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AF 447 Thread No. 5

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AF 447 Thread No. 5

Old 6th Aug 2011, 11:32
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re airtren to lone - I think the word you're looking for to replace "lack" in "lack of lift" is "insufficient". As a matter of fact that is how I interpreted lone's comment.

By the way, what does the water bottle tell you that the pitch display does not? So far as I know that, at least, was still working.
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Old 6th Aug 2011, 11:39
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funfly, you can be falling at mach 20 and not feel it. All you can feel in your ears or your body is a CHANGE in velocity. And there is no known body that, in air, continues to accelerate all the way down from 38000'.

Yeah, I'm picky that way. Please excuse.
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Old 6th Aug 2011, 11:42
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True Air Speed vs other air speeds

JD-EE said:
takata posted the speed graph. ... should have lost just a whole lot more speed than the graph shows,
This graph does not show the velocity of the aircraft. It shows Corrected Air Speed (I think). True Air Speed would be a decent approximation for the velocity but CAS is not anywhere near at the altitudes involved here.

Can the meme that some hand of god is necessary to explain the zoom climb please go away. It has been demonstrated many times that there is about the right amount of energy available including an allowance for manuoevering losses.

Ooh! Just been buzzed, well at 2,000ft, by the Dragon Rapide (from Duxford I believe). Way cool.
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Old 6th Aug 2011, 12:20
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takata commented to A33Zab about the IR data.

Regardless of the IR data from ADIRU the ISIS data existed. And enough data was recorded that the BEA was able to follow altitude and attitude of the plane all the way down. What makes anybody think ISIS data was not presented in the cockpit?

If it wasn't ABI ought to be totally pilloried, if they did not make it available, or AF should be excoriated if they skipped over this as an "unnecessary frill option."
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Old 6th Aug 2011, 12:24
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Mr Optimistic, "I though the 0.5*(v1^2-v2^2)=gh equation had been looked at earlier and found to be broadly consistent ?"

It was - with a speed at the apex of 215 kts, 240 kts maybe....
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Old 6th Aug 2011, 12:26
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Mr O
Indeed - I am a night owl. And I thought I left room in there for cabin pressure sensing in the ears. But the inner ears don't feel even pretty extreme pressure changes unless you've had surgery that exposes the area by drilling through nice thick bone. All the inner ear senses is tilt and acceleration. And those can get mixed up very easily in a dark room.
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Old 6th Aug 2011, 12:31
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I've said too much already but there is an observation I'd like to make.

Here is a simple sentence. "Our speed is 215 kts." This is in English. If I say it with flat or even feminine with the slight upward lilt at the end it means exactly what it says, the speed is in fact 215 kts. It's a statement of fact. If the pitch change at the end of that short sentence is made to sound like a question it is a combination question and statement of incredulity that the speed is 215 kts, "Our speed is 215 kts? (How in (censored) can that be?)" when the unstated part in parenthesis is included.

French adds handwaving to the picture. There's no way we're going to guess precisely what was said dissecting the words given us. And, as noted, even hearing the recordings won't necessarily help much.

Is there a better topic to be entertained about?
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Old 6th Aug 2011, 12:33
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jimjim - accounted for - the energy loss work I did ran from the mach numbers translated back to speeds based on the speed of sound - an approximation. It appears to be about a factor of 2 give or take a bit for the correction.
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Old 6th Aug 2011, 12:44
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Originally Posted by takata
FPV ECAMs fault are due to their selection and rejection (they were unselected before this point) because airspeed was < 60 kt.
There is no such thing as FPV ECAMs fault

But It looks to be set at +/- 10,000 ft in order to show a degraded status.
That's not supported by the traces as posted by A33Zab, something else but what ?

takata, you don't seem interested to address your notion of normality ...
There is a clear internal conflict in the selected vertical speed as there is also one in the selected Mach ... What is it all about ?
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Old 6th Aug 2011, 13:02
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Hi JD-EE,
Re: "Then the PF on AF447 was not a pilot?"

I think you missed the part where I said, "but since recent events have shown us such pilots do exist..."
Of course he was a pilot. Saying I can't imagine it isn't the same thing as saying it can't be.

I've said many times I think these poor folks were in a heck of an ugly situation. One might call it 'the perfect storm' to challenge his abilities... But he was a product of his training. Clearly, we're learning that many pilots don't know how their machine will behave when stalled. In my mind, that points to a serious deficiency in their training. I think it's akin to not knowing how the machine will behave with an engine out.

