But the claim that it should have been reached immediately in that scenario is not.

You still have provided no evidence that the difference in Alpha Max is down to the CONF setting.

Where is such claim ... ?

The words of your Hero is not enough ?

That's your claim - that the system prevented optimum performance by not getting to 17.5deg AoA quickly enough, is it not?

He didn't specify CONF 3 or CONF FULL for the demo - the assumption that there was a difference in the demo config versus that of AF296 has only come from you.

It is not - It is more specific - It still did not change.

If CONF 3 was the setting for the video demo, why alpha max was at 15 when it was at 17.5 for Habsheim ... ?

OK, so let's have a look:

Elevators don't effect an AoA, they effect a pitch attitude.

Therefore, if the pitch attitude is limited by AoA protection and the pitch-up moment from the increase in thrust is expected to exceed that attitude, then the systems will be correct in counteracting that tendency through the elevators. As Capt. Bechet stated, this is normal behaviour, and something that Capt. Asseline should have been aware of.

Nothing in the documentation or the video states that 17.5 degrees AoA is guaranteed upon application of full back-stick. The demonstration in the video was not performed with the engines spooled down, and that would have made a massive difference to systems behaviour.


Which, in the circumstances, the systems could be argued to have done just that.

The systems were designed to keep the aircraft flying and stable even at attitudes which would be considered extreme for a transport aircraft. I'd be prepared to bet money that the combination of Asseline's inputs, had the aircraft been in Direct Law, plus the pitch-up moment from the thrust increase would almost certainly have stalled the aircraft. I'd also be prepared to bet that no human pilot would have been able to take in all the flight parameters and keep the aircraft more stable than the EFCS did.

Can you prove that the extra 2.5 degrees of pitch would have avoided the crash? I know I certainly wouldn't be able to.

We don't know what the CONF setting was for either.

DW, the elevators most definitely control AoA...along withthust setting obviously exempting gliders

Correct - perhaps I should have said that elevators *alone* do not effect an AoA.

The point I've been trying to make is that when the aircraft is decelerating and thrust is not yet sufficient either to arrest the deceleration or power out of the projected flightpath, then either the pilot or the EFCS must take that into account when trying to keep the aircraft aloft. Commanding a pitch attitude equivalent to 15.4 degrees of AoA at timestamp X may well be the equivalent of 17.5 degrees AoA or thereabouts at timestamp X+1s.

The Habsheim Pilot's Problem
 

I haven't read the complete accident report and only wish to offer a quick comment regarding this accident. What I see gives some credence to Confiture’s point of view. For common reference, I'll provide a link to a particular video of the incident and mention some key events. Crash Airbus A320-Vol 296 Air France - YouTube.

The pilot had two problems. He needed to accelerate his engines and needed to clear the trees. Jet pilots cannot forget the spool up time of their engines but at Habsheim that day, use of automation seems to have gotten in the way and created a surprise and a delay in adding power.

After rollout on heading, there are two small pitch adjustments visible. One at T=11 sec, and one at T=14 sec. These are possibly pulls on the stick intended to trigger Alpha Floor (which was not available).
The aircraft began to impact trees around T=26, or about 12 seconds after the second pitch adjustment.
If the pilot had been able to activate Alpha Floor at the second nose twitch, it appears (to me) that he would have cleared the trees.

But let’s look at the problem a little differently, from the viewpoint of what a small increment of g acceleration would have done for the flight path.

If .01 additional g was available at the second nose twitch and for the next 12 seconds, the aircraft cg would be about 23 feet higher-probably not enough to avoid an accident.
If .02 additional g was available at the second nose twitch for the next 12 seconds, the aircraft cg would be about 46 feet higher and would probably have escaped since the engines were spooling up nicely by then. (actually slightly less high since he would have converted some of his kinetic energy to potential energy and it probably would not be possible to maintain all the additional g for the duration.)

Perhaps you suspect that even that that small amount of additional g was not available, but consider that the video shows an alignment turn seconds before the nose twitches up. Was he decelerating that fast that there was absolutely nothing left to maneuver at the end?

