Habsheim

[DozyWannabe]

@CONF iture:

On what evidence are you basing these assertions? To achieve an Alpha Max flypast at or above 100ft RA without Alpha Floor activating and causing the aircraft to climb away, A/THR must be disabled. Therefore there should be no automatic "hunting" of thrust during the manoeuvre, because thrust setting is manual. Any variation of thrust needs to be manually commanded.

As Chris Scott says:
The EFCS targets an AoA of alpha-prot with neutral stick, and alpha-max with the stick fully aft. Nz doesn't rule.

The EFCS *targets* Alpha Max with the stick fully aft - it doesn't *guarantee* it.

Where did you see these sorties being performed?

[Chris Scott]

Quotes from CONF_iture:

"It is not exactly clear why you guys need to introduce notions of "flare maneuver" ..."

Simply because it takes a force to change the trajectory of any vehicle - in this case the FPA. The vertical component of increased thrust alone is not sufficient - extra lift from the wing ** is required. Just for the moment, let's forget about any measures to avoid phugoid oscillations, or whatever. In the case that you are arguing, where the AoA is already at alpha-max, the only way to increase wing lift is to increase the speed. As I have previously reminded you, Valpha-max increases as the load factor (Nz) increases. To put it the other way round, increased speed at alpha-max generates an increase of Nz - which gives an increase of FPA.

In fact, even after the climb has been established, the wing lift requirement will be greater than in level flight, because its vertical component still has to balance the weight. So, at a steady AoA of alpha-max, Valpha-max has to be slightly higher in a climb than in level flight.

"Thrust controls the V/S"

In effect, that's correct, and for the PF to expect the PNF to do that for him would be impracticable.

"Thrust does not control the speed which stays at Valphamax"

For the reasons I have explained, at any given weight, Valpha-max is a variable speed.

** [EDIT]
However, see the reference to "TOTAL aerodynamic lift" in the fourth paragraph of Owain Glyndwr's post (below).

[Owain Glyndwr]

If I may throw in a few thoughts:

The natural phugoid period is approximately 0.23*Vkts TAS, that is about 28 seconds at 120 kts. If you are looking at a transition period of say 3 seconds that is only going to be one tenth of the phugoid cycle and I doubt it you would see much variation in that time. The terms AI have put into alphaprot to stabilise the trajectory also have a significant short term effect, basically by limiting the allowable AOA if the speed is decreasing but also there may be (probably is) a pitch rate term to add damping to whatever short period motion is associated with alphaprot.

WRT the discussion on what happens transiently if you increase thrust at alphamax I can offer two partial explanations; the reality is probably some combination thereof.

If you add thrust you will, of course, get a nose up pitching moment. In steady state conditions to maintain AOA constant this additional pitch has to be balanced by a nose down pitch from the tail. This means a reduction in tail download so there will be an increase in TOTAL aerodynamic lift even if AOA stays constant. In addition of course you will get an increase in total vertical force from the vertical component of the increased thrust.This is why Vs1g is established with idle thrust.

In the transient the increased thrust will cause the aircraft to pitch upwards and the EFCS will react to this changed pitch rate by applying down elevator (or more accurately will reduce the amount of up elevator) and the mechanism described above will come into play. So the total vertical force will be increased a little by increasing thrust even at constant AOA and airspeed.

The other explanation, which I think would be more powerful, rests on the fact that alphamax is not a 'hard' limit. The generation of wings we are discussing does not have an abrupt 'stall' [I cannot answer for the latest generation with sharklets or curved up winglets/wing tips; they may well have different characteristics]. The likes of the A320 start to have flow breakdown somewhere near midspan and this spreads outboard and inboard as AOA is increased above this point. This is true for both the clean aircraft and with flaps deflected. It is the buffet produced by these separations that becomes the limit to useable lift. In effect alphamax is almost a subjective limit, although formally it may be defined by the level of buffet 'g' at the pilot's station reaching a set level.

Now the aircraft is not going to fall out of the sky, or the simulator come off its mountings if the buffet temporarily goes up a little - assuming that is that the simulator has realistic buffet reproduced anyway. Consequently, there will be a margin of AOA available, but not available for general use, beyond alphamax.

Any closed loop control system will need to preserve some margin between the nominal system maximum and any genuine physical limit. The margin will depend on the nature and consequences of that physical limit. If it is a potentially catastrophic 'cliff edge' limit then the margins will need to be carefully set but if it is, as here, a 'soft' limit then one can be a little more relaxed.

To judge by the Gordon Corps video, AI are quite happy to see AOA go as high as 17 deg with full flaps even though the maximum usable AOA is set at 15 deg.

[HazelNuts39]

That's how the alpha protection has been designed.
At full back stick the elevators are all for the AoA control to maintain it at alpha max.That is correct - it is not designed to maintain airspeed. But never mind, OK465 has settled that aspect. Apparently the speed variation is only a few knots for the magnitude of the thrust increase and the rate of change involved.

P.S.
With the natural phugoid period being approximately 28 seconds the speed variation of 'a couple of knots' in that period would be quite slow so it would easily go unnoticed.

[CONF iture]

Any variation of thrust needs to be manually commanded.
And the problem is ... ?

The EFCS *targets* Alpha Max with the stick fully aft - it doesn't *guarantee* it.
A properly flown alpha max demo will deliver alpha max, what make you think the FCS would not comply ?

In effect, that's correct, and for the PF to expect the PNF to do that for him would be impracticable.
I disagree on that as well. For the PF to maintain full back stick for a while is not of all comfort. If he wants to concentrate outside, I find it practicable for the PNF to stay inside and manage thrust versus v/s.

To judge by the Gordon Corps video, AI are quite happy to see AOA go as high as 17 deg with full flaps even though the maximum usable AOA is set at 15 deg.
That's why it is surprising in the Habsheim case, as alpha max was set at 17.5 deg and thrust reached 83% N1, the elevator had no intention to deliver anything closer than 2.5 deg short of alpha max ...

[Owain Glyndwr]

@Confiture

Well of course the elevator doesn't have an intention to deliver anything; it is merely the servant of the control laws. So far as those are concerned the behaviour is not really surprising - you should read the Bilboa report where it says:

Additionally, in these high angle of attack situations, with a tendency towards phugoid movement, studied by longitudinal stability, in which the aeroplane oscillates between two kinetic and potential energy levels, the EFCS behaves as a damper of the oscillations, commanding appropriate variations of angle of attack in a way that, when the aircraft is slowing down, makes it pitch downward and vice versa,"IIRC in the Habsheim accident, the aircraft was still losing speed up until one second before collision with the trees. Although higher power had been commanded, it was simply set too late to arrest the deceleration and remove the damping correction in time for pilots demand for higher AOA to be satisfied safely and in time.

[Chris Scott]

Hi OK465,
Thanks for your detailed, hands-on sim reports. Just to pick up on one:

"The jam engine accels or decels seem to cause the largest AOA variations (both below and above depending) from the stabilized alphamax value, but still resulting in no more than a couple knots above Valphamax on the thrust increases or dipping a couple of knots into the red band on rapid thrust reductions before the available FCS actuated elevator (and AOA control) gets things back under control at Valphamax."

You describe the IAS as varying above or below Valpha-max by "no more than a couple of knots". But did you notice whether the Valpha-max itself remains constant, or if it varies slightly with load factor and/or FPA?

Quote from CONF_iture:
"For the PF to maintain full back stick for a while is not of all comfort. If he wants to concentrate outside, I find it practicable for the PNF to stay inside and manage thrust versus v/s."

So, starting from straight-and-level at alpha-max, let's look at the control of the flight path:
the PF controls bank and can initiate a descent (intentionally or accidentally), but not reverse it;
the PNF controls climb and descent, provided the PF doesn't interfere.

Interesting work-share arrangement, 100ft above the ground. I suppose it might have worked.

[Chris Scott]

Quote from OK465:
"The first obvious change in Valphamax occurs when your wrist gets sore and push forward on the SS resulting in Valphamax noticeably decreasing as the aircraft is unloaded. http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/badteeth.gif "

Yes, perhaps you need to alternate between seats! (Being right-handed, I tended to over-control initially on my occasional visits to the R/H seat.) Any further info on variations in Valpha-max (or lack of) would be most helpful.

Returning to the planned Habsheim flypast (at alpha-max, with thrust effectively controlling VS/FPA while the EFCS adjusts pitch to maintain Valpha-max), I've had another look at the degree of control available to the "PF". As you say, if his wrist gets sore and he releases the stick, the a/c pitches down to target the new AoA that the stick has commanded. If the PNF leaves the thrust constant, the IAS will increase to a figure higher than the 1g-Valpha-max. So, as the PF pulls the stick fully back again, there will be a slight excess of IAS available to flare the a/c as the alpha-max is restored. Until the speed bleeds off again, the lift will be higher than before the disturbance, enabling a climb. In other words, it's the old story of potential energy being converted to kinetic, and then back to potential again.

However, the above scenario illustrates the potential for dis-coordination between the two pilots. As Confit says, the PNF's task is to adjust thrust to keep the VS zero. The PF has initiated a descent by allowing the stick to move towards neutral, but the PNF doesn't know that. Therefore, observing the undesired descent, he is likely to increase the thrust just as the PF is flaring the a/c. The thrust increase will have to be reversed immediately if the a/c is to be prevented from overshooting the 100 ft target height because of the increase in total energy.

Had this pilot-duo ever practised the manoeuvre ensemble?

[Linktrained]

In #410 I did suppose ( with no evidence )


" This may have been a display which had been practiced a number of times successfully, perhaps along a standard R/W...
If there were no trees."


To add dual control, with only the PNF able to increase altitude... And at 100ft ( or could we allow 46ft R ?) might be overstressing the co-operation of the two pilots... without their having had a lot of practice.


And their awareness of the trees.
LT

[CONF iture]

you should read the Bilboa report
Interesting you mention Bilbao as the part you did highlight is applicable to pretty turbulent conditions on final approach phase below 200 ft RA when the aircraft encountered strong and changing vertical and horizontal gusts while descending at a rate of around 1,200 ft/min ...

How smooth was Habsheim ...

So, starting from straight-and-level at alpha-max, let's look at the control of the flight path:
the PF controls bank and can initiate a descent (intentionally or accidentally), but not reverse it;
the PNF controls climb and descent, provided the PF doesn't interfere.
In Habsheim, as the airplane was never slow enough to get to alpha max for the flypast, the altitude control through thrust management by the PNF did not come to the point it was applicable.
Thrust management by the PNF for vertical speed control during a more conventional alpha max presentation by Airbus is surely a good idea and I'm not too sure what you find 'impracticable' about it ... ?

[HazelNuts39]

Just to illustrate what I had in mind when I wrote about a phugoid in post #493.

The following graph shows the variation of speed and height that would result in the following conditions:
- the airplane is initially in level flight at a constant speed of 110 kts TAS
- at t=0 thrust is instantaneously increased to that required for stabilized climb at a flight path angle of 8.5 degrees
- after t=0 thrust and drag are constant and both act in the direction of the flight path, i.e. no thrust component normal to the flight path
- angle of attack is constant, i.e. no damping
- the variation of air density is negligible

This is of course entirely theoretical, but it illustrates the effectivity of the artificial damping in OK465's simulator exercise, combined with the effect of increasing thrust in 2-3 seconds instead of instantaneously and of the thrust component normal to the flight path.

It also illustrates the fundamental difficulty of controlling the flight path with thrust alone, without the ability to control angle of attack.

P.S.
The graph illustrates the point I made in the discussion: the acceleration starts immediately, the flight path changes after some speed increase.

http://i.imgur.com/27eDzJY.gif?1

[Owain Glyndwr]

Originally posted by Confiture

How smooth was Habsheim ...

I am really unsure what point you are trying to make here. AFAIK the same alphaprot law applies no matter what the atmospheric conditions.

Could you please explain what relevance the conditions pertaining to Bilbao have to the behaviour of the system in Habsheim?

[CONF iture]

AFAIK the same alphaprot law applies no matter what the atmospheric conditions.
Apparently Airbus thought otherwise as following Bilbao they developed a new standard for the ELAC, standard L81, to modify the logic in the AOA protection in case of turbulent conditions.

[DozyWannabe]

The post-Bilbao changes related to the phugoid-damping logic, not Alpha Protection. There were no "turbulent conditions" at Habsheim, nor did the EFCS pitch commands at Habsheim reflect what happened at Bilbao.

[Owain Glyndwr]

Originally posted by Conf_iture

Apparently Airbus thought otherwise as following Bilbao they developed a new standard for the ELAC, standard L81, to modify the logic in the AOA protection in case of turbulent conditions.
True, but if you have read the Bilbao report you will also have been aware that the modification was a deletion of the phase advanced AOA term that was part of the logic that triggered entry into the alphaprot mode [and a change to the logic of alphaprot deselection, but that is not relevant here], not a change to the basic alphaprot laws themselves.

You may also know that this post Bilbao change was actually a reversion to the standard that was applicable at Habsheim.

Air Safety Week July 18 2001
The other aspect governing alpha protection is the rate at which AOA is allowed to change before reaching the protection limit. The alpha protection is triggered by two combined conditions: a threshold AOA and the rate of AOA change. To change the outcome in dynamic wind conditions near the ground, Airbus plans to modify the software to eliminate pitch rate as a controlling factor in alpha protection. In plain language, with the rate of change in the value of AOA being removed, the modification basically reverts the software to an earlier standard where pitch rate was not part of alpha protection (the pitch-rate limitation was installed as a result of post-1988 flight tests).
Despite what Dozy has written I have seen nothing to suggest that the basic phugoid damping terms in alphaprot have ever been changed, (and anyway the phugoid damping is an intrinsic part of alphaprot so his remarks make no sense). Consequently I see no reason why the point I was emphasising:

the EFCS behaves as a damper of the oscillations, commanding appropriate variations of angle of attack in a way that, when the aircraft is slowing down, makes it pitch downward and vice versashould not be a valid explanation of the reason why alphamax was not developed at Habsheim. I repeat - the necessary thrust increase was applied too late.

[fizz57]

Owain, you and Dozy are more or less saying the same thing in different words.


A rate factor in the feedback loop provides a damping function - think "D" in a PID controller.


Fully agree with your conclusion though, and glad to see some consensus emerging through all the smoke put up about this affair. Great thread people and thanks from a mostly-lurker for all the info and discussion.

[Owain Glyndwr]

Fizz,

I didn't think Dozy and I were saying the same thing, because he was suggesting that the phugoid damping logic was changed and I am suggesting that it wasn't.
Nice to know that you agree with the conclusions though.
I think that rate of change of AOA signal was in the forward loop not the feedback. The feedback loop I believe still includes pitch rate as a damper.

[Linktrained]

Owain Glyndwr,


" Necessary thrust increase was applied too late..."


Or too low ? Or both ? The planned height was supposed to be 100 ft.

(I do not recall the actual height of the trees.)

[Owain Glyndwr]

Linktrained

A fine distinction!

As a non-pilot I would have said he was flying too low and left it too late. so I suppose my answer is "both".

The BEA report gives the average tree height as 12m (39ft)

[gums]

Interesting graph, Nuts

Although the magnitude of the phugoid seems a bit large, we still see a very rapid increase in FPA and climb rate.

I bet that the pilot would have donated vital parts of his anatomy to gain 100 feet in about 1300 feet of horizontal travel, ya think? 7 seconds at 115 knots +/-

[Linktrained]

O. W.


Thank you for the tree height. Perhaps this was not clear enough to whoever planned this flight.


( Someone born in the late 1840s advised her R.F.C. pupil pilot son "not to fly too high or too fast"... Probably she was thinking of 20 ft. and 20 mph. would be enough. Advice which he did not follow !)

[HazelNuts39]

Hi gums,

the magnitude of the phugoid oscillations is a function of the thrust change from that required for level flight. If thrust had been set for a gradient of 4 degrees the amplitude of the speed oscillation would have been halved and 100 ft achieved after 10 seconds.

A gradient of 8.5 degrees with landing flap and gear down near stall speed is quite healthy for a transport airplane.

[gums]

Good points, Okie.

I also remind folks of Sioux City and the Carmel accidents where the crews used only power once they established a "trimmed" AoA/airspeed that the plane "liked".

I gotta tellya, if we gave out a "Medal of Honor" for airline pilots, the Constellation pilot would have been a sure fire recipient. He was the last troop to try leave the plane once he did his duty to the pax. Sully stayed behind and made it, this guy didn't. Amazing the survival rate.

1965 Carmel mid-air collision - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/1965_Carmel_mid-air_collision)

[Saint-Ex]

Strange how we ignore OO-DLL at Baghdad. Perhaps because "it was just a cargo flight." The crew had to cope with an A300 severely damaged on the left wing by a missile strike so causing extra drag from the damage and still landed at BIAP at less than 2g. A DH structural engineer estimated the wing would have departed after a further 20 minutes.

[DozyWannabe]

@OG - I stand corrected, my apologies.:oh:

[CONF iture]

Consequently I see no reason why the point I was emphasising :
"the EFCS behaves as a damper of the oscillations, commanding appropriate variations of angle of attack in a way that, when the aircraft is slowing down, makes it pitch downward and vice versa"
should not be a valid explanation of the reason why alphamax was not developed at Habsheim.
Simply because you omit the necessary initial conditions :
"Additionally, in these high angle of attack situations, with a tendency towards phugoid movement, studied by longitudinal stability, in which the aeroplane oscillates between two kinetic and potential energy levels"
Such oscillations were taking place in Bilbao due to atmospheric disturbance.
It was not the case in Habsheim.


Air Safety Week July 18 2001
To change the outcome in dynamic wind conditions near the ground, Airbus plans to modify the software to eliminate pitch rate as a controlling factor in alpha protection.
Again, you omit to take in consideration the initial conditions : "in dynamic wind conditions"
Was it the case in Habsheim ?

I bet that the pilot would have donated vital parts of his anatomy to gain 100 feet in about 1300 feet of horizontal travel, ya think? 7 seconds at 115 knots +/-
He didn't need 100 feet but just a tenth of it to survive the situation he put himself in and come back for a landing. It was all in the aerodynamics with still 2.5 deg to grab to get to alpha max and engines already at 83% N1.

[awblain]

The tweak to the flight control laws that damps the phugoid oscillation seems wholly irrelevant to the Habsheim situation. It's also seems irrelevant to Bilbao. A control input to ensure the smooth gain of height on a 20s timescale isn't going to put someone into a hole they're flying towards.

"due to atmospheric disturbance"… then including the tweak to the flight control or otherwise won't stop it. It's not going to make the oscillations worse.

At Bilbao, if the aircraft is being pitched around so that it enters a protection mode, then it's possible that at least briefly it needed protection - not smoothing the flight path, but avoiding stall. This might have caused it to impact the ground, but what if it had been allowed to stall and crash instead?

Is it wise to fly either into a forest, or into horrible record-setting windshear? A non FBW aircraft wouldn't help you in the circumstances either, unless you recognize the impending doom early enough, and maybe the A320 improved the situation in terms of reducing the number of pieces of wreckage to sift.

Would it be possible to argue that without a yaw damper someone might have squeaked themselves out of a particular sticky fix they'd embedded themselves into? Overall, is it a bad thing to have this mechanical protection?

[Owain Glyndwr]

Originally posted by Con_fiture

Simply because you omit the necessary initial conditions :
"Additionally, in these high angle of attack situations, with a tendency towards phugoid movement, studied by longitudinal stability, in which the aeroplane oscillates between two kinetic and potential energy levels"
Initial conditions are irrelevant - the system must be stable for any initial condition and in any atmospheric conditions.

If you want confirmation that phugoid oscillations between two kinetic and energy levels can exist without there being any turbulence just look at the graph that HN39 posted recently. That had at best neutral stability and had no additional phugoid damping - there was no turbulence present. It shows why the phugoid damping terms are necessary.

The point about the software changes made after Bilbao, which you seem to have misunderstood, was that they were made to prevent unnecessary engagement of Alpha Protection in turbulent conditions. The laws that govern the motion once Alpha Protection is engaged have been unchanged from the word go. Other than the logic governing the point of entry into alphaprot the same laws were in place at Habsheim as at Bilbao.

You are simply adding confusion by trying to conflate the two events.

You seem to be using the fact that the system description I quoted came out of the Bilbao report to suggest that it ( the system description) is somehow not applicable for Habsheim. Can we go back to discussing that accident and maybe you could tell us where/why you think the system as described in the Bilbao report, especially that part that describes the effect of speed feedback does not apply for Habsheim? For example, do you have any positive evidence that the basic laws were changed after Habsheim and before Bilbao?

[roulishollandais]

Dear Owain,
You are simply adding confusion by trying to conflate the two eventsIt is easy to be confused when theory of systems are not very familiar. Many pilots and engineers would be happy, feel much more comfortable, and work safer by increasing mutual transdiscipliniraty despite it needs, once again, a sharper selection, and still more time for formation.


Theory of systems and pluridisciplinarity help in all domains of modern life. Isn't ? :)

[HazelNuts39]

Such oscillations were taking place in Bilbao due to atmospheric disturbance.The phugoid oscillation as such has no relation with atmospheric disturbances. The initiating disturbance can be anything, a gust, longitudinal control input, thrust increase ...

QUOTE (http://adg.stanford.edu/aa241/stability/dynamicstability.html)
Phugoid

The long-perioid of phugoid mode involves a trade between kinetic and potential energy. In this mode, the aircraft, at nearly constant angle of attack, climbs and slows, then dives, losing altitude while picking up speed. The motion is usually of such a long period (about 93 seconds for a 747) that it need not be highly damped for piloted aircraft. This mode was studied (and named) by Lanchester in 1908. He showed that if one assumed constant angle of attack and thrust=drag, the period of the phugoid could be written as: T = p V2 U/g = 0.138 U. That is, the period is independent of the airplane characteristics and altitude, and depends only on the trimmed airspeed.P.S.
The formula for the period should read: T = π*√2*U/g, where U is the trimmed airspeed (TAS) and g the acceleration of gravity. With U in ft/s the period in seconds is T=0.138*U .

[Owain Glyndwr]

Dear Roulis

I would be very happy to work towards a better mutual understanding between engineers and pilots - I have been trying to do that all my working life.
But I have found that one essential element for success is that we listen to one another - and yes, I know that is a two edged sword.:D

[gums]

I am with OG on discussion, protocol and such.

@Nuts

How can you "trim" to TAS?
Secondly, what is happens to phugoid phenomena when thrust is greater than drag? I would imagine it would be there, but the time constant/perios/amplitude would be interesting.

I did not get a major in aero, only had the so-called "general" engineering degree, but had maybe 20+ semester hours of thermo and aero and related. Then many hours of physics, chemistry, astro, mechanics, EE, computer science and even civil engineering.

I flew 6 different jets and saw many things that verified about all of the theories I had been taught. But I never had a course about human performance until I actually flew the jets. And that course had very harsh results if you got an "F". Also flew the first "pure" FBW operational jet in the world, while recognizing that a large portion of the Concorde flight control system was FBW. In my little jet, if the electrons went away it was a nylon let down, or worse.

Since I jumped in here with AF447, I have learned an awful lot about both technical and human factors for the commercial pilots. I appreciate all of your acceptance of my "contributions.

[HazelNuts39]

gums,

How can you "trim" to TAS?You trim to CAS or Mach, then calculate TAS to find the phugoid period.
Secondly, what is happens to phugoid phenomena when thrust is greater than drag?It's shown in the graph I posted recently. AFAIK the period does not change, but the natural damping could be different if thrust changes with airspeed.

[gums]

@ Nuts

I can see "trimming" to a CAS/AoA, but not a mach or TAS. For a small altitude delta, the TAS or mach would not vary much. I only flew 2 jets that had a "mach hold" using otto ( F-102A and F-101B) , otherwise we humans had to maintain the mach for our climbs or level flight. In my 1800 hours +/- in straight-wing jets with no otto, I never noticed the phugoid once I had the sucker trimmed. Well, maybe +/- 50 feet and 1 or 2 knots until I had the thing nailed.

I saw your neat graphic for the phugoid, but seems the condition for the model was thrust equals drag. So my question is, "what happens when thrust is greater than drag", especially for a go-around that should have been executed in the incident? I would have preferred a graph of unrestricted FPA using the configuration and commanded gee/AoA.

