CONF iture

Observation of the AoA vanes attitude during walk around tells me that they are not affected by gravity, or they would all display that unique attitude commanded by gravity.

Something else is behind that AoA data invalidity below 60kts ...

bearfoil

BOAC

I think you are right, the limit of evidence based opinion was probably attained some time back. I do think it important that a few people continue to exhaust the possibilities to nil. That is a worthy task, for "out of sight, out of mind", lets the dogs out.

forget

If this doesn't explain the difference then nothing will

http://www.boeing.com/commercial/aer.../whatisaoa.pdf

milsabords

Pitot tubes can be clogged by dust, water or ice cristals because air flows inside from their inlets to their drain holes.

I imagine a tube w/o a drain hole, fed from the aircraft by a variable presssure air pump, controlled to deliver a fixed air flow. The internal pressure is a function of the outside total pressure at the tube inlet, therefore the air speed can be measured.
Side benefit: a simple test on the ground can detect clogging by insects or scotch tape.

wes_wall

And, why do you suppose this is the case? Duh. History shows that their actions were totally predictable. I am sorry to throw a dart, but this is what I feared would occur, and I continue to fear may be the case in future reports to come. What in goodness name is wrong with the truth, or the release of facts. The facts do not have to be judged or editorialized, only reported. Seems the lack of information only promotes the lack of credibility of what is ultimately published. Guess I have been spoiled by the NTSB proceedures.

gums

As most here know, it is not my style to "correct" someone or tell them "they are stuck on stupid" or challenge their lineage. I prefer to iterate my point with data and my anecdotal evidence, experience, if you prefer. Hence...

a) To one poster challenging an estimate of AoA using known pitch /roll attitude and platform inertial velocities at impact:

I am completely familiar with the fact that planes fly thru the airmass, which may be moving with respect to the surface, even a "moving' surface such as the sea, with its currents. Ditto for airmasses moving vertically, as in storms or mountain waves or thermals.

So assuming a reasonable airmass movement within a few hundred feet above the ocean, as well as the current, a few knots here and there are not significant.

Cogsim points out BEA's finding of the horizontal and vertical components of the jet at impact ( last recorded value). Further, BEA claims a pitch attitude of 16 deg or so and 5 deg roll to the left.

If we do the math we see an approx 45 degree descent angle with nose up at 16 degrees. So my estimate is about 60 - 61 degrees AoA with respect to the longitudinal axis of the jet. Actual AoA seen by the wing is prolly a bit different due to the incidence angle of the wing, but close enuf for estimates.

So I return to my graphic of another jet's pitch moment characteristics.



It is quite possible that the 'bus has a similar aero behavior with respect to static stability ( not dynamic or phugoid or .....). So I simply show that the jet could have been in a stabilized deep stall with little or no capability to get the nose down ( call it pitch authority) , regardless of pilot input. Especially with the THS trimmed almost to the max.

A small roll at impact seems logical, especially if the 'bus has great lateral stability or the computers still have some degree of authority in yaw.

b) The skydiver analogy seems close, but realize the later inertials and GPS units are very capable of measuring tiny velocities. The inertials in all three axis, the GPS much better horizontally than vertically ( it's why JDAM quits using GPS several thousand feet above the tgt and prefers a near vertical vector). Further, skydivers DO HAVE A L/D. It ain't much, heh heh, but can be measured if you carry one with you on your next jump.

respectfully,

Gums sends....

bearfoil

wes wall

Any group with a common goal maintains its shape until things go afoul out of balance, a trend that seems to leave one or the other "holding the bag".

The Goal remains the same, so "partners" begin to equivocate, and a slow evolution toward the Truth is attained, partners engaging in damage control until the gig is up.

This happens on the schoolyard, and in the Boardroom.

Virtually all the data is in. The ONLY reason to parse it is to protect one's interests.

Sometimes it is important to comfort the afflicted. At other times, it is necessary to afflict the comfortable.

Who will let the dogs out?

CONF iture

I'm glad to read these words more often than before :

spagiola

I think the value of this thread has been precisely in pointing out how little can be concluded from what BEA has so far published. Some have been eager to make the BEA report fit various theories, and often done so by very selective quotation, or indeed misquotation. It has been useful to have people point out that these interpretations were either wrong or could not be substantiated without more information.

But it does seem we're reaching diminishing returns...

grindles

BOAC
It's a big document. Which bit would you like translated?
BTW thx to all you professionals for your interesting and very enlightening comments which we SLF greatly appreciate!

