Ryanair boss Michael O'Leary has said Stormont is "throwing good money after bad" by bailing out Northern Ireland's direct flight to New York.
The Executive is part-funding a £9m package to keep United Airlines' Belfast to Newark flight - Northern Ireland's only transatlantic route.
"If it were going to encourage United to commit here for a 10-year period it would fine," Mr O'Leary said.
"But you are essentially paying about £160 for every return ticket on that route, and the minute the Government here decides, 'Look, we can't keep subsidising this', United is going to cut the route.
"They acted on APD on the transatlantic routes. But then they throw more good money after bad - they subsidise."
And Mr O'Leary also warned Ryanair is likely to eventually pull out of City of Derry airport entirely, taking out its remaining Liverpool and Glasgow routes.
Mr O'Leary said the scrapping of APD would be "huge" and could double the number of passengers flying in to Belfast through Ryanair.
"If APD had been scrapped we wouldn't be closing the Derry to London route," he said.
He believes a combined £16m aimed at boosting City of Derry airport and subsidising United's Belfast to Newark route would be better spent on plugging the shortfall from axing APD.
Mr O'Leary said if the Executive had removed the £13 a flight duty, his airline would not be cutting services.
And he added that Ryanair would have added a fourth plane to Belfast if the UK hadn't voted for Brexit.
"We were certainly planning to put a fourth aircraft in to Belfast International. We have been made nervous by Brexit," he said.
"That 1.1 million passengers would double to two million, just from Ryanair, if APD was scrapped. The spend from those various visitors over here would be a multiple of the APD."
On Bombardier's C Series jets, Mr O'Leary said the planes were too small and needed to be made bigger in order to pick up more orders.
Speaking about Brexit at a CBI lunch at Titanic Belfast after a press conference, he said: "The EU is not going to make it easy for the UK. All this kind of arrogant nonsense in London - 'we're the fifth biggest economy in the world, they'll give a good deal'... they won't.
"Why would you be a member of the EU if you can have control over your borders? You wouldn't," he said.
"So if the UK gets a good deal, the EU breaks up, and they care less about the UK than they do about protecting and keeping the EU together."
Mr O'Leary also rubbished Government claims that it will secure favourable trade deals, insisting the UK will be "screwed" in negotiations.