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AF447 Thread No. 3

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AF447 Thread No. 3

Old 7th Jun 2011, 22:31
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ADR

@ ChristiaanJ:

AMM - ADIRS 34-12-00 & ADR Operation 34-13-00.
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Old 7th Jun 2011, 22:34
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Originally Posted by alex_brin
From this France Soir article:
Airbus, la descente infernale : Tout s

where the quote is part of the timeline:

"2 h 11 min 45 s. Tandis que toutes les vitesses redeviennent invalides et que l’alarme de décrochage s’arrête, le commandant de rejoint les deux pilotes dans le cockpit. « Je ne comprends rien », lâche l’un d’entre eux, affirme sur France Info Michel Polaco, pilote instructeur et ancien patron de la station. L’avion tombe alors à grande vitesse et il n’est pas sûr que dans la nuit, en pleine turbulence et au milieu des alarmes, les pilotes s’en rendent compte tout de suite."
Where as the English report shows only the following:

At around 2 h 11 min 40 , the Captain re-entered the cockpit. During the following seconds, all of the recorded speeds became invalid and the stall warning stopped. Note: When the measured speeds are below 60 kt, the measured angle of attack values are considered invalid and are not taken into account by the systems. When they are below 30 kt, the speed values themselves are considered invalid.

The altitude was then about 35,000 ft, the angle of attack exceeded 40 degrees and the vertical speed was about -10,000 ft/min. The airplane’s pitch attitude did not exceed 15 degrees and the engines’ N1’s were close to 100%. The airplane was subject to roll oscillations that sometimes reached 40 degrees. The PF made an input on the sidestick to the left and nose-up stops, which lasted about 30 seconds.

At 2 h 12 min 02, the PF said "I don’t have any more indications", and the PNF said "we have no valid indications". At that moment, the thrust levers were in the IDLE detent and the engines’ N1’s were at 55%. Around fifteen seconds later, the PF made pitch-down inputs. In the following moments, the angle of attack decreased, the speeds became valid again and the stall warning sounded again.
The French report seems to agree:
Vers 2 h 11 min 40 , le commandant de bord rentre dans le poste de pilotage. Dans les secondes qui suivent, toutes les vitesses enregistrées deviennent invalides et l’alarme de décrochage s’arrête.

Note : lorsque les vitesses mesurées sont inférieures à 60 kt, les valeurs mesurées d’incidences sont considérées invalides et ne sont pas prises en compte par les systèmes. Lorsqu’elles sont inférieures à 30 kt, les valeurs de vitesse elles-mêmes sont considérées invalides.

L’altitude est alors d’environ 35 000 ft, l’incidence dépasse 40 degrés et la vitesse verticale est d’environ - 10 000 ft/min. L’assiette de l’avion ne dépasse pas 15 degrés et les N1 des moteurs sont proches de 100 %. L’avion subit des oscillations en roulis atteignant parfois 40 degrés. Le PF exerce une action sur le manche en butée à gauche et à cabrer, qui dure environ 30 secondes.

A 2 h 12 min 02, le PF dit « je n’ai plus aucune indication », et le PNF « on n’a aucune indication qui soit valable ». A cet instant, les manettes de commande de poussée se trouvent sur le cran IDLE, les N1 des moteurs sont à 55 %. Une quinzaine de secondes plus tard, le PF fait des actions à piquer. Dans les instants qui suivent, on constate une diminution d’incidence, les vitesses redeviennent valides et l’alarme de décrochage se réactive.
So BEA quotes nothing at all for 2:11:45 in either report. Here are their links, English and French. I choose to discount news reports that include information not in the BEA reports. It may be accurate as a leak. It is not official. And I prefer to go with the actual BEA reports as official data.

Last edited by Jetdriver; 8th Jun 2011 at 03:28.
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Old 7th Jun 2011, 22:42
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Comment to my own lengthy posting with BEA quotes. Here is a link that contains the French that was quoted in the article alex brin quoted.

It bears at best a superficial resemblance to the BEA reports with different times and some data being entirely different.

