Gatwick air traffic control failure explained: This is what caused major disruption

Passengers were left stranded at Gatwick Airport – and at airports across the globe – after a nationwide air traffic control network failure on one of the busiest days of the year.

Transport Secretary Mark Harper MP last month ruled out the possibility that the failure was caused by a cyber attack. Click here to read more.

National Air Traffic Services (NATS) has issued a update on its investigation with followed in the immediate aftermath of the incident.

"NATS’ preliminary investigation has confirmed the root cause that led to the air traffic control incident,” a statement on Wednesday (September 6) read.

"The report confirms that safety was maintained throughout the incident and that a solution has been implemented to avoid any possible recurrence.

"The report, submitted earlier this week to the Civil Aviation Authority, identified an issue with a flight plan processing sub-system called Flight Plan Reception Suite Automated – Replacement (FPRSA-R).

“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.”

Around midday, National Air Traffic Controllers said they were currently experiencing a technical issue, which meant the automatic system – which provides controllers with details of every aircraft and its route – wasn’t working.

Instead, to manage safety, staff had to limit the number of flights they could manage. Thousands of passengers were said to be stranded at airports – including some sat on planes unable to take-off. Passengers reportedly also were unable to get into the UK.

The incident report detailed how 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,” a spokesperson added.

"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.

"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. Steps have been taken to ensure the incident cannot be repeated.”

NATS has reiterated its apology for the associated disruption to passengers, airlines and airports.

CEO Martin Rolfe 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.”

See also: Gatwick Airport air traffic control staff shortages: Everything we know so far about 'airport chaos'