Flight Gimpo International Airport departs from Seoul Gimpo International Airport at 07:10 and arrives at Jeju City International Airport at 08:25.
The flighttime is about 1h 15m. The distance travelled ("as the bird flies"): 271 Km. So the average speed is roughly 217 Km.
The best day to arrive at Seoul is Thursday and it would be best to avoid Sunday, as prices are on average 177.63% higher than on Thursday. (Average prices, based on 818596 datapoints.)
We have a lot more statistics for flights KE 1019 and between Seoul and Jeju City.
