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MH370: How the AAIB and Inmarsat determined the southern trajectory

Mick West

Administrator
Staff member
This update from the Malaysian Ministry of Transport gives a good overview of how the (very) rough location of MH370 final position was determined.

https://www.facebook.com/permalink.php?story_fbid=740971779281171&id=178566888854999&stream_ref=10


NFORMATION PROVIDED TO MH370 INVESTIGATION BY UK AIR ACCIDENTS INVESTIGATION BRANCH (AAIB)

25/03/14

On 13 March we received information from UK satellite company Inmarsat indicating that routine automatic communications between one of its satellites and the aircraft could be used to determine several possible flight paths.

Inmarsat UK has continued to refine this analysis and yesterday the AAIB presented its most recent findings, which indicate that the aircraft flew along the southern corridor.

As you have heard, an aircraft is able to communicate with ground stations via satellite.

If the ground station has not heard from an aircraft for an hour it will transmit a 'log on / log off' message, sometimes referred to as a ‘ping’, using the aircraft’s unique identifier. If the aircraft receives its unique identifier it returns a short message indicating that it is still logged on. This process has been described as a “handshake” and takes place automatically.

From the ground station log it was established that after ACARS stopped sending messages, 6 complete handshakes took place.

The position of the satellite is known, and the time that it takes the signal to be sent and received, via the satellite, to the ground station can be used to establish the range of the aircraft from the satellite. This information was used to generate arcs of possible positions from which the Northern and Southern corridors were established.

Refined analysis from Inmarsat
In recent days Inmarsat developed a second innovative technique which considers the velocity of the aircraft relative to the satellite. Depending on this relative movement, the frequency received and transmitted will differ from its normal value, in much the same way that the sound of a passing car changes as it approaches and passes by. This is called the Doppler effect. The Inmarsat technique analyses the difference between the frequency that the ground station expects to receive and that actually measured. This difference is the result of the Doppler effect and is known as the Burst Frequency Offset.

The Burst Frequency Offset changes depending on the location of the aircraft on an arc of possible positions, its direction of travel, and its speed. In order to establish confidence in its theory, Inmarsat checked its predictions using information obtained from six other B777 aircraft flying on the same day in various directions. There was good agreement.

While on the ground at Kuala Lumpur airport, and during the early stage of the flight, MH370 transmitted several messages. At this stage the location of the aircraft and the satellite were known, so it was possible to calculate system characteristics for the aircraft, satellite, and ground station.

During the flight the ground station logged the transmitted and received pulse frequencies at each handshake. Knowing the system characteristics and position of the satellite it was possible, considering aircraft performance, to determine where on each arc the calculated burst frequency offset fit best.

The analysis showed poor correlation with the Northern corridor, but good correlation with the Southern corridor, and depending on the ground speed of the aircraft it was then possible to estimate positions at 0011 UTC, at which the last complete handshake took place. I must emphasise that this is not the final position of the aircraft.

There is evidence of a partial handshake between the aircraft and ground station at 0019 UTC. At this time this transmission is not understood and is subject to further ongoing work.

No response was received from the aircraft at 0115 UTC, when the ground earth station sent the next log on / log off message. This indicates that the aircraft was no longer logged on to the network.

Therefore, some time between 0011 UTC and 0115 UTC the aircraft was no longer able to communicate with the ground station. This is consistent with the maximum endurance of the aircraft.

This analysis by Inmarsat forms the basis for further study to attempt to determine the final position of the aircraft. Accordingly, the Malaysian investigation has set up an international working group, comprising agencies with expertise in satellite communications and aircraft performance, to take this work forward.

In Annex I (attached) there are three diagrams, showing:

Doppler correction contributions

This diagram shows the Doppler contributions to the burst frequency offset.

Content from External Source




MH370 measured data against predicted tracks

The blue line is the burst frequency offset measured at the ground station for MH370.

The green line is the predicted burst frequency offset for the southern route, which over the last 6 handshakes show close correlation with the measured values for MH370.

