determine the maintenance cost of electrical and plumbing systems of the terminal building, they need to inspect the lighting systems and the plumbing systems of their buildings.

7.1.3 Identifying and Updating Maintenance and Replacement Activities and their Unit Costs

During the condition assessment of the building envelope, the asset managers can also identify the types of maintenance activities that need to be performed to improve the terminal building conditions. If the building envelope components need only regular maintenance to bring in the operating conditions, then the asset managers can prepare a checklist of those maintenance activities to estimate the unit cost of those activities. However, if remodeling or a major overhaul is needed, then the replacement cost of those activities should also be calculated. To calculate the maintenance or replacement cost, those activities should be identified in detail. The building envelope maintenance activities can vary based on the components of the buildings. Some of the activities that should be performed to maintain the building’s exterior wall are: (1) Prevent water filtration in the wall, (2) prevent mold growth in the exterior wall, (3) avoid loose elements falling from the walls, (4) fix the shifted or displaced elements, cracks, spalls, and stains, (5) prevent water entry into a building, (6) repair cracked masonry joints, (7) replace aged flexible sealants, and (8) clean soiled stone or concrete (Facilities Net 2022).

Another important component of the terminal building that needs to be inspected is the roof. Asset managers need to inspect and determine the maintenance activities to be performed on the terminal building’s roof. The key elements of a roof to be regularly inspected are (Schultz 2016):

• The roof covering condition,
• Roof edging,
• Flashing,
• Supporting structures,
• Roof drains and scuppers,
• Roof penetrations, and
• Expansion joints.

The maintenance activities that need to be performed on the roof to keep it durable include:

• Clean the roof debris,
• Clean the drainage system of the roof,
• Protect the roof from water penetration,
• Avoid standing water or “ponding” on the roof, and
• Insulate the roof attic.

Another critical component of the terminal building is the foundation. It is crucial to maintain the foundation of the terminal building to keep the building structure stable. Some of the maintenance activities that need to be performed on the building foundations are (1) slope maintenance for proper drainage, (2) gutter and downspout inspection and maintenance, (3) proper subsurface drainage, (4) proper moisture content maintenance under the foundation, (5) maintenance of vegetation and trees that can damage the foundation, (6) plumbing leak repair, (7) foundation reinforcement steel exposure control, and (8) termite damage control (National Foundation Repair Association 2022). Airport asset managers need to maintain the interior of the terminal buildings in addition to the exterior. Some of the building interior maintenance activities and inspections are (Grainger KnowHow 2022):

• Inspect and maintain floors, ceilings, and interior walls;
• Check and maintain leaks;
• Check and maintain toilets and showers;

• Test and maintain smoke and carbon monoxide detectors;
• Check and maintain the fire alarm system;
• Test and maintain proper door operation;
• Inspect and fix door locks and closures;
• Clean the walkways;
• Inspect and maintain the electrical system;
• Inspect and fix all the lighting systems; and
• Inspect and maintain the plumbing system as required.

After identifying the required maintenance activities of the terminal building envelope, asset managers need to estimate the unit cost of the maintenance of these activities. The maintenance activities mentioned above have two major cost components: the labor cost and the material cost. If an airport needs equipment to perform these activities, then the equipment cost also needs to be calculated. If the airport’s in-house labor performs these activities, they can determine the labor cost by calculating the total labor cost spent on these activities over a year. Then the labor cost per square foot of the terminal building can be calculated by dividing the total labor cost by the area of the terminal buildings. This unit cost can provide the average labor cost spent to maintain the building envelope per square foot. Similarly, to determine the material unit cost, the airport needs to determine the amount of money spent on material costs to maintain the terminal building per year. Dividing that amount by the total area of the terminal building will then provide the unit cost of the materials.

