Enhanced Modeling of Aircraft Taxiway Noise, Volume 2: Aircraft Taxi Noise Database and Development Process (2013)

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1-1   CHAPTER 1. INTRODUCTION 1.1. Project Goals and Overview This aircraft taxi noise modeling research funded by the Airport Cooperative Research Program of the National Academy of Science is in response to a growing understanding that continuing reduction of noise levels related to aircraft flight operations means that previously ignored noise from aircraft ground operations (such as taxiing), now has potentially more of an effect on nearby communities. Taxiing and idling in runway queues, especially during peak hour operations or at night, can significantly contribute to noise contours and Day-Night Average Sound Levels (DNL). This is particularly true when taxiways are very close to the airport property lines and near neighborhoods or other noise sensitive locations. The Federal Aviation Administration’s (FAA) Integrated Noise Model (INM) is the agency’s required tool for environmental impact statements, environmental assessments (Boeker, et al., 2008), and Part 150 studies. Under FAA development is the Aviation Environmental Design Tool (AEDT) (Koopmann, et al., 2012) which will eventually replace INM for such purposes. Currently, INM users who need to assess the contribution of noise from aircraft ground operations must develop a workaround approach within the model or externally. Under ACRP project 11-02 (Page, et al., 2009, Page & Hobbs, 2010), aircraft taxi noise acoustic sensitivity studies were conducted, to document the importance of the modeling elements within INM and AEDT in three areas: source noise, operations, and environmental propagation. Sensitivity studies decoupled the taxi noise into the three areas and exercised each element independently. Under project 11-02, limited opportunistic commercial aircraft taxi operation acoustic measurements were conducted. Independent taxi flight data recorder (FDR) information was queried to determine statistical engine and aircraft operational parameters. The current project, ACRP 02-27, described in this Final Report, builds on the taxi noise and INM/AEDT modeling understanding developed under the prior project. This report documents the technical approach, development, application and the INM / AEDT taxi noise dataset. 1.2. Technical Approach The database developed includes three fundamental components for the INM / AEDT fixed wing Turbofan (Jet) and Turboprop commercial transport fleet:  Noise-Power-Distance tables for the taxi operating condition for each aircraft;  Spectral Classes for the taxi operating condition; and  Fleet-wide Jet and Prop Directivity Functions for the taxi operating condition. Three sources of information from which the taxi noise datasets were developed include empirical taxi noise acoustic data (spectra and directivity), Major European carrier historical Flight Data Recorder (FDR) data, CAEP/8 Best Practice Database - subset of the ICAO NoisedB V2.6.1 (ICAO/CAEP8, 2008), EASA certificated noise database (EASA, 2011) and NASA’s Aircraft Noise Prediction Program, ANOPP (Zorumski, 2006) first principles modeling datasets developed for the Environmental Design Space Model (Kirby, Mavris, 2008 and Barrow et al., 2008). This report describes a prioritized hierarchy of three technical processes which are used to develop a taxi noise-power-distance database for INM and AEDT. The hierarchical process is necessary due to the variability in data availability for each specific aircraft-engine configuration. The INM aircraft types for which the taxi NPD and spectral class data is to be generated will fall into one of three possible NPD development methods: Method I. Empirical Taxi Noise Data and ANOPP data; Method II. Empirical Taxi Noise Data Only; and

1-2   Method III. No Empirical Taxi Noise Data. Method I is a hybrid technique that uses the empirical taxi noise data, assigns a thrust value based on FDR data, applies an ANOPP delta-dB vs. delta-Thrust relationship to develop the Taxi thrust-noise sensitivity and the taxi NPD curve. For this process the empirical taxi noise data trumps any analytical process. Method II is similar to method I, in that the “nominal Taxi Thrust” is based on empirical data, then adjusted to other thrust levels based on a “scaled” ANOPP delta-dB vs. delta-Thrust relationship to obtain a Taxi noise-thrust sensitivity. The scaled ANOPP noise-thrust relationship is based on engine types, categorized by thrust class and bypass ratio. Method III is perhaps the least accurate of the three methods because it has no empirical taxi noise data on which to rely for the absolute level of the “nominal” taxi noise. However, as will be shown in Section 5, it is remarkably successful. This method utilizes combined empirical noise data and ANOPP thrust noise sensitivity data from which a relationship between Max Takeoff Gross Weight and taxi thrust is derived. Applied to this is the thrust-noise relationship between taxi SEL and thrust. The genesis of this method was an inability to correct and extrapolate the existing INM flight noise NPD data to the taxi condition despite exhaustive attempts using a multitude of approaches. Contained in Section 4 are several of attempted procedures to extrapolate the INM flight noise NPD data to the taxi condition. 1.2.1 Report Contents Section 2 describes the assumptions necessary for incorporation of taxi noise within the INM/AEDT modeling framework. Section 3 details the various empirical and analytical taxi data sources utilized in this project. Section 4 lays out the proposed methodology for a taxi noise NPD data set and applies it to a limited subset of aircraft types. Section 5 explains how the taxi NPD development process was extended across the complete INM aircraft fleet. In order to understand the implications of the modeling assumptions, Section 6 describes the uncertainty associated with single spectral class modeling, the chosen process for thrust-noise sensitivity, and application of a hybrid model for those aircraft for which empirical taxi data does not exist. Section 7 documents the NPD process for propeller aircraft NPDs. Section 8 contains the composite directivity pattern development procedures and resultant directivity patterns for both Turbofan (Jet) aircraft and Turboprop aircraft.