O I C. Before 9/11 traffic levels were rising year on year at about 6%, so saturation point would have been very much more quickly reached than at current traffic levels (although they are rising on internal flights with the boom in low cost carriers). I should think that the CBA in '98 was based on the pre 9/11 traffic levels and predictions.
RF congestion has been addressed to some extent by the introduction of 8.33 frequency spacing.
NAS is the UK's Flight Data Processing computer system and is absolutely integral to ATC in the UK. It processes the flight plans it gets from Brussels and distributes the flight data to all the relevant ATC sectors. It allocates the mode 3A code. It sends beacon estimates to units external to the NAS system and internally to NAS equipped units.
The reason it can send estimates is because it is linked into the UK radar system and tracks flights using their SSR code. NAS will 'watch' for an aircraft to get airborne and when it 'see's' the squawk it pairs it to the flight plan which NAS allocated the squawk to. It then tracks the flight and 'knows' its route, hence Flight plan Aided Tracking (FLAT). In addition to using radar NAS has a simple 'idea' of particular aircrafts speed, climb rate, rate of turn etc. plus it uses forecast upper winds to give estimates for beacons along the flights route. As an aside it is this 'idea' which we are very keen to have modernised to vastly improve our trajectory prediction (TP). More upper winds put into the airspace model, more realistic aircraft performances based on length of flight etc. The more accurately we can predict an aircraft's flight profile the more accurately we can predict where it'll be in the future and hence a big step forward to medium term conflict alert instead of our current short term version.
Not unusual for NAS to pair a track to a flight if, say the pilot has input the wrong squawk. Once the aircraft squawks the correct squawk its necessary to 'break' the pairing to allow NAS to correctly pair it up again. I have to admit I did not understand the technical reasons why it is possible to have more than one aircraft on the same squawk and still have the correct callsign etc. showing on the radar. Our 'professor' talks a much higher language than us mere mortals
but he assures me it is feasible.
However I think I may have lead you slightly up the garden path because I'm talking about UK and I suspect the real problem lies within the ORCAM region, but I don't know.
Sorry to burble on at length but couldn't think of a way to precis things. And if anyone can provide a better explanation of NAS than my rather off the cuff one please feel free to correct me
