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Old 15th Mar 2014, 10:23   #3821 (permalink)
 
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There is only one INMARSAT covering ACARS coms over the Indian Ocean. It is IOR located at 64 degrees East, 35890km above the equator, as shown in the Malaysian diagram.

So angle (or equivalently distance) calculations must be being done by using just the one satellite.

I think their diagram shows that they have a very accurate method of calculating that distance. I understand that this can be done via ping latency but there may be other methods.

The distance from the satellite so calculated has given them the 40 degrees altitude as shown. I calculate that this equates to 4840km distance at sea-level around the earth from the point directly below the satellite.
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Old 15th Mar 2014, 10:25   #3822 (permalink)
 
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Quote:
Originally Posted by Sheep Guts View Post
Stormy,

You can see also from this chart that the 40 degree arc highlighted passes thru the southern tip of Veitnam. But they are negating that area now on their Military primary plots data ( which maybe erroneous). I'm sorry but I think they should keep concentrating on the South Veitnam coastline. The New Zealand oil rig worker is still not backing down from his observations.
Somewhere on the 40 degree arc was the last sat communication at 8:11am local time (daylight - sunrise was 7:22am in Kuala Lumpur Sunrise and Sunset for Malaysia ? Kuala Lumpur ? March 2014)

Vietnam is further East so the sun would have been up even earlier.
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Old 15th Mar 2014, 10:25   #3823 (permalink)
 
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Although it often looks like it, this is NOT the Daily Mail discussion forum, but a PROFESSIONAL FLIGHT CREW forum.

Please refrain from commenting if not flightcrew or other aviation professional.
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Old 15th Mar 2014, 10:28   #3824 (permalink)
 
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Quote:
Although it often looks like it, this is NOT the Daily Mail discussion forum, but a PROFESSIONAL FLIGHT CREW forum.

Please refrain from commenting if not flightcrew or other aviation professional.
Absolutely agree iro technical stuff about the aircraft etc. Given scope of this story there's plenty of room for all sorts of other comment whether about history, politics and linguistics or tech background in satellites and radio.
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Old 15th Mar 2014, 10:30   #3825 (permalink)
 
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Smoke on island

US sources are aware of this and have dismissed it as anything significant.
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Old 15th Mar 2014, 10:30   #3826 (permalink)
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That's right stormy from the wreckage not flying.
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Old 15th Mar 2014, 10:32   #3827 (permalink)
 
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Quote:
If this is true, as its an Air Defence system, why were air defence assets not launched to intercept the contact?
TCAS FAN - what makes you so sure they weren't?
As I said many, many posts ago, that particular chain of events could very easily lead to one very unpalatable outcome - one that no country would want to admit to. Such a scenario would best be subsequently handled by having everybody search on one area, whilst you clean up the mess in another.
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Old 15th Mar 2014, 10:33   #3828 (permalink)
 
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Tailgating

Re: the tailgating theory. What's the max separation the tailgater can have from the tailgatee, horizontally and vertically, to appear on radar as a single a/c?
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Old 15th Mar 2014, 10:36   #3829 (permalink)
 
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On Communications

Hello! I'm a telecommunications architect from Australia. I don't work in the aviation industry, so I will endeavor to only discuss components pertinent to my expertise. If anything that I say is incorrect, please notify me so that I can update my correspondence to reflect this.

Both TelcoAG and snowfalcon2 appear to be on the money. Specifically, snowfalcon2 posted:

Quote:
3. A third method may be to utilize the "Time Alignment" procedure that is widely used in e.g. GSM. [snip]
The caveat with this method, hovever, is that it is normally used only when you actually establish a connection to send a payload. For a periodic "ping" you normally don't need to allocate a timeslot.
By my own admission, I am not familiar with the TDMA signalling used on the Inmarsat-C communications platform, but it is my understanding that the signalling channels are also TDMA, meaning that it is highly likely that delta-T between timeslot allocations for handshaking as received by the two birds is how the speculative great circles have been generated.

