Flight Incheon International Airport departs from Seoul Incheon International Airport at 08:00 and arrives at Fukuoka Fukuoka Airport at 09:25.
The flighttime is about 1h 25m. The distance travelled ("as the bird flies"): 518 Km. So the average speed is roughly 366 Km.
The best day to arrive at Seoul is Friday and it would be best to avoid Saturday, as prices are on average 326.57% higher than on Friday. (Average prices, based on 743808 datapoints.)
We have a lot more statistics for flights KE 787 and between Seoul and Fukuoka.
