Apron Planning and Design Guidebook (2013)

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11 Understanding the apron environment is critical to responsive and effective planning and design. This chapter summarizes the different types of aprons, activities (aircraft, passengers, vehicles) that occur on aprons and in the surrounding area, and equipment used to support those activities. This chapter is intended to provide a comprehensive understanding of operations and activities that occur in and around aprons and the factors and influences that should be considered when planning and designing apron facilities. However, it is important to note that airports, by their inherently unique natures, can present diverse apron environments and it is the responsibility of the apron planner/designer to understand the environment of the specific airport apron area. Apron Types Several different types of aprons have been developed at airports. The following sections describe the physical apron facilities and identify the activities that occur on each type of apron. Terminal Area Aprons The terminal area apron is the interface between the terminal building and the airfield and is one of the most congested and active areas at a commercial service airport. Passengers are enplaned on and deplaned from aircraft while GSE used for aircraft servicing, including catering, fueling, deicing, and loading and unloading of baggage and cargo, operates in close proximity. These activities, coupled with aircraft taxiing to and from the gates, drive the need for proper apron planning to enhance safety for ramp workers, aircraft operations, ground vehicle operations, and, in some cases, passengers while maximizing the use of available apron area. Terminal area aprons are identified as any pavement used for the enplaning and deplaning of pas- sengers from an aircraft. There are generally two categories of terminal aircraft parking positions— close-in and remote. Close-in gates consist of contact gates and noncontact gates. Contact gates are those located directly adjacent to a terminal building and passenger loading bridges are used to connect the aircraft to the building. Noncontact gates also have aircraft parking positions suf- ficiently close to the terminal building to facilitate the use of air stairs (stairs built into the aircraft), ramps, or mobile stairs to enplane and deplane passengers. These are referred to as noncontact gates because there is no direct link between the aircraft and the building. Passengers follow designated walkways to doorways into a terminal or concourse building. Ground loading with noncontact gates is common for regional jet or propeller aircraft serving airports with limited or no passenger loading bridges. Ground loading can also be used for narrowbody or widebody aircraft. Figure 3-1 illustrates several terminal area aprons at a variety of airports. As depicted in the exhibit, terminal area aprons can vary substantially in their configuration, size, location relative C H A P T E R 3 Understanding the Apron Environment

12 Apron Planning and Design Guidebook to airfield elements, availability of push-back area, proximity to vehicle service roads, accom- modation of ground vehicle storage and staging, and apron/gate equipment. With the use of remote hardstands, passengers are enplaned or deplaned at a location sufficiently far from the terminal that a bus or other vehicle is used for the safe transport of passengers to and from the terminal. Remote hardstands are also served by air stairs, ramps, or mobile stairs. While passengers are being enplaned and deplaned, several aircraft servicing activities occur on the terminal area aprons: • Fueling: Aircraft fueling entails filling the aircraft fuel tanks with a typically predetermined amount of fuel to meet the requirements of the scheduled flight. Depending on the airport, aircraft fueling is accomplished with fueling trucks or through a hydrant fueling system. Figure 3-1. Terminal area aprons. Source: Google Earth Pro.

Understanding the Apron Environment 13 • Baggage handling: Baggage is typically transferred to and from the aircraft during the servicing of aircraft after arrival and prior to departure. Outbound (departing) baggage is collected, screened, and sorted in the terminal building before being loaded onto the aircraft. Inbound (arriving) baggage is unloaded and either transported to baggage claim units in the terminal or transferred to other flights. Baggage on narrowbody and smaller aircraft is typically bulk loaded, using belt loaders that move bags on a conveyor, into the lower deck of the aircraft. Alternatively, baggage on smaller aircraft may be handled individually by personnel from a manual baggage cart and placed directly into the aircraft. Widebody aircraft bundle baggage into containers, also known as unit load devices, to reduce the time to load and unload baggage onto the aircraft. • Cargo handling: Inbound belly cargo, defined as cargo placed in the belly compartment of the aircraft in addition to passenger baggage, is unloaded and transported to cargo facilities or other aircraft, while outbound belly cargo is prepared and loaded onto the aircraft prior to departure. Similar to baggage handling, cargo on narrowbody and smaller aircraft is loaded individually while cargo on widebody aircraft is containerized. • Ground power: Ground power is required for operation of the aircraft’s electrical equipment while the aircraft is parked and the aircraft’s auxiliary power unit (APU) is shut down. • Preconditioned air: Preconditioned air systems are required to heat/cool an aircraft while it is parked at a gate, depending on the ambient air temperature. The preconditioned air system can also be used to preheat/precool passenger loading bridges in advance of passenger use. • Lavatory servicing: After an aircraft arrives, a lavatory vehicle is used to empty lavatory waste into a tank and replenish the aircraft with a mix of water and disinfecting concentrate, often referred to as “blue water.” The lavatory waste is then emptied at the airport where it is dis- charged into a sanitary waste system. • Potable water: Potable water is provided to aircraft during servicing, typically through a hose connection on the aircraft, which transfers water from a potable water servicing vehicle or through a potable water cabinet located at each gate. • Engine air starts: When aircraft systems (such as APUs) are not available or are inoperative, some aircraft are equipped with pneumatic engine air start equipment, which can be used to start the aircraft engines once aircraft servicing is complete. Air start of the aircraft engines uses high volume air conveyed through an air discharge hose from a mobile power unit to start the aircraft engines. • Catering: Catering consists of restocking the aircraft galley with food and beverages prior to departure and hauling away any garbage. Catering occurs close to the scheduled aircraft departure time. Garbage from international arriving flights must be disposed of and destroyed properly and according to U.S. CBP and U.S. Department of Agriculture regulations and cannot be mixed with garbage from domestic flights. • Maintenance: Light mechanical checks or on-call maintenance work on aircraft is often performed on aprons. • Deicing: Aircraft are deiced to remove frost, snow, and ice contamination from critical aero- nautical surfaces prior to departure and deicing fluid is applied to prevent the accumulation of snow or slush for a period of time. If aprons are not equipped with the proper deicing fluid collection system, deicing fluid recovery vehicles or glycol recovery vehicles are used to recover deicing fluids on airport pavements. Use of these vehicles on the terminal apron may extend gate occupancy time. Airport operators typically use one of three types of agreements to lease terminal gates to airlines, which can be material to the planning and design of apron facilities. Exclusive use agree- ments grant an airline the sole right to use and occupy a gate. This typically provides the leasing airline the maximum flexibility to configure, equip, and mark the apron to best support the opera- tional needs of that user. Preferential use agreements grant an airline the primary right to use a designated gate to support its scheduled operations, but also allows operations by other airlines at

14 Apron Planning and Design Guidebook that same gate, generally subject to gate availability based on the primary airline’s schedule. There can be reduced flexibility associated with preferential use gates/apron based on the expectation that users may have different operating profiles, procedures, physical constraints, and other factors. While the primary airline may dictate the apron configuration, equipment, markings, GSE parking, and other aspects of the terminal area apron, without sole rights to the use of preferentially leased gates there may be requirements imposed by the airport operator to ensure a minimum level of flexibility in assigning other users to these gates when the primary user’s schedule allows. Common use agreements are used for gates that are under the control of an airport operator and allocated or assigned to airlines on a dynamic basis, typically for temporary or short terms. Common-use gates do not necessarily have a primary user, as the airport operator has the ability to assign the gates using what it defines to be appropriate scheduling priorities or preferences. In these instances, apron planning and design will typically follow specific standards defined by the airport operator to ensure required levels of scheduling flexibility. Specific user needs must be accommodated within the standards defined by the airport operator in these cases. Deicing Aprons As mentioned earlier, aircraft are deiced to remove frost, snow, and ice contamination from critical aeronautical surfaces prior to departure and deicing fluid is applied to prevent the accu- mulation of snow or slush for a period of time. This period of time, known as holdover time, is the estimated time that the deicing fluid prevents the formation of frozen contamination on the critical surfaces of the aircraft. Deicing occurs either at the terminal apron (either at the gate parking position or nearby), at a designated remote area, or on other aprons that are properly equipped to accommodate the activity. During deicing operations on a terminal apron, aircraft usually remain in the original parked position with GSE located away from the aircraft to allow for the maneuvering of deicing vehicles. Alternatively, aircraft are pushed away from the specific parking position, but are still adjacent to that position. Deicing is typically accomplished using deicing vehicles that have elevat- ing booms to allow personnel to apply heated deicing fluid on appropriate parts of the aircraft. The deicing vehicles are typically positioned on each side of the aircraft, either simultaneously or alternately depending on aircraft size. Deicing on the terminal apron presents challenges compared to deicing in remote areas. Deicing at the gate can have significant operational consequences, as it can extend gate occu- pancy time and introduces more vehicles to the apron/gate area. In addition, deicing fluids are slippery and potentially create added risk on the apron pavement, both to ramp personnel and to passengers during ground loading operations. These risks are typically managed through operating procedures or the vacuum collection of deicing fluids (resulting from overspray and from fluids that run off the aircraft after application) that pool on the pavement. The fluids can also enter and migrate within pavement joints and utility conduits, potentially causing damage to building environments and airfield lighting systems, and possibly contaminating clean storm water or groundwater. Additionally, deicing fluid overspray may reach the terminal building, which may require it to be cleaned more frequently. A potential benefit of gate deicing is the melting of snow resulting from deicing fluid that falls to the pavement. Remote deicing facilities (often called deicing pads) are provided at some airports, to which aircraft are routed prior to taxiing to the runway for departure. Remote facilities are typically located away from the terminal area, sometimes near the departure end of runways, to reduce the time between treatment and aircraft departure. The use of remote deicing pads reduces vehicular traffic on the terminal and cargo aprons. In addition to the terminal apron, other aprons at an airport are often designated for deicing, such as general aviation, cargo, maintenance or remain

Understanding the Apron Environment 15 overnight (RON) parking aprons. During some types of storm events, aircraft critical surfaces must be deiced (limited deicing) to ensure that the aircraft can safely taxi to these remote deicing locations. In those cases, limited deicing must occur at the terminal gates, but full deicing occurs at remote deicing pads. Figure 3-2 shows remote deicing pads located in proximity to the runway ends at Minneapolis-St. Paul International Airport. The use of deicing fluid can create a number of environmental issues and trigger compliance with specific environmental regulations. At many airports, the runoff of these fluids must be separated from ambient storm water runoff and treated or recycled, or detained and metered into the runoff at regulated (permitted) levels. Storm water collection, detention, conveyance, and treatment systems must be designed to accommodate these requirements. Many aprons where deicing activities occur incorporate pavement drains and piping to route deicing fluid runoff to lined collection/detention ponds. These ponds are used to store runoff contaminated with deic- ing fluid until it is recycled or released to a wastewater treatment facility. Deicing pads usually facilitate a more concentrated collection of deicing fluid runoff, as they tend to encompass less area than a terminal apron and, therefore, accumulate less precipitation. Similar to terminal area aprons, if deicing pads are not equipped with the proper collection system, deicing fluid recovery vehicles or glycol recovery vehicles are used to vacuum deicing fluid runoff and overspray that reaches the pavement. Use of these vehicles on aprons may extend occupancy time. At many airports, deicing fluid recycling facilities are used to process and concentrate col- lected runoff and oversprayed deicing fluids by separating the water and the deicing fluid. The distilled captured deicing fluid is then repurposed for industrial uses as industry regulations and specifications do not support the reuse of the fluids for aircraft deicing. The remaining Figure 3-2. Remote deicing pad at Minneapolis-St. Paul Inter national Airport. Source: Google Earth Pro

16 Apron Planning and Design Guidebook liquid (separated water) is typically processed at a wastewater treatment facility or metered into a receiving waterway consistent with applicable permits and regulations. Although not widely used, aircraft can also be deiced without the use of chemicals, relying instead on infrared heat sources. As shown on Figure 3-3, radiant heating units are installed within an open-ended hangar-type shelter into which aircraft taxi for deicing. These are stand-alone facilities that can be used independently or in combination with liquid anti-icing products to ensure that no icing on the aircraft occurs prior to departure. Deicing operations are usually conducted by airlines or third-party providers. The type of deicing provider is often controlled by the airport operator. The selection of a deicing provider can sometimes influence aircraft deicing operations and procedures. For example, airports with a limited number of deicing pads may benefit from use of a third-party provider because coordi- nation of access by different airlines to the pads can be challenging and inefficient. Also, assigning Figure 3-3. Infrared deicing facilities at Rhinelander/Oneida County Airport, Rhinelander, Wisconsin. Sources: Google Earth Pro (top); Rhinelander/Oneida County Airport, 2013 (bottom).

