Environmental Optimization of Aircraft Departures: Fuel Burn, Emissions, and Noise (2013)

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56 A-1. Overview of Literature A-1.1. Review Process The research team gathered approximately 100 papers, articles, and other materials. Searches were performed using several sources, including Science Direct, the Pennsylvania State University online library, the Georgia Institute of Tech- nology library, conference proceedings, and internet searches. The research team reviewed all materials to determine rele- vance to this project and narrowed the field to approximately 50 items. Then, each item was further reviewed to determine the specific topic areas, keywords, level of relevance, currency (existing operations vs. future/NextGen) and airports studied (domestic vs. international). This data was entered into a database using the Reference Manager™ software. The data- base was used to organize and prioritize the literature and generate a bibliography. A-1.2. Overview Matrix As an initial step, the literature was summarized into tables to provide a quick review of the most pertinent items. Table A-1 presents the interdependencies studies, including scope and variables optimized. These studies are similar to the ACRP research because they include several environmental factors (e.g., noise, emissions, and fuel burn) and/or capacity and optimize the tradeoffs among them. Table A-2 presents the most-relevant environmental studies reviewed and the met- rics and quantitative results as applicable. This table is useful to compare and contrast each study and the results presented. A-1.3. Key Terms In order to frame the discussion in this appendix, several key terms are defined below. NAP (Noise Abatement Procedure). A general term for a flight procedure used by airports, operators, and/or air traf- fic control for arrivals or departures, including ground tracks and profiles. This study focuses on departure NAPs. Profile. The vertical component of an aircraft trajectory (altitude) combined with the corresponding speed and power settings (thrust). Typically defined at distances from aircraft takeoff or landing; sometimes defined by time from takeoff or landing. Ground Track. The projection of an aircraft’s trajectory onto the ground (i.e., the X-Y location of an aircraft trajectory). NADP (Noise Abatement Departure Profile). Departure profiles designed to reduce noise levels either close to an air- port or farther from an airport. In the United States, NADPs are defined and regulated per FAA Advisory Circular 91-53A (which includes two NADP types: close-in and distant). For non-U.S. airports, the ICAO PANS OPS Part V, Chapter 3, defines equivalent close-in and distant NADPs. These docu- ments define the minimum requirements for safe flight and do not specifically define procedures for any given aircraft. Thus, NADPs can vary according to aircraft type, airline, and airport. NADP-1/ICAO-A Profile. The close-in community NADP, which is designed to reduce noise levels near the airport, with the tradeoff of increasing noise in areas farther away from the airport. NADP-2/ICAO-B Profile. The distant community NADP, which is designed to reduce noise levels farther from the airport, with the tradeoff of increasing noise in areas near the airport. NPR (Noise-Preferred Routing). A ground track optimized to reduce noise at sensitive receptors. A-2. Discussion of Literature The relevant literature reviewed was divided into three categories: reports on capacity, airspace, and operations which set the context for this ACRP project and also informed its analysis of runway capacity; studies of environmental interdependencies (similar to this ACRP research) which examine the trade offs among environmental factors for A P P E N D I X A Literature Review

57 airport operations; and studies focusing on noise impacts which study departure procedures, including effects of ground tracks and profiles. A-2.1. Capacity, Airspace, and Operations Studies The need to increase the capacity of the National Airspace System (NAS) because of projected traffic increases has been recognized for almost two decades and some technical papers have addressed this issue. Although some investigations sim- ply state the need for increased capacity (citing various sources of traffic growth predictions), others provide suggested means of achieving the needed capacity growth. In almost every case, it is recognized that it is imperative to mitigate the increases in noise and emissions associated with both existing air traffic levels and future increases in traffic. Aircraft noise is identified as the prevalent deterrent to the construction of new airports and the expansion of existing air- ports (Austrosas 1992 and Upham 2003). Given that local com- munities often form the opposition to expansion, airports must adopt “good neighbor” policies while recognizing that signifi- cant social and cultural factors can affect the perception of what levels of noise are considered a nuisance. Although aircraft and engine technology