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AF447

Old 3rd Jul 2009, 00:03
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Brazilian ATC reports Dakar about AF447

recording here:

http://www.fab.mil.br/portal/voo447/...dio_020709.mp3

Last edited by augustusjeremy; 3rd Jul 2009 at 00:23.
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Old 3rd Jul 2009, 00:18
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The TU154 animation is a characteristic of deep stall with T-tail. If the A330 found itself in full-on stall with attendant nose pitch up, they crew should be able to recover with just the horizontal. If for some reason that wouldn't work, alternating thrust and reverse thrust could rock you out. But of course the FADEC probably wouldn't allow reverse thrust with weight off wheels.

The tail should have been enough. Will pull some conventional tail, low wing, transport wind tunnel data when I get a chance.
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Old 3rd Jul 2009, 00:23
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Originally Posted by LeandroSecundo
If they were trying to ditch (a la Sully) certainly the passengers were fitted with their inflatable lifejackets .
Whilst I very much doubt this was an attempted ditching, the Sully comparison wouldn't prove it anyway, since his pax didn't apparently have lifejackets on, see eg.:

http://newsimg.bbc.co.uk/media/image...sengers466.jpg
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Old 3rd Jul 2009, 00:44
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FWIW, read something about finding a piece of trim from the elevator. Was that what we thought was an aileron segment earlier.
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Old 3rd Jul 2009, 00:45
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FWIW

In free fall in a stable flat attitude at 205t, terminal velocity could be in the region 200 ft/s ~ 300 ft/s - at sea level density. (obviously back of a fag packet calculation, but might give an idea)

Thats as little as 2 minutes from cruise altitide
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Old 3rd Jul 2009, 00:57
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reason to delay ditching...
radio distress call...possibility of ship nearby etc

remain airborne as long as possible

of course, the middle of a storm is a tough place to be.
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Old 3rd Jul 2009, 01:11
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You can get a nose down moment from flaps and deploying the landing gear, more so from the flaps. Redistributing fuel, if possible, would help, but that's time consuming.
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Old 3rd Jul 2009, 01:24
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The real question is whether the pilot flew the aircraft into wx that it couldn't handle or the flight control systems gave the pilot an aircraft that couldn't be flown.

The rest is all consequential ...
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Old 3rd Jul 2009, 01:27
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ttcse re #2830 – “… sit with a long duration stall and not try to recover only because they lacked instruments …”
I did not intend my post to read that way.
The issue, as with the 737 accident/incident (and speculation on the A320 accident), is that with an ‘over-trimmed’ nose-up condition there may be insufficient nose-down elevator power to affect a stall recovery. The stall / trim condition might be further aggravated by the apparent aft cg.
I have sought further understanding in http://www.pprune.org/flight-testing...ml#post5019448

A characteristic of some FBW aircraft appears to be that in comparison with conventional controls there is a lack of control/trim-force feedback on the stick. Thus for pitch trim, the trim position (with respect to balanced flight – auto trim follow-up in normal law) has to be determined from a scale. Thus do pilots need to be aware a suitable trim range for stall recovery, and what effect has ALT law on this situation?
The above is far from fact, hence my questions in the other forum.

The crew might have been aware of a stall if the AOA provided an input for indication / alert.
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Old 3rd Jul 2009, 01:30
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CC...Lowering of flaps and gear might have made a difference, presuming they were in a stall, but, given the time from altitude to surface, would that be your first decision? There was a hell of a lot going on up there, and apparently little time to make any logical decision. Don't get me wrong, your logic is good, but can you imagine the dramatic situation they were in?
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Old 3rd Jul 2009, 01:53
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Originally Posted by Lightning6
CC...Lowering of flaps and gear might have made a difference, presuming they were in a stall, but, given the time from altitude to surface, would that be your first decision? There was a hell of a lot going on up there, and apparently little time to make any logical decision. Don't get me wrong, your logic is good, but can you imagine the dramatic situation they were in?
Sorry, I have to disagree ...

If the main plane was still flying, flaps move the center of pressure forward, causing a pitch up; they permit a nose down attitude at low speeds for this reason.

And, yes, at FL350 the last thing I would think of is gear/flaps.
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Old 3rd Jul 2009, 02:48
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Are we missing something here?

I am keen to understand more about the significance of the “Advisory Cabin Vertical Speed” transmitted at 0214.

Until a few seconds before this message all ACARS related to the suspected loss of reliable pitot information and sequenced deactivation of systems depending on it. Namely A/P , A/T airspeed displays and degraded control law etc.

There has been much discussion on the techniques of handling a loss of reliable airspeed. Power plus attitude maintained at cruise values would generally be expected to suffice and should not readily see the aircraft depart controlled flight. So do we assume that the aircraft should have been right side up and under some degree of control to this point?

But what of the “Advisory Cabin Vertical Speed” which the report states;

Symptoms: Flashing of the cabin vertical speed indicator on the SD’s PRESS page.

Meaning: This message indicates a cabin altitude variation greater, as an absolute value, than 1,800 ft/min for five seconds.

This is cabin rate, not aircraft rate. If the hull was still intact it suggest the Cabin Pressure Controller (lacking good altitude input) had perhaps lost control over pressurization. Did the crew, already facing a dire situation, become aware of a rapidly climbing cabin altitude and initiate an emergency descent?

Turn off track! Lower the nose, Thrust Idle and Speed brakes out!

That severely challenges the “maintain power and attitude for cruise” scenario.

With speed brake the already limited speed range between high mach stall and low speed stall is dramatically reduced. Without displayed IAS and considering the associated buffet and likely turbulence it would have been a difficult task for any pilot in their predicament to stay within normal flight parameters!

