AGL Knowledge Hub

AGL Fundamentals

Airfield Ground Lighting (AGL) is the system of lights, signs and visual aids that allow pilots to identify runways, taxiways and approach paths — particularly at night or in low-visibility conditions. Core AGL infrastructure includes light fittings (elevated and inset), constant current regulators (CCRs), isolating transformers, primary and secondary cabling, and L-823 connectors.

• Series circuits: Most AGL fittings are wired in a series circuit powered by a CCR, which regulates current rather than voltage — every fitting on the circuit shares the same current, and an isolating transformer steps that current down safely to each individual light.
• Constant Current Regulator (CCR): Supplies and regulates the current for a series circuit, with multiple brightness steps for varying visibility conditions, and reports status to the control system.
• Isolating transformers: Provide galvanic isolation between the primary series circuit and each individual light fitting, so a single fitting can be disconnected or fail without breaking the circuit.
• L-823 connectors: The standard plug-and-receptacle connector used to join secondary cable to AGL light fittings and transformers, designed to be watertight when properly assembled.

Runway & Taxiway Lighting

Runway lighting typically includes edge lights (white, transitioning to yellow in the final section before the threshold on some runway categories), threshold and end lights, centreline lights and touchdown zone lighting on precision-approach runways. Taxiway lighting includes edge and centreline lights, together with stop bars and runway guard lights at holding positions.

Approach Lighting & PAPI

Approach lighting systems extend visual guidance beyond the runway threshold, using crossbars, wing bars and sequenced flashing lights depending on the precision category. PAPI (Precision Approach Path Indicator) units give pilots a visual glide-slope indication using a red/white light pattern, and must be sited and angled precisely relative to the runway and any obstacles.

Monitoring & Control

Larger airports typically monitor and control AGL circuits through an Airfield Lighting Control and Monitoring System (ALCMS), which may be PLC or SCADA-based. This allows CCR brightness steps, circuit status and fault alarms to be managed from a central control room.

AGL Standards Overview

AGL design, equipment and installation practice is generally guided by a combination of international and national references. This is a general orientation only — always work from the current, officially published edition of any document you rely on for a real project.

• ICAO Annex 14 (Aerodromes): Sets out international standards and recommended practices for aerodrome design, including lighting systems, spacing and intensity requirements.
• ICAO Doc 9157 (Aerodrome Design Manual): Provides supporting guidance material on visual aids, including AGL, that expands on Annex 14.
• FAA AC 150/5340 series: U.S. advisory circulars covering airport lighting equipment and design, including runway, taxiway and approach lighting.
• FAA AC 150/5345 series: Advisory circulars covering specifications for individual AGL equipment items, such as constant current regulators, isolating transformers and light fittings.
• IS 12290 / national specifications: In India, additional national standards and DGCA requirements apply alongside ICAO guidance for airport electrical and lighting systems.

Precision AGL Academy programs reference these documents for educational purposes so that participants can navigate and interpret them confidently. See our full Standards Disclaimer for how this material should — and shouldn't — be used.

AGL Troubleshooting Atlas

A structured approach to fault-finding is central to AGL maintenance. The patterns below are the general categories covered in our maintenance and troubleshooting modules — they are a starting orientation, not a substitute for your organization's own maintenance procedures, permit-to-work system and manufacturer documentation.

Common Fault Categories

• Open-circuit faults: A break in the series circuit, often caused by a failed connector, damaged cable or a failed transformer winding — typically found through segment-by-segment insulation and continuity testing.
• Short-circuit / ground faults: Insulation breakdown allowing current to leak to earth, usually identified through insulation-resistance testing and progressively isolating sections of the circuit.
• CCR faults: Trips, output/current instability or alarm conditions at the regulator — checked against CCR status indicators, protection settings and load conditions before deeper investigation.
• Transformer and connector faults: Failed isolating transformers or degraded L-823 connectors are among the most common sources of individual light-fitting failure and are checked through insulation testing and visual/physical inspection.
• ALCMS / SCADA alarms: Control-system alarms should be cross-checked against the physical circuit before assuming a control-system fault versus a field fault.

General Method

A consistent troubleshooting method — confirm the symptom, isolate the affected segment, test systematically from the most likely cause outward, and verify the fix before re-energizing — is more valuable long-term than memorizing individual fault signatures. This structured methodology is covered in depth, with practical case studies, in our Airport Lighting Maintenance Engineer Program and the Master Diploma.

Frequently Asked Questions

Quick answers about the AGL Knowledge Hub reference material.