Boeing Co. is closing in on a major order for its 777X widebody model from Emirates, according to people familiar with discussions, in what would provide an important boost to a program that’s years behind schedule.

Already the biggest buyer of the widebody aircraft, Emirates is poised to order a high double-digit number of the 777X, said the people, asking not to be identified discussing private negotiations. As part of the deal, regional affiliate FlyDubai could take on some smaller 787 Dreamliners, the people said. Boeing and Emirates declined to comment.

An accord with the biggest international airline would be a vital endorsement of Boeing’s newest and largest aircraft, which has struggled to pull in sales as it remains behind schedule for entry into service. Any additional purchase of the plane, which comes with novel folding wing tips, would add to a backlog of 115 777X that Emirates previously ordered.

The Dubai carrier is among the largest operators of widebody aircraft, using its hub in Dubai as a global connecting airport between the US, Europe and Asia. With the Dubai Air Show kicking off on Monday, the event will provide a backdrop for major deals as carriers rush to replenish and upgrade their fleets.

Other operators likely to announce major commitments at the event include Turkish Airlines, which is close to an order for about 350 Airbus SE aircraft, including both narrow- and widebody jets, people close to the talks said earlier.

Read More: Turkish Air Order Splash Pushes Dubai Show Into Record Territory

Expanding its fleet with widebody aircraft like the 787 would mark a strategic shift for FlyDubai, which now relies on the Boeing 737 aircraft for shorter routes around the Middle East, parts of Africa and as far as Malaysia, according to the carrier’s website.

Emirates is also in negotiations with Airbus about an order for the European manufacturer’s flagship A350 aircraft. That purchase and the accord with Boeing are still under final negotiations, and terms of the deals and the timing of any announcements could change, the people cautioned.

Airbus declined to comment on discussions with customers.

(Updates with context on accord from third paragraph.)

Author: Siddharth Philip, Julie Johnsson and Leen Al-Rashdan