NATS Blames Prestwick Connectivity Fault for Second UK Flight Disruption in Two Weeks

PRESTWICK, Scotland — A technical fault at NATS's Prestwick Centre forced air traffic restrictions on Monday morning that disrupted flights across Scotland, Northern Ireland and northern England. It came 13 days after a failure that NATS's preliminary report attributed to a software defect disrupted flights across the UK.

NATS said in its statement on the Prestwick fault that "this was a connectivity issue with part of our systems network, specific to the operation in Scotland," and that it was "nothing to do with the problem we had earlier this month." Air traffic regulations were applied "to maintain safety" while engineers investigated, and the issue had "now been fixed," the company said in the statement, published at 10:44 BST.

The fault was fixed by about 10:30 BST, according to The Guardian's report on the disruption. Knock-on delays and cancellations continued into the afternoon. By 14:36 BST, NATS said that "the system is fixed and we are running at full capacity," and that it was working with airlines "to recover their residual delays," according to the BBC's live coverage.

Two accounts of the fault

NATS has described the fault only in general terms. Its statement does not identify the network component that failed, say how much capacity was withdrawn while regulations were in force, or say whether controllers moved to backup systems or manual procedures. It also does not say whether the fault involved the National Airspace System (NAS), the flight data system at the center of the September 8 failure.

Ryanair (FR) gave a different account. In a release calling for NATS Chief Executive Martin Rolfe to resign, the airline said "the same flight data processing system has failed once more." NATS's statement does not describe Monday's fault as a flight data processing failure, and no technical account has been published that would settle the question.

"In the real world we accept technology can and sometimes does fail. Our job is minimising disruption where possible," a NATS spokesperson said, according to the BBC. "What isn't acceptable is any incident where safety is compromised—this is always our first priority."

How far the disruption spread

NATS manages all UK upper airspace from two control centers, at Swanwick in Hampshire and Prestwick in Ayrshire. Prestwick handles traffic over northern England, Scotland and Northern Ireland, about 42% of UK air traffic, according to BBC business correspondent Theo Leggett.

Early on, NATS said airports south of Manchester were "broadly unaffected," while flights heading north and departures from Scottish airports were subject to delay, according to BBC Scotland. Glasgow (GLA) and Edinburgh (EDI) reported delays, Manchester Airports Group reported delays of up to an hour on some flights at Manchester (MAN), and Highlands and Islands Airports said schedules were affected across its 11 regional airports. Several arrivals and departures at Belfast City Airport (BHD) were canceled, including flights to and from Manchester, Amsterdam and London City.

Effects also reached further south. Bristol Airport (BRS) attributed delays and cancellations to the Prestwick fault. London City (LCY) reported "some disruption," Luton (LTN) said domestic flights were disrupted, and Gatwick (LGW) said a small number of flights could be delayed.

The aviation analytics company Cirium counted around 200 flights to and from the UK that had been canceled or did not operate on Monday as of 13:45 BST, 100 arrivals and 99 departures, the BBC reported. That total covers all of Monday's cancellations, not only those caused by the fault. In the same figures, easyJet (U2) had canceled 47 of its 670 scheduled departures and British Airways (BA) 11 of 513.

Ryanair said more than 140 of its flights had been delayed and put the number of its affected passengers above 25,000.

The September 8 failure and NATS's report

The September 8 failure disrupted London Area Control at Swanwick. NATS traced it to a legacy defect in a software module within the NAS that corrupted flight data, and restrictions were imposed across the UK so the system could be restarted. More than 2,000 flights were delayed, canceled or diverted.

NATS's preliminary report into that failure, released on September 18, said a permanent software fix was under test. NATS said it had put in place an "additional engineering framework" to manage link drops between the London Area Control system and the NAS in the meantime, and that "in the unlikely event of reoccurrence, a faster recovery can now be implemented."

Ryanair Chief Operations Officer Neal McMahon cited that language on Monday. "Martin Rolfe's report claimed that another failure was 'unlikely' and that NATS could recover more quickly if one occurred. Those claims have been exposed as completely worthless," he said. The report's wording refers to a recurrence of the September 8 link-drop problem. Whether Monday's fault shares anything with that failure is the point on which NATS and Ryanair differ, and neither has published technical detail to support its position.

Airlines and government respond

EasyJet said the fault "calls into question the resilience of Nats's systems and demonstrates the need for firm actions to prevent these repeated failures," according to The Guardian. British Airways called it "yet another technical fault with Nats" that was "entirely out of our control."

Jet2 Chief Executive Steve Heapy asked, "How many more failures do customers and airlines have to deal with?" and the airline said it would send NATS another bill for the cost of the disruption, the BBC reported. Yvonne Moynihan, managing director of Wizz Air UK, described a "national confidence crisis" in NATS in an interview on BBC Radio 4.

Tim Alderslade, head of the trade body Airlines UK, called air traffic control "critical national infrastructure." He said the upcoming civil aviation bill "must address the underlying weaknesses in the system so that these failures stop happening," according to the BBC.

Transport Secretary Heidi Alexander wrote on X, in a post quoted by The Guardian, that "engineers have fixed the problem and systems are resuming," adding: "I know this will be deeply frustrating for passengers after the previous issue."

Scotland's First Minister, John Swinney, said his government would engage with NATS "to ensure that these issues are addressed," according to BBC Scotland.

The review and what NATS has not said

After September 8, the government asked the Civil Aviation Authority for an independent review of the failure. On Monday, the prime minister's spokesperson said, "There's a review that is ongoing," according to The Guardian's business live coverage. In the public statements Airways reviewed, neither the government, the regulator nor NATS had said by Monday afternoon whether that review would extend to the Prestwick fault.

NATS's public statements also leave open how long the regulations stayed in force, whether redundant network links were available and used, and whether the fault touched systems shared with Swanwick. The company has not said whether it will publish a report on Monday's fault as it did for September 8.