King County officials are in a holding pattern over whether to ask federal permission to change the flight path for incoming airplanes at Boeing Field, which would lessen aircraft noise in Magnolia but turn it up in West Seattle, particularly for people living near Duwamish Head.

King County is balking because a recent study showed the change in flight paths could impede more than a third of the planes approaching Seattle-Tacoma International Airport about five miles south of Boeing Field, also known as King County International Airport.

Secondly, while the change would lessen aircraft noise over Magnolia, it would bring jet planes within a half-mile of Duwamish Head in West Seattle. They fly about 1.5 miles away now.

The King County International Airport Roundtable, an appointed group that offers advice to county officials and departments about Boeing Field, recommended a policy that aircraft noise should not be shifted from one community to another.

Boeing Field is owned by King County and, with about 310,000 flights annually, it's one of the busiest "non-hub" airports in the nation.

For 50 years, most flights arriving at Boeing Field from the north have flown directly over Magnolia and Elliott Bay before touching down. Tired of years of jet noise, Magnolia residents lobbied for years for an approach pattern over Puget Sound instead of their houses.

About 70 percent of aircraft flying into Boeing Field come in from the north.

Currently pilot guidance is provided by an instrument landing system that directs planes to fly over Magnolia at 2,300 feet to avoid interfering with air traffic in and out of Sea-Tac International Airport. They continue south above Elliott Bay, Harbor Island and Georgetown before descending to the runway at Boeing Field.

To change the approach so that it avoids Magnolia and stays above Puget Sound, a "localizer directional aid" system would be installed. But tests indicated that system would cause electrical interference with the existing instrument landing system. In turn, that would force air-traffic controllers to set up a waiting line of airplanes approaching from the north with al least 3 miles between each aircraft.

The result could be a 38 percent decrease in the number of flights able to land at Sea-Tac. Meanwhile, the study predicts Boeing Field will see a 28 percent increase in aircraft flights in the next decade.

The change also would affect the altitude at which planes fly by West Seattle, said Ed Hanson.

Planes would still fly over Magnolia at 2,300 feet but descend to about 1,000 feet as they flew by Duwamish Head, he said.

To maintain these low elevations, jets must fly with their wing flaps and landing gear down, Hanson said. There's a lot of wind resistance on the planes as they fly that way so the jet engines must work harder, which adds more noise, he said.

Under the current system, planes fly about 1.5 miles north of Duwamish Head. If the proposed change were approved, those planes would be a half-mile off Duwamish Head, Hanson said.

"It is a case of shifting noise from one neighborhood to another," Hanson said.

Another problem with the localizer directional system is it wouldn't work for the 30 percent of planes landing at Boeing Field from the south, said Harold Taniguchi, director of the King County Department of Transportation.

The study of the proposal also indicates more research is needed regarding the effects of wind changes, jet noise and the impact of changing Boeing Field's approach route on nearby Sea-Tac Airport, Taniguchi said. He noted there is no money in the county budgeted tagged for more studies about these issues.

The Airport Roundtable recommends using another technique called the "continuous descent approach." It would use the existing route over Magnolia but come in at a higher altitude and descend toward Boeing Field at a steeper angle.

The continuous descent approach would be quieter for Magnolia by keeping planes at a higher altitude longer and using minimal thrust, Hanson said. It would mean little change for people living around Duwamish Head, he added.

Tim St. Clair can be reached at tstclair@robinsonnews.com or 932-0300.