Well, yes you could resume flying and generating lift, but you would be diving at a pretty severe angle and you have to generate enough G to turn the aircraft from that nose down path to horizontal. You have over 100 mph of vertical velocity and it's going to take some positive G to get rid of that. You aren't going to level out right away.

Vertical velocity is 170 ft/sec, and a 2G pullout would subtract 32 fps from that every second. Let's say 6 seconds, during which you would lose quite a bit less than 1,000 feet. Doesn't sound as if pulling out of a 25-degree glide at 250 knots would take that much room. At low altitude it should be possible to pull 2G without risk of a secondary stall. The point is, despite its high vertical velocity the airplane is not descending that steeply.

AoA versus velocity vector, etc
 

Sorry Garrison, but you must add the pitch attitude to the AoA to get the descent angle.

At impact, we know the BEA figures for 107 knots horizontal and vertical. Another contributor came up with same numbers I did, which was a basic 45 degree flight path with a 16 deg pitch attitude at impact. So AoA would have been around 61 degrees. When I use 107 knots vertical, I get about 10,800 feet per minute vertical vector, which seems to agree with BEA's numbers.

I point out the close agreement with my back-of-the-envelope calculations concerning vertical velocity

I can't find a BEA data point of 16 degrees pitch attitude and 35 - 40 degrees AoA in their report.


more on "trust your AoA" later for those debating its value when airspeed is FUBAR.

Lonewolf_50
I'm just looking for the cause of the two stall warnings right at the start, using the hypothesis that a stall warning is triggered not only by AoA but also when the (indicated) air speed falls into a region where a stall in level flight is imminent.

The further conjecture is that the PF acted on these (spurious) warnings according to the manual, and in doing so, perhaps in conjunction with an unfortunate updraft, got himself into a real stall.

So the invalid stall warnings helped get them into a real stall - and the lack of stall warnings (plus the resumption of warnings at times on correct pilot input) when they were in the real stall minimised the chance of them ever getting out of it.

Just a thought.

AoA indication
 

Excuse me for interjecting in a technical discussion as mere SLF (even if it is one who sits on an A340 across the pond rather often):

I am conscious of the various discussions about presence or absence of an AoA indication, and have read this entire thread from day 1 (sad?).
My personal background started in mathematics, moving into engineering, including the much maligned real-time software.

Anyway - a couple of comment on "vector maths", which most pilots should be familiar with from route planning?

If we assume that "pitch and power" were to be maintained, we would have an aircraft with pitch which was likely to be based on inertial reference. At this time, I believe this has not been questioned. A previous post then said that "pitch = airspeed, power = altitude". This makes sense, although I confess I have not had time to search back for the quote (credit to the author, never the less).

Then to the next stage - if you have pitch with reasonable reliability, the AoA is likely to be close to the vector sum of the forward and vertical velocities (not accounting for upward or downward air movement)

Hence - if you have reasonable, or at least some, indication of pitch and a large downward vertical velocity then do you not have a fair indication of a possible stall? The alternative is a very strong updraught - but how long is that likely to last?

Just a thought, I wonder if it is relevant?

Not on this planet. You have to add the pitch angle to the negative of the flight path angle to get the angle of attack (assuming that the flight path angle is negative for a descent).

With regard to the descent angle, the BEA report I am reading (27 May) says 15 to 16.2 degrees deck angle. At 35,000 feet, on the way back down, the angle of attack exceeds 40 degrees but during the 3+30 descent the angle of attack "remained greater than 35 degrees". Now, I suppose you could argue that "greater than 35" means 65, but the use of "exceeds" and "remained greater" strongly suggests that the AoA remained in that neighborhood -- that is, "greater than 35" means 36 or 37, not some much larger number.

I concede that the 107-knot groundspeed at impact is inconsistent with my calculation of 250 ktas, unless there is an improbably huge surface wind; but it is also inconsistent with the reported pitch angle and angle of attack. Maybe something changed in the final seconds; I don't have a good theory handy.

I haven't flown one in many years, but the Stall Horn on the 150 series I believe is nothing BUT an AoA indicator, albeit "aural". Zeroed to exclude angle of Incidence, (the from factory difference in chord line and fuselage longitudinal line) the horn starts to mouth off when air "leaves" the orifice. This I know for I used to test it by inhaling on the hole, and depending on effort, I could almost play it like a flute. Blowing into it accomplishes nothing. When the ANGLE of the airstream starts to impinge on the orifice at a suitable positive AoA, the annoying alert starts to pucker one's own orifice, more so as the AoA approaches the Stall Break.

Dozy. I am in earnest about evidence, something I define as facts, as do you.

Likewise, at Court, facts come with a guarantee, something lacking here.

