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AF 447 Thread no. 4

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AF 447 Thread no. 4

Old 7th Jul 2011, 14:30
  #941 (permalink)  
 
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Originally Posted by BOAC
... not forgetting you are starting at 10,000fpm down and this will increase dramatically during your 'recovery'...
So what? Level at 250?
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Old 7th Jul 2011, 14:34
  #942 (permalink)  
 
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Perspective

Garage Years, # 926

The pictures are nice, but they show a misleading perspective. The photos are taken using a very wide angle lens, in order to capture the whole cockpit in one view. The downside of such a view is that objects seem to be much further away than they really are: you would think it is about a mile to the instrument panel, actually the observers knees are pressed against the pedestal, the view towards the sidestick is obstructed by the broad shoulders of the pilot, etcetera. If the pictures had been taken by a lens more closely resembling the acute field of view of the human eye, about four pictures had been necessary across from left to right and three rows from top to bottom.
Unfortunately, the pictures that I have to demonstrate this, contain recognizable pilots in view, so I will not post them here.

Chriss Scott, # 924

Well said, although I would change your statement
"why did the PF demonstrably embark upon and maintain a clearly unsustainable climb from level flight? "
into "a clearly unsustainable pitch attitude"

I know it runs into semantics, because you can reply that clearly they managed to sustain the pitch attitude all the way down into the ocean, didn't they, but is was the unrealistic pitch attitude that caused the speed loss and subsequently the stalled condition.
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Old 7th Jul 2011, 14:54
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Chris, A33Zab, the photo below, taken from the Right Seat, is of an A330 pedestal/trim wheel/trim indication. The trim indication is smaller than the A320 and is on the outside of the trimwheel. I recall it being highly visible from the front seats but it seems not visible from the Observers seat where the captain likely would have sat down, (cockpit arrangement diagram below).





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Old 7th Jul 2011, 15:19
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Having an AOA indicator in the cockpit doesn't necessarily imply that it be used as a control instrument or even incorporated in one's scan...

But it would be the first place I would look if I heard, "Stall, Stall".

The digital/analog indicator on the PFD in "some" 737 NG's is very unobtrusive...and in the aircraft without it, it's even more unobtrusive.
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Old 7th Jul 2011, 15:22
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Does the trimwheel move when autotrim is active ?
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Old 7th Jul 2011, 15:52
  #946 (permalink)  
 
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Garage Years,
Thanks for the photos and yes, EMIT, there is a perspective problem with that wide-angle lens. Both pilots' seats look to be well-aft of their normal in-flight positions, particularly on the A320 photo. When I sat on the P3 seat in its central position, my knees were almost touching the back of the centre console. The A320 P3 seat is adjustable sideways (but see below).

Lonewolf_50
,
In daylight it would be possible to see if the stick was being pushed or pulled, but it would be difficult at night due to the low illumination of the side console.

PJ2
,
Thanks for that better photo of the A330 centre console, and the seat plan. When sitting in harness in the P3 seat, it is still possible to move your torso to the left or right provided the inertia-reel shoulder harness is not locked. I think that should enable enough sideways head movement to see the left or right THS-position scale, but you may well know better! Do you have access to a sim?

In the seat-plan diagram, do you agree that both P1 and P2 seats are in the full-aft position, provided for ease of entry and exit?
And is the P3 seat moveable sideways, while remaining attached to the rear bulkhead? If so, it looks further aft than on the A320, so viewing the sidestick across the lap of a pilot may not be possible. Is it capable of being locked in more than one position, like the A320?
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Old 7th Jul 2011, 15:55
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Quote from mm43:
It is worth noting that no control surface systems fault warnings entered the the CMC and resulted in ACARS messages. There was plenty of time for them to be transmitted, and due to the manner in which the BEA produced their Note, it may be safe to assume that there were no control faults recorded by the FDR.

Yes, and I agree with the rest of your analysis.
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Old 7th Jul 2011, 15:57
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Originally Posted by OK465
Having an AOA indicator in the cockpit doesn't necessarily imply that it be used as a control instrument or even incorporated in one's scan...

But it would be the first place I would look if I heard, "Stall, Stall".
And what would be the next thing you would do?
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Old 7th Jul 2011, 16:05
  #949 (permalink)  
 
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Doesn't the "what" depend on if you are up high or down low with the gear down?
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Old 7th Jul 2011, 16:21
  #950 (permalink)  
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HN - whatever - it is really irrelevant since we understand NO effective recovery action was taken. Far more interesting (for me) is the answer to my query on #902 which I guess no-one knows? Very reassuring.
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Old 7th Jul 2011, 16:34
  #951 (permalink)  
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DJ77;
Does the trimwheel move when autotrim is active ?
Yes. Like the Boeings (although I can't recall the B767's arrangement), the trim wheel moves with trim changes in either manual or auto flight. It is in motion, quite frequently, with the small speed/pitch changes that normally occur.

Chris;
Thanks for that better photo of the A330 centre console, and the seat plan. When sitting in harness in the P3 seat, it is still possible to move your torso to the left or right provided the inertia-reel shoulder harness is not locked. I think that should enable enough sideways head movement to see the left or right THS-position scale, but you may well know better! Do you have access to a sim?