The red line is the predicted burst frequency offset for the northern route, which over the last 6 handshakes does not correlate with the measured values for MH370.
Content from External Source


Example southern tracks

This shows the southern tracks for a ground speed of 400 and 450 knots ground speed. It should be noted that further work is required to determine the aircraft speed and final position.
Content from External Source
 
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Mick West

Administrator
Staff member
Thanks, is the detailed route available somewhere on the internet? I'm having a hard time finding it.

Just draw a line between the two cities on a globe. It's pretty much a direct flight other than the arrival and departure.

What exactly do you want to know, and why?
 
Just draw a line between the two cities on a globe. It's pretty much a direct flight other than the arrival and departure.

What exactly do you want to know, and why?

Morning. Oh, the trajectory plotted by the guys from Inmarsat looks like a simple inversion(you know, just rotating it 180 degrees) of the flight path that I would expect to Beijing(but not exactly). Maybe just coincidence.
 
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Mick West

Administrator
Staff member
Morning. Oh, the trajectory plotted by the guys from Inmarsat looks like a simple inversion(you know, just rotating it 180 degrees) of the flight path that I would expect to Beijing(but not exactly). Maybe just coincidence.

Probably a coincidence, it's not really that close.
 

Jason

Senior Member

Good morning, Why does this chart show an overlap at 22:30 hours for the predicted north & south track, and what was measured. That is nearly an hour before the plane went ran out of fuel. You would expect those lines to cross when the plane turned around and when it turned south or north, but not 5hrs into the flight. Why is it so? In fact wouldn't you expect both the north and south "predicted" lines to move away from each other while moving outward. They should never cross unless the plane was turning, right?
 

DjjA

New Member
If Malaysia is +8 UTC, and take off is known to be 00.41 Local, then surely the time of take-off according to the graph reproduced above should be 16.41 UTC, not 17.30. If that time is suspect then how can we be certain of the remaining time points?
 

Mick West

Administrator
Staff member
If Malaysia is +8 UTC, and take off is known to be 00.41 Local, then surely the time of take-off according to the graph reproduced above should be 16.41 UTC, not 17.30. If that time is suspect then how can we be certain of the remaining time points?

You seem to have misread it. The first point is a 16:30, the second seems to be at around 16:41. Take off was 16:41. Presumably the 16:30 blip as when it was switched on. There's nothing at 17:30.
 

Mick West

Administrator
Staff member
Good morning, Why does this chart show an overlap at 22:30 hours for the predicted north & south track, and what was measured. That is nearly an hour before the plane went ran out of fuel. You would expect those lines to cross when the plane turned around and when it turned south or north, but not 5hrs into the flight. Why is it so? In fact wouldn't you expect both the north and south "predicted" lines to move away from each other while moving outward. They should never cross unless the plane was turning, right?


What is measured is essentially a function of the angle between the heading of the plane, and a line drawn from the plane to the satellite. (or more technically the component of the plane's velocity along the plane->satellite vector). The geometry involved is a little hard to get your head around unless you do a lot of that sort of thing.
 

DjjA

New Member
Who has prepared these charts? Have they been prepared in-house by Metabunk administrators? Are they based on solid data released by Inmarsat, or are they selective visualisations of what has thought to have occurred? I wonder why in particular the Offset frequency falls so rapidly at the 18.20-1825 time point, where it is thought a change in direction is likely to have occurred. The change in D2 distance from the plane to satellite can not have altered so such an extreme extent.

Why does that make such an obvious off-set frequency change?
 

Mick West

Administrator
Staff member
Who has prepared these charts? Have they been prepared in-house by Metabunk administrators? Are they based on solid data released by Inmarsat, or are they selective visualisations of what has thought to have occurred? I wonder why in particular the Offset frequency falls so rapidly at the 18.20-1825 time point, where it is thought a change in direction is likely to have occurred. The change in D2 distance from the plane to satellite can not have altered so such an extreme extent.

Why does that make such an obvious off-set frequency change?

They were prepared by the UK's Air Accident Investigation Branch based on actual data.
http://www.aaib.gov.uk/home/index.cfm

The fall at 18:00 is labeled "possible turn", and that's what would cause such a dramatic change. The graph represents direction (velocity) relative to the satellite, not distance.
 

