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Gate Demand Model Estimating gate demand requires an understanding of the current capacity and future require- ments based on forecast activity. There are two basic ways to determine the number of gates required: by developing and using a design day flight schedule (DDFS), or by using current and forecast enplanements and departures to estimate the future trends. If a DDFS has been developed for a forecast year (or annual activity level), it can allow a rela- tively detailed study of gate demand. Typically a DDFS is developed when airside simulation modeling is done for an airport. In many cases, a DDFS is produced as separate lists of flight arrivals and departures (records) in a spreadsheet format. To use the DDFS to determine gate demand, arrivals and departures must be matched up. This matched schedule can then be analyzed by various proprietary models to determine the number of gates required during the course of the day. The output is typically a Gantt-type gate chart, and/or a histogram of gate demand by 5- or 10-minute periods. While this type of analysis can be very detailed, it is dependent on the assumptions used to add flights by specific airlines or aircraft types over time. Methodologies without Design Day Flight Schedules When a DDFS is not available, two other approaches can be used: enplaned passengers by gate or departures per gate. These approaches also allow the terminal planner to easily do "what if?" sensitivity checks on basic assumptions, including those which may underlie a DDFS. The Gate Demand model is set up like the other Spreadsheet Models with links to the Table of Contents and the User's Guide, and uses color-coded cells for consistency (see Figure 17). The two methods of determining gate demand without a DDFS are used in the model as outlined in Section V.3.9 of the Guidebook. Annual Enplaned Passengers per Gate Approach The first approach, as shown in Figure 18, uses the current ratio of annual enplaned passengers per gate, adjusted for forecast changes in fleet mix and annual load factors. This methodology assumes that the pattern of gate utilization will remain relatively stable over the forecast period. The changes in passengers per gate would be due to changes in enplanements per departure (due to fleet seating capacity and/or passenger load factors), as opposed to increasing (or decreasing) numbers of departures per gate. The basis for the existing factor is the number of gates in use. This number may be less than the number of gates available at an airport. In rare cases of over-crowded terminals, aircraft may 17
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18 Airport Passenger Terminal Planning and Design Figure 17. Gate Demand model. be double parked at existing gates, so it is important to determine the true demand for active air- craft parking. From the existing passenger activity and annual departures, the current ratios of annual passengers per gate and enplanements per departure are calculated. Similar calculations can be based on total annual passengers, airline operations, or a combination of these, depending on how the airport keeps its statistics and develops its forecasts. Forecasts for annual enplaned passengers and aircraft departures (or total passengers and aircraft operations) are usually forecast separately. Annual departures are typically forecast based on assumptions for fleet size and load factors that are applied to the passenger forecasts. In the model example in Figure 18, the ratio of enplaned passengers per gate for each forecast year is calculated by multiplying the current (2008 in this example) factor by the percentage increase in enplaned passengers per aircraft departure. For example, enplaned passengers per departure increases from 54 in 2008 (actual) to 56 in 2010 (forecast), thus the factor would increase from 94,400 enplaned passengers per gate (2008 data when 36 gates were in use) to 97,500 for 2010, and 102,600 enplaned passengers per gate by the end of the forecast period without any further increase in the number of daily departures per gate. Future gate requirements are then estimated by dividing annual forecast passengers by the estimated passengers per gate factor for that forecast period. For example, in 2010, 4,429,000 enplanements divided by 97,500 enplanements per gate results in a demand for 45 gates. This approach results in a forecast demand for 69 gates by the end of the forecast period. Departures per Gate Approach The first methodology has as an underlying assumption that the future pattern of air service will be stable and will resemble existing conditions. While this may be true at many airports and for some airlines at a given airport, it is often likely that gate utilization will change to some extent for other airlines. With a forecast reduction in mainline jets, for example, additional flights by Figure 18. Example of enplaned passengers per gate approach to determine gate demand.
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Gate Demand Model 19 Figure 19. Example of departures per gate approach. regional aircraft may be scheduled as demand grows. Similarly, airlines may add flights to their hubs from spoke cities. This typically results in higher average gate utilization. However, if an airport attracts service by new entrant airlines, it is often likely that these carriers would initially follow scheduling patterns similar to existing carriers. This could result, for example, in a demand for more gates during the morning departure peak, and a reduction in average daily gate utilization. For the departures per gate approach from the model (example shown in Figure 19), the ratio of annual departures per gate for each forecast year is calculated by multiplying the current (2008) factor by the percentage change in assumed daily departures per gate. In this example, it was assumed that average daily gate utilization would increase from 5.0 departures per gate in 2008, to 5.2 departures per gate by 2010, and gradually increase to 6.5 departures per gate by 2025. Thus, the annual gate utilization factor would increase from 1,750 annual departures per gate (2008) to 2,290 by 2025. Future gate requirements are estimated by dividing annual forecast departures by the esti- mated departures per gate factor for that forecast period. For example, in 2010, 79,500 depar- tures divided by 1,820 departures per gate results in a demand for 44 gates. This approach results in a forecast demand for only 53 gates by the end of the forecast period. For most airports that assume increasing gate utilization, the departures per gate approach will result in a demand for fewer gates than the annual enplaned passengers per gate approach. The model also provides an average of the two methods. The planner then needs to examine the range of values provided and determine the most reasonable and likely outcome. See Figure 20. Once the gate requirements have been determined, the other ground requirements can be further quantified by relating the future DDFS to available gates. If the flight schedule suggests more aircraft than available gates or for early morning high turnover gates due to airline schedules, then additional aircraft parking spots will be required. Average of Both Methods PassengersDepartures Year per Gate per Gate GATES 2010 45 44 45 2015 52 47 50 2020 61 50 56 2025 69 53 61 Figure 20. Comparison of gate analysis approaches.