Investigators have failed to find the root cause of the substation fire that shut Heathrow airport in March, six weeks after the government ordered an “urgent” investigation.
A preliminary report from the National Energy System Operator (Neso) ruled out any suspicious activity behind the outage which cut power to the airport, affecting more than 1,350 flights and almost 300,000 passengers.
But the state-owned body admitted that the “root cause of the fire”, which also left about 67,000 homes without power, still “remains unknown”.
The system operator has promised to continue its investigation into the maintenance history and design of the 57-year-old power substation in west London that caught fire in late March to establish whether it was meeting its legal requirements.
It will also examine the configurations of the airport’s private electricity network, which took hours to repower after the substation outage, even as two nearby substations continued to operate as normal.
Heathrow took a further seven hours to open after the power was restored, according to the report, meaning flights were disrupted for almost 24 hours after the fire broke out on 20 March.
Neso said a dedicated team reviewed more than 600 pieces of evidence from the companies involved in the incident to inform its interim report. It expects to publish a final report by the end of June.
In late March, Ed Miliband, the energy secretary, ordered the system operator to undertake an “urgent” investigation into what happened and provide its initial findings within six weeks of the blaze.
On Thursday, he said: “We now await the full report to understand what happened and learn lessons to strengthen UK energy resilience and protect our critical national infrastructure.”
Heathrow airport said the report raised questions for National Grid – the owner of the substation that caught fire – and Scottish and Southern Electricity Networks (SSEN), responsible for power distribution in the area.
A spokesperson for the airport said: “Further clarity on how the fire started and why two transformers were subsequently impacted can help ensure greater resilience for the UK’s energy grid moving forward.”
The energy companies involved in the power outage will also face an inquiry by the industry’s regulator, Ofgem, which is responsible for approving the investments and revenues of electricity network operators.
after newsletter promotion
Heathrow will also launch an internal investigation into its resilience, led by Ruth Kelly, the former secretary of state for transport and independent board member of the airport.
Executives from the energy and airline industries were summoned within days of the outage to appear before parliament’s cross-party transport select committee.
Heathrow’s chief executive, Thomas Woldbye, apologised for the disruption. He told MPs that a power outage on this scale had been seen as a “very low probability event” and the airport had paid for a “supposedly resilient” supply.
National Grid and SSE said in separate statements that they would continue to work closely with Neso in its investigation and looked forward to the full report.