Understanding the Apron Environment 17 or dedicating deicing positions to specific airlines can result in unused deicing capacity if the dedicated positions are not available to other airlines when not in use by the primary airline. Cargo Aprons The transportation of goods throughout the United States and worldwide provides a necessary link that enables trade between companies, organizations, and people and is an economic engine for the world. One primary method for the transportation of goods, particularly perishable or time-sensitive goods, is air transportation of cargo. Many airports, ranging from large hub to general aviation airports, have infrastructure to accommodate air cargo operations. The type of cargo facilities at an airport is largely dependent on the type and frequency of cargo airline service. Cargo airline service is largely driven by factors external to the airport, such as geographic location, competing airports, the availability of other modes of cargo transport (e.g., rail), supporting transportation networks (highways and railways), and the presence of businesses and industries that drive demand for cargo services. Two categories of cargo services at airports, belly cargo and all cargo, are described here. Belly Cargo While the primary function of the passenger airlines is the transportation of passengers, most airlines use the lower aircraft deck for transporting passenger baggage and cargo. Belly cargo, defined as that transported in the belly compartments of passenger aircraft, is typically processed and sorted at cargo facilities located away from the terminal gates, but with vehicle access to landside and airside facilities. Belly cargo is transported to the terminal apron, where it is loaded onto aircraft parked at the gate(s). Depending on the size or configuration of the aircraft, cargo may be containerized prior to loading onto the aircraft. Container loaders consist of lifts with ball bearings that raise containers level with the aircraft door sill so that containers can be easily rolled into the aircraft. Cargo that is not containerized is loaded and secured within the aircraft similar to passenger baggage. Belly cargo can introduce additional vehicles into the apron area as cargo is brought to departing aircraft and picked up from arriving aircraft. All Cargo All-cargo airlines transport only cargo and are either dedicated to transporting cargo or a division of a passenger airline that transports cargo. As shown in Figure 3-4, aprons for all-cargo aircraft are usually separated from terminal aprons. This is largely due to the landside access and vehicle maneuvering and parking areas needed to accommodate large cargo delivery/transfer vehicles and, in some cases, large numbers of vehicles at peak times (e.g., to support overnight delivery operations). Placement of all-cargo aircraft facilities away from terminal facilities reduces cargo vehicle interactions with passenger-related traffic and allows for better utilization of terminal area aprons required to efficiently accommodate passenger activity that requires proximity to the terminal building. Furthermore, the type and quantity of GSE used to service all cargo aircraft and the facilities that support all-cargo aircraft operations are substantially dif- ferent from passenger terminal facilities and are usually best located in a designated cargo area. Cargo operators use a variety of aircraft types to serve individual markets. The size of all-cargo aircraft serving an airport is largely driven by cargo demand in the local service area, as well as larger cargo collection/distribution networks. Large widebody aircraft typically serve international cargo markets, larger cities, and cargo operator hubs, while narrowbody aircraft serve smaller domestic cargo operations. Turboprop aircraft are also used to transport time-sensitive cargo to smaller communities. All-cargo aircraft facilities at airports generally consist of an aircraft parking apron, fixed or movable GSE, and a cargo building for sortation, screening, and transitioning cargo between the

18 Apron Planning and Design Guidebook secure airside and landside ground transportation connections. Areas adjacent to the aircraft apron are used for storage of GSE. Similar to terminal aprons, cargo aprons are where aircraft are serviced, including fueling, lavatory service, deicing, and maintenance. An airport operator may limit certain cargo activities on the apron, such as the sorting of cargo or the presence of landside vehicles. The established operational and security guidelines at an airport may influence the layout and equipment present on the cargo apron. Figure 3-4. Cargo aprons: (a) FedEx Super Hub, Memphis International Airport; and (b) FedEx cargo facility at Cleveland Hopkins International Airport. Source: Google Earth Pro. (a) (b)

Understanding the Apron Environment 19 Cargo aircraft are equipped with large doors on the left and right sides and upper and lower decks. Some cargo aircraft are loaded through an opening at the front of the aircraft, which is revealed when the nose is lifted. Cargo aircraft with nose-loading capabilities can accommodate large items that do not fit through side cargo door openings. To achieve the proper weighting and balancing of cargo aircraft during loading, and to ensure that the aircraft does not tip (nose up) from unbalanced loading, cargo operators have developed specific plans and procedures for loading each aircraft type to maintain balance and proper weighting throughout the loading operation. Alternatively, a nose tether (linking the aircraft nose to an anchor in the apron) or a tail stand (supporting the tail of the aircraft) can be used to secure the aircraft, allowing greater flexibility in aircraft loading. A variety of GSE is used on cargo aprons, including aircraft tugs, cargo containers and trailers, cargo vehicles, mobile stairs, tail stands, and fueling vehicles or carts. Some cargo aprons contain fixed equipment that includes cargo loading platforms and in-ground nose tethers. The operational characteristics of cargo aprons largely depend on the role of an airport in the all-cargo airline’s network. Many all-cargo airlines operate hub-and-spoke networks, similar to some passenger airlines. For cargo airlines, hubbing airports are used as cargo transfer points and typically result in operations with a high amount of cargo and aircraft activity. Spoke airports may serve one or more cargo hub airports and experience lower cargo volume levels. Spoke airports may also accommodate cargo feeder aircraft. Feeder aircraft are typically smaller, propeller-driven aircraft used to serve smaller nearby destinations. Cargo operations at airports used as hubs for package delivery companies typically experience peak activity during the overnight hours. At these hubs, aircraft arrive in the evening and cargo is unloaded, sorted, and loaded on the destination aircraft. The aircraft then departs in the early morn- ing to reach its destination and to allow sufficient time for unloading, sorting, and loading onto ground vehicles used for door-to-door package delivery. The arrival and departure times of cargo operations at spoke cargo airports largely depend on the airport’s geographic location relative to the hub airport. Feeder aircraft depart shortly after the cargo aircraft arrives from the hub and arrives back to the spoke airport prior to the aircraft departing for the hub airport. This daily schedule usu- ally results in aircraft parked for extended periods of time on cargo aprons, including over weekends when package companies operate on a more limited basis. Cargo operations at airports serving all- cargo airlines that do not operate door-to-door package delivery services, mail operations, or charter operations may vary greatly and are largely dependent on the airlines’ networks. Maintenance Aprons Aircraft maintenance activities include inspections that must be completed on demand or at specific intervals of aircraft operation, such as hours flown or numbers of takeoffs and land- ings (cycles). Each airline is required to prepare an aircraft maintenance program that outlines the activities to be performed during each inspection. Aircraft maintenance facilities, generally consisting of hangar buildings sufficiently sized to accommodate the aircraft fleet, are critical to ensuring that aircraft are adequately maintained and safe for flight. Aircraft maintenance facilities vary among airports and include those serving general aviation aircraft, cargo and passenger airline aircraft, and large maintenance, repair, and overhaul (MRO) operations. As shown in Figure 3-5, maintenance aprons are typically located adjacent to these hangar buildings and are used for performing light maintenance or for aircraft storage and staging. Maintenance aprons are also used for staging maintenance equipment. Some maintenance aprons incorporate run-up areas with blast fences to deflect jet blast, propeller wash, and noise when performing engine run-ups. Jet blast is the thrust-producing exhaust from a running jet engine and propeller wash is the mass of air pushed to the rear of the aircraft by the propeller when in motion. Maintenance aprons are often equipped with lighting, movable stairs, and GSE, such as

20 Apron Planning and Design Guidebook ground power units or engine air start carts. Maintenance aprons are often used more intensely than terminal or cargo aprons as there is less need for GSE to maneuver among parked aircraft and less need for independent aircraft parking on maintenance aprons. Aircraft parking can occur with reduced separations, particularly when the maintenance apron is operated by a single airline. Remote Aprons Remote aprons are located away from terminal or cargo areas and used for storage or staging of aircraft. Most passenger aircraft do not operate overnight and remain parked at the airport overnight. At airports where the number of aircraft parked overnight exceeds the number of terminal parking positions/gates, RON aprons are used to store aircraft overnight. RON aprons can also be used to accommodate aircraft in the daytime during extended layovers to allow the use of gates that would otherwise be occupied by aircraft during these extended periods. These aprons can also be used for light aircraft maintenance and servicing during the day. Aprons located near runway ends are often referred to as holding pads and are used to position aircraft awaiting air traffic control (ATC) clearance. These holding bays are often used in lieu of bypass taxiways and vary in size, shape, and function. Many deicing pads located near a runway end are used as holding pads when not required to support deicing operations. Holding pads can also be located in proximity to terminal areas. These holding pads are used as a pullout area to position aircraft when a gate is not available because of the early arrival or late departure by the aircraft occupying the intended gate. Figure 3-6 shows several types of remote aprons (RON, terminal, and runway holding pads). General Aviation Aprons General aviation is defined as all aviation other than military and commercial airline operations. This category of aviation encompasses private pilots flying ultralight and single-engine aircraft, corporate jet flights, air ambulance activity, forest fire fighting operations, air charters, agriculture spraying, and narrowbody and widebody aircraft transporting sports teams, race horses or other critical wildlife, or dignitaries. General aviation facilities vary in size and configuration, ranging Figure 3-5. Maintenance apron. Source: Google Earth Pro.

Understanding the Apron Environment 21 from facilities at airports that accommodate only small piston aircraft to facilities at larger airports that accommodate widebody jets. At general aviation airports (those without scheduled commercial service), aprons are used either for the temporary parking of transient aircraft or the long-term parking of based aircraft. For light propeller aircraft, general aviation aprons are equipped with tiedowns, which anchor the aircraft to the apron to avoid unintended movement of aircraft during unstable weather conditions. General aviation aprons also provide access to T-hangars and commercial hangars used to accommodate some aircraft. Figure 3-6. Remote pads: (a) remote aircraft parking apron; (b) holding pad near terminal area; (c) holding pad between runway ends; and (d) holding pad near runway end. Source: Google Earth Pro. (a) (b) (c) (d)

22 Apron Planning and Design Guidebook Many general aviation aprons are leased and operated by a fixed-base operator (FBO), which is a business that provides services such as aircraft fueling, maintenance, lavatory service, pilot support and training, and parking. Figure 3-7 shows a general aviation apron collocated with a FBO and T-hangars. On aprons used by FBOs, the marking of designated parking positions is often minimized to maximize the flexibility to accommodate various aircraft types on the apron simultaneously. Typically, mobile GSE is preferred to stationary GSE to maintain flexible use of the apron. To reduce vehicle congestion, general aviation aircraft are fueled at self-service fueling areas operated by FBOs. Most airport operators lease development areas to FBOs, which configure the leaseholds as needed to meet their operational objectives. In order to ensure that FBOs are able to serve all airport users, airport operators often incorporate rules, regulations, and guidelines into leases that require each lessee to configure, operate and maintain their apron(s) to best serve airport users, and main- tain an efficient and secure operating environment. Airport operators may also require FBOs to provide aircraft parking and traffic flow plans for review to ensure that these are compatible with adjacent airport activities. Other lease requirements may include providing a minimum number of tiedowns or parking positions based upon the size of the leasehold or building. Helipads A helipad is an apron that provides a landing area for helicopters. At airports, helipads are used to separate helicopters from fixed-wing aircraft and ensure that proper safety areas and liftoff and takeoff areas are protected. Helipads generally include helicopter parking positions, taxiing routes, and passenger access routes. These features are generally delineated and marked accordingly. Helipads are often located on aprons that also accommodate fixed-wing aircraft or on designated positions on taxiways. Figure 3-8 shows both a helicopter-only facility and a helipad located on a Figure 3-7. General aviation apron. Source: Google Earth Pro.

Understanding the Apron Environment 23 Figure 3-8. Helipads. Source: Google Earth Pro.

