can use these checklists to keep records of their service vehicles. A sample of a checklist is shown in Appendix A (QualityForms n.d.).

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

During annual maintenance and inspection, the mechanics determine the types of maintenance required over the following year to keep service vehicles in good condition. The preventive maintenance activities are performed based on mileage or the number of years in service. The preventive maintenance activities and their frequency based on mileage are provided in Table 6-1. Detailed maintenance tasks are provided in Appendix B (Kansas Department of Transportation 2022).

The preventive maintenance in Table 6-1 needs to be performed as scheduled to extend vehicle life. If these maintenance activities are not performed as prescribed, the vehicles risk breaking down, and repairing them can cost more than regular maintenance. To estimate a pickup truck’s regular and delayed maintenance costs, the unit cost of performing these activities should be estimated. Without the unit cost for performing preventive maintenance, the accurate maintenance costs with or without delay cannot be estimated accurately. The research team contacted airports during the data collection phase to collect the unit cost data for preventive maintenance activities performed on their vehicles. None of the airports were able to provide systematic unit cost data. The team therefore conducted research to determine the cost of performing these maintenance activities on the pickup trucks. Enough maintenance cost data were available for a full-size pickup truck on the web (https://enginepatrol.com/ford-f-150-maintenance-costs-expenses/). Table 6-2 shows the cost data collected for the spreadsheet tool to determine the delayed maintenance costs (Engine Patrol 2021). When the total cost of maintenance is calculated, the team suggests adding 10% miscellaneous cost.

6.1.4 Determining the Full-Size Pickup Truck Failure Probability with Regular Maintenance

As described in the previous section, one of the critical tasks to determine the regular maintenance budget for assets is to find the deterioration rate of the asset in normally maintained conditions. In determining the regular maintenance costs of pickup trucks, it is important to find the cumulative probability distribution of engine failure in a full-size pickup truck under regularly maintained conditions. The research team contacted the case study airports to collect this failure probability but was unable to receive any data. The team searched the engine failure probability

Table 6-1. Preventive maintenance activities of vehicles and their frequencies.

Table 6-2. Unit cost for preventive maintenance of a full-size pickup truck.

or reliability data of a full-size pickup truck online and found the failure probability data, which is shown in Table 6-3 (CarEdge 2022). These vehicles travel an average of 10,000 miles per year. Based on this information, 59% of the full-size pickup truck transmission engines will break at the 12-year mark.

Generally, a full-size pickup truck lasts for 15 years, which is approximately the equivalent of 150,000 miles. Because only 12 years of probability data were available, these data were used to generate a regression equation to predict the failure probability of a full-size pickup truck over 15 years. Figure 6-2 shows scatterplots with cumulative failure probability and the age of the pickup truck. Based on the line of best fit, the regression equation to predict the cumulative failure probability of the full-size pickup truck is shown in Equation 6-1. The line of best fit has an R-squared value of 0.98, which is essentially a perfect fit.

Using Equation 6-1, the probability of the full-size pickup truck can be determined as shown in Table 6-4. The table shows that the probability of engine failure of a full-size pickup truck after 15 years will be 100%. The truck will need to be replaced entirely when it reaches 15 years or 150,000 miles. These failure probability values can be used to determine the replacement cost of transmission engines in full-size pickup trucks.

Table 6-3. Cumulative failure probability of a full-size pickup truck.

none of the airports were able to provide these data. They stated that the engine life of the vehicles reduces significantly when they are not maintained regularly as suggested by the manufacturers. The research team assumes that the vehicle life will reduce significantly when regular maintenance is delayed, meaning that the failure probability of the vehicle engine will likely double compared to the probability of failure with regular maintenance. Based on Table 6-4, a new cumulative failure probability for delayed maintenance of the full-size pickup truck is provided in Table 6-5. Table 6-5 shows that the failure probability increases twofold if the maintenance is delayed during that year. Based on delayed maintenance scenarios, the life of the pickup truck will be reduced to 12 years (120,000 miles) from the original 15 years (150,000 miles).

6.1.6 Estimating the Full-Size Pickup Truck Maintenance Budget without Delayed Scenarios

The maintenance cost of pickup trucks without delayed scenarios can be calculated by determining the types of maintenance that need to be conducted, their frequency every year, and the unit cost of each of these preventive maintenance activities. The research team developed a spreadsheet tool that can determine the preventive activities performed on the full-size pickup truck based on the age or mileage of the vehicles (see Table 6-4). Then, considering the activities that need to be performed, the regular maintenance cost can be calculated using the unit costs provided in Table 6-2. As described in Section 6.1.3, these unit costs are based on data from 2021. To adjust this base cost for future years, however, the research team collected the cost inflation indices of vehicle maintenance from the Bureau of Labor Statistics (2022c). Based on the cost indices available from 2008 to 2021, the average inflation rate of the repair and maintenance of motor vehicles is 2.93%. This default inflation rate can be used to calculate the total maintenance and replacement cost of the full-size pickup truck for future years. The tool also has the capability to use the recent inflation rate, if different from this default rate, to calculate future maintenance and replacement costs.

6.1.7 Estimating the Full-Size Pickup Truck Maintenance Budget with Delayed Scenarios

To determine the total maintenance and replacement costs, the research team calculated the frequency of the maintenance activities to be performed after certain periods of delay using the spreadsheet tool. Based on the frequency of maintenance, the team calculated the total maintenance and replacement costs for delayed scenarios. In the case of pickup truck delayed maintenance calculations, the cost of transmission replacement will generally increase compared to the

Table 6-5. Cumulative failure probability of full-size pickup trucks under delayed maintenance scenarios.

regular maintenance scenarios because the probability of transmission engine failure will be higher. Therefore, the probability of failure shown in Section 6.1.5 for delayed maintenance conditions is higher than that of regular maintenance conditions. Because the transmission replacement costs do not vary greatly, the maintenance and replacement costs in delayed scenarios will not be significantly higher than the base cost. It can also be assumed that, due to delayed maintenance, the entire pickup truck will need to be replaced, if not regularly maintained, and the replacement cost can be calculated using the purchase cost of the full-size pickup truck, which will show significant cost increases in delayed scenarios. It is difficult to predict the impact of the pickup truck engine’s failure on airport maintenance and replacement costs. It is therefore suggested that delaying maintenance is avoided, and, if maintenance is delayed, it should not be delayed by more than 2 years. It is also assumed that the pickup trucks are not replaced unless their life reaches 150,000 miles under normal maintained conditions, or 120,000 miles under delayed maintenance scenarios.

6.1.8 Reporting the Impact of Full-Size Pickup Truck Delayed Maintenance and its Consequences

The research team developed a spreadsheet tool to determine the impact of delaying maintenance on full-size pickup trucks in terms of airport maintenance and replacement costs. The age or the mileage of the full-size pickup truck will have an impact on the maintenance and replacement costs of the vehicle. If the pickup truck is new, then the maintenance costs tend to be lower. However, if the age or mileage of the vehicle is high, the maintenance costs are often high. When analyzing the impact of delayed maintenance on pickup truck maintenance and replacement costs, the research team considered three types of full-size pickup trucks: one with 10,000 miles, another with 50,000 miles, and, finally, one with 70,000 miles. Two- and 5-year delayed scenarios were considered. The team calculated the trucks’ regular maintenance and replacement costs for the year 2023 without delayed maintenance. Then the maintenance and replacement costs for the years 2025 and 2028 with 2- and 5-year delayed maintenance were considered to determine the impact on airport maintenance and replacement costs. It was assumed that the airport owns five full-size pickup trucks.