Hyperveloce

At 2 h 10 min 51 , the stall warning was triggered again. The thrust levers were positioned in the TO/GA detent and the PF maintained nose-up inputs. The recorded angle of attack, of around 6 degrees at the triggering of the stall warning, continued to increase. The trimmable horizontal stabilizer (THS) passed from 3 to 13 degrees nose-up in about 1 minute and remained in the latter position until the end of the flight.
Around fifteen seconds later, the speed displayed on the ISIS increased sharply towards 185 kt; it was then consistent with the other recorded speed. The PF continued to make nose-up inputs. The airplane’s altitude reached its maximum of about 38,000 ft, its pitch attitude and angle of attack being 16 degrees.
(source: http://www.bea.aero/fr/enquetes/vol....mai2011.en.pdf)

Graybeard

Trying to visualize a plane dropping at 107 kt with near zero horizontal speed, and the pitch angle at 16 or some such degrees nose up:

The ailerons would have almost no effect, and the spoilers may even be pushed up by such an abnormal relative wind.

The THS and elevator would not work in a normal manner.

What could the engines do? How would you get the skydiver flying again?

JJFFC

Never-mind to know whether the plane could have recover or not as long as the pilot don't nose down.

henra

That is at least consistent with the way Auto- Trim is supposed to behave under normal conditions and therefore a likely scenario.

At least before probably entering into Abnormal Law when the AoA exceeded 30°, a normal continuous Nose down command by pushing the stick forward should have also reduced THS angle accordingly.
Therefore it is likely that a manual use of the Trim wheel would only have been required when deep in the stall, long after starting the descent.
That point would have been reached somewhere around 2:11:30.
And even after that point Auto Trim could have been regained if continuous Nose Down combined with reduced thrust would have reduced the AoA below 30°.
In that case auto Trim would have been available again.
The fact that a brief Nose Down and Thrust reduction brought back the speed readings indicates that very likely a continuos full Nose Down command would have saved the day, probably even after exceeding 35° AoA.
Unfortunately it seems that was never really attempted, at least not persistently enough.
Sad.
The question remains Why !?
Let's hope the CVR will shed some light on that.

Edit:
Graybeard:
Even at these angles the deflection of THS and elevator will have significant influence on the behaviour, especially in combination.
The combination produces camber which even under high AoA will change the drag coefficient significantly.
That is one advantage compared to the all moving tailplanes on an F-16 for recovery in such a situation.
The other advantage of the 'Bus' is the fact that it is by far more longitudinally stable than the F-16 which was even slightly unstable in the A- Version. It had a negative stability coefficient (albeit very little).
The 'Bus' has definitely a positive longitudinal stability margin even with max aft CG.
Therefore it surely needed the 13° THS (potentially plus Nose Up elevator) to keep it in the deep stall.

CONF iture

PLEASE, Graybeard, do not modify the little data we have been given :
Ground speed (horizontal speed) was at 107kts
CG was at 29%

voyageur9

assume (I fully understand it is a hypothetical) that the pilots had done nothing; no sidestick inputs, no throttle adjustments. Would the aircraft have recovered -- i.e. AP re-engaged, IF valid (or within the computer-acceptable range of) air speed readings were restored?

andreg

English version is here : http://www.bea.aero/docspa/2009/f-cp...90601e1.en.pdf

However, appendixes are book scans left untranslated.

Graybeard

Ok, Confiture, maybe you have a logical explanation why the GS reported was the exact same 107 kt as the vertical velocity. See post #552.

Prior to the report's release, there was a lot of discussion about tail fuel and 39% MAC. There was apparently no requirement to move the fuel forward by the time of the accident, and I saw no mention of it from the report.

I'll go back and generalize my last post.

OPENDOOR

Perhaps at this time we should take a moment to think about the people at the Bureau d’Enquêtes et d’Analyses pour la sécurité de l’aviation civile.

The flight deck crew of AF 447 had slightly over four minutes to try to figure out what was happening. The BEA have spent thousands of hours going over every millisecond of data and CVR information all the way to impact with the ocean at some 55 m/s or 123 MPH.

Not an enviable job. They must have good reasons for releasing the information that they have.

ChristiaanJ

What do you expect?
The investigators are only human, just like the crew of AF447.
They are trying to piece a picture together, even in their own minds, as to what really happened.
If you think that is easy, with a limited amount of complex data in front of you... please shut up... you clearly have never participated in a crash enquiry.

They are being 'pressurised' for at least "something".... So they do release the few confirmed facts..... but not yet their own thoughts on the matter, or equivocal and as yet uninterpreted data.

Get real.

PS Re the previous OPENDOOR post.... Same point I was trying to make.