Southwest Airlines said Tuesday it's ordering almost three dozen of Boeing's smallest 737 Max airliners to add to its fleet as air travel worldwide picks up.

The carrier said in a filing with the Securities and Exchange Commission that the boost in travel and profits has made the upgrade possible.

"Based on improving revenue trends and ongoing fleet modernization plans, the company recently entered into a supplemental agreement with The Boeing Company to increase its 2022 firm orders by 34 Boeing 737 Max 7aircraft," Southwest said in the SEC filing.

The carrier said it also has a number of options to buy more of Boeing's 737 Max 7 aircraft.

"The company accelerated 32 options into 2023, 16 options into 2024, 16 options into 2025, and added 32 new options into 2026 through 2027, bringing the total firm and options order book to 660 aircraft," Southwest noted.

United and Alaska Airlines have also increased orders for the 737 Max this year.

The model was grounded for nearly two years over a problem with its automated flight software that were factors in two deadly crashes overseas that killed almost 350 people.

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