Best Practices Guidebook for Preparing Lead Emission Inventories from Piston-Powered Aircraft with the Emission Inventory Analysis Tool (2015)

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23 5.1 Overview Two worksheets denoted with blue-shaded tabs in the EIAT are used for selecting inventory options for defining operating modes and TIM assumptions. • Worksheet 5.1 is where the options for defining operating modes are selected by the user and parameter values corresponding to the approach option are set. • Worksheet 5.2 is where the option for defining TIM is selected by the user and TIM values corresponding to the approach option are set. 5.2 Mode Definitions and Modeling Parameters: Worksheet 5.1 Worksheet 5.1 is where the user selects the options that determine model operating modes, which in turn define the set of operation modes that will be included in the inventory analysis. There are two required actions for this worksheet: (1) select the inventory option for FW aircraft operating modes and (2) select the inventory option for RC. There are two optional actions for this worksheet where the user supplies additional data if the facility-specific approach option is selected for either FW aircraft or RC. Table 14 summarizes the options for defining FW aircraft operating modes; this table also appears in Worksheet 5.1. The preferred approach is that facility-specific data are collected and entered. In the absence of this, the user must specify the use of one of three screening approaches: current FAA/EPA defaults, FAA/EPA defaults with run-up included, or ACRP 02-34 data. The FAA/EPA default option includes four modes: taxi/idle, takeoff, climb-out, and approach. Table 15 summarizes the options for defining RC operating modes; this table also appears in Worksheet 5.1. The preferred approach is that facility-specific data are collected and entered. In the absence of this, the user must specify one of two screening approaches: use of current FAA/ EPA defaults or use of FAA/EPA defaults with run-up included. The FAA/EPA default option includes three modes: idle, climb-out, and approach. Tables 14 and 15 include the options associated with the standard FAA/EPA default, both with and without the completion of the magneto test (as a pre-flight-check procedure). The magneto test is a required procedure before each leg of a flight during which the engine has been turned off. Whereas the 2011 NEI methods exclude the run-up mode, this EIAT also includes a second approach option of FAA/EPA default with the run-up magneto test included. For FW aircraft, the inclusion of the run-up procedure adds about 5 percent to the lead inventory C H A P T E R 5 Operation Mode Data

24 Best Practices Guidebook for Preparing Lead Emission Inventories from Piston-Powered Aircraft with the Emission Inventory Analysis Tool under FAA/EPA default conditions. It is recommended that the run-up procedure be included in all inventory development, even when using FAA/EPA default operating mode assumptions. Specific parameters are used with the enhanced methodology to define the extent to which continuous operations are observed at the facility, which are implemented based on the approach option selected. As described in Section 2.2.2 of this guidebook, there are two types of con- tinuous operations handled in this enhanced methodology—“taxi-back” and “touch-and-go” operations: 1. The taxi-back operation is an aircraft landing and then taxiing back to a runway and taking off again without turning the engine off. A taxi-back counts as two operations: a landing and a takeoff. 2. A touch-and-go is a landing with a brief ground roll followed by an immediate takeoff, all occurring on a single runway. The touch-and-go operation counts as two operations—a landing and a takeoff—which is important to defining the touch-and-go rate of frequency (defined as a fraction of total operations). These apply only to FW aircraft operations. Continuous operations are typical of pilot training procedures and were observed frequently during airport studies conducted during ACRP 02-34. The FAA/EPA default for operation modes assumes that every two operations consist of a stand- alone landing and a standalone takeoff. These two operations combined are termed a “landing- takeoff (LTO) cycle,” and agency inventory methods are derived and reported on a per-LTO basis with the underlying presumption that every two operations consists of a standalone takeoff and a standalone landing. Inventory Option Title Description Screen 1 FAA/EPA Default Application of the four EDMS operation modes (taxi/idle, takeoff, climb-out, approach) assuming every two operations consist of a standalone landing and a standalone takeoff. Screen 2 FAA/EPA Default with Run- up Included EPA/FAA default (Screen 1) updated to include performance of a magneto run-up prior to takeoff by every piston-powered FW aircraft. Screen 3 ACRP 02-34 Data Application of operation modes defined by the three airport-average results from ACRP 02-34. Incorporates facility-specific data to account for continuous operations and observed run-up frequencies. Facility Specific Facility Data, User Supplied User-supplied input for facility. Table 14. Inventory options for defining FW aircraft operating modes. Inventory Option Title Description Screen 1 FAA/EPA Default Standard EDMS three-mode approach of idle, climb- out, and approach. Screen 2 FAA/EPA Default withRun-up Included EPA/FAA default of three modes (Screen 1) updated to include performance of a magneto run-up prior to departure by every piston-powered RC. Facility Specific Facility Data, User Supplied User-supplied input for facility. Table 15. Inventory options for defining RC operating modes.

