Heathrow airport was completely shut down on Friday after a power outage due to a fire at a London electricity substation, causing travel chaos for passengers around the world and the cancellation or diversion of hundreds of flights from Europe's busiest air hub.
Heathrow plies routes to around 80 countries and some 1,350 flights had been due to land or take off from the airport's five terminals on Friday, according to the online flight tracking website Flightradar24.
Some 230,000 passengers a day and 83 million a year use Heathrow, making it one of the world's busiest airports.
Firefighters were called to a 'highly visible' blaze at the substation shortly after 2320 GMT on Thursday and around 70 were sent to battle the fire, which was brought under control by around 0800 GMT.
UK energy secretary Ed Miliband promised that the government would do all it could to restore power to Heathrow quickly, as questions were raised about the airport's 'resilience'.