Ryanair has suggested it could double the number of flights from Belfast if the tax on flights was abolished.
But Kenny Jacobs, the airline's chief marketing officer, also said uncertainty around the future of the open skies policy following Brexit could hit the company's expansion plans.
"They (the routes) are generally performing well," he added. "Gatwick will always do well. Sunshine routes do well. Anything below 90% load factor and we are going, what's the issue?
"We have a high bar to get over. Generally, we are happy. We wouldn't be growing from zero to 1.3 million (passengers) if it wasn't strong.
"But there are still people driving to Dublin to fly. You get an airport with more frequency and you don't have air passenger duty (APD).
"We have a lot of £19.99 fares and £13 of that is tax. We believe Stormont should do what they are doing in Scotland and take control of the travel tax."
Airline boss Michael O'Leary previously said the airline was cutting expansion due to Brexit, and Mr Jacobs, speaking as the airline announced its winter schedule from Belfast, believes the same could happen here.
"I would urge Stormont to do the same (as Scotland) and grow tourism," he said.
Mr Jacobs claimed City of Derry airport "was the best example of an airport impacted by the travel tax".
Michael O'Leary has already warned that the remaining three domestic flights from the city could be moved to Belfast unless there is a cut in APD.
Mr Jacobs said: "When you are going from Derry to London and the fare is 20 quid, £13 of that is tax. It is punishing regional airports like Derry. That's why we made reductions in Derry.
"It doesn't deliver the return we need. If the tax stays in place, you would expect to see us grow moderately... all with the caveat of Brexit.
"We could probably double flights from Northern Ireland if the tax was removed."
He also warned that if the UK ended up out of the open skies agreement between the EU and US because of Brexit, it could hit the industry. "There is no solution and they need to come up with a solution by March 2018," Mr Jacobs said.
"We will be planning the summer 2019 schedule. We need to know how we are going to operate schedules. The clock is ticking, and it's getting quite tight. It's going to come down to both sides how flying will continue to operate in post-Brexit."
Speaking about the political instability at Stormont, Mr Jacobs said: "I hope a government forms quickly and sets an agenda soon."
Belfast International Airport's Uel Hoey added: "We wholeheartedly support Ryanair's entreaty to the Government to scrap APD as soon as possible.
"The burden of APD has a uniquely negative effect upon Northern Ireland's capacity to boost tourism and general economic growth through the sustainable provision of widely available and affordable airfares."
Ryanair has 13 summer routes and 12 in the winter.