NATS preliminary report traces UK flight disruption to software defect

A preliminary report from NATS, the UK's air navigation services provider, blames a software defect for a September air traffic management failure. The findings were released on 18 September. More than 2,000 flights arriving at and departing from the UK were cancelled.

The report rules out a cyber-attack or any "malicious actor" and rejects suggestions in some media coverage that military intervention played a role. NATS chief executive Martin Rolfe said the problem lay in a small section of code within the flight-data system.

According to the report, the fault sat in software that assigns codes to individual aircraft when manual requests are made. While one such request was being handled, the system received a message for a higher-priority activity, pausing the code allocation. When processing resumed, the defect meant it did not restart correctly, producing corrupted output that affected later flight-data updates. NATS said the sequence unfolded within a millisecond, though the effects took far longer to clear.

The UK transport secretary, Heidi Alexander, had instructed NATS to conduct a full investigation into the 8 September incident and to report back within a week. In the foreword to the 18-page preliminary report, Rolfe said the incident was unrelated both to the 2023 NATS flight-plan processing system failure and to a radar issue the previous July. Incorrect actions by military or civil operators were also not the cause, he confirmed.

Rolfe said the issue has been identified and mitigation put in place while a permanent fix goes through safety testing before deployment.