Conservationists recently won a round in their fight to curb expansion at Mammoth Mountain Ski Area. In April, a U.S. District Court judge ruled that the Federal Aviation Administration violated federal law when it chose not to conduct a full-scale environmental impact statement on the proposal to expand Mammoth-Yosemite Airport on the east side of the Sierra Nevada mountains.

The project would lengthen and widen the airport’s runways to accommodate commercial jets, but environmentalists say the impacts could reach beyond the immediate expansion area. “The overarching concern is that the project contemplates a dramatic increase in the number of people visiting a very environmentally sensitive and geographically remote area,” says Earthjustice attorney Susan Britton. “The FAA didn’t adequately analyze the effects that increase could have.”

Noise pollution from low-flying jets could harm wildlife and tourism in nearby Yosemite National Park and the John Muir and Ansel Adams wilderness areas, Britton says.

The arrival of commercial airline service to the airport, which now serves only charter flights, is critical to the plan to turn Mammoth Mountain into a destination ski resort. Intrawest — North America’s largest ski-resort company, which also owns Colorado’s Copper Mountain and Winter Park, as well as Canada’s Whistler Blackcomb — bought the resort in 1996. In 2000, American Airlines inked a deal with the ski area to provide jet service to the airport.

“Before we’re able to bring American Airlines in here, we need to have the airport expansion approved and completed,” says Joani Lynch, communications director for Mammoth Mountain. “In the meantime, we’re pretty much on hold.”

The FAA would not comment on whether it will appeal the decision.