Flight Narita International Airport departs from Tokyo Narita International Airport at 16:00 and arrives at Seoul Incheon International Airport at 18:35.
The flighttime is about 2h 35m. The distance travelled ("as the bird flies"): 1555 Km. So the average speed is roughly 602 Km.
The best day to arrive at Tokyo is Saturday and it would be best to avoid Thursday, as prices are on average 414.66% higher than on Saturday. (Average prices, based on 3825740 datapoints.)
We have a lot more statistics for flights OZ 103 and between Tokyo and Seoul.
THB
