bearfoil

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.

Graybeard

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.

DozyWannabe

@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?

jcjeant

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 ...

DozyWannabe

@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.

hetfield

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

HazelNuts39

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.

robertbartsch

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.

henra

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.

RetiredF4

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.

henra

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 ?

jcjeant

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 ...

Lonewolf_50

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.

CogSim

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.

MurphyWasRight

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.

infrequentflyer789

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.

RetiredF4

Are you talking about a stalled airfoil or an airfoil in unstalled condition? Iīm 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 doesnīt 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, thatīs necessary to lift the tail, isnīt 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. Iīm 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 itīs limit would be, Imho something like 30° and then its out of authority without some other help.

MurphyWasRight

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.

Yankee Whisky

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.

jcjeant

Hi,

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