AF 447 Thread No. 7
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Mr Idle B - your plea appears to have gone un-noticed. Yes, there are many of us who understand the arrows and hooks and keeping 'rubber side down'. The problem we are facing here is that a particular system of flight (NB no names) appears to engender in some the chance to forget all this and become reliant on the system to look after them. I think you can be assured that many of these have gone away scratching their heads and may now be a little less relaxed about this and hopefully the manufacturers and training systems will also adjust. You will for example, note that the 'drill' taught for stall recovery has been changed following the accident and that I'm sure one large airline will be reviewing the abilities and training of its pilots. Looking at your location I would suggest you have a good chance of being behind someone 'wot knows'.

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Originally Posted by Zorin_75
Because they were trying to get the nose down for four minutes but autotrim didn't let them?
Because once trimmed the airplane was looking quite comfortable in a stalled status.
But before it started to autotrim :
- It was definitely possible to hold the aircraft in the stall with 3 degrees of nose-up trim and full back stick, but it required effort
- The aircraft wanted to nose down and recover itself
- The nose wanted to come down naturally if I released pressure for even a split-second.

While the manufacturer of any simulator will aim for 100% accuracy, the available data is routinely found lacking, hence my cautionary note above. What may seem surprising to some is the fact that the data package supplied by the airframe manufacturer will vary from one customer to another - I recently worked two 737 platforms for different customers, and received different data from each, for the same system. Not entirely different, but 5% was. Eventually I was able to get the same consistent data, but I was lucky since I had access to two sources.
Aside from those parts of the sim using rehosted aircraft code (which has it's own issues), the device trusted for training is the result of hundreds of thousand of lines of code from a motley collection of software engineers, that typically do not follow anywhere near the same rigid procedures and practices employed when writing aircraft-bound code (costs alone would not permit). This is not to say they are not doing a great job, but trusting the sim blindly, in particular in areas extrapolated beyond the aircraft data or figured out by analysis of airframer supplied data, warrant second and third opinions before assuming the behavior is correct.
- GY


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specific edge-case operation should not be trusted on the sim until verified and checked against aircraft operation
You are hitting the wrong sack if you want to blame the autotrim. Autotrim is a perfect tool. They shouldn't have pulled into the stall.

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Dani
This is certainly true, but BEA has tested every steering input on AF447 against the real aircraft parameter and has come to the conclusion that they are completly consistent.
This is certainly true, but BEA has tested every steering input on AF447 against the real aircraft parameter and has come to the conclusion that they are completly consistent.
BEA IR3 P41 The recalculated deflection angles for the elevators and the PHR are consistent with the parameters recorded Comparison.
BEA IR3 P42: Consequently, it would appear at this stage in the work that the bulk of the aircraft movements in the longitudinal axis (attitude, vertical speed, altitude) result from the actions of the PF, with the exception of small variations that are probably due to the meteorological disturbances.
BEA IR3 P42: Consequently, it would appear at this stage in the work that the bulk of the aircraft movements in the longitudinal axis (attitude, vertical speed, altitude) result from the actions of the PF, with the exception of small variations that are probably due to the meteorological disturbances.
To read into those words that the aircraft is sanctioned and freed from having contributed in some way to the outcome looks a bit bold. A systemic inbuilt problem like unwanted behaviour of the THS autotrim (i´m not saying that it is one or isn´t one) would show in the aircraft as well as in the simulation. Only malfunctioning systems in comparison to non malfunctioning systems in the simulation would show as difference.
Where does it leave us then?
It only proves, that concerning the flight control system the aircraft had no malfunctions and that another A330 with the same crew (or with a different crew performing the same inputs) at the same place in the same environment would have ended in the drink too. This recognition might cause more headache for a manufacturer than finding the cause in one faulted part.
franzl

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Originally Posted by CONF iture
No.
Because once trimmed the airplane was looking quite comfortable in a stalled status.
Because once trimmed the airplane was looking quite comfortable in a stalled status.
Originally Posted by RetiredF4
BEA only tells us, that the flight control inputs in the simulator produced comparable outputs to the flight controls and caused comparable flight behaviour. Nothing more, and nothing less.


