Quite often I spot on FR24 flights between BZZ and MPN -- military and civilian. These flights technically traverse COMODORO and EZEIZA FIRs before going into MONTEVIDEO FIR. I have wondered for some time whether these flights file flight plans and interact with the Argentina FIRs. Anyone out there would happen to know?
The civilian airlines that fly the route certainly file flight plans, the routing in on FR24. Now, they don’t have overflight permits for Argentina and remain in international airspace. Both FIRs would control them as Argentina has no sovereign control over them. Curiously, Jepp manual has nearly zero information, all military AIP.
The FIR boundaries don't automatically correlate directly with national boundaries. The flights are operated in international airspace and they are in contact with the relevant ATC units throughout.