Songbird :
An ATC system bases on fixed adherance to the flightplan is always impossible,
I disagree. Of course you may be right in the absolute , especially if you look at today's Procedural environement , when some procedural airspace ( e.g the NAT) move much more traffic that way than some radar airspace ( e.g Albania ).
But what I understood "aviadornovado" said was not that : I think he refered to FL allocation , and there, this is true , this method can be used to separate conflicting traffic procedurally from one another, both on crossing, and when on dual-directions tracks or aiwrways.
In the 1970,s there were aispace ( e.g Greece , pre-radar times or Siberia if you want some examples among many others) which had some airways restricted to a few FL only (250 280 and 350 for instance,) 15 minutes longitudinal. With a system like this you move 10 a/c an hour but it was sufficient and safe enough in those days. If Brazil has opted for a basic system like this on the Amazonas to compensate their lack of radar coverage, we would not be here today discussing their collision.
But then of course , Brazil would not move that many aircraft around as in the current system .