The spreadsheet tool developed to calculate the impact of delayed analysis of the full-size pickup truck is flexible. The tool can calculate the frequency of various maintenance activities performed within a given fiscal year. The user can also adjust the frequency of maintenance activities and enter their own values. The tool uses the unit cost of each of the activities collected during the data collection phase, and, if these unit costs are different from the ones they are using, they can enter their values. The user can also select the number of years delayed and the cost inflation factor for the maintenance and replacement activities. If the user wants to calculate the delayed maintenance costs in present value, they can select the discount rate provided in the tool.

Case Study Results of the Consequence of Delaying Maintenance on Ford Full-Size Pickup Trucks

When analyzing the total maintenance cost of full-size pickup trucks, the research team assumed that the pickup trucks would operate 10,000 miles per year. It was also assumed that, when the pickup truck has 10,000, 50,000, or 70,000 miles on it, the transmission engine has not been replaced. Figure 6-3 shows the total maintenance and replacement costs of five full-size pickup trucks with 10,000, 50,000, and 70,000 miles, with 2- and 5-year delayed scenarios. For a truck with 10,000 miles, the 2-year maintenance delay increases the total maintenance and replacement costs threefold compared to maintenance without the delay. However, when maintenance is delayed by 5 years, there is a 50% increase in the maintenance and replacement costs. The main reason for this is that, in a 5-year delay, the pickup truck mileage reaches 70,000 miles instead of 50,000 miles and the failure probability of the transmission engine increases by 8.4%; the pickup truck will also need to have its alternator changed, which increases the total maintenance and replacement costs. When the mileage in the vehicle reaches about 50,000, the cost of the delayed maintenance for

2 and 5 years will differ by a similar amount due to the previously stated reasons. The same logic applies to a pickup truck that has accumulated 70,000 miles.

6.2 Airport Snow Removal Equipment

Snow falling on runways and taxiways needs to be removed immediately so that airplanes can land and take off safely. Generally, at airports located in areas of heavy snowfall, asset managers need to keep snow removal equipment to remove snow quickly. Airports use snow blowers to remove snow when the quantity is small. If the snow is in large quantities and runways are long enough, airports generally use the wheel loader with an attached snowblower to remove the snow. Some of the airports outsource the snow removal activities to contractors. Airport asset managers must maintain the airport’s snow removal equipment, e.g., blowers, loaders with blower attachments, and wheel backhoes so that snow can be removed quickly. Asset managers must keep an inventory of snow removal equipment. The inventory should consist of types of equipment, age of the equipment, hours of operation, make and model, and date purchased so that the maintenance and replacement costs can be estimated accurately. The FAA (2022d) has developed a tool to estimate the total amount of snow, and the number of front-end loaders, rotary plows, hoppers, and sweepers to remove snow from runways and taxiways based on the size of their airports. This tool is very user-friendly and can be used by asset managers to calculate the number and size of snow removal equipment needed.

FAA AC 150/5220-20A—Airport Snow and Ice Control Equipment discusses requirements for snow and ice removal control equipment (FAA 2014c). This AC provides advice to assist airport operators in the procurement of snow and ice control equipment for airport use. It emphasizes the selection process of snow removal equipment for airports. The main three steps for selection of the equipment are:

• Identifying the type of equipment for a specific task,
• Determining the number of such equipment, and
• Using the recommended equipment specifications to better ensure the equipment performs the required task.

Depending upon the airport and the amount of snow that needs to be removed each year, the airport can use high-speed rotary plows, snowplows, solid and liquid material spreaders, runway brooms with air blasts, and loader-mounted snow blowers. While selecting the snow removal equipment, the airport asset manager must compare the cost/benefit relationship of acquiring a multifunctional piece of equipment offering several attachments versus the acquisition of single units, each designed primarily to accomplish one task. The FAA has developed two other ACs related to snow removal: AC 150/5200-30DAC – Airport Field Condition Assessments and Winter Operations Safety and AC 150/5220-18A– Buildings for Storage and Maintenance of Airport Snow and Ice Control Equipment and Materials. The first AC provides guidelines to assist airport operators in developing a snow and ice control plan, assessing and reporting airport conditions through the utilization of the Runway Condition Assessment Matrix, and establishing snow removal and control procedures. The second AC determines the selection and design of buildings used to store and maintain airport snow and ice control equipment. However, the FAA has not developed any guidelines related to the maintenance of snow removal equipment. Therefore, the team developed a framework to determine the impact of delayed maintenance of snow removal equipment on an airport’s maintenance budget. An asset manager needs to follow the framework provided in Figure 6-4 to determine the maintenance costs of snow removal equipment with and without delayed maintenance.

6.2.1 Establishing Asset Inventory

Generally, large-hub airports located in snow-prone areas will have a large fleet of snow removal equipment. Therefore, airport asset managers need to keep an inventory of all their equipment. The asset manager needs to record the amount of equipment, condition of the equipment, hours used, age, date purchased, and maintenance performed on the equipment. The make and model of the equipment, its horsepower, and whether it is a diesel or gasoline engine also need to be recorded. During the data collection phase, the airports stated that they had these records and provided them. However, the data were insufficient to develop a spreadsheet tool for quantifying the impact of delayed maintenance of snow removal equipment on an airport’s maintenance budget.

6.2.2 Performing a Condition Assessment

The condition assessments of the snow removal equipment and the service pickup trucks were kept in a similar manner. None of the airports that the research team talked with have any rating of their snow removal equipment. The mechanics estimated the condition of the equipment based on their hours of operation and the age of the equipment. Although the mechanics monitor the conditions of the equipment every year, the inspection data for the equipment was not available. Also, the team was unable to retrieve any condition data for the airports’ snow removal equipment. Therefore, it is necessary for airport asset managers to keep the inspection and condition data of snow removal equipment up to date, so that maintenance costs with and without delayed scenarios can be calculated more precisely for budgeting purposes. The New York State DOT has developed a maintenance inspection checklist for front-end loaders, shown in Appendix C (New York Department of Transportation 2022). This inspection checklist covers all maintenance activities performed during the loader inspection. It covers the under hood, interior, and exterior, as well as any attachments. The inspection of the loader using this kind of inspection list will help an asset manager estimate the maintenance and replacement costs for the coming year. This is important in determining the remaining life of the equipment. The inspection checklist will help identify major engines or other parts needing replacement for the coming years. Therefore, airport mechanics should use this type of inspection sheet to evaluate their snow removal equipment and rate their equipment in Excellent, Good, Fair, and Poor conditions. These data need to be entered into the conditional database so that, during the budget preparation process, they can be utilized to determine accurate maintenance and replacement costs of the snow removal equipment.

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

During snow removal equipment inspection, mechanics identify the preventive maintenance activities that need to be performed to keep them in operating condition. These maintenance activities are key in determining the maintenance and replacement costs of snow removal equipment for future years. The preventive maintenance activities that need to be performed depend upon the types of equipment. However, for this research, the team gathered preventive maintenance activities for front wheel loaders with snow blower attachments (see Table 6-6) (Kramlich 2019). Table 6-6 shows the maintenance activities that need to be performed and the frequency of those activities. Generally, the life of a front-end loader with a blower attachment is 15,000 hours or 15 years, which translates to about 1,000 hours of operation every year. Other heavy equipment manufacturers like Caterpillar have developed operation and maintenance manuals for this type of equipment (Caterpillar n.d.).

