Turkish carrier Pegasus Airlines is set to announce an order for 75 Airbus A320neos next week, with an additional 25 options.
Sources close to the deal indicate it will be unveiled on or around 18 December.
Pegasus has previously been an all-Boeing operator, with 37 737-800s in service and a further seven aircraft on order, alongside a pair of older -400s, as recorded by Flightglobal's Ascend Online database.
So far the airline has not indicated an engine choice for the re-engined narrowbody type.
It intends the ordered aircraft to form the backbone of the airline's operation from 2020.