A fault in the air traffic control radar system at Dublin Airport is continuing to cause major flight disruption and delay thousands of passengers.
The Irish Aviation Authority says the airport is operating at around 65% capacity.
Airlines including Aer Lingus and Ryanair have cancelled dozens of flights.
The IAA said this evening that a glitch in the hardware of the radar system has been identified.
It is waiting on an engineering report to assess if this fault is the main cause of disruptions to the radar system. It emerged today the system has been faulty for as long as four weeks.
The Authority has apologised for widespread disruption and cancellation of flights to and from at Dublin Airport due to a safety-based decision to ground flights earlier in the day.
Meanwhile, Ryanair have called for a Government investigation into the failure of the radar system.
Ryanair Chief Executive Michael O'Leary said Ireland is effectively closed for business because of the failure of the system and the lack of a back up system or contingency plan.
He said 74 Ryanair flights had been cancelled and 13,000 passengers have been affected by the systems failure.
Mr O'Leary said it is impossible to know if there will be a knock on effect to tomorrow's schedule as a result of today's disruption.
Earlier, all flights in and out of the airport were grounded for a time because of safety reasons.
Ten flights were diverted to Shannon, Belfast and Cork. A bus service has been provided for those passengers to get them to Dublin.
A spokesperson for Aer Lingus says it is too early to say whether today's disruption will have a knock-on effect to flights tomorrow but she said the airline hopes to restore a full schedule tomorrow morning.
Affected Aer Lingus passengers can rebook their flights free of charge, via the website, www.aerlingus.com, or by calling reservations on 0818 365 044. Passengers that choose not to travel may avail of a refund.
At around 11.45am this morning, a problem occurred with the air traffic management system. Due to a technical fault, air traffic controllers were unable to identify aircraft.
This problem lasted for ten minutes before the system returned to normal. In that time, all departures were held on the ground and some aircraft in the air were asked to remain where they were.
A spokeswoman for the IAA said the cap on flights was put in place as a result of this incident and in the interests of safety.
Passengers are advised to check with their airlines.
Live flight information is available at RTÉ Aertel page 570.
