The Irish Aviation Authority (IAA) says there is nothing to suggest cybercrime was to blame for most of Ireland's airspace being closed last night.
In an update this afternoon the IAA says technical experts are still trying to isolate the root cause of the issue, and the investigation could take some time.
Air traffic control in Shannon and Cork failed yesterday evening causing a number of flights to be diverted.
The backup system was deployed, and it is still running operations.
The IAA says the technical issue was not a radar problem and most likely a simple software issue.
No flights have been impacted today.
Andrew Murphy, Managing director of Shannon Airport said it was fortunate the problem did not happen earlier in the day.
"Had it happened at a different time during the day no doubt it would have been a different level of disruption," said Mr Murphy.
Last night, total radar failure at Shannon Air Traffic Control (ATC) centre forced the closure of Irish airspace to overflights, the rerouting and grounding of dozens of flights, and the deployment of an Emergency Air Situation Display System (EASDS) in an effort to maintain safety in the skies.
The radar collapse affected a state-of-the-art system staff were told could never fail.
It meant air traffic controllers in Shannon were forced to introduce a “zero” flow rate, which means no aircraft were allowed enter Irish airspace for a number of hours while frantic efforts got underway to organise re-routing of hundreds of aircraft due to fly through Irish airspace en route from the US to Europe.
Assistance was sought from neighbouring ATC centres in London, Brest, Scottish control, and Shanwick, which is responsible for oceanic clearances.
Dublin Airport continued to function “due to proximity to UK ATC”.