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

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5 This chapter discusses the framework for initiating and developing the research, including key terminology, a sum- mary of the literature review, and a qualitative discussion of departure NAPs. This background information provides the foundation for the analytical assessments and methods presented in Chapters 3 and 4. 2.1. NADPs and Other Terminology In order to frame the discussion in this report, several key terms are defined below. Additional terms are defined in Appendix A. Noise Abatement Departure Profile (NADP). The FAA’s Advisory Circular AC 91-53A, dated July 22, 1993, provides acceptable criteria for safe NADP operations for civil trans- port jet aircraft. The Advisory Circular (AC) presents two departure methods—one intended to provide noise relief for communities close to the airport (the close-in procedure) and the other to provide relief for communities farther from the airport (the distant procedure). The FAA provided this guid- ance to aircraft operators so that operators would not have to support unique noise abatement procedures at each airport. Although the burden of developing the procedures and sup- porting the training of those procedures was considered to be high, the FAA’s main concern was that lack of standardization resulting from unique departure procedures was a potential safety issue. The Air Line Pilots Association (ALPA) formally supports this policy (Deeds 1996). In addition to the FAA’s recommended procedures, ICAO has also promulgated NADPs in the fourth edition of their PAN- OPS document (ICAO 1993). Instead of using the nomen- clature of close-in and distant, the ICAO document refers to Procedure A and Procedure B, respectively. These procedures are usually referred to as the ICAO – A and the ICAO – B pro- cedures. The primary difference between the FAA and ICAO methods is that the FAA’s AC assumes the use of a thrust cut- back early in the procedure (at an altitude not less than 800 feet AGL) followed by a thrust restoration at 3,000 ft AGL, while the ICAO PAN-OPS assumes the thrust is reduced from takeoff power to climb power at a higher altitude and that climb thrust is maintained throughout the remainder of the departure (no thrust restoration is required). In addition, the National Business Aircraft Association (NBAA) provides a recommended procedure for close-in com- munity relief. NBAA does not explicitly recommend a proce- dure for distant communities, but does recommend a standard departure procedure, which uses the same techniques as the AC 91-53A distant procedure and the ICAO – B procedure. The NBAA procedures can be found at http://www.nbaa.org/ ops/environment/quiet-flying/. The remainder of this section summarizes the procedures contained in AC 91-53A and the ICAO PAN-OPS document. Note that ICAO – A and ICAO – B nomenclature include noise- designated terms (Noise 1 and Noise 2) as indicated below. Close-in (ICAO – A/Noise 1) NADP. The close-in procedure works by delaying the normal retraction of the aircraft’s flaps until the aircraft reaches a clean-up altitude. By maintaining the deployment of the flaps, the aircraft increases its climb gra- dient so that it reaches a given altitude at an earlier distance from the airport. This increases the distance from the aircraft to the receptors on the ground, decreasing the noise received on the ground. Because the flaps are extended, the aircraft can- not perform a normal acceleration and will typically maintain the original climb speed (e.g., V2 + 10 knots) to the altitude where the procedure ends, and the flaps are retracted and the aircraft accelerates. The reduction in airspeed at the end of the procedure means that the aircraft needs to spend thrust accelerating to normal climb speed. Because of the loss of available thrust to climb the aircraft (as well as the increased drag from the extended flaps), an aircraft that has flown a close-in pro- cedure will be lower. A lower aircraft can be louder than an aircraft that has performed a standard procedure at a greater distance from the airport. C H A P T E R 2 Project Background

