The CAA said on Thursday (14 March) it estimated that around 300,000 of these passengers suffered cancellations, 95,000 delays of at least three hours, and 300,000 shorter delays when the systems went down on Monday 28 August last year.

Thursday’s interim report from the independent review panel investigating the outage said the UK’s air traffic control provider Nats had "acted to address a number of findings arising from its own internal investigation", adding the panel had made "good progress" with respect to understanding the cause of the failure.

Last year, preliminary investigations traced the fault to a single flight plan which included two identically named but separate waypoint markers outside UK airspace, described by Nats as an "extremely rare set of circumstances".

In the immediate aftermath, both easyJet and Ryanair estimated the cost to their operations of the failure ran to somewhere in the region of £15 million. The airline sector is understood to have demanded millions in compensation from Nats.

Airlines UK chief Tim Alderslade called for a "deep review" of Nats, while Advantage Travel Partnership chief executive said the episode necessitated a wholesale review of the travel supply chain impact of the outage.

However, the panel said other factors required further evidence and investigation, including into the communications around the incident, the incentive regime for investment and the response by the aviation system.

’Further lines of enquiry’

The CAA said the panel was expected to publish its full report later this year. Its chair Jeff Halliwell said the interim report detailed the panel’s understanding of the root causes of the incident, the effectiveness of communications between Nats, other parts of the aviation sector and consumers, and the regulatory regime underpinning the UK’s air traffic control regime.

"In developing the interim report, the panel has engaged with a wide range of stakeholders to ensure the final report reflects a diverse range of perspectives," said Halliwell.

"In order to produce effective recommendations, the panel has further lines of enquiry it is exploring in order to build a better understanding of how the aviation system can improve."

CAA chief executive Rob Bishton added: "The UK air traffic control system is vital to the safe and efficient management of millions of air journeys each year.

"This interim report helps with the understanding of what went wrong, what worked well in response to this, and importantly what action can be taken to improve the UK’s aviation system for the future."

’Damning evidence’

Speaking on Thursday, Airlines UK’s Alderslade added: “This report contains damning evidence that Nats’ basic resilience planning and procedures were wholly inadequate and fell well below the standard that should be expected for national infrastructure of this importance.

"We welcome the committee’s plans for further investigation to provide recommendations so that this kind of catastrophic failure is not allowed to happen again.”

’Making improvements’

A Nats spokesperson said: "Nats has cooperated fully with the independent panel appointed by the CAA to review the events of 28 August and its repercussions. We will continue to respond constructively to any further requests to support the Panel’s ongoing work.

"We have not waited for the panel’s report to make improvements for handling future events based on learning from the experience of last year. These include a review of our engagement with our airline customers, our wider crisis response and our engineering support processes.
 
"We will study the panel’s interim report and look forward to their recommendations when they publish their final report."