The measurement resolution of noise directivity patterns from acoustic flight tests was investigated. Directivity angle resolution is affected by the data reduction parameters, the aircraft velocity and flyover altitude, and by deviations of the aircraft from the desired flight path. Equations are developed which determine bounds for the lateral and longitudinal directivity angle resolution as a function of the nominal directivity angle. The equations are applied to a flight test data base and the effects of several flight conditions and data reduction parameters on the directivity angle resolution are presented. The maximum directivity angle resolution typically occurs when the aircraft is at or near the overhead position. In general, directivity angle resolution improves with decreasing velocity, increasing altitude, increasing sampling rate, decreasing block size, and decreasing block averages. Deviations from the desired ideal flight path will increase the resolution. For the flight experiment considered in this study, an average of two flyovers were required at each test condition to obtain an acceptable flight path. The ability of the pilot to maintain the flight track improved with decreasing altitude, decreasing velocity, and practice. Due to the prevailing wind conditions, yaw angles of as much as 20 deg were required to maintain the desired flight path. Conner, David A. Langley Research Center RTOP 505-63-51-07...