NextGen for Airports, Volume 1: Understanding the Airport’s Role in Performance-Based Navigation: Resource Guide (2016)

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Metrics for Assessing the Impact of Procedures | 61 Metrics for Assessing the Impact of Procedures10 There are numerous metrics to assess the impacts of PBN procedures on the airport, the local community, aircraft operators, and other stakeholders. Selection of metrics depends upon the primary stakeholders and their objectives for the PBN initiative. Metrics may be used in the design phase of procedure implementation to assess the proposed design against the objectives, and in the post-implementation phase to assess the final implementation against the objectives. When conducting post-implementation assessment, all stakeholders, including airports, aircraft opera- tors, and the FAA should ensure the accuracy of any operational information they provide and that is used by the community, and that the information is understood by the intended audiences. Informa- tion and data that the public accesses related to aircraft flight paths and their impacts, such lateral paths, vertical profiles, timing, noise, emissions, or other characteristics and effects of aircraft arriving to or departing from the airport must be accurate and valid. Inaccuracies may occur, for instance, due to the differences in the accuracy and precision of aircraft position, navigation and timing measure- ments obtained from different surveillance systems. Inaccurate data can generate unnecessary com- munity concern and ineffective responses of the FAA, aircraft operators, and other stakeholders to the concerns of the community. Table 10-1 lists metrics documented in various sources that have been used, or have been proposed to be used, to assess the capacity, flight efficiency, fuel burn, emissions, and noise impacts of PBN proce- dures on airport operations, as compared to current-day or legacy procedures. In addition, the RTCA Blueprint for Success to Implementing PBN (RTCA 2014) describes an extensive set of metrics to measure the local and global impacts of PBN procedures. While the FAA has twelve metrics which have been congressionally mandated for assessing the impact of the FAA’s NextGen Program (Federal Aviation Administration 2013g), many are too broad in scope to assess the local impact of PBN procedures on the airport and its community. Table 10-1. Candidate metrics for airports to assess the impacts of PBN procedures. METRIC DESCRIPTION Capacity • Average hourly operations are the number of aircraft arriving to and departing from an airport in an hour (Federal Aviation Administration 2013g).

62 | UNDERSTANDING THE AIRPORT’S ROLE IN PERFORMANCE-BASED NAVIGATION METRIC DESCRIPTION Flight Efficiency • Average gate-to-gate times or distances are the average of the elapsed times of flights between departing from origin airport gate and arriving to destination airport gate (Federal Aviation Administration 2013g). • Average flight distance or time in the terminal airspace is the average of the actual flown distances or times of flights in the airspace, which is under the jurisdiction of the terminal radar approach control (TRACON) local to the airport. • Level-off flight distance or time evaluates the cumulative distance or time of level-off segments in the vertical profile of an arrival flight between top of descent (TOD) and runway or within an altitude regime [for example, 30,000 to 10,000 feet above ground level (AGL)] (Robinson and Kamgarpour 2010). Similar analysis may be applied to departure flights. Fuel Burn and Emissions • Cumulative gallons of fuel burned and tons of carbon dioxide emitted by all flights within airspace or between pairs of cities (Federal Aviation Administration 2013g). Noise • Day-night average sound level (DNL) evaluates the 24-hour period noise exposure. One event occurring in the evening from 10 p.m. to 7 a.m. is equivalent to ten events occurring in the day outside of those times (Federal Aviation Administration 2015e). NEPA defines thresholds for acceptable noise levels and changes in noise level. • Sound exposure level (SEL) evaluates, for a single flyover, the equivalent sound level if the cumulative exposure is compressed into a 1-second time period (U.S. Government Accountability Office 2008). There are no established thresholds for acceptable noise levels and changes in noise level to assess the impact of noise with this metric. • Time-above evaluates the fraction of a total time period that the noise exposure level exceeds a specified decibel level (U.S. Government Accountability Office 2008). There is no established threshold for acceptable noise levels and changes in noise level associated with this metric to assess the impact of noise. • Number-of-events-above (NA) evaluates the number of noise events above a specified threshold decibel level. This metric may be used to quantify the effect of concentrating flight operations over a particular segment of the community near an airport. There is no established threshold for acceptable noise levels and changes in noise level for this metric to assess the impact of noise. Table 10-1. Continued