improvements have reduced operational noise and emissions, a growing reality is that the projected increase in operations will outstrip the reductions provided by technology (ECAC Conference 1999 and Upham 2003). The conclusions of the investigative reports reviewed pro- pose actions ranging from strategic initiatives with regard to emissions (e.g., improved intermodal transportation between airports and city centers) to ground delay reductions by improvements in high-speed turnoffs and increases in exist- ing ramp areas and gates (ECAC Conference 1999 and Upham 2003). Tactical initiatives predominantly propose development of automation to support changes in the way the airspace is managed. One of the first published investigations recognizing the need for increased capacity (Visser 1992) focused on terminal area traffic management proposing time-based procedures using existing and future airborne and ground equipage. Time-Based Operations (TBO) are seen as a way to absorb delay in a more fuel-efficient manner while increasing capacity by minimizing the actual aircraft separations. Implementation of these types Reference Scope of Analysis Objective function Constraints Variable Optimization method ICAO (2007) profile optimization for departure flights noise N/A N/A flight procedure, spatial management, and ground management SOURDINE (2006) overall assessment of departure and arrival procedures on noise, emission, safety, capacity, user acceptance N/A N/A N/A compare several landing and takeoff procedures King and Waitz (2005) calculate emissions for derated takeoff profile emission N/A profile N/A Rachami (2008) trajectory optimization noise, emission N/A trajectory test of alternative trajectories Visser (2005) trajectory optimization fuel, noise aerodynamic trajectory segments nonlinear programming Hebly and Visser (2008) profile optimization for departure flights noise, fuel aerodynamic, thrust cutback profile nonlinear programming Prats (2008) trajectory optimization noise, fuel, delay aerodynamic, event, path and box trajectory segments nonlinear programming, lexicographic Suzuki et al. (2009) online optimal navigation noise, fuel aerodynamic, terminal, and inequities trajectory segments, time multi stage direct allocation Heblij and Wijnen (2008) Runway allocation noise, delay non negative flight number runway use mix-integer programming Janic (2003) air transport network operations noise, emission, capacity total flight number <=airport capacity network flow integer programming Table A-1. Interdependencies studies matrix.

Noise Emissions Fuel Burn Capacity Noise Emissions Fuel Burn Capacity ICAO (2007) Single flights Lmax (plot dB vs. track dist.) percent NOx; percent CO2 N/A N/A See Note See Note N/A N/A Compares NADP1 and NADP2 to one another. SOURDINE (2006) Single flights Noise Sensitivity Depreciation Index (NSDI); percent change in population exposed percent N/A hourly arrivals N/A N/A N/A N/A A Yes/No metric is used for all the assessments. King and Waitz (2005) Single flights N/A kg CO2, kg HC, kg NOx kg N/A N/A derated procedure created 14.5% reduction in NOx, 99% reduction in HC and 20% reduction in CO derated procedure caused 12.3% increase in fuel consumption N/A Rachami (2008) Single flights SEL (contour area) kg CO2 kg time to fixed point at ~ 10NM 70% reduction in 75 SEL contour areas 20-30% reduction in CO2 100-250 kg reduction 6 - 21% time savings analysis of future engine technology allowing for direct flight paths, compared to existing aircraft and procedures Visser (2005) Single flights % awakenings; population above 65 dB; area above 65 dB N/A kg N/A N/A N/A N/A N/A the different noise metrics and fuel burn metric are not optimized at the same time Hebly and Visser (2008) Single flights % awakenings N/A kg N/A 15% reduction in awakenings N/A 5% reduction N/A Prats (2008) Single flights Lmax; normalized annoyance N/A N/A N/A Minimization N/A N/A N/A Suzuki (2009) Single flights N/A N/A pounds N/A N/A N/A N/A N/A no detailed metrics are used in this paper Heblij and Wijnen (2008) Runway allocation Population noise annoyance N/A N/A N/A 30% decrease in noise annoyed population N/A N/A N/A delay and safety are considered qualitatively Janic (2003) Airport network dB ton N/A flights per day increase noise to allow higher capacity increase emission to allow higher capacity N/A N/A Capozzi (2003) All airport arrivals SEL; DNL 5% to 50% fewer pop. > 55DNL Elmer (2002) Single flights Lmax (contours; plot dB vs. track dist.) 5% reduction in 90 dB contour area Mitsuhashi (2000) Single flights Lmax (plot dB vs. track dist.) plot dB vs. track distance; not specific Includes steepest-climb profile used in Japan Forsyth (2009) Single flights dB; time history Not specific Clarke (2000) Single flights Lmax (contours; area) 15% reduction in pop. > 60 Lmax Winjen and Visser (2002) Single flights Probability of Awakening; SEL 20% fewer awakenings Reference Interdependencies Studies Noise Studies NotesMetrics Quantities/BenefitsScope of Analysis Table A-2. Environmental metrics and results matrix.

