KAI KF-21 Boramae. The KAI KF-21 Boramae (formerly known as KF-X)  is a South Korean-led fighter aircraft development program with the goal of producing an advanced multirole fighter for the South Korean and Indonesian air forces. The airframe uses stealth technology but carries weapons externally, and features such as internal bays will be introduced later with KF-21EX program. The KAI KF-X is South Korea's second domestic fighter jet development program, following the FA-50.

The program is led by the South Korean government, which holds 60% of the program's shares. Indonesia took a 20% stake in the program in 2010 and participate the program through Indonesian Aerospace since the start of KF-21 development in 2011, and the remaining 20% is held by private partners including the manufacturer Korea Aerospace Industries (KAI). Later, in August 2024, Indonesia's stake was reduced to 7.5% when the head of the program, the Defense Acquisition Program Administration (DAPA), cut Indonesia's development contribution.

In April 2021, the first prototype was completed and unveiled during a rollout ceremony at the headquarters of KAI at Sacheon Airport. It was named the Boramae (Korean: 보라매, "young hawk" or "fighting hawk"). The first test flight was on 19 July 2022, with manufacturing scheduled to begin in 2026. At least 40 aircraft are planned to be delivered by 2028, with South Korea expecting to deploy 120 of the aircraft by 2032. It will also be available for export.

Background
The KF-X advanced multirole jet fighter project, intended to produce modern warplanes to replace South Korea's aging F-4D/E Phantom II and F-5E/F Tiger II aircraft, was first announced in March 2001 by South Korean President Kim Dae-jung at a graduation ceremony of the Korea Air Force Academy. In 2002, research and development (R&D) requirements were determined by the Joint Chiefs of Staff. The project was felt to be extremely ambitious, with the Korea Institute for Defense Analyses (KIDA, a defense ministry think tank) doubtful of the country's ability to complete the complicated project.

The development phase had numerous delays and postponements and its economic cost was debated, but the project received renewed interest following a 2008 feasibility study and attacks by North Korea in 2010. Although the project carried risks and the expected per-unit cost would be significantly higher than purchasing from foreign manufacturers, the development of the domestic defense industry was deemed to be of national importance and was expected to have a ripple effect on high-tech industries.

In Indonesia, the KF-X development program is referred to as the IF-X program. The Jakarta Globe reported that the completed aircraft  would have received the designation F-33. On 15 July 2010, a partnership was made with Indonesia, which would provide 20% of the funding for the KF-X project, cooperate with technological development through state-owned Indonesian Aerospace, and purchase 50 of the approximately 150–200 planned aircraft.

Turkey had been considering joining with a 20% share, but wanted more control than South Korea had offered. The South Korean government committed to 60% of the cost. The remaining 20% was provided by domestic and foreign companies. The contract formed a plan for delivery of the aircraft to begin in 2026.

In July 2022, the Polish Armaments Agency said it is closely watching the development of the KF-21 Boramae, potentially paving a way for purchase of future Block 2 version of the fighter jet.

The Philippine Air Force and the Peruvian Air Force have expressed interest in the aircraft.

In May 2023, the Defense Acquisition Program Administration said that the KF-21 had passed the provisional combat suitability evaluation, to begin the initial mass production process in 2024.

Starting with the first prototype on 19 July 2022, six prototypes flew maiden flights until June 2023. The six prototypes will be tested for performance verification.

Design and development

The initial goal for the program was to develop a single-seat twin-engine 
multirole fighter with stealth capabilities exceeding both the Dassault Rafale and Eurofighter Typhoon 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 project requirements were later downgraded by the Republic of Korea Air Force (ROKAF) to a 4.5 generation fighter with limited stealth capabilities.

South Korea possessed 65% of the necessary technology to produce the KF-X, and sought cooperation from other countries. To facilitate technology transfer, the Agency for Defense Development (ADD) proposed two primary concepts for the KF-X: C103, which resembled the F-35, and C203, which resembled European fighters with forward canards. The design chosen would depend upon whether a development deal was reached with the US or European partners.

