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Malaysian Airlines MH370 contact lost

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Malaysian Airlines MH370 contact lost

Old 9th Jun 2014, 21:40
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Originally Posted by Communicator
Based on a basic understanding of the electronics involved (Inmarsat Classic Aero mobile terminal), the fact that this equipment has been around since the 1990s, and discussions of the "BFO" data (e.g. on Duncan Steel's website), it appears that the BFO values are the amount of Doppler-shift pre-compensation applied by the a/c terminal.
Previously in this thread, I described how it was possible to use the offset detected at the AES Rx of the SAT P channel carrier to pre-compensate the AES Tx frequency in the opposite direction, so that the SAT Rx always received the AES on the assigned channel frequency.

It now transpires that the Honeywell SATCOM package installed on 9M-MRO used a software algorithm to calculate the Doppler shift correction to be applied, based on the aircraft position and motion. However, the software assumed that the SAT was actually at its geostationary position of 0° 64.5°E and didn't take into account the eccentric ellipse of +/- 1.63° about the equator performed by the SAT in a siderial day.

Its this eccentric motion which is used by Inmarsat to differentiate whether the aircraft was on a Northern or Southern vector.

So, in this case the BFO is the difference between what the AES calculated, and what it would have calculated if its software used the actual SAT ephemeris values.
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Old 9th Jun 2014, 22:35
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Doesn't the Power Supply Assembly use a dedicated battery to prevent power interruptions during power source transfers?
The "fly by wire system" has dedicated batteries that keep the computers powered during short power interruptions. These "dedicated FBW batteries" are normally kept charged by battery chargers powered by the AC generators.

All AC bus-bars loose power with associated generator failure until the other (or, if running, the APU) generator restores AC power (ignoring the limited AC produced by the static inverter)

However, never in all my years understood why they are called AC generators, not alternators!!
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Old 9th Jun 2014, 23:22
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How is BFO Measured?

Jun stated:
Previously in this thread, I described how it was possible to use the offset detected at the AES Rx of the SAT P channel carrier to pre-compensate the AES Tx frequency in the opposite direction, so that the SAT Rx always received the AES on the assigned channel frequency.
I agree (and also previously stated in less detail) that pre-compensation values could readily be derived from observed Doppler shift in the download signal received from the satellite.

It now transpires that the Honeywell SATCOM package installed on 9M-MRO used a software algorithm to calculate the Doppler shift correction to be applied, based on the aircraft position and motion. However, the software assumed that the SAT was actually at its geostationary position of 0° 64.5°E and didn't take into account the eccentric ellipse of +/- 1.63° about the equator performed by the SAT in a siderial day.

Its this eccentric motion which is used by Inmarsat to differentiate whether the aircraft was on a Northern or Southern vector.

So, in this case the BFO is the difference between what the AES calculated, and what it would have calculated if its software used the actual SAT ephemeris values.
The idea that the BFO is pre-computed based on aircraft location, heading and velocity has recently been mentioned with some frequency here and elsewhere. The approach is certainly possible, but it seems vastly over-complicated (and thus error-prone) as a solution to the Doppler compensation problem compared to measuring the downlink Doppler shift.

Also, what is our basis for thinking that this is ACTUALLY happening in the Aero Classic units?

