Bear.... whatever... it is you who pulled the stunt of changing your user name, not I and then fuddled around in a smog cloud, I can only presume, with the intent to shake off those that had enough of your ramblings. But you were outed. I am not concerned one way or the other regarding how childish I may appear, because you showed all exactly how childish you yourself are - kettle, meet black pot.... Hence my renaming of your current label to "Lyingman" is simply an amusement on my part. No harm intended. As you like to note, these are anonymous forums, so it doesn't seem to matter much what I call the avatar behind the label, within the bound of politeness I grant you.

My most recent post was in response to this:

It is this inflammatory and incorrect statement I bring your attention. Stall had noting to do with the position of the THS, the elevator demand DID. The pilot asked for continuous NU, from 2.10.45... the THS followed, as designed. The pilot asked for NU, what else would it do it do? No trim.... justify? Oh, in this case the cheese was already lined up in a stall, also of the pilots doing, some seconds before. Perhaps some ND inputs from the PF, sufficient to get some ND from the THS might have been a good idea? But, that was not what happened, NU on the SS and TO/GA from the engines was requested, more or less the very worst possible combination at that point.

If you are suggesting in some obtuse way that the automation/protections/limits built into the aircraft should/could jump in at the point a stall is "obvious" (AoA the wrong-side of "bloody-hell" + vertical speed in the "oh, crap" region, and groundspeed in the "I can't believe it" realm), and implement a modern version of the stick-pusher, then may be we agree on something. But it is the manner you get there that is most bloody annoying. The quote above is a perfect example of inflammation, a whiff of truth and good dose of fabrication. It doesn't help your case at all.

Let me take this one...

I know I have, because I know posting here is a privilege, not a right. And for what it's worth, the most respected posters on here have retained their original handles since they first signed up. Most forums I am aware of would have served you with an instant IP ban for doing what you've just admitted to.

Again, no - only autotrim is inhibited from adding further nose-up trim at greater than 1.25g. They didn't need nose-up trim, they needed nose-down trim. The aircraft didn't reach a g-loading low enough to inhibit autotrim completely (0.6 > 0.5), so autotrim was never offline in the direction the THS needed to go. Furthermore, even if the g-loadings are beyond the limits of autotrim functionality, manual trim is always available.

Now - either you've missed my previous post explaining this or ignored it, but I can assure you that I will raise it with the mods if you post the same incorrect information on this technical thread again.

Again incorrect. Svarin, back in a previous thread, claimed that his airline vehemently discouraged use of the manual trim wheel at any time other than a switch to Direct Law. PJ2 said that his airline left use of the manual trim wheel to the pilot's discretion, and indeed trained him quite extensively on it's use. So if we are to take that information at face value, then it appears to be at the discretion of the airlines as to how the manual trim wheel is to be approached.

As of this moment, we do not know what Air France's policy was or is regarding the manual trim wheel, so to state as fact that the pilots were trained to leave it alone is a falsehood, because the only thing we know for sure is that we don't know. (h/t Socrates).

Almost certainly.

Possible, but unlikely.

I doubt it.

No, it stayed there because there was neither a nose-down SS input deflection for a sufficient period of time, nor was there any attempt to manually change the trim.

Sorry - that doesn't wash. Far more likely is an overcontrol response to correct the slight wing-drop at FMS disconnect, followed by PIO as the PF consistently overcorrects, possibly tensing up and inducing the nose-up attitude we see. Look at the FDR traces - now, admittedly I'm working from memory here, but most upset recovery procedures require progressive and sustained control inputs opposite the direction of the upset, until stable flight is resumed (this, incidentally, is why the 737 rudder-reversal failure mode was so deadly, with pilots thinking they were putting in correcting rudder when in fact they were controlling in the direction of the upset and inducing a spiral dive). The AF447 traces show the lateral SS movements going from stop to stop repeatedly over the space of a few seconds at most, classic PIO. Judging by the PF's remarks on the CVR, he seems primarily concerned with lateral control and unaware that he is making pitch demands at the same time - only the PNF seems to notice this ("you're going up - go down"), and reminds the PF to touch the lateral controls as gently as possible.

