7. With the aim of improving the level of performance of air traffic management, several Member States may develop a joint performance plan for en route air navigation services and, as appropriate, for terminal air navigation services. This plan shall at least cover the duration of one reference period, include at least one joint performance target and involve cross-border cooperation. The cross-border cooperation may include joint procurement with a view to improving interoperability and joint governance in order to optimise the use of airspace.