The Federal Aviation Administration lifted an early-morning order to pause domestic departures and said regular air traffic was starting to resume across the country, after a critical system that alerts pilots and crew to safety advisories and other information for flights went down overnight.

Normal air traffic operations were “resuming gradually across the United States,” the FAA said in its latest update on the issue Wednesday. The resumption followed an overnight outage to its so-called Notice to Air Missions, which provides safety information to flight crews. The agency said it continues to look into the cause of the initial problem.