24 Apron Planning and Design Guidebook taxiway. Helicopter operations are controlled by ATC when available at the airport. If the airport is not controlled by ATC, helicopter pilots follow visual flight rules. Helicopters are used for a variety of purposes, including transportation of people and cargo, firefighting, tourism, aerial observation and photography, air ambulance, search and rescue, aerial craning, and military operations. Activities that occur on helipads may vary depending on the use of the helicopter. For example, on aprons used to accommodate forest firefighting helicopters, the aircraft may be refilled with water while positioned on the apron; on aprons serving tourism helicopters, passenger activities that may require walkways and a passenger terminal building must be safely accommodated. Activities on the helipad are generally the same as those on aprons that accommodate fixed-wing aircraft, including, but not limited to, passenger enplaning and deplaning, fueling, maintenance, storage, and cargo loading. GSE for helicopters is either portable or fixed and is typically positioned at the edge of a helipad. Aircraft Maneuvering Three basic types of aircraft maneuvering take place in the apron areas of airports: power in, power out; power in/push back; and tug in, push back. These maneuvers are discussed in the following sections. Power-In, Power-Out Maneuvers As illustrated on Figure 3-9, with the power-in, power-out maneuver, the pilot pulls the air- craft into a parking position under the aircraft’s own power, and sufficient clearance or access to a taxilane or taxiway is available to allow the pilot of that aircraft to subsequently pull out of the parking position under the aircraft’s own power. This maneuver is more common on terminal aprons that accommodate aircraft ground loading and unloading, as no equipment, such as passenger loading bridges, are present to obstruct aircraft movement. Although some aircraft are equipped with reverse thrust to move backward, jet blast or propeller wash can have adverse effects in the apron area, potentially damaging terminal, cargo, or other buildings or creating hazards for personnel or passengers. This type of aircraft maneuver is common on flow-through deicing pads and hold pads near runway ends. A power-in, power-out maneuver is generally more efficient than a push-back maneuver, especially for regional jets or turboprops because tug equipment is not required. Power-In, Push-Back Maneuvers The most common aircraft maneuver used in terminal and cargo apron areas is the power-in, push-back maneuver. As shown on Figure 3-10, this maneuver involves the pilot of an arriving aircraft pulling into a gate or parking position, nose first, under the aircraft’s own power, usually generally perpendicular to a building or a taxilane. When the aircraft is ready to leave the gate or parking position, a tractor or tug is used, attached to the aircraft nosewheel, to push the aircraft to an apron, taxilane, or taxiway, where the aircraft has adequate maneuvering room and can safely be started up without the adverse effects of jet blast. In some cases, aircraft are also pulled forward as part of this maneuver to avoid the adverse effects of jet blast on buildings, equipment, personnel, or other aircraft. The tractor or tug is then detached from the aircraft and moved out of the way. The aircraft is then moved forward under the aircraft’s own power. Although this type of maneuver is the most

Understanding the Apron Environment 25 Figure 3-9. Power-in, power-out aircraft maneuvers. Source: Ricondo & Associates, Inc. Figure 3-10. Power-in, push-back aircraft maneuvers. Source: Ricondo & Associates, Inc.

26 Apron Planning and Design Guidebook labor intensive, it requires the least amount of apron area compared with aircraft taxiing in and out under their own power because the ground crew has better visibility of the apron environ- ment and can more precisely direct aircraft maneuvers in dimensionally tight areas. Tug-In, Push-Back Maneuvers At terminal or other aprons with constrained space and limited dimensional clearance, aircraft are tugged into the gate to reduce the potential for collisions or the negative effects of jet blast. This type of maneuver can be required by airport operational procedures or requested by a pilot. This type of aircraft maneuver takes additional time to allow for the tug vehicle to be hooked onto the aircraft nosewheel and for the aircraft to be towed into the gate. As shown in Figure 3-11, typically, aircraft that are towed into the gate require a tug to push the aircraft away from the apron at the time of departure. There is also a potential for aircraft powering in to a gate to be tugged in if the aircraft unexpectedly had to stop. Powering in is often required because of jet blast concerns where idle or taxi thrust is acceptable and break away thrust is not allowed. Passenger Enplaning and Deplaning When planning terminal aprons, the planners must consider the transfer of passengers between the aircraft and the terminal/concourse. Passengers and baggage can be transferred with minimal use of equipment, or may involve a sophisticated system of equipment. Passengers are generally enplaned and deplaned from aircraft using one of three approaches: bridge loading, ground loading, or remote loading. Bridge Loading A passenger loading bridge (PLB) is a movable enclosure that facilitates the transfer of passengers between the terminal/concourse and the aircraft in a secure and environmentally controlled Figure 3-11. Tug-in, push-back aircraft maneuvers. Source: Ricondo & Associates, Inc.

Understanding the Apron Environment 27 environment. A PLB accommodates differences in elevation between the terminal and aircraft door sill. PLBs also provide a level of security for aircraft boarding and protect passengers from adverse weather conditions, potential jet blast exposure, and other ramp activity, while also pro- viding improved access for passengers using wheelchairs. When aircraft are parked sufficiently far from the terminal building, fixed bridge segments can be used to span the gap between the building and the aircraft, with a PLB placed at the distal end of the fixed bridge segment. These fixed segments are also used when a PLB would not meet maximum slope requirements (typically defined by the Americans with Disabilities Act [ADA]) and a longer bridge length is necessary to lessen the bridge slope. PLBs usually provide the most direct access to a terminal building and generally provide a safer environment compared with ground loading. PLBs almost always interface with aircraft from a left-side door, usually forward of the aircraft wings, but not necessarily the most forward door. Although most aircraft are served by a single PLB, the use of multiple bridges can significantly reduce the time required to enplane and deplane passengers by providing for two streams of enplaning or deplaning passengers, especially for widebody aircraft or dual-level aircraft. Multiple PLBs to serve a single aircraft are most commonly used with widebody and dual-aisle aircraft in which the first and second loading doors are both forward of the aircraft wing. In the case of the double-decked A380, bridges may extend to the upper level of the aircraft. Gates equipped with multiple bridges can often accommodate either one widebody aircraft or two narrowbody or smaller aircraft. This type of gate configuration is referred to as a multiple aircraft ramp system. The two main categories of PLBs are apron drive loading bridges and fixed loading bridges, as described in the following subsections. Apron Drive Loading Bridges Apron drive PLBs provide the most operational flexibility. As shown on Figure 3-12, these bridges consist of a rotating rotunda, typically attached to the terminal/concourse building and usually placed on top of a foundation and pedestal support. The rotunda is connected to two or three telescoping tunnels that extend and retract along their longitudinal axes to connect with aircraft on the apron. A rotating cab is also located at the far end of the tunnels, with the tunnels Figure 3-12. Apron drive PLBs. Source: Kimley-Horn and Associates, Inc.

28 Apron Planning and Design Guidebook and rotunda dynamically elevated by a vertical support under the tunnel section and a set of wheels that can be rotated to move the bridge to meet the door sill of an aircraft. Each bridge has maximum and minimum operational ranges for all three movements (vertical, rotation, and extension), which are defined by the manufacturer. When planning for apron drive bridges, planners must consider these operational limits to determine the slope of the tunneled sections for the bridge interfaces with aircraft on the apron. A three-tunnel bridge provides the greatest range of extension and is usually used on aprons with sufficient apron depth and when aircraft of varying door sill heights must be accommodated. To accommodate apron drive bridges, the apron configuration must reflect consideration of the equipment’s maximum extension and retraction, its maximum rotation at the rotunda, and its maximum vertical range. In situations where a road is located between the parked aircraft and the terminal building, referred to as a head-of-stand road, fixed bridge segments spanning the road are used to connect the terminal building with the rotating cab, which sits on a pedestal mounted to a foundation in the apron. In these situations, sufficient vertical clearance must be provided for vehicles passing beneath the fixed segment of the bridge. On the apron, bridge maneuvering area markings are important to ensure that vehicles or GSE do not interfere with the movement of the bridge. An over-the-wing apron drive bridge is a unique type of loading bridge used to access doors located behind an aircraft wing to provide multiple access points to the aircraft. As shown on Figure 3-13, these bridges are configured with a rotating cab attached to a fixed segment, which is horizontally hinged to allow the bridge to be elevated over-the-wing and then slope down to Figure 3-13. Over-the-wing apron drive bridge. Source: Ricondo & Associates, Inc.

Understanding the Apron Environment 29 a rear aircraft door. A fail-safe stopping or braking mechanism is used to prevent damage to an aircraft wing in the event of bridge failure. The use of over-the-wing PLBs allows two loading bridges to serve an aircraft, potentially reducing the amount of time required to enplane and deplane passengers. While similar to the use of multiple PLBs, over-the-wing PLBs are typically used with narrowbody single-aisle air- craft in which the second loading door is located behind the aircraft wing. The use of this type of bridges reduces the available apron space on the side of the aircraft that the bridge serves, as well as the space for GSE storage. Fixed Loading Bridges Fixed PLBs consist of a fixed link from the building to a stationary pedestal on the apron and a telescoping segment located between the pedestal and the parked aircraft, as depicted on Figure 3-14. These bridges are positioned perpendicular to the aircraft with a tunnel section that extends to the aircraft after it has pulled into the gate and retracts when the aircraft is loaded. With a fixed PLB, the accuracy in the final positioning of the aircraft is more critical, given the limitations in cab movement and the inability for the bridge to move along the axis of the aircraft. This type of bridge is typically more economical than apron drive bridges and is used when reduced flexibility is acceptable, such as when a narrow range of aircraft with similar door sill heights are parked at a particular gate. As fixed bridges are largely stationary, a smaller amount of apron area must be protected compared to that needed to support an apron drive bridge. Door Sill Height Adapters Many PLBs are not able to reach regional jet or turboprop aircraft because the stairs or other equipment on the aircraft exterior can be damaged when a PLB extends to the aircraft. PLBs are also limited in the distance that the cab can drop because of equipment limitations. Adapters are used to reach the aircraft and securely bridge the gap from the edge of the loading bridge to Figure 3-14. Fixed PLB. Source: Ricondo & Associates, Inc.

30 Apron Planning and Design Guidebook the aircraft. These adapters are either portable or integrated into the bridge under the rotunda. With portable bridge adapters, the loading bridge is moved as close to the aircraft as permissible and the portable adapter is extended and lowered onto either the aircraft sill or, if the aircraft is equipped with stairs, onto the top step. Permanent adapters allow for the bridge to approach the aircraft without making contact, and final docking is completed by extending the retractable por- tion of the bridge floor to the aircraft. Figure 3-15 illustrates the two types of adapters. There are also aircraft with passenger door configurations where the bottom of the door is lower than the sill height when it is opened all the way. This may require the PLB to be positioned below the door sill and require special ramps to bridge the vertical difference between the aircraft and the PLB. Ground Loading Depending on the size of the aircraft and the configuration of the terminal/concourse or FBO facility, aircraft may be ground loaded, which entails passengers walking to the aircraft at ground level and accessing the aircraft by using stairs built into the aircraft, also known as air stairs, or a mobile stairway that is positioned at the aircraft loading door. Ground loading is primarily used to enplane and deplane passengers when gates with PLBs are unavailable, aircraft size does not warrant a bridge, or aircraft parking configurations preclude the use of bridges, such as with lower-level facilities. Additionally, regional jet or turboprop aircraft are often ground loaded and unloaded, especially at airports with a large airline hubbing operation where loading bridges are used for larger aircraft. Figure 3-16 provides two examples of apron layouts for ground loading and unloading of passengers. Passengers on regional jets and turboprop aircraft are often enplaned and deplaned using air stairs. Some larger regional jet and turboprop aircraft are not equipped with air stairs and either ramps or movable stairs are used to enplane and deplane passengers. The use of loading ramps enables passengers using wheelchairs to more easily enplane and deplane the aircraft. As shown on Figure 3-17, a variety of ramps can be used. The first photograph shown is a ramp anchored at the base, which remains in position and is rotated into the aircraft during use. Other loading ramps or stairways double back to reach aircraft with higher door sills, as shown Figure 3-17b. Figure 3-15. Low door sill height adapters for regional jets. Source: Ricondo & Associates, Inc.

Understanding the Apron Environment 31 Figure 3-16. Ground passenger loading apron layouts. Source: Google Earth Pro.

