Indian operator IndiGo has tentatively signed for 50 ATR 72-600 turboprops as part of a programme to enhance regional connections.
Deliveries of the aircraft are set to begin by the end of this year.
ATR has confirmed the agreement – still the subject of a term sheet – and says the carrier has flexibility to reduce the number of deliveries.
IndiGo says a firm order will depend on the two sides' reaching a "mutually-satisfactory final purchase agreement".
Up to 20 ATRs will be brought into the IndiGo operation by the end of 2018, the airline says, should the order go ahead.
ATR says the airline is to participate in the Indian government's regional connectivity scheme – known as UDAN – for the subcontinent.
"[IndiGo] is currently preparing for an ambitious development of its regional footprint," it adds.
ATR values the potential order at $1.3 billion.
India's connectivity programme will involve establishing 100 new airports over the next two or three years, says the airframer, while carriers will receive financial support for their operations.
"We are embarking on a journey to build a nationwide regional network and connect cities that have not benefited from the growth in Indian aviation," says IndiGo president Aditya Ghosh.