An unprecedented computer systems failure touched off the recent mayhem that caused delays and canceled flights for thousands of passengers, the U.K.-based air traffic management company said Saturday.
In its first detailed explanation of the computer glitch that led to flight disruptions Friday, NATS said the problems at its control center in Swanwick occurred as more workstations were being brought on line to deal with an increase in traffic.
"In normal operations the number of workstations in use versus in standby fluctuates with the demands of the traffic being controlled," NATS said in a statement. "In this instance a transition between the two states caused a failure in the system which has not been seen before."
The computer failure made it impossible for the controllers to access data regarding individual flight plans. Planes were prevented from taking off, but those in the air and close to airports were allowed to land during the shutdown that lasted about 35 minutes.
Britain's government reacted with fury over the meltdown ahead of the holiday season, when travel demand is particularly high. Ministers are demanding a thorough explanation.
Parliament's Transport Committee chair Louise Ellman said the transport secretary will appear before her panel on Monday and will be asked about the incident.