National Academies Press: OpenBook

LED Airfield Lighting System Operation and Maintenance (2015)

Chapter: Chapter 3 - Maintenance Considerations

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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
×
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
×
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
×
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
×
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
×
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
×
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
×
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Suggested Citation:"Chapter 3 - Maintenance Considerations." National Academies of Sciences, Engineering, and Medicine. 2015. LED Airfield Lighting System Operation and Maintenance. Washington, DC: The National Academies Press. doi: 10.17226/22076.
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7 C H A P T E R 3 Maintenance and care of AGL has been necessary since the first smudge pot was filled with kerosene and lit to assist pilots at night. The need to minimize maintenance and costs soon followed. Throughout the history of AGL, improvements to equipment, training, practices, and technology have moved the industry to provide and maintain systems with minimal inter­ ruptions to operations. The goal of system maintenance is to reduce or eliminate repeated visits to a particular light or system, thus allowing resources to be focused on other issues. This chapter discusses the advantages and disadvantages of LED airfield lighting technology, including the equipment itself, environmental conditions, installation, acceptance testing and warranty, spare parts, and preventive maintenance. Acceptance Testing and Warranty Acceptance Testing An effective maintenance program starts with a well­constructed, compliant, and documented system. Commissioning and acceptance testing of AGL should be conducted in tandem with every construction project to ensure the system is performing to the specified design and to set benchmark performance metrics for the airport’s lighting system before it is turned over to airport maintenance. Operation and maintenance departments can be overburdened by accepting a new LED lighting system which was poorly installed and not thoroughly inspected to meet industry standards. The new system must operate without issues stemming from installation and equipment flaws. This is particularly critical in systems where new technology is implemented and continues to evolve. The implementation of an appropriately stringent acceptance program is vital to the long­term operation and maintenance of an LED AGL system. FAA guidelines already exist for testing and maintaining AGL systems. This guidebook adds recommendations for LED lighting systems to those guidelines, so that maintenance departments receive a fully compliant system with proper test reports, documentation, training, and spare parts. Acceptance Procedure The survey data and case studies suggest that newly installed LED lighting systems face issues similar to non­LED systems when it comes to physical installation. In addition, the survey data indicate potential issues of new LED systems in regards to light brightness and early light fixture failures. Based on this information, a recommended airfield light system’s acceptance testing procedure should include the following elements: • Visual and physical inspection • Electrical testing Maintenance Considerations

8 LED Airfield Lighting System Operation and Maintenance • Photometric testing • System burn­in Visual and Physical Inspection It is a good idea to visually and physically inspect all new AGL and guidance sign systems installed at an airport. Particular features to inspect are presented in the following subsections. Taxi Guidance Signs. The research team recommends inspecting all signs for power and type, orientation, and physical condition. • Power and Type. The type of power feed supplying the sign (i.e., 3­step, 5­step, or a single constant­current feed) and the nameplate data of the sign should be verified. • Orientation. The field location and orientation of all taxi guidance signs should be inspected before acceptance of the system. This inspection should include the lateral and longitudinal distance of the sign from any intersecting taxiway or runway and from the defined edge of the taxiway or runway. Additionally, the angle of the sign legend directional arrows should be verified to ensure it is aligned with the intersecting taxiway centerline orientation. • Physical Condition. Verify that (1) the exterior and interior signs are clean and clear of debris; (2) the power supply is in a sealed enclosure or is encapsulated for protection; (3) the sign legend and frame are free of scratches, cracks, or breaks; and (4) that all bolts and tethers are properly installed and secured. The research team recommends checking a random sampling of 20% of signs to verify the correct installation of the power leg during installation. The research team recommends using a documented pass/fail protocol to do this check. If one sign’s power leg is not installed correctly, the sign fails, and another 20% should be measured. Continue until all signs in a sample pass or all signs have been inspected. All signs that fail should be corrected and re­inspected for compliance. The installation of the power leg frangible coupling, cable clamp, and cable assembly is difficult to verify after completion of work, so these items should be inspected during installation. Visible verification that the total assembly is installed properly is recommended. Elevated Light Fixtures. The research team recommends inspecting all elevated light fix­ tures for proper height and exterior condition. • Height Inspection. Verify the height of the elevated light fixtures for conformance with AC150/5340-30H, Design and Installation Details for Airport Visual Aids, Figure 108, Adjustment of Edge Light Elevation for High Snowfall Areas. • Condition Inspection. Inspect the elevated light fixture for any physical damage, including cracked globes; scratches; dents or abrasions on the fixture housing and stem; and damage to the base plate. Verify that the retaining ring or clips for the globe are present and secure. Verify that all bolts are installed and a base plate gasket is present. Ensure the fixture is level and plumb. Figure 6 provides exterior inspection information. • Light Base Interior Inspection. Visually inspect inside the light base to verify the installation of several components and verify the state of good condition for a new installation. Components to view and verify include the following: – Connectors – Grounding connections – Spacers – Top extension or flange ring – Length of bolts – Transformer

Maintenance Considerations 9 – Cable length – Conduit ends condition In addition, inspect the LED light fixture leads for nicks, cuts, or abrasions because water can penetrate the cable jacket and be wicked into the fixture by the heating and cooling process. This water can damage the circuit board and other electronic components if they are not properly sealed. The research team recommends checking a random sampling of 20% of fixtures. If one fixture fails, then another 20% should be opened and inspected. This should continue until all fixtures in a sample pass or all fixtures are inspected. All failed fixtures should be corrected and re­inspected. Figure 6. Elevated light fixture exterior inspection criteria.

10 LED Airfield Lighting System Operation and Maintenance In-Pavement Light Fixtures • In-Pavement Fixture Height. Often overlooked and highly dependent on the technician’s workmanship, the improper installation of an in­pavement light fixture can adversely affect the performance of a good fixture. A fixture not installed in compliance with the height requirement is susceptible to physical damage and/or noncompliant photometric performance. A fixture set too low will have the lower portion of the beam cut off, making the beam spread smaller and potentially making it noncompliant. If this fixture still meets the photometric output, as the photometric output degrades over time, this fixture will move out of com­ pliance more quickly because of the smaller beam spread. As outlined in AC150/5340-30H, Design and Installation Details for Airport Visual Aids, Chapter 12, paragraph 11.c “The top of the fixture edge must be between +0 and -¹⁄16 inch from the low side of the pavement surface.” This provides the requirement, but gives no guidance on how to verify the installa­ tion. To better understand the issue and a suggested measurement method, refer to Innovative Pavement Research Foundation (IPRF) Report No. 1-G-002-03-1, Constructing In-pavement Lighting, Portland Cement Concrete Pavement. Illustrations from that report are provided for reference in Figures 7 and 8. The research team recommends checking a random sampling of 20% of fixtures, using this method with a documented pass/fail protocol. If one fixture fails, then another 20% should be measured. Continue until all fixtures in a sample pass or all fixtures have been measured. All fixtures that fail should be corrected and re­measured for compliance. An LED light fixture not set at the proper elevation may go out of photometric compliance more quickly than a properly set fixture. As LED light output degrades over time, fixtures at the proper elevation will continue to meet FAA output requirements, while a lower fixture that has part of the light out­ put clipped by the pavement may fail to meet the same criteria, thus requiring poorly installed fixture locations to be addressed by maintenance sooner. • Exterior Light Base Inspection. The exterior inspection of the light base sealant typically indicates the overall workmanship of the light fixture installation. Visually inspect the sealant around the light base to ensure it is evenly distributed and the thickness is no more than 3⁄4 in. Verify that all bolts are installed and properly secured. Note inconsistencies among light fixtures. The light fixture installation indicated in Figure 9 is under suspicion because of two observations: the light reflection and the unevenness of the sealant installation. Figure 7. Height of in-pavement light fixture (IPRF 1-G-002-03-1).

Maintenance Considerations 11 Figure 8. Height measurement of in-pavement light fixture (IPRF 1-G-002-03-1). Figure 9. In-pavement light–visual inspection. Closer examination of the same light fixture (Figure 10) reveals that the pavement is protruding above the edge of the light fixture and causing a reflection of light. This could be an indication that the fixture was installed too low or not plumb. If not verified and corrected, the light could appear to be missing from the pilot’s perspective; additionally, the back reflection of the light could give the appearance that the light fixture is a bidirectional unit, thus providing false information to taxiing aircraft. The only accurate method of determining if the fixture passes is to test the photometric intensity of the fixture using mobile test equipment. Visual inspection along with photometric testing will verify the compliance of this fixture. The uneven and poor distribution of the sealant could cause premature failure of the sealant and allow water into the

12 LED Airfield Lighting System Operation and Maintenance fixture; therefore, the sealant should be removed and reinstalled. The research team recommends visually inspecting the exterior of all newly installed fixtures and recording notes on an inspection form. The form should include a check of, at a minimum: – Fixture ID, if available, or location – Type of fixture – Bolt installation – Sealant inspection – Damage to fixture – Surrounding pavement condition – General observations If an issue is observed, a photograph should be taken and attached to the inspection form. • Mounting Bolts. Mounting bolts are critical to the AGL system. Improper installation (i.e., loose bolts) causes a unique issue for LED light fixtures, given that LED fixtures require servicing so infrequently and loose bolts could result in bolts becoming dislodged, creating foreign object debris (FOD). Although this situation can occur with traditional incandescent light fixtures, those fixtures require re­lamping more frequently, so the risk of severely loosened bolts is less likely. Unless the fixture is clamped down properly, the LED fixture is susceptible to premature failure due to excessive vibration. Additionally, improper bolt installation can cause the fixture to disengage from the light base, potentially causing catastrophic damage. Several bolt characteristics that must be verified are the type, thread engagement, and clamping force (Figure 11). Information on these items is available in several FAA publications including Figure 10. In-pavement fixture–visual inspection 2. Figure 11. Mounting bolt parameters.

