Air France 447 - On topic only!

[Joe H]

There's an awful lot of speculation going on about what went on with the aircraft with us having relatively little data.

When that speculation goes beyond the elusive middle ground, it is customary to suggest that we chill out and wait for the final report.

Hi Sir
I do agree, however, the compression, decompression analogy is correct. (the areas in the post that you omitted are relavent however and we need to be carefull which parts we choose to post)
I just do not appreciate someone questioning my post with slurs on my experience or so called qualifications, discussions ? absolutely.. but it seems this forum is dwindling into the area of 'give me your CV or else' ?

Discuss ! , disagree ! , but do not attempt half hearted slurs on why someone has an opinion (not you SIR, far from it !) ....
If I am wrong, i will be the first to admit it. but I do not suffer fools and trolls. I am open to any form of discussion, but NOT to the above....
Nuff said... chill

[TeeVee]

joe, you are wrong. a full bottle of lemonade will deform because of dissolved gases but the full bottle of water will not? does lemonade have gases we don't know about? a sealed container completely filled with water at the surface will not deform when brought to depth since water does not deform water. the only reason our bodies deform at depth is because of the space we have inside that does get compressed under pressure. and i'm not so sure that human blood vessels contract after death. while there may be dissolved gases in them they will not "contract." what evidence do you have of the state of the bodies, aside from a journalist's description? and we all know how accurate those can be. the blood is no longer liquid? how so? frozen in un-frozen water? solidified while surrounded by liquid under pressure?

too many assumptions i think...

we could continue to argue about physics but you are not going to win since there is no proof of what actually happened. however, i'm reasonably certain that no one survived the descent long enough to make a difference in the relative pressure of dissolved gases in the tissues. the references you made to cns trauma are not relevant given the massive trauma of water impact. oh and what does the fact that the seats were still attached have to do with anything?

my qualifications? absolutely none. i on the other hand, don't speak in the authoritative tone and absolute terms you tend to use about everything in the few weeks you have been here.

so let's get this straight, you are a pilot and general aviation expert, scuba instructor, an expert in gas theory and physics in general. can't wait to see what comes next.

perhaps if you spoke in less absolute terms, people would not question your CV as much. but if you must and you don't like being questioned here, you can always leave. i don't need to have any qualifications to question yours. simply a matter of wanting to know if i should consider your opinion as anything other than that--opinion.

you are not the only one to be questioned and the reason for it is the types and tone of the statements made. i doubt there are too many true "experts" here, although there is no doubt whatsoever that there are at least a few folks on this board that have demonstrated the basis for their opinions. and even they get questioned when they make statements that others don't like.

grow some skin...

[Gabriel]

But not in in this case and you know it. When a respected scientific publication describes something like aerodynamic stall, without mentioning caveats like emergent warm air masses, turbulence or pilot error in raising pitch to hold altitude, it is inaccurate and misleading. That is what I'm objecting to. Because this conveniently titled phenomena called "coffin corner" has been trumped up by every journalist trying to get print out of this, and in the process both coffin corner and stall have been misleadingly represented.

I fully agree, now:

Fly too slow and you stall: Untrue.

Fly too slow and you will "necessarily" stall: I agree it's untrue. But you have to agree that flying too slow is more often than not related to stalling, since a flight cannot be sustained below the 1G stall speed. So my only objection was when you replied to this:

If the lift produced by the flow of air over the wings becomes less than the weight of the aircraft, you are no longer flying, but falling in a "stall".

with this:

Untrue. You are still flying. You are descending. You are not stalled.

The last is as true (or untrue) as the former. You are not necessarily, but might be, stalling. You are not necessarily, but might be, descending. You might be both stalling and descending. You might be neither stalling nor descending. That's why I replied to you with this:

Untrue: [...]

So, in short, if the lift becomes less than the weight you could be:
a) stalled
b) descending
c) both a) and b)
d) neither a) nor b)

The other part that I objected from you was your defense to my criticism saying things like:

Without a change in pitch, how do you stall there? [...]
He never mentioned anything about pilots holding altitude with pitch as a factor. [...]
It is very important to note that there is no mention of pitch input [...]

While that's true, it's biased by partiality.
Ok, he doesn't say that, but he doesn't say the opposite either. He doesn't say that they increased pitch, but he doesn't say that they didn't. He doesn't say that they held altitude, but he doesn't say that they descended either.

Again, I agree with the core of your argument: The S.A. column is poorly written, incomplete, inaccurate and misleading. However, whether they stalled or not is not something that you can argue (for or against) with the arguments presented in the column. Again, with the (incomplete) scenario presented there, they didn't necessarily stall, but they didn't necessarily descend (with no stall) either.

