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AF 447 Search to resume (part2)

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AF 447 Search to resume (part2)

Old 22nd May 2011, 16:06
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look there is a lot at stake here (financially). Nobody wants the blame for this accident.

Airbus have nothing to recommend to its operators following readouts of the CVR and FDR.

It is well known and documented that there was some pretty awful weather that night and ALL other aircraft around that time went around it. That is a pretty powerful comment.

You have 3 systems on this aircraft and we are aware of the warnings that occurred up till a certain point. None of this supports AOA creep or one system speed issues. If a system creeps enough to endanger the aircraft there must have been something seriously wrong with the onboard data comparators.

This was very quick as if someone flew directly into a storm front.
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Old 22nd May 2011, 16:15
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Hi Graybeard,
Originally Posted by Graybeard
The info as presented tries to pack too much into a page, mixing pitot and static pressures together. AFAIK, all the prior events were airspeed errors alone, and did not have altitude errors.
Whilch prior events? Those before Dec. 1999?
Altitude errors are also recorded with pitot issues: variations are not in the same range but still, erroneous altitude will be displayed.

Originally Posted by Graybeard
Airspeed and altitude are separate and unique functions within the ADR, except at low speeds, and their output data bus words are separate and unique. An ADR may flag or put out erroneous airspeed without affecting altitude output.
Each ADIRU module is separated in two: ADR+IR. If you are turning OFF the faulty ADR part because of unreliable airspeed, you will also reject all the associated static and AoA probes. Hence, if all three are rejected, you are only left with your standby instruments.

Originally Posted by Graybeard
The FCOM Bulletin #009 page 3 gives the case for total pitot obstruction, not just drain hole obstruction, although it is known that Thales pitot were prone to drain hole obstruction due to roughness in the holes. Drain hole obstruction without impact air obstruction will give an erroneous higher than correct airspeed.
What is your source for this so-called defective "Thales" probes? Thales C16195AA (know as SEXTANT Av.) were first issued in order to replace the previously "known" clearly defective Rosemount 0851GR (now Goodrich) which was mounted on the first batches of A330. Goodrich developped the 0851HL for fixing the same issue and Thales the C16195BA for improving the C16195AA due to water ingestion (not ice). At the end, this Goodrich 0851HL is now considered to be the more robust to severe icing conditions.

Originally Posted by Graybeard
Total pitot obstruction, per page 3, puts the plane into an unstable situation. Increase of altitude cause increase of IAS. The A/P will try to increase pitch to reduce the IAS, causing even higher erroneous IAS. This is in accordance with Der Spiegel story.
Except the fact that those airspeed discrepancies were obviously correctly monitored by the system, and that would be not very likely otherwise. In your scenario, no ADR DISAGREE would be triggered - the system being "fooled" by undetected probes issues. In AF 447 case, it appears that the system was not "fooled" and what happened was 3 ADRs finally rejected for displaying unreliable airspeed. Get it?
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Old 22nd May 2011, 16:15
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Yes, CB13, impact pressure at the Air Data Module will drop to static level, zero airspeed, if the probe is blocked while the drain is open.

The drain hole is calibrated size with respect to impact hole. If the drain hole clogs, impact pressure at the ADM will increase.
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Old 22nd May 2011, 16:18
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Having said the above, I am unsure where your comments are coming from. In the interest of full disclosure, so I can make an informed opinion: are you a pilot, passenger, lawyer, associated with one of the family on AF447? Or just somebody with some hatred? What exactly is your expertise?

Thank you
I'm nothing particular you describe above.
I'm just a person with common sense .. which followed several trials with the means at its disposal and which thus draws conclusions and evidence.
They may be less visible for some.
Follow the remaining events and I am sure everything will be conducted in the same vein of what happened before in several trials
This is so far my "expertise"
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Old 22nd May 2011, 16:22
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PR team working for "professional release"

Originally posted by Safety Concerns

All BEA are trying to do now is ensure a professional release of the information because it has been established that the a/c was technically fine. Now that doesn't leave many options.
We already know what happened.
And BEA since last weekend as showed by assertive content of "LF leak" delivered very soon

Your feeling IMO is based in a complex "Pattern recognition"

look there is a lot at stake here
Trimming PR work
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Old 22nd May 2011, 16:28
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Der Spiegel today

Pilot war in kritischer Flugphase nicht im Cockpit

"What happened on board the Air France plane that crashed into the Atlantic off Brazil? According to SPIEGEL information to evaluate the flight data recorder is now providing new insights: Marc Dubois pilot was obviously not in the cockpit when the accident took its course".
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Old 22nd May 2011, 16:34
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First, the Der Spiegel article still fits into the category of rumor at this point, so this is comment assuming the rumor has a basis in truth.

