Santa Rosa's airport terminal was a quiet spot when Horizon Air first landed five years ago.
The county airport had been without passenger service for more than five years, after United Express halted flights to Sonoma County in 2001.
Horizon started small on March 20, 2007, flying two daily nonstops from Santa Rosa to Los Angeles and Seattle.
Since then it's grown to five round-trips a day, with added nonstops to Portland and Las Vegas. A sixth flight is coming in June.
Now flying under the banner of Horizon's sister carrier, Alaska Airlines, the service has pumped new life into the regional airport. More than 207,000 passengers took Alaska's Santa Rosa flights last year, up nearly 10 percent from 2010.
There are plans for longer runways, a new passenger terminal and other improvements at Charles M. Schulz-Sonoma County Airport. And there's talk of new carriers and destinations, including a critical eastbound connection.
Sonoma County service has paid off for Alaska and Horizon, said Marianne Lindsey, spokeswoman for the Seattle-based airlines, both part of Alaska Air Group.
"We see Santa Rosa as a strong market and very welcoming since we started service five years ago," she said. "The public response to our Santa Rosa flights has been outstanding."
Alaska will launch a new daily flight from Santa Rosa to San Diego on June 5, dropping its service to Las Vegas. It will also add a third flight to Los Angeles four days a week through Aug. 25.
"San Diego is currently booking strong, ahead of LAX, which is already booking ahead of last year," Lindsey said.
Alaska's daily flights provide a $112 million boost to the county's economy, said Jonathan Coe, part of a Sonoma County group that wants to bring more passenger service to the airport.
"It's a huge plus," said Coe, president of Santa Rosa's Chamber of Commerce.
Alaska's commercial air service supports more than 400 jobs, promotes tourism and makes it easier to attract business, he said.
The airport is talking with Alaska and other carriers about new destinations, but there's nothing definite yet.
"We wouldn't be surprised if we were able to add additional flights in the future, but we don't have anything beyond our new San Diego market planned at this time," Lindsey said.
High on the airport's wish list is a nonstop to Denver, Salt Lake City or Phoenix, three airline hubs with good connections to the East Coast.
Eastbound service would be a boon to economic development, encouraging companies to locate in Sonoma County, Coe said.
"They need to connect to clients or home offices in the eastern part of the country," he said.
The airport is negotiating with Frontier Airlines about starting a Denver route, but it probably won't happen this year, said airport spokeswoman Melinda Gay.
Meanwhile, the airport has won a $650,000 federal start-up grant for eastern service.
Airport expansion is key to getting longer flights. The existing runways are fine for Alaska's 76-passenger Q400 turboprop aircraft, but they're too short for most regional jets, which have up to 99 seats.
In January, Sonoma County leaders approved an $84 million airport expansion project that includes longer runways and a new terminal. The project won strong support from business leaders, but drew fire from critics who said it would cause noise and traffic problems in nearby communities, including Windsor.
The county will extend the main runway to 6,000 feet and lengthen a second runway by 200 feet. The $42 million job could be finished by the end of next year.
The airport's longer-term growth plan would accommodate up to 21 flights a day.
But getting more airlines to Santa Rosa isn't a slam dunk, said Henry Harteveldt, an analyst at Atmosphere Research Group, a San Francisco firm that tracks the air travel industry.
Airlines are still recovering from a travel slump caused by the economic downturn, he said. Faced with higher fuel costs, many carriers are reducing service, Harteveldt said.
"They're cutting back on flying," he said. "It's not going to be an easy win for Santa Rosa."
Still, airlines would be interested if fuel costs fall and they see strong demand in Santa Rosa, Harteveldt said.
"Airlines are looking for new ways to make money," he said.
Alaska's service has made the Sonoma County airport an easy gateway to Wine Country and the North Coast, he said.
"It's a great airport," Harteveldt said. "Other airlines are looking at what they've done."
Alaska performed better than most other carriers in 2011, with passenger revenue up 13.2 percent from the prior year. Under a corporate restructuring last year, Alaska pays Horizon to operate regional flights, including Santa Rosa's service.
Horizon aircraft wear the Alaska brand and Alaska handles scheduling, ticketing, pricing and marketing. The arrangement provides more marketing clout for the company's regional service, Alaska officials said.
Sonoma County is gearing up for Alaska's new Santa Rosa-to-San Diego flights, said Ken Fischang, who heads the county's Tourism Bureau. The bureau is promoting Sonoma wine country in the San Diego market and making contacts with local meeting planners and tour operators, he said.
The San Diego flight also provides a new connection to Mexico, Fischang said.
"There's a tremendous market in San Diego," he said.
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