The stoppage, on 8 September, affected a quarter of all flights due to be handled by Nats that day. Transport Secretary Heidi Alexander called the disruption “completely unacceptable” and told the CAA to conduct an independent review. She initially gave Nats a week to deliver its preliminary investigation.
The outage has left airlines, who must foot the burden, facing hefty bills for disruption. Tim Alderslade, Chief Executive of Airlines UK, the trade body for UK carriers, said this would run “into the tens of millions”.
"Once again, it is passengers who have suffered and airlines who have picked up the pieces – and the tab – of an ATC system failure, while Nats itself faces no real consequences,” he said.
He added Airlines UK wanted “immediate compensation” for costs incurred and a “credible plan” to improve resilience. Carriers escaped paying out automatic EU261 compensation to passengers as the outage was deemed an “extraordinary circumstance” but were still mandated to provide passengers vouchers for food and beverages as a minimum.
EasyJet Chief Executive Kenton Jarvis said airlines were left “as insurer of last resort yet again”. "Passengers deserve more than just another promise lessons will be learned,” he added.
'Legacy software defect'
Nats's preliminary investigation report details how the glitch began affecting flights at lunchtime, soon leading to numbers of aircraft arriving into the UK exceeding numbers departing. This created congestion at airports, which led to diversions and cancellations.
Nats blamed a “legacy and previously unknown software defect” in systems that process codes identifying altitude, speed and direction of a flight. Nats said the issue was not related to a cyber-attack.
Restrictions were lifted at 7.30pm, but many aircraft were in the wrong location to resume schedules and some crews were out of legal working hours.
Nats said that following the outage, the software glitch was identified and a fix put in place, although its report said this was “currently under test”.
The CAA said it would publish its review of the incident within six months. Nats Chief Executive Martin Rolfe, who Ryanair has called on repeatedly to resign, apologised to those affected, adding: “At no point last week was safety in question.”
How many more times?
Julia Lo Bue-Said, Advantage Travel Partnership Chief Executive, said that while it was reassuring to hear safety wasn't compromised, she warned failure would "carry a significant economic cost". "It is simply unacceptable for passengers and the industry to be left to pick up the bill," she said.
"The findings from this failure must now translate into meaningful improvements, and we need Nats, alongside government and the CAA, to ensure the lessons from this incident translate into meaningful improvements in resilience and contingency planning.”
Jet2 Chief Executive Steve Heapy said it was "crystal clear" UK ATC lacked "the necessary resilience". "One has to ask how many times this is going to be allowed to happen?" said Heapy.
"This latest report says that recommendations have been made following previous failures, but it is crystal clear that this critical piece of national infrastructure lacks the necessary resilience. It is time to address this as a matter of absolute urgency, because hardworking customers and families should not have to experience such disruption.
“Our teams worked tirelessly to look after customers and recover operations but, like other airlines, we incurred significant costs because of this latest failure. It is not fair that airlines should be left to pick up the tab on the back of these recurring failures, so we will be seeking compensation from Nats."