I choose to trust BEA and not get worked up over spurious reports.
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Old 7th Jun 2011, 23:03
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rgbrock1

One feels acceleration. One does not feel velocity.
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Old 7th Jun 2011, 23:23
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Howdy rg

What was felt inside by humans has a great deal to do with aspect, and rate, both of entry and exit. BEA claim roll excursions of 40 degrees. I assume they mean each way, so remember that in ALT 2, this a/c is "Twitchy on Aileron", and no one knows if these rollies were co-ordinated (with Rudder). Expect a fair amount of Yaw blended in, and Pitch is by no means nailed. Tail low, descent of 200 knots, with large g value trends. Not a walk in the park. Initially, the Brasilians made note of "flail injuries", those trauma that see extreme accelerations both positve and negative. This was noted of course on those recovered on the surface in the weeks following impact. I doubt there is a Seven Flags e-ticket ride that would come close to the accelerations in the fuselage. CAT can cause broken bones, necks, and serious Skull fractures. And that is simply the bottom falling out and back up.

Those unrestrained were thrown quite violently about. The picture thus far is presented as calm, measured, and conversational (Pilot to Pilot). I hope to God it was like that, but I truly doubt it was. In roll entry and recovery, those situate furthest from the cg (roughly) get the most shaking about. If your pilot is a known goofy foot, don't sit in back.
 
Old 7th Jun 2011, 23:24
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rgbrock,

I think if it´s a constant rate of descent you will not feel it (you might feel it at first when you go from level to a descent). In normal flight you are flying forward at 900 or more km/h, but you don´t feel it (except initial acceleration). Same thing , but vertical motion instead of horizontal.
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Old 7th Jun 2011, 23:28
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Forget AoA, worry about speed

Thanks, A33Z.

ADIRU computes AOAi from sensor resolver cos. and sin. and calculates
AOAc as function of AOAi, FLAPSLAT CONFIG and Sensor position(LH/RH)

If CAS < 60 Kts AOAi & AOAc are set to 0° and SSM (System Status Matrix) is set to NCD (No Computed Data),
this is also valid for TAS 0 Kts if CAS < 60

If CAS < 30 Kts it declares itself invalid and outputs 0 Kts and NCD.
So if we have the confusers not believing speed, or if they sense low speed, they forget about AoA protection? Does this work if the speed is zero or 1000 kts due to iced up pitots?

I can understand a WoW switch and 60 knots on the ground, but inflight???

Guess the engineers designed the system according to spec.
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Old 7th Jun 2011, 23:45
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JD-EE:
I wonder if a vibration feedback to the pilot's back or some other convenient place could give a feel for control stick position without distracting the visual scan. If it was little vibrators...
That's a creative idea, but I won't touch it with a 3.06 Meter pole.
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Old 8th Jun 2011, 02:04
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Originally Posted by gums
So if we have the confusers not believing speed, or if they sense low speed, they forget about AoA protection? Does this work if the speed is zero or 1000 kts due to iced up pitots?

I can understand a WoW switch and 60 knots on the ground, but inflight???
Yeah, you aren't the only one who doesn't understand this bit of logic. Not sure if the fault is in the ADIRU logic or the stall-warning though - or maybe (I think the stall warning is not from ADIRU but higher level) both are "correct" for their inputs and outputs (eg. if the vanes don't work below 60kts maybe the ADIRU is "right" to send out no AOA value), but the overall result makes no sense.

It seems to be:
iAS valid, > 60kts - stall warning on AOA
iAS invalid, > 60kts - stall warning on AOA (but might be spurious)
iAS < 60kts - no stall warning, whether iAS valid or not
That last one seems all wrong - if iAS is valid and <60kts in a big jet then surely you are stalled whatever the AOA vane says ? If iAS is invalid <60kts, then a warning might be spurious - but we run that risk if the speed is invalid but over 60kts, so why change at 60kts ?

It does look like a hole in the design (with the limited info we have at this point) - whether or not it is significant in the outcome in this case remains to be seen. Possibly it was irrecoverable anyway by the time this issue confused them.
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Old 8th Jun 2011, 02:19
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POB Fall sensation

One does not feel velocity
During the near 11,000 fpm from perigee to sea level the cabin pressure was kept quite constant during the few minutes fall? How typically varied?

What kind of "barometric" sensation the POB felt?

And during this fall, the ride was smooth? No bumps? No turbulence?

Just speed (constant)? Or some accelerations, (high AOA buffeting, together the recorded roll oscillations?

Most passengers realized the imminent crash? Felt the fall after perigee?

Or the few minutes "ride" was like a turbulent, same level typical one?

And both engines varying from TO/GA to idle (after the unusual 7,000 fpm climb while "en route") certainly put most POB alert.

And what about the aerodynamic noise (at the recorded AoA)?
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Old 8th Jun 2011, 03:06
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Lonewolf,
Something about using P2 to substitute for pitot air strikes me as very wrong, but I can't put my finger on it.

