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AF447 Thread No. 3

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AF447 Thread No. 3

Old 12th Jun 2011, 17:56
  #1841 (permalink)  
 
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Mach and THS attitude

Salute!

Somewhere in the cobwebs of this old brain it seems that temperature is a big player to get true mach, especially up high. An SR-71 buddy of mine reminded me of this awhile back, but what do WE know? And ask a few Concorde pilots about this. So if the Airbus wants to use only dynamic and total pressures to calculate mach, I am wondering a bit.

Secondly, manually trimming the THS for nose down might not help with a neutral stick. That's leading edge of the THS "up". OTOH, it could be the plane has the same characteristic as the Viper, in which we could command a brief nose up attitude and higher AoA, then the nose would fall down and we could "rock" the thing outta the deep stall. In our case the equivalent of the THS was leading edge up to get the nose down, but we pilots had cleverly managed to get real slow at an extreme pitch attitude and the thing settled into a comfortable deep stall with little wing rock and good directional stability.

jez a thot.
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Old 12th Jun 2011, 17:56
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Originally Posted by MountainWest
What is heartbreaking all the way around is the mode of failure. One moment all is fine, and the next the speed is unknown/unavailable/kaput. There was no opportunity to take note of the situation immediately prior to failure. Had the PF had his eye on speed at the time of pitot icing, he would have known the stall warning was spurius. Is that true?
This is what occured for the Air Caraïbe case.
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Old 12th Jun 2011, 17:59
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In the last moments of the flight what forces were acting on the aircraft...

The tail was stalled so down elevator cannot lower the nose.
The CoG is behind the "center of lift" so that's contributing a nose up pitch.

Seems to be no way to reduce the AoA as per the revised proceedure. Perhaps lowering the gear?
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Old 12th Jun 2011, 18:03
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PFD with a 16° pitch

Hi there,
Does a PFD with a 16° pitch look like this ?



In the affirmative, so much blue on the artificial horizon should be perceived as a big problem in cruise phase ?
PS) the apogee seems not with negative Gs, not even 0-G: the passengers may have been unloaded by the 3/4 of their weight.
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Old 12th Jun 2011, 18:04
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Re bear

Hi bear,


Wie gehts? What do you make of the initial STALLSTALL?

At Mach.82, it takes very little NU to produce the (cricketStall)?
Iīm not in the know there, but have an oppinion. It was a valid warning, caused by reduced mach to .8, the roll to the right and following correction and the nose up travel of the nose ( note, it is not understandable for me how a crew would have done that amount of NU intentionally, but sure PF had his share in it), mixed with some turbulence. Another reason i think it was valid, the crew honored it with the appropriate ND action.

IF PF input of NU caused the alert, could it in some way be related to an unloading of the a/c such that the ensuing climb was negative "g"? Actual Stall?
It was not negative, but it was less than 1 g.

That would make the climb negative g, and ballistic in character. If g = < 1 wouldn't the PF maintain pull? Likewise, would not the a/c follow his input with THS (Leading Edge) DOWN?
As mentioned, maybe .5-.8 gee, just an unload, and i dont think it would have an immidiate effect. In my F4 it would have to be negative gee to get the nose down, with just an unload to .5 or even 0 gee it would continue on the trajectory until out of speed.

If negative, the pilot would feel a profound "falling" sensation, as would the airframe? Hence his pull throughout in concert with THS TRIM? He had no visual reference, and his instruments would not be helping, "No valid indications". He would not feel deceleration (It would also be felt as -g), and at "over the top" the negative would increase rapidly as the a/c started to "fall" having run out of energy? This could explain his reversal to ND at the top, the additional neg. g he may have taken for the Nose falling through at "Stall".
The NU input during the ascent until the apogee at FL 380 could have another reason. The ND was not working, a method to get the nose down is to roll the AC to the nearest horizon. Dont know the bus, we used (if not stalled yet) to pull the nose to the horizon, otherwise the unloaded ship just floated with the bank. In Alt 2 there is no rudder input together with a roll input, am i correct there? If so, the roll may not have worked as planned with the feet on the floor, our ship would be prone for roll reversal.

Was the game over at a/p loss and first "STALL". This is a heavy a/c with beaucoups energy to sustain a short climb of 3k feet?