Above all, the magnitude of the inputs made is more appropriate for batting a Pitts around in VFR conditions at a couple of thousand feet, certainly not appropriate for a widebody at cruise in IMC at night.

Yes it can, and it was explained by several people not long after the black boxes had revealed their first secrets in the lab. In normal flight, autotrim trims the aircraft to maintain a g-loading (in most cases). In the case of Alternate Law with no protections, the autotrim will follow any demand made by the pilot based on the assumption that the pilot knows what he or she is doing - this feature of the design is specifically to support ease of operations in abnormal circumstances. If the pilot does not feel that the autotrim is behaving as they desire it is a simple matter of moving the trim wheel to the desired position and the aircraft will attempt to stabilise around the manually set trim, with the autotrim taking over again from there except in the case of Direct Law or Mech Reversion.

@PJ2 - I completely and unreservedly accept what you are saying and agree totally. However, what bothers me is the knowledge that some journalists are known to either paraphrase or report verbatim some of the things that are posted on here. The BEA and Airbus have spent years trying to overcome the largely undeserved reputation they garnered by the number that Michel Asseline and his enablers in the press did on them, and what worries me is that I'll open the paper one day to find one of Bearfoil/Lyman/Will Fraser's more lurid assertions reprinted as fact in an environment where the general public are more inclined to take such things at face value (which is why we still have people saying that the A320 "overrode the pilot" and hit the trees "because it thought it was landing", and other such nonsense).

Hello AR33Zab,

Thanks for the BUSS information.

I could add the following to your post, from the general perspective of compliance to an engineering, or certification specification :

If the Stall Warning announcement in a Stall approach, or Stall situation is a required - it's a MUST - then the logical formula that is at the basis of the announcement MUST calculate and deliver a TRUE or FALSE result.

If it has an "UNDEFINED" result for a certain condition, than the functioning of the formula, and the Warning announcement corresponds to a SHOULD, not to the specified MUST, and thus it fails to follow or to deliver according to the specifications.

Why the formula failed - which the NCD or AoA zero is - matters in terms of explanation for its failure to comply with MUST, and as an element for considerations in fixing it, so it complies with the MUST.

airtren.

Knowledge of the stall would not help
 

Actually that is NOT what the quote says:

It says ""It is important to know that if such a thrust increase was applied when the aircraft is already stalled, the longitudinal effect would bring the
aircraft further into the stall, to a situation possibly unrecoverable."

It does not say recoverable if the crew recognize they are stalled. It says that a thrust increase at the wrong side of the drag curve when stalled can lead to a situation possibly unrecoverable

Knowledge of the stall would not help ???
 

Ian, this is about pitching moment, the 'wrong side of the drag curve' has nothing to do with it. Let me think, where could it be 'possibly unrecoverable'? I would think possibly when the engines are capable of delivering a high thrust, i.e. at low altitude, low temperature, low speed, flaps down?

@ OK465
GerardC : OK465
In this case I suggest you do some homework : ALL pilots having actually faced flying ALT law2 at high altitude reported :
This is not an "opinion" but established facts. (I have more testimonies on shelf...)

Please see : post 3429 (http://www.pprune.org/rumours-news/4...found-163.html).

Hi GerardC:

I personally do not act on "established facts" from an internet forum.

You're certainly welcome to fly your A330 in whatever manner you feel appropriate. :)

I'm sure this applies to ALL pilots.

(BTW you mean post #3249 and I may be too old for homework)

So, now there are (4) different angles of interest in the pitch plane...? when only 2 are needed. Pitch and AoA

Correct me if I'm wrong... please

Oh yes, another thing...

one good reason for this, is the reduced aerodynamic damping at altitude.

whether this is still taught, explicitly, or left to the control laws to sort out today, would be interesting ;)

Harry Mann. You are not joking I think? I would further explain, but first, do you take exception to the comparison of the HS to a VIW? I think one or the other of us should elaborate, lest some one miss the point? I am concerned that pilots of this a/c are not Trained in the potential dangers of the THS re: PITCH response?

I get this from the apparent lack of care the PF showed in his responses to mere Pitch requirements at the onset of LOC?

