alexd10

Your theory seems a little bit forced . As can be seen on the graph the selected VS value drops ceased to occur at the start of the climb, so it’s improbable to be related to post flight memory damages or data corruption.

If indeed are generated by improper value of the data used for graph, the source it’s highly probable to be a soft/process related to the flight.

So, what can be , and relevant or not for a/c behavior?

rudderrudderrat

Hi Turbine D,

It seems to me that PF may have simply memorised 3 attitudes and power settings, and forgotten the "Below Thrust Reduction Alt" bit.
Once he had selected TOGA power, then he placed the aircraft at 15 degs pitch and waited.

Dohhh!!!

jcjeant

Hi,

A small question about the behavior of the aircraft (A330)
What is the difference at low and high speed for roll control (aileron effectiveness)
I suppose the roll control is more effectiveness ( more sensitive ) at high speed .. ?

Lyman

infrequentflyer789

Thanks for a meticulous and thoughtful reply. I quote the initial BEA text when they sought to describe PF's actions at a/p drop. One can fall back on the dual language, made an issue here, but I prefer to place more confidence in the text as translated, to avoid weasel wriggling.

Some thoughts: The PF's actions were initially "Mostly Nose Down, with alternate roll left and right." Nose down is allowed when the bus is intitially dealing with Overspeed, but gradually ND becomes unavailable, and instead, it is replaced by auto NU, adding to Pilot input, if any.

The THS is also unavailable in Overspeed mode, so that explains the "loss" of THS TRIMOUT after the initial .7 degree TRIMUP. So we are left with a climb of robust nature, and little ND, until just at STALL, where the THS, reinvigorated, cycles all the way NU. Is this from "Memory"?

What does the Bus do if it is in Overspeed after identifying and reacting to it, but then speeds are lost?

Keep climbing? What is the nature of the annunciation of Overspeeding?

I notice your discomfort with a connection twixt UAS and the STALL. I share it. I also am not at all convinced the Pitots misbehaved in any way.

Just as the VSIs were reading "pegged" and "true", these probes could have been legit in their sampling, and the computer confused a "discontinuity" in airspeed with "discrepant" readings at each probe. The a/c apparently can react to these discontinuities as if it is discrepancies, instead. What if the initial airmass shear was additive to IAS? Overspeed determination? What if diminishing in IAS? If sudden, as shear is, could the drop have been 60, 80, 100 knots? Could such a drop in IAS have triggered the "zipper" at VS/SELECT prior to loss of autopilot? There was a WINDSHEAR REPORT on the ACARS, as there was also TCAS alarm?

I mention TOGA and 15 degree PITCH UP not to include it as an option at altitude, but to include it in the PF's muscle memory, and training. It is also possible he selected TOGA to attempt to get the NOSE UP, having not realized the NOSE was UP as high as it was already.

For three minutes, the Pilot was seemingly convinced the a/c had "some crazy speed". The PNF was not convinced, but neither was he ready to take the a/c into a Steep NOSE DOWN recovery. When Captain returned, he never seemed convinced either way, and his presence may have been a fatal distraction to the two at the helm.

So it is possible yet to retain an open mind. Demonstrably it is also predictable to judge the pilots incompetent in the court of easy chair PPRuNe jurisprudence.

jimjim1

Re-posted by someone:-


OK. I give in. Aerodynamics had no part in this incident:-

It was:-

The Hand of God.

Or perhaps you might prefer - A Hand Of God? Since; He has presumably more than one?

infrequentflyer789

Agree with that, and for what my opinion is worth (not a pilot, but I know, or used to, a bit about building stuff that flies) it still looks confusing. And it has no examples for cruise (as you say).

"If safe conduct of the flight is affected" is a critical decision point (memory items vs. level-off) yet seems to me to be vague and not defined anywhere. Plus all those nice big graphics of the horizon at 15deg pitch up, and toga...

Does "safe conduct affected" just mean "if no danger of terrain impact" ?

