Southwest Airlines (WN, Dallas Love Field) plans to retire around twenty B737-700s during the course of 2019 as it prepares to become the launch customer for the B737-7s, Chief Financial Officer Tammy Romo said during the LCC's quarterly earnings call.

"We'll start retiring some of our oldest -700s this year as we continue with our fleet modernization effort, which will help improve our fuel efficiency, operational reliability and maintenance burden," Romo said.

The airline currently operates 513 737-700s and is by far the world's largest operator of the type.

Southwest Airlines plans to replace the -700s with MAX 7s, of which it will become the global launch customer later this year.

"For 2019, we currently have a total of forty-four aircraft deliveries which is comprised of seven owned MAX 7, twenty-one owned B737-8s, and sixteen leased MAX 8," Romo clarified.

The delivery plan for this year is larger than planned due to one delivery of a MAX 8 delayed from December 2018 and nine new orders for leased aircraft of the type.

"These additional nine leased aircraft are earmarked for this year's fleet replacement needs," Romo added.