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AF 447 Thread No. 5

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AF 447 Thread No. 5

Old 26th Jul 2011, 23:08
  #741 (permalink)  
 
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Originally Posted by Dutch M
Yeah, suppose the windspeed goes from 100 knots back to zero, does this change the Ekin of the airplane ? If not, then you will need to take the groundspeed as speed reference.

The energy exchange Ekin vs Epot, is in general only valid for speeds in the direction of the change of Epot (ie Height) and not when trading speed between perpendicular axis.
This is why I use the surface of the Earth as a reference. Then you find it easier to include the effects of thrust, drag, and wind. If the wind stops there is no change in the energy of the aircraft except through changed drag and lift.
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Old 26th Jul 2011, 23:25
  #742 (permalink)  
 
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Originally Posted by Dutch M
Where did the Ekin of (458 - 0.03) m J go ?????
Nowhere. You changed frame of reference. You can't do that when calculating energies unless you take account for the different energy states of the frames of reference.

The glider that lifts and sails backwards relative to the ground is not trading velocity for height. The wind against the glider that is moving at a different rate generates both lift and drag. Those are forces which will change the glider's energy picture relative to its starting point. Rigorous application of forces and frame of reference can tell you what the plane or any other object is going to do.

Without considering the external forces you're hand waving. And, yes, we were hand waving to get a feel for what an ideal energy exchange would give. Once you add the external forces applied to the plane you can account for some discrepancies. If you include enough of the known forces you can deduce what additional force must have been applied to get the final result.

If I knew what climb rate to expect from a 10 degree angle of attack we could probably deduce whether or not there was wind speed, relative to the ground, working to alter the aircraft's energy profile. On doing an obvious estimate (rather than exact math) the plane was moving upwards at something around 80 MPH when it was going 7000'/min. So that motion is slow enough external winds could have been a factor. The climb rate expected for the plane's condition would nail this down a little tighter. And the wind itself would impart forces on the plane which would change it's apparent energy profile.

But, first, keep everything in one frame of reference. As soon as you change frames everything gets all gooey and slippery to think about. It's also best to consider a nice conceptually solid frame of reference so that it's easier to think about what's happening. Referencing the air mass is tricky because it's a changing reference.
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Old 26th Jul 2011, 23:34
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Originally Posted by Dutch M
Let's extend this: Headwind 49.99 kts and the Storch is having a collide with a tower, best would be just above a platform.

What would happen: A very gentle little bump against the tower and then the subtle drop/land on the towers' platform. Nothing bent.
Not quite. The plane would still be "flying" while touching the platform as long as the platform is not applying any force to the plane. If you change the control surface settings you can generate a net downward (and backwards) force on the platform that must be taken into account. Or you can lift off again and ride along 0.2 mm off the surface of the platform. When in that stable condition the forces on the aircraft are balanced, and easiest viewed and determined by considering the ground as your reference.

(Then ask yourself if having said sail plane stationary 0.2mm above the ground neither ascending nor descending is at all realistic.)
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Old 26th Jul 2011, 23:40
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OK465, what wilyflier was saying, in essence, is that the perfect circle relative to the airmass does not change the forces upon the aircraft so it maintains its altitude. If you try to fly a perfect circle relative to the ground that's a different story.

Consider the forces acting upon the plane as well as whatever frame of reference you are using. (And if the airmass is in some way changing the inertia of the aircraft must be considered in your estimates of what is happening.)
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Old 27th Jul 2011, 00:09
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Airtren, IMAO the plane's software declares stalls inappropriately. The stall at 2 h 10 min 05 is likely spurious related to the airspeed indication dropping even though the plane is still flying at altitude with very little real speed change.

If it was real the plane canceled it inappropriately when the real velocity was still high and the indicated air speeds were below 60 kts. It should be 'obvious' to the software that if the plane was really stalled, it's inertially derived ground speed had not changed, that it was still stalled.

If it was a spurious warning the plane should have cross checked inertial data with air speed data and decided the warning was spurious.