59 of operations requires an air/ground data link which permits the rapid exchange of data between the airborne and ground- based automated systems. Although the airborne capability of the Flight Management System (FMS) is considered acceptable, development of a ground-based system is deemed necessary to couple with the FMS in order to optimize available aircraft trajectories so as to de-conflict traffic, thereby ensuring a safe and efficient merge into the existing traffic flow. The result of this investigation identifies improved systems and procedures along with new technologies to eliminate present limitations with regard to communication, navigation, and surveillance, which will enable improved efficiency in the management of terminal area airspace. Many of the capabilities defined in this report are included in the JPDO Concept of Operations (Ver- sion 2, 2007) which is the envisioned strategic blueprint for the overhaul of the National Airspace System (NAS). Visser (1992) defined capacity as the ability to accom- modate demand and separated capacity into three distinct elements: airspace, runway, and control. A distinction between “theoretical” and “practical” capacity is also made with “theo- retical” corresponding to the maximum number of aircraft that can be accommodated within a period of time and “practical” as the level of capacity corresponding to a specific level (average) delay. Available runway capacity is stated to be dependent on the operating configuration of the runway(s) and limitations of the surrounding airspace, including ceil- ing and visibility which dictate required ATC separation standards. Given that arrival operations are considered the most limiting with regard to increasing airspace capacity, most of the investigative reports are focused on mitigation strategies involving improved arrival procedures along precise ground tracks avoiding noise-sensitive areas. The continuous descent arrival (CDA), now more generally referred to as optimized profile descent (OPD), is recognized as a procedure that can provide both noise and emission ben- efits, maintaining the required lateral separation with existing automation requires increased separation between the leading and trailing aircraft because of the differences in speed as the leading aircraft decelerates. Restoring existing capacity requires development of automation relying on improved aircraft tra- jectory method to conduct operations with existing standards of separation (Erkelens 1999). Another proposed mitigation procedure was to extend the current 3-degree ILS glide slope to an altitude of 6,000 feet above the runway elevation and use GPS-aided FMS to conduct the arrival and approach accurately (Clarke 2003). Here again, the problem of separation during a decelerating approach is recognized with development of new automation identified as a solution. As with arrival/approach operations, existing investiga- tive reports regarding departure operations primarily address noise and/or emission mitigation strategies. Again the empha- sis is on conducting the departure via accurately flown ground tracks and avoiding noise-sensitive areas with FMS-equipped aircraft flying published SIDs (Clarke 2003 and Erkelens 1998). An extension of this mitigation strategy is a proposal to develop multiple transitions to a common arrival path, pre-determining the noise impacts along the path for each aircraft type, and then sequencing the arrival stream to either minimize the required separation spacing for capacity or minimize the resulting noise impact (Heblij 2007). The Expedite Departure Path (Jung 2002) is a description of an automated decision support tool that would increase airspace capacity with respect to departure operations by providing controllers with conflict-free altitude, heading, and speed advisory. The objective is to minimize the altitude holds that characterize many of the departure vertical profiles allowing the aircraft to complete a more efficient transition to the en route phase of the operation. This report proposes additional development to integrate the tool with the existing decision support tools for management of aircraft departure queues and departure runway load balancing. Given that separation requirements apply to departure operations, a possible increase in the runway capacity for departures can be realized with the implementation of diver- gent or dispersed headings. A summary published as part of an Operational Assessment Report for the FAA’s NY/NJ/PHL Airspace Redesign (2008) compared departure efficiency rate (scheduled departures/actual departure rate) for a year prior to implementation of dispersed heading with the efficiency rate for a year following implementation. Newark (EWR) Runway 22 reported an increase in efficiency rate from 88% to 107% while Philadelphia (PHL) reported an increase from 107% to 110%. No published literature was found linking the environ- mental impacts of departure operations with runway capac- ity effects. The only capacity-related study for departures was primarily associated with airspace only briefly mentioning future integration with existing decision support tools. A-2.2. Interdependency Studies Environmental mitigation of airport operations has been studied using various optimized procedures. A focal point is airport operating procedures for arrival flights, primarily OPD. However, there is a growing body of literature on the optimization of departure procedures which establish meth- ods to operate aircraft to minimize environmental impact at sensitive receptors. A summary of the current state of the art and the issues for implementation of procedures were given in an ICAO report in 2007. This report gives the results of a survey of established arrival and departure noise abatement procedures. In addition

