AF 447 Thread no. 4
 

Thread no. 3 can be found Here.

As this series of threads has become of epic proportion, the following observation from jpete regarding search filtering may be of interest -

You can achieve a search of only the 4 threads by using the following search string in Google

ths af447 site:http://www.pprune.org/tech-log/

this will search for mentions of THS in the AF447 threads of tech log only. Just change the THS in the string to whatever you want to look for. Adding the site:URL end part is the magic that restricts Google to only searching in the tech log on here



I take your view re: Boyd. So did Schwarzkopf. Your impression is anti OODA. It is also anti (airline) pilot, for the Colonel had other precepts that made OODA, as he taught it, revolutionary. Autonomy, Agility, Mobility. (FFS) are you in Wiki? Have you read Coram? John Boyd's ACM? His "Creation and Destruction"? Read Pierre Sprey on Boyd. The "Acolytes".

Agility is both a cerebral and logistical norm in OODA. As such, it is being applied in Leadership, Military, and economic models. OODA can be deadly without the tools innate in the trained Warrior (combat pilot). It is more than turning inside the scissors, and wasting his tail.

Applied to fbw, it is a disaster, hence my original question. The crew in any modern airliner, to include Boeing, gets immediately into trouble since his vehicle is a thing of mystery in certain regimes. and as PJ2 says, "Wait.....Wait....." etc. That is the antithesis of OODA, don't you agree? Wait until the enemy does something you recognize?

Our PF was reacting to a screen, which is his intel, and he acted. Downhill from there? He wasn't in the loop at all, and his adversary may have been his platform.

Boyd demonstrated new ways to fly in genII a/c, the F-100, specifically. I would dearly love to see an improvement in man/machine. Wouldn't you? I think OODA is a point too far. I would love to hear gums on this, though I think he was in the Branch that disowned Boyd to their distinct detriment. Are you A Marine Pilot? The Marines have a statue built in is honor.

Conclusively, I think OODA would be a disaster for Air Travel. It would be expensive, there would be high washout, etc. Should we start by re-introducing Man to his Machine?

Trimmable Horizontal Stabilizer. For anyone who wishes, take a peek at the pic Machaca posted of the Inner tail cone where the engineer was on a ladder working on the RCU. Look specifically at the Jackscrew and suss which direction it must move to orient the THS in a specific manner. In the pic, it is in ND. To acquire NU, the hydraulic motor turns anti clockwise and the threaded collet distances itself from the fixed motor. As it's Arm increases, the screw itself is in greater torsional stress, and I might entertain that with the enormous feedback of a maximum effort deflection, some damage may result in the threads. If the forces were intermittent, and opposing, the critical point may have been surpassed. HazelNuts39 has posted a graph which should give anyone the willies.

Anticipating a familiar (knee jerk) response from those who have blind faith in the integrity of this airframe, I will even suggest a method to disprove. Without question BEA know the performance of this system, and the actuals will out. The most important evidence for mechanical failure is already in the Public Domain.

1.The THS remained in its near max position for seven miles down.

2. Any pilot who honestly looks at the evidence would say that cannot happen.

747 WW
 

I was told the first 25 747-400 were built with wire wrap interconnects, and they had to run them all back through the factory to change them.

@bear - you've got a funny idea of what constitutes "evidence". "Any pilot who honestly looks at the evidence would say that cannot happen" is not evidence, it's supposition.

There are plenty of alternative explanations for the THS remaining fully nose-up that don't require mechanical failure to be a part of it, the only problem is that some of them will not be especially palatable to those members of the piloting community that are hoping against hope that the PF didn't make a fatal mistake.

With all due respect, you were clinging to the idea of a V/S failure when none of the available evidence supported it, and now you're hoping for some kind of THS failure when any supporting evidence has either not been released or does not exist.

Why is the idea that pilot error played a part (note : I'm not saying that it did) so abhorrent to you, and why do so many assume that there's some kind of conspiracy going on between the BEA, AF and Airbus to blame the pilots?

Hi,

I'm not certain that bearfoil assume it's some kind of conspiracy between BEA AF and Airbus.
But certainly the french government is a big player in the final issue ..
http://www.pprune.org/6513772-post2025.html
BEA ... "aux ordres" ? ... why not ...

