A strong turnout from Portola Valley, Ladera and Woodside is expected at the workshop hosted by the Federal Aviation Administration in the San Mateo Public Library at 55 W. 3rd Ave. at 4 p.m. on Thursday, April 17.

At issue: the noise made by a gradually increasing number of commercial aircraft as they pass over Peninsula communities, some of higher altitude, as they approach the San Francisco International Airport.

At this workshop, one of five identical events to be held in the Bay Area from April 14 to 18, the FAA will have people on hand to explain a draft environmental assessment of an FAA plan to optimize the use of Northern California airspace.

The 953-page draft report, a year in the making, is the work of the FAA and Santa Clara-based ATAC Corp., whose specialties include airspace and environmental impact analysis.

"The materials will include large poster boards depicting some of the graphics and other information that's in the draft environmental assessment," FAA spokesman Ian Gregor told the Almanac. "FAA reps will staff each board and be prepared to help people understand the material in the draft EA."

The report, published March 25, describes "new" routes into major Bay Area airports to save fuel and reduce greenhouse gas emissions. The proposed routes are new only to the extent that they are intended to codify the actual routes now in use. The current routes are not precisely adhered to in practice. Two of the proposed routes appear to converge over Ladera.

The report assumes more use of GPS to

more efficiently guide aircraft, and less use of vectoring -- an air-traffic-controller-directed method employing traditional stepped descents into airports, which generates noise as pilots adjust the aircraft's speed.

The FAA report concludes that the proposed routes "would not result in a significant noise impact" with respect to forecasts of air traffic in 2014 and 2019.

Jim Lyons of unincorporated Woodside and Dr. Tina Nguyen of Portola Valley disagree with that conclusion. They have written to the offices of congresswomen Anna Eshoo, D-Menlo Park, and Jackie Speier, D-San Mateo, calling the report's noise data flawed because it is does not account for differences in computerized projections of noise compared with data from actual noise monitors on the ground.

The report also does not address higher-than-average ground levels in the Portola Valley area, nor does it discuss the continued use of vectoring, they say.

Local governments customarily address controversial issues in public hearings, with live testimony to officials before an interested community. Asked whether there would be public hearings, Mr. Gregor didn't respond to the question. He did say: "One of the purposes of the proposed project is to increase efficiency by reducing vectoring, speed changes, and altitude level-offs during climb-outs and descents. Controllers always have to have the option to vector, but (GPS) procedures reduce the need for it. The noise report has extremely detailed information on noise impacts at literally thousands of locations."

Visitors to the workshop, particularly residents of Portola Valley and Ladera, will have questions on these and other issues, but they must be submitted in writing, Mr. Gregor said. Comment cards will be available at the workshop, with options to write to the FAA via email or regular mail. The 30-day comment period on the draft ends April 24. The FAA will publish responses after the comment period ends, Mr. Gregor said.

A request for a 60-day extension to the comment period has been made from the offices of Ms. Eshoo and Ms. Speier, from the San Mateo County Board of Supervisors, and from Peninsula governments, including the town councils of Woodside and Portola Valley.

Click here to comment and to access the entire FAA report.