After the maintenance activities of snow removal equipment are identified, asset managers must determine the unit costs to perform these tasks. Generally, to determine the unit costs of these tasks, the labor hours to perform these activities need to be estimated, and then the parts needed for these repairs should be calculated. The research team tried to collect these data from the airports; however, the airports failed to provide the data. They performed these preventive maintenance activities but did not collect labor hours and parts data. Therefore, the research team conducted an online search and found labor hours and parts data for a front wheel loader. There are no labor and parts data available for every maintenance activity to be performed on the loader; however, the total labor hours for maintenance of wheel loaders per 1,000 hours of operation and the ratio of labor and parts cost were found online (CASE Construction n.d.). Table 6-7 shows the labor hours for performing these maintenance activities on front wheel loaders for every 1,000 hours or 1-year period, as well as the hours required to replace the tires and transmission engine.

During the data collection phase, the research team could not collect the unit cost data of snow removal equipment maintenance used by the airports. Therefore, the cost available on the CASE Construction website was used to determine the unit cost of maintenance of a front-end loader and

Table 6-6. Preventive maintenance activities of front-end loaders and their frequencies.

Table 6-7. Labor hours required for maintenance and replacement activities of front-end loaders.

Table 6-8. Unit maintenance and replacement cost calculations for front-end loaders.

its tire and engine replacement costs. Table 6-8 shows the cost calculation process for determining the maintenance and replacement unit costs for front wheel loaders. These costs were also verified using the RSMeans Cost Guide (2021). The numbers calculated here are based on 2021 figures.

6.2.4 Determining the Snow Removal Equipment Failure Probability with Regular Maintenance

The failure probability of snow removal equipment used by the airports is not available from asset managers because airports do not keep these data. Therefore, the research team searched the failure probability of heavy equipment online, but was unable to collect any data. Therefore, the research team used the Weibull probability distribution theory to calculate the cumulative probability of engine failure of a front-end loader. As described in the previous chapter, to calculate the cumulative probability of any electrical or mechanical system, the scale and shape factors need to be identified. For heavy equipment failure, a shape factor of 3.5 is considered, which shows the normal distribution of the failure probability of a front-end loader. Because the life of front wheel loaders is generally considered to be 15 years, assuming 1,000 hours of operation every year, the scale factor, which is 63% of the failure value, is assumed as 8,000 hours for regularly maintained loaders. Table 6-9 shows the Weibull failure probability for a front wheel loader for its total life of 15 years or 15,000 hours. This probability of failure can be used to determine the replacement costs of the regularly maintained loader. When the replacement cost is calculated, only the unit cost of installing a new transmission engine will be considered. If the age of the vehicle exceeds 15 years or 15,000 hours of operation, then the front wheel loader is considered in need of replacement.

6.2.5 Determining the Snow Removal Equipment Failure Probability with Delayed Maintenance

The research team used the probability theory to determine the transmission engine failure rate of front-end loaders in regular maintenance scenarios. For delayed maintenance scenarios, the failure rate of the transmission engine of a front-end loader was also determined using the Weibull distribution theory. In delayed maintenance scenarios, the probability distribution shape factor was similar to the one used for regularly maintained cases. However, the scale factor, which is 63% of the equipment’s failure rate, was only 5 years or 5,000 hours of operation. In

Table 6-9. Cumulative failure probability of front-end loaders under regular maintenance.

delayed maintenance scenarios, the chances of failure of the front-end loaders’ transmission will be higher. Table 6-10 shows the cumulative failure probability of transmission engines of front-end loaders in delayed maintenance scenarios. This table was used to calculate the replacement cost of the new transmission of the loader in delayed maintenance scenarios. Once the regularly maintained loader exceeds 15 years or 15,000 hours of operation, a new loader needs to be purchased. The table shows that, under delayed maintenance scenarios, the life of the front-end loader will be about 9 years.

6.2.6 Estimating Snow Removal Equipment Maintenance Budgets without Delayed Scenarios

The total maintenance cost of snow removal equipment can be calculated by determining the labor hours required for maintenance of the equipment and parts. The replacement cost of the front-end loader’s transmission engine can be calculated using the failure probability shown in Table 6-9, and the labor and cost of transmission are provided in Section 6.2.3. After adding the replacement and maintenance costs, the total budget required to maintain the snow removal equipment can be estimated. Because the cost calculated and shown in Table 6-8 is based on 2021 data, these maintenance and replacement costs need to be adjusted based on the inflation factor. Inflation factors (machinery and equipment repair and maintenance) collected by the Bureau of Labor and Statistics (BLS) since 2006 were used (BLS 2022c). Based on these cost indices, the average

Table 6-10. Cumulative failure probability of front-end loader under delayed maintenance.

inflation rate of machinery and equipment repair and maintenance was found to be 2.61% annually. Using inflation cost indices from Statista (2022) for heavy equipment purchase costs since 2005, the annual inflation rate of these purchases was estimated at 2.30%. These inflation factors can be used to adjust the cost of maintenance and replacement of snow removal equipment while preparing the budget for future years.

6.2.7 Estimating Snow Removal Equipment Maintenance Budgets with Delayed Scenarios

The estimated maintenance and replacement cost of snow removal equipment with delayed scenarios was calculated using the unit cost of maintenance and replacement provided in Table 6-8 and the probability of failure of the transmission engine shown in Table 6-10. The only difference in the maintenance and replacement budget between regular and delayed maintenance equipment was that the failure probability was higher in the case of delayed maintenance compared to regular maintenance. Because these delayed scenarios are considered for future years, the unit cost of maintenance and replacement should be calculated based on the inflation rate described in Section 6.2.6. The research team developed a spreadsheet tool to estimate the maintenance and replacement costs of a front wheel loader with a snow blower attachment. For delayed maintenance scenarios, the user can enter a different inflation rate than the default value. Once the cost is adjusted based on the inflation rate, the total maintenance and replacement costs in delayed scenarios can be calculated. The user can also select the number of years the maintenance of snow removal equipment can be delayed. Additionally, the tool can convert the costs to net present value by using a discount rate.

6.2.8 Reporting the Impact of Snow Removal Equipment Delayed Maintenance and its Consequences

The research team developed a spreadsheet tool and used it to determine the impact of delayed maintenance on airport maintenance and replacement costs of snow removal equipment. The age or number of hours the front-end loader with snow blower attachment is used will have an impact on the maintenance and replacement costs of the equipment. If the loader with the attachment is new, the maintenance and replacement costs will be lower. However, if the age or hours of the equipment are high, the maintenance and replacement costs will be very high. While analyzing the impact of delayed maintenance on snow removal equipment maintenance and replacement costs, three types of front-end loaders were considered: one with 1,000 hours, another with 5,000 hours, and one with 7,000 hours of operation. Two- and 5-year delayed scenarios were used. A front-end loader with snow blower attachment’s regular maintenance and replacement costs were calculated for 2023 without delayed scenarios. The team considered the maintenance and replacement costs for years 2025 and 2028 with 2- and 5-year delays to determine the impact of delayed maintenance on airport maintenance and replacement costs of their snow removal equipment. It was assumed that the equipment will be used for 1,000 hours per year.

