A “preventable, technical fault” led to the fire at an electrical substation that resulted in Heathrow Airport being closed for almost an entire day, a report has found.
It was probably caused by moisture that had been present in electrical components for seven years but went “unaddressed”, a review by the National Energy System Operator (Neso) has found.
The review also found the design and configuration of Heathrow’s internal power network meant the loss of one of its three supply points would “result in the loss of power to operationally critical systems, leading to a suspension of operations for a significant period”.
Plans were in place to respond to the event, but these included a network reconfiguration that would take 10 to 12 hours. The loss of a supply point was “not assessed to be a likely scenario by Heathrow due to its expectation of the resilience of the wider network”.
The review said this meant that its internal electrical distribution network was “not designed or configured … to provide quick recovery following such a loss and relied on manual switching”.
No flights operated at the west London airport until about 6pm on March 21 because of the blaze, which started late the previous night.
More than 270,000 air passenger journeys were disrupted by the closure, which led to questions over the airport's energy resilience.
A spokesperson for Heathrow said a combination of “outdated regulation, inadequate safety mechanisms, and National Grid’s failure to maintain its infrastructure led to this catastrophic power outage”.
“We expect National Grid to be carefully considering what steps they can take to ensure this isn’t repeated,” the spokesperson said.
The airport carried out its own review and identified 28 key areas for improvement.
It found attempts to tell Heathrow airport’s sleeping chief executive that the airport had been closed because of the power cut failed because his bedside phone was on silent. Thomas Woldbye was in bed when senior Heathrow staff decided to suspend operations.
Power was restored to terminals around seven hours before flights resumed on the day it was closed.
The National Grid said there were “important lessons to be learned” about cross-sector resilience following the fire. Regulator Ofgem said it was launching an investigation.
The regulator said the cause was a “preventable, technical fault” and will review whether the National Grid Electricity Transmission (NGET) complied with legislation and licence conditions over the development and maintenance of the site.
Ofgem will also commission an independent audit of NGET’s assets and their status and whether “the failings identified in Neso’s report into [the] North Hyde [substation] were one-off in nature, or more systemic across the National Grid estate”.
