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AF 447 Thread No. 10

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AF 447 Thread No. 10

Old 22nd Aug 2012, 10:27
  #21 (permalink)  
 
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Originally Posted by PJ2
The flight data shows that the THS reached the NU limit at the same time that the stall warning occurred, ...
Apart from differences in aircraft, configuration, and altitude (A320 in landing configuration vs A330 clean), there was a difference in the rate-of-approach to the stall. The A320 reduced the speed at 1 kt/second, the A330 at about 1.7 kt/second, increasing.
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Old 22nd Aug 2012, 12:43
  #22 (permalink)  
 
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Originally Posted by HN39
OK465:
Thank you for your post #1392. I understand most of what you are saying, except when you say "a more relaxed SS input". A valid experiment would compare the two cases at exactly the same entry conditions and exactly the same pilot inputs. On 'theoretical grounds' I remain convinced that the resulting airplane trajectories would be identical up to the point where the elevator reaches the stop.
After re-reading your posts and also the one here by OK365 and that other one here by IF789, I can confidently think that I now understand your main idea :

What you're talking about here is maintaining the Nz law but on the elevators alone, without the trim participation.

Such behavior would be in total contradiction with the logical Airbus philosophy where as soon as the THS stops moving automatically, whatever the circumstance, flare, alpha prot range, direct law, the pilot needs to apply a constant deflection on the stick in order to obtain and maintain a desired attitude (as long as he do not manually trim).
To maintain the Nz law on the elevators alone would be totally illogical IMO.
It would be also like masking the reality to the operator.
At this point what is needed is Direct law, why anyhting else ?

People around like to think about more automation, or OTOH to not change anything to the present logic, in reaction to AF447, when the most logical path would be to simply switch to less automation as soon as unreliable data are detected by the system.

If the system had that humility to further switch to Direct law when the UAS was detected, AF447 was an all different game with a probable landing in CDG.
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Old 22nd Aug 2012, 13:13
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Originally Posted by CONF iture View Post
when the most logical path would be to simply switch to less automation as soon as unreliable data are detected by the system.
Autotrim is not automation in the same sense though - and it's only "the most logical path" to those who believe that Airbus should do the same as Boeing and have Normal and Direct only.

If the system had that humility
Systems don't have humility, or arrogance for that matter. They just follow mechanical or digital logic.
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Old 22nd Aug 2012, 13:58
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Originally Posted by CONF iture
If the system had that humility to further switch to Direct law when the UAS was detected, AF447 was an all different game with a probable landing in CDG.
What were the PF's targets, and why would they have been different in direct law? EDIT:: Would direct law have prevented these targets to be achieved? Would there have been less "mayonnaise stirring"? Would direct law have prevented full sidestick deflection?

Last edited by HazelNuts39; 22nd Aug 2012 at 15:05.
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Old 22nd Aug 2012, 15:23
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Just as Autotrim acts over longer term than Stick input (elevators), is there a relationship between the pilots' knowledge of this and an attempt to maneuver without its help? It seems there may be a conscious effort to avoid changing the AoI of the aircraft by using quick inputs, followed by opposites?

Has anyone explained this rapid use of the SS? Does it relate to a 'workaround' of the trim? It is especially odd considering the altitude, and airspeed, to see large and rapid stick displacement. Any Bus pilot care to address?
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Old 22nd Aug 2012, 15:33
  #26 (permalink)  
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CONF iture;

You're an A330 pilot, (captain?) and know and understand the requirement to use and adhere to SOPs and to employ standard CRM communications and problem-solving techniques. The unilateral actions by the PF, within a second of the start of the UAS event do not conform to standard responses to abnormalities, nor did the actions of the PM as the problem rapidly degraded.

