DALLAS — Southwest passengers endured a third straight day of canceled and delayed flights as the airline struggled to resume normal operations on Friday.

Tracking service FlightStats Inc. reported that by midafternoon about 300 Southwest flights had been canceled and 1,200 more delayed. Southwest canceled nearly 1,500 flights and 4,500 others were delayed Wednesday and Thursday.

Southwest Airlines Co. said it was managing through lingering disruptions. It said most of Friday’s cancellations were due to airline crews being unable to get to their flights after being stranded in other cities.

The airline said that a computer router failure caused the breakdown.