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Habsheim

Old 3rd Mar 2014, 03:18
  #581 (permalink)  
 
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The BEA has not produced the extensive data to prove that he did not.
The audio track of the video of the accident shows that he did not get the throttles up until way too late. He should have been sorting out problems with getting the engines accelerated way before he got down in the weeds.
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Old 3rd Mar 2014, 14:45
  #582 (permalink)  
 
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  1. At most, the audio track of the video could tell when the engines accelerated, but not when the thrust levers were advanced.
  2. Which video/audio track are we looking at exactly ?
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Old 3rd Mar 2014, 21:42
  #583 (permalink)  
 
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Thank you, 'bird.


Quote:
Originally Posted by Machinbird
The audio track of the video of the accident shows that he did not get the throttles up until way too late. He should have been sorting out problems with getting the engines accelerated way before he got down in the weeds.

  1. At most, the audio track of the video could tell when the engines accelerated, but not when the thrust levers were advanced.
Exactly right, Confit. And 'bird. The spool up was very late, regardless of what the pilot intended. It was too damned late. The big fans take lots longer to spool up in the commercial jets than the fans in the newer lites flown by the military. If the motors take 15 seconds to spool up, what then? Maybe someone here flew the T- 33 and remembers how careful you had to be when doing a go-around.


Point two: 'bird has a point about getting a degree or two of alpha to get a few feet of altitude. He is also correct - temporary AoA increase, then increase in drag, then settle into the trees further downrange.

Until the commercial dudes have a checkout that shows the limits of the FBW systyems or even the "conventional" ones, we will likely see another crash like this one.

That's my story, and I am stickin' to it.
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Old 3rd Mar 2014, 22:27
  #584 (permalink)  
 
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At most, the audio track of the video could tell when the engines accelerated, but not when the thrust levers were advanced.
Well, the answer is "far too late" to the first, and presumably the same to the second.

Isn't this just back to the heart of the old conspiracy theory that the aircraft failed to respond to the pilots' commands?

The rise in note on the soundtracks is consistent with a ~5s spool up, with the engines roaring as the trees were upon them. I'm sure the video could be analyzed to produce an almost complete reconstruction of the flight path independent of the data recorder, especially given the background clutter from the forest.

The thing that's striking about the video on just watching it again for the first time in ages is the speed of approach. It's not like the displays where an Airbus is held steady at high power, high angle of attack and low speed in a pass, it just comes whizzing in.
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Old 3rd Mar 2014, 23:39
  #585 (permalink)  
 
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Originally Posted by CONF iture View Post
[*]At most, the audio track of the video could tell when the engines accelerated, but not when the thrust levers were advanced.
So to get that information, the CVR audio (which includes the sound of the thrust levers being set to TOGA) and the audio track from the video recording can be synchronised using audio processing techniques (primarily spectral analysis).

That is in fact precisely what the BEA did, and they then synchronised the result with the engine data from the DFDR. Again, please forgive the poor Google Translate grammar:

Originally Posted by BEA report Section 1.16.2.1
1.16.2.1 . Restitution [of] engine parameters during the overshoot

The characteristic parameters of acceleration engines after delivery of gas were returned from three independent means :
- The engine parameters recorded on the DFDR ;
- Spectral analysis of the final seconds of the CVR , the characteristics of engine speeds frequencies being recorded by the micro environment of the cockpit ;
- Spectral analysis of the soundtrack of a made ​​by a viewer on the ground video.
The results of these operations are perfectly consistent and show that the engines are reassembled [regaining] power [normally] from the control overshoot [TOGA thrust setting] .
The last engine speeds returned by the CVR and D.F.D.R. are 84.4 percent respectively . 1 100 N on C.V.R. , 83 and 84 p . 100 N 1 on the D.F.D.R. The soundtrack of the video can reproduce a few extra seconds after the impact on the trees (when the flight recorders stopped working ) : the last value of the maximum speed , clearly identified with this method is 91 percent . 100 N1.
Originally Posted by gums View Post
Until the commercial dudes have a checkout that shows the limits of the FBW systyems or even the "conventional" ones, we will likely see another crash like this one.
Sorry gums, I've got to dissent a bit there. For one thing, we're talking about a crash that happened almost 24 years ago and there hasn't been one like it since. For another, the manufacturer had zero input on the conduct of this flight - this was an AF aircraft with an AF crew flying an AF special charter operation. If we make the reasonable assumption that the "early adopter" line crews were given a demonstration and handling training akin to what was on the Gordon Corps video, then it is also reasonable to infer that the sales bumph should not have influenced them.

