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AF 447 Thread No. 7

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AF 447 Thread No. 7

Old 9th Nov 2011, 20:02
  #41 (permalink)  
 
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Interesting. My A320 FCOM says:

"LATERAL CONTROL
When the aircraft flying in pitch alternate law, lateral control follows the roll direct law associated with yaw alternate or mechanical.

ROLL DIRECT LAW
Refer to Direct Law."

The fact that rudder produces a roll (despite the side stick is not centred) suggests to me that it is not commanding a roll rate in ALT Law.
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Old 9th Nov 2011, 20:28
  #42 (permalink)  
 
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It is quite simple, and said before.

In high AOA and especially in the stall region the aileron is the wrong control surface for roll control.

If you like, use any aircraft model to get a picture from following description.

In normal LAW by a roll action on the side stick, the pilot commands a roll rate, with minimized sideslip (automatic turn coordination), elaborated in the FCPC.
In Alternate 2 LAW the roll control is direct, an order on the side stick directly commands a deflection, according to a kinematic. The yaw control is achieved from the pedals, through a mechanical linkage without automatic sisdeslip correction. A Dutch roll damping function using limited yaw rate data is introduced via the yaw damper servoactuators.
When PF wanted to raise the right low wing with a left SS input, the downgoing aileron on the right wing produced a lot of drag, thus inducing a yawing momentum to the right (into the low wing).

Normally the upgoing spoiler on the left wing would not only help in roll, but would produce drag as well and thus reduce the yawing moment, but under such high AOA the spoiler is blanked out, does not assist in roll and produces not enough drag to prevent the yaw. Sideslip protection was not available, and manual rudder not used.

The induced yaw into the right (low) wing increased the sweep back in relation to the relative wind and thus decreased the available lift on this wing, where on the opposite wing the sweep in relation to the relative wind decreased, thus increasing the lift.

Why did the bank not incrase beyond the 40° (like going into a spiral dive) but oscilated between some left bank and lot of right bank? I don´t know for sure, but it might have something to do with the dutch roll dampening function:

In the event of loss of the inertial data from the ADIRUs, the yaw rate data for Dutch roll damping are provided to the FCPCs via a unit comprising 2 rate gyros. In case of 3 FCPCs loss, the Dutch roll damping is achieved by the FCSCs with yaw rate data coming from the rate gyro unit
Thus left SS input without rudder input produced exactly the opposite what the PF intended to achieve.

One more comment concerning the stall behaviour. It looks like most pilots expect violent maneuvers of the aircraft in a stalled situation, heavy g variations, fast nose position transitions like bank pitch and yaw changes or what so ever. I expierienced the stall violent at the point of departure, but after those initial unpredictable movements nearly stable, but just not logic responsive to the flight controls. AF447 departed and behaved similar, and in combination with a different expectation might also have led the crew to take a stalled situation not into consideration.

Last edited by RetiredF4; 9th Nov 2011 at 20:53.
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Old 9th Nov 2011, 21:06
  #43 (permalink)  
 
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You have it nailed, BOAC.

I have a hard time blaming the crew for 100% of the problem when I see the current training regimen and emphasis upon HAL to "protect" you and the 200 SLF's you are responsible for getting home.

The reversion sequence of the 'bus and its loss of "protections" all along the way disturbs me to this day. Seems the crews are thinking "Normal", and have been "trained" thru hundreds of hours in "Normal" law and "normal" flight conditions. Then when things go Tango Uniform, we see confusion and poor cockpit resource management and..... Also remember that some of us here didn't have the CRM problem, nor could we take a nap someplace aft and hit the bathroom or...

I also have a problem with the warnings and chimes and criteria for them in the 'bus. Many of the flight control functions revert to back-up modes according to loss of speed or whatever. Where should the pilot hang his hat? What's working? And let's forget all the "protections", shall we. I do not advocate a reversion to "direct" law unless there are multiple catastrophic failures of sensors or mechanical systems. It would seem to this old, dumb pilot that we use whatever the jet and/or HAL can give us with clearly defined limits that can be understood by the pilots. For example, who gives a rat's about bank angle limits once outta "Normal" law? Why have two max roll rate limits once reverting from "Normal" to ALT1 and then ALT2 and then "unusual attitude" and then..... Get my point?

Guess/hope the whole affair will result in better crew training, but I would still like to see at least a few concessions by the 'bus folks concerning the reversion sequences, warnings, etc.
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Old 9th Nov 2011, 21:50
  #44 (permalink)  
 
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I do not advocate a reversion to "direct" law unless there are multiple catastrophic failures of sensors or mechanical systems.
gums,
Beware that Direct Law on the bus is nothing worse than any conventional aircraft.
It has also the huge advantage to prevent the risk of any protection to kick in on false information.
It puts back the trim duty on pilot's shoulders and would have prevented AF447 to autotrim full up under STALL warning.
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Old 9th Nov 2011, 22:44
  #45 (permalink)  
 
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A great point, CONF.