To calculate the total unit cost, the cost of labor and materials needs to be added, and, if equipment is used, then the cost of the equipment should also be added. It is a good practice to add 20% overhead and contingency costs to acquire the accurate total cost of maintenance. Once the average maintenance cost per square foot of the building envelope is calculated, this can be used to determine the maintenance cost of the terminal building for the following year. However, if airport asset managers would like to determine the unit cost of labor for each activity, they need to refer to the national unit cost database available from the RSMeans Cost Guide (RSMeans Cost Guide 2021). This cost guide provides the unit cost of labor, equipment, and materials required to perform these maintenance activities. Once the quantity of these activities is determined from the asset inventory database, the total cost can be calculated by multiplying the quantity by the unit cost of maintenance. An overhead or contingency cost of 20% can then be added to get the accurate maintenance cost of the terminal building. Also, these costs should be adjusted based on the year the maintenance was done using the cost escalation factors available from the RSMeans Cost Guide.

7.1.4 Determining the Terminal Building Failure Probability with Regular Maintenance

In any type of asset, there is always the probability that it can fail, even if the maintenance is conducted regularly. In the case of a terminal building, there is always the possibility that the components of the building can fail even with regular maintenance. Generally, failure can occur from natural events such as earthquakes, wind, fire, snow, or rain. In 2004, the terminal building of Charles De Gaulle Airport in Paris collapsed (Craven 2019). Despite being a newly built terminal, it collapsed due to design errors and a lack of construction quality. Although the possibility of terminal building failure is very rare, airport asset managers still need to assume that some components of the terminal building can fail, e.g., parts of the walls, roof, doors, windows, etc.

Some literature shows that the aging of a building can cause significant damage to the building components. In 2013, the University of Michigan found that 72% of all buildings in the United States were more than 20 years old (University of Michigan 2022). A commercial building has an average life of 50 to 60 years (Shingobee 2021), but the lifespan of a building depends on various

factors, including maintenance; external environmental factors like climate hazards and storms, harsh sunlight, heavy rainfall, and snow; internal factors like faulty plumbing, excessive heat, and improper drainage; and usage duration. Concrete decay, roof deterioration, electrical and plumbing deterioration, and door and window damage are some of the major sources of damage (Dansig 2021). Due to the above reasons, airport asset managers need to consider budgeting for emergency maintenance of their terminal buildings. It is highly suggested that these emergency funds be allocated for each component of the building separately and that the budget be based on the age of the building components. There is no accurate method to estimate this emergency budget, but generally 10% to 50% of the total maintenance budget of each component should be allotted for emergency maintenance work of the terminal building. Therefore, the asset managers need to increase the maintenance budget of the terminal building envelope, considering the probability of failure of some components of the building.

7.1.5 Determining the Terminal Building Failure Probability with Delayed Maintenance

As described in section 7.1.4, there is a probability that the terminal building can fail even when regular maintenance is conducted. If maintenance is delayed in terminal buildings, the probability of terminal building component failure significantly increases. Therefore, airport asset managers need to ensure that a significant amount of emergency funds are allocated for building envelope maintenance if the maintenance is delayed by a certain number of years. It is difficult to determine how much money will be needed for emergency maintenance, but asset managers can increase the emergency funds by twofold compared to the regularly maintained terminal buildings. There is no literature available to determine what percentage of the total maintenance budget of the terminal building should be allocated to emergency maintenance work. As described in the above section, asset managers need to allocate more money for emergency maintenance if the component maintenance within the terminal is delayed. Asset managers can also refer to the RSMeans Cost Guide to allocate contingency costs for these kinds of emergency work.

7.1.6 Estimating Terminal Building Maintenance and Replacement Budget without Delayed Scenarios

Once the quantity of each component of the terminal building and their unit maintenance costs are determined, asset managers can determine the maintenance cost per year by multiplying these two factors. Then, the asset managers can add emergency costs (contingency costs) as described in section 7.1.4 to factor into the failure probability of these building components. Depending upon the cost inflation factor, asset managers may need to increase the maintenance cost for the following year. The research team showed how to incorporate cost inflation factors to adjust the maintenance and replacement costs in the spreadsheet tools developed for other airport assets. These cost inflation factors can be found in the RSMeans Cost Guide, or asset managers can search the consumer price index data available on the Bureau of Labor Statistics website.

