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Air Traffic Control Centres (ACC)
Basic Service is also provided by ACCs (Callsign London Information and Scottish Information) through an FIS Officer (FISO) operating on specially allocated RTF channels. In addition to the normal Basic Service, described above the FISO
will:
(a) On receipt of a request for joining or crossing clearance of Controlled Airspace or Advisory Routes either:
• Inform the pilot that he should change frequency in time to make the request direct to the appropriate ATC Unit
at least 10 minutes before ETA for the entry or crossing point
Or
• Obtain the clearance from the appropriate ATC Unit himself and pass it to the pilot on the FIR frequency.