The initial goal for the program was to develop a single-seat twin-engine multirole fighter with stealth capabilities exceeding the
Dassault Rafale,
Eurofighter Typhoon,
F-16 Fighting Falcon, but less than those of the
Lockheed Martin F-35 Lightning II. The Weapon Systems Concept Development and Application Research Center of
Konkuk University advised that the KF-X should be superior to the
F-16 Fighting Falcon, with 50% greater combat range, 34% longer airframe lifespan, better avionics,
active electronically scanned array (AESA) radar, more-effective electronic warfare, and
data link capabilities. Their recommendations specified approximately of thrust from two engines, supersonic interception and
cruising capabilities, and multi-role capabilities. The Block I configuration requirements were later finalised by the ROKAF and DAPA to a 4.5 generation fighter with semi-stealth capabilities. prompting efforts to both develop the remaining capabilities domestically and seek international partnerships to fill critical gaps. and C203, modelled after European fighters with forward
canards. These configurations were outlined for potential partnership with the
United States or European partners. By December 2015, the development team had begun designing the KF-X, with initial research and design based on the C103 configuration. After receiving the basic drawings of the C103, C104, and C105 from ADD, the team built an experimental model of the C105 and conducted wind tunnel tests, which were then repeated on the newly designed C107 featuring a larger airframe and greater maximum takeoff weight. An audit in 2015 estimated that 87% of the technologies required for the KF-X program had already been secured by this time. For the rest of 21 technologies, the U.S. government approved the transfer to South Korea in December 2015, including
avionics operational flight program (OFP) software,
head-mounted displays (HMD), and
aerial refueling control units. Despite its previous partnership on the T-50 design, Lockheed Martin's role in the KF-21 Boramae program was limited. While the company provided guidance to KAI's engineers during the KF-21's development and testing, Lockheed Martin does not possess any design rights to the fighter jet. It later emerged that Lockheed Martin had maintained a skeptical outlook, privately predicting that the KF-X program would eventually be cancelled or fail to reach completion. For the initial armaments, the U.S. government delayed integration approval for the
Raytheon AIM-120 AMRAAM and
AIM-9X Sidewinder, South Korea moved decisively to secure alternatives, quickly integrating the European
MBDA Meteor and Diehl
IRIS-T to maintain the KF-21's development timeline. Following approximately two years of wind tunnel experiments and continued domestic technology development, the C109, jointly proposed by ADD and KAI, was selected in 2018 as the prototype design for the KF-X. and a
critical design review in September 2019, examining 390 technical data sets, confirmed that the KF-X met ROKAF's requirements. The specific mandate for high manoeuvrability, low
radar cross-section (RCS), and the safety of a twin-engine configuration naturally dictated an airframe shape similar to the
F-22 Raptor, as both aircraft were engineered to meet similar stealth-physics and performance benchmarks.
Modular design and evolutionary approach The KF-21 program's core philosophy centers on a spiral development model, where the aircraft is introduced in a series of progressively more capable versions, or blocks. This modular approach allows for incremental improvements, with each block introducing new capabilities and technologies. The initial focus was on developing a highly capable 4.5-generation fighter jet with scalability to be upgraded to a true 5th-generation aircraft in later iterations. AESA radar in
Compact Antenna Test Range (CATR), 2020 By focusing on the in-house development of critical, sensitive technologies like the AESA radar and electronic warfare systems, the program enhances national self-reliance and bypasses potential arms-trading restrictions. In 2020, Hanwha Systems successfully produced a prototype
Saab provided technical advice to
LIG Nex1, which develops Multi Function Radar (MFR) software for AESA radars. On August 5, 2025, Hanwha Systems unveils the first mass-produced AESA radar. The electro-optical targeting pod (EO TGP) was developed by Hanwha Systems, and integrated electronic warfare suite (EW Suite) was developed by LIG Nex1. For the engine,
Hanwha Aerospace signed an agreement with
General Electric to manufacture
General Electric F414 engines for KF-X aircraft. According to the contract, Hanwha is to manufacture key parts, locally assemble the engines, and oversee the installation of the engine on the aircraft. The company will support flight testing and build an extensive support system for the aircraft's operations. As of September 2025, the South Korean government has prioritized the complete localization of the KF-21's propulsion system to mitigate reliance on international supply chains and enhance export competitiveness. In support of this initiative, the Ministry of National Defense allocated ₩86 billion (approximately US$62 million) in the 2026 fiscal budget to replace the US-sourced General Electric F414-GE-400K with a domestic alternative. The development program, led by Hanwha Aerospace and Doosan Enerbility, aims to produce a 16,000 lbf thrust class turbofan engine by the 2030s. For some less critical components that can be sourced more cost-effectively than developing them domestically, KAI and ADD strategically partnered with numerous international companies. For instance,
Texstars was contracted to provide
birdstrike-resistant canopy and windshield
transparencies.
