Plattsburgh’s airport is emerging as a stronger competitor to financially troubled Burlington International Airport (BTV).

PenAir, an Alaska-based carrier, recently started flying 12 times a week between Plattsburgh International Airport (PBG) and Boston. Round-trip fares of $150 are available on the 34-seat propeller planes plying a route that had previously been operated by Colgan Air. A PenAir spokeswoman would not say how full the flights tend to be, but she and PBG manager Christopher Kreig both say the service is popular.

And it’s not just PBG that’s beckoning Boston-bound Vermonters who would rather fly than drive or make the journey via low-fare Megabus. Cape Air recently added a fourth daily flight to Boston from Rutland Southern Vermont Regional Airport. The additional round-trip on Cape Air’s nine-seat Cessnas will be offered in summer only.

BTV, meanwhile, lacks a direct connection to Boston.

Passengers can also book nonstop flights from Plattsburgh to Orlando and two other destinations in Florida. Burlington is scheduled to lose its only nonstop service to Florida in November following JetBlue’s recently announced decision to end its daily run between BTV and Orlando.

Gene Richards, appointed last week as BTV’s interim director of aviation, says he isn’t worried about losing market share to PBG. “We see them as a partner, not a competitor,” Richards insists. He adds, though, “I can’t quite figure out why it makes more sense for some airlines to fly to Boston from Plattsburgh rather than Burlington.”

The key reason is government underwriting. Airlines choose to fly out of small airports such as those in Plattsburgh and Rutland to hubs such as Logan International Airport because they get federal subsidies through the Federal Aviation Administration’s Essential Air Service program. PenAir, for example, is being paid $2.6 million this year for operating the PBG-Boston route. The subsidy arrangement, which also covers most of Cape Air’s flights between Rutland and Boston, is intended to give rural residents access to major U.S. airports.

BTV, which handles almost five times as many departing passengers as Plattsburgh and Rutland combined, is too large to qualify for the subsidy program.

That competitive advantage enables PBG to offer flights to popular destinations unserved by BTV. And Plattsburgh is seeking to capitalize on its direct links to warm-weather getaways by billing itself as “Montréal’s U.S. airport.” It does take less time for many Montréal-area residents to drive to PBG than to BTV.

Canadians accounted for more than 80 percent of the 130,000 passengers who flew out of Plattsburgh last year. BTV also depends heavily on bookings by Canadians lured to U.S. airports by cheaper fares. Airport officials estimate that 40 percent of the 640,000 passengers departing from BTV last year have home addresses in Canada.

PBG has attracted growing numbers of fliers in each of the five years since it began operating on a portion of the former U.S. Air Force base. BTV has meanwhile seen passenger traffic drop or barely rise in recent years.

Kreig says that more Vermonters are starting to fly from Plattsburgh — at least judging from the number of Green Mountain State license plates in the airport’s main parking lot. Daily rates there recently went from $5 to $7 in order to help finance a planned $50 million expansion of PBG’s terminal.