Singapore Airlines will finalize an order for 39 Boeing aircraft worth $13.8 billion when the Singaporean prime minister visits U.S. President Donald Trump in Washington next week.

The national airline first announced the plan to upgrade its fleet in February but no deal has to date been inked in Boeing's order book.

In an interview with CNBC on Thursday, Singapore Prime Minister Lee Hsien Loong confirmed the purchase is ready to be rubber stamped.

"We are hoping to sign an agreement between SIA and Boeing to buy new airplanes. I think that's a done deal," he said.

Singapore Airlines has said previously that it would order 20 777-9 and 19 787-10 widebody planes from the U.S. manufacturer.

Boeing currently leads rival Airbus in orders for the first nine months of the year, with 498 at the end of September compared to 271 for its European rival.