You are not incorrect in your explanation of the Laws, I believe in you completely. Thus far, the bulk of trouble some have here is not in disallowing the Program, or its influences, but in the arena of suitability in crisis. This unsuitability is in discussion, and I warrant it has a basis in fact. something you seem unable to entertain.


I repeat. IF, upon selling a suite of hardware, one does not exhaustively train its usage to the client, one has sold a bill of goods.

one outsider. Please accept my offered apology for twaddle. I agree, though I think your Twaddle Launcher is pointed at the wrong target, just sayin'.

Garrison Absent any need for Pitch or AoA at impact, the Horizontal and Vertical velocities sum for a FLIGHT Path of 45 degrees descent Yes? One wishes for a mental picture of "almost" airborne, but BEA pitch at 16 and AoA at 35 + is discouraging.

ADD. I get an airspeed of about 135-145 knots (at impact) if BEA'S numbers for rate are accurate.

Abnormal Attitude Law
 

PVT
If AOA is available for FDR it should be available for other systems too (benefits of ARINC429),
I've read in system schematics that there is a separate AOA backup signal bus to FCPC's.
On second thoughshould have been activated by AOA >30 @ 2h 11 min 40 ts that may be only on –BUSS- equipped A/C.
I'll come back to you if I got that in hand.

Besides that, if you combine the 3 BEA reports together, the Abnormal Attitude Law before NAV ADR DISAGREE warning msg @2h 12. (Received 2h 12 51)

@Bear:

.

Just trying to clear some operational 'misunderstanding' of FBW and laws from an E&M point of view. If not appreciated just say so.

http://i474.photobucket.com/albums/r...PitchWheel.jpg


@Dozy:

Agree with you.

AoA Utility
 

As I have posted a couple of times before, AoA is highly useful at approach speeds (and in a stall situation) but not for maintaining a desired flight condition while in cruise. When encountering an Unreliable Airspeed condition, flying a specified AoA would not be very effective in cruise. At approach speeds, AoA varies relatively large amounts for relatively small changes in airspeed. At cruise speeds, the variation of AoA is relatively small for relatively large airspeed changes.

The U.S. Navy uses AoA for landing on aircraft carriers because it provides a precision reference for executing a precise approach. AoA indicators have not typically been used in transport category aircraft because that degree of precision is not required, but flying AoA does allow the pilot to fly the correct approach airspeed, regardless of weight and without reference to tables. The P-3, as initially introduced into the fleet, was equipped with AoA indicators but they were routinely ignored because "AoA is for jets". I don't know if those AoA indicators are ever used today.

IMHO, AoA is the single most useful instrument you can have to prevent a stall.

Yes, and with 16 degrees nose up that gives an AoA of 61 degrees as asserted by gums. But the BEA numbers for most of the descent -- pitch 15, AoA 35-40 -- imply a much shallower descent. The airplane was almost uncannily stable during much of the descent -- steady AoA, no spin, and 40-degree wing rock correctable with ailerons is pretty nice behavior with AoA > 35 -- but that may have changed. It is not clear to me whether thrust went above idle again after 2:12:02; at low altitude thrust could affect angle of attack.

Garrison

Bear says:

Quote:
at impact, the Horizontal and Vertical velocities sum for a FLIGHT Path of 45 degrees descentYes?

Garrison says:

Yes, and with 16 degrees nose up that gives an AoA of 61 degrees as asserted by gums. But the BEA numbers for most of the descent -- pitch 15, AoA 35-40 -- imply a much shallower descent. The airplane was almost uncannily stable during much of the descent -- steady AoA, no spin, and 40-degree wing rock correctable with ailerons is pretty nice behavior with AoA > 35 -- but that may have changed. It is not clear to me whether thrust went above idle again after 2:12:02; at low altitude thrust could affect angle of attack.

Sorry, how is 55 degrees a much shallower descent than 61?

I am using BEA derived data re: velocities, basically H/V square. That gives a very simple Pythagorean solution of 45 degrees for hypotenuse, and velocities (integral) that compute to a summed velocity of 140 knots or thereabouts. I don't disagree with your assumption that these figures were or could be different at altitude, but so far no data with which to invest in an opinion?

AF447 - Descent Profile at Impact
 

For those who need some help in envisaging what a high Angle of Attack looks like and how it will affect the pitot data, the following graphic should help.

http://oi51.tinypic.com/201mky.jpg

It should also be noted that during the final stall, the AoA was never less than 35 degrees, and this was probably only achieved with N1 100%, with the AoA increasing once engines were at idle.

"It should also be noted that during the final stall, the AoA was never less than 35 degrees, and this was probably only achieved with N1 100%, with the AoA increasing once engines were at idle."

Que?