Jason

Senior Member
This write-up is quite informative. Covering both the distance calculations, and the heading calculations

http://www.nbcnews.com/storyline/mi...ed-mystery-missing-malaysian-jets-path-n62026
Great article, and I love the basketball analogy, but I wish someone could explain how a ping would sound differently from any other ping. I don't understand that part. I understand doppler shift, and how sound can be used to identify if its moving towards your or away from you, but with respect to a ping, I just don't get it. Maybe its me, but if someone could help explain I would appreciate it. Especially since this is their "major" break through in terms of identifying its approx location
 

Jason

Senior Member
Radio frequencies are like sound waves - the have peaks and troughs over distance.
I get that Balance. But how does a ping's peak or trough relate to distance and direction. Its a ping or better yet a blip. Do they count the number of peaks and troughs in between the satellite and the ping?
 

Jason

Senior Member
Actually, I found a great article that better explains how they determined its location using the doppler shift and the wobble of the F41 satellite.

http://www.extremetech.com/extreme/...ht-mh370-and-why-we-still-cant-find-the-plane
The initial Inmarsat report, which placed MH370 along two possible arcs, was based on a fairly rudimentary analysis of ping latency. Inmarsat 4-F1 sits almost perfectly stationary above the equator, at 64 degrees east longitude. By calculating the latency of MH370′s hourly satellite pings, Inmarsat could work out how far away the plane was from the satellite — but it couldn’t say whether the plane went north or south.


A map showing the location of Inmarsat 4-F1, which received Satcom pings from MH370, and the plane’s radius from the satellite (calculated from the “ping” round-trip time).


Inmarsat’s global coverage. The satellite that tracked flight MH370 is shown in purple.

To work out which direction was taken by flight MH370, Inmarsat, working with the UK’s Air Accidents Investigation Branch (AAIB), says it used some clever analysis of the Doppler effect. The Doppler effect describes the change in frequency (the Doppler shift) as a sound/light/radio source travels towards the listener, and then again as it moves away. The most common example is the change in frequency of a police or fire truck siren as it passes you. Radio waves, such as the pings transmitted by flight MH370, are also subject to the Doppler effect.

Basically, Inmarsat 4-F1′s longitude wobbles slightly during its orbit. This wobble, if you know what you’re looking for, creates enough variation in the Doppler shift that objects moving and north and south have slightly different frequencies. (If it didn’t wobble, the Doppler shift would be identical for both routes.) Inmarsat says that it looked at the satellite pings of other flights that have taken similar paths, and confirmed that the Doppler shift measurements for MH370′s pings show an “extraordinary matching” for the southern projected arc over the Indian Ocean. ”By yesterday [we] were able to definitively say that the plane had undoubtedly taken the southern route,” said Inmarsat’s Chris McLaughlin.
Content from External Source
 

Jeff

New Member
Before war in Irak, there were evidence from satellite images that there were massive destruction weapons... UK and USA were very convincing. Now we know they lied.

Some people in Maldive saw a plane, possibly from Malaysian Airlines... Authorities don't tell it was another plan. They tell they are the liars (and if you think Maldives authorities are really independant from UK or USA, that is a joke). Of course, big governmental organisations necessarily tell the truth.

I would like to know what really happened in Maldive... Especially as the pilot trained for landing in Male (Maldives) and Diego Garcia (US military base).

Satellite data but ... who's satellites ? Which UK organisation do they belong to ? Which organisation processes the data ?

Can we trust them more than real people ?

But, may be something will be found near australia. Just a few pieces of the plane, to make an evidence. I will be convinced that the plane is found when the bodies will be found.
 
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Jeff

New Member
Before war in Irak, there was evidence from satellite images that there were massive destruction weapons... UK and USA were very convincing. No we know they lied.

Some people in Maldives saw a plane... Of course they are the liars. And big governmental organisations necessarily tell the truth.

I would like to know what really happened in Maldive... Especially as the pilot trained for landing in Male (Maldives) and Diego Garcia (US military base).

Satellite data but ... who's satellites ? Which UK organisation do they belong to ? Which organisation treats the data ?

