India’s IndiGo has placed a firm order for 250 Airbus A320neo narrowbodies, confirming a commitment announced in October 2014 and marking the single largest numeric backlog addition in the European airframer’s history, the parties announced Monday. The deal brings to 530 the number of A320-family jets IndiGo has ordered from Airbus, starting in 2005 with an order for 100. In 2011 it placed an order for 180 A320neos, marking the first commitment from an Indian carrier for the re-engined narrowbody.

In business for nine years, IndiGo now ranks as India’s largest domestic airline by market share. It signed this latest purchase agreement on the 69th Independence Day of India, on August 15.

“This new order further reaffirms IndiGo’s commitment to the long-term development of affordable air transportation in India and overseas,” said IndiGo president Aditya Ghosh. “The IndiGo team is even more energized and excited than ever before to herald this new phase of our growth for many years to come.”

Airbus has now collected firm orders for more than 4,100 A320neos. Schedules call for the new single-aisle jet to gain certification ahead of first deliveries by year-end.