A fire at an electrical substation which triggered the shutdown of London Heathrow Airport in March was caused by a ‘preventable technical fault’ which was first discovered in 2018 but had not been fixed, a report has found.
UK energy watchdog Ofgem has launched an investigation after a report by the National Energy System Operator (Neso) said an “elevated moisture reading” had been found in oil samples at the North Hyde electrical substation in July 2018, but action was not taken to replace electrical insulators known as bushings.
In 2022, a decision was made to “defer basic maintenance” at the substation, meaning the issue went “unaddressed”, the final report said.
The fire caused the cancellation of over 1,300 flights to and from Heathrow on March 21, 2025. Heathrow reopened later in the day, operating a very limited flight schedule at Terminals 3 and 5. Throughout the day, airlines operating from Heathrow were expected to transport more than 291,000 passengers.
The review also found that prior to the incident, Heathrow had identified that power disruption could ‘greatly impact' operations. However, the airport assessed the total loss of power to one of its three supply points as a high-impact, low probability event.