All airline traffic within 250 miles (402 kilometers) of Memphis is stopped, because communications equipment had failed at the regional air-traffic control center there.
Air-traffic control centers in adjacent regions handled flights that were already in the air when the problem was discovered, FAA spokeswoman Kathleen Bergen said. "The airspace was completely cleared by 1:30 (p.m.) Eastern time," or 1730 GMT, she said.
High-altitude flights through the region - which includes Alabama, Mississippi, Arkansas, Missouri, parts of Indiana and Kentucky and West Tennessee - were discontinued while the equipment was being fixed.
"What we did is put a ground stop in place for any flight that would transition through that airspace. We held them on the ground wherever they were, whether it was Miami, Seattle, Los Angeles, Boston," Bergen said.
Bergen said the FAA did not know how long it would take to fix equipment at the Air Route Traffic Control Center at Memphis or have an immediate number on how many flights were affected.