With the FBW systems, there are usually "gains" that depend upon dynamic pressure, and I would prefer as a pilot to still have something I could count on. So in the dinosaur FBW I flew we had "standby gains" when the air data went south. Two values - one gear down, one gear up. Sure, if we flying at the speed of stink, the jet was sensitive. Gear down was about the same as normal.

I have yet to see the charts of the 'bus stick commands versus gee or roll rate.

For example, here's mine for roll command:



Now this is just the "command", and the actual control surface deflection could be 2 deg or 25 deg. So non-FBW folks may not completely understand the implementation.

As I understand it, the 'bus "direct" law is just the same as most all planes with 100% hydraulic control wheels/sticks and zero force feedback from the control surfaces. BFD, Been that way for most jets since the 1960's.

I would still like to see some of the control laws on a "block diagram" and I'll try to have one of mine scanned so all can see the inputs to each surface and the commanded movements using the stick.
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Old 10th Nov 2011, 03:52
  #46 (permalink)  
 
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No Conf iture
The fact that the PNF would ask a question shows that he was paying attention. I take it you have gotten your instrument rating? If so, you will recall that you are trained to trust your instruments not your unreliable estimate of what a slanted piece of metal may be doing or your sense of 'feel'. How someone perceives the same event can vary enormously especially under stressful conditions. Rely on the instrumentation (altimeter and artificial horizon) not on your eyes.
The yoke would not have made a blind bit of difference in this case. One can be sure that the PNF would have done nothing except summon the captain. If you take a look at the various reports you can see he perceived a problem but did nothing. Why would the yoke have made any difference to this lack of action? Remember he could see what was happening from his instruments. Do not get led astray by red herrings about yokes or otherwise. Your comments on the sidestick introduce a side issue which is totally irrelevant. The number of Airbuses fitted with sidesticks flying safely demonstrates this.
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Old 10th Nov 2011, 06:20
  #47 (permalink)  
 
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Oh my.
ALTERNATE LAW
(...)
Handling Characteristics (...)
In Roll, depending on the failure level, control is either normal (ALTN 1) or direct (ALTN 2). In roll direct, the aircraft appears to be very sensitive and bank stability is no longer active.

DIRECT LAW
(...)
Handling Characteristics
The handling characteristics are similar to a conventional aircraft. (...) In roll, aileron and spoiler deflection is proportional to sidestick deflection. Direct law works with the yaw damper to provide a minimal turn coordination.
I can't believe we're debating again what flight law they were in.
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Old 10th Nov 2011, 09:27
  #48 (permalink)  
 
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@CONF - "Dozy didn't answer" because he was out at work, so he can continue to pay for the privilege of joining in these delightful discussions. There have been too many LOC accidents in yoke-equipped airliners for the argument that it would have made a difference to stick, and we've already been round that hamster wheel more than once.

@gums - Your aerodynamic knowledge is beyond question, but both Alternate 1 & 2 are "roll direct" [Correction - Alt 2 is roll direct, yay early morning!]. The crews may be "trained in Normal", but in the sim there wasn't that much difference between Normal and Alternate roll handling. It was more sensitive outside the stall, but it took me all of a few seconds to get used to. Also, it looks like the trim is a red herring and the aircraft can be recovered in approximately 5,000ft on sidestick alone *even with full nose-up trim wound in*.

However - in the sim, the TRE noticed that I was trying aileron in the stall sequence and told me to use rudder instead. On this occasion he was standing over the pedestal having just wound the trim on and he could obviously see what I was doing in order to tell me not to do it.

This discussion isn't going anywhere until people start listening to each other and not just making assumptions based on their own prejudice against a specific design. I've never ignored anyone on this forum in my life until Lyman, and if I keep hearing "HAL" used to describe the Airbus system, those that use it are likely to join him.

Last edited by DozyWannabe; 10th Nov 2011 at 12:59.
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Old 10th Nov 2011, 11:35
  #49 (permalink)  
 
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Originally Posted by Old Carthusian View Post
No Conf iture
The fact that the PNF would ask a question shows that he was paying attention. I take it you have gotten your instrument rating? If so, you will recall that you are trained to trust your instruments not your unreliable estimate of what a slanted piece of metal may be doing or your sense of 'feel'. How someone perceives the same event can vary enormously especially under stressful conditions. Rely on the instrumentation (altimeter and artificial horizon) not on your eyes.
The visual contact with the PF's SS, the seeing of where the SS is at any given point of time, would have given to both PNF and Captain, the immediate, DIRECT, unaltered information of what the PF is doing.

