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AF447 wreckage found

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AF447 wreckage found

Old 11th Jun 2011, 11:02
  #1601 (permalink)  
 
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The Duh in Aerodynamics

An airliner on departure, climb, cruise, descent, approach and landing is like a symphony orchestra, with all the components working in concert. The conductor can be the FMS, Fright Management System, or the aircraft commander.

It's all seamless and symphonic until a component hits a sour note. Then you really see the contribution of the other components and what is driving them.

It's basic to conventional airplane dynamics, as taught in Langewieche's "Stick and Rudder" and hundreds of other instructional manuals:

Pitch controls airspeed.
Power controls altitude.

The A330 Flight test accident in 1994 uncovered the flaw in Airbus logic. The plane was on autopilot in Altitude Capture mode when the pilot pulled the power on one engine. The AP responded to lack of power by pulling the pitch up to over 30 degrees. Instead, it should have kept the pitch at desired speed, and told the pilot, "We can't do that."

The TK951 B737 approach accident at AMS in 2007 revealed the same flaw. An undetected erroneous input to the A/T caused it to go to Flight Idle. The autopilot tried to stay on Glideslope by pulling the nose up and trimming to lower speed to make up for lack of power. Instead, it should have kept the desired speed, and let the plane sink below glidepath. If the pilot hadn't caught that, he would have heard, "TOO LOW! GLIDESLOPE." Firewalling the throttles would have stopped the sink, and not have caused such a pitchup, as the elevator would still have been trimmed for the correct speed. The pilot could have intentionally traded some airspeed for altitude, and without fighting full aft trim.

How does this apply to 447? We'll see. Trying to control altitude with pitch is a loser, regardless.
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Old 11th Jun 2011, 11:09
  #1602 (permalink)  
 
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Cool

Hi,

The test should have been carried out at above FL100
Just a tought ... but for me if the tests were conducted at the altitude of 35.000 feet ... the result of Perpignan will be the same than AF447
I don't see that altitude will change the fate of the Perpignan event.
The scenario was set to finish in the sea .. from any altitude over the one of the day.
And indeed the pilots were very experimented on type.
Again .. the hours on type are not a reference for "experience" ... as seen in many accidents.

A) He was applying (inappropriately) his memory items practised recently in the sim?
The memory items were innapropriate (reason why AF changed it after the AF447 crash and sended all their "experienced" pilots to the sim for play again the scenario)

Last edited by jcjeant; 11th Jun 2011 at 11:35.
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Old 11th Jun 2011, 13:03
  #1603 (permalink)  
 
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It's basic to conventional airplane dynamics, ......
Pitch controls airspeed.
Power controls altitude.
I DON'T BELIEVE THIS..
Are you serious?...

We are talking about jets here, it's the other way 'round

(And that makes it adamantly clear: you never flew one)
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Old 11th Jun 2011, 14:06
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Quote:
It's basic to conventional airplane dynamics, ......
Pitch controls airspeed.
Power controls altitude.
I DON'T BELIEVE THIS..
Are you serious?...

We are talking about jets here, it's the other way 'round

(And that makes it adamantly clear: you never flew one)
Its not "black and white", golfyankeesierra, it really depends on the circumstances: for example, when you're on an "open climb" in your A330 (at a fixed power), its pitch/attitude that controls your speed. The same for an open descent.
After more than 1600 posts here, where the main preoccupation was to understand why the AF447 PF didn't lower the nose of its A330 to reduce AoA and therefore to increase "speed", it seems pretty clear that not always "power" is enough to regain speed...

Last edited by aguadalte; 11th Jun 2011 at 16:31. Reason: add "to increase" speed (for better understanding)
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Old 11th Jun 2011, 14:33
  #1605 (permalink)  
 
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iceman you just proved my point.

QED
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Old 11th Jun 2011, 14:38
  #1606 (permalink)  
 
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golfyahnkeesierra makes it plain why modern "airmen" sometimes know nothing about airmanship. Just because his electric airplane's power levers stay in the climb detent, he thinks "You pull back to go up and push forward to go down."

I'd rather fly with Wolfgang Langeweische (or his son William, which I have done) than GYS.

Last edited by stepwilk; 11th Jun 2011 at 16:21.
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Old 11th Jun 2011, 17:23
  #1607 (permalink)  
bearfoil
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Pearpignan

Golf X-ray Lima triple eight
Tango contact tower one one eight decimal three bye
End of stall warning
Single chime

15 h 45 min 54 What’s wrong here
15 h 45 min 55 Flaps up
15 h 45 min 57 (*)
15 h 45 min 58 Flaps up
15 h 46 min 00 End of stall warning
15 h 46 min 00,5(*)
Continuous repetitive chime
15 h 46 min 02 Speedbrakes
15 h 46 min 02,5 End of CRC
15 h 46 min 03 C chord (Altitude alert)
15 h 46 min 04
SV: (*) terrain terrain
15 h 46 min 05 (…) (…)
15 h 46 min 06
15 h 46 min 07 End of recording


Someone unstalled the a/c. Unfortunately, it was pointed at the Ocean. Either the pilots started the Drill too low? (or not). Or the a/c would not allow NU? (what do the g traces say?). Both?
 