I suspect it's an inevitable result of the "cost effective risk management" biz... 'Creating a sim that can teach stall behaviour would cost too much and the aircraft are unlikely to stall anyway, so we won't bother.'

Which brings a question to mind... Somewhere I recall seeing a training aircraft (might have been a helicopter?) that had been designed with the ability to emulate the behaviour of multiple aircraft, depending how it was programmed.... Could such a system, in a small aircraft, be utilized to teach the stall behaviour of transport aircraft, I wonder?
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Old 6th Aug 2011, 13:31
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Originally Posted by 3holelover
Which brings a question to mind... Somewhere I recall seeing a training aircraft (might have been a helicopter?) that had been designed with the ability to emulate the behaviour of multiple aircraft, depending how it was programmed.... Could such a system, in a small aircraft, be utilized to teach the stall behaviour of transport aircraft, I wonder?
I recall seeing the same, although I no longer remember what the aircraft type was.

Howver.... the problem is the same as the sim: if you don't have accurate data for the behaviour of an aircraft well into the stall, there is no way you can program either your sim or your 'training aircraft'.
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Old 6th Aug 2011, 14:52
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Not A helicopter - a converted C131 by Arvin Calspan.

Calspan Retires USAF's Last C-131
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Old 6th Aug 2011, 14:57
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Autotrim

Dozy: Is that because you can't see any instance when it would be useful or because it goes against the methods you were taught flying aircraft with more "conventional" controls?

Autotrim is useful in ensuring that the aircraft remains trimmed when in autopilot so that when the autopilot is disconnected, either by the flight control system or by the pilot, he is not dumped into an out-of-trim situation. However, as I have said several times before, when I am hand-flying, I don’t want the system changing the trim. I want to do that myself. Trimming is not an arduous task. In fact, it is a completely natural act and it is second nature to a properly trained pilot. It would be even easier if the AB side sticks were equipped with “coolie hat” switches. That is my personal opinion as a pilot. You have told us that you are not a pilot so I believe that you have little basis for an opinion as to how you would want to fly an airplane. Apparently you are qualified to offer opinions on how software should be written to meet certain criteria specified by the users (the pilots), but it is those users who are best qualified to set the criteria in the first place. You have stated that there are good and sufficient reasons for the design of the software in the hand-flying mode, but AFAIK you have not offered any reasons why that design is preferable to my reasons for disconnecting autotrim when hand-flying. As a user, I believe that my preferences should take precedence over yours. I am open to reasoned arguments on that subject.

Dozy: IMO (for what that's worth) there's nothing wrong with the autotrim setup as long as the way it works is taught properly.

That’s your opinion as a non-pilot. It seems to be the consensus on this forum that the pilots of AF447 were not taught properly. It is my opinion, as a pilot, that because the autotrim continued to follow the inexplicable nose-up inputs by the PF, stall recovery would have been made more difficult, had they ever attempted stall recovery.


Dozy: If you look at the traces the trim moves minimally under automatic control. What caused it to deviate so strongly was a series of inputs that trended towards nose-up, the majority of which were around half the stick's rearward travel limit, that were sustained for the best part of 45 seconds. What caused it to continue the movement to the stops was a full nose-up deflection that lasted between a further 30-40 seconds - that's more than 1 minute and 20 seconds of nose-up input at a deflection that ranges from halfway to the stops - at cruise level!
I fully agree that the full nose-up trim situation was the direct result of the inexplicable nose-up inputs, but you need to understand the proper technique for hand-flying in turbulence, a technique which has stood the test of time over many decades. As I have previously posted, the technique for flying in turbulence is to first be properly trimmed before entering the turbulence and not to change the trim, allowing the aircraft’s designed positive longitudinal stability to keep you flying properly. That is essentially what the stated procedure is all about: “Fly pitch and power”. Presumably, AF447 was properly trimmed and the power properly set before the autopilot and autothrottle dropped out so they really didn’t need to do anything except take a deep breath and monitor what proper pitch and power was doing for them. If the dynamics of the weather take you off the desired altitude, you simply make small inputs to return to that altitude but you don’t change the trim because you want that proper trim setting to help you minimize excursions from the desired flight parameters. If, as a non-pilot, you think you have a better technique for flying in turbulence, please post that on the forum for the pilots here to consider.