Inferring the positions of the SS from instruments or anything else is INDIRECT information. When the instruments are not reliable it can be lethal.

The yoke would not have made a blind bit of difference in this case.
Of course it would, and not because it's a yoke. Ultimately, it's not about the "yoke" versus "SS", it's about the "SS" problem, which is its positioning in the A330, that can impact an exact, immediate, and precise visual perception of the actions on it.

As I've mentioned it in the past, and will do it again, that using INDIRECT versus DIRECT information, is an elementary system design issue that is known to create problems, where ever is present in any application where immediate and accurate perception of information is critical, one of which happens to be a passenger A/C cockpit.

Originally Posted by DozyWannabe View Post
@CONF - "Dozy didn't answer" because he was out at work, so he can continue to pay for the privilege of joining in these delightful discussions.
You're doing very well with your presence on this Forum. Ironically, the quality of the service brought to Airbus does not depend on how blindly one sticks to his mission.

Last edited by airtren; 10th Nov 2011 at 12:45.
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Old 10th Nov 2011, 12:14
  #50 (permalink)  
 
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@airtren

You and Lyman are sounding even more like you're one and the same - so what am I, a "servant of Airbus" or a "fanatical toady"? For the record I neither work for Airbus nor any of their clients or suppliers. I think modern aviation on a technical level is nothing short of a bloody marvel whether the aircraft come from either side of the Atlantic.

I prefer to think of myself as a neutral party with an inbuilt dislike of bullsh*t and preference for evidence and experimentation over hearsay. I was privileged enough to take part in one experimental session and I'm just telling you what I learned and observed. The response from those determined to hold on to the "AIRBUS BAD" philosophy was to bring control columns up *yet again*, with no evidence that they would make a difference.

Last edited by DozyWannabe; 10th Nov 2011 at 12:25.
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Old 10th Nov 2011, 13:40
  #51 (permalink)  
 
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Originally Posted by Old Carthusian
Rely on the instrumentation (altimeter and artificial horizon) not on your eyes.
So how do you do that now ... you need the Braille !?
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Old 10th Nov 2011, 13:41
  #52 (permalink)  
 
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Originally Posted by DozyWannabe
@CONF - "Dozy didn't answer" because he was out at work, so he can continue to pay for the privilege of joining in these delightful discussions. There have been too many LOC accidents in yoke-equipped airliners for the argument that it would have made a difference to stick, and we've already been round that hamster wheel more than once.
As a politician you twist the question not to address it and then invoke 'the hamster wheel'.
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Old 10th Nov 2011, 13:52
  #53 (permalink)  
 
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No sir, it has already been addressed - by people far more worthy of addressing it than me - in several places on the previous threads, hence the reference to the hamster wheel.

I also found it mildly amusing that my lack of an immediate answer was used as an indication that I did not have one, especially given the fact that a few months ago I left you an open goal to shoot at on another thread to talk about your specialist subject - namely Habsheim - and yet you never replied.

In short, I can't help but suspect that the anti-Airbus brigade "ain't got nuthin'" - to coin a phrase - to go on here, and are simply resorting to calling out their stock phrases.
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Old 10th Nov 2011, 14:20
  #54 (permalink)  
 
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Also, it looks like the trim is a red herring and the aircraft can be recovered in approximately 5,000ft on sidestick alone *even with full nose-up trim wound in*.
This may be a premature pronouncement. In Dozy's case, the trim came promptly back down with nose down stick. If I understand CONF's experience, it did not.

On AF447, it seems to have stayed solidly at its highest value. Was there long enough nose down to get it even moving a bit if it was working? Did the airspeed have to become valid before it would be enabled? Was some interlock stopping it?
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Old 10th Nov 2011, 14:53
  #55 (permalink)  
 
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In Dozy's case, the trim came promptly back down with nose down stick. If I understand CONF's experience, it did not.
According to this Stalled AF447 did not switch to abnormal attitude law
BEA says abnormal attitude law, which could have stopped autotrim, wasn't entered.
Maybe an artifact of the way the sim was forced into alternate in confiture's case ?
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Old 10th Nov 2011, 15:22
  #56 (permalink)  
 
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The A330 simulation referred to by that poster involved a full forward SS input but 'the nose did not come down'.

If the SS input did not change the existing dynamic, why would there be a requirement for the autotrim to change even in ALT2?

