A software defect in the UK’s air traffic control system triggered a shutdown in September 2026, leading to about 2,000 flight cancellations and extensive delays. The issue was traced to a one-millisecond timing bug within a small section of flight data system coding. This fault caused a flight handover request to be interrupted by a higher-priority system request, forcing the activation of backup protocols and manual flight handovers that reduced operational capacity.
Flight Disruptions at Heathrow, Gatwick and Other Airports
The shutdown led to over 250 flight cancellations across Heathrow and Gatwick airports. British Airways cancelled or diverted more than 100 flights, impacting tens of thousands of passengers.
Ryanair cancelled over 50 flights, affecting upwards of 65,000 customers. Other airports including Liverpool, Birmingham, Edinburgh, and Dublin in Ireland also experienced disruption due to the system failure. At Heathrow, flight arrivals were temporarily suspended during the incident.
Official Responses and Accountability
Martin Rolfe, CEO of UK National Air Traffic Services (NATS), acknowledged the software defect and confirmed ongoing mitigation measures while a permanent fix undergoes safety testing and deployment. Rolfe said, “This was a software issue in a specific part of our flight data system that we have traced to a small subsection of coding.”
UK Transport Secretary Heidi Alexander condemned the disruption
as “completely unacceptable.” She demanded urgent investigation and called for an independent review by the UK Civil Aviation Authority. Alexander stated, “We need to urgently understand why this issue was not discovered and fixed before it caused chaos.”
Ryanair Chief Operations Officer Neil McMahon called for Rolfe’s resignation, citing repeated failures and dismissing explanations as inadequate. McMahon said, “Martin Rolfe has run out of excuses. The ‘software ate my homework’ is not an acceptable explanation.” He also urged government action to appoint more competent leadership at NATS.
Technical Cause and System Impact
Investigations linked the cause to a precise timing conflict in software handling aircraft
identification code requests. The fault occurred because a higher priority request interrupted the handover process within exactly one millisecond. Had timing differed by even a millisecond, the operation would have completed normally. This error initiated backup protocols, requiring manual management of flight handovers, which lowered capacity and created cascading delays across the UK aviation network.
NATS stated the failure was unrelated to a separate 2023 outage caused by duplicate waypoints in a flight plan, which forced the system into fail-safe mode, affecting over 700,000 passengers. A previous incident in July 2025 involved a radar fault that caused 150 cancellations. Recovery
from the September 2026 failure is described as complex and ongoing.
Financial and Operational Consequences
Airlines incurred significant costs due to crew and aircraft reallocation and passenger refunds following the cancellations. The disruption created prolonged delays and operational challenges at key UK airports, including London’s two busiest hubs. NATS continues to assist affected airlines and airports in managing the recovery process, while apologising for the disruption experienced by passengers.
