Interview: Testing the Limits of Korea's First Indigenous Fighter Jet, the KF-21

Major Song Min-seok of the Air Force Test Evaluation Group sits in the cockpit wearing a flight helmet and oxygen mask on April 22, 2026. [Photo=Air Force Headquarters]

At low altitudes, the moment arrives unexpectedly. The aircraft makes a sharp turn, subjecting the pilot to intense gravitational forces, and their vision begins to blur. For Major Song Min-seok, a test pilot for South Korea's first domestically developed supersonic fighter jet, the KF-21 'Boramae,' the most challenging task is not simply to fly fast. It is to push the aircraft to its limits and endure the extreme conditions to complete the test.
"When experiencing G-forces during sharp turns, blood starts to pool in the legs, reducing blood flow to the brain. I learned special breathing techniques to overcome this, but maintaining that state while performing the mission is still painful and difficult," Major Song said in a recent interview with Aju Business Daily.
At high altitudes, there is time and space to recover even if one loses consciousness, but at low altitudes, even a moment of distraction can be fatal.
"You have to push the aircraft to the very edge of losing consciousness. If you want to avoid a blackout, you can ease off the stick, but to complete the test, you have to keep pulling. Especially at low altitudes, even a brief drop in altitude can lead to a catastrophic accident, making it the most tense moment," he explained.

Major Song Min-seok poses in front of the KF-21 on April 22, 2026. [Photo=Air Force Headquarters]

Major Song is not your typical operational pilot. He is part of the 281st Test Flight Squadron of the Air Force Test Evaluation Group, the only test flight unit in South Korea responsible for verifying the performance and safety of new aircraft.
Pilots here do not fly aircraft with proven performance; instead, they operate planes that have yet to fully reveal their safety and limits, which they must validate.
His current mission is at the forefront of the KF-21 development, the most ambitious project in South Korea's defense industry history. The KF-21 Boramae is a 4.5-generation medium supersonic fighter developed over a decade through the Korean Fighter eXperimental (KF-X) program by the South Korean Air Force, the Defense Acquisition Program Administration, and Korea Aerospace Industries (KAI).
For Major Song, who flies the KF-21 daily, this national ambition is not just a slogan but a pressing reality. "The KF-21 is the first supersonic fighter developed with South Korean technology. As a test pilot, I feel immense pride in being at the center of this historic moment," he said.
However, with pride comes significant pressure.
"The results we confirm will determine the completeness of the aircraft that Air Force pilots will operate for decades to come," he noted.

The Korean fighter jet KF-21 Boramae is displayed in a hangar on April 22, 2026. [Photo=Air Force Headquarters]

The duties of a test pilot begin long before takeoff. Major Song is involved in the entire flight test process, from reviewing plans and identifying risks to executing the mission and analyzing data post-flight to prepare evaluation reports. After each flight, they collaborate with ground engineers to analyze how the aircraft responded in the air.
When asked about the most impressive aspect of the KF-21 during his first flight, Major Song highlighted its thrust rather than its radar, missiles, or stealth capabilities.
"The thrust is incredibly powerful. It takes off very lightly and has excellent acceleration capabilities," he said.

Major Song Min-seok checks instruments and equipment in the KF-21 cockpit on April 22, 2026. [Photo=Air Force Headquarters]

Next, he was captivated by the cockpit. Unlike older fighter jets filled with analog gauges and complex switches, the KF-21's cockpit gives the impression of stepping into a digital future.
"In older fighter jets, analog instruments are cluttered all around the cockpit, while the KF-21 has what looks like three or four large iPads in front. Everything is touch-screen, making the display layout and operation very intuitive," he explained.
Major Song described the cockpit as 'forward-looking,' likening it to the feeling of first using a smartphone. He also mentioned the superiority of the fly-by-wire system, which converts the pilot's physical inputs into electronic signals to control the aircraft.
Modern supersonic fighters cannot be controlled solely by human strength. When the pilot moves the stick, the internal software comprehensively interprets pressure, angle, speed, and current maneuvering state, then moves the control surfaces in the safest and most precise manner.
One of the most challenging areas for Major Song to monitor during flight is handling quality. This assesses how naturally and safely the aircraft responds to the pilot's commands, and he noted that the KF-21 goes beyond mere obedience, correcting its own control.
"The software onboard adjusts the control surfaces differently based on flight speed and turn angle. It provides perfect corrections during the control process," he said.