HN39 states that a reversion to direct law would not have made a difference in this case. I agree. What should have been a straighforward response to an abnormal event instead took the aircraft rapidly out of stabilized cruise flight and beyond the boundaries of controlled flight. It is no surprise that what the airplane presented them with while well beyond test-pilot territory confused them because they acted outside of expected and trained responses. This kind of response is not specific to the A330, or a Boeing design or a Douglas etc and so making changes to a design only covers this one specific response; where will the next "abnormal" come from which again challenges a crew who may exhibit a similar response?

These are issues to consider and not dismiss in favour of a singular focus on a specific type of aircraft or flight control system.
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Old 22nd Aug 2012, 15:40
  #27 (permalink)  
 
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PJ, this leaves open to question, in my mind, just what it is in the Air France simulator periods that one must demonstrate or practice in order to comply with the sim period requirements.

A hard question to ask the chief pilot at AF:

What tasks and problems am I to stress or require in the limited simulator time for my __ X number __ of pilots and how shall I implement that to get the best training value for the money spent?

I am not sure how the investigation will go, insofar as any legal proceeding vis a vis Air France, but I'd be very, very interested in seeing the answer to

What does the AF training and currency program look like? What is done versus what is on paper?

That's a small piece of the puzzle, as it would address far more than UAS issues.
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Old 22nd Aug 2012, 16:05
  #28 (permalink)  
 
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PJ2

You say... "The unilateral actions by the PF, within a second of the start of the UAS event do not conform to standard responses to abnormalities, nor did the actions of the PM as the problem rapidly degraded."

Not exactly, and that is the first time I have seen a statement of that sort relative to the differences in Flight Law relating to manual flight. You go on to urge the commingling of a/c types other than Airbus A330 when addressing standards of high altitude assumption of manual flight.

I cannot agree. PF took control, and announced it, his inputs were consistent with handling required, and no one will ever know if he sussed ALTLAW2b. Since the outcome of this event resulted in the deaths of 228 souls, I think it is critical that the initial induction of LOC is understood specific to this type.

Respect,
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Old 22nd Aug 2012, 16:15
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Danger Probably a Red Herring (?)

I checked the forums but didn't find a thread about this. Fifty incidents involving total cockpit power loss in A320-series planes. I didn't feel comfortable starting a new thread, so I post this here. Be aware that this is a two-page article:

Airbuses suffer cockpit power failure, await fixes - seattlepi.com

Obviously, not a word about whether this problem occurs in 330/340 flight decks.

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Old 22nd Aug 2012, 16:57
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That's 50 incidents in 23 years. I wouldn't be surprised if similar issues had cropped up on the widebodies (despite the physical implementation being completely different). But I'm convinced that such a failure did not play a part in AF447 because throughout the sequence on the CVR, all the crew are maknig reference to attitudes, altitudes and ECAM messages which would not be visible if a panel failure had occurred.
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Old 22nd Aug 2012, 17:49
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Lyman,
PF took control, and announced it, his inputs were consistent with handling required
Can you explain how this statement is true?
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Old 22nd Aug 2012, 17:59
  #32 (permalink)  
 
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Originally Posted by Turbine D View Post
Can you explain how this statement is true?
It isn't - it's a blatant trolling* exercise, best ignored.

[* - and that's "trolling" in the classic "fishing" sense - a deliberately incorrect statement, fashioned to attract replies - as opposed to the more recent definition, meaning outright inflammatory statements against a person or group.]

Last edited by DozyWannabe; 22nd Aug 2012 at 18:04.
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Old 22nd Aug 2012, 18:22
  #33 (permalink)  
 
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Garbage. Upon loss of Autopilot, PF took controls, and announced it. He then input in two axes, both needing handling, and both correct in direction.

From then on, things went South, But don't you dare try to envelop his initial actions into three years of spin...

Troll? That is a stretch.... For three years on, people have been spinning the accident into ever fanciful and flimsy conclusions of PE, whilst defending and lauding the airframe as perfection personified.....

Hamster wheel under construction, and with odious helpings of wannabe "pilots" waxing scholarly on things that will never be known.

