July 1, 2005 A new landing procedure keeps airplanes higher until they are much closer to the airport. The new procedure, called continuous descent approach, promises to save fuel money while cutting noise levels near airports. Researchers involved in a test study found an average noise reduction of 4 to 6 decibels.
WASHINGTON--You don't have to live right next door to an airport to hear the roar of jetliners cruising overhead. Now, engineers have unveiled a new landing plan that may help our friendly skies be a little quieter.
Tamara Koch, who lives near an airport, doesn't have to see the planes flying overhead to know they are there. "It's annoying, and it disturbs you with whatever it is that you're doing at the time," Koch says.
Koch may not be able to stop the noise overhead, but now, acoustical engineers may have found a way to make that noise a little more bearable. Kevin Shepherd, an acoustical engineer from NASA Langley in Hampton, Va., says, "The idea is to keep the airplanes higher than they conventionally are."
During traditional landings, airplanes descend and fly at low altitudes many miles from the runway. This brings the engine roar closer to more people. The new landing procedure, called continuous descent approach, keeps airplanes higher until they're much closer to the airport. This means planes will still be seen, but less of the noise will be heard.
Shepherd says, "Instead of descending and then flying level and then descending, they just descend the whole way. This is the reduction of six, eight or even 10 decibels."
The noise level of a jet engine could actually be cut in half and that's not all. The new landing plan uses less fuel, which could end up saving jet-setters like Koch some cash.
"It would be great to have a little less air traffic, on the other hand living so close to National Airport for us is very convenient if we want to take a trip," Koch says. So whether she is up there or down here, flying is about to get friendlier.
UPS already uses the new continuous descent procedure at some airports and is interested in implementing the procedure every place it operates.
WHAT CAUSES AIRPLANE NOISE: Airplane noise arises from the basic principles of flight: lift and weight (the pull of gravity), and thrust and drag. An airplane's wings are designed to create an area of fast-flowing air (and hence low pressure) above the surface. A wing is basically an airfoil, with a leading edge that is angled to "attack" the air in such a way that it increases the speed of the airflow above the wing, decreasing the pressure there. When the lift becomes greater than the object's weight, the object will begin to rise. If the lift is less than the weight of the airplane, the plane will descend, while increasing the lift will cause the plane to climb to a higher altitude.
Noise from an aircraft descent comes from two primary sources: the engine, and aerodynamic noise from the drag along the flaps on the edge of the wing. Airplanes typically land in "staircase-like" paths, reducing their altitude in a series of steps towards an airport. Each step requires a noisy engine thrust to level out the aircraft after moving to a lower level. The most noise is generated at the lowest step.
ADVANTAGES: Some airports are already using an alternative "continuous descent approach," in which the aircraft maintains a cruise altitude until it is relatively close to an airport, at which point it makes an even, continuous descent to the runway. This can more than halve the noise level. It can also reduce fuel emissions and slightly shorten flight time, since the plane operates at lower power settings, maintains higher altitudes and speeds, and takes more direct paths to the runway.