nupogodi
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 8:17 pm

Quoting Pihero (Reply 48):
That means that the loci are, instead of lines a set of bands some 2 nautical miles wide

That is an extremely ambitious error margin. They are likely much wider, especially because the plane could have flown for nearly an hour after the last ping.
A man must know how to look before he can hope to see.
 
jox
Posts: 119
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 8:18 pm

Quoting nupogodi (Reply 46):
Select "World Hi" at the top right (for high level airways) and see for yourself.

Excellent! Thanks!

There are no exact match, but on the other hand we don't know the exact end position either. ISBIX and BULVA is close enough to be such candidates for the programming. I just wanted to know if there were such a possibility, and it definitely is.

http://skyvector.com/?ll=-44.0449570...4.04495705232124,91.21984863652585

[Edit: Changed the link]

[Edited 2014-03-21 13:34:58]
 
hivue
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 8:23 pm

Quoting nupogodi (Reply 50):
That is an extremely ambitious error margin. They are likely much wider, especially because the plane could have flown for nearly an hour after the last ping.

I think Pihero's 2 nm margin refers only to the width of the arcs at the exact time of the last ping itself. The 2 arcs are only referenced to that.

[Edited 2014-03-21 13:25:04]
"You're sitting. In a chair. In the SKY!!" ~ Louis C.K.
 
theaviator380
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 8:24 pm

Quoting akberc (Reply 43):

India denied request because,

1. Indian navy and IAF have already looked at area as per proper plan. Didnt find anything.
2. India and China already having issues regarding claiming areas, infiltration etc. So no way they will allow China to sniff around that area.

Cheers.

[Edited 2014-03-21 13:25:45]
 
nupogodi
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 8:25 pm

Quoting capri (Reply 49):
I think what he meant and maybe I am wrong, are those part of initial transition or STAR for Langkawi before final vector, or maybe a company arrival route to Langkawi or any other destination that general public unaware of? ?

Why would you do anything but go back to KUL at that point? What would be the point of overflying the peninsula and looping around to go to LGK?

It's a valid idea though. I would have no idea about routing in S.E.A., I've never even been there.  

[Edited 2014-03-21 13:26:45]
A man must know how to look before he can hope to see.
 
cand
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 8:28 pm

Do we know if the ACARS transmissions before 1:19 were through SAT or VHF? If SAT, there should be more info to correlate with.
Speaking about correlation/calibration of this novel technique to extract position from sat communication: was there some calibration done with known flights in the region (like the SIA aircraft)?
I'm suspicious when info is hidden with no apparent reason.
 
Pihero
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 8:29 pm

Quoting hivue (Reply 52):
I think Pihero's 2 nm margin refers only to the width of the arcs at the exact time of the last ping itself. The 2 arcs are only referenced to that.

Yes. Only it applies to all the *arcs* / *loci* / LOPs ( GRRRrrrr !it bugs me that we can't agree on a single term without error !
Contrail designer
 
nupogodi
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 8:34 pm

Quoting Pihero (Reply 56):
Yes. Only it applies to all the *arcs* / *loci* / LOPs ( GRRRrrrr !it bugs me that we can't agree on a single term without error !

We don't actually know the error margins on those. I suppose it would depend on the accuracy of the timekeeping aboard INMARSAT-3.

It's somewhat irrelevant though, because the aircraft can continue flying, run out of fuel, then glide for quite a distance... Would SATCOM modem be powered in a situation where you are running on batteries? A small question that could use an answer.
A man must know how to look before he can hope to see.
 
Pihero
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 8:35 pm

By the way, I'm not defending this as nmy idea... I'm just trying to explain the NTSB method.
Some interesting points :
- The research is not, for the moment at the end of the NTSB trajectory... It looks like the priority is for finding wreckage, which has drifted for days.
- Once again, a question begs to be asked : Is it that in the minds of the US investigators, crew has been incapacitated, leaving the aircraft to fly on its own ?
It certainly looks so to me... It even looks as the basis of their theory. Otherwise, it does not make sense at all.
Contrail designer
 
Pihero
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 8:37 pm

Quoting nupogodi (Reply 57):
We don't actually know the error margins on those. I suppose it would depend on the accuracy of the timekeeping aboard INMARSAT-3.

