I visited Seoul Incheon on December 10 after my amazing Korean Air B747-8 flight. I have a 100% sunny and clear day in Incheon and it was perfect for photos.
There are some great spots on the south side of the airport in the afternoon. The photo locations are on on a small hill, looking over either the runway threshold or touchdown area. You'd need a 300mm-400mm lens for most of the traffic. From my location, I can photograph both line up and approach (short final) which is perfect!
Although long zoom lens is required, the condition was almost perfect without any heat haze distortion. The local mentioned there were a lot of clear winter days. The weather I had was just one of the typical winter clear day!
The traffic is constant flowing without much downtime. Within a day, you will see most of the Korean Airlines (Korean Air, Asiana Airlines, Jin Air, Air Seoul, T'Way) and quite many interesting foreign movements. There are a lot of heavy movements such as B777, B747 and A380. The photo location is good from 11am till sunset.
Below are what I've caught on my camera during my spotting in the fine afternoon. I took almost 1,000 photos but chose only a handful below in the album to show you.
Special thanks to Jamie Chang, Ricoh Ahn and others for their kind help. Photo would not have been possible without their assistance during my stay in Incheon!