Maintenance Considerations 13 AC 150/5340-30, Design and Installation Details for Airport Visual Aids, AC 150/5340-26, Main- tenance of Airport Visual Aid Facilities, FAA Engineering Brief 83, In-pavement Light Fixtures Bolts, and AC 150/5345-42, Specification for Airport Light Base, Transformer Housings, Junction Boxes and Accessories. Bolt composition varies with the specific installation and materials used; two types of bolts are approved for use, an 18­8 Stainless Steel and an SAE J429 Grade 2 bolt with a ceramic­fluoropolymer coating. Airports may deviate from using these bolts, but they must support their decision with extensive research and comparison for a different selected bolt. The torque value varies depending on bolt type and the application of anti­seize compounds. As indicated in Engineering Brief No. 83, the application of an anti­seize compound will result in an equivalent clamping force with less torque. A bolt should never be over­torqued, as this will lead to premature failure. Follow Engineering Brief 83 guidelines for the proper torque value of the specific installation. The research team recommends checking a random sampling of 20% of the fixtures, using a calibrated torque wrench set at the specified value with a documented pass/fail protocol. If one fixture fails (i.e., one bolt is not properly installed), then another 20% should be mea­ sured. This should continue until all fixtures in a sample pass testing or all fixtures have been measured. All failed fixtures should be corrected and re­measured for compliance. • Light Base Interior Inspection. Visually inspect inside the light base of the elevated light fix­ ture to verify the installation of components and verify the condition for a new installation. Components to view and verify include the following: – Connectors – Grounding connections – Spacers – Flange ring – Length of bolts – Transformer – Cable length – Conduit ends condition In addition, inspect the LED light fixture leads for nicks, cuts, or abrasions as indicated in Figures 12 and 13 because water can penetrate the cable jacket and be wicked into the fixture by the heating and cooling process. This water can damage the circuit board and other electronic components if they are not properly sealed. The research team recommends checking a random sampling of 20% of fixtures. If one fixture fails, then another 20% should be opened up and inspected. This should continue until all fixtures pass in a sample or all fixtures are inspected. All failed fixtures should be corrected and re­inspected. This inspection can coincide with the exterior inspection and these items be added to the inspection form. Electrical Testing. Electrical testing (1) ensures minimum specified values are met and (2) provides valuable initial data that can be used to set a maintenance baseline. These measured values should, at a minimum, include • Circuit Insulation Resistance Measurement. The circuit insulation resistance measurement is the resistive measurement in Ohms of the cable insulation’s ability to resist the passage of stray current through the wall of the insulation to a ground source. Excessive current flow through the insulation wall is categorized as current loss and creates an inefficient electrical system. The larger the resistance value, the better the performance of the electrical system. Periodic measurement of the cable’s insulation resistance will provide a “check­up” of the system. However, this one measurement will not indicate overall condition. The measurement of the cable’s insulation resistance is better used as a trending and tracking measurement to determine the condition and performance of a cable, rather than a static measurement of condition. A high initial measurement reading is desirable, followed by relatively consistent

14 LED Airfield Lighting System Operation and Maintenance Figure 12. Visual inspection inside light base. Figure 13. Light base enlargement. readings over the anticipated life of the cable. This indicates a steady state of performance of the cable and the circuit. A sudden drop of measured value or a slow decrease in measured values typically indicates a failed or failing cable and circuit, at which point further maintenance investigation is warranted. AC 150/5340-30 indicates the minimum insulation resistance value of a cable to be 50 megohms (MW). Typically, higher initial values are achievable. This value should be used unless the initial value is specified in the design documents—then the

Maintenance Considerations 15 more stringent value should be used. Regardless, it is important to obtain this startup value to establish a baseline and trend the data to ensure the health of the series lighting circuit. • Circuit Overall Resistance Measurement. This measurement, which is a function of the length of the circuit and the number of light fixtures on it, is the loop resistance of the circuit after all cable, connectors, transformers, and light fixtures are installed. No specified value should be obtained but, similar to the insulation resistance, it’s a value that can be taken periodically and tracked to determine the state of the circuit. • Circuit Load Measurement. Circuit load is typically calculated during the design stage and is used to ensure that the series circuit is not overloaded. Taking these measurements on completion of design and before turn­over to the airport will verify the circuit is not loaded beyond its capacity. Load calculations assume ideal conditions, but the circuit load can change during installation due to as­built conditions. This load information is also important for maintenance if circuits need to be combined or placed on spare constant current regulators during a failure event. Photometric Testing Once the AGL system is installed, it is impossible to tell by merely visual observation if it is pro­ viding the FAA­compliant photometric output required. Photometric testing evaluates light sys­ tems and identifies performance deficiencies not apparent during visual inspection and measures the light beam output distribution of a fixture, light spread, and intensity. Results can be compared with FAA criteria to determine compliance. Photometric testing equipment is a computer­based system generally composed of a light bar consisting of photometric sensors attached to a vehicle or a trailer. The photometric sensors are positioned to test the fixture’s light beam. The light bar is scanned over energized light fixtures at the various intensity settings, thereby providing real­time data and feedback. Performance issues, such as those that might result from a dirty lens, can be corrected and retested in the same work cycle. Other more­involved performance issues (e.g., a defective light fixture or an improper installation) should be corrected and retested at another time. The research team recommends that each newly installed LED lighting system have photo­ metric acceptance testing performed as part of the project close out. Ideally, the photometric testing for acceptance should be performed by a third­party entity separate from the contractor and the airport. It is preferable that the testing agency be hired by the designer or consultant on the project, rather than directly by the airport, with the cost of the testing agency included as part of the project’s construction budget. However, if no designer or consultant is involved, the airport should hire the testing agency independent of the contractor. If an airport cannot directly secure the services of the testing agency, the testing can be included as part of the contractor’s scope of work. The research team recommends the airport contact the Illuminating Engineering Society, Aviation Lighting Committee (IESALC) at www.iesalc.org for contact information of airfield photometric testing firms. To maintain a state of good repair, the research team recommends an airport perform periodic photometric testing to track the condition and degradation of the AGL system. The research team recommends annual testing for airports with CAT III low­visibility lighting systems. The test should be performed before entering the inclement weather season, with enough time to correct any deficiencies. The research team recommends biennial (every 2 years) testing for CAT II airports with elevated and in­pavement fixtures. The research team recommends testing every 3 to 4 years for CAT I airports. The periodic testing can be performed by a third­party agency or, if the airport chooses to purchase photometric equipment, it can be performed by the maintenance team. System Burn-in The burn­in period is an effective way to identify inferior products of state­of­the­art com­ ponents that are semi­conductor based. LED light fixtures fall within this category. As indicated in

16 LED Airfield Lighting System Operation and Maintenance the survey data, the major source of LED light fixture failure is the electronic component. Although the survey data does not indicate the timeline of these failures, industry studies have identified infant mortality (IM) failures as the main reason for early onset system failures. IM failures are defined as early failures caused by material defects and errors in assembly. A burn­in period introduces stresses to a new system not normally encountered by the system early in its lifecycle. This allows issues to arise from defective parts or poor workmanship and for those issues to be corrected before system acceptance. The research team recommends a burn­in period of 5 to 10 times the normal daily operating period. A normal operating period is typically 12 hours, so this would yield a burn­in period of 60 hours to 120 hours with the system set on the highest intensity setting. Acceptance testing should be fully documented for validation and acceptance by the main­ tenance group. Additional items to be included with the acceptance testing documentation are as follows: • Fixture ID numbers and locations • Installation dates for warranty purposes • Equipment operations and maintenance manuals • Listing of spare parts delivered to the maintenance department Once the testing and documentation is submitted and deemed complete and acceptable, then the maintenance of the system can shift from the construction contractor to the airport main­ tenance group. Key Takeaways • Implement an acceptance testing program for LED lighting systems. At a minimum, perform a physical inspection and a system burn-in. • Depending on the project size and the airport, perform testing in house by the maintenance team or by a third party. Acceptance testing should not be performed solely by the contractor. • Log data collected from the acceptance testing in an acceptance test manual. The manual should include equipment operations and maintenance manuals, record drawings, electrical test results, photometric test results, calculations, inspection reports and photos, fixture inventory list, and manufacturer’s equipment cut sheets. This information will be needed for equipment asset inventory management. Warranty The first LED fixtures to gain FAA approval were the taxiway elevated edge lights. Approval occurred in the early 2000s. Shortly after, in the mid­2000s, in­pavement fixtures such as L­852A­D and L­852T also received FAA certification. Elevated taxiway edge lights (e.g., the L­861T) gained support as a result of their reliability. In one case study, a medium hub airport claimed that they installed the lights as soon as they were FAA­approved and have yet to encounter any issues with the elevated fixtures. This same airport also installed in­pavement LED fixtures.