Are you serious ?
Contrail designer
 
nupogodi
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 8:42 pm

Quoting Pihero (Reply 59):
Are you serious ?

100% serious. The INMARSAT spokesman/VP/whoever he was said that the satellite initiates the ping and the aircraft responds. Therefore by knowing the round-trip time of that signal, taking any processing lag on the receiving end into account, they can calculate the one-way trip time of that signal. This allows you to calculate a distance to the aircraft, which knowing your distance above the ground allows you to use simple trigonometry to solve for the distance across the ground from the satellite. Therefore, accurate timekeeping is essential since at over 30k km in the air, a small error could mean a big difference in the calculated distance across ground (which is used to generate the circle which is then cut down to arcs based on other known data).

GPS satellites are in LEO and have atomic clocks onboard to facilitate exactly the precise timekeeping necessary to facilitate geolocation on the receiver. You are dealing here with a geostationary orbit, a satellite that was never built to do any kind of geolocation, and a round-trip-time that could be influenced by anything from the aircraft's altitude to atmospheric conditions.

So yes I am serious. Why?

[Edited 2014-03-21 13:43:07]
A man must know how to look before he can hope to see.
 
jox
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 8:45 pm

Quoting nupogodi (Reply 57):
We don't actually know the error margins on those. I suppose it would depend on the accuracy of the timekeeping aboard INMARSAT-3.

I am not sure if I follow you here. If the satellite is as bad as microsecond accuracy (I would guess it is much better), that would just give an error (with this method of measuring) of +/- 0.3 km (this is neglecting the atmospheric disturbances, but still), which is nothing in this context. Remember, we are not talking about the accuracy needed in the GPS satellites.

There are other things affecting the error margins much more than the timekeeping in the sat.
 
capri
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 8:45 pm

CNN is having the Australian Ambassador in USA on the show, is giving a real reality check about the search area how difficult will be to find anything due to the nature of the sea
 
nupogodi
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 8:53 pm

Quoting jox (Reply 61):
I am not sure if I follow you here. If the satellite is as bad as microsecond accuracy (I would guess it is much better)

1μs is pretty darn accurate. Let's say they were off by even 1ms in accounting for signal processing time in the modem, and atmospheric conditions, and timekeeping on the satellite, they could be off by 300km.

Remember that there are a lot of assumptions that have to be made. The smallest error in any of them is greatly magnified, even if the clock on the satellite is perfect.

[Edited 2014-03-21 13:54:24]
A man must know how to look before he can hope to see.
 
akberc
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 8:54 pm

Quoting nupogodi (Reply 60):
You are dealing here with a geostationary orbit, a satellite that was never built to do any kind of geolocation, and a round-trip-time that could be influenced by anything from the aircraft's altitude to atmospheric conditions.

1000 miles lateral distance ~= 0.5 millisecond lag. However as you say, it depends not only on the satellite timekeeping but also the lag to an earth station if the data is relayed immediately and not stored on the sat. And finally, if the software in the Satcom is not 'real-time' it may behave differently at different altitudes.

I am quite certain that the smart guys/gals at Inmarsat / NTSB would have taken all those factors into account, but absent hard raw data, we have to speculate a bit . . .
 
nupogodi
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 8:57 pm

Quoting akberc (Reply 64):
I am quite certain that the smart guys/gals at Inmarsat / NTSB would have taken all those factors into account

Yup and they would have calculated the amount of error they expect, too, which we don't know. I just don't think it's quite as tight as 2nm.
A man must know how to look before he can hope to see.
 
WingedMigrator
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 8:58 pm

Quoting Pihero (Reply 59):
Quoting nupogodi (Reply 57):
We don't actually know the error margins on those. I suppose it would depend on the accuracy of the timekeeping aboard INMARSAT-3.

Are you serious ?