6Distant (ICAO – B/Noise 2) NADP. In a distant procedure, the aircraft retracts flaps according to the normal flap retraction schedule. The differences from the standard procedure are usually minor when a thrust reduction is not implemented – these differences are typically in the altitude at which the aircraft transitions from takeoff thrust to climb thrust, in the initial flaps selected, or relatively minor procedural changes. The difference in the climb gradients of the two procedures is presented in Figure 2-1. In addition, the following terms are used frequently in this report: Noise Abatement Procedure (NAP). A general term for a flight procedure used by airports, operators, and/or air traffic control for arrivals or departures, including ground tracks and profiles. This study focuses on departure NAPs. For example, an NADP is a type of NAP. 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). 2.2. Literature Review The research team conducted a thorough review of relevant literature, existing research, published practical guidance, and other appropriate material to identify, list, and describe current or proposed types of noise abatement departure pro- cedures. This review was limited to departure procedures only, from takeoff queuing through climb to cruise. Generation of ground noise during taxi-out was also considered to the extent addressed by existing and proposed noise abatement depar- ture procedures. Published guidance was reviewed for several airports, although there was little available on taxi procedures. The full literature review is presented in Appendix A. In summary, nearly 50 works were reviewed in three rel- evant subject areas: capacity, airspace, and operations; stud- ies of environmental interdependencies which examine the tradeoffs between environmental factors; and studies focus- ing 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. The literature review revealed the following: • 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. • Most of these studies provided detailed technical informa- tion, but lack practical guidance for the implementation of suggested procedures. • There is considerable approach/arrival procedure research, but limited analysis of departures and runway capacity that details the implementation of procedures and impacts on airport operational environments. Figure 2-1. NADP schematic.

7 • Little of the research addresses the environmental impacts of future aircraft technology such as that described under NextGen, CLEEN, and the NASA Fundamental Aeronau- tics Research Program (i.e., N+1, N+2, and N+3 generation aircraft). • Any study of noise abatement procedures must consider and address the public’s likely reactions to changing NAPs. The reality of increased operations equating to increased noise and emissions may result in considerable local com- munity objection and only thorough and valid mitigation strategies will gain acceptance. Although it is not feasible for an airport to completely remove an established set of NAPs, it is possible to optimize the existing procedures to improve emissions and fuel burn. In addition, the literature review highlighted several key modeling issues, including the need to • Model realistic variations of NADPs, which can vary by air- craft type and airport (as discussed in ICAO 2007, SOUR- DINE II, and others). • Study the interrelations between ground tracks and pro- files (as discussed in Clarke 2000, Prats 2008/2009, and Forsyth 2009). • Model ground operation noise and emissions resulting from decreased delays via improved runway throughput when using optimized NAPs. These conclusions from the literature review served as a basis to initiate the research. The following sections address the different types of departure NAPs and a qualitative dis- cussion of tradeoffs. 2.3. Qualitative Assessment of Tradeoffs The goal of the qualitative assessment of tradeoffs was to identify various types of NAPs and the potential inter- dependencies among fuel burn, emissions, noise, and capac- ity. Quantifying such relationships is addressed in Chapter 3 which presents the airport case study analysis. This quanti- fication uses the protocols established in Appendix B, which presents the airport scenario modeling. Appendixes C and D provide information on airport capacity impacts. A comprehensive listing of the various types of NAPs in use and proposed for the future was developed based on the literature review. Known and potential benefits and draw- backs of each individual procedure were discussed, consider- ing qualitatively the range of noise, fuel burn, emissions, and capacity metrics. Next, the Tradeoffs Chart (Table 2-1) was developed, with the goal of ranking the benefits and draw- backs of each procedure considering five key factors: • Community Noise (N) • Local Emissions (E) • Fuel Burn (F) • Runway Throughput (T) • Airspace Capacity (C) Each factor was assigned a score relative to existing (non- NAP) departure procedures. The scores ranged from “++” (high benefit) to “– –” (high drawback). A score of “0” indi- cated no impact and a score of “+/-” indicated a mixed benefit/ drawback. Table 2-1 shows the overall Weighted Score of each procedure computed using a weighted scoring model: Weighted Score = 2*N + E + F + T + C Community noise was double weighted (multiplied by two) for two reasons: (1) to counter the fact that emissions/fuel burn and capacity each have two scores and (2) to account for the higher importance of noise for assessing the effectiveness of a NAP. The individual scores for each factor were determined based primarily on the literature review and also on profes- sional experience. Community noise scores were assigned con- sidering both the tradeoffs involved and magnitude of change in noise. In terms of tradeoffs, fanning and RNAV/RNP SID overlays can reduce noise in some areas, but concentrate and increase noise in other areas; whereas an optimized ground track can be designed to reduce noise in all noise-sensitive areas. In terms of magnitude, single-engine taxi reduces noise without tradeoff, but the magnitude of noise reduction is much less than that of optimized ground tracks. Most scores for emissions and fuel burn were equivalent because changes in fuel burn usually result in the same direc- tional change in emissions. Also, many of these scores are “+/-” because there are inherent tradeoffs in fuel burn: the total energy to takeoff and climb an aircraft does not change— only the balance of fuel used in various stages of flight. Scores for runway throughput and airspace capacity are also often equivalent; however, there are cases when a NAP may have a higher impact on airspace capacity than runway capacity. For example, SID overlays are designed to have a beneficial impact on airspace capacity—they can also improve runway efficiency, but to a lesser degree. In general, NAPs that decrease the effi- ciency of takeoff and climb phases (e.g., noise-optimized tracks and NADP-1) negatively impact runway and airspace capacity. Table 2-1 also shows that most of the highest-scoring NAPs involve new technology and NextGen. These NAPs are not cur- rently implementable, but will come on line over time. The implementation timeframe was estimated based on the litera- ture review. Aside from future procedures, the highest-scoring implementable NAPs include single-engine taxi (which has mild benefits but no drawbacks); NADP-2 (which is already

