Habsheim

[HazelNuts39]

I thought the graph was supposed to be a "Recoupement from Habsheim" but are you now suggesting there is in fact not much to be 'recouped' ... ?The report discusses the difficulty of reproducing simultaneously all elements of the accident flight. My understanding of "Recoupement" is that the objective of Bechet's simulator exercise was to 'replay' the accident flight. The point you are criticising does not concern Bechet's simulation as such, but is about how Asseline's trajectory has been plotted on the graph for comparison with the simulated flight.

I thought you had earlier established the gain at 10 ft ... ?Actually I said 'less than 10 ft' here (http://www.pprune.org/tech-log/528034-habsheim-32.html#post8362739). I do not recall exactly how I arrived at that number, but I may have meant to say that Bechet gained 'less than 10 ft' on Asseline in those 5 seconds. Apologies if my wording was imprecise.

And if you increase your AoA by 5 degrees in 2 seconds what would be the IAS falling rate ... ? If you increase your AoA the loadfactor increases. The IAS continues to fall until the thrust has increased sufficiently to accelerate the airplane.

[roulishollandais]

@roulis - I'm mystified as to what you actually mean there./mystified by me is surely to much. And what about in my posts ? Math model of june 1988 A320 ? Metalanguage ?
Aren't you from the World best Country in logic ? Charles Babbagge, Ada Lovelace, Lewis Carroll, Alan Matison Turing ! France is it for math !

[CONF iture]

The point you are criticising does not concern Bechet's simulation as such, but is about how Asseline's trajectory has been plotted on the graph for comparison with the simulated flight.
I have actually a LOT to criticize :

All the graphs are of the lowest standard. I would not have wasted any time on them if you didn't mention the one on page 9. I do think the BEA made its best effort to make sure nobody would be tempted to read them.
Those flight and simulator tests were purely smoke screens - what was needed was only the DFDR data to be compared with the most detailed programming of the FCS.


If you increase your AoA the loadfactor increases.
Load factor increase should reveal a change of path, from level flight to ... climb.
The IAS continues to fall until the thrust has increased sufficiently to accelerate the airplane.
I still disagree with your concept.
Kinetic energy is transformed in potential energy until the thrust has increased sufficiently to confirm the early but short term positive climb as IAS now remains stable at Valphamax.

[HazelNuts39]

Kinetic energy is transformed in potential energyIndeed, as shown below.
Kinetic energy is transformed in potential energy until the thrust has increased sufficiently to confirm the early but short term positive climb as IAS now remains stable at Valphamax. No. The airplane will start a phugoid motion at alphamax as shown earlier, unless the pilot relaxes the sidestick and maintains the appropriate pitch attitude.

In the following graph KEht and TEht are the kinetic and total energies, respectively, expressed as a height. Total energy is the sum of kinetic and potential energy.

http://i.imgur.com/Revjj8s.jpg

[DozyWannabe]

@roulis - I've explained at least half a dozen times how the software development work was done, most recently in post #740.

The chances of there being a logical error due to a mis-key - as you theorise - are practically zero because the code is not keyed in manually. The chances of there being a logical error aren't much greater because of the pioneering work on testing, regression and reliability metrics. After that there's the fact that every major system "block" was implemented twice using syntactically different methods, and each is cross-checked against the other.

Even CONF iture seems to be accepting the possibility that it might just be a known feature of the system at this point, even if he doesn't much like how that particular mode functioned.

Between OG and HN39's sterling work, we're looking at a very reasonable explanation of how the aircraft functions would have behaved in that scenario.

[Owain Glyndwr]

@roulis

I have to say that I share DW's puzzlement when trying to understand your point. From previous postings:

A simulator stays a simulator today, since they always have commands which don't exist on the plane and use metalanguage

In the simulator a hidden mistake ...... may modify the behaviour of the simulated system (plane, inertial system, aso) without you know it, and you have a bad surprise when you do the same action on the plane, despite your aerodynamic algorithm is OK.

Finally, which was the math model ?


You seem to be saying that you believe there could have been a mistake in programming the simulator [Dozy has been commenting however on errors in the flight EFCS units]


However, I cannot relate to the simulator having "commands" which don't exist on the aeroplane. The simulators at Toulouse are linked to the "Iron Bird" which uses actual flight standard hardware (and its associated software) so the processing of pilot commands is identical on the aircraft and in the simulator. The only difference is that the simulator uses a mathematical model of the aerodynamics and processes the pilot commands in conjunction with that model to produce the aircraft motions which are fed back into the flight standard EFCS units rather than those emanating directly from aircraft response. To quote from the Airbus FAST article on the iron bird:

From the flight deck, the Iron Bird can be flown like a standard aircraft, with a computer generating the aerodynamic model and such environmental conditions as air density, air temperature, airspeed and Mach number.

Since you seem to be accepting that the likelyhood of error in the aerodynamic representation is small, the only source of difference between simulator and actual aircraft that fits your argument is, so far as I can see, the solution of the six degree of freedom equations of motion. Such an error would surely not be confined to the particular case we have been discussing, and in any case the correspondence between the actual flight records and the simulated version of the last few seconds of flight (page 13 of Annexe X of the BEA report) says that no significant error existed.
Also of course the method of solution of these equations has been been around a long time in various simulators so there is no innovation there.


Could you perhaps be a little more specific regarding the reasons why you think the simulator results to be suspect?

[CONF iture]

No. The airplane will start a phugoid motion at alphamax as shown earlier, unless the pilot relaxes the sidestick and maintains the appropriate pitch attitude.
So according to Bechet the airplane has no issue going to alpha max but then, what do you make of the Airbus statement that "the flight protection system operated perfectly and prevented the aircraft from crashing nose first" ?

Also not too sure how you get Valphamax at 113kt ... ?

[HazelNuts39]

So according to Bechet the airplane has no issue going to alpha maxSorry, I should perhaps have written "phugoid motion at approximately alphamax". The phugoid damping terms will reduce the AoA slightly below alphamax when the airplane is decelerating, and increase AoA when the airplane is accelerating, as conceptually illustrated in the chart below.

