Ryanair (FR, Dublin Int'l) will add a "Brexit clause" to tickets sold for flights after March 29, 2019, which will grant passengers full refund rights if these operations would not be allowed to continue due to the United Kingdom leaving the European Union.

"We’ll announce our [2019] summer schedule soon enough and there’ll be a term and condition that this is subject to the regulatory environment allowing this flight to take place," Chief Marketing Officer Kenny Jacobs said on January 31.

Although the carrier is not intending to open sales for the post-Brexit period until September 2017, it is already struggling to plan operations for the next year due to the continuing regulatory uncertainty surrounding the Brexit.

The UK is due to leave the EU on March 29, 2019. It is still unclear whether the country will continue to be a part of the European Open Skies agreement after this date. The European officials recently floated an idea of a two-year transition period, but this also remains vaguely defined.

The European Union and some third countries in the Balkans, Northern Africa, the Middle East and the Caucasus are covered by agreements which allow any carrier registered in any of the countries and owned by nationals of the bloc to operate within the area without restrictions. The law covers both domestic and international operations. The EU has also signed an Open Skies treaty with the United States and Canada.

Should the UK leave the Open Skies agreement, all airlines would need to secure route authorities for services connecting the country with any of the bloc's members. Furthermore, all UK-registered carriers would lose the right to operate within the bloc without specific authorisation. The UK would also cease to be a party to the transatlantic open skies agreements.

The aviation industry has been consistently lobbying for clarity on the aviation regulatory framework after Brexit but so far no agreements have been announced in this regard.

As Ryanair holds an Irish air operator's certificate (AOC) it does not risk losing the rights to operate within the EU but may face difficulties regarding its UK-bound flights. According to the ch-aviation capacity module, London Stansted is the LCC's largest base with 1,021 weekly departures. In total, it currently operates 2,050 weekly departures out of the UK, its third-largest market after Italy and Spain.

In moves widely seen as insurance against the Brexit-related uncertainty, easyJet set up an Austrian-registered subsidiary easyJet Europe last year, while Wizz Air opened a UK-based unit Wizz Air UK.