The warning at 2 h 10 min 51 was probably real. By then the pilot was confused by the on again off again stall warnings and not sure if this one was real.

Couple this with the PF's initial apparently inappropriate action and I'm not sure what I'd expect the PF to do.

What I really want to know is WHY the PF might have might have made this apparently inappropriate action. If he was still thinking he clearly thought it was the right thing to do. Once PF had the plane at 16 degrees pitch and an AoA of 60 degrees I am reasonably convinced it was all over. There was not enough altitude to get the plane back into a flight configuration based on the NASA curves posted here in the past.

So once the pilot made that inappropriate move the plane's responses to his actions certainly did not help. PF needed something to beat into his brain (a physical slap in the face?) to convince him he was stalled. Turning off the warning is not going to do that.
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Old 27th Jul 2011, 00:20
  #746 (permalink)  
 
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PJ2, please forgive an assinine comment or observation here....

My understanding is that in aircraft pull on the yoke is go up. This was true from day one. The joystick handles the same way.

Now, take that joystick and mount it on a panel that is vertical. Diddle it with your fingertips resting on a sturdy arm rest. If you diddle it up the plane should go up, it's the way people normally think. Translate that "diddle stick" back down to mostly horizontal on the arm rest and you have chaos.

Could the pilot have somehow slipped into a thinking mode that had push is up? That's what the little diddle knob on my Lenovo laptop does. Push to move the cursor up the screen.

Is this a hidden danger in joystick aircraft control? Get too used to a laptop or something and when a crisis hits you revert to laptop thinking and do the wrong thing.

Note that in this case I'd expect PNF to take notice. Somebody noted that the stick inputs are indicated on the displays. So if the appropriate display was on the PNF's scan it should have been noticed.
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Old 27th Jul 2011, 00:30
  #747 (permalink)  
 
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Originally Posted by OK465
Energy Management (EM) in a fighter aircraft had nothing to do with the Earth frame of reference, other than avoiding contact with it.

I'm beginning to feel like I was lied to all those years and never noticed it.
Not really. Understanding the forces on the plane requires knowledge of what the plane is doing relative to the air mass. When you have have an air mass that throws curves at you knowing what the plane's going to do may become more difficult due to the plane's inertia. Considering only the air mass is good for estimating which direction the energy will change. For more absolute numbers one must consider that large annoying attractive lump of hard stuff far below. Then you know "how much" the energy changed and what factors are contributing to that change including changes in the air mass.
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Old 27th Jul 2011, 00:30
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Stick input

JD EE

Stick input is displayed ONLY on the ground, to enable flight control check and to monitor stick inputs during ground roll. As soon as aircraft is airborne, the "Iron Cross" and its reference box disappear from the ADI on the PFD (that is the Attitude Director Indicator on the Primary Flight Display).

As soon as the aircraft is airborne, aircraft response indicates what (the hell) the pilot flying is doing with his side stick.

Mix up of sidestick inputs such as you describe does not seem very logical to anybody who has handled aircraft controls.
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Old 27th Jul 2011, 00:35
  #749 (permalink)  
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gums;

First, yes sir, keep it comin'.

Second, why the pitch-up? I think the answer will be straightforward, not complex at all.
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Old 27th Jul 2011, 01:37
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Quote:
Originally Posted by gums
Give me a 'bus and I believe I can duplicate the scenario easily.

DJ77
Not so sure you could.

I think the scenario you describe explains why the “bus” FBW computers calculate a “phase advanced AoA” as mentioned in the A340 zoom climb incident report. Remember the bus has a pitch attitude protection (IIRC: 30 deg NU progressively reduced to 25 deg at low speed). With that limitation and factoring pitch inertial moment and tail effectiveness it must be relatively easy to anticipate and prevent the AoA to become greater than alpha prot. Of course, this works only in normal law.
DJ77, I think we have already seen what can be done with an aircraft when it doesn't have good airspeed information to the computers. I concur with Gums that it would be easy to duplicate this scenario. Wouldn't be that hard to do any number of aerobatic maneuvers that you are not supposed to do with the beast. You would just have to sit down and do the calculations first to avoid breaking things.