... but then, what do you make of the Airbus statement that "the flight protection system operated perfectly and prevented the aircraft from crashing nose first" ?Well, the flight protection system certainly 'prevented the aircraft from crashing nose first'. As to 'operating perfectly' the BEA report notes:
1.16.1.4.2. Réponse de l'avion à une sollicitation à la profondeur à très basse vitesse

La difficulté à reproduire une manœuvre provient du fait qu'il faut se placer dans des conditions identiques ou très voisines de lois de pilotage impliquant le respect de tous les paramètres influents (facteur de charge ou assiette, incidence, gradient de vitesse, positions de manche en profondeur) alors que ces paramètres ne sont enregistré qu'à une cadence faible sur le DFDR (un point par seconde en général) et qu'une restitution exacte nécessiterait de l'ordre de 40 points par seconde.In short, the recorded parameters are too few and too coarse to permit a reconstruction of the operation of the flight control system in a complex situation with variations of windspeed and angle of attack encountered by the airplane as it flew below treetop height in the wake of the forest.
Also not too sure how you get Valphamax at 113kt ... ? I stand corrected: Valphamax should have been the Vs1g of 110 kt.

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

[DozyWannabe]

So according to Bechet the airplane has no issue going to alpha max but then, what do you make of the Airbus statement that "the flight protection system operated perfectly and prevented the aircraft from crashing nose first" ?

In addition to HN39's remarks, I should add that "operating perfectly" in this context seems to refer to the fact that it operated as designed - and based on the analysis both of the report and the work done on this thread, that looks like a reasonably accurate statement.

What Bechet seems to have proved (and others here have explained how and why), is that the aircraft will attain Alpha Max as long as speed is sufficient, but the time taken to do so depends on the flight conditions and the mode. Specifically, the time taken to achieve it will be longer if the command (i.e. full back-stick) is given with the aircraft already in HAP mode and decelerating than it will if the aircraft is in pitch command mode when the command is given.

From a systems perspective this makes sense as, when presented with a decelerating aircraft, HAP mode has to constrain rate of movement in the pitch axis (and elsewhere) in order to fulfil the part of its design brief that demands flightpath stability and trajectory be paramount. Pitch command mode is obviously free of those constraints because airspeed deltas are immaterial if pitch (as opposed to AoA) is what's being commanded by the stick.

As to what impact the earlier increase in AoA might have made in that situation - well, we can only speculate. But my speculation based on reading of the graphs (aided immeasurably by other posters' explanations) definitely indicates that there would still have been some impact with the trees, and at that point there are just too many variables involved (particularly with regard to what part of the aircraft hit the trees, at what angle and what damage that would cause) to make even an educated guess. That said, based on the photographic evidence, I do think that the actual path of the aircraft caused the main gear and later the main spar to absorb more of the impact force from the trees, lessening the subsequent forces on the more fragile empennage and tailcone.

[CONF iture]

I stand corrected: Valphamax should have been the Vs1g of 110 kt.
But again, why do you still persist equalling Valphamax and stalling speed ... ?
And if you do think Valphamax is Vs1g at 110 then what is Vstall ?

True that all these speeds, all of them, including Vls Valphaprot, should have been published in the report for the weight config altitude at the time ... Where are they ?

For the graph, things don't add up.
How do they or you get identical speed traces from so different attitudes ?
An obvious penalty on the speed there must be by pulling the nose up ... but also a benefit to the altitude ... Where are the ?

[HazelNuts39]

But again, why do you still persist equalling Valphamax and stalling speed ... ?
And if you do think Valphamax is Vs1g at 110 then what is Vstall ?This has been discussed extensively earlier in the thread. The Special Conditions for certification of the A320 (published by the FAA and linked earlier on this thread) define Vs1g as Valphamax. The certification requirements consider the airplane stalled when the longitudinal control is held on the aft stop during 2 seconds and there is no further increase of angle of attack. Vs1g is published in the AFM and the FCOM. There is no requirement to determine Vstall, assuming that you mean the speed corresponding to the maximum lift coefficient calculated at 1g. 'Vstall' is not published anywhere, AFAIK.

True that all these speeds, all of them, including Vls Valphaprot, should have been published in the report for the weight config altitude at the time ... Where are they ?All these speeds are irrelevant to the accident, and I can't see any need for the accident report to publish them. The report publishes alphaprot, alphafloor and alphamax, which are relevant.

For the graph, things don't add up.
How do they or you get identical speed traces from so different attitudes ?
An obvious penalty on the speed there must be by pulling the nose up ... but also a benefit to the altitude ... Where are the ? IAs and pitch attitude have been read the graphical presentation of Bechet's simulator exercise. AoA has been determined as the difference between pitch attitude and flight path angle. The vertical speed can be determined from the trace of radio altitude, and FPA is determined from VS and TAS. If there is anything that doesn't add up, please be more specific.

[BARKINGMAD]

This accident was 26 years ago, yet reams of fascinating info regarding the secrets of the 'bus "logic" continue to fill these pages.

And all this in addition to the acres of apparently "new" knowledge following the report on AF447.

I admit I'm an ex-Boeing driver, but the whole process of revelation and presumably education of 'Bus drivers following a major accident, gives me no confidence as l board my next Airbus flight as SLF.

If the beast really is that complicated, and so much info remains in the filing cabinet at Toulouse, then surely those who are NOT 'Bus enthusiasts are entitled to ask is this the best way to go in aircraft design and operator instruction?

787 design team please note?!?! :ugh:

[HazelNuts39]

For an aircraft without a cockpit AOA indication I'm not sure I agree.If I understood Confiture correctly, he was criticising the report, not the lack of cockpit AoA indication. Considering that the cockpit display includes Valphaprot and Valphamax, which speed would you like to add?

[DozyWannabe]

This accident was 26 years ago, yet reams of fascinating info regarding the secrets of the 'bus "logic" continue to fill these pages.

It's not really that complicated to be honest. Ultimately we're talking about differences in mode that didn't really have a great deal of effect in the grand scheme of things.

I think one thing that is coming out of the discussions above all else is that the only guaranteed way that accident could have been avoided was to not point an aircraft full of pax at a forest and chop back the power in the first place! That's an airmanship issue, not a technical one.