This is beginning to look like the X-31 scenario. Once actual airspeed is far enough from system accepted airspeed, the control system gains become set inappropriately and the control system becomes unstable.

The Captain might have had a clue from deck angle when the carts started to roll, or he may just have heard the "Cavalry Charge" through the cockpit door. And I suppose that if I was in the seat, trying to sort out this scenario and my "boss" came in on the middle of it, you can bet I'd mentally pass the situation to him to sort out and then do what he said, whether or not he really understood the situation yet. In this case, the arrival of the Captain in the middle might have worked against this crew.

The swept wing pitch up characteristic works against recovery if a deep stall is achieved from the outset.

My question of a few days ago regarding whether activation of manual THS trim (as during a stall) while in Alternate law, would subsequently be overridden by the system was not fully answered by TAKATA.
Originally Posted by Machinbird
Doesn't it run back to where the computer wants to put it?

Not really, manual-trim mode is activated:
"microswitches, actuated by the override mechanism, ensure that the computers remain synchronized with the manually-selected postion."
Unless manual trim mode involves physically moving the THS trim wheel in some ?Oubtoard? position to achieve manual trim, the more likely method of operation is a force override detection switch to let the computer know that it has been overriden. But then the question is "How does the system know that the crew is done making manual changes?"
If it is a force override detection system, and the system no longer detects a manual override, wouldn't the system return to putting the THS where it "thought" it belonged? Then the next question would be, "Where would the system want to move the THS trim?"

Once in a deep stall, an A330 would likely behave in a manner similar to the F-16 deep stall. The deeper into the stall you get, the more wings behave like flat plates, and less like finely designed airfoils.

Many have assumed that the aircraft would begin to autorotate after a stall, but this general assumption may not prove correct with a FBW aircraft provided sufficient control authority exists to prevent it.

The final question is, whether or not a variation of the F-16 deep stall recovery would work on the Airbus?
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Old 22nd May 2011, 16:39
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In flat plate, the idea is to "spill" flow off one 'side' of the a/c so a 'rolling' moment is instigated. If one can start slow enough, and cleverly instill a "rock" to the a/c, well, if I remember my Boyd, back to flying on bogie's six.

The F-16 cheated, it had rock and roll elevators.

gums ?
Old 22nd May 2011, 16:49
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Even CRM "inside the loop"

In this case, the arrival of the Captain in the middle might have worked against this crew
Highly complex, volatile and extremely dangerous scenario
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Old 22nd May 2011, 17:04
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And I suppose that if I was in the seat, trying to sort out this scenario and my "boss" came in on the middle of it, you can bet I'd mentally pass the situation to him to sort out and then do what he said, whether or not he really understood the situation yet.
Good point. If true, would mean a breakdown of CRM. OTOH, how could the capt. enter through the secured cockpit door unless the situation took minutes to unfold. On the whole, I'll pass on this rumor/leak. Thank you.
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Old 22nd May 2011, 17:12
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How hard would it be to have a crude reaction control system for spin emergencies? Just enough to cancel the spinning tendency and get the nose down.
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Old 22nd May 2011, 17:19
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In Test flight, a spin chute can be fitted. That is absolutely not necessary in a transport category Aircraft. All a/c can stall, and all systems are subject to failure.

447 was lost due influences absolutely designed for. Whether a Training syllabus blindspot, or a glitch in elec/mech, it happened, and BEA know how.

"Why" is different, notably, from how. It will take a judge to determine (jury?).

Why involves the human factor, and as such, we consequently live in a fail/possible realm...

And even then, not all will be satisfied.
Old 22nd May 2011, 17:21
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Originally Posted by deSitter
How hard would it be to have a crude reaction control system for spin emergencies? Just enough to cancel the spinning tendency and get the nose down.
Please explain?
If I understand you right, your question is in the same category as "Why don't all the passengers have parachutes?".
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Old 22nd May 2011, 17:34
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Academically, just for the sake of discussion, let's assume the A330 has a deep stall mode in ALT 2 with a CG near the aft limit. (This has not been determined to my knowledge.)