In other words, if a measly .02 additional g had been available, the Habsheim event likely would not have been an accident. Would an additional.02 g have been available if the maneuver was flown in direct law and the pilot had pulled just slightly past optimum AOA and then eased off to optimum? That is definitely faster than an asymptotic approach to applying g and is the way most experienced manual pilots would lay on rapid g.

Looking at the Gordon Corps video, it seems there might well be some additional g potential/ AOA in the A320 Normal law being held back as a “safety margin”.

How so? Bearing in mind they were not using automation at any point during the approach or flypast, nor were they intending to.

The flight plan included complete disabling of A/THR (and thus A. Floor) - that this step of the procedure was forgotten in the event doesn't alter that.

While taking into account deceleration and the pitch-up movement from slamming thrust back on? I very much doubt a human pilot could have done better.

Originally Posted by Machinbird http://images.ibsrv.net/ibsrv/res/sr...s/viewpost.gif
...but at Habsheim that day, use of automation seems to have gotten in the way and created a surprise and a delay in adding power.
I think I need to clarify that there was apparently a mental 'expectation' that Alpha Floor was going to kick in, thus even though he may have forgotten his specific autothrottle configuration, the expectation that it would operate caused confusion and a delay in actually adding power.

The point is that his point of attempted Alpha Floor activation was not entirely unreasonable from a maneuvering standpoint. It completely failed because he failed to allow for the unexpected non-response.
When maneuvering near the ground, there really isn't much time for goof ups and when doing atypical flying, there is a need for an exceptional level of planning and practice. That was not done in preparation for the Habsheim flight.

Dozy, I'm going to have to tell you to check your 6 'cause you are dealing with a fighter pilot who could lay on extreme g during violent maneuvers without departing the aircraft:}.

Consider basic servo theory for how quickly the output can match a step input. Remember that a human is a variable gain computer, and although not error free, can error correct once trained in error correction.

A computer must use conservative control strategies since it is supposed to operate independently, thus the asymptotic (essentially an overdamped servo approach) control of AOA.
A human can use a variable gain underdamped approach to a step input and even though they may overshoot the ideal AOA they will correct and arrive at the desired AOA sooner, particularly if there is some sort of feedback mechanism for them to observe (such as mild airflow separation causing a slight vibration.) The key is training and practice.

If thrust alone is able to pitch up the airplane, why the system should waste such a potential when 2.5 deg are still to be grabbed ?

No and I have no desire to, but I certainly can prove that preventing the aircraft from getting the available 2.5 deg of AoA made the crash inevitable.

What about you read the Habsheim report ... ?

You're getting some signs of confusion now. Maybe time to take a rest.

Page 35 of the French report:
At 12h 46' 26'' (Crash - 13 seconds)
CDB "Bon Je vais bien la debrayer l'auto-manette."
(Google translate = "Good I'm fine to disengage the auto-throttle").
Radio Altimeter shows 40 / 50 / 40 feet.

I agree. It also seems to me as though he was going to "demonstrate" how clever the aircraft was and that Alpha Floor was going to prevent a crash, despite the thrust levers being closed.
It would explain the crews insistence that they didn't deliberately fly below 100 radio and did not hear the radio call outs because they had both ears covered by their headsets. (From a crash investigator TV program)

This seems to be a good moment to mention Asseline's book. :E It has his own annotated version of the final 60 seconds of the CVR transcript, how he himself remembers the accident flight. Although he seems to be wrong about at least one detail, it may still give an idea about what he was planning to do and what he was expecting. Mentionable items:

• When PNF said "Bon, t'arrives à 100 pieds là fais, fais", this was well above 100 ft, and Asseline is certain that after he levelled off, his pressure altimeter indicated 100 ft exactly.
• For the fly by, he was mainly focused on keeping the vertical speed at zero.
• In the moment when he said "Bon, j'y vais bien là, débrayer l'auto-manette", he pushed the auto-thrust disconnect buttons and advanced the thrust levers to some intermediate thrust setting. (Here the DFDR disagrees: No movement of the thrust levers yet, both still at idle.)
• His original plan for the fly by was to continuously adjust thrust to maintain his intended speed and to apply go-around thrust when passing the control tower. But since his speed was still 160 kts after levelling off, there was initially no need to add thrust.
• Just before passing the control tower, he becomes aware that the engines haven't spooled up from idle. Also he realizes that what looked like just some vegetation of a darker shade of green at the edge of the airstrip is actually a forest.
• This is when he pulled the thrust levers all the way back and pushed them all the way forward again. (The CVR records this as three clacks of the levers moving across their detents.)

