Another try, and then i will shut up :) :

To calibrate the signal path between satellite <-> A/C transceiver, you have to know the exact position of the A/C when a SATCOM transmission is made. My assumption - which may be wrong - is that precise secondary radar fixes where available until 1:21. If the SATCOM transmission, that was used to calibrate the signal path, was made at any other time than 1:07, it would make much more sense to take the secondary radar fix from the time of SATCOM transmission to calibrate the signal path.

The Inmarsat Exec said the statement "the satellite wants to see if you still want service." That indicates to me that the satellite, not the SATCOM, initates the ping. It sounds like, after 60 minutes of silence, the Satellite wants to confirm that you are still on it's network. If you don't respond, it takes you off of its active device registry until you come back online and initiate contact.

Sadly, I think all Inmarsat has to work with is the time of flight of radio waves between their satellite and the aircraft on the hour, plus the uncertain time lag required for the aircraft's satcom box to reply. My understanding is that for a few dollars more, Inmarsat would have an hourly GPS position transmitted from the aircraft in their archives.

The South China Sea information allows Inmarsat to be confident that the 0100 signals were consistent with a "red arc" that goes through that area.

As time goes by, the chances of finding anything in the ocean seems to be fading.

Hopefully, agencies that listen to radio signals from a high orbit, and scan the ocean surface for radar reflections can have a look back through their records and perhaps add something to the conversation.

If any commercial or military imaging satellites happened to be taking pictures of the Indian Ocean at the time (why would they? although Digital Globe seem to have been on 16th - perhaps in response to an order) then there's a possibility that MH370 might have accidentally been spotted traveling through the frame.

With a lot of effort, once it was daylight, it might also be possible for weather satellite data to be handled carefully to look for signs of a contrail in its wake, especially since it took a lonely route.

Perhaps some whole-Earth IR missile launch warning satellite images could be searched in the same way for some warmth from the engines.

Was there really no sign of anything out there on the Australian OTH radar?

mobile phone (NOT Inmarsat) 'pings'
 

I've been thinking....

We all know that on every flight there is a certain number of phones that don't get switched off or put into 'flight mode'.

Now, these phones would try to lock on to a ground-based station during the flight. We've had this discussion here before and know it's perfectly feasible from 30+k feet.

IF the aircraft really headed out into the Indian Ocean, then it must have overflown Malaysia and Indonesia. Does anyone know if the Telcos in these two countries checked their logs for the night in question? If (and again, a big IF) any of the phones on board had tried to lock on to one or more of the cells in either country, then we would at least have proof of two things:

1) MH370 really did fly southwest
2) the time of passing overhead these points

Btw, same goes for the - now largely discounted - northern route.

I agree, this is what I meant by it gets complicated quickly. There's a lot of different parameters that can influence ping time beside distance alone.

Let me give a wild example that I personally witnessed a number of years ago in a related context. Someone had put a wifi relay in a tree with a clear line of sight to a bedroom window in the guest house. During the day the guests kept complaining of congestion on the line, despite the fact they were the only ones at home. It was a puzzle because the ping time got steadily worse during the day and then quickly recovered at night. A full wifi site analysis was done and no radio interference was found.

The culprit that was eventually discovered? The wind. Wait, how can wind affect the radio waves? It can't, directly. But what the wind was doing was blowing the small branches of the tree around. The location experienced a great deal of diurnal heating and as the heat increased during the day so did the wind and so did the amount of interference from the tree branches and so the ping time increased during the day and fell off at night in rhythm to the wind. The owner of the guest house had put the wifi relay in a tree because he felt it was unsightly and so long as there was no wind his plan worked correctly.

The point--radio waves are a tricky thing. In a normal situation there are not many causes of interference between an airplane at 35K and a satellite. But nothing about this situation appears normal. So I think it is something of a leap of faith to say that increasing ping times=increasing distance. It's a decent assumption but we've already seen how other reasonable assumptions have turned out to be wrong.

