Standing in Georgina Kerr's back yard on the banks of the Duwamish River, it's hard not to think about what a nice place it would be with your ears plugged.

From the shade of the trees beyond her back stoop, she can watch river otters and great blue herons navigate the river, just as Native Americans used to on their way to open water.

"This was their I-5," she likes to say when recounting her neighborhood's history.

Disturbing her paradise is the distant rumble of the real Interstate 5. Across the river, a shooting range and Sound Transit bulldozers and dump trucks add to the cacophony.

But all of it is drowned out whenever a jet roars overhead on its way in or out of Boeing Field, just a few miles from Kerr's house in Tukwila.

Kerr is one of about 20 residents who have started organizing to fight a Southwest Airlines proposal to move its commercial flights from Seattle-Tacoma International Airport to King County International Airport, better known as Boeing Field.

Another opposition group, Friends of Boeing Field, has a Web site featuring a graphic of Southwest planes swarming past Mount Rainier like giant orange and blue bees.

If the Metropolitan King County Council agrees to the expansion at the county-owned airport and Southwest competitors Horizon and Alaska airlines, in turn, move some of their flights to Boeing Field, it could mean as many as 370 new takeoffs and landings each day.

Many of the planes would fly over Tukwila and other neighborhoods in the flight path, including Georgetown, Rainier Beach, Beacon Hill, West Seattle, Magnolia and parts of Queen Anne.

There has always been noise in her neighborhood, Kerr said, "but to bring it to a level that people are just going to go loony I think is unconscionable."

Southwest announced plans last month to build a $130 million terminal at Boeing Field, which is now used only for private jets, general aviation and some cargo jets each day.

Southwest says it would start with 60 flights a day — 120 takeoffs and landings — in 2009, eventually ramping up to 85 flights a day. Fewer than 30 cargo jets comparable in size to passenger planes make daily trips in and out of Boeing Field now.

As a general rule, a 50 percent increase in flights makes the noise level much more noticeable to neighborhoods, said Lou Sutherland, a California-based acoustical consultant who specializes in how airport noise affects communities.

Sutherland said Southwest's planes are slightly quieter than the cargo jets used at Boeing Field, and after a preliminary look at the types of planes and flying times at the airport, he said noise impact would be "pretty marginal."

If other airlines follow Southwest, he said, it would be more significant.

The emerging debate over the Southwest proposal is forming alliances between the Port of Seattle, which opposes the airline's move, and some of the neighborhoods that fought the Port over the third runway at Sea-Tac. In some cases, the Southwest proposal is pitting neighborhoods against each other as they consider the impacts of more jets roaring by.

"It would dramatically alter the daily climate of what it means to live in Georgetown or near Boeing Field," said Mark Cooper, who bought his house in Georgetown a year ago.

Although he knew he was moving a few blocks from an airport and would hear some planes, Cooper said the Southwest proposal is a "major repurposing" of the airport that is not fair to residents.

Airport Director Bob Burke said it's not a major shift.

"We have commercial service here now," he said, including some scheduled passenger service.

Tukwila leaders, who just finished fighting the third runway now under construction at Sea-Tac, are livid.

"Now we're getting kicked with the other foot," said Tukwila City Council President Pam Linder.

Normandy Park Councilman Stuart Creighton, formerly a Tukwila ally in the fight to stop the third runway at Sea-Tac, said opponents of the Boeing Field-Southwest deal are overreacting.

"It would seem to me that the communities around Boeing Field are going to get a better deal out of this," he said, because they may be able to negotiate more favorable flight paths over Elliott Bay. Anyway, he said, it's not that many planes.

"The magnitude of what is projected to go in at Boeing Field is really kind of a minor event," he said.

Ed Wojeck, who lives in Magnolia and is a member of the King County International Airport Roundtable, a group that advises the airport about community issues, agreed.

"I personally think that Southwest has worked in other neighborhoods, and I think before they came here, I would insist that they find a way to fly out over the water," he said.

Some of his neighbors are more concerned. Dan Labriola said Boeing Field flights already wake up his month-old baby. He said more would be "devastating."

"The residents are ballistic," he said. "The people that live in this neighborhood are just absolutely unglued over this."

The over-water approach pushed by Magnolia has upset people in West Seattle, since it could mean more noise for them.

"It has the potential of shifting the noise from one community to another, which has always been a concern around town here," said Ed Hanson, West Seattle's representative on the roundtable.

Emily Heffter: 206-464-8246 or eheffter@seattletimes.com