So was the “Advisory Cabin Vertical Speed” merely a further symptom of things going wrong or a contributing factor? Perhaps the straw that broke the camel’s back.
 
Old 3rd Jul 2009, 03:25
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"Inconsistencies between the measured speeds"

*twenty-four automatic maintenance messages were received between 02:10 and 02:15 via the ACARS system. These messages show inconsistency between the measured speeds as well as the associated consequences;

* visual examination showed that the airplane was not destroyed in flight; it appears to have struck the surface of the sea in a straight line with high vertical acceleration.
"Inconsistencies between the measured speeds" was adequately explained by OVERTALK in post 322 on 06 June.
i.e.
1. Port and starboard pitot and static sources will be recording significantly different speeds during a spin
2. A spinning aircraft will strike the surface in a relatively level attitude but also "in a straight line with high vertical acceleration."

Think we're back to a loss of control in coffin corner (for whatever reason).

ALSO RELEVANT (for explanations):

posts 324,

#325 and #2222 and #2412
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Old 3rd Jul 2009, 03:31
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given the time from altitude to surface, would that be your first decision?
The Edwards' test pilots know to extend the gear for spin recovery last chance effort if all else fails, so there is some precedence. The finless B-52 guys figured out gear extension helped due to the aft bogey. Depends on the pilot and his knowledge of the depth of aviation that preceded him. But face it, if you're stuck in a stall, you'd be figuring it out real quick.

There is another precedence though from GA. They interviewed survivors after engines fell off of Buckers, before they cabled them in, asking why they didn't bailout. They replied they still had 3 axis control, where in straight and level descending flight, figured all was well, and didn't grasp the sink rate till they got low. Don't know if this is even applicable in this case, but thought I'd throw it out.

If the main plane was still flying, flaps move the center of pressure forward, causing a pitch up; they permit a nose down attitude at low speeds for this reason.
Flaps down cambers the airfoil and creates a nose down pitching moment in 2D. If that is reversed, then the B-2 would use down elevator for pitch up. Additionally, when applied 3D on an aft swept wing, the 2d effect
still applies, and the outer portion of the wing is making more lift aft of the aircraft cg producing a nose down moment.

The nose down attitude with flaps for landing is because the stall AOA is reduced flaps down.
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Old 3rd Jul 2009, 03:37
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Port and starboard pitot and static sources will be recording significantly different speeds during a spin
Additionally, pitots are accurate for small angles, below 10-15 degrees AOA. Much more than that and you need a flight test boom. Pitots would measure different pressures at high AOA for different waterline locations on the nose, even on the same side.
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Old 3rd Jul 2009, 03:39
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Originally Posted by falconer1
no, "beyond all reasonable doubt" is not possible in a lot of cases, and may not be possible in this case..
Thank you for your reply but, with all due respect, I disagree. The key word is reasonable. We can never be 100% certain and that is why the cause of every accident is always defined as "probable". With data from from the FDR and CVR we can determine the probable cause beyond all reasonable doubt.

I agree with all the dangers you articulate associated with the penetration of convective cells. However, your message infers that you are convinced beyond reasonable doubt that this aircraft did penetrade a deadly cell. With all due respect you have no verifiable data that supports that hypothesis. It is only your assumption.

We do know, beyond all reasonable doubt, that the crew lost control of the aircraft at some point between INTOL and TASIL, but we do not know where that occurred nor why. We can logically presume, beyond all reasonable doubt, that they did not descend 35,000 ft with the deliberate intention of executing a water landing in the Atlantic ocean for the thrill of it.

We can also presume that an involuntary descent of approximately 7 miles in a large T-category transport aircraft, out of control, is most unlikely to have ocurred with no structural damage of significance prior to impact. Such a presumption is not logical. It is a fine aircraft, but it is not immune to structural damage in flight.

Only the FDR and CVR can definitively answer the questions that we all have. IF they are recovered and readable, it is only then that the various hypotheses can be developed into a scientific theory. The probable cause will then have been determined - beyond reasonable doubt.
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Old 3rd Jul 2009, 03:44
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The Edwards' test pilots know to extend the gear for spin recovery last chance effort if all else fails, so there is some precedence. The finless B-52 guys figured out gear extension helped due to the aft bogey. Depends on the pilot and his knowledge of the depth of aviation that preceded him. But face it, if you're stuck in a stall, you'd be figuring it out real quick.
I appreciate what you say CC, but these were not test pilots, they were probably not in a spin, and to drop the gear in the possibility of a ditching is a no, no.
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Old 3rd Jul 2009, 03:48
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For clarifiction.

UNCTUOUS, OVERTALK and Dagger Dirk are one person.
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Old 3rd Jul 2009, 03:52
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Agree L6. But to them dropping the gear would be to gain some control and not for a ditching. I can't imagine these 3 souls would have just ridden it down without reconfiguring. We don't know the sequence yet, maybe they spun, slung the engine/s, were able to recover somewhat, and couldn't unstall because of an aft cg of the reduced configuration. Could we tell if the engines departed through the boxes.
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Old 3rd Jul 2009, 03:56
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Originally Posted by ClippedCub
Agree L6. But to them dropping the gear would be to gain some control and not for a ditching. I can't imagine these 3 souls would have just ridden it down without reconfiguring. We don't know the sequence yet, maybe they spun, slung the engine/s, were able to recover somewhat, and couldn't unstall because of an aft cg of the reduced configuration. Could we tell if the engines departed through the boxes.
Will we ever know?, I have my doubts.
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