Almost 900 passengers travelling from Ireland to the US yesterday were affected by the sudden breakdown of the UK air-traffic control system.

The malfunction, which affected the air-traffic system in Prestwick airport, was fixed by the early afternoon but there were knock-on delays at Dublin airport.

Five flights to the US involving Delta and Continental airlines were affected but Aer Lingus flights to the US managed to depart before the system went down at 8am.

Crews of the grounded flights were on standby throughout the day yesterday as arrangements were made to reschedule cancelled flights after the fault was fixed.

A spokeswoman for the Irish Aviation Authority (IAA) explained it has control of flights up to 250 miles west of Shannon. But Prestwick takes over the control of all transatlantic flights outside the 250-mile limited patrolled by the IAA.

It was reported that the computer system in Prestwick had gone "zero rated", which meant it could not process any routings so everything had to be done manually.

While staff in Prestwick attempted to reboot the system, air-traffic controllers reverted to manual traffic control which severely delayed flights to and from the US across northern Europe.

The IAA said all flights that were in the air at the time of the technical failure continued their flights safely using a back-up emergency air-traffic control system.

Though uninvolved in yesterday's breakdown at Prestwick, in July 2008 there was widespread disruption to all flights in and out of Dublin airport when the IAA's radar system malfunctioned.

What was described as a glitch in the system meant air-traffic controllers could not identify aircraft.

At the time, all aircraft were held on the ground and those in the air were told to remain. Though the fault lasted only for 10 minutes, the knock on effects forced Ryanair to cancel 74 flights.

A week later, Thales ATM, who had only recently installed the hi-tech radar system for the IAA, said this was the first time it had come across such a fault with the system, which had been involved in over 500,000 hours of flight control.