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AF447 Thread No. 3

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AF447 Thread No. 3

Old 1st Jun 2011, 08:55
  #941 (permalink)  
 
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The level-d sim is at least as good as the real aircarft when it come to manouvers and flight controls.
So you know that the A320/A330 sim you have used has "valid" data for deep stalls?

Not exactly sure how the sim can be better than the aircraft, unless it is used as a toy!
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Old 1st Jun 2011, 09:10
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So you know that the A320/A330 sim you have used has "valid" data for deep stalls?

Not exactly sure how the sim can be better than the aircraft, unless it is used as a toy!
No, sure. I was not intending to refer to the deep stall. I was more related to Ventus45 saying that the SIM is not good enough.

The SIM can simulate failures and things alike, no? I can stall the SIM and it happened. Don't know why it happened but anyway I screwed it up at that point. Never analyzed it. I was there for fun. Remember?

At least I can say that the Airbus will not pitch up 7000 ft/m if protections are active. No matter how hard i pull or push on the stick.

I am very unsure if the were in ALT1 or ALT2. Based on the ACARS, with two ADR failed, it's supposed to be ALT2.
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Old 1st Jun 2011, 09:58
  #943 (permalink)  
 
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Originally Posted by MartinM
...At least I can say that the Airbus will not pitch up 7000 ft/m if protections are active. No matter how hard i pull or push on the stick...
Can you recreate the 2000 A340 airprox zoom climb from FL360 to FL384 at up to 6,000 ft/min ?
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Old 1st Jun 2011, 10:02
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At least I can say that the Airbus will not pitch up 7000 ft/m if protections are active
What protection will stop the aircraft climbing at 7000fpm?
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Old 1st Jun 2011, 10:18
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What protection will stop the aircraft climbing at 7000fpm?
Under Normal Law, there is a pitch attitude, as well as a bank angle protection and some other too, like a-floor, ...

Input on the SS that exceeds the Normal Law parameters, will not be executed by the flight control computers. Thats my easy way to explain it. Maybe someone can explain it in a more technical correct way.
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Old 1st Jun 2011, 10:28
  #946 (permalink)  
 
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Stalled AF447 did not switch to abnormal attitude law
By David Kaminski-Morrow


Investigation into the accident sequence of Air France flight AF447 has revealed that the Airbus A330 did not enter the abnormal attitude law after it stalled, despite its excessive angle of attack.
The abnormal attitude law is a subset of alternate law on the aircraft and is triggered when the angle of attack exceeds 30° or when certain other inertial parameters - pitch and roll - become greater than threshold levels.
Alternate law allowed AF447's horizontal stabiliser to trim automatically 13° nose-up as the aircraft initially climbed above its assigned cruising altitude of 35,000ft.
The stabiliser remained in this nose-up trim position for the remainder of the flight, meaning that the aircraft would have had a tendency to pitch up under high engine thrust.
Crucially the abnormal attitude law - if adopted - would have inhibited the auto-trim function, requiring the crew to re-trim the aircraft manually.
After stalling, the A330's angle of attack stayed above 35°. But while this exceeded the threshold for the abnormal attitude law, the flight control computers had already rejected all three air data reference units and all air data parameters owing to discrepancy in the airspeed measurements.
Abnormal law could only have been triggered by an inertial upset, such as a 50° pitch-up or bank angle of more than 125°. "That never occurred," says French accident investigation agency Bureau d'Enquetes et d'Analyses.
The BEA is still attempting to explain why AF447's crew failed to rescue the aircraft after it climbed to 38,000ft and stalled. The pilot's control inputs were primarily nose-up, despite the stall condition.
There has been no indication that the aircraft switched into any other control law, other than alternate, during the accident - suggesting that auto-trim was available throughout the descent.
Failure to realise a need for manual re-trim was central to the loss of an Airbus A320 over the Mediterranean Sea about six months before the AF447 crash.
The auto-trim had adjusted the horizontal stabiliser fully nose-up but, during a flight envelope test involving near-stall, the aircraft switched control laws and inhibited the auto-trim.
Without manual re-trimming, the aircraft pitched up sharply as the crew applied maximum thrust. It stalled and the crew lost control.
In its conclusions over the accident the BEA highlighted the rarity of the need to trim manually, which created a "habit" of having auto-trim available made it "difficult to return to flying with manual trimming".
"One of the only circumstances in which a pilot can be confronted with the manual utilisation of the trim wheel is during simulator training," it said. "However, in this case, the exercises generally start in stabilised situations."
In the wake of the A320 accident, near Perpignan in November 2008, the BEA recommended that safety regulators and manufacturers work to improve training and techniques for approach-to-stall situations, to ensure control of an aircraft in the pitch axis.
Stalled AF447 did not switch to abnormal attitude law
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Old 1st Jun 2011, 10:30
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Sensor validation/ MartinM.

