THE BASIC COMPONENT CHAIN
AGL is not a single lighting product. It is a complete electrical, lighting, control, monitoring and installation system that gives pilots reliable visual guidance during movement, take-off, landing and low-visibility operations. Each component has a specific function, and selection, installation, testing and maintenance all matter.
The CCR supplies a controlled current to the primary series circuit. The isolation transformer electrically separates that circuit from the individual fixture, and the secondary circuit connects the transformer to the fitting through suitable connectors and cable. This lets individual fittings operate reliably while the series circuit stays continuous.
Remember
- CCR → Primary Cable → Isolation Transformer → Secondary Cable → Fixture
- This is the fundamental electrical concept behind a large number of series-circuit AGL installations
MAJOR AGL COMPONENTS
The main components of an airport AGL system fall into six working groups:
| Group | Components |
|---|---|
| Lighting | Runway edge, threshold/wing bar, runway end, centreline and touchdown zone lights; taxiway edge and centreline lights; stop bars; runway guard lights; approach lights; PAPI/APAPI; elevated and inset fixtures |
| Electrical | CCRs, isolation transformers, primary series cables, secondary cables, L-823 / AGL connectors |
| Guidance | Airfield guidance signs and other visual guidance systems |
| Control | Control and monitoring systems, lighting control panels, remote control, fault indication |
| Installation | Junction boxes and cable accessories, pits, frangible mounting systems, earthing and bonding components |
| Assurance | Portable test and maintenance equipment, electrical and photometric testing, inspection, maintenance, compliance |
AGL LIGHT FIXTURES
Fixtures are installed at specific locations on the movement area to give visual guidance to pilots. They come in two broad installation categories.
Elevated fixtures
Installed above the pavement surface on suitable mounting structures. Common uses: runway edge, taxiway edge, approach lighting, runway guard lights and certain threshold and end-light applications.
Inset fixtures
Installed flush or substantially flush with the pavement. Common uses: runway centreline, touchdown zone, taxiway centreline, stop bars, runway intersection lighting, and any location where aircraft clearance needs a low-profile fitting.
Selection parameters to verify
- Application
- Fixture type
- Photometric requirement
- Light colour
- Beam orientation
- Intensity requirement
- Electrical rating
- CCR circuit current
- Transformer wattage
- Installation depth
- Pavement / interface requirements
- Frangibility
- Environmental protection
- Maintenance requirements
RUNWAY LIGHTING COMPONENTS
Runway lighting gives pilots visual information about runway limits, alignment, threshold, touchdown area and runway end.
| Component | Purpose |
|---|---|
| Runway edge lights | Define the lateral limits of the runway. Typically white, with specific colour changes in the final portion of the runway where the governing standard and runway configuration require it. |
| Threshold lights | Identify the beginning of the usable landing runway. Green, visible to an approaching aircraft, arranged (with wing bars where provided) for clear threshold identification. |
| Runway end lights | Identify the end of the runway. Red, visible to an aircraft looking along the runway. |
| Centreline lights | Longitudinal alignment guidance, especially important on precision runways and in low-visibility operations. |
| Touchdown zone lights | Visual guidance in the touchdown zone of applicable precision runways. |
For colours, spacing and distance sequences, see Note 02: Runway Lighting Systems.
TAXIWAY LIGHTING COMPONENTS
Taxiway lighting helps pilots navigate between runways, aprons, terminals and other movement areas.
Taxiway edge lights
Normally blue, identifying the lateral limits of a taxiway where edge lighting is provided.
Taxiway centreline lights
Guidance along the intended taxi route, normally green; especially important on taxiways supporting low-visibility operations.
Stop bar lights
A controlled red holding indication at runway/taxiway holding positions; central to low-visibility operations and runway-incursion prevention.
Runway guard lights
A conspicuous alternating flashing yellow warning at taxiway/runway intersections.
More detail: Note 03: Taxiway Lighting Systems.
APPROACH LIGHTING COMPONENTS
Approach lighting gives visual guidance before the aircraft reaches the runway threshold. A system may contain:
- Approach light bars
- Sequenced flashing lights
- Elevated light units
- Inset light units
- Supporting structures
- Power and isolation equipment
- Control and monitoring equipment
The exact arrangement depends on the runway category, the approach type and the applicable regulatory standard.
PAPI / APAPI
The Precision Approach Path Indicator (PAPI) gives visual vertical guidance to an approaching aircraft. The pilot reads the combination of red and white lights to judge whether the aircraft is above, on or below the nominal approach path.
A PAPI system normally consists of
- PAPI light units
- Mounting structure
- Electrical supply
- Isolation transformers where applicable
- Control equipment
- Cabling and connectors
- Aiming and adjustment arrangement
- Level / installation reference system
Installation and aiming must consider
- Reference elevation
- Runway threshold
- Longitudinal location
- Lateral location
- Obstacle clearance
- Approach slope
- Unit alignment
- Photometric performance
- Manufacturer requirements
- Applicable ICAO / FAA / national authority requirements
See also Note 04: Approach Lighting & PAPI.
