United Airlines is again delaying the earliest possible return of 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 now reduces United's risk of alienating customers by canceling flights closer to the departure date.

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Boeing is working to fix flight-control software implicated in both crashes. The company expects to formally submit its changes to the Federal Aviation Administration in September, although FAA pilots and other experts have been testing new software for several months.