@jcjeant : I pretty much answered the same question here:

http://www.pprune.org/tech-log/45283...ml#post6513849

You only need to see the continuing resentment from some quarters to see that the controversies of 1988 did them little good.

Always remember the Air Inter Strasbourg-Entzheim accident and the influence of the prefecture...

The traces are mutually consistent. They are derived from the assumed vertical acceleration as described. It's an iterative process: assume az/g, look what trajectory and speeds it produces, and how that fits the BEA description. Then modify the az/g to improve the 'goodness of fit' in several iterations, until you're satisfied it is good enough to give a reasonable description of the probable course of events. It's a bit like straightening a table cloth, you pull one corner to flatten a wrinkle, and get more wrinkles in other places, except this has more degrees of freedom. Confidence is a function of 'goodness of fit' in the few corners that BEA gave us. An important caveat that I should have mentioned is that the available cL-alpha data cover only the operating envelope as limited by buffet onset (alpha-max). Everything beyond that is 'educated guess' or pure conjecture.

The zoom climb is partially ballistic whenever 'gee' is less than one. The only way out is to reduce AoA below that at which the stall begins, and that is achieved when stall warning stops (except when IAS<60 kts). Airspeed and thrust are for later. Lift-wise FL375 @ M0.68 is sustainable, but to sustain airspeed the airplane must be put on a descending path (perhaps TOGA would maintain speed in level flight - I don't know). The stall warning threshold is the red dotted line - with valid IAS. BEA has explained the reversion when UAS, but that explanation has been put into doubt because it doesn't fit the Air Caraibes and other UAS incidents.(*)

IIRC in the A340 airprox zoom climb pilot action on the sidestick took the system out of High AoA protection, and the airplane would then recover itself stick-free.

(*)Note: A poster has suggested that in case of airspeed becoming invalid, the stall warning threshold is based on the last valid airspeed, rather than a low-speed value. In my mind, that makes more sense than BEA's explanation. So perhaps you should replace the dotted line in my graph by a horizontal line from the time of A/P disconnect.

PS:: My advice is to look at those traces qualitatively, and not to expect an angle to be accurate within a tenth of a degree.

If BEA allowed AB to say that, after reviewing the data, no modifications to the A330 are needed, that would imply to most people that the accident was caused by pilot error; right?

If BEA intended to avoid making any conclusions in the last preliminary communications, they should not have allowed AB to make any statements since people now believe that BEA must also think that no a/c modifications are necessary.

retiredF4:
It has to be noted that at an AoA of 61° Drag along the Flight path equates to Lift by Factor ,87. So if your tail creates 1000N of Drag along the Flight Path that will eqaute to 870N of lift. Therefore increasing drag on the Tailplane is a good thing. Adding ND elevator will increase camber which again will increase drag and remaining lift.
As has been pointed out lift above the stall decreases bút it doesn't drop to zero.

Slight excursion:
I highly appreciate the fascinating insights of @gums regarding the stall behaviour of the F-16 but it has to be noted that the two designs are very different. In an F-16 much of the lift post stall comes from the strakes (they produce vortex lift which is not susceptible to stall as opposed to traditional wing lift). They are mounted forward of the wing, thereby shifting the CoL forward post stall. That was one of the main reasons for the rather agressive (meaning restrictive, being between 15 and 25°) AoA limitation on the F-16 compared to more conventional designs like F-15 and F-14. High AoA shifts CoL forward on the F-16 therby further increasing longitudinal instability.
/Excursion end

The fact that the Stall warning came back after some Nose Down Input due to the IAS exceeding 60kts again also points to the fact that the control authority was not really lost.
The problem is that reaction probably was quite slow.
So in the heat of the moment it might have appeared as ineffective even if it wasn't.

When GA planes spin it sometimes takes multiple revolutions with opposite rudder to stop it. It is surely not easy to resist the urge to try something else. However those who follow the urge often pay the ultimate price.

On the other hand we still have no clear information if the pilots in this case ever realised their real situation and Flight Path being deeply in a stall. Reading the scarce information we have I have the nagging feeling they didn't.

THS effectiveness with high AOA > 60
 

It is based on my own expierience out of high performance aircraft with a big ugly stabilizer....... which we could stall at less angle than 45° AOA. Fortunately we had a big heavy cannon in the front with lots of weight and favorable cg.

