SEOUL (AFP) - South Korea's biggest airline, Korean Air, on Thursday announced the planned purchase of 12 Boeing passenger jets for US$3.8 billion (S$4.7 billion) over the next five years.

In a regulatory filing, the carrier said it planned to add five 747-8 Intercontinentals, six 777-300ERs and one 787 Dreamliner to its fleet by the end of 2018.

Korean Air currently operates around 155 aircraft, flying to 45 countries.

The airline said it posted a third quarter net profit of 342 billion won (S$400 million), down 1 per cent from a year ago on a decline in passenger traffic.

It said operating profit fell 43 per cent year-on-year to 160 billion won, while revenue was down 3.4 per cent to 3.18 trillion won.

But the company benefitted from a foreign-exchange gain of 597 billion won, it added.

The carrier said outbound travel to Japan had declined sharply due to concerns about radiation.