On 4 November 1969, the L-39 (under the designation "Prototype X-02" – the second airframe to be built) conducted its maiden flight, for which it was piloted by Rudolf Duchoň, the factory's test pilot. Serial production of the initial model of the L-39, designated "L-39C", commenced in 1971. In 1972, the L-39 Albatros was formally recognized by the majority of the countries comprising the Warsaw Pact as their preferred primary trainer, after which point, sizable orders from military customers throughout the bloc proceeded, many of which were from the Soviet Air Forces. In 1974, the first L-39 trainer entered service with the Czechoslovak Air Force.