Travelers walk to their gates in the concourse of Reagan National Airport earlier this summer. (Win Mcnamee/Getty Images)

Dominion Power is investigating the cause of a late-night power outage in and around Reagan National Airport on Wednesday that grounded a couple flights and plunged passengers into darkness at their gates, officials said.

Charles Penn, a spokesman for the utility company, said a preliminary finding showed there was an “equipment failure” involving a switch, but he could not provide more details because the investigation is ongoing.

“It’s highly unusual,” said Rob Yingling, a spokesman for the Metropolitan Washington Airports Authority, to have an airport-wide power outage. About 275 customers in the surrounding area also lost electricity about 9:30 p.m., officials said.

Power was restored a little after 11 p.m., he added.

The impact to airport operations was limited as backup power generators kicked in for critical systems and emergency lighting illuminated terminals. Several arriving flights could not deplane immediately because no gates were available, and at least one flight was canceled. The airfield lighting and the air traffic control tower were not affected.

“They had backup systems and were able to direct landings and takeoff without issue,” Yingling said.