[BARKINGMAD]

Dozy, "It's not really that complicated, to be honest."

Nearly 800 postings on the latest Habsheim thread and almost 1,000 on the last AF447 thread surely scores higher than any Boeing, excepting of course the mystery of MH370?

Admitted it's not an exhaustive analysis of the tech aspects of either breed, but maybe there's something in it?

It would be interesting to know from 'bus line dogs how much more they have learned about their 'frames if they've followed the discussions in these fora.

Yes, l learned things about the 73NG which otherwise would have remained hidden after reading reports various, but doubt that the volume of previously unknowns gets anywhere close to the Airbus genre.

Tin hat is on...........

[DozyWannabe]

Nearly 800 postings on the latest Habsheim thread and almost 1,000 on the last AF447 thread surely scores higher than any Boeing, excepting of course the mystery of MH370?

Actually, I think you'll find a lot of both those threads were invariably the same bunch of people trying to insinuate nefariousness on the part of Airbus, and useful idiots like myself trying to rebut them. I'd say of those threads, about 20% of them were actually worthwhile info - and that's a generous estimate!

In fact, Airbus's original EFCS technology as a whole was somewhat less complex than the T7 - the force-feedback logic being almost as complex again.

The issue with Airbus discussions on here is that there are definitely a core of pilots - usually, though not always, from France and allied with SNPL - that insist Asseline was wronged by a French government cover-up, and no matter what the actual discussion is about, some of them will try to turn the conversation back to that. I'm hoping this thread will answer any remaining issues and end the ridiculous excuses in future...

[EDIT : Put it this way - the level of software implementation we're talking about here would be roughly the equivalent of knowing about the tensile properties of metal cables and hydraulic flow rates on conventionally controlled airliners of yesteryear - which pilots didn't really need to understand in order to fly the aircraft!]

[Owain Glyndwr]

@ OK465

The simulations appear to be well conducted and reasonably high fidelity with respect to that specific aircraft and incident....but as previously noted, the plots not so much. In addition to the pitch attitude inaccuracies, I particularly like the Pg 13 IAS plot that is moved upward halfway thru the simulation and connected with a vertical dashed line.

I think there's possibly a little more pride taken in these type of presentations nowadays.
I take your point, but I do wonder if we aren't being a little harsh when we judge a 1988 presentation by the standards of reproduction equipment available today.

The four "simulator" charts bear all the hallmarks of having been produced on an analogue pen recorder - the sort where paper is drawn past a line of pens which move only transversely across the paper. To analyse the data subsequently one had to annotate and add scales by hand so these are inevitably "untidy" compared to a printed version.

To add to the misery the gridlines on the plotter paper were, IIRC, printed in a delicate shade of pink, which was great if you were reading directly off the plotter paper but which all but disappeared when passed through the sort of copying machine then available.

Both these "faults" are present in the published charts, but they could have been then state of the art :8

About 10 more seconds of the sim plot on Pg 13 might have been interesting and actually I don't see where it would have cost anything to continue it to purported alphamax and present it. The sim was already set up and rolling.I agree it would have been interesting, but it would have been open to the accusation that the extra data was speculative. As it stands the plot stops when the DFDR records stop, so is appropriate for a formal accident report.

I would guess that the extension you advocate was looked at - in fact the BEA report (p.15) talks about "other studies", but these were treated as background material.

If one is prepared to speculate a little it is possible to get some idea of what might have happened - check your PMs.

[DozyWannabe]

@ OK465
I take your point, but I do wonder if we aren't being a little harsh when we judge a 1988 presentation by the standards of reproduction equipment available today.
...
Both these "faults" are present in the published charts, but they could have been then state of the art :8

Quite. I've been saying this for a while, but it's easy to take for granted the relative simplicity in transferring this kind of data and rendering it in different ways today compared to the hassle it was even 20 years ago. For example, in 1990 (when this final report was published) the current spreadsheets could not handle the amount of data that was dumped from the DFDR - and there was no way to even get that data into that format directly other than manual transcription - the risk of miskeys would have been too great.

Even if it were possible, the current version of Windows was 3.0, and the current version of Word was 1.0 (for Windows). In June 1990, these would have been effectively brand new products, and while it was technically possible to insert Excel data into WFW 1.0, Excel could not generate charts - that didn't really come into its own until about 1993-4.

Obviously the realisation that these tools could be used in this way did come, and modern reports use that method routinely these days. However, this was a result of a near-revolution in desktop computing power throughout the 1990s, and simply wasn't available for the publication of this report. As BARKINGMAD says, we're talking about an accident that happened almost 26 years ago, and a final report that is almost 24 years old!

[gums]

@ Barking

It is interesting that we are still here talking about the FCS implementation and such after such a long time.

The point is that many heavy pilots have never flown their planes to within a hair's breadth of the programmed limits.

The accident was caused by a low power setting and lack of practice and plain poor judgement ( demonstrating the jet at its max AoA with pax on board at a ridiculous altitude). Sheesh.

I go with Doze and Okie for the most part. And I think Okie flew the same jet I did in his previous life, which was full FBW and very clear limits defined as to the aerodynamics.

The mentality that the cosmic flight control system will "protect" you is dangerous. We don't all have to be super engineers or test pilots, but we do have to understand the "limits" and then all the reversion modes of both the FCS and the autothrottle ( Asiana).

So I feel that good training in the real jet as well as the sim could help here. I know that $$$ count, but seems to me that a few hours and maneuvers in the real jet would pay off big time.

AF447 PROVED that you could stall the jet if you climbed at such an angle and ran outta speed before the magic FCS could help. The plane was still recoverable, so it was not truly in a "deep stall", it was "deeply stalled".

That's all I gotta say here from the peanut gallery.

[DozyWannabe]

AF447 PROVED that you could stall the jet if you climbed at such an angle and ran outta speed before the magic FCS could help.

To be fair, that particular scenario (i.e. hard protections are void outside of Normal Law) was explicitly highlighted in the manuals from the beginning. Even the most strident Airbus evangelist wouldn't have claimed the protections to be a universal remedy - though the press may have muddied the waters there. The company received a tragic object lesson in that when one of their chief test pilots was killed during a training/demonstration exercise in an A330. From that point onwards, they tended to be even more circumspect.

