. Interesting concept: "Anticipatory Instrumentation". Extrapolation is of limited value, and not to be relied upon.

2. The Updraft could easily have been well in excess of 10k fpm. I used 5000 as a low, and conservative, value.

3. VS not reliable via IR. Airspeed not reliable via IR.

4. In airdata compromised situation, you believe the Baro VS? Let alone a smoothed combination of the two? Especially in the presence of rapidly moving temps and pressures?

5. There is a good deal more evidence to support UPSET caused loss of speeds, than ICE.

6. For that matter, there is plenty of evidence to suggest the upset was caused by this environment, as well as UAS.

7. At Loss of Auto, the airframe was losing altitude, and vertical acceleration. Combined with Nose Low on the screen, what would you do? Wait, right, ask your advisors/instructors?

Challenge. Describe the accelerations on the Pilots' bodies as a result of this maneuvering.
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Old 12th Dec 2011, 15:29
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Originally Posted by Hamburt Spinkleman
I seem to remember the inertial V/S being considered invalid above a certain value. 10 000 ft/min is what springs to mind.
The V/S trace seems to confirm what you remember. Would you have a reference for it?

Last edited by HazelNuts39; 13th Dec 2011 at 08:46. Reason: Re-reading Takata's 7 Aug 2011 post
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Old 12th Dec 2011, 18:49
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Hi DozyWannabe,
we're not going into the force-feedback loop again if we can help it
It's not so much the force-feedback - it's the control surface displacement feed back loop that is missing.

Please see page 7 of http://www.easa.eu.int/rulemaking/do...%202011-09.pdf

“c) The use of side stick controllers together with electronic flight control systems which provide control augmentation and control deflection limiting systems could affect piloting awareness that the aircraft is approaching a control limited flight condition. It may be that return to normal flight condition and/or continuing of safe flight needs a specific crew action. In these circumstances a suitable flight control position annunciation is required to be provided to the crew, unless other existing indications are found adequate or sufficient to prompt that action.
(2) CS 25.777 Cockpit controls
Side stick controller force-deflection characteristics in pitch and roll together with displacement sensitivity and gains need to be evaluated. The intention is to show that normal inputs on one control axis will not cause significant unintentional inputs on the other. Consequently a new paragraph CS 25.777(i) is proposed requiring a suitable assessment.”
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Old 12th Dec 2011, 19:00
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Dunno if it was posted before ...

DÉROULEMENT DU VOL
L’élaboration du déroulement du vol est basée sur l’analyse de l’enregistreur de
paramètres, le compte rendu équipage et les données radio-radar fournies par
la DSNA.
Le 14 Juillet 2010, l’équipage du vol AF 7567 DR effectue le vol Ajaccio-Orly.
La situation est fortement orageuse en région parisienne.
Vers 12 h 49, en approche vers Orly et en contact avec Paris ACC, l’aéronef rencontre
de très fortes turbulences au niveau de vol 180. Elles sont qualifiées par l’équipage
« d’extrêmes » près de l’attente d’OKRIX : l’avion subit un gradient de vent vertical
de 25 kt en deux secondes environ et des facteurs de charges compris entre - 0,03 g
et + 1,89 g en vertical et - 0,15 g et + 0,18 g en latéral. Ces valeurs de facteurs de
charges sont importantes mais toutefois à l’intérieur de l’enveloppe de certification.
La vitesse passe de 202 kt à 178 kt (Vs1g + 7 kt).
Les conséquences de ces turbulences sont une augmentation de l’incidence de
l’aéronef. Cette dernière atteint une valeur de 13 degrés environ. La protection en
incidence Alpha Prot de l’Airbus A321 se déclenche et le pilote automatique (PA)
se désengage. Le contrôle de l’appareil est repris manuellement par le copilote qui
amène les manettes de poussée en position TOGA (butée) et agit sur le manche.
L’aéronef subit des variations d’assiettes comprises entre - 10° et + 14° et également
du roulis entre + 2° et - 46°. L’équipage désengage l’autopoussée. Cette dernière
ainsi que le pilote automatique sont réengagés ultérieurement.
Crude Google translation ......
HISTORY OF FLIGHT
The development of the flight is based on the analysis of the recorder
parameters, reporting crew and radio-radar data provided by
DSNA.
On July 14, 2010, the crew of flight AF 7567 DR Takes Flight Ajaccio-Orly.
The situation is very stormy in the Paris region.
49 to 12 h, on approach to Orly Paris and in contact with ACC, the aircraft encounters
very high turbulence at flight level 180. They are qualified by the crew
"Extreme" about pending OKRIX: the aircraft was a vertical gradient of wind
25 kt in about two seconds and load factors between - 0.03 g
and + 1.89 g vertically and - 0.15 + 0.18 g and g laterally. These values ​​of factors
charges are important but still within the certification envelope.
Speed ​​increases from 202 kt to 178 kt (kt VS1G + 7).
The consequences of this turbulence is an increased incidence of
the aircraft. The latter reached a value of 13 degrees. Protection
Alpha Prot impact of the Airbus A321 is activated and the autopilot (AP)
disengages. The control of the aircraft is taken manually by the co-pilot
bring the thrust levers in TOGA position (lock) and acts on the sleeve.
The aircraft sustains variations of plates between - 10 and + 14 ° and also
Roll between 2 ° and - 46 °. The crew disengaged the autopoussée. the latter
and the autopilot are rehired later.
http://www.bea.aero/docspa/2010/f-zb...74fa196764388a
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Old 12th Dec 2011, 19:39
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Hazelnuts39