Maintenance Considerations 17 The in­pavement fixtures did not perform nearly as well as the elevated fixtures. Because of the number of failures and unreliability of these lights, the FAA implemented a 4­year warranty requirement. This requirement has been successful in controlling unanticipated repair costs to airports, and it motivated manufacturers to identify issues quickly and significantly improve the reliability of LED fixtures. Many of the early problems with LED fixtures were eliminated by product improvements. Several airports that participated in this study and were early adopters of LED airfield lighting reported reliability issues such as electronic failure due to moisture and unprotected circuit boards inside the lights. Others reported vibration issues causing pieces of the circuit boards to break or connectors to become unplugged or dislodged. Obsolescence resulting from product upgrades also created difficulty in finding replacement parts. While man­ ufacturers continued to upgrade fixture components, the FAA revised their standards to hold the manufacturers to a higher design requirement. Improvements included solid­state components that resist vibration, fully potted (meaning encapsulated in an epoxy resin for protection against the elements) circuit boards that protect against moisture, and enhanced adjustable electronics that protect against obsolete diodes. In March of 2012, the FAA superseded Engineering Brief 67C with the release of Engineering Brief 67D. In the updated brief, specific language states the warranty period each manufacturer must provide to gain FAA approval and for airports to gain FAA funding for purchase of fixtures. The following excerpt is from Engineering Brief 67D: 4.0 Minimum Warranties 4.1 All LED light fixtures with the exception of obstruction lighting (AC 150/5345­43) must be warranted by the manufacturer for a minimum of 4 years after date of installation inclusive of all electronics. The replacement criterion for light fixtures is per AC 150/5340­26. The 4­year warranty provides the airport with assurance of a reliable product and time to acclimate maintenance personnel to the equipment. The warranty period starts from the date of installation—not the date of purchase by either the maintenance group or the construction con­ tractor. Make sure acceptance testing documentation accurately records the installation date. If a contractor delivers spare fixtures to the airport after the completion of a construction project, and those fixtures remain in inventory for a year before installation, according to Engineering Brief 67D, the date of installation is when the warranty starts. However, the manufacturer cannot be expected to honor the warranty indefinitely for stockpiled fixtures. This is an important topic to discuss with the manufacturer at the time of purchase or with the contractor purchasing the lights. Warranty claims processing is simplified when an airport maintains an asset management program and can track fixture installations, among other aspects. This approach allows the airport to easily provide the manufacturer with proof of the installation date. The process of warranty claims reviewed in the case studies consisted of airport maintenance personnel being responsible for removing and replacing a failed fixture in the field. Once the light was returned to the shop, maintenance personnel examined it for physical damage and determined whether it was covered under warranty. After it was determined that the light was insured, the light was put in a stockpile area with other failed fixtures to be shipped back to the manufacturer. Airports tended to send fixtures back in groups of 20 to 40 at a time. Once the manufacturer received the fixtures, the manufactured decided whether to either repair the fixture or replace it— depending on what caused the failure. A repaired or replacement light was then returned to the airport. Repairs could take as long as 6 months; however, in most cases, fixtures were returned in less than 90 days, depending on the number of fixtures and the availability of components. Airport personnel must fully understand the coverage of the warranty. A manufacturer warrants the fixture for failure under normal use and does not cover damage inflicted to the fixture due to external causes (e.g., snow plowing operations or grass cutting). Some manufacturers will war­ rant the electronics and the diode for 4 years but other components may only have a 1­ or 2­year

18 LED Airfield Lighting System Operation and Maintenance warranty period. Some manufacturers also stated that they will begin the warranty start date approximately 6 months after ship date, but, in certain cases, there is flexibility to accommodate airport needs. Interviews with airfield light manufacturers made clear that the 4 year warranty is a gray area open to interpretation. The interviewed manufacturers confirmed that only the diode and the electronics are covered for 4 years—components such as external casing, glass (lenses), or couplings are not covered for 4 years. A good relationship between airport and manufacturer is important in efficiently resolving LED issues on the airfield. Most manufacturers will offer an extended warranty or a service contract to outsource fixture repairs when the base warranty expires. Service contracts reviewed in the case studies consisted of the airport removing the fixtures and sending them to the manufacturer for repair. Every airport operator must consider the different options for maintaining fixtures after the warranty period and take into account factors such as the airport’s budget and the size of its maintenance department. Extended warranties vary from manufacturer to manufacturer. One manufacturer interviewed repaired fixtures through an extended warranty or refurbishment program, using a flat rate method. Another manufacturer offered extended warranties based on an asset risk method—they collect data (e.g., the number of LED fixtures on airfield, maintenance practices, age of fixtures, and commonly failed components) and use this data to develop an extended warranty cost. This cost increases proportionately as fixtures age because risk of failure increases with time. Some manufacturers stated that they would rather train maintenance personnel to repair their own fixtures in lieu of providing an extended warranty. It was also mentioned that transport of fixtures can cause damage unknown to the manufacturer. For example, unsecured fixtures moving inside a shipping box is a common reason for cord set failure. The 4­year warranty has been successful in enhancing the reliability of newly installed LED circuits. However, airport maintenance departments need to address repair strategies for when the warranty period expires. Key Takeaways • Current LED fixtures are much more reliable than earlier generations, in part due to the FAA-mandated warranty requirement. • Document the fixture installation date for proper warranty management. • Develop a post-warranty strategy for fixture repairs (e.g., service contract, extended warranty, or perform in-house repairs). • Maintain a close relationship with fixture manufacturer. • Have an asset management program in place. Fixture Obsolescence and Spare Parts Recommendations Fixture Obsolescence LED airfield light fixtures have improved with multiple generations of production. However, because the FAA requires fixtures meet certain photometric requirements, the manufacturer is only allowed to use light fixture components that meet standards set forth by the FAA. Early

Maintenance Considerations 19 generation fixtures are no longer being supported by manufacturers and are considered obsolete. This presents challenges to airport maintenance departments maintaining early generations of LED fixtures. All airfield lighting manufacturers purchase their LEDs, rather than manufacturing them. Diode manufacturers are constantly working to advance their technology to meet the demand for efficiency and to remain competitive. The airfield lighting application is usually not a diode manufacturer’s first concern. The lights are designed to fit and apply to various commercial, automotive, and specialty lighting applications. This means that, once an LED is no longer in production by the diode manufacturer and a replacement is available that is more efficient or requires different electronics, an airfield lighting manufacturer has to revise the design of their fixture to meet the requirements of the new diode. These technological upgrades affect not only the diode but any component of the fixture that the airfield lighting manufacturer does not manufacture in house. This is a challenge for manufacturers trying to continue to fabricate or supply spare parts and achieve backward compatibility with previous generations of fixtures. At some point, manufacturers can no longer support the obsolete fixtures. The obsolescence issue affects incandescent lighting circuits as well. In a few instances in the research, maintenance per­ sonnel complained about the difficulty in purchasing certain replacement incandescent bulbs. Twenty­five percent of survey respondents noted obsolescence in LED fixtures as a concern. Obsolescence is a significant concern for smaller airports because they may not receive FAA funding for lighting fixture upgrades as often and typically do not have the budget to replace obsolete fixtures in a timely manner. In one case study, a medium hub airport stated “The fast­ paced development of LED technology makes fixtures obsolete too quickly.” After further communication with the airport, the research team discovered that this airport was an early adopter of LED fixtures. The generation of fixtures they installed went obsolete shortly after purchase as a result of technological advancements and upgrades to the electronics. The light fixture manufacturer committed to maintaining support for an additional 5 years after purchase and did provide this support. The airport does not have an adequate budget to replace outdated fixtures and faces challenges attempting to repair the fixtures. Although this was only one case study, and was an extreme case because the lights were first generation, it demonstrates the concern with obsolescence of new technology. The fixture manufacturer offered to replace the fixtures with the newer generation fixtures at a reduced cost; however, even the reduced cost was beyond the airport’s budget. The airport is replacing a few fixtures each year as the budget allows, and staff continue to look for spare parts and repair fixtures. Attending maintenance training seminars has proven beneficial in the upkeep of their LED lighting systems. This airport noted that they had no major issues with their elevated fixtures installed more than 10 years ago. Although airfield lighting manufacturers are beginning to notice a slowing down in the pace of advancement of LED technology, no one can foresee what advancements will occur. Airfield lighting manufacturers, in most cases, attempt to maintain fixture backward­compatibility of components for 5 years. Some manufacturers, in order to maintain longer production life for their fixtures as well as provide a sense of security for their consumers, have begun to produce electronics that can work with various diode generations. The best method for ensuring support from a lighting manufacturer is to keep an open line of communication with the manufacturer to understand the production status of an airport’s generation of fixtures. Fixture obsolescence can be mitigated in several ways. One method is continuous upgrade to the latest generation by stockpiling a small number of complete light fixtures. As lights outside of the warranty period fail, they are replaced by newer units. This ensures that the airport is stocking the latest fixtures and avoids the problems of obsolescence. The FAA does not restrict having dif­ ferent generations of LED fixtures on the same circuit or length of pavement if they all conform