The team developed a user-friendly spreadsheet tool to calculate the impact of delayed maintenance of snow removal equipment. This tool can calculate the labor hours required for maintenance of a front-end loader per year. The user can then use those hours instead of case study hours when investing to maintain their front-end loader. They can also use their own labor costs per hour. Similarly, if airports know the parts cost for maintenance of their wheel loader, they can use that cost in their calculations. The tool uses the unit cost of each activity (tire and transmission replacement, new loader, and snow blower attachment) from the data collection phase, and, if these unit costs are different from the user’s, they can enter their own values. The user can also select the number of years delayed and the cost inflation rate for the maintenance and replacement activities

of snow removal equipment. If the user wants to calculate the delayed maintenance cost in present value, they can select the discount rate provided in the tool.

Case Study Results of the Consequence of Delaying Maintenance on Snow Removal Equipment

Figure 6-5 shows the total maintenance and replacement costs of a front-end loader with snow blower attachment with various hours of operations and 2- and 5-year maintenance delayed scenarios. When the snow removal equipment has just 1,000 hours of operation, the delayed maintenance cost for 2 and 5 years increases significantly. The main reason is that the probability of engine failure in delayed conditions will be significantly higher compared to non-delayed scenarios. The same logic is true for equipment with 5,000 hours of operation. However, the equipment with 7,000 hours of operation will have the same probability of engine failure as the equipment with 5,000 hours of operation in delayed scenarios, so the cost of maintenance and replacement for these types of equipment is the same.

6.3 HVAC Systems

Airports require HVAC systems to maintain the temperature in their terminals, administrative, and office buildings. Generally, the commercial types of big HVAC systems are used to cool and heat these buildings. The terminal buildings also use chillers and boilers to cool and heat the spaces. However, these chiller and boiler systems have different kinds of heating and cooling processes. They generally use pipes to send the cold and hot water to cool or heat the rooms. However, in this section, the common rooftop HVAC systems generally used in commercial buildings, like big shopping centers, office buildings, and warehouses, will be discussed. Because of their environmental exposure, rooftop units are built to withstand sunlight, rain, wind, frost, and other conditions.

Rooftop HVAC units are also called packaged units because all the required components are packaged together as one unit (Estes Services n.d.). The roof package system consists of the heating and/or cooling system components, depending on the type of system. Apart from the rooftop units, the air conditioning unit can have split systems, which have separate equipment housed indoors and outdoors. A furnace and/or air handler is installed within the building, while an air conditioner or heat pump is installed outside the building around its perimeter.

Rooftop HVAC units are connected to the building’s ductwork and heat or cool air passing through, then distribute the conditioned air throughout the interior areas. First, the air enters a rooftop unit via the air hood at its side. As air passes through, dampers operate inside to regulate airflow, and the air supply passes through the system’s filters to remove contaminants. Then the air is either heated by a heat exchanger or coils or cooled by cooling coils (depending on the system configuration and operating mode). The conditioned air is circulated through the ducts of the building. All central heating and cooling systems should have an air filter. The air filter is usually located in the return air duct or blower compartment before the return air reaches the air handler. This allows the filter to clean the air from outside of the building before it enters the HVAC unit (Beauchamp and Lopez 2022).

The research team focused on rooftop package units to determine the impact of delayed maintenance on an airport’s total maintenance and replacement costs. Figure 6-6 shows the framework developed to calculate the regular and delayed maintenance and replacement costs for the rooftop HVAC package units.

6.3.1 Establishing Asset Inventory

Airports with rooftop HVAC package units need to keep an inventory of the components of their system. Asset managers should keep a record of the number of HVAC units, capacity of the system in tons or British thermal units (BTU), make and model, purchase date, and Seasonal Energy Efficiency Ratio (SEER) ratings. Additionally, they should keep a record of components of HVAC units, including the condenser, compressor, heating units, air handlers, number of thermostats, number and size of air filters, number and size of ducts, and length of air duct system. These inventory data are critical in determining the maintenance and replacement costs of an HVAC system. The inventory data of these HVAC unit components will help determine the condition of each component so that airport mechanics can determine which components need to be replaced.

If airport asset managers do not have information about the capacity of the HVAC units required for their airport terminals and administrative buildings, they can calculate it using the process provided by the U.S. Environmental Protection Agency. The agency developed a tool to determine the capacity of HVAC units based on the size, number of occupants, and number of doors and windows in a building (EPA 2022). The standard also provides information on selecting HVAC units and their components. Table 6-11 provides the amount of BTU required based on the building square footage, the number of occupants, and the number of doors and windows. Using these values, airport asset managers can determine the necessary capacity of HVAC units for their buildings or terminals.

The number of vents required for the buildings can also be calculated based on the number of occupants in the building. EPA guidelines recommend providing 15 cubic feet per minute (CFM) per person of ventilation. After the number of occupants in the building is calculated, the total ventilation required in terms of CFM can be calculated by multiplying 15 CFM per person by the number of occupants. Assuming one air filter can return 2.5 CFM of air to the blower compartment, the number of return air vents can be calculated by dividing the total CFM required by 2.5 CFM per vent. Similarly, the number of air vents needed to send cool or hot air around the

Table 6-11. BTU requirements based on the building size, number of occupants, and number of doors and windows.

building can be calculated by considering that one air vent is required per 100 square feet of building area. The number of thermostats can also be determined based on the number of HVAC units installed in the building. The research team developed a spreadsheet tool that can perform these calculations to determine the impact of delayed maintenance of HVACs on airport costs.

6.3.2 Performing a Condition Assessment

During the data collection phase, the research team asked asset managers to provide a condition assessment process and rating of the HVAC system used in their airports. None of the airports used systematic condition assessment procedures to rate the condition of the HVAC systems. The airport mechanics, however, assess the condition of HVAC units every year to determine what needs to be fixed to run the system without interruption. Large-hub airports have separate building departments to monitor the assets of terminals and administrative buildings. Most of the airports stated that they have plans to maintain the HVAC system and know what needs to be done. They also prepare budgets based on these requirements. However, the research team found that the airports did not have a systematic way of conducting inspections of their HVAC systems.

The research team searched the HVAC system inspection processes and procedures. There are various HVAC installations and maintenance companies that provide professional services related to HVAC systems. The EPA (2014) has also developed an HVAC inspection form. Other professional HVAC companies have suggested that the following items be inspected every year to make sure that all the components are working properly (ARISTA n.d.):

• Clean or replace filters.
• Clean condenser and evaporator coils.
• Clean drain lines for proper flow and clear clogs.
• Clear drain pans of any standing water to avoid overflows.
• Replace worn pulleys and belts.
• Inspect ducts for mold, dust, and debris.
• Observe humidity levels.
• Check refrigerant charge and for leaks.
• Test thermostats and controls to make sure temperatures and timer functions are correctly set.
• Change batteries.
• Check the electrical system and connections.
• Check the fan motor.
• Check blowers and blades for proper airflow.
• Lubricate motors, bearings, and moving parts.
• Inspect cabinet for leaks and check cabinet door for secure closure.
• Check for debris around the outside unit.