I think the reason this particular accident still causes discussion and debate today hinges - at least partially - on the fact that the report was only ever published in French (which was standard practice when no international body was involved), and most of what the Anglophone world knows about it was filtered through the press.

Asseline's argument was that the aircraft did not respond to his full back-stick command. The BEA research indicates that it did respond, but due to the late application of thrust and even later application of the back-stick command, the rate of response was initially slower than it might have been. This was not a routine operation - far from it - and if it had been, then maybe the details which this thread has uncovered would have been more widely known. As it was, the investigation concluded (rightly so, in my opinion) that the systemic lack of oversight was the primary factor in the accident, with the somewhat poor airmanship during the conduct of the flight also contributing. A radical overhaul of the practices regarding commercial aircraft performing demonstrations at airshows was thus sufficient to prevent a recurrence.

[EDIT : I must say that while I'm appreciative of the namecheck, IMO the dynamite work on this thread has come from Owain Glyndwyr, HazelNuts39 and Chris Scott as well as OK465! :ok:]

[vilas]

gums
447 and Habsheim are two different things. Protection was never an issue in AF447 as the aircraft was in alternate law and you could always stall. It was lack of procedural knowledge on part of pilots was the cause. In normal law you have the protection as was the case in Habsheim but here the issue that was being raised was did the protection cause the accident. Both side have gone considerable distance with interesting inputs although only agreeing to disagree.

[gums]

@ vilas

I don't disagree with you about AF447. My concern is that it appears some 'bus drivers seem to feel that they can't stall the jet, and then the lack of certain "protections" in the various reversion modes comes into play when things go south.

That is why I suggested better training both in the sim and in the real airplane. I know involves lottsa $$$, but sheesh.

In the early days of my experience as an IP in a full FBW jet, we first let the student get used to the side stick, and then we would go to the limits. We did not have a simulator for 3 years after the jet became operational! And you could not demo the gee limiter in a stupid sim.

Habsheim was a great example of poor planning, poor preparation, and poor judgement. Sorry to come down hard on a fellow pilot, but that's my feeling. Even our demo hops for the crowds allowed for some leeway, and the maneuvers were practiced over and over. A degree or two of AoA that the FCS allowed at max command was never a consideration.

Back to my peanut gallery......

[DozyWannabe]

... but here the issue that was being raised was did the protection cause the accident.

I think it's fair to state that the protections didn't "cause the accident" - as there were massive "holes in the cheese" present before the aircraft ever left the ground. Ultimately, I think even the sceptics have to admit that the airline should never have allowed the flight to go ahead without proper review, plus the airmanship and decision-making after getting the airfield visual were questionable.

The question is not about whether the protections "caused the accident" as much as it is whether the slower initial response due to HAP mode made the contact with the trees more substantial than it might have been. At this point I think agreeing to disagree is the best we can manage, because as I said before, there are simply too many variables involved to make a definitive educated guess.

@gums - If there are FBW Airbus pilots who believe they can't stall one under any circumstances (and to be honest I'm sceptical of that), then they clearly haven't read the manuals and training materials properly and require being pulled off the line for immediate remedial training!

I know there's a school of thought that has the AF447 PF pulling up because he was expecting the protections to keep the aircraft in check, but there's no clear evidence of that. The fact is that there have been studies performed into startle response, which found that severe cases of startle will cause a pilot to instinctively pull up in (IIRC) 80% of cases regardless of whether the aircraft has AoA protection or not.

[vilas]

DOZY
I am in agreement with you and I also do not believe there pilots out there who do not know that Airbus can be stalled in alternate law. Pilots are getting complacent on automation and loosing their basic scan. Far too many accidents happen because of not monitoring speed on approach. Take SFO for instance no pilot is going to keep quiet when he sees the speed is 15/20 KTS below Vapp. They simply are not looking at the speed because most of the time automation looks after it. AF447 pilot applied memory items of after take off situation otherwise there is no requirement of TOGA power. Unreliable airspeed is only practiced during type rating and never in yearly or six monthly checks.

[Clandestino]

Tin hat is on...........This thread does not offer anything useful apart from n-th refutation of "Airbus is evil" utterances. These anonymous claims of A brand corruption are based on notions about aerodynamics, thermodynamics and kinematics that are so implausible that not even mixing them liberally with theories of messieurs Einstein, Bohr or Schrodinger can make them look more realistic than average Klee's painting. Sir, if you think there is something of even a bit substantial in them, then your headgear is seriously overbuilt. Material is fine but thickness could be safely reduced down to mere foil.

AF447 pilot applied memory items of after take off situationNo. It says obtain and maintain 15 degrees pitch. It doesn't say "pull mindlessly, change your mind and reduce pitch somewhat then pull mindlessly again." There was no trace of seeking for specific pitch in AF447 case but was a lot of pulling-up-no-matter-what. Just as in Pinnacle (to a point). Or West Caribbean. Or Pulkovo. Or Colgan.

[IcePack]

Barkingmad yep being ex Boeing myself now Airbus for quite a while. I was surprised after AF447 to find out the 330 stall characteristics as all the stalls done in the sim were conventional (buffet then pitch down) no one mentioned it could "deep stall" the bus does require continuous study. They are fascinating however.

[CONF iture]

Considering that the cockpit display includes Valphaprot and Valphamax, which speed would you like to add?
The cockpit displays only include what is believed to be Valphaprot and Valphamax according to the FAC ... but such characteristic speeds have theoretical values, and knowing that Asseline was playing in that area, it should have been the most natural thing for the BEA to communicate those values in their report.

This has been discussed extensively earlier in the thread.
Extensively but erroneously - If Vs1g was Valphamax Airbus would not have called Vs1g "stalling speed".

If there is anything that doesn't add up, please be more specific.
I cannot be more specific than that :
How do they or you get identical speed traces for Bechet and Asseline as they adopt so different attitudes ?

