Korean Air is in talks with Sierra Nevada Corporation, the US aerospace and defense firm, to sell its five B747-8i jets in an apparent move to boost its operational efficiency ahead of its planned merger with Asiana Airlines.

According to industry sources on Friday, Korean Air held a board meeting Wednesday and decided to sell the planes to Sierra Nevada. The deal, valued at about 918 billion won ($674 million), is expected to be completed by September 2025. Currently, the company owns nine units of the B747-8i aircraft.

“The B747-8i model has four engines, which means lower fuel efficiency than the twin-engine aircraft that are more favored recently. The decision comes as part of the airliner’s strategic move toward newer, more fuel-efficiency models,” a source from the aviation industry said.

Earlier in March, Korean Air finalized an 18-trillion-won contract with Airbus for the acquisition of 33 advanced A350 aircraft. The A350 not only promises a 25 percent improvement in fuel efficiency compared to its counterparts but also boasts a corresponding 25 percent reduction in carbon emissions. The company said it aims to adopt the new aircraft in phases by 2032.

In its earnings report on Wednesday, Korean Air posted 3.82 trillion won in sales and 436.1 billion won in operating profits in the first three months of this year, marking 19.6 percent and 5.1 percent growth, respectively, compared to a year ago.