Imagine a 400,000-pound, wide-bodied Boeing 777 gliding over the Peninsula into San Francisco International Airport.
On a recent overnight flight from Honolulu, United Airlines Flight 76 did just that, sailing overhead from the coast to the Dumbarton Bridge at idle thrust using mostly gravity, not mechanical brakes, to cut speed for landing.
For everyone snug in their beds in Woodside, Portola Valley and Atherton, it meant no noise complaints that August morning.
For researchers at SFO, NASA Ames Research Center, Boeing and the Federal Aviation Administration, it means the wave of the future in air traffic control: an aircraft descent pattern generated by computer and flown on autopilot. Researchers say the technology is cleaner, quieter and more fuel efficient than traditional manual landings.
"They didn't hit the speed brakes over land," said Bert Ganoung, manager of SFO's Aircraft Noise Abatement Office. "Spoilers, flaps, landing gear, they all create noise, and they're all speed-braking devices."
The test program, called Oceanic TailoredApproaches, uses computer software to determine the smoothest landing path. A controller sends the path to the plane via data uplink, causing the aircraft to descend with minimal engine thrust and more glide.
Commercial airliners currently fly autopilot at cruising altitude and have auto-landing features. But the vast majority of flights are landed manually by pilots and controllers in heavy traffic to avoid collisions. With tailored approaches, the software determines the path of all planes simultaneously to keep them from colliding, while minimizing the amount of braking and leveling off they normally do to land safely in heavy traffic.
"It's hard for humans to come up with the optimal solution well in advance," said Rich Coppenbarger, Tailored Arrival Principal Investigator at NASA Ames Research Center. "This is ideally suited for automation."
Controllers and pilots liked the system in initial tests, Coppenbarger said. The pilot reviews and approves all computer commands before they're entered into the flight management system.
Scientists working on the highly technical project put it in lay terms this way:
All the bumps, grinds and whines you hear inside a plane as it's descending are noise to people on the ground as well. It also means the plane is cutting, then increasing engine thrust to level off or speed up, keeping the plane in a holding pattern or at a safe distance from other aircraft.
NASA researchers and the SFO Noise Abatement Office tested the automation software every day for three weeks with UAL 76, which arrives at 5:30 a.m. The tests ended last month.
Based on a spate of noise complaints from Peninsula residents in recent years, the noise abatement office has been working with U.S. Rep. Anna Eshoo's office and the Federal Aviation Administration to raise the flyover altitude in Woodside from 6,000 to 8,000 feet.
But in at least one trial, a plane passing at 7,000 feet using a tailored approach made three decibels less noise than a plane with a normal descent at the regular altitude.
"Three decibels is an audible change. You can hear that," Ganoung said.
Researchers said there were no complaints from people on the ground near Woodside and Portola Valley, where the researchers were measuring sound levels. Members of the Airport/Community Roundtable in Woodside and Portola Valley could not be reached for comment Monday.
"What we're trying to tell people is that higher is not always better," Ganoung said. "This is just a snapshot. It doesn't prove anything. But we're analyzing the data."
Preliminary tests also show a fuel savings of about 1,000 pounds per flight, Coppenbarger said.
That may not seem like much, given that a flight burns 100,000 pounds of fuel coming from Hawaii. "A thousand pounds a day on every flight, that adds up," Ganoung said. "Think of the environment, the cut in emissions."
While many agencies are working to test and develop the technology, Coppenbarger says it's at least 10 years from widespread use. Only newer planes carry the Future Air Navigation Systems, or FANS, as standard equipment, allowing transmission of the data used to set flight patterns automatically loaded via computer, Coppenbarger said.
But the team hopes to resume testing in November.
"Any time we can get environmental emissions and noise down, and help airlines stay on time and save fuel, those are all good things for us," Coppenbarger said.
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