Just as importantly, given that Inmarsat, Duncan Steel and others used the BFO values essentially as a proxy for aircraft velocity (subject to some adjustments for three-dimensional heading), the residual error due to movements of the "geostationary" satellite (and uncompensated by the postulated pre-computation system) fails QUANTITAVELY to account for the observed values in the 100Hz - 350Hz range.
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Old 9th Jun 2014, 23:36
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Given the cost of some of the underwater search assets involved, it would seem to be less expensive to charter 2-4 777s with similar satcom installations, wait for an approximately similar moon phase, maneuver the necessary satellite(s) to a similar orbit, and fly the chartered jets along the most likely routes both north and south to generate results for comparison. Even with compensating Inmarsat for maneuvering fuel it would seem to be a more productive use of resources.
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Old 10th Jun 2014, 00:04
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Originally Posted by Communicator
... what is our basis for thinking that this is ACTUALLY happening in the Aero Classic units?
Just read the notes on pages 1 & 2 of the Inmarsat data release. In part -
Inmarsat Classic Aero mobile terminals are designed to correct for Doppler effects on their transmit signals. The terminal type used on MH370 assumes a stationary satellite at a fixed position.
The permanent offset you are referring to, is as a result of Inmarsat creating a "nominal terminal" outside of the satellite.
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Old 10th Jun 2014, 02:33
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ABC (Australia) news also reporting that Australian and Malaysian authorities are "negotiating" on who will pay for the search effort.
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Old 10th Jun 2014, 16:29
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australia signed a contract with fugro survey from the netherlands to map the entire seafloor in the search area. ( 60000 square kilometers )


in german :


Flug MH370: Niederländische Firma soll Meeresboden kartieren - SPIEGEL ONLINE


english :


MH370: Australia appoints Fugro for bathymetric survey of search area - Nation | The Star Online
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Old 11th Jun 2014, 01:32
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@lostinp
A professional survey company with the expertise and equipment to do the job
If they can not fid the damn thing nobody can
These guys are not searching for the plane, they are mapping the ocean depths in the search region to aid the upcoming sidescan sonar search from August onwards.

The tender is still open (until the end of June) for the bottom survey to locate the plane.
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Old 11th Jun 2014, 06:45
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thommo101
Quote:"These guys are not searching for the plane, they are mapping the ocean depths in the search region to aid the upcoming sidescan sonar search from August onwards.

The tender is still open (until the end of June) for the bottom survey to locate the plane."

This video (from a Fugro employee) indicates it "may" be possible to locate the wreckage. They found a shipwreck in the Mediterranean, 9,000ft down, using sonar.

How deep is the Flight 370 search zone? ? Anderson Cooper 360 - CNN.com Blogs
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Old 11th Jun 2014, 09:21
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MH370 - Resolving the Inmarsat Data

On 29 May 2014 the Malaysian DCA released on behalf of Inmarsat an abreviated Communications Log providing both the BFO and BTO data they logged for transactions through their IOR 3-F1 satellite to and from 9M-MRO on its last flight.

There has been a lot a discussion about what this data means, and whether it is possible to draw any definitive conclusions over the path the aircraft took from what is purported to be a Malaysian PSR contact at 1822z on 8 March 2014 near way-point MEKAR in the NW Malacca Strait.

To get the subject away from the speculative nature of the current thread in R&N, will hopefully result in some meaningful discussion.
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Old 11th Jun 2014, 09:23
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There has been a thread established in the Tech Log in which those who have an interest in resolving the issues surrounding the Inmarsat data release are invited to participate.
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Old 11th Jun 2014, 10:50
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BFO values

1)With one exception, all the published BFO values are positive numbers. Has there been any verified explanation of the "-2" BFO?

2) From an engineering prespective, I would have always expressed an offset as a positive value, regardless of the actual computation (leading to a positive or negative result). However in this case if the required frequency shift was positive, that implies one possibility; if the shift were negative that has contrary implications.

So, has it been verified that all the shifts are positive? Or has this been also left to speculation?
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Old 11th Jun 2014, 11:09
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Raw data BTO

Thanks for the opening of this thread!

I have some problem understanding the BTO values published in the "Raw data" PDF (http://www.dca.gov.my/mainpage/MH370...ion%20Logs.pdf)
Perhaps there is a big thing I don't see, but I am looking at those values for a moment without a clue...

