A flight plan filed for a UK military aircraft reportedly introduced anomalous data into the flight-processing system run by National Air Traffic Services (NATS), triggering the failure that cut UK airspace capacity on September 8, 2026.
The Financial Times reported the account on September 11, 2026, citing four people briefed on the incident. Two said the military character of the flight was not the cause.
The UK Ministry of Defence disputed any suggestion of military error. A department spokesperson said there was no indication of a mistake on the military’s part and declined further comment while the NATS investigation remains open, which the ministry said is expected to conclude in the week beginning September 14, 2026.
NATS has not identified the trigger
NATS has not publicly identified the trigger. The operator said at 13:46 local time on September 8, 2026, that it was investigating a technical issue affecting departures, and at 15:25 that the fault lay in its flight processing system.
It reported a fix at 16:40, normal operation at 19:30, and said on September 9, 2026, that a full investigation would establish what happened.
Aviation analytics firm Cirium counted more than 2,000 flights affected across September 8 and 9, 2026, at airports including London Heathrow (LHR), London Gatwick (LGW) and Manchester (MAN).
CAA review to examine NATS resilience
Transport Secretary Heidi Alexander told the House of Commons on September 9, 2026, that she did not believe the failure was unavoidable and asked the CAA to conduct an independent review reporting within six months.
The regulator said the same day that NATS would provide a technical report and that the review would consider how well the operator is set up to deliver a resilient service.