LONDON - London’s Heathrow Airport resumed full operations on March 22 and ordered a probe into how it dealt with a power outage that shut Europe’s busiest air hub for almost a day as airlines warned of further delays and cancellations.

British Airways, whose main hub is Heathrow, said it had operated around 90 per cent of its schedule on March 22 and promised a “near-full” schedule for the next day after chief executive Sean Doyle on March 21 warned the “huge impact” would last days.

The airport, the world’s fifth-busiest, had been due to handle 1,351 flights on March 21, flying up to 291,000 passengers. But the fire at a nearby electrical substation forced planes to be diverted to other airports and many long-haul flights returned to their point of departure.

Britain’s energy ministry said on March 22 it had commissioned the National Energy System Operator to carry out an urgent investigation into the outage that raised questions about the resilience of the country’s critical infrastructure.

Heathrow said it had tasked an independent board member, former transport minister Ruth Kelly, with undertaking a review of the airport’s crisis-management plan and its response to the incident with the aim of boosting resilience.

Aviation experts said the last time European airports experienced disruption on such a large scale was the 2010 Icelandic volcanic ash cloud that grounded some 100,000 flights.

“It has been absolutely insane”, said Amber Roden, a US citizen getting married in three days’ time, after a number of her relatives had their flights cancelled.

Two relatives who were halfway to London from Atlanta had to turn around and go back, she said. Two others will not make it to Britain until the day of the wedding, which she has been planning for two years.

The vast majority of scheduled morning and early afternoon flights departed successfully on March 22, with a handful of delays and cancellations, Heathrow’s departures website showed.

“We don’t expect any major amount of flights to be cancelled or delayed,” Heathrow chief executive Thomas Woldbye told BBC radio.