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Flights to and from the UK were experiencing disruptions after Britain's air traffic control systems were temporarily hit by a technical fault. Image Credit: AFP

London: The UK’s worst air traffic outage in a decade was caused by an anomaly in the airspace manager’s software system, which confused two geographical checkpoints separated by some 4,000 nautical miles.

The UK’s Civil Aviation Authority said Wednesday it will review the technical issue that forced hundreds of flights to be cancelled or delayed last week after an error in processing an airline’s flight plan.

The glitch triggered a shutdown of the software system run by NATS for safety reasons, according to a preliminary report from the public-private partnership formerly called National Air Traffic Services. This forced air traffic staff to input flight plans manually, drastically reducing the amount of air traffic that could be processed.

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The event sent airlines and airports in the UK into turmoil on August 28, leaving planes out of position and passengers stranded. Nearly 800 flights leaving UK airports were cancelled, with a similar number of arrivals scrapped, according to aviation analytics firm Cirium.

The report by NATS showed that on the day of the incident, an airline entered a plan into the system which led through UK airspace. NATS CEO Martin Rolfe declined to discuss details of the flight, such as its route or the airline involved, saying the specifics weren’t pertinent to the outage.

While the flight plan wasn’t faulty, it threw off the system because the software used by NATS received duplicate identities for two different points on the map. There are an infinite number of flight-plan waypoints in the world, and duplicates remain despite work to remove them, according to Rolfe.

In this case, NATS system correctly identified the point at which the plane was to cross into the UK. However, the exit point had a duplicate name that matched a different spot on the map some 4,000 nautical miles away. NATS’ software recognized that this was geographically incorrect.

After the primary system failed to find the exit point, the backup system kicked in and ran into the same problem, leading to the shutdown of NATS’ software for safety, according to the report.

“We’ve never seen this set of circumstances before,” Rolfe said.

NATS said in its report that the manufacturer will update the software to prevent it from shutting down under similar circumstances in the future. Rolfe said this software would be implemented in the coming days, following testing. Meantime, a temporary fix was put in place to prevent a reoccurrence, NATS said.