WinAir attacks Southwest's niche with promo fare.(WinAir Airlines, Southwest Airlines Co.)

WinAir Airlines, which started flying jets between Sacramento International Airport and Long Beach last November, is offering 868 round-trip flights to Southern California, the cheapest in the corridor.

The company is trying to carve out a niche against market leader Southwest Airlines Co. by undercutting its fares to the south state. WinAir said customers are responding by falling seats.

The Sacramento route "is better than what we expected," said Jim Solomon, WinAir's marketing vice president. "We're very pleased with that market."

The "dime-a-mile" fare could continue into July and August if it succeeds, he said.

WinAir of Salt Lake City …