Triumph Group supplies the
airframe mounted accessory drives (AMADs), which transfer engine power to other systems. Other notable collaborations include Aeronautical Systems (CESA) for the
emergency braking system,
United Technologies for the environmental control system, and
Martin-Baker for the Mk18 ejection seat.
Cobham provides missile ejection launchers, external fuel tanks, and oxygen systems, while
Meggitt is responsible for the wheel braking system and internal sensors. standby flight displays, and internal sensors including a fire detection system. The program also benefits from contributions by
Elbit Systems for terrain-following systems and
Curtiss-Wright, which supplies the flight test instrumentation system for data acquisition. This international cooperation for minor systems highlights a pragmatic approach to the KF-21's development, ensuring the aircraft maintains lower unit cost and is equipped with reliable, proven components. The strategic approach taken for the KF-21 program, which involves combining local development of core technologies with some international cooperation for minor components, has been noted by analysts as a practical and effective way to manage a complex project. While other competing programs, such as Turkey's
Kaan and
India's
AMCA, have pursued a more ambitious, fully indigenous development path, the KF-21 model has been credited with achieving its development goals in a relatively efficient manner. The KF-21 program has been recognized for its adherence to its original timeline and budget, a notable accomplishment in a field where major defense programs frequently encounter delays and cost overruns. The local production rate for domestic components of KF-21 Block I has reportedly exceeded 65%. KAI plans to further increase domestic components during the development of future blocks, at which point it expects to produce reliable parts cost-effectively and within schedule.
Open architecture The KF-21 Boramae is engineered with an Open Mission Systems (OMS) architecture, a design philosophy that mirrors the modularity of modern smartphone operating systems. In contrast, the KF-21 grants users greater technical sovereignty, allowing them to customize avionics and strike capabilities to fit their specific national defense requirements.
Manned-Unmanned Teaming and AI pilot The KF-21 Boramae is designed to serve as the central node in a next-generation Manned-Unmanned Teaming (MUM-T) ecosystem. This operational concept involves a manned fighter controlling multiple highly autonomous Unmanned Combat Aerial Vehicles (UCAVs), often referred to as "Loyal Wingmen." The prototypes were designed to be nearly identical to the final production aircraft to prevent delays and save costs. This requirement stemmed from the ROKAF's concern that a program failure could cause a serious gap in their combat readiness. This strategy is consistent with the choice to forgo a flying demonstrator, a phase that was part of other projects, such as the TAI TF Kaan. In February 2019, KAI had begun production on the KF-X prototypes and all six aircraft were completed by 2021. These prototypes then underwent four years of flight trials, with the development process concluding by mid-2026. In addition to the six flying prototypes, KAI built two additional prototypes specifically for ground-based tests. The six flight-test aircraft were scheduled to conduct a total of 2,200 flights. Subsequent prototypes, including the single-seat and dual-seat variants, completed their first flights over the following months. A key milestone was the first supersonic flight on January 17, 2023, where the KF-21 broke the sound barrier at an altitude of 40,000 feet. The prototypes were also tested for various operational capabilities, including night flights, aerial refueling, and weapon separation and firing tests with missiles like the Meteor and IRIS-T. Additionally, they performed tests for high angle of attack stability and endured extreme environmental conditions like heavy rain and icing. By May 2024, the KF-21 had reached a top speed of Mach 1.8, and by late 2024, it surpassed 1,000 accident-free flight sorties, solidifying its safety and reliability. These rigorous trials culminated in the aircraft being declared "provisionally suitable for combat" in May 2023, paving the way for further development and eventual mass production. After three years of flight testing the KF-21 prototype, only one observable design change has been implemented on the initial serial production models being assembled: the sharp, angular sides of the inboard tail booms next to the two GE Aerospace F414 engine nozzles have been flattened. This minor modification was necessary to correct a slight vibration that test pilots had detected while operating the prototype aircraft within specific flight conditions. In March 2022, ground testing was conducted for the AESA radar. The AESA radar of the KF-21 is equipped with about 1,000 transmit/receive modules and electronically steers the radar beam by adjusting the phase of the radio waves. In April 2022, the AESA radar began its domestic