On page 1, we can read (bold from me):
Understanding the Burst Timing Offset (BTO) values:
- The round trip time for a message is a combination of:
1.) Time from the ground station ? satellite ? aircraft ? satellite ? ground station
2.) Processing time within the ground station, satellite and aircraft terminal, which are constant
- The BTO is a value (in microseconds) relative to a terminal at a nominal fixed location. Only R-Channel messages are used.
- The BTO therefore allows the determination of the distance between the satellite and the aircraft. It does not provide the actual aircraft location.
All this seems perfectly clear, and I understand that the BTO is the sum of the round trip of the message (at light speed) and some delay from processing times in the different units.
And because of these processing times, the BTO have to be longer than the time (at light speed) from Perth (ground Inmarsat station) to Inmarsat 3F1 (the satellite) then to the aircraft and all the way back.
How long is this travel? It has to be longer than four times the height of 3F1, which is around 36000 km above the equator, that is about 144000 km, say 150,000 km, which is the distance the light travels in half a second (some maths gives ~159,100 km at 16:00 UTC when the aircraft was on the ground in Kuala Lumpur, so a ~0.5307 second travel time).

But all the BTO values given (for the "R" channel) in the PDF are between 14740 and 14920 microseconds (that is repeated on each page in the column title) when the aircraft was on the ground in KL between 16:00 and 16:30 UTC. Between these times 3F1 moved slightly away from KL : from ~37294 to ~37296 km, that is, in time at light speed, 124399 to 124406 microseconds. For this segment only, the travel time is thus near ten times the given BFO (and ~35 times for the round trip).

So, which distance are those microseconds values given in the "raw data" related to?

Could it be in relation with the distance between a point at sea level under 3F1? At 16:00 UTC, the point at sea level under 3F1 is 13560 microseconds away from KL airport in straight line and ~13790 microseconds along Earth surface. So in the same magnitude order of the "raw data" BTO (14820). But which magic brand could give this kind of "raw data"? Is some unit in the system making this computation, and only this result is filed?

Or I misunderstand all this stuff?



PS: From deleted post of the "main" thread, a "sub"question is: what is the "terminal at a nominal fixed location" (last line of "Raw data" page 1), question which came along with the post of a Canadian whose pseudo is something like ??23 (sorry for forgetting). I supposed it was the ground station near Perth, or, may be, the theoretical position of 3F1, but this obviously erroneous from the published BTO.
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Old 11th Jun 2014, 11:50
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MG23

Originally Posted by Shadoko on R&N
So, which distance are those microseconds values given in the "raw data" related to?
The data logs PDF says:

"The BTO is a value (in microseconds) relative to a terminal at a nominal fixed location. Only R-Channel messages are used."
Originally Posted by MG23
So it's not the actual round-trip time, it's the offset relative to an 'ideal' transmission from the aircraft.
Copy of MG23's R&N post
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Old 11th Jun 2014, 14:00
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I Spy

This video (from a Fugro employee) indicates it "may" be possible to locate the wreckage.
Only if the aircraft is in one piece and not hiding behind a hill or in a canyon. The resolution of this ocean-bed survey is not suited to finding bits if an aircraft.
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Old 11th Jun 2014, 15:24
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Massive Survey With Very Little Time

60,000 sq km is a very ambitious undertaking which must be at least close to completion before the side-scan search begins again in August.
Fugro and the Chinese survey ship Zhu Kezhen will have their hands full to get his done in time. Zhu Kezhen has already done several weeks of survey, but is currently in Fremantle for repairs to their multibeam echo sounder.
Two state-of-the-art survey ships can possibly get it done in tine, but only without weather or technical problems.
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Old 11th Jun 2014, 21:12
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Originally Posted by Datayq1
With one exception, all the published BFO values are positive numbers. Has there been any verified explanation of the "-2" BFO?
The BFO/BTO values have been calculated from a "nominal terminal" outside of the satellite, and this enables the movement of both the SAT and the AES to be taken into account, while ignoring the SAT - GES C-Band link. This "nominal terminal" appears to provide the positive offset.