As with others here, I think the phugoid considerations for the 'bus FCS had negligible effects upon the incident. However, I was surprised that the jet even had some phugoid elements to the laws. Always learning, ain't we?

[HazelNuts39]

I saw your neat graphic for the phugoid, but seems the condition for the model was thrust equals drag.I described the initial condition as level flight, constant speed, i.e. thrust equal to drag. What matters for the phugoid is the thrust set at t=0, which exceeds drag by sin 8.5 degrees times weight.
I would have preferred a graph of unrestricted FPA using the configuration and commanded gee/AoA.Sorry, but I must be misunderstanding what you are saying here. The FPA is unrestricted and the graph is independent of configuration. The only 'aerodynamics' that goes into the calculation is the fact that at constant AoA lift is proportional to airspeed-squared. "gee" is not commanded but is proportional to airspeed-squared. AoA is 'commanded' to remain constant throughout.
As with others here, I think the phugoid considerations for the 'bus FCS had negligible effects upon the incident.What matters is not the phugoid but the control law that reduces the commanded AoA when speed decreases and/or pitch increases.

[gums]

@ Nuts

Sorry, but I must be misunderstanding what you are saying here. The FPA is unrestricted and the graph is independent of configuration. The only 'aerodynamics' that goes into the calculation is the fact that at constant AoA lift is proportional to airspeed-squared. "gee" is not commanded but is proportional to airspeed-squared. AoA is 'commanded' to remain constant throughout.

Yeah, my understanding of the plots was an 8 degree FPA or so. No biggie. I fully understand the relationships between AoA and lift and velocity.

My concerns are that many folks don't understand the actual relationhips of the gee command versus the AoA once at the "limits". You can command all the gee you wish, but the jet will only give you so much due to the FBW control laws. Been there, done that.

Thanks for the civil discourse. And out.

[Owain Glyndwr]

Originally posted by awblain

The tweak to the flight control laws that damps the phugoid oscillation seems wholly irrelevant to the Habsheim situation. It's also seems irrelevant to Bilbao. A control input to ensure the smooth gain of height on a 20s timescale isn't going to put someone into a hole they're flying towards. It's not really irrelevant to Habsheim because although the longer term effects of the 'tweak' could not affect the motion very much in the short time available the speed feedback that provides some of the phugoid damping became operative as soon as Alpha Protect mode became active. Seeing the steady loss of airspeed during the last few seconds this term led to a nosedown signal which offset the pilot's command for more AOA and restricted the aircraft to 15 deg AOA rather than the 17.5 deg of alphamax. As I understand it, it is this restriction that Confiture claims to be a factor in the aircraft striking the trees. The significance of holding AOA below alphamax is best established by a performance discussion rather than one on the system design. As gums has pointed out, when flying close to the aircraft lift limits the available gee for a pull up is very limited.

[awblain]

OG,

OK, but in both cases, if the alternative was a stall, avoided by the system, rather than a flying impact with the ground/trees, I'm not sure that would have been better. Almost everyone did walk away.

Could either crew have honestly said "if only we'd had another 1.5 degrees, our finely planned and executed manouevre would have been a spectacular success."

It's also not clear that the phugoid is avoided by changes to the early control actions, or as it builds a few seconds later. Making a legal excuse based on the flight control systems action just suggests you'd be vulnerable to the question "So, Capt. Asseline, did you know this about the flight control software you were using before you crashed at Habsheim?"

[rudderrudderrat]

Could either crew have honestly said "if only we'd had another 1.5 degrees, our finely planned and executed manouevre would have been a spectacular success."

It's a bit like the Costa Concordia (Costa Concordia disaster - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Costa_Concordia_disaster)) crew saying, "If only we had turned 50 feet earlier".

One has to ask, "why push so close to the limits?"

[Owain Glyndwr]

awblain

Don't get me wrong, we are on the same wavelength. I am only pointing out a mechanism whereby the observed AOA restriction can be explained. Whether it made any difference is another matter. When you write:

Could either crew have honestly said "if only we'd had another 1.5 degrees, our finely planned and executed manouevre would have been a spectacular success."my answer is no. It would have been possible to gain a little more height at the expense of speed if the AOA had followed the pilot's command without any restriction but keeping sidestick movement and timing and throttle movement and timing unchanged, the height gain at the back end would have been no more than half of that required for clearance. Let us remember that the RA height over the last few seconds was only 30 ft and the average tree height 39ft.

[noske]

For some reason, the "Rapport final (additif)" (starting at page 55) consists of odd-numbered pages only, with blank pages in between. So annexe 7 may just have been on one of those even-numbered pages.

That should be easy to verify with a printed copy of the Journal Officiel, volume 1990. (A brief search across libraries in Germany, for example, already seems to indicate seven such copies.) Did anyone ever bother?

Well, now I did. Since none of these libraries was close enough for me to make a visit in person, I made an interlibrary loan. For journal articles, these are routinely handled by copying (which today means scanning, file transfer, and printing at the receiving library).

I received my copy of the "Rapport final (additif)", consisting of odd-numbered pages only, with a handwritten note attached that mentioned a complaint about missing pages, answered by the supplying library (Deutsche Zentralbibliothek für Wirtschaftswissenschaften, Kiel) with an affirmation that they scanned the article as it is.

So regarding preparation of the PDF from the printed "Journal Officiel", I'd say that the BEA did the best they could. Annexe 7 must have gone missing at an earlier stage.

And I'm glad to see that the discussion has already returned to technical matters anyway. :ok:

[Chris Scott]

Quote from Owain Glyndwr (my emphasis):
"Let us remember that the RA height over the last few seconds was 30 ft, the lowest point on the airframe would have been less than that because of the attitude and the average tree height was 39 ft."

For what it's worth, I think not, OG. The two RA TRx antennae are (were) on the bottom of the rear fuselage, around the beginning of the taper point. At an a/c pitch attitude of about +13 or +14 degrees, they are at the same level as the bottom of the main L/G wheels. However, IIRC, the indicators read zero if the a/c is parked on level ground (pitch zero), when the antennae are about 5 ft high. If that is so, the indications are likely to under-read increasingly as the pitch attitude increases, unless there is a correction for changing pitch.

[Owain Glyndwr]

@ Chris Scott

I stand corrected :O

So that means that the recorded RA height was close to being the lowest point on the aircraft? Still well below tree height though

[awblain]

OG, I agree: I think we do agree.

But, the manufacturer sets the flight control rules to seek the best and safest outcome in the operations they foresee.

Should there be a "I'm a test pilot, get me out of here; let me fling it around the sky beyond the physical limits" button across the fleet? Probably not, since non-test-qualified people would surely push it, and get into more trouble. I'd suggest that the skill to train for is to know how the different nature of a FBW airliner means you have to be differently careful. Over many many contributions, I remember Capt Scott has pointed out lots of cases where these differences matter.

Quite the same with the Concordia, as r..t suggested - even of the helmsman had steered counterintuitively left as supposedly instructed, it wasn't going to make the evening's sailing suitable fare for a masterclass in ship handling, even if it might have saved a few tens of lives, and avoided putting 4000 in so much jeopardy in that particular case.

Spot on, the altimeter antennas are at the back. At that point of detail though, it does merit some wariness about the texture, reflectivity and slope of the ground across the radar altimeter beam, the attitude of the aircraft and the chance for stray reflections.

[Chris Scott]

Hello OG,

Yes: more or less. At a pitch attitude of +13.5 deg on T/O (main L/G oleos compressed), most of the length of the tapering part of the rear fuselage scrapes along the runway, and the RA antennae are just forward of it. If my tentative theory is correct, the RA readings in the cockpit at the same time would be a small negative value - perhaps -5 ft. I seem to recall receiving small negative RA readings momentarily on normal take-offs and landings.

So it's possible that the latter RA readings from the DFDR are a few feet lower than the lowest part of the a/c.

BTW, the pilot's eye level at the above pitch attitude (+13.5 deg) is about 27 ft above the lowest point of the a/c.

FWIW, the cockpit cut-off (visual) angle is 20 deg, i.e., the nose prevents the pilots seeing objects straight ahead which are lower than 20 deg relative to the longitudinal axis of the a/c.

So at t -11 - a couple of seconds after level-off, and at a pitch attitude of +12 - any object straight ahead which was more than 8 deg "below the horizon" would not have been visible. The recorded RA was +38 ft. Using the logic of my argument above, the pilot's eye height would have been about 25 ft above the main L/G, which itself would have been about 42 ft high. That makes the pilot's eye height about 65 - 70 ft above the ground.

[CONF iture]

At Bilbao, if the aircraft is being pitched around so that it enters a protection mode, then it's possible that at least briefly it needed protection - not smoothing the flight path, but avoiding stall. This might have caused it to impact the ground, but what if it had been allowed to stall and crash instead?
Don't panic with the stall scenario, at 10 deg of AoA they were just not there yet.
And if you think 4.5 G is not a ground impact, then what is an impact ... ?
Lack of pitch authority in short final was the problem.

Seeing the steady loss of airspeed during the last few seconds this term led to a nosedown signal which offset the pilot's command for more AOA and restricted the aircraft to 15 deg AOA rather than the 17.5 deg of alphamax.
I have nothing against you wanting to state why alpha max was refused in Habsheim, but don't you think that was a task and duty for the BEA to endorse in the first place ... ?
That being said :

1kt/sec deceleration is nothing extraordinary and is precisely the deceleration rate recommended to adopt for testing the protections or voluntarily approaching the stall. The nose down signal in Bilbao was triggered by loosing 13kt for a 2 sec period.
Last second of speed data shows already an acceleration.
Engines were at 83%N1.

Everything was in place to benefit from the widely advertised wonder of alpha max and not simply straight fully fly into the forest.

[CONF iture]

It would have been possible to gain a little more height at the expense of speed if the AOA had followed the pilot's command without any restriction but keeping sidestick movement and timing and throttle movement and timing unchanged, the height gain at the back end would have been no more than half of that required for clearance. Let us remember that the RA height over the last few seconds was only 30 ft and the average tree height 39ft.

5 ft gain and the aircraft is probably back but not without leaves in the landing gear.
10 ft gain and the aircraft is back.


The phugoid oscillation as such has no relation with atmospheric disturbances.
Except that the system can interpret the external disturbance as a phugoid movement, which can result as in Bilbao in an automatic nose down input that the pilot cannot counteract.

So regarding preparation of the PDF from the printed "Journal Officiel", I'd say that the BEA did the best they could. Annexe 7 must have gone missing at an earlier stage.
As the crucial Annexe 7 is missing but part of Annexe 8 has been labelled Annexe 7 I see here a deliberate attempt for camouflage.

[Owain Glyndwr]

Originally posted by Con_fiture
5 ft gain and the aircraft is probably back but not without leaves in the landing gear.

10 ft gain and the aircraft is back.


5 ft gain - maybe; but it is a bit speculative isn't it? At a pitch attitude of 17 deg the elevator hinge and the lowest point of the gear are at the same height, so with a 5ft gain you are just as likely to end up by tearing the elevators off accompanied by a vicious ND pitch and no hydraulics.

10 ft gain - again maybe - the AVERAGE tree height was 12m (39ft) so you have something like a 50% chance of going clear.

[Owain Glyndwr]

Originally posted by Con_fiture

Everything was in place to benefit from the widely advertised wonder of alpha max and not simply straight fully fly into the forest.Everything that is except time and space for the system to do its job

[roulishollandais]

1. From the CVR it is unclear if the F/O understood that Asseline wanted to fly at 100 FT height . He acted how if he understood 100 FT RA.

Final report Habsheim : Journal Officiel Documents administratifs Année 1990 N°28 Mardi 24 avril 1990 ISSN 0242-6773

12 h 30' 20" CDB Bon alors, décollage, virage à droite, on laisse le volet 1, enfin on fait un décollage normal, on rentre le train et avec les volets 1, tranquillement on va chercher notre truc. Dès qu'on l'a formellement identifié, on sort la tôle jusqu'à volets 3 train sorti, 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.

12 h 30' 59" CDB Et alors après on rentre toute la tôle, on s'éloigne, on s'accélère comme des bêtes à 340 noeuds et le deuxième tu te le passes aussi à 100 pieds, et là, c'est pas la peine de leur foutre 2,5 g dans la gueule parce que derrière, y vont pas aimer.


2. Nowhere do I find the reference to alpha prot ? (12° in Asseline's book)

[Chris Scott]

Bon soir roulis,

Because my French is faible, I still have not finished Mr Asseline's book!

1) I also see nothing in the captain's briefing to stipulate (sorry!) which instrument would be used to maintain 100 ft. But, long after the flight, Mr Asseline explains it very clearly to all his readers, and he makes at least two good arguments for not using the RA. Unfortunately, as you know, baro indications are not accurate enough for his stated purpose.

But, whatever the co-pilot thought the captain meant, the a/c does not seem to have been levelled at 100 ft on the barometric altimeters - and certainly not on the radio altimeter. So it seems strange that the copilot made no call after the height-bust.

Here is a part of your quote from le Rapport Final BEA:
" '[...] 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.' "

This is my rough understanding of it:
"[...] one does a pass at a hundred feet, gear extended and there, you leave it to me. I get you to alpha max, I disengage alpha floor and at that point, if I tell you that it's too hard, you help me and you [adjust] the thrust at [for] V/S zero."

The captain goes on, if I understand the transcript correctly:
"...V/S zero and me, I'll hold alpha-max. At the signal, you [select] TOGA and me, I pull, and if you are there I bank away."
Co-pilot:
"You want to make to shine [?] there, eh?"
Captain:
"[?] there. I've done it twenty times, that one."
Co-pilot:
"OK, agreed."

That brief dialogue leads me to think that the co-pilot was not familiar with the technique that he was being briefed to perform. If he had done it before, I reckon he would have said so - if only in response to the captain's boast. However, CONF_iture seems to think that this task assigned to the co-pilot was a cinch. I wonder.


2) I do not understand your point at the moment. Was there any need to define alpha prot in the briefing?

[roulishollandais]

1. Finaly I found in the Final report §1.16.1.2 the reference to "Alpha Prot". But the report says the incidence of alpha prot is 14.5°. That point is reached at tgen 333.0-334.0 , speed was 114 kt
Asseline says alpha prot incidence is 12° (page 420 of Asseline's book) . That point was reached a tgen 326.0 (speed was 120 kt).
Twelve seconds separate these two points.

In the report we find one time "alpha prot", and six times the word "incidence" concerning alpha prot 14.5° : "loi d'indidence" or "protection en incidence"

2. The Report §1.16.1.2 says that the end of the flight is done in alpha prot law " since t-4s :

"A t-4s, commutation sur la loi de pilotage en incidence, la valeur de 14.5° ayant été atteinte, cette loi étant ensuite conservée. (At - 4s, switching on the incidence law, thevalue of 14.5 ° has been reached, this law is then maintained)"

With alpha prot = 12° it would have been t-16s... (not better without thrust !)

Since alpha prot is reached, without thrust, I assume the EFCS modifies the THS to decrease incidence, and altitude is decreasing too :}

3. "100 FT" : What Asseline was asking to the F/FO was surely easy in any case (height or RA), but I think too they never trained that together. And the FO was unable to push the levers too.

[CONF iture]

5 ft gain - maybe; but it is a bit speculative isn't it? At a pitch attitude of 17 deg the elevator hinge and the lowest point of the gear are at the same height, so with a 5ft gain you are just as likely to end up by tearing the elevators off accompanied by a vicious ND pitch and no hydraulics.
No visible vicious ND pitch for at least 400 ft at 30 ft height through the forest so at 35 ft and climbing I think the elevators could have survived even better.

Everything that is except time and space for the system to do its job
If the system is that inefficient, better give the elevator control to the pilot when he needed to get alpha max ...

CONF_iture seems to think that this task assigned to the co-pilot was a cinch.
I can't remember saying it was a walk in the park but performing such presentation by assigning the thrust management to the PNF is a judicious move instead of exclusively relying on the PF.
Now if you want to suggest the Habscheim crew was ill prepared for such an ambitious and already highly questionable program ... I fully concur.

[Owain Glyndwr]

@Conf_iture

I think the elevators could have survived even better.

If you want to so speculate feel free....

better give the elevator control to the pilot when he needed to get alpha max ...

It was of course poor judgement on the part of a pilot that produced the problem in the first place.

[roulishollandais]

It is clear that that flight would not have been scheduled. Many people had to refuse it. But we had already seen such crazy flight in La Ferté Allais, over the Park of Vincennes, aso.
Belonging to a parachutists union, they sent me regularly SINCE YEARS before Habsheim to watch airshows around Paris to verify if parachutists jumping during the airshow had the legal license which was only the Professional parachutist license depending from DGAC, or a military order. Infractions (missing license is not nothing !) were the rule. They only sent me when we had the Notam who showed who was jumping the next morning.The Union President wrote a great number of letters to complain, to DGAC, to GTA, to PAF, to Préfets, to organisers of airshows too, etc. Everybody from these people signed clearance and NOTAM they knew illegal. DURING YEARS !
The evening of Habsheim crash I thought to all that work we had done for nothing. The Prefet in Colmar had allowed that flight, DGAC, AF, aso.
But it was the last time. After Habsheim the rules for airshows have been radicaly modified and verified, included the Paris Le Bourget Airshow.
and finaly our Union won at the Cassation Court (the highest level in France)

[roulishollandais]

@Paul :
Thanks to double the size of our PMs during your hardware maintenance... Are you?

@Others:
I wonder why Asseline want to fly his Airbus at "alphamax" and uses that word in his briefing?

Why doesn't he mention Alpha Prot? Both pilots seem to have approximative knowing of their plane?

Why is the value of Alpha Prot from the BEA final report for Alpha Prot incidence 14.5° and differs from Asseline's book shematic p.420 where Alpha Prot is 12° ?

From the same book, page 432, why does Bernard Ziegler requests to R.DEQUE, G.PICHON, B.BISSEY, P.BAUD an improvment of Alpha Floor to alpha 12° (14 feb 1990, two months after Bengalore) and the Habsheim final report is giving Alpha Floor =15° ?

How many degrees incidence are given in books today to A320 pilots and correspondant speed for steady level flight, in the conditions of Habsheim flight and MLW for :
- Alphamax?
- Alpha Floor?
- Alpha Prot?
- Vs1g?
- Vref?

[gums]

Thank you, Rouli.

I jump back in from the peanut "light" gallery.

Good grief, we can go over all the control laws for years. As Doze and I and others seem to agree, it wasn't the control laws that caused the crash.

- Why in the world would you fly past the crowd at the max AoA? I will bet $1,000 that only one or two folks there would understand what was being demonstrated, and only with a narrator describing what you were seeing.

- Why did you not practice one or two times for the demo? Sheesh. The T-birds and Blue Angels come in a day or two earlier and do two or more practice demos for the particular venue. Same for the Red Bull and other acrobatic pilots at an airshow. Called professionalism, airmanship, and more. You just don't improvise, period. We even had a military flight lead resign from his position after he made a mistake on a maneuver and got too low with his three wingies. Had the guts to call an abort, and no harm done.

- Mission briefing? What's that? No evidence from documents or testimony or whatever that the planned flyby was briefed in detail. If the captain was solo, I might have a better understanding. With another crewmember, it is beyond my understanding.

- If the approach to the flyby was not going as planned ( that's a joke, as there seemed to be no plan), then turn around and give some excuse and set up correctly.

Trust me, I did my share of buzz jobs in fighters. I even "planned" some. If things didn't "look right" I went home. This guy at Habsheim was a "showboat" and I am still not sure about what he was trying to demonstrate, especially with SLF aboard.

Sorry to rant.

[DozyWannabe]

@Others:
I wonder why Asseline want to fly his Airbus at "alphamax" and uses that word in his briefing?

Because that was the point of that part of the sortie as briefed.

Why doesn't he mention Alpha Prot? Both pilots seem to have approximative knowing of their plane?

Alpha Max is the maximum achievable AoA when in High AoA Protection mode, whereas Alpha Prot (the value) is the AoA it will achieve without additional back-stick. It follows that if his intent was to achieve Alpha Max, then Alpha Prot would not require coverage in the briefing.

What can be confusing to people who are not as obsessive over the technical details as many of us is that some parties, when referring to the *mode* that Airbus name in their own documentation as "High AoA Protection", abbreviate that name as "Alpha Protection".

The "High AoA Protection" mode and "Alpha Prot" value are two very distinct things, and should not be confused.

It should be noted that Airbus themselves do not, to the best of my knowledge, use that particular abbreviation in their technical documentation.

Why is the value of Alpha Prot from the BEA final report for Alpha Prot incidence 14.5° and differs from Asseline's book shematic p.420 where Alpha Prot is 12° ?

Honestly, I don't know - it would depend on the sources Asseline is using, particularly with regard to the publishing dates.

I'm also unsure as to what point Asseline is trying to make, as the AoA of the aircraft during the phase where the protection logic commanded nose-down elevator was a little over 15 degrees, which is in excess of both stated values.

From the same book, page 432, why does Bernard Ziegler requests to R.DEQUE, G.PICHON, B.BISSEY, P.BAUD an improvment of Alpha Floor to alpha 12° (14 feb 1990, two months after Bengalore) and the Habsheim final report is giving Alpha Floor =15° ?

Presumably because that request (which - if accepted - would have reduced the Alpha Floor AoA trigger by some three degrees) was made over a year after Habsheim. Alpha Floor behaviour is somewhat moot in any case, because A/THR (and thus Alpha Floor) was supposed to have been disabled in order to maintain Alpha Max at a steady altitude - and in the event was inhibited by allowing the aircraft to descend below 100ft RA.

How many degrees incidence are given in books today to A320 pilots and correspondant speed for steady level flight, in the conditions of Habsheim flight and MLW for :

If you look at the graphs posted earlier in the thread, degrees incidence (at least of the Alpha values) are neither specified nor annotated in Airbus's recent pilot documentation, and I'd guess that they weren't then either.

The graphs can therefore convey only a qualitative idea of how the High AoA Protection responds, and this makes sense for at least two reasons I can think of off the top of my head.

Firstly, production A320s are not fitted with an AoA gauge - and so to annotate the graph with precise values would be of little use to flight crews.

Secondly, and as the general direction of the thread has indicated, the values themselves represent only what can *possibly* be achieved - i.e. in optimum conditions. In the case of Habsheim, the aircraft was low, slow - and with the engines spooled down until far too late it was continuing to decelerate until possibly a second or so prior to impact. These are pretty much the polar opposite of optimum conditions, and in such events the systems will comply as best they can with what they have to work with.

There's also (IMO less important) the aspect that the precise trigger values may change due to operational experience and feedback from the line, as the A. Floor request you mentioned hints at, but the overall behaviour pattern will not. No need to republish the FCOM if the values aren't specified.

[noske]

Why did you not practice one or two times for the demo? Sheesh. The T-birds and Blue Angels come in a day or two earlier and do two or more practice demos for the particular venue. Same for the Red Bull and other acrobatic pilots at an airshow. Called professionalism, airmanship, and more. You just don't improvise, period.
An explanation for this puzzling lack of preparation is, once again, in Asseline's book, p. 22 - 26.

The year before, the Habsheim flying club had chartered an Air France Concorde for roughly the same job: A sightseeing round trip from and to Bâle-Mulhouse, including a flyby over the Habsheim airfield. This Concorde crew arrived a day early, parked their bird at Bâle-Mulhouse, picked up their rented car, drove out to Habsheim airfield, had a look at the grounds and chatted with those in charge, then drove back to their hotel. That's not exactly "practice", but far better than nothing, and probably would have saved the day for Asseline. He wasn't given such an opportunity, because everyone in his flight division was on a tight schedule, working to put the A320 into service.

Then the book has some written statements (made in the context of the internal investigation at Air France) by Monsieur R. Simon of AF flight operations, tasked with the preparation of the charter flight, and Captain André Groppo of the A320 flight division, to whom he presented the results of his work. Captain Groppo says (my translation): "Feeling M. Simon slightly worried about the fact of not having gotten into contact with the captain of the flight, I recall telling him that this crew was particularly qualified for this kind of flight and that there was no reason for him to worry." On which Asseline himself comments: "Alas! No way were we particularly qualified for flight shows."

