Noting forecasts about economic disruption in the UK in the event of a vote to leave the EU, airline president Tim Clark said he was also worried about political and economic volatility in the rest of the 28-nation bloc.

"My concern is what will happen in the rest of the EU," Clark told reporters at the annual IATA airline industry meeting in Dublin.

"Instability means lowering demand, lowering in demand means less people travelling on aeroplanes. How long that would last, I don't know," he said.

The CEO of German carrier Lufthansa (>> Deutsche Lufthansa AG) also said he expected demand to fall if Britain leaves the bloc.

"We have already brought down our growth plans," CEO Carsten Spohr said when asked whether the airline was making capacity adjustment plans in the event of a Brexit.

Airlines are among those that have benefited the most from EU agreements on open airspace and free movement of people, and airline executives fear Brexit's resulting long-winded renegotiation period between governments which would need to take place to ensure that their current access to the skies was retained.

If Britain votes to leave, bilateral agreements allowing unlimited travel between Britain and the rest of the EU would have to be renegotiated. Britain would also have to agree other deals, such as with the United States, which has an open skies arrangement with the EU.

But for Irish carrier Aer Lingus, owned by UK-based International Airlines Group (>> International Consolidated Airlns Grp SA), chief executive Stephen Kavanagh said a Brexit could create opportunities.

"If Heathrow or the UK becomes difficult to transfer through from the European perspective, then that again accelerates the opportunity for us in expanding Irish airports as a gateway," he said.

(Reporting by Tim Hepher and Victoria Bryan; Additional reporting by Sarah Young; Editing by Jason Neely and David Evans)