Yes, that's the typical set up. I'd be surprised if it was any other way.

- well, I went back 5 and lost heart - it was 6 back. Also if you had bothered to scroll back you would have seen that both brika and Blue Amber had already answered. .....and it is cynar ....but thanks anyway.

-indeed, but IF there is more precise information it should be possible to analyse and form a reasonable assessment. It would be nice to see a bit more from Inmarsat. - yes, but what makes it more likely that the southern arc is in focus? Can this be deduced from the Inmarsat data or is there (probably) some more int to point at that arc?

172,

Phantom phone tie ins from air to ground could perhaps rule out the "Northern Route". The phone providers of the missing passengers should know whether anything was received or sent from a live phone after take off.

In any case, a better look at the Thai and Malaysian (and Singaporean and Indonesian?) radar records should eventually be able to work out whether the reported zigzags over the Andaman Sea actually happened.

However, there's no mast to talk to from a cellphone all the way from Java to Antarctica on the "Southern Route", and while Three Letter Agencies are supposed to be able to listen to calls from a distance, a phone inside a 777 is not nearly as clear to listen to as a phone outside a 777.

BOAC,

I think the only thing that rules out the "Northern Arc" is the lack of any reported radar returns that way consistent with a mystery 777, and also a lack of a wrecked 777 out that way, but then there's a lot of nothing in central Asia.

It could have avoided radar coverage on an early weekend morning, and be waiting to be found in a hole in the desert or mountains somewhere.

But if it impacted on land, you might expect to have heard from the ELT beacon?

Well, that's part of my point. So far we assume the observed radar return was MH370. Connecting phone lock-ons to this route would eliminate any doubt.

Thanks TelecoAg. It does make much more sense to me that the satellite initiates the ping each hour.

In any case, the satellite has to send a message and get a return message as part of the ping exchange in order to be sure of the identity of the plane. Typically it would encrypt a random number using the specific plane's public key and check that the supposed plane was able to decrypt that message and return it encrypted with the satellite's public key.

The satellite's accurate clocks can then record timestamps for the sending and receiving parts of that message.

The journey of the message each way would take about 130 millseconds while it would only take 1-2 millseconds for the plane's equipment to process the incoming message and send a response back. Thus most of the 262 milliseconds difference in timestamps would be travel time.

This gives a pretty good estimate of distance between satellite and plane.

Mountain Bear,

But you were looking through a tree in that example, and there are none between a 777 and the satellite.

The "ping time" in that example I think is also a time required to transmit a certain amount of data across your network, so you were measuring a data rate being slowed by the whirling tree, and not a time of flight/path length increased with time like Inmarsat were.

Inmarsat have many hundreds of thousands of flight records that they can test their method against. I'm sure they wouldn't broadcast faulty information.

It is noteworthy that ELTs are not mentioned in the official accident reports re. TWA 800, Swissair 111, PanAm 103 or Egyptair 990.

Thus one does not know whether the Emergency Locator Transmitters were activated or not in these instances.

But if it is a one-way transmission from a/c to satellite then this is subject to error based on the clock drift between the satellite and the a/c. Even using the most accurate clocks drift with say one part per million stability would drift 3.6 milliseconds an hour. A millisecond clock error translates to roughly 300km position difference. Over seven hours, the location information based on a single, one-way ping would be useless. The satellite would have a high accuracy clock, but the a/c would have something normal, say 10ppm. Therefore, I guess they must to be talking about a two way communication, but I haven't seen the protocol spelled out anywhere. The details of this protocol matter a lot to determining the accuracy of the distance measurements.

Edited:
Ok I found this on the WSJ

To get a handle on the error we need to know where and how the ping transmit/receive time was measured and the total round trip time.