flight tests. By the first half of 2023, all developed functional and performance requirements of the AESA radar were verified through flight tests. Various flight scenarios and repeated tests improved the completeness and reliability of the AESA radar. In
South Africa, a civilian aircraft (
Boeing 737-500) was modified to create a
test aircraft (FTB: Flying Test Bed) equipped with the AESA radar. From November to December 2021, a total of 10 sorties were conducted to test the basic functions and performance of the radar, including its most critical performance, maximum detection range. On 6 July 2022, the first prototype of the KF-21 conducted a ramp
taxi test in preparation for its maiden flight. On 7 July 2022, the final engine run test. and a high speed taxi test was conducted in preparation for its maiden flight. On 19 July 2022, the KF-21 successfully completed its maiden flight. The KF-21 took off at 3:40 PM and landed at 4:13 PM, marking a successful 33-minute first flight. It will undergo approximately 2,000 flight tests in the future to verify various performance aspects and weapons compatibility. On 28 September 2022, the ROKAF released a video demonstrating the KF-21's
landing gear operation during flight, addressing public curiosity about the mechanics of the landing gears and caps. On 10 November 2022, the second prototype took off from
Sacheon Air Base in
South Gyeongsang Province, tested its flight performance for 35 minutes, and landed safely. On 3 January 2023, the third prototype successfully completed its first test flight. The third prototype took off from the 3rd Training Wing in Sacheon, South Gyeongsang Province at 1:01 PM and landed at 1:38 PM. The first test flight recorded a maximum speed of 370 km/h and a maximum
altitude of 4,600 meters, which is similar to the levels achieved by the first and second prototypes. The third prototype is equipped with speed and structural load expansion measurement systems. It is expected to facilitate smoother speed and structural load expansion tests, which constitute a significant portion of the KF-21 system development flight tests. On 17 January 2023, the KF-21 successfully achieved its first
supersonic flight. The KF-21 first prototype took off from the ROKAF's 3rd Training Wing and broke the sound barrier (Mach 1.0, approximately 1,224 km/h) for the first time while flying at an altitude of about 40,000 feet over the South Sea. On 20 February 2023, DAPA announced that the fourth prototype of the KF-21 successfully completed its maiden flight, taking off from the 3rd Training Wing in Sacheon at 11:19 AM and landing at 11:53 AM after a 34-minute flight. The fourth prototype is a two-seat aircraft with seats arranged in tandem, accommodating two pilots. The two-seat KF-21 will primarily be used for training new pilots (prototype composition: 4 single-seat (prototypes 1, 2, 3, 5), 2 two-seat (prototypes 4, 6)). Despite being a two-seat aircraft, only one pilot flew the fourth prototype for this initial flight to verify early flight stability. Until the completion of system development in June 2026, the fourth prototype will undergo various flight tests to assess the impact of design differences on the aircraft, perform AESA radar
avionics tests, and more. The livery of the fourth prototype features an image of four aircraft simultaneously ascending into the sky on the vertical tail, similar to the third prototype, but with yellow-colored ascending aircraft. With the fifth and sixth prototypes starting flight tests in the first half of 2023, all six prototypes will continue expanding the flight envelope and verifying aircraft performance through continuous flight tests. On 9 March 2023, KF-21 prototypes 3 and 4 successfully completed a night flight test and landed safely. During this test flight, the proper functioning of both internal and external lighting systems on the aircraft was verified in a low-light environment. The lighting on the aircraft plays an important role in night flights, including collision avoidance and identification of instruments for the pilot. With this successful test, it is expected that the KF-21 will be capable of performing nighttime missions. On 28 March 2023, DAPA announced, 'The KF-21 successfully conducted air-to-air weapon separation tests and aerial gun firing tests over the South Sea, taking off from the Air Force's 3rd Training Wing in Sacheon.' The second KF-21 prototype conducted weapon separation tests with Meteor medium-range air-to-air missile test round, while the third prototype performed aerial gun firing tests with around 100 rounds. These tests aimed to verify the safety by checking changes in the aircraft's structure, engine, and aerodynamic characteristics that can occur when weapons are separated or guns are fired from the fighter jet, and to confirm the normal operation of avionics systems related to weapon operation. Since its maiden flight in July 2022, the KF-21 has conducted approximately 150 flight tests, successfully verifying its supersonic flight capabilities and the performance of advanced avionics including the AESA radar. On 4 April 2023, the KF-21 successfully conducted a weapon separation test with