Operation Mode Data 25 For FW aircraft, the approach option selected in Table 14 then corresponds to setting the values for the following four parameters within the enhanced methodology: • Touch-and-go rate—the fraction of facility operations that are touch-and-go; • Taxi-back rate—the fraction of FW landings that then taxi-back and takeoff again without turning off the engine; • Run-up frequency (for a taxi-back takeoff)—the fraction of occurrence of a taxi-back opera- tion performing a run-up test prior to takeoff; and • Run-up frequency (for a standalone takeoff)—the fraction of occurrence of a standalone takeoff (one that begins with the engine off and is not a continuous operation) performing a run-up test prior to takeoff. Accordingly, the values assigned for each of the three FW screening inventory options are presented in Table 16. If continuous operations are not expected to be significant, then the FAA/EPA default with run-up included is the recommended approach option. If continuous operations do occur at the facility, then the recommended approach is for the user to supply the parameter values based on local observation. Because the proportion of continuous operations will be facility specific, the ACRP 02-34 values are not recommended for inventory development, but are included here for informational purposes. It is expected that the touch-and-go rate and the taxi-back rate would be based on local obser- vations. Collecting a representative sample is critical, with the following considerations: 1. In collecting these data, the proportion of continuous activity can vary by time of day, day of week, and season (as the commercial instruction proportion of activity may vary temporally). 2. In collecting these data at facilities with more than one runway, the proportion of continuous activities may vary by runway. It was observed in ACRP 02-34 that facility traffic management often favored certain runways for continuous operations. If locally observed run-up frequency rates are not collected, it is reasonable to assume no run- ups are performed for taxi-back operations and that all standalone takeoffs include a magneto- test run-up. Finally, it should be understood that capturing continuous operations in the inventory method is a critical element because the default FAA/EPA assumption that every two operations consists Parameter Description Screening Inventory Option FAA/EPA Default FAA/EPA Default with Run-up Included ACRP 02-34 Data Touch-and-Go Rate Fraction of total FW operations that are from touch-and-go operations 0 0 0.180 Taxi-Back Rate Fraction of FW landings that taxied back to the runway and took off again 0 0 0.219 Run-up Frequency, Taxi-Back Takeoff Fraction of taxi-back operations that completed a magneto-test run-up procedure before takeoff (assessed for piston-powered equipment only) 0 0 0.026 Run-up Frequency, Standalone Takeoff Magneto-test run-up frequency per standalone takeoff (assessed for piston-powered equipment only) 0 1 0.877 Table 16. Operating mode defining parameters by screening inventory option for FW aircraft.