So it would be kind if you could proof it with numbers for the AF 447, otherwise its just an oppinion of yourself.

Although in an F-4 with its tiny VS and the Anhedral/Dihedral I would assume the main danger was not so much the stall itself but the spin.

With the CG and aerodynamic Design of it I would expect rather swift Nose Drop at the Stall. The thrill being not to spin it (unrecoverable?) and therefore not to drop a wing.
Am I right ?

Hi,

Last OT on this sensible matter :)

We must keep in mind that all press releases and BEA release are mainly read by the general public and not only by the Pprune contributors ...
General public don't go on all kind of deep analyses on such press articles or BEA note ...
With only a few words and explanations .. they form their own opinion
Public sentiment in general by reading the note and press articles can't be ambiguous .. the way is clear ...

bear, please stop mixing apples and oranges in your OODA soup, rather than any useful OODA loop. PD: I learned of OODA before the Endless September arrived. It has aged well.

The OODA loop is what it is. It remains as what Boyd first laid out when he was teaching how to improve air combat maneuvering. (Dogfighting, if you prefer). Of interest is the question of whose decision cycle prevails, robot or pilot, but there is only limited evidence to support them being in that much conflict in alternate law. It remains at some points an open question.

(Or was there more conflict? Not sure, appears to apply to normal law, which sat on the bench_.

Taking the OODA framework and applying it to other disciplines requires adapting the basic model and flow, since the patterns and value in the iterative process, and the speed of the iterative process, lead to a form of the continuous improvement model.

That doesn't change what the Decision Cycle is.

When you fly, you are a living breathing decision cycle the whole time you are flying ... otherwise, YOU ARE CARGO. That doesn't mean you have to act or decide fast, but you do have to make good decisions, and your Observe and Orient need to be accurate. If I observe and misorient, my odds of a bad Decide or Act move goes up.

Each time you get to the Act node you can decide to do as PJ2 suggests ... wait for the next cycle is an action. (This also works when sitting in an ambush and waiting for the right time to pull a trigger, light infantry style).

Or, per the spin recovery in smaller planes, wait for the second or third turn (and sometimes tightening spin rate) to see that your opposite rudder was effective ...)

The other point in Boyd is avoiding tunnel vision, which means not just look at your target, but your whole battlefield ... enough on OODA extensions.

Chris's recent posts suggest to me that the pilots in AF 447 may have gotten behind the decision cycle somewhere in between 35000 feet level, and 35000 feet on the way down. The 11 seconds or 45 seconds PJ2 and you were discussing a while back can lead you to a root cause regarding an Observe-Orient problem which led to Decisions and Actions that may have been based on faulty input, based on faulty pitot probe input.

OODA as anti pilot?

Stuff and Nonsense.

OODA came from pilots. It is what we do. (It is what flight computers to a large extent try to mimic, in their own special way).

That Boyd took an idea and went beyond its origin speaks well of him: he was one smart guy. He did that "out of the box" and "cross discipline migration" thing very, very well.

The movement of THS; 10 degrees in 60 seconds (if continuous) strikes me as very very gradual. In my mind this fits the bill of inadvertent NU input while trying to correct for right roll (especially if being flown from right seat).

OTOH, it is indeed puzzling how the pilots seem to display good awareness of bank angle (judging by a/c not departing into a spin) but not check the pitch attitude.

henra:
A prior post (cant find it at moment) comments that the "ride" coould have been relatively smooth when fully stalled and would likely get rougher as AoA decreased when ND inputs where applied.

So we have:

A: Slow response to ND input
B: Possibly rough ride as AoA starts to get better.
C: Return of stall warning as AoA is improving.
D: Highly suspect air speeds, even though at this point they were valid (when over 30kts) but likely not beliveable: 60Kts, that cant be right, we wouldnt be flying...

Given the above items it is hardly surprising that the PF might have thoughts along the lines "well that is not helping things" and return to NU inputs.
Whether persisting with ND at that point could have saved things is impossible to tell from the BEA "note".

It is usefull to remember that BEA knows a lot more that what has been released and likely had a strong working theory when deciding what information to include.

They knew that when matched with final report the note would need to be seen as:

1: Factually correct
2: Not containing true but deliberatly misleading information.

A (made up) trivial example for #2 would be "then the PF sneezed", unless that was going to be a significant factor in the final report including it in the note would be seen as deliberately misleading even though true.

