Complete Electrical Architecture of Airfield Ground Lighting Systems

The electrical architecture of an airport lighting system is designed to:

• Supply uninterrupted power to visual aids
• Maintain constant lamp brightness
• Isolate failures without affecting the entire circuit
• Allow centralized control and monitoring
• Ensure safe aircraft movement during low-visibility operations
• Meet applicable ICAO Annex 14 requirements and the equipment standards specified for the project (FAA, IEC, IS)

A complete AGL electrical architecture generally includes: the primary power source, backup power systems, the CCR room, Constant Current Regulators, circuit protection panels, control and monitoring systems, primary series cables, isolating transformers, secondary cables, airfield lighting fixtures, earthing and lightning protection, and redundant power and communication systems.

Unlike normal commercial lighting systems, AGL circuits are series-current systems designed specifically for aviation safety.

The incoming electrical supply may come from the airport substation, the utility grid, or dedicated HT/LT feeders. To maintain uninterrupted operations, airports back this up with Diesel Generator (DG) sets, UPS systems, Automatic Transfer Switches (ATS), and redundant feeders — critical airfield lighting circuits cannot tolerate power interruption during aircraft movement. Annex 14 Chapter 8 sets the permitted switch-over times to secondary power — as short as 1 second for certain CAT II/III elements — which is why UPS or no-break arrangements are used alongside DG sets.

The CCR Room is the heart of the electrical architecture. It houses the Constant Current Regulators, circuit protection panels, control and monitoring systems, PLC/SCADA interfaces, relay logic systems, and field monitoring equipment. The Air Traffic Control (ATC) tower or control center communicates with the CCR room for brightness selection and operational control.

A Constant Current Regulator is one of the most important electrical components in an AGL system. Its function is to maintain constant current throughout the entire series circuit despite changes in cable length, number of lamps, voltage variations, and load changes. Brightness is selected by changing the regulated current step; the CCR then adjusts its output voltage as needed to hold that current.

A 5-step CCR typically uses 2.8 A, 3.4 A, 4.1 A, 5.2 A, and 6.6 A; a 3-step CCR uses 4.8 A, 5.5 A and 6.6 A. In both cases 6.6 A is the maximum (full-brightness) current of the standard series circuit.

The CCR is what allows a runway of dozens or hundreds of lamps to behave, electrically, as a single predictable circuit.

Unlike conventional parallel street-lighting systems, airport lighting uses a series circuit architecture: all lamps are connected in series, the same current flows through every fitting, and each fitting is connected through an isolating transformer. This gives uniform brightness, simplified monitoring, better fault detection, and reduced voltage-drop issues.

The primary circuit is the high-voltage series loop running from the CCR to the field fittings and back. It typically uses 5 kV-class AGL series-circuit cable — single-core, with XLPE or equivalent insulation, shielded where the specification requires — routed through ducts, trenches, HDPE pipes, or cable pits, with the loop eventually returning to the CCR.

Each airfield light fitting is connected using an isolating transformer, which provides electrical isolation, a separate secondary circuit for the lamp, fault containment, and protection of the primary circuit. If a lamp fails, the transformer keeps the primary series loop intact, so the rest of the circuit stays lit. Because the primary is a constant-current loop, the transformer behaves as a current transformer: Ip / Is = Ns / Np. Standard series-circuit types are most commonly rated 6.6 A / 6.6 A (1:1), with the secondary voltage set by the connected lamp load.

Common transformer ratings include 30 W, 45 W, 65 W, 100 W, 150 W, 200 W, and 300 W. The secondary side connects directly to the lamp or LED fitting through a low-voltage, short-length circuit using water-tight connectors — commonly FAA L-823 connectors, plug-and-receptacle systems, or heat-resistant cables.

The isolating transformer is the component that keeps a series loop from failing every time a single lamp does. Fittings should still be disconnected only with the circuit isolated and locked out.

The electrical architecture ultimately powers different types of visual aids, typically fed from dedicated series circuits:

• Runway lighting — edge lights, threshold lights, end lights, centreline lights, touchdown zone lights
• Taxiway lighting — edge lights, centreline lights, stop-bar lights
• Approach lighting — approach lighting systems, flashing lights, sequenced flashers
• Guidance systems — PAPI and sign boards (powering varies by make and design); obstruction lights are normally fed from a separate mains supply, outside the CCR circuits

Modern airports use intelligent control systems integrated with SCADA, PLC, HMI panels, and remote monitoring. Operators can turn circuits ON/OFF, select brightness levels, detect field failures, monitor insulation resistance, and track CCR performance — with advanced systems also providing alarm history, fault location, energy monitoring, and redundancy switching.

Because airfield lighting is highly exposed to lightning and electrical surges, the architecture includes dedicated earthing grids, Surge Protection Devices (SPDs), lightning arrestors, shielded cables, and equipotential bonding. Improper grounding can result in CCR failures, lamp damage, communication errors, and transformer breakdown.

Airport lighting systems are designed with high redundancy because lighting failure can directly affect aircraft safety.

Modern airports are increasingly moving from halogen to LED technology, gaining lower power consumption, longer operating life, reduced maintenance, better photometric stability, and smart monitoring capability. LED systems also introduce intelligent drivers, monitoring electronics, remote diagnostics, and integrated failure reporting. LED loads change the electrical behaviour seen by the CCR (power factor, harmonics, low load), so CCR and transformer compatibility must be confirmed for every conversion.

However the fundamental series-circuit philosophy remains unchanged — LEDs sit inside the same CCR-driven, isolating-transformer-protected architecture as their halogen predecessors.

• AGL circuits are series-current systems, not conventional parallel lighting networks
• The Constant Current Regulator holds current steady at the selected brightness step (6.6 A at full brightness), adjusting its output voltage as needed
• Isolating transformers give each fitting its own isolated secondary, so a lamp failure does not interrupt the series loop
• The primary circuit runs on 5 kV-class, single-core series-circuit cable in a loop back to the CCR
• Earthing, surge protection, and lightning arrestors protect the network from a highly exposed operating environment
• Redundancy — dual CCRs, standby generators, parallel feeders, spare circuits — is built in because failure directly affects aircraft safety
• LED technology changes the fixture, driver, and monitoring layer — but not the underlying series-circuit philosophy