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Malaysian Airlines MH370 contact lost

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Malaysian Airlines MH370 contact lost

Old 21st Mar 2014, 18:25
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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.
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Old 21st Mar 2014, 18:28
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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.
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Old 21st Mar 2014, 18:38
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Originally Posted by FE Hoppy
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!
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

After not receiving new data from the 777 after its automated reporting system was switched off, the automated satellite pings—the digital equivalent of a handshake—originated at a ground stations and was transmitted up to the orbiting satellite high above the Earth's equator. The satellite relays the ping down to the aircraft below, effectively asking the jet if it is still able to send and receive data. After receiving it, Flight 370 transmitted a return ping back up to Inmarsat, which in turn relayed it to the ground station.
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.

Last edited by glenbrook; 21st Mar 2014 at 18:53. Reason: found a ref
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Old 21st Mar 2014, 18:40
  #7004 (permalink)  
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Originally Posted by awblain
I think the only thing that rules out the "Northern Arc" is the lack of any reported radar returns that way
- 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.
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Old 21st Mar 2014, 18:42
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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.
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.
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Old 21st Mar 2014, 18:43
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Originally Posted by MountainBear
Ping time can increase for multiple reasons not related to distance. One obvious confounding factor is interference of some type.
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.
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Old 21st Mar 2014, 18:45
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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.
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Old 21st Mar 2014, 18:53
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Originally Posted by awblain
Lockerbie, The aircraft also vanished from the full radar coverage,
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.
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Old 21st Mar 2014, 18:54
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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?
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Old 21st Mar 2014, 18:54
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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.
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Old 21st Mar 2014, 18:55
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Something which disturbs and saddens me about this, other than the probable loss of life, is the apparent unwillingness of various agencies to share information which may be of help. I'm thinking particularly of the "We didn't tell them because they didn't ask" situation with Thailand. Surely common decency should dictate that any possibly relevant information should be shared as a matter of course without having to be asked and as soon as possible after an event? I appreciate that security needs to be preserved but ways can usually be found of circumventing specific detail which might betray particularly sensitive information which the country of origin might wish to preserve.
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Old 21st Mar 2014, 18:56
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@ JG1

It kept pinging and made course changes.
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Old 21st Mar 2014, 19:02
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The Imersat Arc

The imersat track is shown as an Arc if transposed onto a globe does it become a direct great circle track as normally flown? I assume the track was calculated this way. Perhaps they should release the timing data for others to have a look.
Checking with the search aircraft should give a comparison timing.

How many way-points exist in the southern area that can be programmed into the 777 Internal navigation system?

After depressurization is it possible to open the doors and bale out the 777 did any crew have a unusual carry on bag?
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Old 21st Mar 2014, 19:03
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@ Bono
Appeal: Please Do Not Reveal Critical Security Info

Some one raised a very pertinent question about discussing cockpit door security procedures on an open forum. I believe that information that can reveal crucial security procedures related to aircraft operations such as access to vital areas, disabling any aircraft equipment by any manner, interfering with flight/cabin crew, ability to tamper with any equipment, etc. whether related to MH370 incident or not, must not be allowed on this forum. Posters and moderators please use caution, as innocent questions could be masking less than friendly intentions.
In principle just about anyone would agree with you, but try a Google search.
It is all available on the Internet.
I think ill minded people have Internet too.
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Old 21st Mar 2014, 19:04
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But after the initial turn westbound, if it did come back over Malaysia/Indonesia would there not have any cell phone sign in attempts as Mr172 points out? Especially if it, for whatever reason, was at a lower altitude? As was pointed out before, plenty of people leave their phone on after closing the door.
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Old 21st Mar 2014, 19:04
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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.
"Ping", which judging from the interview with the Inmarsat VP isn't a term they actually use, clearly implies a ping-and-response sequence in this context. Except in the case of the final ping, of course.
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Old 21st Mar 2014, 19:05
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How many way-points exist in the southern area that can be programmed into the 777 Internal navigation system?
You can create a waypoint anywhere you like so gazzilions! And there and lots of ways to define a waypoint.
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Old 21st Mar 2014, 19:11
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The imersat track is shown as an Arc if transposed onto a globe does it become a direct great circle track as normally flown? I assume the track was calculated this way.
The arc isn't a track.

It's the set of possibilities for the position at the time of the final exchange with the satellite. And no, it's not a Great Circle.
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Old 21st Mar 2014, 19:12
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Originally Posted by FE Hoppy
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.
The other explanation for prioritising the southern arc was that a northerly route would have taken it over several countries' radar systems that - as yet - have drawn a blank. But I guess they may yet come up with something who knows ?

That said, the Malaysian's have continued to say they're keeping their options open, not ruling anything out without a fact-based reason to. There really are still very few facts, that we know of anyway.
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Old 21st Mar 2014, 19:12
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Originally Posted by glenbrook
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.

ground to sat two fixed positions, sat to aircraft, aircraft to sat one fixed one moving, sat to ground two fixed items.

sat ground and vice versa absolutely irrelevant (the should be a constant). it matters not one jot whether the satellite has an hourly clock or the ground has the hourly clock, the only part that can measure the distance in time and relate it to distance is the sat-aircraft section.

The timing is almost certainly on the satellite why depend on extra transmissions from/to GS which may be down.

You fly into the coverage of a satellite, your presence is detected just like you going to an area of a new phone mast, it knows your there and both of them periodically check to see if you still are. So the satellite has detected a potential service user why tell the ground , it just logs it and checks in an hour
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