The UK air traffic system failure that resulted in more than 2,000 flights being cancelled has been blamed on “an extremely rare set of circumstances”, as the aviation regulator opened an inquiry into the meltdown that caused chaos for passengers. The Civil Aviation Authority announced its own independent review as it submitted an initial report from Nats, the air traffic control services provider, into the incident to the transport secretary, Mark Harper. Hundreds of thousands of passengers, including families on summer holidays, faced disruption due to cancellations and delays linked to the system fault. The technical report from Nats confirmed that a single flight plan with confusing waypoint data brought its bespoke software system to a halt on 28 August. An error triggered by the plan – which was correctly submitted by an incoming airline – forced the system to stop processing flight plans automatically, leaving controllers to handle operations manually. Nats said the failure was due to “an extremely rare set of circumstances” with two identically named but separate waypoint markers outsidethe UK’s airspace – a scenario that has not occurred in more than 15m flight plans previously processed in the five years that the current system has operated. Nats said its report confirmed that the failure did not present any danger and that it had now found a fix to prevent it happening again. The company apologised again for the disruption to passengers, airlines and airports. The CAA said it agreed that safety was not compromised. However, it will now review wider problems around the system failure and assess how Nats responded to the incident. The regulator warned that if there was any evidence that Nats may have breached its licensing obligations it would take “appropriate steps”. Airlines have called for a shake-up of compensation and passenger rights rules after the incident, which may have left them up to £100m out of pocket in customer care costs and lost revenue, according to the global airline lobbying body Iata. Rob Bishton, the acting CAA chief executive, said: “Millions of passengers every year rely on air traffic control to work smoothly and safely. “The initial report by Nats raises several important questions and as the regulator we want to make sure these are answered for passengers and industry. “If there is evidence to suggest Nats may have breached its statutory and licensing obligations we will consider whether any further action is necessary.” Martin Rolfe, the chief executive of Nats, said: “Keeping the sky safe is what guides every action we take, and that was our priority during last week’s incident.” He said that the failure came from “data that had never been seen before and generated a logic error” in the Nats system, but confirmed that the unnamed airline’s flightplan was “perfectly compliant”. Rolfe added: “We welcome any further review of the incident that the CAA wishes to conduct.” The scale of the disruption affected an estimated 250,000 passengers and many had to wait several days for alternative flights. Details of the independent review will be published by the end of September, the CAA said. Ryanair said on Monday that the system failure had caused it to cancel more than 350 flights, affecting 63,000 passengers.