infrastructure and connectivity · the national record
UK air traffic control failures: the record, the cost and what changed
On 8 September 2026 the NATS flight data system failed for the second time in three years and the airlines cancelled flights for two days. This page puts the incident against the official record: what the reviews of 2014 and 2023 found, what NATS delivers on a normal day, how UK airspace compares with Europe, and why an afternoon's fault at Swanwick becomes a weekend of cancellations at Heathrow.
How to read this
Every figure comes from an official document: NATS's own incident updates and annual reports, the CAA's independent review reports, the NESO review of the Heathrow substation fire, Eurocontrol's Performance Review Unit data and the CAA's airport and punctuality statistics. Press estimates of flights cancelled this week conflict by a factor of two and are quoted only as reported, never charted. NATS's own delay metric counts only delay NATS caused; Eurocontrol's counts all en route delay in UK airspace including weather. The two are shown separately and never combined.
13:46 to 19:30
NATS first notice to "operating normally", 8 September
4
NATS technical failures with published figures since 2014
NATS technical updates 8 to 9 September 2026, Hansard 9 September 2026, the CAA statement of 9 September 2026 and NATS Annual Report 2026 (year to 31 March 2026, published 26 June 2026); CAA CAP2993 (published 14 November 2024) and the 2015 Swanwick enquiry; NESO North Hyde review (May 2025); Eurocontrol PRU en route ATFM delay by ANSP, 2010 to July 2026; CAA UK airport data 2019 to 2025 and punctuality statistics to June 2026. Built 10 September 2026.
8 September 2026
What happened, in NATS's own words
NATS posted timed updates through the afternoon and evening of Tuesday 8 September. The fault was in the flight processing system, the same class of system that failed on 28 August 2023. No official count of flights cancelled or passengers affected across the network has been published; British Airways has published its own.
NATS technical issue updates, Tuesday 8 September 2026
13:46"We are investigating a technical issue which is causing some disruption to flight departures."
15:25"We have identified that the issue was in our flight processing system."
16:40"Our flight system is starting to recover."
19:30"Our system issue is now resolved, we are operating normally."
22:10"This has been a very complex recovery and has created difficulties for the whole aviation network, from which it will take time to recover."
12:55, 9 Sep"We apologise unreservedly" to passengers, airlines and airports, with a fuller investigation to follow.
"A four-hour air traffic outage yesterday left hundreds of thousands of passengers facing cancellations, diversions and delays. I apologise wholeheartedly to passengers for that disruption. [...] While my understanding from that is that we can rule out a cyber-attack on this occasion, I do not believe this issue was unavoidable. [...] I have therefore asked the Civil Aviation Authority to conduct an independent review, to establish cause and ensure that our air traffic control systems can get passengers where they need to be. The review will report to me within six months."
"When we had the major outage in 2023, it took two years for the CAA to make a similar report. In that report, it made 34 recommendations, of which 32 have been implemented, so a six-month timeframe is a much shorter, sharper window in which to get definitive answers to these questions. NATS is also required to provide a report to the CAA within a week of the incident taking place, to fully explain the implications of what has happened." Later in the debate he corrected the count: "not 32 but all 34 of the recommendations have been implemented."
"The technical issue led to delays and the cancellation of hundreds of UK arriving and departing flights on 8 September. [...] We consider that disruption caused by the NATS outage is likely to be considered the result of 'extraordinary circumstances' under passenger rights rules. This means that although passengers should be looked after by airlines, they are unlikely to be entitled to compensation for delays or cancellations that were directly caused by the incident."
One airline's own count: British Airways, 9 September
almost 550
BA flights cancelled by the failure
85,000+
BA customers affected
60,000+
rebooked on alternative flights by 9 September
190+
further BA flights cancelled on 9 September, aircraft and crew out of position
British Airways media centre, 9 September 2026. These are one airline's figures for its own schedule and cannot be scaled up to the network.
Reported, not official: press and wire coverage put UK flight cancellations at "close to 1,000" (PA), "more than 1,000" (Euronews) and "at least 2,000" (other outlets). Neither NATS nor the CAA had published a figure by 10 September. This page does not chart any of them.