Btw., the flight presentation as envisaged by M. Simon would have been first a flyby at 600 ft in clean configuration, then at 100 ft in landing configuration.

[roulishollandais]

Could Asseline refuse to do that scheduled flight, presold to the Newspapper l'Alsace and their readers, without to be fired by Air France ?

[DozyWannabe]

Could Asseline refuse to do that scheduled flight, presold to the Newspapper l'Alsace and their readers, without to be fired by Air France ?

Almost certainly. Asseline wasn't the only senior A320 captain at AF, so it would likely have simply passed to someone else on the duty roster.

Let's not beat about the bush here - Most indications (mainly thinking of the apparent confidence on the CVR) prior to the accident convey that Asseline was more than happy to operate the flight. His later (and IMO correct) view that the preparation was poorly handled seems to be a case of 20/20 hindsight.

[CONF iture]

It was of course poor judgement on the part of a pilot that produced the problem in the first place.
We all know that for a while, don't we ?
How does it justify to not look one step further ?
If you want to so speculate feel free....
Why speculation should be your exclusivity ?

In the case of Habsheim, the aircraft was low, slow - and with the engines spooled down until far too late it was continuing to decelerate until possibly a second or so prior to impact. These are pretty much the polar opposite of optimum conditions, and in such events the systems will comply as best they can with what they have to work with.
What would be the point to benefit from alpha max only in case of 'optimum conditions' ?
That's when you're in deep problem you want to rely on it and that's how Airbus is selling it.

I wonder why Asseline want to fly his Airbus at "alphamax" and uses that word in his briefing?
Asseline writes on Page 29 :
C'est dans cette ambiance particulière, très différente de celle du travail habituel d'un pilote de ligne, que j'ai reçu la mission de présenter cet avion à Habsheim. Il me semblait indispensable de le faire du mieux possible, en démontrant ses extraordinaires qualités de vol, tant vantées par son constructeur. La seule documentation de vol complète dont nous disposions était celle d'Airbus. Il y était écrit en toutes lettres que, si nous voulions utiliser l'avion en volant aux grandes incidences (c'est-à-dire à très faible vitesse), nous pouvions le faire, la seule condition étant de maintenir le manche à fond en arrière, les ordinateurs assurant la totale sécurité de la manœuvre. Les pilotes d'essai d'Airbus usaient et abusaient de cette caractéristique à chaque sortie publique de l'avion. Les pilotes en entraînement en recevaient la démonstration en tour de piste à Toulouse, au-dessus des agglomérations. Seul cet avion pouvait voler dans ces conditions en toute sécurité, les enseignements des pilotes d'essais nous confortaient dans cette idée. Le Titanic ne pouvait pas couler, l'A 320 ne pouvait pas décrocher (tomber par perte de vitesse).

[DozyWannabe]

How does it justify to not look one step further ?

Haven't we all been looking at least one "step further" for nearly 30 pages and nearly 600 posts now?

Why speculation should be your exclusivity ?

That makes no sense - OG's specifically inviting you to speculate there.

What would be the point to benefit from alpha max only in case of 'optimum conditions' ?
That's when you're in deep problem you want to rely on it and that's how Airbus is selling it.

"Optimum conditions" in this case meaning only enough airspeed and time for the systems to stabilise at or as near as possible to 17.5deg AoA. Asseline had neither, largely down to his own decision-making. The systems can't defy the laws of physics.

Airbus promoted the systems as being able to help pilots get themselves out of trouble, and in that respect they do. But by disabling A/THR/Alpha Floor or getting the aircraft so low that Alpha Floor is inhibited, a pilot is going outside of Airbus's recommended operation techniques and will therefore be responsible for the consequences.

Asseline writes on Page 29 :

Apologies for rough Google translation:
It is in this particular atmosphere, very different from the usual work of an airline pilot, I have been tasked to present this aircraft [at] Habsheim.
...
The test drivers were using Airbus and abusing [highlighting?] this feature each public release of the aircraft. Pilots received training in the demonstration lap in Toulouse, above cities.

Such equivocation stands in marked contrast to Asseline's confident attitude during the briefing on the CVR:

Bon alors, décollage, virage à droite, on laisse le volet 1, enfin on fait un décollage normal, on rentre le train et avec les volets 1, tranquillement on va chercher notre truc. Dès qu'on l'a formellement identifié, on sort la tôle jusqu'à volets 3 train sorti, 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.


where in response to a query from his F/O as to how to increase thrust and escape:

Tu veux t' faire reluire là-hein ?

he says:

Ben, ça. J' l'ai fait vingt fois, c'lui-là.

Which I believe is along the lines of "I've done this twenty times". If he had indeed done it twenty times over Toulouse, I strongly doubt he'd have been doing it at 100ft.

Note also this phrase in the briefing itself :
...je débraye l'alpha floor et à ce moment là...

Which clearly indicates that his intent *was* to disable Alpha Floor, and it seems he missed it in the event.

[CONF iture]

"Optimum conditions" in this case meaning only enough airspeed and time for the systems to stabilise at or as near as possible to 17.5deg AoA. Asseline had neither, largely down to his own decision-making.
To provide performance is to rapidly deliver alpha max whatever the conditions and to do so, a temporary overshoot of alpha max can naturally be part of the process, as demonstrated by the test pilot in the video.
No PERF when the AoA is restricted between 14 and 15 but should target 17.5 deg instead.
Then you'll need to explain what "enough airspeed" has to do as a criteria to properly stabilize at alpha max ... ??

The systems can't defy the laws of physics.
It does not have to defy any laws of physics to stabilize at alpha max ... what a strange concept you have here ...

Airbus promoted the systems as being able to help pilots get themselves out of trouble, and in that respect they do. But by disabling A/THR/Alpha Floor or getting the aircraft so low that Alpha Floor is inhibited, a pilot is going outside of Airbus's recommended operation techniques and will therefore be responsible for the consequences.
We are instructed to use alpha max and to totally rely on the capacity of the system to deliver alpha max when needed. That's how the protected aircraft is able to outperform the non protected one.
That you disable alpha floor has nothing to do with the capacity to deliver alpha max.

Which clearly indicates that his intent *was* to disable Alpha Floor, and it seems he missed it in the event.
Nothing new here ... but he did not miss anything - They just came in too fast, and TOGA was selected before the alpha for an eventual alpha floor activation was reached anyway.

For the rest of your partial translations, sorry, but it is very unclear to me what your points are ... ?

[roulishollandais]

We are instructed to use alpha max and to totally rely on the capacity of the system to deliver alpha max when needed. That'show the protected aircraft is able to outperform the non protected one. That you disable alpha floor has nothing to do with the capacity to deliver alpha maxReally in 2014! With very limiting gusts values? And are you instructed for deepstall (AF447 style) after alphamax?
Which are your alphaprot,alphafloor,alphamax and steady level speeds and Vs1g at MTOW and MLW?
Thank you CONF_iture . You are from the few Posters here testing with your life these undescribed figures...:(

[roulishollandais]

Better is the enemy of the good.

We see here all the perversion from protecting pilots against themselves.
Magic stall protection pushed these pilots who where able to avoid stall by their traditional learning to put themselves and the SLF in the mouth of the wulf, and replace a nice airshow afternoon in a catastrophic way.:ugh:

[gums]

Thank you, Rouli. Well stated.

I flew two jets with AoA limiters, and I never failed to notice what was happening, nor did I depend on the limiters to "save" me because I flew into a dire situation.

It's called airmanship, piloting skills, knowing your own limits and that of the jet. The FBW systems can only do so much to protect you from yourself. It is not supposed to be a system to protect you from the results of your poor judgement.

Going back to the peanut gallery, now.

[RetiredF4]

It's called airmanship, piloting skills, knowing your own limits and that of the jet. The FBW systems can only do so much to protect you from yourself. It is not supposed to be a system to protect you from the results of your poor judgement.

Gums, amen to that. :D

[CONF iture]

You are from the few Posters here testing with your life these undescribed figures...
To be honest, never had to experience the protection system. Up to now, all I got was one SPEED low energy audio warning for not following the FD under auto thrust - My fault - For me, to go to the limit, has been a simulator experience only.
You're correct to mention how in the every day operation we know nothing about the speeds associated to the different protection alpha values. They are accurately displayed on the PFD, of course as long as the probes work correctly and the system don't silently discard the only reliable data to ultimately lie to the crew ...

That seems to me to be a misrepresentation of training objectives. You are instructed, in situations of immediate danger, to rely on the the stall protection to prevent stalling.
No - We're instructed to not think to go and get the maximum performance by applying full back stick.
And that is precisely what the FCS accomplished at Habsheim.
Absolutely not - The FCS had simply no intention to deliver anything more than 15 deg when the max performance had been established at 17.5 which is alpha max for CONF 3 and not alpha stall.
The FCS did not prevent the stall in Habsheim. That is pure Airbus propaganda to not have to detail why the FCS limited directly or indirectly the AoA between 14 and 15 deg.

[DozyWannabe]

Magic stall protection pushed these pilots who where able to avoid stall by their traditional learning to put themselves and the SLF in the mouth of the wulf...

The airmanship stuff is true, and I wholeheartedly agree with that, but the above statement is not.

Asseline's own words indicate that Airbus's test pilots only performed the Alpha Max manoeuvre with *other pilots* on board over the Toulouse region (and probably the French Alps as well), which would have necessitated a much higher altitude than 100ft RA. Thanks to alonso1986's detective work, we've seen a video of their chief test pilot demonstrating the technique, again at a much higher altitude. Some displays were flown by Airbus test pilots at or near 100ft RA (though no lower), but I'd be prepared to wager that none of those flights were carrying pax.

Neither Airbus nor AF mandated that the Habsheim flight demonstrate Alpha Max at 100ft RA, and given his confidence on the CVR prior to the accident I wouldn't be surprised if it was Asseline himself who likely suggested doing so. If this was the case, regardless of where he got that level of confidence from, the responsibility for the decision to perform that manouevre that low and with pax on board must ultimately rest with him. The poor level of preparation can largely be laid at AF's door, however - as we've discussed - Asseline could have used his airmanship and judgement to improve safety margins at several points during the flight, which he did not.

For all his words about prior Airbus FBW demonstrations, as far as I know the fact remains that he was the only pilot who ever attempted that technique at an altitude that low with no prior recce and with pax on board. That he still can't accept that this was shaving the safety margins far too close continues to astonish me.

@CONF iture - We've been over this several times. 17.5deg AoA is the absolute value for Alpha Max. The FCOM not only does not give specific quantitative values on the graph, it states in black and white that with full back stick, Alpha Max "may be achieved". Not "will be", much less "will immediately be" - and we've had input from engineers involved with the programme as well as line pilots who, like Asseline, were A320 "early adopters" giving very useful input as to why that is.

I know you harbour an argument that Asseline could, given direct elevator control, have finessed the aircraft over the trees, but given the slipshod approach to the flypast as a whole I have to argue that this is highly unlikely (particularly with no AoA gauge fitted to the aircraft).

The FCS did prevent stall, *because the aircraft did not stall*.

[roulishollandais]

as far as I know the fact remains that he was the only pilot who ever attempted that technique at an altitude that low with no prior recce and with pax on board. Still happy it was not!! Flying the first A320 delivered to AF certified two days before and n°9 of the manufacturor nobody should have performed such a flight!And after the crash noboddy should have imagined such a flight!:mad:
That he still can't accept that this was shaving the safety margins far too close continues to astonish me. Pedagogy does not worry about words said or written in books , magazines or said during talks , courses, and lectures, but how these words are understood by the learning people. Greatest part of Instructors' work needs to know and preview how a particular person is interpreting instruction words, gestures, process and will reproduce or modify them. Airbus has been master in creating trouble in pilots' mind, sometimes near of schyzophreny. Using such words like "Concierges", "can't stall", "test pilots", "fools", "as designed", etc. or letting think -or worse imagine- AoAs, speeds, algorithms, aerodynamic knowledge, and desorganisation of working experience to create a new paradigm is the worst pedagogy I have ever seen in my whole life.

[DozyWannabe]

@roulish:

It is part of the job of a technically competent operator to differentiate sales and promotional bumpf (and the press interpretation of it) from the reality.

BZ's "concierge" reference was purely a promotional aside and not part of formal training. I'd argue that he might have had a point, as this non-pilot who hadn't been privy to flight controls since he last got out of a Chipmunk in 1993 managed to land an A320 simulator successfully (if not particularly elegantly) on the second attempt.

The FCOMs clearly delineate the limitations of the systems and always have. In this case, no amount of quibbling over systems specifics can alter the fact that the aircraft crashed because it collided with terrain that it should have been clear of if the approach had been handled correctly.

[CONF iture]

17.5deg AoA is the absolute value for Alpha Max. The FCOM not only does not give specific quantitative values on the graph
But the BEA did ... 17.5 deg for CONF 3
The graph is generic only - values vary with configuration

it states in black and white that with full back stick, Alpha Max "may be achieved".
As you like that much that "may" ... show me that black and white FCOM reference ... ?

The FCS did prevent stall, *because the aircraft did not stall*.
Impressive logic really ...
Actually the FCS made sure the crash was going to happen.

[DozyWannabe]

But the BEA did ... 17.5 deg for CONF 3
The graph is generic only - values vary with configuration

And for other reasons too I expect.


As you like that much that "may" ... show me that black and white FCOM reference ... ?

See post #23 in this thread:
http://www.pprune.org/tech-log/528034-habsheim-2.html#post8200752

Actually the FCS made sure the crash was going to happen.

That's your opinion only, and one that doesn't seem to be widely held.

[Bidule]

I doubt that the "tours de piste" were flown at 50 ft height! Same for the Airbus shows. It is what makes a large difference.

[CONF iture]

And for other reasons too I expect.
Which are ... ?

See post #23 in this thread:
http://www.pprune.org/8200752-post26.html
The Airline has some latitude to customize the Airbus FCTM - If Cathay wants to word it that way, that is their responsibility.
Still expecting your black and white FCOM reference ...

That's your opinion only, and one that doesn't seem to be widely held.
That an opinion is widely held is not a criteria of veracity - What matter are the facts, and the fact is that the FCS refused to follow the pilot orders despite the possibility for the aircraft to accept an AoA increase of 2.5 additional degrees.

I doubt that the "tours de piste" were flown at 50 ft height! Same for the Airbus shows. It is what makes a large difference.
Strictly speaking about the alpha protection behavior, what is that large difference ?
Are you going to reveal something Airbus did not want to mention ... ?

[DozyWannabe]

@CONF iture:
Why would Cathay rewrite what is essentially a universal technical fact across the Airbus FBW types?

The EFCS *absolutely* complied with the command, it's just that you have chosen to interpret things such that you believe that full back stick will immediately command and deliver an AoA of 17.5 degrees, which is not supported by any documentation that has come to light.

The point Bidule seems to be making is that Asseline cut safety margins much more significantly than Airbus's own test pilots, which is a fair criticism.

[Machinbird]

As one who formerly earned his living by being able to milk the last bit of performance from swept wing jet aircraft, I would like to offer the following opinion regarding the Habsheim accident.

Other than poor pre-planning, the direct cause of the accident was mismanagement of the aircraft's engines. Asseline needed to have been waking up those engines much earlier to avoid the acceleration lag. One should be gradually walking the throttles forward from idle as the ground gets nearer until arriving at a stabilized power at the desired minimum altitude.

It is quite possible that if given direct control of the elevator, Asseline could have developed sufficient g a bit earlier to clear the trees, but in so doing, the aircraft would likely be entering a stall over the tops of the trees (but with the engines coming fully up to power). If he was good and he was lucky, he might have been able to fly out of that without losing altitude. If he was unlucky or not so good of a stick, then the accident would have been moved a bit further from the airfield. Elevator response is thus a secondary issue to the mismanagement of the engines.

The idea is to avoid having to use your superior airmanship to extricate oneself from the consequences of your inferior planning.:}

[DozyWannabe]

The idea is to avoid having to use your superior airmanship to extricate oneself from the consequences of your inferior planning.:}

Exactly (agree with the whole post - with the caveat that he'd have had to have been *extremely* lucky). :ok:

[CONF iture]

Why would Cathay rewrite what is essentially a universal technical fact across the Airbus FBW types?
What wrote Cathay is not in my Airline FCTM and I doubt my Airline would take the liberty to remove such information if it was part of the Airbus FCTM ...

The EFCS *absolutely* complied with the command
No it did not - If it had it would have commanded the elevators to permit some pitch up for an AoA increase.

it's just that you have chosen to interpret things such that you believe that full back stick will immediately command and deliver an AoA of 17.5 degrees, which is not supported by any documentation that has come to light.
Where is the documentation to state that the AoA will be restricted to 15 deg when alpha max is at 17.5 ?
Is it part of the same FCOM you still have to quote ... ?

Other than poor pre-planning, the direct cause of the accident was mismanagement of the aircraft's engines. Asseline needed to have been waking up those engines much earlier to avoid the acceleration lag. One should be gradually walking the throttles forward from idle as the ground gets nearer until arriving at a stabilized power at the desired minimum altitude.
Asseline has always said that's what he did.
The BEA has not produced the extensive data to prove that he did not.

If he was good and he was lucky, he might have been able to fly out of that without losing altitude. If he was unlucky or not so good of a stick, then the accident would have been moved a bit further from the airfield.
But if the high AoA protection feature had simply worked as advertised, he could have been bad but still lucky.

[Machinbird]

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.

[CONF iture]

At most, the audio track of the video could tell when the engines accelerated, but not when the thrust levers were advanced.
Which video/audio track are we looking at exactly ?

[gums]

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.



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.

[awblain]

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.

[DozyWannabe]

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:

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.

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. ]

[CONF iture]

Dozy, you make statements (http://www.pprune.org/8348739-post587.html) but when time comes to back them up you're unable.

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 ?

[DozyWannabe]

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?

[CONF iture]

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 ?

[mm43]

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. :ok:

[DozyWannabe]

@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.

[Linktrained]

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..."

[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.
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 ...

[AlphaZuluRomeo]

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.

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.

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.

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.

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.

[HazelNuts39]

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.

[DozyWannabe]

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.

[roulishollandais]

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

Thank you HazelNuts39

[gums]

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.

[HazelNuts39]

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 ToulouseBe 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".

[DozyWannabe]

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. :)

[HazelNuts39]

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.

[Chris Scott]

Quote:
"@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."

IMO, that has to be one of the most patronising comments I've seen on this thread - from someone who is inclined to bluster in areas of which he understands little.

[DozyWannabe]

Believe me, it wasn't meant to sound like that! Honest and heartfelt apologies if it came across that way.

I felt it was important to make the distinction because, as I've learned from you all, a simulator's behaviour around the edges of the flight envelope will usually be approximate, whereas doing it for real would give a more accurate picture.

As far as I'm aware, I knew it was Bechet who flew the reconstructions at Toulouse because he said he did on the ACI/Mayday programme on the subject.

[gums]

Thank you, Doze. What I wanted to confirm. I feel we are on the same page, and I have actual experience flying the "limiters" or "protections" in a FBW system.

[roulishollandais]

???!!!what!?

[roulishollandais]

I felt it was important to make the distinction because, as I've learned from you all, a simulator's behaviour around the edges of the flight envelope will usually be approximate, whereas doing it for real would give a more accurate picture. Today all the airline pilots are type rated on these simulators for all their training and formation!!!!

[Chris Scott]

That's true today, but not on the A320 at Blagnac in February/March 1988. The Thomson-CSF flight simulator was very unreliable, and certainly not approved for zero-flight-time type-ratings! Admittedly, it would have been a bit better 6 months later.

[roulishollandais]

Bonsoir Chris,

Thank you for your time reference.

Asseline said he trained his 100 FT height flight on the Thomson simulator (with sealed software) used to train AF first A320 pilots. Isn't ?

Which informations and simulator quality had Asseline, Bechet, the BEA, about AoA in Alpha protection and flight laws ?

So You were type rated by Test pilots who had to do instruction and qualification ?

[Chris Scott]

roulis!

More of a history reference, after 26 years! Sorry, I should have explained better, so today I have been looking at the Aeroformation course information, the schedule (with many amendments), and my own notes annotated on them.

Capt Asseline was, I now understand, to be in charge of A320 flight training for Air France, and would have been on Aeroformation (later renamed Airbus Flight Training) A320 course #1 ("FC1"). I was one of two ordinary line captains (each of us paired with a line first-officer) on course FC2 - the first BCAL/BA course - a week behind FC1. (It is sometimes forgotten in French aviation circles that there were three launch-customer airlines for the A320, and Air Inter was the lowest in the pecking order.) The rest of my course members were training and management pilots, and two pilots from the CAA. We did not mix socially with the AF pilots, which I now regret; but we would occasionally meet them briefly at the simulator platform on handover, or at the drinks machine.

After a couple of weeks of self-tuition on the VACBI, and passing the technical exam, we started the FBS (fixed-base simulator) - originally planned to be 14 three-hour sessions - on the third Monday in January. The two FBSs were hors-service (u/s), so the first half of the series was cancelled and we started at FBS session #8, using the FFS (full-flight simulator). I cannot remember if we used one or both FFSs, but I think only one was available most of the time. It or they were unreliable - throughout our 7 FBS and 7 FFS sessions. Neither of my two instructors for the 14 FBS and FFS sessions was A320 type-rated, as far as I know. We lost 1h40 on the first two FFS sessions, and regained 0h45 on the next three; lost 0h45 on the sixth, and regained 0h10 on the seventh.

We then went home to England to wait for the A320 to be type-certificated, returning to Blagnac in March for our type-rating training. The latter consisted of one FBS session for re-familiarisation; 3 FFS sessions with instructors who were A320 TRE/IRE-rated, during which we did our instrument ratings; and one base-training sortie on the a/c for our type ratings.

Quote:
"So You were type rated by Test pilots who had to do instruction and qualification?"

Most of the TRE/IREs were Aeroformation trainers, not test pilots. There were, however, two or three test pilots who were involved in our refresher sim sessions in March. They may not have been TRE/IRE-current, but I'm not sure. They included GC, UE, and maybe NW. (Later, GC and NW were closely involved in our line training from Gatwick.) My single sortie on the a/c for base-training and type-rating was with an Aeroformation training captain, Dick Steele (who later conducted my "final" line check out of Gatwick). We reached alpha-max at an altitude of 4000 ft...

Quote:
"Asseline said he trained his 100 FT height flight on the Thomson simulator (with sealed software) used to train AF first A320 pilots. Isn't?"

That's quite possible, as he would have been able to negotiate extra sim time in his capacity as chief trainer for AF. But I cannot comment on "sealed software". What is that?

Quote:
"Which informations and simulator quality had Asseline, Bechet, the BEA, about AoA in Alpha protection and flight laws?"

I think the simulator(s) had been increased in number and reliability by the end of June. I know little about the working of sims, but all the necessary information would surely have been available from the Aerospatiale EFCS design team to create the necessary algorithms? Perhaps someone else can comment.

[CONF iture]

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.
You have clearly no idea what would be to reproduce such a flight for real with the necessary required level of detail, accuracy, and fidelity, to have any value. The flight over the Toulouse runway was not meant to be a "reproduction" but was merely a wish by members of the commission to personally assess the behavior of the aircraft during maneuvers near the ground, to see if the switching of control laws could cause difficulties for a pilot.
HN39 is referring to the 'graph' on page 63 of the PDF which refers to a simulated flight not a real one.

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.
As you seem ready to give any value to those graph, how Bechet and Asseline would still keep the same speed after obtaining so different alpha ?
Nevertheless, Bechet would still have hit the trees if he had not been in a simulator.
According to the poor quality ... graph we are presented, not if he had started the maneuver at the same altitude that Asseline did, and not 10 ft lower ...

[roulishollandais]

Bonsoir Chris Scott,

Thank you for your long description of the A320 launch-customers pilots type rating. I could compare it to my own MD-80's TR at the same moment. Despite the MD-80's were already "old" aircrafts our TR had many similarities, but of course no flight with test pilots, not alphafloor flight. But like you, only one base-training sortie on the a/c, after VACBI, FBS and FFS. That only one flight was around 1 hour or less, verifying that the real plane felt still easier than the FFS, and to say we did a real flight !

