**Cause of Heathrow Shutdown Fire Remains Unknown, Interim Report Indicates**
A recent interim report has shed light on the significant operational disruption caused by a fire at Heathrow Airport, revealing that the exact cause of the incident remains undetermined. The fire occurred on March 20th, 2025, at an electrical substation located near the airport, leading to extensive power outages and the cancellation of over 270,000 journeys worldwide, significantly impacting travelers and airline operations.
The substation fire caused a total shutdown of Heathrow for most of March 21st, with power outages affecting not only the airport but also 66,919 domestic and commercial customers connected to the National Energy System Operator (Neso). The airport only reopened to flight operations after power was restored approximately seven hours after the outages began. Neso’s final report, expected by the end of June, may provide further details regarding the fire’s cause and root failures.
Notably, the Metropolitan Police’s counter-terrorism unit conducted a preliminary investigation but found no indications to suggest that the fire was suspicious in nature. The absence of identifying factors that could hint at foul play led to a more comprehensive inquiry being ordered by Energy Secretary Ed Miliband. He emphasized the necessity of understanding the fire’s nature to avert similar occurrences in the future.
The timeline released by Neso revealed that the incident started around 23:21 GMT on March 20, resulting in a significant loss of power. The fire was linked to one of three supergrid transformers that enable the efficient distribution of electricity by regulating voltage levels. The transformer caught fire after becoming detached, leading to a simultaneous loss of connection, which further complicated the emergency response protocols that would have provided backup power supplies.
Neso’s chief executive, Fintan Slye, expressed the importance of learning appropriate lessons from this incident to prevent future occurrences. Heathrow Airport officials stated that they welcomed the interim findings, adding that clarification on how the fire started is vital for ensuring the security of the UK’s energy infrastructure.
The logistical challenges following the fire were substantial, prompting a complete closure of the airport by 1:11 AM on March 21st. The prolonged power outage triggered significant criticism of Heathrow’s initial response strategy; despite available back-up power supplies intended to maintain safety systems, the airport chiefs cited that it was not merely a power shortfall but operational delays in switching to alternative electricity supplies that prolonged the shutdown.
Upon assessing the situation, Neso reported that the flow of electricity to Heathrow’s four passenger terminals was reestablished around 10:56 AM on March 21, with the wider airport network receiving power later by 14:23. This reinstatement was followed by safety checks to ensure all critical safety systems were operational before passengers were permitted to re-enter the airport.
Heathrow Airport has indicated that further clarity regarding the fire’s cause, along with insights into why two transformers were impacted, could bolster resilience and safeguard the functioning of UK energy grids in the future. Miliband remarked on the necessity of the ongoing investigations to ensure that vital infrastructures remain secure and robust against potential threats.
As the inquiry progresses, the aviation and energy sectors will be looking closely at the findings to draw conclusions and implement necessary enhancements in safety and operational readiness, with the hope that this incident will yield critical lessons for preventing similar disruptions in the future.