MurphyWasRight...

Re your post #864: :ok:

‘Human – Technical’ thoughts
 

Some ‘Human – Technical’ thoughts … … and questions, … mainly questions.

It is widely assumed that the event was triggered by ice particle blockage of the pitot tubes. With all three blocked it is also likely that the TAT probes suffered blockage, probably simultaneously; ref previous events and see VH-EBA (not simultaneous), #692 graphic and report link.

If the ‘sudden failure’ of airspeed (an erroneous low value) was accompanied by an erroneous low altitude (as with VH-EBA), then the indicated altitude deviation could also attract the crew’s attention. Would the altitude alerter sound?
Thus with apparent simultaneous failure of all air data and logical auto-flight disengagement, the crew’s initial thoughts might have been of a system failure – a technical issue.

The PF took the controls, but with the perception above, may have concentrated on altitude. In every day operation there is significant focus on altitude – ‘beware altitude bust’, TCAS, interview, loss of license, etc; these could easily be hidden (subconscious) operational and social pressures which might have influence the initial action; pitch up to recover the assigned altitude, back stick and follow-up trim.
I assume that the trim datum is still attitude (flt path?) and zero control input. Would the control law be attitude or flight-path stable with these system errors. If flight-path, how is flight-path computed, inertial or with air-data mix, and if air-data and the air-data is erroneous … … ?

Would the FD still be active, if so, in which modes and what command might be shown?
We should recall the many discussions of how modern crews depend on the FD; a general low experience level of basic instrument flying. Was an erroneous FD command followed resulting in an inappropriate manoeuvre?

Would an abnormal TAT (rising towards zero, based on previous events, A/B and other aircraft types) affect any other instrument display systems of flight guidance computation?

If airspeed was erroneous, and the altitude is also affected by this and also possibly from ‘abnormal’ temperature, what about Mach, and any residual protections (MMO pitch-up bias), i.e difference between computed Mach (and rate) vs computed MMO.
From what has been describes so far it may be impossible to take any of the quoted air-data values as representing the true condition of the aircraft; except perhaps the vane derived AOA. What source of information does the FDR record, is this always the same as what the crew will see?

Roll deviation might be considered a separate but confusing issue. If the YD ‘froze’ (fail-safe) with air data ‘failure’ (as designed?), then an offset rudder would induce roll and a permanent roll bias, but its effect varying with actual airspeed – need to use rudder. But who uses rudder in normal (symmetric power) flight?

With these distractions and concerns of system failure, then any more speculation about crew thought and behavior would be unjustified without further data.
However, the trim position is a dominant issue, and without awareness of this offset, basic flying could be difficult and probably added further confusion.

At a late stage, nose down control action did effect a pitch change and an apparent speed increase (a semblance of stall recover but with the confusion and aerodynamic complications of mis-set trim). The speed increase was sufficient to reinstate the previously inhibited AOA driven stall warning; probably further confusing the mental picture – nose down pitch apparently caused a ‘stall’ ??? … what next; undo what you have just done, back stick? Perhaps this is normal (to be expected) human behavior.
Also, think about how the industry discusses stall – some thread discussion, education, and training. Virtually every aspect is speed related – stall ‘speed’, warning ‘speed’, stall displayed on a ‘speed’ tape, the importance of gaining / maintaining ‘speed’; even if a crew had been taught that the stall warning was AOA driven and that the aerodynamics of a stall involve AOA, is this information recallable, or would ‘speed’ dominate our thoughts.

There is much more to come, much to be learnt, and probably all intermixed in technical, human, and social system (operational/organizational) interactions.
At this early stage, we might consider how crews are educated / trained, and what is currently expected of them. How might everyday operation influence encounters with a very rare and unusual events? Are modern norms based on a remarkably benign (safe) operation so that it is now unrealistic to expect extremes of experienced-based innovative behavior? Has the industry overlooked ‘change’, and retains old, inappropriate assumptions?