Quote:
4. It is quite conceivable that the Inmarsat satellite can measure the "elevation angle" of the received signal directly. Newer satellites have narrow individual "spot beams" to increase capacity, and obviously the system can keep track of which beam is allocated to any particular transmission.
Spot beams tend to be focused over areas where capacity constraint becomes an issue. Shaped beams (covering greater surface area) are used over sparely populated areas (such as oceans) because of the lower capacity requirements in these areas and the lack of business case for cost recovery in investing in additional hardware and power requirements on the space platform to accommodate underutilized transponders.

There has been a lot of speculation in the thread regarding the use of the SATCOM on the AC to communicate with ground crew in a hypothetical scenario where the person or people who have intervened in the operation of the aircraft intended to land it. Whilst it is true that the airframe of an aircraft is a decent Faraday cage, a pair of 5W VHF radios with a small antenna near the window of the flight deck would be sufficient to establish voice communications with a ground crew.

Last edited by TelcoAUS; 15th Mar 2014 at 10:47.
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Old 15th Mar 2014, 10:37   #3830 (permalink)
 
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Is it just me or does that satellite diagram fail to support the 'flight into the Indian ocean' theory?
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Old 15th Mar 2014, 10:37   #3831 (permalink)
 
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Spot on TelcoAg

Quote:
I'll guarantee you one thing though - every hour spent by an RF engineer to limit that range saves somewhere on the order of half a day's worth of ocean to cover.

This is an incredibly complex system with limited knowledge of all of the variables.

To describe the difficulty, it would be like me asking you to find out which cows your hamburger came from after visiting a random McDonalds. You could probably limit it down to a few slaughter houses, but you'd never be able to pinpoint the cows.
Thanks TelcoAg - I agree with you. Too many people are criticising those involved in the investigation for taking "too long" to figure out "probable outcomes" from the sparse data involved. This is a difficult and imprecise science - it takes a lot of skill, mathematical modelling and , yes, time, to make sensible deductions from the sparse information available. I would feel sure that there a lot of dedicated engineers (both inside and outside government organisations) who are putting in a lot of hours trying to figure things out. Let them do their job without levelling accusations at them that they ar intentionally hiding things.
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Old 15th Mar 2014, 10:42   #3832 (permalink)
 
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Quote:
Is there any valid reason why transponders can be switched off?
If not then all transponders should be armed and locked immediately so they cannot be switched off ever again!!
This has been discussed repeatedly during the last 24h but I'd like to summarize.

I have seen two reasons so far.
1. in case of equipment fire there has to be a means to cut electrical power to the equipment.
2. malfunction of the transponder sending out garbled signals that block the radar system and may create chaos for ATC.

Now, as the question is very likely to be addressed in the accident report,
how could these risks be mitigated?

Re (1), while I concur the fire risk is high priority, I think electronics design has made significant progress since the 777 was designed and certified in the early 90s. Power consumption is less, "design for safety" has improved, and it is becoming commonplace to design circuitry that monitors over-temperature and shuts down automatically. Just look at all effort done in electric cars nowadays. (Yes there have been some well publicized fires, but they mask the fact that in the vast majority of events the overtemp protection works. And a transponder draws far less power than an electric car.)

Re (2), unfortunately the type certification processes tend to hamper innovation and progress. But there are some potential relatively easy design fixes such as replacing "hard" power on/off switches with momentary reset buttons, such as e.g. in laptop computers.
Going one step furher one may have a networking between devices so that a shutdown or standby of the active transponder automatically turns on the redundant transponder, or at the very least sends a fault message on ACARS.

Considering the whole world's attention to this incident, it seems certifiers may come under some strong pressure to establish more tamper-proof datalinks in order to not let any more airliners vanish. The technology is already existing.

Last edited by snowfalcon2; 15th Mar 2014 at 10:55. Reason: typo
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Old 15th Mar 2014, 10:43   #3833 (permalink)

Rotate on this!
 
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Quote:
Please refrain from commenting if not flightcrew or other aviation professional.
This forum has mods.