To analyse the data subsequently one had to annotate and add scales by hand so these are inevitably "untidy" compared to a printed version.
Sorry but there is ample way to do it professionally ... or you can always choose to do it unprofessionally.

To add to the misery the gridlines on the plotter paper were, IIRC, printed in a delicate shade of pink, which was great if you were reading directly off the plotter paper but which all but disappeared when passed through the sort of copying machine then available.
Tell me ... is it that same sort of copying machine that swallowed Annexe VII ?

[HazelNuts39]

How do they or you get identical speed traces for Bechet and Asseline as they adopt so different attitudes ?Firstly, speed and attitude are independent variables. You can have any speed at any attitude.

Secondly, one of many explanations is that Asseline flew into a forest and Bechet did not. Asseline's IAS would have been higher that Bechet's if he had not lost 5 kt of headwind in the 5 seconds before he hit the trees:

http://i.imgur.com/JeHgmNn.jpg?1

[HazelNuts39]

If Vs1g was Valphamax Airbus would not have called Vs1g "stalling speed".Compared to the certification requirement, that is a lame argument. Vs1g is the official definition of "stalling speed" for this airplane, and it is obtained with the sidestick on the aft stop at the corresponding AoA. How would you define Valphamax?

Furthermore, in Bechet's simulator test, at about 6.8 seconds after moving the thrust levers forward, the AoA is 17.5 degrees and the airspeed is 116.5 kIAS. According to the FCOM, Vs1g is 109.5 kt at a weight of 59,000 kg, so 116.5 kt is 1.064 times Vs1g. The loadfactor at an AoA is proportional to airspeed-squared, and should be 1.064*1.064 = 1.13. That value is a perfect match with the loadfactor shown in the graph below, that is derived from the altitude trace (or the radius of the flight path) of the simulated flight.

In other words, Bechet's simulation confirms that Vs1g corresponds to alpha-max of 17.5 degrees at 1g.

http://i.imgur.com/JiAfjEg.jpg?1

[DozyWannabe]

Sorry but there is ample way to do it professionally ... or you can always choose to do it unprofessionally.

Given that we've established that the tools to generate and annotate the material digitally were not readily available in 1990, how would you propose they do it differently?

Tell me ... is it that same sort of copying machine that swallowed Annexe VII ?

Annexe VII is there. It was either mis-labelled by the clerk who compiled the paper copy, or the sheet inserted by the clerk who did the original compilation made a mistake in describing it. What the document scanning hopper *has* done is get the occasional pages scanned in the wrong orientation, but they do all appear to be present.

The way to check this would be to go and have a look at the original paper copy in the Republic archives, but I wouldn't know how to go about doing that (and as a foreign citizen may not be able to access it anyway).

[Agnostique75]

Dear Dozy & al.

The Republic's archives will come to you !
The reports published by the BEA on their website merely serve an informative purpose. The "genuine" reports are those published in the paper version of the french "Journal Officiel", a publication that regroups all official french communications, such as newly promulgated laws, minor and major administrative changes or reports of importance.

The "Journal Officiel"'s publication relating to Habsheim is available here:
Journal Officiel 24 Avril 1990 (http://www.bea.aero/docspa/1988/f-kc880626/pdf/f-kc880626.pdf)

As anyone can see, annex VI devoted to the CVR transcription is there in its entirety, starting page 29 of the report. A technical error has placed the pages 27 & 28 after page 29 instead of before. But the CVR transcript continues on page 30 and following.

I hope that this puts to bed the now mythical "dissapearance of annex VI" and that everyone realises that the inversion (not the omission) of two pages in a document cannot constitute the grounds for accusations of "tampering".

[DozyWannabe]

@Agnostique75:

That's kind of you to provide that link, but that's the same one we've been using since the start of the thread.

CONF iture is referring to a different Annexe - number 7 (VII), which is listed on p.23 of the PDF as "Corrélation DFDR-CVR", but appears (on p.36 of the PDF) to actually be a different portion of the DFDR trace.

[Agnostique75]

Oops ! I shall copy 50 times "Fully engage brain before writing" :\

[HazelNuts39]

The cockpit displays only include what is believed to be Valphaprot and Valphamax according to the FAC ... but such characteristic speeds have theoretical values, and knowing that Asseline was playing in that area, it should have been the most natural thing for the BEA to communicate those values in their report.It seems reasonable to me that the BEA saw no need to communicate them because neither pilot made any reference to those speeds, not in the briefing nor in the execution of the demonstration. That in itself may be considered a a major flaw in their preparation of the flight. What if they had arrived at Valphamax, the throttles still at idle, the sidestick on the aft stop, at a height of 30 ft?

In the energy plot shown in post #772 (http://www.pprune.org/tech-log/528034-habsheim-39.html#post8422768) it can be seen that Bechet lost 89 ft of total energy after he started to move the thrust levers until 5 seconds later the engines had spooled up sufficiently and the total energy started to increase. Bechet could absorb most of those 89 ft out of his kinetic energy, but if the speed drops below Valphamax it is not possible to arrest an increasing rate of descent.

[737Jock]

What are you guys exactly trying to determine? Apart from reenacting the event...;)

Simply what happens when you pull the stick fully aft and keep it there?

Could it be that airbus decided to write that valpha-max may be reached by pulling full aft sidestick, because of the habsheim accident?
To me the sidestick input certainly does not look like he wanted to reach valpha max throughout. According to the figure in page 7 he only reached max aft side stick in the last few seconds.
With loadfactors changing, engines spooling up, wind changing... the flight control computers might simply not have had enough time to reach valpha max (before crashing).

Therefore some lawyer decided to write may be reached.

[DozyWannabe]

With loadfactors changing, engines spooling up, wind changing... the flight control computers might simply not have had enough time to reach valpha max (before crashing).

Valphamax is a minimum airspeed requirement, and the aircraft never dipped below it prior to impact according to HN39's analysis.

Therefore some lawyer decided to write may be reached.

Lawyers don't write manuals.

I love how there's always this assumption of skullduggery in the case of this event, when the general drift of this thread indicates that there probably wasn't any.

