Speed of sound in water is APPROX 1500 mps but it varies with temperature, salinity, surface conditions and half a dozen other things

You use 1500mps as an approximation but it could be +/- 5%

ACARS, Disabled or Switched off
 

Bilby, Desparing Traveller et al,

ACARS "was deliberately turned off" was reported early on. Now ACARS 'logs on' and 'logs off' usually on aircraft systems power up and power down. ACARS using VHF often (regularly) loses contact as the aircraft flies out of line-of-sight. There is a difference to the system between just not getting any more transmissions and receiving a log-off. So it would be possible to know if the system was shut down via a pilot input or just 'stopped' as it would if out of line of sight of VHF, fire had burned through the power supply, or the pilot had tripped a circuit breaker.
The repeated statements that someone had "switched ACARS off" rather than we received no more ACARS transmissions after the last one at cruise, implies that there is evidence of a tidy log-off. This evidence is crucial as it would settle several hypotheses - a pilot with a cockpit fire or some other emergency, does not find the correct place to log off from ACARS. SITA/ARINC should have that evidence and it should have been in the initial report.

@IanW

The Curtin University receivers are based off Rottnest Island, pretty much due west of Perth. I gather these receivers serve a scientific purpose (whales etc).

He explained the data had been cross referenced with data obtained from different receivers based quite a way south of Perth (off Cape Leeuwin). The purpose of these receives is to help monitor compliance with the comprehensive test ban treaty. He was a little vague regarding precise details at this point, perhaps deliberately so. But I got the impression differential timing suggested a source well to the south (he did specifically mention Antarctica as a likely source).

@IanW
As mentioned, the first acoustic transient, if originating from the final Inmarsat ping ring would have been produced approximately 50 minutes after the time of last Inmarsat ping.

The second acoustic transient was much later and would have originated approximately 4.5 hours after the last Inmarsat ping

Both signals received contain only low frequency energy, suggesting a large propagation range, and have rather different characteristics (frequency and time spread).

Glide from 35,000ft?

Less than 15 mins.

Hello, a first-time poster here with a couple of points I would like to contribute:

When Tim Clark talks about 3 systems disabled, he probably refers to the transponder, ACARS and SATCOM. Please note that ACARS and SATCOM are separate systems.

Transponder being disabled (turned off or failed) is self-evident.

Last ACARS transmission from the plane through SATCOM was at 1707 Z and none received after that, thus ACARS disabled.

In the Inmarsat logs, there is a gap of SATCOM transmissions between 1707 Z (after the last ACARS transmission) and 1825 Z (when the SATCOM in the plane initiated a handshake). In particular, the SATCOM modem didn't respond to a satellite query at 1803 Z. We can deduce therefore that SATCOM was disabled at least between 1803 Z and 1825 Z, and enabled at 1825 Z.

Curtin University researchers find possible acoustic trace of MH370

IanW, a brief media presentation by Dr Duncan. The 15 minute interview I heard was much more in depth, but you might be interested in this.

Dale C. Acars was VHF only. The systems off: VHF (Acars), HF, transponders, satellite phone. This reply will disappear soon along with your comment.

I don't think there is any 'Official' statement that ACARS was switched off or logged off. I believe the position/time of last ACARS on the various plots is that of a complete and normal ACARS transmission and there is no indication of a log off ACARS message.

The log ons at 18:25 (from memory) and the 7th ping, are the satellite communication system itself, not the ACARS communications. Further, I believe it is established fact that MH370 was not configured to have the ACARS system use the satcom link, Satcom was only onboard to provide telecommunications for Business/First class (and potentially available to the flight crew for calls).

I have little technical knowledge of the ACARS system, but it appears to not intrinsically require a log on/log off process. It seems to just be a VHF/HF/Satcom store and forward system where individual data packages are sent to the central service for storage and then periodically polled or pushed until an ACK is received or a retry limit is hit.

It is also not clear to me that the Satcom system itself has any 'logoff' function and therefore if there would be anything to distinguish between the device being turned off/ put into standby/ loosing power/ being destroyed

The logon sets up the store and forward system and checks that you are a subscriber to ARINC or SITA messaging systems. Similarly, the SATCOM sets up a link at the lower protocol layers that also allow check of subscription against the aircraft ID, or you would not be able to start the SATCOM phone or other uses of the SATCOM system. These actions all happen on power on and are 'transparent' to the pilot. This is what was meant by the Earlier statements about 'pilots not knowing how to switch the comms systems off'. From the pilot perspective the comms can be switched off - but they are actually still connected at the network level in case the pilot wants to switch the higher level application on again.

@IanW

Thank you for the explanations.

What I've taken away from this very interesting discussion is that possible the ground would know if the system had been tidily shut down because a logoff message would have been received, but that the existence of such a message hasn't been explicitly disclosed publicly. As you quite rightly say, if that evidence exists, it is crucial.

The preliminary report simply states:I was a bit surprised to read that paragraph, as I had been under the impression that ACARS was VHF only on this flight. Like others, I've also been under the impression that the 1:07:49 message was a routine engine report.