Metrics for Assessing the Impact of Procedures | 63 The details and considerations regarding these metrics to assess the impacts of PBN procedures at an airport are described as follows: • Regarding capacity, the average hourly operations can be computed to track airport capacity and any changes due to PBN procedures. • Regarding flight efficiency, PBN procedures can help to reduce the flight time and distance in the terminal airspace. Reductions in flight time and distance may also improve other aspects of flight efficiency, such as fuel burn, emissions and noise exposure. Variability in flight time corresponds to flight predictability for aircraft operators. The flight distance or time of level-off segments in the trajectory of an aircraft indicates the degree to which optimized profile decsents (OPDs) are being realized among arrivals as well as the climb efficiency of departures. • Regarding fuel burn and emissions, flight efficiency improvements enabled by PBN procedures can reduce the fuel burn and emissions from aircraft. Capacity increases enabled by PBN procedures may also reduce fuel burn and emissions, for instance, by reducing departure queuing and taxi time at the airport. The FAA’s FAR Part 150: Airport Noise Compatibility Planning Program, An Overview (FAA 2014j) cites DNL as the primary noise metric for airport noise compatibility planning. The RTCA NAC recommend- ed to the FAA use the DNL metric in conjunction with its proposed net noise reduction method. The New York/New Jersey/Philadelphia airspace redesign identified that supplemental noise metrics would have provided information that may have been more readily understood by decision makers and the public than the DNL metric. The SEL and time-above were cited as alternatives. However, while alter- natives such as SEL capture noise level and duration, there are no accepted criteria or thresholds for evaluating impact, and, in addition, the selection of points on ground and noise threshold complicate application. The FAA Aviation Environmental Design Tool (AEDT) is the tool for evaluating noise, fuel burn, and emissions of instrument flights procedures (IFPs). Estimates may be obtained from analysis of simulated or actual flight tracking data. FAA Order 1050.1F, Environmental Impacts: Policies and Procedures (FAA 2015e) describes comprehen- sively the FAA policies and procedures for complying with NEPA and regulations issued by the Council on Environmental Quality (CEQ). It describes the regulations, affected environment, environmental consequences, supplemental noise analysis, additional noise guidance, and noise mitigation. Evaluating the Noise of PBN Procedures In accordance with FAA Order 1050.1F, noise screening tools and methodologies may be used to de- termine if a proposed action may be categorically excluded with respect to noise. Detailed noise analy- sis is employed if the action cannot be categorically excluded, or for post-implementation. Standard noise analysis is done using the FAA AEDT tool, and DNL is the noise metric recognized by the FAA. Regarding the evaluation of noise of aircraft flying PBN procedures that may be categorically excluded as per the FAA Modernization and Reform Act of 2012, the net noise reduction method for noise screening is the RTCA NextGen Advisory Committee’s (NAC’s) recommendation for comparing an existing procedure to a proposed PBN procedure (RTCA 2013a). The purpose is to identify (1) the number of people who experience a reduction in noise compared to the number of people who expe- rience an increase in noise, at noise levels greater than DNL 45 dB and (2) any increase in the number of people experiencing DNL 65 dB or greater. The process may be summarized as identifying the areas around the airport where people might be impacted and the points representing the centers of the populations (otherwise known as census block centroids) of those areas, computing the DNL at the census block centroids, and determining the overall (not centroid-by-centroid) change in the number

64 | UNDERSTANDING THE AIRPORT’S ROLE IN PERFORMANCE-BASED NAVIGATION of people exposed to noise in individual DNL bands with the PBN procedures versus the conventional procedures. Regarding the detailed evaluation of noise of aircraft flying PBN procedures, which may not be cat- egorically excluded or have already been implemented, detailed noise assessment may be performed using computer models approved by the FAA. The FAA AEDT is the foremost tool for airports to use in their analyses. Data input to the model should accurately reflect the previous and current conditions; that is, flight tracks from the legacy procedures, and flight tracks from the current PBN procedures. The computer models generate noise contours corresponding to 65, 70, 75, and other user-specified decibel levels, as well as grid point and/or change of exposure noise data. Evaluating the Emissions of PBN Procedures The FAA is required to prepare an environmental document for federal actions that have the potential to affect air quality, as defined in two applicable laws: NEPA and the Clean Air Act (CAA). FAA guidance for evaluating the effects of air traffic actions on air quality, including greenhouse gas emissions and climate, are prescribed in FAA Order 1050.1F. The FAA AEDT tool is the approved model for air quality analysis. Analysis of emissions first and foremost focuses on pounds of carbon dioxide (CO2). For purposes of greenhouse gas emissions disclosure, carbon dioxide equivalent (CO2e) emissions are estimated from fuel burn as a proxy for actual CO2 emissions estimates. The CO2e emissions are computed directly from fuel burn analysis as 9.7438 kilograms of CO2e per gallon of fuel. In addition, the EPA states that emissions of PBN procedures are to be assessed for areas that have been designated as non-attainment (not meeting) or maintenance (having previously not met, but now meeting) with respect to the National Ambient Air Quality Standards (NAAQS) for one or more criteria pollutants. The 6 “criteria pollutants” are carbon monoxide (CO), lead (Pb), nitrogen dioxide (NO2), ozone (O3), particulate matter (PM10 and PM2.5), and sulfur dioxide (SO2). All air traffic between the ground and “mixing height” of 3,000 feet AGL or mixing height specified in a state implementa- tion plan (SIP) must be evaluated against the air quality standards.