Community Noise Local Emissions Fuel Burn Runway Throughput Airspace Capacity Weighted Score 1 Optimized ground track which avoids noise sensitive locations ++ +/- - - -- 0 Now Prats 2008; LGA; BOS; SFO Distribute ground tracks over area (fanning) +/- +/- +/- + + +2 Now Capozzi 2003 PHL; EWR; MSP RNAV/RNP overlays of SIDs +/- +/- +/- + + +2 Now Mayer 2008 DFW, ATL Preferential routing for low-noise jet aircraft + +/- +/- + + +4 NextGen Rachami 2008, JPDO 2007 NADP 1 Close-in procedure + - - - - -2 Now ICAO 2007; PBI, SNA NADP 2 Distant procedure +/- +/- + + + +3 Now ICAO 2007; MSP Climb over unpopulated land or water near airport to gain altitude ++ - - +/- - +1 Now BOS Temporal Vary ground tracks by time-of-day ++ +/- +/- - - +2 Now Prats 2008; SDF Single-engine taxi + + + 0 0 +4 Now Preferential runway system ++ +/- +/- - -- -1 Now Heblij and Winjen 2008; BUF, LGA, SFO Automated thrust reduction for NADP 1 ++ - - - - 0 Now + 5 Years Forsyth 2009; SNA Low-noise and emissions engines ++ ++ ++ 0 0 +8 5 - 10 Years Rachami 2008 Trajectory-Based Operations (TBO) +/- +/- + + + +3 NextGen JPDO 2007, Visser 1992 Legend: ++ + 0 - -- +/- Profile Aircraft/ ATC Technology Relevant Literature/ Example Airports Qualitative Assessment Estimated Implementation Timeframe Category Ground-Based Operational Measures NAP Ground Track Mixed Benefit/Drawback High Benefit Note 1. Noise score is multiplied by a weight of 2 and all other scores are multiplied by a weight of 1, then the individual scores are summed. Low Benefit No Impact Low Drawback High Drawback Table 2-1. Tradeoffs chart.