None of the Three, (apparently) monitored the Trim Wheel?

Certainly, an alternate to THS would be a TMP? ('TRIMMABLE' MAIN PLANE?)

I don't say the THS is inherently unwise, of course! Perhaps the builders need the discussion?

Also, are you sure mere mention of reduced aerodynamic damping is sufficient to convey the caution needed in handling?

Perhaps an elaboration?

It has dawned on me why some folks aren't particularly concerned re: AutoTrim in recovery/AL2, when some pilots here have voiced some strong exception to the concept?

@AZR:
 

By Joelle Barthe

Flight Operations Engineer

Published on SafetyFirst #5
December 2007



And this why AF didn't installed the BUSS option:

Frankly, I don't entirely disagree with AF' decision not to fit this kit.

What is frustrating, though unproven, is that had AF installed it, the glaring lack of altitude skills would probably have gone unaddressed.

Horse gone, corral closed.

Thanks A33Zab. :ok:

Can anyone comment on:
- the relative precision of the AoA "from an ADR" and "from an IR"?
- the relative failure rate (whatever reason) of an ADR vs an IR?

I'm trying to understand why the ADR AoA was used on planes, if IR AoA is/may be available too, and the latter not being subject to AoA probes icing (Perpignan), nor speed problems "pollution" (AF447).

Concur on the thanks to A33Zab.

It's a step in the right direction, and acknowledgement that something needed be done.

But with a use limited to FL250, it seems improvements are in order.

Further on the question of ADR AoA and IR AoA on the same plane:

Why not to have a compound formula, a logical summ of the two formulas/calculations, and use the result which is most efficient if it is valid, and fall back to the other, if the first result is not valid.

Aren't they the same probes, just piped through the aircraft systems differently?

Compared to an airspeed system, an AOA system is significantly more accurate at low (approach) speeds and much less accurate at cruise speeds.(Assuming proper calibration and design.)
Remember that your approach speed is used primarily to infer an angle of attack for the approach.

