A military flight plan is reported as the cause of the UK air traffic shutdown
More than 2,000 flights were cancelled when the Nats system went down for four hours on Tuesday. The Financial Times reports the trigger was "spurious" data in a military flight plan; the Ministry of Defence says it sees no error on the military side.
The air traffic control outage that grounded thousands of flights across the United Kingdom this week was caused by a military aircraft entering "spurious" flight data into the system, according to a report in the Financial Times.
More than 2,000 flights were cancelled on Tuesday when the system used by the National Air Traffic Services shut down for four hours, affecting hundreds of thousands of passengers.
What the report says happened
Four people briefed on the incident told the Financial Times that the shutdown was caused by a flight plan submitted by a UK military aircraft, which triggered a failure in the flight processing systems used by Nats. The fault remained unresolved for several hours.
The paper also reported that Nats operations officer Kathryn Leahy called the operations managers of numerous airports and airlines, and that tensions boiled over after she told them the flight processing system had no dedicated backup.
Two reasons were given for that, according to the report: Nats was in the middle of a complete overhaul of its systems, and the volume of data held meant duplicating it would cost vast amounts.
The Ministry of Defence response
The Ministry of Defence has said there was no wrongdoing on the part of the military.
"We do not believe there's any indication of an error on the part of the military," a spokesperson said. "This is subject to the live Nats investigation, so it'd be inappropriate for us to comment further while that's ongoing."
The two positions are not necessarily in conflict. A correctly submitted flight plan that a system cannot process is a failure of the system rather than of the submission — which is the distinction the investigation will have to settle.
Pressure on the Nats chief executive
The crisis has put pressure on Martin Rolfe, the Nats chief executive, who was summoned to a meeting by transport secretary Heidi Alexander on Wednesday.
Alexander said she did not believe the issue was unavoidable. She was understood to have given Rolfe a week to report on the causes, and has also commissioned an independent review by the Civil Aviation Authority.
Rolfe ruled out a cyber-attack, which was initially suspected. He said he believes Nats has never seen an incident happen more than once, so this would be something different that had not been seen in 50 years of operation.
Several airlines have called for Rolfe to resign or be dismissed. Ryanair chief executive Michael O'Leary accused him of "telling lies to save his own skin" and said his position was "untenable".
O'Leary dismissed the process now under way: "We don't need more investigations, we don't need more reports and we don't need another parliamentary committee hearing." Rolfe, he said, "will promise change, will promise resilience and will promise an effective backup system".
The 2023 precedent
The outage is the most serious to affect British commercial airspace since August 2023, when a technical problem led to almost 1,600 flights being delayed.
Nats came under criticism after that episode, and the Civil Aviation Authority set out 34 recommendations to improve its systems and avoid a repeat. All 34 were said to have been fully implemented.
That is the fact the current review will have to account for. A set of recommendations designed to prevent this class of failure was completed, and a larger failure followed three years later.
The effect on passengers
Some aircraft full of passengers were left waiting for information for more than four hours. Flights due to arrive in the UK were diverted to other airports, with some forced to land in Germany.
Despite the scale of the disruption, it was understood that affected passengers were unlikely to be able to claim compensation, because the delays fell under extraordinary circumstances — the category in UK and EU air passenger rights rules that removes the airline's liability where the cause was outside its control.
What is still open
The Financial Times account rests on four people briefed on the incident rather than on any official finding. Nats has not published its own conclusion, and the report Alexander requested was due within a week of Wednesday.
The Civil Aviation Authority's independent review sits alongside that, and will take longer.