Station 1 is the free stream, PT2 is total pressure at the engine inlet. Total pressure is total pressure, whether you measure it at the engine inlet face or with a pitot tube, so long as it is properly derived and calibrated it’s the same.

A33Zab
Wouldn't do it for GE. Sensor in inlet is Temp sensor T12, PS1.2 is static pressure ports just IFO fan. The only probe measuring dynamic pressure is P2.5 just after the booster, but this is only used for conditioning monitoring and that's an option.
That’s actually enough. If you have inlet temp, static pressure at the inlet, fan rpm and total pressure after the booster you have to use a fan map model and look up the pressure, but it can be calculated, and probably already is being calculated by the FADEC already and compared with the ideal map for condition monitoring. What you would do is, using the inlet temperature and rpm, you know how much pressure is being made by the fan and that allows you back calculate the free stream total pressure. Can be done pretty accurately (within a couple of knots) if you know the altitude.
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Old 8th Jun 2011, 03:57
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Deep stall demo

Deep stall demo, described as bring "like falling onto a cushion", and "like falling onto a feather bed". (Maybe over-stated?)

Videos System > Viewing Video > SpaceShip Two Re-Entry Test - PestGaming

Last edited by PickyPerkins; 8th Jun 2011 at 04:20. Reason: Spelling
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Old 8th Jun 2011, 04:49
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PJ2, thanks for your answer, very informative as always.
Do you think the QAR would have recorded the data for the #2 IAS ?
Would you know if all data available from the ACMS are automatically recorded in the FDR and/or QAR ?


Originally Posted by mm43
have you any personal ideas of how best to ensure that the PNF knows what the PF is doing with the side-stick?
I’m afraid the only option would be to link both sidesticks.
I think the sidestick as it is, is a great tool for a single crew operation, but for a multi crew … it is a sure way for wasting very valuable information.
For now I think some fighters have adopted a similar sidestick philosophy, also a Dassault Falcon, but I still don’t know what kind of sidestick the Bombardier CSerie will adopt … ?


Originally Posted by Sciolistes
How such firm conclusions about pilot training can be reached on the basis of the massaged information that has already been released is beyond me - well actually it isn't beyond me as such, it is simply depressing.
Absolutely share your view.
The article you mention is not even signed ...
Flightglobal - Comment : AF447's new puzzles
"The investigators' decision to release a detailed picture of the accident sequence ended the mystery for many who had followed AF447's extraordinary story ... "
Which 'detailed picture' ... !?
And apparently the problem is already solved !

What about this one :
Aviation Week - Air France Crash Suggests Inadequate Training
Full of inexactitudes and extrapolations.

Those aeronautical specialized media use their notoriety to misinform.
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Old 8th Jun 2011, 08:47
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I'm not a jet pilot or engineer but..

Has the possibility of a fault with the PF stick been ruled out? Suppose that fault added a constant nose up. Presumably that would cause the THS trim to exagerate the problem? A stuck bit fault in a digital system can appear to add a constant to an otherwise correct value (eg it adds 1,2,4,8,16 etc) but you would hope error detection catches such faults.

Anyway Google finds..

Chapter 5. Flight controls

Airbus A320 Family Non-Normal Notes

5.19. Sidestick unannunciated transducer faults

It is possible for a failed sidestick transducer to cause uncommanded control inputs. If no fault is detected, the result is that the aircraft behaves as if that input had actually been made. Generally, the autopilot will disconnect and any attempt to control the aircraft with the failed sidestick will fail. The aircraft should be recovered with the other sidestick using the takeover button. Keeping this button pressed for 40 seconds will lock out the failed sidestick, and the autopilot can then be re-engaged. The autopilot should not be disconnected in the normal manner as pressing the takeover button will re-introduce the failed sidestick and the uncommanded input; use the FCU instead.
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Old 8th Jun 2011, 09:21
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Cool

