Observed cause-effect relationships between measured aircraft sound exposure levels and various predictor variables

Abstract

Sound exposure levels of in-service jet aircraft departures at a single airport were measured along with a number of potential explanatory variables to determine the extent of cause-effect relationships under typical uncontrolled operating conditions. Explanatory variables included aircraft type, installed engine type, aircraft gate weight, aircraft operator, 10-meter wind velocity, temperature, relative humidity, and barometric pressure. The two factors having the greatest influence on measured SELs (within aircraft type) were (1) a linear association with gross weight and (2) a logistic association with air density (or density altitude). The logistic relationship with air density shows an asymptotic functional form at extreme density values suggestive of full takeoff power under low air density conditions, and lower power settings under high air densities. Together, gross weight and air density alone explained 80 percent of the measured SEL variance. The remaining variables appeared to show little affect for the aircraft types investigated, with the exception of headwind component at speeds in excess of 15 knots. These relationships, along with the integrated noise model’s (INM) ability to predict them, are presented. Also presented are differences in computed annual average SELs using single, annual average predictor values of the variables versus separate, seasonally averaged ones.