ICAO provisions require that the implementation of specified reduced separation minima, e.g. 50 NM lateral separation based on PBN RNAV 10, 50 NM longitudinal separation based on PBN RNAV 10 and Direct Pilot Controller Communication (DCPC), and PBN RNP 4 based 30 NM lateral and longitudinal separation abased on Automatic Dependent Surveillance – Contract (ADS-C), Controller Pilot Data Link Communication (CPDLC), must first meet Annex 11 safety management system requirements and undergo a safety assessment based on collision risk modelling to confirm that the regionally established target level of safety (TLS) for the airspace has been met. Additionally, periodic safety reviews must be performed in order to permit continued operations. To, date the performance of safety assessments and continued monitoring for reduced horizontal separation minima had been carried out by a few specialized teams of technical experts and contractors supporting States within the region.

The recent inclusion of the previously independent RNP and RNAV concepts under ICAO’s global PBN concept has led to some uncertainty amongst States regarding the monitoring requirements for reduced horizontal separation minima implementations where these minima are based on PBN approvals. The Asia/Pacific Air Navigation Planning and Implementation Regional group in 2004 established the Regional Airspace Safety Monitoring Advisory Group (RASMAG) to achieve a regional approach for coordination and harmonization of airspace safety monitoring activities, and to provide assistance to States in this respect. RASMAG agreed that there was need to standardize the principles and practices of assessing the safety performance of implementations utilizing reduced horizontal plane separations, in order to ensure the continued safe application of reduced horizontal separation standards in international airspace.

In anticipation of more widespread use of the PBN RNAV 10 and RNP 4 navigation specifications within the international airspace of the Asia/Pacific Region, the EMA Handbook was provided to identify the safety assessment and monitoring requirements and related EMA duties and responsibilities associated with those navigation specifications, as well as the reduced separation minima which may be implemented based upon compliance with them.