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

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14 3.1. Approach The goal of the case study analysis was to provide detailed data on the tradeoffs among noise, emissions, fuel burn, and capacity by modeling single departure events at several air- ports. Although it is unlikely that an airport would remove an existing NAP, an airport could optimize that NAP in terms of emissions, fuel burn, or capacity at the expense of noise exposure (i.e., given that an existing NAP is already optimal for noise exposure in the eyes of both airport and commu- nity, any changes to a NAP would be undesirable, unless sup- porting data can be used to show the benefits of making such changes). The Testing Protocol included in Appendix B specifies the parametric optimization process in which many combina- tions of departure ground tracks and profiles were modeled for each airport. These tracks covered variations of existing NAPs, as well as the most direct ground track from takeoff to a departure fix. Environmental analysis was carried out for each case study and capacity was modeled by simulating runway throughput for each airport. Assessments of tradeoffs were then compiled by comparing each of the result sets against the existing NAPs for all modeled variables. Figure 3-1 illustrates the process detailed in the Testing Protocol. After an individual review of 81 U.S. airports with existing NAPs, 9 airports were selected for case study analysis. These airports represent different types of airports with various NAPs and local noise and air quality issues. These airports are listed in Table 3-1 along with a description of the NAP and additional information on why the airport is of interest (e.g., airport type, air quality concerns, annual operations, and proposed baseline aircraft type). Although details are provided, descriptions are generalized and the actual airport names have been replaced with code names (e.g., APRT1) to respect airport sensitivities to the presentation of such infor- mation. A detailed explanation of the airport selection pro- cess is provided in Appendix B. The airports listed in Table 3-1 were used to determine the trade offs for different types of NAPs. In the following sec- tions, NAPs are discussed as detailed in Table 3-2, which shows the type of NAP studied in each section and highlights the way each was implemented in the case studies. This chapter presents a summary of results for each type of NAP studied; the impacts of airport capacity are presented in Appendixes C and D. The population data used for these analyses were obtained from Arc GIS data. 3.2. Turn Restrictions A turn-restriction NAP puts a constraint on the departure ground tracks used for a given runway at a given airport. This constraint is typically used to keep aircraft flying at runway heading after takeoff until reaching a certain distance (or alti- tude) relative to the runway end, after which the aircraft can turn toward the destination or fix as directed by air traffic con- trol. Such procedures are in use at APRT6, APRT1, and APRT5 (distance based) and at APRT9 and APRT8 (altitude based). To model the effects of optimizing these procedures, alter- nate ground tracks were created for each of these airports following the schematic shown in Figure 3-2. Beginning with the distance or altitude location where the NAP allows turns to be initiated, additional ground tracks were developed at 0.5 NM intervals working back toward the runway end. Each of the tracks was constructed to reach a common conver- gence point representing the destination fix of the existing NAP ground track. The most-direct ground track represents an immediate turn from the runway end. For example, Fig- ure 3-3 shows the ground tracks and NAP for APRT6, and Figure 3-4 shows the tracks for APRT9. The procedure at APRT6 for runway 7L is designed with a “gate” located 5 NM east of the runway. Turns made after the gate may head north or south; however, for this analysis, a south turn was modeled, converging at a point southeast of the airport. The differences in noise, emissions, fuel burn, C H A P T E R 3 Case Study Analyses

