Ryanair boss Michael O'Leary jets in for key talks with the transport secretary Chris Grayling today as concerns mount over airlines' flight rights post Brexit.
From March 2019, the UK no longer automatically has the same flight permissions as an EU member, meaning the right of its carriers to fly to the EU and beyond will have to be renegotiated.
The aviation industry has warned repeatedly that flights from the UK could be disrupted and even grounded if a new legal framework is not agreed by then. The situation has become increasingly urgent because the industry and its regulators have to finalise flight timetables many months in advance.
"There is a real prospect, and we need to deal with this, that there are going to be no flights between the UK and Europe for a period of weeks, months beyond March 2019," O'Leary told the European Parliament's Transport and Tourism Committee last month.
This has prompted the UK-based easyJet to apply to Austria for an air operator's certificate, which would enable it to establish a new airline in the country.
In Ryanair's case, it may have to create a UK subsidiary to operate from its Stansted base post Brexit. There could also be ramifications for the Irish airline's Prestwick operations.
It is thought that the low cost airline, which could move more flights to Central and Eastern Europe, is seeking more clarity from UK ministers before it acts.
In a statement, a spokesman for the Department for Transport said: "Aviation is absolutely crucial to the UK's economy and we are committed to getting the right deal for Britain.
"Our aviation industry is the largest in Europe, and both we and the EU benefit from the connectivity it provides."