As I alluded to earlier, Airbus's own demonstrations appear to have been performed *either* at higher altitudes with persons other than crew (e.g. pilots in training, press, VIPs) aboard - *or* at lower altitudes with only crew aboard. I can find no evidence that they ever combined low altitude demonstrations with non-essential people on the aircraft as this AF sortie did.

On top of this discrepancy in approach, there is also the sense that the unexpected deviation from the briefed sortie led to rushed decision-making and a level of improvisation that many would consider unacceptable, particularly given the crew's unfamiliarity with the airfield.

Regardless of what CONF iture seems to have interpreted the details around Alpha Max to mean, the undeniable fact is that the EFCS did not point the aircraft at the trees, nor did it command the excessive reduction in thrust which necessitated such a drastic escape.

[EDIT : I'm not demonising or casually disregarding Asseline here, and as I said I do sympathise with the guy. However, the sympathy tails off somewhat after a point because as far as I know he has not publicly acknowledged that there were several points where he could have done things better - maybe because that requires at least entertaining the notion that there was no cover-up and conspiracy. That he apparently continues to refuse to at least entertain the thought is troubling to me. After a while, it just seems to come across as making excuses. ]

Last edited by DozyWannabe; 4th Mar 2014 at 00:34.
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Old 4th Mar 2014, 21:34
  #586 (permalink)  
 
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Dozy, you make statements but when time comes to back them up you're unable.

Originally Posted by Dozy
So to get that information, the CVR audio (which includes the sound of the thrust levers being set to TOGA) and the audio track from the video recording can be synchronised using audio processing techniques (primarily spectral analysis).
Which video/audio track are we looking at exactly ?
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Old 5th Mar 2014, 01:49
  #587 (permalink)  
 
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Frankly, I'm a little bit tired of playing this game. I think I've provided enough info to satisfy reasonable enquiry, but you're unlikely to ever be satisfied. So how about we turn it around a bit? If *you* can find a single piece of documentation from Airbus which states that full back stick will instantly (or thereabouts) deliver 17.5 degrees AoA in that configuration, then I'll sit up and take notice. I don't believe it was ever, as you put it, "advertised" as such.

The sources of the video and audio as well as the methods used to synchronise them are all documented in the BEA report, but then I suspect you know that already. What more is there to say?
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Old 5th Mar 2014, 04:18
  #588 (permalink)  
 
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Originally Posted by Dozy
Frankly, I'm a little bit tired of playing this game.
Of course you're tired as you cannot back up your statements - And you don't have to stick around either.
So how about we turn it around a bit? If *you* can find a single piece of documentation from Airbus which states that full back stick will instantly (or thereabouts) deliver 17.5 degrees AoA in that configuration, then I'll sit up and take notice.
So sit-up and take notice :

BEA Report Page 14
A tout moment, si l'incidence atteint 14,5°, la loi de pilotage est modifiée et le terme en facteur de charge ou le terme en assiette (modifié ou non par l'ordre de dérotation) est remplacé par un terme en incidence (écart entre l'incidence mesurée et la valeur de 14,5°). Cette loi de pilotage assure en particulier une protection automatique empêchant l'avion d'atteindre une incidence supérieure à 17,5°, pour conserver une marge suffisante par rapport au décrochage, même si le pilote maintient sa demande au plein cabré.
Note that it is NOT written :
This flight law provides in particular an automatic protection preventing the aircraft to achieve an AoA greater than 15 degrees, to keep a sufficient margin with the stall, even if the pilot maintains his request to the full nose-up.
And nobody said it had to be "instantly".

