The Irish Aviation Authority has said it still does not know what caused the issues with itsair traffic management system that led to the temporary closure ofIrish airspace last night.
Cause of radar failure still unknown - IAA
An investigation is under way this morning into the technical problems with the Shannon Air Traffic Control flight radar system, which caused disruptionto flights to and from Shannon and Cork.
Director of Commercial Technology with the IAA Philip Hughes told RTÉ's Morning Ireland thattechnical issues do occur, which is why there is an independent back up system, which came into effect last night.
He apologised for any inconvenience caused but said that safety had to be put first. He added thatit was very rare for these problems to occur, and thatit could be a relatively simple problem.
Mr Hughes said it was a fairly new system which is frequently maintained.
While the problem is being resolved, operations will continue to run on the back-up system.
"These technical issues arise from time to time so we have complete plans in the event this happens that we move to back-up systems. It's highly rare for us to have this particular type of problem. The equipment is relatively new and it's maintained and it's updated very frequently. We have one of the most modern ATM (Air Traffic Management)systems in Europe so it's not an issue in terms of age or anything like that."
Mr Hughes said a "handful"of flights were affected, adding that very few over flights were affected because the busy period is usually after midnight.
Both Cork and Shannon airports sayflights are operating as scheduled this morning.
A number of flights in and out of Shannon and Cork airports were affected for a time last night, whileDublin Airport was not affected.
A back-up system was deployed to allow a phased resumption of take-offs and landings at the airports.
In a statement, the IAA said safety was its main priority and it had restricted air traffic while the issue was being investigated.
Alternative travel arrangements are being made for around 420 passengers on three flights cancelled in and out of Cork last night.
Speaking on RTÉ's Morning Ireland,Managing Director of Shannon Airport Andrew Murphysaid that "everything is back to normal" this morning.
He saidthat there have already been a number of arrivals at Shannon and departures this morning are due to leave on time.
Because flights are still operating on the back-up radar system, Mr Murphy asked that customers continue to monitor their flights on social media and keep in contact with their airlinesif due to travel today.