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AF 447 Search to resume

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AF 447 Search to resume

Old 1st Dec 2010, 13:48
  #2521 (permalink)  
bearfoil
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Tokyo Geoff

Perhaps Two hundred and one. Everything about this accident is speculation thus far.
There are missing pieces from any and all "conclusions". Not even the first report made conclusions, only informed speculation. So it remains.

Compared to established routine, some informed speculation has been offered. If the Fuselage impacted as BEA have said, the cockpit would have hit almost exclusively in the vertical, and the cockpit/nose area is reinforced beyond that of the "Tube". So right off a suggestion of pilots being trapped in situ. If the Captain was resuming his Left Seat, or walking forward from rest, he may have tumbled out the front shattered section of Fuse. There have been no reports of identifying injuries for those unseated. The only injuries referenced have been those concluded by BEA to have been of seated passengers.

Seats occupied have been noted on graphic, so one can unwind name/seat by manifest.

There is a strong possibility we have all the evidence we shall ever have. So, as you say, all will remain speculation. Let's simply hope the speculation will remain objective.

cheers,
bear
 
Old 1st Dec 2010, 13:56
  #2522 (permalink)  
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JD-EE

When viewed dispassionately, all hidden data hurts the hider, that is the impetus of the hiding?
 
Old 1st Dec 2010, 14:05
  #2523 (permalink)  
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Once flying my Manta Wing, I was overcome by an updraft that lifted the 'nose', I ended up on my back. Overrotated. I was an observer, not a pilot at that point.

The Autoflight has limits designed into it. As these limits pass the designed value, the Autoflight trips out. This introduces Alternate Law. Manual Flight. Dark as Coal, no Horizon, No Airspeed, two dozen warnings and alerts, Turbulence of "Fortes".

Sky King would be perplexed.
 
Old 1st Dec 2010, 14:41
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For cpp6f and vortex:

Not sure I'm the right guy to say this, but I got here first so here goes.

The airplane was flying in 'coffin corner'. This is a strange part of the flight envelope where stall speed and the maximum mach number converge. The stall speed is a constant indicated airspeed, based on 'q' or 'half rho vee squared'. And this is the problem, rho, the air density, decreases with altitude so the true ground speed for stall progressively increases. At the same time the speed of sound in air decreases with lower density and so with higher altitude.

At the flight level they were flying, I think it was fl370 or 37,000ft, the margin between airplane stall speed and structure maximum mach number was only 25 knots. Go slower and you stall. Go faster and you disintegrate. Don't know your airspeed and you sure as heck will do one or the other.

I hope this is a valid explanation, others greater than I will come after and will surely correct me.
 
Old 1st Dec 2010, 15:07
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Correct me if I'm wrong, but isn't indicated airspeed directly determined by the AoA which is directly controlled by the trim setting of the horizontal stabilizer and completely independent of engine power? So if I'm the pilot and I lose airspeed data in such conditions, I would assume I was already at a safe airspeed and AoA and not touch the trim, and then cut engine power to descend to a safer altitude. Of course, severe turbulence would cause temporary deviations from the equilibrium airspeed and AoA, but would a functional autopilot be able to correct these deviations faster than aircraft would by itself, thus reducing the possibility of a catastrophic deviation?

Now this is coming from a hang glider pilot with absolutely no experience in powered aircraft much less a 100 ton state-of-the-art transport so I may have no idea what I'm talking about.
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Old 1st Dec 2010, 15:19
  #2526 (permalink)  
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Let's simply hope the speculation will remain objective.
By its nature, speculation is subjective.
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Old 1st Dec 2010, 15:33
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I am intriqued by this talk of pilot (in)action in the face of contradictory evidence to the pilots

I always understood that Airbus was fly by wire and that the computer CANNOT be disabled under any circumstances.

momie sait mieux - as they say in Toulouse
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Old 1st Dec 2010, 15:52
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Common Mode Failures

This is quite a bit oversimplified, but with Airbus, until you degrade fully to direct law, the computer is still trying to fly the aircraft as it sees fit, up to and including overriding the aircrew's input. All that "Autopilot" really means is that the aircraft is holding heading and altitude in accordance with its instructions, but the computer is still flying the aircraft.

