A major air traffic control failure led to the cancellation of more than 2,000 flights, impacting hundreds of thousands of passengers earlier this month.
The disruption, which occurred on September 8, was caused by a software defect in the system that assigns identification codes to aircraft, according to a preliminary report from National Air Traffic Services (Nats).
The fault led to the cancellation of more than 2,000 flights in and out of the UK, affecting hundreds of thousands of travellers.
Martin Rolfe, chief executive of Nats, said: "I can also confirm that it was a software issue and not caused by any incorrect actions by either military or civil operators."
He apologised to passengers and the aviation industry for the disruption.
The affected software automatically allocates codes to aircraft when manual requests are submitted.
These codes are used to identify flights on radar while they are airborne.
Transport Secretary Heidi Alexander described the disruption as "completely unacceptable" and acknowledged the frustration it caused for passengers, airports, and airlines.
Ms Alexander said: "I have now received Nats’ report and, while I am pleased to see that the safety of passengers was protected, it’s clear we need to urgently understand why this issue was not discovered and fixed before it caused chaos."
She has asked the Civil Aviation Authority (CAA) to conduct an independent review of Nats’ findings and to examine its investment plans for improving future resilience.
The CAA’s report is expected within six months.
Mr Rolfe has faced renewed calls to resign following the incident, which affected major airports including Heathrow, Gatwick, Manchester, and Stansted.
The disruption follows other recent technical failures.
In July 2023, a radar-related issue led to more than 160 flight cancellations.
A month later, a technical glitch in Nats’ flight plan processing system disrupted travel for more than 700,000 passengers.
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