An experimental study has been performed to investigate the sound-propagation losses associated with aircraft ground operations. Downwind propagation was emphasized in this study, because the highest levels observed on the ground generally occur when the receiver is downwind from the source. The noise from the initial part of jet-aircraft takeoff roll was found to be the most reliable high-level source for the study. The results show a pronounced increase in low-frequency range of 125–250 Hz. They indicate also that the “standard” values of atmospheric absorption are too large above 1000 Hz. A simple engineering procedure for estimating downwind propagation is given. [Work supported by the National Aeronautics and Space Administration.]