United Airlines, which lost the distinction of being the world's biggest carrier after shrinking for several years, plans to regain lost ground by adding more flights from key airports this summer, but John Glenn Columbus International Airport won’t be one of them.

The airline, which announced the expansion plans Monday, says it wants to upgrade facilities at key airports and trim the use of smaller planes on important business routes.

United is in fourth place among the big four carriers in terms of passengers flying in and out of John Glenn Airport. For 2016, United had only 13 percent of the airport’s passengers, a little more than a third of the number of passengers on Southwest Airlines, John Glenn’s top carrier.

And while Delta Air Lines and American Airlines have been adding flights nationally, United hasn’t been.

"We've been shrinking, and our competitors have been growing at our expense," says Scott Kirby, who jumped from president of American Airlines to the same job at United in August. "We're going back on offense."

Reducing the number of delays and cancellations will be crucial, said airline analysts, who note that United consistently ranks worse in on-time flights and cancellations than its top three competitors.

After a 2010 merger with Continental Airlines, United alienated important customers with cost-cutting initiatives that backfired.

A decade ago, for instance, United flew eight daily flights on Boeing 737s between Atlanta and Newark, a big business route where it competes with Delta. By 2013, United flew six times a day on small regional jets or turboprops.

Business travelers detest the small planes because they are more likely to be delayed or canceled, and their lack of enough overhead bins can mean carry-on bags get gate-checked — adding a time-consuming trip to baggage claim.

"Our best customers started abandoning us and flying on the competition, who had a better product," Kirby said. "We have to turn that around."

Kirby thinks that new routes from hubs will win over, or win back, passengers. If traffic picks up, and as United takes delivery of new planes, it should eventually be able to phase out small planes on key business-travel routes, he said.

United announced that this summer it will add four new destinations in smaller cities including Rochester, Minnesota, and Santa Rosa, California, add new connections to other medium-sized towns, and add daily flights on 15 other routes that connect with the big hubs. It will add seasonal flights between San Francisco and Munich.