To reassure any PAX Ppruners (and the media), the industry remains very safe. Incidents such as this are very rare and the assumed precursor (high confidence) – ice particle blocking is generally understood. Safety action is in place – changing the type of pitot tube, manufacturers have refreshed crew dills for loss of airspeed and stall recovery, and operators are applying these training aspects. The industry is not (must not be) complacent; a thorough and tenacious investigation is underway from which we expect ‘lessons to be learnt’; but it’s still up to us to learn.

You meant that ACARS at reciept time only shows when the CMC was able to dispatch them thru the satellite link.

ACARS sequence/order/time is due to the processing time logic, being queued, and to protocole limitations as nothing (so far) is indicating that she could have reached an attitude that would broke the satellite link: up to +20 deg pitch and +/-40 deg bank angle combined should make any ACARS sending possible every time from the begining to the end.

Now, it is also possible that the satellite could be, at one point, busy with other aircraft sendings (as there is not so many satellites above this place and the total bandwith was not illimited). That is also how I interpreted the BEA quote "that the satellite link could be broken" (due either to aircraft attitude or satellite not available for login).

Wondering what the proceedure syllabus AF uses for application of TOGA. Would assume that at some point, the airplane would wish to climb, and that the THS would move to nose up.

Begs the question also, is there any system , irrespective of whatever Law may be active, which effects the THS if and when TOGA is enabled?

Only if the A/P was enabled, which in this case it wasn't.

Actually there are two time stamps. The first on is the sending time stamp. The second one, within the message, is the time of the generation.

HN39 #847: "First three sentences agreed. However at FL375, 215 kCAS, AoA=4° the airplane is not stalled: the normal acceleration is less than 1 (approx. 0.8) hence v/s is decreasing."

That brings us back to spurious stall warnings, doesn't it?

Not exactly: the first one (precise stamp, like 0210:10) is the time stamp at "reception" of the ACARS. The only clue about the sending time is that it takes about 6 seconds to be processed between the aircraft and the satellite (both way). Hence, it was sent about 6 seconds before the receipt time stamp (an acknowledgement "successfully sent" is recieved by the aircraft 2 seconds later). By this way, it was assumed that the aircraft had crashed at the earliest at 0214:28 because the last recieved ACARS (0214:26) was processed up to the "successfully sent" return acknowleged by aircraft.
Now, the BEA confirms that she crashed in the same second at 0214:28.

Readers of thisforum may want to refer to fcom page 3.01.20p4a which shows a graph for determining high and low speed buffet

Hi JD_EE,
Right. This first stall warning seems to be due to a change in stall function (it is mach based above Mach 0.75) to AoA based function. Unreliable airspeed seems to affect everything like static pressure, which is mach sensitive, AoA indication which is mach sensitive... Then when you lose the mach function for a while, this become a real issue. Beside, the stall warning is kicking above VSw1g with some margin for taking into account any possible overshooting.

MurphyWasRight; Grizzled;

Re post #864... :ok:

HN39;

Thanks for the TE Plot.

Takata, re the A340 AIRPROX, you wrote:
Hmm, the flight controls were in normal mode and no sidestick controller input was made until 28 sec. after AP diconnection when they were already a thousand feet above their assigned level.

I thought that in normal law, compensation for thrust variation was provided.

Anyway, except for human factor aspects, this incident appears unrelated to AF447, this one being in ALT law.

Why would that be? At M=0.8 stall warning is set to occur (see 2nd Interim Report) at approx. AoA=4°, alpha-max = 5°, and the real stall is probably between 6° and 7°. The second stall warning occurred "around 6°" at M=0.68, where alpha-max=7.3° and stall probably beyond 9°. I suspect that people who stubbornly maintain that these stall warnings are 'false' don't really understand what they mean. An intermittent warning such as may occur due to AoA- and hence g-variations due to turbulence may be considered 'inappropriate' since it doesn't require recovery action from the crew, but that doesn't mean it is false. It means that the AoA has temporarily exceeded the stall warning threshold.

