The prototype took off from an air base in Sacheon-si, some 300 kilometers (186 miles) southeast of the capital city of Seoul. As it was flying over the waters off the country's southern coast, the South Korean air force's KC-330 tanker refueled the jet, Yonhap reported.
One refueling session could extend the jet's operational range by up to 50%, DAPA was cited as saying. The state arms procurement agency will continue refueling tests of the KF-21 prototype at various flight altitudes and speeds.
South Korea has been developing the KF-21 project since 2015 together with Indonesia, seeking to build a supersonic jet to replace the aging fleet of F-4 and F-5 jets. To date, six prototypes have been built, with the first production model expected to be ready in 2026.