Airport asset managers need to make sure that the HVAC units are inspected yearly so that the required preventive maintenance can be performed and the airports can remain open without compromising travelers’ comfort. They must also keep a record of these inspections to estimate the HVAC unit maintenance and replacement budget based on the conditions. A short HVAC unit

checklist developed by the professional companies that provide HVAC services is shown in Appendix D (HousecallPro 2022). During the inspection period, the mechanics can determine whether the parts need to be replaced or if regular maintenance is required. The form provided in Appendix D shows that, when the inspection is done, it is necessary to determine whether the components of the system are in good condition. If the inspection record helps determine the level of attention needed, it will be easier to prepare the maintenance budget for the HVAC system. HVACs can operate up to their full lifespan if preventive maintenance is performed on the HVAC units annually.

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

If airports perform inspections of HVAC units as mentioned in Section 6.3.2, then it will be easy to determine what major maintenance activities need to be performed. Those inspection records should focus on the necessary maintenance activities so that HVAC units can reach peak performance. There are specific maintenance activities related to each component of an HVAC unit to keep an HVAC unit in good condition. Some of the maintenance activities are shown below. For more details, please refer to the City of Lake City HVAC repair and preventative maintenance services invitation to bid (OpenGov Procurement 2021).

• Check and change filters if needed (filters shall be supplied by the contractor);
• Inspect the entire system;
• Check all controls, including thermostats, and damper operators when necessary;
• Check the operation and condition of all components;
• Adjust and check motors, starters, valves, drives, and accessories;
• Lubricate all moving parts, motors, bearings, etc., add compressor oil as needed;
• Replace or maintain compressor belts;
• Clean and check blower assembly;
• Clean ignition system; and
• Clean duct system.

After identifying all the preventive maintenance activities that need to be performed in HVAC units, the airport should record the labor hours and parts spent maintaining them. During the data collection phase, the research team found that some labor hours and money spent on parts were recorded, but not all data were available to determine how many hours were spent and on which activities. So, the team conducted an internet search to determine the labor hours required to perform these activities and their frequency. The data are shown in Table 6-12, and these labor hours were estimated using HVAC company websites. The website links are provided in the spreadsheet tool in Section 3.3 of the Quick Guide. Because other activities need to be performed besides those mentioned above, a 20% miscellaneous cost was added to the maintenance cost calculations.

Table 6-12. Maintenance activities, frequency, and labor hours required of HVAC units.

To calculate the maintenance cost of HVAC units, the research team first calculated the labor hours for each maintenance activity. The labor cost was then calculated using a $60/hour rate for mechanics. After the labor cost was calculated, the cost of the parts was determined by taking 70% of the labor cost and 30% of the parts cost and adding them. Then a 20% miscellaneous cost was added to the total maintenance cost of the HVAC units. Table 6-13 breaks down the component costs, labor hours required for installation, and total costs for each component for the replacement of HVACs and their major components. The cost is calculated assuming that 25 tons of commercial HVAC units are installed. These numbers are based on 2021 figures.

6.3.4 Determining the HVAC Components’ Failure Probability with Regular Maintenance

To determine the replacement costs of HVAC components, it is necessary to determine their failure probability. HVAC companies have not provided these failure data; thus, the research team used the probability failure theory of machinery to determine the chances of HVAC components’ failure during their life cycle. One of the probability theories the team primarily used to determine the cumulative probability of failure was the Weibull distribution theory. Researchers have used this theory successfully in various types of machines and electrical systems. The research team applied this theory to determine the failure probability of HVAC components, e.g., compressors, condensers, and air handlers, which most often break down in normal operating conditions. The shape and scale factor of these machines need to be determined to use the Weibull distribution probability theory. The shape factor is the probability distribution shape of the HVAC components. The shape of the probability distribution for these components will likely be normal, so the shape factor value used was 3.5. Because these three components are part of the HVAC system, the life of these components will be similar to the HVAC unit as a whole. The team found that the HVAC unit life is generally 15 years, so the scale factor (which denotes when 63% of the components will fail) was assumed to be 12 years in normal conditions given regular maintenance is performed annually. Table 6-14 presents the cumulative failure probabilities of these regularly maintained HVAC components using the Weibull probability theory. These cumulative failure probabilities help determine the regular replacement costs of the compressors, condensers, and air handlers.

6.3.5 Determining the HVAC Components’ Failure Probability with Delayed Maintenance

As described in Section 6.3.4, the team could not find the failure probability of HVAC components tracked by any professional HVAC companies under regular maintenance conditions. Similarly, predicting the failure probabilities under delayed maintenance scenarios is difficult. Regardless, the life of HVAC components will reduce significantly if HVAC units are not regularly maintained. Therefore, the research team assumed that the Weibull distribution’s scale factor would be reduced and used 6 years instead of 12. Using 6 years as a scale factor, the failure probabilities of these HVAC components were calculated. As Table 6-15 demonstrates, the life of

Table 6-14. Cumulative failure probabilities of regularly maintained HVAC components.

Table 6-15. Cumulative failure probabilities of HVAC components under delayed maintenance.

HVAC components will only last 10 years in delayed maintenance scenarios. These failure probabilities in delayed maintenance conditions can help calculate the HVAC component replacement costs when the system maintenance is delayed.

6.3.6 Estimating the HVAC Maintenance and Replacement Budget without Delayed Scenarios

The maintenance budget of HVAC units can be determined by calculating the labor hours required to perform the regular maintenance activities stated in Table 6-12. Based on the frequency of these activities on an annual basis, the research team calculated the total labor hours required to perform these activities for the HVAC units. Using the base cost of a mechanic per hour, the team calculated the total labor cost to maintain an HVAC unit for a year. After the total labor cost was determined, the team calculated the parts cost based on 70% labor and 30% parts distribution. Due to maintenance activities not mentioned in Table 6-12, 20% in miscellaneous costs were added to the budget to reflect the total maintenance cost in a year. The research team used the failure probabilities from Table 6-14 to determine the replacement costs of the compressor, condenser, and air handler.

The unit cost determined in Table 6-13 was used as a replacement unit cost for these components. If the HVAC life exceeded more than 15 years, then it was assumed that the entire HVAC would be replaced. The unit cost of maintenance and replacement was calculated based on the 2021 figures, meaning that these costs need to be adjusted to calculate future maintenance and replacement costs. To adjust the base cost, the research team used two types of cost indices. The first cost index shows the equipment cost inflation rate (BLS 2022c) and is determined as 2.95% per year. This cost inflation rate is used to adjust the cost of parts and the replacement components, e.g., compressors, condensers, air handlers, and the HVAC unit itself. The research team used the second cost index to determine the inflation rate of machinery and equipment repair and maintenance (BLS 2022c). The inflation rate for repairs and maintenance of HVAC units was calculated as 2.61% per year. The spreadsheet tool used to prepare the regular maintenance and replacement costs of HVAC units applies these two inflation factors to adjust the maintenance and replacement base costs.

6.3.7 Estimating the HVAC System Maintenance and Replacement Budget with Delayed Scenarios

The maintenance cost of an HVAC system can be calculated by multiplying the unit cost of maintenance items and the frequency of maintenance activities in delayed conditions. There is little difference in preventive maintenance costs inside or outside of delayed scenarios. However, the cost of replacing HVAC components will be higher due to higher probabilities of the failure of these components in delayed maintenance scenarios. The maintenance cost of an HVAC unit can be calculated as described in Section 6.3.6. To calculate the replacement cost of HVAC components, the research team used the failure probabilities under delayed maintenance stated in Table 6-15. Due to high failure probabilities, the total maintenance and replacement cost of HVAC systems was higher for delayed maintenance scenarios compared to regularly maintained HVAC systems. To calculate the total maintenance and replacement costs, the base cost used in the spreadsheet tool needs to be adjusted. The cost adjustment for maintenance and replacement can be completed as described in Section 6.3.6. In delayed scenarios, the user can either use the default inflation rate or enter the inflation rate they expect to occur in the future.

