At that time Balkan Bulgarian were using the Tu134A, Tu154B and also the Ilyushin IL18 on IT services from the UK. I was a Traffic Officer/Load Controller at Stansted then, and we used to see all of these on services to both Bourgas and Varna in the summer and ski flight services to Sofia in the winter season. The type was always determined by the booked loads at the time. Sometimes we would only have confirmation of the type we were going to get when the departure signal from Sofia operations came through, which would only gave us around 3 hours to match the load planning to the aircraft type that was coming. I used to look foreward to the apple juice that the cabin chief always offered to us on the turnround:)