Ground Track Procedures NAP Benefits Drawbacks Implementation Control Optimized ground track which avoids noise-sensitive locations ▪ Contains noise exposure to specific areas, and avoids noise-sensitive receptors ▪ Can optimize procedure to minimize noise- exposed population ▪ May concentrate noise in selected areas ▪ Not always possible to avoid all populated areas ▪ May cause reduction in airspace capacity if path is not optimal ▪ May cause increase in fuel burn and emissions if path is not optimal ▪ Recommend: Airports (via planning studies) ▪ Implement: FAA Distribute ground tracks over area (fanning) ▪ Distributes noise over broad area ▪ Can be designed to create a “fair” share of noise among communities ▪ Allows for airspace flexibility ▪ Improved capacity and runway throughput ▪ Noise increases in some areas ▪ May not provide any benefit for fuel burn or emissions ▪ Recommend: Airports (via planning studies) ▪ Implement: FAA RNAV/RNP overlays of SIDs ▪ More accurate than conventional navigation ▪ Accurate routing can improve airspace capacity ▪ Contains noise exposure to specific areas ▪ Can be designed to avoid noise-sensitive receptors ▪ Concentrates noise in selected areas where flights occur ▪ Emissions and fuel burn have negligible or small change compared to conventional navigation ▪ Not all aircraft have necessary navigational equipment ▪ Implement: FAA Preferential routing for low- noise jet aircraft ▪ Allows lower-noise aircraft to fly direct routing to departure fix, reducing fuel burn and emissions ▪ Increases airspace and runway capacity for existing aircraft types ▪ Provides incentive for operators to upgrade to low-noise technology ▪ Cannot implement until NextGen ▪ Capacity benefits proportional to the number of low-noise aircraft ▪ No improvement in noise, fuel burn and emissions for existing types of aircraft ▪ Implement: FAA via NextGen Table 2-2. NAP descriptions. (continued on next page)

Profile Procedures NAP Benefits Drawbacks Implementation Control NADP 1 Close-in procedure ▪ Redistributes noise away from areas near the airport (from brake release to 5-10 miles away depending on aircraft type) ▪ Tradeoff of larger noise reduction than corresponding noise increase farther from airport ▪ Useful where ground tracks cannot be changed ▪ When compared to NADP2, lower NOx ▪ Airlines and most airports prefer NADP 2 (distant procedure) ▪ Only in use at few airports with exceptional close-in residential areas, noise monitors, or geographic features ▪ Takes more time to reach top of climb altitude when compared to NADP2 due to delayed acceleration segment to retract flaps (reduction in capacity) ▪ When compared to NADP2, higher GHG due to shorter time to climb to 3000’ ▪ Recommend: Airports ▪ Implement: Airlines/operators NADP 2 Distant procedure ▪ Redistributes noise away from areas farther from the airport (beyond 5-10 miles away from brake release depending on aircraft type) ▪ Useful where ground tracks cannot be changed ▪ Airlines and most airports prefer this NADP. In some cases, airlines have adopted NADP 2 as their standard procedure ▪ Takes less time to reach top of climb altitude compared to standard profile (due to increased acceleration at lower altitudes) ▪ Increase in runway and airspace capacity due to increased acceleration during initial climb ▪ When compared to NADP1, higher NOx but lower GHG due to longer time to climb to 3000’ but shorter time to reach cruise altitude ▪ Recommend: Airports ▪ Implement: Airlines/operators Climb over unpopulated land or water near airport to gain altitude ▪ Reduce noise exposure in noise-sensitive areas by climbing to higher altitude first ▪ Shift higher noise exposure levels to non- noise-sensitive areas ▪ Increase in emissions due to longer flight time ▪ Increase in fuel burn due to longer flight time ▪ May have impacts on runway throughput ▪ Can only be implemented at certain airports with adjacent land or water ▪ Recommend: Airports (via planning studies) ▪ Implement: FAA Table 2-2. (Continued).

