The Bk-534 was designed to carry one 20 mm (0.79 in) Oerlikon FFS-20 cannon firing through the nose, along with a pair of 7.92 mm (0.312 in) machine guns to the sides of the fuselage. By the summer of 1938, Czechoslovakia, sensing rising political tension caused by German claims to Czechoslovak border territory, was eager to get more aircraft in the service, thus Avia decided to use a third machine gun in the nose. However, there have been claims that the company had encountered substantial difficulties in adapting the aircraft to accommodate the additional weapon and these were not quickly resolved. Judging by the size of the gun magazine, the nose machine gun was matched with an increased supply of ammunition. Consequently, however, the fuel load was decreased