Paraphrased from pp. 5-8 in the book: http://www.crashdehabsheim.net/livre...20coupable.pdf . Annotations in () are mine.

What I make of this:

1. If you're surprised by a forest in your intended flight path, there's something seriously wrong with your flight preparation. Duh.
2. It looks like Asseline made one serious omission (meant to adjust thrust right after levelling off, but didn't), but could never admit it.

Why would he pull the throttles all the way back? I'm not an Airbus guy so I'm curious as to the reasoning.

Jet engines decelerate very rapidly, and if there was any RPM above idle prior, that was undoubtedly lost and that would cause/contribute to a long engine accelerate time.

Time to get the engines spooled up was one of the critical problems on that flight.

But disabling A/THR (and thus Alpha Floor) was central to the entirety of the attempted demonstration - there would have been no expectation of Alpha Floor operating.

Understood, sir. But we're not talking about a fighter here, we're talking about a jetliner which, as you know, has a considerably lesser thrust to weight ratio and considerably greater inertia. The reason the EFCS makes the A320 an exceptionally nimble jetliner when handflown is because the systems are designed to take that into account and have been precisely calibrated to do so.

EDIT : In fact, the whole reason Airbus (as opposed to AF, who were responsible for this flight) used the high alpha demonstration to show off and sell the A320 was because no other airliner at the time could perform that manoeuvre precisely enough to be safe! In terms of risk, barrel-rolling the Dash 80 - while a superlative example of aircraft control - was a Sunday stroll compared to a low-speed high-AoA manoeuvre without EFCS backup.

@noske: While the Captain undoubtedly made mistakes as a result of the improvised approach, at least part of the reason the forest was "surprising" can be laid at the door of AF's operations department - they only had one copy of the airfield chart, so the chart supplied to the crew was a B&W photocopy. Unfortunately, the graphics indicating trees at the far end of the grass strip were of a light grey which did not transfer to the photocopy.

Dozy,
In the right hands and without all the "protections," your genteel A320 could be made to do a low g airshow on the order of what Bob Hoover did with his Aero Commander.

To make it fly in the genteel mode, they have provided some safety margin from the performance boundaries. What people are not talking about is how big the safety margins are (that is closely held data because in the wrong legal hands, it could be said that AI took away a pilot's maneuvering margins and thus caused an accident.

But I'll bet that there was .02 g available from the airframe that the computers were not letting the pilot obtain in the Habsheim accident.

Surely you must recognize the need for some safety margin from an engineering standpoint. There is variability between aircraft after all. Surface contamination of the wings does happen.

What a properly trained pilot can do is to operate an aircraft right up to the boundaries and if the boundaries are slightly exceeded, he will maintain control and correct back toward the actual boundary. (Unless an intervening computer limits this performance.:E)

[QUOTE=DozyBut disabling A/THR (and thus Alpha Floor) was central to the entirety of the attempted demonstration - there would have been no expectation of Alpha Floor operating.[/QUOTE]
I might suggest that you modify 'would' into 'should' in the above sentence. It is probably closer to the truth.

That's as may be - however not every pilot is on the order of a Bob Hoover, Roly Beamont or "Tex" Johnson. In this case we're talking about an AF line pilot - technically capable, certainly - but nowhere near on the order of a Bob Hoover.

The A320 is not particularly "genteel", particularly in airliner terms!

That's a rather cynical way of thinking about it

Popping back to HN39's graph near the beginning of the thread:
I've got to say I'm not entirely convinced. Admittedly I'm unversed in the knowledge you're using to come to that conclusion, particularly with regard to CoG height and relationship to lift...