32 Apron Planning and Design Guidebook Many of these ramps or stairways are towable and use brakes to prevent slippage. Aircraft stair vehicles are also used to enplane and deplane passengers. These vehicles are equipped with stairs that can be raised or lowered to meet the sill of the aircraft and can accommodate both narrow- body and widebody aircraft. Other ground passenger loading equipment includes wheelchair lifts that are used to provide access to an aircraft that has built-in air stairs. Ground loading of aircraft, which may require more or less time to complete than enplaning and deplaning through a PLB depending on the size and sill height of the aircraft, introduces safety and security concerns because passengers must transit an area occupied by operating aircraft and GSE. In addition, ground loading of aircraft often does not provide meaningful protection for passengers during adverse weather conditions, although, in some cases, a fixed or movable covered walkway extending at least a portion of the distance between the building and the aircraft can be installed. Remote Loading/Hardstands At airports where space is not available in the terminal area for passenger enplaning and deplaning, remote aprons are used to supplement terminal gates. Also known as hardstands, these remote aprons are usually located sufficiently far from the terminal that walking is not desirable or acceptable (particularly in an active operating environment). Although the construc- tion cost of these remote hardstands can be lower than that for a terminal gate, the operational costs are higher because of the need to transport passengers to and from the terminal building. In addition, remote loading often increases bus and vehicle activity on the airfield. Remote hard- stands require the use of air stairs or mobile stairs (as described in the previous section) to enplane and deplane passengers. Hardstands can be equipped with hydrant fueling systems, but typically require cart-mounted ground power units (GPUs) and preconditioned air (PCA) units, thus increasing the amount of equipment on the apron. Passengers are transported between the terminal and remote hardstands using shuttles or buses, which can vary in size. The larger vehicles accommodate approximately 130 passengers. The size and frequency of bus service depends on the size (seating capacity) of the aircraft and the passenger load. Although not common, mobile lounges are specialized vehicles that are used to enplane and deplane passengers at remote hardstands. Mobile lounges have ramps on one end that can be raised or lowered to meet the door still of an aircraft. A variation of a mobile lounge Figure 3-17. Ground passenger loading equipment. (a) (b) Source: Ricondo & Associates, Inc.; Airport Development Group, Inc.

Understanding the Apron Environment 33 is a plane mate which consists of a passenger compartment that can be raised or lowered using a screw assembly to meet the height of an aircraft loading door and terminal dock. An example of a plane mate mobile lounge is shown on Figure 3-18. Some remote hardstands contain supporting structures that are equipped with a PLB and ramps, escalators, or stairs that provide vertical circulation to a bus station on the apron level. These structures typically protect a vertical corridor to the aircraft and may provide some pas- senger facilities, such as restrooms. Figure 3-19 shows remote hardstands at Los Angeles Inter- national Airport. Figure 3-18. Plane mate mobile lounge. Source: Ricondo & Associates, Inc. Figure 3-19. Remote hardstands at Los Angeles International Airport. Source: Google Earth Pro.

34 Apron Planning and Design Guidebook Vehicle Roadways Vehicle roadways are of vital importance to the efficiency of daily airport operation. A well- designed and properly maintained roadway system enhances safety; reduces delays for airlines, cargo operators, and other aircraft users; and facilitates the controlled and channelized movement of vehicles throughout the airport. Vehicle roadways are best described as a path (or means) of channelizing the flow of vehicles to enhance safety, reduce vehicle and aircraft interactions, control vehicle traffic, support wayfinding, and connect various parts of the airport. The follow- ing describes the types of apron service roads, emergency access roads and busing operations on aprons. Apron Service Roads Apron service roads serve as the main vehicle circulation arteries in and around the terminal core and other apron facilities. The purpose of apron service roads is to channelize the movement of vehicles so that pilots know where these vehicles are and to prevent conflicts with aircraft or engine jet blast. Apron service roads provide access to aircraft parking positions for GSE and other vehicles and connection to other terminal, cargo, or GSE storage facilities via airfield service roads. There are three generally accepted locations for apron service roads: head-of-stand, tail stand (apron edge), and between aircraft. A number of newly constructed airports, with ample space available, have incorporated a combination of both head-of-stand and tail-stand designs. These service roads are defined by the position of the service road in relation to parked aircraft. Head-of-Stand Road A head-of-stand road is located between the nose of the parked aircraft and a terminal or cargo building. This configuration allows for uninterrupted access to aircraft as vehicle movements are not stopped for aircraft entering or exiting a gate. With this configuration, vehicles and GSE can travel from storage/staging areas around the gate areas directly to aircraft for servicing without accessing taxiways or taxilanes, having to wait for aircraft pushing back or pulling into a gate posi- tion, or other potential interactions. Head-of-stand road alignments also tend to increase apron depth and require additional PLB segments. As shown on Figure 3-20, fixed bridge segments Figure 3-20. Head-of-stand service road configuration. Source: Google Earth Pro.

Understanding the Apron Environment 35 must span head-of-stand service roads and must provide adequate clearance to allow the tallest vehicles to pass beneath them, which can affect the planned floor elevation of the terminal building. Head-of-stand roads require aprons with greater depth, especially to accommodate aircraft tugs without interfering with vehicle movements on these roads. These roads can create conflicts with apron level door exits for personnel and ground loading of passengers. Overall, the head-of-stand configuration enhances safety by limiting interactions between vehicles and moving aircraft. Tail-Stand Road A tail-stand road is located at the tail of the aircraft, at times referred to as an apron edge service road because the road can delineate the limit of the leased areas. As shown on Figure 3-21, the layout of this type of service road usually reflects the physical limits of aircraft parking areas, but may also reflect the taxiway/taxilane alignment. Tail-stand roads can result in potential conflicts between vehicles and aircraft, as aircraft must cross the tail-stand roads to enter or exit gates. To avoid operational consequences, tail-stand service roads must be located outside all taxiway and taxilane object free areas (OFAs), as penetrations of these areas can result in limitations on the size of aircraft that can use the affected taxiways/taxilanes. On aprons with tail-stand roads located on each side of a taxiway or taxilane, it is common for these tail-stand roads to be con- nected across the taxiway/taxilane by a service road marked on the pavement to provide vehicles a defined route to cross what can be expansive pavement areas. Figure 3-21 illustrates marked vehicle roads crossing dual taxilanes between concourses. Roads Between Aircraft It is not uncommon for tail-stand roads to be supported by a vehicle pass-through of the apron level of the terminal/concourse or cargo building, allowing ground vehicles of a limited size to drive into or through the apron level of a building rather than around the building. Such a pass-through can be particularly beneficial in the case of linear concourse piers when an air- line operates gates on both sides of the pier. Vehicle pass-throughs are typically supported by defined vehicle routings, enhanced with traffic control signage and markings on the pavement. These routings often pass between parked aircraft positions, linking a tail-stand or other service road with the building pass-through entry/exit point. As shown on Figure 3-22, when a vehicle Figure 3-21. Tail-stand service road configuration. Source: Google Earth Pro.

36 Apron Planning and Design Guidebook pass-through is planned with aircraft parked on both sides of the vehicle routing, aircraft wing- tip separation increases. These roads can also provide access to the building for emergency and delivery vehicles. Roads between aircraft routings can also support airside employee bus stops, concessions delivery/storage facilities, and other non-GSE vehicle movements. Emergency Access Roads Emergency access is required in all apron areas to allow swift and effective response to emer- gencies involving aircraft, personnel, passengers, medical illness or trauma, structural damage/ fires, law enforcement response, security issues, and other emergent situations. In the event of an emergency, response can originate on the airside or landside, including airside ARFF vehicles, landside police or fire department vehicles, ambulances, and other types of vehicles. The effec- tiveness of an airside response, irrespective of vehicle type, is maximized when the responding vehicle(s) can proceed as close to the emergency scene as safely possible. In some situations, response vehicles or equipment will have to drive between parked aircraft and among apron equipment and parked GSE. Emergency response is a function of the type and severity of the triggering incident, but, in all cases, the highest priority of the responder is providing assistance, even if that temporarily interferes with apron activities or operations. Busing on Aprons Busing operations on aprons are either scheduled or unscheduled. Some airport operators provide scheduled buses to transport airport and airline employees to and from remote parking Figure 3-22. Service road between aircraft. Source: Google Earth Pro.

Understanding the Apron Environment 37 facilities and terminal or other airport buildings, often using apron roadways to access these facilities. Buses may also be used to transport passengers between terminal buildings or con- courses on a recurring schedule, particularly when a hubbing airline operates from multiple terminals or concourses. Mobile lounges and plane mates are also used to transport passengers between terminals and concourses. Figure 3-23 shows a passenger and employee bus stop on a terminal apron. Bus stops for passengers provide access to secure portions of the terminal while employees may be dropped off in nonsecure areas. Separate bus stops are provided for arriving international passengers because these passengers must be connected to a sterile corridor system connecting to U.S. CBP arrival facilities. Unscheduled bus operations can be provided in response to airfield incidents that require the transportation of passengers from an aircraft back to the terminal or other facility. Such incidents would usually be the result of an aircraft emergency or act of nature. Where terminal gates are not available, passengers may be deplaned at remote aprons and bused back to terminal facilities. Busing is also used to transport passengers when the primary form of transportation between a terminal and concourses, such as an automated people mover, is unavailable. Unscheduled bus operations are either escorted (e.g., if transiting the airfield to meet a disabled aircraft), particularly if the bus is operating on or crossing taxiways or runways, or unescorted following marked and signed service and access roads. To the maximum extent possible, bus drivers will be trained in the safe operation of buses in the secure environment; however, an airport operator may opt to require escorts even in these cases. Figure 3-23. Terminal apron bus stop. Source: A.S.S.E.T., LLC.

38 Apron Planning and Design Guidebook Apron Equipment and Systems Various types of apron equipment and systems, such as aircraft towing equipment, pre- conditioned air units, GPUs, potable water system, aircraft fueling systems, other aircraft servicing vehicles, and baggage vehicles, are used to service aircraft parked on the apron. Aircraft Towing Equipment Gating, parking, or other limitations can preclude aircraft from vacating their parking positions under their own power. Only a limited number of aircraft types can power in reverse (i.e., power back) out of their parking positions, such as the DC-9 aircraft series, but they are usually restricted from doing so (by the FAA, airline, or airport operator) because of foreign object debris damage concerns, increased noise, increased fuel consumption, weather conditions, and other safety-related factors. The method preferred by the airlines is the use of tug tractors or towbarless tractors to push aircraft away from the gate/parking areas to a location where it is safe and efficient for the aircraft to taxi forward under its own power. Tug tractors and towbarless tractors are also commonly used to reposition aircraft to other gates, hardstands, or RON positions; tow aircraft to or from aircraft maintenance facilities; and move or recover aircraft on the airfield that are unable to move under their own power. Tug Tractors Tug tractors, also known as conventional tugs, are a specialized form of apron equipment used to push or pull aircraft from parked or stationary positions, as shown in Figure 3-24. These conventional tugs use a pivoting towbar to connect the tug to the nosewheel of the air- craft. The tugs must have a low profile to avoid coming into contact with the nose of the aircraft to which they are connected, while also being heavy enough to maintain the traction needed to move the aircraft. Conventional tugs used for A380 pushbacks, for example, can weigh more than 155,000 pounds. Conventional tugs use high torque engines and low gear ratios to slowly push aircraft back from the gate or parked/stationary positions. The towbars that connect conventional tugs to aircraft are aircraft-type specific. Conventional tug operators must have a variety of towbars available to connect their tugs with different aircraft types. Towbars are commonly equipped with wheels to allow transport of the towbar and to Figure 3-24. Tug tractor. Source: Ricondo & Associates, Inc.

Understanding the Apron Environment 39 assist tug operators in positioning heavy towbars. Shear pins are designed to prevent damage to aircraft by breaking if the tug operator places too much stress on the aircraft nosewheel during tugging operations. The length of the tractor and the bar connected to the aircraft can influence apron depth. Towbarless Tractors Towbarless tractors, also known as towbarless tow vehicles (shown in Figure 3-25), are used in addition to conventional tugs to tow and push back aircraft, ranging from regional jets to wide- body aircraft. Instead of relying on a towbar, towbarless tractors rely on a pickup device located in the center of the vehicle to lift and cradle the nosewheel tires to move the aircraft. The lack of a towbar removes two pivot points in the connected aircraft-tug mechanism, resulting in simpler maneuvering of the aircraft. Similar to conventional tugs, towbarless tractors must also have a low profile and sufficient weight appropriate for the aircraft they are designed to move. These tractors are typically larger and wider than tug tractors, with vehicle widths up to approximately 15 feet. In addition to gate maneuvers, towbarless tractors are also used to move aircraft on the airfield (between gates, remote hangars, runway departure ends) because their use reduces jet fuel consumption and resulting engine emissions during taxiing. The absence of various towbars and the ability to operate at higher speeds than conventional tugs mean that aircraft movements, pushbacks, repositioning, and maintenance towing can be conducted faster than with conventional tugs. PCA Units PCA units provide conditioned outside air for ventilation and temperature control (heating or cooling) in parked aircraft. The PCA unit is attached to an aircraft via one or more air hoses through a port typically located on the underbelly of the aircraft. PCA units can be engine driven (using diesel or jet fuel) or electric, connected to an airport’s electrical distribution system. The use of PCA units for passenger aircraft is common at most airports. The main benefits associated with PCA units, in conjunction with GPUs, is a reduction in jet fuel use, which reduces aircraft emissions, as the use of this equipment allows the APU engines to be shut off while the aircraft is parked for cabin preparation, aircraft servicing, or maintenance. PCA units are generally categorized as mobile, stationary/bridge mounted, or centralized. Figure 3-25. Towbarless tractor. Source: A.S.S.E.T., LLC.

