A US Navy maritime patrol plane took off from Varna and kept watch off the Bulgarian coast on Wednesday, 4 November. A NATO AWACS early warning plane and an air tanker were also flying over the Black Sea and south-eastern Europe at the time, according to flight-tracking data analysed by a specialist aviation website.
The Varna plane is a US Navy Boeing P-8A Poseidon, registration number 170269. It flew a series of routine patrol routes along the Bulgarian coast and tracked ship traffic and the situation in the western Black Sea.
More on this story: Radev: US plane is already scouting for risks over the Black Sea
The P-8A is built mainly for maritime surveillance. The website calls its flight the most important of the three missions. It says the mission appears to have focused mainly on the sea, unlike reconnaissance flights further from the region. The base in Bulgaria gives the plane access to the country's territory and logistics, and to the Black Sea at the same time, the website adds.
The second plane is an Airbus A330 MRTT, registration number T-058, call sign MMF18. It belongs to NATO's Multinational Multi-Role Tanker Transport Fleet. The tanker took off from Cologne, flew a mission over Romania and made holding patterns near Brasov. The website says this suggests air-to-air refuelling or related training.
MRTT planes let combat and reconnaissance aircraft stay in the air longer and operate far from their bases.
The third is a NATO Boeing E-3A Sentry AWACS, registration number LX-N90442, call sign NATO001. It took off from Geilenkirchen air base in Germany. The plane handles early warning, air surveillance and coordination between military units.
The three types of aircraft, for sea patrol, early warning and refuelling, complement each other and together give a fuller picture of the situation, the website says. The flight-tracking data alone cannot show whether the three missions were directly coordinated.
Military activity in the western Black Sea is closely watched, and shipping lanes there are protected. Russian attacks continue to hit commercial shipping linked to Ukraine.
The website says the flights show how important Bulgaria and Romania are to NATO surveillance in the region. It says they also show that the alliance can monitor the area continuously by combining reconnaissance planes and air support aircraft.