"> I thought hard about the wisdom of posting this, but in the end decided to take the plunge. This chart takes the AOA values listed as valid in the notes accompanying the CVR transcript together with some additional data read off a digitised version of the traces and combines them with elevator and THS deflections. It has been said several times on this thread that the THS is more powerful than the elevators, usually with a ‘much’ adjective. In fact, for the A330 geometry and using standard aerodynamic calculation methods it turns out that 1 deg of THS is roughly equivalent to 1.5 deg elevator. So if we multiply the THS deflection by 1.5 and add that to the elevator deflection (with appropriate signs of course) we get an ‘equivalent elevator deflection’. This is what I used to get the graph.">http://i1081.photobucket.com/albums/...avsequivDq.jpg">
I have plotted it with the AOA as the X axis because in that way it doubles as a qualitative pitching moment curve – if the aircraft is in equilibrium then the tail pitch will be equal and opposite to the wing/body contribution. Obviously, this hides any pitch damping or thrust contributions to pitching moment. We can’t do much about the damping, because the scale of the traces doesn’t allow one to get anything like credible values of pitch rate and we know nothing at all about pitch damper gains. One can try to assess the thrust effects, although without access to actual engine thrust variations with rpm, altitude and airspeed it is going to be rather rough and ready. Don’t shoot the messenger – he is only trying to get a ROM. The second line on the chart shows such a ROM. Beyond the AOA limit shown the thrust effect increases sharply, due to a combination of increased thrust as a result of altitude changes and the drastically reduced airspeed which makes thrust effects much more powerful. Unfortunately, this is an area where the speed indication becomes unreliable.
Apart from the fact that this graph gives some indication of the AOA you can expect for a given set of tail deflections, the important thing for me is that there is no indication of any stall. OK, there is the faintest trace of a pitch break at 30 deg AOA, but in no way can that be considered as “ a nose down pitch that cannot readily be arrested” since it was clearly possible to go to even higher AOAs by the application of more NU commands. There is another possible pitch break at around 19 deg AOA, but just before this point there was a lot of sidestick activity and pitch response, so the damping terms may be important. also the same comment that it was not a nose down pitch that could not be arrested.
So when we talk of the PF not recognising that he was stalled, one of the classic indications was missing.
The other criterion specified in the rule book [and incidentally the A330 was not certificated to CS25, but to JAR25 Change 13 – similar but not exactly so] is buffet. If you look at the plot in 1.16.5.2 of the BEA report the main change at the stall seems to be the appearance of a 5 Hz component. The report does mention that the ‘g’ at the cockpit would be significantly greater than that at the CG, but this must also be true to some extent for the turbulence generated accelerations. Both relationships will depend on the fuselage structural modes, but from what I remember of mode shapes it would be primarily the first bending mode that generates high motions up front and that would not be a 5 Hz mode.
I will bow to any pilot opinion that differs, but it seems to me to be perhaps expecting too much for a pilot to distinguish a change in frequency content of cockpit motion when he has been experiencing turbulence and was expecting more severe turbulence to come shortly. I note that the AI Chief Test Pilot has said that it is very difficult, even for experienced test pilots, to distinguish the transition into stall.
If there is no pitch break and the buffet is difficult to interpret, he would have been thrown back on symptoms that do not appear in the JAR description of stalls – high attitude and inability to arrest the rate of descent – but over to pilots to evaluate those.
One other thing that is hardly rocket science either but will probably surprise many people is the THS behaviour. THS AOA is just the body AOA less downwash and THS setting. The downwash is usually expressed as a value at zero AOA plus a downwash gradient relating downwash and AOA. I have used 1deg and 0.4 if anyone cares.
The aircraft first went into the final stall at about 02:11:55 at which time the AOA was around 10 deg and the THS at -3.4. Downwash was 5 deg, so the THS angle of attack was 1.6 degrees positive. The THS arrived at -13.6 at 02:12:27, when the AOA was over 40 deg. With the above assumptions the downwash would have been 17 deg and the THS angle of attack 9.5 deg positive. There are arguments to suggest that this is an overestimate of downwash behind a stalled wing, so the THS AOA would have been at least this positive value.
For virtually the whole of the event, and certainly for the whole time the aircraft was stalled, the THS had a positive AOA so that it was generating upwards lift and a nose down pitching moment despite the fact that it was set at -13.5 degrees!. This is consistent with it being a stable aeroplane as shown by that pitching moment curve.

Of course the net HS lift was negative and the net pitching moment positive (nose up), but this was made up of a very large downwards lift from the elevators partly offloaded by the positive lift from the THS itself. If the elevator had been returned to neutral the THS lift would have given a ND pitch and attitude reduction. Look at the traces - that is exactly what happened!

The nose was being held up by the application of elevator.

Of course, the THS setting made the elevator’s job easier, and if the THS had been (sensibly in my view) restricted to 3 deg the eventual AOA would have been lower, How much lower you can get from the first chart – with 3 deg THS and 30 deg elevator you could expect to arrive at 35 deg AOA – big deal! – you are still well stalled and although the descent would have been shallower the end would have been the same unless he had recognised early on that he was in a stall.

OwainG,

Thanks for a truly fascinating analysis, and particularly for expressing it in a manner which we ordinary mortals can understand. In my case, most of it. Could you clarify a couple of points?

(1) Downwash assumptions

Quote:
THS AOA is just the body AOA less downwash and THS setting.
Should that read "... body AoA LESS downwash PLUS the THS setting? (Given that the THS angle is negative.)

Quote:
The downwash is usually expressed as a value at zero AOA plus a downwash gradient relating downwash and AOA. I have used 1deg and 0.4 if anyone cares.
Is the 0.4 multiplied by the degrees AoA?

(2) Effect of sidestick fore/aft on elevator position (dq)

Can you confirm that, with stick neutral in the descent phase, Pitch Alt law would still have provided substantial up-elevator (i.e., a minus dq)? Any idea how much forward stick would have been required to neutralise the elevator? I also wonder how much down-elevator could have been achieved by full forward stick, and if that might have been enough to stall the THS.

You make a particularly significant point when you state that, elevator authority being two-thirds as much as THS, stopping the THS running beyond (say) minus-3 would probably not have made any difference until the AoA reached +35.