The Secretary of State's statement opened the second reading of the Civil Aviation (Consumer Protection and Regulatory Reform) Bill; the Official Report was retrieved through the Hansard API. No Department for Transport press release on the incident had appeared on gov.uk by 10 September.
The record
Four NATS technical failures since 2014, and one substation fire
Each card carries only figures the official review or the operator itself published. Where an official count does not exist the card says so.
12 December 2014
Swanwick: a latent software fault from the 1990s
System
Flight server at the London Area Control Centre, Swanwick
Duration
14:44 failure to 20:30 last restriction lifted
Both channels of the System Flight Server failed at once for the first time in its history, because of a latent software fault present since the 1990s in a check on the maximum number of controller and supervisor roles.
All departures from London airports were stopped at 14:55, and from European airports routing through UK airspace at 15:00. The system was back with controllers at 15:49 without full redundancy; full redundancy returned at 20:10.
NATS calculated 14,863 minutes of delay across 353 flights, about 150 cancellations and up to 20 diversions, with 65,000 passengers directly affected. Counting knock on effects NATS's own upper estimate was 1,900 flights and 230,000 passengers.
Flight plan processing cut from about 800 an hour to about 60 for several hours; disruption ran into the following weekend
A single flight plan from Los Angeles to Paris Orly carried two waypoints with the same abbreviation. The software could not resolve it, raised a critical exception, and both the primary and the backup system put themselves into maintenance mode.
The CAA estimated over 700,000 passengers affected: about 300,000 by cancellations, about 95,000 by delays of more than three hours and at least 300,000 by shorter delays.
The CAA put the cost to airlines at about £65m and the wider cost of the incident at £75m to £100m. None of the passengers were entitled to fixed compensation, because the failure was treated as an extraordinary circumstance outside the airlines' control.
NATS's own investigation report put the count at "likely that the number exceeds 1,500" flights cancelled on 28 August, with more the next day; of the 5,500 flights that did operate in UK airspace around 575 were delayed by the incident. About 75 per cent of planned flights operated.
The Independent Review Panel made 34 recommendations to NATS, the CAA, airlines, airports and government.
North Hyde 275kV substation, National Grid, feeding Heathrow through SSEN's network
Duration
Closure decided at 01:11; reopened for some repositioning flights that evening; normal operation on 22 March
A high voltage bushing on a supergrid transformer failed catastrophically and the transformer oil caught fire. NESO found that a fire risk assessment in July 2024 had said a fire on any of the three transformers "would not be suitably suppressed", and the resulting high priority action was still outstanding in March 2025.
Power returned to the North Hyde 66kV substation at 09:49 on 21 March, more than eight hours after Heathrow decided to close. Heathrow reopened for some repositioning and repatriation flights that day and for business as usual on Saturday 22 March.
NESO's review is an energy system review. It does not publish a count of flights or passengers affected, and Heathrow's own commissioned Kelly review PDF was no longer at its published address when checked on 10 September 2026, so no official aviation count is shown here.
Capacity restored within 42 minutes by switching to a backup; flow restrictions while the issue was investigated
NATS's annual report describes it as the one material impact on service in the year: "a radar-related technical incident in July 2025 which required us to regulate the flow of air traffic temporarily while the issue was investigated and resolved."
NATS's own estimate: 26,134 minutes of delay and approximately 150 cancellations, equivalent to an average of 3.5 minutes of delay for every flight that day.
The Transport Secretary met the NATS chief executive the following day. The same report records that "all actions arising from the August 2023 and July 2025 incidents were completed".
13:46 first notice to 19:30 "operating normally"; network recovery ran into 9 September
NATS identified the fault in its flight processing system at 15:25, reported recovery under way at 16:40 and the system resolved at 19:30, then at 22:10 warned of "a very complex recovery" for the whole network.
British Airways cancelled almost 550 flights affecting more than 85,000 of its customers, and more than 190 further flights on 9 September.
No network wide count of flights cancelled or passengers affected had been published by NATS, the CAA or the Department for Transport by 10 September. NATS has promised a fuller investigation.
