Abstract
In 1971, field noise measurements were made during two 10-day periods at locations under the ILS approach path to Runway 21R at Detroit Metropolitan Airport to evaluate proposed changes in glide slope intercept altitudes [FAA-RD-71-117 (Dec. 1971)]. Over 1400 recorded flyovers were analyzed to obtain effective perceived noise level (EPNL) values and other noise measures. Regression lines correlating noise levels with slant distance over observed distances to aircraft ranging from about 1500 to 6000 ft show good agreement with published noise curves frequently used for noise exposure forecast (NEF) calculations. There is relatively large variability in data, however; 95% confidence intervals about the regression lines ranged from approximately 7 to 9.5 dB. Also examined is the observed variability in noise levels at a single ground position under the approach path. Standard deviations of the order of 5 to 8 dB were noted. Of the several sources of variability in noise levels at this position, distance variations appeared to be the most important.
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