United Airlines resumed operations on Wednesday night after a technology issue grounded all mainline flights, leading to over 1,000 delays.

United Airlines resolved a “technology issue” that triggered a ground stop for the carrier’s flights at major U.S. airports Wednesday evening that led to hundreds of delays and some cancelations, although the airline was still tackling residual delays triggered by the outage.

United Airlines on Wednesday night was dealing with a backlog of delayed flights because of a technology issue that grounded planes nationwide.