The 2018 Gatwick drone closure is left out: the one primary source that carries a reconciled official count, the House of Commons Library briefing on civilian drones, was behind a bot check on every attempt and the press figures conflict.
The 2023 review
Thirty four recommendations, all implemented
The CAA's Independent Review Panel, chaired by Jeff Halliwell, reported in November 2024. Its recommendations went to NATS, the CAA, airlines, airports and government. The 8 September failure lands against a record in which every recommendation has been signed off as implemented, by NATS in June and by the minister on 9 September.
What went wrong in 2023
"In the case of both the primary and the secondary systems, processing of the flight data resulted in critical exception errors being generated which triggered firstly the primary system and then the secondary system to enter maintenance mode."
On resilience
Recommendation 20: "NERL should review its strategic approach to resilience, as is common among other safety-critical regulated sectors, recognising the importance to the public of resilience alongside safety and efficiency."
On counting the damage
Recommendation 16: "The CAA should explore ways of measuring cancellations and knock-on delays attributable to NERL for use in its incentive framework." The panel "attempted in vain to get objective quantitative information about the extent of the impact" and airlines declined to share passenger lists.
On who pays
"None of the over 700,000 passengers estimated to have been impacted by the incident were entitled to such compensation since it was considered to be an 'extraordinary circumstance', though they were entitled to reimbursement of reasonable costs incurred."
July 2025 · Department for Transport, written statement
"NATS has delivered its recommendations with many of these already having been confirmed as completed by the CAA." The CAA expected "most of the recommendations made by the panel will have been validated and completed by the end of 2026."
"All actions arising from the August 2023 and July 2025 incidents were completed. The CAA subsequently noted in the report to the Department for Transport, that NATS response to the 30 July 2025 incident effectively mitigated the risk of a recurrence and confirmed that recommendations from the 2023 independent review have been embedded within regulatory oversight."
9 September 2026 · Keir Mather, aviation minister, House of Commons
"In that report, it made 34 recommendations, of which 32 have been implemented." Corrected later in the same debate: "I should add that I was slightly remiss in what I said earlier: not 32 but all 34 of the recommendations have been implemented."
The same annual report records £215.5m of capital spending in the year, "including to accelerate the replacement of the National Airspace System Flight Data Processor". The replacement had not arrived by 8 September 2026.
NATS in normal times
Very efficient on the average day
The regulator's headline metric for NATS is average delay per flight attributable to its en route operation, in seconds, against a target set in the CAA's NR23 price control. On that measure NATS has beaten the target in each of the last two years. The metric is an average across every flight in the year, so an afternoon that cancels a thousand flights moves it by a few seconds.
Average delay per flight attributable to NATS, seconds, against the CAA target
20238.8s target 8.5s
20244.4s target 8.3s
20257.8s target 9.0s
Calendar years. NATS's own description of 2025: "within the CAA's target of 9.0 seconds but slightly up on the prior year following a brief technical incident". The 2023 figure includes the 28 August failure. The tick marks the target.
2.41m
flights handled, year to 31 March 2024
2.48m
flights handled, year to 31 March 2025
2.54m
flights handled, year to 31 March 2026
The CAA's capacity incentive also carries a separate metric for major outages: NATS's remuneration report explains it "is based on weighted delays exceeding pre-determined thresholds on a daily basis" and "is intended to capture the impact of major service outages", and that if it scores above 250 points "no incentive will be payable for delay performance".
£1,076m
NATS revenue, year to March 2026
£213m
profit before tax
£215.5m
capital spending, including the flight data processor replacement
2.54m
flights handled
Against Europe
UK airspace is among the least delayed in Europe
Eurocontrol's Performance Review Unit publishes daily en route air traffic flow management delay for every air navigation service provider in Europe. This counts all en route delay in the provider's airspace, whatever the cause, so it is broader than NATS's own attributable figure. In 2025 the UK's continental airspace ran at about a quarter of Germany's delay per flight and an eighth of France's.