Takata,
the stall warning threshold has to maintain a certain margin below alpha-max which defines the 1g stall speed. For all Mach numbers greater than 0.275 alpha-max reduces with increasing Mach, and therefore also the stall warning threshold AoA. Just take a look at the FCOM page presenting Vs1g.

Amazing amount of material posted in the last few days. I was out of town, :E and so did not FOD the thread.

A thought on AoA probes and 60 knots.
Aye, but here is a thought: if the mission designed approach and takeoff speeds are typically 150 kts and more, maybe the design criterion can accept them not being as swift as the nautical brand at less than half of the operating speeds? :confused:

Two thoughts I see bubbling up, the answers to which are not clear to me.
Is there an unambiguous answer to those nested questions?

What I don't see from the latest BEA narrative is how many attempts to move the stick down, or move the nose down, were in play. Two are mentioned. Was that all?

This related to an earlier observation: a continuing attempt to move the stick down (though they mention some instances of stick movement toward nose down, the event flow is hard to discern) to unstall also runs into temporal distortion and its effects on pilots handling upsets.

Many pages ago, one of our posters pointed out that he was suprised to learn how long it takes for his inputs to unstall one of the big jets. With that in mind, was the crew in AF 447 (if and when they finally figured out "we are stalled!") not aware of how long it takes to get the AoA to start increasing again for the position they were in when "we are stalled and falling" became evident?

We may never know. CVR might tell.

Aside/musing. (Not sure how applicable this is to the mishap underdiscussion).

FWIW, from a pilot, but not an Airbuss 330 pilot.

If I command the nose down or up with the stick, and the nose does not go up or down, there is something horribly wrong, and I am by definition, in a condition known as out of controlled flight.

I am using a very simple definition of out of controlled flight.

You are in the aircraft, you make inputs with the stick and rudder and throttle, and the plane does not respond as you command it to. (Or, as you expect it to). Recovering from out of controlled flight is a skill set that relies on the flight controls working as they are known (or designed) to work in response to your inputs, so you have to get to that state. As an emergency or recovery procedure, out of controlled flight recovery means taking a set of steps that gets you to the point where the flight controls respond to your inputs to go up, down, left, right, etecetera. It often takes time and altitude to get through those steps.

From a pilot and human factors point of view, and the flight regime the cockpit crew found temselves in ...

Given the flight regime they were in, and considering the likely concerns about not overspeeding or going to fast in turbulent air present due to envirnonemt, the crew was in the condition for a surprise upset:

You don't expect to be stalled, which means you have to spend "x" seconds (or fractions thereof) overcoming the denial stage, and getting to the action stage. (Responding to your training and knowledge of your equipment and situation).

That some of the cues were either ambiguous or at odds with previous training looks to have led to counterintuitive responses ... but we don't know what PF was seeing.

Further thought on aerodynamics and degree of stall.

If the answer to the two nested questions is "no visual alert" and "yes, you need to take over manually to get THS to work the nose attitude to your advantage" then there is a possible training improvement to be harvested.

To the question of ineffectiveness of elevators, as aircraft speed decreases, due to V^2 ... the slower you are in the airstream, the more pronounced the effect of THS overwhelming the elevators in pitch control. (I hadn't considered the masking due to high pitch/AoA). Does this make sense, in terms of me understanding that characteristic of the flight controls?
The deeper into stall you go, particularly if THS running most of the way up was a factor, the harder it is to unstall with your stick control.

Maybe my math on that is off, and it washes out and is a linear relationship.

Yes, pitch and power brigade, the basics are important.

data access
 

Thanks for the reference grizzled.
So is it correct to say that for the time being the data belong to the BEA and the BEA has the liberty to give access to the parties that could provide expertise for the good of the investigation ?
I believe, us, as people of what is called a 'free society' should have access to those data. There is a lot of expertise on the net too ...
Anyway, what would be the downside to publish them ?