Can we trust them more than real people ?
 

Mick West

Administrator
Staff member
I get that Balance. But how does a ping's peak or trough relate to distance and direction. Its a ping or better yet a blip. Do they count the number of peaks and troughs in between the satellite and the ping?

They count:
A) The time taken for the plane to respond to a signal (i.e. related to the distance to the plane)
B) The frequency, which is essentially the number of peaks per second, which relates to the direction the plane is moving in.
 

Jason

Senior Member
Before war in Irak, there was evidence from satellite images that there were massive destruction weapons... UK and USA were very convincing. No we know they lied.

Some people in Maldives saw a plane... Of course they are the liars. And big governmental organisations necessarily tell the truth.

I would like to know what really happened in Maldive... Especially as the pilot trained for landing in Male (Maldives) and Diego Garcia (US military base).

Satellite data but ... who's satellites ? Which UK organisation do they belong to ? Which organisation treats the data ?

Can we trust them more than real people ?
Don't fall down the rabbit hole to far because once your in it to deep, its so hard to climb back out.
 

WeedWhacker

Senior Member
Especially as the pilot trained for landing in Male (Maldives) and Diego Garcia (US military base).

This has been verified?

And point of order: There is no need to "train for a landing" at an airport. (Only exception are certain designated "Special Airports", so named because of particularly difficult or challenging terrain, or unusual procedures associated with the arrival and go-around contingencies).
 

Jason

Senior Member
And point of order: There is no need to "train for a landing" at an airport. (Only exception are certain designated "Special Airports", so named because of particularly difficult or challenging terrain, or unusual procedures associated with the arrival and go-around contingencies).
So what is the simulator for? Is it more for learning how to navigate from location to location, or how to land in different locations, or even how to avoid thunderstorms or how to deal with turbulence.
 

WeedWhacker

Senior Member
So what is the simulator for? Is it more for learning how to navigate from location to location, or how to land in different locations, or even how to avoid thunderstorms or how to deal with turbulence.

Landing, although certainly an important part of a successful flight ( :D ) isn't the primary purpose of a simulator (and the one being discussed RE: MH370 was a home set-up anyway --- no motion, no control feedback feel, etc).

A typical simulator training session (full blown full motion, the whole shebang) is about standard procedures and orientation and repetition, and Emergency and Abnormal drills. (Engine failures before V1 and an RTO, engine failure after V1 and the profile and procedures to follow, etc).

Also, a modern Level-D simulator is "Landing Certified", but this pertains to the regulatory requirement for currency --- at least three landings every 90 days is the minimum. What this means is a pilot transitioning to new equipment can accomplish all training and landing currency requirements without ever having to fly the real thing. In the past we would go out (usually late at night) on what we called Airplane Trainer flights, just to do the landings and complete the requirement. Expensive for the airline, in terms of fuel and added maintenance and airframe "cycles".
 

Jason

Senior Member
Landing, although certainly an important part of a successful flight ( :D ) isn't the primary purpose of a simulator (and the one being discussed RE: MH370 was a home set-up anyway --- no motion, no control feedback feel, etc).

A typical simulator training session (full blown full motion, the whole shebang) is about standard procedures and orientation and repetition, and Emergency and Abnormal drills. (Engine failures before V1 and an RTO, engine failure after V1 and the profile and procedures to follow, etc).

Also, a modern Level-D simulator is "Landing Certified", but this pertains to the regulatory requirement for currency --- at least three landings every 90 days is the minimum. What this means is a pilot transitioning to new equipment can accomplish all training and landing currency requirements without ever having to fly the real thing. In the past we would go out (usually late at night) on what we called Airplane Trainer flights, just to do the landings and complete the requirement. Expensive for the airline, in terms of fuel and added maintenance and airframe "cycles".
So basically the flight simulator he had in his house, is no more sophisticated than a Playstation 4 flight simulator game or even a PC flight simulator game at home. It seems like based on what you said above, only the full blown motion simulators actually simulate emergencies, and abnormal drills.
 

WeedWhacker

Senior Member
What is the procedure after a "Total Electric Failure"?