France (DSNA)114.1s
Germany (DFS)53.3s
United Kingdom (NATS)14.1s
Spain (ENAIRE)59.6s
Italy (ENAV)4.7s
Maastricht UAC (Benelux and north west Germany upper airspace)16.6s
Turkey (DHMI)0.0s
Austria (Austro Control)23.5s
Switzerland (Skyguide)17.8s
Hungary (HungaroControl)33.2s
Greece (HASP)54.0s
Bulgaria (BULATSA)3.2s
SMATSA43.2s
Eurocontrol Performance Review Unit, 2025, all causes, providers with at least one million flights in the year. Ordered by flights handled.
UK continental airspace, en route ATFM delay per flight, seconds
910
412
414
1816
1718
1319
120
021
1722
1923
824
1425
2026
NATS (Continental), seconds of en route ATFM delay per flight, all causes. 2026 covers January to July only. The 2023 bar includes the 28 August failure; 2025 includes 30 July.
The airports
Heathrow has almost no room to catch up
A three hour restriction at Swanwick becomes two days of cancellations because the airports it feeds run close to full. Heathrow's planning permission caps it at 480,000 air transport movements a year. In 2025 it flew 477,870, leaving 2,130 spare, and scheduled more than the cap before cancellations. There are no empty slots in which to fly a lost afternoon later.
Heathrow air transport movements against the 480,000 cap
Year
Scheduled
Cancelled
Flown
Headroom under cap
2019
479,811
3,952
475,859
4,141
2023
463,854
9,789
454,065
25,935
2024
482,143
8,344
473,799
6,201
2025
484,340
6,470
477,870
2,130
CAA UK airport data, Table 04a. The cap is the Terminal 5 planning condition quoted by the Department for Transport: "the number of air transport movements at the airport shall be limited to 480,000 each year". Scheduled means all planned movements including those later cancelled.
296.8m
UK terminal passengers, 2019
272.8m
UK terminal passengers, 2023
292.5m
UK terminal passengers, 2024
299.4m
UK terminal passengers, 2025
Flights on time, the 15 largest airports combined
74.3%
2019
63.2%
2023
66.5%
2024
72.4%
2025
75.3%
Jan to Jun 2026
Flights on time by airport, per cent
Airport
2019
2023
2024
2025
Jan to Jun 2026
Passengers 2025
Liverpool
82.7
73.4
76.4
80.9
82.2
5.6m
Belfast International
72.8
68.2
75.1
78.6
79.7
6.7m
Glasgow
77.2
70.1
72.4
77.3
78.6
8.2m
Heathrow
77.3
63.9
67.3
76.7
78.0
84.5m
London City
72.4
71.7
73.1
76.4
75.5
3.7m
East Midlands
80.0
72.2
75.4
75.0
76.7
4.0m
Leeds Bradford
81.0
70.4
72.1
73.6
76.3
4.4m
Luton
70.4
63.1
69.4
73.4
75.9
17.8m
Newcastle
78.8
66.0
69.2
72.4
77.6
5.5m
Edinburgh
76.2
61.9
67.3
71.4
74.8
17.0m
Bristol
66.5
61.6
66.2
70.3
75.3
10.8m
Gatwick
67.5
54.8
59.9
69.8
74.9
42.8m
Stansted
77.1
64.4
63.6
69.7
74.6
29.8m
Birmingham
72.5
65.5
65.8
68.0
70.8
13.7m
Manchester
74.2
61.8
64.0
64.5
67.0
32.1m
CAA punctuality statistics, share of flights arriving or departing any degree early or up to 15 minutes late, the CAA's own "on time" definition, reconciled at build time against the CAA's 2025 On Time Performance Table. 2026 is January to June, weighted by flights each month, and predates 8 September. Ordered by 2025.
Who runs it and who pays
A regulated monopoly the state half owns
NATS is a public private partnership formed in 2001. Its subsidiary NATS (En Route) plc holds the licence for en route air traffic control over the UK under Part 1 of the Transport Act 2000, with the CAA as its economic regulator.
UK Government, holds the golden share49%
The Airline Group, a consortium of UK airlines and pension funds42%
NATS staff, through the employee share trust5%
LHR Airports Limited (Heathrow)4%
Shareholdings as stated on NATS's company page. The annual report records four shareholders and no ultimate controlling party.
