Dick, it wasn't a radar/non-radar division. ATC had huge non-radar areas. As for the low level FS areas, it had a lot to do with radio coverage. ATC needed to use reliable VHF radio to keep in constant communication. Any ATC instructions relayed through FS HF and VHF were time consuming. The technology just didn't exist for nationwide VHF coverage. As VHF coverage improved, FS was no longer required. As FS wound down, training courses stopped an the FS average age increased. Another reason why the majority of FSOs took redundancy.