7.1.7 Estimating Terminal Building Maintenance and Replacement Budget with Delayed Scenarios

If an airport needs to delay the maintenance of its terminal building components due to financial constraints, it should determine which terminal building maintenance component can be delayed first, considering the lowest impact on the structural damage of the building. Once asset managers identify the building components in which maintenance must be delayed, they should predict the condition of each component after the delay. Because the deterioration models of the building with delay are not available, the airport asset manager must increase the contingency cost for emergency maintenance in the case of delayed scenarios. The emergency maintenance

cost due to delay needs to factor in the probability of failure as explained in section 7.1.5. Then the maintenance cost to correct that component after the delay needs to be calculated by multiplying the unit cost and the quantity of the component and adding the contingency costs. The unit cost also needs to be adjusted based on cost inflation factors. These cost inflation factors can be found in the RSMeans Cost Guide or the consumer price index data available on the Bureau of Labor Statistics website. An airport can use its own cost inflation factors for maintenance work if they are available.

7.2 Airport Hangars

The hangar is a building or structure designed to house an aircraft. Most airports own aircraft hangars. These hangars are used to keep the aircraft protected from weather and direct sunlight, and are also used for maintenance, repair, and storage. Hangars are one-story structures built of metal, wood, or concrete. Depending on the size of the airport, small or large hangars may be used. Large-size airports usually own multiple hangars to house their aircrafts for maintenance or storage. If the hangar is used for aircraft maintenance, they are generally called aircraft maintenance hangars (Tronair n.d.). The aircraft maintenance hangars are generally large, open, and have ample space for major repairs. These types of hangars also have maintenance stands, tool stands, scaffolding, and other equipment required for aircraft maintenance. The hangar should have firm, solid foundations made of concrete. The walls of the hangar can be steel columns with masonry walls, concrete, or drywall. Generally, the roof of the hangar should be made of shockproof and fireproof materials (SAFS Steel Structure n.d.). The FAA has developed a policy on the non-aeronautical use of airport hangers. If the airport received an AIP grant to build the hangar, they should abide by these rules. The hangar should be used for aeronautical purposes, however, with the approval of the FAA, the airport can designate some areas for non-aviation use (FAA 2016b). The main purpose of an aircraft hangar is aircraft storage. If the hangar is used to store the aircraft, then storage of non-aeronautical items in the hangar does not violate FAA policy. Maintenance of the hangar is critical to keep the structure of the building intact. Like terminal buildings, airport asset managers need to maintain these hangars. Asset managers can determine the maintenance cost of the hangars with and without delayed scenarios by dividing the hangars into the following building components:

• Foundation,
• Floor,
• Wall structure, and
• Roof.

Asset managers can follow the steps provided in the following section to determine the maintenance cost of each component of the hangars with and without delayed scenarios. Then the total cost of the maintenance and replacement of the hangar can be calculated by adding these costs for each component. As mentioned for other airport assets, asset managers need to follow seven steps to determine the maintenance and replacement costs of the hangar with or without delayed scenarios.

7.2.1 Establishing the Asset Inventory of an Airport Hangar

The airport asset manager should keep the inventory of each hangar separately. If the hangars are of the same size and height, then one inventory can be used for multiple hangars. The asset manager should have the dimensions and types of materials used for each of the four major components of the hangar, keeping data related to length, width, depth, and the material used for the foundation. They should also keep the dimensions, wall size, and type of materials used on the hangar floor. The asset manager needs to collect detailed information about the

roofing structures, including dimensions and types of material used for the roof structure and roof shingles. In addition to this, the airport must also keep the inventory of the exterior drainage to keep the water out of the foundation. The asset manager must also keep the inventory of the door and windows related to size and material type.

7.2.2 Performing a Condition Assessment of an Airport Hangar

The aircraft hangar consists of components similar to a building. Therefore, airport asset managers can perform condition assessments of the hangar similar to the terminal buildings. However, the airports do not need a detailed assessment of the plumbing provided in the kitchen and restrooms. Asset managers can follow a process similar to the one used for terminal buildings to assess the condition of the aircraft hangars. The airport should assess the conditions of the following main components of the hangars: (1) structural system, (2) building envelope, (3) interior, (4) mechanical system, and (5) electrical system (S2 Architecture et al. 2017).

