An Airborne SpacingApplication (ASPA) instruction,and more specifically an ASPAS and M (for enhanced sequencing and merging) instruction contains an ASPA SandM manoeuvre as an element indicating the way the time spacing has to be acquired. Three manoeuvres can be requested from the trailer aircraft: - Remain behind, - Merge then Remain behind, and - Vector then Merge (then Remain) behind. Once the spacing is acquired, the three manoeuvres behave the same way i.e. maintain the requested spacing within the requested tolerance.