The Korean fighter jet KF-21 Boramae dual-seat prototype 4 conducts a test flight on April 22, 2026. [Photo=Air Force Headquarters]

This automatic correction feature shines in extremely delicate situations, such as aerial refueling, where minor movements can be life or death. Major Song stated that the KF-21's excellent stability allows pilots to focus entirely on the mission rather than struggling with aircraft control.
This stability signifies a greater meaning for the KF-21 in South Korea. While foreign fighter jets can be purchased, domestic fighters can be modified as needed.
The KF-21 can integrate new weapons, software, and even future AI-based manned-unmanned teaming systems at any time, making it a significant platform for South Korea as it prepares for a larger leap in the global defense market.
Major Song's flights are forming the backbone of that platform. The data obtained from test flights reveal gaps between design goals and actual performance, prompting engineers to modify flight control software, improve avionics, or adjust the pilot interface. Through this iterative process of flying and refining, the fighter jet gets closer to perfection with each moment.
Thus, Major Song defines his work not merely as flying an aircraft but as 'translating the aircraft's language.' He flies, feels, and tests in the sky, then comes down to explain what this massive machine has communicated to the engineers.
Becoming a test pilot took nearly two years. Major Song began his training in 2021, undergoing about a year of domestic education involving repetitive flying, data analysis, and presentations. After completing approximately 13 challenging tasks, he also had to complete an overseas training program evaluating foreign aircraft and avionics systems.
He noted that the most challenging aspect was not the physical training familiar to existing fighter pilots but the endless routine of flying, analyzing, and logically explaining.
"After flying, I have to extract data and continuously present it. It’s a cycle of writing reports and presenting them," he said.

Major Song Min-seok sits in a flight simulator on April 22, 2026. [Photo=Air Force Headquarters]

His journey into this field was inspired by his instructor, Ki Ye-ho, the oldest test pilot at age 70. The instructor often shared insights about the world of test flying and encouraged Major Song when he considered applying.
"The instructor said it was a very rewarding and interesting field. He also mentioned that if you truly love flying, it’s the best job to hold onto the stick for a long time," Major Song recalled.
Major Song still loves flying. When asked about his goals, he provided a concise yet profound answer.
"I enjoy flying. My goal is to continue test flying until the KF-21 is more complete," he stated.
However, he does not romanticize his profession. To young people dreaming of becoming pilots, Major Song advises that the cockpit is not just a glamorous place.
"The profession of a pilot may seem cool on the surface, but in reality, there are many incredibly tough and dangerous moments. Without a strong sense of mission, it’s a difficult path to endure," he cautioned.
The sense of mission he speaks of goes beyond the desire to 'fly in the sky' and must start with understanding the responsibility of contributing to national defense as a military pilot.

Major Song Min-seok explains the armament mounted on the KF-21 on April 22, 2026. [Photo=Air Force Headquarters]

"Both a sense of duty as a soldier and as a pilot are necessary," he emphasized.
While his daily life is governed by danger, data, and strict discipline, there is an exception during the moment of soaring above the clouds. When the aircraft glides smoothly over the white carpet of clouds, Major Song encounters the pure joy that this demanding profession offers. Pilots refer to this experience as 'cloud skiing.'
For the test pilot writing the future of the KF-21, this remains the greatest gift that flying can provide.

* This article has been translated by AI.

Heesu Kim