Washington National Airport yesterday morning lost power for the radios that air-traffic controllers use to communicate with pilots.
The incident occurred at 7:39 a.m. when a backup generator failed. Controllers in National's tower were already using a backup generator because a cable was cut on Monday, the National Air Traffic Controllers Association said.
National's controllers switched to a second backup system but it did not have enough power for all primary radio functions, said the association's vice president, Mike McNally.
Some planes were held on the ground, but three were delayed, the longest delay lasting 23 minutes, Federal Aviation Administration officials said.
"This [incident] was transparent to passengers. They should not have been aware of the delay," FAA program manager Dave Canoles said.
Controllers used some radio frequencies from Andrews Air Force Base to keep in communication with planes, "using backup facilities that were already in place," FAA spokesman Anthony Willett said.
A replacement generator was in place within 90 minutes, returning air-traffic opearations to normal, according to Deputy FAA Administrator Linda Hall Daschle. Radar and computer automation equipment were not affected, she said.
National's transmitter was using backup power because of a break in a 6,000-foot power cable buried under the runway, Mr. Willett said.
The backup system, which is an engine …