ACARS being turned off, means that data would no longer be sent, however the onboard satellite transmitter continued to get a baseline connection to the satellite just incase it needs to transmit the same as a mobile phone searches for cells so its ready to go when you needs to make a call. Like a mobile phone, ACARS is a two way communication....it can receive data as well like weather reports... (I think the receiving of data requires firstly a request for data from the planes ACARS system especially with regards to weather reports) - Aircraft Communications Addressing and Reporting System - Wikipedia, the free encyclopedia

It would appear that the time has come for the FAA or NTSB to take over the investigation of this incident as the Country of the aircraft manufacturer Boeing until the aircraft is found.

If the ACARS pinging stopped at 0811 local time (00.11 UTC.) it would be interesting to check the mobile phone records of all the passengers as some will inevitably have left them turned on. If that is the case it should be possible to track those phones when they ping to establish contact with a ground base station if the aircraft flew over land or by intel. satellites.

The next question is did any flight deck crews flying the suspect routes pick up an aircraft without their transponder turned on? Routing scanning of the radar for weather frequently brings up aircraft returns.

INMARSAT uses geostationary satellites.

is it just me or is it a pretty damning indictment of the worlds military's that a plane that size can fly for 7.5 hours and not be noticed?

what happened to air defence?

They know exactly what transmissions came from that aircraft. They aren't amateur satellite operators.

ACARS location information is transmitted in clear text, i.e. its not encrypted & can be received at home by anyone with a receiver & decoder (software based)

https://www.google.com.au/search?q=a...sm=93&ie=UTF-8

I think you're the one who needs a performance course mate. :rolleyes:

This is a quote from someone who does fly the 777 from the Aviation Herald website.

Air defence Primary radar range is 200NM (Nautical Miles)....that is not very far from land base radar station compared to the size of the seas in that area.

ACARS on HF or VHF may be, but even though you can receive it, can you decode all the "non text" packets to determine what the engines are doing? I don't think so.

You've got zero chance of intercepting a satellite uplink transmission.

StormyKnight
 

Why is everybody assuming the comms was from ACARS?

I presume, that if it is switched off, it is off, i.e. no polling or handshaking with a ground station or satellite?

I also presume that whoever was flying the a/c would need to communicate with a ground team somewhere where they were heading. That would need SATCOMs, surely?

Is it beyond possibility that the signals picked up by the satellite(s) were voice comms between the 'pirate' and a ground team?

I can't see the 'pirate' just swanning off in the plane without a support team somewhere to help with getting the a/c on the ground. That team would have no way of knowing if the op was a 'go' unless the 'pirate' could communicate with them, would they?

So you now agree Inmarsat have no idea what the payload they carry holds, they only act as a relay service for their customers (as I originally said).

Interpretation of the SATCOM signals is key. What radios were the signals received on, which beams, was there a pattern visible in signal strength that can be attributed to potential terrestrial weather attenuation or triangulated to a track?

Rule out where the aircraft could not possibly be.

Hell of a thread you guys have going. Don't want to interrupt, but thought you might like a general understanding of the sat location process.

When the satcom transmitter checks in with the satellite, the satellites keep a registration of what the received signal level was. It's obvious that this is all they are going off of now.

When you've got an object moving in the third dimension it will significantly expand the range that you have to consider for the transmitter to be in. What they are doing here is building an area within a received signal level (RSL) threshold where both satellite A and satellite B would be receiving a range of signal levels. For instance, you limit it to an area where sat A receives between -85 to -90db and Sat B receives between -40 to -45 DB. There are lots of other considerations such as interference levels and noise to be considered.

Once you have that area mapped, you have to mirror it across the line of latitude shared by the two satellites in geo. This is because you only have two satellites, and points where similar signal strengths intersect would happen in both places. It's kind of like picking the two spots where the circumference of two circles in a Venn diagram would cross.

Great stuff on this thread.

A few posters have suggested that if, indeed the aircraft was hijacked/stolen, the hijackers/thieves would likely want to communicate with a ground crew somewhere, and for this they would need the aircraft's SATCOM capability.

I beg to differ. A simple satellite phone would do nicely. They are small enough to easily be taken on as hand luggage.

Coincidentally, a satellite phone call could well be handled through Immarsat.

Immarsat haven't said precisely what data they handled. Read into it what you will.

why is that obvious?

Its obvious to me that the aircraft is "pinging home" sending packets of data back to a control centre, where they get distributed to various people depending on what they are and who subscribe to them.

MAS do not subscribe, so they don't get them.

Exactly right. My initial guess in this case is that those exact satellites were the ones being pinged. That's based on the bandwidth needed and general age of the tech. This was a quick drawing a put together when explaining it to someone earlier, hopefully it makes sense:

http://i.imgur.com/9ZWNnEk.png

Telco
 

I kind of suspected that they can't triangulate, so they have only been able to narrow it down to two corridors.

Based on the size of the area given. and the mirroring of the areas, it's obvious to me that's what they are doing. Sorry for the confusion.

I don't think the transmitted data is carrying anything meaningful in terms of the location, or they'd be going off of that.

What I've seen so far indicates RSL measurements from 2 receiving antennas.

p.j.m.
 

That is not at all obvious, especially as the Malaysian PM specifically said that ACARS had been SWITCHED OFF.

So what packets of data are you referring to?

I agree with LongTimeInCX, the logistics of having to look after 239 pax and crew on some bush airstrip, with or without the heightened interest of the whole World watching, is just inconceivable. A friend has suggested that North Korea could, and might have, coped with such a problem, and certainly the aircraft had the fuel to reach there, assuming that all ATC units en route ignored a silent target and also that North Korea was expecting it - else they would have shot it down as it crossed the border - but there seems to be incontravertible evidence that it went the other way.

I think it is now undoubtedly at the bottom of the Deep Blue Sea - but where?

Location of the FDR will confirm how it got there, but only the CVR ( voice recorder ) will determine why, and if that is never found we might just as well consign the event to history right now and get on with Life.