40 Apron Planning and Design Guidebook Mobile PCA Units As shown in Figure 3-26, mobile PCA units are mounted on trailers allowing for movement/ repositioning around the apron and are not limited to serving a single gate. The advantages of mobile PCA units are that they can be moved out of the way when not in operation and can be used at multiple locations as needed. Typically, mobile PCA units are plugged into an airport’s electrical distribution system at dedicated receptacles, but some units have built-in engine gener- ators that locally produce electricity to power the aircraft air conditioning (refrigeration) system and blower, and for the electric heating of the outside air, if necessary. The main disadvantage of mobile PCA units is that they add to gate congestion. Trailer-mounted PCA units can be as large as 150 square feet, which is significant in already congested gate areas. Engine generator mobile units are generally usable in any location throughout the airport, but may be prohibited in certain locations because of noise restrictions. Engine generator units typically produce noise in the 80 dB range, which is just below the National Institute of Occupational Safety and Health threshold for an 8-hour shift before hearing damage can occur. In addition to employee concerns, this level of noise is typically undesirable near passenger areas. Engine generator PCA units may also be prohibited in some locations because of exhaust and combustibles associated with diesel engines. Battery-operated units eliminate noise and emissions concerns, but require recharging and battery maintenance. Battery units are typically useful up to 2 hours before recharging is required. Electrically powered PCA units sacrifice flexibility because they rely on connection to an electrical distribution system. Limitations associated with receptacle locations can often be mitigated by increasing the discharge hose length; however, this approach adds to the equipment congestion and introduces trip hazards around the gate area. The airport’s electrical distribution system must also be designed and sized properly to allow electrically powered PCA units with varying electrical demands to simultaneously be plugged in at different locations. Stationary/Bridge-Mounted PCA Units Stationary PCA units are fixed on a pad mounted near the aircraft parking location or attached to the underside of a PLB. Stationary PCA units attached to a PLB are powered by a standard electrical distribution system. The main advantage of PCA units attached to a PLB is the reduc- tion in gate area congestion. PCA units can be mounted under a PLB, as shown in Figure 3-27, or mounted to the top of the bridge. Figure 3-26. Mobile preconditioned air unit. Source: Ricondo & Associates, Inc.

Understanding the Apron Environment 41 Figure 3-28 shows a stationary PCA unit mounted on the apron. Apron-mounted units can be installed when there is not sufficient space available on a PLB. These units are also typically powered by the airport’s electrical distribution system, but can also be powered by a diesel engine generator. The PCA units, which vary by aircraft size and required cooling capacity are usually sized for the largest aircraft that is reasonably expected to be accommodated at the gate. Sufficient hose length is usually provided to serve a range of aircraft sizes. Hoses can be extended to aircraft parked away from the PCA unit, such as regional jets or propeller aircraft not using the PLB and parked away from the bridge. Both bridge-mounted and stationary PCA units can be equipped with diverting valves that provide conditioned air to the PLBs. Higher-capacity PCA units may be required to sufficiently heat or cool the PLB and the aircraft. Centralized PCA Systems Centralized PCA systems differ from stationary/bridge-mounted units in that the refrigera- tion is generated remotely (e.g., within the terminal building) and distributed via chilled and Figure 3-27. Bridge-mounted preconditioned air unit. Source: Kimley-Horn and Associates, Inc. Figure 3-28. Stationary preconditioned air unit. Source: Ricondo & Associates, Inc.

42 Apron Planning and Design Guidebook heated liquid to the individual point-of-use air handling units. The individual PCA units are smaller and lighter because their function is limited to blowing outside air past the heating or cooling coils. Some centralized PCA systems use an underground distribution system and pop- up hatch pits that reduce the amount of equipment on the apron. GPUs GPUs provide the 400 Hz power required by aircraft electrical systems, rather than the stan- dard 60/50 Hz power available from utility companies; 400 Hz power is used in aircraft as the power supply equipment is smaller and lighter, thereby reducing the weight and amount of space required in the aircraft. Traditionally, 400 Hz power has been motor-generated (i.e., 60 Hz or 50 Hz electric motors drive a 400 Hz generator) or engine generators directly produce 400 Hz power. However, with advancements in electronics, solid state 60/50 Hz to 400 Hz frequency converters are becoming the standard for GPUs. GPUs connect to the aircraft via specialized seven-conductor cables plugged into receptacles on the aircraft fuselage. The number of recep- tacles is dependent on the aircraft size and diversity demands. Most commercial aircraft use only a single receptacle, but larger aircraft, such as the A380, use up to four receptacles. Airline-specific requirements often dictate the quantity of GPU receptacles assembled on an aircraft, which may result in differences in the number and configuration of the GPU receptacles on the same aircraft type among various airlines. Many regional jets require 28.5 volts direct current (DC) power supply at the gate. This type of power is supplied by equipment that either converts 60/50 Hz power to 28.5 volts DC or produces DC from an engine generator. One of the main benefits associated with GPUs is the reduction in aircraft emissions, accom- plished by allowing aircraft to shut down the APU engines while the aircraft is parked for cabin preparation, aircraft servicing, or maintenance. The FAA initiated the Voluntary Airport Low Emissions (VALE) Program in 2004, which includes gate electrification, to help airport operators pay for these low emission products. GPU equipment can be categorized as mobile, stationary, or centralized. Mobile GPUs A mobile GPU is typically mounted on a trailer and can be moved among gates or to storage when not in use, as shown on Figure 3-29. These units are either plugged into an airport’s tra- ditional 60 Hz or 50 Hz electrical distribution system at dedicated receptacles or coupled with a diesel engine generator. The main advantage of a mobile GPU is that a single unit can be used Figure 3-29. Mobile ground power unit. Source: Kimley-Horn and Associates, Inc.

Understanding the Apron Environment 43 in various parking positions, making them popular for both cargo and terminal aprons, as well as RON aprons. Engine generator mobile GPUs are technically usable in any location throughout the air- port, but may be prohibited in certain locations because of noise restrictions. Similar to PCA units with engine generators, these GPUs can produce noise in the 80 dB range, which may be bothersome to passengers and detrimental to personnel working in the apron environment. Engine generator units may also be prohibited because of exhaust and combustibles associated with diesel engines. Solid state frequency converters typically operate in the 60-65 dB range, which makes them more desirable in areas where passengers or apron workers are present. However, solid state or electric motor-generator units sacrifice flexibility because they are dependent on a connection to a 60/50 Hz power distribution system. Trailer-mounted GPUs can occupy up to 40 square feet of apron space. Mobile units also introduce trip hazards caused by connections to the aircraft or the 60/50 Hz distribution line being strung along the apron to the point of connection. Stationary/Bridge-Mounted GPUs Stationary GPUs are installed on the apron or mounted to the underside of a PLB. GPUs installed on the apron are either hardwired into a traditional 60 Hz or 50 Hz electrical distribu- tion system or coupled with a diesel engine, as shown on Figure 3-30. A GPU mounted on a PLB is shown on Figure 3-31. This type of GPU is usually a solid state frequency converter and relies on a dedicated 60/50 Hz electrical distribution system. These GPUs and the electrical distribution system need to be sized to accommodate the largest aircraft that could reasonably park at the gate where the GPU is located. However, smaller aircraft that may not use a PLB and are parked further from the bridge-mounted or stationary GPU must also be considered. In these cases, longer aircraft cables may be needed. The main advantage of a bridge-mounted GPU over a mobile GPU is a reduction in equipment on the apron, which results in the increasing popularity of bridge-mounted units for gate areas. Figure 3-30. Stationary ground power unit. Source: Ricondo & Associates, Inc.

44 Apron Planning and Design Guidebook Centralized Ground Power Centralized ground power systems differ from mobile or stationary/bridge-mounted GPUs in that the power distribution to multiple gates is provided at 400 Hz rather than the traditional 60/50 Hz. Some centralized GPU systems use pop-up hatch pits or other underground distri- bution systems that reduce the amount of equipment on the apron compared with mobile or apron-mounted GPUs. The aircraft is connected to the receptacle in the hatch pit. The benefit of a centralized ground power system is the reduction of equipment on the apron. Centralized systems present some challenges that mobile or stationary units do not, such as requiring specialized distribution equipment, large cooling demand, possible voltage decreases, and magnetic interference. Potable Water System Potable water supplied to aircraft for consumption is jointly regulated in the United States by the Environmental Protection Agency (EPA), the Food and Drug Administration (FDA), and the FAA. As a World Health Organization member, the United States supports international guidelines on aircraft drinking water to comply with international health regulations. The underlying focus of these regulations is the provision of hygienic water for public consumption onboard aircraft. The cleanliness of the water is regulated to prevent the transfer of disease and illness. The main elements of a potable water system affecting aircraft aprons include water source location, connection to the public water system, underground routing of utilities, utility location relative to aircraft and aircraft main gear, water transfer equipment, and GSE access/operation. The source of aircraft potable water is generally a public water system, controlled by the airport operator. All water source connections are required to be an approved FDA watering point. Several types of water transfer equipment can be used to transport potable water intended for consumption onboard aircraft. Water transfer equipment consists of trucks, carts, and water cabinets. The type of water transfer equipment used depends on the aircraft’s relative location to the watering point, aircraft water capacity, availability at an airport, and airline/FBO ground handling procedures. Figure 3-31. Bridge-mounted ground power unit. Source: Ricondo & Associates, Inc.

Understanding the Apron Environment 45 Transfer Vehicles Several types of vehicles are used by airlines and ground support providers to transfer potable water from an approved watering point to an aircraft. The type and size of each transfer vehicle is based on the aircraft being serviced, as well as provider preferences. Vehicles used include small hand carts (low capacities of 20 to 50 gallons), towable tanks and carts (capacities of 50 to 300 gallons), truck bed-mounted tanks (capacities of 200 to 300 gallons), and self-propelled vehicles (capacities of 200 to 500 gallons). Figure 3-32 shows a potable water tank trailer. Tank transfer vehicles are routed to the approved public water system watering point for supply filling. Tanks are then staged at the aircraft gate location in accordance with each airline’s operational access plan. Towed or self-propelled vehicles access the aircraft at the potable water access panel. The access location varies based on the aircraft type, but is typically located on the belly of the fuselage at the wings or tail. Safe ground handling requires consideration of the height of the transfer/tow vehicle operating near aircraft. Water Cabinets A potable water cabinet is connected to a public water system and is an approved FDA water source. Water cabinets are either mounted to a building, mounted on the apron, or mounted onto a PLB. The cabinet is typically insulated to prevent the water from overheating or freezing. The cabinet contains a pump system, pressure regulation, backflow prevention, and system shut off and drainage. Water is transferred via a hose and reel system, which are required to meet FDA requirements. As shown on Figure 3-33, water cabinets are typically mounted a few feet off the ground and located near the PLB or at the head of the parking position. The location of potable water service connection on an aircraft varies, but is typically located on the underside of the aircraft near the front or tail of the aircraft. An aircraft may have more than one potable water service connection. Aircraft Fueling Systems Aviation fueling includes many different components, distribution methods, categories, and fuel grades. The number one concern regarding any fueling system and operation is fire protection. Aircraft fuel is distributed by fuel trucks, hydrant fueling system, or self-service direct from a stationary fuel tank. Figure 3-32. Potable water tank trailer. Source: Ricondo & Associates, Inc.