It will certainly climb at 7000'/min if its in a sufficiently powerful updraft, indeed it could be hard to stop it doing so.

That climb must have been a combo of pilot input, weather and maybe aircraft input if speed too high.
 
Old 1st Jun 2011, 10:33
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MartinM,

I think you'll find the aircraft can climb at more than 6000fpm and remain in normal law!
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Old 1st Jun 2011, 10:37
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Sensor validation/ MartinM.

It will certainly climb at 7000'/min if its in a sufficiently powerful updraft, indeed it could be hard to stop it doing so.

That climb must have been a combo of pilot input, weather and maybe aircraft input if speed too high.
Yes, agreed.
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Old 1st Jun 2011, 10:39
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I think you'll find the aircraft can climb at more than 6000fpm and remain in normal law!
Maybe, yes.
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Old 1st Jun 2011, 11:06
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ACARS Messages – time-stamps

Salut encore takata,

Am catching up, currently only 40 hours behind in this plethora of mess ages...

Re the time-stamp on the ACARS warning/failure messages:

is it your understanding that the timing is to the nearest whole minute? For example, does a time-stamp of "0210" mean that the event was generated between 02:09:31 and 02:10:30 (inclusive)?

Up until I read one of your posts this week, I was assuming that a time-stamp of "0210" would mean that an event took place between 02:10:00 and 02:10:59 (inclusive).

On the off-chance that you spot this post, I would appreciate your clarifying this important (30-second) ambiguity.
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Old 1st Jun 2011, 11:30
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Hi Chris,
Nice to see you.
Originally Posted by Chris Scott
Salut encore takata,
Am catching up, currently only 40 hours behind in this plethora of mess ages...
Re the time-stamp on the ACARS warning/failure messages:
is it your understanding that the timing is to the nearest whole minute? For example, does a time-stamp of "0210" mean that the event was generated between 02:09:31 and 02:10:30 (inclusive)?
Yes, the "nearest minute", is what I thought:
02:10 = 02:09:31 - 02:10:30.

But after reading you and checking again the French report it is writen: "précis à une minute près".... not what I remembered "à la minute la plus proche".
Hence, it is more probably what you said:
02:10 = 02:10:00 - 02:10:59
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Old 1st Jun 2011, 11:48
  #953 (permalink)  
 
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Cool

Hi,

About all those posts on "blaming the pilots or not" "blaming the constructor or not" "blaming the airline or not" (on the basis of available fragmented informations so far ..)
A straight report will be
If the pilots are in fault on the AF447 ... the case is simple and the final conclusion of BEA will not contain any recommendations concerning the aircraft.
If the pilots are not at fault .. and so it will be recommendations concerning the aircraft
But I'm sure it will be not so straight ... and certainly it will be recommendations about the pilots and airline (training SOP .. etc...) and recommendations for the constructor(s) and recommendations for the regulators
Seem's to me a usual and honest scenario and it will be no different for the AF447 case.
So .. it will be also many food for the court of justice
Nobody will go out white from this accident.
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Old 1st Jun 2011, 11:53
  #954 (permalink)  
 
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Stalled AF447 did not switch to abnormal attitude law

Tubby:

The abnormal attitude law is a subset of alternate law on the aircraft and is triggered when the angle of attack exceeds 30° or when certain other inertial parameters - pitch and roll - become greater than threshold levels.
........
Abnormal law could only have been triggered by an inertial upset, such as a 50° pitch-up or bank angle of more than 125°. "That never occurred," says French accident investigation agency Bureau d'Enquetes et d'Analyses.
From the BEA report:

"The angle of attack, when it was valid, always remained above 35 degrees."


More questions to answered by BEA!!!


From the AMM:

"Abnormal attitude law,
This FCPC law is engaged when certain aircraft parameters exceed pre-determined values.
This law ensures that the flight control law will never hinder aircraft recovery.

The laws available are:
- in roll: the yaw alternate law,
- in pitch: an adapted Nz law, without autotrim.

After aircraft recovery, and until landing, the laws available become:
- in roll: the yaw alternate law,
- in pitch: the Nz law (with recovered autotrim)"

"The Nz law is such that the aircraft response is quasi independent of aircraft speed, weight, and CG location.
If both ADIRUs are failed, the Nz law is kept, but with limited pitch rate and gains.
A consolidation of the vertical acceleration and pitch attitude rate is then performed via the two accelerometer units."
From the FCOM:

"An abnormal attitude law in pitch and roll is provided, if the aircraft is in flight and in any of these
conditions :


Pitch attitude > 50° nose up or 30° nose down

Bank angle > 125 °

Angle of attack > 30° or < 10°

Speed > 440 knots or < 60 knots

Mach > 0.96 or < 0.1



The law in pitch is the alternate law without protection (except load factor protection) and without auto trim.

