Correct me if I'm wrong but isn't the VHF ACARS transmission uplinked from a ground station to the Inmarsat anyway so the fact that it is eventually received by the satellite doesn't necessarily mean it was sent by SATCOM?

It's not sending black box data, just position updates including GPS coords more frequently.

odd
 

That's an odd choice of a word. I assume that by longer he means the time delays between each hourly ping, in milliseconds. If so, it is wrong to construe that delay with distance alone. Ping time can increase for multiple reasons not related to distance. One obvious confounding factor is interference of some type.

What would be interesting to do is some type of statistical smoothing. For example, if the plane was flying a consistent speed one would expect the increasing ping delay to follow a consistent, not random, pattern. OTOH if the ping delays were increasing at an increasing rate then distance alone might not explain it. The forensic calculations get complicated quickly having to take into account so many parameters. I'm going to assume that they go it right and have had many different eyeballs look at it. But I do not think we should treat the result of such calculations as a certainty, more like an educated guess.

- don't forget a ?sinusoidal? rate of change if the TX crosses the concentric signal elevations.

brika - no more help in that link!

They have a very accurate position at 07 due to the VHF ACARS transmission. They use that datum with the next ping to work out the return time at that known range. High school maths then allows you to work out future ranges based on ping return times.

It's not rocket science although they are capable of that too!

I'm struggling with the concept too, but imho Chris McLaughlins statement only makes sense if there was some kind of SATCOM between the inmarsat satellite and the A/C, at 1:07 which was used to calibrate the signal return path between them.
An ACARS message between ground station and satellite wouldn't doe any good to calibrate the path between satellite and A/C transceiver.

ACARS update
 

Yancey Slide #7045

IBT said "You really do need to know the height, distance, direction and a record of what has been going on the flight deck in a regular burst every 15 to 30 minutes," said McLaughlin. "If the box had been configured to send out these bursts, we would have located the plane by now."

Of course one also needs to prevent someone turning off transmissions otherwise its not am improvement

MountainBear:

By "getting Longer" he is referring to the fact the ping sends a timestamp with its ping, and the satellite adds its own timestamp on arrival; so in this case the difference between these timestamps (in milliseconds) would be increasing, implying a longer distance between the sender and the satellite.

I think some are getting confused between the INMARSAT link and ACARS... there isn't one, except if you pay for a certain service the SAT link will carry ACARS data.

REMEMBER folks the SAT transceivers on the aircraft are also voice capable, and the pings are used as a "stay-alive" status at the SAT-end of this link. In other words if the crew decided to make a SATCOM voice call, the satellite needs to be ready to relay the message.

What he's inferring I believe is that the last ACARS transmission DID include precise positional info, so the 1.11 SATCOM ping will closely correlate with the 1.07 ACARS report, and from thence the following pings can be traced/located (at least to ping arcs).

But it doesn't make sense to take the GPS position at 1:07 for calibration, if for the next ping - which probably was exchanged at 1:11 - secondary radar position from 1:11 was available. Why then take the GPS fix from 4 minutes earlier and not the SR fix from that same minute ?

Inmarsat
 

Megyn Kelly´s interview with Mr. Chris Mclaughlin, Senior Vice President at Inmarsat; the most articulate / informative one to date.

Satellite company official speaks out on tracking missing jet after it lost contact | Fox News

The Inmarsat guy has six hourly ping times to work with. It should be clear whether the aircraft was heading towards his satellite or away from it over that time to an accuracy of somewhere in the region of 100 km per hour.

It could be confounded by a delay in the transponder reply, but there's no other factors that can affect it. Inmarsat must know a great deal about transponder delays, and they could run the same test on every flight since MH370 to see how wrong they are against actual flight tracks.

He has no information apart from the round-trip time to the aircraft, and his satellite over the Indian Ocean sees the whole Earth disk.

It is possible that some other mysterious geostationary satellite might have collected the signals too, which would help a lot in locating them, but I doubt the Inmarsat guy would talk about that on the TV.

If he had six hourly GPS positions reported in the replies, this uncertainty would all be gone. For a few cents per seat per trip, this would seem to be a good idea in future. Then again, the wreck of AF447 still took 2 years to find, despite much more comprehensive satellite signaling.

You need to ask him not me!

"On average once an hour"

I don't understand the endless confusion between SATCOM pings and ACARS data...

SATCOM pings and ACARS data transmissions are completely independent.

The article states that the ACARS data transmitted included GPS coordinates from the plane. It doesn't matter how it was sent - the GPS coordinates were part of the data.

Those coordinates were then used to 'calibrate' the interpretation of the SATCOM ping sent (independently) around the same time.

Interesting article.

He seems to be talking about an upgrade to the INMARSAT SATCOM box, not the ACARS system? Which would make sense since he works for INMARSAT...

HMS Echo
 

Broadlands - you would know! I can't find the post but somebody said that HMS Echo is equipped with one, maybe two, sounding lines with lead weights on them. I thought these went out with Capt Cook and Admiral Nelson? Perhaps it was a bad joke!

It is probable that each ping is actually an exchange satellite to aircraft and back, or vice versa. This is the only way to ensure a secure identity check within each ping.

It is not clear which end initiates the communication. There are conflicting statements by experts.

In any case it does mean that each individual ping operation does get longer to conclude as the distance from satellite increases.

Along the published southerly path the distance from the satellite is increasing for the last several pings, at least. However, other possible paths can be matched as well.

yes there is and if you had bothered scrolling back a few pages you would have found posted by cyanr

Satellite company official speaks out on tracking missing jet after it lost contact | Fox News

BREAKING: The Telegraph has obtained the transcript of the last 54 minutes of comms
 

Malaysian Airlines MH370: live - Telegraph

16.38 The first was a message delivered by the cockpit at 1.07am, saying that the plane was flying at a cruising altitude of 35,000 feet. This message was unnecessary as it repeated a call that had already been delivered six minutes earlier.
Steve Landells, a former British Airways pilot who flew Boeing 777s, told The Telegraph that this second message was not required but he did not regard it as suspicious.
“It could be as simple as the pilot forgetting or not being sure that he had told air traffic controllers he had reached the altitude,” he said. “He might be reconfirming he was at 350 [35,000 feet]. It is not unusual. I wouldn’t read anything into it.”
16.25 BREAKING: The Telegraph has obtained the transcript of the last 54 minutes of communication aboard Flight MH370.
Related Articles
How MH370 vanished - and how it could have been avoided 21 Mar 2014
The final communication between the Malaysia Airlines flight cockpit and ground control can be revealed, from its taxi on the runway to its final message at 1.07am of “Alright, good night”.
The Telegraph's Jonathan Pearlman has seen the full communication record of MH370, including the crucial moments in the lead-up to the disappearance of the Boeing 777 and its 239 passengers. It reveals the messages relayed between the cockpit and air traffic controllers during the period when the plane is believed by investigators to have already been sabotaged.
More to follow...

P3 S&R
 

These true experience revelations about the discomfort of low level S&R are most enlightening. There is no way you can get this kind of insight from conventional media sources. So let me express my thanks to all you professional posters whose original comments keep me coming back to this site every day.
:D