26 Best Practices Guidebook for Preparing Lead Emission Inventories from Piston-Powered Aircraft with the Emission Inventory Analysis Tool of a standalone takeoff and a standalone landing significantly overestimates fuel consumption for both taxi-back and touch-and-go operations. Using the average statistics from ACRP 02-34, a FW aircraft that completes a standalone landing and takeoff (i.e., two operations) spends 15.3 minutes on the ground with the engine running and consumes 5.1 pounds of aviation gasoline (ground operation modes only). In comparison, the time and fuel consumed on the ground for a taxi-back (i.e., two operations) are 3.7 minutes and 1.5 pounds, respectively; and for a touch- and-go (i.e., two operations), 0.3 minute and 0.3 pound, respectively. 5.3 Time-in-Mode Data: Worksheet 5.2 Worksheet 5.2 is where the user selects the inventory options and values for TIM data. There is one required action for this worksheet, which is the selection of the option for defining TIM in the inventory analysis. There is one optional action for this worksheet where the user supplies additional data if the facility-specific inventory option is selected. Table 17 summarizes the three options for defining TIM; this table also appears in Work- sheet 5.2. The preferred approach is that facility-specific data are collected and entered. In the absence of this, the user must specify use of one of two screening approaches: current FAA/EPA defaults or ACRP 02-34 data. Note that the FAA/EPA default option is not valid for use in mod- eling scenarios that include continuous operations (as defined by the user in Worksheet 5.1), as FAA/EPA default TIM values do not exist for touch-and-go and taxi-back operations. It is the user’s responsibility to ensure consistent selection of options between Worksheets 5.1 and 5.2. If continuous operations are selected as part of the inventory modeling on Worksheet 5.1, then the user must apply the ACRP 02-34 data or input facility-specific results for the TIM assump- tion shown in Table 17. Table 18 presents TIM data for the two screening inventory options. The FAA/EPA defaults are applicable to the current 2011 NEI approach, but the 2011 NEI documentation does not report TIM assumptions other than to cite the 1992 EI guidance (U.S. EPA 2013b). The 1992 EI guidance should be consulted, if needed, to better understand the background behind the values (U.S. EPA 1992). For the aloft operation modes (i.e., climb-out and approach), the FAA/EPA defaults assume a maximum altitude of 3,000 feet above ground level (AGL). Comparatively, the ACRP 02-34 values for climb-out and approach are capped at the “traffic pattern altitude” or TPA of each facility. The maximum vertical extent of the aloft modes of operation is discussed further as part of the remaining discussion of how to develop and apply TIM values. Inventory Option Title Description Screen 1 FAA/EPA Default EPA default TIM rates for piston-powered FW aircraft.a Screen 2 ACRP 02-34 Data Average TIM rates observed for three airports (FW aircraft only); RC values based on Swiss FOCA study (Switzerland Federal Office of Civil Association 2009). Facility Specific Facility Data, User Supplied User-supplied input for facility. a The FAA/EPA default option should not be used if there are continuous operations at the facility. Table 17. Inventory options defining time-in-mode assumptions.

Operation Mode Data 27 In order to correctly collect and apply the TIM values to the inventory analysis, several key background elements need to be considered as relevant context. Five topics are covered in this remaining discussion: operating mode definitions, differences with the 1992 EPA guidance, ACRP 02-34 TIM data, maximum altitude assumptions, and other considerations for facility- specific data collection. 5.3.1 Operating Mode Definitions for Time in Mode The modes of operation to which the TIM data apply must be clearly defined, as shown in Table 18. It is recommended in applying the enhanced methodology that the following specific operating mode definitions, corresponding to each TIM value, be determined. • Idle/taxi time (takeoff)—aircraft time spent from engine-on to the initiation of takeoff, except for the time of the magneto-test run-up. • Run-up—time needed strictly to perform the high RPM magneto test (because the fuel con- sumption rate assignment to this mode is reflective only of the magneto test). During the ACRP 02-34 field studies, the average aircraft spent about 5 minutes in the run-up area, of which about 1 minute was spent performing the magneto test. The remaining time in the run-up area (about 4 minutes) related to other preflight checks (or for waiting on runway clearance) is included as part of the taxi/idle time (takeoff). • Takeoff—time from the initial runway ground roll