15 Figure 3-1. Case study analysis process. 1. Airport Selection and Data Collection 2. Develop Ground Tracks 3. Develop Profiles 4. Environ- mental Modeling 5. Capacity Modeling 7. Tradeoff Assessments 6. Analyze Results Airport Type of Airport Existing Departure NAP (1) Air Quality Concerns(2) Approx. Annual Operations(3) Baseline Aircraft Type(3) APRT1 CargoHub - Airport goes to single direction operation at night - Departure turns based on distance from airport Ozone, PM2.5 100,000 – 200,000 A300 APRT2 Hub,Coastal - RNAV NAP procedures Ozone, CO 300,000 – 400,000 757-200 APRT3 Hub - Community close to airport Ozone, CO, PM2.5 300,000 – 400,000 MD-88 APRT4 Hub - Fanning NAP CO, SO2 400,000 – 500,000 DC9-30 APRT5 Hub,Coastal - Multiple turn restrictions on departure Ozone, CO, PM2.5 300,000 – 400,000 747-400 APRT6 Hub - Departure heading gate (distance-based turns) Ozone, CO, PM10 500,000 – 600,000 737-700 APRT7 GeneralAviation - Distance-based turns Ozone, CO, PM10, PM2.5, NO2 < 50,000 Gulfstream GIIB (Noise Stage 2) APRT8 Regional - Heading restriction based on altitude Ozone < 50,000 CRJ-200 APRT9 Regional - Altitude-based headings Ozone 100,000 – 150,000 EMB-145 Sources: (1) Boeing NER Database 2009; (2) VALE Airport Status List 2009; (3) ETMS 2006 Table 3-1. Case study airports. Sec. NAP Study Airport(s) Method Utilization 3.2 Runway-heading Turn Restrictions APRT1, APRT5, APRT6 Study varies initial turn by distance from runway end, progressively reducing distance Alternated NAP with straight- out ground track to represent flights in other directions APRT8, APRT9 Study varies initial turn by altitude of aircraft, progressively reducing altitude All aircraft follow NAP 3.3 Multi-turn NAP track APRT2, APRT3, APRT5 Study varies NAP ground track geometry for more- direct routing All aircraft follow NAP 3.4 Climb Procedures APRT2 Study lengthens ground track over water to increase altitude reached at shoreline crossing All aircraft follow NAP 3.5 Close-in NADP APRT3, APRT5, APRT7 Determine how close-in NADP can mitigate noise increases due to a different ground track All aircraft follow NAP 3.6 Fanning APRT4 Noise abatement fanning procedure distributes noise to different areas Alternated use of fanning tracks Table 3-2. NAP studies matrix.

16 Figure 3-2. Illustration of turn-restriction ground tracks. Each earlier turn spaced at 0.5 NM Most-direct Runway Fix NAP ground track NAP turn point and capacity resulting from each ground track turning earlier than the existing NAP are discussed below. Noise level analysis was conducted by computing the dif- ference in single-event SEL contours for each ground track. The difference in SEL values and population counts for each track were computed in comparison with the existing NAP track. As an example, the difference in SEL comparing the track which turns 2.5 NM sooner than the NAP is shown in Figure 3-5. This map shows the range of SEL increase and decrease over the local area, including a maximum increase of 18 dB and a maximum decrease of 14 dB. Noise differences were also computed for the other ground tracks modeled for APRT6, and maps of these differences showed similar trends with different values of increase and decrease. Throughout this chapter, noise difference maps are presented using dif- ferent color scales to reflect varying levels of noise change appropriate to each airport and aircraft type. Figure 3-6 shows the capacity curves for APRT6. The mod- eled ground tracks affect runway throughput according to the length of the common path shared by successive departures. The capacity simulation was used to alternate aircraft flying south along the modeled ground tracks (DIR, NAP, and INT) and aircraft flying in other directions through the departure gate (STR). The direct ground track, DIR, increases runway throughput by approximately 1.5 to 2 departures per hour (x-axis), depending on the arrival rate (y-axis). This increase is due to the fact that once a departure turns immediately south on the direct track, the following departure can be more quickly cleared to take off. Noise, emissions, fuel burn, and capacity were then plotted on a graph designed to summarize the tradeoffs. Figure 3-7 shows the population exposed to SEL greater than 75 dB, which increases by varying amounts over the baseline of 59,167 per- sons for the NAP. Each ground track is indicated on the x-axis. Emissions of CO2 and fuel burn are shown in terms of total kilograms (from beginning of takeoff roll to reaching the departure fix). Capacity is shown in terms of the number of hourly departure operations for the runway for a constant level of arrival operations. Although not shown, SEL increases from 0 dB for the NAP (left side of graph) up to 29 dB for the direct ground track. Figure 3-7 illustrates the same trends exhibited by fuel burn and CO2 emissions. Although not as closely as CO2 emissions, NOx emissions also follow fuel burn and, therefore, would show similar trends. NOx emissions are often used as an indicator of impacts on local air quality. There are several conclusions which can be drawn from Figure 3-7. First, the tradeoffs between increasing noise and decreasing emissions and fuel burn are readily apparent. Com- paring the extremes of the ground track nearest to the NAP (which turns 0.5 NM before the gate) and the direct track, CO2 emissions decrease from 1,363 kg to 961 kg – a decrease of 30%. In addition, fuel burn decreases from 432 kg to 305 kg, also a 30% decrease. An increase in capacity is expected: there is an improvement from 37 operations to 39 departures per hour. In terms of the effect on the local area, the population count must also be considered, and, unlike the other variables, there is not a steady rate of increase or decrease. For APRT6, the baseline for the NAP is 59,167 persons within the single- event 75 dB SEL contour. The population counts for all other modeled tracks are higher; however, the greatest increases occur between the 2.5 and 4 NM turns. In fact, the direct- track population count is 61,362 – only 4% higher than the NAP population count. Certainly, the decision to change an existing NAP would have to be weighed carefully against decreases in emissions. For example, selecting the “NAP minus 2 NM” ground track would increase the population exposed to 75 dB SEL by 13%; however, this would decrease the CO2 emissions by 11%. Local airport decisions can be better informed by considering the tradeoffs and trends in noise levels, population counts, emissions, fuel burn, and capacity. Similar results were generated for APRT9, a much smaller airport with a fleet consisting mainly of regional jets. The NAP consists of a runway-heading turn-restriction of 3,000 ft

