U.S. airlines began canceling hundreds of flights Thursday due to the Federal Aviation Administration’s order to reduce traffic at the country’s busiest airports starting Friday because of the government shutdown. More than 760 planned Friday flights were cut from airline schedules, according to FlightAware, a website that tracks flight disruptions. That number, already four times higher than Thursday’s daily total, was likely to keep climbing. The 40 airports selected by the FAA span more than