The Irish Aviation Authority has said that an irregular software occurrence caused a failure of the primary Air Traffic Control (ATC) system at its facility in Co Clare on Tuesday evening.
The IAA said that there was no danger to any flights in the air at the time as the back-up network kicked in immediately.
Provision of the service has been transferred back to the main system again following the fixing of the fault.
It said a comprehensive testing and safety analysis was done on the system to ensure its safety before it was returned to operations.
The IAA reiterated that the fault was not in a radar, with radar coverage maintained at all times.
The issue impacted one module of the ATC system, which had an impact on its performance, and regulations governing the transfer to the back-up system meant air traffic flow had to be restricted.