CONSTANT CURRENT REGULATOR (CCR)
The CCR is one of the most important electrical components in a series-circuit AGL system. Its primary function is to supply a controlled constant current to the series circuit.
Typical CCR functions
- Constant current output
- Multiple brightness / intensity steps
- Current regulation
- Circuit protection
- Fault indication
- Remote control
- Monitoring
- Interface with AGL control systems
Select the CCR according to
- Required circuit current
- Circuit load
- Number of transformers
- Transformer wattages
- Cable length
- Voltage requirements
- Circuit impedance
- Brightness steps
- Control / monitoring requirements
FAA designations (AC 150/5345-10)
- L-828 = regulator without monitoring; L-829 = regulator with monitoring; L-827 = regulator monitor
- Class 1 = 6.6 A output; Class 2 = 20 A output
- Style 1 = 3 brightness steps; Style 2 = 5 brightness steps
More detail: Note 07: Constant Current Regulators.
ISOLATION TRANSFORMER
The isolation transformer is fundamental to a series-circuit AGL system. It electrically isolates each light fixture from the high-voltage primary series circuit.
Main functions
- Electrical isolation
- Transfer of energy from primary to secondary
- Individual fixture connection
- Maintaining series-circuit continuity
- Matching the secondary supply to the fitting
Parameters to confirm
| # | Parameter | # | Parameter |
|---|---|---|---|
| 1 | Transformer wattage | 7 | Insulation level |
| 2 | Primary current | 8 | Installation type |
| 3 | Secondary current | 9 | Connector arrangement |
| 4 | Primary voltage rating | 10 | Connected fixture load |
| 5 | Secondary voltage / current | 11 | Applicable standard |
| 6 | Frequency | 12 | Environmental requirements |
A transformer may be specified, for example, as 200 W – 6.6 A / 6.6 A or 200 W – 20 A / 6.6 A. The correct transformer must always be chosen from the actual AGL circuit and fitting requirements. FAA designations: L-830 = 60 Hz, L-831 = 50 Hz, so check the frequency of your supply. See Note 08.
PRIMARY AND SECONDARY CABLES
The two cable types belong to different parts of the system and must not be confused.
Primary series circuit cable
Forms the continuous electrical circuit connecting the CCR and the isolation transformers. It must suit the operating voltage, the series-circuit application, insulation requirements, underground installation, mechanical stress, moisture, temperature and the airport specification.
Secondary cable
Connects the isolation transformer to the individual fixture. Select it by transformer secondary output, fixture requirements, length, insulation, connector configuration, installation method and environment. The secondary circuit is normally much shorter than the primary.
More detail: Note 09: Primary & Secondary Circuits.
L-823 / AGL CONNECTORS
AGL connectors provide reliable electrical connections between primary cables, isolation transformers, secondary cables, light fixtures and other field equipment. Common arrangements are plug, receptacle, inline connector and transformer lead connector.
Verify before selecting
- Voltage and current rating
- Cable size
- Conductor material
- Insulation and sealing
- Mechanical compatibility
- Connector type
- Applicable standard / specification
A poor connection can cause
- High resistance
- Heating
- Voltage drop
- Intermittent operation
- Insulation failure
- Circuit faults
More detail: Note 10: L-823 Connectors.
AIRFIELD GUIDANCE SIGNS
Signs give pilots mandatory, location, direction and information guidance. Types include mandatory instruction, location, direction, destination, runway designation, taxiway designation and apron / stand-related signs.
A typical internally illuminated sign is built up as:
Important sign parameters
- Sign dimensions
- Letter height
- Character design
- Colour
- Illumination
- Visibility
- Housing material
- Structural strength
- Frangibility
- Mounting arrangement
- Electrical supply
- Environmental protection
JUNCTION BOXES AND CABLE ACCESSORIES
These provide protected locations for cable connections and system interfaces. Depending on the installation they include junction boxes, cable pits, cable glands, cable joints, terminal arrangements, protective conduits, cable markers and sealing materials.
FRANGIBLE MOUNTING SYSTEMS
AGL equipment near aircraft movement areas may need frangible mounting. The objective is to reduce the hazard created if an aircraft or vehicle strikes the equipment. Frangible arrangements may apply to elevated lights, signs, PAPI units, approach lighting structures and other airfield equipment, and must be compatible with the applicable airport design and regulatory requirements.
CONTROL AND MONITORING SYSTEM
Modern AGL systems can include centralised control and monitoring that provides light switching, intensity control, circuit selection, fault indication, CCR monitoring, remote status, equipment alarms, interfaces with ATC and airport systems, and maintenance information.
