Cause of Heathrow Airport fire that saw more than 1,000 flights affected still unknown

UPDATED 9 MAY 2025

The cause of the London Heathrow Airport (LHR) electrical substation fire is still unknown according to an interim report from the National Energy System Operator (Neso). According to Neso, a transformer at the substation disconnected and caught fire. The final report is due at the end of June.

A spokesperson for the Heathrow Reimagined campaign, said: “Heathrow Reimagined welcomes today’s commitment by NESO to investigate “the resilience of energy infrastructure” at Heathrow and we look forward to reviewing the recommendations next month.

“For too long, inefficient spending has been enabled by a flawed regulatory framework and resulted in a lack of basic operational resilience. The time for a fundamental review by the UK Civil Aviation Authority (CAA) to investigate what has gone wrong and to address the root causes, is now.”

What happened?

Heathrow Airport was closed all day on Friday March 21 2025 as a result of a fire at a nearby electrical substation, grounding flights at the airport and causing disruption around the world. More than 1,350 flights are thought to have been affected. Passengers were told not to travel to the airport and to contact their airline for further information.

The fire was brought under control and the UK’s counter-terrorism unit investigated, but concluded that there was no evidence to suggest that the fire was suspicious. However, as airports are a key part of national infrastructure, this must be ruled out immediately. The counter-terrorism unit have specialist forensics in their skillset and can look for any evidence of an explosion or other deliberate act.

The fire is said to have started in a transformer in the substation in Hayes around midnight.

However, it has come to light that Heathrow bosses were warned about vulnerabilities in the airport’s power supply just days before a major outage, UK MPs have heard. 

What has been said of the incident?

Willie Walsh, the Director General of the International Air Transport Association, said: “Today’s closing of Heathrow will inconvenience a huge number of travellers. We thank those affected for their patience as airlines focus on getting them to their destination as quickly and efficiently as possible.

“This is yet another case of Heathrow letting down both travellers and airlines. And that begs some serious questions. Firstly, how is it that critical infrastructure—of national and global importance—is totally dependent on a single power source without an alternative. If that is the case—as it seems—then it is a clear planning failure by the airport. And, from that arises the question of who bears the costs of taking care of disrupted travellers. We must find a fairer allocation of passenger care costs than airlines alone picking up the tab when infrastructure fails. Until that happens, Heathrow has very little incentive to improve.” 

Tara Spielhagen, CEO of Swiipr, the compensation payment partner of several major global airlines, including the UK’s largest operator out of Heathrow, said: “It is another day of travel chaos with the closure of Heathrow and over 1300 flight cancellations. Passengers impacted by the shutdown are unlikely to be eligible for compensation payments if their flight is delayed or cancelled, as the fire will almost certainly be considered an extraordinary event. 

“We remain on high support alert with all our clients, as under UK regulations, airlines still have a duty of care towards passengers who experience significant disruptions, and must provide them with assistance – including the provision of food and drink and accommodation for overnight delays. Many other UK airports are likely to have increased traffic as travel to and from Heathrow spills over.

“Affected airlines will be under pressure to not only reschedule flights, but ensure they are meeting both their passengers’ needs and their regulatory requirements. As payment partner to many airlines, including the UK’s largest operator out of Heathrow, we anticipate a large amount of payments for passengers over the coming days. When last year’s global IT outage grounded thousands of flights, we saw a 200% rise in payments to passengers from airlines on the first day alone.”