ARLINGTON, Va. (AP) — A power outage at Reagan National Airport is being blamed on an equipment failure and the disruption of two electrical feeds to the airport.

Dominion Energy spokesman Chuck Penn said Friday in an email that when equipment in an underground cabinet failed Wednesday night, one of the two feeds was interrupted. When the airport's automated equipment tried to switch to the second feed, the Dominion source for the feed was also disrupted, leaving most of the airport without power.

Backup generators powered critical functions and emergency lighting until power was restored about 90 minutes later. The airport said flights were operating but unpowered mechanical systems slowed boarding and deplaning

Penn says Dominion is still investigating to fully understand the sequence of events that led to the outage.