Autotrim is a 'TRIM' function for dynamic pressure changes which would alter the existing 'G'/longitudinal command and doesn't 'necessarily' follow the direction of SS movement unless the SS has some effect on the existing flight conditions.

These are two very different simulations, neither of which can positively be confirmed as representing either aircraft faithfully. Both posters may well want to monitor the SD FLT/CNTL page the next time they get a chance to do this.

The other side of the coin is that one or both of the simulations MAY actually represent the aircraft characteristics and certainly will up to the point that actual stall flight data was accumulated and incorporated in the simulator flight package. Beyond that, well there are a number of posters here that are sure they know what will occur...
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Old 10th Nov 2011, 15:37
  #57 (permalink)  
 
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There is (to me) a lack of technical discussion of the TRIM operation prior to its travel to NU stop at (near) the top of climb. The accepted wisdom is at 3 degrees NU (-3), the THS stopped moving. The rest of the climb was not followed (augmented, commanded) by TRIM.

It is said that it stopped because the elevators had requisite authority to change PITCH w/o the slab. This infers a data point at which the THS inhibits, leaving to the stick, commands that do not "require" THS follow.

This implies (to me), a computer generated point at which "maneuvering" is left to elevators alone. This is inconsistent (at least to me) with AB philosophy, even in ALTLAW2.

Had the TRIM continued, would we see less mayonnaise, and more stability in the climb to 38k? Was PF "hunting"? I think he was, and though that may be improper, I certainly see how that could happen. Afterall, we know he lost SA with PITCH/POWER from the git, with his intitial input.

The THS was articulating to, (and through) handoff to manual flight, why did it stop? It moved as the PF was ordering a climb, what was different about his initial input from the regime that prompted the FC to stop the THS in the zoom? Again, his initial input caused STALLWARN, so it wasn't for lack of emphasis, or authority, that the airframe sensed the lack of a need for continued THS?

What separates PITCH command (NOT LAW), in auto from PITCH command in ALTLAW2? In the time it takes (took), to climb 3k feet, the PF became accustomed to elevators/results? I realize there is room here for slandering the crew, but it seems to me, the computer was little help in the transition.

I'm looking for an honest answer to an honest question, not flames or politics.
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Old 10th Nov 2011, 15:42
  #58 (permalink)  
 
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Originally Posted by DozyWannabe View Post
...
For the record I neither work for Airbus nor any of their clients or suppliers.
I strongly believe that sentence. If you worked for Airbus, you would have been long ago silenced, in a way or another, as I know the perception of de-service to Airbus, and dislike of your type of defense.
I prefer to think of myself as a neutral party with an inbuilt dislike of bullsh*t and preference for evidence and experimentation over hearsay.
Your not recognizing the difference between DIRECT and INDIRECT information transfer combined with the advertising of a software engineering background is again, as it was in past posts of yours a clear indication of BS.
I was privileged enough to take part in one experimental session and I'm just telling you what I learned and observed.
As far as I am concerned the BEA report information on the Airbus simulation of the AF 447 case is sufficient, and any simulation on a non-A330 may be a valuable personal experience, but cannot bring true scientific value - it's rather a source of more speculation, and self-serving argumentation.

You may pretend to be, or would like to think as "neutral", but it's so obvious were you stand. Your personal attacks, ....
The response from those determined to hold on to the "AIRBUS BAD" philosophy ....
In short, I can't help but suspect that the anti-Airbus brigade "ain't got nuthin'" - to coin a phrase - to go on here, and are simply resorting to calling out their stock phrases.
the "anti-Airbus brigade" obsession, and your self assigned mission of defending Airbus at any cost, even those elements that are scientifically indefensible, for anyone that is a professional, and wrongly extrapolating faults with certain few Airbus elements, as being applied to the entire Airbus design, is a good indication of the type of alignment you're driven by.
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Old 10th Nov 2011, 16:17
  #59 (permalink)  
 
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Originally Posted by CONF iture
Sidestick is a sure way to waste valuable information in a multi crew operation.
Can anyone provide any verifiable source for this statement? If we were to believe it then right now thousands of FBW Airbi currently airborne are operating with considerable wastage of valuable information in a multi crew operation.

Originally Posted by Old Cartusian
The yoke would not have made a blind bit of difference in this case.
Probably wouldn't make a lot off difference in the accident sequence but it would make a whole lot in analysis phase: with independent sidesticks, there is no doubt who made which controls input.
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Old 10th Nov 2011, 16:34
  #60 (permalink)  
 
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Originally Posted by Lyman
The accepted wisdom is at 3 degrees NU (-3), the THS stopped moving.
Not true, see Interim #3, page 42.
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