17 Figure 3-3. APRT6 ground tracks.

18 Figure 3-4. APRT9 ground tracks. MSL. For this procedure, it was assumed in the model that all operations would follow the procedure before turning westbound. The noise difference map shown in Figure 3-8 shows the areas of noise decrease and increase when shifting an EMB-145 departure operation from the NAP to the direct track, and Figure 3-9 shows the tradeoffs summary chart. Both figures reflect the maximum noise increase of 17 dB SEL comparing the NAP to the direct track. For the intermediate tracks, the increase in population exposed to SEL above 75 dB increases gradually at first, from 6,342 for the NAP to 6,632 for the “NAP minus 1.5 NM.” The difference between these ground tracks is a reduction of 11 kg of CO2 and 4 kg of fuel, and 0.5 operations per hour impact on throughput. Over- all, the relative differences shown for APRT9 are much less than for APRT6 due to the smaller aircraft type and different ground track geometry modeled. 3.3. Multi-Turn NAP Routing A multi-turn NAP ground track is designed to avoid densely populated and noise-sensitive areas near airports. The modeling of such NAPs was performed on the basis of published information for APRT3, APRT2, and APRT5. Similar to turn restrictions, once multi-turn NAPs termi- nate, ground tracks proceed to a destination-specific fix in the airspace. To model the effects of optimizing these pro- cedures, alternate ground tracks were created following the schematic shown in Figure 3-10. The airspace between the existing NAP and the most-direct feasible ground track was filled with alternate tracks spaced 0.5 NM apart. Figures 3-11 and 3-12 show the specific ground tracks modeled for APRT3 and APRT2, respectively. For APRT3, a tradeoffs summary chart was developed to determine the optimal alternate flight tracks for the utilized runway using an MD-88 aircraft type for analysis (see Fig- ure 3-13). The direct track, which turns immediately left instead of following the NAP initial right turn, results in a noise increase; however, the total population exposed to 85 dB SEL is lower. Although CO2 and fuel burn are reduced by 27%, there are significant changes in noise exposure. In addi- tion, capacity is affected by the varying ground tracks, due to the interactions between the multi-turn trajectory near the runway end and the departure profile of the MD-88. Effects of profiles at APRT3 are discussed further in Section 3.5. The ground tracks modeled for the APRT2 runway RNAV NAP departure procedure vary from the published NAP to a

19 Figure 3-5. APRT6 noise difference map.

20 Figure 3-6. Capacity of runway pair at APRT6 with base departure profiles. Figure 3-7. APRT6 tradeoffs summary. CO2 (kg) Throughput 800 900 1,000 1,100 1,200 1,300 1,400 1,500 Ki lo gr am s 36.0 36.5 37.0 37.5 38.0 38.5 39.0 39.5 De pa rtu re O pe ra tio ns pe r Ho ur Fuel Burn (kg) Population > 75 dB 250 300 350 400 450 500 NA P NA P - 0. 5 NM NA P - 1. 0 NM NA P - 1. 5 NM NA P - 2. 0 NM NA P - 2. 5 NM NA P - 3. 0 NM NA P - 3. 5 NM NA P - 4. 0 NM NA P - 4. 5 NM NA P - 5. 0 NM D ire ct Ki lo gr am s 50,000 55,000 60,000 65,000 70,000 75,000 Nu m be r o f p er so ns