[Gabriel]

I think he is referring to the sidestick for of control that Airbus use.

As the Sidestick is not a feedback device, the pilot will not have the traditional feel for the controls as a pilot in a Boeing.
Boeing's Control Yokes always move in direct proportion to the flight control and vice versa. So Autopilot engaged or hand flying the controls always move so the pilot has a direct visual and tactile feel for the aircrafts controls

Airbus's sidestick does not move and control inputs do not necessarily translate to the same degree of movement of the control surface. There is no tactile feel and visual indication is on a screen.

Even with 787 though fly by wire, the control column will move like a traditional column via servo motors, Embraer do the same with the E jets.

Yes, I understand that. What I don't understand is why he said "with the lack of a "feel" sense for where the controls are located"

That said, there is a couple of things to add to your comments:
1. The AP was off, so there would not be any control surface movement unless the pilot moved the stick (yoke) himself, both in an Airbus and a Boeing.
2. The control law reverted to abnormal alternate, meaning that the movement of the elevator was proportional to the movement of the stick, just like in a Boeing.
3. The sidestick is spring-loaded, so there is a force feedback of how much you are displacing the stick and hence, in alternate law, how much you are displacing the elevator. That's not exactly like in a Boeing because the "feel" system computes both displacement and speed for the force feedback, although I don't know how would that work in an unreliable speed condition. Anyway, at a given speed, the stick (yoke) displacement, the force needed for such displacement, and the displacement of the control surface are all proportional to each other, both in an Airbus in alternate law and in a Boeing.

[Evan]

2. The control law reverted to abnormal alternate, meaning that the movement of the elevator was proportional to the movement of the stick, just like in a Boeing.

In both alternate law (1) and (2, I think this is what you refer to as "abnormal alternate law"), the pitch is still a load factor demand law, similar to normal law. To get a direct stick-to-elevator relationship, you have to degrade to direct law (which may very well have happened).

But I don't quite understand the point MCM is making, because you don't fly the Airbus by feel, you fly it by instruments, and the HSI should give you your pitch response to sidestick inputs (and/or THS setting). However I do understand his earlier statement that the A330 is not designed for precise manual flight at cruise altitude, and to do so would be very difficult in severe turbulance.

[Evan]

Ok, he doesn't say that, but he doesn't say the opposite either. He doesn't say that they increased pitch, but he doesn't say that they didn't. He doesn't say that they held altitude, but he doesn't say that they descended either.

I think here is where you are not following me: in the part of the article I am objecting to, he is not specifically speaking about AF447. He has taken an aside to explain 'coffin corner' in general. And here is where he states that stall WILL occur due to lack of airspeed. Will occur, not might occur. And regardless of what aircraft or what set of exacerbating circumstances.

If the lift produced by the flow of air over the wings becomes less than the weight of the aircraft, you are no longer flying, but falling in a "stall".

That's "you" are "falling in a stall", not "they, or AF447, may have been falling in a stall".

This sort of misleading statement addressing air travel in general, coming from a respected scientific authority, is what breeds ignorance-based fear of flying in the general public. That is the problem I have with it.

If he was merely speculating that insufficient airspeed may have led AF447 to stall (leaving other factors as implied in the statement), I would not take issue with that, but here he is defining general aerodynamics incorrectly and thereby instilling fear in general. Do you follow me?

[Fear_of_Flying]

Again, I agree with the core of your argument

I do not. The core of Evan's argument is not about AF447 per se, or even about aircraft stalling, but that this article is an example of sensationalism, distorting the truth about coffin corner and feeding on our misconception that one wrong move could send the plane plummeting to the ground. On that basic point, which is the reason we are having this discussion, I don't think Evan is correct, and I invite anyone on this forum to read the article (http://www.scientificamerican.com/bl...ner-2011-05-12) and tell me if you think this is a case of media sensationalism, or simply an unclear and perhaps flawed explanation of coffin corner (which was also, by the way, pointed out in the comments section of the article). And, not to belabor the point, but when Evan continues to use expressions such as "so-called expert", he is basing that description at least partially on the author's qualifications, making fun of the fact he is a registered massage therapist.

The referenced article is a blog, i.e. akin to the op/ed section of a newspaper. The opinions expressed do not necessarily reflect those of Scientifc American. Now, hopefully the article was selected because it has some merit, and I think it does, namely, helping a novice - someone who isn't going to pick up on or comprehend the nuances of stalling that a more knowledgable reader might - understand coffin corner. And frankly, I think it is enlightening for some people to find out that even though cruise is vastly safer than take-offs and landings, there is a tiny but inherent risk at high altitude - when extraordinary circumstances occur - that I certainly hadn't heard about prior to AF447.