Of course - however the margins are not particularly restrictive, again, especially for an airliner. Ultimately, though, the reason the aircraft crashed has nothing to do with the technology. Human factors aside, the overarching reason the aircraft crashed was because where it was going, there was a forest in the way.

EDIT - re:would/should, I think the wording is reasonable as it stands - the crew were briefed to have Alpha Floor disabled in order to perform the manoeuvre, and while the approach was improvised and the Captain's physical SA seems to have been compromised by that, he seemed to be pretty sure that A.Floor was out of the equation.

While I disagree with 'bird about using "direct law", I find a flaw in your logic, Doze.

You point out two factors that are essential to understanding the final outcome.

- "improvised" ???? Huh? Flying a multi-zillion $$$ jet without having done a dozen practice profiles? BEAM ME UP!!!!

- thinking that the magic FBW system with all the "protections" and limits and such would "save" him and all the folks on-board? Give me a break.

- Not using manual throttle throughout the flyby? Sheesh. All the automation and such can only compensate for so much.

- blaming pictures of the field? Good grief!!! Just two or three practice missions would have made a huge difference.

I enjoyed flying my first fully-FBW jet, and we always had one place to hang our hat upon - max AoA was always there if we pulled full back on the sidestick. No auto-throttle, but that was up to us. The jet gave you everything it could.

Since Gen 317 seconds RA<52 Ft, the longitudinal law is pitch law until Gen 327 (RA <32 Ft), and then incidence law with derotation. Both are nearly direct and no more Nz law.
There is a problem between Gen 312 and 315 due the trees BEFORE the runway. (These trees have been cut very quickly after the crash!) The expert Max Venet said at the first trial they did not exactly knew how much time was needed to switch the law to "flare" (incidence law with derotation).
It seems descending 2 Ft is enough to switch the law. But Machinbird is talking about 36 Ft which is much more due to loss of. 02 g. We know that stall is achieved on the A320 with g<1 (plane descending!) due to beeing "protected against stall" (rudderruddererrat link post 269). But AF447 learned us that the A330 (and probably the A320) DOES STALL. Using the stall definition with g<1 (.94?, .97?) is transfering ≈50 ft or more from the pilot's margin toward system margin, as Machinbird was arguing.
Contradiction accepted but wih proofs.:O

In theory, the Airbus is not different, as the procedure is to rely on the protections to get the most out of it, but as I wrote earlier :
What strikes me is how in Habsheim, New-York or Bilbao, the pitch authority has been compromised by features built into the system, whenever the aerodynamic had still more to deliver.

Here is what Asseline writes in his book on page 105 :

And pushing the thrust levers to said intermediate position would have taken place about six seconds before TOGA thrust was commanded. Unfortunately there is no evidence of it on the flight recorders. As the Airbus presentation on Habsheim phrases it:

Possible explanations for this discrepancy (ignoring the extreme assumptions that Asseline ist just a liar or that the whole investigation was rigged to protect Airbus):

1. Asseline honestly believes that he commanded intermediate thrust at the transition from descent to level flight, but he never really did.
2. He did, but the thrust levers failed in such a way that not even thrust lever angle as recorded by the DFDR reflected the change.

And no, I don't think that both scenarios are equally likely.

@conf

WRT to my comment about getting max performance when commanding max performance in the Viper....

Which features compromise the pilot's command for max performance?

I also wonder if there were connections with the throttle implementation ( think Asiana) that the pilot did not expect, hence trying to "re-cycle" the system?

Secondly, our primitive system did not require full stick forward or back to command max AoA. As with the 'bus, it was a gee command, and of approx one gee per 4 pounds of stick pressure ( no movement, just pressure sensors), limited by AoA, so at max AoA all we could command was one gee even with 34 pounds of back stick pressure! In short, we could have duplicated the crash into the trees if power-limited and too slow. Hence my question about the throttle implementation.

Thanks ahead of time.

• Hudson - Phugoid damping
• Bilbao - Logic in the AOA protection in case of turbulent conditions
• Habsheim - Radio silence ...

