The Chicago Department of Aviation announced Sunday hundreds of Southwest Airlines flights were canceled due to issues with deicing fluid at Midway International Airport.According to the Chicago Tribune, ice storms forced the cancellation of more than 200 flights Sunday after the airline’s supply of glycol ran low, which is a fluid used to de-ice planes.The official Twitter account of Southwest announced the airline’s issues with its deicing fluid were actually caused by a malfunctioning pump.We're sorry for the frustration surrounding your son's flight cancellation, Rick. We are unable to utilize our deicing fluid due to a malfunctioning pump. That said, if we fly into Chicago, we are unable to deice those planes for the next journey. We appreciate your patience. ^NG— Southwest Airlines (@SouthwestAir) February 12, 2018The carrier also revealed operations returned to normal Monday once the supply of deicing fluid was replenished and the pump was repaired.Hey Maria - Yes, we have de-icing fluid on hand now, and our operations are back to normal today. ^KM— Southwest Airlines (@SouthwestAir) February 12, 2018READ MORE: Are ‘Rowdy’ Kids Enough to Get You Kicked Off Flight?Sunday’s temperatures in Chicago were in the mid-20s, causing icy conditions at the Chicago airport.Sunday’s cancellations weren’t the first at Midway caused by deicing fluid. In December, a total of 90 Southwest flights were canceled due to delays associated with de-icing planes, which the carrier blamed on freezing conditions at the airport.