[Chris A]

Wenn man lange sucht findet man auch was.
Auszug aus einem Booklet von Eurocontrol:

The FUA concept is based on airspace and route structures that are especially suited to temporary
allocation and utilisation on a daily basis by the national Airspace Management Cells (AMCs) such
as:
• Conditional Routes (CDRs) which are non-permanent ATS routes subdivided into three
categories CDR 1, CDR 2 and CDR 3 according, mainly, to their flight planning possibilities;
CDR1 : Permanently plannable CDR during the times published in the AIP
CDRs 1 will be flight planned the same way as permanent ATS routes during the times
published in the AIP. In the event of a short notice unavailability of a CDR 1, rerouting around an
associated AMC-Manageable Area will be made on ATC instructions.
CDR 2 : Non-permanently plannable CDR
Flights may only be planned on CDRs 2 in accordance with conditions published daily in the
Conditional Route Availability Message (CRAM). Details of the availability, conditions and use of
CDRs 2 will be published in the CRAM and disseminated to operators for flight
planning purposes.
The CRAM will cover the 24 hours time period between 0600 the next day to 0600 the day after.
CDR 3 : Non-plannable CDR
CDRs 3 are published in the AIP as CDRs usable on ATC instructions only.
Therefore flights cannot be planned in advance on CDRs 3.