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AF 447 Search to resume (part2)

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AF 447 Search to resume (part2)

Old 10th May 2011, 14:30
  #1081 (permalink)  
 
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Originally Posted by JD-EE
The problem with the short ping time is you cannot get the bandwidth down very far or you attenuate signal energy along with noise energy. The signal energy is coherent and the noise energy is not. So increased averaging times decreases your ability to detect the signal once you hit the threshold. Filter ringing, as it is called, screws you if you try really narrow bandwidths.
I was hoping you'd add some reality to this discussion. Agreed on all points. I was only pointing out that there is some room for improvement, given that the frequency spec is +/-1000Hz and the bandwidth of a 10ms pulse is on the order of 100Hz. Thus if you divide the potential 2kHz band into 100-200Hz slices, you stand to improve detection.
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Old 10th May 2011, 14:56
  #1082 (permalink)  
 
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"Cannot speak for Tubby, but most of you seem still to be convinced that pitot icing always leads to the related ASI over-reading. This presumption is unfounded. Further homework is called for."
Chris I do have practical experience of pitot icing in a non fbw Airbus and in my case it led to a false underspeed indication.The first ecam was for Fuel aft transfer!
In severe icing,if the drain holes of the pitot are blocked,the sensed pressure is trapped and remains constant ,whatever the changes in airspeed or altitude.If the holes are free the airspeed varies or may quickly drop to Vss until exiting the severe ice area.
See diagrams below for an explanation.Oddly these do not appear in the 330 fcom!

Last edited by tubby linton; 10th May 2011 at 15:53.
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Old 10th May 2011, 15:08
  #1083 (permalink)  
 
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Tubby, could you be talking about a static port hole in a combined pitot/static probe?

[edited]
Ah, I think I see now... Your "trapped pressure" threw me. I think may have that bit a little skewed.... If the "vent hole" was plugged, but the pitot opening was not, that would lead to a greater pitot pressure, causing a higher a/s reading, until the blockage cleared... but if both were blocked (on the pitots only - static vents still open) your airspeed would only change according to whether you flew up/down/into different pressure air.

Last edited by 3holelover; 10th May 2011 at 15:22.
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Old 10th May 2011, 15:29
  #1084 (permalink)  
 
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Tubby,

Thanks for confirming what I believe to be the case - having "never-knowingly" experienced it myself.

We don't know how subtle the onset might have been, nor if the PF would continue to be influenced by ASI readings even after the SPD-LIMIT warnings appeared on the PFDs. His pushing the nose down cannot be ruled out yet, in my opinion. This could be a case of high-speed LOC, followed by a recovery which ended in a normal stall at medium-to-low altitude, at which stage the pitots might still be de-icing themselves.

Initiating pitch-thrust is reasonably straightforward in level flight; in a steep descent it might lead to a high AoA.

Regards,
Chris

PS
3holelover, I rest my case!
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Old 10th May 2011, 15:45
  #1085 (permalink)  
 
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Chris?
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Old 10th May 2011, 15:46
  #1086 (permalink)  
 
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Old 10th May 2011, 15:46
  #1087 (permalink)  
 
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Old 10th May 2011, 16:55
  #1088 (permalink)  
 
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Originally Posted by JD-EE View Post
The submarine had no chance of reception unless it's crush depth is WAY below that of anything I could find on the Internet a couple years ago.
Hum, does this statement also apply to submarines equipped with towed array sonars (which can be towed lower than the ship's depth)?

Originally Posted by Chris Scott View Post
culs-de-sac. (Think the French don't call them that, preferring "Impasses".)
Well, I use both
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Old 10th May 2011, 17:41
  #1089 (permalink)  
 
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Cool

Hi,

Originally Posted by Chris Scott
culs-de-sac. (Think the French don't call them that, preferring "Impasses".)
Well, I use both
Why not "voie sans issue"
French is a language very rich .. and has many different words to describe the same thing (synonyms)
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Old 10th May 2011, 18:04
  #1090 (permalink)  
 
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mm43,

"ballonné et endommagé par la morsure de requin étrange"
Please, from where did this phrase come from?

I can´t "google" it from any other place than this forum...

Thanks!
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Old 10th May 2011, 18:53
  #1091 (permalink)  
 
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Originally Posted by JD-EE
The submarine had no chance of reception unless it's crush depth is WAY below that of anything I could find on the Internet a couple years ago.
Hum, does this statement also apply to submarines equipped with towed array sonars (which can be towed lower than the ship's depth)?