I wanted to point that flying alpha prot or alpha floor on A320 FFS is reliable, as the FFS has the exact reproduction of the EFCS rules. That is very different from trying to test i.e. stalls who have never been done in flight, and whose behaviour is still unknown and could not be "reproduced" on the FFS.

My purpose was to say to DozyWannabe that the FFS simulation from BECHET/BEA was totally reliable, and consequently too that the Hazelnuts39's demonstration perfectly applies (about "sealed software", see (1)).

Continuing the demonstration, it suggests that the fact that pulling the stick three seconds later and getting in alpha prot which had not been previewed by Asseline -and missing in the short "briefing" (gums You are right, that was a very poor "briefing" !) - modified seriously the pitch control reponses.

I don't forget that Hazelnuts39's conclusion reminds that it was not enough to replace the late thrust of Asseline.

Asseline is writing many times in his book that he surely was wrong to trust his altitude. we know from the crash itself and the videos that the plane's real altitude was nearly the same that the RA. The question seems still to be open : did Asseline read 100 FT on his baro-altimeter, when the DFDR records an altitude complying with the Radar altitude, and Mazières telling him clearly about RA ?

The BEA report is saying too that the crew did not contest the FCS (at the time of the enquiry, which is some years earlier than Asseline's book).

(1) re:"sealed software" : Asseline said that working with Thomson they first asked to AI -or AS ?- they needed the copy of the EFCS software. Asseline said they recieved a negative answer, but AI-or AS?- accepted to give them an original EFCS software in a box they could not open or read or copy

[HazelNuts39]

As you seem ready to give any value to those graph, how Bechet and Asseline would still keep the same speed after obtaining so different alpha ?I see no reason to doubt the accuracy of the simulator used by Bechet. He gained less than 10ft height in the five seconds after he went to full throttle and full back stick. That is equivalent to less than 1 kt of airspeed. In the accident flight the wind was light and variable (5 kt +/- 2kt headwind component), and in those last few seconds the airplane entered the lee of the forest. Those wind varations were evidently not represented in the simulator.

P.S.
Just before hitting the trees, the DFDR recorded RA was 24 ft, possibly even less because the recorded values are rounded to the nearest 2 ft. The average tree height is reported as 12 m (40 ft).

[Chris Scott]

Thanks roulis,

My main purpose was to explain to anyone interested in these matters that - at the time Capt Asseline was doing his conversion course - the A320 sim was unreliable, and that zero-flight-time conversion was impossible.

Quote:
I wanted to point that flying alpha prot or alpha floor on A320 FFS is reliable, as the FFS has the exact reproduction of the EFCS rules. That is very different from trying to test i.e. stalls who have never been done in flight, and whose behaviour is still unknown and could not be "reproduced" on the FFS.

I think the a/c would have been stalled during the test programme. But it would not be necessary to incorporate any stall data into the FFS, because the aerodynamic stall is not part of the training syllabus. And, of course, it did not occur at Habsheim.

Quote:
re:"sealed software" : Asseline said that working with Thomson they first asked to AI -or AS ?- they needed the copy of the EFCS software. Asseline said they recieved a negative answer, but AI-or AS?- accepted to give them an original EFCS software in a box they could not open or read or copy

Thanks - that is interesting, and would make sense commercially.

[DozyWannabe]

Regarding the test flights at Toulouse, I'm going from Captain Bechet's interviewed statements on the ACI programme, and he at least seemed to be confident that it was close enough to the actual event (though obviously with some variation) to be useful. Other than that I make no claims whatsoever, other than HN39 (as usual) seems to be on the money regarding the effect of earlier vs. later application of full back-stick.

As for the software in the original simulators, it would have been standard practice at the time to provide complete and working hardware/software combinations as a unit - as long as the interface of the simulator and that of the aircraft was the same it should have been like-for-like. As such, the behaviour of the EFCS would have been one-and-the-same on the simulator and the real aircraft, but the simulator's flight model behaviour would still likely have been undergoing refinement. The "black box" (in engineering terms, i.e. meaning a 'sealed unit') was and still is for commercial considerations only - Airbus's competitors would have likely been very interested in the implementation of their systems, and - especially at that time - the fear of industrial espionage was a real one.

I know that the flight model was essentially fed with the data gleaned from the flight testing performed on the A320 prototypes, and I've been told that those prototypes were the most heavily instrumented and monitored machines of their type at the time. I don't know whether they were flight tested beyond the stall boundary, but wouldn't be surprised if they were at least taken as close as possible in order to gather data on airframe characteristics.

From my brief experience, I can say that modern A320 simulators do provide a plausible representation of behaviour going into stall and recovery, but can't vouch for how precise a representation that is.

[CONF iture]

I see no reason to doubt the accuracy of the simulator used by Bechet. He gained less than 10ft height in the five seconds after he went to full throttle and full back stick. That is equivalent to less than 1 kt of airspeed.
In 2 sec the airplane gains 5 deg of AoA without altitude gain and without losing speed ... That A320 is a very special bird indeed ...

In the accident flight the wind was light and variable (5 kt +/- 2kt headwind component)
Yes, the atmosphere was calm.

Just before hitting the trees, the DFDR recorded RA was 24 ft, possibly even less because the recorded values are rounded to the nearest 2 ft.
Not what is in the report text and not what is on the graph you're commenting ...
1.11.4.
Les points les plus bas de la trajectoire sont à une hauteur voisine de 30 pieds : entre 12 h 45 mn 32 s et 12 h 45 mn 39 s la radiosonde indique 32, 32, 32, 32, 30, 30, 24 et 34 pieds (une valeur par seconde).
How do you explain again such confusion in the report ... ?

[HazelNuts39]

Yes, the atmosphere was calm.The reports states that the wind was 5kt at the time of the accident. Comparison of the recorded airspeed and groundspeed shows variations of +/- 2kt of airspeed that can only be explained by variations of the wind speed.
How do you explain again such confusion in the report ... ?The last value of 34 feet is obviously a typographical error and should read 24 ft as shown in the CEV print of DFDR data. In addition, the recorded accelerometer data show that the airplane cannot possibly have climbed 10 ft in one second between TGEN 333 and TGEN 334.
http://i.imgur.com/jOmWmjz.jpg

[gums]

I thot Doze or another contributor tried to duplicate the stall/recovery for AF447 in the sim.

Unless early flight tests showed a poor pitch co-efficeint at a high AoA, as we had in the Viper, then an approach to stall at 20K would seem to provide great data for the simulator. No need to reach the AF447 complete stall conditions, but at least show the ability of the alpha protect and such to help the pilot. From the AF447 data, seems to me that the 'bus has poor nose down authority once past 15 or 20 degrees AoA. Our problem in the Viper was similar, in some ways. We had plenty of nose up, but our AoA limiter would not let us use it. Nose down was FUBAR due to the design of the jet and its pitch co-efficient at 40 - 50 degrees AoA. Hence, we had the manual pitch override switch that would only work if AoA was above 30 degrees.

I still feel the accident, if you can call it that, was the result of poor planning and practice, and improvised changes in the "plan". I won't comment any further on the airmanship of the pilot.

[CONF iture]

The last value of 34 feet is obviously a typographical error and should read 24 ft as shown in the CEV print of DFDR data.

If it was one they would not have used it for the graph drawing
Tome 2 is more inclined to depict 34RA for TGEN334 than 24 ...


http://i55.servimg.com/u/f55/11/75/17/84/image12.jpg (http://www.servimg.com/image_preview.php?i=160&u=11751784)

I still feel the accident, if you can call it that, was the result of poor planning and practice, and improvised changes in the "plan". I won't comment any further on the airmanship of the pilot.
Still nothing new here gums - We still all agree - But what we're looking for is the FULL story not only the part on the crew.
As HN39 is avoiding the question, you probably could bring your thought on that :
In 2 sec the airplane gains 5 deg of AoA without altitude gain and without losing speed ... That A320 is a very special bird indeed ...

[HazelNuts39]

In 2 sec the airplane gains 5 deg of AoA without altitude gain and without losing speed ... That A320 is a very special bird indeed .That is not what I said in post #622 based on the graph in the report. In the simulation the airplane gained 10 ft and that is equivalent to 1 kt of airspeed.The graph is a computer/plotter generated record of the simulated flight. How accurately were the plotter pens aligned with the millimeter raster on the paper ? The scales and the Habsheim points have been handwritten on that plot with lesser accuracy. The wind at Habsheim was variable. Thus a difference of one or two knots is easily masked by other factors. It is ridiculous to dismiss the simulation for no other reason than that you can't see a difference of one knot on that plot.

[awblain]

"It's a special bird indeed"

Well… Maybe.

During that time was it gaining thrust? If so, then increasing the angle of attack, and thus drag, keeping the potential and kinetic energy constant, but matching the increasing drag and thrust? That doesn't seem an unreasonable proposition.

[Chris Scott]

Hello Confit,

I think many of us were already aware of the discrepancy between the figure of 34 ft in 1.11.4 of the BEA "Rapport Final", and the 24 ft shown in the DFDR "Tome 1" table of the same document.

Thanks for bringing to our attention that DFDR Tome 2 of the same document appears to show a figure of 34 ft, in line with the narrative. The version you show magnified in your post is, I presume, the PDF copy, the poor quality and assembly of which we discussed earlier on this thread.

Another curious aspect of this matter is that an HTML version of the BEA report - Habsheim F-GFKC (http://wnoeker.de/kc/) - clearly shows a figure of 24 ft in both Tomes 1 and 2.

TGEN 334 seems to represent the last second of flight before the RA antennae (rear fuselage) reached the treeline. The ground between the northern extremity of the grass Rwy 34R and the treeline - a distance of about 70 metres - seems to have been flat, with minimal slope. One cannot, however, entirely rule out the possibility of a vehicle or other temporary obstruction being present within the wide, conical lobe of the aircraft's RA TRx. As the ground-speed of the a/c was slightly less than 60 m/s at that point, the RA values at both TGEN 333 & 334 could have been affected by vehicles or superstructure between the grass runway and the treeline.

Therefore, determining the precise RA datum at TGEN 334 would not in itself enable us to prove the trajectory of the a/c in the final second of free flight.

[Chris Scott]

Confit,

I think you are wrong to argue that the wind was calm, if only for the reasons HN39 has pointed out.

Also, if you look again at the Andre Karsenty video, you will see a large balloon in the backround about 7 seconds before the a/c reaches the treeline. It is leaning slightly towards the south, suggesting some kind of headwind component for the A320.

And, as you and any pilot of any size of a/c know well, the proximity of trees is always associated with some degree of wind-shear.

Wind components (W/Cs) can, of course, be estimated from a comparison between the TAS and the GS. (Any error in the GS readings from the IRS are likely to remain constant for the short period of the straight-line flypast. In this case, allowing for pressure altitude and temperature, adding 3 kt to each IAS value gives the approximate TAS.)

Starting from level-off at TGEN 321 and finishing with TGEN 334, the estimated W/Cs at one-second intervals are as follows:
-7, -4, -8, -9, -7, -7, -6, -4, -6, -5, -7, -7, -3, -3.

The above variations are consistent with small gusts of a light headwind.

[CONF iture]

That is not what I said in post #622 based on the graph in the report. In the simulation the airplane gained 10 ft and that is equivalent to 1 kt of airspeed.
Good ... then from the 30 ft with a gain of 10 ft at 17 deg of alpha and speed at 119 kt the BEA and yourself agree that the airplane was surviving the 40 ft forest ...

It is ridiculous to dismiss the simulation for no other reason than that you can't see a difference of one knot on that plot.
I am certainly not looking for any kind of "one knot difference" or other 2 kt gust theory to dismiss such ridiculous simulation when they want you to believe that taking 5 additional degrees of alpha in 2 seconds to bring it to alpha max won't make a difference in term of altitude and speed compared to the same aircraft that remains between 14 and 13 of alpha as computed on the graph.

I think you are wrong to argue that the wind was flat calm, if only for the reasons HN39 has pointed out.
Where did I argue so exactly ... ?
The atmosphere was calm, and the wind less than 5 kt according to the Air Traffic Controller.

Thanks for bringing to our attention that DFDR Tome 2 of the same document appears to show a figure of 34 ft, in line with the narrative. The version you show magnified in your post is, I presume, the PDF copy, the poor quality and assembly of which we discussed earlier on this thread.
Another curious aspect of this matter is that an HTML version of the BEA report - Habsheim F-GFKC - clearly shows a figure of 24 ft in both Tomes 1 and 2.
Here is the ultimate purpose of my concern. This Official Report has a typographic quality of the 60s at most but certainly not one of the 90s standards. All the "graph" as presented as they are, are a pure joke or an insult to the reader. Too convenient for blurring data and bringing confusion. One crucial Annexe is nowhere to be seen and manipulation in Annexe labeling is even created in an attempt to mask its absence. As the BEA is that unprofessional, we clearly do not need them.

I am concerned that a guy with your background seems to give more credibility to such piece of cr@p from the BEA than to Ray Davis ...

[gums]

C'mon, Confit.

The jet and its FCS worked as advertised. And then the laws of physics and aero came into play.

It could be that 'bus folks did not do enough testing at altitude to examine all the "protections" and "floors" and such using flight idle, TOGA, etc. The jet did not have the pitch coefficient problem we had in the Viper, so it had plenty of nose down authority at high AoA ( although we saw with AF447 that the THS position had to be compensated for to get the nose down). Nose up is "limited" by the flight control laws WRT AoA, not the actual capability of the plane, and we had that in the Viper. You can command everything, but HAL is only gonna let the jet "obey" the laws, best it can.

[noske]

Another curious aspect of this matter is that an HTML version of the BEA report - Habsheim F-GFKC (http://wnoeker.de/kc/) - clearly shows a figure of 24 ft in both Tomes 1 and 2.

Well, that's the risk you take with an unofficial publication. That document was probably derived from the BEA PDF, and transcribing those DFDR printouts must have been especially error-prone. I'd say that the evidence offered by CONF iture (the magnified scans, and the values as they appear in the narrative) is sufficiently convincing.

[Chris Scott]

Quote from noske:
"Well, that's the risk you take with an unofficial publication. That document was probably derived from the BEA PDF, and transcribing those DFDR printouts must have been especially error-prone. I'd say that the evidence offered by CONF iture (the magnified scans, and the values as they appear in the narrative) is sufficiently convincing."

Yes, I agree with all of that. It is ironic, however, that the RA figure of 24 ft at TGEN 334 in the HTML version of Tome 2 is more plausible than the 34 ft figure in the PDF copy of the BEA report. The Karsenty video rules out any inference that the a/c might have climbed 10 ft in the last second.

Whichever of the two figures is correct, students of the report might expect that its final edition would have corrected an unnecessary anomaly that undermines the authority of the whole document. If that and other less imperative amendments were done, it is unfortunate that the BEA has not made the amended document accessible via their website.

In public transport, the Habsheim accident has unique aspects and complexities, and continues to provide a basis for the study of a broad range of aeronautics. In recent years, the BEA has published several very informative papers relating to flight safety matters in general. Its valuable contributions to the subject are somewhat undermined by the continuing deficiencies of the Habsheim document.

Hi gums,
Just a reminder to you and others that, in AF447, Pitch Alternate Law allowed the THS to continue auto-trimming to full nose-up trim. At Habsheim, starting with Pitch Normal law, the THS auto-trimming was disarmed first (briefly) by the premature, 2-second engagement of Flare mode at TGEN 313 (t -21) - triggered by flying over trees; and, secondly, when Flare mode was entered again at TGEN 317 (t -17). Finally, it remained disarmed when Alpha Protection mode took over from Flare mode at TGEN 330 (t -4). Earlier, in fact, it had had no need to trim between TGEN 306 (t -28) and t -21. So, to sum up, it remained at U04 (4 degrees nose-up trim) for about the last half a minute of flight. Full deflection in the nose-up trim sense is 13 degrees.

[roulishollandais]

In France the official version is not the BEA file, but the "JOURNAL OFFICIEL" copy of the BEA file. Probably the BEA had two versions : 24 and 34 Ft. They have to verify and ask to the J.O. to register the true number. The J.O. would not modify such a number.

[Chris Scott]

Bon soir roulis,

The Journal Officiel is the document, available via the BEA website, which Confit shows.

http://www.bea.aero/docspa/1988/f-kc880626/pdf/f-kc880626.pdf

Can you explain more? Are you saying that, once the document has been published as the Journal Officiel, the BEA is completely powerless to publish any necessary corrections?

[DozyWannabe]

The Ray Davis angle was covered earlier in the thread more than once - here:

http://www.pprune.org/tech-log/528034-habsheim-4.html#post8209613

and here (click the arrow to go to the original post):

Notably, the ACI programme got this wrong too - it was not ATC's discrepancy with the CVR, it was a misinterpretation of the DFDR. [Davis] seems to have treated the DFDR's transmit/receive flag as referring to the call from ATC (which would be almost 5 seconds adrift from the ATC recording and unacceptable). In fact the DFDR does not flag incoming, only outgoing transmissions, and the DFDR referred to the crew's response (just shy of 1 second adrift from the ATC timestamp, and within the margin of error).

All this and more is in the Airbus document...

One thing that I didn't mention before and may have some bearing is that Mr. Davis was hired by a UK TV production company making a documentary on the subject - not of the crash itself, but of Asseline's attempt to clear his name. The Airbus document explaining where Davis may have erred does not allude to this, but there is a distinct possibility that the information supplied him may have been missing some of the details mentioned in the above posts.

We also know that the Loral DFDR units fitted to the early A320s were later known to be susceptible to write errors when subjected to unexpected shock or vibration. The estimated value of +0248 RA at TGEN335, which CONF iture has helpfully provided in magnified form, is clearly erroneous - therefore it is within the realms of possibility that the previous value is also in error. That the video evidence clearly does not demonstrate an altitude gain of 10ft before impact with the trees supports this hypothesis in my opinion.

Hi gums,
Just a reminder to you and others that, in AF447, Pitch Alternate Law allowed the THS to continue auto-trimming to full nose-up trim.

Hi Chris - I hope you find this interesting, though it's on a bit of a tangent. When we tested the AF447 scenario in an A320 sim (the best we could do as there were no A330 sims available), the autotrim was limited by the system well before we got into difficulties - to simulate the scenario, the TRE had to manually wind on full nose-up trim with the wheels. If such behaviour was consistent with the A320, it follows that autotrim behaviour on the A320 series is different from that on the A330/340.

[roulishollandais]

Can you explain more? Are you saying that, once the document has been published as the Journal Officiel, the BEA is completely powerless to publish any necessary corrections? In France the official version is not the BEA file, but the "JOURNAL OFFICIEL" copy of the BEA file. Probably the BEA had two versions : 24 and 34 Ft. They have to verify and ask to the J.O. to register the true number. The J.O. would not modify such a number.@Chris Scott,
1. My last sentence was perhaps at a wrong place?
Once the document has been published in the Journal Official any necessary correction is possible in a similar form and level of law hierarchy, probably in a short but accurate description of the modification but with the signature of the original administration . If the modification is not published you may ask a Court to apply the wrong text. The Journal Officiel does the maximum to avoid such mistakes and many verifications are done and redone before publishing, to respect every comma or space, but in the JO typography, design , with absolute rules of registering, diffusion, existence of copy. It often needs much time which brings a delay between the BEA text who has its own design, and rules, published so quickly as possible and the JO tex
It is unusual that the BEA text provides a copy of the Journal Officiel which gets a BEA report.. Why, when was the original BEA report replaced in their files?

2. The numbers provided by the sensors must not be replaced, the BEA may only comment them in his report

[CONF iture]

The jet and its FCS worked as advertised.
Absolutely not - The advertisement is to do the necessary in order to expect alpha max 17.5 deg in this configuration, but certainly not to restrict it to 15 at most.
You can command everything, but HAL is only gonna let the jet "obey" the laws, best it can.
The law in this case is to permit 17.5 deg of alpha and not to restrict it to 15, or even 14 depending on where you look into that BEA Official Report ...

That document was probably derived from the BEA PDF, and transcribing those DFDR printouts must have been especially error-prone.
I'm not too sure how such document as you posted it is actually obtained ?
Don't you think the transcribing to obtain such format must be part of an automatic process ?

We also know that the Loral DFDR units fitted to the early A320s were later known to be susceptible to write errors when subjected to unexpected shock or vibration. The estimated value of +0248 RA at TGEN335, which CONF iture has helpfully provided in magnified form, is clearly erroneous - therefore it is within the realms of possibility that the previous value is also in error.
Then you should have said that that type of DFDR was also susceptible to write errors when anticipating a shock ... the emotion maybe.
BTW any data from TGEN335 has already no value has the tape is labelled as de synchronized.

That the video evidence clearly does not demonstrate an altitude gain of 10ft before impact with the trees supports this hypothesis in my opinion.
Not more than it demonstrates an altitude loss of 6 ft the second before ...

[DozyWannabe]

The advertisement is to do the necessary in order to expect alpha max 17.5 deg in this configuration, but certainly not to restrict it to 15 at most.

Where does it say this? It doesn't say this in any of the documentation.

To my mind it's two separate pieces of information out of context that you have yourself combined to come up with this ludicrous theory that the FCS was to blame, and not the arrogant*, incompetent** and stubborn*** (on that day at least) Capt. Asseline.

* - In blithely assuming that he was skilled enough to take a greater level of risk with pax on board than Airbus's own test pilots
** - Thoroughly making a hash of the approach with very poor thrust management
*** - Going ahead with the flypast on the first attempt when it was obvious that the briefing was wrong (regarding which runway to follow)

[CONF iture]

Where does it say this? It doesn't say this in any of the documentation.
Of course it does as already posted in #599 (http://www.pprune.org/8353278-post599.html) and #603 (http://www.pprune.org/8354978-post603.html).

To my mind it's two separate pieces of information out of context that you have yourself combined to come up with this ludicrous theory that the FCS was to blame, and not the arrogant*, incompetent** and stubborn*** (on that day at least) Capt. Asseline.
* - In blithely assuming that he was skilled enough to take a greater level of risk with pax on board than Airbus's own test pilots
** - Thoroughly making a hash of the approach with very poor thrust management
*** - Going ahead with the flypast on the first attempt when it was obvious that the briefing was wrong (regarding which runway to follow)
Finally showing your true colors after initially playing false demagoguery by pretending "having some sympathy for Capt. Asseline".

[DozyWannabe]

Neither of those posts state 17.5deg as being a guaranteed swift response upon full application of back stick, and in fact the Airbus documentation does not mention 17.5 degrees at all. You're taking the absolute value given in the BEA report out of context and grafting it to the Airbus documentation in a way that is not consistent with the way the documentation is written in order to claim that there should have been an expectation of 17.5 degrees, when that doesn't seem to be the case.

And I *am* sympathetic to Asseline in some respects, particularly the lack of oversight and poor preparation materials given him by the airline. This does not alter the fact that the conduct of the flight seems to be consistent with the negative traits sometimes ascribed him, and *on that particular day*, as I said, he seemed to be displaying those traits during the conduct of the flight. The two positions are not mutually exclusive.

[HazelNuts39]

That the video evidence clearly does not demonstrate an altitude gain of 10ft before impact with the trees supports this hypothesis in my opinion.
Not more than it demonstrates an altitude loss of 6 ft the second before ...
The DFDR recording offers three sets of data that can be used to reconstruct the trajectory:

-- radio altitude
-- pressure altitude
-- x, y, and z accelerations

When comparing these three sources, the different heights of the respective sensors must be taken into account. The radio altimeter antenna is on the lower rear fuselage, the ambient pressure is sensed by Air Data Modules close to the static pressure ports on the front fuselage, and the three-axis accelerometer is located near the center of gravity. The relative height of the three sources varies with the pitch attitude of the airplane, and for the radio altitude also with the elevation of the terrain. The following graph shows the height of the CG taking those factors into account. The elevation of the terrain can be taken as 781 ft at TGEN=334 with a downhill slope of 0.15%. The pressure altitude depends on the local pressure, given in the report as QNH=1012 hPa and QFE=984 hPa. If the pressure has been accurately measured and properly rounded the QNH must then lie between 1012.1 hPa and 1012.5 hPa. The graph shows the CG height based on the pressure altitude for both values of QNH.

http://i.imgur.com/4v6E9D3.jpg?1

[gums]

Gotta tellya, Confit, that until I see the actual FCS charts/functions for modes and such, I'll stay with Doze and others that the plane gave everything it was "programmed " do.

