NATS’ preliminary investigation has confirmed the root cause that led to last Monday’s air traffic control incident, and the company has reiterated its apology for the associated disruption to passengers, airlines and airports.

The report emphasises that safety was maintained throughout the incident and that a solution has been implemented to avoid any possible recurrence. Submitted earlier this week to the Civil Aviation Authority, the report identified an issue with a flight plan processing sub-system called Flight Plan Reception Suite Automated – Replacement.

A small but important part of NATS’ overall air traffic control technical infrastructure, it was found to have encountered an extremely rare set of circumstances presented by a flight plan that included two identically named, but separate waypoint markers outside of UK airspace. This led to a ‘critical exception’ whereby both the primary system and its backup entered a fail-safe mode.

The report details how, in these circumstances, the system could not reject the flight plan without a clear understanding of what possible impact it may have had. Nor could it be allowed through and risk presenting air traffic controllers with incorrect safety critical information. On the day, the time taken to recover was driven by the need to identify the problem and the specific data, isolate and remove it in a controlled way, and then test it to ensure it could be returned safely into operation.

NATS says that this scenario had never been encountered before, with the system having previously processed more than 15 million flight plans over the five years it has been in service. It added that steps have been taken to ensure the incident cannot be repeated.

Martin Rolfe, CEO of NATS, said: “Keeping the sky safe is what guides every action we take, and that was our priority during last week’s incident. I would like to reiterate my apology for the effects it had on so many people, including our airline and airport customers. Incidents like this are extremely rare and we have put measures in place to ensure it does not happen again.

“Our preliminary report, provided to the CAA this week, details what caused the incident, how we responded and the steps already taken to prevent recurrence. We welcome any further review of the incident that the CAA wishes to conduct.”

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