on 29 july 1985, the prototype for the type, designated as the "xt-4", performed its maiden flight. reportedly, test pilots of the air proving wing who flew the xt-4 observed the type to have greater subsonic manoeuvrability than the mcdonnell douglas f-15 eagle, an agile aerial supremacy fighter. speaking in the months before the xt-4's maiden flight, kawaski publicly claimed that the aircraft possessed the highest performance of any subsonic trainer aircraft then available. despite the limited available of the f3-ihi-30 engine, it proved to be fortuitously reliable, preventing any serious limitation being imposed on the wider test programme. flight testing with the four xt-4 prototypes ended after two and a half years and roughly 500 individual flights made; in response to the feedback produced, only minor changes, such as improved brakes and refinements of the hydraulically actuated flight control system, were made.