NORTH BEND — If Horizon Air hadn’t canceled service between Portland and the Bay Area, it stood to lose a fifth of its passengers to its new competitor.

An estimated 15,000 passengers will switch to San Francisco flights via SkyWest Airlines once SkyWest begins offering twice-daily flights on July 7, according to Mike Boggs, an air service consultant for Mead & Hunt in Eugene.

Airport officials turned to Boggs after Horizon Air’s announcement Friday that the airline would end its service at Southwest Oregon Regional Airport on Oct. 11.

Boggs provided a sobering analysis to the Coos County Airport District board of commissioners on Wednesday. He said a number of factors led to Horizon’s decision.

Horizon’s airplanes were 74.9 percent full in 2007, a number that compares well with similar markets. The airline offers four daily flights to Portland, providing valuable scheduling options to business travelers, Boggs said.

“Business travelers are 40 percent of the customers that produce 70 percent of the revenue,” Boggs said. “This market cannot survive without business travelers.”

But Horizon Air is switching to larger, more fuel-efficient Q400 aircraft, which hold more than twice as many passengers as its current Q200s. The change will save Horizon about one-third of its cost per seat, Boggs said.

On the other hand, Horizon’s current passenger volume in North Bend would fill only two planes a day.

Having just two Portland flights a day would become a matter of convenience for business travelers. If the number of passengers per year falls to 60,000, as Boggs predicts, Horizon’s two daily round-trip flights would be only 58 percent filled. Airlines like to see the planes 70 percent full.

“The fewer frequencies you have in your market, the less convenient it is,” Boggs said. “Our conclusion is they weren’t sure they could get that with a two-trip-a-day schedule. It looks to us like it’s very difficult for them to make it work with Q400s.”

This problem is compounded by the potential 15,000-passenger loss to SkyWest. But competition with Skywest wasn’t the only factor in Horizon’s decision.

“With or without SkyWest, we would have problems in our market with the larger aircraft,” Boggs said.

It’s a combination of things, including seasonal tourism in the area.

Overshadowing everything, not just in this area, but in communities across the entire nation, is the price of fuel, which has gone up 50 percent in the past six months.

Small airports are the hardest-hit. Of 413 commercial U.S. airports, the 267 smallest handle only 11 percent of air traffic. This makes them expendable.

“It’s coast to coast,” Boggs said.

In addition to the 15,000 passengers lured away from Horizon, SkyWest’s San Francisco service is expected to about 6,700 local passenger bookings. Another 9,100 will begin flying out of North Bend instead of driving to surrounding airports such as Eugene.