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AF 447 Search to resume (part2)

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AF 447 Search to resume (part2)

Old 9th May 2011, 00:29
  #961 (permalink)  
 
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Would you keep full throttles, once having already a very large AOA exceedance , and all your way down during about four minutes?
from, say 40,000+ feet down to sea level?
Who said anything about full throttles? I'd pull power back toward idle until I began to lose pressurization.
Some of the the F-4 aircrews were issued Moon suits and as part of their syllabus were supposed to zoom up to 70,000 feet. The throttles had to be pulled back to keep from exceeding 100 % RPM, and if you got high enough, you had to shut them down to keep from exceeding RPM limits at altitude. Fortunately for me-they didn't have a moon suit in my rather common size.

Below quote in reference to engine operating envelope charts availability.
Not at hand.
But say 50-60 degrees AOA without much forward speed remaining at all (in order to stay into your 8000 m zone) will make such an angle for the airfoil to bypass in order to reach the compressors that I really doubt of the tolerance. I'm not even talking about all the tropical storm ice/water you will ingest at lower than cruise levels in the process.
It seems that the crew somehow was able to keep the engines running for the majority of the descent, at least some of which must have been at very high AOA. Perhaps the fan creates local airflow straightening in front of the engine at high AOA. Perhaps the power settings were low enough to avoid stall.

What make you think Direct Law may be lost?
The rudder would be still limited (could be an issue at low speed for stall recovery) but other surface control would still move freely.
I don't think that Direct Law would be lost. Just that the crew would not deliberately try to achieve Direct Law as a result of their training. Even with Direct Law, it would not be easy without an Airbus demonstrated procedure. You would probably have to dial in full nose down trim, and then quickly undo it on recovery. Something like what the F-16 has to do to recover.

The F-16 has to rock itself out of a deep stall if it gets stuck there.
Read "Semper Viper" in this link http://www.codeonemagazine.com/image...49318_2157.pdf
to see all the fun you have been missing.
Link courtesy of Gums.
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Old 9th May 2011, 00:51
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infrequentflyer789;
I think you missed a bit of the intro:
I think you might be right, and possibly, "there is a need...".

32 of rudder would be nice to have - if it was going to get you out of an otherwise "no win" situation that apparently you shouldn't have gotten into.
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Old 9th May 2011, 00:56
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Originally Posted by JD-EE
That is what troubles me with the simple scenario of pitch to a fatal point and actually slide down backwards at least part of the way. Wouldn't that put the candles out? And isn't a tail down stall recoverable using the elevators? Maybe they were in the middle of recovery when they hit?
These theories are getting more & more bizarre the nearer we get to hearing from the CVR and FDR
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Old 9th May 2011, 00:59
  #964 (permalink)  
 
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Back to Cabin VS...

grity, quote:
"if the bird is without any control but starts with an extrem climb mayby 60 deg, this (~balistic) path will reach a maximal high of ~12700m (full change the kinetic horizontal energie into potencial energie), while reducing the speed to very low untill it will deap stall and if it then fall with a stable AOA of 50-60 deg. back to 10500m and afterwards down to zero....."

Although this violent pitch-up would be an effective speed-loss mechanism, and looks to be the best (maybe the only) way of greatly exceeding the normal-stall AoA, there is evidence that suggests it couldn't have involved a climb as high as your ~12700m (~FL416).

The cabin altitude and differential pressure in the cruise at FL350 could not have coped with a sudden climb of 6000ft without maximum differential pressure being reached. Shortly after that, the safety valve would operate and the cabin VS (cabin climbing) would increase to something well over the +1800ft/min required to trigger a warning identical to that generated at 02:14z, the subject of the last ACARS message received.

Regret to say that I cannot calculate the flight-level where this would occur, nor the relationship between aircraft VS and cabin VS at the safety-valve differential pressure; but a ball-park figure would be between 2:1 and 2.5:1. So I think an aircraft climb VS of about 4000ft/min would suffice. The passing flight-level where this would start might be about FL370 - FL380. Sorry I cannot be more helpful.

