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(CNN Business) —  

American Airlines now won’t use its fleet of Boeing 737 Max planes any time this summer.

The world’s largest airline, which has 24 of the 737 Max jets in its fleet, said it is canceling about 115 flights a day through September 3 as a result of the grounding. It previously had canceled flights through August 19. The plane was grounded in mid-March after two fatal crashes, putting focus on a particular safety feature on the plane.

American’s canceled flights are the most extensive among US airlines. Southwest (LUV), which has 34 of the 737 Max jets in its fleet, has canceled flights only through August 5 at this time. United Airlines’ cancellations also run into August.

Not all of the American flights scheduled to be flown by the 737 Max will be canceled outright. Some will be flown with other aircraft. American is also canceling some flights scheduled to be flown by different aircraft, such as the original 737, to shift those resources to other flights.

American said it is adjusting its schedules to affect the fewest number of passengers possible, and passengers whose flights are canceled will be able to rebook at no cost or get a full refund if they don’t wish to take their trip.

The 115 flights and 24 planes represent about 2% of American’s overall operations. The airline operates about 6,800 flights a day during the busy summer travel season, including those flown for it by regional feeder airlines. Its mainline operations include a total of more than 900 aircraft.

Late summer is one of the busiest times of the year for air travel, so the lost flights will hurt the airline — although Boeing (BA) is expecting to find ways to compensate airlines hurt by the Max grounding. It is seeking to win approval for a software fix that is designed to address the automatic safety feature that is the focus of the investigation into the two fatal crashes.

“American Airlines remains confident that impending software updates to the Boeing 737 MAX, along with the new training elements Boeing is developing … will lead to recertification of the aircraft soon,” American said in its statement. “We are pleased with the progress to date.”