Hundreds of flight cancellations spread across the U.S. on Friday as airlines began complying with the Federal Aviation Administration 's unprecedented order to scale down routes nationwide because of the government shutdown.

While the FAA order left some passengers scrambling to figure out backup plans, most were relieved to find their planes still on schedule as airlines slowly phase-in reductions at the nation's busiest airports.

The 40 airports selected for the slowdown by the FAA span more than two dozen states and include hubs such as Atlanta, Dallas, Denver, Los Angeles and Charlotte, North Carolina, according to the order.

More than 800 flights were called off nationwide — four times the number canceled Thursday, according to FlightAware, a website that tracks flight disru

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