Commercial aircraft pass over Woodside, Portola Valley and parts of Atherton every day on their way into major Bay Area airports, often to the intense annoyance of residents who live in elevated neighborhoods and thus in relatively close proximity to the noise from the jet engines. According to the Federal Aviation Administration, there's good news ahead.

Now in the first year of a decade-long implementation at some airports, including Bay Area airports, the Next Generation Air Transportation System (NextGen) will alter the manner in which aircraft approach airports for landing. These changes should reduce noise levels, the FAA says.

One FAA goal: "Reduce the number of people exposed to significant noise around U.S. airports in absolute terms, notwithstanding aviation growth, and provide additional measures to protect public health and welfare and our national resources."

NextGen guides aircraft by satellite instead of radar. Satellite-based procedures keep aircraft from straying from a prescribed flight path, something they can do with a radar system. These "tighter flight tracks ... reduce the ground noise footprint," FAA spokesman Ian Gregor told the Almanac.

Traditionally, an aircraft's descent is punctuated by loud engine power thrusts, similar to gear changes, as the aircraft arrives at incrementally lower altitudes in its stepwise approach to landing.

This noise pattern goes away with tailored arrival, another NextGen innovation. With tailored arrival, the aircraft is assigned a 200-mile-long glide path to the runway, "like sliding down a bannister rather than walking down steps," Mr. Gregor said. Aircraft using this method "burn less fuel, emit fewer pollutants and make less noise because they are using minimal power."

There may be more planes. "(Air traffic) controllers will be able to safely reduce the separation standards between aircraft, which will provide increased capacity in the nation's skies," a NextGen fact sheet says.

The Almanac asked a number of questions regarding the new system:

• Will NextGen raise the number of flights over Woodside and Portola Valley?

• If aircraft are kept to one tightly controlled flight path, some houses might no longer have aircraft crossing above them, but others may have more. The ground noise footprint may be tighter, but what about houses located directly under that tighter footprint?

• If a jet engine is on reduced power on a 200-mile glide, it's hard to argue that it would be louder, but what if the aircraft flies closer to the ground? What will the net effect be for people on the ground?

Mr. Gregor said he could not talk about "hypothetical impacts from Bay Area procedures that are still in development. We're going to do a draft environmental assessment for the new NextGen procedures we're developing as part of the Northern California Metroplex process. Until we complete the draft EA, we won't know what the possible impacts of the new procedures will be. The draft EA will be a public document that we'll likely post online so anyone can access it."

As for NextGen raising the numbers of flights, the most important determining factors of airport capacity are runway configuration and the workload of air traffic controllers, Mr. Gregor said. "NextGen technology improves efficiency, reduces delays, increases capacity in higher altitude airspace and creates a smoother and more balanced flow of aircraft into an airport," he said.

Does the FAA measure noise under flight paths? "We do, in fact, do noise modeling for new procedures," Mr. Gregor said.

"We will do full environmental reviews of all new NextGen procedures, and we will comply with all applicable provisions of the National Environmental Policy Act (NEPA)," he added.

The FAA claims NextGen could save up to 5.6 million gallons of fuel annually (about $15.5 million) and could reduce greenhouse gas emissions by 56,000 metric tons annually.

8,000 feet?

On a clear patch of ground in the forested hills of unincorporated Woodside sits a navigation beacon over which many Bay Area-bound aircraft pass. Between 1998 and 2001, Rep. Anna Eshoo, (D) Menlo Park, reportedly got air traffic officials to agree that aircraft crossing over this beacon would stay at an altitude of at least 8,000 feet above sea level.

It's the rare flight that keeps to this standard, records show. Between January 2009 and June 2012, 75,705 flights crossed the beacon and about 66,620 of them (88 percent) were flying at less than 8,000 feet, according to data provided by Woodside resident Jim Lyons and Portola Valley resident Vic Schachter. Some 20,895 flights were below 6,000 feet, they said. Mr. Lyons' house sits at 2,300 feet above sea level in Skylonda.

Their source was the noise abatement office of the San Francisco International Airport, which publishes statistics on incoming flights.

Ms. Eshoo met with local air traffic control officials again in July. Asked to comment, she replied in an email: "The meeting was productive. All parties are working in good faith to reduce aircraft noise, as well as maintain safe flight levels. At this time, we are still taking a close look at the data to determine if and how many aircraft are flying below the 8,000-foot minimum altitude."

Asked about the 8,000-foot standard, Mr. Gregor replied: "There is no firm requirement that airplanes fly at 8,000 feet over the Woodside (beacon). Air traffic controllers direct pilots; pilots do not randomly decide what altitude or route to fly. The airspace in that area is extremely complex, and we use the Woodside (beacon) for a number of different airways and purposes — not just for San Francisco (SFO) arrivals.

The aircraft could be headed into San Jose or somewhere out of the Bay Area, he said. "While we keep almost all SFO arrivals at 8,000 feet at night, it is not possible to keep all SFO arrivals at that altitude during the day because of conflicts with other aircraft using that airspace."

Will the glide path used in tailored arrivals result in consistent altitudes? Yes, Mr. Gregor said, "but we have to maintain the flexibility to vector aircraft to different altitudes or routes to keep them safely separated from other aircraft and moving efficiently in the system."

Mr. Lyons said he appreciates the importance of getting an aircraft on the ground quickly and safely. "Why is it necessary for a plane to be at 5,500 feet when another is at 7,900," he asked. "I've never gotten a clear answer to that. It can't always be traffic issues."