60 to technical requirements for modeling noise, emissions, and fuel impacts, the report stresses that better collaboration among research organizations, airports, airlines, manufacturers, and governments is needed. The report concedes that most research has focused on the effects and implementation of arrival proce- dures. NADP use by various U.S. and international airlines for many aircraft types is collected in a survey. A total of 14 different departure profiles, all conforming to the definitions of NADP-1 and NADP-2, are listed in detail for the relevant aircraft types (including many common air carrier jets and two regional jets). This data was valuable to this ACRP project. Following this report, the ICAO working group completed an environmental analysis of the varying NADPs presented in the survey report (Circular on NADP Noise and Emissions Effects–Working Paper CAEP/7-WP/25, 2007). This analysis was commissioned to resolve a major limitation of the PANS OPS (and the FAA Advisory Circular) which lacks quantitative data to assist an operator or airport in selecting and designing a specific NADP. Unique elements of this research include deter- mination of the “cross-over point” where an NADP changes from reducing noise to increasing noise and analysis which includes full-thrust profiles as well as reduced-thrust profiles. Reduced thrust is an important feature of the study, because it relates more directly to actual flight procedures used most often by airlines. Comparisons are made among four types of NADPs and the relative differences in noise and emissions are computed. The study concludes that close-in noise differences are generally greater than distant noise differences and that the magnitude of noise difference is less for reduced-thrust takeoffs than for full-thrust takeoffs. For emissions, the study concludes that NOx generally increases while CO2 generally decreases when flying NADPs. As such, tradeoffs must be made on a per airport basis, as no single procedure can reduce both noise and emissions. This study is limited to the analysis of flight profiles and does not investigate changes in ground tracks and does not focus on any specific airport. Several different methods are evaluated for noise abatement for airports in the SOURDINE project (Muynck 2001). Exist- ing rules in flight management and new rules are investigated and the procedures for taking off and landing are updated based on the chosen rule for certain airports. For departure flights, gradual increase of cutback thrust during climb out helps to maintain a low noise at ground level. In the following SOURDINE II Final Report (2006), methods are reported to mitigate noise impact and emissions around airports by defin- ing new departure and approach procedures. The project aims to develop optimized departure/takeoff trajectories to mini- mize noise impact without loss in capacity/safety and other environmental benefits including emissions. The new proce- dures are then validated through the air transport manage- ment lifecycle. Four European airports are chosen and capacity is modeled using TAAM and SIMMOD, noise is modeled in INM, and emissions are modeled in TBEC. Three departure and five approach procedures are assessed. The departure procedures include ICAO-A, SII close-in, and SII distant. The effects on environmental impact as well as feasibility are assessed for all the procedures. Recently, emission mitigation has become increasingly important. In current models, emissions are calculated based on full-thrust assumption for departure flights. King and Waitz (2005) discussed the emissions from de-rated departure flights. Although most flights use reduced thrusts when taking off, the emissions are calculated at full thrust in most emission models, and this leads to overestimated emissions. The study uses the actual flight trajectory to estimate the actual thrust and uses this thrust to calculate fuel flow and emissions. When using this method for the flights at London-Heathrow (LHR) and Gatwick (LGW), a 10% overestimation of emission is found. This study indicates the necessity to use realistic power settings for departure flights to calculate emissions. For departure and arrival flights, certain practices can reduce both emissions and noise levels, due to progress in engine designs. Rachami et al. (2008) reported a series of tech- nical