The ASBUs make it possible for air navigation service providers to form their independent implementation and investment strategy by selecting and implementing only those modules appropriate for their individual operational needs. The development of a business case is necessary to determine module cost benefit. The business case is discussed later in this booklet. The required technologies for Block 0 exist, and the associated operational capabilities of Block 0 have been implemented in some ICAO Regions. The Block 0 modules have initial operational capabilities (IOC) of 2013. They are therefore available for ANSPs’ and operators’ implementation. The modules assigned to Block 1 through Block 3 represent emerging operational improvements with IOCs for 2018, 2023 and 2028 respectively. The typical navigation planning approach normally addresses only the concerns of ANSPs. However,the ASBU methodology addresses standards,regulatory and user requirements as well.