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36 9.1 Implications The primary implications and recommendations arising from this guidance are summarized below. 1. Piston aircraft lead inventory development needs to incorporate the emissions occurring during flight-check run-up procedures (i.e., the magneto test). High lead concentrations were observed in the ACRP 02-34 air quality modeling, specifically in the run-up areas. The guidance provides a method and supporting data such that this inventory element can be addressed with no addi- tional user input. 2. Currently, there is no reliable data source for airport-level piston operations, whereas total airport operations are widely available. The piston-engine share of aircraft activity is poorly quantified by publicly available data and current methods. It is recommended that airport collection of activity-based aircraft tail numbers be completed for purposes of calculating the piston-engine share of aircraft operations and improving the accuracy of fleet-average aviation gasoline consumption rates (based on the locally observed fleet). The guidance is designed to incorporate these piston fleet data, if collected, into the inventory analysis method. 3. It is recommended that airport sampling of aviation gasoline be completed to determine typical, local lead content of fuel dispensed. Current inventory methods model lead content as the maximum allowable, whereas the limited data available show that there is considerable variation in lead content from airport-collected gasoline samples. This guidance allows for modeling with airport-specific gasoline lead content. 4. The standard modes of operation included in existing inventory methods are not adequate to address commercial flight school activities, which are common at many general aviation airports. For the three airports of study in ACRP 02-34, âcontinuousâ operations (i.e., those associated with training procedures) accounted for about 40 percent of all piston operations. The emissions characteristics of continuous modes are distinct and not modeled adequately by current inventory methods. The guidance can handle these modes of operation; however, the frequency of occurrence will be airport specific and should be based on locally collected data. 5. The amount of time spent in each mode (TIM) is locally variable and depends on the airport configuration and the individual fleet of piston-engine aircraft. Local collection of TIM data is a means to improve the airport-specific inventory, and the guidance facilitates the incor- poration of TIM data into the inventory method. 6. If airport-specific fuel consumption rates are not calculated from a local aircraft fleet assess- ment (i.e., the primary recommendation), then the secondary recommendation is that average fuel consumption rates from ACRP 02-34 be used in place of FAA/EPA defaults. The under- lying data, fuel rate assignment method, and activity-weighting assumptions of the ACRP 02-34 averages are all significant improvements over the methods used to create the FAA/EPA default fuel consumption rates. C H A P T E R 9 Implications and Limitations
Implications and Limitations 37 9.2 Limitations The following list discusses some noteworthy limitations of this guidance methodology: 1. Airport extrapolationâGeneral aviation airports are not homogeneousâthere is consider- able variation in the uses and characteristics of these facilities. Caution should be applied in extrapolating results across facilities. FAA recently completed an assessment and classifica- tion of all general aviation airports nationally, which provides a benchmark for grouping facilities by common criteria. Of the three facilities studied in ACRP 02-34, two fell under the ânationalâ and one under the âregionalâ classification. In extrapolating the results of ACRP 02-34 to other airports, it is advisable to take these categorizations into consideration (FAA 2012, FAA 2014). 2. Other modes of operationâAdditional modes may be possible locally beyond those included in this enhanced methodology (e.g., military training procedures may differ from the civilian practices observed). Along those lines, âmaintenance run-upsâ are separate run-up procedures that are not coupled with a takeoff event and are often completed in conjunction with engine maintenance for specific testing purposes. Airports have guidelines where maintenance run- ups are to occur. The field studies completed as part of ACRP 02-34 did not comprehensively evaluate the frequency/duration of maintenance run-ups, but maintenance run-ups were observed. This may be an important local source of lead emissions not accounted for in the enhanced methodology. Note that fuel consumption rates of maintenance run-ups would not be the same as documented herein for the magneto-test procedure (fuel consumption rates would be less). 3. The EIAT is limited to a single user-supplied, detailed FW piston aircraft inventory (input through Worksheet 4.3). It is possible that detailed, separate aircraft fleet data can be obtained for subsets of the piston fleet at a given airport. Examples include (1) differentiating âgeneral aviationâ from âair taxiâ piston fleets and (2) differentiating piston aircraft by mode (con- tinuously operating modes versus standalone modes). ACRP 02-34 did determine that the piston share and the type of craft used in continuous operations were distinct. This level of detail could be handled in the EIAT by creating separate spreadsheet versions for each distinct piston fleet. The final airport inventory would be the sum of the individual EIAT models.
