Habsheim

[Chris Scott]

Dozy,

Are you arguing that he levelled off 40 ft lower than he intended, despite that being a potentially-hangable offence, and did absolutely nothing about it for nearly 10 seconds?

Or are you suggesting his barometric altimeter was over-reading by at least 40 ft, due to an error in an ADC or DMC?

[noske]

Originally Posted by Chris Scott

At level-off (TGEN 321, or t -13 sec), the rad alt showed a height of 40 ft. At the same time, the pressure altitude was +869 ft, from which I calculate the pilots' altimeters (set to the QFE of 984 hPa) would have been indicating about 60 ft.

It's kind of annoying that the report leaves those calculations as an exercise to the reader (I used this Pressure Altitude Calculator), but yes, it shows that the QFE value received from Habsheim must have been correct.

Capt Asseline may have planned to fly below 100ft all along. This was certainly not incompetence, because his height-keeping after level-off at t -13 (see my post to roulishollandais above) was remarkably accurate – whether you study the baro readings, or the heights recorded from the rad-alt. Although he did lose height, it amounted to no more than 10 ft on his baro-altimeter, and the same on the rad-alt. He has stated that he was using only his baro altimeter throughout, and claims that it must have been giving false readings, but – other than his own testimony – I’m not aware of any evidence to support that.

But Asseline seems honestly upset about the investigators not believing him ("Do they think that both of us are too stupid to read an altimeter?").

To reconcile the DFDR values with an indication of 100 ft on the captain's PFD, one could assume that the crew had erroneously entered a QFE value of 985.5. Now that seems totally unlikely. On the CVR, they repeat the correct value three times (and "cinq" and "quatre" don't even sound similar).

Asseline has another explanation, that the reference value for his altimeter must have shifted somehow, and he has indeed a hair-raising story to tell, where this happened to him on a flight from Paris to Geneva, and he ended up 1000 ft too low, almost (as in "too low, terrain") striking some mountains.

While I have some sympathy for this particular theory of his, it still leads back to the basic problem: the flight crew being unfamiliar with the airfield. Had they been aware that Habsheim control tower is not a good 100-ft-reference, and had they known about these trees that are just about as tall as the tower, it wouldn't have mattered if their altimeter reading was off by a lousy 40 ft.

[DozyWannabe]

Originally Posted by gums

From the "light" peanut gallery...

Hah. Don't be daft, you're always welcome and your input is always thought-provoking in a good way.

..."pride" gets in the way one or two times, but usually only once. Our aviation mistress is harsh in that regard.

No doubt, though on occasion it can be about other things - for example, a tendency to stick to the plan even though some aspects have already gone awry.

The "press on" attitude may apply in combat, but otherwise it is not a smart thing ... I know about the combat reference from one mission, but I digress.

An interesting point and one with which I'd agree, with the caveat that in today's cut-throat business world I'd be surprised if most airline captains haven't been concerned at one time or another about the potential fallout from disgruntled pax complaining to the firm when deciding whether to go-around and/or divert. With airline management consisting mostly of MBAs, many of whom don't appreciate the risks involved, the worry that making a safe call could harm or even end your career might be palpable.

In this case though, I'd be surprised if the schedule wasn't more flexible than the majority of airline ops.

Let's face it, the dude had a poor setup and tried to "save" it.

Yup, and the 'setup' was poor all the way back to the airline's briefing. However, at the same time there were opportunities to make a more stable approach which were not taken, so some responsibility for the need to "save" the aircraft remains with the captain.

The "magic" protections and limiters can only do so much, and flying at the "limits" when carrying SLF and such is not very "professional" to this old pilot.

As you well know from your FBW fighter experience, such systems are a result of hard-nosed engineering practice - far from "magic" on closer inspection! Whatever one's views on the technology, the laws of physics remain immutable and if you can't avoid solid objects in your path you are going to hit them...

One of the outcomes was a move to ban pax from the general public on display flights.

