A number of Southwest Airlines Boeing 737 MAX aircraft are parked at Southern California Logistics Airport on March 27, 2019 in Victorville, California. Southwest Airlines is waiting out a global grounding of MAX 8 and MAX 9 aircraft at the airport.

Uncertainty over when regulators will allow the Boeing 737 Max to fly again following two deadly crashes prompted Southwest Airlines, the largest U.S. operator of the jets, to remove them from its schedules through early November — a month longer than it estimated in late June.

Southwest's move follows similar schedule changes announced over the last week by American and United.

Southwest said Thursday it will cancel about 180 flights a day out of about 4,000 flights because of the schedule change. Last month, the Dallas-based airline said it was targeting October for the planes' return, which would have meant 150 daily flight cancellations.

The planes have been grounded since mid-March after two fatal crashes within five months killed 346 people.