21 Figure 3-8. APRT9 noise difference map. Figure 3-9. APRT9 tradeoffs summary. Fuel Burn (kg) Population > 75 dB 148 150 152 154 156 158 160 162 NA P NA P - 0. 5 NM NA P - 1. 0 NM NA P - 1. 5 NM NA P - 2. 0 NM NA P - 2. 5 NM NA P - 3. 0 NM Di re ct Ki lo gr am s 6,000 6,500 7,000 7,500 8,000 8,500 Nu m be r of p er so ns CO2 (kg) Throughput 460 470 480 490 500 510 520 Ki lo gr am s 32.0 32.5 33.0 33.5 34.0 34.5 35.0 De pa rtu re O pe ra tio ns pe r H ou r

22 Figure 3-10. Illustration of multi-turn ground tracks. Each gap is ≤ 0.5 NM Most-direct Runway Fix NAP ground track direct ground track. The resulting changes in SEL are shown in the noise difference map in Figure 3-14. This map indi- cates that the maximum increase of 35 dB is located north- west of the airport, while corresponding noise decreases to 32 dB are located southwest of the airport. The intermediate noise increase values are shown in the tradeoffs chart in Figure 3-15. Both APRT2 and APRT3 are airports surrounded by dense populations, as shown in Figures 3-13 and 3-15. Therefore, there is great sensitivity of population counts to changes in ground track locations at these airports. Although there is a potential to reduce emissions and fuel burn at each of these airports, a balance must be struck with changes in noise levels. For example, the population exposure for APRT2 increases gradually until after the “NAP minus 3 NM” alternate track; up to this point, reductions in CO2 and fuel burn are 23% and there would be a 0.6 operations per hour increase in runway throughput. 3.4. Climb Procedures The NAPs studied in the previous section are designed to avoid noise-sensitive areas by turning at several points along a ground track. However, a multi-turn ground track can also be used when a runway is near an unpopulated area or body of water. For example, APRT2 has implemented a procedure for runway departures because the airport is contiguous with an ocean. As shown in Figure 3-16, the existing conventional departure procedure was previously used to direct departing aircraft with a destination to the north. A new RNAV procedure was implemented recently to extend the segment of the ground track located over the water, so that aircraft can climb to a higher altitude before turning north and crossing the shoreline. A pen- insula (not shown) to the northeast of the airport is still exposed to departing flights, but the longer flight track allows aircraft to climb higher before crossing this area, thus reducing noise. However, the longer RNAV ground track results in higher fuel burn and emissions. Figure 3-17 shows the tradeoffs chart for each ground track out to a cutoff near the point where the tracks converge towards the fix. The result of the longer RNAV departure track (left side of the chart) is a 10% increase (243 kg) in CO2 emissions (with a similar increase in NOx emissions) compared to the conventional departure (right side of chart). Conversely, the RNAV departure reduces noise levels by as much as 16 dB for a single event. Thus, the benefit of reducing noise in the vicinity of the airport comes at the cost of increased emissions and fuel burn, although there is no measurable effect on capacity. 3.5. NADP Profiles In addition to the NAP ground track procedures discussed above, Noise Abatement Departure Profiles (NADP) are also used to mitigate noise near airports. This section dis- cusses the effects of NADPs on noise, emissions, fuel burn, and capacity. First, NADPs will be discussed independently of flight tracks. Then, the interactions between profiles and ground tracks will be discussed, particularly the case in which an NADP can mitigate noise increases that result from chang- ing ground track locations. In practice, the distant NADP-2 procedure is very similar to aircraft manufacturer’s standard procedures—many airlines have adopted NADP-2 as their standard procedure. The close- in NADP-1 is different than standard procedures, particu- larly below 3,000 feet above field elevation (AFE). Figure 3-18 shows a schematic diagram of these profiles, with NADP-2 assumed to be similar to the standard procedure. The noise benefit of NADP-1 occurs above at least 800 feet AFE and below 3,000 feet AFE: the aircraft climbs higher sooner and reaches 3,000 feet AFE sooner than the standard profile. NADP-1 also