Originally Posted by Chris Scott

Are you arguing that he levelled off 40 ft lower than he intended, despite that being a potentially-hangable offence, and did absolutely nothing about it for nearly 10 seconds?

Or are you suggesting his barometric altimeter was over-reading by at least 40 ft, due to an error in an ADC or DMC?

I'm not arguing or suggesting anything, because it's outside my area of expertise!

I think it's not a simplistic either/or proposition though. It could be that he moved to level off at 100ft, but the inertia of the rapid, improvised descent profile coupled with an abnormally low thrust setting caused the aircraft to continue to sink while he was heads-up, looking out of the windscreen. The rapid increase in workload due in part to continued improvisation could have lead to confirmation bias and misreading of the altimeter when he looked heads-down again. I'm not saying that's what happened as much as asking you if you think it plausible.

Originally Posted by noske

But Asseline seems honestly upset about the investigators not believing him ("Do they think that both of us are too stupid to read an altimeter?").

And in my personal view, that - namely taking things personally and reflexively defending with counter-attacks - has always been his Achilles' heel when it comes to the credibility of some of his claims. For their part, the investigators certainly believed that *he* believed the baro alt was showing 100ft - but every bit of hard evidence staring them in the face made it unlikely.

Interesting use of "both of us" as well. To the best of my knowledge, the FO has never spoken up publicly on the subject. I may try hunting for material there.

Asseline has another explanation, that the reference value for his altimeter must have shifted somehow, and he has indeed a hair-raising story to tell, where this happened to him on a flight from Paris to Geneva, and he ended up 1000 ft too low, almost (as in "too low, terrain") striking some mountains.

Which rather begs the question of why, that issue being known to and experienced by him personally, he neither used the RA display as a backup himself, nor - given his claim that the RA display was difficult to read - asked his FO, as pilot monitoring, to do his best to cross-check both baro and radalt.

While I have some sympathy for this particular theory of his, it still leads back to the basic problem: the flight crew being unfamiliar with the airfield.

It's one fundamental issue certainly, but there seems to be a general sense of creeping complacency about the operation as a whole.

20/20 hindsight is a wonderful thing.

[roulishollandais]

Rules of computer art 1988

So we do agree about the passage of more than 50 FT RA to the unexpected less than 30 FT RA before the runway threshold.

Being particularly concerned in flying systems as a former manager of mathematics and computational methods, the comment of the expert Max Venet indicates to me a lack of computational methods. From memory, he said the following sentence: "We do not really know why the aircraft did not set in flare passing below thirty FT RA, or how long he should stay less than thirty feet. "
This sentence shows that Venet did not found in Airbus a person who could tell him that or a document with this information. He could not access either to a history of the evolution of the software before its certification, and he did not find the information in the certification documents.

I believe that these serious gaps do not correspond to the state of the art computer at that time (or today!). If indeed at that time certain documents required to decode a specific 0 and 1 know-how it was even more to accompany these documents and comments in everyday language. In any case it is so that AS or AB (or any other designer of the system) should proceed.

The absence of such documents can only be accompanied by operational documents being incomplete and unsafe to the user (airlines, pilots, mechanics).

I say that as a computer specialist who had to put up this kind of working methods among researchers and engineers. And it had nothing difficult, but it is of course a constraint.

I do not see the point either to keep secret the software description. The fight against the copy is much easier to exercise if everyone puts their workon the table in daylight in a reasonable time. Only that can serve as engineers who wish to sell their know-how and pilots who wish to return alive from flight when they flew as we taught them

[DozyWannabe]

Originally Posted by roulishollandais

Being particularly concerned in flying systems as a former manager of mathematics and computational methods, the comment of the expert Max Venet indicates to me a lack of computational methods. From memory, he said the following sentence: "We do not really know why the aircraft did not set in flare passing below thirty FT RA, or how long he should stay less than thirty feet. "

We've covered a lot of this ground before, and I believe you had a look at my old Prof's overview from his 1993 visit, where he saw use of advanced software engineering and reliability techniques in person.

