XTENSIVE use of noise-absorbi ng materials in the inlet and exhaust ducting of modern high bypass ratio turbo fan engines has reduced the noise generated by fans, compressors, turbines, and burners to the level that the jet noise (noise generated in the exhaust plume by mixing the high velocity jet with the ambient air) is an important part of the total noise signature of current aircraft. The characteristics of jet noise from turbojet and turbofan engines have been well documented under static conditions. However, aircraft noise certification limits must be satisfied under actual aircraft flyover conditions during takeoff and approach operations. Thus, it is important that methods be developed to more accurately predict the jet noise under flight conditions. The effect of flight on jet noise of a circular jet exhaust has been simulated by testing in wind tunnels.1'2 Noise measurements obtained in wind tunnel tests show that the jet exhaust noise of nozzles operating subsonically is reduced in flight from the static levels at all measurement angles. However, noise measurements obtained from some flyover tests3 have shown less noise reduction than the results of the wind tunnei tests. In order to help resolve the differences in wind tunnel and flyover results, it is necessary to understand the effects of flight on the fundamental mechanisms of jet noise generation. Measuring the changes caused by flight in the aerodynamic parameters responsible for noise generation and relating these changes to the measured noise reductions caused by flight will provide a more basic understanding of the effect of flight on jet noise than is currently available. This understanding will allow eventual improvements in our ability to develop more accurate in-flight predictions. The noise reduction in flight is generally attributed to changes in the strength of the acoustic sources distributed throughout the jet shear layer. The acoustic source strength at a point in the jet shear layer is determined from the local aerodynamic flow properties. The mean and turbulence flow quantitites needed to determine the acoustic source strength are mean velocity, mixing layer growth, turbulence intensity, integral length scale, eddy convection velocity, and integral