Cause of fire that brought Heathrow to a standstill still unknown
May 9, 2025
An interim report into the substation power outage that brought London Heathrow to a standstill in late March has concluded that cause of the fire remains unknown, although counter-terrorism and investigations confirmed “no evidence to suggest that the incident was suspicious in nature”.
On 20 March, a fire broke out at a transformer in an electricity substation in West London’s North Hyde; one of three independent supply points feeding the airport. The inoperability of this facility (‘Substation A’) resulted in the loss of all power from the 275kW substation and “impacted thousands of customers including Heathrow Airport,” wrote the National Energy System Operator (NESO).
NESO was subsequently commissioned by the Secretary of State for Energy Security and energy regulator Ofgen to review the incident, including identifying recommendations to manage and prevent similar future failures.
With Heathrow closed for the majority of Friday 21 March, the airport did partially reopen later that afternoon, using its two other connections to the Scottish and Southern Electricity Networks (SSEN Distribution) system. This also including reconfiguring its own internal electrical distribution network before re-opening for ‘business as usual’ the following day. However, with Heathrow’s three independent supply points (feeding different systems and areas across the airport) not normally connected, reconfiguring a different power setup required “significant network switching” in a process “understood to take a number of hours”.
The Metropolitan Police Service, supported by the Metropolitan Police Counter Terrorism Command, concluded that “no evidence to suggest that the incident was suspicious in nature” has been found and subsequently closed its investigation. However, the National Grid Electricity Transmission Network’s and London Fire Brigade’s forensic fire investigations remain active.
With multiple lines of enquiry now focusing on a variety of areas – including maintenance history, incident management coordination, and the implementation and legal requirements of design standards for substation sites – a final report will be filed by the end of June. Heathrow Airport’s “private network configuration, its operational characteristics and its resilience” will also form an area of attention, concluded NESO.