Would this be the same Max Venet who was President of the SNPL from 1979 to 1982? If so, in which area of expertise was he qualified to comment?

This sentence shows that Venet did not found in Airbus a person who could tell him that or a document with this information.

No it doesn't, it shows that he didn't have the information - whether this was because he didn't try hard enough to get it or because Airbus were wary of supplying (at the time) very commercially-sensitive data to a representative of a hostile organisation is unknown.

The absence of such documents can only be accompanied by operational documents being incomplete and unsafe to the user (airlines, pilots, mechanics).

M. Venet stating that he didn't have those documents is not the same thing as those documents not existing. Again, we're back to Prof. Mellor's visit where he saw contemporary best practice in action.

I say that as a computer specialist who had to put up this kind of working methods among researchers and engineers.
...
I do not see the point either to keep secret the software description. The fight against the copy is much easier to exercise if everyone puts their workon the table in daylight in a reasonable time.

And I respond as a professional software engineer and aviation nerd who had the good fortune to be educated by someone who saw behind the curtain.

These days it's clear to those with an interest that some of the techniques pioneered with the Airbus FBW systems have percolated down into more mainstream software practice (test-driven development and regression testing in particular). The kind of source-code sharing you describe has also become well-known, spawning the Open Source movement. However in 1988 the legalities surrounding software copyright and ownership were still something of a grey area, and the people dictating commercial policy guarded all aspects ferociously.

Getting back to the point, we've already discussed that Capt. Bechet organised an accurate real-world replication (minus the trees that were hit) of the flight at Toulouse. Flare mode was not activated, but Alpha Prot was.

Based on my understanding of how the systems were designed, it's likely the reason Flare Mode was not activated was because the brief RA reductions were not consistent with the overall trend of the values. M. Venet appears to have been working on the assumption that a value of 30ft RA will immediately trigger Flare Mode under all circumstances. This in turn suggests an overly simplistic understanding of software in general and indicates that his expertise was not in software, real-time or otherwise.

If Flare Mode had been (completely - h/t HN39) activated by overflying the copse, the DFDR would have indicated the elevators down shortly after crossing the strip threshold. Instead, the EFCS complied with the sidestick commands until shortly before impact, where Alpha Prot mediated the pitch-up demand to avoid stall.

And as rudderrudderrat said all the way back in post #45, Flare Mode can be overridden at any point:

Originally Posted by rudderrudderrat

The baulked landing procedure (Select TOGA power and rotate to 10 degs pitch) allows you to fly away from any attempted landing - even after touch down.

[noske]

Originally Posted by DozyWannabe

Interesting use of "both of us" as well. To the best of my knowledge, the FO has never spoken up publicly on the subject. I may try hunting for material there.

I was referring to Asseline's book, p. 35/36. Scattered all over that book, there are a few passages where I can imagine Mazières putting down his copy, muttering "Will you please just speak for yourself, Michel?", and this is one of them. But all in all, Asseline was reasonably cautious about that issue.

[HazelNuts39]

From the FCTM: "When reaching 50 ft, auto-trim ceases and the pitch law is modified to flare law.
(...) The system memorizes the attitude at 50 ft, and that attitude becomes the initial reference for pitch attitude control. As the aircraft descends through 30 ft, the system begins to reduce the pitch attitude at a predetermined rate of 2 ° down in 8 s."

This aligns with paragraph 1.16.1.2 of the accident report where it says:
"Pendant la phase de descente entre 50 et 30 pieds, la loi de pilotage est modifiée et prend progressivement en compte (1), au lieu du terme en facteur de charge, un terme en assiette longitudinale (écart entre l'assiette constatée au passage à 50 pieds dite assiette de consigne et l'assiette réelle instantanée) ; Au passage à 30 pieds, un ordre supplémentaire destiné à simuler un effet de sol conventionnel est introduit en complément à la loi de pilotage en assiette précédente : cet ordre ramène progressivement l'assiette de consigne (constatée à 50 pieds) à - 2° en 8 secondes, créant un moment à piquer que le pilote doit contrer (« dérotation »)".