FCOM DSC-27-20-10
HIGH ANGLE OF ATTACK PROTECTION
In normal law, when the angle-of-attack becomes greater than α PROT, the system switches the elevator control from normal mode to a protection mode, in which the angle-of-attack is proportional to sidestick deflection. That is, in the α PROT range, from α PROT to α MAX, the sidestick commands α directly. However the angle-of-attack will not exceed α MAX, even if the pilot gently pulls the sidestick all the way back. If the pilot releases the sidestick, the angle-of-attack returns to α PROT and stays there.
Note that it is NOT written :
However the angle-of-attack will not exceed α PROT

The sources of the video and audio ... are all documented in the BEA report, but then I suspect you know that already.
No I don't know - Do you have that documented reference ?
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Old 5th Mar 2014, 09:36
  #589 (permalink)  
 
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I must say as a "lurker" throughout the course of this thread, I have found it compelling reading. The tidbits that have been added by other than the main protagonists have added to the value of the thread overall.

The hidden algorthmns used by AI in their application of αPROT have certainly been "teased" and "tormented" for the benefit of all.
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Old 5th Mar 2014, 16:54
  #590 (permalink)  
 
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@CONF iture:

Again, you're taking selective quotes and turning them around. In the case of Habsheim, it would have *had* to be a near-instant response, because the Captain did not apply full back-stick until a few seconds (exact values are earlier in the thread) before impact.

And the supposition that the AoA was restricted to A. PROT is also unsubstantiated. As I recall from earlier in the thread, the AoA was in fact slightly more than 15 degrees - 15.4 if memory serves me correctly. You have the Gordon Corps demonstration video showing that even keeping the thrust on, full back stick will initially get you a little more than 15 degrees AoA. You've had other posters tell you that the transition from that state to full A. MAX takes time to achieve in order to maintain stability and to allow for introduction of bank if necessary.

You put the difference down to CONF FULL vs. CONF 3, but have not substantiated that with hard evidence.

The video would have been the original cassette from the camcorder which filmed the flypast and subsequent crash.
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Old 6th Mar 2014, 00:43
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Dozy #596


" We're talking a crash that happened almost 24 years ago and there hasn't been one like it since."


In the 1950s and 1960s many of the accidents were regular " repeaters". They happened again and again, somewhere, not always " Type specific".

The local AAIBs may have been unable to produce reasonable reports before memories had faded and any lessons passed on before the next similar accident occurred.


Habsheim had the advantage of actual video coverage which has been repeated, until the lessons are absorbed.


"DON'T DO THIS..."

Last edited by Linktrained; 6th Mar 2014 at 00:51. Reason: punctuation !
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Old 6th Mar 2014, 02:18
  #592 (permalink)  
 
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Originally Posted by Dozy
Again, you're taking selective quotes and turning them around. In the case of Habsheim, it would have *had* to be a near-instant response, because the Captain did not apply full back-stick until a few seconds (exact values are earlier in the thread) before impact.
That it was a few seconds or ten changes nothing to the fact that the elevators for that period just did the opposite of the pilot request. The FCS had simply no intention to let the pilot increase both the attitude and the alpha whenever 2.5 deg were still avail.

And the supposition that the AoA was restricted to A. PROT is also unsubstantiated.
As I recall from earlier in the thread, the AoA was in fact slightly more than 15 degrees - 15.4 if memory serves me correctly.
15 deg even at TGEN 334 and that value seems to have been the limitation the FCS was ready to accept.

You have the Gordon Corps demonstration video showing that even keeping the thrust on, full back stick will initially get you a little more than 15 degrees AoA.
Right on, alpha max all the way for CONF FULL, no hesitation, even possible alpha max transient overshoots. That's how the alpha protection feature is supposed to work.

