U.S. flights cleared to take off again after ground stop order caused thousands of delays and cancellations

Travellers wait at a United Airlines terminal at Los Angeles International Airport on Friday. (Ethan Swope/The Associated Press)

Flights across the U.S. were grounded for more than four hours on Friday, causing travel chaos across the country and beyond.

Thousands of flights were cancelled or delayed, including in Canada, after aging air traffic control systems in the U.S. were overloaded, triggering a ground stop order by the Federal Aviation Administration.

The ripple effect of the FAA's order, which was in effect for more than four hours, will likely last many days as airlines work through the backlog of delays.

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