BANGOR, Maine — United Airlines’ decision to return to Bangor after a 20-year hiatus hinged on a number of factors, including the city’s promising economy, according to those familiar with the airline industry.

On Monday, Bangor International Airport announced that United Airlines was returning to the airport to offer seasonal, round-trip service to Chicago effective June 5. It will be the airport’s first direct service to Chicago since United pulled out in 1993 because low passenger numbers made the service uneconomical.

Mary Clark, a United spokeswoman, told the Bangor Daily News on Tuesday that several factors led to United’s decision to give Bangor another shot. She cited the city’s size, its strong business community and its “tremendous” summer tourism season among the factors that attracted the airline.

“It is one of the largest cities we don’t currently serve,” Clark said. “That’s the type of growth we look for, and that tremendous seasonal tourism business you have there makes it very attractive.”

While Clark wouldn’t go so far as to say it was solely Bangor’s economic promise that attracted United, Bob Ziegelaar, a veteran of the airline industry who was director of Bangor International Airport throughout the 1990s, suspects that economic development efforts in the Bangor area have helped the city look more attractive to airlines.

“I’ve always maintained we need to grow our economic base to attract the air service we really want,” Ziegelaar told the BDN on Tuesday.

Last summer, he was at Bangor’s Sea Dog restaurant when he met some people who had flown from Chicago to see Phish perform at Darling’s Waterfront Pavilion.

“You can never dismiss even the smallest economic factors,” Ziegelaar said. “The more local activities we have, whether it is a business producing items for sale or whether it’s rock concerts or it’s tourism promotion, it all builds the case for air service.”

Tony Caruso, current director of the Bangor International Airport, said the economic health of a region is certainly a factor.

“There’s myriad factors that go into the airline route planning, but certainly the economic stability of an area does come into the conversation and the decision making,” he said on Tuesday.

But it’s not just changes in Bangor that have made it more attractive to airlines. Changes in the airline industry have made it more economically feasible for large airlines to serve small- and mid-size airports, according to Ziegelaar. One of the biggest changes is the rise of the regional jet, he said.

During the 1990s, United was using Boeing 737s for its service to Bangor, which were large planes with more than 100 seats to fill. That proved uneconomical because fares had to be too high to cover fuel costs and to make up for the fact the flights were often below 50 percent capacity.

United will now be using Bombardier CRJ700, which holds up to six first-class passengers and 64 coach passengers. Besides being smaller than the 737, the CRJ700 also has more fuel efficient engines, Ziegelaar said.

“The regional jets have been a blessing for Bangor,” he said.

United’s new Chicago-Bangor service is scheduled to begin June 5 and run through Dec. 2. During that time, there will a 1:10 p.m. flight from Chicago to Bangor, with a return flight from Bangor to Chicago at 5:15 p.m.

United will add a second daily flight from July 1 through Aug. 31. That will leave Chicago at 7 p.m., with a return flight from Bangor leaving at 6:45 the next morning, according to Caruso.

At this time, United has no plans to make the service year-round, but Clark said that could always be a possibility if the service is well received.

“Any route is dependent on traffic. So if there’s a demand for [expanded service], I think that’s something that could be a possibility,” she said.

Bangor’s principal problem in attracting year-round airline service has always been the seasonality of its market, Ziegelaar said.

“If Bangor could produce on a year-round basis the monthly passenger numbers that it produces June 1 to Nov. 1, there would be no question that flights like this would be year-round,” he said. “The seasonality has always plagued us, which is unfortunate. If we could ever develop a ski industry like Colorado, it would be a different story.”

BGR did receive a $500,000 grant from the federal government in 2010 to help entice United to return and provide service to Chicago or Washington, D.C. The Small Community Air Service Development Program is designed to help reduce an airline’s risk in entering a new market by providing a minimum revenue guarantee.

Clark at United, however, said the grant “was not a major factor in our decision.”

While Bangor has come a long way since 1993, Ziegelaar said in the end an airline’s decision to provide air service to the region is all about economics.

“It’s a dog-eat-dog world in aviation today,” he said. “At the end of the day, the airline has to make a profit on its flights.”

Whit Richardson

Whit Richardson is Business Editor at the Bangor Daily News. He blogs about Maine business, entrepreneurs and the economy.