Can anyone clarify for me the operation of the AoA system? The real angle of attack must be obtained from a lookup table that translates the vane position into actual alpha. How far does the lookup table go? The interim report says that (my translation) "The angle of attack, when it is valid [or reliable], remains above 35 degrees." (Emphasis mine.) What limits the validity of the reading? Is the AoA recorded by the FDR and reported by the BEA valid/reliable for purposes of visualizing the attitude and flight path of the airplane?

If the horizontal component increased due to additional power and the RoD remained essentially the same, the AoA will have decreased. Do you want me to stretch the graphic to prove it?

bearfoil...
I feel like Alice in Wonderland, except I'm a guy.

It's not 55, it's 25. Please please please draw a picture of an airplane, side view, nothing fancy, with its nose tilted upward 15 degrees. Then take a protractor and draw a line at a 40-degree angle downward from the airplane's longitudinal axis (which stands in, for purposes of discussion, for the mean aerodynamic chord). That is the flight path angle -- definition of angle of attack. It's 25 degrees.

Granted, the BEA numbers could be wrong -- garbage in, garbage out.

Maybe I should draw the picture. I'm not very good, but I'll try.

I think mm43's picture is cool, have you seen it? The long line is the Flight Path, from data via BEA. That qualifies as (Angle of) descent for me. Pitch and AoA are important how? Ride?

bear

mm43, hey two against one, no fair. With N1 100 %, doesn't the Pitch increase? and since increasing Pitch separates the AoA , it increases also? Lowering Thrust therefore closes the two (or...... This is a ballistic projectile. A brick with fins.

How do you post a picture? I drew one, it's a JPG, but I don't know how to insert it into a message. The "Insert image" icon asks for a URL.

MAC? maybe it's in Direct Law. You are entertaining a ballistic projectile, yes?

airfoilmod@sbcglobal. net. attachment?

I'm looking at 15 seconds before, and fifteen seconds after a/p disconnect. Here is where it happened.

AoA and pitch attitude one mo' time
 

Sorry, all, I misplaced two of the vectors in my explanation. So I'll stick with my story, and only place I find a no-kidding AoA and pitch attitude and both velocity vectors was the one I quoted from the BEA report.

This is what I was trying to depict.

http://i120.photobucket.com/albums/o...ingums/aoa.jpg

As shown here on my chalkboard, the AoA is the sum of the pitch attitude and the velocity vector ( assume airflow is opposite the velocity vector in the air).

Bear is correct about total velocity, 'cause if both horizontal and vertical velocities were identical, the total vector would be about 1.414 times either of them ( square root of two).

Need a real geometry wizard to make the call. Winner ( and referee) gets a free slug of Jeremiah Weed at my fishing cabin in Colorado in a few weeks.

I throw my hat in with the AoA mafia.

I don't understand why it isn't used more often, as it reflects the basic characteristics of the wing and its lift capability. In other words, weight of the jet is inherent, as the AoA must be greater to get the extra lift for the same speed. High lift devices, flaps, etc can change the stall AoA value, but that's an easy thing to depict on a display.

I call 'bird to the stand re: AoA indexer and gauges for the Navy jets.

Hate to hijack the thread from the "who was in what seat" discussion, but thot we could use a break.

That pitcher, that one.........

Pitch and AoA are important how? Ride? What is the AoA in flat Plate?

Or for simple folk... http://img.photobucket.com/albums/v3...330Diagram.jpg Note that the ground speed for the given pitch angle, angle of attack, and 10,000 fpm rate of descent is about twice the BEA number...

Whew! Thanks a million. But what do you mean about 10,000 fpm being twice the BEA number? It is the BEA number.

Great graphic, Tailspin
 

Yeah, Tailspin, just show for the impact velocities BEA has published.

I also got the same numbers using an AoA of 40+/- and pitch of 16 and vertical of 10,000 feet per minute

For Garrison: He says the groundspeed, not the vertical velocity. He is also using some numbers from early in the description of the descent. I am using the ones at impact, which are very specific in the report.

That pitcher, that one.........

Pitch and AoA are important how? Ride? What is the AoA in flat Plate?

I am still stuck on Flight Path, ok? Ballistic flightpath. Not "line of Flight" when there is none.

Ballistic. Some few seconds after 2:10:04, Aero was out the door, and Rocketry wandered in. Ballistic.

Rocketman? Where fore art Thou?

Well, that's the point. The numbers BEA gives for the steady-state descent are incompatible with the groundspeed at impact. Either something changed at low altitude, or the numbers are not reliable.

I think, as above, what went out the glass ("changed at altitude") was aeronautics, at ~ FL360.

One cannot fly a brick, no matter the architecture. And Stall is a point in time, once broken, Stall is left behind. It is Flight, Stall, or NOT Flight. At no time can two of the above be happening concurrently. One at a time. "Breaking the Stall" is misleading, what one does, is become airborne again. "Take off".