'Locked' THS
 

I believe that Lyman was trying to say somewhat less than concisely, was that with the aircraft established in the stall and dropping at over 100 kts, that the g could have been less than .75g leading to the THS software logic locking in position.

or to put it another way

If the software driving the THS uses g sensimg
and moves the THS with the intent of maintaining 1 g then
0.9 g would be enough for the software to continue commanding full NU.

airtren, "Being disruptive once, or twice, to gain attention is perhaps enough."

Me, "Perhaps a two day old pizza across the face is needed in some cases where there is a persistent lack of attention."

You need to be persistent until a randomly chosen acknowledgement is performed. Then you know you have their attention, however briefly.

The object is not to avoid distraction. Sometimes one must distract the over focused attention of people ignoring warnings.

Yes, sorry for any confusion.

Again yes.

I think so. As I understand it, with neutral stick the system would have tried to maintain the 'g' present at the time the stick was neutralised, on the assumption that the pilot was satisfied with the situation at that time. Trouble is that there were periods of time (02:11:06 to 02:12:06 for example) where the 'g' was less than 1.0 but quite a lot of up elevator was being applied (and presumably needed). Since stick movement even in Alternate is a 'g' command not a direct elevator command I don't see how to easily translate that into how much stick would neutralise the elevator. Given though that even in the worst case that the THS AOA was only 9 or 10 deg I don't think that full down elevator would have stalled the THS.

I didn't think I said that in quite that way, but yes, I agree http://images.ibsrv.net/ibsrv/res/sr...lies/wink2.gif

Most of which is factually incorrect, particularly the 0.75 value, which should read 0.5, a value the aircraft NEVER achieved.

For once an for all, the THS followed the PF demand applied for NU. Once the elevators were consistently held NU the integrating function that looks at the demand, determined a constant NU offset was being applied to the controls and followed the demand in an attempt to off-load the elevator (as designed, trim, hello!). I don't know what else to say? The PF asked for NU, the system delivered. The PF also decided that TO/GA was a good idea, again assisting in NU.

BTW - Owain Glyndwr - nice work, helps understand things and also reaffirms the point that the THS was NOT the 500lb gorilla in the room here. The elevator demand alone was enough to put the aircraft in the ocean.

I can't help but equate the THS sysetem to the power steering assistance on most cars - yes, if you turn the wheel to point the car over the edge of the precipice the car will dive over the edge to it's doom, the power steering just makes it less hard to do the pointing, but over you will go, whether the power steering works or not, if that is where you point the car in the first place. In fact the THS is LESS intrusive than the power steering analogy, but you get my point...

A little off topic
 

Lone, I noticed this, "Alt 2 latched does not mean "flight control locked and no longer able to be moved."" before I noticed it was to bear and ignored the message.

I have an idle question that does not bear on this crash. Why might Alt 2 latch in and not be able to be escaped back to normal once the aircraft is flying normally again? Permanently latching out the aircraft safety systems for half of a long (10 hours?) flight seems counter productive.

DozyWannabe

Actually full motion simulators are useful to teach pilots NOT to trust their somatic senses when flying purely on instruments. It is extraordinarily easy to fool somebody into thinking they are accelerating forward simply by tipping them back. This is done in amusement park simulator rides all the time. Heck, even simple manipulation of the seat's configuration can lead to a feeling of (slight) upwards acceleration.

A full motion simulator can drive that point home to pilots who do not quite get it. PF apparently did not get it. He remarked about high speed. He was tilted back and drew the wrong confusion from his senses.

Quote from Owain Glyndwr:
I didn't think I said that in quite that way, but yes, I agree

Whoops, I take your point. Apologies for putting words into your mouth.

One would think that this is one of the basics of flying that class of aircraft, just as the "in out and down" pattern is taught to helicopter pilots first learning to hover. (Or something like is mentioned here Visual Cues When Hovering Helicopters | helicopterblog.com)

'Nuther silly question --
A33Zab, does the BUSS report a line of flight component of airspeed or does it report the square root of the sum of the squares of the three dimensional velocity vector components? (Or ideally, does it report both?)

Nope.

Trim is not implicated in the climb into the stall, so wouldn't change that.
To get out of stall, the first step is the pilots recognizing it. That didn't happen, and trim (or lack of) wouldn't change that.

