The quantification of the effects of forward flight on jet noise has practical importance. Boeing’s open-jet wind tunnel has an octagonal shape, produced by filleting the four corners of a rectangular cross-section. This non-axisymmetric geometry introduces complications in the application of the correction procedure for sound transmission through the shear layer, for microphones placed outside the tunnel flow. Appropriate guidelines for the proper application of shear layer corrections have been developed and validated first with simple circular single-stream and dual-stream nozzles, with three polar microphone arrays at different azimuthal angles. The sound field is axisymmetric for dual-stream nozzles, both for simple and complicated internal geometries, so long as the exit plane is axisymmetric. With this validated procedure, the effects of forward flight and external pylons on the noise field from realistic geometries have been assessed, with the aim of incorporating these effects in a prediction method. The following effects of forward flight have been established: (1) at the lower inlet angles and up to 110, the magnitude of the noise reduction due to forward flight is nearly uniform at all frequencies, at all velocity ratios and area ratios; (2) more complicated effects of forward flight are observed at large aft angles: ~10 dB reduction at the lower frequencies and ~3 to ~4 dB at the higher frequencies; (3) the area ratio plays no role at high Vs/Vp but becomes important at lower Vs/Vp. In general, two effects are anticipated due to the presence of the pylon: the first one pertains to the introduction of azimuthal variations in the spectra. Surprisingly, the sound field in the azimuthal angular range of =0o to =60o is axi-symmetric, except at very high engine power and low As/Ap for which there is an increase in level at large aft angles. The second effect of the pylon pertains to modifications to the spectra, relative to an axisymmetric nozzle system. There is a noise reduction of ~2 dB to ~4 dB for the pylon nozzle at large aft angles, and an increase of ~2 dB at the lower inlet angles. In general, the pylon effect is most pronounced at high engine power and gradually diminishes as engine power is lowered progressively.