assessments of the relationships among various aviation environmental and operational factors, including noise at the source, aircraft emissions, fuel burn, and flight trajectories. The study includes an initial phase focusing on single-event opera- tions and a second phase focusing on all airport operations. Alternative trajectories are assessed for emission reduction and noise impact through Integrated Noise Model (INM) and emission calculation based on INM trajectory for two indi- vidual airports. This study shows how fuel burn, emission, and capacity can be improved without worsening noise impact. Mathematical methods have been used to find the optimal solutions regarding the different aspects of airport operations (e.g., noise, emissions, capacity, economy, and safety). For an actual airport operation, all these factors have to be consid- ered, and there are various strategies in handling these multiple objectives mathematically. As an optimization issue, some of the factors considered are the objective function that needs to be minimized (or maximized) and other factors that can be treated as constraints. The most common variable to adjust for better environmental impact is the flight trajectory (usually segmented into smaller pieces either spatially or temporally). Visser (2005) developed the NOISHHH model, includ- ing a noise model, a geographic information system, and a dynamic trajectory optimization algorithm. Fuel consump- tion, site-specific noise impact (probability of awakenings), and generalized noise impact (population within contour areas) are weighted and summed into one objective function, and tradeoff analysis is performed by adjusting the weights. The variables are the segments of the trajectory, but the optimi- zation is subjected to constraints of aerodynamics so the trajec- tory will be realistic. The optimization process consists of cycles

61 among several modules, including an optimization engine that implements a nonlinear programming method, a performance model and noise model, and a database to store all the data. The author states that the method is not ideal for real-time navigation purposes and proposes a database of optimal and sub-optimal profiles for operators to select. Hebly and Visser (2008) used the NOISHHH model to minimize noise impact in terms of total awakenings and fuel consumption by finding the optimal profile for a departure flight; the optimal profile is then compared with ICAO-A reference profile. Prats (2008) introduced a similar model to NOISHHH to optimize trajectories to minimize noise impact. The major difference from NOISHHH is that a hierarchical optimiza- tion problem (Pareto type) is used, rather than the weight and sum method. Airliner cost and Air Traffic Management (ATM) efficiency are taken into account in addition to noise to form a multi-objective optimization problem. Suzuki et al. (2009) developed trajectory and 4D naviga- tion applications to study safe, clean, and quiet operations. Their model optimizes the trajectory for the total fuel burn of a B747 and a B737 descent. The single-flight optimization confirms that flying higher for longer time results in better fuel savings. Although when two aircraft are considered, the best solution is to let the heavier aircraft be close to its single- flight optimal trajectory. The above methods are designed for the best trajectory or profile for a given runway. For airports with more than one runway, flights can be allocated to different runways to mitigate environmental impact. Heblij and Wijnen (2008) proposed a multi-objective optimization solution of runway allocation at a generic airport. The objective function consists of noise, third-party risk, and delay. The multiple objectives are summed using weights automatically adjusted. When reaching the final optimum, the three objective functions will be equally important. The optimizing process is interactive so users can adjust the weights. The optimization problem is solved by a mix-integer programming method. At a higher level, for an air transport network, including air- ports and air routes connecting them, Janic (2003) describes the use of integer programming techniques to maximize the total network profits for given environmental constraints and operational capacity. The decision variable is the maximum number of flights in the network. The objective function is the net profit expressed as the difference between revenue and cost. The constraints include capacity, noise impact, and air pollution. The air transport network with London-Heathrow airport as the center is chosen as a case study. To reduce the decision variables, the high diversity of air routes was col- lapsed into seven clusters and four aircraft types. By varying the constraints level, the impact on profit is investigated. The model has found the noise constraints had more effect on profit than the emission constraints. A-2.3. Noise Studies As noise has traditionally been the most studied environ- mental concern for airports, many studies were found in which, while discussing the optimization of