Stanev, Hristo. “STATUS OF AIR NAVIGATION MANAGEMENT SYSTEMS WITH STATE AIRCRAFT IN THE REPUBLIC OF BULGARIA AND ITS NEIGHBORING COUNTRIES”. KNOWLEDGE - International Journal 53, no. 1 (August 15, 2022): 215–222. Accessed June 9, 2026. https://ojs.ikm.mk/index.php/kij/article/view/5502.