For the record, going back to my post #26 - "may be reached" comes from the FCTM for the A330, not the A320. The A320 doc is worded thus:

If the PF then pulls the sidestick full aft, a maximum AOA (approximately corresponding to CL Max) is commanded.

The wording there suggests that it is commanded, but nothing at all about whether (or how quickly) it will be achieved.

I think you are right that the important factor was time, but it had more to do with the belated realisation of the danger they were in (as a result of an approach which was in itself belatedly improvised and, for want of a better word, botched) and the late application of TOGA thrust than it did any issue with the computers.

[737Jock]

Valphamax is a minimum airspeed requirement, and the aircraft never dipped below it prior to impact according to HN39's analysis.

Yes that is what I said, never had time to reach Valphamax, as in decelerating towards Valphamax with stick pulled fully aft.
The maximum aoa was never reached, but the sidestick was only fully aft for about 2 seconds.

During those 2 seconds a lot happened and the FCS might not have had enough time to actually provide the commanded maximum aoa and associated valphamax. Certainly considering, thrust spooling up, loadfactor changes and wind change.
I would imagine valphamax being reached more easily in circumstances that are more "stable".


Manufacturers certainly are concerned by litigation regarding their manuals. The only way to determine would be to find an old FCOM/FCTM. But since we don't have that we will never know.

Anyway im not even saying, nor did I imply that the system has a fault that needed to be clarified, it might just be a rewording to emphasize its not a guarentee that valphamax will be reached.
But I am sure that it is commanded. Success depends on many factors, some internal and many external.

I'm sure those pilots just pulled the stick as they saw the forrest come closer. All the detailed info is nice, but those sidestick inputs do not suggest they wanted to fly at max aoa, evident from not having sidestick full aft. Just somewhere close to it. They had no idea what their exact speed, aoa or vs was.

[DozyWannabe]

I would imagine valphamax being reached more easily in circumstances that are more "stable".

But the aircraft was flying *faster* than Valphamax throughout - the EFCS didn't have to "reach" anything, and there was no impediment to the aircraft reaching Alpha Max other than time.

What seems to have made the response slower than it might have been was the significant deceleration with the stick half-back and thrust still at idle - then staying half-back until a few seconds after TOGA was commanded, because in that scenario HAP mode restricts pitch rate change to maintain stability and trajectory.

The test flight being discussed by HN39 (as part of the original investigation) involves a slightly different scenario where the stick was moved full-aft simultaneously with TOGA being applied, thus the aircraft was in pitch command mode, which allowed pitch (and AoA) to increase more rapidly - initially. However what effect this might have had - if any - regarding impact with the trees can only be a matter of speculation, as the initial faster pitch change is arrested until the thrust starts bringing the airspeed back up again.

[737Jock]

But the aircraft was flying *faster* than Valphamax throughout - the EFCS didn't have to "reach" anything, and there was no impediment to the aircraft reaching Alpha Max other than time.

You seem to try very hard not to understand me. That is what I said!
They never flew at Valphamax, they never commanded Valphamax until they were about to kiss the trees, evidenced by the lack of full backstick until the last 2 seconds before crash.

What seems to have made the response slower than it might have been was the significant deceleration with the stick half-back and thrust still at idle - then staying half-back until a few seconds after TOGA was commanded, because in that scenario HAP mode restricts pitch rate change to maintain stability and trajectory.

I think this is really far fetched and cannot be reliably be concluded, certainly not from the habsheim plots. And to draw this conclusion from the bechet plots is highly questionable.
They only applied a full aft input on the sidestick in the last 2 seconds. Just in those 2 seconds, loadfactors, engine thrust and wind were changing rapidly. This would lead me to simply think the flight control computers did not have enough time.

If you want to reach Valphamax, the simple matter of fact is that you have to decelerate significantly. If you do this with idle thrust and then smack on toga thrust, the change of force on the airframe will be much more significant then if you had for example 40% N1 on. Lets not forget the pitch-up effect from underslung engines that needs to be compensated for, which happened to really kick in when the sidestick reached full aft position (habsheim).
Combine that with a constantly changing altitude, and you see significant thrust changes and loadfactors.

In more stable conditions (bechet) the FCS will have less of a problem reaching Valphamax (on applying full backstick) as the required output is not constantly changing. P.is he clearly had the benefit of time.

I dont think it has anything to do with some sort of sluggishness of the flightcontrols that only happens after a prolonged time in HAP, it is just the system managing the changing forces as best as it can. Although its a computer it is still a reactive system.
A human certainly could not fly at Valphamax under those circumstances with any accuracy.

[DozyWannabe]

Why would you want to "reach" Valphamax? The intent was to perform a high pitch flypast at relatively low speed, not take it to the absolute limit as far as I was aware.

[737Jock]

Is that even a serious question? Why do you think he pulled full aft stick in the last seconds?

Maybe he realised he ****** up his original plan and needed max performance to escape from terrain contact?
What would you do in an airbus if you are about to hit the ground involuntarily?

Maybe you have a read through the QRH and see what they want you to do in case of imminent terrain contact.

I haven't met someone who tries so hard to misunderstand another person.

[HazelNuts39]

Synopsis: Résumé de l'accident :

Dans le cadre d'une manifestation aérienne, l'avion effectue un passage au-dessus de la piste 34 R à une hauteur voisine de 30 pieds, moteurs réduits, avec une incidence croissante jusqu'au maximum possible compte tenu du taux de décélération de l'avion.

Annexe VI:
12h30'20'' - CDB: (...) on fait un passage à cent pieds, train sorti et là, tu me laisses faire. Je t'amène en alpha max, je débraye l'alpha floor et à ce moment là, si je te dis que c'est dur, tu m'aides et tu tiens les gaz à vario zéro. (...)

Short summary of the captains briefing of the copilot: I'll take her to alphamax and then you control thrust to maintain zero vertical speed ...

[CONF iture]

Interesting stuff watching you playing with numbers and graphs ... now how do you justify Bechet, according to your graph (http://www.pprune.org/8433802-post801.html), gains 2.5 deg of alpha in 2 sec, reaches 1.1g but still manages to lose altitude ... ?
Load factor increase should reveal a change of path, from level flight to climb ... where is that altitude gain ?