Where does it leave us then?
I think it leaves us with this, from page 77:
throughout the flight, the movements of the elevators and the THS were consistent with the pilot’s inputs,
up to the exit from the flight envelope, the airplane’s longitudinal movements were consistent with the position of the flight control surfaces,
(my bold above)
So that although the movements of the control surfaces were consistent with pilot inputs throughout the entire event, there is no direct statement of finding to the effect that after the aircraft exited the flight envelope the aircraft longitudinal movements were still consistent with these pilot inputs even though control surface positions were. Nor does this appear to imply anything further.
I would imagine this is still being investigated.

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up to the exit from the flight envelope, the airplane’s longitudinal movements were consistent with the position of the flight control surfaces,

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So that although the movements of the control surfaces were consistent with pilot inputs throughout the entire event, there is no direct statement of finding to the effect that after the aircraft exited the flight envelope the aircraft longitudinal movements were still consistent with these pilot inputs even though control surface positions were. Nor does this appear to imply anything further.

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You are hitting the wrong sack if you want to blame the autotrim. Autotrim is a perfect tool. They shouldn't have pulled into the stall.
Ninety-nine point nine nine nine percent of your flight time or more has been in Normal Law. Just because your regular autotrim has been so sweet doesn't mean she does not have an ugly sister.


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Zorin75
The THS did not travel to (-) stop. It stopped short, something less than a degree. Neither did it "start" after one minute of SW.
Take a look back at Takata's pic of the Recovered THS. Note the damage to the NU end of the screw. Impact? Possibly. But the damage suggests collapse of the thread collar opposite the implied direction of travel at water impact. Something like an airload, not a water contact.
The THS did not travel to (-) stop. It stopped short, something less than a degree. Neither did it "start" after one minute of SW.
Take a look back at Takata's pic of the Recovered THS. Note the damage to the NU end of the screw. Impact? Possibly. But the damage suggests collapse of the thread collar opposite the implied direction of travel at water impact. Something like an airload, not a water contact.

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Originally Posted by RF4
BEA only tells us, that the flight control inputs in the simulator produced comparable outputs to the flight controls and caused comparable flight behaviour.
At the request of the BEA, Airbus conducted a simulation of the operation of the flight control computers,
Originally Posted by OK465
there is no direct statement of finding to the effect that after the aircraft exited the flight envelope the aircraft longitudinal movements were still consistent with these pilot inputs even though control surface positions were.
Last edited by HazelNuts39; 18th Nov 2011 at 19:35. Reason: text in italics

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Ninety-nine point nine nine nine percent of your flight time or more has been in Normal Law. Just because your regular autotrim has been so sweet doesn't mean she does not have an ugly sister.

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What is the purpose of "zero force"? Pilot feels nothing anyway, and the elevators can sustain and withstand the forces on their own. What the THS adds is lethargy when perhaps an abrupt input is necessary.
It's great for cruise. What is the need in ALTERNATE LAW?
Does the computer get sore muscles?
It's great for cruise. What is the need in ALTERNATE LAW?
Does the computer get sore muscles?

Zorin_75:
Correct - my point really was that jumping in the next available A320 or A330 simulator and wringing the cr*p out of it into an upset condition (outside of flight data) puts you entirely at the mercy and competency of the individual simulator engineer responsible for that aspect of the simulator performance - so in the case of flight modeling you might happen upon a model built with sensible extrapolations and cleanly interpolated behavior, while other models may simply 'straight-line' the performance once the flight test data runs out. It is unlikely such a flight regime was tested beyond a joy ride or unintended upset from the less capable engineers testing the sim - the last thing on a persons mind at that point is the accuracy of the simulation. The same would be true of any other aspect of the modeling, be it hydraulic systems, electrical or whatever.
So, taking the trim behavior in a simulator, once into an upset condition, with possible invalid airspeed, etc, probably shouldn't be regarded as definitive. I'm one of those engineers and I wouldn't trust it. As noted before, the sound models I produce would NOT include a vertical speed component as a contribution to the aerodynamic noise 'hiss' model. I have not data to model it and would be guessing. I could probably make a pretty good guess and have something representative, but:
(a) I've never been asked for it
and
(b) I'll bet if I ask 3 pilots for a subjective assessment, I'll get at least 4 opinions....
I suspect the Airbus "simulator" referred to in the interim report was an engineering simulator based on flight modeling the aircraft behavior versus control inputs, not what we all know as a full flight sim - perhaps the final report will define this more specifically.
- GY
Dani and GY were discussing the fidelity of simulators. Nothing more, and nothing less.

