In a highly unusual incident described as a "one in 15 million" event, the UK's air traffic control system experienced a major disruption during the August bank holiday, affecting hundreds of

flights. The incident occurred on August 28th, causing chaos in the skies and leading to flight delays and cancellations the following day.

Nats, the company responsible for controlling the UK's air traffic services, disclosed that the disruption was triggered by an unprecedented occurrence: the reception of duplicate "markers" on a flight plan. This unexpected event prompted the automatic shutdown of a part of the air traffic control system within a matter of seconds.

Martin Rolfe, the Chief Executive of Nats, emphasized that the system acted as intended, ensuring safety by shutting down when it encountered data it couldn't process. He described the incident as "a one in 15 million flight plan," which took engineers several hours to address.

Nats, formerly known as National Air Traffic Services, has taken corrective measures to prevent a recurrence of this incident. Additionally, the Civil Aviation Authority (CAA), the UK's aviation regulator, has announced an independent review to assess whether Nats breached any "statutory and licensing obligations," with the findings expected to be released in the coming months.

The Unprecedented Event:

According to Nats' initial report, the disruption occurred at 08:32 on August 28th when the system received flight details for an aircraft scheduled to cross UK airspace later that day. Airlines typically submit flight paths to the national control center, which are then shared with Nats controllers responsible for managing UK airspace.

The system detected that two markers along the planned route had identical names, despite being located in different places. Consequently, it couldn't comprehend the UK portion of the flight plan, prompting an automatic safety shutdown to prevent incorrect information from reaching air traffic controllers. The backup system followed suit, and this entire sequence unfolded in just 20 seconds.

Engineers faced a significant challenge in resolving the issue and had to seek assistance from the system's manufacturer. This marked the first occurrence of such an incident in the five years of operation during which the software processed more than 15 million flight plans.

Apology and Consequences:

Martin Rolfe expressed his apologies to the affected customers, acknowledging the disruption caused to their holidays. He recognized the significant inconvenience experienced by travelers, particularly during the busy bank holiday period, with planes and crews dislocated and many individuals stranded abroad.

In response, airlines arranged additional flights to clear the backlog of passengers and return them home. However, questions persisted regarding how a single flight plan could lead to such extensive disruption. At one point, manual processing of flight plans was necessary, reducing the handling capacity from the usual 400 flights per hour to only 60.

Nats assured that a software update would prevent a similar reaction in the future if a comparable situation were to arise. Both Nats and the CAA emphasized that safety had never been compromised throughout the incident.

Impacts and Resolution:

According to Nats' report, Eurocontrol data indicated that 5,592 flights operated in UK airspace on August 28th, which was 25% fewer than anticipated, including canceled flights and those that bypassed UK airspace. Approximately 1,500 cancellations occurred on the day of the disruption alone, affecting all airlines operating in the UK.

Although the outage lasted less than four hours, its repercussions lingered for several days. The CAA affirmed that this unprecedented scenario had never been encountered before and that it is now understood and can be promptly resolved should it recur.

Transport Secretary Mark Harper welcomed the confirmation that no safety issues arose during the incident and highlighted that the independent review by the aviation watchdog would explore potential steps to enhance the resilience of the air traffic control system. Photo by nats.aero.