According to the footnote to this paragraph, the transition to flare law is progressive and takes one second to complete. In the same paragraph the report states that flare law (loi de pilotage en assiette) was active between t-21s and t-20s (i.e. when the airplane was overflying the 'bosquet').

RA, sidestick and elevator position are recorded once per second. Even if 'loi de dérotation' was momentarily activated, the time below 30 ft was probably too short (considering the ramps of 1 second and 8 seconds) to result in a movement of the elevator that would have been observable in the DFDR data.

[DozyWannabe]

@HN39 - That's interesting. So the transition began, but the 'drop' below 30ft was probably too brief to complete it? OK - that makes sense (and is in keeping with the 'trends and deltas' nature of the systems as I was taught).

Sometimes I really wish I'd taken French alongside German - it'd make this so much easier. It also means that the question of Flare Mode was in fact asked and answered in the report, which somewhat dents Asseline's assertion that they didn't check for it/someone was hiding something.

[Chris Scott]

Effects of Flare Mode

Hi HN39,

Thanks for recapping the information from the post-1988 FCTM.

My English-language FCOM from 1988 is in agreement that the first stage of what it calls Landing Mode involves two things passing 50R (50 ft on the radio altimeter): memorising of the pitch attitude; and freezing of the THS setting.

The BEA report indicates that this first stage would have been engaged as a result of the ramp of height to 32R at t -21 (TGEN 313), as the a/c passed over the copse ("bosquet") before the airfield boundary.

As you know, the second stage of what is now called Flare Mode, which begins crossing 30R, introduces a slow bias of pitch that modifies the zero-stick pitch progressively from what it was at 50R to minus-2 degrees - this during a period of 8 seconds. That sub-mode would probably have been engaged by the recorded height of 24R at t -20.

The BEA states that, because the rad-alt height in the following 2 seconds was over 50 ft, flare mode was disengaged back to Normal Law for that period. AFAIK, there is nothing in the recorded data to suggest otherwise.

By t -17, however, the height had once again fallen below 50R, which would have re-engaged the first stage of Flare Mode, freezing the THS at its current setting of U04 (4 deg nose-up trim). The second stage of Flare Mode would never have engaged, because TOGA thrust had been selected by t -4 (see Tome 4), at which point the height had not crossed 30R. (A second later, the AoA exceeded 14.5 deg, and Alpha-Prot Law would have engaged.)

In summary, the only adverse effect of the regime of the first stage of Flare Mode between t -17 and t -5 would have been the freezing of the THS at 4 deg nose-up trim. After levelling off at t -13, the PF had to pull back slightly and increasingly on the sidestick as the a/c decelerated. However, in my experience, pilots of a/c with conventional flight controls flying deliberate approaches to the stall do not continue pitch-trimming below Vref. At level-off, the IAS was already below the Vref for Flaps 3.

Bon soir, roulishollandais,

Does the above interpretation address any of your concerns?

[roulishollandais]

Originally Posted by DozyWanabee

Sometimes I really wish I'd taken French alongside German - it'd make this so much easier.

Sometimes Iself really wish I'd taken English alongside German as first foreign language - it'd make this so much easier.
Specialy here, where we are walking on eggs.
I shall take some time to write my answer in English.
Already Thank you to Hazelnuts39 and Chris Scott for analysing these sequence over the bosquet, to gums for global analyse of the flight, to Dozy for the interest he finds now in that forum who could never take place since 25 years, for any reason. Thank you to Conf_iture who shows us that not retired pilots are not all ectoplasms, to John who allowed that forum to exis, and to all the excellent contributors, and to the followers.

My last posts don't want to comment the crash itself (I removed my pilot's cap) but what did me wonder as computer guy, as it may be a chapter of factors in the lessons to learn from Habsheim. But we need a good analysis of the facts.

