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.

The blackout caused the airport to close for an hour until electricity was restored. It reopened at 12:33 p.m. and began operating with delays of 30 minutes to an hour for all flights.

Nearly 60,000 people were affected by the closure, according to the ministry, which said the airport’s power company, Tokyo Electric Power Co., likely had nothing to do with the incident.

The airport has two main power transmission lines, one of which transfers electricity to the tower. Power was halted due to a malfunction in the uninterruptible power supply units, which provide temporary power during blackouts, the officials said.

Power was restored by diverting electricity around the UPS units, they said.

According to Kyodo News, the transport ministry said a drop in voltage about 50 minutes before the blackout caused the tower to switch to emergency battery power.

But the airport staff did not notice the switch, and the batteries eventually ran out, resulting in the power failure, according to the transport ministry.

Japan Airlines Corp.’s 16 flights heading for Haneda had to be rerouted to Narita airport in Chiba Prefecture and Chubu airport in Aichi Prefecture, according to the transport ministry. Most of the diverted flights later reached Haneda, a JAL spokeswoman said.

Six All Nippon Airways flights were diverted to Narita and Chubu but all later reached Haneda.

Skymark Airlines Co. said two of its flights were canceled.

Check-in procedures were also delayed.

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