Sometime back, someone here offered that the pilots of AF447 only needed to let go of the controls and the aircraft would have returned to normal flight on its own. While that is true with conventional flight control systems and a properly trimmed aircraft (for cruise), it was not true with AF447 because the autotrim had changed the pitch trim from a stable, level-flight setting. With a century of manned flight under our belts, the consensus of pilots is that aircraft should exhibit positive longitudinal stability. But the AirBus flight control system changes that, overrides the natural aerodynamic stability of the airframe and introduces neutral longitudinal stability when hand-flying. As a result, when a pilot moves the stick in pitch, the nose stays right there and will stay there even if the pilot lets go. It is my opinion as a pilot that an aircraft that exhibits neutral longitudinal stability is more difficult to fly properly than with positive longitudinal stability. If you have a different opinion, it will have to be as a non-pilot.

Dozy: The trim doesn't move in any noticeable way as long as the inputs are relevant to the flight regime. The PNF notices that the PF's lateral inputs seem to be extreme, and admonishes his counterpart. He then further upbraids the PF for commanding a climb when it is unnecessary. This is why the BEA recommend training for manual aircraft handling at altitude, because in this case the sidestick inputs are repeatedly way beyond what is reasonable at that altitude and airspeed.
It is my opinion that the pilots of AF447 were so poorly trained that they really didn’t know what had happened to the trim. For AB pilots, trim seems to be out of their notice in any situation except takeoff where they set it and forget it. Actually I believe that even if the AF447 pilots had known what had happened to the pitch trim, they would not have understood the consequences. They clearly didn’t understand much about flying an aircraft.

Dozy, it you have relevant arguments on why autotrim should not drop out with the autopilot, I will be glad to consider them.

There are other subjects which would be appropriate for separate threads such as the lack of tactile feedback in the side sticks, and whether or not it is appropriate to use the autopilot in heavy turbulence. I did not bring these up at this point because I wanted only to address your opposition to having the autotrim drop out when the autopilot drops out.
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Old 6th Aug 2011, 15:26
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A flying variable stability testbed for recent posts by 3HL & CJ ?

2011: Edwards AFB test pilot school has a variable stability F-16.

It is a one-of-a-kind VISTA (Variable stability In-flight Simulator Test Aircraft).

The VISTA can be configured to fly and behave like any aircraft, from a UAV to a C-17 Globemaster. It also has enhanced data recording capabilities.

Article at TPS's Test Management Program brings real-world projects to classroom
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Old 6th Aug 2011, 15:59
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Well said, Smilin_Ed! Being a know-all is so endemic in the computer world that it's refreshing to hear the other side put the foot down.
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Old 6th Aug 2011, 16:10
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curvedsky,
Many thanks for that very interesting link.

And no, it was not an F-16 I was remembering, more like a large twin jet. Might have been a DC-9, a 737, or a large business jet.

Slightly O/T, but IIRC NASA has a few T-38s that can be reconfigured to "fly like a space shuttle" and that the shuttle pilots used to "stay current" and practise the approach.

Maybe they're for sale now?
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Old 6th Aug 2011, 16:27
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Cool

Dozy: Is that because you can't see any instance when it would be useful or because it goes against the methods you were taught flying aircraft with more "conventional" controls?
http://www.pprune.org/rumours-news/4...ml#post6623524
Know the aircraft you are flying ... it's help in some situations ....
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Old 6th Aug 2011, 18:13
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Hi Smilin Ed

You are far too gracious. I won't belabor this, and won't stay, but this needs to be writtern.

Since the few days after the crash, a few PILOTS have noted the problem w/trim in Alternate Law.