6.3.8 Reporting the Impact of HVAC System Delayed Maintenance and its Consequences

The research team developed a spreadsheet tool to determine the regular maintenance and replacement costs of HVAC systems. This tool can also calculate the impact of delayed maintenance on maintenance and replacement costs of airport HVAC systems. As described in previous sections, the tool uses the labor and parts cost data available from the case study and the CASE Construction website to calculate the maintenance and replacement costs with and without delayed scenarios. The tool can determine the amount of HVAC units required for the buildings. It can also calculate the number of air filters and air vents based on the area and number of occupants in the building. If an airport is already aware of these data, it can directly input the data to calculate the total maintenance and replacement costs of its HVAC systems. The same is true for the parts cost and labor hour data. The miscellaneous cost can also be changed if airports have their own data. These options provided in the tool can help airport maintenance managers calculate accurate HVAC system maintenance and replacement costs. When calculating the cost in a delayed maintenance scenario, the user can select the number of years maintenance of the HVAC system is delayed. They can also select a discounted rate to convert their future maintenance and replacement costs to net present value costs. This option helps to compare the present and future costs.

increase the cost significantly for HVAC systems of any age. The increase in the maintenance and replacement costs of a 5-year-old HVAC unit are significant when maintenance is delayed by 2 years. However, the total cost increase of 2- and 5-year-old HVAC units is not significantly different when maintenance is delayed by 5 years. When maintenance is delayed by 5 years, a 5-year-old HVAC unit will reach 11 years of age. The probability of failure in delayed scenarios reaches 100% for an 11-year-old HVAC unit (Table 6-15). Thus, delaying the maintenance of 5 years or older HVAC units by more than 5 years will not have a significant impact on the total maintenance and replacement costs.

6.4 Baggage Handling System

The airport baggage handling system is one of the most important pieces of infrastructure in the airport. The airport baggage handling system transfers baggage from ticket checkpoints to airplane loading areas, or from airplane unloading points to carousels. The FAA has not issued any AC related to baggage handling systems. Generally, the baggage handling system consists of conveyor belts that move over motors so baggage can be transported from one point to another. The baggage handling system consists of motors, belts, guard rails, frequency inverters, and photocells. The baggage handling system is continuously moving to transport baggage, and these parts function almost all hours when the airport is open. These systems are expensive and need regular maintenance and replacement of parts as they wear. If the system is not regularly maintained, it will break and need replacement entirely or new parts for the conveyor belt, which can cost thousands of dollars. Airport asset managers need to make sure that these systems are regularly inspected, and that a budget is available to maintain them. The research team collected the maintenance and replacement labor and cost data of baggage handling systems from specific airports. Based on these data, the team built a framework and a spreadsheet tool that can assist airport asset managers in calculating the regular maintenance and replacement costs of this system with and without delayed maintenance. Figure 6-8 shows the framework to determine the maintenance and replacement costs of the baggage handling system. Each step involved in this framework is described in the following sections.

6.4.1 Establishing Asset Inventory

The baggage handling system consists of various components. The conveyor belt is a major part of the system. Depending on the size of the airport, the length of the conveyor belt can range from a few 1,000 feet to a few miles. In large airports, the length of conveyor belts can be 15-20 miles long. The conveyor belt has motors that help to move the belt over the guardrails so baggage can be transported from one place to another. In addition to conveyor belts, the baggage handling system includes baggage screening points, X-ray units, pushers, power benders, power turns, merges, diverters, and nodes (loading, unloading stations, and junctions). Airport asset managers need to keep an inventory of all the components of the system so that they can track, inspect, and maintain it or replace parts on time. Airport asset managers should record the date of purchase of these components, their brand and manufacturer’s name, the age of the parts, and the types of spare parts required to maintain the system. In a large airport with many terminals, these systems may be complicated. There is often a room with computers to monitor and control the movement of the conveyor belts, and these control rooms also need to be maintained efficiently. Any information related to baggage handling system components should be stored in the database.

6.4.2 Performing a Condition Assessment

Assessment of the condition of various parts of the baggage handling system is critical because the inspection and assessment of conditions will provide enough information to plan for system

maintenance and replacement. During the data collection phase, the research team did not find any specific written procedures to inspect the baggage handling system in airports. The team found that a specific department dedicated to the baggage handling system was created in large airports. Because the system consists of motors and rotary parts, the maintenance of these components is crucial. If the system breaks, it can be disruptive for air travelers. Airport mechanics monitor and regularly inspect various parts of the baggage handling system to ensure they are working properly. Some of the airports outsource baggage handling system maintenance work

to third parties. The following inspections should be conducted regularly to keep the baggage handling system safe and moving (Ravnholm n.d.):

• Conveyors, including check-in collection, curbside input, load and unload, and transport conveyor segments.
• Power turns, merges, high-speed diverter units, and plow diverters.
• Motor control panels and field control devices (e.g., photocells, limit switches, control stations/devices, audio/visual alarms, etc.).
• Motors, motor starters, disconnects, and push buttons.
• Baggage handling system-related computers, controls and control hardware, and control rooms.

The research team did not find an inspection checklist developed by any of the airports or other companies that provide operation and maintenance services for the baggage handling system. Because the system is complex, professionally trained people are required to conduct the system component inspection in order to execute proper maintenance.

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

As mentioned in the previous section, the baggage handling system is so complex that identifying all maintenance activities poses a challenge. Some of the regular maintenance activities are as follows:

• Cleaning all parts of conveyor belts to keep the dirt, litter, dust, spills, grime, or chemical residue away from the surface.
• Oiling and greasing the rotary parts of the conveyor belts.
• Maintaining conveyor belts including motors.
• Maintaining baggage screening areas.
• Maintaining carousels.
• Maintaining X-ray units and RFID sensors.
• Maintaining automation control hardware and software.

The frequency of these activities depends on an airport’s hours of operation and the environment of the terminal given how much dirt and litter will infiltrate the system. The research team gathered the maintenance frequency of some of the key maintenance activities of the baggage handling system for the airports. These data are shown in Table 6-17. Companies like Siemens (2019) have started a condition-based maintenance plan to increase the efficiency of the baggage handling system. Various types of intelligent sensors can be installed in the components of baggage handling systems. These sensors can acquire information related to wear and tear, use, environment, and maintenance history of the system, which can be used to maintain the system

Table 6-17. Frequency of major maintenance activities of baggage handling systems.

components. Airport asset managers can prepare and plan the system maintenance and replacement budget using the data from these sensors.

The research team contacted several airports to collect the labor hours used in the maintenance of their baggage handling systems. None of the airports had collected these data. However, the research team found that some of the large-hub airports have a department dedicated to the operation and maintenance of baggage handling systems. The team was able to determine the number of electricians and mechanics working in this department to find how many man-hours are spent on the maintenance and operation of the baggage handling system. The cost of maintenance was calculated using a ratio of 60% for labor and 40% for parts. Then the installation cost of a new baggage handling system was retrieved from one of the large-hub airports that had recently installed the system. Table 6-18 shows the unit cost calculation for maintenance and replacement of a new baggage handling system. The research team estimated the unit costs of maintenance and replacement from the case study airport data with 20% in miscellaneous costs added to reduce variability.