The C501 ( KFX-E) was a third design, proposed by KAI and supported by the Defense Acquisition Program Administration (DAPA), which attempted to reduce costs with a smaller, single-engine fighter, but it had inferior performance to the F-16 and was unsuitable for the large airspace of Indonesia. ROKAF preferred the benefits of a twin-engine design, with better combat performance and safety, and a larger airframe with room for upgrades. These upgrades could lead to a future reclassification as a fifth-generation fighter, while the C501 was closer to fourth generation.

When the development team started designing the KFX in December 2015, research and design was conducted based on the C103 configuration. Upon receiving the basic drawings of the C103, C104, and C105 from ADD, the development team built an experimental model of the C105 and began a wind tunnel experiment on the newly designed C107, which increased the size of the aircraft and increased the max takeoff weight. After about 2 years of various wind tunnel experiments, in 2018, the C109 proposed by ADD and KAI was decided to be the prototype design of KFX.

In May 2016, the U.S. government and Lockheed Martin tentatively agreed to transfer 21 technologies to KAI under the terms of offset trade, which is part of a contract for South Korea to introduce the F-35A. Later, The US government blocked the transfer of four vital technologies: AESA radar, infrared search and track (IRST), electro-optical targeting pod (EO TGP), and radio frequency jammer (RF jammer) technology. South Korea was required to develop these technologies domestically. A 2015 audit estimated that 87% of technologies for the project had been secured. The preliminary design was finalized in June 2018. In September 2019, a critical design review examined 390 technical data sets and confirmed that the KF-X was adequate to ROKAF's requirements.

Differences between design configurations

Prototypes

In February 2019, KAI began production work on the KF-X prototype, with six expected to be completed in 2021. These will undergo four years of trials, and complete the development process by mid-2026. The first prototype was publicly rolled out on 9 April 2021. In addition to the six aircraft for airborne tests, two will be made for ground tests. The first test flight occurred on 19 July 2022. The aircraft bore the flags of South Korea and Indonesia and took off from Sacheon Airbase for 33 minutes.

Six flying prototypes, including two two-seat versions, will conduct 2,200 flights until mass production begins in 2026. 40 Block-1 jets will have an interim capability limited to air-to-air duties, then the following 80 Block-2 jets from 2028 will add air-to-ground engagement. Later developments will include equipping the KF-21 with a domestically developed air-launched cruise missile (ALCM) and hypersonic missile.

A second KF-21 flew in November 2022 and a third in January 2023, achieving the aircraft's first supersonic flight in January. The first two-seat KF-21 prototype flew in February 2023. The two-seater's primary role will initially be type conversion. DAPA is considering other operational missions that would be more suited to a two-seat platform including electronic warfare.

Tests

In January 2022, the final assembly of the KF-21 occurred.

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 July 6, 2022, the first prototype of the KF-21 conducted a ramp taxi test in preparation for its maiden flight.

On July 7, 2022, the final engine run test and a high speed taxi test was conducted in preparation for its maiden flight.

On July 19, 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 September 28, 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.

The second prototype took off from Sacheon Air Base in South Gyeongsang Province on November 10, tested its flight performance for 35 minutes, and landed safely.

On January 3, 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 January 17, 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 February 20, 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 March 9, 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 March 28, 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 April 4, 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 May 16, 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 May 23, 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 June 28, 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 July 19, 2022.

On October 12, 2023, the KF-21 prototypes 3 and 4 conducted a formation flight.

On October 20, 2023, at the Seoul ADEX, the KF-21 showcased its technological capabilities during a five-minute demonstration, performing maneuvers such as horizontal sharp turns and inverted flights. This was the first time the aircraft's flight performance was revealed to the public.

On January 12, 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).

DAPA announced that on the morning of the March 19th, 2024, 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 April 22, 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 May 8, 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.

Budget

R&D expenditures

A 2015 government audit placed the development cost of the project at . In an agreement signed at the end of 2015, Indonesia agreed to provide 20% of the development costs. KAI would provide an additional 20%, and the Korean government would support the remainder.

