United Airlines reported strong second-quarter profit growth and announced Wednesday it will buy 19 used Boeing 737-700 jets to fill the gap created by the worldwide grounding of 737 MAX aircraft.

The strong earnings report -- United said second-quarter profit increased to US$1.05 billion from US$683 million a year earlier -- suggests that fatal crashes of two MAX jets have not deterred customers from flying. The 737-700 is an older, less fuel-efficient plane introduced in 1993. United said it hopes to take delivery of the used jets by December. It did not disclose the airline it is buying the airplanes from.

"I see United's action as an opportunistic buy to supplement its domestic fleet," aviation consultant Robert Mann told China Daily USA. "Remember that taking delivery of the planes and inducting them into service are two different things."

United has 14 MAXs and planned to add another 16 by the end of the year with 28 more in 2020, but deliveries have slowed following the crashes of MAX jets flown by Lion Air in Indonesia and Ethiopian Air.

United hopes to have its MAX jets back in service by December, but Boeing has not submitted the software update for the airplane's anti-stall system to federal regulators for review, and it's unclear how long the review will take. Initially, airlines hoped to get their MAXs back in the sky by early summer, but technical and regulatory issues have created lengthy delays. Some analysts believe the MAX will not return to service until 2020.

"This is a stop-gap measure until the MAX is returned to service," John Cochran professor emeritus of aerospace engineering at Auburn University and CEO of aviation consulting firm Eaglemark, told China Daily.

"The 737-700 is an older, but a proven, plane. It doesn't have all the attributes of the MAX, but it functions well. I think the FAA will recertify the MAX, but the question is when," he said.

Ryan Air, an Irish discount carrier, said on Wednesday that it expects to cut flights and may close some European hubs following the grounding of the Boeing 737 MAX.

The airline said it expects to receive only 30 new MAX jets by next May rather than the planned 58 that would have allowed it to provide full service. The airline expects reduced capacity will cut the number of passengers it carries through March 2021 to 157 million from the previously forecast 162 million.

Boeing MAX jets were grounded worldwide following crashes on March 10 in Ethiopia and Oct 29, 2018, in Indonesia that killed a total of 346 passengers and crew.