20 LED Airfield Lighting System Operation and Maintenance to the photometric and chromaticity requirements. For this method to work properly, the air­ port must maintain a meticulous asset management program to track fixture stock, including installed location and warranty periods. Unfortunately, however, this approach is more costly than repairs. In addition, if airports want to repair fixtures and have used this method, they will have multiple generations in place, which could increase their spare parts budget for stockpiling parts. Another method is to stockpile critical spare parts and train personnel to repair the fixtures so they can maintain the equipment after the warranty has expired. This method requires the air­ port to keep a record of the components that experience the highest failure rates and keep those replacement components on hand. Before the manufacturer discontinues support, based on the airport’s repair experience, the airport must stockpile an appropriate number of spare parts with that generation of fixtures. This method, although it is cheaper than replacing full fixtures, is not a long­term solution to obsolescence. Eventually, the components will be discontinued from production, forcing the airport to purchase the newer generation of fixtures. Most airports require at least a 10% spare fixture stockpile whenever a lighting project is completed. This stockpile, however, should not be the only stockpile the airport carries and should include a separate inventory of components such as circuit boards, power supplies (if not part of circuit boards), and LEDs, based on repair experience. These components will come in handy if the manufacturer stops supporting the fixtures after the warranty period has expired. Manufacturers should notify airports when a fixture is going out of production. Some manufacturers post a list of obsolete fixtures and component compatibility. As technology matures, obsolescence becomes less of an issue because manufacturers have typically solved the field problems and begun to standardize designs for greater compatibility. LED light fixtures are following this progression and the research team expects that obsolescence will be less of a concern in the future. Key Takeaways • Product obsolescence is an inevitable trend with all technological advancements. • Obsolescence is often a larger concern at smaller airports. • Fixture obsolescence has decreased due to more adaptable electronics. • Maintain a close relationship with the manufacturer to stay updated on manufacturer support status for fixtures. • Asset management programs can help airports match budgets with maintenance needs. • Airports should maintain a stock of complete fixtures along with a stock of parts that have typically failed. Spare Parts Recommendations Developing an Inventory An airport should maintain an adequate number of replacement fixtures and spare parts to facilitate quick repair so as to maintain the operational status of the AGL system and the air­ port. AC 150/5340-26C, Maintenance of Airport Visual Aid Facilities, provides guidance and outlines the process in Chapter 3, Maintenance Management. The AC indicates three factors that can help

Maintenance Considerations 21 determine a sufficient inventory: effect of downtime to operations, part availability, and component failure rate. Understanding LED Fixture Components An LED light fixture has various components. Components found in both in­pavement incandescent and LED fixtures include fixture housings, lenses, seals, gaskets, cord sets, and mounting hardware. Although components such as fixture housings, lenses, and gaskets are similar, they may not be interchangeable. The physical configuration of LED fixtures may vary from an incandescent counterpart from the same manufacturer and should be verified to determine if a separate stock of parts is needed. The major difference between an LED light fixture and an incandescent fixture is that an LED light fixture contains electronic components. Although the exact configuration of the components may vary slightly from manufacturer to manufacturer, they contain similar major components. The two major components are an LED light engine assembly and LED printed circuit board (PCB) with integral power supply (PCB/PS). As shown in Figure 14, the top housing has been removed. The light assemblies detach from the housing and plug into the PCB. The PCB and power supply are in the bottom of the fixture. Newer generations of PCB/PS are being potted. Given the location of the electronics for LED fixtures, the bottom of the fixture may be larger than that for a standard incandescent fixture. This may cause issues when performing a direct light fixture substitution on existing shallow or overcrowded light bases. This size varies between light fixture manufacturers and should be verified before selecting a light fixture for direct replacement. Elevated incandescent light and LED light fixtures also contain similar parts including frangible couplings, elevated stems, fixture housings, glass domes, seals, gaskets, cord sets, and mounting hardware. Again, although similar, the physical configuration of these fixtures varies from their incandescent counterparts and the potential to interchange parts should be verified with the manufacturer. As with the in­pavement fixture, the main differences between the incandescent and the LED fixtures are the LED light assembly and LED PCB/PS electronic components. Refer to the taxiway elevated edge light fixture in Figure 15 for illustration. The components of an elevated fixture sit in the upper housing of the fixture and sometimes in an enlarged fixture stem. The light engine assembly and the PCB/PS are sometimes integrated to form one unit. This is solely a manufacturer’s design preference. Light manufacturers’ websites often contain useful information on each type of LED fixture they manufacture. Typical websites provide assembly drawings, replaceable parts lists, and guidelines Figure 14. Typical in-pavement LED fixture components.

22 LED Airfield Lighting System Operation and Maintenance on how to test and replace the parts. It is important to become familiar with this information as it pertains to a particular light fixture. Determining Availability Early generation LED light fixtures, through changing LED technology, have become obsolete. Spare parts may not be available for these early­generation fixtures if they were not purchased at the time of installation or before being discontinued by the manufacturer. Maintenance depart­ ments should contact the fixture manufacturer to determine the availability of LED and PCB components to determine if repair or refurbishment is an option for the light fixture. If parts are not available through the manufacturer and the manufacturer is no longer supporting the fixture, the fixture is obsolete and a complete replacement is required. Be cautious if repair parts are obtained through an exchange with another airport, because these may not be the certified parts associated with the fixture and may adversely affect the performance of the light fixture. Such exchange is not a recommended practice. Newer generation lighting fixtures are now available with an intelligent PCB/PS that can sup­ port the light fixture through several changes of the LED technology and is interchangeable among types of light fixtures. A one­power­supply­fits­all scenario will reduce the need to stock different versions of power supplies and help reduce fixture obsolescence. The number of available spare parts depends on the business and fabrication practices of the various manufacturers. Manufacturers maintain a supply of fabrication parts to produce light fixtures and those quantities depend on their current procurement and fabrication schedules. However, discussion with several manufacturers has revealed that a small quantity of fixtures is usually available with a delivery timeframe of 2 to 3 weeks. Available Spare Parts Each lighting fixture manufacturer website indicates a list or provides drawings for the available spare parts associated with a particular light fixture and a maintenance guideline for each fixture. Spare parts that are typically available for light fixtures are as follows: In-pavement Elevated Signs PCB/PS Light Assembly Light Assembly Light assembly PCB/PS PCB/PS Cable clamp Cable clamp Power Cable Assembly Cord Set Cord set Exterior Switch Cord set grommet Cord set grommet Seals and Gaskets Figure 15. Typical elevated edge light LED components.

Maintenance Considerations 23 In-pavement Elevated Signs O­ring Stem Tether Prism Frangible coupling Frangible coupling Prism gasket Globe Seal, prism keeper Arctic kit heater Arctic kit heater Several manufacturers are moving toward standardizing parts among types of light fixtures and among the types of signs. Standardization will allow a single type of item to be used for various fixtures or signs, thus eliminating the need to carry redundant parts for all types of fixtures. Airports that refurbish fixtures and signs may continue to do so with LED fixtures and LED signs. LED fixture refurbishment tends to be more successful in a workstation environment, rather than out in the field, because electronic components can be degraded if exposed to poor environmental conditions. Additionally, it is a good practice to perform the work in a separate clean environment, rather than where the refurbishment of non­LED light fixtures is performed. L­858 Guidance signs, unlike lights, are generally repaired in the field; in this case, the work must be performed diligently to ensure components are kept clean. Working on electronic components requires specific precautions to prevent damage from handling. Such precautions include preventing static electric discharge and preventing transfer of oil and grease to the components. Refurbishment of light fixtures and signs should follow the recommended guidelines set forth by industry standards and the manufacturers. The survey data indicates the major reason for light­out failures of LED fixtures is the electronics/ printed circuit board. The initial versions of LED light fixtures and signs contained model­specific LED components. Manufacturers have addressed this issue and are offering newer generation fixtures and signs with standardized and universal components. Quantity of Spare Parts Method Regardless of the size of an airport (e.g., general aviation, regional or major hub) and the capital investment it makes to maintain an inventory of spare parts/stock, an inventory of spare parts must be maintained. The current practices established at an airport for maintenance of light fixtures can be followed for LED light fixtures, whether that practice involves full fixture replace­ ment, refurbishment of light fixtures, or a combination of both. There are numerous theories for determining the ideal number of spare parts for a given type of fixture. However, only the individual airport can decide what approach works best. A typical rule of thumb is 10% stock for spare parts but, with the longevity of LED fixtures, this may be reduced to 5% for an initial inventory. That percentage may be increased for elevated fixtures that are more prone to physical damage from vehicle traffic. Airports can adjust the value as they gain experience with LED lighting systems and the physical and environmental stresses of their particular location. As more LED lights are installed during rehabilitation projects, airports should use those opportunities to adjust inventory to maintain the new lights. Additionally, airports should build a relationship with their lighting manufacturer to better understand the manufacturer’s parts and stock inventory practices and to develop an emergency lighting replacement plan. Spare parts inventory will vary from airport to airport, depending on the service duration of the fixtures. An airport that has been using LED fixtures for only 2 years will not have the same parts inventory as an airport that has been using them for 6 years, where the fixtures may be out of warranty. Figure 16 shows how often surveyed airports needed to replace components within LED fixtures; however, duration of service was not accounted for.

