The F.IX, a 20-passenger airliner, two of which went into service KLM, was built under license in Czechoslovakia.
Though the Avia works produced some of Europe's best fighters between the world wars, it was not judged economically feasible to attempt a heavy bomber. Accordingly, Avia, obtained a licence for the Fokker F.VII/3m, the pre-eminent civil transport of the 1920s, and while producing this for civil use also schemed a bomber version. The Czech army/air force, however, judged this aircraft too small. The upshot was a further licence for the Fokker F.IX, considerably bigger and weighing more than twice as much.
In 1932, Avia built 12 F.IX bombers, powered by three Walter Jupiter VII engines rated at 450 hp, carrying an internal bomb load of up to 1500 kg (3307 lb) and with any of a variety of armament schemes involving manually-aimed Vickers 7.92-mm (0.312-in) Mk 30 guns above and below the fuselage and firing from beam windows. Some aircraft had a retractable ventral 'dustbin'.
The Avia F-IX was used only in a bomber version through the 30s until the March 15, 1939 German Occupation.
Jugoslavia bought two slightly modified aircraft designated F 39, powered by 560 hp Gnome-Rhone Jupiters, and obtained a sub-licence for this version.