Following on from development of the L-39ZO, in 1976 the ninth and tenth prototypes were engaged in tests of the GSh-23 twin barreled machine gun and designated L-39ZA's. These two prototypes were complemented by the eleventh L-39 prototype X-11 on 16 May 1977. This was the first aircraft to be shown in the West at the 32nd Paris Air Salon in the same year. The L-39ZA can also be utilized for reconnaissance.