Lyman

Did you try without failing the ADR's? See, if PITCH (elevator) can induce a STALLWARN, transient, then the a/p has no business remaining active, wouldn't you program it that way? My point is that the a/p can quit without UAS.

Just on the prowl for negative synchronicity, aero style

DozyWannabe

Careful TD, your source is not exactly known for impartiality.

It took a lot of pitch input to induce that stall warning - way in excess of what the autopilot would order in terms of magnitude and speed.

Autopilots *can* quit as a result of extreme maneouvres, but that doesn't seem to be the case here - it was designed to cope with worse than what it was facing.

Lyman

One does not need PITCH input to trigger the STALLWARN, only "G", as you say.

If so, and you say it is, we would be looking for sufficient turbulence to trigger G that triggers the STALLWARN. This can happen in a/p, obviously, and the STALLWARN will remain silent. So I seek the data that conclusively shows us the PITOTS were clogged, and in failure. Powdery ICE is thus far unknown to me. Perhaps it is hitherto not well understood by others?

I do submit that STALLWARN can trigger without my touching the controls. No "extreme maneuvers" needed. The STALLWARN can be a TURBWARN as well? Even a WINDSHEARWARN ?

HazelNuts39

The brief stall warnings at 02:10:10 were the result of a combination of control inputs and turbulence (vertical gusts). That is evident in the traces of normal acceleration shown on page 42 of interim report no.3.

The gust velocities that can be derived from the DFDR data were posted here.

The meteorological analysis by Tim Vasquez points to the possibility of a gust velocity of 23 m/s = 75.5 ft/s = 4527 ft/min based on the atmospheric temperature profile obtained in a radiosonde ascent from Fernando de Noronhas.

Snow?

DozyWannabe

But Lyman, Stall Warning *did not* trigger until *after* the PF had taken manual control - that's a documented fact, down in black and white.

It would take considerably more external force to trigger Stall Warning or trip autopilot off than the aircraft was facing - this was all laid out in the TRE's debrief. This TRE is not an Airbus fanboy and I hold him in the highest regard.

I know you want to believe that the aircraft handed itself over in a practically uncontrollable state, but the evidence simply isn't there to back that hope up - not even slightly.

@HN39 - possibly. All I can tell you is that we got the transitory stall warning when I pulled the stick halfway back - so either the impact of turbulence was relatively negligible, or our simulated condiitons happened to hit a randomly-generated pocket that matched the conditions AF447 faced (which is on the face of it very unlikely). I don't believe the turbulence alone would have been anywhere near enough to trigger it, and neither did our TRE.

Lyman

What are the margins for error? A gust that does not impinge on the airframe sufficient to upset the Inertials can displace the AoA vanes, is this so?

DozyWannabe

At a guess, not enough and not for long enough to trigger a warning or autopilot disconnect. Remember that the AoA vanes are responding to the forward velocity of the aircraft and as such are subject to more inertia from those forces than an updraft could provide.

Lyman

Doze. No, not uncontrollable, not at all, I am trying to establish that the degrade could be the result of issues other than UAS. If turbulence was sufficient, and short cycling quickly enough to be masked by the inertial lag with airframe displacement, the AoA could be wack, short term, but disguised as unaffected in longer time cycles (seconds).

The 330 hasn't a part to play in this, except to say, she was there....

The vanes are every bit as sensitive to vertical as horizontal gusts....

DozyWannabe

Lyman - all I can say with any certainty is that what you're proposing is extremely unlikely. Which is to say none of us can know for certain, but based on the information we have it does not seem to be a plausible scenario.

The AoA value could be "wack" on one vane (which appears to be the case for a period), but as long as two of them are providing good data, it's not going to mess the systems up.

You'd need to be talking about a near-supersonic updraft to overcome the normal operation of those vanes, and the data suggests that the forces weren't even close to that.

