Investigators have not pinpointed the cause behind the substation incident that led to the closure of Heathrow Airport in March, following a government-ordered emergency inquiry around six weeks ago.
A preliminary report from the National Energy System Operator (NESO) found no evidence of suspicious activity linked to the outages that disrupted power at the airport, impacting 1,350 flights and around 300,000 passengers.
However, the NESO acknowledged that while the fire affected about 67,000 homes, its exact cause remains unclear.
The state agency has committed to continue investigating the maintenance history and design of the 57-year-old power substation in West London, which triggered the fire in late March, to ensure it complies with legal standards.
There will also be a review of the airport’s private electrical network, which took hours to stabilize after the substation failure, even though two nearby substations were functioning normally.
The report indicated that it took Heathrow an additional seven hours to resume operations after power was restored, meaning the airport remained out of service for nearly 24 hours following the fire on March 20.
NESO mentioned that a dedicated team will analyze over 600 pieces of evidence from involved companies and inform the interim report, with a final report expected by the end of June.
In late March, the energy secretary, Ed Miliband, requested an urgent investigation from the system operator to determine what transpired and to provide initial findings within six weeks of the incident.
He stated on Thursday that a complete report is eagerly anticipated to gather insights, enhance the UK’s energy resilience, and safeguard critical national infrastructure.
Heathrow Airport noted that the report raises questions about National Grid, the owner of the affected substation, and the Scotland and Southern Power Networks (SSEN), responsible for distribution in the region.
An airport spokesperson mentioned that clarifying the fire’s origins and the impact on the transformers could assist in advancing the UK energy grid.
Energy firms involved in the outages could face investigations by OFGEM, the regulator overseeing investment approvals and revenues for power network operators.
Heathrow will also initiate its own internal investigation into resilience, led by Ruth Kelly, the former Secretary of State for Transport and a member of the airport’s independent committee.
Executives from the energy and aviation sectors were called to appear before the Congressional Cross-Party Transport Selection Committee shortly after the incident.
Heathrow CEO Thomas Waldy expressed his apologies for the confusion, explaining that incidents of this scale were deemed “very low probability events,” and that the airport was investing in what was considered a “probably resilient” power supply.
A spokesperson for National Grid confirmed that the company will continue collaborating closely with NESO throughout the investigation and looks forward to the comprehensive report. SSE has been approached for comment.