Old 11th Jun 2011, 17:58
  #1608 (permalink)  
 
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GYS
Quote:
It's basic to conventional airplane dynamics, ......
Pitch controls airspeed.
Power controls altitude
.

I DON'T BELIEVE THIS..
Are you serious?...

We are talking about jets here, it's the other way 'round
I presume you are a Flight Sim wannabee if you don't understand how we can control airspeed with pitch (which you do everyday on an airliner, well any aircraft, in both climb and descent)
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Old 11th Jun 2011, 18:28
  #1609 (permalink)  
 
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I am an aircraft engineer with nearly two decades of experience in the industry. I am not a pilot. What I find SHOCKING is that many professional pilots in this thread disagree so strongly on such basic issues as flight dynamics or what a variation of throttle will do to you in level flight. This is really scary. I know quite a lot about airframe design as well as flight control system design having done both for many years. But this thread is proving that as automation proceeds flying IS going to become more and more dangerous. And if that were not enough, they've now started to make airplanes from plastic!
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Old 11th Jun 2011, 19:27
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Cool

Hi,

(what do the g traces say?)
If you find G traces in the BEA report .. you lucky man
Myself found nothing about G traces in the BEA report.
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Old 11th Jun 2011, 19:50
  #1611 (permalink)  
bearfoil
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jcjeant

No traces of gee? How is that possible? Is the report available through the FAA? I can't imagine not, the A320 is everywhere over here.

complexman

As to resin, 447 had few composites in structural places. If it actually did, please don't tell me. As one who has designed and built in composites for ~40 years, I am most apprehensive about two things. Elasticity, and Fire.
 
Old 11th Jun 2011, 20:01
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Airbus has the obsession to use composites in much of the tail in most of its models. Joining a metallic component with a composite one is like asking for trouble. Always. (e.g. see section 19 on the A380). But that is not what is worrying me - I am scared of the 787. Rumors indicate that it actually would be lighter had it been built of Al instead of composite. This is because composite have never been used on such scale before so large safety margins are used to absorb the uncertainty.
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Old 11th Jun 2011, 20:20
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NOD, stepwilk, aguadalte,
Pitch controls airspeed.
Power controls altitude.
I was reacting to above statements

Yes, in a climb or descent pitch=speed, but then power becomes rate

But otherwise:
In a prop: pitch=speed, power=altitude
In a jet: pitch=altitude, power=speed

When you fly an ILS and you get a little high, you don't pull the power, you put your nose down.

What I am objecting to is GB's notion that the 2 mentioned accident are attributed to this pitch/power thing, and what I object most to is his "advice":

Trying to control altitude with pitch is a loser, regardless.
Now back to the AF447 and all this discussion about the stall recovery "procedure".
Stalls aren't trained anymore, they are such basic flying skills that the only time you do them is as mandatory items during type conversions,
but on every type conversion from the very beginning of my flying career they are (with the exception of the option of flapextension on some types) the same: lower your nose (on the horizon will do most of the time) and put on some power and you're out of it.


I can't believe that a pilot with the experience that equals the AF447 least experienced pilot consciously counteracts a stall with pitch-up command.
The big issue here is what the pilots felt and saw, and the BEA statements are a bit puzzling here.
I don't understand the sequence of AP and ATS dropping of before the airspeed indications became faulty. You only get alternate law after ADC's become unrelaible but the aircraft was already in alternate law before the speed dropped from 275kts to 60.
I don't understand the low speeds; I would expect speed increasing with altitude with blocked pitots.
I also don't understand the pilots perseverence in maintaining pitchup command; in his situation I could understand a temporary wrong input, but why so long?
Personaly I think the BEA has not given the full picture regarding actual flight laws; I am also afraid some unknown pitch protection feature played a role, pulling the nose up, while we are thinking it was the pilots doing...

Anyway the pilots were most likely overloaded, spatially disoriented and fooled by their indications, as we all would be.

I don't think an industry wide change of flying technique "Pitch equals speed", as GB suggests, would have saved the day here.
And as much as I like to be a "hands on" pilot, I think the prevention of this happening again will be a technical/engineering solution and not a piloting skill.

BTW, no, I am not a FS wannabe
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Old 11th Jun 2011, 20:56
  #1614 (permalink)  
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golfyankeesierra

I more or less resent the ease with which pilots are doubted, and the fall back is "It did what it is programmed to do". Fine, perhaps because pilots can think and
innovate, there is some residual resentment that programming gets a look once in a while. For what it's worth, any discussion should have some (alot) of room to wander, we're stuck with fbw. Not that it is poor, it is fine, but it gets this knee jerk defense where professionals get the magnifying glass.