In the seat-plan diagram do you agree that both P1 and P2 seats are in the full-aft position, provided for ease of entry and exit?
And is the P3 seat moveable sideways, while remaining attached to the rear bulkhead? If so, it looks further aft than on the A320, so viewing the sidestick across the lap of a pilot may not be possible. Is it capable of being locked in more than one position, like the A320?
Sitting in the center seat it is entirely possible to move sideways slightly and observe the trim position. Other considerations in reading the trim setting would be turbulence, the fact that the indication and pointer are on the top of the indicator and one is viewing from the rear, (there is no parallax however).

Yes, the forward seats appear to be in the full-aft position - the rails take each seat slightly outboard for more room - still, it is a bit of a step across the inboard part of the seat to get in.

The third (center) seat in the A330/A340 is on rails, well ahead of the rear bulkhead and cockpit entrance. The rails take the seat from the full forward position, which is about eight to ten inches behind the aft edge of the pedestal, rearwards about two feet behind the pedestal and thence to starboard about two feet, maybe a bit more. The fourth observers seat is well to starboard, behind, and to the right of the F/O position, and fixed to the bulkhead.

In my opinion one cannot adequately see or judge what movements on the stick are occurring. Most movements are tiny - a pitch-up such as this one might take a two, maybe three centimeter movement aft.

When I first checked out on the A320 I really liked the "Iron Cross" feature because it told me what the other stick was doing. On my first takeoff, the symbol disappeared at lift-off and I distinctly recall being surprised because I thought it was a natural and needed bit of information. Over the years I grew used to using many other cues as to what the other stick was doing and the Iron Cross would not indicate the tiny movements referenced above, but the airplane would. Communication between crew members on this type is vital where any possibility of confusion exists - it is a "cerebral" airplane in that sense, displacing physical cues with digital cues which must go through an interpretive process first. That was "the veil" that I felt when I first sat in the A320's cockpit. The "interpretive process" becomes natural and as swift as in a conventional cockpit after a while and one can get very good at it, all subconsciously of course.

I don't know the arrangement of controls in fighters, so let me ask those who flew them - do fbw fighter aircraft have a way of conveying to the pilot in the front or the back seat, what control inputs the other pilot is making or do both sticks move, (via mechanical connection, etc)? Are there back-driven autothrottles in any types - how is thrust control arranged? Is it standard to display AoA in every fighter?
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Old 7th Jul 2011, 16:38
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Svarin, #848
Do you mean subsystems inside one given computer/unit, inside one PRIM or
inside one ADR for example ?
I'm thinking about something that has one function. An adr is probably a
good example, as it's function is simply to measure air data parameters
and send the results elsewhere. It's functionality is quite limited and
the only thing the internal software must do is produce accurate results
when the inputs are within range and an error message when it finds that
the inputs exceed the limits of the measurement hardware. That may be a
little oversimplified, but it's basically a box that converts barometric
pressures to electrical signals that other parts of the system can
understand. Because of the limited functionality, it's not too difficult
to devise tests that provide a high degree of confidence that the thing
is working to spec.

The complexity problem arise when many of these individually reliable
boxes are connected together, as you then have time as an added variable
thrown into the mix. Depending on conditions, the various boxes send
their messages with slight variation in timing, so that, for example a
data or error message may arrive at one box before, or after, a message
from a third, or fourth. The testing and validation problem is one of
how to model or prove the system correct when timing variation, together
with all possible system operating and failure modes, probably gives
millions of possible combinations / sequences to test against.

You might compare an adr to a fiddler in the local pub, while a complex
interconnected system is more akin to a symphony orchestra. If the
orchestra is playing Bach, then you're probably ok, so long as everyone
is in tune and in sync. Jazz, and you might be in big trouble :-)...
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Old 7th Jul 2011, 17:20
  #953 (permalink)  
 
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Hi BOAC,
Originally Posted by BOAC
Originally Posted by A33Z #902
The system compensates almost 100% for trim changes, due to speed and configuration changes.
- still hoping someone can enlarge on this please? Anyone?
Far more interesting (for me) is the answer to my query on #902 which I guess no-one knows? Very reassuring.
What is it you don't understand about maintaining a pitch attitude (modified for 1g) by auto-trimming out the load due to changes in air speed?
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Old 7th Jul 2011, 18:49
  #954 (permalink)  
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Well, rrat - it is to see HOW exactly it does it, do you see? More to the point, do you know? Are there ADC inputs to THS setting? Do I assume you know?

