Noise certification of subsonic jet aeroplanes, heavy propeller-driven aeroplanes and helicopters is carried out using the procedures described in the International Civil Aviation Organization (ICAO) document Annex 16. Measured noise levels are corrected to reference atmospheric conditions to allow for differences in air attenuation resulting from variations in ambient temperature and relative humidity. The attenuation is calculated using the Society of Automotive Engineers standard ARP 866A. This procedure does not include the effect of ambient atmospheric pressure. This Report discusses the influence of atmospheric pressure on the attenuation of sound transmitted to the ground during noise certification tests carried out using airfields at altitude. ARP 866A and three alternative procedures that include the effect of atmospheric pressure are assessed, and calculations are made of air attenuation rates based on reference atmospheric pressure and pressures that are representative of those that occur at airfields located at altitudes of up to 10000 feet (3048 m). Comparison of these attenuation rates shows differences that are dependent on temperature, relative humidity, frequency and altitude. For combinations of low temperature/low humidity or high temperature/high humidity, attenuation rates calculated using ARP 866A are greater than those predicted using the other three procedures. For combinations of temperatures less than about 10 degrees Celsius and relative humidities less than about 70%, attenuation rates are larger at altitude. The effect of these differences on EPNL evaluation is difficult to assess as it is dependent not only on meteorological conditions, but also on spectral shape and propagation distance. The effect is likely to be small. However, in order to draw definitive conclusions about EPNL evaluations and the significance of neglecting the effect of atmospheric pressure on attenuation rates, further work is required using a representative sample of certification test data.

"TRB's Airport Cooperative Research Program (ACRP) Synthesis 9: Effects of Aircraft Noise: Research Update on Select Topics includes an annotated bibliography and summary of new research on the effects of aircraft noise. The report is designed to update and complement the U.S. Federal Aviation Administration's 1985 Aviation Noise Effects report"--Publisher's description

This report examines three particular problem areas associated with the measurement of noise levels of propeller-driven small airplanes required to comply with FAR Part 36, Appendix F. These problems are directly related to effects of atmospheric conditions on (1) the performance capabilities of an airplane when tested at various barometric pressures and altitude densities; (2) the noise signature generated at such conditions; and (3) the propagation of sound from the airplane to the measuring station. The first two of these have been addressed by deriving potential correction procedures which could be applied to noise levels obtained by tests not in strict compliance with Appendix F. These corrections are based on aircraft operations conducted within a specific margin of power setting. The corresponding measured noise levels are subsequently corrected for variation of propeller tip speed, forward velocity and barometric pressure relative to predetermined reference conditions. The third effect, that of sound propagation, si examined by applying SAE ARP 866A to a typical propeller airplane noise spectrum and demonstrating the range of A-weight noise levels that would result within a range of ambient conditions. (Author).

Aircraft noise has adverse impacts on passengers, airport staff and people living near airports, it thus limits the capacity of regional and international airports throughout the world. Reducing perceived noise of aircraft involves reduction of noise at source, along the propagation path and at the receiver. Effective noise control demands highly skilled and knowledgeable engineers. This book is for them. It shows you how accurate and reliable information about aircraft noise levels can be gained by calculations using appropriate generation and propagation models, or by measurements with effective monitoring systems. It also explains how to allow for atmospheric conditions, natural and artificial topography as well as detailing necessary measurement techniques.