All power to the radar and radios at the Honolulu International Airport control tower were lost for 20 minutes on Sunday night during an annual electrical systems check, but no damage occurred and just four flights were delayed, a spokesman for the Federal Aviation Administration said today.

Portions of the radar room also lost some radar and radio frequencies during the outage, but no flights were affected, said Ian Gregor, FAA spokesman.

"The air traffic controllers and supervisors performed flawlessly in switching to emergency plans," Gregor said. "The outage happened during a planned maintenance check scheduled for when there would be little air traffic and good weather. It's never a good thing to lose power, even during a check, but everyone handled the situation perfectly and the problem has since been fixed."

Gregor said the outage occurred at 7:47 p.m. during annual testing to ensure the switch to a backup generator goes smoothly if power is ever lost at the airport.

While most of the power transition was seamless, Gregor said something happened to prevent the backup power from reaching some electrical systems, particularly all power at the tower and some radar and radio frequencies at the control center. The outage lasted 20 minutes. Twelve planes were in the air at the time and four departures, two from Honolulu and one each from Maui and the Hilo, were briefly delayed.

Controllers in the air traffic control tower immediately began using emergency radios to communicate with airborne aircraft. In the radar room, they transferred operations to sectors that retained radar and radio capabilities, Gregor said.

"We had full radar and radio capabilities back by 8:07 p.m.," Gregor said. "All in all, the impact was very minimal. The planes in the air were never in danger. None came close close together. We were able to keep them safely apart."

Gregor said FAA investigators and technicians have already reconfigured the power delivery system so the blockage won't happen again.