Flight Incheon International Airport departs from Seoul Incheon International Airport at 10:20 and arrives at Tokyo Narita International Airport at 12:50.
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 Sunday and it would be best to avoid Tuesday, as prices are on average 116.32% higher than on Sunday. (Average prices, based on 5616791 datapoints.)
We have a lot more statistics for flights TW 213 and between Seoul and Tokyo.
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