If read with the above in mind the BEA note likely provides clues to the causes beyond the bare stated facts.

It might if they had done that, but they haven't, so it doesn't.

AB released a statement saying that at this point in the investigation no new modifications were advised. That does not preclude modifications coming out of the detailed investigation further down the line. It also does not preclude modifcations that have already been advised, and in fact in this case modifications already have been advised (and in fact were advised before the accident - AF had not implemented).

Even if the only thing that went wrong with the a/c was the pitots, that is still the a/c as part of the causal chain.

Only idiots can believe that since it directly contradicts the evidence - BEA have already recommended a/c modifications as a result of this accident (and previous incidents). BEA might believe that no further modifications are necessary - but that is an entirely different proposition.

Are you talking about a stalled airfoil or an airfoil in unstalled condition? I´m sure there is a lot of difference in it without being an aerodynamic specialist. Otherwise any object producing drag would also produce lift. A stalled airfoil at 60° AOA is nothing more than a door in the wind producing disturbances and drag of uncalculated ammount. I bet, even EADS doesn´t know what kind of lift the THS would produce at that AOA. It has never been expected and therefore never been tested. And even if it produced some lift, in what direction in relation to the airfoil would that be? How much of it would be directed 90° to the fuselage, that´s necessary to lift the tail, isn´t it?

.

It only points to the fact, that airspeed was not stable below 60 KIAS (if that speed was the real one and not some falsified indication by pitot icing or high AOA).


Why do you assume that there was some spinning present? Do you have any source? Everything is pointing on a stable high AOA descent without much rotational input or even rolling input.

In comparison to the overall size of the F4 it was nothing compared to tiny. We had lots of stab- authority, up to the point of stall. Then it was gone. By the way, stall was accompanied by a dominant nose rise, indicating loss of lift (stall) on the stabilator.

Not quite. As already mentioned, nose drop due to cg and weight on the nose (canon or camera equipment) helped to get the nose down. The aerodynamic design however (swept wing) made it prone for turning departure to stall and therefore spin. Not an issue on modern GA aircraft.

I repeat our stall recovery procedure to picture the problem (the spin recovery was different):

- Stick forward (it was not full forward, due to danger to stall the stabilator)
- ailerons and rudder neutral (not to induce any rolling moment)
- if not recovered maintain full forward stick and deploy drag chute (this assumes, you go forward with the stick until you feel the reaction of the aircraft, If you dont feel it and reach full forward stick you are out of options with the stabilator alone. The dragchute establishes itself in the relative wind and causing a violent up-movement of the tail and bringing the stabilizer back into the working regime, it unstalls the stabilator)

The F4, and the F16 are no A330, but aerodynamics are similar and fundamental. I´m wondering why this knowledge of aerodynamic behavior of airfoils got lost between bit and bytes.

On the other hand modern aircraft like A330 have a very stable aerodynamic design and are flown with a managed CG. When those aircraft are flown into very high AOA, the aft shift of CG settles the ship in a stable nose high attitude, when not immidiate corrective action is applied.

Just picture the THS in its normal working regime, on takeoff, in cruise, on approach and during landing, then it is more then logical, that it was never ever built to recover the ship out of an 60° AOA. I dont know what it´s limit would be, Imho something like 30° and then its out of authority without some other help.

R F4:The BEA note seems to me to strongly imply that the ND input did in fact cause the AoA to improve as would be expected, hence the input did have some effect.

Too much speculation going on !
 

I am waiting for the final report and documentation of the real facts
as saved on the flight recorders and circumstantial evidence.

Any speculation makes for interesting writing, but in no way reveals what
in fact caused the apparent flight crew control anomaly and the write off of a planeload of crew and passengers !

Too many "why's" remain unanswered so as to reach any kind of conclusion.

Hi,

http://www.bea.aero/fr/enquetes/perp...4x768.xvid.avi

The initial estimate of 37% was probably erroneous :
http://www.pprune.org/tech-log/45283...ml#post6484163


You did not oversimplify anything, you make up technical stuff on your own and obviously not able to back up by the appropriate Operation Manual reference when requested.
"The only way autotrim is activated is if the stick is fully deflected and held there past the elevator travel limit"
Give me your reference that I learn something … or retract it !

If it’s getting personal or insulting to challenge what appears to be unfounded statements, so I am.