HN39 #894
That is why I used "spurious" rather than false. I thought 215kt and 4 degrees would likely calculate into an imminent stall, if stall warning pays attention to speed at all. (Off hand I'd be surprised if it didn't in my non-pilot naivete.)

That suggests that things broke down with that stall warning at 37500 feet. The PF appears to have made an inappropriate action, full throttle and pull up - the apparently prescribed action to take before a stall. But it never seemed to help but the PF kept the stick back fatally long even as the thrust was, at some time, reduced to idle. It was at idle at 2 h 12 min 02, and TOGA at 2 h 10 min 51. That's all I can extract from the report.

It would also be nice to know how long and how much "up" was asserted at 2 h 10 min 05. That could tell a lot more of the story just in itself.

Graybeard;
You are right, it didn't.

I was aiming more at the ALT erroneous speed correction component, and its rate of change which may have been too much for the TCAS. The problem right now is we don't know whereabouts in the 0210 minute the NAV TCAS FAULT occurred, and it could be related to a combination of the speed error correction and the zoom climb, i.e. both were heading in different directions. Or the changes occurring between valid and invalid data.

Here's a clearer copy of the VH-EBA FDR print-out for reference.

Hi DJ77,
Well, in fact, even in Normal Law, it is not really able to compensate for thrust change as it is described in the A330 FCOM (3.04.27):
http://takata1940.free.fr/A330_NOR%280%29.jpg

Certainly, beside human factor aspects. But maybe it is an issue that those human factors appears to be seriously challenged when several crisis are declared at the same time (TCAS event/turbulence/overspeed for this A340 crew).

Well, immediately before that stall warning, we know that the aircraft was climbing. The report states the rate of climb had been reduced and the VS was recorded as +700ft/min. The altitude was reported as FL375.

The report is clear that the descent started 3m30 before the end of the recoring - so that would be 2h10m58s. So, my guess is that there was about 7s between the warning and the actual stall.

Now, they reached a max altitude of FL380 - so there was some climb energy left before the actual stall and we know the two immediate actions at the stall warning by the PF were TOGA and nose up sidestick.The engines would have taken time to spool up. I reckon that they were too close to the stall and the nose-up at the warning pushed them into an actual stall.

Takata, tks for pointing me to FCOM3

mm43, graybeard;

The TCAS has numerous system inputs. One of the inputs is the stall warning system. I think the NAV TCAS FAULT message was triggered by a programmed inhibition of the TCAS warning.

When certain other systems require a higher priority in terms of pilot attention and aircraft systems/performance/energy, they inhibit warnings which would compromise such priorities. Here, the priority would be aircraft energy to recover from a stall, so a TCAS warning is set aside as the lesser danger and is inhibited during such an event. The AUTO FLT REAC W/S DET FAULT warning has the same source.

The BEA Second Report seems uncertain regarding the source. Even though the second reason, (altitude differences > viability of data) makes a bit more sense than the electrical notion, the above reason should be examined as possible or dismissable. The inhibition isn't strictly a fault and if the two messages, (stall/TCAS) were ever "in competition" for attention/energy, perhaps the TCAS would simply remain silent.

Anyway, just thinking...always hazardous!

Ignorant question. It has been surprising that the PF control input almost throughout this incident has been NU. Could it be related to the bank that he appeared to be offsetting pretty much throughout as well? The note in the basic control law that suggests keeping the nose up in a tight turn was interesting to this layman.

Looks to me that the initial climb may have been due to a combo of flight through uplifting air, pilot induced pullup to avoid wx or possible a/c induced pullup due high speed, perhaps only flight director commanded if AP already OFF.

It's hard to see why else they would do that initial pullup and there seems to be a precedent in that other 'airprox' uncommanded pullup.

After that, when they ran out of energy, it seems clear that no-one on the FD realised that 'nose down' on the sidestick wouldnot be enough. They needed to trim.

Ah.....'trim' the basis of good piloting! Completely ABSENT in Airbus normal ops.