- don't forget that Transponder off wipes out a whole stack of ATC radars which look only at those codes. Also trying to fathom truth from fiction, deception and 'reluctance' to share info begs the question - can we be SURE there are no radar returns? I cannot see mil radars on that track readily sharing info even if they saw the 'blip' and chose to investigate it - there would be a load of traffic on that route at that time of night and would a sleepy scoper notice no transponder code if indeed checking? Look how long it appears to have taken various agencies to pass on info.

I believe their data. It's the fact that they are not accident investigators that concerns me. Any good accident investigator knows to be wary of projecting their own bias onto the data instead of letting the data takes it where it leads them. In fact, the fact that the normal assumption is that delay=distance makes me even more wary of it.

Several people have suggested that the plane flew low over the water in order to avoid radar detection. Flying low over the water could cause what is known as "tidal fading" which is interference as a result of multipath reflection off the surface of the water. It's theoretically imaginable that this tidal fading could cause the distance calculations to be messed up in unpredictable ways.

So I'm not wary of their data, I'm wary of their assumptions they are making in analyzing the data.

They're talking about differences of a few milliseconds over the course of a flight, so the only way I could see interference affecting it would be to add noise to the signal that would make identifying those signals harder and increase the error bounds on the timings; I'm not sure exactly where the delay is measured, but, for example, a noise spike could presumably cause misidentification of the first bit, if that's the point used to determine delay.

So there's no 100% certainty here, but if the delays are consistent with an aircraft moving over time, particularly one moving at a constant speed, and the delays on earlier flights are consistent with position reports on those flights, then we can be pretty sure they're good positions. Bigger issues are probably things like transmitter synchronization drift over the course of a flight, which, again, can be checked by looking at earlier flights of the same aircraft.

Edit: just saw your post above mine about low-level multipath reflections: yeah, there certainly could be oddities like that which would affect the timings. I'm guessing no-one's going to offer a 777 to fly low-level over the ocean to provide calibration data.

BOAC,

I entirely agree, it would have to be military radars doing the finding, and silly o'clock on a weekend is probably not the best time to keep a keen look out.

Nevertheless, the timings of the Inmarsat round-trips should give a range of plausible tracks north too, and would help anyone to run back through saved data to look out in hindsight. The problem with the Southern track is there's absolutely nothing to run into.

Mr 172 has noted the plausible possibility of cellphone sign ins over more populated areas, and I suspect the lack of those should be able to rule out a northern route, making a trip south with no cell towers until Patagonia the default.

It did not vanish. There was a vast return which took a long time to disappear as the wreckage slowly glided did. It was very obvious what had happened, although immediate thought was that it had hit something.

In August 2005 a 777 also Malaysian Airways, encountered an upset caused by the autopilot pitching the aircraft to FL 410 before the aircraft stalled.

Investigation: 200503722 - In-flight upset; Boeing 777-200, 9M-MRG, 240 km NW Perth, WA

Recently there was a warning about cracks in 777 fuselages.

I put it to you that perhaps a similar incident occurred here with MH370 withe the autopilot causing it to pitch to FL450 or higher with the aircraft structure actually failing explosively a la Aloha Airlines, incapacitating the crew but leaving the aircraft in a flyable state. Further Partial destruction, for example of the comms systems, could happen over time as loose pieces of the fuselage ripped away. The damaged aircraft sans crew somehow resumes level flight after the upset, (stranger things have been know to happen to ghost aircraft),but pointing in the wrong direction. It flies off and continues to do so.

After this 2005 incident it was discovered that sudden accelerations during the incident had damaged an accelerometer in the ADIRU and that an other accelerometer had failed previously.

Could it be that MH370, with the flight crew incapacitated, the passengers dying, flew an erratic track because the ADIRU was damaged and intermittently commanded turns which ultimately resulted in this aircraft flying south until it crashed in the sea due to fuel exhaustion?

From todays press brief it's clear that the southern route has some priority due to the time constraints in locating the recorders. The same doesn't apply to the north.