For this, the a/c would not have fallen off the Nose, so was the THS stalled, and Center of Gravity aft enough to prevent the Nose from falling through?
Not at the first stall, but when the ship went into the stall regime in an unloaded attitude with the nose up, the chance to recover got minimized. I think it just quit flying at FL 380 when the speed was gone and was picking up descent rate in the same attitude NU as it had gotten to that height. Our F4 would have pitched down due to the heavy nose (i had been there, just let go of all controls and wait till its heading down).

When I trained, we practised "maintaining Stall". Instead of releasing the HS and Pushing, we held it back, sufficient to continue the Stall, the effect was a MUSH, a way to lose gobs of altitude in short order.
An expierience, most nowadays pilots are not granted anymore.


As mentioned, just my thinking out of a lot of practicing of stalls and falls (on the stick and observing / instructing), might well be totally wrong.

So lets wait and see.

Last edited by RetiredF4; 13th Jun 2011 at 11:35.
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Old 12th Jun 2011, 18:26
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Black Sheds, take a look at post #1, it has the links to the latest report. From memory, one of the pilots warns that they will soon be at 10000 feet, so he believed the altimeter and it was falling.
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Old 12th Jun 2011, 18:31
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Early warning of Air Speed sensors "failure"

Considering the importance of Air Speed (critical to "advanced planes" Systems) why not to implement an "EW AS resource" to alert the crew, before the System actions.

Pitotīs failure (e.g. at cruise) are not sudden ("digital"). They start to be transformed, in altimeters for example, gradually. Thiells 727 (NW N274US) showed this gradual deterioration. I think that an encounter of a dangerous icing condition when cruising, is also gradual, technically allowing a warning (of this crucial info) before "law switching" by the Systems.

And this perhaps could be a "band aid" before we have better AS sensors.

Last edited by Jetdriver; 13th Jun 2011 at 00:39.
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Old 12th Jun 2011, 18:42
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ND using an special type of APU

How many pounds of thrust an "augmented" special type APU would need for the task for this class of a/c? With a 45° degrees tilted nozzle.
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Old 12th Jun 2011, 18:44
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Why AOA is disabled <60 kts?

@MB.

A33Zab
Quote:
Maybe, not sure! this lower CAS speed limit is introduced for maintenance.
That would be an unfortunate tail wagging the dog approach to a minor engineering problem.

With a computerized aircraft you no doubt have maintenance modes you can enter (that are locked out during flight operations). Besides, how do you test the stall warning system on the ground then?

The 60 knot limit below which AOA is disabled more than likely results from another corner of the envelope. Something such as flow impingement from thrust reversers at low speed (on the ground of course).
Valid and logic too.

MCDU System Tests mode option is disabled after you entered your flightnumber. But hey.....because its a computerized aircraft it can be fooled even in flight! Just have to know how to set the proper bit.

Depends on the type of test: Stall Warning system is tested through MCDU, drives AOA to predetermined test angle by means of the -dual purpose -dampingmotor and set a false speedsignal.
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Old 12th Jun 2011, 19:05
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Mr.O

"Black Sheds, take a look at post #1, it has the links to the latest report. From memory, one of the pilots warns that they will soon be at 10000 feet, so he believed the altimeter and it was falling."


I propose that this statement was Made by PNF. It is an 'observation', and the PF was.......flying. F/O (RHS), was PF, he had duff (and unrecorded) data, this made him the one flying with displays that will not be known. Later, at dual ss input, the PF gives the ss to LHS (relief pilot). This is an intuitive notion, a "maybe you should try something" action?

RR_NDB

"Pitotīs failure (e.g. at cruise) are not sudden ("digital"). They start to be transformed, in altimeters for example, gradually. Thiells 727 (NW N274US) showed this gradual deterioration. I think that an encounter of a dangerous icing condition when cruising, is
also gradual, technically allowing a warning (of this crucial info) before "law switching" by the Systems."

With no liquid water available, the assumption is entry of ice crystals? If so, the likelihood is they collected at the drain, and slowly plugged it. This increases the pressure sensing and increases ias.; the aperture then plugged, and stabilized the pressure, then the plugs melted, and the actual pressure became available? This happens over a period of time, as you say, and since in solid state, the water has slower Thermodynamic behaviour, lengthening the event?
 