With unreliable inputs in what would probably be a fairly "locked" stall situation, would not ALT 2 logic position the elevator to cope with what it thought was occurring? In a deep stall with not much aerodynamic change taking place could not the elevator effectively be "frozen" in one position with fore or aft SS inputs possibly having little or no effect?

The A330 does not have a pitch override switch (ala the F-16) to allow the pilot to gain full movement of the elevator and use the SS to "rock" the aircraft.

Manual THS input in the nose down direction might result in additional nose up elevator to preserve the same dynamics. (BTW the THS manual trim wheel will remain where it is positioned by the pilot in ALT 2)

Could not flap extension provide a required pitching moment?

(As 'Hoot' Gibson said, "Gear down.")

If this has been discussed before, my apologies.

edit: by the pilot
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Old 22nd May 2011, 17:40
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Very funny No, I mean something like hydrogen peroxide thrusters on the outer reaches of the wing. Just enough to get the airplane out of the stalled configuration, hopefully with the nose down.
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Old 22nd May 2011, 18:01
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John the Mod;
Originally Posted by JT #2069
gums has made some comments on the F16 stick. I recall from a course years ago (so it might be scratchy) that the initial test article had a zero break out stick arrangement which was unflyable due to low level muscular tremors. If I recall correctly, the initial mod was to introduce a 4lb break out load to get rid of the non-commanded small perturbations.
In manual flight, the A330 sidestick has a breakout force. It is enough to prevent small motions. However, the experience I've had in heavy turbulence is that, even when the elbow and lower arm are planted firmly on the armrest and the sidestick is moved only through the wrist or more likely through just the fingers, it is difficult to not "stir the pot" or more importantly to achieve consistent, steady in puts in one direction, (subtle or large inputs).

The inertia of the arm/hand responds as one would expect in heavy turbulence, and if the stick is gripped firmly instead of being ridden loosely, (while trying to achieve steady inputs in one general direction), the stick inputs will follow the movements of the hand/arm.

In the meantime, the flight controls, even in ALT2, will all be trying to satisfy all movements of the stick (within the limits of ALT2) while trying to satisfy the commands of the flight control laws in keeping the aircraft at its last-commanded attitude. gums mentioned this phenomenon earlier but it didn't get much play. In FBW, the flight controls are not in a steady, fixed state...they are always moving, attempting to keep the aircraft in its last commanded attitude. In manual flight, these inputs are blended with the commands from the sidesticks, to produce what, in flight data work, looks like a mashup instead of steady state control.
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Old 22nd May 2011, 18:08
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Stabilators and flaperons and rudder


Bear is right about the Viper stabilators - they moved independently and were used for both pitch and roll. Funny, and most folks don't realize this, but the flaperons and stabilators were interchangeable WRT left-right. made maintenance easy and reduced procurement costs, ya think?

The flaperons were the ailerons that also moved independently but could be cranked down as "flaps". In that case, a roll command would raise one while the other remained down. Of course, the tail surfaces helped and we had a good aileron-rudder-interconnect until WOW.

In our deep stall, both stabilators were full leading edge up as they tried to reduce our AoA. Unfortunately, as as you can see from that graph I posted, our pitch moment at 50 - 60 degrees AoA was zippo for nose down. Above 29 degrees AoA, our rudder was taken away from us - GASP!!! It countered any yaw we had, according to the designers, and guess what? It worked as advertised. That's why first deep stall was hard to recognize by the test pilot. As he recalled, smooth as silk except altimeter was unwinding at max display value!!! Other than that, and no pitch control, a Sunday drive.

While we wait, I would point out that an aspect of the 'bus control laws in one of the very deepest reversions seems to place more emphasis upon speed than upon AoA. This puzzles me. Maybe TK can explain.