I suspect that the report conflates the Satcom infrastructure (which logged twice in flight, and is the source of the pings), with the ACARS system (which provides store and forward text and data messaging from the flight deck and various aircraft systems). But ultimately, it is irrelevant in that we know when the last ACARS message was transmitted and we know the Satcom infrastructre was connected for many hours after that.

IanW,
Understood - My point was more on the logoff side. It doesn't appear that either system (SatCom or the ACARS store/forward network) have any intrinsic need to have a logoff function. From those with more technical knowledge, is there a logoff message the would or would not be expected in certain circumstances?

I have believed that both are like a transponder in that you know it is not 'on' when it stops responding/sending rather than something like a logout messaging being sent. As such, it is not possible to to deduce the 'Why' from a loss of ACARS or Satcom (or transponder) data. It is intinguishable between the device being shut down in a controlled way (i.e turned off in the normal way), suddenly issolated from power, failed, or destroyed.

logon and logoff
 

I think you will find that the reason for a logon and log off is so that the network knows the aircraft is available to receive traffic in the ground - air direction.

Can't work out how to paste the image here.

I have calculated the solar terminator for 0018 UTC on March 8 2014, and the link below seems to work.

http://www.timeanddate.com/scripts/s...=20140308T0018


So if plan was to ditch around first light, this would suggest a long way SW along the final (7th) arc. Somewhere close to the initial air search area a long way WSW of Perth.

The further NE along the 7th arc the flight ended, the longer the plane was flying in daylight.

The level of presumption here is really quite surprising. Tim Clark, President of the company that operates the largest B-777 fleet, and might just have access that we don't mentions, in an apparent off-the-cuff interview, that there were three things that his qualified crews would not know how to do, THAT WERE DONE and the presumption here is - OH! he must mean VHF com, Transponder(s), and ACARS? So how many 777 qualified pilots don't know how to manage those things? For example, do all aircrew know how to access the flight deck of an aircraft to which they are not assigned?

Isn't it time for a reality check?

Clearly, there is something else and I suspect that as a major operator with the responsibility he has, Mr Clark may know more that he can openly say? So what you, or we, should really be thinking about is what three things could have contributed to the loss of this aircraft that aircrew would not likely know about,but others might? And why is it he assumes that this knowlege boarded the flight and could do so again? Seems to discount all of those fire theories, meteors and structural failure too.

There are far more important issues in play here than LF noise picked up on hydraphones and an anxious lady sailor seeing an aircraft in the early dawn (when it is still dark at sea-level).

It seems that Tim Clark is still asking exactly what was below deck in the hold; amongst other things? That seems to have been brushed aside; as soon as someone found batteries. What else is there that remains unknown about the freight and the people onboard?

Why, then, is it assumed all will be known once the aircraft is found, if it is? Just what do you think the DFDR will reveal about the how and why?

It is time to stop sweating the small stuff and consider the bigger picture.

Astra Mike makes a good point in closing:

quote "It is time to stop sweating the small stuff and consider the bigger picture"

The big picture now is the 29th May press release by JACC, where we are informed the next steps are as follows:

1. A review of all existing information and analysis to define a search zone of up to 60,000 square kilometres along the arc in the southern Indian Ocean.
2.Conducting a bathymetric survey to map the sea floor in the defined search area.
3. Acquiring the specialist services required for a comprehensive search of the sea floor in that area.

Simply put, this means.
1. Try and decide where to look next, then having made up their minds where to look,
2. have a peep to see where it is flat and where it is not, then
3. get the boys and their equipment on site.

It will take them till end of August to do No1 and at least another 12 months to do the rest.

Could it be that in the interim some debris may wash up on someone`s shores.

AstraMike writes, "The level of presumption here is really quite surprising." Well, that's the nature of investigation into mysteries, collecting data and trying to fit the bits of the jigsaw together, ideas followed by testing against reality.

You presume that Clark is an authority and hiding stuff, rather than accept what he says at face value. Well, we know it wasn't engine management, control surfaces or undercarriage he is talking about. I put Clark into the same category as many other highly paid executives.

I would suggest no Emirates pilots have disappeared with a B777, not because they can't, but because so far, none of them have wanted to. Professionalism, stability and a stake in the community.

We're not permitted to talk about the different cultures (including their religions), formerly called races, their attitude to life and other individuals ...

Marty
 

At 320 kts or so you might be correct - however at best glide speed you would be wildly out.

The timezone was most likely UTC+8 (the software her husband used to create the plot uses local time), in which case that section of the plot missed MH370 by a couple of hours or so.

However since the yacht only does 3 knots so it would definitely been possible to see the airplane assuming that the ATSB estimated track is correct.

At 02:50 the yacht was on a northern tack so MH370 would have appeared over the bow, then swung around the port side and disappeared off to the stern. Her eyewitness account saw something over the stern and traveling from port to starboard, so that would be West to East, completely wrong for MH370

As for what she saw it was dawn so it may have been a plane catching the red glow of sunrise. The 'other aircraft' she saw could have be low-earth orbit satellites, which would have been clearly visible at that time of day.

Well, it clearly didn't catch up with it, did it. I'd file this bright idea with the claim by the lawyer brother of Kiwi Paul Weeks lost on the flight, "It's either incompetency or a cover-up." Wouldn't just be that this caught everybody napping, nobody had a clue what happened or where it went...