The topic came up in a discussion with a tech rep some time ago. The discussion had veered off the main topic at that point so I didn't pursue it any further.

Thinking about it a bit more, 10 000 ft/min seems a bit low as a cut-off value. I would expect the IRs to be able to provide valid data at higher vertical speeds.

With regards to the PF and the V/S display, there are two slighly different layouts of the display. One where the only visible part of the pointer is the one covering the V/S scale, and one where the full lenght of the pointer is visible.

I do not know which version AF has, but if it is the first one the position of the pointer is less obvious when pegged at one end of the scale.

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Old 12th Dec 2011, 20:12
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HN39,The vertical wind speeds in this graph have been derived from the recorded AoA, pitch attitude and the aircraft horizontal and vertical speed components. The calculation is very sensitive to small errors in AoA and pitch attitude, and should therefore perhaps not be taken too seriously.
how sensible is your calculation for smal changes in AoA? the elevator flys about 0.1 sec behind the wing, if you fly with CAS 250 into this sort of fast increased updraft the elevator had ca.160 feet/min lower updraft than the wing-----> the result in AoA is about 0.2 deg aditional-diference between elevator and wing

the bird pitch up, as if you pull 0.2 deg, if he fly into this strong updraft

(and visavers pitch down 0.2 deg if you fly outta)

is your calculation so sensible that this effect plays a role???
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Old 12th Dec 2011, 20:54
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grity

along those lines, which surface has the greater moment arm to affect Attitude? And how is this accomodated?

Up Elevator. Per PF
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Old 12th Dec 2011, 21:13
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Grity,

The sensitivity of the calculated updraft velocity to errors in AoA or pitch is evident from the formula given in the header of the graph. For example, for GS + HW of approx. 500 kt, the updraft velocity changes by 88 fpm for 0.1 deg error in the recorded AoA.

Quite another matter is the pitch response of the aircraft when traversing an updraft zone of increasing or decreasing vertical velocity. That effect exists and has been discussed on an earlier AF447 thread, but is smaller than you suggest: The updraft increases about 2000 fpm in 5 seconds, and 40 fpm / 500 kt is about 0.05 degrees. The actual effect is even smaller due to the downwash behind the wing and other damping effects.
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Old 12th Dec 2011, 22:49
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@RRR

It's not so much the force-feedback - it's the control surface displacement feed back loop that is missing.
The F/CTL page - showing the control surfaces position - was automatically callled and in view on the System Display @ triggering of the F/CTL RUD TRV LIM FAULT (02:10:19).

Which could be in compliance with:

“c) The use of side stick controllers together with electronic flight control systems which provide control augmentation and control deflection limiting systems could affect piloting awareness that the aircraft is approaching a control limited flight condition. It may be that return to normal flight condition and/or continuing of safe flight needs a specific crew action. In these circumstances a suitable flight control position annunciation is required to be provided to the crew, unless other existing indications are found adequate or sufficient to prompt that action.
Next,

(2) CS 25.777 Cockpit controls
Side stick controller force-deflection characteristics in pitch and roll together with displacement sensitivity and gains need to be evaluated. The intention is to show that normal inputs on one control axis will not cause significant unintentional inputs on the other. Consequently a new paragraph CS 25.777(i) is proposed requiring a suitable assessment.”
Not very demanding IMO, SS is equipped with dampers, springs (Roll) & spring rods (Pitch) in all axis.
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Old 12th Dec 2011, 23:40
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For me, the supposition that aft stick at a/p release was inadvertent was put to bed long ago. I have to give a minimum amount of credit to PF, and I do believe still the a/c required aft stick as well as Roll left at drop.

