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 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

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:

HN39

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!

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

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).

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

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.

Where do you see such definite short delay ... ?

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

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 ...

... with maintaining altitude, speed not being dependent on the level of thrust.

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.

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.

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

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?

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.

I was under the expression that you had accepted the explanation I offered in post#605:
There was also a difference in the way the sidestick was pulled back - Bechet in one quick move and Asseline more hesitating.

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.

Classical vs digital design reliability
 

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

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.

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 did not dispute, you pretended the config for Habsheim was unknown.

Already answered here and here.

What a delay if not a restriction ?

Same graph mentioned by HN39 earlier.

For someone who wanna stay blind, surely.

If you're satisfied with it, then it shows how the concept is poor and inefficient.

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:

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.

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.

Asseline should be relieved to hear that.

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

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.

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

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.

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.

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.

As far as I know YOU set the initial conditions in YOUR post #652 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

Where I said

OG out

To which I replied

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

Windshear in the lee of the trees?
 

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. 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:
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.)

This thread has been quite interesting to read, lots of factual information and explanations. But there are exceptions:
Say what? Since when?

It is when the AoA is constant.
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).

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.

If they do, they control speed by using the elevator to change pitch and AoA.

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. ;)

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?

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.

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?

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.
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.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.

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.

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.

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.

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

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:

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.