Heathrow’s chief executive has defended the airport’s response to the power outage and shutdown that sparked global travel chaos, apologizing to stranded passengers and confirming the airport is “operating as normal” Saturday.

Heathrow Airport said it expected “significant disruption" over the coming days due to the power outage caused by the fire at a nearby electrical substation. The airport had previously said it would be shut until at least midnight local time, with no flights leaving today.

London’s Heathrow Airport—one of the world’s largest travel hubs—said Friday it would resume flights after a fire at a nearby electrical substation caused a power outage, which halted operations and disrupted global travel.