Every nanosecond of timing error contributes 15 cm of error to the distance (accounting for two way travel of the ping from the satellite followed by the response from the aircraft). There may be numerous nanoseconds of error, but probably not milliseconds. 1 ms error = 1e6 ns is equivalent to 150 km of range error.
 
dtw2hyd
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 8:59 pm

Quoting nupogodi (Reply 60):
100% serious. The INMARSAT spokesman/VP/whoever he was said that the satellite initiates the ping and the aircraft responds.

INMARSAT 3F1 has a round trip ping time of 0.25 seconds. Its signal is susceptible to solar flux, ionospheric and radio interferences. So I would think its error margin will be 100+ NM.

It is not built to provide location services, it is a communications satellite.
 
nupogodi
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 9:00 pm

Quoting WingedMigrator (Reply 66):
1 ms error = 1e6 ns is equivalent to 150 km of range error.

1/1000 sec * c ~= 300km

unless you are talking about 300km/2 because the round-trip time would have been divided by two, halving the error in the one-way time.
A man must know how to look before he can hope to see.
 
jox
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 9:01 pm

Quoting nupogodi (Reply 63):
Let's say they were off by even 1ms in accounting for signal processing time in the modem, and atmospheric conditions, and timekeeping on the satellite, they could be off by 300km.

Exactly my point! The time it takes for the modem to react and answer is going to be significantly larger than the propagation time. You have to distinguish between the *accuracy* of the clock in the satellite and the RTT!
 
WingedMigrator
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 9:02 pm

Quoting nupogodi (Reply 68):
1/1000 sec * c ~= 300km

That's 300 km on the round-trip signal, or 150 km of range error to the aircraft.
 
nupogodi
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 9:07 pm

Quoting jox (Reply 69):
Exactly my point! The time it takes for the modem to react and answer is going to be significantly larger than the propagation time. You have to distinguish between the *accuracy* of the clock in the satellite and the RTT!

It depends on what kind of clock is up there and what kind of data from it is logged. There's no need for it to be extremely fancy, with microsecond resolution. And the SATCOM modem software might give a contract, defined by the protocol, of the maximum time it can take to respond and still be in-spec. But only the designers of that specific modem would know if it's likely for it to significantly exceed the requirements of the spec. All in all, this gives you a fairly wide range of errors for very crucial assumptions.

That is why I said a 2nm error margin is extremely optimistic.
A man must know how to look before he can hope to see.
 
akberc
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 9:08 pm

Quoting WingedMigrator (Reply 70):
That's 300 km on the round-trip signal, or 150 km of range error to the aircraft.

Not exactly. Pythagoras' theorem would apply and range error would be on the base and the round-trip on the hypotenuse. It should be much more sensitive than that.
 
rcair1
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 9:08 pm

Quoting Pihero (Reply 48):
It would be very difficult for me to assume that the FAA, Boeing and the NTSB,
Quoting jox (Reply 61):
I am not sure if I follow you here. If the satellite is as bad as microsecond accuracy

I think we need to be talking about "precision" not "accuracy".

The accuracy of the clock relates to how close to it is to a given standard, and how much it may drift with time. That is irrelevant in this case.

The precision is related to how small a difference we can measure and with how many significant bits. The clock could be very inaccurate (drift a minute per day), but very precise in terms of measuring short periods.

-rcair1
rcair1
 
hivue
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 9:13 pm

Quoting Pihero (Reply 56):
Only it applies to all the *arcs*

Right. But the last "ping" is the only data released publically so far.

Quoting Pihero (Reply 58):
It even looks as the basis of their theory.

Are you referring (as I think you did earlier) to the NTSB's curved tracks as possibly being due to winds aloft with no pilot(s) awake to notice and correct (i.e., sort of a drifting course)?

[Edited 2014-03-21 14:15:48]
"You're sitting. In a chair. In the SKY!!" ~ Louis C.K.
 
nupogodi
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 9:13 pm

Quoting rcair1 (Reply 73):
The precision is related to how small a difference we can measure and with how many significant bits. The clock could be very inaccurate (drift a minute per day), but very precise in terms of measuring short periods.

