Software defect caused six hour UK air traffic control outage

A software defect in the United Kingdom’s air traffic control system corrupted flight data within a millisecond, resulting in a six hour outage that led to widespread airline cancellations and delays, National Air Traffic Services has confirmed. The preliminary report into the incident indicates that the error originated in a legacy component of the National Airspace System, which is responsible for allocating identification codes to aircraft for radar tracking. The failure caused significant disruption to hundreds of thousands of passengers and resulted in the cancellation of more than 2,000 flights across the UK and beyond.

According to the findings, the initial error occurred at 10am on Tuesday, 8 September. Engineers were notified at 10.02am that the link between the National Airspace System and the London area control system had dropped. By 10.06am, the engineering team reported that the system had apparently recovered with no operational impact, although investigations continued. The report states that the fault manifested when a manual request for an aircraft code was paused for an unspecified higher priority activity. When processing resumed, the software defect prevented correct resumption, corrupting the output and affecting subsequent flight data updates. This corruption occurred in the space of a millisecond.

The situation escalated at 12.32pm when the link between national and London airspace management dropped again. A major incident was declared at this time, forcing air traffic controllers to conduct certain tasks manually. By 12.45pm, National Air Traffic Services began restricting flights as the system continued to malfunction, before failing completely at 1.32pm. Airlines were advised of the restrictions at 1.40pm. Between 2.50pm and 4.09pm, the system was rebooted, and full operations were eventually resumed at 7.30pm. However, the disruption left significant congestion, displaced aircraft, and hundreds of thousands of delayed passengers. It took more than two days to clear the backlog of passenger disruption.

Transport Secretary Heidi Alexander stated that the disruption was completely unacceptable and acknowledged the frustration experienced by passengers, airlines, and airports. She noted that while the National Air Traffic Services report provides details, it leaves questions unanswered regarding why the issue was not discovered and fixed before causing chaos. Consequently, she has tasked the Civil Aviation Authority with conducting an independent review to check the findings and investigate investment plans for enhancing resilience and regulatory accountability. The review is expected to be published within six months.

Martin Rolfe, the chief executive of National Air Traffic Services, confirmed that the incident was unrelated to previous failures and was not caused by incorrect actions by military or civil operators. He stated that the issue has been identified and mitigation is in place while a permanent fix is safety tested and deployed. Rolfe apologised sincerely to those affected, emphasising that safety was never in question. However, industry leaders have called for stronger measures. Tim Alderslade, chief executive of Airlines UK, urged the regulator to mandate real investment in resilience to prevent a single fault from causing nationwide disruption. Airlines are demanding immediate compensation for costs incurred and a credible plan to improve system reliability.

Kenton Jarvis, chief executive of EasyJet, stated that passengers deserve firm actions rather than just promises of lessons learned, and that airlines should not be left to bear the financial burden. Neil McMahon, chief operations officer at Ryanair, criticised the explanation as insufficient and questioned how many times the system must collapse before the chief executive accepts responsibility and resigns. The incident marks the third major air traffic control failure in the UK since the summer of 2023, prompting calls for a fundamental investigation into whether the provider is fit for purpose.