Navigator wanted
 

Pontius Navigator. Thanks for the excellent explanation, I did not consider the ground speed changing the track. You did remind me to consult my 1975 Ground studies for pilots, and perhaps navigators used to 50s and 60s radio and star navigation could solve the problem.

Thanks for clearing that up, I knew about the Poseidon capability and saw the first post about AMSA Orions, I missed the second

UK telegraph claims to have ATC transcript.

Has anyone seen it?

Agreed, just as with B-777 pax O2, don't assume all P-8's have the same inflight refueling capability or that the crews are current and trained.

For example, most P-3's don't have inflight refueling capability, the P-3F's sold to Iran do (or did, its been a long time since they were delivered).

Sadly that was simplified. You would also have to consider the width of each arc. You could also refine (complicate) the groundspeed
vector by applying wind to assumed airspeed.

Aerials
 

Rather than some catastrophic loss of transmitting devices (VHF/HF radios, transponder/ADS-B, ACARS etc, is there any event that could cause all the relevant aerials to become inop, for eg does their wiring converge on some point, but would still enable the aircraft to be flown (albeit erratically) by a hypoxia affected pilot ? #clutchingatstraws

Has been debunked by another eyewitness having seen it on the Andamans .:eek:
Malaysian woman 'saw missing MH370 in water near Andaman Islands' | Mail Online

The Andaman Island question:

Trying to figure out why the Malaysian lady and her "sighting" from an aircraft (up high) near the Andaman Islands, as reported in a link further up, is being discounted. (There may be a lot of good reasons to do so).

Is the estimated position of her reported sighting too far from the north arc?

Her reported time of seing something is six to seven hours form the last "ping" that the Inmarsat folks have reported as registering on their satellite.

If the assumptions of last speed, or last altitude, or both are wrong ... is the locale where she thinks she saw it close enough to that arc/estimation to be worthy of investigating?

I am looking at maps, thinking about times, and that if the aircraft descended, and/or slowed down, for some reason, the furthest on circle shrinks a bit, and the fuel would run out sooner.

Some (Inconclusive) INMARSAT Info
 

A few definitions:

In the following the aircraft can be referred to as the UT (user terminal) or the AES (Aircraft Earth Station).

In the FCC documents, "downlink" is from the satellite, "uplink" is to the satellite. Don't guarantee that other documents follow that, have seen the terms reversed elsewhere, so one needs to skim any given document to get the sense of how those terms are used.

A few caveats:

The satellite antennas are not angle sensing, per se (e.g., no 4-horn feed or whatever). Spot beams and regional beams would have nominal angles relative to a satellite-fixed frame that would be known to the satellite operator. The documents linked do not contain a detailed frequency plan, but it seems reasonable that any pair of adjacent beams would employ some frequency separation.


A 4 MB "INMARSAT 101" briefing from 2009:

http://www.satcomdirect.com/connect/...rsat%20101.pdf

Slides 32-33 show coverage for IOR and POR. Slide 17 says that Generation 3 satellites have 7 spot beams, so the numbers in the plots on Slides 32-33 appear to be the spot beams.

Slide 33 is actually moot, since the current POR satellite is Generation 4, located nearly 40 degrees further West in longitude:

LIVE REAL TIME SATELLITE TRACKING AND PREDICTIONS: INMARSAT 4-F1

MH370 should have been closer to the POR satellite at takeoff, and possibly within its field of view throughout much of its flight.

Haven't seen any "credible" statements of which INMARSAT satellite was providing the "ping" data. It could make a big difference, since the Generation 4 satellites (e.g., POR) have many more spot beams, which could help in the aircraft location.

FCC document that describes INMARSAT Block 3 communications (the Indian Ocean Region satellite is a Block 3):

https://licensing.fcc.gov/myibfs/dow...nt_key=-136047

FCC document that describes INMARSAT Block 4 communications (the Pacific Ocean Region satellite is a Block 4):

https://licensing.fcc.gov/myibfs/dow...ent_key=-94644

"The Inmarsat 4F2 satellite, licensed in the United Kingdom, will provide Mobile-Satellite Services to small User Terminals (“UTs”) . . .