AIM-2000 short-range air-to-air missile test round. This test aimed to verify the safety by checking for changes in the aircraft's structure, engine, and aerodynamic characteristics that can occur when weapons are separated from the fighter jet, and to confirm the normal operation of avionics systems related to weapon operation. On 16 May 2023, DAPA announced that the fifth prototype successfully completed its maiden flight, taking off from the 3rd Training Wing in Sacheon and flying over the South Sea. With the successful maiden flight of the fifth prototype, all four single-seat KF-21 prototypes have now completed their first flights. The fifth prototype will primarily conduct avionics performance verification tests, including those for the AESA radar, and is scheduled to undergo aerial refueling tests in the second half of 2023. On 23 May 2023, DAPA revealed the site of the mounting demonstration for the Meteor medium-range air-to-air missile and the AIM-2000 short-range air-to-air missile. On May 16, 2023, DAPA announced that the KF-21 Boramae had been declared "provisionally suitable for combat." After over two decades of development, including more than 200 flight tests, the KF-21 has proven its capabilities, such as supersonic and night flight, and has successfully tested its Active Electronically Scanned Array (AESA) radar and AIM-2000 air-to-air missile separation. On 28 June, DAPA announced that the sixth prototype successfully completed its maiden flight, taking off from the 3rd Training Wing in Sacheon, and flying for 33 minutes from 3:49 PM to 4:22 PM. With the successful maiden flight of the sixth prototype, all six KF-21 flight test prototypes have now completed their first flights. This milestone comes 11 months after the first prototype's successful flight on 19 July 2022. On 12 October 2023, the KF-21 prototypes 3 and 4 conducted a
formation flight. On 20 October 2023, at the Seoul ADEX, the KF-21 showcased its technological capabilities during a five-minute demonstration, performing manoeuvres such as horizontal sharp turns and inverted flights. This was the first time the aircraft's flight performance was revealed to the public. On 12 January 2024, the KF-21 second prototype successfully conducted a high
angle of attack (AOA) flight stability test. The aircraft maintained a maximum pitch angle of approximately 70 degrees, flew to an altitude of over 38,000 feet, and then successfully returned to a stable flight condition after reaching a low-speed state (below approximately 20 KCAS). On 19 March 2024, DAPA announced that the fifth prototype (single-seat) successfully completed an aerial refueling flight over the South Sea after taking off from the Air Force's 3rd Training Wing in Sacheon. This achievement has secured the KF-21's long-range operational capability. On 22 April 2024, the KF-21 fourth prototype conducted a "full-scale environmental test" at the Agency for Defense Development's Haemi Test Center. This test verifies the aircraft's normal operation in extreme environments (low temperature, heavy rain, and icing). The test simulated extreme rain and icing conditions on the ground to check the KF-21's waterproof and anti-icing performance. The test results were successful. In May 2024, the KF-21 surpassed Mach 1.8, the highest speed achieved by a domestically produced fighter jet, during a test flight. On 8 May 2024, a KF-21 equipped with a Meteor missile successfully completed its test from Sacheon Airport. The same day, it also aced an AIM-2000 missile test, tracking a drone 87 km away and passing within 1 meter using AESA radar. Later that month, a KF-21 successfully fired an IRIS-T missile for the first time, following earlier tests with an unguided dummy missile of the same type in 2023. On 24 October 2024, Prototype 6 of the KF-21 Boramae demonstrated exceptional stability and agility at Sacheon Airshow 2024, performing advanced manoeuvres with precision. On 28 November 2024, KAI's KF-21 Boramae achieved a milestone of 1,000 accident-free flight sorties, showcasing its outstanding safety and reliability. On 19 February 2025, Air Force Chief of Staff Lee Young-su participated in a KF-21 Boramae test flight at Sacheon Air Base, becoming the first non-test pilot to fly aboard the aircraft. Gen. Lee flew at an altitude of approximately 4,500 meters over the southern coast at a speed exceeding 1,000 km/h, assessing the KF-21's stable aerial operational capabilities. Additionally, he flew alongside a KF-16 to verify its tactical interoperability with other aircraft. On 8 April 2025, the KF-21 Boramae successfully conducted its first nighttime aerial refueling trial with the KC-330 tanker. Performed using the fourth prototype, the test was completed on the first attempt under low-visibility conditions, demonstrating the aircraft's all-weather and long-range operational capabilities.