You take the freaking cake. Presumption piled on assumption...
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Old 22nd Aug 2012, 18:53
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Originally Posted by Lyman View Post
He then input in two axes, both needing handling, and both correct in direction.

For three years on, people have been spinning the accident into ever fanciful and flimsy conclusions of PE, whilst defending and lauding the airframe as perfection personified.....
Two more statements of (at best) dubious provenance, intended to elicit a response. I'm not biting this time - I wonder what will hapen if people stop biting altogether?

Last edited by DozyWannabe; 22nd Aug 2012 at 18:54.
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Old 22nd Aug 2012, 19:12
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I agree with PJ2 about his analysis of the crew reactions and our discussions about control law reversion, as well as the function of the THS.


The thing that bothers me is the lack of "feel" that the system provides to the pilot. I fully understand the Nz law, which seems to me primary for the 'bus, and corrected for pitch attitude with little regard for AoA. That's important - corrected for attitude.

So you don't really have a one gee command if not fairly close to zero pitch attitude. Hence, HAL is trying to achieve 0.87 gee at a 30 degree pitch attitude, and less if you figure the sine/cosine/etc .

The big deal with the THS is that it is trying to relieve the required stick pressure/displacement if the pilot is holding a command other than the one gee corrected for pitch attitude. For a commercial airliner, this makes perfect sense to this dinosaur.

The problem is that simply releasing pressure/displacement does not give you the "feel" that we used to have when the basic aero of the jet tried to achieve a trimmed AoA. In other words, going too fast or pulling too hard, the jet would try to go back to the trimmed AoA/gee if we relaxed the pressure/displacement ( NOTE: Our primitive FBW implementation used pressure , not stick displacement, so simply relaxing pressure would command the jet to go back to the trimmed gee). . So the THS concept seems to get in the way of what we old farts "felt" when we were commanding something that the jet was not trimmed for. Does this make sense?

The Boeing FBW implementation appears to use a mechanical "artificial feel" that requires ever-increasing pressure/movement to maintain other than trimmed gee/AoA. I don't see this on the 'bus.

My opinion after these last three years of discussion and analysis of the 'bus flight control laws leads me to this :

- The jet performed exactly as designed.

- The THS logic and lack of increasing stick pressure to command an unusual pitch attitude/AoA "helped" to maintain a condition that made a recovery very difficult for the average or even above average pilot that had not thought this scenario through. The 'bus has postitive longitudinal stability thoughout it's envelope unless the fuel trim system is completely FUBAR. So the jet would appear to act as we old folks would expect in the so-called "direct law". Unfortunately, the system keeps trying to achieve a gee-command ( corrected for pitch attitude) and there's no obvious indication/feeling via the stick that the plane wants to achieve an AoA versus a gee.

- The AoA inputs to the flight control logic should be emphasized more IMHO, and good AoA sensors work well down to 50 or 60 knots of actual dynamic pressure, regardless of what the pitot-static system(s) is telling the system.

- Crew coordination and a clear "chain of command" is essential if you are flying a "crewed" airplane that allows more than one pilot to have a control input. My only experience in "crewed" planes was as an instructor in a family model of two jets ( ultimate authority!) or in the VooDoo, which had a radar operator in the back seat with no flight control inputs. So I defer to those here who have thousands of hours dealing with the "CRM" issue. All I ever had to do was ask, "Gums? What the hell are you doing?"
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Old 22nd Aug 2012, 19:12
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Originally Posted by DozyWannabe
Two more statements of (at best) dubious provenance, intended to elicit a response. I'm not biting this time - I wonder what will hapen if people stop biting altogether?
What if that knife cut both ways?
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Old 22nd Aug 2012, 19:23
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Then maybe the spectre of a thread 11 - in which we all go over the same ground, discussing nothing new - would be banished.

I for one am more than comfortable with that.

