Shares of the Dallas airline closed Wednesday trading 0.7% lower at $58.51.
Starting Thursday Southwest will add 10 Boeing 737 MAX jets to its schedule; the planes will make as many as 44 flights to 15 cities, media reports say. The airline plans a wider expansion starting in April.
The company is the last major U.S. airline to resume using 737 MAX jets, after the global fleet was grounded in March 2019, the Dallas Morning News reported.
The grounding followed two crashes, in Indonesia and Ethiopia, that killed a total of 346 people. The cause of the crashes was traced back to a faulty software system that left pilots unable to control the planes.
Boeing has been diligent about getting its 737 MAX jets through the regulatory process. The Chicago aerospace giant redesigned its flight-control software and has tested 6,900 active pilots with flight-simulator and computer training, Bloomberg News reported.
In November, the Federal Aviation Administration approved the 737 MAX to fly again.
Since then, American Airlines (AAL) - Get Report was first to reintroduce the aircraft in the U.S. in December, while United Airlines (UAL) - Get Report began using the jets again in February, and Alaska Airlines (ALK) - Get Report added them to its fleet last week.
Reestablishing Southwest as a partner would be a major benefit to Boeing as the airline is its largest operator and customer, Bloomberg reported. The carrier is set to expand its fleet to 65 MAX jets by mid-April, and 69 by year's end.
Members of the Southwest Airlines Pilots Association have spoken publicly about their confidence in the updated aircraft, media reports say. Analysts have also noted that passengers appear comfortable with the 737 MAX despite its history.