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AF 447 Thread no. 4

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AF 447 Thread no. 4

Old 8th Jul 2011, 19:11
  #1041 (permalink)  
 
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If -hypothetically - the altimeter showed a declining altitude when they were level in the cruise, I suppose that could have caused a NU command ? No reason to think it happened but .... Could icing do that ?
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Old 8th Jul 2011, 19:16
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could icing do that ?
afaik, no......
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Old 8th Jul 2011, 19:37
  #1043 (permalink)  
 
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Originally Posted by bearfoil
The BEA report "a" left, nose up input. Not continuous. Doesn't the 30s mimic a rate similar to Manual? IOW, .65 degree/second? That gives a total of 20 degrees NU, but with some pauses on the way up, why not a total of Ten total excursion in 30 sec.?
Bearfoil,

The first Input I did not consider continuous.
However I did not understand the BEA Note as implying that the move up of the THS would have started upon the initial NU Input, but rather the continuous 'To the Left and Nose-Up Stops' as initiating the move of the THS.
I agree the rate of the THS move is a bit mysterious.
Maybe it is a wording problem and in reality there was a time delay included in the overall timespan of 1 minute that it supposedly took for the THS to move from 3 to 13°.
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Old 8th Jul 2011, 19:44
  #1044 (permalink)  
 
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I have read all four of the threads on this subject so I might have missed something (there's a lot of chaff amongst the wheat here) but has it been established that with the THS at the end of its range (13), with full nose down SS, the elevator would not have enough effect to lower the nose?

There have many posts about using the trim wheels but has it been confirmed that the only way to lower the nose would be to move the THS?

Just curious.
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Old 8th Jul 2011, 20:19
  #1045 (permalink)  
 
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Hi A33Zab,
Originally Posted by A33Zab
NAV ADR DISAGREE needs 10s monitoring to trigger.
ACARS msg was received @02:12:51; CMC has 60s maximum to correlate
to any failure message ~02:11:51 - 10s monitoring = ~02:11:41.
I'm not that sure of your interpretation of this timming.
NAV ADR DISAGREE was time-stamped at 0212 during the ACARS sequence. As I understand it, this is a cockpit effect (WRN) and not a fault (FLR), then, I do not think that it needed a correlation window to open before being displayed and an ACARS triggered.
Consequently, as it takes 5-6 seconds for ACARS protocole and 10 seconds to trigger, I would rather time it at 0212:51 less 15-16 seconds -> 0212:35.

Everybody seems to interpret ADR DISAGREE solely in relation with airspeed issues. So far, I don't know if it was only airspeed related as both AOA or pitot probes measuring values outside of their valid envelope could have basically the same effect.

Last edited by takata; 8th Jul 2011 at 21:33.
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Old 8th Jul 2011, 22:08
  #1046 (permalink)  
 
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Originally Posted by Idle Thrust
There have many posts about using the trim wheels but has it been confirmed that the only way to lower the nose would be to move the THS?
I don't think it has. According to BEA's Update:
At 2 h 12 min 02, the PF said "I don’t have any more indications", (...) Around fifteen seconds later, the PF made pitch-down inputs. In the following moments, the angle of attack decreased, the speeds became valid again and the stall warning sounded again.
Also, there are two ways to move the THS. The first is to push the sidestick forward sufficiently to cause the elevator to move to an AND deflection, the other is to move the trim wheel on the center pedestal.
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Old 8th Jul 2011, 22:15
  #1047 (permalink)  
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henra

hey. The three degrees I take to be THS position at trimmed cruise.The PF initially called for climb, but may have become impatient with response in Pitch coupled with his unfamiliarity with cruise/manual flight. If he kept inputting climb whilst awaiting a Pitch up, he could have been commanding the kind of abrupt Pitch up that is suggested by BEA's statement of "The aircraft, at 10 degrees Pitch up, finally began to climb." If, with the eventual rotation of the airframe, the THS and elevators were approaching max Pitch UP deflection, the rapid climb with alarming Vs would be explained. The ND inputs are in there until the second STALLSTALL, we just don't know when in the sequence they occurred. Thus far, so far, so explained.

