For years, the Sonoma County airport has been angling to get passengers to Denver on a nonstop flight.

Now, pending the approval of a recent grant proposal, it could happen this year, a United Airlines spokesman said.

The airport’s proposal to the Department of Transportation asks for $650,000 in startup funds to partner with United Airlines to make the route a reality, said Charles M. Schulz-Sonoma County Airport manager Jon Stout. If approved, it would mean United would transition some of its current 66-mile Santa Rosa-to-San Francisco flights, which operate up to three times a day, to the Denver route, said airline spokesman Jonathan Guerin.

It is the second time the airport has applied to the federal Small Community Air Service Development Program, which aims to help small airports identify air service deficiencies and propose solutions. Denver is the sixth most popular destination for North Bay air passengers, Stout said, which makes the lack of a direct route from Sonoma County just such a deficiency.

In 2011, a similar $650,000 award allowed the airport to launch its popular Phoenix route, operated by American Airlines. Of that, $500,000 was given to American Airlines in revenue guarantees and the other $150,000 was used for marketing purposes. Stout said the new grant would follow the same model, if awarded.

A maximum of 40 SCASDP applicants are awarded grants each year, with up to four grantees per state. There is no limit to the individual grant sizes, though the amount depends on available funds. The number of applications submitted by the December 2017 deadline was not available, but Stout said it is likely far more than 40. For this grant cycle, $10 million in federal funds are up for grabs, the DOT said.

Stout expects to be notified of the airport’s application status later this spring.

“There’s a lot of interest in Denver from the local community,” Stout said. “Denver’s a really good hub, so if you want to go east, it’s a good way to connect.”

The Sonoma County-to-San Francisco flight operated by United Airlines has been running about 50 percent full, lately, Stout said — much lower than the airport’s goal of 70-80 percent flight load capacity.

At 17 minutes flight time, the route is United’s shortest, which makes it inexpensive to operate frequently, despite low passenger numbers.

“What would happen is we would reduce the number of frequencies between San Francisco and Sonoma, as that Denver service would potentially launch,” Guerin said. “We’re still kind of analyzing what that timing would look like.”

The airport currently operates only one route to a top-10 destination, Stout said: Los Angeles. The list of top 10 destination cities is compiled through a survey of ticket purchases made by credit cards with billing addresses associated with North Bay zip codes, Stout said. The last time the airport paid for such a survey, Los Angeles ranked No. 1, with New York City, Guadalajara, Chicago, Newark, Denver, Mexico City, Atlanta, Dallas and Boston following.

“A Denver flight would open up the New York, Newark and Atlanta markets, and also Boston, and that would give us a one-stop (flight) to a lot of our top 10 (destinations),” he said. “Denver’s been our focus for the last couple of years, and we’re eager just like everybody else.”