United Airlines is again delaying the expected return date for its grounded Boeing 737 Max jets.

The airline said Friday that it has removed the Max from its schedule until Dec. 19, six weeks longer than previously planned.

United owns 14 Max jets, which have been grounded since March after the second of two accidents that together killed 346 people.

Taking the Max out of the schedule reduces United’s risk of alienating customers by canceling flights close to departure if the plane does not return to service as quickly as Boeing hopes.

United’s announcement means it could be flying the Max during the week before Christmas — a period when heavy travel and bad weather can snarl airline operations. By contrast, Southwest Airlines is delaying its earliest possible use of the plane until early January.

Robert Mann, an aviation consultant and former airline executive, said United’s timing is possible if computer-based training for pilots and some “confidence-inspiring” demonstration flights can be wrapped up in November.

With each passing month, the loss of the Max results in more flights being dropped from United’s schedule — from 70 a day in September to 96 a day for most of December — because it’s not getting any new deliveries either.

United expected to have 27 Max jets by the end of September and 30 by the end of the year. The Chicago-based carrier has nearly 800 planes in its fleet.

Airlines haven’t been able to quickly replace the missing planes, so they are cutting back on growth — or in the case of Southwest, actually shrinking.

Boeing is working to fix flight-control software implicated in crashes off the coast of Indonesia and in Ethiopia and solve another problem that Federal Aviation Administration test pilots discovered in June.

The company has shown its changes to FAA over the past several months and expects to formally submit a recertification package in September. CEO Dennis Muilenburg predicted last month that the plane will return to service early in the fourth quarter.

Boeing’s 737 assembly plant near Seattle is still running but at a slower rate, and completed jets are going into storage. A Boeing spokesman said Friday that the company believes it can gradually increase 737 production from 42 a month now to 57 a month next year.

Separately, the FAA said Friday that a committee of international aviation experts will need more time to complete its review of how the agency certifies planes. The group faced a deadline Friday, but FAA said it now expects to wrap up “in the coming weeks.”

The panel is looking into FAA’s original approval of the Max and its use of designated employees at aircraft manufacturers like Boeing to evaluate some aircraft parts. Some lawmakers and safety advocates have criticized that approach and questioned whether FAA understood software that was new on the Max.

The panel’s members represent nine aviation authorities including those of Europe, China and Canada, and is led by a former chairman of the U.S. National Transportation Safety Board. Its review is separate from FAA’s decision about when the Max is safe to fly again.