IndiGo is placing a massive order for 180 Airbus A320s and, in the process, becomes the first customer for the “new engine option” configuration launched in December.

Airbus notes that the deal is the single-largest A320 commitment. The deal so far is only a memorandum of understanding and still has to be finalized and would hit the order book likely this year.

The first 30 aircraft will be regular A320s, with the remaining 150 in the NEO configuration which only becomes available in 2016.

Unusually, Airbus launched the NEO program without a launch customer, arguing it wanted to avoid the deep discounts such buyers usually receive. Still, IndiGo’s deal will be far below list price given the magnitude of the commitment.

The airline has still to announce whether it is buying the CFM International Leap-X or Pratt & Whitney PW1100G. The order will likely dictate the order in which the A320NEO engine offerings come to market.

In a statement, the airline’s co-founders, Rakesh Gangwal and Rahul Bhatia, say “this order for industry leading fuel efficient aircraft will allow IndiGo to continue to offer low fares.”

The airline is already an A320 operator and “ordering more... was the natural choice to meet India’s growing flying needs,” the executives say.

Airbus notes the NEO and traditional A320 will have a high degree of commonality, including for pilot operations. The NEO also features winglets Airbus plans to introduce next year.