UK air traffic management agency NATS has said that it has resolved the technical issues it was experiencing earlier today, which resulted in restricted flights across the south of England.
The agency told Computerworld UK that the 'rare' problem was caused by 'out of sync' software tools.
It is still unclear whether or not Lockheed Martin, which has recently been awarded a seven-year contract extension to support NATS' air traffic management systems, was responsible for the system fault.
A spokesman for NATS said: "[The fault] was caused by the processing of a piece of flight data, which resulted in some of the software tools our controllers use to get out of sync.
"This is known as a 'race condition'. The resolution required the removal of the data for the specific flight and the rebooting of affected work stations."
He added: "This was a very rare combination of events that has not happened in the three years since this system was introduced, during which time it has successfully handled over six million flights."
Operations are now back to normal and NATS is working with airports, airlines and Eurocontrol to clear the backlog of flights.
A statement from NATS said that outbound delays from the UK have generally been limited to 20 minutes.
"We regret any inconvenience this technical problem has caused, however our first priority will always be the safety of the flying public," said the agency.