You've had other posters tell you that the transition from that state to full A. MAX takes time to achieve in order to maintain stability and to allow for introduction of bank if necessary.
Gordon Corps just proved them wrong.

You put the difference down to CONF FULL vs. CONF 3, but have not substantiated that with hard evidence.
Part of the reports you don't read but comment ...

The video would have been the original cassette from the camcorder which filmed the flypast and subsequent crash.
Is it "documented" or not ?
A few camcorders have filmed the event ...
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Old 6th Mar 2014, 09:44
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Originally Posted by CONF iture View Post
That it was a few seconds or ten changes nothing to the fact that the elevators for that period just did the opposite of the pilot request. The FCS had simply no intention to let the pilot increase both the attitude and the alpha
Yes, clearly that is fact, and amply demonstrated.
Noteworthy is that "that period" is quite short.

Originally Posted by CONF iture View Post
whenever 2.5 deg were still avail.
OTOH, that is not.
From an aerodynamic point of view, there were probably more than 2.5 deg before stall. From an FCS point of view, for this to be correct, the FCOM should read that alphamax was to be attained immediately and without any damping.
Does the BEA report or the FCOM read this? No. You just quoted both.
The NTSB report on Hudson event, and numerous other discussions here and there have put forward several explanations as to why alphamax(17.5) would, in certain circonstances, not be reached immediately.

Originally Posted by CONF iture View Post
Right on, alpha max all the way for CONF FULL, no hesitation, even possible alpha max transient overshoots.
Yes, clearly that is fact, and amply demonstrated.

Originally Posted by CONF iture View Post
That's how the alpha protection feature is supposed to work.
No. That's the way it works when in the conditions of the test flight. Which are different from the conditions of Habseim flight.

Originally Posted by CONF iture View Post
Gordon Corps just proved them wrong.
No. See above.

I'm sorry to be a bit harsh, CONF. I have no certainty myself as to why precisely the FCS did what it did on the last few seconds before the crash at Habseim. I would like to be sure, but I'm not.
The BEA says it's normal behavior, Airbus says nothing (or more or less rephrase the BEA report), and external experts don't have access to the code or specifications of the A320 FCS.

But there have been a number of attempts from contributors here (and elsewhere) to explain this "why" (sometime using the NTSB contribution, which had access to whatever it needed to explain Hudson).
I judge those explanations convincing.
You seems not, but don't explain yourself on that matter.

As neither of us can proove them right, or wrong, without access to the code and specifications of the A320 FCS, we can either agree to a "stalemate", or you can try and explain why you (seem to) dismiss each hypothesis.

Cheers.

Last edited by AlphaZuluRomeo; 6th Mar 2014 at 14:16. Reason: precisions on 2nd point
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Old 6th Mar 2014, 12:02
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From the NTSB Performance Group Chairman’s report on the Hudson river ditching:

At 15:30:39, as the airplane descends through 50 ft, the stick moves aft more
abruptly, reaching its aft limit (16°) at about 15:30:41, and remaining there about 2
seconds, until touchdown at 15:30:43.
The elevator response plotted in Figure 15b indicates that during this time, the elevators
move trailing-edge up starting at 15:30:37, reaching about 4° at 15:30:38, and then move
abruptly down to about -1° at 15:30:39 before increasing again to about 4.5° at 15:30:41. In
the last 2 seconds of flight, the elevator deflection increases about 1°, from 4.5° to 5.5°.
Figure 7 shows that between 15:30:36 and the touchdown at 15:30:43, the pitch angle
increases from 9.5° to 11° and then settles back to 9.5°, even though in the last two
seconds the left longitudinal side stick is at its aft limit, and α is below αmax.
It seems to me that the elevator response to the sidestick input at Habsheim was quite similar, except that the sequence was interrupted by the airplane striking the tree tops.

What is puzzling to me is that the simulator did not reproduce it when capt. Bechet flew it to duplicate the accident sequence. In that simulation the elevator moves immediately nose-up, and the airplane pitches up 5 degrees in 2 seconds. Why is it different?

