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20 Airport Passenger Terminal Planning and Design Remain Overnight Aircraft Parking At many airports, the pattern of airline service results in more aircraft being on the ground overnight than number of active gates. This situation is more pronounced at "spoke airports" where an airline may have, for example, hourly service to its hub for the first few hours of the day. Because it may take until mid-morning before aircraft begin to arrive, a single gate may accommodate two to three aircraft departures for which the aircraft must be parked overnight. These remain overnight (RON) aircraft are usually parked remotely or, in some cases, double parked on contact gates where the apron geometry allows. If RON aircraft are parked remotely, the aircraft are typically towed to a contact gate for departure, and towed off a contact gate to the RON parking area after the evening arrival. Estimating the number of RON positions should take into account the airport's air service pattern, the forecasts for cities to be served in the future, whether these are hubs or direct desti- nation flights, and the relative utilization of gates. Gate Equivalents Airport comparisons are also frequently made on the basis of passengers per gate or terminal area per gate, but these comparisons lack a consistent definition of the term "gate." To standardize the definition of "gate" when evaluating aircraft utilization and requirements, two metrics have been developed: narrowbody equivalent gate (NBEG) and equivalent aircraft (EQA). The model includes a Gate Equivalencies Table (see Figure 21) to serve as a gate inventory dur- ing the gate demand process, showing available leased or forecast gates. This inventory is useful to other model segments where the EQA or NBEG values may be needed as factors that help deter- mine other space requirements. The user needs to input the number of gates for each design group, and the total and equivalent values will be calculated. The calculated values are the cumulative sum product of the gate share and the index values. Narrowbody Equivalent Gate This metric is used to normalize the apron frontage demand and capacity to that of a typical narrowbody aircraft gate. The amount of space each aircraft requires is based on the maximum wingspan of aircraft in its respective aircraft group. FAA Airplane Design Groups used to define runway/taxiway dimensional criteria have been used to classify the aircraft as shown in Figure 22. Group IIIa has been added to more accurately reflect the B757, which has a wider wingspan than Group III but is substantially narrower than a typical Group IV aircraft. A wingspan com- parison is illustrated in Figure 23. Figure 21. Computing EQA and NBEG gate equivalents.
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Gate Demand Model 21 FAA Airplane Maximum Typical NBEG Design Group Wingspan Aircraft Index Feet Meters I. Small Regional 49 15 Metro 0.4 II. Medium Regional 79 24 SF340/CRJ 0.7 III. Narrowbody/Lrg. Regional 118 36 A320/B737/DHC8/E175 1.0 IIIa. B757(winglets) 135 41 B757 1.1 IV. Widebody 171 52 B767/MD11 1.4 V. Jumbo 214 65 B747,777,787/A330,340 1.8 VI. A380 262 80 A380/B747-8 2.2 Source: Hirsh Associates Figure 22. NBEG index. Feet Meters Code A Code A 15 24 CR J-2 00 0 -2 0 CRJ 36 41 00 00 7 -2 7 -2 B75 B75 52 00 00 7-3 7-3 B76 B76 65 0 -3 0 300 77 77- B7 B7 80 GP GP 00 00 0-8 0-8 A38 A38 Source: Hirsh Associates and Landrum & Brown Figure 23. Wingspan comparison.
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22 Airport Passenger Terminal Planning and Design In developing terminal facilities requirements, the apron frontage of the terminal, as expressed in NBEG, is a good determinant for some facilities, such as secure circulation. Terminal concepts can also be more easily compared by normalizing different gate mixes. Equivalent Aircraft The concept of EQA is similar to that of NBEG, i.e., a way to look at the capacity of a gate. EQA, however, normalizes each gate based on the seating capacity of the aircraft that can be accommo- dated. The EQA measure was originally developed in the early to mid-1970s as a technique for sizing terminal facilities. The EQA measure was originally included in The Apron & Terminal Building Planning Manual, for U.S.DOT, FAA, by The Ralph M. Parsons Company, July 1975. When the Manual was devel- oped, the majority of jet aircraft had 80 to 110 seats, thus the EQA measure centered on the 80- to 110-seat range with an EQA of 1.0. Smaller aircraft had an EQA of 0.6, and larger aircraft fell into seating ranges with the center of the range determining the EQA of that range. One hundred seats was equal to 1.0 EQA, aircraft in the 211- to 280-seat range had an EQA of 2.4, etc. In considering the modern fleet mix of regional and jet aircraft, and in order to have some rela- tionship with the physical parameters associated with the NBEG, the basis of EQA has been revised from the 1970s definition. The current EQA is also a Group III narrowbody jet. Most of the larger aircraft in this class typically have 140 to 150 seats. This establishes a basis of 1.0 EQA = 145 seats. As with the concept of NBEG, smaller aircraft may use a gate, but the EQA capacity is based on the largest aircraft and seating configuration typically in use. While most terminal facility requirements are a function of design hour passenger volumes, some airline facilities are more closely related to the capacity of the aircraft. For example, while the total number of baggage carts required for a flight are a function of design hour passengers (and their bags), the number of carts staged at any one time are generally based on the size of the aircraft. Thus, the EQA capacity of the terminal can represent a better indicator of demand for these facilities. The number of seats in each design group, as shown in Figure 24, can vary considerably from the basic definitions. For example, larger "regional jets" in Group III can be in the 100- to 110- seat range, while a Group III A321 narrowbody can have over 180 seats. Similarly, as fuel econ- omy and range becomes more important, most new widebody aircraft are being designed with wider Group V wingspans than the Group IV aircraft they replace, but may have less than 250 seats. For a given airport, it may be appropriate to modify the EQA metrics to better match the fleet mix expected when using EQA to determine some terminal facilities. FAA Airplane Typical Typical EQA Design Group Seats Aircraft Index I. Small Regional 25 Metro 0.2 II. Medium Regional 50 SF340/CRJ 0.4 III. Large Regional 75 DHC8/E175 0.5 III. Narrowbody 145 A320/B737/MD80 1.0 IIIa. B757 (winglets) 185 B757 1.3 IV. Widebody 280 B767/MD11 1.9 V. Jumbo 400 B747,777,787/A330,340 2.8 VI. A380 525 A380/B747-8 3.6 Source: The Apron & Terminal Building Planning Manual, for U.S. Department of Transportation FAA, by The Ralph M. Parsons Company, July 1975. Figure 24. EQA index.