The same month, General Director of Tactical Missiles Corporation (KRTV) Boris Obnosov reported, a contract for serial production of ammunition for Su-57 fighters was signed, and is being inducted. Serial production of the aircraft began in July 2019, with the first production aircraft scheduled to be delivered by the end of the year; following the crash of the first production aircraft, the Russian Aerospace Forces took delivery of its first Su-57 in December 2020. By May 2022, four more aircraft were delivered, and production has progressed slower than planned. Further developments In 2004, Sukhoi anticipated that the Su-57 could become the basis for a family of combat aircraft for the Russian Aerospace Forces, similar to the Su-27 family. Under the program name Megalopolis (), the company is developing a new variant, designated Su-57M, that augments the base Su-57 design with improved mission systems, reliability and maintenance enhancements, incorporation of electromechanical drives, and the new NPO Saturn izdeliye 30 engines. The formal contract was signed in 2018, although preliminary work had begun earlier. In 2020, flight test of the improved variant was planned to begin in 2022, with serial production in the mid-2020s. The second flying T-50 prototype was used to test the new izdeliye 30 engine starting in 2017; the third prototype was configured for teaming tests with the Okhotnik UCAV in 2018. Additionally, work is underway to make a variant of the aircraft that can operate on aircraft carriers. Sukhoi has also used technology from the Su-57 to produce a mockup of a more affordable lightweight single-engine aircraft, designated as the LTS (, ). At the 2021 Moscow Air Show (MAKS-2021), Sukhoi revealed its LTS mockup, named Checkmate, which shares many systems with the Su-57, including radar, main weapons bay, vertical stabilizers, and wings. , international sanctions on Russia's defence industries may hamper development of the Su-57, as Russia could not import semiconductors and high-tech machining equipment from the European Union. Potential export sales of Russian products -including military aircraft- also stalled because Russia cannot trade using U.S. dollars. The UAC reported that an upgraded Su-57 aircraft made its first flight on October 21 2022. It is yet unclear whether this airframe represents a Su-57M, as the "second-stage engine" (alluding to the Izdeliye 30) was reportedly not mounted. The flight was carried out by Russian test-pilot Sergey Bogdan. Design The Su-57 is a fifth-generation multirole fighter aircraft and the