In this provided photo taken on Nov. 10, 2022, the second prototype of South Korea's homegrown KF-21 fighter makes the maiden flight at the Air Force's 3rd Flying Training Wing in Sacheon, about 300 kilometers southeast of Seoul. Courtesy of Defense Acquisition Program Administration

South Korea plans to conduct a test of its homegrown KF-21 fighter to achieve supersonic speeds this month should the weather permit, multiple sources said Thursday, in what would be a key milestone in the high-profile warplane development project.

Securing the supersonic capability is a major part of the development efforts, led by its manufacturer, Korea Aerospace Industries Ltd. (KAI), as it means key functions, including avionics, work smoothly irrespective of flight speeds.

"We plan to conduct the test (for supersonic speeds) sometime in January, but we cannot tell you the exact date as it could be pushed back due to weather conditions," the source told Yonhap News Agency on condition of anonymity.

On Thursday, the third prototype of the fighter successfully conducted its maiden flight, signaling progress in the high-profile fighter project. The testing authorities plan to conduct some 2,000 flight tests through February 2026.

Launched in 2015, the KF-21 project worth 8.8 trillion won (US$6.9 billion) seeks to develop the 4.5th-generation fighter to replace the country's aging fleet of F-4 and F-5 jets waiting to be decommissioned following decades of service. (Yonhap)