So be it. My baseline is that this crew were eminently qualified, and perhaps more so than the bus. If there is a fault, it may be (probably) that the orchestra hit some sour notes, whether flute or conductor, no matter. The deal is that not enough practice leads to "Prior Planning Prevents Piss Poor Performance". Will the Bus surprise? It is certain, for there is simply no way this crew flew to STALL without some mitigating events. I think this should continue, for it is only the pressure of the folks that will goad the sloth.
 
Old 11th Jun 2011, 21:42
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Bear, not doubting the pilots, nor the plane.
I think the 'bus is as safe as any other plane, probably even more.
But I do think there will be some "discoveries" in the course of the investigations revealing a) new notions in passing through weather in that particular area of equatorial Atlantic, and b) new insights in the A330's FBW system.

BTW, remember the Lufthansa A320 tipstrike at Hamburg? In the course of that investigation it showed that most pilots were unware of a specific behavior in the roll-authority at touchdown:
The pilots could not have been aware of the specific flight system control response characteristics
during a landing with a gusty crosswind ...
BFU report page 62

I guess the AF447 final investigation report will spit out similar words..
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Old 11th Jun 2011, 23:15
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There is no enormous debate about the THS, it behaved correctly and if the correct actions had been taken I am sure the A/C would have been recoverable.
Iceman(appropiate enough),

So you dont think autotrim will feature in the report then?You're quite confident that the automatic application of full ANU tim followed by auto-cutout is a good example of "fail-safe" design?And that the transition from auto to manual (when how why it occurs) is intuitively understood by the poor pilot?So why perpignan and now AF?or the tarom or taipei?
It behaved correctly?It behaved as designed.

You might think your oh-so-clever destruction of Gretchenfrage's points were on the nose but you forget one thing;those planes crashed and Im afraid the pilots didnt really know why they were crashing.THEY DIDNT UNDERSTAND WHAT THEY HAD/HADNT DONE.If a design is ambiguous,then it is deficient.

Do you have anything to say about the stall warning inhibit?Id love to hear your thoughts on this one.Over to you ace.
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Old 12th Jun 2011, 01:42
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Cool

Hi,

So far as this accident is concerned, the adjustments in thrust and trim that were computer-directed
In alternate law with auto-throttle off (read BEA note !)
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Old 12th Jun 2011, 02:08
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Hi,

A little of topic but an interesting table ....
By the ACARS ... the BEA ?? .. and many people of this forum had concluded that the plane was falling rapidly (a stall or spin condition)
So (I already commented) I still puzzled with the management of the researches by the BEA (almost two years spend in thin air ..)

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Old 12th Jun 2011, 05:58
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RWA
 
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It used to be said that the only really silly question is the one you don't ask.

I'm wondering WHY the autotrim 'decided,' in both accidents, to go to 'THS full up' in the first place? And then STAY there, even though both pilots were in the end pushing the stick forward? Anyone know what the 'system logic' that could cause that reaction is?

The BEA gives us no guidance at all on the point. For the Perpignan accident - even though it's the final report - the BEA just says:-

The auto-trim system gradually moved the horizontal stabilizer to a full nose-up position during the deceleration. The horizontal stabilizer remained in this position until the end of the flight.
In the case of AF447, it says even less - it just tells us 'what' happened, and doesn't even tell us when it happened (i.e. which minute):-

The trimmable horizontal stabilizer (THS) passed from 3 to 13 degrees nose-up in about 1 minute and remained in the latter position until the end of the flight.
No mention of 'why?' in either case.

So here's my 'silly question.' Despite the fact that the autopilot and autothrust had 'signed off' on AF447, and the pilot at Perpignan was most certainly seeking to get the nose down all the time, and the AF447 one much of the time - is it possible that the autotrim in both cases was still trying to regain the previously-commanded altitude?

Never flown anything with autotrim (in fact, I've only flown anything with an autopilot twice in my life). But as far as I know, that (keeping the aeroplane exactly to a given altitude) is the main 'everyday' function of an autotrim?

Last edited by RWA; 12th Jun 2011 at 06:17.
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Old 12th Jun 2011, 07:20
  #1620 (permalink)  
 
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Flying Basics, straight and level:
Pitch attitude controls altitude
thrust controls airspeed
This for prop, jet, rocket any type of propulsion in fixed wing aircraft, but only on the front, right side of the thrust versus speed curve.

Left side of the curve- opposite. This because of negative speed stability, where a given power setting doesn't have one but two correct speeds, and the aircraft would always fly away from the desired speed on the left side..

Last edited by opherben; 12th Jun 2011 at 10:54.
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