The DANUBE FAB airspace structure became more flexible and adaptable, enhancing capacity, with a balance between the requirements of civil and military use.
Environmental requirements were taken into account in the process of redesigning the route network. Reconciliation of the different requirements is met through different airspace configurations. Each airspace configuration consists of different sectorisation adapted to the traffic structure and free route configuration was applied to a maximum extent.
The rationale of Cross Border Provision (CBS) of ANS was set out in the Article 20 of the DANUBE FAB Agreement. The intent of DANUBE FAB to implement CBS and further optimise the airspace boundaries of the States was clear throughout the development phase of the project.
Following the establishment of DANUBE Functional Airspace Block (DANUBE FAB) the two partner States of Romania and Bulgaria implemented two cross-border sectors on 11 December 2014, the first time that cross-border sectors have been implemented under a FAB framework.