The BGAN UT’s start by searching for the global beam signaling carrier. When acquired, the global beam holds information on any underlying regional beam channel the UT can use for registering on the network. No return communication is carried out in the global beam. The selection of regional beam channel is based upon UT GPS position and spot-beam maps or carrier C/No scanning. Once the correct regional beam has been acquired, the UT will attempt to register using either slotted aloha random access or un-slotted (in case the UT does not have its GPS position available) aloha random access on dedicated logical channels.

After registration the UT is handed over to a spot beam whenever a communications session is started. After the communications session has ended the UT is moved back to the regional beam to preserve resources in the spot beams."

"Regional Beam Signaling:
In the regional beam, two 50 kHz signaling carrier types are used for the BGAN. The modulation
is either 16QAM or QPSK.

The Return direction is used for the UT’s to register onto the network. Depending on the UT Class (1, 2 or 3), the UT will register using any combination of burst characteristics that closes the link. The return signaling carriers are either 25 kHz or 50 kHz and the modulation can either be QPSK or 16QAM."

It's not all that relevant, but if anyone gets hung up on the aloha protocol:

ALOHAnet - Wikipedia, the free encyclopedia

A draft RTCA spec with some system description for the latest version of ACARS (SBB, the broadband service with lots of spot beams):

http://www.icao.int/safety/acp/ACPWG...20Material.pdf

On pg. 35, it mentions "performing link tests (keep alives)". Using those keywords in web searches doesn't seem to turn up much more than using "pings".

The document also mentions an "ICAO 24-bit aircraft address". That allows over 4 million unique addresses, though the bits may be allocated less efficiently (e.g., using BCD). Whatever, that identifier is likely part of the aircraft response to a "ping", hence uniquely identifying MH370.

Civilian aircraft won't have an IFF.

Sure they will: it is called a transponder, Mode 3/C.

"IFF" is a term used for transponder. Most mil transponders I worked with had modes I, II, III/C, and IV. The kit someone was painting your with would determine what part of the system responded to you.

Mode III/C interacted with standard air traffic control radar systems. A mil operator can refer to a standard civil transponder's response as an IFF (Mode III/C) reply to his interrogation. The advantage of this is that you only need one piece of kit to send out replies to interrogations via the antenna.

Anything to add? Anybody? Please feel free!
 

I'm sure most of us ("real" ppruners) recognized a long time ago: this topic is going around and around circles without anything valuable added for a long time now. Obviously, nobody takes the nuisance to read previous posts.
So: Anybody to come up with a timeline again... and again? More self made maps? More wild ideas? Conspiration theories repeated dozen times? Something again on "PINGS" ( oh, God I learned to hate this tiny world)? Something technical again on transponders? And you, search and rescue experts, want to repeat your opinion on awashed containers? Preconceptions on poor pilots experimenting with flight simulators at home (I know a couple of them, including myself) just for fun and because they love their jobs, addicted to aviation? I just hope we are not terrorists.. eeer.. I have to double check that...
PLEASE FEEL FREE TO POST THE SAME RUBISH AGAIN and AGAIN! We could barely wait to read the same thing again. Hey, PPRUNE hase a huge server, they can cope with it I'm sure.
PPRUNE (and us, "real experts") wasted 350 plus pages of this topic for nothing. Nothing new, nothing to learn, no knowledge to share, absolutely nothing.
Only one consolation: It seems that most of the professional ppruners left this topic for good reason...and I will do the same.

Hoegh St. Petersburg should have been in the area for a while now and no news from them. Perhaps the only way to find MH370 is if the US Navy sends a sub into the area. They would have the technology to hear the pinger a long ways off.

Timing "pings" and accuracy
 

My first post on this site :O – please be gentle! :uhoh:

I am a telecoms engineer, nothing to do with aviation.


Pings – let’s see if we can sort this out.