They are linked though. Assuming the drift is linear with time, that's a maximum resolution of ~0.7ms. Pretty awful.
A man must know how to look before he can hope to see.
 
jox
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 9:14 pm

Quoting nupogodi (Reply 71):
That is why I said a 2nm error margin is extremely optimistic

We don't disagree on that, but the reason is not mainly due to (lack of) precision, thanks rcair1, of the clock in the satellite.
 
ryu2
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 9:19 pm

Quoting liquidair (Reply 5):

http://www.telegraph.co.uk/news/worl...s-of-communication-from-MH370.html

apparently, they have a transcript of the last 54 minutes of communication....

If that's indeed the real transcript, both pilots and ATC are using very non ICAO-standard phraseology.
 
nupogodi
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 9:23 pm

Quoting ryu2 (Reply 77):
If that's indeed the real transcript, both pilots and ATC are using very non ICAO-standard phraseology.

That is extremely common though.
A man must know how to look before he can hope to see.
 
dc9northwest
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 9:24 pm

Quoting hivue (Reply 74):
NTSB's curved tracks

I understand they're straight lines, but the map projection gives them that curvature.
 
akberc
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 9:25 pm

Quoting jox (Reply 76):
We don't disagree on that, but the reason is not mainly due to (lack of) precision, thanks rcair1, of the clock in the satellite.

Based on this: http://www.inmarsat.com/wp-content/u..._Classic_Aeronautical_Services.pdf

It is a 10kbps data stream, so the pings may even originate from the ground, bounce off Inmarsat, to the Satcom modem, and back up through Inmarsat to the ground station.

I strongly believe now that it took them a few days to calibrate/compare the received pings to similar equipment/flights, and not rely on purely unprecedented mathematical analysis. That would explain the accuracy claim and the 4-8 days of 'refinement' of the data.

[Edited 2014-03-21 14:44:41]
 
rheinwaldner
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 9:26 pm

Quoting rcair1 (Reply 42):

Quoting rheinwaldner (Reply 33):No, the mathematical function laid through the radius samples alone will reveal a lot:
E.g. if it is the negative peak of a sinus, this means that the flight track has actually been steady and straight, approaching the closest point to the satelite and after that departing again.
Can you please elaborate - I would like to understand what you are saying and I do not.

Imagine a histogram, each bar with the ping radius after another hour.

That histogram shows a curve, which must be (part of) a trigonometric function (my first bet was a sinus, but maybe a tangens), if the plane flew steadily on one track and with constant speed.

It is now a simple mathematical task to find out where the plane flew.
Many things are difficult, all things are possible!
 
jox
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 9:27 pm

Quoting ryu2 (Reply 77):
If that's indeed the real transcript, both pilots and ATC are using very non ICAO-standard phraseology.

Read the last line in the transcript! This is English translation of Mandarin translation of English.
 
User avatar
Dalavia
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 9:46 pm

Quoting akberc (Reply 43):
South arc end - straight/constant zombie flight on auto-pilot or a single suicidal pilot who had successfully killed/neutralized everyone.
North arc end - intentional successful hijacking. If it reached the mainland and evaded radar and landed secretly, then senior pilot was at controls and part of the hijacking.

Perhaps there is a third possibility for the southern arc - maybe an attempted hijacking but the pilots fooled the hijackers into thinking they were taking them to the correct destination, but to save some some of wider catastrophe (terrorism?), steered the plane south away from land as an act of self-sacrifice.

Whether the Northern or Southern arc seems more realistic seems to depend on which parts of conflicting information one is more willing to dismiss.

Personally, I am still favouring the northern route as being more likely.

Time will tell - I hope.
 
aw70
Posts: 138
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 9:59 pm

Quoting Dalavia (Reply 83):
Perhaps there is a third possibility for the southern arc - maybe an attempted hijacking but the pilots fooled the hijackers into thinking they were taking them to the correct destination, but to save some some of wider catastrophe (terrorism?), steered the plane south away from land as an act of self-sacrifice.

