All three U.S. carriers that use Boeing’s 737 Max jetliner have again put off returning the plane to their schedules.

On Friday, United Airlines said it would operate without the jet until Sept. 4, while American Airlines said it would do so through Aug. 17. Southwest Airlines said Thursday that it would do likewise through Aug. 10.

The three airlines had previously said they expected to bring the 737 Max back in June, but none had provided a formal update since Boeing said last month that it did not expect regulatory approval to fly the jet until June or July. Once approval is granted, airlines will have to prepare the planes and train pilots, which would take weeks.

United said Friday that its decision allowed it to plan service during the peak summer travel season with greater certainty, even if regulators clear the 737 Max to fly sooner.