Dublin Airport is operating at reduced capacity today after a virtual shutdown yesterday afternoon due to a serious radar fault.
The Irish Aviation Authority is awaiting an engineer's report into the fault before deciding whether to return the airport to normal service.
It says the airport was operating at around 70% capacity this morning, handling 20 departures and 16 incoming flights per hour, compared to the 25 planes usually allowed in and out of the facility.
The IAA says the fault has been identified, but further tests are needed before operations can return to normal.
Passengers are being advised to turn up to the airport as planned and to contact their airline for details on specific flights.
Aer Lingus is warning passengers to expect delays, but says it does not expect to cancel any of its 155 flights into and out of the airport.
Ryanair, however, says the IAA is not telling the full truth and is warning that the continued disruption will lead to major back-ups by midday.
It says significant flight cancellations are a virtual certainty.