An aircraft in an updraft will drop her nose, and in a downdraft, the reverse. By herself, it is basic to the geometry of the architecture. I could not tell you whether or how much attention was paid that fact by the software, (DOZY?). But in this a/c, if in an UP with the kind of energy I believe was in play, her Nose wanted down on the natch. The a/p may have "known" this, but it would not have abated at a/p quit. This may have been a major player in the PF's insistence on Nose UP, when in fact, Nose Down would be needed. Nose down is also contrary to g demand in PITCH, and the PF may have had help in Pitching this mama UP. NO?
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Old 13th Dec 2011, 00:51
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Lyman, your constant restating of your theory is somewhat annoying to me. Saying the same thing many times does not make it correct. Flying at night, in turbulence, should not be overly challenging. If the aircraft needed a bit of nose up at AP disconnect, then 1/2 to 3/4 seconds of aft stick would have been sufficient. What PF was doing must have been quite different.

From the control position graphs of the first 10 seconds, PF was badly over-controlling the aircraft in roll. The energy and force required to make these lateral control inputs were likely substantial.

The Airbus stick is angled forward in its neutral position (to discourage cross channel inputs I understand). I suspect that with the drag from the roll channel viscous damper, PF could not get adequate leverage on the stick to keep up with his perceived need for fast lateral input. Once the stick is canted back towards vertical, there is higher mechanical advantage available. Please note, I am only discussing the control inputs up to the stall. Afterwards, there were different reasons for his aft stick input.

If someone (perhaps A33Zab) could come up with the force/velocity characteristic for the lateral channel viscous damper, then we could look at the energy and force required to make those lateral inputs. It might be very educational when looked at in terms of human energy expenditure.
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Old 13th Dec 2011, 04:13
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I must confess a certain scepticism about such a suggestion. It suggests, to my mind, an unfamiliarity with the controls worthy of a tyro which whatever his reactions I don't think we can claim the PF to be. One shouldn't get too wrapped up in trying to find a mechanical explanation (red herring fillets). Rather there should be more examination of the psychological elements of this accident.

Last edited by Old Carthusian; 13th Dec 2011 at 22:01.
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Old 13th Dec 2011, 08:21
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HN39, the pitch response of the aircraft when traversing an updraft zone of increasing or decreasing vertical velocity. That effect exists and has been discussed on an earlier AF447 thread, but is smaller than you suggest: The updraft increases about 2000 fpm in 5 seconds, and 40 fpm / 500 kt is about 0.05 degrees.
I mesured in your calculation at 2:10:13 increases of updraft 1000 fpm in 0.7 seconds, that was my base for delta AoA ca. 0,2 deg

but you are right this is not so much......
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Old 13th Dec 2011, 23:44
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AF447's initial altitude drift went virtually unchallenged

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Old 14th Dec 2011, 03:17
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AF447 Roll Oscillation & PF's control inputs.

Originally Posted by OC
I must confess a certain scepticism about such a suggestion. It suggests, to my mind, an unfamiliarity with the controls worthy of a tyro which whatever his reactions I don't think we can claim the PF to be. One shouldn't get too wrapped up in trying to find a mechanical explanation (red herring fillets). Rather there should be more examination of the psychological elements of this accident.
OC, So what are your thoughts about the following definition?
Pilot-induced oscillations, as defined by MIL-HDBK-1797A,[1] are sustained or uncontrollable oscillations resulting from efforts of the pilot to control the aircraft and occurs when the pilot of an aircraft inadvertently commands an often increasing series of corrections in opposite directions, each an attempt to cover the aircraft's reaction to the previous input with an overcorrection in the opposite direction.
Do only tyros experience PIO? Was the aircraft's sustained roll oscillation before the stall a PIO? Had PF ever flown in Alt 2 Law at altitude?
Why would a somewhat experienced pilot be unable to fly smoothly?
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