In other words, which data are erroneous and/or 'adjusted' ?

Yours
Bechet
Habsheim
All of them

[HazelNuts39]

In other words, which data are erroneous and/or 'adjusted' ?

5. None of them

But you are constantly changing the subject. The issue was Valphamax, where you disagreed with me, and you have not answered my question: How would you define Valphamax?

P.S.

RE:: "Load factor increase should reveal a change of path, from level flight to climb ... where is that altitude gain ?"

The story begins with a descending path. At t=2.5 seconds the descending path has changed to level flight, then begins to climb. At t=4.75 seconds the altitude has increased 5 ft and is again equal to that at t=0. Between t=0 and t=4.75 the vertical speed changes from approximately -2.5 ft/s to +4 ft/s, i.e. a change of 6.5 ft/s in 4.75 seconds is 1.37 ft/s/s. Divide that by the acceleration of gravity (32.17 ft/s/s), add 1 and you get an average loadfactor of 1.043 in that period.

However, allowance must be made for the resolution of the graph in the BEA report. The whole graph is 1550 x 965 pixels. The scale of the radio altitude trace is about 1 foot per pixel, and the pen trace is about 3 pixels wide.

[Owain Glyndwr]

@HN39

I must say I admire your patience and tolerance - and I wholly agree with your analysis!

[IcePack]

Love all this pulling the stick back etc. on an AB the side stick commands G. So if you hold say 1/2 side stick back you command say 1 3/4 g. The flight controls will then move to give you that G up to their max deflection if required. So permanent back stick will get you to Alpha Max. The only way to stop the continued demand for G is to centre the stick. In theory the aircraft then holds the pitch you were at then. In practice it usually "nods" down AA degree or so.
So if he was holding the stick aft of ctre he would be pitching up until alpha max.
(note lateral stick is a roll rate demand)
The above is a simplified description I know. :ugh:

[DozyWannabe]

Love all this pulling the stick back etc. on an AB the side stick commands G.

99.9(rec)% of the time in practice, yes. In pitch command mode it commands pitch angle directly, and in HAP mode it commands AoA.

As far as the human pilot is concerned, in almost every scenario one can think of the distinction is so transparent as to be immaterial - i.e. at its simplest, the aircraft will go where you point it, and the tech will do its best to keep the shiny side up. The only reason the modes are being scrutinised so closely in this case is because questions have been asked as to why the aircraft behaved as it did at a level deeper than the original report was required to go.

Certainly as far as I can tell with the benefit of extra analysis from those who are experienced in the aero end of things, the EFCS was complying with the control demands to the best of its ability, but with the aircraft in such a low-energy state, neither technology nor manual handling finesse would have been sufficient to defy the laws of physics.

[BARKINGMAD]

I say again, " 'bus linedogs", how much more are you learning about your vunderplane from these pages than what you've managed to extract from the official OM/FCOMs?

Somewhere in the murky depths of my memory I recall the great surprise in the 'bus world, following the VA A340 tailscrape accident at Gatwick, that the 'frame would behave differently above 50' radio height than below it.

If memory serves me right, that quirk was unknown to the early 'bus drivers until after that accident, but I wait to be corrected?

[CONF iture]

The scale of the radio altitude trace is about 1 foot per pixel, and the pen trace is about 3 pixels wide.
Never mind, you still make miracles from such a botched graph when you read tenths of second or half of a foot ...

The story begins with a descending path.
Not too good for a simulated flight that was supposed to simulate Habsheim ...
Is it new to the BEA as they did not mention such discrepancy ... ?
1.16.1.4.1.
Dans le deuxième cas, où le pilote du simulateur était le président de la commission d'enquête, le recoupement de l'évolution de la vitesse en fonction de temps est également excellent, l'altitude du vol simulé étant toutefois toujours très légèrement supérieure à celle du vol réel (+ 8 à 10 pieds).
Never mind the graph shows exactly the opposite, the altitude for the simulated flight being très légèrement inférieure à celle du vol réel (- 8 à 10 pieds).
It must be the same clerk (http://www.pprune.org/8434297-post802.html) that messed up again ...

At t=2.5 seconds the descending path has changed to level flight, then begins to climb. At t=4.75 seconds the altitude has increased 5 ft and is again equal to that at t=0.
I won't argue with or confirm the data you're ready to see ... but you're telling me that Bechet would have gained 10 ft by commanding PULL UP TOGA from level flight.

But you are constantly changing the subject. The issue was Valphamax, where you disagreed with me, and you have not answered my question: How would you define Valphamax?
Not differently that the FCOM :
"It represents the speed corresponding to the maximum angle of attack that the aircraft can attain in pitch normal law."

[HazelNuts39]

Not differently that the FCOM :
"It represents the speed corresponding to the maximum angle of attack that the aircraft can attain in pitch normal law."How does that differ from the definition of Vs1g?

P.S.

The special conditions for certification of the A320 (and associated guidance material) define Vs1g as the minimum speed (corrected to 1g and zero thrust) obtained in the following maneuver:

- forward center of gravity
- idle thrust
- normal law except deactivated alpha-floor
- decelerate at 1 kt/sec until sidestick reaches aft stop
- maintain sidestick on aft stop for 2 seconds or until pitch attitude does not increase further, whichever occurs later
- recover

[CONF iture]

How does that differ from the definition of Vs1g?
Quite different as Vs1g is the stall speed at 1g.
If Airbus wanted no safety margin they would have set alpha max to alpha stall at 1g and modified their graph accordingly.

http://i45.servimg.com/u/f45/11/75/17/84/hud_0210.png (http://www.servimg.com/image_preview.php?i=115&u=11751784)

[HazelNuts39]

Quite different as Vs1g is the stall speed at 1g.So how would you demonstrate it in normal law in a certification flight test?

P.S.

The diagram you posted is a schematic illustration that alpha-max is just shy of alpha-CLmax. Alpha-CLmax would define Vs1g for a conventional airplane, but not for a FBW airplane with a flight control system that is designed to prevent achieving and exceeding alpha-CLmax. The difference between alphamax and alpha-CLmax (the safety margin) is the performance penalty that must be paid for having a 'hard' stall protection, and Airbus has never made a secret of that fact.