So the implication of this is that the French Navy are idiots then? Otherwise they were just tooling around the ocean for a bit of fun, since they obviously have a better idea of whether or not there was any chance of reception.... I vote there WAS a reasonably good chance.

A typical FAA approved pinger or beacon attached to the FDR will send out a continuous acoustic 160.5dB, 9ms pulse at 37.5 kHz for a minimum of 30 days, usually up to 90 days or longer at a slightly reduced dB level.

Sound propagates in all directions from the source - sound traveling vertically will be largely unaffected by thermal layer effects, so would suffer attenuation due to salt water (chemical content affects absorption), which at 37.5kHz would be roughly 5.5dB/km. Now I have no idea of the acoustic noise floor of the ocean or the sensitivity of the detection array on the sub, so I can't even guess what might have been the theoretical picture, but there seems to a very good chance of picking up a fully working pinger assuming the sub passed nearly overhead... at greater angles of incidence then thermal layers start to hide sounds and bounce them around, so may be there is significantly less chance of finding them at say greater than 30 degree off-vertical.

However I do wonder why the pinger frequency is so high?

37.5kHz = 5.5dB/km attenuation

9kHz = 0.5dB/km <<< 10 times less, or potentially 10 times the detection range.

- GY
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Old 10th May 2011, 19:18
  #1092 (permalink)  
 
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Pingers

Pingers are VERY simple devices. And not costly.

It´s "performance" can be (easily) improved.

Why not (for longer range airliners) use extra pinger(s) with specs. like:
  • Better (mech.) survivability (not a tiny one attached to a CSMU)
  • Increased duty cycle (allowing RX DSP)
  • Better frequency spec. (<1%)
  • At another (lower) frequency
  • Battery capacity (also) up to 90 days
The technology to this "new" device was available more than 30 years ago.

Mac
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Old 10th May 2011, 19:38
  #1093 (permalink)  
 
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The UK AAIB have just re-published the 2001 report of the October 2000 near miss between an A330 and a A340

Airbus A330 C-GGWD and Airbus A340 TC-JDN

including the DFDR figures in the Appendices

Air Accidents Investigation: Airbus A330 C-GGWD and Airbus A340 TC-JDN

Discussed here because of the involuntary "zoom" from FL360 through FL384 carried out by the A340 due to incident with turbulence.

Last edited by sensor_validation; 10th May 2011 at 19:55.
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Old 10th May 2011, 19:55
  #1094 (permalink)  
 
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Pingers

How about an option where if the pinger receives a signal at a different defined frequency it broadcasts a continuous tone for 30-60 secs to allow for better DF? This would allow for max battery life if no one was in the area, but give another option if someone was able to hear the ping but having trouble localizing it.

I am still a big fan of some sort of distributed storage as discussed previously, where either CVR and DFDR data are mirrored on both devices, or there are other devices with copies located in areas prone to survival. With all the advances in storage technology it would seem this could be done in a cost and weight effective way.

It has been very lucky that both recorders were found, and appeared to be in relatively good shape, lets hope that luck extends to the data itself, otherwise we will be wishing there had been a redundant system.

RR_NDB: Pingers are VERY simple devices. And not costly.

It´s "performance" can be (easily) improved.

Why not (for longer range airliners) use extra pinger(s) with specs. like:
  • Better (mech.) survivability (not a tiny one attached to a CSMU)
  • Increased duty cycle (allowing RX DSP)
  • Better frequency spec. (<1%)
  • At another (lower) frequency
  • Battery capacity (also) up to 90 days
The technology to this "new" device was available more than 30 years ago.

Mac
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Old 10th May 2011, 20:02
  #1095 (permalink)  
 
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Coherent sampling should work, if the frequency is stable and the ping time interval is well controlled. I would assume that both are XTAL based which would get you easily in the 1e-6 to 1e-8 territory on long and short term stability. If it is not XTAL based, then they should change that design, because then you have all the problems you describe.

Regarding filter ringing you will use digital filters anyway. That will give you a long delay, but who cares, you can turn around your ship anytime if you detect something.
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Old 10th May 2011, 20:13
  #1096 (permalink)  
 
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GarageYears;
So the implication of this is that the French Navy are idiots then?
I don't think anyone was implying that, but it transpired during the Phase 1 search that the SNA (Nuclear Attack Submarine) L'Emeraude's sonar detection equipment was not up to the task. It was apparently optimised for 8~9kHz and tests were undertaken onboard another Rubic class sub in the Mediterranean to optimise the detector for 37.5kHz. The new settings were transmitted to L'Emeraude and applied.

