3,000 feet above the elevation at the airport. Each time an aircraft descends to an intermediate altitude and levels off, thrust must be applied to maintain level flight. And, increasing thrust increases noise. The resulting noise impact on the ground is even greater in communities such as those in southern Indiana where the nearby residential elevation is more than 850 feet higher in relation to the local runways than the residential elevation in Louisville. Our experimental procedure addresses both the thrust and elevation issues by keeping planes higher longer and then bringing them down in a continuous descent. The aircraft are quieter, both because they are operating at reduced thrust levels and because they are higher as they pass over the affected com-
THE AIRCRAFT ARE QUIETER BOTH BECAUSE
munities. Calculations indicated that the new procedure would
THEY ARE OPERATING AT REDUCED THRUST
reduce noise from about 69-70 decibels to 62-63 decibels, a
LEVELS AND BECAUSE THEY ARE HIGHER AS
significant difference. Because we were examining identical airplanes equipped with identical engines during the same time
THEY PASS OVER THE AFFECTED COMMUNITIES.
period, we eliminated variables that could potentially corrupt the noise measurements. And, because we had a complete picture of what the pilot and airplane were doing, and what the noise level was on the ground, we could look at most of the issues associated with how good our predictions were (in terms of both aircraft performance and noise impact). Additionally, we could determine how easy it is to fly this type of procedure. Our flight tests occurred during a two-week period beginning on October 28, 2002. For eight nights, two UPS Boeing 767 aircraft on their way to Louisville from West Coast cities were selected (once all aircraft were airborne) to participate in the flight test based on their scheduled arrival time in Louisville. Both aircraft needed to be close enough in the sequence so that the weather conditions would be the same during both approaches. One 767 was instructed to perform the standard approach, which involves a series of descents
An innovation in Aircraft Noise Reduction
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