United is buying used planes to add capacity as the 737 Max remains grounded

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 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.

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The used planes aren't meant to replace the Max 9 jets because they are slightly smaller. The Boeing 737-700's currently in United's fleet has 126 seats, while the Max 9 can fit 179 passengers.

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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Boeing's CEO said he thinks the newly-designed planes are so safe, he took two test flights himself.

It has bolstered its fleet by buying used planes in the past, because purchasing them outright is more financially feasible than leasing them. Last year, it bought 20 used Airbus 319s.

Despite the issues surrounding the Max grounding, United had a strong quarter. Revenue jumped to $11.4 billion, up more than 6% compared to the same quarter a year ago. That was slightly above analysts' expectations. The stock is a bit higher in premarket trading.

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Last week, Delta Air Lines also reported a strong earnings report and raised its 2019 profit forecast. The Atlanta-based carrier doesn't use any Boeing 737 Max planes.

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