FAA’s Integrated Noise Model (INM) is the agency’s required tool for NEPA-related studies and also for FAR Part 150 Noise Compatibility Studies. The transition of INM into the Aviation Environmental Design Tool (AEDT) is a prime example of the commitment of FAA to improve aviation environmental assessment computational capabilities. The AEDT program will achieve an important milestone in integrating FAA legacy tools and improving on their accuracy and functional capability to assess airport noise. For instance, improvements include changes in acoustic, emissions, and performance modeling capabilities, as well as improvements to noise-power-distance (NPD) curves, lateral attenuation algorithms, and relative-humidity absorption. ACRP recently contributed a key improvement to the set of available noise modeling tools as reported in the recently published ACRP Web-Only Document 9: "Enhanced Modeling of Aircraft Taxiway Noise—Scoping.” The objective of this scoping project was to determine the best way to model airport noise from aircraft taxi operations and, based on that assessment, to create a plan for implementing a taxi noise prediction capability into INM in the short term and AEDT in the longer term. One study outcome revealed that the primary weakness for taxi noise modeling is related to a definition of engine source noise characteristics, including level, spectra, and directivity.   In fact, there is no direct noise database for taxiing operations. Within the current INM/AEDT models, source noise is obtained through an approximate extrapolation of NPD data. For long-term requirements, the study suggested that additional measurements be made for taxi operations to obtain synchronized noise and engine operating parameters which can then be used to determine noise sensitivity at low thrust settings and allow a realistic evaluation of break-away thrust impact. This approach would require a considerable field measurement effort with extensive coordination with cooperating airlines. A short-term solution to the problem, suggested in the ACRP Web-Only Document 9, is to develop a noise, spectral class, and directivity database for a nominal taxi state by processing existing measurement data [e.g., data from ACRP "Web-Only Document 9”; data from a study conducted at Madrid Barajas International Airport, “Aircrafts’ Taxi Noise: Sound Power Level and Directivity Frequency Band Results,” C. Asensio, I. Pavón, M. Ruiz, R. Pagán, M. Recuero, Universidad Politénica de Madrid, Grupo de Investigación en Instrumentación y Acústica Aplicada (I2A2), INSIA – Ctra. Valencia km 7, 28031 Madrid, Spain; and data from other available sources]. As a follow-up to this effort, the next step is to fully populate a taxi noise database for input to INM/AEDT. It is not feasible, however, to acquire the necessary data for all the aircraft types found in the INM database. Efforts are therefore needed to derive a method(s) that would allow extrapolation of noise levels associated with higher thrust levels to those relevant to taxi conditions. This method would enable taxi conditions of current and future aircraft to be included in INM/AEDT. Should this method prove unsuccessful, then a modest measurement program should be undertaken to record a sufficient number of taxi operations to develop statistically valid source characteristics for aircraft commonly in use. The resulting database would remove the gap in the current INM noise database and allow for much improved taxi noise estimates.

The objective of this research is to develop a NPD and spectral class database for nominal taxi, break-away, and idle thrust levels for use in FAA’s INM as it transitions into the AEDT. The database will be presented in a spreadsheet format and will encompass the fixed-wing fleet mix provided in INM/AEDT.

STATUS: The report has been completed and published as Volume 2 of Web Only Document 9.