I still think the PF and PNF thought the a/c to be ND and oversped when commencing the 10fpm descent, hence the continual NU inputs.

If, at 10k feet, the PNF saw the a/c's true orientation, (assiete), his over command may have been a ND to the stops. "You have control".
 
Old 8th Jul 2011, 22:27
  #1048 (permalink)  
 
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ALT-1, ALT-2 or ABNORMAL ATTITUDE LAW

I thought the June 01, 2011 David Kaminski-Morrow article in Flight Global had been accepted as a genuine BEA leak to counter forum posts etc. that had deduced that the aircraft was in Abnormal Attitude Law.

Furthermore, there are still references being made to ALT-1, whereas the general consensus is that ALT-2 is the law applicable.

From post #1567 Thread No.3 - the FCOM provides the following statement on ABNORMAL ATTITUDE LAW -

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° node 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 laws are:
In pitch : Alternate law.
In roll : Direct law with yaw alternate.
First reading of the above leads one to believe that each of the conditions is mutually exclusive, but if the Flight Global report is to be believed, that is not the case. The new interpretation is that the conditions are mutually exclusive PROVIDED all the ADRs haven't been rejected, but should all the ADRs be rejected, then an inertial upset involving either of the first two items will revert the aircraft to ABNORMAL ATTITUDE LAW.

If this was the case, the MAN PITCH TRIM ONLY was not displayed, as auto trim was still available.

Don't take it all as "gospel", as that is not what the FCOM currently says.

See post #1571 by A33Zab for details.
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Old 8th Jul 2011, 22:39
  #1049 (permalink)  
 
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Hi,
Originally Posted by Idle Thrust
I have read all four of the threads on this subject so I might have missed something (there's a lot of chaff amongst the wheat here) but has it been established that with the THS at the end of its range (13), with full nose down SS, the elevator would not have enough effect to lower the nose?
There have many posts about using the trim wheels but has it been confirmed that the only way to lower the nose would be to move the THS?
The THS was set very close to the end of its range (14 deg NU). The only clue given by the aircraft manual about elevator authority is that, they are powerfull, but it depends also on airspeed and THS settings: in case of a jammed THS above 8+ deg NU, the elevators control would be ok (say for a landing) if the aircraft airspeed is below 185 knots.

In AF447 case, the airspeed, once stalled, went far below 185 knots. Consequently it should be assumed that the elevator authority was not the main issue despite having the THS at 13 deg NU. Nonetheless, the airflow at one point into such a stall could also affect elevators control. Only Airbus could tell us if it is recoverable without moving the THS trim wheel.

Originally Posted by YRP
It seems that the crew made little or no ND inputs (apart from briefly shortly after the captain's return). So the THS position was not have been a factor. Whether there is enough elevator authority to recover is only a factor if they actually attempted it, no?
(I'm not making a statement on whether or not there was enough authority.)
Spot on.
This THS settings would be a non issue (beside an academic discussion about crew training to use it) if it would be confirmed, in the next interim report, that there was no real attempt to recover from this fully developed stall.

That was also my point from the last report. At any point before impact, did they really acknowledged that they were stalled? So far, it is leaked: NO.
If not, why this persistence in error? What really confused them?
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Old 8th Jul 2011, 22:39
  #1050 (permalink)  
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So, that would explain how the Roll excursions were easily handled, but PITCH/AoA were a mystery? 447 did not revert after recovery from <60 knots? Or, it did, but AoA was not protected, and load protection was not necessary? (Unlike Perpignan?) PF was expecting a pedestrian AL? No Stall? rapid descent due to "dive"?
 
