Optimum Profile Descents Allow For Lower Power Levels

A generation’s worth of gains in aerodynamics and aircraft engine technology has dramatically reduced the number of people exposed to high noise levels near U.S. airports, but future noise reductions will depend largely on advances being developed through the Next Generation Air Transportation System (NextGen).

In the late 1970s, noise from aircraft affected about 7 million people. That number has dropped to fewer than 500,000, according to the FAA’s Office of Environment, Noise Division, which tracks the agency’s progress on noise-reduction targets.

The assessment is based on computing the areas surrounding U.S. airports that are exposed, over 24 hours, to an average noise level of 65 decibels or more — at or above the level of normal conversation. The computation takes into account the number of takeoffs and landings, the noise level of each, and whether the activity took place during the daytime or at night.

Since the late 1960s and the advent of aircraft engines with higher bypass ratios — which increase the percentage of air that goes through an engine but not through its combustor — aircraft noise levels have dropped 20 decibels. That translates into making only one-fourth as much noise as they did 50 years ago.

Although the impact of noise is at a minimum, the FAA predicts that it will start to increase again soon and continue climbing. Why? Aviation forecasts see continuing growth in traffic in the years ahead. More traffic means more noise. Unless flight operations can be made even more quiet than they are now, noise exposure will increase.

The Noise Division continues to investigate ways to keep aviation quiet, notably through the CLEEN (Continuous Lower Energy Emissions and Noise) program, which provides incentives for manufacturers to develop lower-noise aircraft. NextGen initiatives being fielded now offer additional gains. New Optimum Profile Descents (OPDs) enable pilots to reduce power, nearly to a glide, as they land their aircraft. This eliminates the noise from throttling the engines during step-down approaches near the airport. Additionally, Required Navigation Performance allows pilots flying OPDs to maneuver in areas around the airports to avoid congested housing areas on the ground.

FMI: www.faa.gov