It might have made for a faster recovery, but there was no recovery attempt, and had there been a timely recovery attempt, the trim wouldn't have been full up anyway.

In contrast, the behaviour you suggest (autotrim drops out) is a contributing factor in several fatal accidents and near-accidents, on both A & B. Particularly when the automatics have trimmed the a/c up into the stall in the first place. One more thing too many for the pilot to remember in a recovery.

Hi

My guess: having encountered once a HARD failure (i.e. not intermittent), the system cannot be sure its sensors are back to normal.
OK, we (human) may analyse that a priori the speed (pitots) are back to normal.
But a computer cannot be sure of that (unless implementing complicated/prone to failure cross checks). So, as long as a real check of the once faulty part(s) (here: the pitots/ADR) has been done (on the ground, that is), the computers considers their functionnality (here: airspeed values) ​​as unreliable ; or, at last, not enough reliable to revert back to NORMAL LAW and its associated protections.

Just an (educated?) guess, though. If anyone knowledgable can/may confirm or infirm, I'll be glad. :)

Well, the pilot was asking for 'more G' actually, a moot point maybe, but true... and when not sensed (howsover) as 'more g' maybe that was the clue to something being very wrong... possibly, subject to poor buffet and nose-down.. the only (tactile) clue at all.

On the power steering analogy, I find myself helpless not to comment, as I find too that has completely destroyed many driver's ability to steer accurately, or hold the wheel properly with two hands (at 10 to 2 O'Clock) such that in a moment of crisis, any meaningful avoiding action could ever be taken; some drivers, seemingly bunched up behind the wheel, with a laissez faire one-handed grip in the most strange of places (even right down the bottom) are unlikely to be able to input more than 10 or 15 degrees wheel input... even after 2 to 3 whole seconds of reaction time:ugh:

NB. The steering wheel will save your life easily as often as the brakes, sometimes more so...

NB2. IMHO, this is 'on' topic.. witness the likely appalling stick handling skills... treating the stick as just another appendage, is somewhat akin to the modern power steering driver's complete failure to honour the steering wheel as a vital life & death control (usually though its not them in their massive heavy & expensive energy absorbing steel box who suffers, but a pedestrian or occupant of an older or smaller car !)

IF789 I am NOT suggesting AutoTrim 'dropout'. That is a bad idea. It should not have begun in the first place, but once present, an immediate loss of AoI aspect could be deadly.

If THS dialed in NU to accommodate PF input, there is a big problem with that, and the main reason recovery most likely was impossible. The fact that PF did not recover the flight Path is not relevant for the general discussion.

If THS was loading NU to re-gee the airframe, same story, it was out of its program, functionally. The a/c had to have ND, and just cause the PF didn't grok that, it is ok for the THS to blow it also?

At the onset of climb, PF had elevators loaded with airstream, and THS was unnecessary. He was barred from over loading the tail via 'g' protection, but that wasn't necessary either. He was allowed (or input himself) nibbles of NU sufficient to STALL. Because it took so long to STALL, he had zippo energy (~ or, 'not enough') left to allow a rapid break, and the MUSH brigade began. Now without cue, no-one gets that the airframe is STALLED, and TOGA is still proper (in the BOOK) per procedure, Bob's yer uncle. Done, done, done.:8

REPEAT... I do not advocate 'dumping' trim in the guise of recovery.

per LATCH AL2. Why do we have to go back to NORMAL LAW from AL2?

How about just a simpler version of it, like an autopilot. Is that to Ludditic?

JD-EE, re yr #460 -
From Joelle Barthe's text: Leaving out the more subtle details for readability, this is how I think it works in principle:

If one knows the airplane's aerodynamic characteristics (in particular, lift coefficient versus AoA), and the airplane's mass and airspeed, one can calculate the normal load factor for each AoA. I think the BUSS essentially uses the same equation in reverse, solving for airspeed from sensed LF and AoA.

P.S. For two reasons this doesn't work very well at high altitude. Firstly, the slope of AoA vs airspeed becomes rather shallow at high airspeed. Secondly, the aerodynamic characteristics vary with Mach number, i.e. (pressure) altitude.