ground tracks or profiles, the environmental analysis was limited to noise. Some studies also include qualitative discussions of navigation or capacity effects of noise abatement procedures. Furthermore, because of the advanced stage of research into OPD procedures, many studies focus on approach procedures with less information on departure procedures. This section discusses the noise analysis studies in three categories: studies of ground track optimiza- tion; studies of vertical profile optimization; and studies discussing both ground tracks and profiles together. Several studies analyze ground tracks and specific effects on noise. Erkelens (1999) sets forth the essential points regarding ground track locations: advanced navigation capabilities allow for more precise locations of ground tracks, which can con- tain noise exposure to specific areas. Erkelens discusses both approach and departure procedures, including Precision Navi- gation Instrument Departure (PNID), in which RNAV is used to define departure ground tracks with greater precision. RNAV is now used at several U.S. airports to “overlay” SIDs, thereby making them more precise. Capozzi (2003) explores the optimization of ground tracks to improve noise exposure. Although the research focuses on approach procedures, the method is relevant to this ACRP research. The goal of the optimization process used by Capozzi is to minimize both noise and delay. The focus is on ground track geometry; altitude and speed are not varied in the analy- sis. Capacity is discussed in terms of the tradeoff between air- space efficiency and noise impacts for arrivals. Several noise metrics are used to compare and contrast the effects of vary- ing trajectories, including population impacts. A set of arrival paths fill in the “boundaries” set by the most direct (least delay) ground track and noise abatement (higher delay, more circu- itous) ground track. These varying ground tracks are overlaid on a map showing population density at Census centroids. Then, the noise impacts of each ground track are compared according to SEL values. In addition, an attempt is made to integrate all arrival events over a day to minimize the popula- tion exposed to DNL above 55 dB. This is accomplished using various optimized ground tracks judged by overall DNL impact (and not individual flight impact). The goal is to reduce popu- lation exposed to DNL above 55 dB at the expense of increasing population below DNL 55 dB. One interesting conclusion is that the best method for improving noise exposure is to select abatement ground tracks based on difference in sound level due to individual events compared to a baseline procedure. Several noise studies focus on profiles and NADPs. Elmer (2002) discusses a study of departure and arrival procedures flown using a flight simulator replicating a Boeing 747 operat- ing at London-Heathrow airport. Noise impacts are assessed

62 for the ICAO-A NADP and two variations. Lmax contours for single flights are compared and the Lmax is plotted as a func- tion of track distance on Cartesian coordinates, similar to the results presented by ICAO (2007). In addition to noise, pilot flying accuracy and workload are studied. This study lends valuable data on noise effects of different reduced-thrust pro- files as compared to standard NADPs. Mitsuhashi (2000) also discusses a comparison of varying profiles, using Lmax versus track distance to compare profiles. Mitsuhashi focuses on noise abatement profiles used in Japan, where the primary procedure is steepest-climb profile. The author determines that a thrust-cutback procedure similar to the close-in NADP is in some instances louder than the steepest-climb. Although this is country-specific, steepest-climb may be possible in the United States under NextGen. Forsyth (2009) adds a new element to the discussion of NADPs: the focus is made on cutting back thrust when the aircraft is at a noise-sensitive ground location and not a set altitude. This can be accomplished using the Boeing Quiet Climb System (QCS) cockpit software, which automates departure profiles for the close-in NADP. This software is an on-board thrust management function to reduce noise at spe- cific points on the ground. Typically, NADPs are defined and executed based on aircraft height: thrust is reduced when a certain altitude is reached. However, altitude will vary accord- ing to aircraft weight, as a lighter aircraft (less fuel/passenger/ cargo load) will climb faster, reaching a noise-sensitive point on the ground at a higher altitude than a heavier aircraft. The QCS has already been deployed to some Boeing aircraft. The author also notes that airlines prefer the distant NADP because it saves fuel and time (as the aircraft can make initial climb more efficiently and quickly). Several noise studies focus on the interrelations among ground tracks and flight profiles. Clarke (2000) investigates the tradeoffs between noise abatement profiles and ground tracks. A NOISIM model is developed to use flight simulator performance data to feed noise and population impact mod- els. Three