The March date will mark nearly a year since regulators around the world issued a safety ban on Boeing Co's fastest-selling aircraft, the 737 MAX, following two fatal crashes in Indonesia and Ethiopia.

Boeing said on Monday that the U.S. Federal Aviation Administration could approve in December fixes to software that played a role in both crashes and approve fixes to new pilot training in January, though the agency has insisted it has no set time frame.

Major airlines have said they will need at least a month after approval to complete training and install revised software before flights can resume.

Since the grounding, airlines have cancelled flights or put other aircraft on routes that would have been flown with the 737 MAX in a hit to profits.

"We are continuing to work through the schedule to try and swap and upgauge aircraft to mitigate the disruption caused by the grounding of the MAX," United said in a statement.

Airlines have been automatically booking affected passengers on alternate flights or offering other options.

United had previously cancelled 737 MAX flights through early January. The new timeline, which could still change depending on the timing of FAA approval, will lead to more than 8,500 flights being cancelled between November and the first few days of March.

The other two U.S. airlines that operate the MAX, American Airlines Group Inc and Southwest Airlines Co, last week announced extended cancellations through March 4 and March 5 respectively.

By Tracy Rucinski