Accurate prediction of sound levels around airports and below flight paths can help faithfully represent the impact of aviation noise on communities. However, for large scale assessments, as are often performed by the U.S. Federal Aviation Administrationis environmental models, the accuracy of a model must be weighed against its efficiency. The hybrid propagation model (HPM) is capable of predicting propagation through complex environments. It is a composite of three methods-the generalized terrain parabolic equation (GTPE), fast field program (FFP), and straight ray models-each utilized in a different region of elevation angles from the source. If propagation conditions do not warrant use of the full model, one of the component models with faster runtime can be chosen as a surrogate. Analyses of cases using different source heights and including uneven terrain, refractive atmosphere, and ground type transitions, indicate when a detailed propagation model is needed, or when a simpler model is sufficient.

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The current Federal Aviation Administration (FAA) aircraft noise modeling tools, Aviation Environmental Design Tool (AEDT) and Integrated Noise Model (INM), do not consider noise below 50 Hz in their computations. This paper describes a preliminary study to determine the effect of including low-frequency data on the accuracy of AEDT/INM results. Expanded aircraft noise spectra containing one-third octave band data to 12.5 Hz were analyzed using methods adapted from AEDT/INM. Results from expanded spectral data are compared with results from the historical AEDT/INM spectral data (one-third octave band data from 50 Hz to 10 kHz). This comparison showed a range of differences, from increases in overall un-weighted sound pressure levels, to negligible changes in A-weighted and time audible metrics. These changes may be particularly important for helicopters, with dominant low-frequency rotor noise below 50 Hz. Following the comparison, the potential implementation of expanded spectral data in AEDT/INM is discussed.