Even the direct hydraulic control A-4 Skyhawk and F-4 Phantom could run out of control effectiveness and end up back sliding/falling at higher nose up attitudes.

I would hate to take an F-4 in autopilot Control stick steering mode (which is very much like the mode that AF447 was in when it lost control) and do anything but essentially level flight. (You former F-4 flyers should remember what this was like). It would be too easy to set an unstable attitude and decelerate/accelerate. (basically a pure attitude hold).

The control inputs made by the AF447 crew as presented to date by BEA only seem to make sense WRT seat of the pants flying. I hope BEA has been able to make some sense of the control inputs and their rationale when they give their next interim report.
I'm having trouble believing that there was almost no scan of the instrument panel going on.

JD-EE. That was a very respectable explanation for the problems with Dutch_M's "paper." Newtonian Physics should work properly in any frame of reference and give consistent results. When it doesn't work out that way, then there is a problem with the analysis.
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Old 27th Jul 2011, 01:47
  #751 (permalink)  
 
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Originally Posted by PJ2
Second, why the pitch-up? I think the answer will be straightforward, not complex at all.
Maybe the PF just applied a bit generously the Airbus recommended procedure for UAS ...
But I think svarin is really on something ... Of course I don't expect the BEA to 'study' in that direction.

Full data to the victim's families - Make sure no data are left behind.
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Old 27th Jul 2011, 03:15
  #752 (permalink)  
 
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Hello jd_ee

You've been quite a prolific poster today.

Your reply has triggered more thoughts, and comments here:

Originally Posted by JD-EE
Airtren, IMAO the plane's software declares stalls inappropriately.
The problem with the Stall Warning, which I've already mentioned, can be split, IMO, in two parts, each part being a problem on its own.

These may not look as problems to those people that are inside the box, engineers or pilots that were educated/trained to accept the SW, think of it, use/operate with it, as it is.

From outside of the box though, the Stall Warning looks unreliable, and incomplete, to say the least.

First it is the limited number of parameters used for calculation and triggering the Stall Warning, and the high risk of having major parameters, and thus the calculations invalided by adverse weather, inducing a total failure of the Stall Warning.

Second is the single Stall Warning message in itself.

There seem to be 3 types of distinct Stall related situations.

1. Entry/approach to Stall (transition from NON STALL to STALL, or entering the Stall ZONE)
2. Stall per see (Stall, or Stable STALL, or in the middle of Stall Zone)
3. Exit Stall. (transition from STALL to NON STALL, or exiting the Stall Zone)

The current one Stall Warning message seem to be designed to apply for both situation #1 and #2, but not for situation #3.

In the case of AF 447, the Stall Warning didn't work for any of the situations it was designed for, which is #1, and #2, but it was triggered for situation #3, in which case its interpretation as #1, or #2 was misleading, making the PF think that his actions were wrong, inducing a Stall, when in fact, his actions were in the right direction.

So:

The first problem can be addressed, by extending the number of parameters/sensors, with parameters/sensors that cannot fail, and become invalid at the same time with the others, under the same conditions, so to reduce the risk of failure, and increase redundancy. This also implies a change of the algorithms, and perhaps have several parallel ones, for calculating the Stall conditions.

The second problem, is ideally resolved by adding two more Stall messages, and creating a distinction, so there would be one message for each of the 3 situations, which would make each of them clear, and unambiguous.

1. Warning!!! A/C Entering Stall
2. Emergency!!! A/C is in Stall
3. Information!!! A/C Exiting Stall

Originally Posted by jd_ee
What I really want to know is WHY the PF might have might have made this apparently inappropriate action.

….Once PF had the plane at 16 degrees pitch and an AoA of 60 degrees I am reasonably convinced it was all over. There was not enough altitude to get the plane back into a flight configuration based on the NASA curves posted here in the past.

