Half of all flights in European airspace could be delayed following a technical glitch at the Eurocontrol centre in Brussels.
Eurocontrol coordinates airspace over all 41-member states and expected to process 29,500 flights today.
However, approximately half of those could have some delay as a result of the system outage, the organisation said.
“The issue with the ETFMS system has been identified and action is underway to return to normal operations,” explained a statement.
“However, flight plans filed before 10:26 UTC were lost, and aircraft operators have been requested to refile these flight plans for all aircraft that have not yet departed.”
The ETFMS system matches demand from airlines with capacity in the skies above Europe.
When airlines file flight plans, ETFMS calculates a pathway according to data on available airspace and allocates slots accordingly.
The relevant national air-traffic providers are notified, reducing the complexity of communication.
Eurocontrol said the ATFM contingency plan will be maintained for the coming few hours until it was certain that there is sufficient data is in the system to allow it to operate correctly.
Normal operations were expected by late this evening.
There has been a failure of the Enhanced Tactical Flow Management System at Eurocontrol which also had an impact on the associated flight plan system.
Contingency procedures are in place which will have the effect of reducing the capacity of the European network by approximately ten per cent.
Work is underway to solve the issue.
The ETFMS is central to the flow management function of the network manager, which regulates the flow of flights around Europe.
Air Traffic Control has not been directly affected and there are no safety implications arising from this incident.