46 Apron Planning and Design Guidebook Fuel tanks are generally located in the wings of an aircraft. Aircraft refueling is through grav- ity feed ports on the top of each wing or through a pressure connection port generally located at or under the wing edge. Many aircraft have fuel tank vents on top of each wing tip, which is considered a potential fuel spill point. Although many different grades of aviation fuel are used worldwide, two main types are used commercially, jet fuel and aviation gasoline (avgas). Jet fuel used at commercial service airports is usually type Jet A or Jet A-1. General aviation aircraft typically use avgas that is 100 octane, low lead (100LL) or Jet A. In addition, airports with military aircraft activity may provide military grade fuels, which are similar to commercial jet fuels and are com- monly identified as JP-4, JP-5, and JP-8. The FAA allows passengers to be onboard an aircraft during fueling, but requires supervision and protection of passengers during fueling. Fuel Trucks Fuel trucks are specially designed with a fuel tank to transport fuel to and from aircraft, as shown on Figure 3-34. These trucks range in capacity, with avgas trucks typically having a capacity of 1,000 gallons. Jet fuel trucks have capacity to serve aircraft of different sizes, ranging between 3,000 gallons and 17,500 gallons. Fuel trucks refuel an aircraft by parking next to an aircraft fuel port. After the truck is secured, it is grounded to the aircraft by connecting a wire (to prevent sparks during refueling caused by static electricity), a fuel hose is coupled to the air- craft, and fuel is then pumped into the aircraft. After the correct amount of fuel is pumped into the Figure 3-33. Potable water cabinet. Source: Ricondo & Associates, Inc. Figure 3-34. Fuel truck. Source: Kimley-Horn & Associates, Inc.

Understanding the Apron Environment 47 aircraft, the hose is disconnected and reeled back onto the truck. Fuel trucks are refilled at stations that are connected to an airport’s fuel tanks or fuel farm. Given the large size of these trucks, a large area of the apron adjacent to the aircraft wings must be vacated to accommodate the trucks. Fuel trucks are often used at airports with small aircraft or low activity and at older facilities where it is not economically feasible to install a hydrant fueling system in existing apron areas. Hydrant Fueling System Hydrant fueling systems consist of in-ground piping from airport fuel farm tanks to aircraft gate locations. System elements include looped distribution piping, hydrant fuel pits, high point vent pit assemblies, isolation valves, emergency shutoff valves, and low point drainage pits. As shown on Figure 3-35, a hydrant fueling cart is used to transfer fuel from a hydrant fueling system to an aircraft. Hydrant fuel pits are located near the fuel ports of aircraft parked at a gate. The vehicles or carts are positioned near the in-ground hydrant pit and connected to the aircraft fuel tank port via a pressure coupling system. Once the hydrant fueling system is connected to the cart and grounded, fuel is transferred to the aircraft from the in-ground piping system. Most aircraft fueling systems allow fuel to be transferred to all tanks on the aircraft so that the aircraft can be fueled through a single fuel port, even though a second fuel port may be available. A fuel pit system is equipped with a hose and reel and is contained under the apron. This hose is attached to the hydrant fueling cart in fueling the aircraft. Self-Service Fueling Self-service aircraft fueling is typically available at general aviation airports with limited FBO services. The fuel is dispensed into the aircraft by an individual other than an FBO or fuel service operator. A self-service storage tank is a self-contained unit that is generally located at the edge of an aircraft parking apron, as shown on Figure 3-36. A separate taxilane with OFA clearances is often provided for aircraft access to the fueling location. Self-serve fueling is most commonly available for avgas. Given the relatively small amounts of fuel dispensed as avgas, self-fueling facilities limit the number of fueling staff and reduce vehicular traffic on general aviation aprons. Source: Ricondo & Associates, Inc. Figure 3-35. Hydrant fueling cart.

48 Apron Planning and Design Guidebook Other Aircraft Servicing Vehicles In addition to the apron equipment discussed above, FBOs, airlines, airline contractors and service providers, and the military may use additional equipment to assist with the servicing and operation of aircraft. These additional aircraft servicing vehicles include lavatory servicing vehicles and carts, cabin/galley/catering vehicles, air start vehicles and carts, mobile stairs, and aircraft maintenance vehicles. Lavatory Servicing Vehicles and Carts Lavatory servicing vehicles are used to empty waste from lavatories and refill the flush/fill tanks onboard aircraft. These vehicles are either small carts that can be towed behind other vehicles or powered vehicles that can be the size of large pickup trucks, as shown on Figure 3-37. Figure 3-36. Self-service aircraft fueling facility at Centennial Airport, Englewood, Colorado. Sources: Ricondo & Associates, Inc.; Google Earth Pro.

Understanding the Apron Environment 49 These vehicles or carts are equipped with waste tanks for storing the waste removed from aircraft lavatories and separate tanks to refill the flush/fill tanks onboard the aircraft with “blue water.” These tanks, depending on the size of vehicle or cart and the type of aircraft being serviced, can range in size from a few gallons to hundreds of gallons. Hoses are used to connect the waste and fill tanks to the aircraft’s lavatory servicing ports, which are located along the bottom or sides of the aircraft fuselage. These vehicles are not aircraft specific and can generally be used to service multiple aircraft types. Lavatory servicing trucks dispose of the collected aircraft waste at a triturator facility, typically located in general proximity to the terminal/gate area. A triturator is a sanitary sewage facility equipped to accept, hold, and pulverize aircraft waste prior to its discharge into the sanitary sewer system for eventual wastewater treatment. The facility is typically covered and includes measures to minimize the potential for sanitary waste to reach the storm water system. Cabin/Galley/Catering Vehicles Cabin/galley/catering vehicles are used to service the cabins of passenger aircraft, which may include cleaning the cabin environment, emptying and restocking the onboard kitchens (galleys), and delivering other goods or catering supplies to aircraft. Vehicle size generally depends on the aircraft type being serviced; however, small corporate aircraft are serviced by small trucks, and air carrier aircraft are generally serviced by large box-type trucks equipped with scissor lifts, allowing the rear portion of the servicing truck to be raised to cabin height, as shown on Figure 3-38. Figure 3-37. Lavatory servicing vehicle. Source: Ricondo & Associates, Inc. Figure 3-38. Cabin servicing vehicle. Source: Ricondo & Associates, Inc.

50 Apron Planning and Design Guidebook The servicing crew can then use the additional doors on aircraft (generally opposite the enplaning door or in the rear of the aircraft) to enter and exit directly into the galley/cabin without inter- fering with passenger enplaning or deplaning processes. Because of the ability to raise and lower the servicing vehicle height, these servicing vehicles are not generally aircraft specific and can be used to service a range of aircraft types. Cabin servicing vehicles are also used to remove garbage from aircraft. Local and state health and agriculture codes may require garbage to be disposed of properly or incinerated. Air Start Vehicles and Carts Air start vehicles are used to generate high-velocity air for starting aircraft jet engines. Air start vehicles, commonly known as “start carts,” are usually small- to medium-sized carts that are towed behind other vehicles. While the engines of most civil aircraft now in service can be started using onboard power and air, external assistance from the start cart may sometimes be necessary, such as when an aircraft’s APU is out of service. When a start cart is necessary to assist in starting an aircraft, it is positioned near the aircraft (generally near an engine). Start carts contain either a piston or turbine engine, which produces high-velocity air that is then delivered via hose to the aircraft to spool up the jet engine, beginning the starting process. Mobile Stairs Mobile stairs are used to enplane and deplane passengers from aircraft when jet bridges or onboard stairs (or air stairs) are not available or may be inconvenient to use. Additionally, mobile stairs are commonly available at remote hardstands, and cargo and maintenance aprons where no other enplaning facilities are available. As shown on Figure 3-39, mobile stairs can vary from a simple metal staircase with wheels to covered telescoping stairs mounted on vehicles. Simple mobile stairs that are fixed in height are generally aircraft specific, as they cannot be adjusted to reach the varying door levels of multiple aircraft types. More complex mobile stairs can be adjusted in height, allowing a single staircase to serve multiple aircraft types. When the use of mobile stairs is necessary to access parked aircraft, the stairs are rolled or driven into position near an aircraft door and locked into place to prohibit movement, thus allowing passengers to enplane and deplane at the apron level. Figure 3-39. Mobile stairs. Source: Ricondo & Associates, Inc.

Understanding the Apron Environment 51 Figure 3-40. Conveyor belt baggage loader. Source: Ricondo & Associates, Inc. Aircraft Maintenance Vehicles Aircraft maintenance vehicles are used to transport aircraft mechanics and their tools to parked aircraft for servicing. Aircraft maintenance vehicles can vary from simple pickup trucks to large box trucks and vans. Typically these vehicles, which move between aircraft maintenance facilities and parked (or disabled) aircraft, use signed and marked access and service roads. Baggage Vehicles Different types of baggage vehicles are used to load, unload, and transport baggage between the terminal and aircraft. These vehicles generally include conveyor belt loaders, used to load and unload baggage from aircraft, and tugs pulling baggage cart trains, used to transport baggage between the terminal/baggage sortation facilities and the aircraft. Baggage is typically bundled into containers and loaded onto widebody aircraft. The equipment for loading and unloading containers is the same used for cargo. Conveyor Belt Loaders Conveyor belt loaders are used to transfer baggage to and from the apron level and the baggage compartment of an aircraft. Two common types of loader belts are used in the apron environ- ment: induction belts that are rolled or towed into place and belts that are self-driven, as shown on Figure 3-40. Both types of vehicles generally have a motor-driven conveyor belt mounted on a frame that allows the loading height to be adjusted to reach the varying heights of aircraft baggage doors. These belts/conveyors may be equipped with railings that rotate upward to prevent baggage from falling off the sides of the conveyor belt. To load or unload baggage from an aircraft, the induction belt operator positions the vehicle near the baggage compartment and raises the con- veyor belt to the appropriate height. The conveyor belt can then be operated toward the aircraft, allowing baggage to travel into the baggage compartment from the apron level, or away from the aircraft, allowing baggage to travel to the apron level from the aircraft baggage compartment. Tugs Pulling Baggage Cart Trains Baggage carts and containers are used to deliver outbound baggage to the aircraft where it is placed on a belt loader that moves the bags up to the aircraft for loading. Similarly, arriving bags

52 Apron Planning and Design Guidebook and bag containers are removed from the aircraft and transported to the terminal baggage claim devices or for sorting to a connecting flight. At airline hubs, bags are often “ramp transferred” from aircraft to aircraft without being taken to the terminal/baggage sortation facilities in order to meet minimum connection times, which increases apron vehicle activity as a result. Ramp-transferred bags are moved among aircraft using tugs and carts. As shown on Figure 3-41, baggage tugs are generally the size of small tractors and pull trailers or carts in which the baggage is transported. The tugs are commonly used in conjunction with induction belts to load and unload aircraft. The most frequent uses of baggage tugs and carts are to transport baggage between aircraft and baggage claim facilities, and to transport baggage among aircraft for connecting flights. To aid in operational flexibility, the number or trailers or carts that the baggage vehicle tows can be adjusted according to need, with larger aircraft requiring more carts to accommodate larger passenger and baggage loads. Aircraft may be served by more than one cart train depending on the flight. Baggage handling personnel may load one cart train of baggage onto the aircraft and then pick up the last load of baggage shortly after the check-in deadline has passed. Similarly, upon aircraft arrival, baggage handlers may deliver an initial load of baggage to the assigned baggage claim device and drive back to the aircraft for a second load. Baggage Handling System Induction on the Apron Baggage handling systems can also incorporate induction belts on the apron. These systems contain input and/or output belts to move outbound baggage directly from the baggage system input to the gate and to move inbound baggage from the apron induction point to the baggage claim device or to another induction location in the terminal or concourse. Instead of driving tugs between an aircraft and baggage makeup facilities in a terminal area, baggage handlers only drive tugs between these baggage induction facilities and the aircraft, as shown in Figure 3-42. By incorporating baggage induction facilities, the amount of vehicle traffic is greatly reduced because the number of tug trains would be substantially reduced. Other Baggage Equipment It is not unusual for passengers to check carry-on baggage at the gate prior to boarding the aircraft, either because of a lack of available overhead bin space, dimensional limitations of the overhead bins, or requests by the airline gate crew. During aircraft ground loading, the airline ground crew often positions a baggage cart alongside the passenger walkways to collect bags as passengers head to the aircraft for boarding. In these instances passengers often carry their bags Source: Ricondo & Associates, Inc. Figure 3-41. Baggage vehicle and carts.