Interesting theory. Except that hijackers would have had some notion of when land should have become visible on the way to their intended destination. Or if any of them happened to have a smartphone with GPS on it, and checked their location, they would have seen in an instant what was up. And would have acted accordingly once they realised they were being taken for a ride.

Maybe they could not have done much to fly the a/c themselves, but it would be unlikely that hijackers did not notice the entire time, and that the plane would have flown that long in such a scenario.

[Edited 2014-03-21 15:00:05]
 
YoungMans
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 9:59 pm

This may now 'Stir the Possum' as we say it in Australia; but ....

The authorities may be searching out there for something that does not exist, at least not in the area where they are looking.

The Indian Ocean is a big body of water. In that area the swell is probably at least a couple of metres at the best of times. As soon as you get a bit of wind, you get waves and they are for most of the time at least some two to four metres or so; until you get real wind, 50, 60 knots when the waves will be easily ten metres and more.


Travelling on a ship down there many a time, as a passenger, I have never had it where the waves were less than three metres; in fact that is considered really calm.

Every so often you get breakers, right in the middle of the ocean, for no apparent reason and unpredictably. With breaking waves you almost always get lots of white wash, kind of foam (I don't even know the exact word for it). These breakers can be quite large and, hence, the area of white-wash can be easily 24 metres and a lot more.

Now, if the pictures we have been shown are only single photos, they will not tell us if it was just a breaking wave or, indeed, if something was floating there with the water washing over it.

If there is no series of photos, taken at intervals of a minute or two, whatever it is that looks like an object could simply have been white-wash from a breaking wave. In fact, that is what it looks like to me.

But.., I'm definitely no expert on any of this but I have seen heavy seas and 'Breaking Waves' with a lot of white-wash.
 
rheinwaldner
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 10:05 pm

Quoting nupogodi (Reply 63):
1μs is pretty darn accurate.

Time duration measurements tend to be high resolving and accurate.

Quoting rcair1 (Reply 73):

The precision is related to how small a difference we can measure and with how many significant bits. The clock could be very inaccurate (drift a minute per day), but very precise in terms of measuring short periods.

If we are talking about pings, we are talking about IT networking in the widest sense. And IT network gear is indeed measuring and resolving times very accurately.
Many things are difficult, all things are possible!
 
nupogodi
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 10:08 pm

Quoting YoungMans (Reply 85):
If there is no series of photos, taken at intervals of a minute or two, whatever it is that looks like an object could simply have been white-wash from a breaking wave. In fact, that is what it looks like to me.

It looks like that to me too, but considering their confidence a) in the NTSB most-probable tracks and b) in the satellite imagery, I would have to give the authorities the benefit of the doubt and assume they know something we do not.

Regardless, it is still the most reasonable place to send SAR at the moment, don't you think?
A man must know how to look before he can hope to see.
 
capri
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 10:08 pm

What is being said or speculated and leaked sources on CNN, this is one reason why Malaysia was not releasing anything until full outcome of investigations become clear
 
nupogodi
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 10:10 pm

Quoting rheinwaldner (Reply 86):
If we are talking about pings, we are talking about IT networking in the widest sense. And IT network gear is indeed measuring and resolving times very accurately.

Yes, on internal timers and counters that may not be actually stored or written anywhere. Even on plain old consumer hardware, you don't get a tick for every oscillation of the crystal. It's a communications satellite, they may not have a clock that ingests and records such a precise resolution, even when individual components may count time at far greater resolution.
A man must know how to look before he can hope to see.
 
ikramerica
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 10:14 pm

Quoting canoecarrier (Reply 8):

Of course they are. That's what FAR 121.344 was created for, to set the requirements for a CVR/DFDR. That's what I was suggesting...to amend that FAR. But, it won't be retroactive and EASA would have to make the same change in their regulations.

They can absolutely be retroactive just as were reinforced cockpit doors and other safety and security rated items.

