A software defect in part of the UK’s air traffic control system corrupted flight data “in the space of a millisecond”, National Air Traffic Services (Nats) has said, after a malfunction that led to a six‑hour outage and widespread cancellations and delays.
Immediate impact and political reaction
The failure, which began on Tuesday 8 September, left airlines scrambling and passengers stranded as flight information used to identify aircraft on radar was corrupted. Ministers said the Nats preliminary report still left unanswered questions and demanded urgent explanation of why the fault had not been identified and fixed before it caused major disruption.
"to urgently understand why this issue was not discovered and fixed before it caused chaos"
The transport secretary, Heidi Alexander, announced that the Civil Aviation Authority (CAA) would now review the findings and carry out a wider investigation into whether Nats is operating effectively. A government source described the CAA review as an opportunity to “fundamentally investigate” the service’s fitness for purpose.
How the fault unfolded
Nats’ preliminary account says the fault was a legacy, previously unknown software defect that combined with a specific sequence of events in the National Airspace System (NAS) — the system that assigns identification codes to aircraft for radar tracking.
The company reported that the error first occurred at 10:00 GMT and engineers were alerted within minutes. Although the system appeared to recover shortly afterwards, a repeat failure at 12:30 GMT prompted Nats to declare a major incident and led to the prolonged disruption that spilled over into the following day.
| Time | Event |
|---|---|
| 10:00 | Initial software error in NAS reported |
| 10:02 | Engineers notified of link drop between NAS and London area control |
| 10:06 | Engineers reported apparent recovery, continued investigation |
| 12:30 | Repeat occurrence; major incident declared |
Airlines and leadership under pressure
The disruption affected hundreds of thousands of passengers and sparked demands from airlines for compensation and a credible recovery plan. Low‑cost carrier Ryanair called for the dismissal of Nats’ chief executive, Martin Rolfe, after what the airline framed as the third major UK air traffic control failure since summer 2023.
Rolfe responded by drawing a distinction from earlier incidents, saying the cause was technical rather than operational. He said he could:
"confirm that it was a software issue and not caused by any incorrect actions by either military or civil operators"
Technical explanation and next steps
According to the preliminary report, the fault resulted from a combination of a legacy software defect and “very specific events occurring simultaneously” in the NAS, which allocates codes to individual aircraft. Nats said engineers first noted the link between the NAS and the London area control system had dropped at 10:02 and that staff believed the system had recovered by 10:06, although they continued to investigate.
In response to the findings, the CAA will now undertake its own review of Nats’ report and investigate the organisation more broadly. Ministers have emphasised the need for urgent answers about why the defect persisted undetected and what steps will be taken to prevent recurrence.
- Scale: Hundreds of thousands of passengers affected by cancellations and delays.
- Cause identified: Legacy and previously unknown software defect in the NAS.
- Regulatory action: CAA to review Nats’ report and carry out a wider investigation.
The incident has intensified scrutiny of the resilience of the UK’s air traffic infrastructure as the industry and government demand a credible plan to restore public confidence and prevent further disruption.