Lyman

Unlikely? More so than Pitots filling with powdery ice? Prolly. Can you quote me a velocity for UP/DOWN air mass in a fully developed Cell? Or in its vicinity? I'm going to guess 100 knots. You? If not symmetrical, this movement can be quite a threat to life in the Flight Level?

Hardly supersonic, 100 knots (vertical) can deflect an AoA vane (s) what, five degrees?

DozyWannabe

This was a known issue with the Thales AA pitot tubes, so not at all unlikely.

No.

In which case it's going to come up against the inertia of 500+kts horizontal airflow and come off worse.

Lyman

NO. The airmass (flow) is no longer horizontal, relative to the a/c. The AoA is the new result of the relative displacement of the airmass.

And ground speed decreases...

DozyWannabe

Lyman, prior to climb, it's more horizontal than it is vertical. These vanes and the systems connected to them are *designed* to cope with conditions like this, otherwise you'd have minor emergencies as a result of every moderate turbulence encounter, which just isn't the case.

The Stall Warning comes after the initial pitch up command by a matter of a couple of seconds. The aircraft disconnected autopilot due to UAS and followed the PF's commands into the climb, not vice-versa.

HazelNuts39

Simple: 11.3 degrees

DozyWannabe

With no other force acting on them, right?

HazelNuts39

@Dozy,
I'm thinking in terms of flow angle. What forces are thinking of?

DozyWannabe

@HN39

The sharp up- or downdrafts that Lyman is describing against the flow generated by the aircraft's forward motion, and whether they would be enough to have a significant impact on the AoA value supplied to the systems.

Lonewolf_50

If I may revisit a tidbit about AoA from Retired F4

AoA is information related to airflow over your flying surfaces, more or less a snapshot of "How is my aircraft (wing) flying?"

There is a bit of pilot scriptural canon, oft cited on these pages and in particular in the first two or three threads on AF 447, called Fly the Wing. Your AoA can tell you how your wing is doing, flying wise.

The A330 already detects and uses AoA information ... at least the robot does.

Why it is not considered by designers, airline companies, and others to be useful to the pilots remains a matter of design attitude, and conceptual attitude.

Choosing not to make that info available for the pilot's display looks to me like an attitude problem. (And again, I appreciate that the real estate in "display area" is precious, and is (allegedly) allocated with great care, particular in modern design processes. )

So who needs an AoA gage? What you don't know won't hurt you, eh?
Sorry, I disagree, with data point AF 447 a supporting tidbit.

Would a discreet AoA display have made the pilots aware, as they were flopping about, that they were in stall, a fact that seems to have escaped their notice?

Maybe, maybe not. Given my previous remarks on scan breakdown, there is ample argument against.

HazelNuts39

@Dozy,

An airplane moving forward at 500 kt encountering a sharp-edged upward gust of 100 kt would see the AoA increase by 11.3 degrees, and airspeed by 2%. That would increase the lift/weight ratio to about 1.8 and put the airplane in a stall. If the airplane maintains its pitch attitude, it would be accelerated upwards at initially approx. 0.8 g. As the airplane vertical speed increases the AoA reduces. The stall warning operates until the AoA is below the threshold. If the updraft lasts long enough, the airplane V/S will increase until it is equal to the updraft speed. The increased drag in the stalled condition would decelerate the airplane horizontally.

DozyWannabe

OK, so taking this statement as the basis for our raw numbers and the fact that we know moderate turbulence does not as a rule lead to stall warnings or loss of AP, this means :

• Either moderate turbulence does not reach 100kts vertical
• Or the vanes and systems are designed to cope with this kind of anomaly

Personally I'm leery of getting too theoretical in this manner, as we begin to diverge from the facts on the ground.

Probably more a case of "no-one else does it" than anything else. The FPV display option comes pretty close.

My position isn't too far from yours. If they couldn't diagnose a stall from the information they were provided, then it leaves the question open. That said, if it's easy enough to implement (and I'm pretty sure it is), that option should be exercised if for no other reason to provide more defence-in-depth than already exists.