24 LED Airfield Lighting System Operation and Maintenance Preventive Maintenance and Refurbishment/Repair Preventive maintenance is essential to maximizing the life expectancy of any AGL system. Preventive maintenance includes regular inspection and refurbishment of light fixtures to avoid failure. For an airfield to operate under safe conditions, the FAA mandates a maximum lights­out requirement for each lighting system. System requirements are provided in Appendix A. Along with lights­out requirements, the FAA also mandates a schedule for maintaining the lights. Table 1 is one of many maintenance schedules in AC 150/5340-26, Maintenance of Airport Visual Aid Facilities, used to guide airports in establishing a cost­effective preventive maintenance program. Appendix A contains all the schedule tables for easy reference by maintenance personnel. A common misconception about LED lights is that, given their claimed longer life span in comparison with their incandescent counterparts, they require little or no maintenance. However, How oen do you need to replace the light engine/electronics/diode of your LED light fixtures (not including premature failures)? Figure 16. Survey results for the need to replace parts on LED fixtures. Key Takeaways • Maintain an initial minimum of 5% stock items, whether full fixtures or spare parts. • Refurbishment of LED fixtures should be conducted in a clean area, following manufacturer’s guidelines and industry practices for work on electronic equipment. • To maintain the quality of LED light fixtures, use only parts received from manufacturers for the particular light fixture. • Maintain a relationship with a lighting manufacturer to gain knowledge of part availability and to develop an emergency lighting plan in the event of major light fixture failures.

Maintenance Considerations 25 an LED fixture needs to be well­maintained to maximize life expectancy. From the data collected, it was evident that maintenance personnel believed that if a fixture illuminates, it needs no attention. This belief, however, conflicts with most manufacturer recommendations and the minimum requirements of AC 150/5340-26. AC 150/5340-26 describes the minimum maintenance requirement for AIP­funded airports and provides guidance and recommendations for airports funded through other sources. The following excerpt is from the AC: Applicability. The FAA recommends the guidance and specifications in this AC for the Maintenance of air­ port Visual Aid Facilities. In general, use of this AC is not mandatory. However, use of this AC is mandatory for all projects funded with federal grant monies through the Airport Improvement Program (AIP) and with revenue from the Passenger Facility Charges (PFC) Program. The AC should be followed in order to maintain airfield visual equipment properly. The AC covers every visual aid system on the airfield in detail, providing requirements and intervals for maintaining the equipment. The AC also includes a table that breaks down maintenance into time MAINTENANCE REQUIREMENT D A I L Y W K L Y M T H L Y S M A N Y A N N L Y U N S C H 1. Inspect for outages; repair as necessary X 2. Check cleanliness of lenses X 3. Perform photometric testing (HIRL) and check light alignment and orientation X X 4. Re-align lights as needed X X 5. Clean fixtures and sockets X 6. Check light elevation X 7. Check for moisture in lights X 8. Inspect fixture for rust, deterioration X 9. Check lamp fitting and clean contacts X 10. Check gaskets X 11. Remove snow and/or vegetation from around lights X Table 1. AC 150/5340-26C, Table 5-5, preventive maintenance inspection schedule for runway and taxiway elevated edge lights. Yes 51% No 49% Is the maintenance schedule idencal for incandescent and LED lights? Figure 17. Survey results for difference in maintenance schedules for LED and incandescent fixtures.

26 LED Airfield Lighting System Operation and Maintenance periods (e.g., daily, weekly, monthly, semi­annually, and annually). The circular goes through step­by­step detail in each section and discusses the tasks to be completed in each timeframe. However, these requirements are set as a minimum and may require alteration in response to local airport conditions. The AC also repeatedly advises users to consult manufacturers maintenance manuals. AC 150/5340-26 is not a replacement for manufacturers maintenance manuals. Based on the airport and the airfield category, a specific number of lights have to be turned on and functioning for the airfield to operate safely. For example, a CAT I runway can operate with only 85% of the edge lights on. Based on the availability of maintenance personnel, labor costs, and the stockpile of spare parts or fixtures, maintenance procedures must be established for the airport that are not cost prohibitive. Such procedures may evolve over years of planning and recordkeeping of maintenance tasks and labor hours associated with each task. As LED AGL becomes a more prominent part of the visual aid system, the preventive main­ tenance practices once used with incandescent fixtures will, in some cases, differ from those for LED fixtures (see Figure 17). To preserve the life of LEDs, a specific maintenance schedule has to be implemented because fixtures no longer require frequent re­lamping. Lack of attention can quickly result in a small problem becoming a bigger problem that can result in permanent failure to the fixture. For example, in one case study, a spider gained access to the housing of a fixture and created a web on the circuit board. Although the fixture continued to operate, over time the web held moisture and, ultimately, short circuited the electronics—this problem could have been avoided by periodic inspection of the fixtures. Although preventive maintenance can reduce fixture failures, it will not eliminate them. Airports rely on their fixture failure maintenance procedures. The surveys and case studies revealed several methods for failure maintenance. Some airports found that it was best to replace fixtures as they failed. If the fixtures were within the warranty period, the fixtures were returned to the manufacturer for repair or replacement. If fixtures were out of warranty, they were replaced with new fixtures and the failed fixtures were discarded. This method reduced some of the preventive maintenance mentioned in the table above and allowed maintenance personnel to be used in other ways; it also reduced concern about retaining obsolete fixtures. Other air­ ports repair fixtures as they fail. At almost all airports surveyed, maintenance personnel did not troubleshoot or repair any LED fixtures in the field. They replaced the fixture with a functional one in the field and brought the failed fixture back to the shop. This is also the recommended procedure as stated in AC 150/5340-26: Do not disassemble LED­type light fixtures in the field–follow the manufacturer’s recommendation for maintenance if any is required. A potential method conceived by the research team through case studies with airport person­ nel would be to establish a refurbishment schedule for portions of the airfield throughout the year. For example, every other June, a hypothetical airport might remove runway centerline lights and bring them to the shop for refurbishment, which would include replacing gaskets, seals, lenses or prisms, among other components that can sustain wear, and running each fixture through different tests, including photometric and chromaticity testing, pressure testing, and PCB output. Components would be repaired as needed. This refurbishment would be conducted in conformance with the maintenance manuals provided by the manufacturer. In most cases, the diode will not fail; other components around it fail or degrade due to vari­ ous reasons including moisture, vibration or simple wear and tear due to vehicular and aircraft movement and weather. A maintenance supervisor from a medium­hub airport in a cold climate remarked: We haven’t started yet, as most LEDs are less than 4 years old. However, we need to set up a PM plan to rebuild sections of LEDs at a time. With incandescent fixtures, we (remove and replace) them as

Maintenance Considerations 27 the lamps burn out. At that time, usually a year or so, they get an overhaul. Since the LEDs are lasting much longer, the prisms and gaskets will not be addressed in a timely manner, without a rebuild time period. Although most airports refurbish or repair fixtures in their own shops (Figure 18), some airports use a service contract with the light fixture manufacturer for repairs or refurbishment of fixtures. These airports package the fixtures and return them to the manufacturer. The extent of in­house repairs varied from airport to airport. Some replace internal components and seal the fixture back up while others fully refurbish the fixture including the housing. Given that LED technology is evolving, receiving proper training is necessary for the per­ sonnel who maintain these lights. Many training opportunities for airfield lighting are offered. Many airports have staff attend training courses provided by the fixture manufacturers or ask the manufacturer to conduct in­house seminars (Figure 19). These training opportu­ nities include attending airfield conferences, classes offered by lighting manufacturers, and AAAE certification programs. Proper training ensures that maintenance personnel are handling fixtures in an approved manner and that preventive maintenance measures recommended by the manufacturer are being adhered to by the consumer. A good way to ensure airfield personnel receive training is to include training costs in the scope of large construction projects. Although preventive maintenance routines differ, the following elements are considered the minimum essential by the FAA, as stated in AC 150/5340-26, in establishing a maintenance program: a. Document the service checks that comprise the maintenance program. b. Record the performance of each maintenance action, scheduled or unscheduled. How are your LED fixtures maintained? Figure 18. Survey results indicating how many surveyed airports use each method of fixture maintenance.