23 Figure 3-11. APRT3 ground tracks.

24 Figure 3-12. APRT2 ground tracks.

25 CO2 (kg) Throughput 1,000 1,100 1,200 1,300 1,400 1,500 1,600 1,700 1,800 Ki lo gr am s 34.5 35.0 35.5 36.0 36.5 37.0 37.5 38.0 38.5 39.0 39.5 De pa rtu re O pe ra tio ns pe r Ho ur Fuel Burn (kg) Population > 85 dB 300 350 400 450 500 550 600 NA P NA P - 0. 5 NM NA P - 1. 0 NM NA P - 1. 5 NM NA P - 2. 0 NM NA P - 2. 5 NM NA P - 3. 0 NM Di re ct Ki lo gr am s 50,000 70,000 90,000 110,000 130,000 150,000 170,000 190,000 210,000 230,000 Nu m be r of p er so n s Figure 3-13. APRT3 tradeoffs summary. entails a thrust reduction at the beginning of the procedure, from takeoff thrust down to climb thrust. However, this thrust reduction is not as drastic as the “deep cutback” or minimum thrust level used in some special cases. It is far more typical for aircraft to reduce thrust to climb power early than to reduce thrust to the minimum level. In addition to the effect of reducing noise, emissions are also reduced for below 3,000 feet AFE, which is the mixing layer cut- off used for computations of air emissions for a local area (for pollutants such as CO, PM, HC, and SOx). Figure 3-19 shows that CO emissions and fuel burn accumulated to 3,000 feet AFE are less for NADP-1 than for the standard (base) proce- dure at APRT3. However, as shown in the schematic, after the procedure ends, the NADP-1 must retract flaps and accelerate, result- ing in lower altitude farther from the airport. When the air- craft reaches a common departure fix, the total fuel burn and emissions are greater than the standard procedure, as shown on the right side of Figure 3-19. This tradeoff is important to consider when weighing the benefits of NADP-1: this trend was also found for other aircraft types and airports. The lower airspeed of NADP-1 below 3,000 feet AFE, while allowing for reductions in noise and local emissions, affects runway capacity. Figures 3-20a and 3-20b compare the runway throughput for APRT3 for standard (top) and NADP-1 ( bottom) profiles. The departure curves are lower for the NADP-1 case, with approximately four fewer operations per hour; this is due to the lower airspeed of NADP-1 near the runway end. This tradeoff must also be considered when assessing NADPs. The combination of changing ground tracks and using NADP-1 can be used to develop an optimized 3-dimensional trajectory. That is, implementing an NADP can partially mit- igate the noise increases due to a change in a ground track and can reduce the local air emissions below 3,000 feet AFE. Continuing with the APRT3 case study as an example, Fig- ure 3-21 shows the noise differences for a combination of NADP-1 and an alternate ground track which turns to the fix 1 NM sooner than the NAP. A noise reduction of 5 dB is shown at the location of the NAP track and a noise increase of 5 dB is shown at the location of the alternate early-turn track. In addition, the noise reduction of the NADP can be seen close to the runway end directly under the flight track during the initial segment of the ground track. However, there is a noise tradeoff involved in the use of NADP-1. Directly south of the runway end there is an area of noise increase; this is due to the lower airspeed of the aircraft during the climb to 3,000 feet AFE. Although the aircraft is at a higher altitude than the standard profile during this climb seg- ment, the lower airspeed results in more accumulated noise added to the SEL metric in areas to the side of the ground track near the runway end. This effect is highly dependent on ground track geometry; however, there is always a tradeoff between reducing noise directly under the ground track and increasing noise on the sidelines when using an NADP-1. This