Once the computer accepts bad data as gospel, it can start doing stupid things with the aircraft. All it needs is a trigger for all heck to break loose.

The computer gets its data primarily by accepting the middle (median) value of the 3 input channels for key flight information.. When some situation occurs that affects 2 or 3 of these data inputs channels in some common (but bogus) manner is when Airbus gets confused.

ACARS information from the flight indicates that all the Airspeed information channels were considered bogus at some point.

Sheer speculation below but possible initiators for loss of control are:

1. The Aircrew being confused by erroneous airspeed indications and stalling the aircraft in Alt (2) law.
2. The aircraft being confused in Normal Law, and applying the wrong dynamic laws for the aircraft and thus dynamically diverging from controlled flight.(Think servo system that is stable but too much gain.)
3. The aircraft being confused in Normal Law, and applying Mmo/Vmo protections inappropriately, then degrading to Alternate law and stalling.
4. Something even stranger that I haven't considered.
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Old 1st Dec 2010, 16:27
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Originally Posted by mike-wsm
The airplane was flying in 'coffin corner'. This is a strange part of the flight envelope where stall speed and the maximum mach number converge. (...)
At the flight level they were flying, I think it was fl370 or 37,000ft, the margin between airplane stall speed and structure maximum mach number was only 25 knots.
Actually, the airplane was flying at FL350, its 'coffin corner' was at FL460, and the margin between max. speed (Mmo=0.86; 295 kCAS) and low speed buffet (M=0.58; 192 kCAS) was 162 kTAS.

regards,
HN39

Last edited by HazelNuts39; 1st Dec 2010 at 17:07. Reason: low speed buffet correction
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Old 1st Dec 2010, 17:06
  #2530 (permalink)  
 
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HN39,

Thanks for injecting some sanity back into the discussion.

We know the aircraft lost the ability to maintain stable speed and altitude, but how that came about and the apparent inability of either FBW protections or crew inputs to rectify the situation is why this thread exists. Hopefully by mid 2011 we will have factual answers to this conundrum and a resolution to an intriguing puzzle.

mm43
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Old 1st Dec 2010, 18:57
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I always understood that Airbus was fly by wire and that the computer CANNOT be disabled under any circumstances.
I believe that one can force the system to a lower law by pulling CB's / intentionally disabling systems.
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Old 1st Dec 2010, 19:12
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Once the computer accepts bad data as gospel, it can start doing stupid things with the aircraft. All it needs is a trigger for all heck to break loose.
The Perpignan A320 accident is a prime example, especially the out of trim condition following an unexpected law change.

mm43
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Old 1st Dec 2010, 21:44
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Human vs. Machine

I have tried to keep up with this thread, but don't recollect having seen this discussion, so here goes.

Re the comments about PRIM, SEC related messages in BEA reports. The reports state it has not been established if the messages in question were the result of pilot action.

IMHO, if this information is available to the system, it should be differentiated on their ACARS signature. I'd think this is a pretty important piece of "maintenance" information.
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Old 1st Dec 2010, 23:53
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HN39, as you have explained they were nowhere near coffins corner. Speculation on this thread is the only thing we have been reading other than some acars data transmitted during the incident. Does anybody else think by holding attitude angle, maintaining GPS GS and cruise power was the only option they had with total pitot/static freeze up? I hope they find the black boxes so they can find out what really happened. If
that was their only option even though GPS GS changes with prevailing winds it is better than nothing.
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Old 2nd Dec 2010, 02:44
  #2535 (permalink)  
 
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Hi p51

There is no shortage of speculation. But there are also a few fairly hard facts. The best chance of finding AF447 is to find an explanation that unifies these few facts.

1. We have bodies drifting North when they were found - in fact just a little west of north (357). Not ENE or NE as the current charts showed. This suggests that the point of impact is somewhere to the SE of where we have looked so far. How far SE is speculation, but I am fairly convinced that SE is the direction to look next. I believe this information provides the single best indicator of where AF447 may have ended up.