Two different things related to the thrust system happened earlier :

1. During the take off run, the system bizarrely requested to set the thrust levers to the CLB position.
2. At 1000 AGL when it was time to set the thrust levers to the CLB position, the N1 command did not follow the request and remained to the previous setting. Asseline had to retard the levers behind the CLB position, only then the N1 command was elaborated but not without delay.

• Nothing of this is mentioned in the BEA report.
• The final report does not even include the FDR data for that flight portion.

Thanks, Conf

I'll have to dig out my FCOM stuff from the AF447 files and see how that throttle works.

Of course, a few practice flyby runs may have shown any problems with the throttle mechanization.

You would have thought then, that Capt. Asseline would have made doubly sure that the engine thrust was following his TL position, by flying at alpha MAX earlier in the demonstration (say 500 ft agl) and descending towards the runway using a controlled amount of manual thrust. To do a flight idle fly pass and hope the engines spooled up when requested (with the knowledge of the known thrust problem on take off), does not seem to be prudent to me.

They did interpret the initial situation as a temporary bug, but I do agree with you, it should have been a signal to not go and play at very low altitude ...

Second observation is :
Why the BEA is hiding the malfunction ?
What else are they hiding ?

It did not, it's all in the CVR transcript. At 12:41:19 the captain comments that he knows about that 'bug' and at 12:42:12 that it is because he has reduced below a certain N1.

Was this discussed in the Body of the BEA report?

I'd think they would want to address how that specific feature works and what influence it may have had with respect to the delayed power response.

The comment at 12:42:12 is not related to the thrust 'bug' but to the landing gear status.
Nowhere - Totally ignored ...

As often when the BEA does not want to comment anything they only write without discussion they did not think that is linked to the accident!

Report approved with unanimity by the members of the enquiry commission :
Claude Bechet, François Gonin, Bernard Farthouat, Robert Auffret, Philippe Gourguechon, Paul Arslanian, jean-Paul de Villeneuve:suspect:

Alleged thrust discrepancies (1)
 

Quote from CONF_iture (my clarification in square brackets):
"Two different things related to the thrust system happened earlier :
(1) During the take off run, the system bizarrely requested to set the thrust levers to the CLB position.
(2) At 1000 AGL [roughly top of climb] when it was time to set the thrust levers to the CLB position, the N1 command did not follow the request and remained to the previous setting. Asseline had to retard the levers behind the CLB position, only then the N1 command was elaborated but not without delay."

Before I read the captain's memoir, I may be able to explain (1), and I've some observations on (2).

(1) In the early months of A320 airline operation, we had quite a lot of minor glitches on the FMGS. The PERF page includes separate figures for thrust-reduction and acceleration altitudes, the defaults of which are either 1000 ft or 1500 ft above the departure aerodrome, but each can be amended manually before T/O. Basle (LFSB/BSL) is 883 ft amsl, so the default settings may have been 1900/1900. AFAIK, the only function of the THR RED function is to provide an aide-memoire for the crew to reduce to climb thrust (if both donks are still running), which it does by a flashing "CLB" in amber on both pilots' thrust FMA.
The glitch was that the THR RED figure would be lost just after take-off thrust was commanded on T/O, leading to an immediate flashing CLB prompt. This was distracting, but had no effect on engine performance.

(2) After T/O the L/G was retracted in the normal way. After climbing only 1100 ft, the short cruise was conducted at 2000 ft QNH, i.e., roughly 2000ft amsl, maintaining the T/O Flap setting of 1+F (Slats 18 deg, Flaps 10), so ALT* (altitude-capture mode) would have been triggered well below it, pre-empting the acceleration phase for the FDs, which seem to have been in use. "Alt Star" was called by the copilot at 12:41:47, about 17 seconds after airborne, and his call may have been some seconds after the mode change.
At ALT*, the thrust would have needed to be reduced immediately and substantially below CLB thrust, to avoid exceeding the flap limiting speed. (With Habsheim so close, an IAS of about 185 kt would have been reasonable.) In fact, the CVR recorded sounds of thrust reduction starting 5 sec after reaching 2000 ft. At that point, the A/THR was still engaged, and would have changed to SPD (speed) mode because of ALT*. So the thrust reduction would have been achieved by resetting the speed to a figure at or below the current IAS, and/or by retarding the thrust levers well behind the CLB gate, thereby introducing an upper thrust limit less than CLB. (Partially retarding the thrust levers to the desired N1 would in either case have been desirable before changing to manual thrust.)
A/THR was in fact disengaged about 8 sec after start of thrust reduction, and happened to coincide with a L/G CRC warning. The latter would have been caused by a combination of N1 < 75% and radio height < 1000ft, (as the captain intimated, although my 1988 FCOM states < 750 ft). There were some low hills to their left at this point.