Temporal NAP Benefits Drawbacks Implementation Control Vary ground tracks by time- of-day ▪ Flexibility to reduce noise during sensitive periods such as nighttime ▪ Typically lower traffic levels at nighttime, thus low impact on capacity ▪ Minimize reductions in capacity by implementing only at certain times of day ▪ Noise abatement flight tracks may be longer and increase fuel burn and emissions ▪ Recommend: Airports (via planning studies) ▪ Implement: FAA Ground-Based Operational Measures NAP Benefits Drawbacks Implementation Control Single-engine taxi ▪ Reduced noise during taxi ▪ Reduced fuel burn and emissions ▪ No benefit to runway or airspace capacity ▪ FAA safety concerns at some airports ▪ Recommend: Airports ▪ Implement: Airlines and Operators Preferential runway system ▪ Minimize noise by directing flights towards less sensitive areas ▪ Can implement at specific times such as nighttime, when traffic levels are lower ▪ Decrease in airspace capacity compared to most optimal configuration ▪ May increase fuel burn and emissions if distance to departure fix is increased ▪ Recommend: Airport ▪ Implement: FAA Aircraft/ATC Technology Measures NAP Benefits Drawbacks Implementation Control Automated thrust reduction for NADP 1 ▪ Optimal use of NADPs which reduce noise at sensitive locations ▪ Provides automatic cutback to minimum required thrust at specific user selected altitude or noise-sensitive location on ground ▪ Technology under development/ not widely in use; will take time for operators to upgrade fleets ▪ Tradeoff of noise close and distant from airport ▪ Implement: Manufacturers and Airlines Low-noise and emissions engines ▪ Decreases noise and emissions impacts throughout all phases of flight ▪ Engines also consume less fuel ▪ Although under development, not currently available ▪ Will take time for operators to upgrade fleets ▪ No inherent effect on capacity, unless preferential routing is possible ▪ Implement: Manufacturers and Airlines Trajectory-based operations (TBO) ▪ Can be adjusted with time and traffic levels ▪ Optimized to improve capacity and reduce delays and fuel burn ▪ May decrease noise by combination of ground tracks and profiles ▪ NextGen technology needed to implement (4-dimensional trajectories) ▪ May increase noise during peak traffic levels ▪ Implement: FAA via NextGen

Ground Track Profile Temporal/Traffic Level Ground-Based Operations Aircraft/ATC Tech Ground Track Profile NADP 1 or 2, to reduce effect of increased noise in new areas due to changed ground track Temporal/Traffic Level Combine ground track with peak demand procedures NADP 1 or 2, to reduce effect of increased noise Ground-Based Operations Queue aircraft according to low- noise versus existing types to more efficiently route aircraft on ground tracks NADP can add to environmental benefits of ground-based operations Implement preferential runways on a time of day basis, depending on demand and noise sensitivity Aircraft/ATC Tech In future, low-noise engine technology can allow for smaller increase in noise and more-direct routing Automated thrust reduction for NADP 1 In future, low-noise engine technology can allow for smaller increase in noise Preferential routing for low- noise aircraft to increase capacity Table 2-3. NAP combinations matrix.

13 used by many operators); RNAV/RNP overlays of SIDs (which have high benefits to airspace and runway capacity but mixed environmental benefits); and, varying ground tracks either temporally or over an area using fanning (both of which have weighted scores of +2). All other NAPs in Table 2-1 have scores of +1 or below, with preferential runways and NADP-1 having negative scores. Table 2-2 describes each NAP in greater detail and includes a list of the benefits and drawbacks considered in assign- ing the individual scores shown in Table 2-1. Thus, a more detailed description of the decision process behind the devel- opment of the weighted scores is provided. In addition, Table 2-2 discusses the entity that controls implementation of each NAP—given that control affects an airport’s ability to implement NAPs successfully, this is a key consideration. Finally, Table 2-3 provides an assessment of NAPs that can be used in combination to further reduce or counteract negative environmental impacts. This table provides a basis for under- standing how several types of NAPs can be used in conjunction to best optimize procedures for a given airport.