2. Takata extrapolated the observed drift of the bodies, and came up with an impact position of 1.915 N, 30.390 W. His theory to explain this was that the aircraft turned right to the SE an attempted to divert to Fernando de Noronha. This extrapolation was based on the assumption that the current was exactly the same for the 5 days prior to bodies being recovered as it was for the period when they were being discovered. In the absence of any definitive information, this assumption is as reasonable as any other. However my guess (speculation) is that the impact is not that far to the SE. If the aircraft had a significant period of controlled flight after turning, then you would have expected a radio call of some sort, evidence of life-jackets, and cabin crew secured in their seats. None of this appeared to have happened, and so it is likely that the end was faster than Takata's theory.

3. There was at least one (possibly more) submarines searching for the pingers. The mission and the very survivability of these submarines depends on finding things that are trying not to be found. How could they search for weeks and not locate something trying to be found? Sure the pingers have limited range - more so if you are listening several miles above them. Yes I appreciate the challenges posed by extreme depths and that submarine sonar is probably not designed to find enemy submarines that deep (there being no point). And multiple thermoclines and mountain ranges will complicate the task greatly. But nothing definite identified. I could accept not localised due to the complexity of pinning the source down. But not even heard. No other civilian assets heard anything either. We they all listening in the wrong place?

4. No life-jackets. No radio call. Cabin crew seats that were not used. All this suggests things went very bad very quickly.

I have left the pollution spot out of this as I do not think we really know its origin - thank you to mm43 for clarifying that. If you chose to include the pollution spot as a reliable datum point however, then this would also support a crash SE of last known position. Not very far however due too the proximity of this when found on the 2nd.

Can anyone produce a credible explanation of the aircraft turning (either controlled or not) to the SE, flying for some distance south of 3 N, and no pilot able to get out a radio call, nor cabin crew get to their seats, nor life jackets utilised?

Last edited by slats11; 2nd Dec 2010 at 04:49.
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Old 2nd Dec 2010, 04:25
  #2536 (permalink)  
 
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question

If a NAV IAS DISCREPANCY ECAM MSG has/had been triggered, would/should it figure on the ACARS list ?
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Old 2nd Dec 2010, 04:42
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YouTube - Lost - The Mystery Of Flight 447 - Part 5

The BBC documentary speculates that the failure to increase thrust after the loss of AIS led to the stall. Correct me if I'm wrong, but on a simple aircraft with no automation, reduced thrust should not change the AoA - thus a stall should not occur - the only thing that would happen is the aircraft would descend in a controlled manner. So what are they really trying to say? Are they just dumbing it down for a non-technical audience?

I don't have much expertise here, but I'd still like to understand what might have gone wrong. Are these the possible scenarios that could have caused the crash?

(a) Severe turbulence caused the plane to stall or overspeed - thus the crash was caused directly by flying the plane into a powerful storm and the malfunction of the pitot tubes did not play a significant part. Thus it is suicidal to fly into such a storm even if you have a perfectly functioning flight control system and improvements in radar or interpretation are needed to safely fly through the ITCZ.

(b) It is reasonably safe to fly through such a severe storm if one maintains a large enough airspeed cushion above stall speed and below mach buffet speed. But without accurate airspeed data, this cushion could not be maintained and the severe turbulence caused the plane to stall or overspeed.

(c) The autopilot is unstable (in severe turbulence) with loss of airspeed data and caused the plane to stall. Had the pilots been in direct control of the aircraft the entire time, this would not have happened. This is corroborated by the incident on Quantas flight 72. Thus the flight control system of the A330 has design flaws that need to be corrected.

Any other scenarios that could have led to the crash?
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Old 2nd Dec 2010, 11:47
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bearfoil, "When viewed dispassionately, all hidden data hurts the hider, that is the impetus of the hiding?"

That is what is known as a tautology. It ignores the affects on third parties when the secret information is released. Your view is one I associate with people "who just want to see the world burn." That's not a healthy viewpoint. It ignores how most people would be quite unhappy to see the world burn, especially as they take part in the "festivities" as nice Roman Candles of ambulatory fat deposits.

