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Old 9th Apr 2014, 14:55   #9581 (permalink)
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The latest TV news briefing said that the frequency received was 33.331 kHz, which is very precise.

Back of the envelope calculations assuming speed of sound in sea water at 4 degrees C and 4000 metres is around 1500 m/s, and the ship is towing at around 1 m/s, gives me a maximum doppler shift to the signal of around 20 Hz, which is an order of magnitude greater than the resolution indicated by the news report.

This is best case and assumes movement directly towards or away from the source, that there aren't effects due to currents, and that I haven't got my maths and assumptions wrong. Also, with 10 ms pings and the small windows of acquisition, there aren't that many waves to measure. Further, the signal seemed quite broad on the waterfall on the news report, but I couldn't make out bandwidth.

But - is it possible or even plausible that some further geometric information about the pinger's location wrt the receiver could be obtained this way? Perhaps the thread readers with DSP/hydroacoustic experience could comment...
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Old 9th Apr 2014, 14:55   #9582 (permalink)
 
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One question has occurred to me. It seems that MH370 may (and I say MAY) have been following airways towards Perth. Would an MH 777 have had a Kuala Lumpur - Perth route stored in the FMC library?
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Old 9th Apr 2014, 15:24   #9583 (permalink)
 
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wow! that TPL 25 is a LOT smaller than I thought. Never saw it in reference to another object before till now next to humans. I thought it would be perhaps the size of an automobile or something!@ LOL
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Old 9th Apr 2014, 15:34   #9584 (permalink)
 
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Quote:
One question has occurred to me. It seems that MH370 may (and I say MAY) have been following airways towards Perth. Would an MH 777 have had a Kuala Lumpur - Perth route stored in the FMC library?
Malaysian operate direct flights between Kuala Lumpur and Perth so the answer must be yes.
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Old 9th Apr 2014, 15:45   #9585 (permalink)
 
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Quote:
One question has occurred to me. It seems that MH370 may (and I say MAY) have been following airways towards Perth. Would an MH 777 have had a Kuala Lumpur - Perth route stored in the FMC library?
Given that MAS fly a scheduled non-stop service from KUL-PER (MH125) I'd say there was an excellent chance that the route was available in the FMC.
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Old 9th Apr 2014, 15:53   #9586 (permalink)
 
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I42,

They will use as much cable as possible and when mowing the lawn, will have to make large turns. The towed array is rated with a static depth, so the dynamic load of the towed speed and turn is important.
Due to the time required, they will not raise and lower the array when turning.

The distance between the parallel tracks is a function of the overlap at depth.

There are also Bluefin 21's in use.


They may also be towing a magnetometer, or multiple beam sonar array to image the bottom. I am sure if Ocean Shield isnt, others are.
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Old 9th Apr 2014, 15:56   #9587 (permalink)
 
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Doppler signature

Re: 9679

Agreed. Doppler signatures were used for ELT locating by satellite before GPS's were integrated with ELT's. The relative doppler shift is a tenth of the under water case.

The lower duty cycle ping pulse will make it challenging. A fellow on the Reddit MH370 group used matlab to find a 0.4 millisec slowing down during a playback of 20 seconds of pings from a news broadcast. Lets put Inmarsat on the case.

Last edited by Rollleft; 9th Apr 2014 at 16:20.
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Old 9th Apr 2014, 16:09   #9588 (permalink)
 
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Quote:
Originally Posted by underfire
Due to the time required, they will not raise and lower the array when turning.
Ocean Shield reels the TPL in to to a shallower depth when turning and then lowers it again. They in fact heard one of the first pings at a shallower-than-cruise depth after a turn. Turns take around three hours.
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Old 9th Apr 2014, 16:20   #9589 (permalink)
 
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Legislation

Further to post by Sheep Guts 9 Apr 03:24 regarding SAFE Act:

I am reliably informed that in fact the SAFE Act (Safe Aviation and Flight Enhancement) bill has not yet been introduced. It is in the process of being revised, extended and/or upgraded by certain relevant legislative staffs. It is my understanding that with respect to similar measures introduced in prior Congresses, committee hearings were not held.
Of course the state of facts about what happened with the recorders on the Malaysian T7 is as yet indeterminant. It would be a wiser course not to legislate a mandate for FAA to amend all type certificates until such time as the (reasonably) full impact of this on-going event has been assessed and understood.
At the very least, when it comes to aeronautical technology as the subject of Congressional action....one can always hope.

Last edited by WillowRun 6-3; 9th Apr 2014 at 18:11. Reason: Cross - reference to prior post on same subject, for clarity
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Old 9th Apr 2014, 16:43   #9590 (permalink)
 
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Acoustic Signal Strength

No Cookies | Perth Now

" 'It looks like the signals we’ve picked up recently have been much weaker than the original signals we picked up, so that means probably we’re either a long way away from it, or in my view more likely, the batteries are starting to fade and as a consequence, the signal is becoming weaker,' he [Angus Houston] warned.

'So we need to, as we say in Australia, make hay while the sun shines.' "


DK-Series Underwater Locator Beacons | Radiant Power Corp


"Acoustic Output, Initial: 1060 dynes/cm2rms pressure at 1 meter (160.5 dB)



Acoustic Output, After 30 days: 700 dynes/cm2rms pressure at 1 meter (157.0 dB)"
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Old 9th Apr 2014, 17:52   #9591 (permalink)
 
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Legislation

WillowRun6-3

Quote:
I am reliably informed that in fact the SAFE Act (Safe Aviation and Flight Enhancement) bill has not yet been introduced. It is in the process of being revised, extended and/or upgraded by certain relevant legislative staffs. It is my understanding that with respect to similar measures introduced in prior Congresses, committee hearings were not held . . .
Reliably informed? You're a lawyer - right? The SAFE Act was introduced and referred to committee twice before (2003 and 2005) and died there. A first year summer clerk could have told me no such act has been "introduced" this year. No need for any inside baseball here - please.

