"There were two planes affected - one trying to take off and one trying to come in," airport spokesman Bob Parker said Monday.
The unexplained silence, which started at 3:15 a.m. that day, ended at 3:40 a.m. when a Port of Seattle staff member drove to the guard shack at the base of the control tower.
"They went over to the guard shack at the tower and he (the guard) was able to raise someone," Parker said.
Airport officials said that a Boeing 747-400 flown by Taiwanese carrier EVA was on its final approach to Sea-Tac at around 3:15 a.m. when it radioed the control tower for permission to land.
There was no response. Eventually, the airliner reached a dispatcher at the airport's departure control facility, who is not in the control tower, and made a plan to remain airborne until a controller could be reached.
Meanwhile, a Delta Airlines jet attempting to back away from the airport's south satellite got no response when it sought clearance to leave.
The airfield - the runways and taxiways - was cleared of maintenance workers until the tower resumed communications, Parker said. "They followed procedure and left the immediate area," he said.
The EVA plane landed safely once contact was reestablished. The matter is being investigated by the FAA, which oversees air traffic control, Parker said. The FAA would not comment on the incident.