There usually is not a "total" failure, there is so much redundancy built in.

Here is an example of one page in a B767 QRH (the B777 will be similar):

Gen767.jpg

If you had two "Gen Off" simultaneously, then you would do this procedure for each. Meanwhile, you have the Standby Power from the airplane batteries, for essential controls and instruments and lighting.

Edit: I found the B767 QRH at the link below. It's a big file, over 4 1/2 mb:
http://fly.shanghai-air.com/flyiis/handbook/B767/767_QRH.pdf
 
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WeedWhacker

Senior Member
So basically the flight simulator he had in his house, is no more sophisticated than a Playstation 4 flight simulator game or even a PC flight simulator game at home.

That's right. Not certain what all he had, but there are many hobbyists who get very sophisticated (except for motion, and control feel I suppose).


You can buy all of those components --- instrument panels, control wheels and columns, center pedestal, the MFD (Multi-Function Display) screens (they're LCD panels), the FMC, the CDU, etc. Not cheap, though!!

Or, this might seem off topic, but I found it and thought it was interesting:
 
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Jason

Senior Member
There usually is not a "total" failure, there is so much redundancy built in.

Here is an example of one page in a B767 QRH (the B777 will be similar):

Gen767.jpg

If you had two "Gen Off" simultaneously, then you would do this procedure for each. Meanwhile, you have the Standby Power from the airplane batteries, for essential controls and instruments and lighting.
What is the procedure in a hijacking? Are the pilots supposed to let the hijackers take control of the plane, as in sitting in the pilot's seat, or are they supposed to talk the hijackers into letting them fly them to where ever they want to go? Or are they supposed to fight them fist and hand..
 

Jason

Senior Member
That's right. Not certain what all he had, but there are many hobbyists who get very sophisticated (except for motion, and control feel I suppose).


You can buy all of those components --- instrument panels, control wheels and columns, center pedestal, the MFD (Multi-Function Display) screens (they're LCD panels), the FMC, the CDU, etc. Not cheap, though!!
Wow, that really sums things up nicely. So the media went way over board with this simulator business, and it wasn't necessary...
 

WeedWhacker

Senior Member
What is the procedure in a hijacking?

Rather than write an answer here, I'll just say that what used to be (prior to 9/11) kept confidential within the industry is now actually public, and can be found online. Better course of action is to not blurt out things like that.

And also, I forgot which thread I was in, I thought it was the MH370 "speculation" thread (until I looked up top again) which is probably where this line of posts better belong (?)
 
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Jason

Senior Member
If these 'handshakes' were recorded by another device anywhere a much more accurate trajectory can of course be plotted.
I agree. Was this satellite the only satellite to receive these handshakes is a major question. Now they are saying the location of the downed plane might be north east by as much as 1100 miles due to the "newer" interpretation of the data. I think its a monumental task looking for this plane in the Indian ocean but there needs to be a better and more cost effective way of doing this. Especially if they are not totally sure about the data they are interpreting.
 
This update from the Malaysian Ministry of Transport gives a good overview of how the (very) rough location of MH370 final position was determined.

INFORMATION PROVIDED TO MH370 INVESTIGATION BY UK AIR ACCIDENTS INVESTIGATION BRANCH (AAIB)

25/03/14

....
From the ground station log it was established that after ACARS stopped sending messages, 6 complete handshakes took place.

The position of the satellite is known, and the time that it takes the signal to be sent and received, via the satellite, to the ground station can be used to establish the range of the aircraft from the satellite. This information was used to generate arcs of possible positions from which the Northern and Southern corridors were established.
....

I'm curious about the way Inmarsat drew the Northern and the Southern corridors.

For each handshake, Inmarsat must have recorded the time it took the signal to be sent and received, via the satellite, to the ground station. Then, the distance from the satellite is known. Which allows us to draw those arcs.

But, if we look at the map, neither the Northern nor the Southern corridor match the period when the plane suposedly flew west.

Moreover, when we add the Burst Frequency Offset analysis and plot it over the map, shouldn't it fit exactly over one of the two corridors?
 
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