Korean Air Lines Co. plans to order up to 50 Boeing Co. widebody jets, including 20 each of the 777-9s and 787-10s, the carrier announced at the Farnborough air show on Monday.

The transaction, which includes an option for 10 more 787-10s, is a boost for the US planemaker, which has had to slow production over concerns around its manufacturing safety standards.

The deal was unveiled by Korean Air Chairman Cho Won-Tae and Boeing Commercial Airplanes President and CEO Stephanie Pope.

“The addition of the Boeing 777-9 and 787-10 aircraft marks a significant milestone in our strategic objective to expand and upgrade our fleet,” Cho said.

For Boeing, signing a new airline customer to the 777X shores up confidence in a troubled plane program that’s already running several years behind schedule and is yet to gain certification. It’s an important endorsement of the twin jet intended to replace Boeing’s four-engine 747 by an airline that was once a major operator of the iconic, hump-backed jumbo.

Korean Air would use the 777X jets to replace its two other biggest jets — the Boeing 747s and Airbus A380s — the largest passenger planes in the world.

Boeing’s Korean Air deal is a bright spot at Farnborough, a commercial air show that this year is expected to be light on marquee transactions.

While the current Boeing deal is at a memorandum of understanding stage, after finalizing the transaction, Korean Air will have a total of 203 new-generation aircraft in its fleet by 2034.

In March, Korean Air ordered 33 Airbus A350s and last year added 20 A321neos to bring its total order backlog to 50 of the single-aisle jets.