The satellite is always transmitting. Think of it as a steady “tick” from above. The receiver, not the ACARS system, or any other similar higher function in the plane, just the receiver is always listening to the tick. IN fact the receivers on all the planes and boats are listening to the "tick". By clever encoding the “tick” carries information to say “this is the start of my sequence of messages” at defined intervals, and then it sends data intended for specific receivers in various time slots. Of course, all receivers "hear" all the messages, but they only actually “listen” to the ones intended for them. But the background “tick” keeps going all the time, so every receiver can synchronise itself all the time, keeping track of where the sequence of messages starts, just listening and waiting for a message from them. When a receiver recognises a message is for that particular receiver (i.e. plane), of course it “listens” to the message and acts accordingly, passing the message on to the appropriate unit where necessary. But one of these messages it watches for is a message saying “are you still there”. When it gets that message the receiver has to reply in the correct “slot” to say “still here”. So now the sat system on the plane has to transmit to reply. In this case the reply is effectively an automatic response from within the satellite receiver – nothing else needs to be involved.



But notice the response to the “are you still there” message has to be sent in the correct time slot. Remember the receiver is listening to the “ticks” from the satellite all the time – not just when there is data to exchange. All the time, so the plane has a “clock” ticking at the same rate as the satellite’s clock. But, the plane’s clock is running late all the time as it takes time for the “tick” sent out by the satellite to travel the 35,000 km to the receiver. The equipment on the plane then has to reply in the correct slot after it has received the “are you there” message and so it replies. Now, the satellite has a problem. Because it does not know how far the plane is away, it actually does not know when the reply to its message is going to arrive. It cannot do what the plane has done and keep a “copy” of the plane’s clock ticking away because, firstly, the plane is not transmitting its own “tick” for the satellite to follow, and in any case it would need to have a similar clock running for every plane and ship using the service. In any case it does not need to.


What it does is allow a window for the return message to arrive. It has a petty good idea since it knows the earth is 35,000 Km away as a minimum, less the altitude of a plane, of course. It knows that the “receiver” has to respond so many ticks after receipt of the request. It knows the receiver has a good clock tick signal – it is the very signal the satellite is transmitting. So it has a time window when a response can be expected. The reply will arrive at the early end of the window if the message is from a transmitter directly under the satellite, later from one at the edge of the coverage, earlier from a plane than from a ship etc.
Now, here is the bit I have not seen mentioned before. The “tick” is related to the frequency of the satellite’s radio band. It has little to do with the relatively slow rate at which data can be sent over the communications channel. The frequency of Inmarsat C is around 1600 MHz. That is 1,600,000,000 “ticks” a second. So the timing resolution the satellite can see is to an accuracy of 1/1600000000 of a second. Light is fast. But the amazing speed of electronics we now have is such that we can measure time with astonishing precision. Just think about those laser tape measures you can buy. You can measure a distance to a millimeter, and they work by timing pulses effectively, all in something you can buy for a few £/$/Eu. Think about a GPS set. An ordinary GPS set will give you a position with in a few metres, limited not by the ability of measure time, but by various vagaries in the transmission of the signals. A “pro” surveying GPS set does clever things to reduce the vagaries, and while it may take a few minutes to give a good “fix” they can give your position to typically 15mm accuracy. Given longer to analyse and process the signals, weeks in some cases, to an accuracy of considerably less than 1mm. Note, accuracy, not resolution. Absolute accuracy, and all without a fantastically expensive atomic clock at the “user end” though there are several in each orbiting GPS satellite.


So, back to our satellite. It was expecting a response at “tick” number XYZ and it actually arrives at “tick” number XYZ + whatever. It knows, because it is in the standard, that the receiver on the plane is obliged to reply exactly N ticks after receipt of the request, so by subtracting N from XYZ + whatever it knows how long the message has taken to transit to the receiver and back again in “ticks”. Halve that and you have how many ticks away the plane is. One “tick” is 1/1600000000 of a second. In a vacuum- and remember part of this journey is not in a vacuum – 3 x 10 to the eight metres. So, divide this by 1600000000 i.e. by 1.6 times 10 to the nine and you get about half a metre as the potential accuracy (the satellite will have a VERY accurate clock onboard) and resolution of ths measurement. In principle the satellite could determine how far away the responding receiver/transmitter was to a precision in the order of a metre. In practice there would be no point in measuring this accurately and in any case the presence of the atmosphere and variations in the precise timing in the receiver makes this rather “optimistic”. These are, after all, communications systems not navigation systems. The satellite does not need to know to this level anyway, it can work with signals arriving in the allocated window.


