United Airlines Holdings Inc. is removing the 737 Max from its schedule until Dec. 19, the carrier’s sixth adjustment since aviation regulators grounded the Boeing Co. jet in March following two fatal crashes.

Chicago-based United said the schedule change would affect about 9,500 planned flights through December, with the largest impacts expected in October and November. United flew 14 Max aircraft at the time of the grounding but had expected 30 in its fleet by year’s end.

The largest operator of the jet, Southwest Airlines Co., has removed its 34 Max aircraft from its schedule through Jan. 5. Air Canada has adopted a similar timetable. American Airlines Group Inc. has set the Max’s return for Nov. 2, with about 115 daily flights affected by the plane’s absence from its fleet.

Whenever the Max is cleared to fly, U.S. airlines have said they will need several weeks or even months to transition the jets back into their operations.

Federal regulators grounded the plane after two accidents in Indonesia and Ethiopia within five months killed 346 people.