And if you want us to discuss Habsheim, start a thread on its own, or stop making redundant innuendo.

So many questions about stalls
 

More:
1. Why did the pitots ice up?
2. Why did the A/P and A/T disconnect?
3. Why the zoom climb without clearance from ATC?
4. Why the sudden reduction of speed at top of climb?
5. Why when at the same time the plane went into the thunderstorm?

Any connection?

The unanimous comment from my group of old retired pro's: Why didn't they deviate?

Comment: When an airplane comes out at the top of an uncommanded zoom climb almost 3000 feet above their max altitude below 60 kts, it is out of control! The flight controls do not have ANY effect. As we have seen until it hit the bottom.

Thunderstorms are known to contain strong up and down drafts. For 50 years we in the pilot community have been warned to avoid, avoid, avoid them.

Thunderstorm do's and don'ts
 

full text of the classic FAA guide


DO'S AND DON'TS OF THUNDERSTORM FLYING

Above all, remember this: never regard any thunderstorm as “light” even when radar observers report the echoes are of light intensity. Avoiding thunderstorms is the best policy. Following are some Do's and Don'ts of thunderstorm avoidance:

1. Don't land or take off in the face of an approaching thunderstorm. A sudden wind shift or low level turbulence could cause loss of control.
2. Don't attempt to fly under a thunderstorm even if you can see through to the other side. Turbulence under the storm could be disastrous.
3. Don't try to circumnavigate thunderstorms covering 6/10 of an area or more either visually or by airborne radar.
4. Don't fly without airborne radar into a cloud mass containing scattered embedded thunderstorms. Scattered thunderstorms not embedded usually can be visually circumnavigated.</I>
5. Do avoid by at least 20 miles any thunderstorm identified as severe or giving an intense radar echo. This is especially true under the anvil of a large cumulonimbus.
6. Do clear the top of a known or suspected severe thunderstorm by at least 1,000 feet altitude for each 10 knots of wind speed at the cloud top. This would exceed the altitude capability of most aircraft.
7. Do remember that vivid and frequent lightning indicates a severe thunderstorm.
8. Do regard as severe any thunderstorm with tops 35,000 feet or higher whether the top is visually sighted or determined by radar.

If you cannot avoid penetrating a thunderstorm, following are some Do's Before entering the storm:

1. Tighten your safety belt, put on your shoulder harness if you have one, and secure all loose objects.
2. Plan your course to take you through the storm in a minimum time and hold it.
3. To avoid the most critical icing, establish a penetration altitude below the freezing level or above the level of —15° C.
4. Turn on pitot heat and carburetor or jet inlet heat. Icing can be rapid at any altitude and cause almost instantaneous power failure or loss of airspeed indication.
5. Establish power settings for reduced turbulence penetration airspeed recommended in your aircraft manual. Reduced airspeed lessens the structural stresses on the aircraft.
6. Turn up cockpit lights to highest intensity to lessen danger of temporary blindness from lightning.
7. If using automatic pilot, disengage altitude hold mode and speed hold mode. The automatic altitude and speed controls will increase maneuvers of the aircraft thus increasing structural stresses.
8. If using airborne radar, tilt your antenna up and down occasionally. Tilting it up may detect a hail shaft that will reach a point on your course by the time you do. Tilting it down may detect a growing thunderstorm cell that may reach your altitude.

Following are some Do's and Don'ts During thunderstorm penetration:

1. Do keep your eyes on your instruments. Looking outside the cockpit can increase danger of temporary blindness from lightning.
2. Don't change power settings; maintain settings for reduced airspeed.
3. Do maintain a constant attitude; let the aircraft “ride the waves.” Maneuvers in trying to maintain constant altitude increase stresses on the aircraft.
4. Don't turn back once you are in the thunderstorm. A straight course through the storm most likely will get you out of the hazards most quickly. In addition, turning maneuvers increase stresses on the aircraft.

Table of Contents
Previous Section: Thunderstorms and Radar
Next Section: Common IFR Producers

Direct (K.I.S.S.*) questions
 

Hi,

Because the a/c flew into a region with certain characteristics, equipped with 3 identical Air Speed sensors (Pitot tubes) not adequate for this "region". These sensors (Thales) presented some anomalies before (in other flights) and were scheduled to be replaced by BF Goodrich ones. The accident occurred before the change in the F-GZCP plane.