My problem is with the "flare mode", which requires increasing back stick once the jet is "x" feet above the ground. Could it be that the "flare mode" prevents the jet from reaching the advertised max AoA?

I swear, the 'bus has more "laws" and functions and everything else that the space shuttle, the Viper or the F-22 do not have. For a pilot, I want to know exactly what to expect without having to go thru modes, sub-modes and then sub-sub-modes. Sheesh.

I am not an advocate of "direct" laws, as some have mentioned on our discussion. But you can only do so much to prevent/help some hamfist to fly the jet.

[DozyWannabe]

Could it be that the "flare mode" prevents the jet from reaching the advertised max AoA?

No - aircraft was not in flare mode from shortly (as in under a second) after it overflew the "copse"/"bosquet". Well out of flare mode when the trees were spotted, and as other A3x0 rated pilots have attested, flare mode can be cancelled simply with application of TOGA thrust*. As OG attested to (If I read him right, it's related to EFCS phugoid damping) - the Alpha Max command in High AoA Protection gives as much as it can, then likely waits a fraction of a second to stabilise before determining whether the remaining AoA is to be used for extra pitch or for bank input.

Oops - got the above regarding OG's post completely wrong - apologies!

EDIT : As I said earlier, I have a suspicion that the airspeed deltas have an effect on how long it takes to consider the attitude "stable", and in a case such as this one where the aircraft was decelerating almost right up to impact, the duration would likely be longer than if it had airspeed in reserve.

I swear, the 'bus has more "laws" and functions and everything else that the space shuttle, the Viper or the F-22 do not have.

The 'bus systems have three primary laws only. Alternate Law has a number of sub-modes, but the overall performance isn't a great deal different between them - the sub-mode is determined by which of the myriad systems has suffered a failure. It goes without saying that this will be more complex than a fighter, possibly even the F-22, because an airliner is a much more complex piece of engineering mechanically.

* - This aspect is discussed in more detail earlier in the thread.

[roulishollandais]

@Hazelnuts39
What is still unknown is the altitude read on the altimeter on the cockpit

[DozyWannabe]

@Hazelnuts39
What is still unknown is the altitude read on the altimeter on the cockpit

I think this has been covered before, but if I may attempt to recap...

The only way to be 100% certain would be to have had a camera trained on the PFD, but since we don't have that, a degree of assumption will always be necessary. Folks, correct me if I'm wrong - but I think from recollection of the AF447 thread that the DFDR altimeter trace is fed from the ADIRU selected on the Captain's side (LHS).

As others have demonstrated, the DFDR trace seems to tally well with other data when it comes to actual baro altitude. QNH seems to have been correctly set, and all things considered the likelihood is that the baro alt on the PFD was showing the values recorded on the DFDR. For there to have been a discrepancy would mean a fault on the data bus between the ADIRU and the LHS PFD, for which no evidence seems to exist (though, admittedly, such evidence would be difficult to trace later on).

Asseline insists that the baro alt was reading 100ft throughout, and furthermore frames the possibility that it wasn't as tantamount to accusing him of lying. He mentions earlier baro alt misreadings on test flights and argues that may have happened in this case. I believe he states elsewhere that he was relying on the baro alt and external references because he found the digital RA display difficult to read.

I'm sure that Asseline believes fervently that the baro alt was reading 100ft, and if it wasn't, he may have still perceived it as such through confirmation bias - as the workload on the flight deck was significantly higher than anyone had anticipated due to the briefing errors. If the baro alt was in fact consistent with the DFDR, that doesn't make him dishonest - it just raises the possibility that he made a (completely understandable) mistake under pressure.

On the other hand, his own input raises further questions about the conduct of the flight as a whole - particularly with regard to the wisdom of relying solely on one instrument if you consider that instrument to be unreliable, with the only safeguard being external references at an unfamiliar airfield.

[CONF iture]

You're taking the absolute value given in the BEA report out of context and grafting it to the Airbus documentation in a way that is not consistent with the way the documentation is written in order to claim that there should have been an expectation of 17.5 degrees, when that doesn't seem to be the case.
As 17.5 deg value for alpha max at CONF3 given by the BEA is not good enough for you ... where do you think the BEA got that value if not from Airbus ?
True I should always remember that you still don't know which config (http://www.pprune.org/8254085-post289.html) was used in Habsheim ... !?

As OG attested to - the Alpha Max command in High AoA Protection gives as much as it can, then likely waits a fraction of a second to stabilise before determining whether the remaining AoA is to be used for extra pitch or for bank input.
Another nice piece of disinformation. Who should I credit it to, OG or you ... ?

As I said earlier, I have a suspicion that the airspeed deltas have an effect on how long it takes to consider the attitude "stable", and in a case such as this one where the aircraft was decelerating almost right up to impact, the duration would likely be longer than if it had airspeed in reserve.
Then Bechet in his simulator just proved your suspicion wrong ...

Gotta tellya, Confit, that until I see the actual FCS charts/functions for modes and such, I'll stay with Doze and others that the plane gave everything it was "programmed " do.
Sorry gums but I go by the book, now if the the plane behaved as per an unpublished program ... it was the BEA duty to detail it afterwords.

[DozyWannabe]

As 17.5 deg value for alpha max at CONF3 given by the BEA is not good enough for you ... where do you think the BEA got that value if not from Airbus ?
True I should always remember that you still don't know which config (http://www.pprune.org/8254085-post289.html) was used in Habsheim ... !?

If you say it was CONF 3 and the report says it was CONF 3, then it was CONF 3. I've been aware of that for a while.

Of course the BEA would have got the value from Airbus. But the issue I have with your position regarding 17.5deg is not the value itself - it's your interpretation of combining the absolute value as given in the BEA report with the less-specific (regarding values and how they are used by the EFCS) documentation that Airbus provided to flight crew.

Your argument seems to be that Airbus - to use your own word - "advertised" that in CONF 3, 17.5 degrees AoA would definitely be achieved under any circumstance with the application of full back-stick, when the documentation says no such thing.

AZR said much the same thing to you a couple of pages back:

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.



Another nice piece of disinformation.

On what are you basing that accusation? There seems to be a definite short delay between acquiring 15 degrees AoA and going further. OG reckoned it was related to damping.

Then Bechet in his simulator just proved your suspicion wrong ...

How so? Please elaborate. For one thing, you yourself said that Bechet's work in the simulator and real-world testing did not involve a precise reconstruction of the event - so I'm puzzled as to how they could disprove an assertion if that was the case.

[Owain Glyndwr]

Another nice piece of disinformation. Who should I credit it to, OG or you ... ?Let me first say that I strongly object to it being suggested that I would present disinformation!
Now let me repeat what I have said previously - the AOA was held down by the phugoid damping term in the Alphaprotect law. I said nothing about waits a fraction of a second to stabilise before determining whether the remaining AoA is to be used for extra pitch or for bank input. I think that is :mad:. The EFCS doesn't decide whether to add pitch (AOA?) or bank; the pilot does that, the EFCS merely decides whether it is safe to fulfill his commands. The system was designed to facilitate this by adding thrust if the energy management needed such thrust to maintain safety. By switching off alphafloor Asseline transferred that responsibility for safety to himself.
Apart from the fact that I have never seen an Airbus statement "advertising"* any specific value of alphamax, they would certainly not have made any claim that this could be safely achieved by simple action on the sidestick with only part of the system working.
Although Airbus test pilots routinely made high AOA demonstrations with alphafloor switched off they invariably compensated for that by selecting a level of thrust commensurate with maintaining speed and altitude.
When test flying to establish Vs1g, which must be done with idle thrust they were (are) careful to do this at a safe altitude so that the aircraft can be allowed to sink.

Edit:

* "advertising" as in writing for publicity or sales purposes intended for a general audience as against writing in a technical publication intended for knowledgeable persons

[DozyWannabe]

Sorry OG - *extremely* poor phrasing on my part (on top of an initial howler to start with - I'm a bit at sea when it comes to grasping the damping part). I did go back and try to correct it. :oh:

[Owain Glyndwr]

HN39

The graph shows the CG height based on the pressure altitude for both values of QNH.

There is also an unknown effect coming from any difference between static pressure position errors established in free air (up to alphamax) and those which would apply at the same AOAs in ground effect. So far as I am aware, no company has been zany enough to try to establish PEs near stall conditions at 30ft AGL!

[HazelNuts39]

Owain Glyndwr,

I agree with that. The last five seconds seem to indicate a change of PEC as the airplane gets nearer to the ground at increasing AoA.

However, in the preceding 20 seconds we see the opposite trend: the airplane seems to descend steeper based on pressure altitude than indicated by the radio altimeter + terrain profile. Do you have an explanation for that?

http://i.imgur.com/K6FieGw.jpg

[Chris Scott]

Quote from roullishollandais:
What is still unknown is the altitude read on the altimeter on the cockpit

That is correct, strictly speaking, for two reasons:
(1) there is no video of the cockpit altimeters;
(2) we only have the testimony of the pilots that they had set their altimeter sub-scale settings to the transmitted QFE of 984.

However, as you know, it is a simple process to convert the DFDR readings of pressure altitude ("FINF") to the reading of an altimeter set to 984 hPa, simply by subtracting 808 ft.
For those who have not already done that, here are the readings at one-second intervals,
starting at TGEN 310 (t -24), and finishing at TGEN 334 (t -0):
126, 115, 111, 104, 101, 89, 85, 75, 70, 69, 68, 61, 60, 60, 60, 54, 54, 56, 53, 51, 52, 55, 56, 60, 56.

As I have stated in an earlier post, it appears that the a/c levelled off at 61 ft on the QFE at about t -13, gently lost indicated height from about t -10, and then recovered most of it by t -1. It is likely, however, that the accuracy of the readings available to the crew would have suffered from increasing position-error in the last seconds, because of the high AoA. Also, the static ports are between the cockpit and the CG, so the increasing pitch-attitude means the CG is increasingly lower than the static ports (whereas the pilot eye -height is increasingly higher).

[CONF iture]

If you say it was CONF 3 and the report says it was CONF 3, then it was CONF 3. I've been aware of that for a while.
... but never have acknowledged it since JAN 8th when you pretended otherwise.

Your argument seems to be that Airbus - to use your own word - "advertised" that in CONF 3, 17.5 degrees AoA would definitely be achieved under any circumstance with the application of full back-stick, when the documentation says no such thing.
I have not such argument - But if I had one it could be how the Airbus documentation describes the normal high AoA protection functioning but not when under given circumstances further additional restrictions apply.

There seems to be a definite short delay between acquiring 15 degrees AoA and going further.
Where do you see such definite short delay ... ?

How so? Please elaborate.
Under similar deceleration Bechet had obviously no delay to go straight to alpha max.

For one thing, you yourself said that Bechet's work in the simulator and real-world testing did not involve a precise reconstruction of the event - so I'm puzzled as to how they could disprove an assertion if that was the case.
Until you publicly acknowledge how the BEA work is questionable, I won't miss the opportunity to make you face their and your own contradictions ...

Although Airbus test pilots routinely made high AOA demonstrations with alphafloor switched off they invariably compensated for that by selecting a level of thrust commensurate with maintaining speed and altitude.
... with maintaining altitude, speed not being dependent on the level of thrust.

[DozyWannabe]

... but never have acknowledged it since JAN 8th when you pretended otherwise.

No, I was asking where you were getting the evidence for your claim that the demonstration flown by GC on the video was at CONF FULL - I never disputed the contents of the report that I can recall.

I have not such argument - But if I had one it could be how the Airbus documentation describes the normal high AoA protection functioning but not when under given circumstances further additional restrictions apply.

It's not a restriction, but a delay - thanks to a timely explanation offline (given slowly and carefully so that even I could understand), the damping effect goes some way to explaining that delay, and I won't embarrass myself by trying to reword it - OG and HN39 seem to have covered it.

Under similar deceleration Bechet had obviously no delay to go straight to alpha max.

On which graph do you see that? I must confess that I can't follow the hand annotations at the current resolution.

Until you publicly acknowledge how the BEA work is questionable, I won't miss the opportunity to make you face their and your own contradictions ...

Ultimatums - really?

Look, I'm not qualified to comment in any detail on the BEA report, but from a layman's perspective, and especially taking into account that this was the first public investigation of a commercial airliner crash that used digital technology in flight controls as well as data recording, the report seems to be at least fit for purpose and certainly as good as reports of the same vintage from other investigative authorities.

I'm sure there are some areas that could have been improved, but on the whole it seems solid.

What would you have had them do differently?

[Owain Glyndwr]

Originally posted by Confiture

speed not being dependent on the level of thrust.

An interesting interpretation of the laws of aerodynamics; but I was taught that to maintain constant speed in level flight (constant altitude) thrust has to be set equal to drag and since drag varies with speed it follows that speed and thrust are interlinked.

[HazelNuts39]

Under similar deceleration Bechet had obviously no delay to go straight to alpha max.
I was under the expression that you had accepted the explanation I offered in post#605:
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.

There was also a difference in the way the sidestick was pulled back - Bechet in one quick move and Asseline more hesitating.

[Owain Glyndwr]

Originally posted by HN39

However, in the preceding 20 seconds we see the opposite trend: the airplane seems to descend steeper based on pressure altitude than indicated by the radio altimeter + terrain profile. Do you have an explanation for that?

The short answer is no - or at least nothing really convincing, just a couple of thoughts.

There may be two effects with opposing trends involved; the effect of height at more or less constant AOA and the effect of AOA at constant height. This will be complicated by the fact that the AOA effect is very possibly more powerful at low heights than far off the ground. The motion seems to consist of one part with reducing height at more or less constant AOA and the other part increasing AOA at more or less constant height. OTOH, ground effect is rather weak above, say, 50ft so one would not expect any significant effect from the first trend over much of the relevant sequence.

[roulishollandais]

What is still unknown is the altitude read on the altimeter on the cockpit
That is correct, strictly speaking, for two reasons:
(1) there is no video of the cockpit altimeters;
(2) we only have the testimony of the pilots that they had set their altimeter sub-scale settings to the transmitted QFE of 984.

However, as you know, it is a simple process to convert the DFDR readings of pressure altitude ("FINF") to the reading of an altimeter set to 984 hPa, simply by subtracting 808 ft.k
For those who have not already done that, here are the readings at one-second intervals,
starting at TGEN 310 (t -24), and finishing at TGEN 334 (t -0):
126, 115, 111, 104, 101, 89, 85, 75, 70, 69, 68, 61, 60, 60, 60, 54, 54, 56, 53, 51, 52, 55, 56, 60, 56.

As I have stated in an earlier post, it appears that the a/c levelled off at 61 ft on the QFE at about t -13, gently lost indicated height from about t -10, and then recovered most of it by t -1. It is likely, however, that the accuracy of the readings available to the crew would have suffered from increasing position-error in the last seconds, because of the high AoA. Also, the static ports are between the cockpit and the CG, so the increasing pitch-attitude means the CG is increasingly lower than the static ports (whereas the pilot eye -height is increasingly higher).
I know all that Chris Scott ! I am able to do substractions... but please accept that we don't know how the pressure (total and static) are 'handled' by the software to appear as a graduated scale on the PFD on the glass cockpit.
AEROSPATIALE/AIRBUS INDUSTRY chosed to keep the A320 and next types software secret/private/hiden.
Not a post from Dozy Wanabee assessing that option as legitim, not a post from Iself assessing the opposite option that responsibility of the pilots need they may have access to ALL algorithms used on the aircraft.
Dozy thought it was in the sense of Open Source Software, free of copyright ; no, it is with protected copyright, as you may protect your rights when you are an author of published text or music that you would not hide !!!
What is different with digital design has been well pointed by the JACQUES-LOUIS LIONS report after the ARIANESPACE rocket ARIANE 501 crash. That crash and that report came much later than HABSHEIM, eight years later, but just before the HABSHEIM trial.
Since the beginning of the Airbus project Aérospatiale was growing on a paranoid way of writing software (ie the A320 simulator with the 'locked software' used to train the AF pilots) and some typical method failures were done by that community .
These many many method failures have been studied with a great accuracy (and diplomacy) in the report but read between the lines as a software professional I was in a highly challenging science ' the conclusions were just terrifying, and some sentences are absolute rules we just NEVER can jump over after that référence report.
Here is the link to the english traduction of the 12 pages report, followed by the most important sentences that no line of code may ignore.
Owain G already said me that Aérospatiale teams in the both projects were not the same, but from what I know from that history of software methods, both were involved in similar software design ... temerity. That temerity is a natural result of the fact that human brain does not work so logicaly as it seems, engineers -happily- incluses. They are many ways to do the altimeter figures and scale wrong via hiden software... Alas

ARIANE 5 Failure - Full Report (http://www.ima.umn.edu/~arnold/disasters/ariane5rep.html)

the Board wishes to point out that software is an expression of a highly detailed design and does not fail in the same sense as a mechanical system. Furthermore software is flexible and expressive and thus encourages highly demanding requirements, which in turn lead to complex implementations which are difficult to assess.

An underlying theme in the development of Ariane 5 is the bias towards the mitigation of random failure. The supplier of the SRI was only following the specification given to it, which stipulated that in the event of any detected exception the processor was to be stopped. The exception which occurred was not due to random failure but a design error. The exception was detected, but inappropriately handled because the view had been taken that software should be considered correct until it is shown to be at fault. The Board has reason to believe that this view is also accepted in other areas of Ariane 5 software design. The Board is in favour of the opposite view, that software should be assumed to be faulty until applying the currently accepted best practice methods can demonstrate that it is correct.

[CONF iture]

An interesting interpretation of the laws of aerodynamics; but I was taught that to maintain constant speed in level flight (constant altitude) thrust has to be set equal to drag and since drag varies with speed it follows that speed and thrust are interlinked.
Not in the high AoA demonstration world to which you made reference where Airbus test pilots routinely fly alpha max and use thrust to control altitude but not speed ...

I never disputed the contents of the report that I can recall.
You did not dispute, you pretended the config for Habsheim was unknown.

No, I was asking where you were getting the evidence for your claim that the demonstration flown by GC on the video was at CONF FULL.
Already answered here (http://www.pprune.org/8251341-post262.html) and here (http://www.pprune.org/8253980-post288.html).

It's not a restriction, but a delay
What a delay if not a restriction ?

On which graph do you see that?
Same graph (http://www.pprune.org/8362095-post620.html) mentioned by HN39 earlier.

I'm sure there are some areas that could have been improved, but on the whole it seems solid.
For someone who wanna stay blind, surely.

I was under the expression that you had accepted the explanation I offered in post#605
If you're satisfied with it, then it shows how the concept is poor and inefficient.

[Owain Glyndwr]

Originally posted by Confiture

Not in the high AoA demonstration world to which you made reference where Airbus test pilots routinely fly alpha max and use thrust to control altitude but not speed ...You are wrong there. They know that to make a correct demonstration of alphamax it is necessary to have enough thrust not only to maintain altitude but also to maintain speed. If that is not so the EFCS will apply a nose down corrective pitch command that will prevent achievement of alphamax.

That is why I wrote:

invariably compensated for that by selecting a level of thrust commensurate with maintaining speed and altitude.

[HazelNuts39]

Not in the high AoA demonstration world to which you made reference where Airbus test pilots routinely fly alpha max and use thrust to control altitude but not speed ...It depends. If you do the demonstration at low altitude you have to set the thrust that maintains level flight.

If you do the demonstration in free air there is no need to maintain altitude, but maintaining alphamax implies constant speed and pitch attitude. Vs1g is demonstrated with engines idle, and the sidestick held on the aft stop for 2 seconds or until there is no further increase of AoA.

So in both situations it is constant speed and attitude, therefore no phugoid damping.

[noske]

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.There was also a difference in the way the sidestick was pulled back - Bechet in one quick move and Asseline more hesitating.

Asseline is well aware of this hesitation, and in his book (in his timeline of the accident in the first chapter) he volunteers an explanation (my translation):

"The mental image I had made for the fly by falls apart. Instinctively, in the fraction of a second, I move the thrust levers to idle (*), then to full thrust. I maintain level flight by visual reference. The forest approaches. Still no thrust. [...] I must not pull the stick all the way back too soon, for, if the thrust doesn't come, we'd only fall from a greater height."

(*) Because, as he recalls the events, he had already added some thrust six seconds earlier, when levelling off after the descent.

Nevertheless, Bechet would still have hit the trees if he had not been in a simulator. Asseline should be relieved to hear that.

[CONF iture]

You are wrong there.
Am I ?

Thrust deficit you go down
Thrust surplus you go up
But alpha remains at alpha max
And speed remains at Valphamax
Only elevator controls speed through alpha
Thrust has no say on speed

[Owain Glyndwr]

Originally posted by Confiture

Am I ?Yes because if you generate a situation where speed decays whilst in alphaprotect and trying to fly at alphamax you will not get to or remain at alphamax so your equalities break down.

Only elevator controls speed through alpha

So when he applied up elevator at the end of the flight he was actually trying to slow down?

[CONF iture]

Yes because if you generate a situation where speed decays whilst in alphaprotect and trying to fly at alphamax you will not get to or remain at alphamax so your equalities break down.
Now you come up with the "if" situations ...
So "if" the speed decays below Valphamax it would mean you're over alpha max and that's the elevator job to correct back to alpha max and its corresponding Valphamax, not the thrust job.

So when he applied up elevator at the end of the flight he was actually trying to slow down?
Unfortunately Asseline had not the power to apply up elevator, only to apply back stick.
Hopefully a cooperative FCS would have commanded the required up elevator necessary to increase alpha up to alpha max and decrease the speed to the corresponding Valphamax.

[Owain Glyndwr]

Now you come up with the "if" situations ...
So "if" the speed decays below Valphamax it would mean you're over alpha max and that's the elevator job to correct back to alpha max and its corresponding Valphamax, not the thrust job.If you don't like if, change it to when.

As for the rest, you are distorting my words to suit your own purposes. I made no mention of Valphamax, those are your words. I made no mention of flight at more than alphamax, in fact I said that you could not achieve alphamax, so in my world the situation you describe could not happen. I could perhaps have been more specific, and stated that the restriction to alpha can occur at any AOA between alphaprot and alphamax. You choose to interpret it as being at and only at alphamax.

I made no mention of speed falling below Valphamax, I simply spoke of speed falling - again at any AOA between alphaprot and alphamax.

[Chris Scott]

Quotes from roulishollandais:
"I know all that Chris Scott ! I am able to do substractions..."

Forgive me... But your posts are usually so cryptic that it is sometimes difficult for a simple soul like me to estimate your experience and knowledge of aeronautical matters in general, and glass cockpits in particular. You talk of an MD80 pilot course, and then you say you are a software professional. If you read my posts, you know exactly my experience in the context of Habsheim, but I know little of yours. So I have no alternative but to take your questions on face-value, and answer them as well as I can. I have also to consider other readers who may have less knowledge of altimetry than you. (By the way, I admire your courage in posting on an English-language forum, because I would not want to try a French-language one.)

"...please accept that we don't know how the pressure (total and static) are 'handled' by the software to appear as a graduated scale on the PFD on the glass cockpit."

That is true, but how many pilots of a/c with mechanical or electro-mechanical altimeters know the precise mechanism that drives the needles, or the chances of them misreading? In my case, altimeters had already become more and more sophisticated as my career gradually progressed from the DC-3/C-47 to the A310 and DC10. Pilots have to take many things on trust, unless and until they find a problem. The A310 of 1983 had a PFD and ND, on which we relied for most of our flight parameters, except altitude and VS. So the DMC and other links in the display system were not unprecedented in airline service. I was flying A320s before this accident, and experienced no altimeter indication problems that I was aware of.

We know that Capt Asseline had had a problem on a previous flight, in a descent over the Jura mountains, when the selected sub-scale settings had changed spontaneously. That later resulted in the a/c being lower than he intended. But, as far as I know, there is no suggestion or likelihood that the same fault happened at Habsheim, and the pilots had both set the QFE of 984 less than a minute before they levelled off at 61 ft. Therefore, it is most likely that the indications on the PFDs were precisely 808 ft lower than the pressure altitudes recorded by the DFDR.