From the time I first flew a Luscombe ( Earth was still cooling and I fought raptors during pre-flight), I was taught and learned that AoA is what causes a stall, not speed. I fully understand a design consideration for mach, as a high mach can reduce or even reverse aileron and spoiler inputs. But pure CAS seems a poor input for major attitude commands by "otto".Considering that previous 'bus incidents had erroneous airspeed as a major contributor to the ends results, why would Airbus not consider AoA the primary consideration in an "upset"? I wonder....

p.S. Maybe TK can find the pitch moment graph for the 'bus like the one I posted for the Viper. We ain't proud, heh heh, and our discovery led to better FBW control schemes down the road.
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Old 22nd May 2011, 18:27
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For the techies on this thread, I've managed to dig up this report from my old Software Engineering/Reliability professor, Peter Mellor. In it, he details the visit he made to Airbus Industrie in January 1993:

Peter Mellor's visit to Airbus.

Interesting snippets include (emphasis mine):

The building block of the EFCS (and many other systems on the A3xx family) is the Command and Monitoring fail-safe (or fail-passive) computer, which has been in use for around 30 years. (One of the points that was repeatedly stressed was that the design approach used on the A320 is "evolutionary'' not "revolutionary'': the ideas have been introduced gradually over many years, building on experience with many models of aircraft.)

This device consists of two channels, each with its own microprocessor, RAM, ROM, watchdog timer, I/O ports and power supply. The two channels are electrically separated and physically separated by a bulkhead. Each channel contains its own software, diversely developed to the same functional specification, and the output of the command channel is compared to the output of the monitor channel. Any mismatch or time-out results in a shut-down of the one computer. There is an asymmetry between the command and monitor channels due to the existence of time-dependent functions in the servoloop.

The design is intended to ensure that the only failure mode is ``stop'', after
which other computers in the EFCS take over the function (possibly with a
change in the flight control laws and a degradation of automatic protection).
The EFCS life cycle involves requirements capture resulting in an equipment specification, including hardware, software, and functional specifications. The pilot is very definitely "in the loop'' for requirements capture, which is an iterative process using rapid prototyping and flight tests. Emphasis is placed on validation of functional requirements, which is clearly distinguished from verification.
The tool used to express functional requirements is ``Specification Assiste par Ordinateur'' (SAO) or ``Computer Aided Specification''. This tool is far more powerful than I had previously realised. It allows the precise definition of sequences of control actions in graphical form with a library of symbols to represent individual actions such as integrate, switch, etc.
To achieve diversity, the development of hardware and software for the A320
and A340 was contracted out as follows:-

Aircraft    Computer   Chip       H/W Development   S/W Development
--------    --------   -----      ---------------   --------------- 

A320:       ELAC       Motorola   Thompson-CSF      Thompson-CSF 

            SEC        Intel      SFENA             Aerospatiale
                       80186                        Atelier Logiciel

A340:       FCPC       Intel      Aerospatiale      Aerospatiale
                       80386      ADL               Atelier Logiciel

            FCSC       Intel      Sextant           Aerospatiale 
                       80186      Avionique         Atelier Logiciel
Showing, as syseng68k pointed out, that while later generation processors were used in later models, they were still a few generations earlier than the state-of-the-art (which in 1993 would have been the Intel i486, with the first Pentium P5 coming out that year).

It should be pointed out that judging by his posts on RISKS going back to the late '80s, Mellor was definitely willing to be sceptical about the use of computers in aircraft, but it would appear that the more he learned about how it was done, the more comfortable he became with the concept.
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Old 22nd May 2011, 18:30
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Airbus FBW Sidestick

Quote from Garage Years:
"my understanding of the side-stick is that the Airbus stick is quite a different design to that of the F-16. The F-16 stick only moves a very small physical deflection and is more of a force sensor (I worked F-16 simulators about 17 years ago!), while the 'bus stick is a position sensor. That in itself though is merely interesting."

Quote from Smilin Ed:
My instructor, Nello Infanti, asked which I preferred. I preferred minimal stick motion with aircraft response determined by stick forces. Nello informed me that the vast majority of pilots also preferred that configuration. I would think that, when finding it necessary to fly current FBW aircraft using the stick, that precise control would be more difficult using stick deflection rather than stick forces. Is Garage Years correct in his characterization of the AB side stick?

You, gums, Machinbird, Flexible Response, and others may find some thoughts of mine on the use of the Airbus sidestick (from experience on the A320) of some interest:

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Old 22nd May 2011, 18:38
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From a layman's point of view I was surprised that there appears to be no 'split cuff' or similar to hold the forearm in place. Isn't there anything to provide a positive anchor for the wrist -must be a reason why not but curious.
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