Because the Airbus SAS System requires reliable information from the sensors in order to work at full specifications. When entering (a region with certain characteristics) and the sensors start to present anomalies, the System change the a/c operation mode (LAW) disconnecting A/P and A/T, etc. We don´t yet have information on other (possibly) occurred sensor anomalies that could also lead to this "disconnection" (due mode change, LAW).

In this region they were capable to use HF and Data comm. They tried to use Data comm with DKR ACC for 3 times, some minutes before. During the sudden zoom climb they certainly were not able to even think on comm for FL change.

The a/c changed speed by altitude and with THS "going" to 13° UP with/and NU commands, she eventually stalled. And they were facing non reliable air speed in their displays and also in the ISIS (3rd and redundant resource). So the real speed (during many moments) after icing up nobody will ever know. Just estimate, based at other data, (risky estimate). The info was just lost (simply not measured, due "sub heated sensors" :}:8:E).

The decision making to go straight (and not deviate) was made before. "Inside" the WX they started a 12° LH deviation, then the zoom climb started. We don´t have the CVR info to understand on the "decision" to go in the straight route. Other planes deviated. On this particular aspect see BEA reports and Tim Vasquez

Nobody has the "real" speeds during many moments during this phase. The sensors were just not working properly. The FDR will show us the moments when the speeds were correctly measured. (Again, the a/c was equipped with air speed sensors not compatible to the region she entered)

The (very little) information BEA released on that suggest they had "some control".

Several cases of Unreliable Air Speed occurred during deviations from WX.


(*) KISS principle - Wikipedia, the free encyclopedia


CVR certainly will help us to understand why.

This is simple stuff, you use your remaining instruments and return to basics: use pitch and power. And you certainly do not continue pulling. Scary stuff,. You don't use the stall warning to calibrate your response, you use your remaining instruments and your knowledge of your aircrafts pitch/power settings. Your solution puts you at an unnacceptable risk of secondary stall and that is another opportunity to enter a spin. If you do not know your aircraft's pitch/power settings for level flight then you are not competent to pilot it/manage its autopilot and take over if/when that autopilot fails.Of course not, you are not born with the ability to recover from unusual attitudes using partial panel. You learn this when you take your instrument rating. If you have lost your scan you are not competent to fly in clouds.

It really is that simple.

I'm struck by the fact these guys managed to "fly" and reverse course at what is essentially under minimum controllable airspeed, for five minutes, in turbulence, and they hit the water belly side down and reasonably flat. That is a huge credit to the designers of the airframe, must be inherently incredibly stable.

@RetiredF4: As I mentioned previously, an aerofoil doesn't cease to be an aerofoil and stop producing lift just because it's at high AoA and stalled. Yes, it produces a lot of drag (component of force parallel to the airflow) as your barndoor would, but there is still significant lift (component of force normal to the airflow). Since you don't want to just take my word for it (fair enough), here's a link to a study specifically of post-stall aerofoil behaviour; it has a good set of Cl/Cd/Cm-alpha graphs going up to extremely high AoA. You'll notice that the motivation for this study wasn't aircraft behaviour, but wind turbines; there's been a lot of interest in post-stall aerofoil chracteristics because they spend quite a bit of their time operating in a stalled condition!

Attitude stable yes - pity it was not speed stable.

Stability
 

Hi,

And Airbus SAS learned something not "testable" before. The airframe designers received (from the FDR) an important information.

And now are being able to learn other very important "things" on the a/c.:}

Stability in a downward 'mush' is no advantage unless you have the power or pitch authority to then accelerate back into normal flight. Indeed, if the aircraft had rolled over to 90 degrees through instability, possibly aided by some agressive rudder input then may that have allowed a recovery?

OUCH!!
 

OUCH, previous poster.

Agressive rudder input in a transport category airplane? No thank you, has been tried before (New York, nov 2001), wasn't an overwhelming succes.

Why not just push the stick forward, instead of full aft, would most probably work like a charm. Forward trim might be used as well, to make life easier.

Unreliable airspeed, alright, but there never was any unreliability in the ATTITUDE: four independant sources available (IRS 1, 2, 3 and ISIS attitude).