28 LED Airfield Lighting System Operation and Maintenance c. Document repairs and troubleshooting performed on each piece of equipment and the results of those actions, as well as the symptoms related to the malfunction. This allows for more rapid troubleshooting of similar problems later. The AC also states that a maintenance program is essential to the safety and reliability of the lighting system, especially if a failure occurs at a critical time. The following is a summary of paragraph 5.3, Light Fixture and Base Maintenance, which is the FAA’s minimum requirement for maintaining runway and taxiway lights, including scheduled and unscheduled inspection checks: • Airport lighting fixtures for runway and taxiway use are broken into two general categories: elevated and in­pavement. • In­pavement fixtures typically require more maintenance than elevated fixtures. Elevated Fixtures • Do not disassemble LED­type light fixtures in the field. • Elevated fixtures are more likely to be damaged because of snow plowing, operation, or grass cutting. For this reason, many airfields use in­pavement edge fixtures. • If elevated fixture are struck, proper measures must be taken to prevent foreign object debris (FOD) hazard. • When repairing edge lights, ensure proper aiming. The beams of runway edge lights are aimed toward the runway centerline at 3.5 degrees. The beam is also aimed up 4 degrees from horizontal. Refer to the manufacturer’s manuals. If the globe is opened, gaskets/seals should be replaced. • Control the vegetation growing around elevated edge lights. • Never repair fixtures with the circuit energized. • Only use parts approved by the original equipment manufacturer of the fixture. If you conduct connuous maintenance training for your staff, do you conduct: Figure 19. Survey results for how many airports use each type of training.

Maintenance Considerations 29 In-pavement Fixtures • Rubber deposit on the lens is the main cause for poor photometric performance. • Jet fuel, deicing fluid, and other contaminants can collect on/in a fixture, thereby causing deteriorating light output. • When maintaining a fixture, remove and replace with a refurbished or new unit. Bring fixtures back to the shop for required maintenance. • For maintenance purposes, maintain a quantity of spare fixtures equal to 5% of the installed quantity for each type of fixture at the airport. • Airports are encouraged to build specially modified trailers or vehicles for fast removal and replacement of fixtures. Maintenance vehicles or trailers can be equipped with generators, air compressors, and proper tools to perform almost any task. • Bench­test fixtures after refurbishment. • Replace all gaskets/seals during refurbishment to avoid water intrusion. • Some newer light fixture designs come from the factory with a Schrader valve stem attached to the bottom of the fixture. This fitting is used at the factory to pressure test the fixture during final assembly and can also be used during maintenance. Consult the fixture manufacturer for recommended air pressure settings. • When reassembling a fixture, follow all manufacturers’ instructions. • When reinstalling the fixture, use new bolts and locking washers. Many of the maintenance requirements can be simplified if the airport maintains an asset management system. An asset management system also allows the airport to budget properly, maintain a safe operating stock, and develop a plan for replacing outdated fixtures. Ensuring that a stock of functioning lights is always available is paramount to the safe operation of an airfield. The case studies revealed that some airports keep electronic records while others keep paper records. Manufacturers are beginning to use electronic methods to record hours of operation completed on fixtures. Airport records must be kept current and an understanding of the warranty must be established with the manufacturer. Keeping records current and understanding the warranty will help ensure that the airport maximizes its investment. For new fixtures, the asset management database should log vital information (e.g., fixture type and serial number, date of purchase, date of installation, and fixture location). For refurbished or repaired fixtures, the database should include repair/refurbishment date, fixture location, tests, measurements conducted, and parts replaced. By documenting fixture repairs at problem areas on the airfield and noting components susceptible to higher failure rates, airports can stock more of the components they need. Other data deemed necessary by individual airfield maintenance teams should also be recorded. To maintain efficiency on the airfield and ensure personnel are repairing equipment properly and to the standards and recommendations of the manufacturers, maintenance personnel are encouraged go through applicable training. AC 150/5340-26 states the following: Maintenance personnel should have a thorough knowledge of the equipment, experience with high voltage, and should be able to perform inspections and repairs. Special training is available and may be desirable, as most well­qualified electricians can be trained on­the­job if suitable supervision and instruction are provided. Qualified maintenance individuals should be present, or on­call, during the operating hours of the airport to correct any deficiencies that may develop. Airport visual aid maintenance personnel should be specialists in the field. Conferences and tradeshows occur all over the country throughout the year. Attending these events may help keep airfield personnel current on issues, studies, and technological develop­ ments. Staff can attend these events and bring information back to their respective airfield main­ tenance teams.

30 LED Airfield Lighting System Operation and Maintenance Key Takeaways • Preventive maintenance is regular inspection and refurbishment of light fixtures to avoid a failure. • AC 150/5340-26, Maintenance of Airport Visual Aid Facilities, describes the minimum maintenance requirements for AIP-funded airports. (All the schedule tables are in Appendix A of this guidebook.) • To preserve the life of LEDs, a specific maintenance schedule has to be implemented given that fixtures no longer require frequent re-lamping. • Based on the availability of maintenance personnel, labor costs, and the stockpile of spare parts or fixtures, maintenance pro- cedures must be established for the airport that are not cost prohibitive. • A typical rule of thumb is 10% stock for spare parts, but with the longevity of an LED fixture life, this may be reduced to 5% for an initial inventory. However, only the individual airport can decide what works best. • Do not troubleshoot or repair any LED fixtures in the field. Replace fixtures and bring failed ones back to the shop. • Stay ahead of fixture obsolescence by replacing failed fixtures with the latest generation or keep a stockpile of commonly failing components to allow for fixture repair after a fixture is out of production. • Airports should maintain asset management systems to allow for proper budgeting and a safe operating stock and to help in developing a plan for replacing outdated fixtures. • The asset management database should log in vital information (e.g., fixture type and serial number, date of purchase and date of install and fixture location) for new fixtures. For refurbished or repaired fixtures, the database should include repair/ refurbishment date, fixture location, tests, measurements conducted, and parts replaced. • Airport personnel must fully understand the coverage of the warranty. • Fixture manufacturers may offer an extended warranty or a service contract to outsource fixture repairs when the base warranty expires.

Maintenance Considerations 31 Maintenance Practices During Pavement Repair Airfields undergo long­term construction improvement projects, such as rubber removal, striping, or full pavement rehabilitation. During such projects, fixtures may be affected. Several methods can be used to protect lights during construction. While pavement is being rehabilitated, repaired, or newly constructed, protecting the light fixtures must be part of the project. In most cases, part of the electrical work is performed first before civil work can proceed. It is highly recommend that lights be removed, tagged, and stored or disposed of as the airport sees fit. Leaving lights in the pavement during civil work may cause severe damage to the fixtures. Some of the issues mentioned in the airport survey and case studies for elevated fixtures occurred due to construction equipment and vehicles being close to the activities. In­pavement fixtures often get damaged during rubber removal when chemicals can enter the fixture or lenses can be scratched. In­pavement fixtures sometimes get painted over, which affects their photo­ metric integrity. Maintenance activities can also affect fixtures. When fixtures are removed during pavement maintenance, they can be mishandled, thus resulting in damage to the fixtures or identification tags being misplaced, which ultimately affects the maintenance log. The following steps, as illustrated in Figures 20 and 21, are general procedures for protecting fixtures during pavement overlay construction: Pre/During Paving • Remove fixture, transformer(s), and top section. Remove P­606 sealer, cement compound, or epoxy around the perimeter of opening. Remove extension or top section. • Take coordinate location (northing and easting/latitude and longitude). This will be used to locate the fixture after final paving is complete. Key Takeaways • To maintain efficiency on the airfield and ensure personnel are repairing equipment properly and to the standards and recom- mendations of the manufacturers, maintenance personnel are encouraged to go through the applicable training. • When repairing edge lights, ensure proper aiming. Refer to manufacturers manuals. If the globe is opened, gaskets/seals should be replaced. • Only use parts approved by the original equipment manufacturer of the fixture. • Replace all gaskets/seals during refurbishment to avoid water intrusion and bench-test fixtures after refurbishment. • When reinstalling a fixture, use new bolts and locking washers. • AC 150/5340-26 requires airports to check the torquing of in-pavement light fixture bolts bi-monthly at a minimum. If an area experiences repeated failures, that area should be checked more frequently.

32 LED Airfield Lighting System Operation and Maintenance • Furnish and install a temporary mud plate on the fixture. Mud plates should be 1⁄8­in.­thick steel or 5⁄8­in.­thick plywood. • While paving operations are in progress, perform preventive maintenance on fixtures. • Refurbish damaged fixtures in house or ship them to the manufacturer. • Dispose of failed or obsolete fixtures and purchase new replacement fixtures as part of the construction budget or the airport’s budget (budget dependent). Post Paving • Using coordinates previously recorded, locate the light base. • Core drill the full­size hole for the top section and fixture installation. The gap between fixture and pavement should not exceed 3⁄4 of an inch. • Remove the temporary mud plate. Figure 20. Fixture to be removed prior to paving. Figure 21. Fixture removed during paving.