… PF needed something to beat into his brain (a physical slap in the face?) to convince him he was stalled.
Based on the division of the time from the AF 447 A/P and A/THR disconnect to the final impact to the Ocean, in two major steps:

1. Transition from Normal to STALL.
2. Attempts to exit Stall, and return to Normal.

On Step 1, based on the current BEA report, I perceive a confluence of causes.

IMO, a PF/PNF failure alone cannot stand, as it has immediately great, and grave implications on Air France, as well as the industry. The Captain and two pilots were employed, were trained, were accredited, and they were tasked to fly the plane by Air France according to its standards, Airbus, and the industry's international standards.

The second step, is not easier to judge. But among all of the failures, one of its contributors is the Stall Warning, i.e. not having it when it was needed, and then having it at the wrong time, with the wrong meaning for the actions of the PF at the time.

Would have been possible to get out of the Stall?

I think there was a chance.

There are two cases of Stalls and successful recovery that come to mind, with no passenger injury, or plane damage, albeit not A330, but rather A310 – Interflug, approaching Sheremetievo, Moscow, in 1991, and Tarom approaching Orly, Paris in 1994.

I consider them relevant, as 310 is still part of the 300 family, and would expect a number of similarities in their aerodynamic attributes.

The captain and pilots on the Tarom Airbus 310 approaching Orly, Paris, France in 1994, realized the problem they were getting into very early, before the stall, and worked very hard, and were very quick to bring the plane out at 800ft above ground, from the Stall at 4100 ft, 30 knots airspeed, and 60 degree pitch attitude. So, it was possible within 3300ft.

Considering that the AF 447 had its highest stall point at 38000 ft (33000ft more than 4100ft, which is also about 9 times more) , somewhere around 185 knots airspeed (155knots more than the 30knost), and 16 degree pitch (a lot more than the 60), I think that with appropriate awareness – which a correct Stall Warning would have helped - and quick, aggressive actions, the plane would have had hope and chance to recover.

Last edited by airtren; 27th Jul 2011 at 05:28.
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Old 27th Jul 2011, 03:18
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side stick? no biggie

There is no big deal using the side stick.

A few thousand, well maybe hundreds, of pilots have flown the Viper since the mid 70's. Our ops chief demanded we all have one ride in the back seat of the family model to check out the stick. That requirement went away after about 6 months or less. I flew an old pilot ( hadn't flown in ten years or so) one day, and it took him all of ten seconds to get the "feel" of it.

The 'bus stick moves, and ours didn't/doesn't. Personally, and having flown PC sims and real aircraft sims, I prefer a stick that uses pressure more than actual movement.

As with the 'bus, the Viper stick is "canted" to help minimize roll inputs with pitch inputs and vice versa. Both jets' computers revert to trimmed gee and zero roll rate if you just let go of the stick. That's gear up, for the most part. Ours had a healthy AoA and pitch rate input with gear down, making the thing seem more like the "old" jets.

So I am not gonna blame the side stick for any contribution to this accident.
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Old 27th Jul 2011, 04:54
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So I am not gonna blame the side stick for any contribution to this accident.
Hi Gums, I plan on looking at the control input traces, looking for synchronization between lateral inputs and nose up inputs. If so, wouldn't that infer cross channel inputs?

My understanding of the Friday BEA report is that it will be an interim report that will provide (almost) full presentation of the raw data, and early factual conclusions.
I expect they will then kick the can around for a year or so in the process of writing the final report and trying to make sense of that which is presently illogical data from their analysis. Is this a realistic assessment? If so, there will be plenty to chat about and analyze for the next year.
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Old 27th Jul 2011, 08:07
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Originally Posted by CONF iture
But I think svarin is really on something ...
Be honest CONF, is it that you *think* he's on to something, or is it that you *want* him to be on to something, given a track record of wanting a smoking gun to stick it to Airbus for over two decades?