Serial production In June 2024, 20 units of KF-21 Block I ordered for a value of US$1.41 billion. In July 2024, the serial production of the 20 KF-21 Block I started. On May 20, 2025, the Defense Acquisition Program Administration (DAPA) marked the start of final assembly for the first mass-produced KF-21 Boramae fighter jet with a special ceremony. In June 2025, additional 20 units of KF-21 Block I ordered with the delivery of 40 units to begin in March 2026 (since delayed) and to be completed by 2028. On August 5, 2025, Hanwha Systems rolls out the first mass-produced AESA radar. The resulting domestically produced radar, the
APY-016K is equipped with approximately 1,000 transmit-receive modules, enabling it to detect targets from 150 to 200 km away and track about 20 targets simultaneously, allowing the KF-21 to engage multiple enemies effectively. On October 17, 2025, during the first public day of the Seoul ADEX 2025, the KF-21 Boramae successfully demonstrated a series of high-difficulty aerial maneuvers at Seoul Airport, showcasing its advanced combat agility. Unlike previous exhibitions, this flight was conducted with G-force restrictions lifted, allowing the indigenous supersonic fighter to perform high-speed sharp turns, inverted flights, vertical climbs, and rolls, as well as a low-altitude flyby reaching speeds of approximately 1,000 km/h. Military officials and observers noted that while the KF-21 had appeared at the previous year's event, this latest performance utilized more sophisticated piloting and intensified maneuverability to definitively prove the aircraft's operational stability and superior flight performance to the public. On December 23, 2025, the Defense Acquisition Program Administration (DAPA) officially launched the KF-21 Additional Armament Test Project during a kick-off meeting at Korea Aerospace Industries (KAI) in Sacheon. This 700 billion KRW initiative is dedicated to transforming the KF-21 into a full-scale multirole fighter by integrating and verifying more than 10 types of air-to-ground munitions by December 2028. Building on the success of earlier air-to-air tests and flight stability trials, the project aims to fast-track the deployment of ground-strike capabilities by approximately 18 months, with the first certified weapons expected to be integrated into mass-produced units starting in 2027. Additionally, the DAPA made public a video documenting "pit drop" testing for several key munitions, including the
GBU-12 Paveway II, the GBU-56
LJDAM, and the domestically developed
KALCM Cheonryong. These trials signify that the integration process for the Block II phase—which focuses on multi-role air-to-ground capabilities—is already well underway even before Block I development reaches its conclusion. On January 13, 2026, South Korea's Defense Acquisition Program Administration (DAPA) announced the successful completion of the flight testing phase for the KF-21 Boramae. Over a 42-month period, the project achieved approximately 1,600 accident-free flights and verified 13,000 test conditions, including advanced maneuvers, air-to-air weapon launches, and the nation's first-ever aerial refueling tests. By expanding test sites and improving operational efficiency, DAPA shortened the development timeline by two months, concluding the final verification with Prototype No. 4 over the South Sea. On March 25, 2026, Korea Aerospace Industries (KAI) held the official rollout ceremony for the first mass-produced KF-21 Boramae, marking a significant milestone in the transition from development to active deployment. On April 15, 2026, the first mass-produced KF-21 Boramae successfully completed its maiden production test flight at the 3rd Training Wing in Sacheon, occurring just 21 days after its official rollout ceremony. This flight, conducted by Republic of Korea Air Force personnel, served as the final validation to ensure that the mass-produced airframe accurately replicates the performance and reliability established during the prototype phase's 1,600 test sorties.