Chris

PS
For new readers, there has been a broad consensus on previous threads that the cabin VS warning at 0214z was the result of the aircraft "catching the cabin" in its last descent, causing the inward-relief valves to open and allowing the cabin to descend at a VS exceeding -1800ft/min. This would have happened at about FL060.
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Old 9th May 2011, 01:13
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JD-EE
That is what troubles me with the simple scenario of pitch to a fatal point and actually slide down backwards at least part of the way. Wouldn't that put the candles out? And isn't a tail down stall recoverable using the elevators? Maybe they were in the middle of recovery when they hit?
I have never lost an engine during tail slides in multiple types of aircraft. Only once had a compressor stall going to full AB during a high AOA scissors at FL290, and that quickly cleared. So tail slide does not necessarily mean flameout or stall.
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Old 9th May 2011, 01:19
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takata, quote[FONT=Verdana][SIZE=2]:
AF447 - timed cases for one upset from cruise level:
01.06.2009..35,000..FL350...60s..~5 NM..A-330 (1 mn)
01.06.2009..23,000..FL350...90s..~5 NM..A-330 (1.5 mn)
01.06.2009..17,500..FL350..120s..~5 NM..A-330 (2 mn)
01.06.2009..12,000..FL350..180s..~5 NM..A-330 (3 mn)
01.06.2009...9,000..FL350..240s..~5 NM..A-330 (4 mn)
01.06.2009...7,000..FL350..300s..~5 NM..A-330 (5 mn)
01.06.2009...6,000..FL350..360s..~5 NM..A-330 (6 mn)

Monsieur, can you explain what these figures mean, and from what data they were derived?
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Old 9th May 2011, 01:51
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Originally Posted by Machinbird
It seems that the crew somehow was able to keep the engines running for the majority of the descent, at least some of which must have been at very high AOA. Perhaps the fan creates local airflow straightening in front of the engine at high AOA. Perhaps the power settings were low enough to avoid stall.
The problem of such form of reasoning is obvious to me:

Axiom 1: ACARS sequence (pitots icing) started at 0210; consequently, it would certainly cause an unrecoverable upset at nearly the same time (or even before if you want to make the Normal Law pulling up this zoom climb all by itself).

Axiom 2: This unrecoverable single upset was followed by a massive loss of altitude, but at a very slow rate of descent, from 0210 to crash time; during those four to five minutes, while a very small linear ground distance was nonetheless covered.

Axiom 3: As ACARS sequence ended at 0214:26, this aircraft crashed no later than 0215:14.

While I'm questionning Axioms 1, 2 & 3 altogether, your point will become fully circular if your answer is that those engines could not have stalled at very high AOA because they obviously did not have stalled during all the descent down to sea level, which some part of it should have been at very high AOA.

Don't you think?

As for the "full power", a response (at this time) to low speed stall was supposed to apply (full?) power and to reduce AOA -now revised the other way, if I remember it correctly.
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Old 9th May 2011, 02:13
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Even if he crew did nothing and the engines stalled they would still keep running.

A stall does not equate to a failed or dead engine. It is only a symptom as a sneeze is to a human.
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Old 9th May 2011, 02:28
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Axiom 1: ACARS sequence (pitots icing) started at 0210; consequently, it would certainly cause an unrecoverable upset at nearly the same time (or even before if you want to make the Normal Law pulling up this zoom climb all by itself).
Takata (Olivier) What if it wasn't pitot icing that caused the ACARS message at 0210 but an actual stall that caused erratic airspeed data in the same way that the Perpignan aircraft experienced bad airspeed data at the stall? No one his been able to discount this possibility yet. Can you?
Thank you for the spirited discourse.
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Old 9th May 2011, 02:31
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Hi Chris,

Originally Posted by Chris Scott
Monsieur, can you explain what these figures mean, and from what data they were derived?
Sorry if this was not clear.
I formated the columns exactly like the table above including 9 historical cases of LOC in order to compare them easily with 1 to 6 minutes rate of descent from FL350 for AF447 in case of a single upset leading to the crash.
So, the headings are the same like in the first table:
1. Event date
2. Rate of descent (ft/mn)
3. Flight Level (departing)
4. Duration (seconds)
5. Distance covered (Nautic Miles)
6. Type of aircraft
7. Known cause of upset