Understanding the Apron Environment 53 to the pre-positioned cart, which is ultimately rolled to the aircraft for loading once all passenger bags have been deposited. These carts are used to transmit the traditional carry-on bags to the aircraft prior to departure and to transmit the bags to passengers on the arriving aircraft upon deplaning. It is typical for arriving passengers to claim their gate-checked bags directly from the cart rather than at baggage claim facilities. When loading bridges are used with regional jet or turboprop aircraft, passengers may leave their gate-checked bags at the end of the bridge near the entrance of the aircraft in the bridge cab. The bags are then manually lowered to the apron level using the bridge stairs, a bag elevator, or a bag slide located adjacent to the stairs. Some PLBs designed specifically for regional jets are equipped with a baggage cart on an enclosed elevator located at the entrance of the bridge, just outside of the terminal or concourse building. Passengers deposit gate-checked bags on the cart during the boarding process. This type of system is typically enclosed to maintain security and protection from weather conditions. Prior to aircraft departure, the cart is lowered and moved to the aircraft for baggage loading. Upon aircraft arrival, the cart is loaded by airline personnel and placed on the elevator where it is lifted to the loading bridge for passengers to access their arriving bags. Cargo Loading Various types of equipment are used to move cargo around an airport and to and from air- craft. Once departing cargo is positioned near the aircraft, cargo loading equipment is used to lift cargo containers or pallets into aircraft. In general, this equipment can be operated by FBOs, airlines, airline contractors, or freight forwarders, and consist of either vehicles or stationary equipment. Belly cargo is typically loaded and unloaded on the terminal apron, while the all- cargo airlines use dedicated cargo aprons for loading and unloading. Vehicles Cargo loading vehicles include, but are not limited to, tractors, forklift trucks, and cargo plat- forms. The tractors used to transport cargo cart trains are similar to those used to transport baggage. Belly cargo is typically transported in carts similar to baggage carts, while containerized cargo is placed on a cargo dolly. Cargo dollies are equipped with rollers, wheels, or ball bearings Source: Google Earth Pro. Figure 3-42. Baggage induction.

54 Apron Planning and Design Guidebook that allow cargo containers to easily slide onto the dolly and then be locked into placed. Figure 3-43 illustrates different examples of cargo transportation equipment. Forklift trucks range from non-powered hand trucks the size of a wagon to diesel-powered telescoping trucks capable of lifting thousands of pounds more than 15 feet. Cargo loaded by a forklift truck is typically positioned on a pallet, which is a flat transport structure that supports the cargo while it is being lifted by the truck’s tines. Narrowbody and widebody aircraft usually consist of a main deck and a lower deck, also known as the lower lobe. The main deck is typically larger than the lower deck and can accom- modate a larger volume of cargo. The lower deck is usually separated into a forward and aft compartment by the wing structure, landing gear, and fuel tanks. Cargo platforms consist of two movable platforms that can be raised and lowered to the level of an aircraft cargo hold, as shown on Figure 3-44. Cargo platforms are generally available in two sizes: (1) lower lobe/narrowbody loader and (2) main deck loader. Lower lobe/narrowbody platforms have the ability to load cargo onto the main and lower decks of a narrowbody aircraft and the lower deck of a widebody aircraft. Main deck loaders are more adaptable and can be used to load both upper and lower decks of narrowbody and widebody aircraft and typically can lift heavier loads than lower lobe/narrowbody loaders. Both types of cargo platforms have two separate areas that can be independently raised and lowered. Cargo containers are moved Source: Ricondo & Associates, Inc. Figure 3-43. Cargo transportation equipment. Figure 3-44. Cargo platform. Source: Ricondo & Associates, Inc.

Understanding the Apron Environment 55 onto the platform via integral rollers or belts. The platform is then raised or lowered to the desired height and the cargo is loaded or removed using the same roller system. Stationary Equipment Stationary equipment includes semi-fixed cargo platforms, floors lined with ball bearings, and aircraft tilt prevention apparatuses, all necessary for the safe and timely loading of cargo onto aircraft. Airports with express cargo operators may use semi-fixed dedicated cargo platforms for load- ing at each aircraft parking position. These cargo platforms can be moved forward or backward to match the aircraft door sill height. Often, the platforms are connected to a ball-bearing-covered area at the apron level, as shown on Figure 3-45. Cargo pallets and containers can be pushed across the ball-bearing-covered area by cargo handling personnel without the use of tugs or other equipment. As cargo aircraft are loaded, they can become “tail heavy” (imbalanced as the result of more weight behind the main gear than in front of it), causing the aircraft to tip back on the main gear and rest on the tail of the aircraft. To prevent the aircraft from tipping, two types of tilt prevention apparatuses are used: tail stands and nose tethers. A tail stand is a pole or tripod that is temporarily positioned under the aircraft tail, preventing the tail from tipping down toward the apron; a nose tether anchors the nosewheel of an aircraft to fasteners mounted in the apron pavement. As nose tether anchors are built into the apron, their use reduces the amount of equipment on the cargo apron. Aircraft Docking Systems Aircraft docking systems provide visual cues to pilots parking aircraft. The cues aid pilots in remaining clear of obstructions and ensure that the aircraft stops in the correct position. Docking systems are most often used when aircraft docking precision is critical, such as in Figure 3-45. Stationary cargo equipment. Source: Google Earth Pro.

56 Apron Planning and Design Guidebook congested and constrained gate areas. The most advanced systems in use today have three three-dimensional scanning lasers to monitor aircraft position and provide visual feedback to the pilot via an electronic display mounted at the head of the stand. Prior to an aircraft enter- ing the parking position, ground crew input the aircraft type to the docking system. The system then checks compatibility with the parking position, including the location of the PLB. As an aircraft begins to enter the parking position, the system alerts the pilot to the aircraft position relative to the lead-in line and stop bar. Figure 3-46 shows an aircraft docking system. In addition to providing guidance for aircraft maneuvering, aircraft docking systems can be used to track and analyze gate use. Such information can be used to quickly determine which gates are occupied or available and to integrate various airline and airport information systems. Use of an aircraft docking guidance system can facilitate more precise aircraft movements in the apron/gate area and enhance the efficiency of apron use. These systems reduce dependence on wing walkers, which may allow gates to be used during adverse weather conditions when apron/airline personnel are evacuated from aprons (e.g., during lightning conditions). Deicing Equipment There are generally two categories of deicing equipment: mobile deicing vehicles and stationary equipment; mobile equipment is far more prevalent, particularly at U.S. airports. This equipment is described in the following subsections. Mobile Deicing Vehicles As shown on Figure 3-47, mobile deicing vehicles have maneuverable vertical booms, which are equipped with hoses that provide the ability to spray deicing solution on all critical parts of the aircraft. These vehicles typically have two heated tanks that contain different types of deicing fluid. Type I and Type IV deicing fluids are the most widely used. Type I deicing fluid (typically dyed orange) generally has a low viscosity and is heated and sprayed at higher pressures Source: Ricondo & Associates, Inc. Figure 3-46. Aircraft docking system.

Understanding the Apron Environment 57 to remove snow and ice from aircraft. Type IV deicing fluid (typically dyed green) is used as an anti-icing agent, as it is more viscous and typically provides longer holdover times. Within their holdover time limits, these fluids protect the aircraft from snow and ice accumulation and frost formation until the aircraft reaches a specific speed at which the fluid shears off the surfaces of the aircraft. Both Type I and Type IV deicing fluids are diluted with water at concentrations that vary, depending on the outside air temperature, approximate holdover time, and precipitation (snow, drizzle, rain, fog) conditions. Many mobile deicing vehicles are equipped to apply forced air or a forced air/fluid mix to remove snow and ice contaminants from aircraft. During certain weather conditions, forced air can be used to remove snow and ice, which typically reduces the amount of deicing fluid required. Mobile deicing vehicles vary in size. Vehicles used to service small general aviation and regional jets have fluid capacities of 200 to 500 gallons; larger widebody aircraft may require several deicing vehicles, with fluid capacities up to 2,200 gallons each. Mobile deicing equipment is usually staged close to the deicing aprons (at terminal gates or deicing pads) to allow for the quick initiation of deicing operations when conditions warrant. During non-winter months, this equipment is often remotely parked or staged away from the terminal and deicing pads. Fixed Fluid Applicators As shown on Figure 3-48, fixed fluid applicators consist of telescopic booms mounted to a deicing pad. These applicators have an enclosed cab at the end from which deicing personnel can control the height and extension of the cab and the spray hoses. The spray hoses are connected to pumps and fluid tanks that control the dilution of the fluid. Although these applicators do not require refilling, their fixed nature may restrict the size of aircraft that can use the deicing pad. When fixed fluid applicators are used, aircraft taxi into predefined positions on the apron, stopping to allow the deicing operation to be completed before taxiing out of the deicing pad. Tanks and Buildings Deicing operations require storage tanks for deicing fluids and pumping stations to refill mobile deicing vehicles. Typically, these tanks and pumping stations are located adjacent to deicing pads or near the terminal areas if aircraft are deiced at gate positions. Vehicle refueling areas or fuel tanker trucks may also be located near deicing pads to allow for more efficient vehicle Source: A.S.S.E.T., LLC. Figure 3-47. Mobile deicing vehicles.

58 Apron Planning and Design Guidebook refueling during deicing operations. In close proximity to many deicing pads, small buildings are available for coordinating and managing deicing operations and providing restrooms and break rooms for personnel. Other Equipment In addition to the equipment mentioned, several other aircraft support areas and GSE are often located on or near apron areas. These include GSE fueling islands and gas pumps; charging units for electric-powered vehicles; and waste-related containers, such as trash compactors, trash con- tainers, and waste oil containers. All equipment placement requires consideration of convenient access for service and operation and adequate and safe separation from other apron functions and parked and maneuvering aircraft. In many cases, curbs or bollards are required for protection around fixed equipment in the apron environment. Types of Airline Operations Airlines typically operate their systems in one of two ways: hub-and-spoke, and point-to-point. Hub-and-spoke airlines utilize hub airports as passenger transfer points between flights from spoke airports or other hub airports in their network. Airports that operate as an airline hub typically have more activity (passengers and operations) than spoke airports. Spoke airports may serve one or more airline hub airports and accommodate lower activity levels, both overall and on an individual airline basis, than a hub airport. Point-to-point airlines transport passengers directly between city pairs rather than routing them through hub airports and generally operate with schedules similar to those of spoke airports, with activity occurring relatively evenly throughout the day. Terminal aprons at airports with an airline hub tend to experience peak periods of demand during which nearly all gates and parking positions are occupied. During these peak periods of connecting operations, there is a commensurately high level of GSE activity, especially related to the movement of baggage tugs between aircraft and the terminal. The amount of GSE in use at Source: City and County of Denver, Department of Aviation. Figure 3-48. Fixed fluid applicators.

Understanding the Apron Environment 59 hub airports is generally higher than at non-hub airports because of the peaking characteristics and the need to simultaneously serve many gates. At non-hub airports, aircraft activity typically occurs more evenly throughout the day. International Arrivals The CBP controls and processes passengers, baggage, and cargo on aircraft arriving from origins outside the United States, which require special consideration. Some of these aircraft arrivals affect apron markings and operations. Passengers on arriving international flights (from airports in countries that do not have preclearance agreements with the United States and that do not have CBP preclearance facilities) must be isolated within a sterile corridor system to prevent commingling with secure passengers in the terminal until they have been appropriately processed. If aircraft arrive at an airport’s remote hardstand, secure transport to an isolated dock connected to a sterile corridor system is required. Additionally, to prevent the spread of agricultural or animal disease, all arriving international garbage must be incinerated or sterilized properly. Specialized vehicles or dumpsters may be required to ensure that the garbage is not com- mingled with garbage from domestic flights. Terminal aprons are usually equipped with closed- circuit television (CCTV) systems that allow CBP personnel to monitor passenger and baggage on aprons used for international arrivals. General aviation facilities that accommodate arriving international passengers traditionally consist of a building adjacent to an apron, usually isolated from the terminal building and airfield, as shown on Figure 3-49. Aprons adjacent to CBP facilities often have multiple marked parking positions, including helicopter landing pads. These aprons often accommodate searches Figure 3-49. U.S. CBP general aviation facility. Sources: Google Earth Pro; DigitalGlobe, 2013.