P.S.
Sorry for posting when I should have thought a bit longer. Both moved the thrust levers forward at 120 kts, 12 deg alpha. The difference is in pulling the sidestick back - Bechet at the same instant and Asseline 3 seconds later. So Bechet was still in pitch control law when he pulled the stick back while Asseline was in alpha-prot. Nevertheless, Bechet would still have hit the trees if he had not been in a simulator.

Last edited by HazelNuts39; 6th Mar 2014 at 15:45. Reason: P.S.
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Old 6th Mar 2014, 20:57
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Originally Posted by HazelNuts39 View Post
Nevertheless, Bechet would still have hit the trees if he had not been in a simulator.
Awesome explanation - though I should point out that the reproduction was not flown in a simulator, it was flown in a real A320 over the test runway at Toulouse, with (I believe) obstacles set up reproducing the "bosquet" at the start of the reconstruction.
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Old 6th Mar 2014, 21:50
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Devil

Important knowledge of flight laws figures, understanding with great precision how they work actually, real suffisant briefing including alpha prot mention and preparation.

Thank you HazelNuts39
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Old 6th Mar 2014, 21:54
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Forgive me, but I can't find the reference to a re-enactment of the crash, Doze. Where?

I also go with 'bird and others that another degree of AoA would only have increased drag unless the power was sufficient to overcome that extra drag.

Sheesh.

I don't think many here have actually flown at the "edge of the envelope". You have to see it to believe it, and learn. We can't do that for most commercial jets, and sure as hell not try it with pax aboard on a poorly planned/practiced demo. Practice was the key, IMHO.
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Old 6th Mar 2014, 22:29
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Originally Posted by Dozywannabe
I should point out that the reproduction was not flown in a simulator, it was flown in a real A320 over the test runway at Toulouse
Be that as it may, but I was basing my observation on the graph on page 9 of the 'Additif' of the Final Report bearing the notation "Essai simulateur 20/7/89 Recoupement Habsheim CPT. C. Bechet".
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Old 6th Mar 2014, 22:30
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Originally Posted by gums View Post
Forgive me, but I can't find the reference to a re-enactment of the crash, Doze. Where?
BEA report section 1.16.1.4.3. Approximate (Google) translation below:

Some members of the Commission of Inquiry, pilots themselves , wished to personally assess the behavior of the aircraft during maneuvers near the ground, to see if the switching of control laws could cause difficulty steering . Tests above track Toulouse were conducted for this purpose , in steps between 100 and 50 feet ( C * ) between 50 and 30 feet (Act trim ) and below 30 feet ( law trim and " rotator "). These [test] cases, which do not correspond to a normal approach , have led to the recognition [of] no problem driving : switching C * - control law in [pitch] - has no significant effect on the behavior of the aircraft seen by the driver , the effect of the term " rotator " is perceptible ( must exert increasing back pressure to keep the landing) without presenting any delicate and we must remember that this mode has not been activated during the flight of 26 June.

Switching on the control law in effect does not affect the behavior of the aircraft as felt by the driver.

These tests also establish that very momentary switching control laws that have occurred between t and t - 21 seconds - 20 seconds because of erratic indications given by the radiosonde [radio altimeter] when passing over a grove are not likely to have affected the behavior of the aircraft.

In conclusion, the inquiry found that the operation of the flight controls was consistent with the data of the certification during the flight of 26 June 1988 and considers that the control laws of the device have no feature likely to create a particular difficulty driving , even under the conditions of this flight which differs significantly from a normal approach.
@HN39 - Understood, and it wasn't a criticism, I just wanted to make sure that as the thread meanders to its late stages we got as many of our facts in a row as we can.

Last edited by DozyWannabe; 6th Mar 2014 at 22:41.
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Old 6th Mar 2014, 23:32
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Some members of the Commission of Inquiry ...
IMHO, since you want to 'get your facts in a row', that doesn't refer to Bechet, who was president of the Commission of Inquiry.
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