Your shame still stands out, bearfoil, for not considering the collateral damage of satisfying your ego trip from the information release.
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Old 2nd Dec 2010, 12:26
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Slats11, some nits

Rather than a straight line approximation look into a second or higher order curve that better fits. The maps Saturn has put up show weak currents to the NE that turn into slightly stronger currents to the N and then even stronger currents to the NW in that region at that time. I'd expect them to have gone down to the West of the over simplified straight line estimate.

Fernando de Noronha is to the SW and has roughly a mile of runway. So that part of your comment raises a huge, "But, WHY?"

Regarding life jackets, I've noted it's really hard to reach that silly object in its storage under the seat cushion while I am strapped in to keep from kissing the overhead due to turbulence.

Pinger range is very short compared to the depth of the ocean where the plane went down. As you mention multiple likely thermal discontinuities make it even less likely a mere submarine at even twice its Wikipedia estimated maximum survivable depth would get close enough to hear the pinger.

Missing radio is a little unlikely. If the current setup was for transmit on DAKAR's frequency when the microphone switch on the joystick was pressed that could explain a lot. While the world is turning to (oops) around you reaching to reset the console to transmit on some other pre-tuned radio would be unusual. So I'm merely uncomfortable with missing radio calls, well before the situation turned bad. Once it went to perdition setting up to transmit a mayday on 121.5 or the like seems somewhat like the little mouse raising its middle digit as the owl swoops in for dinner.
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Old 2nd Dec 2010, 13:43
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Pick away JD.

The Fernando de Noronha theory was Takata's explanation for his drift analysis. Takata assumed the current was constant from the time of impact. As such he plotted the crash site to 1.9 N - a log way south of the last known position. I guess he could only explain the plane being that far south as being due to controlled flight - and I presume he therefore suggested a diversion to Fernando de Noronha as a possible explanation for this.

I buy Takata's drift analysis (in part). However I doubt that the plane was as far south as 1.9 N. There is no logical reason for it to be that far south, and if they did reverse course there should be some corroborating evidence to support this. Therefore the current was not constant from the time of impact. It was fairly constant (speed and direction) from day 6 when the bodies were first discovered. But it was doing something else for the first 5 days - who knows what.

The real point is that the bodies were not drifting in accordance with the current charts when they were discovered. At 3.5 N on the 6th, these charts suggest the current was to the NE. The bodies were drifting slightly west of north.

Therefore, the best thing to do with these charts is to ignore them. And keep an open mind as to where the bodies were drifting over the first 6 days. Don't attempt retrospective drift analysis based on charts which could only be tested once (days 6-10) and were shown to be inaccurate.

I have long forgotten whatever I ever knew about 2nd order curves. However that does not matter here. We have no idea what the currents were really doing. I am sure some datum buoys were thrown out by the FAB. But if they were not thrown out in the right area then they are pretty meaningless also.

Life-jackets? I can accept that not everyone would get a jacket on. I find it strange that no one got one on - these are the bodies that would most likely be found, and I feel that if 50 recovered bodies did not have a jacket on then probably no one put one on.

No Mayday or other call?

Very importantly, cabin crew seats were not used. The cabin crew are all taught the importance of using their seats - rear facing with shoulder as well as lap belts.

Any one of these factors? Shrug shoulders. However putting these 3 things together, it is hard to escape the conclusion that things went from routine to totally out of control very quickly. So nope, I don't buy the controlled flight to the south theory. There is nothing at all to support it.

So what are we left with. At some point soon after last known point, the most likely sequence of events appears to be a pitot blockage leading to stall and loss of control and a spin. Probably recovery of spin at some point (if we accept the BEA analysis of the impact). Then a rapid descent with some forward motion. The plane could have been pointing in any direction at that time, and so possibly a few miles were covered during the descent. My guess is that this was to the south. Based on 2 factors:
i) we have not found it and we have looked in most other directions
ii) a few miles SE does incorporate the pollution spot (that is pretty thin however).

Any unsecured cabin crew would likely have been incapacitated by this stage and hence would not have got to their seats. Any restrained pax that were still conscious were probably beyond doing anything as organised as putting on a jacket. And the pilots are probably not going to transmit anything at that point either.
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