(Reuters) - Southwest Airlines Co said its operations mostly returned to normal at Chicago Midway Airport on Monday after the breakdown of one of its plane de-icing machines forced the cancellation of some 250 flights on Sunday.

A weekend winter storm in the region had blanketed the city in snow and ice, leading to hundreds of cancellations at its major airports.

Dallas-based Southwest ran into trouble de-icing its planes when a pump on one of its glycol tanks stopped working, leaving workers unable to access some of the antifreeze solution onsite.

Southwest was forced to cancel nearly all of its Sunday flights as it waited for the pump to be repaired.

“Southwest has resumed operations at Chicago (Midway) and expects to operate a close to normal schedule. The glycol has been replenished and the airport de-icing equipment is fully functional,” the carrier said.

“Those developments, coupled with a more positive weather forecast for Chicago position us to safely operate our more than 250 departures out of Chicago Midway.”