|Quoting Pihero (Reply 36):|
He said that in his experience, the Satcom never ( stress never ) stops exchanging data with the satellite. the so-called "call every hour at fixed times" is a load of bull and these "handshakes" happen several times every minute.
To him, it is disingenuous to say that we only have ten loci... It could be one hundred and probably more...
(I went back to downloaqd the BFO diagram made public) and he said :"You see ? In the space of two minutes, they acknowledge at least thee *pings* and as far as I know, no message was exchanged then !
To counter such rather strong comments, we need to know for sure the satcom configuration of 9M-MRO
. Something the Malaysian Minister of Defense and/or MAS could have provided without breaching too much secrecy. But they never did.
Mandala499 discussed the configuration several times, starting in part 15, post 60:
9M-MRO does not have the High Gain Antenna.
It may have the Low Gain Antenna... but I can't confirm it due to its size, but there is a 3rd 'blade' (the front most) between the wing's trailing edge and the tailfin along the top of the fuselage.
There are many snapshots of 9M-MRO
on A.net. Some clearly show an Omni-directional Blade satcom antenna on top of the fuselage, for instance:
What I believe is a low gain satcom antenna is on the picture above the word "Malaysia" in red. I could not identify for sure the make and model of that antenna although I really tried (if you do know, please share!). Some antennas by Cobham, Honeywell and EMS look similar. My guess is that 9M-MRO
has an old ARINC 741 type antenna that is no longer sold. It was probably installed when 9M-MRO
was manufactured around 1998,
With that antenna and operating on Inmarsat 3 satellites, I surmise that 9M-MRO
was using a reliable but very low speed Aero L service (one of the Classic Aero possible services) , that offers packet data but nothing else.
Low speed means really low speed. The P channel continuously transmitted by the GES using the global beam to inform a/c and request actions by the a/c would operate at best at a speed of 1,200 bits/s. And since satellite transmissions can be affected by significant bit errors, I would guess that Inmarsat uses a strong coding rate (rate 1/2?) meaning that half of the bits transmitted are used to correct the other half that carries the actual message(s) from GES to a/c. 600 bits/s is indeed low speed.
Keep in mind that the P channel is not just for 9M-MRO
, but for all a/c in the footprint (about 1/4 of the earth surface).
When the GES generates what is referred to as a "ping", it is IMO just to determine whether the resources allocated to the a/c should be maintained or released. How does 9M-MRO
respond when it receives a message on the P channel with its own id. Within a set delay (essential for RTD measurements), the a/c must send a response on the R channel which is organized as a slotted Aloha channel. A slotted Aloha channel is like a roulette wheel. To send a response, the a/c must pick an empty slot and send its response in that slot. Easy enough you think except that the a/c has to pick a slot while being bind folded. The a/c cannot listen to the R channel (only the satellite at its position and with its large antenna can), therefore It cannot know which slots are empty or already filled or being filled by other a/c's somewhere, maybe many thousands of miles away. The a/c just has to chance it. Statistical analysis has shown that as long as the fill level is much lower than 30%, slotted Aloha channels work pretty well. Of course with unavoidable collisions and lost messages from time to time.
This rather long presentation is my attempt at convincing anyone who thinks that there might be 100's of hidden messages with 9M-MRO
in the background that Inmarsat is unlikely to have done anything that would incredibly reduce their already minuscule capacity.
I must admit that their is one possibility where such messages could actually exist but only for 9M-MRO
, not for other a/c's that were in the air at the same time. In my post #115, thread 48, I suggested the following:
ATCs around the world would only need to know how to perform an https logon to a central site where they could designate the aircraft to be added to the emergency watch list, together with its last known location. Inmarsat could automatically pick up that emergency watch list and via the appropriate earth station for each aircraft in trouble request a "enhanced ping" response.
The enhanced ping would just require that Inmarsat's GES keep one timer increment per aircraft rather than the same timer increment for all a/c's.
I don't believe that this is implemented today (ICAO would have to know and organize it ). Besides someone would already have boasted that they implemented and actually used such a neat feature..