This is a very simplified explanation, not always desperately accurate, but basically shows how it works. For example the frequency used for the plane to reply is actually slightly lower, but it will be locked to the satellite’s transmission clock tick.


As a further explanation, think of a lighthouse flashing away constantly with a constant beat. It flashes white. You sit and watch holding a torch. You watch and watch and tap your foot to the beat of the white light. You are told that if the light flashes red you MUST flash your torch back three beats later. And you do exactly that, exactly three beats later. The man at the lighthouse is watching and from his point of view he sees a torch flash back not three beats later, but three and a bit beats later. The three beats if the time you have been allowed to wake up, get your finger on the flash button, the “and a bit” is the time it has taken the light to get from his lighthouse to you plus the time it has taken your torch light to get back. Clearly in this case you could not measure the distance in this way, but you can see the principle.


As has already been shown, the satellites are at a very precisely known height over the earth, so equal distances from the satellite are where concentric cones intersect with the earth – circles on the earth’s surface representing equal elevations of the satellite.


My suspicion is, and I say no more than a suspicion, that the satellite’s system can also measure the frequency of the reply accurately and so have some estimate of the relative velocity of the plane relative to the satellite, but the geometry will limit how much use this would be. Clearly the plane’s altitude when transmitting is relevant; you would not be able to differentiate between a low plane nearer the point the satellite sits over and a higher plane further away.


I also suspect that the satellite would keep a log noting that it had received a response the “are you there” messages at such and such times, but it would only keep the technical details of the latest transaction, as this would help in allocating its time slots efficiently. Remember, while memory to hold this sort of data is cheap, on a satellite power is the limiting factor all the time, and weight adds to the “delivery” cost of getting these things up there. So the commercial birds would not want to retain data that they did not need to hold for longer than necessary. The logs may be downloaded to the ground too, but even downloading takes power.


Hope that helps. I have been reading all the posts since this thread opened. There are some on here that simply waste effort – and show complete disrespect, but there are some incredibly insightful and helpful posts here conveying real information. Not all are “hard” facts, but many are fascinating, like the description of what it is really like in a search plane. Many thanks to the posters.

Nope. Transponder Yes
IFF NO

I imagine she was directed there to go to anything the aircraft found. For her to spot anything herself would be most unlikely. From a ship, spotting something awash in the water, not a 24 m item, such as a seat cushion or small debris more than 200 metres from the ship would be very lucky indeed.

If a aircraft spotted something they would drop a sonobuoy to mark on top and then direct the ship to the spot while remaining on top until either relieved by the ship or another aircraft.

And Balaton, some of us are trying to fill gaps or correct media comment while trying to avoid feeding parrots and trolls.

Ozlander, the OP concerned how military radar could identify an aircraft without IFF. Lonewolf beat me to it so I deleted my post but is contextually correct.

Not so. If the inputs are screwed up, because a sensor is thrown out of calibration from heat or other damage, you could get a specific fault. Heat can cause added resistance, that makes 5 volts, which would be a "1" in binary, low enough, where it shows up as 0 volts, which is a "0". This could feed some radical numbers into the brains of your "complex electronic systems", and cause an intermittent, as the sensor heats up or cools, or consistent, but specific failure, , due to ambient temperature change. I think such a failure of some acceleration sensors was the cause of the Malaysian 777 stall in 2005.

Lazier dog

10 minutes ago was listening to the owner of the ship who gave an update on what the ship was doing, weather etc. he also said the ship was taking instructions from AMSA and all communication was with or via them and they were following their instructions.

Mk 1 eyeball was being used with binos. Weather ok, sea fog was a problem yesterday.

A backtracking exercise from the 40° arc positions supplied to AMSA using 470 kts ground speed, leads to a likely position outside PSR range west of Banda Aceh. The hourly positions have the appropriate SAT elevation circle drawn through them, though the actual elevation is not shown.

A previous post has been updated.

Note the comments about the projection used.