WASHINGTON (Reuters) - U.S. air traffic controllers used personal cell phones to sort out flights on Tuesday when a major communications systems failure in Memphis knocked out radio and radar, officials said.

The three-hour midday disruption in a telephone line prompted the Federal Aviation Administration to clear all commercial flights over an eight-state area in the Southeast and Midwest while the problem was fixed, the agency said.

The FAA said it did not know why the communications line failed, but there was no evidence of sabotage. Three long-range radar units were knocked out as well as radio communications.

Controllers used personal cell phones to call other air traffic control centers that still had radio contact with planes that they could not reach, a union official said.

“They had to use personal cell phones to talk to other air traffic control facilities about specific flights that they could not communicate with themselves,” said Doug Church, a spokesman for the National Air Traffic Controllers Association.

There were 150 planes in the affected air space at the time of the outage around 12:30 p.m. EDT, the FAA said. The agency could not say how many aircraft were affected, but the air traffic controllers union said the number exceeded 1,000.

The regional air traffic control center in Memphis monitors flights passing between 40 miles and 250 miles of Memphis.

AGING SYSTEM

The outage was the latest in a string of embarrassing air traffic equipment and other problems this past spring and summer that spotlighted the aging system that handles thousands of flights daily.

On Tuesday, jetliners planning to fly through the area were grounded at airports around the country, and those already in the air were diverted.

Air traffic controllers said there were delays in Atlanta, Dallas and Charlotte -- hubs for American Airlines, Delta Air Lines, and US Airways. Delta said it canceled 10 flights, while American canceled 88 flights. US Airways reported eight cancellations.

FedEx Corp., which is based in Memphis, said it diverted a small number of flights. But the cargo giant’s air operations occur mainly at night, so it did not expect any additional problems.

Flights had resumed at Memphis International Airport and communications were restored at the regional air traffic control center, an airport spokesman said.