CVRs are serviceable and replaceable items. Certifying a flash based 25 hour model would be trivial, even taking into account the various aircraft families out there. And the cost per aircraft would be less than reinforced cockpit doors
Of all the things to worry about... the Wookie has no pants.
 
nupogodi
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 10:19 pm

Quoting ikramerica (Reply 90):
CVRs are serviceable and replaceable items.

The beacons are necessary to replace every 6 years, I believe, or after operating for more than 30 days (not likely you'll be replacing that one in the same airframe anyway).

ELTs I believe have a much shorter timeframe on necessary battery replacement, and they have to be replaced after operating for 1 hour.

So basically these devices go through maintenance frequently-enough anyway.
A man must know how to look before he can hope to see.
 
Pihero
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 10:22 pm

Quoting dc9northwest (Reply 79):
Quoting hivue (Reply 74):
NTSB's curved tracks
I understand they're straight lines, but the map projection gives them that curvature.

If anything, the projection is a Mercator type ( see the elongation the further you are from the equator )

Quoting akberc (Reply 80):

I strongly believe now that it took them a few days to calibrate/compare the received pings to similar equipment/flights, and not rely on purely unprecedented mathematical analysis. That would explain the accuracy claim and the 4-8 days of 'refinement' of the data.

I certainly agree with you.
For those disregarding the precision of the track because of an inferior time keeping system : Innmarsat has a very accurate clock, based on a set of crystal oscillators... But that's not all : the time-keeping is backed by atomic clocks on the ground,. Precise time keeping is primordial to coding.
Secondly, from a geostationary orbit, the influence of atmosphere is relatively speaking less than for a Nav Sat, which is on a much lower orbit.
Thirdly, there is a far less influence of Doppler shifts, as the Geostationary satellite is apparently motion-less.
As I said earlier, the only uncertainty is the aircraft altitude, in this case introducing an error of less than 10km/42000. In fact, with the tools the Americans have at their disposal, I'd be surprised to have an error of more than a lateral 2 km .

Quoting rheinwaldner (Reply 81):
It is now a simple mathematical task to find out where the plane flew.

I agree.
Contrail designer
 
hivue
Posts: 2052
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 10:23 pm

Quoting YoungMans (Reply 85):
Travelling on a ship down there many a time, as a passenger, I have never had it where the waves were less than three metres; in fact that is considered really calm.

Every so often you get breakers, right in the middle of the ocean, for no apparent reason and unpredictably. With breaking waves you almost always get lots of white wash, kind of foam (I don't even know the exact word for it). These breakers can be quite large and, hence, the area of white-wash can be easily 24 metres and a lot more.

I would think that those kind of seas wouldn't leave behind 24m parts (or conglomerations of parts) of an airframe for very long.
"You're sitting. In a chair. In the SKY!!" ~ Louis C.K.
 
YoungMans
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 10:26 pm

Quoting nupogodi (Reply 87):
Regardless, it is still the most reasonable place to send SAR at the moment, don't you think?

Yes, I agree with that. A search on site may show up what the satellite hasn't seen yet.
At the same time, though, other leads should also be followed.
 
nupogodi
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 10:38 pm

Quoting Pihero (Reply 92):
Precise time keeping is primordial to coding.

Indeed. But just because certain circuits may have very high-frequency timers, does not mean that kind of resolution is recorded in whatever logs they fished these pings out of. At any given moment in a modern household, for example, there are dozens if not hundreds of extremely accurate timekeeping devices and yet that precision is never written anywhere. No networking hardware I've ever worked with has written logs to microsecond precision. Accurate timekeeping is something the network hardware itself needs, it's not something it needs to report to the processor. Since the satellite was never built for this purpose, the question of the precision is a valid one.

I personally don't think the error is as small as you think it is. But, it is OK for us to disagree. And it is irrelevant anyway because the aircraft could have flown powered for ~59min and glided quite a distance unpowered after 0811L.

edit: And it would be nice if you could source your claim that the ground stations are equipped with atomic clocks. I don't doubt you, that just seems excessive.

