The impacted system, called Unimatic, houses flight information that is fed to other systems including those that calculate weight and balance and track flight times, according to United. It’s not clear what caused the problem, which was resolved late Wednesday, though some service disruptions continued into Thursday.

An alert on the Federal Aviation Administration website said all United flights destined for Chicago were halted at their departing airports. Flights to United hubs at Denver, Newark, Houston and San Francisco airports also were affected.

The system outage, as the company described it, lasted several hours, the statement said. It wasn’t related to recent concerns about airline industry cybersecurity.