The National Aeronautics and Space Administration (NASA), Langley Research Center (LaRC) and the Environmental Measurement and Modeling Division of the United States Department of Transportation's John A. Volpe National Transportation Systems Center (Volpe) conducted a noise measurement study to examine the sound level directivity pattern behind aircraft start-of-takeoff roll. This report discusses the procedures and methodologies used to measure and quantify data acquired from the Study.

The Federal Aviation Administration (FAA) and National Park Service (NPS) jointly requested that the Federal Interagency Committee on Aviation Noise (FICAN)"provide advice on some matters related to the measurement and assessment of the effects of aircraft noise due to overflights of units of the National Park System." FICAN findings and recommendations are included.

Two procedures for adjusting as-measured test-day spectra to reference day conditions - the Society of Automotive Engineers' (SAE) Aerospace Recommended Practice (ARP) No. 866A (866A) and a procedure utilizing pure-tone absorption equations, developed in support of the International Organization for Standardization's (ISO) 9613-1 and the American National Standards Institute's (ANSI) S1.26-1995, and refined for application to one-third octave-band data- were evaluated and compared. The ISO and ANSI pure-tone absorption equations are identical to each other. The 866A procedure historically has been used for atmospheric absorption corrections for Federal Aviation Regulations (FAR) Part 36, Noise Standards: Aircraft Type and Airworthiness Certification and similar regulations of the International Civil Aviation Organization (ICAO). The ISO/ANSI procedure analyzed herein is under consideration for inclusion into harmonized regulations. This document presents a comparison of data corrected to several distances using the two different methodologies.