So, taking the trim behavior in a simulator, once into an upset condition, with possible invalid airspeed, etc, probably shouldn't be regarded as definitive. I'm one of those engineers and I wouldn't trust it. As noted before, the sound models I produce would NOT include a vertical speed component as a contribution to the aerodynamic noise 'hiss' model. I have not data to model it and would be guessing. I could probably make a pretty good guess and have something representative, but:
(a) I've never been asked for it
and
(b) I'll bet if I ask 3 pilots for a subjective assessment, I'll get at least 4 opinions....
I suspect the Airbus "simulator" referred to in the interim report was an engineering simulator based on flight modeling the aircraft behavior versus control inputs, not what we all know as a full flight sim - perhaps the final report will define this more specifically.
- GY

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Dani
When you pull for a long time it trims this position to zero force. That's the definition of trim.
When you pull for a long time it trims this position to zero force. That's the definition of trim.
As we know, autotrim not works on behalf of the SS inputs, but on the order of the FCPC, which has an ordered load factor of 1 g (no SS input) or a change (decrease or increase ) of this loadfactor (SS input).
Example (and this is not far away from AF447):
When in ALT2 and the aircraft is in a climbing trajectory (make it shallow or steep, the difference is only time) and the speed decreases (no autothrottle), the FCPC´s will position first the elevators and then the THS in order to maintain 1 g in the climb to compensate for the decreasing speed, even when SS is in neutral / untouched position.
Without preotections in ALT2 THS trim might even drive NU with a SS-ND input, if the increase in descent rate (like in the stall of AF447) decreases the loadfactor more than a small SS ND command would demand and elevators are already full NU.
Therefore machinebird got it right:
Dani, I would normally fully agree with your assessments, but the autotrim you know and love in Normal law is not the same autotrim in certain critical respects when in ALT2 law.

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Originally posted by Machinbird...
...the autotrim you know and love in Normal law is not the same autotrim in certain critical respects when in ALT2 law.
...the autotrim you know and love in Normal law is not the same autotrim in certain critical respects when in ALT2 law.
On approach to stall and taking into account the dynamic of the flight and of the complexity of the displays, the automatic changes in the control laws can fail to be perceived and their consequences can sometimes be misunderstood by pilots. In this case, the passage to direct law rendered the auto-trim function inoperative. Even if the amber USE MAN PITCH TRIM flag was displayed on the two PFD artificial horizons, the crew did not notice the position of the stabilizer and did not command the trim wheel manually during the twenty-five seconds in direct law between 15 h 45 min 15 s and 15 h 45 min 40 s. From this time on and for the rest off the flight, as a result of passing into abnormal attitudes law, the amber USE MAN PITCH TRIM flag was no longer displayed. The systems thus functioned in a degraded manner, without the real overall situation of the aeroplane being known by the crew.
In short, the Human Factors were dominate in this accident.

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RetiredF4:
no, it trims not for zero force, it trims to maintain or achieve an ordered load factor.
no, it trims not for zero force, it trims to maintain or achieve an ordered load factor.
Remember: You give a sidestick input, that's the load factor you order. Now fbw computers calculate the necessary load factor. When you release your side stick (normal law), you maintain the ordered load factor.
What trim does is that it "neutralizes" long term load factor orders, so the flight control surfaces can go to neutral position.

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Originally Posted by Organfreak
The Russian pilot who let his son 'steer' that A300 was 'qualified' too, and yet everybody died.
Dozy:
Oh, it was an A310? My mistake.
But I wouldn't call that detail "little-known." Hell, I saw it on Air Emergency on the idiot box just the other night! But, in their defense, they never knew what was wrong in the first place. I doubt they would have trusted (my speculation) the protections at that point. Did the A310 really have that feature?
The Russian pilot who let his son 'steer' that A300 was 'qualified' too, and yet everybody died.
Dozy:
There's a little-known coda to that accident, and that is the story of how the pilots successfully recovered the aircraft from the initial stall, but overcorrected by pulling up too long and caused a second stall that sealed their fate. What the investigators discovered in the sim was that if the pilots had simply let go of the control columns, the A310's protections would have stabilised and righted the aircraft on their own. Sadly, the Russian pilots were not trained on this feature of the A310's design.
But I wouldn't call that detail "little-known." Hell, I saw it on Air Emergency on the idiot box just the other night! But, in their defense, they never knew what was wrong in the first place. I doubt they would have trusted (my speculation) the protections at that point. Did the A310 really have that feature?