Asset managers should visually inspect the foundation of the hangar every year and determine its condition. If any structural damage issues are found in the foundation, the structural engineers should perform a detailed engineering analysis to determine the root cause of the issue. If any types of non-destructive tests need to be performed to determine the stability and loading capacity of the foundation, the structural engineering consultant should be contacted. As in the terminal building, the asset manager should also assess the condition of the building envelope every year. The building envelope consists of the exterior and the roofing of the hangar. If the exterior wall has extensive moisture-related deterioration, it should be fixed immediately. Similarly, if the asset manager finds that the roof is leaking or the roof rafters are damaged, then they should also be fixed immediately.

Airports should also assess the interior condition of their hangars. Asset managers should inspect and assess the condition of interior wall finishes, any issues related to building envelopes, water penetration affecting the hangar floor, ceiling finishes, etc. The airport should also assess the interior wood doors, frames, and plumbing fixtures. Another item to be inspected regularly is the mechanical and plumbing system in the hangar. The hangar does not typically have extensive mechanical and plumbing systems like in the terminal building. However, the plumbing required to provide a water and sewage system in the hangar must be inspected regularly to check whether it is working properly. Similarly, HVAC units in the hangar need to be inspected every year. The process of quantifying the impact of delayed maintenance of HVAC units can be found in Chapter 6. The airport also needs to assess the condition of the sewage system provided in the hangar along with the electrical system of the hangar every year. During the assessment of the electrical system, asset managers should inspect all lighting wires, light bulbs, power distribution systems, receptacles, electrical devices, and fire alarm panels. When assessing the condition of the hangar components, asset managers can divide the condition into four categories e.g., excellent, good, fair, and poor, depending on how quickly they need to be fixed.

7.2.3 Identifying and Updating Maintenance and Replacement Activities and their Unit Costs

The maintenance activities identified in the airport terminal building can be used to maintain the hangars. Because most of the building components in these two assets are similar, asset managers can use similar maintenance activities to those used in terminal buildings to maintain the hangar. Some specific maintenance activities that can be performed in the hangar building envelope are (S2 Architecture et al. 2017):

• Change exterior cladding, including associated flashing.
• Repair wall insulation.

• Repair walls, mortar joints, etc.
• Maintain or replace exterior doors and frames.
• Maintain or replace hangar doors.
• Maintain or replace hangar windows.
• Maintain or replace roofing, including cap flashings, etc.
• Maintain or replace insulation and roofing membranes on the top surface.

Airports should also assess the condition of electrical systems provided in the hangar. Some of the maintenance activities airports can perform related to electrical systems are:

• Maintain or replace existing power distribution system, including conduits and feeders.
• Maintain or replace branch circuit wiring.
• Maintain or replace lighting fixtures, including exit lights, emergency lighting, and lighting controls.
• Maintain or replace receptacles, mechanical starters, and other electrical devices.
• Maintain or replace fire alarm devices and panels.

Asset managers should determine the unit cost of these maintenance activities. As described in section 7.1.3 for terminal buildings, the airports can use their existing unit cost of maintenance, or they can determine the unit cost by using the RSMeans Cost Guide. If these maintenance activities are carried out by contractors, the airports can ask for a bid cost for maintenance budget preparation purposes. If the airports perform these maintenance activities using their in-house manpower, they can estimate the number of personnel involved in these activities per year and determine the labor cost per square foot of the hangar. Then the asset managers can determine the material costs for hangar maintenance by using the ratio of labor and materials found in the RSMeans Cost Guide. These unit costs need to be adjusted based on the budget preparation year. Cost inflation factors can be found in the RSMeans Cost Guide, or asset managers can search the consumer price index data available on the Bureau of Labor Statistics website. It is a good practice to determine the unit cost for each component of the hangar and estimate the maintenance cost of hangars with and without delay. Asset managers can also use the overall unit cost of maintenance for the hangar to determine the total maintenance cost for budgeting purposes.

