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AF 447 Thread No. 12

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AF 447 Thread No. 12

Old 25th Feb 2015, 08:23
  #1061 (permalink)  
 
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Originally Posted by Lonewolf_50
If that wasn't your intended meaning, then perhaps what you meant to say didn't come across.
True. Point I tried to make gently but unsuccessfully: intended public of manuals is pilots who fly or will fly Airbi and they do understand their FCS enough for everyday use and abnormals. Participants in anonymous fora and bloggers who complain about it have to demonstrate they don't, in order to make their unrealistic ideas look plausible. That's all there really is to it.

Originally Posted by Lonewolf_50
if your assertion behind that line is that one or two of the three in that AF crew were unworthy of certification and unable learn this oh so complicate thing, but became regular crew at AF, that is another matter. Is that your position?
No. This is very crude (and unsurprising) falsification of my position.

AF crew was qualified and experienced on 330, thence they must have known something about their flight controls and apply it in practice to be let to play with their aeroplanes and then survive flying them. Issue is that at the crucial moment they forgot everything they learned not just about A330 but about basic aerodynamics and performance also and that's what killed them. BEA's report does not hide modern psychology's helplessness when faced with task to explain a pilot who suddenly tries to unreasonably go against the fundamental laws that keep him aloft, with inevitably tragic outcome.
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Old 25th Feb 2015, 10:00
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Originally Posted by vilas
Dutch roll on B707 has no similarity in Airbus. 707 was notorious for that and whatever little time I had on 707 I experienced it on a commercial flight, yaw damper failure kept causing vicious yaw and turn till I think the weight and altitude reduced to a certain level. I was trained for yaw damper failure in A310 simulator and it was nothing as compared to 707. Airbuses are not prone to this. So KC 135 comparison is futile.
Dutch roll is a normal oscillation regulated by yaw damper. Divergent dutch roll is another thing, one way among others toward PIO/APC on three axis, who have a great variety of causes and dynamic, often aggravated by unadapted pilot's response.
Learning from any of these accidents or incidents is never futile !
Switching the yaw damper to ON if OFF, or OFF if ON is far to be enough following a correct rapid diagnostic.
Pilots are mostly untrained to reduce or stop oscillations in their actual and always surprising form. A whole culture to understand unsteady dynamic is missing to pilots. Engineers building Y/D and Stability Augmentation systems who have that closed loop culture don't imagine all the cases of oscillations -rarely pure sinusoids- involving pilots by actions or only effects in flight in real and short time.
That must be improved and cooperation and communication between pilots and aeronautic and systems engineers enhanced and not limited to test flights. The solution is not replacing true test pilots and test flight engineers by airline pilots. Oscillations need to be studied by pilots in many forms.
Military are concerned as well as civilian pilots, both have their flight envelope limit where understanding a little more in the marge may switch life to death.
Of course it has a cost, not decreased by ultra-modern FBW or aging planes. But accidents have greater cost.
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Old 25th Feb 2015, 11:57
  #1063 (permalink)  
 
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Originally Posted by Clandestino
True. Point I tried to make...
Thank you for explaining what you meant.

Points raised on training, proficiency, and currency in the original threads I won't repeat here.

The "why" of the crew's decision and actions remains up in the air, unlike the aircraft and the souls who were traveling from Rio to Paris.
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Old 19th Mar 2015, 05:10
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'Ullo, everybody...

Originally Posted by Machinbird
Maybe they really should tell you something that you really might need to know like "Alternate Law" or as in the case of the Perpignan A320, "Direct Law."...
The Flight Control Law shouldn't really matter that much. In real terms, Alternate Law means "take extra care with your inputs, as it's now possible to stall your aircraft" and Direct Law means exactly the same with the addition of "...and you have to do the trim yourself". No matter what control law one is in, you should never deflect your stick to the stop unless you've got a damned good reason to do so.

Originally Posted by Machinbird
All circumstantial except for one thing. Just why was AF447 oscillating in roll during those first 30 seconds?

Didn't we cover this a few months ago?

Originally Posted by DozyWannabe

It may be possible that the roll direct aspect of Alt2B might have thrown Bonin initially, but consider these points:
  • Bonin had *no* training or experience in high-altitude manual handling in Normal Law, let alone any of the Alternate configurations - how could he have known what to expect (put another way, how could he be 'thrown' or 'confused' by the control law change when he had no prior experience with which to compare it)?
  • Take a close look at the "Lateral Wind" graph alongside the pink trace on the "Roll Attitude" graph. At the moment Bonin took manual control, a 25kt right crosswind with an updraft component suddenly dropped sharply. The pink trace indicates that even with no input, the simulated aircraft actually rolls about 2 or 3 degrees to the left from inertia.
  • The right crosswind returns and averages around 30kts for the next 12 seconds, but at this point, Bonin's initial overcontrol to the left has him disorientated and making input reversals.
No matter what control law you are in, or even if you're in a type with traditional controls, I'd imagine that kind of initial quick reversal would be very tricky to damp out manually, and practically impossible if you've just been handed control from the AP with little warning. The return of a near-constant right crosswind for the next 12 seconds can only complicate matters further.
Originally Posted by Goldenrivett
Better tell BAE they are wasting their time then.
...
"The biggest drawback of the “passive” sidesticks now used in civil aircraft is the lack of control feedback from the aircraft or the other pilot."
Of course, being sales literature, they don't enumerate the potential benefits (e.g. what happens when someone wires one side up backwards?)