So, prior to reading Capt Asseline's account, I see no evidence of anomalies of engine performance in the T/O, climb or cruise phases. I agree with CONF_iture, however, that it would be good to see the DFDR for the whole flight.

Achieving actual ultimate performance
 

Gums-re, the underlined portion:
That would only apply to level flight. I would hope you could still pull a fractional g load if headed straight up and needing to ease the nose over-
A related question however:
Did your system allow you to pull right into buffet, or did it keep you out of the buffet boundary? How much of your ultimate potential performance did it let you have? Did some Vipers turn a little bit better than others?
I ask this from the vantage point of a Phantom Pflyer where if the outer wing panels weren't shaking, you were not asking for maximum performance!:}

I'd think that the A320 would not be allowed to enter the buffet boundary to keep from scaring the cargo, but I could be wrong. (Normal Law)

Buffet would more likely be encountered in clean configuration if it is possible to achieve the buffet boundary.
With flaps/slats down, there may not be a buffet boundary or a very minimal one.

Extracted from VFW614 ATTAS Hi AoA protection tests: LINK

http://i474.photobucket.com/albums/r...pscd279ac2.jpg

erratum post 304
 

I just edited my post 304.
I replaced (Chris Scott link) to "rudderrudderrat link post 269".
Apologize to both.
That link with the 3 definitions of stall was :
http://lessonslearned.faa.gov/Indian...0Condition.pdf
... new edit : after rereading all that, I find NO definitive definition of stall, only rumours

Hi A33Zab,

Long time no see! Thanks for the graph amd the link to the DASA/NLR report on the ATTAS-SAFIR research project. A valuable contribution to the never ending Habsheim debate and the intriguing questions still posed 25 years later.

@ 'bird: Sorry, I needed to make it clear that I could have duplicated the crash, as even with max back stick, my jet would only hang at 27 deg AoA and 1 gee. No way to command a higher AoA or gee. Biggest difference was no autothrottle modes and such. Push forward, motor spools up. Pull back, motor spools down. Unlike the GE J-79, both the fans I flew ( A-7D and F-16A) spooled up very slowly, in comparison. At max AoA and low altitude, I had plenty of thrusties left over, so a go around was easy. Aftr reading the India 605 discussion, I got a better understanding of the autothottle, and I see why the Captain under scrutiny here pulled back and then advanced to ensure he was out of the autothrottle system. Too late. He had plenty of excess thrust available, but "pressed" too hard and too long.

Secondly --- No real buffet in the Viper at max AoA. Kinda a low freq buzz. This was due to the leading edge flaps moving all the time, eventually reaching full down above a certain AoA. Provided excellent directional and lateral stability - like full aileron command and 250 - 300 deg/sec roll rate all without departing.

Last answer for the 'bird -- - could always push to a lower gee unless in a deep stall. The lack of pronounced buffet and the loss of the nose down pitch authority we had in a deep stall was the main reason I joined the AF447 crowd. Although the 'bus still has nose down authority when deeply stalled, our contributors here have shown it takes a long time to finally get flying again. Unlike the 'bus, we trimmed for a gee with either a small wheel or the coolie hat. We did not have the 'bus implementation. If I let go of the stick, the sucker tried to get to whatever gee I had it trimmed for. Did this at any attitude.

Didn't mean to repeat what I had posted on AF447, but simply answered the 'bird's question and added an opinion of the Captain's actions/judgement.

A33zab

Yes, thanks for that link and graph. I see that for quite a time the elevator was moving downwards and the AOA dropping even though the sidestick was being held fully back. Hmmmm!