Just a word about Venet :
He did the mentioned declaration during the first Trial, answering to the President of the Court (dec 1997) . When he says "We" it means himself and Belotti.
Retired AF airline pilot, and former (elected by the members) President of the SNPL the most important pilots Union in France. That does not make him the Devil! Pilots are never on the ground... and sleep (after night flight) when ground People are working hard in Office, etc. We know that old story between Navigants and Rampants So pilots need to be represented in Unions when they are not on the ground, despite someone don't like existence of Unions.

Four enquiries have been done :
1. 27. june 1988 BEA : President Bechet, Gonin, Auffret, Farthouat, Arslanian, Gourguechon, Villeneuve
2. Judiciary expertise from the Juge d'instruction Mrs Marchiani : Auffray and Bourgeois
3. 11.january1990, from Mrs Marchiani, two supplementary experts : Venet and Belotti
4. 28. june 1988, Air France investigation Commission :
Richer the President, Vuillard, Gauthier, Merloz, Bourbon, Conrozier and prof. Org. (Chatelain, Scattolin, Thiébaut, Brédy, Edelbloude)

[DozyWannabe]

Originally Posted by roulishollandais

Just a word about Venet :
...
Retired AF airline pilot, and former (elected by the members) President of the SNPL the most important pilots Union in France. That does not make him the Devil!

Didn't say it did. However he is not an expert in the field of computing, and the statement showed a lack of understanding of how such a feature is implemented in terms of real-time safety-critical software disciplines.

The issue with the SNPL regarding any action against Airbus is that the union has held a long-standing animosity against the company ever since the A300 went into service as the first long-haul widebody to do away with the Flight Engineer's station. An evolution of design which their members fought tooth-and-nail, and seemingly never forgave.

As such, there will be an understandable suspicion of bias against Airbus in such representations. In Asseline's case, it seems his union-supplied legal representatives steered him in the direction of pursuing claims of technical issues against the aircraft despite a lack of supporting evidence, when he would have been better served by pursuing the airline's poor operations practices which put him in a bad position in the first place, and for which there was significant evidence and potentially a much stronger case when it came to mitigating factors.

I have to say my personal opinion is that all this political nonsense has served only to hinder understanding of the incident and the issues involved, and furthermore has led to a significant number of people developing entrenched opinions that are, in some cases, still held with an almost religious fervour. This in turn means that there's a degree of personal animosity and ad hominem to the discussion that saddens me immensely.

[gums]

Well, we get to replay the incident over and over......

Before I return to the "monitor mode", I think Doze summarized the whole thing, and it wasn't "flare mode" or altimeter settings or anything else except:

I think it's not a simplistic either/or proposition though. It could be that he moved to level off at 100ft, but the inertia of the rapid, improvised descent profile coupled with an abnormally low thrust setting caused the aircraft to continue to sink while he was heads-up, looking out of the windscreen. The rapid increase in workload due in part to continued improvisation could have lead to confirmation bias and misreading of the altimeter when he looked heads-down again. I'm not saying that's what happened as much as asking you if you think it plausible.

I have personally lost friends that did stupid things like "pressing" when they should have done a "go around" or broken off the attack ( fighter stuff). Pride is a player, and "get the job done" is also there on most of the losses. Then there is loss of situational awareness and basic failure to use all the displayed data of your flight path and such. On the civilian side, I knew the Cali pilot and the guy at Little Rock ( not like Cali, but still sad to lose a student of mine). Didn't cross paths with Sully, but might have, and he did it right. I got tired of going to memorial services my last two years in the "business" - 4 pilots that were of my age and experience that screwed up, and were all pilot error.

Sorry for the personal stuff.

Let's face it, the accident/crash happened due to poor judgement, and the jet did everything it was designed to do. Not enough to compensate for a sorry execution of a simple flyby, but you play the cards you are dealt.

I am not sure about the purpose of a low, slow flyby at a ridiculous altitude for a big jet and at a high AoA. But the captain tried it. Poor planning and practice. Then getting behind the jet's capabilities. Sad, sad.


I relish the info on the flight control laws and such. Also like the insight I see from professional "heavy" pilots and a few engineers.