profiles are modeled: a baseline full-thrust takeoff, the ICAO reduced-thrust takeoff, and a deep thrust-cutback departure. Peak A-weighted sound level contours are plot- ted for each profile for varying aircraft altitudes to compare the noise levels at different stages of flight. A specific study of noise exposure at Boston Logan International Airport is conducted. A combination of a thrust-cutback procedure and a modified ground track results in lower population exposed to noise. One key element of the study is the deter- mination of the ideal altitude for thrust cutback specific to the airport and corresponding adjustments to the ground track. Huber (2003) also used NOISIM to assess weather effects on aircraft noise. A Boeing B767 flight test is used to show that weather can affect the climb rate of an aircraft and, therefore, noise exposure. Two studies by Prats (2008, 2009) also focus on the noise impacts of modified ground tracks and profiles for depar- tures. A novel scheme is developed to design ground tracks based on sensitivity to noise in terms of Lmax levels at different times of day. “Fuzzy logic” and optimization are used to create the most equitable ground track in terms of noise sensitivity: different tracks are optimized for specific receivers (hospital, residential, industrial – for varying hours of day and night). For example, since schools are only in use during daytime hours, they can be subjected to higher levels of overflight noise during nighttime. However, the author does not consider that flying various procedures based on time of day and noise sen- sitivity would not be possible under the current U.S. air traffic system. Currently, procedures are defined as day or night and cannot be modified in real time or over finer time intervals. NextGen would allow for customized and time-varying tra- jectories. In addition, Winjen and Visser (2002) contribute to this topic by using a different noise metric, based on probabil- ity of awakening. This work laid the foundation for Visser’s later papers which used the NOISHHH tool to perform interdependencies modeling for flight trajectories. A-3. Conclusion The literature reviewed covered three relevant subject areas: capacity, airspace, and operations; studies of environ- mental interdependencies that examine the tradeoffs among environmental factors; and studies focusing only on noise impacts. In addition to providing valuable information, the review of these studies identified gaps in the current research and the need for this project to fill the gaps. First, many of these studies were conducted outside the United States and focus on non-U.S. airports. Although these studies provide relevant data, they do not address the same operational environment, regulatory standards, and socio-political environment found in the United States. This project will fill a need for detailed analysis of U.S. airports. Second, most of these studies have provided detailed tech- nical information, yet lack practical guidance for the imple- mentation of suggested procedures. Although some guidance is discussed for airlines, this ACRP project will fulfill the need for guidance for airports. Third, due to the predominance of OPD-related research, there is a lack of analysis of departures and runway capacity that details the implementation of procedures and impacts on airport operational environments. This project will link the potential for environmental benefits to the constraints of runway and airspace capacity. Fourth, little of the research addresses the environmental impacts of future aircraft technology such as that described under NextGen, CLEEN, and the NASA Fundamental Aero- nautics Research Program (i.e., N+1, N+2, and N+3 generation

63 aircraft). This ACRP project will provide such forward-thinking analysis and discussion. Finally, any study of noise abatement procedures must con- sider and address the public’s likely reactions to changing NAPs. The simple reality of increased operations equating to increased noise and emissions will result in considerable local commu- nity objection and only thorough and valid mitigation strate- gies can hope to gain their acceptance. This project will focus on the implementation of procedures at airports and the potential for environmental benefits, beyond changes in noise exposure. Although it is not feasible for an airport with an established set of NAPs to abolish them, it is possible to optimize the existing procedures to improve emissions and fuel burn. In addition, the literature review has highlighted several key modeling issues that the environmental analysis conducted during this study will need to address, including the need to • Model realistic variations of NADPs which can vary by aircraft type and airport (as discussed in ICAO 2007, SOURDINE II, and others). • Study the interrelations between ground tracks and profiles (as discussed in Clarke 2000, Prats 2008/2009, and Forsyth 2009). • Model ground operations noise and emissions due to the effect of decreased delays with better runway throughput when using optimized NAPs.