How's that for pedantic. Garrison, you are a writer, does that work for you?

Barkeep, two aspirin and an ROC cokola, boy howdy.

The graphic I put up on the previous page is using the BEA's data at impact. You are not telling me they read that data out incorrectly?

mm43

and my velocity was low by 11knots. Apologies, and good night.

Smilin_Ed (Another USN guy)
And also the single most useful instrument in recovering from a stall. Otherwise, at low speed, how do you know how much to push the nose down? Suppose you are actually inverted? Which way do you pull (push) then?

I didn't always look at my AOA while flying my Navy jet, but if I was maneuvering, it was definitely in my scan. If you ever get AOA in your airliner, try real hard to use it. You don't need it in cruise of course, but when you start to dirty up, you can observe the beneficial effects of slats and flaps very clearly, and with a little practice, you can tell when you need some flap to fly slower.

How to best mechanize AOA presentation has some contention, but it is probably time to develop a standard for airliners. It would be silly to have to train to recognize different types of presentations for each aircraft you fly.
A little bit of software and some free space on your PFD should be all most jet aircraft will need.

The AOA gauge directly answers the question, "How close am I to stalling the aircraft. " You can accurately fly an aircraft below stall speed in a ballistic trajectory and not stall the aircraft if you mind your AOA. (Of course, you do need some control authority-this doesn't work with tail slides.:})

I'm also thinking the first two "beeps" of stall warning on AF447 were quite possibly caused by the g incurred in the initial pull up! It will be interesting to see the pitch rates developed.

deSitter, two comments about that link about demanding all A330s be grounded:
1) It's Speigel, which news service does not have a sterling reputation for their handling of this crisis, so far.
2) The A330 has a safety record that any earlier airliners more than a few years older than the A330 can only dream about. Shutting it down on a 1 in a million accident is past foolish. It's damn foolish.

I'm tempted to add a third item - it's Spiegel.

I wish there were some aero guys contributing to this thread. It's interesting, and revealing, that a bunch of Airbus pilots hunched over their keyboards in the safety of their homes can argue so long and hard about the meaning of the various "laws"; imagine trying to figure it out in a cockpit headed toward the ocean. But the laws that really count in the end are the laws of nature and physics, and I think a lot of the commentary here has been lacking in understanding of the aerodynamics of a stalled airplane. It's much more complicated than just "brick". It appears that the wing is providing sufficient downwash, in spite of being "stalled," to keep a download on the horizontal stabilizer. If it were not, the airplane would pitch down naturally, because it is a conventionally configured airplane, it's not in a spin, its CG is not excessively far aft, and that's what they do. So the stabilizer is actually working. Furthermore, the wing, although largely stalled -- but note that the ailerons continue to be effective -- is still producing a lot of lift -- probably a CL of 1.0 at least -- but just with a ton of drag to go along with it. It's the drag that's making the airplane sink -- not lack of lift.

I'm just an amateur at this, but I've talked with a few experts and they all agree that it's highly unlikely that the airplane was in a stable "deep" stall. Much more probable that it was being held nose-high by its own wing and stabilizer.

Bearfoil
Bear, I used to fly a brick-like object aboard ship routinely. The secret was maintaining control.:}:}:} Well, that and lots of thrust too.

mm43
No no, your graphic is great (don't quite agree about pitot behavior, but that's a small matter when they're frozen anyway) but if you compare it with Turtle's you see that the two sets of numbers are incompatible. So either some of the numbers are wrong to start with, or the flight conditions changed as the airplane neared the surface.

My bad. The BEA report doesn't give an angle of attack at impact. Solving for it: http://img.photobucket.com/albums/v3...roundSpeed.jpg

Hello, bingo.

Two graphics showing exactly the same data, just in different ways.;)

mm43
You mean your graphic and his second one. Agreed. I'm talking about the differences between his first one and his second one, which are quite significant.

Consider my first graphic to be the general case on the way down and the second to depict the flight condition at impact with the difference being the angle of attack. Of course, the actual angle of attack at impact will be dependent on surface wind speed and direction, but it was clearly much more than 40 degrees for the stated rate of descent and ground speed at impact and might even have been more than 61 degrees.

The modern jetliner gets its vertical speed from the IRU, Inertial Reference Unit. The IRU measures in 3 axes, as that's how the plane travels. It is apparent that all the velocity was in the Z axis, so the plane was dropping at 10,912 fpm, or 107 knots. There must have been near zero horizontal velocity when the plane hit.

AOA vane has physical stops. It has to be 35-40 degrees, so greater than 40 degrees AOA can only be calculated from the IRU, which data has apparently not been released, and the BEA are quoting AOA only from the vanes. I'm betting real AOA at the end was 100-120 degrees.