26 Figure 3-14. APRT2 noise difference map.

27 CO2 (kg) Throughput - 500 1,000 1,500 2,000 2,500 Ki lo gr am s 36.4 36.6 36.8 37.0 37.2 37.4 37.6 37.8 38.0 38.2 De pa rtu re O pe ra tio ns p er Ho ur Fuel Burn (kg) Population > 75 dB - 100 200 300 400 500 600 700 800 NA P NA P - 0. 5 NM NA P - 1. 0 NM NA P - 1. 5 NM NA P - 2. 0 NM NA P - 2. 5 NM NA P - 3. 0 NM NA P - 3. 5 NM NA P - 4. 0 NM NA P - 4. 5 NM NA P - 5. 0 NM Di re ct Ki lo gr am s 60,000 70,000 80,000 90,000 100,000 110,000 120,000 130,000 Nu m be r of pe rs on s Figure 3-15. APRT2 tradeoffs chart. noise tradeoff must be considered in any situation when an NADP-1 is implemented. 3.6. Fanning Fanning procedures are implemented by FAA air traffic control to improve runway throughput, particularly for periods of high traffic levels at an airport. In addition, airports such as APRT4 use fanning as a noise abatement procedure in order to distribute noise more widely over an area. For one of the runways at APRT4, a fanning depar- ture procedure is in place because areas directly in line with the runway are affected by arrivals to the opposite runway end. Figure 3-22 shows the departure tracks from the run- way, including straight-out departures, left and right fanning headings immediately at the runway end, and left and right fanning headings 1 NM from the runway end. These ground tracks were modeled to assess the changes in noise and capacity when using fanning procedures. Emissions were not computed because the tracks do not converge at any point beyond the terminal area. Figure 3-23 shows the SEL difference between a straight- out departure ground track and fanned tracks and shows this difference when switching from the fanned tracks to the straight-out departure ground track. Although the maxi- mum SEL difference is 36 dB, the differences closer to the airport are smaller. Nonetheless, the increase in noise along the extended centerline of runway 30L is significant. Further- more, the capacity curves in Figure 3-24 show that only the immediate-turn fanning tracks result in an increase in throughput because a departure must be on a heading 15 degrees off of the previous departure profile by 1000 ft. above the runway for the trajectories to be considered to diverge immediately. The 1 NM turns modeled for APRT4 did not meet this condition. Thus, an important conclusion is that fanning can improve runway throughput only when the turns are made immediately after takeoff, which is not possible for some larger aircraft types. 3.7. Conclusions Nine airports were modeled using single-event case studies to determine the tradeoffs of noise, emissions, fuel burn, and capacity. These airports represent a sample of different sizes and types of airport, with varying levels of population den- sity and different types of aircraft. The case studies showed that even relatively small changes in noise exposure have an appreciable impact on reducing fuel burn and emissions, although the benefits to runway throughput were minor and, in some cases, negligible (with the exception of fanning). The impact on local population varied from airport to air- port, and, in some cases, a small population impact could be

28 Figure 3-16. APRT2 climb procedure ground tracks.

29 Figure 3-18. NADP schematic. CO2 (kg) Throughput 1,750 1,800 1,850 1,900 1,950 2,000 2,050 2,100 2,150 Ki lo gr am s 35 35.5 36 36.5 37 37.5 38 38.5 39 39.5 40 De pa rtu re O pe ra tio ns pe r Ho ur Fuel Burn (kg) Population > 75 dB 540 560 580 600 620 640 660 680 700 RN AV De pa rtu re NA P - 0. 5 NM NA P - 1. 0 NM NA P - 1. 5 NM NA P - 2. 0 NM NA P - 2. 5 NM Co nv en tio na l De pa rtu re Ki lo gr am s 5,650 5,700 5,750 5,800 5,850 5,900 5,950 6,000 6,050 Nu m be r o f p er so ns Figure 3-17. APRT2 climb procedure tradeoffs chart.

