The European Union Aviation Safety Agency has published a regulatory proposal to enable and support operations in the single European sky (SES) airspace. Notice of Proposed Amendment (NPA) 2023-04 addresses two different subject matters: the use of airborne collision avoidance system (ACAS) Xa and the harmonised use of performance-based navigation (PBN) specifications for oceanic operations. The proposal enables the use of ACAS Xa in the SES airspace, as one of the Single European Sky ATM Research (SESAR) solutions that has been standardised and adopted as an International Civil Aviation Organization (ICAO) standard. The ACAS X technical specification order, installation requirements for ACAS II (including ACAS Xa) as well as updated ACAS-related Air OPS material are included in the proposal. The proposed amendments on ACAS X transpose related ICAO Standards and Recommended Practices (SARPs), improving harmonisation and introducing operational and safety improvements.This NPA also proposes amendments to the airspace usage requirements in Regulation (EU) 2018/1048 to transpose additional ICAO PBN specifications in support of oceanic and remote continental operations, in particular the RNP 4 and RNAV 10 specifications. The guidance material to the Regulation is also proposed to be amended to be consistent with the regulatory requirements. This proposal would ensure an effective transition to a PBN operational environment in the SES airspace.The proposal is open for public comments until 28 August 2023.