When ever, in a big lumbering airliner, is 15 degrees pitch up an appropriate ATTITUDE? Only after lift-off, with take-off thrust set on all engines. NEVER around FL350.

@CONF - I have never "made stuff up" on this subject in my life, and I always make a point of checking what I'm saying beforehand - with others if possible, some of whom are pilots. My knowledge is strictly engineering and systems design.

So I oversimplified and rendered the information badly - that said, I've still yet to see any proof that an "inadvertent" pull back on the stick would command a nose-up so aggressive that 13 degrees of THS up-trim is required for full elevator authority, or proof that neutral stick would do the same - Chris's theory notwithstanding (for which there seems to be some debate about which speed neutral stick switches from "G-load" command to "Zero Pitch"). I think the only way we'll know for sure is when the BEA release the interim report. Only problem there is that there are those on here, yourself included, that will never believe anything the BEA says regarding an Airbus aircraft - so I fear that these arguments will go on and on and on...

EMIT

My post / question was based on the theory (admittedly unproven) that there was insufficent pitch authority to escape from this situation.

I just don't buy the idea that they were scared away from their one attempt at corrective pitch action by the restart of the stall warning and consequently maintained pitch up inputs for the remaining two minutes plus. The BEA report leaves large gaps but surely they must have tried everything?

AF 447 Elevator trim
 

Is there a determination of how the elevator trim came to be so high, nose up? The trim has more authority than the elevator and I doubt it is possible to recover from a deep stall with the trim full, or nearly full, in the nose up condition. My reading of the Airbus control laws is that automatic pitch trim is "available" in the Alternate Law mode. Did the trim go to the nose up position from pilot input or is there some envelope protection or other reason for it?

In the jet upset cases, it is hypothesized, that an updraft or headwind increase from penetrating an upper frontal boundary caused the aircraft to pitch up; the pilot pushed over but also trimmed nose down then the aircraft developed a steep descent with the pilot pulling hard to resist; the elevator force was sufficient to jam the elevator trim jackscrew so nose up trim could not be accomplished; the aircraft developed a steep dive which could not be corrected. Is it possible in this case, the pilots were attempting to cause a nose down condition and the elevator force was sufficient to jam the elevator trim?

There is a dynamic stall condition, discussed by S.S. Horner in his book on Fluid Dynamics where the AOA at which airflow re-attaches to the upper surface of the wing is significantly less than the AOA at initial stall.

wmelvin and several recent posters: Please read the thread, particularly Part 3 (found here> http://www.pprune.org/tech-log/45283...ad-no-3-a.html). I believe every aspect of your question(s) have been examined, discussed, re-examined and turned inside out through the course of those posts. Re-hashing those same discussions will not further our understanding unless new information comes along with such posts. I don't mean to be dismissive, but many here have been with this thread since the initiating event and I am sure you will find an enormous amount of info (along with a lot of dross, it is true) in the tens or hundreds of pages that make up the body of work here.

@wmelvin

Time-consuming as it may be, I recommend you read the earlier thread(s) - a lot of your questions will be if not answered, at least debated there.

THS post stall lift
 

Good reference, with witch i was familiar already. But i´m unable to see how you would prove your point of enough THS authority being available at 60° AOA.

Lets start on page 153 of your reference with the lower graph, which shows how drag is a function of AOA. The more AOA, the higher the drag. To reduce drag, you have to reduce the AOA.

Now lets look at the upper table, Coefficient of lift versus AOA. Lift increases with AOA, until stall AOA is reached. In that graph that is at about 20°AOA. This drop in Lift continues till 30° AOA. From a max CL of 1.4 at 20°AOA CL has dropped to CL 0.9 at 30° AOA. If we continue to increase the AOA to 45°AOA, CL would increase to 1.2 again. But remember and check the lower graph, we just have increased the CD by the factor of six from stallspeed until 45° AOA. ! If we increase the AOA above 45° to 60° AOA, CL decreases again and CD continues to increase.

What does it tell for the A330?
First of all i dont know what kind of profile the THS represents, but your reference shows, that most mentioned airfoils have a similar behavior, just the numbers change. So lets use what we got until someone comes up with the correct profile.

