Complex sentence: The aircraft's maiden flight occurred at Zhukovsky on 2 April 1996, at the controls of Yevgeni Frolov; the nozzle, however, was locked fully aft, and it was not until the sixth flight that tests on the thrust-vector nozzles commenced.
Split into simpler sentences: The aircraft's maiden flight occurred at Zhukovsky on 2 April 1996, at the controls of Yevgeni Frolov. The nozzle was locked fully aft throughout the flight, and it was not until the sixth flight that tests on the thrust-vector nozzles commenced.