Old 8th Jul 2011, 23:04
  #1051 (permalink)  
 
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Just a reminder when talking about the THS - this is what you should be thinking about:-



With the direction of airflow relative to the THS as shown, a ND input to the elevator will create a reasonable degree of increased leverage. Forget any idea of lift - the THS is stalled.
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Old 8th Jul 2011, 23:05
  #1052 (permalink)  
 
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Quote from Idle Thrust:
"...has it been established that with the THS at the end of its range (13), with full nose down SS, the elevator would not have enough effect to lower the nose?
There have many posts about using the trim wheels but has it been confirmed that the only way to lower the nose would be to move the THS?"

Don't think anyone can give a reliable answer to that. The problem is that, by the time the THS had reached 13NU (an incidence of minus 13 deg), the aircraft AoA was very high indeed, but we don't have a figure yet. It seems to have been around +40. The THS was no longer producing negative lift as it normally does; it was producing positive lift.

In my piece this morning, I argued that if the PF had selected full forward stick,
"...the EFCS would have selected full down-elevator, and started trimming the THS in the nose-down-trim direction."

The minute taken for the THS to return (if by auto-trim) to 3NU would have involved a very big height loss. Normally, the THS retrim would increase pitch authority. What I did not add, however, were some tough questions.
Was the THS already stalled (aerodynamically)?
If so, was it beyond its CLmax?
Would down elevator have therefore reduced THS lift, causing aircraft pitch-up?
If pitch-down by down-elevator didn't work, the movement of the THS towards a more neutral setting would increase its own AoA, deepening its stall.

Too many unknowns...

PS: mm43, guess you just beat me to it?
PPS [EDIT]: Just a reminder that mm43's super graphic uses an aircraft AoA of over +60, which represents the situation at the end of the flight.

Footnote [EDIT]
Having slept on this one, now realise that I foolishly omitted the other important nose-down input that was available to the crew at the time we are discussing: thrust reduction from TOGA to idle. This they did...

Last edited by Chris Scott; 9th Jul 2011 at 09:17. Reason: 1st: PPS added. 2nd: Footnote added.
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Old 8th Jul 2011, 23:25
  #1053 (permalink)  
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At ~full up deflection (THS) any down elevator would produce additional drag, as the elevators would trap airstream, ala Flap? This would also produce ND, but not due lift. As airstream became more LE on, the drag would dramatically change to lift, and the a/c would almost PitchPole over the nose. This obviously did not happen, and who says the PF input ND elevator? Both directions of elevator deflection would produce attitude change in the proper direction, but only to a slight and ineffective degree, yes? Doesn't this 'school' the crew (erroneously) into doing the wrong thing? Perhaps irrelevant; at this point, there is no correct solution? Could they conceivably have been waiting for lower thicker air to regain Tailplane "Authority" Holding Backstick and patiently waiting for it to dig in?

This comes back to CG? With an aft loaded cruise (trim tank), what would the THS aspect be at cruise?

Last edited by bearfoil; 8th Jul 2011 at 23:44.
 
Old 8th Jul 2011, 23:54
  #1054 (permalink)  
 
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bearfoil;
As airstream became more LE on, the drag would dramatically change to lift, and the a/c would almost PitchPole over the nose.
Not exactly the case; the airfoil has bottom camber and a current patent application by AI is for a THS with equal top and bottom camber.
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Old 9th Jul 2011, 00:10
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For purposes of 447, camber is not relevant? Surely for low speed, and a way to shade the Tail Down force w/o so much elevator? At cruise speed, its drag does not mean so much? As with the Vertical Stabilizer, why not a symmetrical airfoil, since lift is supplied by an active surface without the thickening of asymmetrical chord?

When THS stalls, aren't elevators just spoilers in costume? As in, when in 447's type of descent, a little ND elevator will slightly slow the Tail's vertical velocity by adding drag to the longitudinal? As the tail regains some airflow with a diminishing AoA, so gains the THS some lift to merely lift the nose to some stabilised (STALLED) value?

