The FAA took down a national ground station on Friday after a communications failure at air traffic control centers caused chaos at US airports and caused the longest shutdown since the Sept. 11, 2001, attacks. More than 6,600 flights were canceled and 8,600 delayed, with another 1,500 already canceled on Sunday, according to FlightRadar24. Aviation analysts said a four-hour slowdown across the country could disrupt the airline's schedule for days. Watch:

The FAA took down a national ground station on Friday after a communications failure at air traffic control centers caused chaos at US airports and caused the longest shutdown since the Sept. 11, 2001, attacks. More than 6,600 flights were canceled and 8,600 delayed, with another 1,500 already canceled on Sunday, according to FlightRadar24. Aviation analysts said a four-hour slowdown across the country could disrupt the airline's schedule for days. Watch: