Air Transport World

Research, not regulation. (aircraft noise)

One person's music is cacophonous to another. Sound can be measured objectively but noise is a subjective matter. According to one simple definition, "noise is unwanted sound." By that definition, the sound emanating from jet aircraft is noise to most ears.

Noise it may be. But at least, those aircraft are producing a lot less of it than they once did. From first-generation commercial turbojets to the latest high-bypass turbofans, perceived engine noise at full power for a 150-seat aircraft has been cut about 22 dB, roughly a 5-fold decrease. Yet, such gains have prompted scant celebration. Instead, with air traffic rising and airport perimeters hugged by more and more housing developments, the demand is for still quieter aircraft. Even while the world's commercial jet fleet upgrades from Stage 2 to Stage 3, noise foes are pressing for a Stage 4 or more stringency by some other name.

In reply, both the airline and manufacturing industries say that's like moving the goal posts in a football game. Such a move, they contend, would provide little discernible benefit to that minority of the population who five near airports but by undercutting the value of the current fleet, it would have a devastating impact on an already weakened sector of the economy. What's needed at this time, they insist, is more research, not more regulation, since most of the noise reductions possible already have been wrung out of the current technology. The showdown likely will come in December, at the third session of the Committee on Aviation Environmental Protection, ICAO's environmental standard-setting body.

In 1959, soon after the start of commercial jet operations, the Federal Aviation Administrator had to get an unlisted phone number as protection from the outraged citizens who were calling each night to harangue him about aircraft noise. At that point, the levels were such that prolonged exposure would cause hearing damage even at points 4 tai. beyond takeoff rotation.

When bypass ratio was increased on some engines to improve fuel efficiency, one beneficial byproduct was reduced noise. Later, design teams began tackling noise more directly, so that by now, noise impact is a primary design parameter for any new engine or airframe. The Boeing 777, for example, was built with the restrictions at London Heathrow Airport in mind. The 737-300 was guided by the limits at Orange County, Calif. …

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