If I immediately have problems controlling roll, is safe conduct affected and should I therefore apply the pitch memory items ?

If in RVSM airspace and I'm struggling to level off, is safe conduct affected and should I therefore go to pitch up ??? [ mind you I should be getting out of RVSM anyway without an A/P ?]

If different pilots on here have different answers, then yes, it's all dangerously unclear.


I'm still not sure 447 ties with any of the procedures though. If they were going for the memory items, and recalled the wrong pitch/power, then FD should have been turned off (in, I think, all versions) - and it wasn't.

On the other hand, if they were going for "level off and troubleshoot"... where does the climb come from ?

It could be misapplied proceudre, it could be inadvertent - I think PNF's comments lean towards the latter, but not conclusive.

What might clinch it woudl be the details of the rumoured (posted on here) AF sim tests shortly after the accident. If most of their crews crashed when faced with the scenario on the sim, then something systematic is wrong at AF and not (only) with the guys on the night. If we knew why they crashed in the tests, then we might be much clearer about why 447 climbed.

I wonder if that info (assuming we believe the rumours) will ever see the light of day, or will AF manage to bury it ?

infrequentflyer789

Me, I'll go for numbers every time (blame it on engineering or software background, take your pick). Text has been written by a frenchman, edited by a lawyer and translated by a linguist - the numbers have far less room to wriggle.

As to overspeed, it could have been - but I don't think it was. Overspeed is shown in the trace on P111, and doesn't trigger in the time region shown, which includes the A/P drop.

Also, PF pitch actions were NU first (see same page, below the line is stick-back, above is forward) - whatever the text might say

I think they probably did, but my concern is more that beyond causing A/P drop and Alt Law, pitot failure may have no bearing on what happened. Which means that any other failure leading to alt law could lead to the same result - and fixing the pitots is a convenient scapegoat that leaves larger problems unaddressed.

I judge them not (or try not to) - and am not qualified to do so anyway. I try to understand their actions from a user-interface / controls / human-factors perspective, and I await the human factors report with interest.

If I have come to any judgement so far, it is that there were major systemic operational failures that put this crew up there (along with other AF crews if the sim test rumours are true) unprepared to cope with this scenario. And it was a known scenario, precisely known, but clearly not assessed - until after the crash. To quote AF (from Press Releases ):But did they train, or even assess, their A330/40 crews to handle a loss of airspeed in cruise ? It would appear not (according to the BEA).

infrequentflyer789

Was discussed in several posts some time ago, e.g. http://www.pprune.org/tech-log/45687...ml#post6621079 and http://www.pprune.org/tech-log/45687...ml#post6618515 and http://www.pprune.org/tech-log/45687...ml#post6621079

infrequentflyer789

One reference point is that the ADs allowed for replacing only two out of three probes with Goodrich initially, leaving one Thales.

Didn't find my original remembered source, but did find others including this:
EASA and FAA Airbus Pitot RequirementsWhich probably means everyone was right in that argument - could have grounded planes but didn't because risks were assessed and timescales were managed.

Zorin_75

Regardless of what a certain person will make up, the text is pretty unambiguous in this matter. Just DFTT.

CONF iture

Solved, not, discussed at most as just reminded by infrequentflyer789 here.
Diagnostic also kindly sent me some references of interest, but more related to the spiky traces phenomena in general. here and here.

I share your analysis alexd10.

IMO this has to be seen as a general comment only. As a matter of fact, the flight was not proceeding in NAV anymore but in HDG.

The FD/AP VERTICAL MODE is a critical parameter for the all event, after, but also before the AP disconnect.
BEA ... where is the trace ?