In roll, it is a full authority direct law with yaw alternate.
After recovery, the flight controls laws are:
In pitch : Alternate law.




In roll : Direct law with yaw alternate law."




I think we already all concluded that it did enter -abnormal attitude law- but only after THS was auto-positioned in 13 ANU, and never recovered from this law.
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Old 1st Jun 2011, 12:05
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Originally Posted by tubby linton
Stalled AF447 did not switch to abnormal attitude law
I don't see this statement from BEA - not even from an alleged "source close to the investigation". About as reliable as the media reports who was PF in which seat? The BEA report states that the "The inconsistency between the speeds displayed on the left side and on the ISIS lasted a little less than one minute" and 2 out of 3 means they agree - even though we don't know what RHS was displaying.

Maybe possible abnormal attitude law not triggered because of the cross-link between real and indicated airspeed and AoA - at high AoA IAS much lower than TAS, and low IAS suppresses use of AoA?
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Old 1st Jun 2011, 12:06
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Takata, it may take a hand to trim the rudder, but if you are a pilot, you are taught to fly with your feet. (I understand that some people are taught to stop doing that ... ) The point of the trim (particularly if we are discussing manual trim versus auto trim) is to set a new rudder position so that you don't have to keep making smaller and smaller inputs.

From the diagrams I have, there are rudder pedals on the Airbus 330.

Using your feet to move the rudder is a skill taught from Hour Zero in anyone's flying career ... a skill that appears to atrophy with disuse.

Last edited by Lonewolf_50; 1st Jun 2011 at 12:18.
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Old 1st Jun 2011, 12:11
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Hi tubby,
Originally Posted by tubby linton
Thank you for posting this. IMO, it changes everything.
Their source is the BEA and I presume that it is a very serious matter if the BEA informed them at this stage of "no switching to abnormal attitude"= no trace of it in the DFDR. Those technical informations are too precise for being another "rumor".
It means that autotrim was available all the way down.
It means also that:
a) either they never really pushed the stick in order to recover as the THS did not move back.
b) The THS was jammed (but they should be able to say it).

Consequently, a) being much more probable, it would also mean that they never acknowlegded the real situation (being stalled).
My opinion is that one may make a serious mistake (bad reflex, etc.) but it doesn't fit with 3 pilots confronted to a situation lasting four and half minutes.

I'm pretty convinced now that there was an unknown factor involving instruments that fooled the PF, hence more specifically the Right Hand Seat which is feeded by ADIRU2. Also, by deduction, the pilot flying was David Robert, 37, with 6,547 flying hrs including 4,479 on type. He was by far the more experienced A330 jockey on the deck and was PF from take-off. His reaction was immediate, he was not asleep, and he should have been fooled by something.

Last edited by takata; 1st Jun 2011 at 12:27.
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Old 1st Jun 2011, 12:15
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From the diagrams I have, there are rudder pedals on the Airbus 330.
Yes. And those pedals are used as wheel brakes too, on ground, of course

Rudder Trim, is a small knob on the center pedestal console, while elevator trim is a large trim wheel besides the Throttle.
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Old 1st Jun 2011, 12:25
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Hi Lonewolf,
Originally Posted by Lonewolf_50
Takata, it may take a hand to trim the rudder, but if you are a pilot, you are taught to fly with your feet. (I understand that some people are taught to stop doing that ... ) The point of the trim (particularly if we are discussing manual trim versus auto trim) is to set a new rudder position so that you don't have to keep making smaller and smaller inputs
Your comment is irrelevant with the point I was making about trimming the rudder for addressing the sensitive roll axis being direct. It takes a hand, nothing more. Read again what I was talking about before jumping in.
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Old 1st Jun 2011, 12:26
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Yes, Martin, I also gathered that from the cockpit and flight controls layout available in the public domain.
Originally Posted by takata
Read the part of the FCOM I posted above and you'll see that it is mentioned that you may have to re-trim the rudder in order to stabilize your roll axis.
takata, I'll suggest to you that pilots know that because that is part of flying.

The mental and congnitive process, when you are doing this on instruments (which I presume AF 447 crew were, as it was night and the Wx was bad) is to set an attitude in balanced flight and trim to hold that attitude in all three axes. (Plural of axis)

What I was taught and used to teach was to trim nose and rudder first, aileron last, to avoid cross trimming, but such technique is probably model dependent.
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