A collapse of online services, check-in and boarding systems caused major disruption at the carrier.
Aer Lingus blamed “a break in connectivity in services from a UK network provider” for the cancellations, which affected services from Dublin to European and UK destinations.
The airline said it had operated all its transatlantic routes from Dublin, “albeit with delays and reduced passenger numbers in some instances due to security restrictions applying as a result of the systems outage”.
Transatlantic flights from Shannon were unaffected but Aer Lingus Regional flights also suffered delays.
Aer Lingus is offering free rebooking “on available flights” until Tuesday.
It will also allow passengers to rebook for a later date with change fees waived or issue refunds. Aer Lingus said it was contacting affected customers directly.
