A preliminary investigation found that a software glitch in NATS’s air traffic control system caused widespread disruption on 8 September, grounding more than 2,000 flights and affecting hundreds of thousands of passengers. The malfunction occurred when an aircraft identification-code request was interrupted by a higher-priority task and failed to restart correctly, triggering restrictions on UK airspace.

The report said the incident was not caused by human error, military or civil operators, or previous system failures. Transport Secretary Heidi Alexander has ordered the Civil Aviation Authority to independently review NATS’s findings, while NATS chief Martin Rolfe has promised a full report within two months; calls for his removal have so far been rejected despite earlier failures and £2.2 million in bonuses and incentives.