[Edited 2014-03-21 15:40:21]
A man must know how to look before he can hope to see.
 
Backseater
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 10:39 pm

Quoting akberc (Reply 80):
so the pings may even originate from the ground, bounce off Inmarsat, to the Satcom modem, and back up through Inmarsat to the ground station.

Of course they would.

There was much discussion about the ping measurement process.
Don't expect to see clocks on board communication satellites. Think of them as a bidirectional mirror with very little to no processing on board.

Pinging would be a purely ground process running in the Earth station computers based on profiles in databases and the realtime status of the aircraft modem .

For an accurate measurement you need in principle:

- precise time stamping upon generating the ping request

- estimating any delays that may occur if messages are queued according to priority before being transmitted

- knowing the position of the satellite as accurately as possible. Yes, geostationary satellites are not absolutely stationary. They oscillate in longitude and latitude around their nominal station. Their fuel on-board is used to keep them within their "box" so that they don't go mess up their neighbors.. 3F1 is an old satellite operating beyond its nominal life but it only has a small orbital inclination (only 1.6 Deg), I am sure Inmarsat tracks its real-time position very well as that is essential for station keeping and now for RTD measurements (for instance apogee-perigee difference around 40kms )

- qualified software of the satcom modem on-board the aircraft as to latency in response to a message ping. It does not matter how long the modem takes to respond as long as it always answers with the same latency

Now the answer goes back through the satellite and reaches the earth station. Several operations have to occur to decode the message including error correction and assess its time of arrival. That time has to be measured AND recorded with enough precision (I hope no worse then 1msec). Just like for the aircraft modem, the receive chain has to operate with constant latency.

The problem I see is that a precise RTD operation was probably never envisioned and therefore never specified for that satellite, aircraft modem and earth station.

There are payloads on other GEO satellites that have been designed specifically to allow for precise ranging using appropriate waveforms and algorithms. For a ground target i.e. the altitude of which can be inferred from a DEM (Digital Elevation Model), positioning to a few tens of meters can be obtained.

In our case, only Inmarsat knows from their analysis and calibration data what can be expected in practice.
 
iberiadc852
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 10:41 pm

Quoting aw70 (Reply 84):

Interesting theory. Except that hijackers would have had some notion of when land should have become visible on the way to their intended destination. Or if any of them happened to have a smartphone with GPS on it, and checked their location, they would have seen in an instant what was up. And would have acted accordingly once they realised they were being taken for a ride.

That post brought me a question. Maybe if I were a telecomminications expert I would know the question is absurd, but as I am not, I ask.
Would the telephone/telecom companies with networks along the supposed northern and southern routes could guess from their internal data if there were any mobile devices receiving data in the heights those 7 hours MH370 was flying?
variety is the spice of life; that's what made the "old times" so good
 
nupogodi
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 10:45 pm

Quoting iberiadc852 (Reply 97):
That post brought me a question. Maybe if I were a telecomminications expert I would know the question is absurd, but as I am not, I ask.
Would the telephone/telecom companies with networks along the supposed northern and southern routes could guess from their internal data if there were any mobile devices receiving data in the heights those 7 hours MH370 was flying?

This has been discussed but basically

- Yes, if there was a connection attempt made by a mobile device even in the flight levels, they should have that logged somewhere
- No, all information the public has is that no such connection attempts were made, but that efforts were being made to engage more carriers
- There would be no chance of this occurring over the ocean i.e. the southern arc
A man must know how to look before he can hope to see.
 
chaseus1
Posts: 77
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RE: MH370 Malaysia Airlines B772 Missing Enroute KUL-PEK Part 42

Fri Mar 21, 2014 10:56 pm

If the plane was off by too much, it would be in another "distance ring" so to speak. The error in time, if any, from the planes response lag time, could probably be ascertained by the differences as the angles changed, as its effect would become greater or less as it flew further away (as a percentage of the total response time). I think mathematics can determine the error, and make some adjustment for it. I'm not saying they will get an exact location, because there are some variables, and we don't even know the exact crash time. But I think the math will get them closer than many realize.

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