Indonesian investment

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. In August 2011, a joint research center was opened in Daejeon, South Korea. 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. FlightGlobal reported in July 2019 that Indonesia was exploring payment in Indonesia-produced armaments instead of cash. By July 2019, Indonesia was approximately  billion in arrears.

Yonhap reported in October 2019 that, according to DAPA Korea, there were 114 Indonesian engineers participating during the peak of the KF-21 design phase in July 2019 and the development was ready to go to the prototyping stage after it met all of the requirements in September 2019.

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.

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. The rumors about the United Arab Emirates joining the KF-21 program was denied by DAPA Korea based on Korean government-owned media, Yonhap. Indonesian Defense Ministry Technology Director Air Vice Marshal Dedy Laksmono confirmed to the press on 29 October 2023 that the budget for 2024 cost share payment had been set aside at 1.25 trillion rupiah (US$80 million).

On February 21, 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 Korea Aerospace 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.

Polish investment
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.

According to a South Korean government official, in May 2023, during a visit to Korea in mid-April 2023, Sebastian Chwałek, chairman of the PGZ, expressed Poland's desire to participate in the KF-21 project. Specifically, the Polish government wanted to join the project as a development partner in 2026, after the KF-21 Block-1 is developed and when Block-2 begins development. It is reported that the Polish government is discussing the possibility of acquiring Indonesia's stake in the program by paying the ₩800 billion in overdue contribution funds that the Indonesian government has failed to pay. PGZ reportedly plans to deliver a letter of intent to participate in development partners to the South Korean government soon through the Polish government. The South Korean Defense Acquisition Program Administration said it will begin a full-fledged review once it receives a letter of intent from the Polish government.

Project partners 

While KAI was the primary builder, numerous other domestic and foreign companies were contracted to provide aircraft components or support. Several of these firms had worked with KAI on the T-50. For certain sensitive technologies, such as AESA radar, EO TGP, IRST and RF jammer, foreign companies were only consulted for testing support and technical advice in order to avoid arms-trading restrictions.

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.

AESA radar was co-developed with Hanwha Systems under the leadership of the ADD. Elta Systems helped to test the demonstrative prototype hardware of the AESA radar developed by Hanwha Systems. Saab provided technical advice to LIG Nex1, which develops Multi Function Radar (MFR) software for AESA radars.

IRST is based on the processor unit (PU) designed by Hanwha Systems and a Leonardo sensor head unit (SHU) called the SkyWard-K with modified back-end and a Korean software that replaces the original program.

Integrated electronic warfare equipment including RF jammer was developed by LIG Nex1.

US aerospace contractor Texstars was selected by KAI to develop canopy and windshield transparencies for KF-X. Under the contract, Texstars will work alongside KAI to provide the KF-X fighter with birdstrike resistant transparencies with high-quality optics.

Triumph Group was selected by KAI to provide airframe mounted accessory drives (AMADs) for the KF-X. Triumph will develop and manufacture the AMADs, which transfer engine power to other systems.

 (Spanish: Compañía Española de Sistemas Aeronáuticos, CESA), a subsidiary of Héroux-Devtek, was contracted to develop the emergency braking system.

United Technologies announced in February 2018 that it was providing the environmental control system, including cabin pressurization and liquid cooling systems, as well as the air turbine starter and flow control valve.

Martin-Baker was contracted to provide the Mk18 ejection seat escape mechanism.

Cobham received contracts to provide missile ejection launchers, communications antennae, external fuel tanks, and oxygen systems.

Meggitt was contracted to provide a wheel braking system, standby flight displays, and internal sensors including a fire detection system.

MBDA was contracted to integrate the Meteor beyond-visual-range air-to-air missile (BVRAAM) onto the aircraft.

Elbit Systems was contracted by Hanwha Systems to provide terrain-following/terrain avoidance (TF/TA) systems for the aircraft.

Curtiss-Wright was contracted by KAI to Provide complete flight test instrumentation (FTI) system, it is data acquisition system (DAS) for use in flight-test campaigns.

