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The interior noise within the relatively small space of civilian or military rotorcraft results from exterior and interior noise sources. Interior noise measurements may be required in order to develop or evaluate acoustical treatment designs that will provide a necessary degree of crew and passenger comfort. This document describes recommended methods and procedures for uniform measurement, analysis and reporting of sound pressure levels in the interior of rotorcraft. Satisfactory measurements of noise in personnel-occupied rotorcraft cabins may require test techniques different from those prescribed for other types of aircraft (ARP1323) because rotorcraft operate under significantly different flight conditions. Recommendations of this ArP apply to the recording of acoustical data on magnetic tape and the subsequent processing and analysis of the recorded data.