PJ2 has the right of it here, and so (for the most part) does Clandestino.
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Old 19th Mar 2015, 10:19
  #1065 (permalink)  
 
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Having flown a number of different piston, turbo props and jets in my time, I am a big fan of the Airbus FBW philosophy. It does not react as a conventional aircraft does, but I have personally adapted, and have no problems with that - I prefer it actually.

However, I think that where Airbus FBW IS deficient is that the side sticks are not mechanically or otherwise linked.

This causes problems with CRM and SA, and for example training cadets to flare and land. With ever other type I have flown, I have been able to "follow through" by softly holding the controls to learn what inputs the Trainer was making at each stage of the flare and landing. However, with the Airbus FBW, this is not possible. It is difficult to even see the side-stick on the other side of the cockpit, let alone assimilate what inputs are being made.

Those poor b@stards in AF 447 never really had the chance to realise what Bonin was doing, (and why the hell was he doing it anyway?), but with linked side sticks, they could have.
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Old 19th Mar 2015, 11:56
  #1066 (permalink)  
 
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Linked side sticks
S/S inputs are summed. PF moves his, if linked PM's moves as well, doubling the input.
To avoid doubling the demand, software is required to recognise when a sidestick is being moved by the pilot, and when it is being moved by the linking mechanism. Anyone fancy writing that, or explaining how they can be linked?
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Old 19th Mar 2015, 12:25
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Anyone fancy writing that, or explaining how they can be linked?
Just a guess but how about something like:

When both Active Side Sticks move together, the inputs are summed and the controls move the normal amount (full & free).
If the override button is pressed, the side sticks become passive. The take over side's input is then doubled (full and free controls again) and the locked out side's input is ignored.
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Old 19th Mar 2015, 12:58
  #1068 (permalink)  
 
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Forget the override button... I will rephrase the question...

I move my sidestick. If the other one moves because they are linked, how will the FCS know it should ignore the input, yet not ignore the input when the other pilot moves that sidestick?
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Old 19th Mar 2015, 13:49
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If the other one moves because they are linked, how will the FCS know it should ignore the input, yet not ignore the input when the other pilot moves that sidestick?
I will rephrase my answer.
The FCS doesn't ignore the input - it sums both active side sticks (which are moving together) it doesn't matter if the other pilot is moving the side stick or not.
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Old 21st Mar 2015, 13:37
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We recently had an experience in A330 SIM when ADRS were blocked for unreliable speed pilot raised the pitch to deal with increasing airspeed. The aircraft went in deep stall and the nose dropped. The aircraft went in dive and could not be pulled out as the elevators had lost their effectiveness. it shook up the pilots but then we realised unless the data of that specific manoeuvre flight path is in the software the SIM behaviour cannot be taken as realistic of the aircraft flight path. So using SIM for AF447 type testing will be erroneous.
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Old 22nd Mar 2015, 21:56
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Originally Posted by Dozy
The Flight Control Law shouldn't really matter that much. In real terms, Alternate Law means "take extra care with your inputs, as it's now possible to stall your aircraft" and Direct Law means exactly the same with the addition of "...and you have to do the trim yourself". No matter what control law one is in, you should never deflect your stick to the stop unless you've got a damned good reason to do so.
Dozy, as you intimated, mostly the flight control law doesn't matter that much with respect to the way you make your control inputs.

When you start getting into Direct modes such as Alt 2B with Roll Direct, or into full Direct Law that assurance breaks down. If your attention is directed elsewhere (like outside the aircraft or at controlling a roll oscillation) you might well be setting off down a wrong path in controlling your aircraft.

In Bonin's case, he began flying with one set of roll gains expected and experienced a much higher roll gain with lessened damping than he was accustomed to. If the aircraft had the ability to enunciate: Alternate Law-Roll Direct, right at the A/P drop, that would have helped his situational awareness.

In the XL Airways A320 at Perpignan, that Captain needed to know that his aircraft had dropped to: Direct Law-Manual Trim in the initial stall, but he was looking out the window at a rapidly rising nose, holding the stick full forward and waiting for the automatic trim to lighten the load on the stick.

Maybe we need an automated Flight Engineer in the Airbus that you can talk to and which will inform us of changes to aircraft status by the verbal channel instead of the highly loaded visual channel. Might help in the Boeing as well.

There is no doubt that the Airbus human interface is eminently flyable, but it could probably be improved.
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Old 27th Mar 2015, 04:49
  #1072 (permalink)  
 
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Originally Posted by Machinbird
In Bonin's case, he began flying with one set of roll gains expected and experienced a much higher roll gain with lessened damping than he was accustomed to.
With respect, riddle me this; how do you expect Bonin to have a feel for what the "normal" roll gains are and therefore be thrown by the difference in Alt2B when it is on record that he had no training and likely little or no experience in manual handling at high altitude?