Hi,

OT about the feeling of the passenger
I jumped in the future and makes me in the court at the trial of the AF447
The potential feeling that had passenger and their knowledge of their fatal destiny can make a big difference in terms of money compensation to the families.
I'm sure it will be part of discussions among lawyers for the families of victims to demonstrate with the data of the flight that the victims had the knowledge of their fate.
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Old 8th Jun 2011, 09:35
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Generally, the autopilot will disconnect and any attempt to control the aircraft with the failed sidestick will fail.
And could that explain the initial disconnection of the autopilot? But what about the Auto Throttle? Could this be a case of extremely bad luck, with both the pitot probes and sidestick failing at the same time?
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Old 8th Jun 2011, 10:03
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That’s actually enough. If you have inlet temp, static pressure at the inlet, fan rpm and total pressure after the booster you have to use a fan map model and look up the pressure, but it can be calculated, and probably already is being calculated by the FADEC already and compared with the ideal map for condition monitoring. What you would do is, using the inlet temperature and rpm, you know how much pressure is being made by the fan and that allows you back calculate the free stream total pressure. Can be done pretty accurately (within a couple of knots) if you know the altitude.
And there are a couple of other ways of cross-checking the pitot based airspeed. Inertial reference has already been mentioned, how about force required to deflect control surfaces, relationship between pitch/power/vertical speed (static/gps based)? The problem I think lies not in coming up with new ways to calculate airspeed, but how do we design and certify the software to work out which is valid? Simple voting between the various systems would probably not do - the system would need to cross-check the values and trends from the individual sources and estimate the probability of particular airspeeds being reliable. But how do we then present all this information to the pilot? Does any further advancement of the automation imply we need to take the humans out of the loop?


The BEA report did not mention anything about GPWS messages. Were the final seconds of what went on in the cockpit simply omitted from the report, or does this suggest that the ADIRU faults also led altitude measurements to be automatically deemed invalid?
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Old 8th Jun 2011, 10:09
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Have read most of the technical discussion in these threads but one thing that seems strange is that there are no VS inputs recorded by the FDR ,if it records them at all,yet looking at the BEA released final track and 3 D graphic there was a reasonably tight turn to starboard presumably needing the rudder inputs -unless Bearfoil's suspicion re the VS is correct. I'm not aircrew but interested and impressed by the amount of expertise and the arguments between the experts.
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Old 8th Jun 2011, 10:20
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Alternate with Manual Trim Law

Hi Golf-Sierra,

And there are a couple of other ways of cross-checking the pitot based airspeed.
There may be lots of "very clever technical ways" of measuring airspeed. The aircraft has it's own natural way of flying a constant airspeed - simply don't change the power or stab trim.

I think it's a great pity that the stab trim didn't remain where it was once the system recognised spurious airspeed.
Do you think they will add another Law "Alternate with Manual Trim"?
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Old 8th Jun 2011, 10:35
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Speed indication lower limit.

AOA / Speed lwr limits.

In the digital world they need to set a upper and lower limit.
You have only limited bits in a binary word and have to deal with accuracy, resolution, standarisation and......odds.

E.g. the odds to get into ALTERNATE LAW = 10^-5 per Flighthour (10^-3 under MMEL) as advertised.

The Speed indicating limits of ISIS (directly connected to Pt/Ps) are 5 - 600Kts, so backup is available.

AIB did develop the Back-Up Speed Scale. (Article dated Dec. 2007 - sorry can't get direct link working.)

5 Back UP Speed Scale (BUSS)
In order to decrease the crew workload in case of unreliable speed, Airbus has developed the Back-UP Speed Scale (BUSS) that replaces the pitch and thrust table. The BUSS is optional on A320/A330/A340. It is basic on A380, being part of the ADR Monitoring functions.
This indication is based on angle of atack (AOA) sensor information, and is therefore not affected by erroneous pressure measumements.
The BUSS comes with a new ADIUR standard (among other new system standards), where the AOA information is provided through the IRs and nor through the ADRs. This enables selecting all ADRs off without loosing the STALL WARNING PROTECTION.
The AOA information provides a guidance area in place of the speed scale. When the crew selects all ADRs OFF, then:
- The Back-Up Speed Scale replaces the PFD speed scale on both PFDs,
- GPS Altitude replaces the Altitude Scale on both PFDs.

The Back-Up Speed Scale then enables to fly at a safe speed, i. e. above stall speeds, by adjusting thrust and pitch.



The BUSS will be displayed once all ADRs are switched OFF. Therefore, on aircraft that have the BUSS, when the flight crew cannot identify the faulty ADR(s) when performing the troubleshooting, or when all ADRs are affected, the flight crew will switch OFF ADRs, and will fly the green area of the BUSS.

However, if the safe conduct of the flight is affected, the memory items must still be applied before troubleshooting.
As the BUSS is associated to the ADR monitoring funcitions, some unreliable speed situations can be automatically detected (e. g. new ECAM warning "NAV ADR 1+2+3 FAULT"), and some ECAM procedures will lead to the BUSS activation by requesting to switch OFF all ADRs.

****************************************************

But all of that wouldn't make any difference to this SWISS CHEESE case.

BTW ADIRS are also common in modern B brand airliners.

Last edited by A33Zab; 8th Jun 2011 at 15:53.
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