Flight Incheon International Airport departs from Seoul Incheon International Airport at 22:35 and arrives at Haikou Haikou Meilan International Airport at 02:25.
The flighttime is about 4h 50m. The distance travelled ("as the bird flies"): 1988 Km. So the average speed is roughly 411 Km.
There is an 1 hour time difference between Seoul and Haikou
