The low-cost airline said aviation should be treated as a matter of urgency in Brexit negotiations, as summer schedules for 2019 must be finalised by March next year, reports the Telegraph.
Without a bilateral agreement being struck with the EU, Britain will have to revert to historic WTO regulations that do not cover aviation, Ryanair said.
The airline added that there was a “distinct possibility of no flights between Europe and the UK” for a period from March 2019.
Airlines plan their flights a year in advance, so will finalise their schedules for the summer of 2019 in the spring of 2018.
“Some nine months on from the Brexit referendum, we are no closer to knowing what effect it will have on aviation,” said Ryanair’s chief marketing officer Kenny Jacobs.
“With Britain planning to leave the EU and its Open Skies agreement, there is a distinct possibility that there may be no flights between the UK and Europe for a period of time after March 2019.”
Open Skies is an agreement between the EU and the US, which the UK will potentially be outside of if it leaves Europe without a replica of the deal.
“The best we can hope for is a new bilateral agreement between the UK and EU,” Mr Jacobs added. “However, we worry that Britain may not be able to negotiate such a bilateral in time for the release by airlines of summer 2019 schedules in mid-2018.”
Ryanair said it will carry more than 44m customers to and from British airports this year. It has already shifted growth into Europe and away from the UK, and will base no additional aircraft at its 19 airports in the country this year.