You are not one of them.
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Old 15th Mar 2014, 10:44   #3834 (permalink)
 
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Quote:
I have operated SIN LHR for the last few years routing over KL, Port Blair then over Calcutta. The new info about this flight being flown over this similar route makes we wonder if it "tailgated" such a flight heading towards India.
SQ068 was speculated as being a possible "Shadow" many pages ago. But nobody ever confirmed its actual flight path that evening. This was not an amateur job, whatever happened, so I wouldn't rule that out.

Last edited by philipat; 15th Mar 2014 at 10:58.
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Old 15th Mar 2014, 10:45   #3835 (permalink)
 
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Position lines - estimated roughly

The images do NOT show tracks.
The images do NOT show tracks.
The images do NOT show tracks.

The primary purpose of this post is to indicate using symmetry the location of the southern position line. It is a LONG way from anywhere.

The diagram shows a representation of an estimate of the two position lines (with uncertainty) described in the press conference as being the position lines indicated by the last received "ping".

Since the satellites are geostationary, that is above the equator, I have assumed that the two lines are symmetrically disposed about the equator.

The two lines are based on the PMs statement; "a northern corridor stretching approximately from the border of Kazakhstan and Turkmenistan to northern Thailand", a *random* line between the two points (generated by Google Earth), and a southern copy of that line reflected in the equator.

The last image shows an additional alternate random position line between the two points. The white rectangle was drawn with the Google Earth "add polygon" tool with four points and the orange line with the "add path" tool with four points.

Please note:-


The images do NOT show tracks :-)))))

Hopefully a mathemetician will be along in a minute to explain the correct shape of the lines.

Two estimated position lines for the LAST "ping".





Northern





Southern





Alternate northern - showing an alternative estimated line.




Higher resolution versions are available at (hopefully):-
http://i783.photobucket.com/albums/y...copter/malasia
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Old 15th Mar 2014, 10:46   #3836 (permalink)
 
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Spectators Balcony

I have started a new thread in Spectorors Balcony for those of us who are not Professional Flightcrew to ask questions and speculate. Hopefully that will reduce the number of posts here and make the thread more useful.
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Old 15th Mar 2014, 10:47   #3837 (permalink)
 
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Update

A quick update to keep us focused:

Official Confirmed

01:07 Last routine engine data transmission
XX:XX ACARS disabled
01:17 Sign off Subang ATC
01:21 Xpndr switched off (near IGARI)
01:21 Malasian military PSR picks up MH370 at IGARI
XX:XX MH370 moves towards VAMPI and then towards GIVAL
02:15 MH370 turns towards IGREX and is lost on Malasian military PSR
08:11 Last ACARS handshake signal detected

Official Unconfirmed

08:11 A/C somewhere between border of Kazakhstan and Turkmenistan to northern Thailand
08:11 A/C somewhere between Indonesia and the southern Indian ocean

Unofficial Unconfirmed

XX:XX Altitude excursions at IGARI of unidentified PSR target (leak, via NYT)

Rumors

Everything else

Last edited by CogSim; 15th Mar 2014 at 11:09. Reason: Formatting
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Old 15th Mar 2014, 10:47   #3838 (permalink)
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What I am saying Stormy is that final ping to the Satellite at 8:11 am came from the wreckage in the South China off Veitnam. Which is on the 40 degree line. It doesn't show up on your picture because it's faded. But I saw it when Jim Clancy showed his picture in front cameras this afternoon after the news conference.
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Old 15th Mar 2014, 10:48   #3839 (permalink)
 
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The pilot thickens.

Just out of curiosity, is there any public record of the last known conversation beyond the "Roger that" bit we've been allowed to know of? What was being acknowledged by that phrase?
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Old 15th Mar 2014, 10:51   #3840 (permalink)
 
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Nigel post 3922
once again,so it`s understandable for everybody.
Your guess is the same 1 was thinking about LAST evening.
Could it be a long planned revenge for OBL?
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