It's a logical certainty that one cannot be wrong-footed by a change in response when one has no experience of what the normal response is, surely?
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Old 27th Mar 2015, 17:23
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That's interesting ... Any official report somewhere ?
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Old 27th Mar 2015, 17:43
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@CONF iture:

Investigation and final reports incident involving Voyager ZZ333 9 February 2014

Last edited by A33Zab; 27th Mar 2015 at 19:12.
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Old 28th Mar 2015, 03:58
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riddle me this; how do you expect Bonin to have a feel for what the "normal" roll gains are and therefore be thrown by the difference in Alt2B when it is on record that he had no training and likely little or no experience in manual handling at high altitude?
Dozy, very simple. He was expecting a Normal Law type roll response. What he received was very different and much more vigorous. The scanty information I've seen on his training indicated that he had never flown in Alternate law at altitude. That does not exclude flying in Normal law at altitude. I would also expect Normal law at altitude to fly about the same as Normal law at lower altitudes due to the intervening computer magic.

Bonin began flying when the autopilot dropped, before he knew the nature of the causal malfunctions and their implications.
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Old 28th Mar 2015, 05:11
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Originally Posted by Machinbird
Dozy, very simple. He was expecting a Normal Law type roll response.
How could he have been expecting a Normal Law roll response when he had no experience of what that response was?

Originally Posted by Machinbird
The scanty information I've seen on his training indicated that he had never flown in Alternate law at altitude
What I've read suggests that he had no training or experience whatsoever on high altitude handling in any flight law.
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Old 28th Mar 2015, 13:58
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Has the replacement pitot programme completed yet? Were there any other changes, eg to the stall warning logic?
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Old 28th Mar 2015, 18:01
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Originally Posted by Dozy
How could he have been expecting a Normal Law roll response when he had no experience of what that response was?
Dozy, you are making this more complicated than it is supposed to be. In Normal law, Full lateral stick is supposed to deliver 15 degrees/second roll rate, period. See FCOM. The computer magic makes it seem to roll the same everywhere, even though you are up at altitude. The roll damping even seems to be the same. When you neutralize the controls the roll rate stops the same way up high and down low.
When you are in a roll direct law, Your control deflection is proportional to stick deflection. When you neutralize the stick, the aircraft roll momentum keeps it rolling dependent upon its roll rate damping factor and you actually have to make a counter roll input to stop it. That is a big difference, but if you have flown that type system before, the adjustment is quick.
(From FCOM)
LATERAL NORMAL LAW
When the aircraft is on the ground (in "on ground" mode), the sidestick commands the aileron and roll spoiler surface deflection. The amount of control surface deflection that results from a given amount of sidestick deflection depends upon aircraft speed. The pedals control rudder deflection through a direct mechanical linkage.
When the aircraft is in the "in flight" mode, normal law combines control of the ailerons, spoilers (except N° 1 spoilers), and rudder (for turn coordination) in the sidestick. While the system thereby gives the pilot control of the roll and heading, it also limits the roll rate and bank angle, coordinates the turns, and damps the dutch roll.
The roll rate requested by the pilot during flight is proportional to the sidestick deflection, with a maximum rate of 15° per second when the sidestick is at the stop.
When the aircraft is in "flare" mode, the lateral control is the same as in "in flight" mode.
This is not to say that making a turn at altitude is identical to making a turn down low. At altitude, you are going much faster and Mach effects reduce the available AOA. You also have less reserve thrust available. The result is that turns at altitude are less aggressive than turns down low. You have to use lesser bank angles at altitude if you are going to avoid the stall boundary and maintain airspeed.
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Old 31st Mar 2015, 23:29
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Originally Posted by Machinbird
This is not to say that making a turn at altitude is identical to making a turn down low. At altitude, you are going much faster and Mach effects reduce the available AOA. ... You have to use lesser bank angles at altitude if you are going to avoid the stall boundary and maintain airspeed.
Which is kind of the point I was trying to make. Far from making things more complicated, I think my position is fairly simple - namely that the lack of training or experience in high-altitude manual handling *in any law* had a far greater impact on Bonin's ability to control the aircraft than the difference in roll response in Alt2B vs. Normal Law.

Fundamentally, whether you're getting 15 degrees/sec roll rate, or whatever you get when stick input commands deflection, the point is that the aircraft must be handled differently at altitude than it does closer to the ground. Bonin's inputs in roll were excessive from the get-go, and I think the control law would have made little difference in how he perceived the aircraft's reaction.
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Old 1st Apr 2015, 15:06
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Lack of high level handling is the common feature in commercial flying for all aircrafts. Actually non FBW are more tricky to handle as they are very sensitive at altitudes. FBW aircrafts high altitude handling does not differ in pitch in normal and alternate law. In alternate roll is conventional but when aircraft holding the flight path it becomes easier. The point is roll or rate of roll was not the cause. The aircraft was pitched up and held there otherwise there is sufficient margin from VSW even at FL350 for the rock n roll.
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