Thanks for replying, by the way.
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Old 7th Jul 2011, 18:57
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PJ 2 #944

In F-16, no feedback from one sidestick to the other.
Even more, in the F-16 the sidestick cannot be moved like in the Airbus. The signal is the FORCE that is exerted on the stick, not the angular displacement.
In the original, F-16 the stick was really as rock solid as an iron pipe, it turned out that that configuration was not so nice for finer control, so a little bit of play was built into the versions from Block-10 onwards (maybe 2 or 3 millimeters of movement at the top of the stick).
Philosophy for the non-moving stick is as follows: there is a "perfect" relaxed steering attitude for your hand, the stick is built in that attitude. If the stick had to be displaced angularly for generating steering signals, that would mean rotating your hand out of the perfect steering attitude - would be a painful exercise under a 9 g load.
In the Rafale, the French originally built a sidestick akin to the Airbus setup. It took some rough remarks from an F-16 pilot to get the factory to switch to an F-16 type stick, after that the Rafale was a fine flying machine.
Info on what the other guy is doing comes from aircraft response. No such thing as "Dual Input" calls as in Airbus. Does it always work out fine that way? No, there has been a case in F-16 history when a non F-16 rated backseater kept his feet well away from the rudder pedals; unfortunately that brought his knees very close to his sidestick. When his G-suit inflated during a dive pull-out, the expanding suit pushed the sidestick sidewards, unexplained sudden roll, didn't work out well.

Autothrust in a fighter, no, everything is done manually. Exception, I believe, Saab Viggen, for landings on short runway strips.

Angle of Attack indicators in fighters? YES.
And, yes, they are actively used.

AOA in civil airplanes - unfortunately, mostly in disguised form: the red minimum speed indication on the speed tape is actually AOA driven, ever notice how it moves up as you increase g-load? (OK, that is observed mostly in the SIM, e.g. during unusual attitude recoveries). Too bad, that when the speed tape is taken away because of system errors, you also loose your disguised AOA indication.
So yes, I would like an AOA indicator in civvie aircraft.
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Old 7th Jul 2011, 19:07
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Trim

PJ 2 #944

In the 767, there is no trim wheel and no trim actuation noise. Trim position is indicated on a tape style indicator on the pedestal, approximately next to the throttle quadrant. Only time you really use it, is for setting of take-off trim, after that, trim more or less disappears from your conscious memory.

(PJ 2 knows, but info for others)
When flying manually, you trim as needed. A/P trim works without pilot involvement.
Tricky thing is, autopilot may trim very much nose up without your conscious knowledge. Results are not only awkward in this AF447 case, but also in the B-737 Turkish 1951 stall accident in Amsterdam, and in many stall incidents.
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Old 7th Jul 2011, 19:09
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Originally Posted by BOAC
The last para regarding 'lock' at 8+ is particularly alarming.
May I point you to the fact that similar statements would have to be made for most if not all types of airliners ?

Full NU Trim will overpower the elevator not only in the A330.

And please don't assume it can only happen in an Airbus that you are handed an Aircraft with Full NU trim. AP commanding full NU Trim quitting and handing over a plane with 10 + NU Trim.
Has happened on different types.


I would also appreciate an explanation of how the trim compensates for 'speed' (and which 'speed') ie is its response a direct function of 'neutralising' the resulting elevator input required for speed change or is there a direct 'speed' function for the THS?
Although I don't know for sure how it is technically solved in the A330 the system behaviour strongly points to an inertia based (read IR) system rather than anything ADR.
As always happy to stand corrected.

Last edited by henra; 7th Jul 2011 at 19:40.
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Old 7th Jul 2011, 19:12
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PJ2,
Thanks for confirming that the THS-position indicator is visible from the P3 seat, as I expected. However, I should admit that, on entering the low-lit cockpit from the front vestibule (or galley?) area, there is a potential problem of adjustment to night vision. (I know that the vestibule lights probably dim automatically when the cockpit door is opened, but that only serves to protect the night vision of those already in the cockpit.)

Quote:
In my opinion one cannot adequately see or judge what movements on the stick are occurring. Most movements are tiny - a pitch-up such as this one might take a two, maybe three centimeter movement aft.

You are right, particularly in the case of pilots who prefer to hold the stick continuously in the palm of the hand, rather than making inputs and then releasing. With the roll problems the PF was experiencing, and the reversion to Roll-Direct law, he may well have been holding it in the palm of the hand. As I've previously commented, the low illumination of the side console at night would also make it very difficult to see the stick.

[EDIT] There is another slight possibility re cockpit illumination. Being in a remote area, and in the vicinity of thunderstorms, the crew might have elected to put the dome light on. This would not be my choice, but I've seen it done. It floods the whole cockpit with light.

Last edited by Chris Scott; 8th Jul 2011 at 00:05. Reason: Para added.
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Old 7th Jul 2011, 19:22
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Cool

Hi,

Sitting in the center seat it is entirely possible to move sideways slightly and observe the trim position. Other considerations in reading the trim setting would be turbulence, the fact that the indication and pointer are on the top of the indicator and one is viewing from the rear, (there is no parallax however).
Well .. as the THS was in full deflection .. honestly .. regarding any error of interpretation .. we can put the eventual parallax out of the game.
I assume if one check the pointer of the THS wheel .. it will see immediately that the pointer indicate a full deflection ....
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Old 7th Jul 2011, 19:32
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Hi BOAC,

In Direct Law it's like a Boeing, you don't need any ADC input to manually trim the elevator stick load out.
In Normal or ALT LAW the autotrim works in a similar way to maintain the (modified) pitch attitude. I can't see why it would need any ADC input either.
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