gradual descent: that's one way to save fuel...

From Alex Kingsbury in U.S. News & World Report...

Once or twice a week, airplanes landing at the UPS transport hub in Louisville, Ky., chart a new course to the runway. Using the latest in GPS tracking technology, the planes glide toward their destination in a maneuver called a "continuous descent," which brings planes to the ground on a direct line, rather than through a gradual approach.

New aircraft maneuvers rarely make news, but UPS's testing of the new technique...could substantially reduce skyway congestion, noise, and pollution—and save money on jet fuel costs. Recent testing at Hartsfield International Airport in Atlanta found that each continuous-descent landing saved 1,300 pounds of carbon dioxide.

With oil costs soaring, every drop of jet fuel counts....

In January, the Federal Aviation Administration gave UPS, the world's largest package carrier, the green light to begin testing the new landing procedure at the Louisville facility, which handles some 100 cargo planes per night. One or two of those flights a week use the new technique, says Mark Giuffre, a UPS spokesman in Louisville. Tests over the past few months indicated that each landing using the continuous descent system saves an average of 50 gallons of jet fuel, or about $200 per flight. "That adds up, especially these days," says Giuffre. Indeed, the company estimates it will save $400 million on jet fuel costs each year for its entire fleet of planes.

In a traditional landing, pilots glide the plane through a series of predetermined elevations in their approach to the runway. This practice makes noise and uses more fuel as planes rev their engines to level off at each of the elevation intervals. Think: moving down a series of steps.

With continuous descent, the airplane relies on GPS guidance to essentially coast on idle in a direct line from its cruising elevation to the tarmac. Think: sliding down a ski slope.

The GPS system that makes continuous descent possible is part of the FAA's Next Generation Air Transportation System, nicknamed NextGen, which also enables planes to fly in straight lines rather than following the twisting paths of the current radar-based system—another fuel saver. In addition, NextGen allows planes to fly closer together, land more planes in quicker succession, and be rerouted more quickly. With some 7,000 planes aloft over the country at any one moment, the new system should also ease congestion and flight delays....

But the GPS systems aren't cheap. Every plane needs reprogramming of its onboard computers and other systems, putting the cost to refit some older planes at $300,000....

While the FAA and trade groups estimate that NextGen could reduce fuel consumption by more than 10 percent, it is unlikely to be in place until 2025 because of cost and technology issues. Meanwhile, Congress and the airlines are still bickering about who will foot the bill for the new system, expected to cost perhaps as much as $20 billion to implement. The airlines are clamoring for tax credits and subsidies to offset the cost....

Yet while fuel savings and the decline in carbon dioxide output are important to the shipping company, the residents of Louisville are most likely to notice something else: a reduction in noise. Because airplanes using continuous descent need not rev their engines, the noise output is 30 percent lower than that of a traditional landing.