Air routes from Belfast to London Heathrow could be ringfenced to protect regional services, the UK Transport Minister has said.
This would require European agreement and a significant change in EU law, Theresa Villiers added. She said the coalition's options for intervening were limited.
Recent consolidation of airline groups has prompted fears for the future of Northern Ireland's air link with Heathrow but the minister said there were grounds for hopefulness.
Ms Villiers said: "The current situation I think gives cause for real optimism. There are lots of flights to Heathrow and every indication that these flights are commercially viable."
The Northern Ireland Affairs Committee of MPs at Westminster is investigating air transport links to and from Northern Ireland. It is also probing the implications of the recent takeover of BMI by British Airways' parent company IAG in a £172.5 million deal.
The Belfast to Heathrow route is protected but about 100 staff employed by BMI, which operates the service, at George Best Belfast City Airport were told earlier this year their jobs could be threatened. In 2001, BA pulled out of its London Heathrow to Belfast route with the loss of 160 jobs.
There are fears that, in the long term, BA wants to use the Heathrow slots provided by the Belfast route but may not continue with the Belfast-London services.
The minister told the committee the link from Belfast to Heathrow was commercially attractive for BA but how long into the future this could be maintained was unclear.
She said: "There is a case for looking at whether there is any scope within the debate in Europe at the minute with how slots are allocated as to whether there is any scope for ringfencing certain flights to Heathrow to ensure and have a guarantee that these flights remain in the long term."
DUP Upper Bann MP David Simpson said BA had "walked away" from Northern Ireland in 2001. "Despite the assurances that Willie Walsh is giving there is still that doubt, lack of trust, that in the not too distant future BA will pull out of the Belfast routes," he said.