Program funding The funding for the KF-X project is a multi-party effort, primarily led by the South Korean government. The development phase, with an initial cost estimated at 8.8 trillion won (approximately US$7.8 billion), is a joint venture. The remaining 20% was to be funded by Indonesia;
Indonesia's contributions and financial challenges In July 2010, the
Indonesian government agreed to fund 20% of the KF-X project cost in return for prototype 005 (designated IF-X), system development participation, technical data, and production sharing. The second agreement between Indonesia and Korea was a work assignment agreement between KAI and Indonesia's state-owned aerospace manufacturer PT Dirgantara (PTDI). As per this agreement, PTDI sent 100 engineers to South Korea to take part in the structural design of the KF-21, to play a role in its development over time. In November 2017, Indonesia, through state-owned Indonesia Aerospace, failed to pay its share of the latest round of development costs, prompting criticism from South Korea. As of 2019, Indonesia was renegotiating its involvement in the program. According to a September 2023 report from Yonhap, the South Korean state news agency, Indonesia had paid only US$208 million since 2016 on the research and development stage Another report stated that Indonesia paid US$205 million for research and development and owed about US$420 million. In December 2020, a report showed that Indonesia was likely to pull out of the project. Another stated that South Korea and Indonesia planned to move forward on the KFX/IFX project. In August 2021, Indonesia reaffirmed its interest in the KF-21 program, with Indonesian engineers returning to South Korea to continue their work. Further agreement on the costs has been reached between the two countries. According to reports in May 2022, the issue of Indonesia's unpaid US$4.2 million in development costs had not been resolved. In November 2021, Indonesia and South Korea agreed to draw up a new sharing agreement for development costs by March 2022, but it had not been implemented so far. In November 2022, reportedly Indonesia has resumed payment for its share of the cost for a joint fighter development project. At the Polish-Korean Defense Industry Cooperation Conference in
Warsaw in November 2022,
Sebastian Chwałek, chairman of
Polish Armaments Group (PGZ), a state-owned defense company, expressed his desire to participate in the KF-21 project. In September 2023 it was reported that Indonesia did not make its payments, and South Korea had signed a
memorandum of understanding with the United Arab Emirates (UAE), that the UAE would buy Indonesia's KF-21 shares and be part of the KF-21 program as a partner. On 21 February 2024, on the sidelines of the G20 meeting in Rio de Janeiro, Brazil, Indonesia foreign minister Retno Marsudi and her counterpart South Korean foreign minister, Cho Tae-Yul, discussed the KF-21/IFX program, and both parties once again reaffirmed their commitment to continue the joint development program between the two countries. The KAI CEO said in the Korean media that Indonesia entering the program is pretty significant for KF-21 development and the program could have been stalled if there was no continued Indonesia participation. On 16 August 2024, the 163rd Defense Acquisition Program Promotion Committee readjusted the development contributions Indonesia was supposed to pay from
₩1.6 trillion to ₩600 billion, and Indonesia's stake was reduced to 7.5% as the shortfall was decided to be covered by the
Korean government's additional budget. but under this new adjustment Indonesia will not receive a prototype of the aircraft. On 27 June 2025, Colonel Ferrel "Venom" Rigonald of the
Indonesian Air Force became the first Indonesian pilot to fly the aircraft. He flew the aircraft for an hour long test flight accompanied with KAI test pilot, Koh Hwi Seok. The test flight by an Indonesian pilot reaffirms Indonesia's participation in the program. This flight is Sugiyanto's first flight from the pilot seat after he previously fly the aircraft from the rear seat on 16 May 2023. South Korea mulled on transfering a single seated prototype of the aircraft to Indonesia. DAPA announced that they will decide on the transfer schedule once Indonesia has fulfilled their 600 million won contribution. As of 8 April 2026, Indonesia has paid 536 million won and is expected to pay the remaining 64 million won in June 2026 in order to make the transfer possible. == Challenges and setbacks ==