functional airspace block
as defined in Regulation (EC) N o 549/2004 of the European Parliament and of the Council of…, Article 2, point (25) (Definitions)
25.
‘functional airspace block’ means an airspace block based on operational requirements and established regardless of State boundaries, where the provision of air navigation services and related functions are performance-driven and optimised with a view to introducing, in each functional airspace block, enhanced cooperation among air navigation service providers or, where appropriate, an integrated provider;