I mean, if you NEVER trim, how are you expected to realise that you are badly out of trim?

According to the victims association, the Ile de Sein has recovered 75 bodies, bringing the total bodies recovered to about 125.

Not clear whether this concludes this phase of the recovery process, or whether Ile de Sein has retrieved any parts of the plane (other than seats).

Also nothing said on whether there would be any future attempt (phase) to recover other parts of the plane.

TCAS Fault
 

Good thought on the Stall Warn priority, PJ2, but Windshear Warn, GPWS Pull Up and GS Warn will merely silence the TCAS audio and put the TCAS in to TA, Traffic Advisory mode while the Warn is active.

IIRC, Stall Warn will not silence the TCAS, as they may go hand in hand. At any rate, it will not cause a TCAS Fault. Stall Warn could possibly take priority over the GPWS, but I'm not certain of that. I'll dig.

Graybeard, yeah, I think you're right...the "fault" makes no sense. I'll dig too.

It doesn't look like if they attempted a "tight turn" in normal law. The bank oscillation was certainly due to AP going off with an induced right roll momentum that should have been trimmed by rudder corrections. The control law switch to alternate caused the roll axis to be direct (and sensitive) as the controls are powerfull (hence, stick moving left and right).

Read below, effect in roll direct and trimming the rudder:
http://takata1940.free.fr/A330_ALT%280%29.jpg
http://takata1940.free.fr/A330_ALT%281%29.jpg
http://takata1940.free.fr/A330_ALT%282%29.jpg
http://takata1940.free.fr/A330_ALT%283%29.jpg

Takata.

What about trimming?

Was the trim wheel moved?

Trim Controls
 

Do I understand this correctly:
1. Auto Trim continues to function even though the autopilot has disconnected?
2. There are no trim buttons on the sidesticks?

Absence of "ICE DETECTED MESSAGE"
 

As in the BEA report is stated 'uneventfull' before 0210:05'
and then suddenly Pitot Probes clogged due to ice.

I'm wondering why the ice detection system didn't trigger an ICE DETECTED (0,5 mm ice aggretion within 60 sec.) WARNING MESSAGE?

Can accept that within the timeframe a SEVERE ICE DETECTED (7 times 60 sec.) is never shown.
I can also imagine that the visual ICE Indicator between the windshields is not in direct view during all the mess,
but the ICE DETECTED message should have been there!



http://i474.photobucket.com/albums/r...99/ICE_DET.jpg

Hi BarbiesBoyfriend,
Why should I bother to answer you after your very informative first post here. You obviously posted without even reading a couple of pages from this thread, don't you?
Read it.
All the questions you asked (airprox, trim, etc.) were already answered, some of them only a couple of post ago, some further back.

1. Yes - Autotrim is part of the FBW systems as opposed to the A/P and A/THR systems.
2. No, but there's a big manual trim wheel just like on the other airliners in exactly the same place. The questions being raised involve training to use it.

In that part of the atmosphere what you're dealing with is not ice as it is generally considered, but supercooled water. This is water that is below freezing point, but still liquid because it has almost zero contaminants. Stick a big piece of metal into that water and it freezes into ice in less than a second. This was demonstrated in the BBC/NOVA documentary.

Hi Dozy,
More likey, some very small ice crystals (which are not detectable by radar) and not supercooled water at this level flight (which is detectable).

Takata

I've not seen much on how the Airbus normally trims for you. But I might have missed a bit here and there.

I think that while Airbusses design is great when it's all working , it's notso when in ''not normal' mode.

But hey, what do I know?

Sorry to disturb you.

Call me 'old fashioned' but I prefer to look after the trimming myself, and I'm used to doing so- unlike the AF447 pilots.

Frankly, I think the Airbus is the aircraft the erodes piloting skills more than any other. Anyone care to disagree?