Each time the THS moves, The airframe starts behaving like a different a/c. One reason I think the PILOT had problems with PITCH is at least because this ship did not want to lower her nose. Besides, when he did attempt it, He needed WAY MORE ND than he was comfortable with. WHY? because, as DOZY WANNABE has said... "The THS COMPENSATES for the elevator position". Go look up compensate, and think about if you would like to have a massive set of wings ON THE TAIL, "taking away" your elevators..... AUTOMATICALLY, and without any prompt on the Flight Deck.......
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Old 6th Aug 2011, 18:18
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Originally Posted by henra
Originally Posted by xcitation
The inexperienced PF did try stick forward however a/c still stays nose up no response, as elevator is at -30 deg due to full THS! So behaviour is bizarre and only explained if you have a full understanding of the situation in 60 seconds.
Hmmm, where did you find this situation in the plots ????
Where was any indication the PF was trying to get the Nose down ??
In contrary the Nose descended a couple of times despite continued NU commands from the PF, albeit slightly reduced from full NU to half NU a couple of times.
In the last minute the PF even fought the ND commands of the PNF by himself applying Full NU.
Having a look at the traces I do not see anything there which would confirm your assertion that the PF was seriously trying to get the nose down.
English BEA #3, Page 111, t>=02:11:00

Locate the 4 lines conveniently next to each other.
brick read, purple, cyan and green.

(brick-red line) look at PF nose downs (+ve above zero),
(purple) elevator max deflection down (forcing nose up)
(cyan) because the THS is auto trimming.
(green) the pitch stays nose up,

Example
t=02:12:17
stick 2/3 (10/16) forward deflection.
elevator -30 deg
THS -13 deg
pitch +4 deg.

My point is that the a/c sometimes did the opposite of inputs (pitch up with stick forward and pitch down with stick back). This was because a/c was dancing around edge of the stall from the outside of the flight envelope.
I stated this because someone said that you could just fly it by behaviour. The behaviour was terrible i.e. inconsistent and at times contrary to stick inputs. A/c needed to be flown by pitch and power with manual THS trim not by its behaviour.
Another point to make is that the instruments were impared, e.g. IAS, altitude etc. The true air speed and true altitude could have been different as noted by the QF72 incidents CPT.
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Old 6th Aug 2011, 19:05
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Originally Posted by Smilin_Ed
Autotrim is useful in ensuring that the aircraft remains trimmed when in autopilot so that when the autopilot is disconnected, either by the flight control system or by the pilot, he is not dumped into an out-of-trim situation. However, as I have said several times before, when I am hand-flying, I don’t want the system changing the trim. I want to do that myself.
Fair enough, that's your opinion - but have you ever actually flown a FBW Airbus? Plenty that have state that the autotrim is completely unobtrusive when hand-flying and that the aircraft as a whole handles rather well.

You have stated that there are good and sufficient reasons for the design of the software in the hand-flying mode, but AFAIK you have not offered any reasons why that design is preferable to my reasons for disconnecting autotrim when hand-flying.
In fact I did, but it's several threads back - one of the reasons was the ability to have hands on throttle and stick in a pilot incapacitation scenario.

That’s your opinion as a non-pilot. It seems to be the consensus on this forum that the pilots of AF447 were not taught properly. It is my opinion, as a pilot, that because the autotrim continued to follow the inexplicable nose-up inputs by the PF, stall recovery would have been made more difficult, had they ever attempted stall recovery.
And it is my opinion that had the pilots been taught how to use the manual trim wheel then they would have had an option for correcting the position it ended up in due to the overcontrolling that occurred just after FMC disconnect. Of course, more fundamentally than that had they been taught how to handle the aircraft properly manually at cruise flight even that knowledge would have been a mere "nice to have".

And for the record, while I am a non-pilot and have never flown solo, I have been at the controls of gliders and trainers in my youth. I'm not just some techie trying to dictate the way you should fly, I'm just saying that there are valid reasons why the design is the way it is.

Sometime back, someone here offered that the pilots of AF447 only needed to let go of the controls and the aircraft would have returned to normal flight on its own. While that is true with conventional flight control systems and a properly trimmed aircraft (for cruise), it was not true with AF447 because the autotrim had changed the pitch trim from a stable, level-flight setting.
And had they let go of the controls then the elevator demands would have ceased and the trim would have returned to neutral. In addition, the trim wheel is available to move the THS back to a neutral position far quicker than the autotrim would have. There were plenty of ways to recover, but the overriding problem is that the crew failed to recognise the situation they were in and the reason they were in that situation (overcontrolling at altitude). The reason they overcontrolled was because their training was lacking, which is the fault of the airline and the industry.

Originally Posted by deSitter
Well said, Smilin_Ed! Being a know-all is so endemic in the computer world that it's refreshing to hear the other side put the foot down.
Not helpful -the only one showing a dismissive and arrogant attitude is you.
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