7.2.4 Determining the Hangar Component Failure Probability with Regular Maintenance

The airport can use a process similar to the one mentioned in section 7.1.4 to incorporate failure probability costs in the total maintenance costs of the hangar. Because terminals and hangars have similar components, the percentage of contingency costs can be factored into the maintenance cost to incorporate the failure probability of the hangar. There is no systematic method of incorporating the hangar failure cost in the maintenance budget, but asset managers can use the contingency cost procedure to cover the failure of the hangar in normally maintained conditions.

7.2.5 Determining the Hangar Failure Probability with Delayed Maintenance

The research team could not find any literature or process that explains how to determine the failure probability of the hangar in a delayed maintenance scenario. When the maintenance is delayed, it will have an adverse effect on the condition of the hangar components. However, it is difficult to predict how fast the hangar components will deteriorate. As described for terminal buildings in section 7.1.5, asset managers can increase the contingency cost to incorporate the failure probability of hangar components in delayed scenarios. Airports can use similar percentages of contingency as described in the terminal building case.

to this guidebook, some of the major inspection and maintenance activities to be performed on rail tracks are (American Public Transportation Association 2017):

• Inspect and replace defective rails;
• Inspect the continuous welded rail track and fix it if found defective;
• Inspect the track geometry;
• Inspect mainline switches, track crossings, and moveable bridge lift rails and fix them if found defective;
• Inspect and replace the yard switches; and
• Inspect and fix the rail tracks in the event of a fire, flood, severe storm, or seismic activity.

If the APM guideway system has special structures like tunnels, bridges, and fences, then the following maintenance activities need to be performed annually:

• Inspect the bridges’ sub- and superstructure for any defects and maintain them if found defective.
• Inspect the tunnel structure and maintain it if found defective.
• Inspect the fencing structures and maintain them if found defective.

The maintenance facilities and stations of the APM system should also be maintained. The maintenance activities involved in these facilities and stations are similar to that of the terminal buildings. If any special equipment is used, the airports also need to maintain the special equipment housed in the facilities. Command and communication facilities are critical to the APM system. In these facilities, asset managers need to perform regular maintenance, software maintenance, and upgrades. Software is key to operating the APM system effectively. Asset managers should also maintain the hardware of the APM systems.

After identifying the maintenance activities of the APM systems, airport asset managers need to determine the unit cost of these maintenance activities. Airports can refer to the RSMeans Cost Guide to determine the cost of these maintenance activities. Also, asset managers can determine the number of labor hours used to maintain their APM systems per year and convert the cost into feet or mile unit costs. Airports can determine the ratio of labor and materials spent on maintaining their APM systems and find the unit cost of materials. The total unit cost of maintaining the APM system per linear foot or mile can be calculated by adding the labor and material costs and the overhead cost. These unit maintenance costs can be used to estimate the future maintenance and replacement costs of the APM systems with or without delayed maintenance.

7.3.4 Determining APM Components’ Failure Probability with Regular Maintenance

The APM system consists of physical structures as well as mechanical and electrical systems. Therefore, asset managers need to determine how to incorporate the probability of failure of these components in regularly maintained conditions. The airports can use processes similar to those in terminal buildings to determine the failure probability of structures like bridges, tunnels, guideways, stations, etc. Because there is no exact theoretical method to calculate failure probability for physical structures, the contingency cost addition method can be used to incorporate the failure costs of these structures. After calculating the maintenance and replacement costs of these structures, asset managers can add appropriate contingency costs in case of structure failures.

Asset managers can use the probability theory to determine the electrical and mechanical systems failure probability of APM systems. The Weibull distribution theory can be used to determine the failure probability of an APM system’s train and guideway mechanical systems. Asset managers can determine the life of an APM system’s passenger cars and guideway systems. They can estimate the duration at which 63% of the passenger cars and guideway systems will fail when

they are regularly maintained, and they can use these values in a Weibull probability distribution equation. Asset managers can use a shape factor of 3.5, considering the failure probability as normally distributed. They can refer to section 6.4.5 under the baggage handling system delayed maintenance cost calculator to determine the cumulative failure probability of passenger cars and guideway systems of APMs.

