>So they have calculated such an angle of 40 degrees for the last ping.

Not being an RF engineer I'd like to know what sort of error margin they have on that reading. My gut feel is that once you start taking into account a possibly damaged antenna and damaged transmitter (lower voltage maybe) the time to get a response might be a little longer. When the talk was around GPS packets in the ping and triangulation it seemed more solid.

I'm having a hard time seeing the satellite reading as the smoking gun that the media and SAR teams are making it out to be. Unless there is another source we aren't being told about.

StormyKnight
That's an interesting picture but I'm not sure the signal strength method is the only method available for "triangulation" in this case. I'll outline some general methods that are used in various systems, commenting also on TelcoAG's posts at 07:39 and 09:02 UTC today:

1. The signal strength method is a possibility but I believe its accuracy may be rather poor.

2. Another possible method is to measure the signal timing differences from two satellites, if data from both are available ( "reversed GPS principle" as someone said).

3. A third method may be to utilize the "Time Alignment" procedure that is widely used in e.g. GSM. Here, the system makes a signal timing adjustment to align the arrival time of radio packets from each active transmitter so that they align with the time slots in the receiver's (the satellite) TDMA (time division multiplex) channel frame. This adjustment value is an indication of the transmitter-receiver distance and can be used to plot a circle where the transmitter is located. Use 2 satellites and you get two cross bearings, one north and one south.
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.

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.

5. Finally, the "ping time" itself (i.e. the roundtrip delay), if measured with enough precision, tells the distance between transmitter and receiver and can conceivably be used to plot a range circle as with the time alignment method.

A lot of weight is indeed being put on the sat pings. I hope the engineers have thoroughly checked for latency issues or time stamp errors to ensure everything is as it seems. There are a lot of protocol levels in that system.

Have just heard the Malaysian PM's statement on SKY, he indicated that the SSR transponder was switched off and Malaysian Air Defence primary radar data indicated a track change in a westerly direction, flying back over the Malaysian peninsula. If this is true, as its an Air Defence system, why were air defence assets not launched to intercept the contact?

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.

With respect to ultimate flight path, one can create possible corridors after subtracting out the effective ranges of military radars of various governments in the region, and depending on whatever judgments one cares to make about how alert the operators were.

And sitting due south of the Maldives is Diego Garcia, possibly having the most powerful radars in the whole region, with a 360 field of view, whose operators are unlikely to be sleeping.

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.

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.

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.:mad:

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.

Smoke on island
 

US sources are aware of this and have dismissed it as anything significant.

That's right stormy from the wreckage not flying.

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.

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?

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:

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.

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.

Is it just me or does that satellite diagram fail to support the 'flight into the Indian ocean' theory?

Spot on TelcoAg
 

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.

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.

This forum has mods.

You are not one of them.

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.