Dietrich E. Riemer, Bulgarian Badges Witnesses of History, BM-Trade , Sofia, 2007, p. 133 writes this could be a WW II Air Force Flight Instructor badge, but strongly suggests this could be a fake or a fantasy badge made up with parts of authentic badges.
Prof Petko Pavlo does not mention it in the Air Force section of his Bulgarian Military Decorations, PHP Publihing House, Sofia, 2007.
Sorry for the bad news ....