UK air traffic outage caused by ‘legacy’ software bug, says review
Under-fire air traffic agency says it is planning to invest £1bn in its systems by 2033
The UK’s air traffic control operator has blamed a “software defect” buried in its systems that led to the outage that grounded thousands of flights last week.
An instruction issued to a single aircraft became “corrupted” by a “legacy and previously unknown defect in a software module”, the National Air Traffic Services (Nats) said on Friday, in its initial report into the incident that sparked days of chaos.
The outage saw more than 2,000 flights cancelled and hundreds of thousands of passengers delayed or stranded. Airlines have warned it will cost them tens of millions of pounds.
The Nats report said the computer system that processed the single aircraft’s request for a flight code paused the process to deal with another request at exactly the same millisecond.
This spiralled into a problem that forced the operator to take its entire system offline for several hours.
“Investigations are ongoing as to the precise millisecond timing involved in the very specific interactions encountered,” it added.
Nats is under fire from airlines, which have criticised the agency for repeated outages over the years, and from the government.
It stressed that last week’s failure was a separate issue from a 2023 meltdown, which was also caused by a flight plan being submitted to its systems.
Transport secretary Heidi Alexander on Friday said the incident was “completely unacceptable”. She said a six-month investigation by the regulator, the Civil Aviation Authority, will also look at the agency’s investments as well as the underlying cause of the problem.
“We need to urgently understand why this issue was not discovered and fixed before it caused chaos,” she said. “It is crucial that our national infrastructure is fit for the future.”
Nats chief executive Martin Rolfe, who has faced calls from several airlines to be fired after the chaos, apologised for the disruption but stressed that the agency’s first responsibility was to ensure safety.
“Our primary role is to keep our skies safe, and everyone who flies through them,” he said. “At no point last week was safety in question.”
He said Nats has invested “well over one billion pounds in systems and technology” over the past decade, “and we will soon submit plans to the Civil Aviation Authority to invest a further billion pounds by the end of 2033”.
The FT last week reported that the plane involved was a military aircraft. The Ministry of Defence issued a statement afterwards that it did not believe it was at fault in the incident, without confirming its involvement.
Nats stressed in its report on Friday that the plane’s request “was made correctly and there was nothing abnormal or invalid about the associated flight plan”.