How long is the flight from Seattle WA to Osan Korea?

Answer 1

If there were a direct flight, . . . about 12 or 13 hours depending on time of year, as seasonal jet streams can affect flight times. Still, there is no direct commercial flight. At best you would have to route yourself through Incheon, Korea's main international airport. Once you arrive in Incheon, you will need a 2 hour bus ride to Osan, which is just south of Seoul. With a destination such as Osan, I suspect you may be in the military. Osan Air Force Base may have military flights strictly for military personnel, but even those are probably routed through Japan. Good Luck!