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 but calling the incident “unprecedented.

Hundreds of additional employees were on duty, and flights were added to the schedule to accommodate thousands of extra passengers, the airport said.

Flights at Britain's Heathrow resumed late on Friday after a fire knocked out its power supply and shut Europe's busiest airport for the day, stranding tens of thousands of passengers and causing travel turmoil worldwide.