Assessment of Noise Variability of Landing Aircraft Using Phased Microphone Array

Abstract

Enforcing noise control environmental laws around airports is a difficult task due to the large variability in the noise levels observed for flyovers of the same aircraft type under similar conditions. These variations are not properly considered by the current models, such as the noise-power-distance tables. In this research, noise measurements of aircraft flyovers were used to assess this variability and investigate its causes. 115 flyovers of landing aircraft were recorded using a 32-microphone phased array. It was assumed that the main cause of this variability is the change of the emitted aircraft noise, as previous studies showed that the effect of the variable atmosphere (for the distances considered) is negligible. The noise-level variability for the Boeing 737 and Fokker 70 cases was approximately 7 dB. The fan rotational speed of each flyover was determined by analyzing the spectrograms. Functional beam forming was applied to the acoustic data. For the Boeing 737 case, it was found that the engines are the dominant noise source for all flyovers and that over 75% of the variation of the noise levels can be explained by variations in the engine settings. The Fokker 70 flyovers were dominated by airframe noise sources. Differences in the aircraft velocity explain almost 70% of the noise-level variability in this case.