Archive · 18 Sep 2026
UK Flight Chaos Traced to Millisecond Software Defect
A computer problem disrupted the system that helps control airplanes in UK airspace.
The problem happened when the system was handling an aircraft identification code.
A paused computer task restarted incorrectly and damaged some flight information.
This happened in less than a thousandth of a second.
The system later stopped working properly and had to be partly operated by people manually.
Thousands of flights were cancelled, and many more were delayed.
The system was working again that evening, but the travel problems continued for more than two days.
Nats said flight safety was never at risk.
The government and airlines want an independent investigation and better protection against another failure.
A previously unknown software defect disrupted UK air traffic control operations on September 8.
The failure caused more than 2,000 flight cancellations and affected hundreds of thousands of passengers.
Nats said corrupted aircraft data triggered restrictions, a complete system failure and widespread congestion.
The system was restored by 7:30pm, but the resulting backlog took more than two days to clear.
The Civil Aviation Authority will independently review the incident, while airlines seek compensation and stronger safeguards.
- Who
- National Air Traffic Services, UK aviation authorities, airlines and affected passengers.
- What
- A previously unknown software defect caused a major air traffic control outage, leading to cancellations, delays and congestion.
- When
- September 8; the system was fully restored by 7:30pm, while the backlog took more than two days to clear.
- Where
- Across the UK and beyond, after the link between the National Airspace System and the London area control system failed.
- Why
- A legacy software defect corrupted aircraft and subsequent flight data after a manual aircraft-code request resumed incorrectly.
Officials and Nats
Airlines and Industry Critics
Cause of the failure
Officials and Nats
Nats said the disruption was caused by a previously unknown legacy software defect and specific simultaneous events, not incorrect actions by military or civil operators.
Airlines and Industry Critics
Airlines said the explanation was insufficient and questioned how a single software fault could produce nationwide disruption.
Safety and accountability
Officials and Nats
Nats said safety was never at risk, apologized to passengers and said mitigation was in place while a permanent fix was tested and deployed.
Airlines and Industry Critics
Airlines called for firm action, stronger resilience and greater accountability, with Ryanair demanding that Martin Rolfe be dismissed.
Financial responsibility
Officials and Nats
The government announced an independent review of Nats's findings, resilience investment and regulatory accountability before determining further action.
Airlines and Industry Critics
Airlines sought compensation from Nats for costs incurred and said passengers and carriers should not bear the consequences of the failure.
- Initial error detected
- 10:00am on September 8
- Major incident declared
- 12:32pm
- Complete system failure
- 1:32pm
- Full operations restored
- 7:30pm
- Flight cancellations
- More than 2,000
- Passenger impact
- Hundreds of thousands of passengers experienced disruption
- Independent review
- The Civil Aviation Authority review is due within six months