Tokyo's Haneda airport, the nation's busiest domestic air hub, was forced to shut down for an hour after the control tower lost power during an inspection of its electrical switchboard.
As of 5 p.m., 45 flights had been scrubbed, 22 had been rerouted and 242 others delayed.
The power failure halted the tower's operating systems, including radar, computers and radios, rendering it unable to handle air traffic. But a backup radio system allowed the tower to re-establish contact with aircraft, officials from the Land, Infrastructure and Transport Ministry said.