Southwest Airlines Co.’s cancellation of 250 flights at Midway Airport Feb. 11 was the third time in two months that a shortage of de-icing fluid has complicated the carrier’s Chicago operations.

Heavy snows forced Southwest to use much more than the normal amount of glycol Sunday morning to remove ice and snow from planes that parked at the airport overnight, eating away at the carrier’s supply, Anthony Gregory, vice president of ground operations and provisioning, said in an interview Monday.

Matters were made worse when air seeped into pumps, blocking Southwest from accessing some of the remaining glycol in storage tanks. Unable to secure more, and with additional icing in the forecast, the airline decided to cancel most of Sunday’s flights at Midway.

“What we saw this weekend in Chicago was because of the supply challenges we’ve had with our vendor,” Gregory said. “We’ve had to secure additional vendors to bring Midway sufficient supply.” Midway is Southwest’s largest airport by number of flights.

Some of the suppliers Southwest hired after similar problems in December have also had trouble securing sufficient quantities of glycol, and new regulations that enforce work limits on truck drivers has meant some drivers aren’t available to make deliveries, he said.

Southwest first began to hear about the supply and delivery problems on Dec. 24. At the same time, a glycol pumping station was left inoperable after an equipment malfunction allowed water to enter and freeze in a fueling line. Delivery and supply issues again arose on Dec. 28, forcing the carrier to cancel about 90 flights.

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Photo Credit: An employee guides a Southwest jet into a Chicago Midway gate during a 2013 snowstorm. Southwest had to cancel 250 flights on Feb. 11 because of a shortage of de-icing fluid. Armando L. Sanchez / Chicago Tribune/MCT