6.4.4 Determining the Baggage Handling System Failure Probability with Regular Maintenance

The research team contacted the airports to determine how often the baggage handling system breaks down; however, the asset managers were not able to provide any data related to system breakdown. The team also searched online to determine whether any academic or professional organizations have developed probabilities of baggage handling system failure in normally maintained conditions but could not find any literature. The team instead used the Weibull probability function theory to determine the system failure probabilities. As described previously, two major parameters of baggage handling system failure are required to use this probability theory. These include scale factor and shape factor. Because none of the academic or industrial researchers had developed these parameters for the baggage handling system, the team assumed a normal distribution of failure probability. Therefore, the shape factor used was 3.5. During the data collection phase, the airports were asked to estimate the life of the baggage handling system. They stated that, generally, it is about 15 years. So, the team considered that 63% of system failures will occur within 10 years. A 10-year scale factor was used to calculate the cumulative failure probabilities of the baggage handling system. Table 6-19 shows the failure probabilities of the baggage handling system under regular maintenance scenarios. The cumulative probabilities show that, by year 16, the system will break down and need replacement.

Table 6-18. Unit maintenance and replacement cost calculations for the baggage handling system.

it is regularly maintained because the failure of a mechanical or electrical system can happen even when the system is maintained. Based on the system failure probability, some funds need to be set aside to cover breakdown scenarios if the system fails. To determine the regular maintenance costs of the system, the labor hours and parts required to maintain the system need to be calculated. The research team collected the labor and parts costs based on 2021 figures, which are provided in Table 6-18. The cost should be adjusted based on the year the budget is prepared. The research team then collected the inflation cost indices from the Bureau of Labor Statistics (2022c) to determine the inflation rate per year. Since 2006, the average inflation rate of machinery and equipment repair and maintenance has been about 2.61% per year. This inflation rate was used to determine the maintenance cost of baggage handling systems for future years. The team also considered replacement costs due to the probability of failure. To determine this replacement cost, the replacement cost per unit of the system was multiplied by the total length of the baggage handling systems and the probabilities shown in Table 6-19. The unit replacement cost is based on 2021 figures and needs to be adjusted for future years. The cost indices of new equipment since 2004 were used to calculate the average inflation rate of equipment per year (FRED 2022d). The cost indices showed that the average inflation rate of equipment is about 2.95% per year. This inflation rate was used to determine the future replacement costs of the system.

6.4.7 Estimating Baggage Handling System Maintenance and Replacement Budget with Delayed Scenarios

The research team used similar procedures described in the previous sections to estimate the total maintenance and replacement cost of baggage handling systems for delayed scenarios. The difference with the baggage handling system is that the high probability of a system failure will increase the replacement cost. The system replacement cost can be calculated by multiplying the unit cost of replacement by the probabilities of failure of the system provided in Table 6-20 for delayed scenarios. The cost of replacement will be higher in delayed scenarios because the probability of failure of the system will be higher compared to regularly maintained systems. The maintenance and replacement costs also increased due to the inflation rate as described in section 6.4.6. The team developed a spreadsheet tool to determine the maintenance and replacement costs for the system. The airports can enter their own expected inflation rates in the tool for the maintenance and replacement activities when calculating the delayed costs.

6.4.8 Reporting the Impact of Baggage Handling System Delayed Maintenance and its Consequences

The research aimed to determine the impact of delaying asset maintenance on the airport’s budget. This research did not address other impacts of delayed maintenance, e.g., safety, security, and the comfort of the passengers. The research team only considered the impact of higher maintenance and replacement costs due to delayed maintenance. The team used the spreadsheet tool to determine the financial impact of delayed maintenance. The team also developed a hypothetical airport case study to calculate the impact of delayed maintenance on total costs. Table 6-21 shows the hypothetical airport data used to determine the maintenance and replacement costs of baggage handling systems with and without delayed scenarios. The delayed scenarios used were 2 and 5 years. The age of baggage handling systems was assumed to be 1 year, 3 years, and 5 years. The team used the default inflation rates to calculate the impact of delayed maintenance on baggage handling system maintenance and replacement costs.

The research team developed the spreadsheet tool with a case study airport’s labor hours and parts cost used to maintain the baggage handling system per year. If the airports know the labor hours used to maintain their baggage handling system, they can use those hours instead of the case study

Table 6-21. Case study data of baggage handling systems.

hours. They can also use their own labor cost per hour. Similarly, if the airports know the amount they are spending on parts to maintain their baggage handling system, they can use that cost instead of the case study parts cost. The airports can also enter their own baggage handling system unit replacement and miscellaneous costs. If they want to calculate the delayed maintenance cost in present values, they can select the discount rate provided in the tool.

The Consequence of Delaying Maintenance on the Baggage Handling System Case Study Results

The research team used the spreadsheet tool to calculate the impact of delayed maintenance on total maintenance and replacement costs of baggage handling systems. Using hypothetical case study data available in Table 6-21, the team calculated the total maintenance and replacement costs of regular maintenance for 2023. The team then hypothesized that no funds were available for the following 2- and 5-year periods and calculated the total maintenance and replacement costs for 2025 and 2028. The budget increase reflected the impact delaying baggage handling system maintenance has on airport budgets. Figure 6-9 shows the change in the total maintenance and

replacement costs of 1-, 3-, and 5-year-old baggage handling systems when the maintenance is delayed by 2 and 5 years. The results show that, when the system is 1 year old, the maintenance and replacement costs significantly increase at delayed maintenance scenarios of 2 and 5 years. However, for 3- and 5-year-old systems, the maintenance and replacement costs for a 2-year delay will increase significantly (but not for a 5-year delay). When the system is 7 years or older, the failure probability under delayed maintenance scenarios indicates that 96% of the system will need to be replaced (Table 6-20). This is why a 5-year delay did not significantly increase the total maintenance and replacement cost.

6.5 Passenger Boarding Bridges

The passenger boarding bridge is also called a jet bridge. The passenger boarding bridge helps passengers board the planes. Passenger boarding bridges are generally attached to terminal buildings; however, they can be extended and moved side to side to connect with the plane gates. Generally, a passenger boarding bridge has a hydraulic system, which helps the bridge extend and contract to fit into the plane doors. Passenger boarding bridges consist of five components as shown in Figure 6-10 (Aviation Learnings 2020). They include (1) the cabin unit, (2) the telescopic tunnel, (3) the elevation system, (4) the bogie, and (5) the rotunda. Manufacturers use various terms to identify the parts of passenger boarding bridges. The cabin is the part at the end of the bridge that connects with the airplane doors. The cabin is generally fitted with an operator panel, and an operator controls the movement of the bridge inside this cabin. The telescopic tunnel connects the cabin and rotunda. Some of the bridges have more than two tunnels, and intermediary tunnels are assembled between the cabin tunnel and rotunda. The elevation system supports the cabin tunnel and consists of two columns side by side. This column can collapse or elongate. The elevation system rests on the bogie, also called a traction system. This part helps the bridge to move on the ground. The rotunda is fixed over the rotunda column and anchored into the ground. The main function of the rotunda is to connect the terminal building to the mechanical bridge.