MFgeo

To me, there is a much bigger issue than the "sawtooth" trace of selected vertical speed values prior to 2:10:06 (in reference to the graph in posts #1186 and #1195) -- WHY is the selected vertical speed shown as being constant in those graphs after 2:10:42? If what the PF saw on the VSI during that period was a constant, slightly positive value, completely unresponsive to his pitch inputs, it seems likely that he would conclude that the VSI reading was erroneous.

jcjeant

Hi,

I asked before

And no answer ..
I asked this because in the BEA report N°3 the PF tell " seem's we have a crazy speed"
If the PF know how react the A330 to the roll command ( he give many .. reference PF SS mayonnaise graph) he must also know if it was high or low speed ...
Logic ?

rudderrudderrat

Hi jcjeant,

99.99% of the PF's manual flying experience will have been in Normal Law, where stick deflection controls a roll rate independent of air speed. When he was faced with ALT Law, he had direct control of the ailerons. You get full deflection of the ailerons with full side stick - independent of the airspeed. The roll rate at high Altitude is very rapid, I've never experienced this this for real - but I am reliably informed that it is "very twitchy".

PF seems to have been struggling to maintain wings level whilst he was over controlling. Whether he was flying fast or slow could not be part of his evaluation - because he probably had no previous experience of ALT Law at high FLs to base his judgement.

HazelNuts39

Hi jcjeant,
When the PF made that remark, the real airspeed was about 125 kCAS: BEA Interim Report no.3, p.76: At 2 h 12 min 04, the PF said that he thought that they were in an overspeed situation, perhaps because a strong aerodynamic noise dominated in the cockpit.

AlphaZuluRomeo

Yes, and that was reported. I assume: no change reported, then no change occured in vertical mode. You assume differently, that's your call.
Let's hope for more traces in the final report.

It's constant... for some time... but changed again at ~02:12:50

Didn't you mistake selected vertical speed (shown on the MCP) and the current vertical speed (shown on the VSI) here?

ChristiaanJ

CONF,

I admit to being baffled by the SEL'D VS trace.
The 'zipper' before the AP disconnect looks like an FDR or postprocessing graph software artefact (as suggested), but why does it jump to +5000ft/min shortly after the disconnect, and then drop abruptly back to approx. zero?

I seem to remember somebody saying earlier that it was not the 'raw' MCP setting, but an 'intermediate' parameter.

Isn't it a red herring, if the AP/FD was in ALT CRZ mode?

I'm not 'au fait' enough with the Airbus FCS.

Lyman

Hazelnuts39. It would be interesting to imagine a wind tunnel with the forward ten metres of A330 fuselage mounted level and subjected to 200knots of airstream impacting the belly at 35 degrees AoA.

PF makes his comment, and it was discussed at length, re: motive, CRM, etc. Clearly, at least one airman was baffled by the noise.

A discussion of the zipper trace would be interesting. An understanding of vertical speeds, commands, and events that had an effect on autopilot would be progress. Thus far, no possibilities are broached, and I for one would be grateful if some one would take it on.

A novice' question might be: the VS select 5,000fpm UP just post a/p drop; is that related to the ensuing climb? Because that would mesh with Pilot's inputs to produce 7,000fpm.

Is there evidence of the absence of the a/c having a role in the climb? It would be necessary prior to conclusion that the PF acted alone.

ChristiaanJ

Thanks, Lyman, for confirming you do not have the slightest notion of aeronautical engineering...

Give it a break, mate... you're trying to play way outside your league.

HazelNuts39

The airstream in windtunnels is horizontal (except in spin tunnels where it is vertical). You would need a relatively small airplane model to mount it at 35 degrees AoA without getting too close to the tunnel walls. What would you be interested in? I would be interested in the pressure near the static port, and in the pitching moment at various angles of elevator and THS. I take it that the noise registered on the CVR is generated by the flow separation on the wing. And why 200 kt? The airplane wasn't stalled until the speed was much less.

Though I'm curious about the cause of the 'zipper trace', I don't see any effect of it on the airplane. As the AB simulation shows, the airplane behavior is entirely consistent with the SS control input. There is no delay in the response in pitch attitude.