 The development of the T-10 was marked by considerable problems, leading to a fatal crash of the second prototype, the T-10-2 on 7 July 1978, due to shortcomings in the FBW control system.Extensive redesigns followed (T-10-3 through T-10-15) and a revised version of the T-10-7, now designated the "T-10S", made its first flight on 20 April 1981.It also crashed due to control problems and was replaced by T-10-12 which became "T-10S-2".