After the second prototype was delivered, the aircraft was placed in the hands of a different test pilot, "Poručnik" (1st Lieutenant) Janko Dobnikar, who conducted its first flight on 24 August 1934. Dobnikar had worked closely with the designers and Ikarus during its construction and static testing, and his suggestions had resulted in an improved cockpit layout. He strictly followed a completely new test program, while installed testing equipment recorded the various characteristics of the aircraft. After gaining complete mastery of the aircraft, he conducted some aerobatic manoeuvres during a visit by the future Turkish president İsmet İnönü, which included a complete inverted loop. In mid-October 1935, Dobnikar used the second prototype to break the unofficial European air speed record for an aircraft with a fixed undercarriage, attaining a speed of , which was also a Yugoslav air speed record. The aircraft was able to achieve greater than expected power at altitudes of . Dobnikar completed the testing program and submitted his report to the VVKJ on 23 May 1937.