The National Air Traffic Control System is said to be "back to normal" after a computer error caused nationwide flight delays.

Richard Everitt, the chief executive of the service, says an investigation will be launched into what had gone wrong.

Most UK airports are suffering delays. The worst affected are around London and at Birmingham where many flights are running over an hour late.

Mr Everitt said: "We had a problem with our flight data processing computer in West Drayton at just after 6am this morning, and that was sorted out within about 20 minutes, but there was a period obviously where we had to make sure all the data was correct, safety being the paramount consideration.

"So we gradually brought the capacity back up. We were back up to 70% by 8 o'clock this morning, and I am pleased to say we are now at 100%.

"We were reduced to about 30% of capacity fairly soon after this problem occurred and obviously we are very sorry for the inconvenience that that's caused to passengers and the airlines, and we are going to investigate this very thoroughly this morning.

"It is a managed process, our systems are very closely monitored. If we see a problem occurring with the flight data processor, then the system can be managed down and managed down very rapidly, to a manual operation rather than a computer-based operation.

"If we know there's a problem then we go straight into a manual mode.

"We've had a very stable period over the last 12 months, particularly with our flight data processing which has caused problems 18 months ago.

"We did have a problem in the evening of March 27, which was not actually with the system itself, it was with some data that was put in incorrectly, and that caused the system to reject it."

Ananova

-- Anonymous, April 10, 2002