BEA states that the AoA "when valid" was never below 30 degrees NU. Were they hinting that the AoA was fluctuating in descent? Were the pilot's trying to porpoise the nose to gain what they thought was nose up to terminate the (natural, and flying) descent? If they believed they had ALTERNATE LAW, and had Pitch Protection, they were then attempting the decrease in "Speed" that would have been their responsibility w/o A/P, and A/T ?

take care mm43.

Last edited by bearfoil; 9th Jul 2011 at 00:26.
 
Old 9th Jul 2011, 00:25
  #1056 (permalink)  
 
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The Real Problem

It seems to me lately that what everyone on this site seems to forget or ignore is what got this flight into the mess in the first place. They went dead on into a thunderstorm. And shortly after, pitots iced up, auto pilot and throttles clicked off, airspeed info out, and then a zoom climb, out of airspeed, in a stall condition, with the controls innefective, and out of ideas.

With all that, was the crew confused? Were they trained for that? Was it turbulent? What is the AF policy regarding thunderstorm avoidance? Make small steady movements. How, if you've never hand-flown the aircraft in smooth air? Has anyone ever been trained for stall recovery in a deep stall?These seem to be the questions we should be addressing.
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Old 9th Jul 2011, 00:32
  #1057 (permalink)  
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wallybird

At great risk to my tender self, I have offered that ICE had nothing whatever to do with UAS. That the A/P loss was due to its insufficiencies in controlling the a/c in very turbulent airflow due the weather. If the a/p was lost due to being voted out of the loop by its mama, and the Pilot(s) "chosen" to take over, NORMAL LAW would have obtained, at least until further asym flow could confuse the Pitot heads, eliciting UAS and ALTERNATE LAW. ROLL DIRECT (UNPROTECTED) and PITCH DIRECT (PROTECTED) would have been the regime the Pilots would have assumed afaik. From there, a tug of war ensued, and the pilots lost, though they won a battle or two.
 
Old 9th Jul 2011, 01:19
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wallybird7;
They went dead on into a thunderstorm.
What's your definition of a thunderstorm? There was no lightning reported by other flights or observed by satellite.
Was it turbulent?
We don't know exactly, but the evidence presented so far doesn't point at that. They were using the radar to select a path between Cb's and became victim (or the pitots did) to the latent heat content in the out-flowing and sinking air from nearby towering Cb's.
Has anyone ever been trained for stall recovery in a deep stall?
Stall Warnings are provided and the training given is for procedures to be used to avoid stalling. Air Transport aircraft are not designed for, nor is their ultimate performance in a stall known, and therefore avoidance is the appropriate training.

Remember, this aircraft was lost because the correct procedure of pitch and power was not used when unreliable airspeed data became an issue. Becoming stalled was a by-product of that, and the logic associated with "how" and "why" this happened is really the issue.
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Old 9th Jul 2011, 01:33
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Chris Scott #924
Said "even half the possible THS of 13 NU is a frightening thought"
It has also been suggested that the PF may have inadvertently gripped the SS with his fingers gently, (more strongly than with his whole hand ?). From the threads that I have read inly a few mm of movement would cause the THS to try to compensate by increasing from the initial cruising figure of 3 or 4 NU.
PF may have concentrated on his hand flying but without his accustomed air pressure instruments - they have always been there in the past. He does not look at the THS, indeed it is something which has always "done its own thing" ( In some airlines it is a "don't touch-me " item).
PNF does not notice that all THS movements are in one direction ( the "N" means he has other duties...)
Taking CS's half the possible as 7NU, lights which came on, adjacent to the trim wheels, ONLY when this figure was exceeded. I recall that automatic fuel transfer happens around 20,000 ft. Perhaps the activation of this simple circuit might use the same figure.
In HAL BASIC " You are making me work too hard"
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Old 9th Jul 2011, 02:38
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bearfoil;
When THS stalls, aren't elevators just spoilers in costume?
The colloquial expression would be, "In drag!"

However, treating their action as more like that of the rudder is probably the best way of looking at it. The effect would be small to start with and increase rapidly as the THS also started its ND journey.
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