Old 12th Jun 2011, 19:22
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Hyper-V.... That would be pretty close. But the stall was pretty mushy up at 37,000 feet so the passengers probably felt little, as did the flight crew on a turbulent night. The big clue should have been that display you depict ALONG WITH the altimeter dropping. Even without reliable airspeed, it should have indicated that the nose needs to go down to get the airplane flying again. The cockpit voice recorder transcripts will be telling. It will be interesting to see if the vernacular involved is about flying the airplane or system observations.
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Old 12th Jun 2011, 19:38
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The passengers would have felt the 40 degree rolls, but I do agree with this "The cockpit voice recorder transcripts will be telling. It will be interesting to see if the vernacular involved is about flying the airplane or system observations."
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Old 12th Jun 2011, 19:41
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Dealing with Pitot data, sometimes unreliable

Hi,

I am assuming that most of Pitot discrepancies (among the 3) takes some time to stabilize in a condition capable to trigger a "switch law".

I am just imagining as "technically feasible" an EW resource that could warn the crew, before a major System change, any discrepancy and itīs rate of unstabilities, i.e. characterizing the differences between the (odd) number of AS sensors.

I consider an almost "useless" redundancy (for cruise level) the 3 identical Pitotīs and capable to trigger a "law switch". Doing that, (scanning and processing the 3) the System is almost like "amplifying" the Pitot problem.

Certainly Airbus SAS is working in better processing the info presented by current available Pitot, data. And also doing R&D on this issue. The Laser AS sensor filed patent by them shows it.

Last edited by Jetdriver; 13th Jun 2011 at 00:40.
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Old 12th Jun 2011, 19:55
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Yes, I saw that but I was not convinced that it was a factual statement, nor that it fitted the current (at the time) situation.
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Old 12th Jun 2011, 20:03
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POB "feelings" after sudden climb

What plane "attitudes" was probably mostly felt by PAX?

1) Sudden climb at 7,000 fpm
2) perigee deccel together high pitch
3) perigee zero (vertical speed) to > 10,000 fpm, speed variation
4) Rolls
5) Increasingly aerodynamic noise (and buffeting) of stalled a/c at > 10,000 fpm
6) TO/GA to idle noise engine variations
7) Turbulence during perigee to SL travel

I guess most "realized" the "deep trouble" after the above combined points. Even the pax sleeping before the sudden "climb", at high rate.
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Old 12th Jun 2011, 20:09
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BlackSheds: trouble is the released transcript extracts have been selected on unknown criteria, however the crew weren't slow to say when they had what they took to be no valid indications. Without any spoken caveats the phrasing sounds like it was information being given by PNF as Bear deduces, with the intent of relaying information taken as fact at the time. However it is like reading a story with two out of every three lines blanked out so it's filling in the dots.......
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Old 12th Jun 2011, 20:14
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Why AOA is disabled <60 kts?

Could it be a mod post 346 in the wall in Toulouse ...
http://www.pprune.org/rumours-news/3...ml#post4594759
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Old 12th Jun 2011, 20:22
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Mr.O

"However it is like reading a story with two out of every three lines blanked out so it's filling in the dots......."

It is more challenging, and more interesting, to have too little, than 'enough.'

Not even Perpignan is "Safe". Cold Cases are the best cases.
 
Old 12th Jun 2011, 20:27
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Redundancy is a fossil left over from the days when engines could last 2000 hours on the wing, and radios were "crystal".

A back step from that old worn out bromide is necessary to save lives, and modernize design. Better a redundant system but anomalous design than the false security of "numbers". Hard to believe that "More is better" is still around....
 
Old 12th Jun 2011, 20:30
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Bear, true enough. Can't understand why the whole transcipt minus anything upsetting or not relevant wasn't released but there will be a reason (maybe give the lawyers a head start ?). Since the whole story will be known at some stage the extracts and commentary must be factual, as far as they go. Can't release something now and have to contradict it later.

I remember a statement that the Captain announced (en francais) 'this is a stall' or similar. That must have been in a newspaper 'leak' as I can't now find it. Odd, but the leaks seem to have stopped.
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