Heathrow Airport saw more than 1,000 cancelled flights on Friday following a fire at an electricity substation in Hayes.
The blaze broke out on Thursday night, leading to a major power outage that forced Europe’s busiest airport to close for hours.
Roughly 200,000 passengers were affected by the west London airport being brought to a standstill.
London Fire Brigade deputy commissioner Jonathan Smith said: “The fire involved a transformer comprising 25,000 litres of its cooling oil fully alight.
“This created a major hazard owing to the still live high-voltage equipment and the nature of an oil-fuelled fire.”
Energy Secretary Ed Miliband has ordered the National Energy System Operator (Neso) to “urgently investigate” the power outage caused by the fire. He is working alongside Ofgem and using powers under the Energy Act to formally launch the grid operator’s investigation.
Is Heathrow back to normal?
Over the weekend, a Heathrow spokesperson said the airport was open and fully operational as it was expected to run a “full schedule” on Sunday.
A statement said: “Today we will operate another full schedule of over 1,300 flights.
“We apologise for the inconvenience caused by our decision to close the airport on Friday following a significant fire at an off-site power sub station.
“Yesterday, we served more than 250,000 passengers, with punctual flights and almost all passengers waiting less than five minutes for security.”
A representative added that there were hundreds of additional colleagues to assist in terminals on Sunday as operations picked up.
Transport Secretary Heidi Alexander said: “This incident caused significant disruption but Heathrow, National Grid, and our emergency services have worked swiftly to get people travelling again.
“Heathrow is a massive airport that uses the energy of a small city, so it’s imperative we identify how this power failure happened and learn from this to ensure a vital piece of national infrastructure remains strong.
“Whilst Heathrow is back to business, some disruption is expected over coming days as things get back to normal so I encourage anyone travelling to check with their airlines and plan their journeys.”
The comments came after Heathrow served more than 250,000 passengers on Saturday and operated about 90 per cent of scheduled flights, according to the airport.
Meanwhile, British Airways said it expected it would run a “near-full schedule” on Sunday.
