Flight Incheon International Airport departs from Seoul Incheon International Airport at 08:35 and arrives at Tokyo Narita International Airport at 11:05.
The flighttime is about 2h 30m. The distance travelled ("as the bird flies"): 1555 Km. So the average speed is roughly 622 Km.
The best day to arrive at Seoul is Tuesday and it would be best to avoid Thursday, as prices are on average 297.83% higher than on Tuesday. (Average prices, based on 6968843 datapoints.)
We have a lot more statistics for flights TW 241 and between Seoul and Tokyo.