Let's not use big words to state the obvious - or what is otherwise breakfast table newspaper information . . .
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Old 9th Apr 2014, 17:56   #9592 (permalink)
 
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Something doesn't add up

I've been following the whole thing closely and reading many of the excellent posts made on this thread.

Not one for the conspiracy theories at all.

However, there is something that I can't help but find strange and that is why they were suddenly able to focus on these areas and miraculously discovered the pings.

First the Chinese then the Aussies/US.

I was under the impression they were searching huge areas, and then suddenly they decide to try the ping detectors and Lo and behold they get what seems like a result.

Isn't that a bit strange?
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Old 9th Apr 2014, 17:59   #9593 (permalink)
 
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Echo in transit?

While the most recent JACC media release at the moment I am typing advises that Haixun 01 and Echo are at the southern end of the underwater search area, with Ocean Shield at the northern, the current display of Echo position, track, and speed made good on marinetraffic.com shows Echo making 15.5 knots on a 37 degree course appearing to aim very closely at Ocean Shield's current position.

Meanwhile Haixun 01 shows as 16.7 knots on course 333, having made much progress toward the current surface search area.

They may never say this, but the disposition (and transit speeds, which are inconsistent with acoustic search) of the ships suggests to me that the much-discussed Chinese pinger contact is no longer being prosecuted, and that Echo may be transitting for sidescan sonar or other service at the site of the Ocean Shield contacts.
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Old 9th Apr 2014, 18:04   #9594 (permalink)
 
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Dunno, WillFly...Sheep Guts' post on prior page included specific statement that the bill had been reintroduced on March 12 of this year in response to this incident. It hasn't been. Period.
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Old 9th Apr 2014, 18:17   #9595 (permalink)
 
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oviano: I should have been less cryptic. Sorry.

There was nothing "sudden" about their progress in the search. This search has been going on for over a month. We in the public are not priviy to all of the details of what they consider, what they reject, and what their cueing and trigger information have been.

Part of what they are doing involves the process of elimination, and making the most of such clues as are available. If we let the drama infested media influence our understanding of this search, we can fall into the trap of assigning traits like 'sudden' to events that unfolded over time for the search team and various national authorities.

They were indeed searching huge areas, but the areas have been shrinking every few days. Nothing strange, nothing sudden.

What took a lot of people by surprise (myself included) was the public announcenment that the early searches in the South China Sea and Malucca Straits needed to be abandoned, and a search far off the coast of Australia in the middle of nowhere granted precedence.

As I understand the background of this search, the indicators that this was a better course of action did not arrive suddenly, but were derived from the process of vetting and analyzing the sparse information available. No drama: plodding detective work.
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Old 9th Apr 2014, 18:18   #9596 (permalink)
 
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Quote:
Originally Posted by James7 View Post
of

Something told them to look there...
I thought it was the 'boring' work of ongoing detail analysis of the Inmarsat data coupled with more refined analysis of 777 performance characteristics that fit to the pattern of known arcs and dopplers that lead to deploying listening assets in the 'small arc' where Haixun 01 and Ocean Shield were operating.

It seems quite likely that after a lot more hard analysis of the acoustic data they will have localised a reasonable search area and then in several weeks will have found the wreckage with the side scan sonar.

Nothing particularly sinister in all of this analysis and thinking taking a lot of time.
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Old 9th Apr 2014, 18:28   #9597 (permalink)
 
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IATA code coincidence...

Using IATA codes instead of ICAO reveals a bizarre coincidence:


Originally heading for PEK
Turned west to PEN
Turned south to PER


All of which are MH served destinations, alphabetically ordered same as above...


772 FMC uses ICAO codes though, does it not?
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Old 9th Apr 2014, 18:56   #9598 (permalink)
 
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Why new location

Quote:
Weebobby:

There was something that led them to that spot in the Indian Ocean, some clue or intelligence that meant Ocean Shield heard the first pings on the very day the black box batteries were due to start weakening. Something told them to look there... I doubt we will ever find out!

It was the realisation that the aircraft was flying lower.

The resulting faster IAS, slower TAS, and thus slower groundspeed - and the resulting shorter range - meant that the search location had to move along the last ping-ring towards the northeast. Simple, really.

What we don't yet know, is why they suddenly realised that the aircraft flew at low-level.


P.S. If someone can post the fuel-burn/altitude tables for 1,000' and 10,000', it would be fairly easy to calculate roughly how low it flew.
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Old 9th Apr 2014, 19:03   #9599 (permalink)
 
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Also it is possible a classified asset heard it first and a hint was dropped to get everyone in range of the pinger
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Old 9th Apr 2014, 19:18   #9600 (permalink)
 
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Quote:
Originally Posted by silvertate View Post
It was the realisation that the aircraft was flying lower.

The resulting faster IAS, slower TAS, and thus slower groundspeed - and the resulting shorter range - meant that the search location had to move along the last ping-ring towards the northeast. Simple, really.

What we don't yet know, is why they suddenly realised that the aircraft flew at low-level.


P.S. If someone can post the fuel-burn/altitude tables for 1,000' and 10,000', it would be fairly easy to calculate roughly how low it flew.
I think the reasoning was the reverse. Assume last ping was at out-of-fuel. That gives a fuel burn rate which can then be reverse looked up to find the cruise levels/speeds that would result in that burn rate now fit those speeds/levels to the several INMARSAT rings the one that most closely fits tells you where on the final ring the aircraft was out-of-fuel. Use simulation of aircraft behavior when fuel is out at that level/speed, then generate a new search area. Pingo
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