Lets start with the 46.5°AOA of the THS (60° Aircraft AOA minus 13.5° NU trim) , which gives us a CL of 1.2 and a CD of 1.2. Lets do some ND input by trimming the THS to 0° and let´s see what it does to our numbers. We end up at 60° AOA at the THS, a CL of 1.0 and a CD of 1.6! Our upforce on the THS needed for lowering the nose has decreased and the drag has increased, our ND trim has caused the opposite of our desired outcome.

But that´s not all, lets start again at 47.5° AOA with CL1.2 and CD 1.2 and let us pull full aft stick. That decreases the AOA of the THS for example to 30°AOA, but at the same time we are loosing CL to 0.9, (loosing upforce on the THS again) but we improve CD to 0.5.

Conclusion in this simulated case with this airfoil: Somehow you are stuck between max CL pre-stall and max CL post stall and the airfoil itself has no authority to change that.

To make matters worse, the same applies to the other airfoil, the wings. There´s probably a similar change in CL and CD and any positive change on the THS (somehow generating ND force for the aircraft) might bring the AOA of the wing into the region, where the decrease of AOA initially causes an increase of CL thus rendering your success on the tail usesless for the complete fuselage.

As mentioned before, i´m no aerodynamics guy and might be completely wrong, but i like to make the point that the crew most probably had no conventional way to get AF447 out of a 60°AOA stall and that their behavior described by the BEA in the last 3 minutes of the fall might reflect the helpless situation they found themselves in due to normal aerodynamic layout and behavior of the aircraft, which has never been tested in that flight region.

Another point to remember: That THS has never been designed and tested to generate negative g or great nose down pitching momentum (like in a fighter aircraft), but to keep the nose up in cruise and especially during approach to land.

Another point: CG might have travelled aft (some fuel in the tanks not equally distributed, but now in the aft parts of the tanks, Some cargo in the belly falling to the rear part of the hold, and shift of the center of lift due to high AOA, a mixture which ruins your day.

Retired F4, 35
This is way I see it as well and mentioned in a previous post. If the
a/c has never been tested in such a situation, how can the crew be
expected to recover ?.

Testing the water here, but is that an argument for a tail chute to be
fitted to civil transports, or is that too far off the wall and would
it add to problems in that it might cause structural damage to the
airframe ?.

Another thing that's been nagging me about the last bea report is that
when the ap and ath disengaged, there was a "roll to the right". This
strikes me as odd as one would expect that at the point of disengagement,
they should hand back without change of ap or ath settings. Thus,
no immediate change. Why the uncommanded roll to the right, systems
fault, or what ?...

LG´s, drag chutes, etc
 

Hi,

Considering the fact "prevention" can fail what kind of resource could be used to "remedy"?

Unfortunately the "bean counters", ROI considerations are against us, technicians.

It would be better "written off" a/c´s than other similar tragedies.

If even for "sub heated Pitot´s" we have long delays for "fixing" one could easily imagine what will happen for airliners "stall recovery resource(s)". Probably no chances and probably there are better approaches to the issue. Like the ASAP introduction of "real redundant" air speed sensors. So, Airbus SAS seems to be working on that important issue, vital (AF447 is showing this) for their "advanced planes" reliable operation.

Probably the simplest fix would be just "hotter Pitot´s. And this can be "tested" by the "players". With benefits to A, B and other companies (and a/c operators, etc.)

syseng68k,

Presumably a tail-chute could be fitted, perhaps to a strengthened APU bulkhead. How its getting tangled-up with the APU (which might be running) could be prevented, I'm not sure.
Other problems
(1) It would have to be certificated for public transport, and presumably deployed on a test-flight.
(2) Would it be deployed automatically or manually (by crew action), and what criteria would be used?
(3) Would it subsequently be jettisoned automatically or manually (by crew action), and what criteria would be used?
(4) In the event of jettison failure, which might have followed unwanted deployment, would the aircraft be capable of maintaining level flight? (The second prototype BAC 1-11 had to make a very sudden forced landing on Salisbury Plain when it suffered this problem during deep-stall testing,)
Hard cases make bad law?

Re the uncommanded roll to the right as the AP disconnected, the BEA does not quantify it. Turbulence?

Like some others, I have a feeling that the PF may have experienced some difficulty in achieving left-stick without up-stick when unexpectedly handed the baby at 4am CET. I also hang on to the faint hope that the BEA may acquire ASI 2 data from the QAR. Unless it was over-reading, I cannot understand why he perpetuated the mistake as the aircraft climbed.