Of course I don't expect the BEA to 'study' in that direction.
Why not? Accident and incident investigations have discovered problems with Airbus software which Airbus have gone on to fix several times in the past.

Originally Posted by airtren
IMO, a PF/PNF failure alone cannot stand, as it has immediately great, and grave implications on Air France, as well as the industry. The Captain and two pilots were employed, were trained, were accredited, and they were tasked to fly the plane by Air France according to its standards, Airbus, and the industry's international standards.
The Dutch investigators thought very much the same way after the Tenerife disaster in 1977. It was a painful thing to accept, but by and large it is accepted today. That said, AF447 can never be put down to human factors alone because of the known pre-existing issue with the Thales AA pitot tubes fitted to that particular airframe.
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Old 27th Jul 2011, 08:10
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What I really want to know is WHY the PF might have might have made this apparently inappropriate action. If he was still thinking he clearly thought it was the right thing to do. Once PF had the plane at 16 degrees pitch and.....
I don't think the pilot was able to think clearly, being overloaded with unreliable airspeed, ECAM Dings, ALT LAW, etc. I suspect that once he selected TOGA power, he simply went for an inappropriate combination of power and attitude with which he was familiar:
UAS: TOGA/15 degs pitch. ...................Cl/5 degs above FL 100
Wind Shear: TOGA/17.5 degs pitch.
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Old 27th Jul 2011, 08:18
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Cool

Hi,

My understanding of the Friday BEA report is that it will be an interim report that will provide (almost) full presentation of the raw data, and early factual conclusions.
I expect they will then kick the can around for a year or so in the process of writing the final report and trying to make sense of that which is presently illogical data from their analysis. Is this a realistic assessment? If so, there will be plenty to chat about and analyze for the next year.
Indeed .. there will certainly be a matter for debate that I hope it will be contradictory and impartial.
For my part I'm not expecting much more of this new interim report ...
Nothing more than we already know .. according to the 2 other reports and the last note of the BEA
More .. I'm not 100% sure of the integrity and independence of BEA from the other actors implicated ...
How to be confident in an organization whose members are at the origin of repeated leaks to the benefit of the press
How can you trust when you know that the parent organization of BEA (the French state) gives the findings of an investigation not even finished (Secretary Ministry of Transport Mariani which states that pilots are responsible for 95%)
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Old 27th Jul 2011, 08:56
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I concur with Gums that it would be easy to duplicate this scenario.
I understand Gums' proposed scenario was to try to confuse the confusers, specifically the AoA protection (normal law, correct speed data) as he did with the Viper. Apparently not directly related to AF447 but there may be a subtle link.
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Old 27th Jul 2011, 10:03
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gums As with the 'bus, the Viper stick is "canted" to help minimize roll inputs with pitch inputs and vice versa
hi gums, exist a stick for left-handet pilots in the viper?

i trying to creat this post with my left hand........ it is horrible for the brain using the mouse with lefthand push the button with the third finger

how fast can an airbuspilot chang his hand-skills for the stick if he change the seat from right to leftside?
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Old 27th Jul 2011, 10:26
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EMIT, I'd call the two modes of thought for joysticks as "attitude" and "motion".

Traditional sticks in aircraft control attitude. The image in your head could be a model of the aircraft on top of the stick handle. Push is nose down.

Computer "mouse" joysticks think position and translate that diddle stick I mentioned down to a horizontal platform. Push is "go up" as opposed to "pitch down".

I'm still vaguely wondering what it would take to get an even moderately experienced pilot to mentally switch modes of thought from "change the attitude this way" to "Dangitall I'm telling you to go up! Please go up!" I can't see what would do it. It'd be an interesting thing for some college psychology type to study for his thesis, I suspect. I can't shake that image in my head of the pilot pulling the stick to go down rather than pushing it to pitch nose down and being confused further when the plane did the wrong thing. And once a simple mistake is made it's quite natural for people under stress to keep repeating the same mistake over and over thinking they just didn't do it hard enough. ("This time, Rocky, for sure!")
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