Chicago ? Hundreds of flights from across the nation bound for O’Hare International Airport were delayed for about 3 1/2 hours Monday when a telephone link used by air-traffic controllers was accidentally shut off during routine maintenance, the Federal Aviation Administration reported.

Radar serving the airport was never lost, but the line that was downed by a telephone company about 3:30 p.m. linked the air-traffic control tower at O’Hare to a radar facility in Elgin, Ill., where controllers direct flights arriving and departing the Chicago area, FAA spokesman Tony Molinaro said. The line was restored about 7 p.m.

Airports across the nation were forced to hold dozens of flights on the ground to accommodate the reduction in O’Hare’s ability to land planes until the problem could be fixed.