EDIT:

Originally Posted by gums View Post
The Boeing FBW implementation appears to use a mechanical "artificial feel" that requires ever-increasing pressure/movement to maintain other than trimmed gee/AoA. I don't see this on the 'bus.
The designs are fundamentally different in their approach, despite both being underpinned with digital technology - I've gone into detail on the differences in approach before, so won't bore you with it again. An (admittedly rough and incomplete) analogy would be comparing the Viper with the original F/A-18 Hornet. Both used FBW - but whereas the Viper's flight deck layout was a significant departure from what had gone before, the Hornet's layout was more traditional.

Last edited by DozyWannabe; 22nd Aug 2012 at 20:12.
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Old 22nd Aug 2012, 19:57
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Hi gums,

I agree with PJ2 as well, there doesn't appear to be any reason to believe there was anything wrong with the aircraft. Regarding the Viper that you flew, is there any change to the latest F-16 models as to handling and "feel" via the sidestick? Is sidestick pressure rather than displacement still used?
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Old 22nd Aug 2012, 20:16
  #39 (permalink)  
 
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Originally Posted by MachinBird
Not really a surprising result. In Normal and Alternate 1&2 Laws, holding the trim wheel can result in inadequate control effectiveness for proper operation of the flight control system.

Of course, if the flight control system is off in La La land, you still can seize control, but it will be at the expense of someones free hand and (apparently) smooth control. If you do this, you are fully responsible for observing all aircraft limits, so I can understand a bit of caution in applying this technique, but ultimately you do have the "hammer" should you want to use it. The crew of AF447 could have stopped the trim from its run to the nose up trim limits if they had been aware of the motion.

Just as there isn't any good reason to point the nose high in the air at cruise altitude, there is also no good reason to have full nose up trim dialed in at cruise altitudes.
Maybe you meant to say "touching the trim wheel" vs "holding the trim wheel". If you go back and read what I wrote, I spoke of attempting to trim the Bus with the manual trim wheel. I only "held" the trim wheel in an attempt to manipulate it for its primary purpose of trim control.

Can you confirm that the AF447 crew could have held the trim wheel and stopped the trim from its run to nose up limits? In my experience in a 320, I was able to eventually force a small pitch "bobble" when moving the trim wheel to the limit of the available "one hand grip" travel. The wheel feels like it's attached to a bungie cord and with a hundred fifty souls behind me, I had no intention of going anywhere further with trim than that initial "one handful movement".

Can anyone confirm what would happen if a pilot, on a test flight of course, just held the trim wheel?

Why weren't they aware of the continuous trim motion?

Why no "trim in motion" claxon, or other indication?

The system can warn of a jammed stab, but not a run away stab.

Oh I know, it wasn't run away, it was just doing as it was told. And a find job it did.
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Old 22nd Aug 2012, 20:30
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Originally Posted by TTex600 View Post
Can you confirm that the AF447 crew could have held the trim wheel and stopped the trim from its run to nose up limits?
...
Can anyone confirm what would happen if a pilot, on a test flight of course, just held the trim wheel?
From an earlier post by A33Zab:

Originally Posted by A33Zab, thread 4, post 327
"An override mechanism, which is installed in the PTA (Pitch Trim Actuator),
makes sure that the mechanical control through the trim wheels cancels the electrical control.
When a manual command is made with the trim wheels, the override
mechanism gives priority over the electrical command from the FCPCs.
It mechanically disconnects the PTAoutput from the mechanical input(via
electro-magnetic clutch) and also operates the overriding detection
switches which in turn signal the FCPC's to stop any electrical command
from the FCPC's."
Why weren't they aware of the continuous trim motion?
They should have been - continuous trim motion in the FBW Airbus design is a given in Normal and Alternate laws.

Why no "trim in motion" claxon, or other indication?
Because the trim is more-or-less constantly in motion, it would quickly become a nuisance. A warning that the trim is exceeding a certain value, on the other hand, would be a viable proposition.
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