[3WE]

...perhaps if you spoke in less absolute terms..

Shoud one always be careful when speaking in absolute terms, or ususally be careful when speaking in absolute terms?

[3WE]

If the lift produced by the flow of air over the wings becomes less than the weight of the aircraft, you are no longer flying, but falling in a "stall".

Going to play devils advocate here and support this statement- and it's all about context and inference.

To some extent- you might infer that flying means "maintain altitude". And, if the airspeed drops below what you need to keep the plane flying and you (or the autopilot) is doing what is normally done to maintain altitude, a stall is what is going to happen almost all the time.

And, if you aren't maintaining altitude, you are gliding (and maybe not flying). (Before someone says anything, yes a glider and glider wing is a beautiful flying machine).

And, let's remember, the most important way to avoid stalling is to maintain adequate airspeed and most inadvertent stalls are attributed to poorly-managed airspeed... (Heck, even the Colgan stall is related to mis-managed airspeed).

Sensational journalism, or dumbed-down journalism?

While it's wrong for the puppy-mill curiculum, it's not that terribly wrong to tell the general public that flying too slow will lead to a stall.

[3WE]

Coffin corner

If you try to slow down, you break up and die.
If you try to speed up, you break up and die.
Try to climb or descend....break up and die.

All you can do is maintain airspeed and altitude until the plane has burned off some fuel (weight) and then ever so slowly slow and descend.

[Evan]

I do not. The core of Evan's argument is not about AF447 per se, or even about aircraft stalling, but that this article is an example of sensationalism, distorting the truth about coffin corner and feeding on our misconception that one wrong move could send the plane plummeting to the ground. On that basic point, which is the reason we are having this discussion, I don't think Evan is correct, and I invite anyone on this forum to read the article (http://www.scientificamerican.com/bl...ner-2011-05-12) and tell me if you think this is a case of media sensationalism, or simply an unclear and perhaps flawed explanation of coffin corner (which was also, by the way, pointed out in the comments section of the article).

I don't mean to say that the article itself is written in a sensationalist style. I mean to say that the aspect of 'coffin corner' continues to be sensationalized in the media, and that this is a very subtle version of the sensationalism. In the article he described the low side of coffin corner as a place where the aircraft is no longer flying, but falling in a 'stall'. To the average reader, that means dropping out of the sky like a stone. No effort is made to explain that this is not the case.

The referenced article is a blog, i.e. akin to the op/ed section of a newspaper. The opinions expressed do not necessarily reflect those of Scientifc American.

Yes, and they do state this in the fine print, but this is the problem I see with blogs that are presented under the 'brand' of a respected journal. Articles written in the main journal are carefully fact-checked, while blog entries are rarely if ever subject to this kind of scrutiny. The trouble is that the readership often does not perceive these blog articles as outsider contribution to be taken with appropriate skepticism, but rather with the same level of trust and authority as the main journal.

[Evan]

If you try to slow down, you break up and die.

Can you explain that?

[Fear_of_Flying]

I don't mean to say that the article itself is written in a sensationalist style. I mean to say that the aspect of 'coffin corner' continues to be sensationalized in the media, and that this is a very subtle version of the sensationalism. In the article he described the low side of coffin corner as a place where the aircraft is no longer flying, but falling in a 'stall'. To the average reader, that means dropping out of the sky like a stone. No effort is made to explain that this is not the case.



Yes, and they do state this in the fine print, but this is the problem I see with blogs that are presented under the 'brand' of a respected journal. Articles written in the main journal are carefully fact-checked, while blog entries are rarely if ever subject to this kind of scrutiny. The trouble is that the readership often does not perceive these blog articles as outsider contribution to be taken with appropriate skepticism, but rather with the same level of trust and authority as the main journal.

Subtle sensationalism?

And you want a better, more sophisticated explanation of aerodynamic stall, but the readers are too dumb to distinguish a blog from an article?

[Fear_of_Flying]

Subtly sensationalist headline: "Previously Unknown Virus in Northern China Causes Symptoms Inconsistent with Life: 4 Affected!"

[3WE]

If you are at coffin corner and try to slow down, you break up and die

Can you explain that?

Sure- a valid question.

If you are at coffin corner, maintaining altitude and you slow up, you are going to stall.

(Doesn't answer your question though, does it?)

The other part of this is that high-perormance aircraft tend to have crummy stall/spin behavior, and often go into uncontrolled high-speed death-dives, where they shed various parts, including assorted big, flat aerodynamic thingies.