OBS_VALUE: https://ec.europa.eu/transport/modes/air/ses_en; see also Regulation (EC) 550/2004 on the provision of air navigation services in the single European sky (the service provision Regulation) and Regulation (EC) 551/2004 on the organisation and use of the airspace in the single European sky (the airspace Regulation); also Presedential Decree 143/2017 on the EUROCONTROL