New York (CNN Business) United Airlines is getting creative in its plans to maintain capacity as the grounding of the Boeing 737 Max enters its fifth month.

The Chicago-based carrier said Tuesday it has signed an agreement to buy 19 used Boeing 737-700 aircraft. It expects the planes to be delivered starting in December. It didn't disclose the airline it's buying the planes from.

United UAL has 14 Boeing 737 Max 9 jets in its fleet. Like other airlines , it is being forced to cancel flights until at least early November because of the grounding. It didn't disclose the cost of the Max grounding.

But the extra planes will help fuel United's growth. The airline expects to boost capacity between 3% and 4% this year.

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