It is showing that a 1-3 minutes duration event might have fit with the historical table (12,000 to 35,000 ft/mn); that the covered ground distance of 5 NM is also coherent with other historical cases; but that a possible 4-5-6 minutes event (6,000 to 9,000 ft/mn) do not match the precedent cases.
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Old 9th May 2011, 02:54
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Hi Lomapaseo,
Originally Posted by Lomapaseo
Even if he crew did nothing and the engines stalled they would still keep running.
A stall does not equate to a failed or dead engine. It is only a symptom as a sneeze is to a human.
Right!
Nonetheless, such a sneeze would have been reported via ACARS -even loss of thrust, and there is no trace of it in the sequence... Then, I asking what the chance really are that they will keep managing perfectly those throttles all their way down to the sea and avoid it?

A/THR off, FADEC compromised (ADM feeded), heavy tropical rain, airfoil critically turbulent... ice ?

S~
Olivier
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Old 9th May 2011, 03:02
  #972 (permalink)  
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takata

howdy. The limits accepted and proposed in your post differ from A330 A/P limits only in ND. The 330 a/p limit for ND is nine degrees. This I recall from data posted by PJ2. I think that given the data supplied by ACARS and the requisite times, it is premature to eliminate other than ICE in Pitot Tubes as the cause of 'upset', a/p drop, or LOC. Something is not right about PF allowing a/p to exceed its limits and decouple involuntarily. He knew what was in store (ITCZ), was alert, and something happened to paint both pilots into a corner. ACARS suggests an attitude locking with the satellite for those four minutes.

At the impact point I think 447 was travelling as slow as she ever did; iow, she was decelerating perhaps continuously from upset and/or loss of control??

Still she could have been travelling at 160knots down, and 80knots forward for an actual airspeed of ~220Knots?? At this speed, with perhaps an AoA of 80 degrees plus, does this fit??

JD-EE I think the debris field we see, from the few photos, suggests that it is composed of mostly "heavy stuff" so lighter objects would be well to the West, elsewhere, or may have left prior to impact. An A330 at touchdown and flaps extended carrying 140 knots with a deck angle of 16 degrees (17 is tailstrike time) has an angle of attack (Flap) of 45 -50 degrees. At 210plus knots (AF447), even with flaps stowed (BEA), and an AoA of 80 degrees, well, one starts to see the stress on the Flap. If the Flap is Prised loose and leaves, the spoilers will follow quickly, having lost their "Prot" from the massive flap. Their plane of stress is opposite stress from beneath.

This is as close as I'll get (at this point, having softened my admitted alarmist views at the outset) to suggesting that the a/c was other than completely intact at impact. My suggestion is that as much as I appreciate and admire your courage in suggesting it, not even bear thinks this airframe had greater than 90 degreees of AoA ('backward' flight)...

Last edited by bearfoil; 9th May 2011 at 05:03.
 
Old 9th May 2011, 04:26
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"As Close as I'll get..."

Bear,
I've been following this and the other threads since June '09. I'm sure many will agree that you've been a lot closer than that to suggesting the A/C was not intact before impact.
Andrew
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Old 9th May 2011, 05:13
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Cool

Hi,

Returning far away in the past .....



I still feel very frustrated when I look at this map ...
It shows the very first search (aerial) and then those incurred by the BEA
The abyssal plain where you found the wreck was known (from a hydrographic point of view)
I always wondered why the BEA has not started his research in this area .. that was easy enough to explore .. compared with the rugged surroundings.
Over the means used during the aerial search (detection signal pingers) was not very efficient.
The negative results of the aerial search in this area (other than find some floating debris) should not be considered conclusive IMHO
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Old 9th May 2011, 09:15
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Originally Posted by Chris Scott
The cabin altitude and differential pressure in the cruise at FL350 could not have coped with a sudden climb of 6000ft without maximum differential pressure being reached. Shortly after that, the safety valve would operate and the cabin VS (cabin climbing) would increase to something well over the +1800ft/min required to trigger a warning identical to that generated at 02:14z, the subject of the last ACARS message received.
Sorry, don't follow - the cabin alt is controlled at max 8000ft equivalent, this will only rise rapidly due to a breach in the pressure vessel - potentially triggering that ACARS message. Surely this variant A330 certified for cruise at more than 40,000ft and no need for cabin air pressure controller to dump cabin air to protect max pressure differential (9psi)?