Hi HN39,

It's not that clever.
It simply displays a sensible angle of attack as the "green" sector. Other angles of attack as orange and red. It is orientated so that the red sector (with high angle of attack) is at the bottom of the scale, etc.

Hi JD-EE,
Pilots can only sense accelerations - not speed. The sensation of high speed was due to the unusual air noise around the cockpit sounding like they were going very fast.

rrr. They were going fast. Wicked fast. Far faster than the airframe was designed to go. In that aspect. Very, very fast, given so dirty.

:ok:

HarryMann,

Your reference to power steering, brings forward the "feedback question again". As one that spends time racing cars at speeds that are well above those that normal drivers do, the steering feedback is a very important sensory element in terms of wheel adhesion, or lack of adhesion - the lightness/hardness of the steering is an adhesion indication - if no other sensing mechanism is included in the system, to replace it.

Qwain Glyndwr,

Thank you for constructing the graph, and curves, illustrating, and explaining what appears to be the science behind some of the interpretations and assumptions made based on the existing BEA Report graphs in earlier posts .

Your post is substantial, while also dense, and at a quick reading - I don't have much time now - I can react with some quick questions, but I may have more later....

1. Regarding the Elevator to THS 1:1.5 ratio, what is the ratio between the surface/area of the Elevator versus surface/area of the THS?

2. Is this 1:1.5 ratio the reason (or are there more?) behind qualifying the THS as the "most powerful control surface on the plane" - paraphrasing text from some earlier posts on this thread, related to the THS?

The explanation above seems to emphasize the role of the Stall Warning as being by far the most important element present among the Stall Warning mechanisms at the time, and thus the need for it to be reliable.

The THS reached the 13 degree NU when the airplane was already in STALL, so the effect of the max 13 degree deflection can be counted on from that moment, and not earlier - I would think.

3. At what AoA, and Elevators max NU, would the THSmaxNU pitching moment switch into becoming a NU moment?

While at 40 degrees AoA, the THSmaxNU ND momentum (in spite of its NU position) opposed the Elevators NU momentum; at this switching point, it would start helping the Elevators NU pitching moment, or opposing the Elevators ND pitching momentum, if Elevators were moved to be deflected ND.

You seem to have taken in consideration a first important element regarding the THS contribution to the pitching momentum, which is the THS angle in itself.

But there is a second element, which I think may be, or is important, which depends on the question:

Is the Elevator swing action relative to the THS surface, that is, Elevator max NU and max ND angle relative to the THS surface?

If the answer is yes, than in that case, in absolute value relative to the airplane longitudinal axle (absolute - for shortness):

a) Elevators max NU (absolute) angle is at
- maximum at THSmax NU
- minimum at THSmax ND
and

b) the Elevators max ND (absolute) angle is
- minimum at THS max NU,
and
- maximum at THS max ND.

This implies a difference between the absolute Elevators ND angle relative to the a/c longitudinal axle:
- Elevators max ND angle with THS max NU, versus
- Elevator max ND with THS at 3 degree NU (call it Neutral), and further
- Elevator max ND with THS max ND.

4. I would be interested in reading your comments extended to these above elements.

The combination of answers to 3. and 4. would explain further, I think, your conclusion above.

5. At AoA 40 degrees, are the THS + Elevator, Thrust, (and Cg) the only (force) factors contributing to the pitching momentum?

I am confused. Is perhaps my first reading. I read "first chart", but I don't see more than one chart, so I must be missing something.
Or are you perhaps referring to first curve? Also you mentioned in your text "traces", or "trace" which I read as "curves" or "curve" on the graph, but I want to make sure my reading was correct.

Overall things are very complex, but it is nice to peal off one by one the layers involved.....

Without having a Normal Acceleration in the picture, is there any indication that in order to being able to quickly and effectively react and have full control of the control surfaces at Stall, would have been better achieved by being in Direct Law?

