Instead of dividing the terminals into rational categories, the plans will put passengers on Korean Air, Delta Air Lines and Air France-KLM through the second terminal, while fliers on other carriers will keep using the first.

Concerns are rising that the opening of the second terminal at Incheon International Airport next January will sow confusion among passengers.

One airline staffer said, "This is the first time in Korea that a single airport will operate multiple terminals, so there's a chance that lots of passengers will go to the wrong terminal."

The distance between the two terminals is more than 15 km, and travel from one to the other will take about half an hour by shuttle bus, which could mean that any passengers who arrive at the wrong one could miss their flights.

Industry insiders said code-sharing among carriers could add to the chaos. Around 794 code-sharing passengers a day went through the airport last year, transferring from a foreign airline to onward domestic flight on Korean Air. And 1,188 code-sharing passengers a day bought tickets for a foreign airline through Korean Air.

"This will create many instances where passengers who buy a ticket through a foreign carrier arrive at Terminal 1 but end up having to go to Terminal 2 to board their onward flight," one airline staffer said.