[CONF iture]

As for the rest, you are distorting my words to suit your own purposes. I made no mention of Valphamax, those are your words.
As far as I know YOU set the initial conditions in YOUR post #652 (http://www.pprune.org/8380004-post652.html) I did not.
The objective for an Airbus test pilot when making high AOA demonstrations with alphafloor switched off is to demonstrate the capacity of the airplane to safely maintain alpha max at the corresponding Valphamax.

Trough the elevator the FCS controls speed by maintaining the proper alpha
Trough the thrust the pilot controls altitude ... not speed

[Owain Glyndwr]

Originally posted by Confiture
As far as I know YOU set the initial conditions in YOUR post #652 (http://www.pprune.org/8380004-post652.html)
Where I said

Although Airbus test pilots routinely made high AOA demonstrations with alphafloor switched off they invariably compensated for that by selecting a level of thrust commensurate with maintaining speed and altitude.

OG out

[CONF iture]

To which I replied
... with maintaining altitude, speed not being dependent on the level of thrust.

[HazelNuts39]

Trough the thrust the pilot controls altitude ... not speedI'm disappointed that you still don't seem to grasp a point I made more than once (see f.e. my post #520 on page 26):

When flying at alphamax, thrust controls altitude through speed:

Increase thrust - speed goes up - lift goes up - airplane goes up
Decrease thrust - speed goes down - lift goes down - airplane goes down

[Chris Scott]

Quote from HN39, in reply to CONF_iture:
"I'm disappointed that you still don't seem to grasp a point I made more than once (see f.e. my post #520 on page 26)
When flying at alphamax, thrust controls altitude through speed:
Increase thrust - speed goes up - lift goes up - airplane goes up
Decrease thrust - speed goes down - lift goes down - airplane goes down"

You're not the only one to be disappointed! In fact, for the benefit of new readers, you had earlier made the point on page 24 (http://www.pprune.org/I'm disappointed that you still don't seem to grasp a point I made more than once (see f.e. my post #520 on page 26):). It was picked up by others including myself, although the vertical component of thrust at high pitch-attitudes may assist the pilot somewhat.

The co-pilot, without any previous experience of the task, had been briefed to take control of the throttle levers if and when Capt Asseline found the task too onerous. Commenting on the knife-edge accuracy of control required by the co-ordinated efforts of the two pilots to maintain (even) the briefed height of 100 ft at alpha-max, I then wrote:

"Clearly, low flight at alpha-max is hazardous, for at least one reason: wind-shear, which is inevitable over and near trees and buildings, unless the wind at all levels is flat-calm (a rare event). Any loss of headwind or increase of tailwind leads to a loss of IAS. Recovery of IAS requires an increase in GS, i.e., kinetic energy. With no surplus of potential energy to convert, that increase in kinetic can only be supplied by an increase in thrust."

So was there any windshear on the day? A few days ago, I wrote (http://www.pprune.org/tech-log/528034-habsheim-32.html#post8371711):
Starting from level-off at TGEN 321 [t -13] and finishing with TGEN 334, the estimated W/Cs at one-second intervals are as follows:
-7, -4, -8, -9, -7, -7, -6, -4, -6, -5, -7, -7, -3, -3.

(TGEN 334 represents t -zero, the approximate second at which the a/c reached the treeline)
The Karsenty video shows a tall balloon on the west side of the airfield leaning slightly to the south, suggesting a light headwind for the accident a/c. The above wind-components are based on the usual comparison of the IAS-derived TAS, and the inertial ground-speeds (GSs). Any errors in the recorded GSs are likely to be consistent, but the IAS may have suffered increasing position-error in the last few seconds at higher AoAs.

The free-air W/C seems to be between -5 and -9. As the a/c CG was roughly the same height as the approaching treetops, it is likely that the loss of headwind component indicated in the above figures is genuine, and due to slight windshear in the lee of the trees.

Between TGENs 332 and 333 (t -2 and t -1), the recorded IAS drops by 4 kt (116 to 112), although there is no change in AoA, pitch, or GS. That would suggest a loss of wing-lift of the order of 7%, partly offset by the increasing vertical component of thrust as the N1 increased? (There may also be a slight reduction in HS downforce as the elevators unload slightly, one at a time.)

[Turbine D]

This thread has been quite interesting to read, lots of factual information and explanations. But there are exceptions:
with maintaining altitude, speed not being dependent on the level of thrust.
Say what? Since when?

[HazelNuts39]

Folks it is not necessary that speed change to change flight path angle up or down with thrust.It is when the AoA is constant.
You're making the assumption AOA stays constant which is not true. It is in alpha-protect mode because the FCS commands the elevator to maintain the AoA commanded by the sidestick position (leaving aside the phugoid damping terms, and the inclination of the thrust vector, to keep it simple).

[gums]

Salute!

It's good for some to realize that you do not have to increase speed/AoA to climb or descend.

Now, ya gotta be gentle with the throttle(s), but a well-trimmed plane (or one with max AoA command in the FBW planes) will climb or descend nicely using only power changes.

Would be interseting if any of the "modern" planes with "speed" mode on the AP would allow throttle/power changes made manually to control climb rate.

[HazelNuts39]

Would be interseting if any of the "modern" planes with "speed" mode on the AP would allow throttle/power changes made manually to control climb rate. If they do, they control speed by using the elevator to change pitch and AoA.

[roulishollandais]

I'm glad to watch that old piloting debate about how controlling path and speed. If we stop to forget the shape modifications and to forget that the aircraft is mostly in unsteady transient dynamic everybody will agree to common equations. ;)

[Chris Scott]

Hello gums,

If you were asking about ops in the normal range of AoAs, the answer is yes on most current transports.

With the A/THR off, but the AFS in speed mode, the AFS controls speed with elevator. So, if (s)he wants to do it that way, the pilot can adjust VS by changing the thrust manually. The most common scenario might be in a descent at idle thrust, if the a/c is going low on the profile and the pilot doesn't want to reduce the IAS/Mach, but it would work the same in a climb.

if the AFS is in altitude-hold, VS, (or FPA) mode, the pilot would of course be controlling IAS/Mach with thrust. And, if the A/THR was restored, it would use thrust to achieve whatever IAS/Mach the pilot calls for.


Returning to topic, you say:
"It's good for some to realize that you do not have to increase speed/AoA to climb or descend."

I would argue that the only way to initiate an increase in the FPA is to increase total lift. We are considering a case where the AoA is already at the maximum permitted. In a steady atmosphere - without briefly increasing the IAS - total lift can only be increased by increasing the vertical component of thrust, and/or reducing the HS downforce.

Re the vertical component of thrust, the high attitude obviously provides some effect in this case.

Re reducing the elevator downforce, the pitch couple with increasing thrust on an aeroplane with under-slung engines means that - bearing in mind that the A320 is not a canard ;) - the HS downforce has to be reduced to counteract the pitch-couple. So the elevators move down accordingly, which - as I pointed out yesterday - can be seen on the Habsheim DFDR.

Does that make sense?

[CONF iture]

When flying at alphamax, thrust controls altitude through speed
Negative - Alpha max is an AoA that the FCS maintains at the fixed value Airbus decided to adopt depending on the configuration.
The corresponding speed to that fixed alpha max value is called Valphamax and remains the same as well, be it in level flight descent or climb ... The amount of thrust will decide the V/S but the speed will remain at Valphamax.

[Chris Scott]

Quote from CONF_iture:
"[...] Alpha max is an AoA that the FCS maintains at the fixed value Airbus decided to adopt depending on the configuration.
The corresponding speed to that fixed alpha max value is called Valphamax and remains the same as well, be it in level flight descent or climb ... The amount of thrust will decide the V/S but the speed will remain at Valphamax."

The process of changing the FPA requires a force. Can you go on and explain how that force is produced?

[HazelNuts39]

Alpha max is an AoA that the FCS maintains at the fixed value Airbus decided to adopt depending on the configuration.
Agreed, I don't remember how many times I wrote that. It is the reason that the lift is proportional to airspeed-squared. Lift can only increase by increasing the airspeed.
The corresponding speed to that fixed alpha max value is called Valphamax and remains the same as well, be it in level flight descent or climb ... That is basically correct also, but only in 1-g condition (lift equal to weight). Strictly speaking the load factor in steady climb and descent is less than 1, but that difference can be ignored for small flight path angles. The point is that changing the flight path angle requires a net force normal to (at an angle to) the direction of movement. In steady level flight lift equals weight. To increase the flight path angle requires a lift force greater than weight. At constant angle of attack (i.e. constant lift coefficient) you can only increase lift by increasing speed.The amount of thrust will decide the V/S but the speed will remain at Valphamax. That is basically correct for the steady climb at constant V/S and airspeed, but not for the transition from level flight to steady climb. During that transition the V/S increases from zero to the steady climb value due to the vertical acceleration resulting from the net vertical force of lift minus weight.

[DozyWannabe]

...the only thing that can be stated for sure is that with the SS on the aft stop, pilot input to the FCS is taken out of the picture.

I'm a little reticent to contradict you, as I'm aware of your knowledge and experience - but I'm a little unsure about that statement. As far as I know, with the SS on the aft stop, pilot input is very much *in* the picture, it's just that the input is commanding the maximum until the SS is moved forward or released...

CONF is correct in stating that Alpha Max "...is an AoA that the FCS maintains at the fixed value Airbus decided to adopt depending on the configuration", but before the value can be maintained, it must be *attained*, and, if I read things correctly, the rate of attainment of that value will clearly be affected by other aspects, for example the phugoid damping if already in High AoA Protection mode.

[HazelNuts39]

OK465,

I don't disagree with what you are writing, but it does not change the physical law that increasing the V/S requires a vertical force that exceeds the weight of the airplane.

Secondly, the airspeed will increase or decrease at any instant during the transition at which the thrust is greater or less than that required to sustain the FPA at that instant. Therefore the FPA has to increase faster than the thrust to avoid any speed increase during the transition.

[gums]

I do not disagree that lift must change for a flight path change.

The point is that the change in lift does not have to be due to even a tenth of a gee or a knot or two. And it only has to change for a few seconds to have an effect. Then the plane tries to resume trimmed condition with thrust equal to drag and so forth.

I fully understand the "point the nose and use power for speed" technique. I also understand the "Navy" technique where AoA is very important to get the plane on the boat. I personally used a blend of the techniques depending on the plane I was flying. The low aspect ratio wings and high drag suckers were easier to use the throttle for descent or climb changes. The cleaner ones with high aspect ratio wings and low induced drag were more like an Aeronica or Cessna.

Still a good, if not great discussion.

[HazelNuts39]

The point is that the change in lift does not have to be due to even a tenth of a gee or a knot or two. And it only has to change for a few seconds to have an effect.The point is that it has to increase first before it decreases.

To achieve a FPA of 10 degrees at 115 kTAS takes roughly:

10 seconds at one tenth of a gee
5 seconds at two tenths of a gee
3 seconds at three tenths of a gee

[roulishollandais]

gums didn't fly in wind tunnels, nor in perfect gas, nor in a totally rigid plane, always in complex transient combinations.
Perhaps other physical models than official models do the plane fly . ie viscoplastic model is never used, where the chains of molecules brake partially, or scratched molecules like Velcro patches, or ....!
Any math model is worthful only if it is confirmed by accurate experience. gums is speaking from 1/10 of gee ,and probably less, and one knot difference, a part of a second. We still have much to learn from our best military pilots ...:ok:

[CONF iture]

The process of changing the FPA requires a force. Can you go on and explain how that force is produced?
During high AoA demo where full back stick has to be maintained the FCS is constantly working at maintaining alpha max, therefore the FCS will not use a thrust increase or additional aport of energy to increase the speed but to increase the pitch and the FPA.

The initial comment that started our discussion :
"Although Airbus test pilots routinely made high AOA demonstrations with alphafloor switched off they invariably compensated for that by selecting a level of thrust commensurate with maintaining speed and altitude."
had to be corrected as the FCS is dealing with speed through AoA and the pilot is dealing with altitude through thrust.

The later comment :
"They know that to make a correct demonstration of alphamax it is necessary to have enough thrust not only to maintain altitude but also to maintain speed. If that is not so the EFCS will apply a nose down corrective pitch command that will prevent achievement of alphamax."
had also to be corrected as the level of thrust is strictly to maintain altitude and not speed. You could be idle thrust and still maintain alpha max at Valphamax.

[Chris Scott]

Quote from CONF_iture:
"During high AoA demo where full back stick has to be maintained the FCS is constantly working at maintaining alpha max, therefore the FCS will not use a thrust increase or additional aport of energy to increase the speed but to increase the pitch and the FPA."

Okay, then what increases first - the FPA, or the pitch?
If the pitch, how can that be done without initially exceeding alpha-max?

[CONF iture]

Okay, then what increases first - the FPA, or the pitch?
If the pitch, how can that be done without initially exceeding alpha-max?
Hard to tell ... who came first, the hen or the egg ?
The FCS mission is to maintain alpha max whatever the amount of energy brought to the equation. The goal is alpha max and punctual under or overshooting of the alpha max value is part of the process too, the time for the FCS to absorb a variation of energy.

[DozyWannabe]

The FCS mission is to maintain alpha max whatever the amount of energy brought to the equation.

That's only partially true - you're looking at it from the assumption that Alpha Max has already been achieved, in which case the system will maintain it as speed continues to wash off, though eventually if airspeed is not sufficient to fly, ground contact is a certainty (however as the Habsheim and Hudson incidents showed, the aircraft will "fly" right up until impact). This is why, as OG correctly pointed out, Alpha Floor is an integral part of the combined systems protections - and why disabling it effectively transfers the responsibility for maintaining airspeed and thrust solely to the flight crew.

The part you've now skipped over twice is how the EFCS works to *achieve* Alpha Max if it's not there already, and the rate at which it does so seems to be contingent on the mode (pitch normal vs. high AoA protection) and how the latter mode brings the phugoid damping aspect into the equation.

It seems to be generally accepted that the TOGA thrust was applied too late, as was the SS back-stick command. In the case of the latter, HN39 brings up the interesting fact that the back-stick command was not only late, but somewhat hesitant as well.

To me, OG's discovery regarding the phugoid damping system and HN39's careful parsing of the DFDR data regarding application of back-stick both provide good technical explanations of why acquisition of Alpha Max was slower than it might have been with more favourable conditions (as you pointed out, Bechet achieved it much more quickly and HN39 reckons that was because he was still in pitch normal at the time). [EDIT : It also raises the slightly ironic possibility that if AF296 had pulled the SS back to attain Alpha Max earlier in the sequence (before crossing the threshold), the more rapid loss of airspeed would have necessitated thrust application sooner and might have put them in a better position.]

Add to that the low-energy state of the aircraft in general, and I'd say we now have more technical detail, but that ultimately it comes back to the original conclusion - the aircraft was too low, too slow and corrective action was applied too late.

[gums]

Yo!

Direct hit, Doze.

Add to that the low-energy state of the aircraft in general, and I'd say we now have more technical detail, but that ultimately it comes back to the original conclusion - the aircraft was too low, too slow and corrective action was applied too late.

It all comes back to a poorly executed, poorly planned/practiced "display".

Sheesh.

Even 200 feet and adding power to maintain decent speed should have "satisfied" the crowd, most of whom did not understand what the 'bus was trying to demonstrate.

The guy screwed up. All the flight control laws discussion is "noise".

I would have been fired had I done something like that unless I demonstrated the manuever with HHQ review. The Birds and Angels do hundreds of practices, and all of their maneuvers are reviewd/approved by HHQ. Look at the Angels' loop with the gear down. Then see the inverted passes with a wingie tucked in real nice on the other plane.

The flight control laws on the 'bus seem very realistic for a heavy. The engine performance is about like what I saw back in 1971 when moving to a "fan" ve5rus a pure turbojet motor. Big deal. Spool up time is a bit longer, so you must anticipate, and not wait until you realize that your power setting is too low for what you are trying to do - go around, maintaining proper descent on a precision approach, etc. Sheesh.

[DozyWannabe]

Direct hit, Doze.

Heh - while I must admit that I was going for a collegial tone rather than aggression, your support and sentiment are very welcome all the same.

The guy screwed up. All the flight control laws discussion is "noise".

To be honest, and I've said this before, I've gained so much more understanding of the systems design as it relates to flight mechanics from this thread that the discussion was definitely worth having anyway in my book.

And to play a bit of Devil's Advocate, while "screwed up" is a reasonable - if strongly-worded - conclusion to draw if you're looking purely at the conduct of the flight, if I'd been looking at it at the time I would have been deeply troubled by the apparent lack of oversight from - and shoddy preparation by - the airline. Obviously he was one of their top pilots on the A320 programme, and that implies a certain amount of trust and leeway - but he wasn't the only AF Captain in that position (indeed Capt. Bechet, who headed the investigation, was of equal seniority on the same programme). To me it just beggars belief that management didn't seem to require a peer review of the intended flight plan, because I'd be very surprised if such a review wouldn't have considered the level of risk unacceptable. At the very least I'd expect such a review to have triggered discussions with Airbus as to how it compared to their own practices.

I would have been fired had I done something like that unless I demonstrated the manuever with HHQ review.

Good practice, no question. But that dreadful B-52 accident demonstrated that even military practice can lapse if the person involved has a track record of making things difficult.

Anyways, nowt more to add - cheers again!

[Chris Scott]

Quote from gums:
The guy screwed up...

As a general observation, I think even the A320's strongest critics in this discussion have never disagreed that no flypast should be conducted with passengers, that 100 ft is too low at any speed, and that this one was ill-conceived, badly planned, and poorly executed - in a number of ways. The Karsenty video proves that beyond reasonable doubt each time we replay it.

...All the flight control laws discussion is "noise".

Given the general consensus that has been evident since the first couple of pages of this thread, some of us have taken the opportiunity to try and improve our understanding of flight at high AoAs in general, and the characteristics of the Airbus alpha-prot mode in particular - including aspects of its certification. Not only was this a unique accident in public transport, but all the gathered evidence provides unique opportunities for study.

Quote from Dozy Wannabe:
"... ultimately it comes back to the original conclusion - the aircraft was too low, too slow and corrective action was applied too late."

Assuming you are referring to the execution in relation to the plan, you are right on your first and last "conclusions", but wrong again on the second. The reason the crew decided to keep the thrust at idle - and then left it there until too late - was that the a/c arrived over the display area too fast - not too slow. :ugh:

[roulishollandais]

. Quote from Dozy Wannabe:
"... ultimately it comes back to the original conclusion - the aircraft was too low, too slow and corrective action was applied too late."

Assuming you are referring to the execution in relation to the plan, you are right on your first and last "conclusions", but wrong again on the second. The reason the crew decided to keep the thrust at idle - and then left it there until too late - was that the a/c arrived over the display area too fast - not too slow
Important observation. Agreed.

[DozyWannabe]

The reason the crew decided to keep the thrust at idle - and then left it there until too late - was that the a/c arrived over the display area too fast - not too slow. :ugh:

Of course - perhaps I should have qualified the statement as "*ended up* too slow". I've certainly never argued that the aircraft wasn't fast and high on the approach initially!

[gums]

Agree with Chris and Doze.

He was too fast, and had to keep power low to finally reach max AoA or whatever some want to call it. Then was slow getting the power back in.

As with others here, I have learned a lot about the "laws" and details about the nuances of the "laws". IMHO, they ain't so straight forward as some might think, huh?

[DozyWannabe]

IMHO, they ain't so straight forward as some might think, huh?

Well, from a technical standpoint they have to be complex by their very nature - they were designed to be as transparent and easily-learned as possible for the end-users (i.e. pilots) though. Of course, there's only so much simplification one can do!

That said, I think it's fair to state that at or below 100ft RA at an unfamiliar airfield is definitely not a suitable time to start probing around the limits of the systems, one's experience with those systems or both - regardless of whether or not you've got pax behind you!

[Chris Scott]

Quote from Dozy Wannabe:
" - perhaps I should have qualified the statement as "*ended up* too slow". I've certainly never argued that the aircraft wasn't fast and high on the approach initially!"

Even that statement would require to be qualified with something like "for the current power setting". During 35 pages of reading and contributing enthusiastically, you have evidently not fully grasped the fundamentals of the basic scenario, nor those of the developing argument.

The game plan was to display the a/c in stabilised flight at an AoA of alpha-max, meaning that - using a fairly high thrust-setting - the airspeed would have remained roughly constant at Valpha-max in level flight and during a spectacular go-around.

The essence of the accusation repeatedly made by CONF_iture is that the a/c failed to achieve alpha-max after the PF called for it. That means that its IAS remained ABOVE Valpha-max until the treetops slowed it down. He argues, understandably, that the slight, residual surplus of speed above Valpha-max could have been traded more immediately for height.

Contributors who are expert in aerodynamic performance have explained that the refusal of the EFCS to respond immediately to the stick-command ** was due to the lack of thrust, and the decaying IAS. The latter may have been exacerbated by a slight loss of headwind component at about t -2: that crucial moment when the N1s were still low, although spooling-up.

Therefore, the unqualified statement "ended up too slow", is simplistic, to say the least. Strictly speaking, it is incorrect and misleading. I'm sure that's not what you intended?


** (that is, increase the AoA as soon as physically possible to the commanded value of alpha-max)

[PJ2]

A fine and for me definitive response Chris Scott, thank you.

[CONF iture]

That's only partially true - you're looking at it from the assumption that Alpha Max has already been achieved
Because that's part of the alpha max demo and that's where (http://www.pprune.org/8381705-post657.html) our discussion with OG initially started.

in which case the system will maintain it as speed continues to wash off, though eventually if airspeed is not sufficient to fly
Obviously you still didn't get what alpha max is ...

you simply cannot "wash off speed" and "maintain alpha max" at the same time
Airspeed is always sufficient to fly at alpha max


ground contact is a certainty (however as the Habsheim and Hudson incidents showed, the aircraft will "fly" right up until impact).
As a start, neither Habsheim or Hudson were at alpha max.

This is why, as OG correctly pointed out, Alpha Floor is an integral part of the combined systems protections - and why disabling it effectively transfers the responsibility for maintaining airspeed and thrust solely to the flight crew.
Alpha floor is an auto thrust function only and has nothing to do with maintaining speed for a flight crew.

The part you've now skipped over twice is how the EFCS works to *achieve* Alpha Max if it's not there already, and the rate at which it does so seems to be contingent on the mode (pitch normal vs. high AoA protection) and how the latter mode brings the phugoid damping aspect into the equation.
I have not skipped anything, but the BEA obviously has.
The US and Spanish teams have underlined the lack of pitch authority given to the pilots - They made some research and proposed possible explanations.
The BEA did ... nothing : "normal functioning of the aircraft"

It seems to be generally accepted that the TOGA thrust was applied too late
That part is a ALL chapter on its own as Asseline pretends TOGA was applied 4 seconds earlier than the BEA has concluded ... But we can keep that chapter for later as we have already enough to discuss on alpha max for now.

The essence of the accusation repeatedly made by CONF_iture is that the a/c failed to achieve alpha-max after the PF called for it.
Actually it is more specific : the elevator movements show that the FCS had no intention to deliver anything closer than 2.5 deg short of alpha max.
And the BEA has not provided any reason for such restriction.
But I mainly agree with the way you write the conclusion :
"That means that its IAS remained ABOVE Valpha-max until the treetops slowed it down. He argues, understandably, that the slight, residual surplus of speed above Valpha-max could have been traded more immediately for height."

Contributors who are expert in aerodynamic performance have explained that the refusal of the EFCS to respond immediately to the stick command was due to the lack of thrust, and the decaying IAS.
Then our "experts in aerodynamic performance" are in total contradiction with the BEA who conducted the simulated flight at the hands of Bechet.

The latter may have been exacerbated by a slight loss of headwind component at about t -2: that crucial moment when the N1s were still low, although spooling-up.
We need something more substantial than an hypothetical 2 kt wind shear to justify a drastic difference in the FCS response between the simulated flight and the Habsheim one.

