Annotation: Abstract. Due to the current situation in the Eastern part of Ukraine and Autonomous Republic of Crimea (ARC), there was an urgent need to introduce changes of the Ukrainian air traffic management (ATM) system and to the air navigation services (ANS). Those ATM/ANS changes concerned both the Ukrainian national airspace and the airspace over the High Seas, where the responsibility for ATS is delegated to Ukraine by international agreements (hereinafter - airspace under the responsibility of Ukraine). Those changes were aimed at ensuring safe and continuous provision of air navigation services in the airspace under the responsibility of Ukraine. The airspace under the responsibility of Ukraine is that within the boundaries of the Flight Information Regions (FIRs) in accordance with the basic principles of the Convention on International Civil Aviation. Ukraine provides air traffic management in the airspace over the High Seas on the basis of valid bilateral and multilateral agreements with the neighboring countries, including the Russian Federation, based on the ICAO Council Decision of February 17, 1997 (No. EUR/NAT96/38-ATS).