DALLAS (CBSDFW.COM) — Southwest Airlines is expanding its footprint in Houston and Chicago.

On Monday the Dallas-base airlines announced its return to Houston’s George Bush Intercontinental Airport. The location was one of three airports where Southwest offered service on its first day of operation in 1971. The carrier moved to Hobby Airport shortly after though it operated service from both airports between 1980 and 2005. Southwest provides an estimates 4,000 jobs in the City of Houston.

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Work is already underway to add new service from Chicago O’Hare International Airport, alongside existing service from Midway International Airport, which is one of the busiest airports in Southwest’s network. The airline employ more than 4,800 Chicago-based employees.

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“Southwest owes decades of success to our Employees and Customers who have supported our business in Chicago and Houston,” said Southwest CEO Gary Kelly. “Today’s announcement furthers our commitment to both cities as we add service to share Southwest’s value and Hospitality with more leisure and business travelers.”

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Service to both airports is expected to be up and running by the first half of 2021.