60 Apron Planning and Design Guidebook of arriving aircraft and cargo. At airports with less activity, a portion of an apron may be identified for CBP use only. Alternatively, at airports where the CBP is not routinely staffed, arrangements for the aircraft to be met by CBP personnel can be made ahead of the arrival; however, the arriving aircraft and its passengers and cargo must remain isolated until the CBP inspection and processing are complete. At airports where this situation occurs, a dedicated apron position is often designated as a place for an arriving international aircraft to await CBP inspection and processing. Ground and Ramp Tower Control At airports with an airport traffic control tower (ATCT), areas of the airport that support aircraft operations are categorized as either movement or nonmovement areas. In movement areas, aircraft are maneuvered under the direction of ATC ground control personnel working in an ATCT. An airport’s runways and the taxiways serving those runways are typically classified as movement areas and are under the strict control of FAA ATC personnel. In nonmovement areas, aircraft are moved at the discretion of the pilot, sometimes under the guidance of a ramp tower controller, if present. ATCT controllers do not control aircraft in nonmovement areas. Taxilanes and terminal and cargo aprons are typically classified as non- movement areas. The location where responsibility for the safe movement of the aircraft transitions from the pilot in command of the aircraft to the controlling entity (ATC or ramp control) is referred to as a hand-off point. The location of hand-off points varies depending on the layout of aprons and access points to the airfield. Aprons directly adjacent to taxiway movement areas may be controlled by ATC and defined hand-off points may not be designated. The control of aprons and the locations of hand-off points for aircraft departing from aprons vary by airport and are influenced by apron configuration and local ATC preferences. Hand-off points can also function to meter aircraft awaiting departure at peak times to avoid creating airfield congestion due to the near simultaneous push-back of aircraft from multiple gates during the peak. Aprons in the terminal area or near runway ends may be used by ATC for metering aircraft for departure as aircraft are held on the apron until sequenced into the departure queue. Control Towers ATCTs are used by the FAA to house air traffic controllers with responsibility for the control of movement areas at airports. Ramp towers are used by airlines, airport personnel, or third-party operators to house ground traffic controllers with responsibility for controlling aircraft in non- movement areas of an airport. Generally, ramp towers are used at airports with higher levels of activity on the apron. As shown on Figure 3-50, ramp towers are often co-located with terminal, concourse, or cargo buildings to provide sufficient line-of-sight to non-movement areas in the vicinity of the associated building. Most ramp tower controllers are able to view the top of aircraft fuselages or, at a minimum, an aircraft tail in the areas under their control. Surface Management Software Surface management software is used by airport, airline, and ramp tower personnel to track aircraft using surveillance data from airport navigational aids and sensors located throughout an airport. The software often uses aircraft departure and arrival information to predict gate and parking position demand and to aid in ramp tower controller decision making. The software provides a visual map of aircraft movements and locations and can be enhanced with additional capabilities that support decision making related to managing apron traffic. For example, the Additional Guidance U.S. CBP, Airport Techni- cal Design Standards Passenger Processing Facilities, August 2006.

Understanding the Apron Environment 61 software can be used to reduce queues and delays at deicing pads by predicting demand and informing ramp controllers as to the optimal time to push back and taxi aircraft to the deicing pads. Interface with Nonapron Areas The FAA requires the accurate and clear definition of the interface between the nonmovement areas and the movement areas of an airport. As defined by the FAA Advisory Circular 150/5300- 13A, the movement areas include “the runways, taxiways, and other areas of an airport which are used for taxiing or hover taxiing, air taxiing, takeoff, and landing of aircraft, exclusive of loading ramps and aircraft parking areas.” Many aprons are located within or near movement areas. The configuration of aprons and taxiways/taxilanes reflects the configuration of the terminal and airfield, especially the locations of runways. At airports with an ATCT, the transition of aircraft from nonmovement areas to movement areas is controlled by FAA ATC. Figure 3-51 depicts a terminal apron located adjacent to a single taxiway as part of a movement area. In this apron configuration, the pilot must obtain permis- sion to push back onto the taxiway. This type of apron configuration is the most operationally restricted and can cause delays because of the time needed to push the aircraft back, decouple the tug, and start up the aircraft. This delay may prevent other aircraft from passing through the area or from pushing back from adjacent gates. Many terminal aprons are configured with push-back areas that allow aircraft to push back without blocking the movement of aircraft on taxiways or taxilanes, as shown on Figure 3-52. Aprons are also configured with either single or dual taxiways or taxilanes. Dual taxiway/taxilanes allow for more flexible operations, as one aircraft can pass another while being pushed back or taxiing in the opposite direction. Aprons configured with dual taxiways/taxilanes often use one taxiway/taxilane as a push-back area, while using the other for the directional movement of air- craft taxiing through the area. An apron with both dual taxiways/taxilanes and push-back areas provides the greatest operational flexibility, but requires the most pavement area. Security Safety and security are two of the most important aspects of operations at any airport. Airport security is very detailed, complicated, and comprehensive, with procedures, rules, and require- ments that are continually evolving and changing. Each airport is unique in terms of size, location, and layout. A portion of security relates to protection of the terminal core and apron area. Source: Ricondo & Associates, Inc. Figure 3-50. Ramp tower.

62 Apron Planning and Design Guidebook Source: Google Earth Pro. Figure 3-51. Apron adjacent to movement area. Source: Google Earth Pro. Figure 3-52. Apron with push-back area.

Understanding the Apron Environment 63 Security of apron is largely controlled by ensuring that only authorized individuals or vehicles are provided access through security gates at the edges of the air operations area (AOA) or in terminal or cargo buildings. Beyond this, security on aprons is largely the responsibility of apron personnel and security personnel monitoring the apron environment. Badged personnel at most airports are required to challenge individuals not displaying proper security badges and to report any suspicious or unusual behavior. Access to aprons is provided through security gates at the edges of the AOA or in terminal or cargo buildings. The threat of intrusions onto an airport through a perimeter fence line or security access gate has resulted in many airports using CCTV to provide views of aprons to security personnel. Coordination with the TSA is recommended to ensure that apron planning and design do not introduce security weaknesses or vulnerabilities. Snow Removal and Prevention Snow removal is a complex operation that must be managed by airport operators to ensure a safe operating environment. This is especially true for apron areas that are typically expansive and require the removal of large volumes of snow. The variables and dynamics of a snow storm can change the means and methods of snow removal from one day to the next. For this reason, a fleet of different types of snow removal equipment is usually available to handle a variety of weather scenarios. Airports differ in responsibility for apron snow removal operations. General aviation and small hub airports may rely solely on airport maintenance personnel for all snow removal, while the oper- ators of medium to large hub airports may contract apron and hold pad snow removal operations to a third party. In most cases, lease agreements between airlines and airport operators clearly identify each party’s responsibilities. At medium to large hub airports, agreements may designate respon- sibility for the removal of snow within leased areas to the leasing airline, with airport personnel or third-party contractors responsible for snow removal outside of the leased areas. Snow removal on aprons, especially on terminal aprons, is challenging given the presence of aircraft, the amount of equipment in the apron environment, and reduced visibility during snow storms. Depending on the timing of the snow storm event, snow removal may occur during aircraft loading, unloading, and servicing. GSE is usually required to be relocated out of the way, if not in use, to allow effective snow removal operations. Snow Removal Vehicles Terminal aprons are usually cleared by vehicles with snow plow attachments or brushes, as shown in Figure 3-53a. The snow is pushed to a designated location, usually the end of the aircraft parking area or a closed gate. Larger snow plows or front end loaders (Figure 3-53b) are used to remove the snow from these locations to stockpiles or snow melters. Aprons outside of the terminal area are usually cleared of snow by airport staff or contractors that use snow removal equipment similar to that used on taxiways and runways. Small trucks used for snow removal are often parked on the terminal apron while larger snow removal vehicles are staged at facilities located away from the terminal because of their size and the relative infrequency of use. Haul Routes and Stockpile Areas In most instances, snow removal vehicles operate on existing service or access roads to either enter or exit the apron area to access snow stockpiling areas. During heavy snow conditions, alternative routes may be necessary as primary routes can become impassable. Safety during Additional Guidance Transportation Security Administration, Security Guidelines for General Aviation Airports, May 2004. Transportation Security Administration, Recommended Security Guidelines for Airport Planning, Design and Construction, May 2011.

64 Apron Planning and Design Guidebook snow removal operations greatly increases when snow removal vehicles can be kept away from the tails of aircraft and avoid aircraft pulling in or departing from a gate or the effects of jet blast from taxiing aircraft. Apron size and location must be considered for snow stockpiling. Smaller airports usually have stockpile locations of 1,000 square feet to 2,000 square feet, while larger airports may need several areas up to several thousand square feet for adequate snow stockpiling, as shown on Figure 3-54. Snow Melting Snow melting at airports has been occurring for many years. Melting operations allow for the fast and effective removal of snow from apron and other areas of the airport with minimal disruption to aircraft or airline operations. Snow melting equipment is placed near snow piles and one or two front end loaders are used to load the snow melters. Many benefits are associated with snow melting rather than trucking snow from the apron areas. Melting reduces the need for large numbers of trucks to move snow and also reduces the need to stage or park trucks. There are two types of melters: stationary and mobile. (a) (b) Source: Ricondo & Associates, Inc. Figure 3-53. Snow removal vehicles.

Understanding the Apron Environment 65 Stationary melters are permanent units installed in the apron. These units are limited because they cannot be moved and snow must be pushed to the location of the melter. The current maxi- mum capacity for a stationary snow melter is approximately 350 tons of melted snow per hour. Mobile melters are built into trailers that can be pulled around the airport by semi-trailer trucks, as shown on Figure 3-55. Mobile melters must be operated near sufficiently sized drains to accept the melted snow runoff. The melters provide more mobility and operational flexibility as they can be easily moved where needed. Mobile melters have a higher snow melting capacity, typically up to 500 tons per hour. Heated Pavement Heated pavement, while not a new concept, has mainly been used in private and residen- tial applications. Heated pavement aids in the prevention of snow/ice accumulation without mechanical or chemical actions. It can have the benefit of reducing the amount of vehicular activity during adverse weather conditions. The heated pavement system may incorporate a “sandwich” method of construction, with the electrically conductive asphalt insulated between Figure 3-54. Snow stockpile. Source: A.S.S.E.T., LLC. Figure 3-55. Mobile snow melter. Source: A.S.S.E.T., LLC.

66 Apron Planning and Design Guidebook layers of pavement. As current passes through the conductive layer, heat is generated to a cycled temperature of approximately 34°F, melting the surface snow. The system may also incorporate tubes or pipes in the pavement, wherein a heated fluid is pumped through the system. Heat for the system can come from traditional heat sources or a geothermal heat pump that uses heat from the ground. Both systems typically involve a complex installation process and require high initial costs, although these costs may be offset by a reduction in personnel needed to mechani- cally clear snow with plows and sweepers. The benefits of these systems include a reduction in the use of chemical deicers and a reduction in the time required to remove snow from priority areas. While the construction of large expanses of heated pavement for aircraft aprons has not occurred, smaller-scale applications, in which limited sections of heated pavement are used for apron walkways, have been proposed. The loading and unloading of passengers in the apron area can contribute to hazardous conditions during snow events. The benefits of heated pavements in walkway areas are that they tend to stay free of snow/ice accumulation for longer periods during snow/ice events. Pavement Deicing Products At many airports, pavement deicing products are used on runways, taxiways, and aprons. These chemical products help mitigate snow and ice formation and accumulation on pavements. Common pavement deicing products used on airfield pavement include urea, sodium formate, sodium acetate, potassium acetate, and propylene and ethylene glycol-based fluids. In selecting pavement deicing products, consideration must be given to the compatibility and acceptability of the use of these chemicals in the vicinity of aircraft and airfield equipment, given concerns with potential corrosion and adverse environmental impacts. Automated spray deicing systems have been used by highway departments for many years as a self-contained and fully automated means of deicing bridge decks in remote locations. Limited testing for airfield use has not yielded sufficient benefits to warrant larger-scale installation in the apron or airfield environment. Additional Guidance FAA Advisory Circular 150/5370-17, Airside Use of Heated Pavement Systems, March 29, 2011. FAA Advisory Circular 150/5200-30C, Airport Winter Safety and Oper- ations, December 9, 2008.