The indigenous fighter KF-21 of South Korea’s KF-X project had its first test flight after more than 6 and a half years of research and manufacture.
The flight test took place on July 19 at the 3rd training flight school of the Republic of Korea Air Force in Sacheon city, about 300 km south of Seoul, according to an announcement from the Korea Defense Acquisition Program Administration (DAPA).

The KF-21 Boramae took off at 3:40 p.m. and landed at 4:13 p.m. “This is the moment when Korea’s ability to develop 4.5-generation fighters has become a reality,” DAPA said. Major Ahn Jun-hyun of South Korea’s Air Force piloted the KF-21 prototype No.1 featuring the national flags of South Korea and Indonesia.
The maiden flight was aimed at examining KF-21’s basic flight performance such as takeoff and landing. It was also intended to examine the jet’s structural integrity before kicking off the thousands of test flights to follow. Ground tests including low, medium and high-speed taxi testing and engine ignition testing took place before the first flight.
According to DAPA, the KF-21 is a 4.5-generation fighter because it does not have features to increase stealth such as a weapon compartment hidden in the fuselage. However, analysts say that this fighter model can fly faster and higher than the US F-35 fifth generation fighter.
This test turns South Korea into one of the few countries in the world that has successfully developed a modern supersonic fighter. The KF-21 was developed as part of an 8.8 trillion won project ($6.67 billion) to replace aging F-4 and F-5 fighter jets. Thereby strengthening air defense capabilities to cope with nuclear and missile threats from North Korea.
The KF-21 Boramae is expected to be a cheap and stealthy alternative to the US-made F-35. South Korea said it will service at least 40 KF-21s by 2029 and increase to 140 by 2032. KF-X is the largest and most expensive fighter program in South Korean history.
South Korea and Indonesia agreed in 2014 to jointly develop a $6.3 billion fighter project, of which Jakarta will contribute 20% of the budget. However, the Indonesian government in 2018 sought to renegotiate the project terms to reduce pressure on foreign currency reserves, in the context of the project costing up to 8 billion USD. Indonesia has also been slow to pay contributions many times, making it difficult for KAI Group.
KF-X or Korean Fighter eXperimental, is a next-generation stealth aircraft program that combines the features of a 5th generation fighter. KAI started system development in December 2015, underwent a Preliminary Design Review in 2018, began machining the first part in February 2019, and passed the Critical Design Review in September 2019.
In addition, KAI is localizing the main avionics part to improve products with domestic technology. Observers said that South Korean domestic aircraft were heavily influenced by the US F-22 Raptor. It is not clear how much of the US has assisted in technical issues for Korea to perfect this 5th generation fighter, all parameters related to KF-X are still a secret.
The KF-X project consists of two stages over 13 years, from 2015 to 2028. The first stage focuses on developing aircraft and integrated logistics systems between 2015 and 2026. The second phase aims to develop aircraft capabilities to carry out air-to-surface missions between 2026 and 2028. The KF-21 program has also paved the way for South Korea to locally develop and produce fifth-and sixth-generation fighter aircraft with stealth and other advanced capabilities.