New York (CNN Business) Southwest Airlines is prepping for a summer travel season without its Boeing 737 Max planes.

Southwest LUV The airline said Thursday that it was extending changes to its flight schedule to account for the grounded aircraft's absence.last month modified its timetable up to June 7, but will now further tweak it through August 5.

The move aims to "reduce the amount of last-minute flight changes" and bolster schedule reliability, Tom Nealon, the airline's president, said in a statement

"While the timing for the return to service of the MAX remains unclear, what is very clear is our commitment to operate a reliable schedule," he added.

Investigators are still probing both crashes, which killed 346 people in total. The 737 Max was grounded in March after one of the planes flown by Ethiopian Airlines crashed, killing everyone on board. It was the second accident involving the jet model in less than six months, after another flown by Indonesia's Lion Air crashed last October.Investigators are still probing both crashes, which killed 346 people in total.

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