to the wheels leaving the ground. • Climb-out—time aloft from 0 feet AGL (i.e., airport level) to the maximum altitude tracked. • Approach—time aloft (on approach) from the maximum altitude tracked down to the wheels-down event at the airport. • Idle/taxi (landing)—time from the landing ground roll, including all subsequent taxiing and idling time, until the engine is turned off. • Idle/taxi (taxi-back)—time from the landing ground roll, including all subsequent taxiing and idling time, until reaching the head of the runway for takeoff. • Ground roll (touch-and-go)—time on the ground for a touch-and-go operation. Aircraft Type Operation Mode Screening Inventory Option FAA/EPA Default (minutes) ACRP 02-34 Data (minutes) Fixed-Wing Aircraft Idle/Taxi (Takeoff) 12.00 9.89 Run-up 0.96 0.96 Takeoff 0.30 0.33 Climb-out 5.00 1.76 Approach 6.00 2.19 Idle/Taxi (Landing) 4.00 4.08 Idle/Taxi (Taxi-Back) N/A 3.32 Ground Roll (Touch & Go) N/A 0.28 Rotorcraft Idle/Taxi (Departure) 3.50 4.00 Run-up 0.96 0.96 Climb-out 6.50 0.92 Approach 6.50 0.67 Idle/Taxi (Arrival) 3.50 4.00 Table 18. Time-in-mode values by screening inventory option.

28 Best Practices Guidebook for Preparing Lead Emission Inventories from Piston-Powered Aircraft with the Emission Inventory Analysis Tool 5.3.2 Differences Between Guidebook Modes and EPA Guidance It should be noted that three of the operating mode definitions described above differ from the 1992 EI guidance, as follows: 1. There is a difference in the point at which the transition between takeoff and climb-out assumption is applied. There is an error in the 1992 EI guidance as it describes the takeoff mode, which it describes as including the climb-out to 500 feet AGL (U.S. EPA 1992). This is an error because it is physically impossible for an FW piston aircraft to include both a takeoff and a 500-foot climb-out in 0.3 minute, followed by a 5-minute period to complete the remaining 2,500 climb-out—the 500-foot climb-out can be approximately scaled and would take 1 minute. The 1992 EI guidance transition elevation of 500 feet between takeoff and climb-out may be accurate for commercial jet engines, but it is not for FW piston aircraft takeoff. A review of piston aircraft operations manuals, which provide fuel use and rate of climb data, was completed as part of ACRP 02-34 and the default EPA TIM values for takeoff and climb-out are typical for a single-engine, carbureted piston aircraft assuming a transition point at the wheels-up moment. This transition definition is also consistent with how the terminology is applied in aircraft manuals (for the purposes of fuel management strategies). The transition from takeoff to climb-out at the wheels-up moment is recommended for piston aircraft inventories, and that is the transition assumption applied in the enhanced methodology. 2. The time during which the aircraft is completing the landing ground roll is assigned to differ- ent modes. Under the FAA/EPA default, the landing ground-roll time is part of the approach mode; in the enhanced methodology, the landing ground-roll time is part of the taxi/idle (landing) mode. This is a small correction, but it is one that is made because the engine is idling during the landing roll. The enhanced method thereby assigns the correct fuel con- sumption rate to the landing roll. 3. FAA/EPA default assumptions do not include the run-up mode; the run-up data from ACRP 02-34 were assumed in Table 18 under the FAA/EPA option as a reasonable extra- polation. This was done so that the FAA/EPA default case with run-up could be included as a modeling option (see Worksheet 5.1). The run-up mode TIM is not highly variable (the procedures are standardized and specific). It should be noted that the FAA/EPA default value for run-up is strictly a construct for the enhanced methodology and is not an agency- assumed value. 5.3.3 ACRP 02-34 Time-in-Mode Data It is noteworthy to document additional assumptions behind the ACRP 02-34 (Heiken et al. 2014) TIM values shown in Table 18. 1. The ground-level modes of takeoff, taxi/idle (takeoff), taxi/idle (landing), taxi/idle (taxi- back), touch-and-go ground roll, and magneto-test run-up for FW aircraft were determined by on-site data collection. 2. The RC TIM values (except run-up) were taken from the Swiss FOCA study of helicopters (Switzerland Federal Office of Civil Aviation 2009). 3. The run-up TIM was measured only for FW aircraft. The same value of 0.96 minute was assumed to apply to RC. 4. The aloft modes of climb-out and approach were capped at the TPA. The TPA varies by air- port and equipment. RC was 500 feet AGL at all three airports; FW piston aircraft varied from 1,000 to 1,500 feet AGL. FW aircraft climb-out and approach TIM values used in ACRP 02-34 were FAA/EPA defaults (for 3,000 feet AGL) scaled to the TPA.