Controversies

Foreign bribery allegations 
In October 2009, a retired ROKAF general was arrested for leaking classified documents to Saab. The general was alleged to have been given a bribe of several hundred thousand dollars for copies of a number of secret documents that he had photographed. Saab officials denied any involvement.

The Defense Security Command (DSC) found evidence that another foreign defense firm had also bribed a member of the Security Management Institute (SMI). President Lee Myung-bak believed that such corruption resulted in a 20% increase in the defense budget.

Opposition 
In 2017, the Korean defense think tank KIDA told a public meeting that South Korea is not technologically equipped to develop the KF-X aircraft, that the project is economically unviable and that the KF-X would not be a successful export product. It also questioned the ADD cost estimates. DAPA's estimated  trillion development cost was criticized by some analysts, who said the project could cost up to  trillion.

Defense researcher Lee Juhyeong held a seminar on the program, stating that the KF-X development would cost more than  trillion (US$9.2 billion) and could cost more than twice as much as an imported aircraft over the life of the program.

Critics noted that the KF-X would cost up to twice as much as a top-end F-16 model and that Japan had encountered a similar situation with its Mitsubishi F-2.

EADS funding pullout 
In May 2013, EADS (European Aeronautic Defence and Space Company), the defense subsidiary of Airbus, offered a US$2 billion investment into the KF-X program, if South Korea selected its Eurofighter Typhoon for the F-X Phase 3 fighter procurement program. The US F-35A was selected instead. EADS repeated its investment offer, for a split-buy of 40 Eurofighters and 20 F-35As. In September 2017, South Korea confirmed purchase of 40 F-35 fighter jets, causing EADS to withdraw its offer.

Postponements and delays
The KF-X project had a history of delays and postponements since its announcement in 2001. Foreign partners were sought to share costs and guarantee purchases, and several failed attempts were made to entice Sweden, Turkey, and the United States to join the project. Design concepts and requirements frequently changed while trying to appeal to prospective partners. In March 2013, following the election of President Park Geun-hye, South Korea postponed the project for 18 months, due to financial issues.

In February 2017, Indonesian Vice Minister of Foreign Affairs Abdurrahman Mohammad Fachir said that the KF-X project was further delayed because the US government had refused export licenses for four key F-35 technologies. This disapproval was reaffirmed in October 2015 talks, though the US military stated that there was an agreement to form an interagency working group on such issues and that the US Secretary of Defense would "think of ways for joint cooperation" with technology for KF-X.

In November 2017, state-owned Indonesia Aerospace was overdue in its funding payment, which National Assembly Defense Committee member Kim Jong-Dae said would further delay, or suspend the project. Kim said that the Indonesian government had disclosed its difficulty in paying and did not include the payment in its budget. DAPA stated that it was in talks with Indonesia regarding the payment, which would be discussed at a summit between leaders of the countries. Indonesia stated that it was an administrative error, as it was falsely thought that the payment would be made from the "side defense budget". Parliamentary approval was required to correct the error, and the payment was delivered along with a statement of hope that the program would continue without further delinquencies.

Indonesian renegotiation
On 1 May 2018, it was reported that Indonesia had complaints concerning the contract rules surrounding technical benefits and export licensing. Indonesian state media announced that the defense ministry would renegotiate the joint development program in an attempt to gain a larger share of local production, as well as export rights. The Indonesian defense ministry added that it hoped that the program would continue despite setbacks.

Renegotiation talks continued into 2019. According to the agenda of a January 2019 meeting, Indonesia sought to extend its involvement in the program to 2031, and was interested in making part of its payments in trade for Indonesian-produced defense equipment. By August, Indonesia had transport aircraft on offer along with commodities.

In August 2021, Indonesia reaffirmed its commitment to the KF-21 program. Cost negotiations were achieved and agreed by both parties in 2021. In May 2022 it was reported that the issue of development payments had not yet been resolved. In November 2022, it was reported that Indonesia had resumed payment for its share of the costs. As of February 4, 2024, Indonesia is still in arrears of around US$1 billion in payment.

