Engineers working remotely took 90 minutes to arrive and restart a crucial part of UK air traffic control’s IT system during the August bank holiday meltdown, according to an independent report.

The flights of more than 700,000 passengers were disrupted after planes were grounded across UK airports on 28 August, when the computerised flight planning system at National Air Traffic Sreervices (Nats) shut down because of a glitch.

An independent panel highlighted a “significant lack of pre-planning” at Nats, without “any multi-agency rehearsal of the management of an incident of this nature and scale”.

Airlines said the report, which was commissioned by the Civil Aviation Authority (CAA), showed Nats’ procedures were “wholly inadequate”. Ryanair repeated its calls for the Nats chief executive to be sacked.

When technicians on site were unable to solve the problem, the on-call specialist engineer found they could not carry out the fix working remotely. The report found it took 90 minutes for the on-call engineer to “arrive on-site in order to perform the necessary full system restart that was not permitted remotely”.

The interim report said: “It is clear there is a significant lack of pre-planning and coordination for major events and incidents that targets the alleviation and remediation of major incidents.”

Most flights were grounded for hours during one of the busiest days of summer, with subsequent disruption leaving some passengers stranded for days. Many were required to pay upfront for alternative flights, food and accommodation and submit claims to airlines for reimbursement.

The financial cost to passengers was “very considerable” and the report said the stress and anxiety was “at least as serious”.

The report found the incident was triggered by the inability of the Nats computer system to process unusual, but correct, data in a flight plan submitted for a plane crossing UK airspace to Paris from Los Angeles.

Two waypoints with an identical code triggered a “critical exception error” that caused the primary and secondary systems to disconnect themselves and stop working.

Tim Alderslade, the chief executive of Airlines UK, the industry body representing UK-registered carriers, said: “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.”

Michael O’Leary, the chief executive of Ryanair, said: “The fact that key Nats engineers were sitting at home during one of the peak travel weekends, combined with findings that Nats has a fundamental lack of pre-planning, documentation, and coordination, clearly demands senior management changes. Overpaid Nats CEO Martin Rolfe’s position in untenable. He should be removed.

“In Ryanair’s case, we pay over £100m per annum and we are entitled to expect an efficient, well-run service, rather than mismanagement and incompetence we suffered on 28 August 2023 due to the Nats system collapse.”

A spokesperson for Nats said it had cooperated fully with the review, adding: “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.”

The inquiry is being led by Jeff Halliwell, a veteran executive across various industries. He is expected to set out full recommendations in a final report.

The interim report noted that contingency rehearsals were “best practice” and “regularly conducted in other sectors”, adding: “The panel expects to recommend that the CAA should review and lead such multi-agency planning. This is especially important as some relationships between aviation sector stakeholders appear to be adversarial … This is not to the benefit of passengers, especially in a crisis situation such as this incident.”