Piloting skills
 

The MBA's that run commercial aviation to generate maximal shareholder value would rather not have any bodies on the flight deck. Silicon Valley assures us that cybernetics transcends human behavior in anomalous situations so that pilots are an unnecessary expense. Hull losses are a cost of doing business the bottom line impact of which is mitigated by aggressive legal action and publicists smoke and mirrors. How many airlines have failed because of accidents or flight crew errors? How many airlines have failed because of MBA incompetence? How many airlines were reborn under a different corporate name with the same MBAs managing them to carry on the pattern?

Please....can we just keep to the topic at hand and not launch yet one more 'eroding skills' discussion...it's been done to death and never resolves a thing.

Sorry, BBB, but dang, it gets a tad tiresome and will only produce another round of A vs B, Colgan vs the FAA and whatnot.

I flew (almost always manually to cruise, the descent, approach and landing) the A320, then A330/A340 for fifteen years. One doesn't lose one's skills, one permits flying skills to be lost, and THAT is a professional standards matter, not an airplane, airline, regulator or other matter. Disconnect the damn airplane and the autothrust and stay familiar with the airplane.

There's far too much blame about "loss of skill" directed elsewhere when the real one responsible for any loss of one's skills and professionalism is in the mirror. If your airline wont' let you hand-fly because they like automation, to hell with them and their MBAs, fight them on it!

Take a look at the stats: we've had far too many fatal accidents resulting from the most basic failure of all and which we're trained to avoid and prevent from Hour One in our first flight...stalling the airplane. If the training isn't there in the syllabus, demand it.

Sorry, but enough is enough.

Takata
Would you pull up to max deflection while trimming down your nose at the same time?
Certainly not.
If their THS was trimmed close to max (+13/14 deg), it was because autotrim followed their NU imputs. Once AoA overshoot +30 deg, autotrim was not working anymore: it could only be applied manually by the trim wheels (see my post above and parts about trimming manually in direct law).

Basically, it means that they didn't aknowledge to be in a developped stall at the first place, hence, trimming down was not their main issue: their lack of nose down imputs certainly was before they reached such an high AoA while falling from FL380.
Even so (without manual trim imputs), elevators (if not fully stalled) should have had enough power to recover below +30 deg AoA (due to low airspeed) and autotrim would then follow their nose down imputs. When and how much did they try? we still don't know yet from the release of informations.

PJ.

OK. After this I'll never mention it again.....but...the trimless Airbus helps its pilots all the time trimwise, right up til when it stops. And then it leaves them precisely where?:rolleyes:

I know you can practise 'manual flight' in an Airbus just like any other a/c, but please don't forget a bus ain't like a non-bus. In many ways.

Takata, to answer your first question, of course not, but the pilot held the stick back, the bus trimmed the tail 'nose up' (almost to max) and then stopped trimming.

So now, the pilot had to manually reverse, using his manual trim wheel that he never uses, a trim input that he never made!

Youre second point, that they ought to be able to push over even with the tail trimmed for full nose up I dispute (but only from experience of non-buses, so dismiss it if you like. These tails are really powerful though).

Third point, if implied, 'why not stick full forward til impact'. I'm as baffled as we all are.

I see you are from Toulouse.
I just think the bus rather isolates its pilots from what's actually happening. That's just an opinion.

Uhh... No we don't.

(At least this Brit working for a Silicon Valley firm doesn't!)

PJ2 - Don't sweat it, they'll get to the bottom of this sooner or later, anything anyone says now is just conjecture. :)

BarbiesBoyfriend - The trim wheels are there and if airlines aren't training the pilots when and how to use them correctly that is not Airbus's fault. Old school "communion with man and machine" was lost as soon as the first widebodies came along, maybe even earlier - even the old 747 Classic, DC-10 and L-1011's feel was entirely artificial.

Anyone,

Is "auto-trim" a feature of the B777? I think auto-trim is a function of Airbus' design which does not trim to hold a sped, but trims to maintain a set flight path. Nothing wrong with that, but different.

Gums

Any comments on the Viper's auto trim?

GF