The fire that shut down operations at London Heathrow in March 2025, is still unexplained, according to an initial report on the event from the National Energy System Operator (NESO).
Over 1,350 flights and nearly 300,000 passengers were affected by the fall out from the fire that started in a nearby electricity substation and effectively closed Europe’s busiest aviation hub for 16 hours. That lengthy blackout came despite power being restored to all four terminals as early as 10:56 am on 21 March. The investigation has yet to explain why flights could not resume until around seven hours later, almost 24 hours after the blaze began.
🚨Heathrow Airport Fire🚨
— Taymur Malik (@Taymur959) March 21, 2025
Heathrow Airport shuts down until midnight due to a massive fire at a nearby power substation! Over 1,350 flights grounded, 16K+ people without power. #Heathrow pic.twitter.com/oxcErJmgnc
Over 600 pieces of evidence have been examined by the operator so far and the final report is not expected to be released until June 2025. While concerns have been raised over the airport’s electricity network configuration, the “root cause of the fire remains unknown” NESO said.
Read our interim findings from the review into the North Hyde Substation outage on 20 March which resulted in the closure of Heathrow Airport and over 60,000 customers and businesses losing power. We were commissioned to conduct an interim review within six weeks and will share… pic.twitter.com/osgUqvrxov
— National Energy System Operator (@neso_energy) May 8, 2025
Having described the impact of the incident as “major disruption to thousands of people and many businesses”, on Thursday, the UK’s Energy Secretary Ed Miliband, said: “We now await the full report to understand what happened and learn lessons to strengthen UK energy resilience and protect our critical national infrastructure.”
Incredulity over the airport’s vulnerability and lack of a working power back-up were expressed by commentators and Members of Parliament at the time of the incident. Heathrow airport meanwhile said the National Grid – which owns the affected substation – as well as distributors Scottish and Southern Electricity Networks (SSEN), had questions to answer. Industry regulator Ofgem is will investigate the network operators involved.
Set to conduct its own internal inquiry, Heathrow said: “Further clarity on how the fire started and why two transformers were subsequently impacted can help ensure greater resilience for the UK’s energy grid moving forward.”
The Metropolitan Police has previously said that there is “no evidence to suggest that the incident was suspicious in nature”, something echoed by Miliband, who noted: “The National Energy System Operator’s initial summary of the incident rules out the possibility of any suspicious activity.”
When the final report comes out in June, it is expected to make a series of recommendations about energy infrastructure resilience at the airport and nationally, as well as examining and advising on how the airport responds to critical incidents of this nature.
The Heathrow blackout is not the only energy incident to have hit Europe in recent months. An unprecedented transnational power outage swept across Spain and Portugal at the end of April, plunging millions of people into darkness, causing severe disruption to transportation, communication, and essential services, and triggering a state of emergency. Authorities are still looking into the reason for the outage.