Originally Posted by takata
Hi Lomapaseo,

Right!
Nonetheless, such a sneeze would have been reported via ACARS -even loss of thrust, and there is no trace of it in the sequence... Then, I asking what the chance really are that they will keep managing perfectly those throttles all their way down to the sea and avoid it?

A/THR off, FADEC compromised (ADM feeded), heavy tropical rain, airfoil critically turbulent... ice ?

S~
Olivier
I do not think it is the engines management system responsibility to report on flight envelope issues, and if the ADM feeds of Temperature, Pressure, Mach Number etc are marked as suspect wouldn't the FADEC be forced to just look at its own data? - can't be FA if critically dependent on external systems! Isn't it possible that from engines own measurements of total pressure inlet, EGT etc the engines themselves were operating within expected performance parameters, and just reporting rotational speeds and effective thrust output back to the higher level systems as normal. 'Rollback' due to ice build up would be different, with the engine able to sense that it wasn't working as expected, so maybe this didn't happen.

Last edited by sensor_validation; 9th May 2011 at 10:21.
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Old 9th May 2011, 09:56
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There is an interesting story in the online edition of the New York Times (the former International Herald Tribune website) about the search for the aircraft and what has happened since then - here is the link:
What Happened to Air France Flight 447?.

It's not a scholarly article, but it is of a much higher quality than most stories that have been published about the search. Makes for interesting reading.
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Old 9th May 2011, 09:57
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Originally Posted by Chris Scott
Regret to say that I cannot calculate the flight-level where this would occur
For flights longer than 2.5 hours the cabin altitude is 7350 ft (*), pressure 11.19 psi. The safety relief valve setting is 8.85 psi (*), so it would open when the ambient pressure passes through 11.19 - 8.85 = 2.34 psi, i.e. FL429.


EDIT:: (*) Reference FCOM 3.01.21 p.1; Operating Limitations; AIR COND/PRESS/VENT; Cabin Pressure.

Last edited by HazelNuts39; 9th May 2011 at 11:00.
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Old 9th May 2011, 09:59
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jcjeant, machaca,

I don't remember anyone at the time thinking that the bodies and recovered debris could have drifted so far from where we now know the wreckage is located. IMO the mistake was to waste the time pursuing the spurious pinger signals "discovered" by Thales. Without this diversion the wreckage might have been found in phase three.
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Old 9th May 2011, 10:35
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Cool

Hi,

IMO the mistake was to waste the time pursuing the spurious pinger signals "discovered" by Thales.
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Old 9th May 2011, 10:44
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'Morning, sensor validation,
Quote:
"Sorry, don't follow - the cabin alt is controlled at max 8000ft equivalent, this will only rise rapidly due to a breach in the pressure vessel - potentially triggering that ACARS message. Surely this variant A330 certified for cruise at more than 40,000ft and no need for cabin air pressure controller to dump cabin air to protect max pressure differential (9psi)?"

As I implied in my post, I'm suffering from:
(a) not knowing the A330 pressurisation schedule;
(b) lack of expertise in calculating the diff-press for different pairings of cabin-altitude versus aircraft-altitude;
(c) lack of ability to calculate precisely the cabin-VS versus aircraft-VS at a fixed diff-press.

From experience on the A320, A310 and other jets, however, I can tell you that at the medium cruise altitude of FL350, the cabin altitude would not be scheduled as high as the maximum-permitted 8000ft. My GUESS was that it would have been about 6000ft, for passenger comfort. This would keep the diff pressure below the normal maximum of eight-point-something. During even a brisk step-climb in normal operations, that gives the controller a relatively easy task to climb the cabin at the maximum desired rate of 500ft/min without max-diff being reached.

You are quite correct to point out that, in normal (planned) flight at the max cruise alt of FL410, the cabin altitude would be about 8000ft, and the differential pressure would be just below maximum.

Chris

PS
While I've been drafting this, HN39 has kindly provided us with some figures that are significantly different from what I had in mind. As you can see, if he is right (and he normally is!) grity's zoom climb to FL416 would not trigger the cabin VS warning.
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