Indonesian engineers' alleged technology theft
On 2 February 2024, the South Korean National Intelligence Service (NIS) and the Defense Counterintelligence Command (DCC) announced a joint investigation into whether Indonesian engineers dispatched to KAI violated the Defense Technology Security Act for allegedly attempting to steal classified KF-21 technical data after storing it on an unauthorized USB drive. According to the investigation authorities, on 17 January 2024, an Indonesian engineer was reported to have been caught attempting to take eight USB drives containing 49 confidential data related to KF-21 out of the company, and also included sensitive data of the European and U.S. subcontractors with restricted exports to third countries and avionics only accessible to KAI officials.

On 11 March 2024, the Korean National Police Agency (KNPA), which is investigating the case at the request of DAPA, decided to expand its investigation after circumstantial evidence emerged that another Indonesian engineer was involved in the crime, and an initial investigation result report by NIS and DCC revealed that about 4,000 to 6,600 KF-21 data, including 3D design drawings of the aircraft, were stored on USB drives.

On 15 March 2024, for an in-depth investigation, the security investigation department of the South Gyeongsang Provincial Police Agency dispatched 10 investigators to the Indonesian engineer's home and KAI office to conduct a search and seizure.

Variants

South Korean variants

KF-21 Block I 
The block I focuses on the air-superiority capabilities.

KF-21 Block II 
After further developments, the KF-21 will become a swing role fighters with attack and reconnaissance capabilities added.

Potential variants

KF-21N 
In September 2022, KAI unveiled a model of the KF-21N, a carrier-based version of the fighter. In May 2022, the Ministry of National Defense (MND) decided to drop funding for the CVX, a planned small aircraft carrier capable of operating STOVL F-35B jets. It was later clarified that the MND would consider purchasing a larger aircraft carrier design, if a maritime jet fighter could be developed indigenously. Anticipating this, KAI began a preliminary design concept to make the KF-21 carrier-capable. The wings are 20% larger to ensure safety and stabilization when taking off and landing, and they fold for more compact storage. Structural changes would make the airframe capable of CATOBAR and STOBAR operations.

If the Republic of Korea Navy (ROKN) decides to procure an aircraft carrier large enough to operate fighters and identifies a requirement, KAI claims it would be able to build the KF-21N "in a few years."

KF-21EA 
One of the three new variants revealed in June 2024. Will serve as an electronic warfare aircraft comparable to the EA-18G Growler. This variant would be based on the two-seat KF-21B, with a position at the back for the electronic warfare officer.

KF-21EX 
One of the three new variants revealed in June 2024. Will reportedly be a fully stealth variant with reduced radar cross section and internal weapons carriage. It is also expected to integrate the Next Air Combat System (NACS), a combat network for the air force.

KF-21SA 
One of the three new variants revealed in June 2024. Will reportedly be a variant specifically dedicated to the export market, with opportunities for the client to modify the aircraft.

Operators

Current operators 

 
 Republic of Korea Air Force
 Air Force Test & Evaluation Wing
 281st Flight Test Squadron

Potential operators 
 
 Indonesian Air Force
 As of May 2024, Indonesia is reducing its contribution to the development. Indonesia previously had 20% of stake but reduced into 7%

 In 2024, the Philippines announced its interest to purchase 40 jet fighters. The Gripen E/F and the F-16 block 70/72 were pre-selected and South Korea joined the bid in September 2024 with the following jets:
 10 KF-21 Block I
 12 FA-50 Block 20
 12 FA-50PH

Specifications (single seat aircraft)

See also

 Chengdu J-20
 Lockheed F-117 Nighthawk
 Lockheed Martin F-22
 Sukhoi Su-57
 Fifth-generation fighter

References

Notes

External links

 Korea Aerospace Industries' future plan for the KFX
 Oxley Group wins development contract for KAI KF-X Fighter
 

KF-21
Twinjets
Stealth aircraft
Mid-wing aircraft
4.5-generation jet fighters
Aircraft first flown in 2022
ADD research and development projects
Indonesia–South Korea relations