The air traffic control failure that shut down departures and stranded passengers at Heathrow for several hours on 8 September, with disruption lasting days, was triggered by a single military aircraft's flight plan, according to new reports citing people briefed on the incident.
A flight plan submitted by a UK military aircraft introduced what insiders described as "spurious" data into the flight-processing system run by National Air Traffic Services (NATS), triggering a chain of technical failures, the Financial Times reported, as cited by the Mirror and GB News on Thursday evening.
NATS operations director Kathryn Leahy told industry bosses about the source of the fault during a briefing on the evening of the outage, an insider told the Financial Times. Four people briefed on the incident said the flight plan set off the sequence of events that caused chaos at airports across the country, including Heathrow, Gatwick, Stansted, Manchester and Birmingham.
At Heathrow specifically, queues stretched through terminal corridors as passengers waited for information, and British Airways cancelled its remaining short-haul services that evening in an effort to protect the following day's schedule, GB News reported. The Ministry of Defence declined to comment, and sources stressed the military origin of the flight plan was not itself considered responsible for the failure; investigators are focused instead on why the system could not handle the data safely.
More than 2,000 flights were cancelled across the UK network within three days of the fault. Transport Secretary Heidi Alexander has told the House of Commons she believes the disruption was avoidable, and gave NATS chief executive Martin Rolfe a week to report on the cause. The Civil Aviation Authority is also running an independent investigation, though its findings are not expected for six months.
The revelation adds to pressure on Rolfe, who has faced calls to resign from airline bosses including Ryanair's Michael O'Leary, while Wizz Air UK managing director Yvonne Moynihan has said NATS needs to demonstrate meaningful changes to restore confidence. Airlines say they were previously assured that lessons from a similar 2023 NATS outage had already been implemented.
As reported this week, the CAA has confirmed that passengers affected by the disruption, including those who flew through Heathrow, are unlikely to receive compensation, since ministers rejected a plan to make NATS reimburse airlines for the costs.
What this means for your journey: Heathrow has been operating close to normal schedules since the fault was resolved, and this update does not affect current departures. If you are still waiting on a rebooking or refund from the outage, our public transport guide has current advice on getting to and from the airport.