Originally Posted by
IRpilot2006
Surely any flight plan sent to Eurocontrol goes to all the sector controllers? What exactly is it that achieves the implicit enroute clearance?
The "implicit enroute clearance" is achieved by remaining in controlled airspace throughout the flight. If you leave controlled airspace, you need a new clearance to reenter.
The CFMU will anticipate the flight passing through standard airway sectors, without a detailed knowledge of what goes on at low level. It doesn't anticipate that at FL50 you will be talking to Solent rather than London, which looks after the airspace above.