NATS, the company that runs UK air traffic control, published its preliminary report on 18 September 2026 into the flight data failure of 8 September. It blames a legacy software defect, not a cyber attack, a military error or an invalid flight plan. A manual request to identify an aircraft was interrupted by higher-priority processing, and when the system resumed, a timing gap of about one millisecond corrupted data.
NATS had forecast around 8,000 flights that day and handled 6,094. The report describes more than 2,000 flights delayed, cancelled or diverted, which is a wider group than cancellations alone. Passengers felt the effects from 12:45 and all restrictions were lifted at 19:30, with departures halted for about four and a half hours within that period. It took more than two days for the disruption to clear.
Passengers in a Heathrow departure lounge. Earlier photograph, not the September disruption.
For families caught up in it, the Civil Aviation Authority’s guidance of 9 September sets out the rights. Passengers whose flight was cancelled can choose a refund, or re-routing at the earliest opportunity, or re-routing later. Airlines should provide meals and refreshments and a hotel when a delay needs an overnight stay. If the airline can’t provide that, it should reimburse reasonable costs the passenger arranged themselves, so receipts are worth keeping, although not every expense is guaranteed to be repaid.
The Authority considers the outage and the disruption it directly caused likely to count as extraordinary circumstances. That makes the fixed compensation payment under UK261 unlikely, though each claim depends on its own facts. UK261 covers departures from the UK on any airline and arrivals into the UK on UK or EU airlines.
NATS is due to publish its final investigation report within 60 days of the incident, which works out at 7 November 2026, and it may change the preliminary findings. A separate Civil Aviation Authority review of air traffic resilience is due to report within six months.
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