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.