[HazelNuts39]

Confiture,

In my post #605 (http://www.pprune.org/tech-log/528034-habsheim-31.html#post8355502) I noted the difference between Bechet's simulation and the accident flight. Bechet went to full side stick before entering alpha-prot, and Asseline after, 3 seconds later.

The difference between the two flight control modes is decribed in the Final Report, 1.16.1.2 Lois de pilotage de l'Airbus A 320:

Pendant la phase de descente entre 50 et 30 pieds, la loi de pilotage est modifiée et prend progressivement en compte (*), 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)

(*)Cette prise en compte est progressive : le changement de loi s'effectue en une seconde.

(...)

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.

Ce dernier mode de pilotage, dénommé Alpha Prot (protection d'incidence) est un mode prioritaire dès que l'incidence atteint 14,5°. Il ne constitue pas un mode dégradé et ne peut pas être désactivé par l'équipage.
(...)

Entre t - 18 s et t - 4 s, loi de pilotage en assiette (écart par rapport à la valeur de 6° mesurés lors du passage à 50 pieds) ;

A t - 4 s, commutation sur la loi de pilotage en incidence, la valeur de 14,5° ayant été atteinte, cette loi étant ensuite conservée. If you see a contradiction with the BEA report please explain where you see it.

EDIT:: Phugoid damping is a feature of the alpha-protection mode, because an airplane is prone to develop phugoid motions when constrained to a commanded angle of attack. Flying an airplane to a commanded pitch attitude does not result in phugoid motion, and therefore pitch-command mode does not require phugoid damping.

[CONF iture]

HN39,
I do salute your effort to provide what the BEA and Airbus should have dealt with ... but as you quote part of the Report, absolutely nothing in 1.16.1.2 details or even mentions why the FCS response in its capacity to command alpha max should be different whether full back stick is applied before or after Alpha Prot is reached.
The paragraph in question had no intention to deal with such aspect but is purely an attempt to justify why what they call the de rotation law or the ground effect simulation law could not have negatively interfered during the event.

[HazelNuts39]

Confiture,

There is no discussion of alpha-protection phugoid damping in the BEA report, it doesn't go into that level of detail. Many more details have been discussed in later reports of BEA and other investigators.

I'm well aware of your views regarding the BEA, but where is the "total contradiction"?

[CONF iture]

There is no discussion of alpha-protection phugoid damping in the BEA report, it doesn't go into that level of detail.
Then why do you quote at length a paragraph that says nothing on the topic if you want to use it to justify your hypothesis ... ?

I'm well aware of your views regarding the BEA, but where is the "total contradiction"?
Before, at, and after thrust levers are advanced to TOGA position, both Bechet and Asseline suffer from the same "lack of thrust and decaying IAS"

Our "experts in aerodynamic performance" explain that's the reason why the FCS did not comply
The BEA demonstrates how the FCS fully complies

It is what I call total contradiction ...

[DozyWannabe]

The US and Spanish teams have underlined the lack of pitch authority given to the pilots - They made some research and proposed possible explanations.
The BEA did ... nothing : "normal functioning of the aircraft"

The Bilbao and Hudson investigations were of a very different scope though. Bilbao highlighted an unforeseen 'gotcha' (for want of a better phrase) in the EFCS design when subjected to a tail gust - Airbus themselves admitted as much - and therefore a degree of research would have to focus on what precisely caused this unwanted behaviour. The Hudson investigation would have been interested in focusing on every detail of what was an exemplary bit of piloting, and therefore would want to go over the technical aspects with a fine-toothed comb. It's also worth pointing out that the behaviour of the phugoid-damping aspect of HAP mode was known in the industry by that time as a result of Bilbao, and would have been something they'd want to test anyway.

Overall, what distinguishes those incidents from Habsheim is that they occurred on what were routine ops, and in both cases the airmanship from the crews couldn't be seriously faulted.

With Habsheim, what the BEA were faced with was a system-wide failure. Even setting the airmanship question aside, there should have been red flags raised within the airline and by the crew well before the aircraft ever left the ground.

Ultimately, the main aim of the investigation was to ensure that something like that never happened again. I'm happy to concede that an argument could be made that the BEA missed an opportunity to look further into the phugoid-damping aspect in the course of that investigation, however at the same time when looking at the circumstances of the accident holistically, that would have been a small, tangential issue at most when compared to the obvious shortcomings of AF regarding the handling of the operation and the conduct of the flight itself.

I would also be inclined to argue that Capt. Asseline himself bears some responsibility for the way that part was covered - after all it was he who made the decision to disengage from the investigation as soon as the scope moved in a direction he didn't like. I think it's a distinct possibility that if he'd been able to swallow his pride and continue to work with Bechet and the other investigators, then more technical detail may have been uncovered. But by retreating behind his lawyers, openly briefing the press against the investigation with claims of a cover-up and an increasingly bizarre veil of excuses, he left the investigators with no option but to try and work things out on their own.


Our "experts in aerodynamic performance" explain that's the reason why the FCS did not comply
The BEA demonstrates how the FCS fully complies


You're parsing things again. The BEA said that the EFCS behaviour was *normal*, it did not (as far as I know) say anything about complying with the demand.

whether full back stick is applied before or after Alpha Prot is reached

Unfortunately the report in that sentence uses the term "Alpha Prot" (which as you have stated is a value rather than a mode) to refer to High AoA Protection mode (to give the mode its correct nomenclature in English Airbus documentation), which can cause confusion. If you'll excuse Google Translate again:

The latter control mode , called Alpha Prot ( [AoA] protection ) is a priority mode when the incidence reached 14.5 ° . It is not a degraded mode and can not be disabled by the crew.

If you combine this with what HN39 was saying:

Phugoid damping is a feature of the alpha-protection mode, because an airplane is prone to develop phugoid motions when constrained to a commanded angle of attack. Flying an airplane to a commanded pitch attitude does not result in phugoid motion, and therefore pitch-command mode does not require phugoid damping.

It can therefore be deduced that - based on the assertion that it was the phugoid-damping feature which slowed acquisition of 17.5deg AoA - the difference between pulling the SS back in HAP mode versus pitch normal is that there is no phugoid-damping in pitch normal, thus less potential impediment to the rate the system can acquire 17.5deg AoA.

PS - @Chris Scott - many thanks for the clarification.

[Chris Scott]

Quote from Dozy Wannabe:
"[...] the difference between pulling the SS back in HAP mode versus pitch normal is that there is no phugoid-damping in pitch normal, thus less potential impediment to the rate the system can acquire 17.5deg AoA."

No. The EFCS would never permit the AoA of alpha-prot (in this case 14.5 deg) to be exceeded in Normal Law without introducing High-AoA Protection mode. Therefore, to imply that alpha-max might be achieved in a shorter time from Normal Law than from an AoA in High-AoA Protection mode is a non-sequitur.

[DozyWannabe]

No. The EFCS would never permit the AoA of alpha-prot (in this case 14.5 deg) to be exceeded in Normal Law without introducing High-AoA Protection mode. Therefore, to imply that alpha-max might be achieved in a shorter time from Normal Law than from an AoA in High-AoA Protection mode is a non-sequitur.

Perhaps I should elaborate. While pulling the SS all the way back in Pitch Rate Normal will, as you say, engage HAP mode upon reaching 14.5 degrees, the rate at which pitch-up is commanded will - if I have this right* - be somewhat more rapid than if the aircraft has been put into HAP mode with partial back-stick for some time before full back-stick is commanded. Based on discussions offline, I believe the phugoid-damping aspect of HAP mode relies in part on airspeed deltas recorded at certain time frames prior to that point. Because, as HN39 pointed out:

...an airplane is prone to develop phugoid motions when constrained to a commanded angle of attack. Flying an airplane to a commanded pitch attitude does not result in phugoid motion, and therefore pitch-command mode does not require phugoid damping...

It is therefore reasonable to infer that the EFCS only uses these deltas (and possibly only stores them) after HAP mode is triggered.

One possibility is because the change in pitch is more rapid from Pitch Rate Normal, there is less time for these deltas to be interpreted as phugoid motion by the EFCS (and because pitch changes due to phugoid motion tend to be more gradual). Certainly in the sim, full back-stick from straight and level seemed to induce a very rapid pitch change.

Another (which could complement the first) is that the decaying airspeed along with the more minor pitch change due to the hesitant back-pressure prior to 3 seconds before impact could also be interpreted as phugoid motion. The damping would then progressively introduce pitch-down in order to counteract this, increasing the time required for the full back-stick command to deliver Alpha Max.

In any case, the damping feature requires a period of time to come into effect, and the faster the aircraft is rotated, the less time that feature has to make any immediate changes to the elevator command.

[* - As stick deflection in Pitch Rate Normal commands rate of pitch change rather than AoA or load factor]

[HazelNuts39]

Capn Bloggs in another thread (http://www.pprune.org/tech-log/536616-thrust-during-flare-q-airbus-test-pilots.html#post8399672):
"Always remember and forever take heed: left hand for glidepath and right hand for speed!" (Reverse for first officers).Fits well into our thread indeed.

[CONF iture]

You're parsing things again. The BEA said that the EFCS behaviour was *normal*, it did not (as far as I know) say anything about complying with the demand.
The simulator experiment alone demonstrates what they didn't want to say.

No. The EFCS would never permit the AoA of alpha-prot (in this case 14.5 deg) to be exceeded in Normal Law without introducing High-AoA Protection mode. Therefore, to imply that alpha-max might be achieved in a shorter time from Normal Law than from an AoA in High-AoA Protection mode is a non-sequitur.
Amen

[DozyWannabe]

So what do you think happened, and what is it you think "they" didn't want to say?

[CONF iture]

A clear restriction in the FCS that prevented the aircraft to get the optimal performance when most needed. If it is part of the normal functioning, then everything should be apparent in the decoding of the algorithms ...

[DozyWannabe]

So are you then suggesting that a fix was devised in secret and subsequently applied to the simulator and aircraft Bechet used for his own testing?

If so, given the timeframe, I don't think that's plausible - but as always I can't be certain. Having said that, why would there be a deliberate restriction there in the first place? It all seems a bit too cloak-and-dagger to me.

EDIT : Furthermore, in practical terms it seems unlikely - the software engineering processes made extensive use of regression testing and other techniques that maintained a record of changes made to the implementation over time. If a change was made, then every software engineer working on the project for Airbus at the time would have to have known about it, and with a team of that size it would be a massive gamble that they'd all keep their silence in perpetuity. As with all conspiracy theories, the fact that so many people would have to have known about it and subsequently keep schtum is a major roadblock to plausibility.

Additionally, if such a restriction was found and fixed, surely it would have been better PR for Airbus to tell the world that they had found and fixed the problem, would it not?

EDIT 2 : As for "decoding" the algorithms, the program source code is machine-generated from a graphical layout system - machine-generated code tends to be very difficult to reverse-engineer. You'd have better luck with the schematics, though you'd still need a qualified EE/Systems Engineer to decipher them for you.

[DozyWannabe]

I ... have noticed that when a 'required' simulator update is installed for some specific reason, or even when a completely new Ops package version is installed to update a whole host of functionality, occasionally you will find other supposedly unchanged systems and characteristics to be affected...

From a software engineers' perspective I don't think that's anything out of the ordinary. Modular software design tends to inherently create "dependencies" between modules, so if a change is made in one module, then there will usually be at least some code affected in other modules - sometimes in quite surprising areas, depending on how the system architecture is laid out.

Your point also adds to why I think a surreptitious update scenario is unlikely, because it's not just Airbus's own software guys that would have to keep quiet, you've then got the sim engineers who have to install and test the update, the aircraft techs who had to do the same on the A320 Bechet used, and so on. Any one of them blowing the whistle at a later date would do far more long-term damage to the reputation of the company and the project than simply "'fessing up" to a mistake - as proven by the case of MD's DC-10 and the notorious "Gentlemens' Agreement".

[CONF iture]

So are you then suggesting that a fix was devised in secret and subsequently applied to the simulator and aircraft Bechet used for his own testing?
Asseline had to face a restriction in the FCS that Bechet did not.
Now, suggest whatever you like ...

As for "decoding" the algorithms, the program source code is machine-generated from a graphical layout system - machine-generated code tends to be very difficult to reverse-engineer. You'd have better luck with the schematics, though you'd still need a qualified EE/Systems Engineer to decipher them for you.

I figure Airbus has all the necessary ressources
It was not a time to reveal or detail any shortcoming
Airbus preferred propagating the myth that the envelope protection had prevented the aircraft from a catastrophic stall

[DozyWannabe]

Asseline had to face a restriction in the FCS that Bechet did not.

No, something was different, we don't know what. We do know that Bechet's handling of the SS (emphatic and direct) was different to Asseline's (hesitant). I still think that's a better place to look than a nebulous "restriction" or "bug" in the software for which there is no evidence of it's existence or removal before Bechet came to do his tests.

The problem with Asseline is that he's been invested in this idea of a cover-up for so long that neither he nor his supporters are capable of seeing it any other way.

[roulishollandais]

@DozyWannabe & CONF_itureEDIT 2 : As for "decoding" the algorithms, the program source code is machine-generated from a graphical layout system - machine-generatedcodetendsto bevery difficult to reverse-engineer. You'd have better luck with the schematics, though you'd still need a qualified EE/Systems Engineer to decipher them for you. Algorithms need to be encoded not decoded. They describe the system in the nearest form of natural language (math included:p).Shematics already need to know System theory tools. Pilots need to know algorithms. Asseline seemed to don't know them. Did Chris Scott knew them?

[CONF iture]

The problem with Asseline is that he's been invested in this idea of a cover-up for so long that neither he nor his supporters are capable of seeing it any other way.
The data show he's not necessarily wrong ... but Dozy has been invested in this idea for so long that no Institution and/or Corporation would ever protect their interest First that he is unable of seeing it any other way.

[DozyWannabe]

Not at all, but based on the complete lack of any evidence that there was anything untoward going on, no whistle blown at 25 years and counting, Dozy thinks it's a fairly unlikely possibility.

Also, it's a pretty tenuous claim that pretending there was no issue when there was one would be in the interest of the corporation or the institution involved. Bear in mind that the last company to try that ended up with their project given the nickname "Death Cruiser", and eventually went out of business - their assets becoming part of Boeing.

[CONF iture]

Also, it's a pretty tenuous claim that pretending there was no issue when there was one would be in the interest of the corporation or the institution involved.
Obviously they got out from it pretty well as not only they managed to hide the FCS restriction but in the meantime they pushed for their favorite myth :
"the envelope protection has prevented the aircraft from a catastrophic stall"

[Turbine D]

Original quote by Dozy:
Also, it's a pretty tenuous claim that pretending there was no issue when there was one would be in the interest of the corporation or the institution involved. Bear in mind that the last company to try that ended up with their project given the nickname "Death Cruiser"
A little bias seeping through?

Airbus was a little more astute than MD when it came to sweeping issues under the carpet. This was the lesson they learned from the DC-10s.

The Aviation Safety Network reports a total of 32 hull-loss incidents, which are incidents where the aircraft had to be scrapped. Over the life of the model, there have been 1,439 deaths as a result of the aircraft. In comparison, the Airbus A300 has been involved in 31 hull-loss incidents, claiming a total of 1,436 lives. While fewer A300′s than DC-10′s were delivered, the A300 is a much newer aircraft than the DC-10, and would have the benefit of lessons learned from the DC-10.

[DozyWannabe]

A little bias seeping through?

Nope, just a reasonable point as to why keeping things schtum is more likely to cause further problems down the line.

Airbus was a little more astute than MD when it came to sweeping issues under the carpet. This was the lesson they learned from the DC-10s.

Sorry, I don't see what that has to do with "sweeping... under the carpet". The DC-10 got a bum rap because of the notoriety of the early accidents, but its later record was actually as good as or better than many other types. It was the damage to their reputation as a result of being caught trying to solve the cargo-door problem while avoiding an AD (and failing to fix it on the THY DC-10 that crashed) that caused the loss of confidence.

As you said - Airbus tended to be savvy and astute PR-wise. They'd have been unwise to go down the same route as MD did in the early days of the DC-10.

@CONF - *or* there was no "restriction" in the FCS, and the aircraft did indeed prevent a stall, because it didn't stall! The stall might still have happened after clearing the trees without active protection...

I'm wondering if you think that somewhere in the code, the A_MAX variable was transposed with A_PROT. Because of the way the systems were developed, this is unlikely because the unit and regression tests (both written separately from, and chronologically before, the code itself) would also have had to carry the same error, otherwise the tests would fail. The presence of regression tests also means that a later change would have shown up in the reports - something that every software engineer on the project would have seen. As OK465 says, the change would also have shown up in the sim logs, so everyone involved in the update would also have had to be sworn to secrecy. To me that's just too many potential loose ends for Airbus to consider taking the risk.

[CONF iture]

*or* there was no "restriction" in the FCS, and the aircraft did indeed prevent a stall, because it didn't stall! The stall might still have happened after clearing the trees...
*or* one day you might understand what alpha max is ...

[DozyWannabe]

CONF, with all due respect - if you could just ease off on the insults and listen to what I'm saying, it might help us get somewhere.

I know what Alpha Max is, I know it wasn't reached and I suspect that the reason it wasn't has something to do with a combination of phugoid damping and Asseline's tentative stick input compared with Bechet's. I can't be certain, in fact none of us on either side of the argument can - all we can do is try to work out what's likely and what is less likely.

The assertion that the protections may have "prevented a stall" is based on Asseline's control inputs prior to impact, had they been applied to an unprotected aircraft. Without protections, full back-stick would have caused the pitch (and AoA) to increase regardless of whether there was sufficient airspeed. Without an AoA indicator to guide him, it's likely that the instinctive pull would have caused an unprotected aircraft to exceed alpha-stall (to use your nomenclature). Of course, Bechet's inputs during the test were even more immediate and positive, so he'd likely have stalled an unprotected aircraft as well.

I'm still learning about the aero side of things, but what I'm certain of is the methods used in developing the FCS software - and I'm telling you that it is *extremely* unlikely that there would have been a logical error limiting AoA to the A_PROT value, because there were around three layers of test harnessing that would have caught such an error, and each of those layers would have had to separately been developed with the same mistake - hence why I believe it's so unlikely.

EDIT:

Furthermore, whether the aircraft did or did not clear the trees is really just a footnote in terms of the investigation as a whole. Clearing the trees would have avoided the deaths, meaning Asseline would not have been prosecuted for manslaughter, but the existence of the video, whether it showed a crash or a close call, would still likely have ended his career. The investigation as a whole was more concerned with the lack of oversight from the airline and the decisions made during the approach phase than it was the mistakes made during the conduct of the last few seconds of the flight - as such, Airbus would have had no reason to cover up any technical problem. As the MD experience proved, it's far better PR for a manufacturer to put their hands up to a mistake and fix it than to risk being exposed trying to hide it.

EDIT 2: I'm surprised that you haven't picked up on the fact that I've gone from thinking phugoid damping wasn't a factor to being fairly convinced that it was. There's nothing wrong with changing one's mind if new information becomes available!

[DozyWannabe]

I've got a question....if you're trying to duplicate something in a simulator, why would you do something 3 seconds early and more aggressively?

At a guess, I'd say the sim run that generated that particular data was not an attempt to duplicate the accident sequence, but to determine the limits of system behaviour. In this case they were probably trying to ascertain what difference more prompt and decisive action may have made, if any.

If I've understood previous posts on the subject, the simulator available at that time was still being refined in terms of aerodynamic response when compared to the real aircraft. If this is correct, then sim runs would really only have been of use in terms of defining systems behaviour. The real world run over the Toulouse runway would probably have been more along the lines of an attempt to duplicate the flightpath.

[CONF iture]

CONF, with all due respect - if you could just ease off on the insults and listen to what I'm saying, it might help us get somewhere.
Take it as an insult as you wish, it was merely the observation that contrary to what you're pretending, you still don't get what alpha max is (http://www.pprune.org/8394710-post706.html), and a stall could not have happened after clearing the trees as alpha max is not alpha stall.

I'm wondering if you think that somewhere in the code, the A_MAX variable was transposed with A_PROT.
Don't bother thinking for me, just read what I write, you will spare me theories I did not ask for.

I'm surprised that you haven't picked up on the fact that I've gone from thinking phugoid damping wasn't a factor to being fairly convinced that it was.
Good for you ... what I was expecting is a BEA + Airbus analysis.
By the way if phugoid damping was involved, they could have detailed why Bechet was miraculously spared from it ... ?

[Owain Glyndwr]

@OK465

I've got a question....if you're trying to duplicate something in a simulator, why would you do something 3 seconds early and more aggressively?Actually, if you have access to a development simulator you wouldn't involve pilots at all; you would simply set up the initial conditions and feed in the actual control movements [sidestick; TLA]. This is what Aerospatiale did to produce the comparison shown on p13 Annex X of the BEA report.

The calculated response in the last couple of seconds (from just after the time where the IAS is marked as 114kt) is rather interesting - [Sidestick held fully back at -16deg, TLA at TOGA position]

[roulishollandais]

Actually, if you have access to a development simulator you wouldn't involve pilots at all; you would simply set up the initial conditions and feed in the actual control movements [sidestick; TLA]. A simulator stays a simulator today, since they always have commands which don't exist on the plane and use metalanguage :bored:

EDIT 1 : "real system" replaced by "plane", but it is the case too if you simulate a rocket or another computer,aso.

[DozyWannabe]

...and a stall could not have happened after clearing the trees as alpha max is not alpha stall.

You clearly didn't read what I wrote, because I said they were comparing it to a *conventionally-controlled* aircraft. Alpha Max is irrelevant in that situation because full back-stick/yoke does not command Alpha Max in a conventional aircraft, it just moves the elevators to the stop - if the aircraft is moving fast enough, it will pitch up and climb, but if it is not, it will pitch up and stall.

Good for you ... what I was expecting is a BEA + Airbus analysis.
By the way if phugoid damping was involved, they could have detailed why Bechet was miraculously spared from it ... ?

As HN39 said, phugoid damping is not used when in pitch command (i.e. the mode Bechet was in), only in HAP mode (which Asseline was in).

As I said before, the fact that the investigation went as far as confirming the behaviour as normal, but no further, could be argued as a point that they missed an opportunity to further explore the mode switches (and consequences of those changes) involved. However, the events of the last three seconds in the context of an accident investigation could equally be considered a minor point when compared to the major systemic failures that led to the aircraft being put in that position. Namely:


The airline provided woefully inadequate briefing materials
The airline failed to perform even a cursory review and risk assessment of the flightplan
The airline failed to check the flightplan against DGAC regs regarding minimum altitude for display flights
The airline did not require the crew to submit an effective "Plan B" for each stage of the flight plan
The airline did not require the flight crew to familiarise themselves with the airfield, other than how it appeared on the chart (i.e. no prior recce flight was required)
Neither the airline nor the flight crew attempted to confirm which runway was in use for the airshow on that day


The result of these failures was that the flight crew were effectively entirely reliant on their ability to improvise at short notice - which, given the inherent riskiness of the manoeuvre, should have been completely unacceptable on the face of it. Even more so when you take into account that there were pax on board.

To the best of my knowledge, "Priority One" of accident investigation is working to ensure that the incident is never repeated.

Now, I'm no accident investigator, but if I were I'd be inclined to consider getting to the bottom of how the aircraft was permitted to get into that position in the first place as a much higher priority than getting too far into why the Alpha Max command was complied with more slowly than it otherwise might have been (especially given the fact that the flight had been woefully mismanaged long before Asseline pulled that stick back).

Put another way, if the mistakes and loopholes in the list above can be prevented and closed, then with all other things considered there should never be another aircraft put in that position again, making the assessment of precisely why the aircraft was slow to achieve Alpha Max somewhat of a moot point.

Again, I said before that Asseline's best hope of being able to get the investigation to look further into the matter of what the EFCS was doing in those last few seconds would have been to take his lumps and remain positively engaged with the investigation throughout. By disengaging from the investigation and subsequently actively briefing against it, he did his own cause more harm than good.

[DozyWannabe]

If I'm reading it correctly, I am guessing that what you're referring to here is the fact that in the simulation, the elevator smoothly continues to trend leading edge less down (less negative)/aircraft less nose up until the end of the plot.