In the -2Hz BFO case, either the offset is not enough or the figure is a result of an incomplete handshake; the later being more probable. The BTO associated also looks "off".
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Old 12th Jun 2014, 01:25
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AMSA have issed a time line (with a click for details) covering their involment and related news from17/3/>31/3

Search for flight MH370 - Timeline of AMSA's involvement
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Old 12th Jun 2014, 01:51
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Crumble - apple or rhubarb?

The whole Inmarsat edifice seems to be crumbling. Sadly.

They have previously stated that they have round trip times for the signals. This I understand very well as I am a data network engineer as my day job. I have been measuring network delays (let's call them) for decades.

Now they appear to be saying that they do not have those times. They only have the "offset" times. These are the differences between the times expected of a notional satellite and a notional aircraft and the actual times measured.

As far as I recall they have not released the position of the notional (I refuse to use the inexplicable 'nominal') satellite. They have not stated how they think they know the position of the notional aircraft.

They of course know where the notional satellite was. But they do not appear to know where the notional aircraft was. So any offset from the round trip time from the notional satellite and via the notional aircraft is meaningless without further information about the location of the notional aircraft.

I of course must be missing something - hopefully.

At present I have no inclination to even start on the BFO.
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Old 12th Jun 2014, 03:29
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Hope this "nominal" thing will be resolved... Just a thought: the first things Inmarsat published were "arcs" which seemed based on angles. Perhaps this angle was found using arctangent from satellite altitude and BTO "converted" to distance (after taking away some time constant)?

Another remark. Just looking at the data, there is a strange similitude between the last data and the ones of 18:25. And they show the two highest BTO values:
07/03/2014 18:25:27,421 IOR-R600-0-36E1 8 R-Channel RX 0x10 - Log-on Request (ISU)/Log-on Flight Information (SSU) 142[BFO] 17120[BTO]
07/03/2014 18:25:28,852 IOR-P600-0-36FC 10 P-Channel TX 0x11 - Log-on Confirm
07/03/2014 18:25:29,572 IOR-P600-0-36FC 10 P-Channel TX 0x40 - P-/R-Channel Control (ISU)
07/03/2014 18:25:29,572 IOR-P600-0-36FC 10 P-Channel TX Subsequent Signalling Unit
07/03/2014 18:25:30,213 IOR-P600-0-36FC 10 P-Channel TX 0x41 - T-Channel Control (ISU)
07/03/2014 18:25:30,213 IOR-P600-0-36FC 10 P-Channel TX Subsequent Signalling Unit
07/03/2014 18:25:34,461 IOR-R1200-0-36ED 4 R-Channel RX 0x15 - Log-on/Log-off Acknowledge 273[BFO] 51700[BTO]
07/03/2014 18:25:35,408 IOR-P10500-0-386B 10 P-Channel TX 0x15 - Log-on/Log-off Acknowledge
and
08/03/2014 00:19:29,416 IOR-R600-0-36F8 10 R-Channel RX 0x10 - Log-on Request (ISU)/Log-on Flight Information (SSU) 182[BFO] 23000[BTO]
08/03/2014 00:19:31,572 IOR-P600-0-36FC 10 P-Channel TX 0x11 - Log-on Confirm
08/03/2014 00:19:32,212 IOR-P600-0-36FC 10 P-Channel TX 0x40 - P-/R-Channel Control (ISU)
08/03/2014 00:19:32,212 IOR-P600-0-36FC 10 P-Channel TX Subsequent Signalling Unit
08/03/2014 00:19:32,852 IOR-P600-0-36FC 10 P-Channel TX 0x41 - T-Channel Control (ISU)
08/03/2014 00:19:32,852 IOR-P600-0-36FC 10 P-Channel TX Subsequent Signalling Unit
08/03/2014 00:19:37,443 IOR-R1200-0-36F6 10 R-Channel RX 0x15 - Log-on/Log-off Acknowledge -2[BFO] 49660[BTO]
08/03/2014 00:19:38,407 IOR-P10500-0-386B 10 P-Channel TX 0x15 - Log-on/Log-off Acknowledge
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