The BEA have already tabled for a ULB change of frequency to 8 ~ 9kHz with the ICAO at a meeting in Montreal in 2010. I suspect that the change will only gain traction once the reason for lack of detection of the AF447 ULBs is determined.

Some of these matters were previously discussed in Part 1 of this thread and can be found around page 90.
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Old 10th May 2011, 20:22
  #1097 (permalink)  
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Salute!

I wish to make it clear that I do not believe the plane was in a deep stall all the way down from cruise altitude. I do believe it was in a stall or deep stall at impact.

- Proximity to impact position from last known seems reasonable for a deep stall all the way down, but impact heading seems to show an intentional or unintentional turn from course. The plane may have even been in a spin for a turn or two or experienced a no-kidding "wahoo!!!" after encountering severe turbulence. Serious problems with the air data sensors is another explanation for an unusual attitude/flight condition due to all the "laws" this plane has.

- The impact damage and wreckage pattern indicate that the aircraft hit the water with a higher vertical velocity than horizontal velocity, such as the French interim reports claim. So a 60 or even 70 degree angle seems possible. Only other reason I can imagine than a stall is that the crew regained control and couldn't quite make the recovery in time. However, with the standard aft c.g. the plane flies with, the stall seems more likely,

- There is also a possibility that it was not sensor problems as much as an extreme aft c.g. that caused loss of control after the plane experienced only a moderate amount of turbulence. Any warnings or displays in the cockpit for c.g.???

On a personal note, the FBW system I flew acted like the Airbus for forward stick with respect to AoA protection.. We only had a positive AoA limit with gear up and that was 25 degrees ( no "protect" mode/value, just max AoA). Our system also had "standby gains" if the air data sensors were deemed unreliable. So two values for total pressure - one for gear up and one with gear down. This didn't limit gee or AoA, but limited the rate and amount of deflection of the control surfaces.

later,

Gums sends...
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Old 10th May 2011, 20:28
  #1098 (permalink)  
 
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Originally Posted by GarageYears
However I do wonder why the pinger frequency is so high?

37.5kHz = 5.5dB/km attenuation

9kHz = 0.5dB/km <<< 10 times less, or potentially 10 times the detection range.
The figures for detection have been discussed before, recently and a year ago. At 4km depth the probability of detection from Emeraude, even from directly above, was probably less than good. I expect that they were using every vessel they had available.

30-50kHz falls in an area of decreasing or minimum ambient noise (depending on depth). That is a good thing for typical scenarios where a plane goes down in shallow water near an airport; also the attenuation is not as big a factor in shallow water.

Certainly 9-15kHz would be a better range. This is the band commonly used for deep water transponders. The problem is that the typical transducers are about 1/2 liter in volume and weigh a kilogram or more. Aircraft designers are concerned with weight. BEA (or some other agency?) has called for lower frequency as a result of this accident.

Originally Posted by RR_NDB
Pingers are VERY simple devices. And not costly.

It´s "performance" can be (easily) improved.

Why not (for longer range airliners) use extra pinger(s) with specs. like:
  • Better (mech.) survivability (not a tiny one attached to a CSMU)
  • Increased duty cycle (allowing RX DSP)
  • Better frequency spec. (<1%)
  • At another (lower) frequency
  • Battery capacity (also) up to 90 days
Weight. All of the items listed add weight; some add a lot. I'm not saying that they aren't good or possible things to do, but I'm sure that's why they have been avoided in the past.
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Old 10th May 2011, 20:36
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Perhaps a bit late, but how do we know the time and altitude of the LKP? How was this seemingly well accepted information acheived? All speculation and calculations of what the airplane did or did not do has been based on two important things as fact. In reality, is altitude and position a confirmed fact? Just wondering.
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Old 10th May 2011, 20:55
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Originally Posted by wes_wall View Post
Perhaps a bit late, but how do we know the time and altitude of the LKP? How was this seemingly well accepted information acheived? All speculation and calculations of what the airplane did or did not do has been based on two important things as fact. In reality, is altitude and position a confirmed fact? Just wondering.
AF447 reported position to AF HQ via ACARS Satellite comms, every 10 mins. In amongst the alarm messages in one of the BEA interim reports is the 02:10 entry received at 2:10:34

2:10:34#0210/+2.98-30.59

Position only accurate to nearest 0.6NM in each direction, time 'nearest minute' but assumed close to 2:10:30.

Significantly this was ~3NM west of planned route, altitude, heading, velocity all 'assumed' until the black boxes reveal all.
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