Conventional aircraft having a stickpusher pay a similar price in performance if the pusher is set to fire before alpha-CLmax.

[CONF iture]

The diagram you posted is a schematic illustration that alpha-max is just shy of alpha-CLmax.
Therefore Valphamax is not Vs1g.

Alpha-CLmax would define Vs1g for a conventional airplane, but not for a FBW airplane with a flight control system that is designed to prevent achieving and exceeding alpha-CLmax.
Actually the FCS is designed to achieve alpha max without exceeding it.
Nevertheless temporary overshoot could happen due to turbulence but without significant effect.
Also Gordon Corps demonstrated how temporary overshoots seem to actually take place and so without negative effect.

The diagram I posted is from the Airbus documentation and is applicable to their FBW airplanes.

So how would you demonstrate it in normal law in a certification flight test?
This is a question Airbus and/or the airworthiness authorities could answer.

[roulishollandais]

a 'hard' stall protection...like AF447 ?
Didn't we agree we must no more say the mantra "Airbus cannot stall" ?

[HazelNuts39]

This is a question Airbus and/or the airworthiness authorities could answer.Indeed ...

[DozyWannabe]

Also Gordon Corps demonstrated how temporary overshoots seem to actually take place and so without negative effect.

That's based on your assumption that he was in CONF FULL, which is not explicitly confirmed in the video or elsewhere.

Actually the FCS is designed to achieve alpha max without exceeding it.

But it makes no promises about the rate at which it is achieved.

@roulis : That's not what's being said - the aircraft is protected from stall provided that the required features are operational. Without that, it definitely can stall - no-one on this thread has argued otherwise.

[gums]

@ Doze

@roulis : That's not what's being said - the aircraft is protected from stall provided that the required features are operational. Without that, it definitely can stall - no-one on this thread has argued otherwise.

The AF447 was not in the "primary" control laws. And seems that the crew at Habsheim did something to avoid the "primary" laws for their slow, high AoA pass.

It appears that the Habsheim problem was not a flight control computer problem, and the jet did everything it was supposed to do. The AF447 accident showed that the jet can get into a stall if you "do it right". And we learned that in the Viper, after being assured you could not stall the jet. NOT! With a high pitch attitude you could run outta smash and overshoot the progrmmed "protections". Unlike the 'bus, we actually got into a "deep stall".

My feeling is we should let this thread go. It seems obvious that the crew screwed up and crashed a perfectly good jet into the trees.

[CONF iture]

That's based on your assumption that he was in CONF FULL, which is not explicitly confirmed in the video or elsewhere.
Has been already addressed here (http://www.pprune.org/8382254-post663.html).
You have been unable to counter my argumentation.

But it makes no promises about the rate at which it is achieved.
Actually it is fast enough that the FTCM states :
"This immediately provides maximum lift"

[DozyWannabe]

Has been already addressed here (http://www.pprune.org/8382254-post663.html).
You have been unable to counter my argumentation.

Yes - your inference and assumption that because he specifies 15 degrees, therefore it must be CONF FULL. What I said was that the actual config is not explicitly confirmed in the video or elsewhere - you may be right, but there's no definitive way to tell.

Actually it is fast enough that the FTCM states :
"This immediately provides maximum lift"

Which FCTM, which page? Can you provide more context? HAP mode is described in the FCTM I posted at the beginning of the thread as providing maximum aerodynamic lift, but the word "immediately" is not used.

[CONF iture]

Yes - your inference and assumption that because he specifies 15 degrees, therefore it must be CONF FULL. What I said was that the actual config is not explicitly confirmed in the video or elsewhere - you may be right, but there's no definitive way to tell.
Your lack of argumentation proves my point.
Thank you

Which FCTM, which page? Can you provide more context? HAP mode is described in the FCTM I posted at the beginning of the thread as providing maximum aerodynamic lift, but the word "immediately" is not used.
FCTM A320 OP-020. P 12/16
In case of GPWS/SHEAR:
• Set the thrust levers to TOGA
• Pull the sidestick to full aft (For shear, fly the SRS, until full aft sidestick).
• Initially maintain the wings level
This immediately provides maximum lift/maximum thrust/minimum drag. Therefore, CFIT escape maneuvers will be much more efficient.

[DozyWannabe]

Your lack of argumentation proves my point.
Thank you

Er, no it doesn't. It just means that I don't have any way to confirm whether your supposition is in fact correct, and frankly, neither do you.

Given that this thread started largely as a result of your requests, I have to say that regardless of what you think of me or my input, there are a significant number of qualified and knowledgeable people who have taken the time to sift through the data and attempt to provide answers to your technical questions - and I'm frankly staggered at your dismissive attitude towards them if the results don't fit your preconceived notions of what happened.

FCTM A320 OP-020. P 12/16

Got it - and you're playing fast-and-loose with context again.

You're quoting from the "Operational Recommendations" section, which includes the warning:

The PF must not deliberately fly the aircraft in alpha protection, except for brief periods, when maximum maneuvering speed is required.

Not only does the nature of the Habsheim flight fall outside the parameters of normal ops, thus rendering this particular section (which goes on to assume an airspeed of Vapp) somewhat irrelevant - but Asseline's handling of the aircraft after crossing the threshold completely contravenes that warning.

As HN39 has pointed out, in such circumstances "maximum lift" may not initially be a great deal.

[CONF iture]

If CONF 3 was the setting for the video demo, why alpha max was at 15 when it was at 17.5 for Habsheim ... ?
What about simply answering the question Dozy ...

[DozyWannabe]

Hi CONF,

Look - all I am saying is that in the video, the configuration is not explicitly specified. Nothing more, nothing less.

[steamchicken]

12h30'20'' - CDB: (...) on fait un passage à cent pieds, train sorti et là, tu me laisses faire. Je t'amène en alpha max, je débraye l'alpha floor et à ce moment là, si je te dis que c'est dur, tu m'aides et tu tiens les gaz à vario zéro. (...)

"plus kéké que moi, tu meurs. autant, c'est plutot les passagers"