[DozyWannabe]

Originally Posted by gums

Sorry for the personal stuff.

Don't be - it's all good. There's no shortage of examples where otherwise excellent pilots paid dearly for a single call that turned out to be poor with 20/20 hindsight, and it goes without saying I'm sorry for your loss.

I am not sure about the purpose of a low, slow flyby at a ridiculous altitude for a big jet and at a high AoA.

Because no other jet of that kind at the time could do it safely. I have little doubt that had the crew been properly briefed on the terrain surrounding the airfield we wouldn't be having this discussion.

[Machinbird]

Quote:
I am not sure about the purpose of a low, slow flyby at a ridiculous altitude for a big jet and at a high AoA.

Because no other jet of that kind at the time could do it safely. I have little doubt that had the crew been properly briefed on the terrain surrounding the airfield we wouldn't be having this discussion.

Without A/T engaged and Alpha Floor, the A320 couldn't do it safely either.
So what were they thinking?

[DozyWannabe]

Originally Posted by Machinbird

Without A/T engaged and Alpha Floor, the A320 couldn't do it safely either.

Surely it could do that perfectly safely without either as long as there were no obstacles in the way! A caveat which was firmly in the hands of the operator and crew...

(referring strictly to the aircraft capabilities, not the advisability of the sortie itself)

[HazelNuts39]

Surely it could do that perfectly safely without either as long as there were no obstacles in the way!

I concur with Machinbird. The demonstration as planned: a fly-past at Valphamax and alpha-max, therefore with thrust control the only means for controlling the height of the flight path, could not be done safely at 100 ft above terrain, let alone 40 ft. In any case it could not have been done with the level of safety required for a passenger-carrying flight.

Just imagine: To achieve alpha-max you have to pull the sidestick to the rear stop and keep it there. To maintain level flight at alpha-max you have to slow down to Valphamax. The only way to 'pull up' in that situation is to increase thrust to accelerate to a speed greater than Valphamax.

[gums]

Thanks 'bird and Nuts

We pilots must remember that rate of climb is the delta between thrust available and thrust required for the AoA and weight and...... ( power required)

It's why the nasal radiators tend to use throttle for glide path rate of descent to land on a boat. They trim for an AoA/speed and control the flight path with power. Just look as the Asiana fiasco, much less this one we are re-hashing.

Besides going well below the planned altitude, and a screwed up approach, the power side of the equation was not even close to what was required to "save" the screwed up flyby. Sheesh. I don't like being harsh about a fellow pilot, but this one really bugs me, and I am thankful that so many folks walked away from it.

Lastly, who in the world on the sidelines would have appreciated a high AoA, slow speed, extremely low altitude flyby? I'll bet 99% of the witnesses didn't have a clue about what the pilot was trying to demonstrate.

[HazelNuts39]

Originally Posted by gums

Lastly, who in the world on the sidelines would have appreciated a high AoA, slow speed, extremely low altitude flyby? I'll bet 99% of the witnesses didn't have a clue about what the pilot was trying to demonstrate.

I still have a vivid memory of the demonstration at the Farnborough airshow of the high angle-of-attack protection by Gordon Corps on the A300 serving as a flying testbed for the FBW system developed for the A320. The speaker didn't inform the audience about the altitude observed in the demonstration but, from memory, it must have been closer to 1000 ft than to 100 ft.

[DozyWannabe]

As I said,

Originally Posted by DozyWannabe

(referring strictly to the aircraft capabilities, not the advisability of the sortie itself)

Theoretically speaking, at 100ft over a flat landscape and with the power set correctly the A320 would be capable of safely maintaining Alpha Max indefinitely until it ran out of fuel.

With 20/20 hindsight the sortie shaved safety margins to the bone, but the responsibility for that didn't lay with the aircraft.

[Linktrained]

TREES

Farnborough had NO trees exceeding 500 ft. ( QFE ) along the extended centre line of the R/Ws ( IIRC ).
THAT factor alone, would have made a lot of difference for Gordon Corps' demonstration, if done at 1000ft.