Operation Mode Data 29 5.3.4 Maximum Altitude of Aloft Modes It is important to understand the different maximum altitude assumptions for the aloft modes of climb-out and approach that impact the TIM values for these modes. FAA/EPA defaults include the assumption of 3,000 feet AGL maximum altitude. The FAA/ EPA default allows for scaling the maximum altitude based on mixing height. Mixing height is the height of the ground-level air layer in which pollutants will be dispersed and is temporally variable. The 1992 EI guidance includes methods for scaling the TIM aloft (for climb-out and approach) based on the average mixing height. This is pertinent to air pollution studies because the emissions occurring at or below the mixing height will become dispersed, impacting ground- level pollutant concentrations. Incorporating mixing height into annual inventory development is problematic because mixing height is temporally variable, and EPA guidance does not specify how this variable can be treated on an annual timescale. For ACRP 02-34, the TPA of each airport was used as the maximum altitude for the aloft modes of climb-out and approach. The use of a pattern at airfields is for air safety management (i.e., consistent flight patterns) and is specific to the type of aircraft (e.g., rotorcraft, single-engine piston, etc.). The TPA defines the altitude for initial climb-out and final approach at the airport. Significant local operations may be flying a circuit at the TPA, such as touch-and-go operations. Although use of the TPA is recommended to achieve the most accurate result, use of 3,000 feet AGL may be required for inventories being submitted to EPA. For ACRP 02-34, climb-out and approach TIM for FW aircraft were estimated by scaling the FAA/EPA default TIM by the ratio of the airport-specific TPA to the FAA/EPA default assump- tion of 3,000 feet AGL maximum altitude, as follows: TIM min TIM min TPA feet AGL 3,000 feet AGL airport FAA EPA dafault airport( ) ( ) ( )= × In the above equation, the FAA/EPA default TIM values are 5.0 minutes for climb-out and 6.0 minutes for approach. Airport-specific TPA can be obtained from sources such as air- port directories or the Aircraft Owners and Pilots Association database (http://www.aopa.org/ airports/). 5.3.5 Considerations for Facility-Specific Time-in-Mode Data Collection Local data collection of TIM should consider the following elements: 1. Data collection can focus on the modes that are most likely to be locally variable, and thereby a combination of local data and screening values could be implemented by the user. More- over, it is not readily possible to get TIM of aloft modes from on-the-ground observations. The idle/taxi modes are the ones most likely to be locally variable; run-up (magneto test) is the least likely to vary locally. Takeoff times can vary with the altitude of the facility. 2. TIM of idle/taxi modes will have temporal and spatial variability, and effort needs to be applied to get a representative sample. Congestion and use are temporally variable; traffic pat- terns at facilities are not symmetrical, and runway assignments are based on meteorological conditions. 3. A typical ground speed of 20 mph for taxiing was observed, which can be used to approximate taxiing times (if the distance is known) or validate taxiing time measurements [as part of quality assurance/quality control (QA/QC)].