A flight plan submitted by a UK military aircraft is reported to have introduced "spurious" data that caused a four-hour shutdown of the National Air Traffic Services (Nats) system on Tuesday, grounding more than 2,000 flights and stranding hundreds of thousands of passengers. Nats reportedly had no dedicated backup for the affected flight-processing system, as the organisation was midway through a full overhaul and said duplicating its data volume would cost "vast amounts." Transport Secretary Heidi Alexander, who said she did not believe the outage was unavoidable, has given Nats chief executive Martin Rolfe one week to report on the causes and commissioned an independent review by the Civil Aviation Authority, while airlines including Ryanair have called for Rolfe's resignation.