Aer Lingus has said it is confident that technical problems impacting online check-in and booking management have been resolved.
The airline said it is aware that yesterday and earlier today, some customers experienced issues checking-in online via its website and mobile app and managing their bookings.
"Following earlier intermittent availability, we are now confident that the issues have been resolved," the airline said in a statement.
"For customers who were unable to check-in online earlier, online check-in is now fully available and we would encourage customers to use it."
"Check-in at the airports is also available," the company said.
Aer Lingus apologised for the inconvenience caused to customers and said that there was no impact on its services today.
"We expect that services will also operate normally tomorrow."
"Customers should arrive at the airport 2 hours before departure for European flights and 3 hours before departure for transatlantic flights," Aer Lingus said.
The airline said that the issue is not connected to last week's IT outage which led to the cancellation of more than 60 flights.
Last Saturday, construction work in the UK caused damage to a fibre-optic cable which led to a break in connectivity between Aer Lingus and a cloud service provider.