Malaysia’s AirAsia X has converted a memorandum of understanding covering 50 Airbus A330neos to firm status and added another five airplanes to the total in the largest single order ever placed for a member of the European airframer’s twin-engine widebody family. With the firm order, confirmed on Monday by Airbus, AirAsia X has placed firm orders for 91 A330s, making it the type’s largest customer. Plans call for deliveries of the latest batch of airplanes to start in 2018.

“This latest deal with Airbus will enable AirAsia X to consolidate its growth rate in 2015-2017 before ramping up deliveries from 2018 onwards,” said AirAsia X cofounder and director Tony Fernandes.

Launched during the 2014 Farnborough Air Show, the A330neo drew commitments for 121 examples worth $33.2 billion at the event. Launch customer AirAsia X led all takers with a $13.8 billion commitment for 50 airplanes. The addition of the five airplanes to the firm order this week raises the value of the deal to $15.1 billion at list prices.

The A330neo drew its first firm orders late last month, when Delta Air Lines signed for 25. On December 3 CIT Group—one of the three leasing companies to sign an MOU at Farnborough—announced it had converted on its commitment for 15.