The World's Busiest Air Routes: Korean Routes Rank #1 for Both International and Domestic

According to OAG International data
The world's busiest air routes by passenger volume for September 2026
Domestic: Gimpo-Jeju route at 1.08 million passengers/month (unchanged at #1 for about 15 years)
International: Incheon-Narita route at 550,000 passengers/month
For reference, Incheon-Narita ranked 4th throughout 2025, but hit #1 for the first time this month
Additionally, the Incheon-Osaka and Incheon-Fukuoka routes also ranked within the top 10.
Japan is the country most visited by Koreans, and Korea is the country most visited by Japanese
Since Japan's Silver Week and Korea's Chuseok holiday overlap in late September
There is a synergistic effect
Also, since the pandemic, Incheon has been used extensively as a hub
If you take a Korea-Japan route
You'll notice more multinational and multi-ethnic passengers than expected, traveling from distant home countries through Incheon transfers to various regions in Japan
Just as Koreans used to transfer through Dubai or Amsterdam when traveling to Europe in the past