FAA AC 150/5220-21C discusses the performance standards, design, manufacture, and testing of passenger boarding bridges. This AC does not review the maintenance requirements; however, it does discuss the manufacturing specifications of the bridge in detail. This research is focused on developing a framework and a tool to determine the impact of delayed maintenance on total maintenance and replacement costs for airport passenger boarding bridges. The research team only focused on the agencies’ direct costs, incurred by the rapid deterioration of the bridge when regular maintenance is not conducted. Figure 6-11 shows the framework for calculating the consequences of delaying maintenance on passenger boarding bridges. The following section discusses a step-by-step process to calculate the total maintenance and replacement costs based on delayed scenarios. The team also developed a spreadsheet tool to help airport asset managers calculate the impact of delayed maintenance on passenger boarding bridges.

Table 6-22. Frequency of major maintenance activities of passenger boarding bridges.

the data collection phase, the research team identified some of the major maintenance activities that need to be performed. The research team also searched online to identify these maintenance activities and their frequency. Table 6-22 shows the types of maintenance activities and their frequency to maintain the passenger boarding bridges (Louisville International Airport 2022).

Identifying maintenance activities helps to determine the unit cost of the activities performed every year and the total maintenance and replacement budget. However, none of the airports had determined the unit cost of these maintenance activities for the passenger boarding bridges. The research team successfully gathered the number of mechanics and electricians working in one case study airport who maintain and operate the passenger boarding bridges. Some large-hub airports have an entire unit of people responsible for maintaining passenger boarding bridges. During the interview, the asset managers were also able to estimate the percentage of the cost for labor and parts to maintain the passenger boarding bridges. The team used the case study data of this airport to determine the maintenance cost per passenger boarding bridge per year. Table 6-23 shows the unit cost calculation of the maintenance, as well as the unit cost of replacing a passenger boarding bridge. All costs are based on 2021 figures.

Table 6-23. Unit maintenance and replacement cost calculations for the passenger boarding bridge.

was therefore considered to be reduced by half if regular maintenance was not performed. Given this, the scale factor used was 7 years. The research team selected a shape factor value of 3.5, assuming the probability will be normally distributed like a regularly maintained bridge. Using these shape and scale factors, the Weibull probability distribution yielded the failure probabilities of passenger boarding bridges as shown in Table 6-25. The table shows that the bridge will fail 100% when it reaches 10 years of age.

6.5.6 Estimating Passenger Boarding Bridge Maintenance and Replacement Budget without Delayed Scenarios

As described above for other airport assets, the total maintenance and replacement costs of passenger boarding bridges can be calculated by the number of bridges and their unit maintenance cost, as well as the failure probability based on the age of the bridge and unit replacement costs. The maintenance cost is based on the condition of the bridge and the replacement cost is based on the probability of failure of a passenger boarding bridge. The team developed a spreadsheet tool to calculate passenger boarding bridges’ total maintenance and replacement costs. These calculations were based on 2021 figures. The cost needed to be adjusted when calculated for periods after 2021. The research team gathered cost index data for machinery repair and maintenance and new equipment to adjust the cost. The team used an inflation rate of 2.61% per year to adjust the maintenance cost of the passenger boarding bridge. The team calculated this inflation rate using cost index data from 2003 to 2021 (BLS 2022d). Similarly, for new equipment purchase and installation, the team collected cost index data from 2006 to 2021 and calculated an inflation rate per year of 2.95% (FRED 2022d). These inflation rates assisted in adjusting the cost for future years.

6.5.7 Estimating Passenger Boarding Bridge Maintenance and Replacement Budget with Delayed Scenarios

The research team used procedures similar to those described in section 6.5.6 to estimate the maintenance and replacement cost of passenger boarding bridges for delayed scenarios. The difference was the higher cumulative failure probability of bridges due to neglected maintenance. During the data collection phase, the team found that most airports do not delay the maintenance of passenger boarding bridges. If budget constraints cause a delay, however, the airport should consider that an extended delay in maintenance could lead to the entire passenger boarding bridge needing replacement. The spreadsheet tool created by the research team has the flexibility to delay maintenance up to 10 years. The cost used in the tool needs to be adjusted based on future inflation rates when maintenance is delayed. The tool uses default inflation rates for maintenance and replacement, which are 2.61% and 2.95%, respectively. The tool allows the user to enter their own

Table 6-25. Cumulative failure probabilities of the passenger boarding bridge under delayed maintenance.

inflation rate to calculate the total maintenance and replacement costs for delayed scenarios. The tool can also convert the future maintenance and replacement costs to the present value using a discounted rate.

6.5.8 Reporting the Impact of Passenger Boarding Bridge Delayed Maintenance and its Consequences

As described for other assets, this spreadsheet tool helps determine the monetary impact of delayed maintenance of passenger boarding bridges on an airport’s total maintenance and replacement costs. The research team created a hypothetical airport case study to estimate the impact of delayed maintenance of passenger boarding bridges on total maintenance and replacement costs. Table 6-26 shows the hypothetical airport case study project data. In the case study scenario, there is one passenger boarding bridge. The scenario considers that the age of the bridge is 1, 3, or 5 years old. The delayed scenarios show how the total maintenance and replacement costs will change based on the age of the bridge. The delayed scenarios used were 2 and 5 years. Default inflation rates were used in this case study. The discounted rate was not used.

The spreadsheet tool developed can calculate the labor hours required to maintain the bridge per year with and without delayed scenarios. The tool uses the labor hours calculated from the case study airport. If the airports know the labor hours needed to maintain their passenger boarding bridges, they can use those hours instead of the case study hours. They can also use their own labor costs per hour. Similarly, if the airports know the parts cost to maintain and replace their bridges, they can use that cost instead of the case study cost. The tool uses the unit cost of each passenger boarding bridge replacement recorded during the data collection phase, and, if these unit costs differ, they can enter their own costs. A 20% miscellaneous cost was added to the maintenance and replacement budget to cover unforeseen costs. The airports can also use their own miscellaneous prices in this tool. They can also use their cost inflation rates for the maintenance and replacement of passenger boarding bridges. If they want to calculate the delayed maintenance costs in present value, they can select the discount rate provided in the tool.

The Consequence of Delaying Maintenance on the Passenger Boarding Bridge Case Study Results

The research team used the spreadsheet tool to calculate the total maintenance and replacement costs of a passenger boarding bridge. Using the case study data available in Table 6-26, the team calculated the total maintenance and replacement costs of a regularly maintained bridge for 2023. The team hypothesized that there would be no funds available for the following 2 and 5 years and calculated the total maintenance and replacement budget for 2025 and 2028. The budget increase demonstrated the impact of delayed maintenance of passenger boarding bridges on airport costs.

Table 6-26. Case study data for a passenger boarding bridge.

Figure 6-12 shows the change in the total maintenance and replacement costs of 1, 3, and 5-year-old passenger boarding bridges when the maintenance is delayed by 2 and 5 years. The results show that the impact of 2- and 5-year delays on annual maintenance and replacement costs is significantly higher when the age of the passenger boarding bridge is 1 and 3 years old. The impact of maintenance and replacement costs of passenger boarding bridges is not as high when the maintenance is delayed by 5 years for 3- and 5-year-old passenger boarding bridges. The cumulative failure probability of the passenger boarding bridges under delayed maintenance conditions at 9 years reaches 91% (Table 6-25). If the passenger boarding bridges are not maintained regularly, then they will fail after 10 years. This indicates that any maintenance delay beyond the total life of the bridge at 10 years will have a similar impact.