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1 CHAPTER 1. INTRODUCTION Historically, the analysis of airport noise has generally been limited to the flight operations of aircraft arriving and departing, as these are the operations that produce most noise, and therefore, determine the shape and size of the overall airport noise contours. Over recent years, since the phase-out of Stage 2 aircraft and the replacement of these aircraft by the quieter Stage 3 and Stage 4 models, noise exposure at most US airports has decreased significantly. Projections indicate that the noise contours from flight operations will continue to shrink as the noisier Stage 3 retrofits are retired, until later in this decade when the growth of operations will cause a leveling off and an eventual increase in exposure. Noise contours will however still be smaller than those computed for pre-2000 conditions. It might be expected that as noise levels from flight operations decrease over time, noise exposure from ground operations (i.e., taxiing) will decrease proportionally. As such, taxiway noise would remain a relatively small contributor to airport noise. The reductions in flight noise resulting from the introduction of new engine technology are, however, not necessarily reflected in the noise at the low engine thrust settings that are typical of taxiing operations. Furthermore, as traffic grows, and airports approach capacity, the resulting ground congestion will mean that aircraft will be spending more time on the ground in hold short positions and waiting queues. Fuel heavy departing aircraft will be producing more noise as they accelerate to taxiing speed from hold short positions. The overall result is that ground operations may, in fact, become a larger contributor to airport noise, hence, the need to include them in future airport noise estimates required in Part 150 studies, master plans, Environmental Assessments (EA) and Environmental Impact Statements (EIS). There are, of course, other sources of noise at an airport. These sources, which include taxiing, APUâs, ground support and other gate operations have generally been minor contributors to the overall airport noise contours. As such, these sources have generally not been included as contributors to the airport noise contours. There are exceptions, however, such as at Boston Logan, where the nearby water surface reduces the propagation losses, and at Chicago Midway, where residential dwellings are very close to the airport boundary. The purpose of the sensitivity work described in Chapters 1-4 in this report is to develop an approach for modeling taxiing and ground noise, and for incorporating the necessary algorithms into the INM and AEDT. In order to properly model taxi operations at airports, one must first characterize the elements of such operations and determine which features are important from the perspective of noise modeling. A holistic approach requires an understanding from the operational level (how the aircraft move from the gate to the runways, and how the bigger picture of congestion and weather affect aircraft movements) through the detailed aircraft motion level (what thrust is being used, how fast do aircraft accelerate and decelerate) and down to the source details (noise directivity, levels and spectral content). We have approached the project in the following manner: ⢠Define the requirements of a taxiway model. ⢠Acquire noise and operations data for taxiing operations where available. ⢠Develop models for the source and propagation of noise from taxiing aircraft at appropriate thrust levels.
2 ⢠Perform sensitivity analyses of the source and propagation models to determine the influence of model components on the acoustic predictions. ⢠Identify the critical components and operations that need to be included in a taxiway noise model and assess the capability of the current INM7 and AEDT Local structure to incorporate these components, and make suggestions for their inclusion. Data and information was sought from a variety of sources including airframe manufacturers, engine companies, airlines, airports and government agencies such as NASA and DOT Volpe Center. Several examples of operations were examined in detail in order to understand and extract pertinent operational information. These examples include historical flight data recorder records from a major European airline, taxi modeling protocol and procedures approved for use in the Boston Logan Airport Noise Study, and operational scenarios developed for a benchmark emissions study under CAEP. The findings from the sensitivity study led to a suggested system design and architecture for incorporating a taxiing noise model into INM7 / AEDT Local. At project initiation, the ACRP project review panel communicated that the first priority was to determine if a taxi noise model can be incorporated into INM 7 in the short term and if so, to determine and document the necessary acoustic modifications. The second priority was to design a taxi noise module for AEDT and identify any longer term research items. The design presented here may therefore be implemented in two steps: ⢠Step 1: Targeted acoustic modifications and database extensions to INM Version 7 (1) and ⢠Step 2: A taxi module for AEDT Local (2), which builds upon features of EDMS (3) including longer-term improvement recommendations for taxi noise modeling. The taxi noise modeling system design presented in Chapters 5 and 6 incorporate maximum input flexibility providing the user with the option of selecting a suitable level of fidelity for their needs. The taxi model architecture suggested for AEDT Local has been constructed such that it is compatible with and leverages capabilities and data contained within both INM and EDMS. The Step 2 AEDT Local taxiway noise module is presented both in isolation and with the supposition that the Step 1 taxi noise modeling acoustic extensions suggested for INM 7 will also be available and implemented in AEDT Local, specifically within the Aircraft Acoustics Module. Chapter 7 gathers together the specific taxi modeling pieces and identifies a path forward.