30 CO Std. (g) CO Std. (g) CO NADP-1 (g) Fuel Burn Std. (kg) Fuel Burn Std. (kg) Fuel Burn NADP-1 (kg) Fuel Burn NADP-1 (kg) CO NADP-1 (g) 0 100 200 300 400 500 600 Ground to 3,000 AFE Ground to Fix Mass Figure 3-19. Emissions and fuel burn for MD-88 at APRT3. traded for larger reductions in emissions. In terms of profiles, NADP-1 was found to have tradeoffs in noise and emissions, but consistently reduced throughput. In addition to the conclusions drawn in each preceding section, an analysis which considers all airports together was completed. Figure 3-25 summarizes tradeoffs in terms of noise increase in decibels versus CO2 emissions decrease in kilograms. A curve was plotted for most of the airports using the data generated for the ground tracks modeled relative to the existing NAP, with the direct track result- ing in the greatest noise increase and corresponding CO2 reduction. The variability of the curves results from three factors unique to each airport: aircraft type, ground track geometry, and departure fix (cutoff) location. For example, regional jet emissions are much lower in overall magnitude than heavy jet emissions, so the potential for reduction is also smaller. Ground track geometry was also an important fac- tor: large, sweeping NAP turns (i.e., APRT2, APRT1, APRT3, and APRT6) showed greater changes when compared with smaller, incremental track changes (i.e., APRT5, APRT9, and APRT7). To characterize the range of noise changes shown in Fig- ure 3-25, a list of noise reductions due to fleet replacement using various existing and planned aircraft technology was tabulated. Table 3-3 shows the approximate ranges of noise reductions relative to existing marginal noise stage 3 aircraft. The differences in cumulative noise level for stage 3 and 4 are based on FAA certification requirements and the future aircraft cumulative levels were reported by Rachami (2008). Takeoff and sideline levels were assumed to be equivalent and were approximated from existing certification data trends. Overall, this analysis shows that, for single-departure opera- tions modeled in the case studies, replacing a stage 3 with stage 4 would result in a 3 to 4 dB reduction throughout all noise contour levels, with even greater reductions possible with future technology. Therefore, fleet replacement, limited to a single-event basis, has the potential to mitigate the increases in noise reported in Figure 3-25. The case studies generated single-event data from which the most optimal procedures were determined by comparing results with the existing NAPs. Although the goals of the case studies were met, there were some limitations to the analy- sis. Given that the case studies focused on single-departure events, the following limitations were observed: • Cumulative effects, such as daily or annual average noise and emissions inventories, could not be computed based on the case studies. The environmental and capacity effects of departures on other runways and arrivals were not included. • The runway throughput model was simplified to focus on individual runway operations and ground tracks. In addi- tion, the effects on throughput reported in this chapter are representative of IFR conditions; VFR conditions results showed no changes as a result of NAPs because the separa- tion limits are smaller. • The ground tracks and profiles modeled for single events are idealized to match precise procedures; in practice, there are deviations from these procedures (e.g., the dispersion of ground tracks throughout an airspace corridor). • Each case study considered only one aircraft type per air- port, limiting the ability to compare aircraft with different noise levels directly.

31 Figure 3-20a. Runway capacity for MD-88 at APRT3 with base profiles. Figure 3-20b. Runway capacity for MD-88 at APRT3 with Noise1 profiles.

32 Figure 3-21. APRT3 noise difference for NADP-1 (1 NM turn).

33 Figure 3-22. APRT4 ground tracks.

34 Figure 3-23. APRT4 noise difference.

35 Figure 3-24. APRT4 runway capacity with base profiles. -1,000 -800 -600 -400 -200 0 0 10 15 20 25 30 Maximum Noise Increase (dB) CO 2 De cr ea se (k g) APRT7 (Gulf-2) APRT9 (EMB-145) APRT5 (747-400) APRT6 (737-700) APRT1 (A300) APRT2 (757-200) APRT3 (MD-88) 5 Figure 3-25. Comparison of noise and CO2 change levels for multiple airports.

36 Aircraft Technology Difference in Cumulative1 Noise Level Relative to Stage 3 (dB) Approximate Difference in Takeoff and Sideline Noise Level Relative to Stage 3 (dB) Stage 3 0 0 Stage 4 -10 -3 to -4 Advanced Stage 42 -30 -9 to -11 N+12 -42 -12 to -15 N+23 -52 -16 to -18 N+34 -81 -24 to -28 1: Cumulative noise certification levels are based on the sum of takeoff, sideline, and approach noise measurements. Typically, takeoff accounts for 30-35% and sideline accounts for 30-35% of cumulative. 2: Currently under development. 3: Development through 2020. 4: Development through 2035. Sources: Rachami 2008; FAA Advisory Circular AC36-1H Table 3-3. Noise reduction levels for aircraft technology horizons.