Boeing will receive a $9.2 billion contract to produce more than 350 T-X trainer jets in addition to simulators and other equipment.
KAI sought for a joint bid for the U.S. T-X APT program where overall purchase could reach 1,000 jets given the average age of aircraft.
The goal is to have the new trainer aircraft at full operational capability by 2034.
The USAF contract also ensures Boeing maintains a presence in military fast jets as its F-15 and F/A-18 Super Hornets are retired in the coming years.
"This is all about joint warfighting excellence; we need the T-X to optimize training for pilots heading into our growing fleet of fifth-generation aircraft", said Air Force Chief of Staff Gen. David Goldfein. Lockheed, the manufacturer of the F-35 Joint Strike Fighter, is the world's largest defense contractor by a wide margin, taking in $50 billion in USA contract dollars a year ago compared with Boeing's $23 billion.More news: USA sanctions Chinese military for buying Russian weapons
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The award from the US Air Force comes after Boeing has had some problems delivering to the Air Force its new in-air refueling jet, which is the KC-46.
Boeing was the only competitor to pitch a clean-sheet design for T-X, which increases the likelihood that it will have to pay out of pocket to correct any issues that emerge as the program proceeds. The Air Force offered further information in its own statement and in comments to reporters, according to Defense News.
St. Louis, Missouri, has been awarded. Lockheed Martin and Korea Aerospace Industries had teamed up to offer the T-50A, which has already been used to train pilots in Korea, Indonesia, Thailand, the Philippines and Iraq.
The Air Force's original cost estimate for the T-X program was $19.7 billion.
The T-38 replacement program has been under development for 15 years now.
The Boeing T-X at its official unveiling in 2016.