Maintenance Considerations 33 • After properly cleaning all debris from the light base, including the bolt holes, reinstall the extension onto light base. • Fill the gap between the extension and pavement with appropriate materials (e.g., P­606 sealer, cement compound, or epoxy). • Make all necessary connections and reinstall the light fixture. • Final fixture installation will resemble the installation shown in Figure 21. There are several ways to protect fixtures during a construction project. Elevated lights can be protected by enhancing their visibility to reduce the likelihood of vehicles or equipment hitting them. This can be done by placing construction cones around the light fixtures. If possible, ensure that edge lights are outside of the construction limits to reduce accidental damage. For in­pavement fixtures, fixtures should be removed during major paving operations. If pavement marking is being applied, fixture lenses should be masked to avoid getting paint on the lenses or light channels. The same procedure applies to rubber removal. Rubber should be removed from the fixture by separately cleaning each fixture lens after rubber removal procedures have been completed for the pavement. Protecting the fixtures also extends to storage and inventory. The research team recommends that fixtures removed during paving be properly labeled. Fixtures should not be stacked on top of one another in large piles because this may damage the electrical leads (which could promote water infiltration). Because most LED fixtures are more expensive than incandescent fixtures, airports tend to refurbish fixtures out of warranty. In general, if an LED fixture is opened for any kind of repair, the research team recommends that gaskets and prisms be replaced. After the fixture is repaired and reassembled, a pressure test is recommended to verify the light’s assembly integrity. The research team also recommends photometrically testing the light to confirm that it meets FAA standards. Many airports are now obtaining photometric testing equipment to test lights after refurbishment or repair. Lights should also be tested through the five intensity steps using a benchtop constant current regulator to ensure proper functionality. Some airports completely rebuild fixtures, meaning that all components are either cleaned or replaced depending on condition, including sandblasting and repainting of the housing. This refurbishment can be done either by a trained contractor, trained airfield maintenance personnel, or the manufacturer of the fixtures. Once a fixture is refurbished, a maintenance log should be prepared or updated explaining what was repaired or replaced on the fixture. Follow these general steps during refurbishment: • Visually inspect the housing for cracks or deformities. • Inspect the globe/prism for cracks, pitting, or other damage. • Inspect for evidence of moisture infiltration. • Disassemble the fixture and inspect internal components for damage or moisture. • Replace parts as needed according to the manufacturer’s recommendation. • Reassemble the fixture and pressure test. • Run the fixture through the five intensity steps. The fixture should be tested for an adequate period of time to ensure it will not prematurely fail in the field. • Photometrically test the fixture on the highest step. Other steps can be tested; however, the FAA only requires testing on the highest step. For major paving projects, the age of the fixtures should be assessed along with the generation, availability of spare parts, and failure rate. These will all help determine whether the fixture should be refurbished or replaced as a part of the rehabilitation project. As previously stated, in­pavement fixtures should be protected during rubber removal. Enforc­ ing this precaution is essential in touchdown zones where rubber accumulation is more severe.

34 LED Airfield Lighting System Operation and Maintenance In 2008, TRB released ACRP Synthesis 11, Impact of Airport Rubber Removal Techniques on Run- ways. The document briefly discussed some of the effects rubber removal has on the lights. From all the different methods used for rubber removal, water blasting was deemed most harmful to lights. One of the main contributors to damage occurred when an inexperienced operator was using the equipment. ACRP Synthesis 11 states, “However, in those cases where operator skill or experience was not adequate, damage to runway lighting, pavement markings, and crack sealant was experienced.” Table 2, from ACRP Synthesis 11, shows that any method for rubber removal could damage the lighting system. It may be cost effective to remove the lights and plate their cans prior to rubber removal operations. Possible Damage Water Blasting Chemical Removal Shot Blasting Mechanical Removal Groove damage X X X Spalling of concrete X Damage to asphalt pavements X X X X Microtexture degradation (polishing of aggregates) X X Loss of aggregate/fines X X Damage to expansion joints and crack seal X X X Damage to patches X X X Damage to equipment from caustic chemicals X Damage to runway lighting X X X X Damage to paint/markings X X X X Table 2. Possible damage from rubber removal methods. Key Takeaways • Pavement rehabilitation projects, or whenever pavement is shut down for a prolonged period, is an optimal time to perform preventive maintenance on LED light fixtures. • Airport should have a protection plan for fixtures during pavement construction projects. • Fixtures should be protected during pavement marking and rubber removal operations. Environmental Factors Environmental factors are a greater cause of concern when comparing LED with incandescent fixtures, because LED fixtures contain electronics that can be more susceptible to environmental effects than standard lampholders and incandescent lamps. During the project, the research team noticed that, although vibration and moisture are the more common reasons for fail­ ure, other environmental aspects (e.g., insects) were also cause for concern. As the technology evolves and improves, these environmental factors are beginning to be reduced. In many cases,

Maintenance Considerations 35 manufacturers have worked closely with the airports to resolve issues and then took the neces­ sary steps to prevent the failure from occurring in future fixtures. Vibration Vibration is typically associated with the airfield operating environment due to moving air­ craft and the forces they generate. As use of LED fixtures began to gain momentum in airfield applications, vibration became a concern given the various electronic components incorporated in the fixtures. The FAA requires airfield lighting manufacturers to subject in­pavement fixtures to vibration and shock tests. AC 150/5345-46, Specification for Runway and Taxiway Light Fixtures, states that fixtures must be subjected to a sinusoidal vibration along three mutually perpendicu­ lar axes. The first part of the test vibrates the fixture over a frequency range of 20 to 500 Hz with a maximum acceleration of 10Gs. The second part of the test vibrates the same fixture from 500 to 2,000 Hz, with a maximum acceleration of 15 times the force of gravity. Each part of the test must have a duration of 10 minutes. At the conclusion of the test, the fixture is thoroughly inspected for mechanical damage, loosened components, loss of continuity, or movement of the diode which is cause for rejection of the fixture. For shock testing, which applies to runway in­pavement lighting, the fixture is mounted to a 1­in.­thick steel plate or a 4­in.­thick concrete base. Steel or concrete must not be less than 3 square feet in size. Once assembly is complete, the fixture is set to the highest brightness level for 2 hours prior to the start of the test. With the fixtures still at highest brightness, a 5­pound steel ball is dropped on the center of the light from a height of 6 feet. This step is repeated 10 times at 5­minute intervals between drops. At the conclusion of the test, the fixture internals are inspected for failures or displaced components. Any evidence of damage or LED failure is a cause for rejection. Vibration due to aircraft impacts is believed to be one of the causes for premature failure of LED airfield fixtures. Pinpointing the effects of vibration is difficult because clear data does not exist on what happens to fixture internals as an aircraft runs over it. Some of the airport personnel who completed the survey mentioned that vibration was a cause of LED failure on the airfield shortly after installation. In cases where lights failed due to vibration, the fixtures were typically still under warranty and issues were repaired by the manufacturer. Fixtures failing due to vibration were most commonly taxiway centerline lights at runway high­speed exits. Taxiway centerline lights are not required to comply with the rigorous impact testing that runway centerline lights are subjected to. The following survey response from a medium­hub airport in a cold­climate environment demonstrates how vibration has affected LED fixtures: When we first installed L­852 LEDs on a high speed taxiway, off a runway, we had a high rate of failures. We had not experienced the same issue on slower taxiways. Ultimately, we attributed this to the high number of 747s and MD11s . . . causing high rates of vibration in the fixtures. Basically, the leads were breaking off the light engines. [The lighting manufacturer] pursued the problem and repairs, under warranty. After a couple of rebuilds and product improvement, the LEDs are holding up. A large­hub airport stated the following: We have had a lot of runway fixtures go out in the first couple months of operations. Specifically centerlines and some touchdown fixtures. Earlier generation fixtures were more susceptible to vibration damage. Resistors, capacitors, and other circuit board components would break away from the circuit board, causing the fixture to immediately fail. However, product improvement, for example, by potting the electronics and reducing the number of “moving parts,” has resolved many of the problems. Some light manufacturers established test beds to determine whether LED fixtures were more susceptible to vibration in comparison with their incandescent equivalents. For example, one manufacturer