Airlines
Airlines carry the direct cost of rerouting, care and assistance whatever the cause. For 2023 the CAA estimated their cost at about £65m.
Passengers
An air traffic control failure has been treated as an extraordinary circumstance under UK Regulation 261, so passengers get refunds, rerouting and reasonable expenses but not the fixed compensation of £110 to £520 that applies when the airline is at fault.
NATS
NATS is exposed through the CAA's delay and outage incentives on its price control and through enforcement. The CAA's penalties policy allows a fixed penalty of up to 10 per cent of the licence holder's qualifying turnover and a daily penalty of up to 0.1 per cent. In February 2021 the CAA found that NERL "contravened its statutory and Licence duties and obligations in the period January 2019 to March 2020 in relation to the provision of sufficient staffing resilience in the London Approach Service for users of Stansted and Luton airports".
What is not published
The numbers that should exist by now
How many flights were cancelled on 8 and 9 September 2026?
Not published
The CAA said "hundreds" of flights; the Secretary of State said "hundreds of thousands of passengers". Press figures range from about 1,000 to at least 2,000 flights. NATS's report to the CAA is due within a week. The 2023 review had recommended the CAA "explore ways of measuring cancellations and knock-on delays".
How many flights were cancelled on 28 August 2023?
Only NATS's own estimate
The CAA's review gives passengers (over 700,000) and cost (£75m to £100m) but shows daily cancellations only as a chart. The count in the record is NATS's own: "likely that the number exceeds 1,500". The widely quoted 1,585 does not appear in either report.
How many passengers did the Heathrow closure affect?
No official count found
NESO's review is an energy review. Heathrow's Kelly review PDF was not at its published address on 10 September 2026.
What did the 8 September failure cost?
Not yet known
For 2023 the CAA produced an estimate in its final report, fourteen months after the event.
Questions this raises
What the investigation should answer
1.
Was the 8 September fault in the same flight data processing system that failed in 2023, and if so which of the 34 recommendations was supposed to prevent a recurrence?
2.
When will the replacement flight data processor that NATS was "accelerating" in its 2026 annual report enter service, and what runs in the meantime?
3.
Why is there still no official count of flights cancelled and passengers affected, two years after the review asked the CAA to find a way to measure exactly that?
4.
Should a failure inside a regulated monopoly still count as an extraordinary circumstance that removes passengers' right to compensation?
5.
Does the CAA's outage metric, which only removes NATS's delay bonus above 250 points, put a price on a failure that costs airlines tens of millions?
6.
If Heathrow schedules above its 480,000 movement cap and flies within 2,130 of it, what is the plan for recovering a lost afternoon at the hub?
No official count of flights cancelled or passengers affected by the 8 September 2026 failure existed on 10 September 2026. Press figures are quoted as reported and not used in any chart or calculation.
NATS's average delay per flight is a calendar year regulatory metric counting only delay attributable to NATS's en route operation. Eurocontrol's en route ATFM delay counts all en route delay in the provider's airspace, weather and staffing included. They are different measures of different things and are never combined.
NATS flights handled are financial years to 31 March and include oceanic traffic; Eurocontrol's UK count is calendar year continental IFR traffic. They agree within a few per cent, as expected, not exactly.
The CAA's on time definition is any degree early through 15 minutes late. The computed 2025 figures reproduce the CAA's own On Time Performance Table to within 0.001 of a percentage point and the build fails if they do not.
The 2026 punctuality figures cover January to June 2026, the latest month published, and do not include the September failure. The CAA publishes with a lag of two to three months.
The Heathrow cap comparison uses movements flown (Table 04a, total excluding cancelled), which is what a planning condition on movements restricts. Scheduled movements are shown for context only.
The December 2018 Gatwick drone closure is omitted because no primary source with a reconciled count could be reached.
The Kelly review commissioned by Heathrow was not at its published address when checked; the Heathrow card relies on the NESO review, which does not count flights or passengers.
Every figure on this page traces to its official source. Share it as it stands.
One email a month: the national resilience score, what moved, and the newest analyses like this one, plus The Quarterly Record four times a year. Every figure traced to its official source.