Flight Incheon International Airport departs from Seoul Incheon International Airport at 09:00 and arrives at Tokyo Narita International Airport at 11:20.
The flighttime is about 2h 20m. The distance travelled ("as the bird flies"): 1555 Km. So the average speed is roughly 666 Km.
The best day to arrive at Seoul is Sunday and it would be best to avoid Thursday, as prices are on average 65.86% higher than on Sunday. (Average prices, based on 6764575 datapoints.)
We have a lot more statistics for flights NH 6972 and between Seoul and Tokyo.