36 LED Airfield Lighting System Operation and Maintenance installed their fixtures at a Naval Air Facility to subject them to a more severe environment than on a typical airfield. After many landings and tail­hook strikes, no fixture failures due to vibration were reported. (http://www.adb­air.com/media/10333/ADB­Tech­Corner­Answers­ High­Intensity­Airfield­Lighting.pdf) The results showed that newer generation LED fixtures are more stable and durable in high vibration areas. By incorporating more solid­state and passive components, fixtures are now more resilient to vibration. In comparison, incandescent fixtures still incorporate a wire filament. When exposed to vibration, these filaments are susceptible to failure. If an airfield is experiencing repeated failures in certain areas, specifically if these areas are runway centerlines, high­speed taxiways or touchdown zones, it may be due to vibration. A good practice is to discuss this topic with the airfield lighting vendor to better understand how equip­ ment will perform in high­vibration areas. The case studies revealed that the areas mentioned above were typical areas for premature failure due to vibration and shock. There are industry concerns regarding loosening in­pavement fixture hold­down bolts, regard­ less of the fixture type. Although FOD damage is the primary concern, loose bolts can amplify vibration damage. After being exposed to the various forces of aircraft movement, the bolts holding in­pavement fixtures down have been known to loosen if not fastened properly or have sheared off when fastened too tight. Whenever a fixture is not properly fastened, vibration to the fixture increases, which inherently increases the probability of damaged fixture electronics, disconnection of wiring, or loosening of components within the fixture. AC 150/5340-26 requires airports to check the torquing of in­pavement light fixture bolts bi­monthly, at a minimum. If an area experiences repeated failures, that area should be checked more frequently. Vibration issues were not as evident in incandescent lights because the fixtures were visited more often for re­lamping. LEDs do not require re­lamping and, therefore, are not visited as often. A good practice, especially for airfields with high LED usage, is to have a work plan and special crews assigned only to bolt torquing. Some of the airports included in the case studies stated that they have special crews that go out, usually at night, to check bolt torquing. These airports had different parts of the airfield testing scheduled at different times of the year to accommodate the work load. Although this may seem like an additional maintenance requirement for LEDs, it is not. The same amount of maintenance, if not more, is required when re­lamping an incandescent. Furthermore, AC 150/5340-26 requires the same torquing checks for incandescent fixtures. More research is being conducted on bolt torquing issues, but a solution is yet to be determined. Maintenance records should be maintained by the airport to ensure that bolt main­ tenance schedules are followed. Key Takeaways • Fixtures in runway centerlines, high-speed taxiway centerlines, or touchdown zones may experience greater failure rates due to vibration from more consistent high-impact aircraft movement. • Discuss vibration with the manufacturer to better understand technological advancements and how issues can be alleviated. • Maintain proper bolt torquing on light fixtures by creating a testing schedule and stocking the correct tools.

Maintenance Considerations 37 Moisture In-Pavement Light Fixtures The responses to the surveys and case study questionnaires indicated that moisture is a common issue and area of concern that airports are experiencing with LED fixtures and that the presence of moisture may result in the failure of the fixture. Moisture is not unique to LED fixtures; in fact, incandescent equivalents experience similar water infiltration. The difference is that LED fixtures use a printed circuit board (PCB) in lieu of the gas­encapsulated filament used in traditional lamps. Once water migrates into a PCB, it quickly corrodes conductive material, resulting in a circuit short that is difficult to pinpoint and impractical to repair. When water is present at the base of an incandescent lamp, corrosion is accelerated; however, due to the shorter life span of lamps in incandescent fixtures, lamps require replacement long before corrosion is an issue. Additionally, lamp replacement is far less expensive than the replacement of the PCB. The project research indicates that most airports have water in their light bases as well as conduit system. Newer LED fixtures have better coatings on the circuit boards and other electrical components to prevent corrosion; however, in older fixtures that is not the case. Other airports reported that water injected into the light fixtures as aircraft rode over them. Figures 22 through 24 show an incandescent light fixture that had been in service over 40 years and was still operational. As Figure 22. Water surging through lighting infrastructure. Figure 23. Primary cabling flooded by storm water.

38 LED Airfield Lighting System Operation and Maintenance the fixture was removed, the research team could see the damage done to the fixture assembly and primary cabling. LED fixtures cannot be sustained in this environment. If groundwater or stormwater reaches the light fixture itself, the infrastructure should be drained or else LED fixtures will be more susceptible to failure in these locations. Many airports require their AGL systems to be drained to the nearest stormwater structure. For example, a light base will have a 2­inch PVC or HDPE pipe running from the bottom of the can. Unfortunately, as time goes on, these drainage lines may become clogged. In addition to water being present in the lighting infrastructure, there are various reasons why moisture penetrates the actual fixture. Although fixtures leave the factory with an airtight seal that prevents water entry, the surveys and case studies revealed that water penetrates these fixtures through worn gaskets, cracked lenses, and damaged cord sets. Opportunities for water to penetrate fixtures are magnified by the longevity of LED systems. LED fixtures require little to no re­lamping and are, therefore, visited less often than their incandescent counterparts for repair. Many airports the research team interviewed stated that as long as a light is operational, it is not touched by the maintenance team. After several years, with the fixtures having gone through the different seasons, the gaskets on the lights began to blister and crack. The lenses subjected to jet blast and aircraft tires began to get scratched and cracked. Cable insulation on cord sets began to break down. Such issues that would typically be inspected during a re­lamping phase are often left untouched, causing their effect on the LED light fixture to be amplified. Figure 25 was taken at Portland International Jetport (PWM) in Portland, Maine by mainte­ nance personnel. Although this fixture clearly shows moisture, other fixtures may fail before show­ ing any signs. If a light begins to appear dimmer than surrounding fixtures, it is usually a good indication that the light requires further investigation. Figure 26, also taken at PWM by maintenance personnel, shows a disassembled light fix­ ture that failed because of water within the fixture. This picture was taken prior to a complete refurbishment of the fixture. Research findings proved that the most common method of inspecting lights is with a low­speed drive­by review, noting lights that are not illuminated or are dim. Such fixtures are removed from the light base to allow staff to inspect the damage and to determine the repair or replacement proto­ col at the first available opportunity. This method, although effective, is substandard to some manu­ facturers’ recommendations. Most manufacturers recommend a much more thorough inspection that usually involves pulling all fixtures out of the light bases on a schedule. This solution is difficult Figure 24. Accumulation of silt and corrosion on cabling.

Maintenance Considerations 39 to achieve because the procedure would take weeks, if not months, to complete when considering allowable runway and taxiway closures. Although moisture is an ongoing issue, maintenance personnel had success with fixture life when they thoroughly inspected a failed light. This included replacing gaskets, testing boards, and cleaning fixtures, among other steps to ensure a fully functional, properly sealed fixture. Guidance Signs L­858 runway and taxiway guidance signs subject to environmental factors (e.g., jet blast, vehicle damage, and ground maintenance damage) require diligent maintenance. Based on the survey data, approximately 55% of the airports have some LED lighted taxiway guidance signs. Manufacturer documentation indicates all standard signs are available in three­step or five­step operation. Figure 25. Moisture build-up inside fixture. Figure 26. Water inside light fixture.

40 LED Airfield Lighting System Operation and Maintenance As with the LED­type AGL, the LED lighted signs offer extended lamp life, which significantly reduces re­lamping maintenance compared with non­LED signs. The survey data indicated the most common issue faced by the LED signs is exposure of the electronic power supply inside the sign structure to environmental conditions. Given that the sign housing is not sealed, the power supply is susceptible to dust and dirt. Dirt on the electronic components can cause overheating and premature failures. This condition has been indicated in case studies for the early generation of guidance signs. Manufacturers have revised the design of the signs by either encapsulating the electronic power supply or providing a sealed box to house the power supply. Some manufacturers are using a universal power supply that can be used with both ground lighting and signs with only minor adjustments. Additional Factors Figures 27 through 30 present the survey results on LED fixtures performance versus incandes­ cent fixture performance in various conditions. Much of the feedback the research team received reiterated the toll taken from high­ impact areas, making vibration and moisture two standout factors for discussion. Addition­ ally, the research team also learned that insects and spider webs that hold moisture have penetrated light fixtures and shorted out PCBs. Although insects typically coexist with most systems in industrial locations, unprotected PCBs are fragile and susceptible to many forms of deterioration. Figure 27. Insect resistance. Figure 28. Operation in snow. Figure 29. Operation in extreme cold. Figure 30. Operation in extreme heat.

Maintenance Considerations 41 Although this data seems to be an overwhelming endorsement for the performance of LED systems, the reality is that decades of using incandescent fixtures were being compared to a relatively new product. Although this may skew the perception in favor of LEDs, early reports on these fixtures indicate no inherent flaw with the use of this equipment that would restrict its use in any region or climate. Key Takeaways • Refer to the preventive maintenance section to develop a plan to inspect LED fixtures independent of light failures. • Inspect all material susceptible to moisture entry during repair. • Areas that have a higher susceptibility to moisture damage include touchdown areas, high-speed exits, deicing areas, and areas at a low elevation. • LED PCBs are much more sensitive to environmental conditions than legacy incandescent systems.

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TRB’s Airport Cooperative Research Program (ACRP) Report 148: LED Airfield Lighting System Operation and Maintenance provides guidance for operating and maintaining light-emitting diode (LED) airfield ground lighting systems, including taxi guidance signs, elevated light fixtures, and in-pavement light fixtures.

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