Sukhoi Su-57 T-50

The T-50's maiden flight was repeatedly postponed from early 2007 after unspecified technical problems. In August 2009 Alexander Zelin acknowledged that the engine and technical research issues remained unsolved; that same year Mikhail Pogosyan announced first that the airframe was almost finished and the first prototype would be ready by August, then in August that the flight would come by year's end. After Sergei Ivanov announced in December 2009 that trials would begin in 2010, the first taxi test was completed on 24 December 2009 and T-50-1 flew on 29 January 2010 with Sukhoi test pilot Sergei Bogdan at the controls, a 47-minute flight from KnAAPO's Dzemgi Airport in the Russian Far East.

Prototype construction progressed more slowly than planned: by the end of October 2013 the test programme had amassed more than 450 flights across five aircraft. Ten flying and three non-flying T-50 prototypes were built in total for preliminary flight tests and state trials, against the six initially planned before serial production. Testing revealed that the early prototypes lacked adequate fatigue life, with structural cracks forming early in the airframe.

That finding forced a structural redesign: increased composite usage, a reinforced airframe meeting full life-cycle requirements, an elongated tail sting and slightly greater wingspan. The sixth flying prototype was the first of the redesigned "second stage" aircraft, with the five earlier ones consequently treated as "first stage" vehicles needing extra reinforcement to keep flying. The last two flying prototypes were test articles of the production Su-57 with full mission systems on board. Although the redesign curbed weight growth, normal takeoff weight still rose to roughly 26,700 kg.

The fifth flying prototype, T-50-5, was severely damaged by an engine fire after landing on 10 June 2014; it was written off and its salvageable parts were cannibalized to finish the sixth "first stage" prototype, which inherited the fifth's bort number and was redesignated from T-50-6-1 to T-50-5R. The second flying prototype was used from 2017 to test the izdeliye 30 engine and the third (bort no. 053) was configured in 2018 for teaming trials with the Sukhoi S-70 Okhotnik UCAV. T-50-4 went on static display at China's Zhuhai Airshow on 4 November 2024. Issues and accidents during testing pushed delivery of the first production aircraft back from 2015 to 2020.