Now look at the thrust and IAS, and what the pitch is actually doing. :)

[roulishollandais]

Metalanguage = object formal language in semantic brackets.

Example of semantic brackets in character strings is using a special character which is never used in the object language.
As the number of characters is very limited, the special character is often an unused string of characters, like : = , http://www , Ctrl Z, [/quote] and [quote], etc.

Building an object language vs metalanguage may use different gramatic too but it is not mandatory.

Children playing to be master or parents or king mostly build metalanguage to be considered as master, parents or king! Sometimes they forget to use the metalanguage and suddenly they are no more king, and everybody is laughing.

In the simulator a hidden mistake (forget the space between ":" and "=" and you discover a smiley no-no instead of the string ": =" ) in the metalanguage semantic brackets may modify the behaviour of the simulated system (plane, inertial system, aso) without you know it, and you have a bad surprise when you do the same action on the plane, despite your aerodynamic algorithm is OK.

It is always difficult to test the semantic brackets, you would mostly need a meta-meta-language!

All that applies well on well structured simple systems using formal language. Graceful degradation brings a greater complexity .... KISS!

[DozyWannabe]

@roulis - I've said before, the computer code is not manually keyed in in that manner. Code blocks are tested in situ against the formalised function, then assigned to an element in a graphical development environment, which then generates the logic path from those individually-tested blocks of code. Each subsystem is then itself tested against the required behaviour pattern, and as the subsystems are linked together to form an overall program "module", that module and its functions are tested individually and in conjunction with others.

These tests are run *every single time* a change is made, and the results of the tests plotted against a regression graph. Any change in that graph is immediately apparent, and will point to exactly where the program deviates from the specified behaviour.

[CONF iture]

You clearly didn't read what I wrote, because I said they were comparing it to a *conventionally-controlled* aircraft.
Typical Dozy disinformation again - where is the quote ?

As HN39 said, phugoid damping is not used when in pitch command (i.e. the mode Bechet was in), only in HAP mode (which Asseline was in).
Speculation only from HN39 that would demonstrate how the system is inefficient but you're happy to take it for cash ... Where is the official reference ?

[DozyWannabe]

Typical Dozy disinformation again - where is the quote ?

Here's a novel idea, why don't you find it and prove me wrong?

EDIT : Certainly whenever I've heard that factoid referred to in the past, I got the impression that they were talking about an unprotected (i.e. conventional) aircraft - not least because I can't see how it makes sense any other way!

Speculation only from HN39 that would demonstrate how the system is inefficient but you're happy to take it for cash ... Where is the official reference ?

It's not inefficient, it's a necessary consequence of an aircraft being commanded to achieve or hold a specific AoA - namely a tendency to begin a phugoid motion.

On a different subject, I strongly recommend you have a look at OG's post #734, then look at the graphic on Annex 10 p.13. Bear in mind that what you're looking at (I think) is a simulation of how the aircraft and systems would have responded to the commands as they were prior to impact had there been no collision (114 kt being very close to the airspeed achieved just prior to impact).

[CONF iture]

Here's a novel idea, why don't you find it and prove me wrong?
Assume the disinformation you're spreading around or retract it.

It's not inefficient, it's a necessary consequence of an aircraft being commanded to achieve or hold a specific AoA - namely a tendency to begin a phugoid motion.
Knowing both are starting from identical parameters, why Asseline should be subject to it but Bechet not ... ?

[DozyWannabe]

Assume the disinformation you're spreading around or retract it.
Why?

(Or more to the point, how is it fair that you get to make unsubstantiated claims of a "restriction" in the EFCS (and insinuate that it may have been surreptitiously removed) unchallenged, whereas I must retract any statement with which you disagree out of hand?)

Knowing both are starting from identical parameters, why Asseline should be subject to it but Bechet not ... ?

They're not starting from identical parameters. As stated:

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.

Check the graphs on Annexe X, page 9. Look at the bottom of the page (when rotated lengthwise), and you'll see a graph indicated "Manche Longitudinal". Asseline's inputs are the broken, dotted plot and Bechet's are the unbroken plot. Note that on this particular run, Bechet snaps the stick back almost immediately approximately 3 seconds prior to when Asseline did the same. Bechet's action is just prior to when the mode switched from pitch command to HAP mode. Asseline's motion is also more gradual.

[CONF iture]

Why?
That's what responsible adults would do.

They're not starting from identical parameters.
Yes they are, according to the graph at the remise des gaz, except that Bechet is 10ft lower ...

Note that on this particular run, Bechet snaps the stick back almost immediately approximately 3 seconds prior to when Asseline did the same. Bechet's action is just prior to when the mode switched from pitch command to HAP mode. Asseline's motion is also more gradual.
Then if I had to guess the one who could be more prone to phugoid motion I would go for Bechet not Asseline.

[DozyWannabe]

according to the graph at the remise des gaz, except that Bechet is 10ft lower ...

Not quite 10ft, and Bechet pulls back roughly at the same point as "remise des gaz", whereas Asseline waits for around 3s before doing the same.

Then if I had to guess the one who could be more prone to phugoid motion I would go for Bechet not Asseline.

How? Asseline was in HAP mode when he pulled full-aft, Bechet was in pitch command.

[CONF iture]

Not quite 10ft
How much then ?

How? Asseline was in HAP mode when he pulled full-aft, Bechet was in pitch command.
It does not change anything - they still have to deal with the same level of energy.
Still waiting for the reference stating phugoid damping under high AoA protection but none under pitch command ...

[HazelNuts39]

Speculation only from HN39
Still waiting for the reference stating phugoid damping under high AoA protection but none under pitch command ...
Phugoid damping is a feature of the alpha-protection mode, because an airplane is prone to develop phugoid motions when constrained to a commanded angle of attack. Flying an airplane to a commanded pitch attitude does not result in phugoid motion, and therefore pitch-command mode does not require phugoid damping.
Firstly, both the Bilbao report and the Hudson river report mention phugoid dammping explicitly for the high angle of attack protection mode. If you have a reference stating that it is a feature of the pitch command mode then please provide that reference.

Secondly, I explained in post #707 why phugoid damping is necessary in alpha-prot and unnecessary in pitch command mode. I showed a phugoid motion that results from maintaining AoA after a disturbance of a steady flight condition. On the AF447 thread I showed similar simulations of airplane motion at constant pitch attitude after a pitch change, for example:
http://i.imgur.com/mYVPqZz.gif?1

[CONF iture]

If you have a reference stating that it is a feature of the pitch command mode then please provide that reference.
Not my point - What makes phugoid damping a feature of high AoA protection but irrelevant when high AoA protection is activated from pitch command initially ?
In other words, by which subterfuge Bechet is not subject to phugoid damping as he is obviously hitting high AoA protection too ?

The point has been brought here (http://www.pprune.org/8396979-post712.html) but you did not comment.

[Owain Glyndwr]

OK465

What's at play here? Is this solely due to the engine's increasing thrust pitching moment?That's the way I read it. A quick sum suggests that at 118kt (the end of the simulator run) 2 CFM56s at full chat would give a nose up pitch equivalent to about 10 deg up elevator.

Why wouldn't the elevator show reversals of direction or at least pauses during the pitching to stabilize AOA, if AOA is truly the driver?For the reason given above, the net pitching moment (thrust plus elevator) at the end of the run was equivalent to about 7 deg nose up. There is an indication that the elevator is starting to move back up at the end of the run, but even at that point the pitch is barely sufficient to be consistent with the commanded alphamax of 17.5 deg plus a bit of climb. [The pitch scale appears to be incorrectly labelled which doesn't help!] It looks to me as if for most of the time the thrust is supplying more than enough pitch to satisfy the demand but towards the end the thrust contribution is levelling off and it is from that point onwards that one would see elevator movement alone doing the controlling/stabilising job. Unfortunately (for this discussion at least) there isn't enough time in that state to form a judgement.

[HazelNuts39]

BTW I notice on HN39's presented graph that what is referred to as alphamax is actually higher than alpha SW, I assume that reference is to alphaCLmax and not the conceptual protection alphamax which is lower than alpha SW. For the A330 in clean configuration alphamax (normal law) is greater than alpha_SW (alternate law) at all Mach numbers less than 0.86. I do not know the value of alphaCLmax, except that it is greater than alphamax as explained in numerous Airbus documents. At high Mach number alphamax is actually buffet onset, as explained in the FCOM.

P.S.
I forgot to mention that we know one point of the alphaCLmax vs Mach curve: AF447 stalled at 10° AoA / M.67.

[HazelNuts39]

Not my point - What makes phugoid damping a feature of high AoA protection but irrelevant when high AoA protection is activated from pitch command initially ?
In other words, by which subterfuge Bechet is not subject to phugoid damping as he is obviously hitting high AoA protection too ?
"Not my point"? IIRC you made it a point.

Bechet pulls the sidestick abruptly fully back at an AoA where the FCS is in pitch command mode and there is no phugoid damping. Therefore the airplane starts to pitch up achieving a rate of 2.5°/second one second later. About again one second later the AoA exceeds 14.5° and the FCS goes into alpha-protection mode. The elevator then moves to more nose-down positions in a way that is quite similar to the accident sequence and the rate of rotation starts to decrease. However, the inertia of the airplane pitching up at 2.5°/second and the nose-up pitching moment of the thrust increase allow the airplane to continue pitching up to about 16.5° while it begins to climb. That is what I see in that plot, although the resolution of the plot is not sufficient to show the AoA that is achieved.

[CONF iture]

"Not my point"? IIRC you made it a point.
My point was more precise and needed to be detailed :
What makes phugoid damping a feature of high AoA protection but irrelevant when high AoA protection is activated from pitch command initially ?
In other words, by which subterfuge Bechet is not subject to phugoid damping as he is obviously hitting high AoA protection too ?

However, the inertia of the airplane pitching up at 2.5°/second and the nose-up pitching moment of the thrust increase allow the airplane to continue pitching up a few degrees while it begins to climb.
No stall - Alpha max - How great is it really !
You just confirm here that everything was in the aerodynamics but only the FCS restricted Asseline at 2.5 deg short of alpha max and deprived him the opportunity to survive the poor situation he initially put himself in.

[DozyWannabe]

but only the FCS restricted Asseline...

Why do you keep calling it a "restriction"? It isn't - it's a deliberately engineered damping feature to ensure stability when in HAP mode which is, after all, concerned with protection from stall and stabilising trajectory.

Asseline wasn't restricted by the EFCS, he was restricted by his own actions in the previous 30 seconds or so - chopping back too much thrust, and then seeming indecisive about whether to actually go for Alpha Max (while constantly bleeding off airspeed). The EFCS doesn't know there's an obstacle three seconds away, it just tries to comply with the commands as best it can, and in this case both the TOGA thrust and full back-stick came too late.

The A320 and its systems were designed for ferrying passengers between airports, and the protections were designed to fit that function - it was not designed for "playing chicken" with forests at low altitude and low speed!

[Owain Glyndwr]

OK465

If I'm reading it correctly, I am guessing that what you're referring to here is the fact that in the simulation, the elevator smoothly continues to trend leading edge less down (less negative)/aircraft less nose up until the end of the plot.

Excuse my jumping back a couple of posts, but what I was actually describing as interesting was, starting from 114 kt, the sequential increases in thrust, airspeed, pitch and height. Each lags its predecessor as it must, but the end point is that the simulator run showed that the aircraft would have got to alphamax by about TGEN 336 and (with a reasonable extrapolation) 40 ft about two seconds later. This would be an elapsed time of around 7 or 8 seconds from the application of maximum back sidestick. The two other simulator exercises, Bechet's and an un-named pilot's show very similar times.

If we accept (as I think you do) that this simulator was a 'high fidelity' representation of the aircraft then these figures must mean something in terms of the actual aircraft behaviour on the day of accident. One might conclude that the EFCS was carrying out the pilot's command, but that the physics of the flight conditions were such that it would have needed around 7 or 8 seconds to complete the task.

[HazelNuts39]

You just confirm here...That is a strange twist - many posts ago I first suggested that phugoid damping was a possible explanation for the 'attenuated' response of the airplane to full back sidestick.

[CONF iture]

That is a strange twist - many posts ago I first suggested that phugoid damping was a possible explanation for the 'attenuated' response of the airplane to full back sidestick.
... and I did not (http://www.pprune.org/8233579-post161.html) oppose it, but what you confirm here is that the phugoid damping (if it is actually the guy behind the restriction ...) was useless and detrimental performance wise.

Bechet did much better without it than Asseline with it.

[Owain Glyndwr]

Looking at the totality of the evidence from the four graphics presented in the BEA report it seems to me that the situation is as follows:

The HAP mode of the EFCS has no knowledge of what the engines are doing. Indeed, with thrust control switched to manual no part of the EFCS uses thrust information. Consequently any aircraft motions produced by thrust changes are treated in exactly the same way as perturbations coming from any other “outside” source such as atmospheric disturbances.

The HAP mode contains logic that in effect says: “Do not allow pitch to increase if the speed is falling”. Introduced to ensure trajectory stability in the phugoid mode, it has its own logic – if flying at or near alphamax with a falling airspeed the last thing one wants to do is allow changes that might take the aircraft over that limit and nearer to alphastall.

The “job” the EFCS was being asked to do has been stated as “Provide the commanded alphamax”, but although at first reading that seems a straightforward objective, it is in fact simplistic. A more accurate task description would be “Provide the commanded alphamax in a controlled manner so as to minimise the risk and potential magnitude of overshoots above alphamax”

The details vary a little depending on the timing of thrust and sidestick applications, but basically when starting from a condition of level flight in the HAP operative AOA range with idle thrust and a reducing airspeed and applying maximum thrust and full back stick the sequence of events would be as follows:

Because the speed is initially reducing, the HAP logic requires that a down elevator signal be added to cancel the pilot’s nose up command. At this point the thrust is low and increasing only slowly, so the pitch remains constant whilst the speed builds up slowly.
As soon as the thrust has increased enough to arrest the deceleration, the HAP logic changes to allow the aircraft to pitch up. By this time though,the thrust has increased enough to provide a noticeable nose up pitching moment so the pilot’s demand can be satisfied without much change to the elevator command. At the end of this phase the speed is still building up slowly and the aircraft has just started to climb. [Note**]
The engines are by now accelerating quite rapidly, being on the steep part of the “S” curve, and if left uncorrected the associated pitching moments would increase the pitch rate to a level where there would be a very real risk of overshooting alphamax. The HAP therefore applies corrective elevator (actually a reduction of ‘up’ elevator) as shown on the graphs.
The aircraft, at this point, is pitching up towards alphamax and starting to climb more steeply.
As the engines near TOGA power their acceleration tails off along with any increase in pitching moment. The HAP elevator command depends on the details of the pitch rate and the proximity to alphamax at this point. If it seems that the pitch rate could be safely increased then the HAP might apply a small nose up correction, but if the pitch rate means that the aircraft is approaching alphamax too rapidly it might need to do the reverse to avoid an overshoot.
It is quite difficult to see exactly what is driving the elevator at this time because it is trying to control the difference between pitch and flight path angle, but we don’t have direct information on either alpha or FPA from the simulator records, although it could in principle be calculated from the data available.

Under this line of reasoning the only substantive difference between any of the four “flights” would be that F-JFKC’s was truncated (literally!)

[Note**] It was at about this point in the sequence that F- GFKC entered the trees.

[DozyWannabe]

but what you confirm here is that the phugoid damping (if it is actually the guy behind the restriction ...) was useless and detrimental performance wise.

Not quite - as OG says:
The “job” the EFCS was being asked to do has been stated as “Provide the commanded alphamax”, but ... [that] is in fact simplistic. A more accurate task description would be “Provide the commanded alphamax in a controlled manner so as to minimise the risk and potential magnitude of overshoots above alphamax”

This is because it's an airliner, not a fighter - HAP mode is designed to maintain stability and trajectory, and Alpha Max is the upper AoA limit of that mode - it is *not* necessarily for use as an escape manoeuvre. In fact it can only really be expected to perform that function in concert with either sufficient airspeed, sufficient manual thrust applied (and available) or with Alpha Floor enabled. Asseline set the situation up so as to have neither.

Bechet did much better without it than Asseline with it.

As the graphs demonstrate (and OG has helped describe), Bechet initially got to a higher AoA in less time, but the overall performance was more or less similar. Whichever way you slice it, the fundamental aspect that cannot be ignored is that, possibly as a result of task saturation, Asseline did not recognise the danger in time and therefore did not act swiftly and decisively enough. That in itself is not the main reason he shoulders the responsibility he does - it's more to do with his decisions prior to then, when he had ample opportunity to turn around and do the run with more margin for error - but instead elected to press on and continue improvising with an ever-narrowing safety margin.

Airbus's own Alpha Max demonstrations were performed with sufficient thrust to achieve and maintain Alpha Max while preserving trajectory, and they were properly prepared such that they had a clear path ahead of the aircraft while in that state, because in that mode and at higher alphas, the room for evasive manoeuvre is significantly reduced.

[CONF iture]

The HAP mode contains logic that in effect says: “Do not allow pitch to increase if the speed is falling”.
Bechet got no restriction to obtain more than 17 deg of pitch even if he was under high AoA protection 1 sec after selecting TOGA.
True that speed was bizarrely not falling ... especially compared to Asseline who kept his sidestick in the same position for 3 more seconds ...
if flying at or near alphamax with a falling airspeed the last thing one wants to do is allow changes that might take the aircraft over that limit and nearer to alphastall.
If flying at or near alpha max, there is no such thing as "falling airspeed", but there is flying at or near Valphamax.
"Falling airspeed" would be associated to rapid increase of alpha.
If it seems that the pitch rate could be safely increased then the HAP might apply a small nose up correction, but if the pitch rate means that the aircraft is approaching alphamax too rapidly it might need to do the reverse to avoid an overshoot.
It would do that but brief temporary overshoot of alpha max is part of the protection too as demonstrated by the Airbus test pilot.

This is because it's an airliner, not a fighter - HAP mode is designed to maintain stability and trajectory, and Alpha Max is the upper AoA limit of that mode - it is *not* necessarily for use as an escape manoeuvre.
To the contrary it is specifically designed with that in mind.
In fact it can only really be expected to perform that function in concert with either sufficient airspeed
Alpha max is necessarily associated to "sufficient airspeed" called Valphamax.
As the graphs demonstrate (and OG has helped describe), Bechet initially got to a higher AoA in less time, but the overall performance was more or less similar.
Anything between 5 and 10ft is a lot of performance ... if it's all it takes to survive the bush ...

[DozyWannabe]

True that speed was bizarrely not falling ...

Are you sure? Annexe X - page 9, right?

If so, then I'm seeing from "Remise des gaz"/full back-stick:

An immediate increase in pitch for approximately 1 second (about the time it takes to transition between pitch command and HAP mode)
The speed continues to decay from approx. 120kts to 113kts
As the mode transition finishes (at approx. 115kts), the pitch increase stops, then actually decreases slightly as the speed decays
As the speed builds up from the lowest value of 113kts (presumably due to the thrust kicking in), the pitch angle starts to increase again


To the contrary it is specifically designed with that in mind.

Only in conjunction with sufficient airspeed and/or thrust. Alpha Floor is intended to provide a degree of fail-safe functionality in the event that airspeed/thrust is insufficient, which is why turning it off or otherwise preventing its function is not advisable unless precautions regarding minimum altitude and a clear path ahead of the aircraft are strictly adhered to.

Alpha max is necessarily associated to "sufficient airspeed" called Valphamax.

Yes, but unless you know how that's calculated, it's something of a moot point.

Anything between 5 and 10ft is a lot of performance ... if it's all it takes to survive the bush ...

Page 9 indicates that Bechet's altitude was in fact slightly lower than Asseline's at the point of impact, but even if you transpose it to match it doesn't really suggest that it would have made much difference.

[EDIT : Actually, hold that thought - I just remembered something from a while back (cheers for this info Chris)...

The four rad-alt TRx antennae on the A320 were mounted on the bottom of the rear fuselage, just forward of the fuselage tapering area ... At the final pitch angle of about +15, the tail-cone and tapering part of the rear fuselage would have been the first to touch any horizontal series of treetops.

The RA of Bechet's pass diverges significantly below that of Asseline's roughly around the same time Bechet gets his initial "bump" in pitch (before HAP mode/damping arrests it as a result of an airspeed delta of approx. -5kts/sec). I'm wondering if this increase in divergence is down to the higher pitch angle and consequent lower physical altitude of the RA antennae. ]

Also, as others have pointed out, the increased pitch angle would have meant that the empennage made contact with the trees lower down and at a more acute angle, increasing the risk of the airframe breaking up before it came to rest and a significant increase in casualties as a result.

[CONF iture]

Yes I am sure that speed was bizarrely not falling ... especially compared to Asseline who kept his sidestick in the same position for 3 more seconds ...
And obviously you don't have any explanation to justify that so different attitudes obtained by Bechet and Asseline are supposedly still producing an identical speed decrease ... ?

Alpha Floor is intended to provide a degree of fail-safe functionality in the event that airspeed/thrust is insufficient, which is why turning it off ...
Asseline applied TOGA before alpha floor would have kicked in ... what's you point again ?

Page 9 indicates that Bechet's altitude was in fact slightly lower than Asseline's at the point of impact, but even if you transpose it to match it doesn't really suggest that it would have made much difference.
Knowing that Bechet started the procedure 10ft lower than Asseline did, it does suggest that it could have made all the difference.

Also, as others have pointed out, the increased pitch angle would have meant that the empennage made contact with the trees lower down and at a more acute angle, increasing the risk of the airframe breaking up before it came to rest and a significant increase in casualties as a result.
Just another typical unsubstantiated catastrophic scenario à la Airbus.

[HazelNuts39]

True that speed was bizarrely not falling ... especially compared to Asseline who kept his sidestick in the same position for 3 more seconds ...On the timescale of the chart on page 9 of BEA's 'Additif' (synchronized at the time the flight path passes through 100 ft RA ?), Bechet advanced the thrustlevers between 1 and 1.5 seconds earlier than Asseline.
"Falling airspeed" would be associated to rapid increase of alpha.Actually, at nominally 1g, with IAS falling at 1.7 kt/second, AoA is increasing at 0.5 degrees/second.
Anything between 5 and 10ft is a lot of performance ... if it's all it takes to survive the bush ... Knowing that Bechet started the procedure 10ft lower than Asseline did, it does suggest that it could have made all the difference.The accident report puts the impact at about 5 seconds after the thrust levers were advanced. Bechet's radio altitude was 27 ft when he advanced the thrust levers, and 5 seconds later it was again 27 ft. Asseline's radio altitude was 32 ft when he advanced the thrust levers.

[roulishollandais]

Finaly, which was the math model ? :}

[CONF iture]

On the timescale of the chart on page 9 of BEA's 'Additif' (synchronized at the time the flight path passes through 100 ft RA ?), Bechet advanced the thrustlevers between 1 and 1.5 seconds earlier than Asseline.
I thought the graph was supposed to be a "Recoupement from Habsheim" but are you now suggesting there is in fact not much to be 'recouped' ... ?

Bechet's radio altitude was 27 ft when he advanced the thrust levers, and 5 seconds later it was again 27 ft.
I thought you had earlier established the gain at 10 ft (http://www.pprune.org/8371240-post629.html) ... ?

Actually, at nominally 1g, with IAS falling at 1.7 kt/second, AoA is increasing at 0.5 degrees/second.
And if you increase your AoA by 5 degrees in 2 seconds (http://www.pprune.org/8355502-post605.html) what would be the IAS falling rate ... ?

[DozyWannabe]

@CONF - I notice you're avoiding the question over whether the slight increase in pitch would account for the marginally lower RA value given that the increase in pitch angle would cause the rear-mounted RA antennae to be physically closer to the ground.

The IAS drops from 120 at the point Bechet set TOGA to 113kts 5 seconds later. How is that "not falling", let alone "bizarrely"?

And regarding "unsubstantiated catastrophic scenario[s]", it's no such thing - it's basic physics. A flat-ish sheet of metal subjected to an opposing physical force will bear a greater degree of that force as the angle becomes more acute.

@roulis - I'm mystified as to what you actually mean there.