DALLAS — The three big U.S. airlines that own Boeing 737 Max jets don’t expect the grounded plane back in their fleets until after the peak summer travel season, and that promises to lead to thousands more canceled flights and higher costs well into another year.

On Thursday, American Airlines executives said they canceled 10,000 flights in the fourth quarter because of the idled planes.

Southwest Airlines said the grounding cut its 2019 operating income by $828 million. The airline expected to own about 75 Max jets by now — 10 percent of its fleet — and the shortage is creating “a crisis-like challenge,” said CEO Gary Kelly.

The airlines planned to add more flights in 2020 to take advantage of strong demand for travel. Now Southwest figures to shrink by up to 2.5 percent in the first quarter, compared to early 2019. Beyond that, the airline isn’t sure because it all depends on when the Max returns.

Max operators say they are still confident in the plane, which they bought with its promise of better fuel economy and larger size than previous versions of the venerable Boeing 737, which has a good safety record.

“We know it will fly again some day,” American Airlines CEO Doug Parker said of the Max. “When it does, we’ll be ready.”

The comments, which echoed those by United Airlines executives the day before, came as American and Southwest reported fourth-quarter profits.

The Max has been grounded since last March after two crashes killed 346 people. Boeing, which is working on fixes to software and other items, said this week that it doesn’t expect federal safety regulators to clear the plane to fly until June.