Aer Lingus announced today that it had struck a code-sharing deal with British Airways for its new service from Belfast International to London Heathrow.
The move means that aircraft operating the four flights a day service will carry both BA and Aer Lingus numbers.
Enda Corneille, Aer Lingus' commercial director, said passengers travelling onward with BA on long-haul flights from Heathrow would be able to book tickets and baggage through to their final destinations.
He said this would give the airline a distinct advantage over bmi, which operates an eight flights a day service from Belfast City Airport to Heathrow.
Aer Lingus is due to launch its Heathrow service on January 14 and has been advertising fares from £23 single including taxes.
But Mr Corneille said that in a couple of weeks' time, the lead-in fare for certain off-peak dates would be reduced to £19.
He denied that this was a sign of panic and insisted that the airline was " very encouraged" by the level of bookings to date.
Mr Corneille, who was hosting a Press conference in Belfast, said that the fares being charged by bmi on its London service at present were " criminal".
He said: "The fares being charged by bmi are up to £160-£170 one way, whereas we will be offering fares at £12 or £13 for certain dates."
He also said Aer Lingus "wanted to achieve" a later flight back from Heathrow to Aldergrove.
The final Aer Lingus departure of the day will be at 7.25pm, while bmi's last flight is at 7.45pm.
There have been many calls from the business community for a late-evening departure from Heathrow, which would enable people flying from abroad into London at teatime to get home.
The Aer Lingus service is set to kick off on December 10 with new services from Aldergrove to Amsterdam and Barcelona.
Mr Corneille said that Aer Lingus would be basing three Airbus A320 aircraft - two of them brand new - at Belfast, an investment of £100m.
He said that following the settling of the dispute with IALPA, the Irish pilots' trade union, recruitment was under way for Aldergrove, with 1,000 applications having been received for the 100 vacancies.
Aer Lingus is set to fly to nine destinations from Aldergrove, with Nice having been added earlier this month to the list.
The airline hopes to carry 500,000 in its first full year of operations from Belfast, and be profitable within year one.
? Pat Shanahan, the executive chairman of Shannon Airport Authority, yesterday resigned his post in protest over the failure of the Dublin Airport Authority to inform him about Aer Lingus' plan to axe its service from Shannon to London.