Aer Lingus has confirmed that it is in talks with George Best Belfast City Airport.
The airline is believed to be planning to switch its operations from Belfast International Airport to Belfast City.
A spokesman said: “We are engaged in a confidential process with both airports which is not complete yet.”
It follows the City’s loss of BMI Baby, which carried 400,000 passengers a year. The airport is expected to confirm details of new airlines soon.
Aer Lingus flies to Heathrow and seven European destinations, but could expand routes to regional UK airports from the City, filling some of the lost BMI Baby routes and competing with Flybe.
The move would make George Best Belfast City Airport Belfast’s only Heathrow connection.
With the takeover of BMI by British Airways there had been concerns about that route.
BA has confirmed its commitment to the route but there remains speculation that there may be long-term plans for both airlines to work together on the Belfast-Heathrow connection.
Aer Lingus currently operates flights to Alicante, Barcelona, Faro, Lanzarote, Las Palmas, London Heathrow, Malaga and Tenerife.
Budget airline BMI Baby was taken over in April by the International Airline Group, parent company of British Airways.
Belfast City has said 420,000 of its passengers last year had flown with BMI Baby.
IAG said it had to act in the face of big losses, and promised to provide full refunds after flights stop this month.