Airports can also use the Weibull probability distribution theory to determine the cumulative failure probability of APM electrical systems. Similar to the mechanical system described above, asset managers can determine the duration at which 63% of their electrical system will fail in regularly maintained scenarios. Asset managers can consider that the failure probability distribution of the electrical system of the APM will be normal and use a value of 3.5 as the shape factor. The process of determining the failure probability of electrical systems under normal conditions is shown in section 5.3.4.

7.3.5 Determining APM Components’ Failure Probability with Delayed Maintenance

Asset managers can use the contingency cost estimation process to determine the impact of delayed maintenance on the physical structures of the APM system. For delayed maintenance scenarios, asset managers can double the contingency cost percentage compared to regularly maintained structures. They can increase the contingency cost based on the age of the structures as described in the previous section.

Airports can also use the Weibull distribution theory from the previous section to determine the cumulative probability of an APM’s mechanical and electrical component failure in the delayed maintenance scenarios. The process is similar to the one described in section 7.2.4, however, the duration at which 63% of the components will fail when their maintenance is delayed will decrease. Asset managers can assume that this value will decrease by 50% depending upon the types of components. The cumulative probability distribution can then be determined for the mechanical and electrical components of an APM by using a shape factor of 3.5. The research team developed a spreadsheet tool for determining the delayed maintenance and replacement costs for baggage handling systems and passenger boarding bridges. Airports can refer to that sheet to determine the delayed maintenance cost of mechanical components of their APM system. They can also refer to the spreadsheet tool developed for runway lighting systems to determine the delayed maintenance costs of the electrical components of their APM system.

7.3.6 Estimating the APM Maintenance and Replacement Budget without Delayed Scenarios

Airport asset managers can use their inventory, condition assessment, unit cost of maintenance, contingency cost percentages, and the failure probability of mechanical and electrical components of the APM system to determine regular maintenance and replacement costs for the following year. They must adjust the unit cost of these maintenance activities for the subsequent year. Asset managers can use their own airport’s cost inflation factors for labor and material costs or get these cost inflation factors from the RSMeans Cost Guide or the consumer price index of the Bureau of Labor Statistics. Once the unit cost of maintenance for each component of an APM system is calculated, airport asset managers can multiply this adjusted unit cost with the quantity to estimate the total maintenance and replacement costs. Airports should always consider contingency costs for the physical components of their APM system in case some components fail during operation. As described in the previous section, asset managers can estimate this contingency cost based on the age of the structures.

Asset managers should also add the cost related to the probability of failure of the mechanical and electrical components of the APM system. To determine this cost, they can multiply the replacement cost and the failure probability of these components. Airports should have some leverage in their maintenance and replacement budget in case some components fail abruptly during the operation of the APM system.

7.3.7 Estimating the APM Maintenance and Replacement Budget with Delayed Scenarios

Airports can use a similar process to the one described in section 7.3.6 to determine the maintenance and replacement cost of APM systems with delayed scenarios. The only difference is the failure probability cost of the APM system components. This failure cost will increase significantly depending on the number of years by which maintenance and replacement are delayed. The research team developed spreadsheet tools for other airside and landside assets for up to 10 years of delay. However, asset managers should understand the overall implication of delaying APM system maintenance on the performance of the airport. When calculating the delayed maintenance and replacement costs, the cumulative failure probability of mechanical and electrical systems will increase significantly compared to regularly maintained APM systems. Therefore, the delayed maintenance cost will increase significantly, and the incremental cost will depend on the age of the APM system. The older an APM system is, the higher the delayed maintenance and replacement cost will be because the probability of failure increases exponentially. Asset managers should use appropriate future cost inflation factors to determine this future cost. Asset managers can refer to other spreadsheet tools developed by the research team to adjust inflation factors.