OwainG;
Great post, thank you - it is taking me some time to absorb and think it through. I would like to offer what I can by way of response.
Yes, I think that is a very good point. I think it is probably expecting too much to distinguish between the character of turbulence and buffet under the circumstances described. Confirmation bias may play a role in this, for as you say, "more turbulence" was expected. I have asked and I think simulators, even D-Level, do not replicate turbulence and either high or low speed buffet differently. Perhaps that will be one of many changes that will emerge in the learning.
Again yes, I think that is a good place to start the change in the teaching/checking of stalls in all conditions. Despite the fact that simulators do not currently replicate the aerodynamics of the actual stall, (once past the approach to the stall), they could certainly replicate these two symptoms and training stall recovery techniques as per the revised "Stall Warning or Aerodynamic Stall Recover Procedure" (Airbus, Boeing, Bombardier, Embraer document), revised published procedures could be scripted in recurrent training. In fact, I would expect such training and checking are already being implemented as is the UAS procedure (including clarifications on how to do the drill and checklist).

I'm sure that the various regulatory authorities are examining all this and will change their PPC (Pilot Proficiency Check) mandatory requirements concerning the approach to the stall from "minimum loss of altitude" to the current wisdom. Currently in Canada even teaching/checking the approach to the stall, and the stall itself, are not required if the PPC is for FBW aircraft, (not sure if this includes the B777 or not - anyone?).
The one question I have on this then, is about the elevator which clearly had aerodynamic authority all the way down. If, after the stall was fully-developed and even with the THS at -13.5deg, if the SS had been placed in the full ND position and held there, depending upon when this was done, (earlier the better of course!), and given the ND pitching moment afforded by the THS, would such elevator position be sufficient to eventually get the nose down or would it partially/fully stall given the already-positive AoA of the THS, and lose all effectiveness thereby?

Fascinating post, thank you sir.

Air noises
 

Do you think it might be possible that these sounds reminded him of the sounds heard in a glider going at high speed with which he was probably familiar, and that in this respect his glider experience to some extent misled him?

Just an idea.

Hello,

What about his experience seeing full blue area in the artificial horizon
The pilots had a very good horizon indication .. it's even the last words of the captain ....

http://i.imgur.com/DOF51.jpg

airtren

The elevators are full span and the hinge line is at 70% chord, so the elevator area is 30% of the exposed HS area


I know this has been said, but I think it is based on a misinterpretation of the facts (as is quite a lot said herehttp://images.ibsrv.net/ibsrv/res/sr...lies/wink2.gif)

The THS limits are 14 deg NU to 2 deg ND and the elevator limits are 30 deg NU to 15 deg ND. Taking my 1.5:1 power ratio the elevator/THS power would be 30/21 and the ND power 15/3. I rather suspect people have been thinking of the ability of the elevator to overcome the THS when they are in opposition, but since the THS is slaved to the elevator it is difficult to see how this could in any way be relevant particularly when you consider the main thrust of my arguments on THS behaviour.

So far as I can see, never. To give a NU moment the THS would have to experience a negative AOA. It might get this in cruise at fwd CG, but then the elevators would be neutral, since that is why the THS would be so positioned. As soon as full NU elevator was applied the AOA would go up and you would be back where we started.

To be honest I am not sure what you are asking here.http://images.ibsrv.net/ibsrv/res/sr...s/confused.gif

Elevator deflection is always quoted relative to the THS chordline.

For the rest it is probably easiest just to give the numbers:

Maximum NU deflection relative to body axis is (14+30) = 44 deg
Maximum ND deflection relative to body axis is (2+15) = 17 deg.

It is usual to take moments around the CG, so that doesn't figure in the calculation of moments except through variations in the relevant moment arms. The pitching moment is then affected by THS+elevator, Thrust and pitch rate, although this last is a minor term compared to the others.

Sorry - minor typo - my first version of the post included two charts, the second of which was THS AOA vs aircraft AOA. For "first chart" read "the chart above"http://images.ibsrv.net/ibsrv/res/sr...s/embarass.gif


I don't think it would stall, because even at 40 deg aircraft AOA the THS AOA was only about 10 deg. After all, you don't very often see wings stalling at that sort of AOA with plain flaps deflected do you?

OwainG;
I was in the process of working on all the relative angles (a la mm43) and this instantly cleared it up, thank you. QED!