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Habsheim

Old 14th Apr 2014, 20:59
  #781 (permalink)  
 
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Habsheim Report / French Official Journal

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

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".
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Old 14th Apr 2014, 21:15
  #782 (permalink)  
 
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@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.
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Old 14th Apr 2014, 21:19
  #783 (permalink)  
 
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Oops ! I shall copy 50 times "Fully engage brain before writing"
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Old 15th Apr 2014, 08:45
  #784 (permalink)  
 
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Originally Posted by CONF iture
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 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.

Last edited by HazelNuts39; 15th Apr 2014 at 09:10. Reason: Last sentence added
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Old 15th Apr 2014, 19:57
  #785 (permalink)  
 
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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.

Last edited by 737Jock; 15th Apr 2014 at 21:16.
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Old 15th Apr 2014, 22:00
  #786 (permalink)  
 
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Originally Posted by 737Jock View Post
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.
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Old 15th Apr 2014, 23:21
  #787 (permalink)  
 
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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.
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Old 16th Apr 2014, 00:16
  #788 (permalink)  
 
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Originally Posted by 737Jock View Post
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.
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Old 16th Apr 2014, 07:57
  #789 (permalink)  
 
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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.

Last edited by 737Jock; 16th Apr 2014 at 08:52.
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Old 16th Apr 2014, 12:37
  #790 (permalink)  
 
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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.
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Old 16th Apr 2014, 13:55
  #791 (permalink)  
 
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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.
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Old 16th Apr 2014, 13:55
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Originally Posted by BEA Final Report
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 ...

Last edited by HazelNuts39; 16th Apr 2014 at 14:01. Reason: "then" added
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Old 17th Apr 2014, 16:50
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Interesting stuff watching you playing with numbers and graphs ... now how do you justify Bechet, according to your graph, 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' ?
  1. Yours
  2. Bechet
  3. Habsheim
  4. All of them
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Old 17th Apr 2014, 18:44
  #794 (permalink)  
 
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Originally Posted by CONF iture
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.

Last edited by HazelNuts39; 19th Apr 2014 at 21:23. Reason: P.S.
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Old 18th Apr 2014, 05:29
  #795 (permalink)  
 
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@HN39

I must say I admire your patience and tolerance - and I wholly agree with your analysis!
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Old 19th Apr 2014, 23:15
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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.
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Old 20th Apr 2014, 00:21
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Originally Posted by IcePack View Post
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.
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Old 20th Apr 2014, 11:45
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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?
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Old 21st Apr 2014, 01:45
  #799 (permalink)  
 
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Originally Posted by HN39
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 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."
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Old 21st Apr 2014, 06:48
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Originally Posted by CONF iture
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

Last edited by HazelNuts39; 21st Apr 2014 at 11:38. Reason: P.S.
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