Typical control chain
EARTHING AND BONDING
Proper earthing and bonding are essential for electrical safety and equipment protection. The installation should address equipment earthing, metallic structure bonding, control-panel earthing, transformer-related requirements, surge / lightning protection where specified, and cable system requirements. Arrangements must be designed and tested to the applicable electrical and airport standards.
COMPONENT SELECTION: QUICK METHOD
Before ordering any AGL component, work through six questions.
- What is the application? Runway, taxiway, approach, PAPI, sign or stop bar.
- What light type is required? Elevated, inset, omnidirectional, unidirectional, bidirectional or multidirectional.
- What is the electrical requirement? CCR current, primary circuit, transformer rating, secondary requirement, frequency, voltage / current and power rating.
- What are the photometric requirements? Colour, intensity, beam spread, vertical and horizontal distribution, aiming and photometric compliance.
- What are the installation requirements? Elevated or inset, mounting, frangibility, pavement interface, cable routing and connector arrangement.
- What standard applies? ICAO, FAA, national civil aviation requirements, airport specification, project technical specification or approved manufacturer specification.
COMPONENT MATCHING CHART
| Component | Main function | Typical electrical connection |
|---|---|---|
| CCR | Controls series-circuit current | Primary circuit |
| Isolation transformer | Electrical isolation and energy transfer | Primary → Secondary |
| Primary cable | Carries series-circuit current | CCR → Transformer |
| Secondary cable | Supplies individual fitting | Transformer → Fixture |
| Connector | Field electrical connection | Cable / Transformer / Fixture |
| Runway light | Runway visual guidance | Secondary circuit |
| Taxiway light | Taxiway guidance | Secondary circuit |
| Stop bar | Holding-position guidance | Secondary / controlled circuit |
| Runway guard light | Runway warning | Dedicated AGL circuit |
| PAPI | Vertical approach guidance | Series circuit via transformer, or a dedicated supply, per design |
| Approach light | Approach visual guidance | AGL circuit |
| Sign | Surface movement guidance | Series circuit via transformer, or a constant-voltage supply, per design |
| Control system | Control and monitoring | CCR / field equipment |
| Junction box | Protected cable connection | Field circuit |
| Frangible mount | Safe equipment support | Mechanical |
| Earthing system | Electrical safety / protection | Grounding / bonding |
COMPONENT FAILURE: WHAT HAPPENS?
Understanding failure modes helps maintenance engineers narrow down a fault by its extent.
| Symptom | Possible causes |
|---|---|
| One light not operating | Failed lamp / LED module, failed fixture, secondary cable fault, connector problem, isolation transformer fault |
| Multiple lights not operating, others still lit | The loop is intact: look for a shorted or bypassed primary section, a double earth fault, water in a shared pit or junction, or several transformer or connector failures |
| Complete circuit failure (all lights on the circuit) | CCR failure, primary cable open circuit, major insulation failure, control command failure, protection trip, power supply failure |
| Flickering or intermittent light | Loose connector, high-resistance connection, cable insulation problem, transformer issue, fixture electronics fault, moisture ingress |
Think
- The wider the failure, the closer the cause is to the common part of the chain (power, control, CCR, primary loop)
- The narrower the failure, the closer it is to the fixture end
COMPONENT TESTING
Test according to the applicable equipment standard, the project specification and an approved test procedure.
Electrical tests
- Insulation resistance
- Continuity
- Dielectric withstand
- Earth / bonding verification
- Transformer tests
- Cable tests
- Connector inspection
Photometric tests
- Intensity
- Beam distribution
- Colour
- Alignment
- Uniformity
- Light output
Functional tests
- Switching
- Brightness levels
- Control commands
- Monitoring
- Fault indication
- Emergency / backup functions where applicable
Visual inspection
- Cracks and corrosion
- Water ingress
- Damaged lenses
- Loose hardware
- Cable and connector damage
- Incorrect installation
- Physical obstruction
PREVENTIVE MAINTENANCE
A good AGL maintenance programme includes:
Daily / routine inspection
Lights operating, visible damage, foreign object / debris concerns, sign condition, abnormal indications.
Periodic inspection
Fixture, connector and transformer condition, cable system, CCR performance, sign illumination, PAPI alignment, approach lighting, control and monitoring system.
Photometric maintenance
Measure with appropriate calibrated equipment and procedures to verify the installed lighting still meets the required performance.
PRACTICAL SELECTION EXAMPLE
Requirement: a runway inset light must be connected to a 6.6 A series circuit.
- Fixture type: Inset runway fitting.
- Fixture power requirement: For example, 100 W.
- Primary circuit current: 6.6 A.
- Secondary requirement: Confirm from the fixture manufacturer.
- Transformer: Select the appropriate 6.6 A primary transformer with the required secondary characteristics.
- Connector: Select compatible AGL connectors for the transformer and fixture.
- Cable: Select suitable primary and secondary cables.
- Photometric requirement: Verify the fitting meets the runway application and photometric performance.
COMMON SELECTION MISTAKES
1. Selecting only by wattage
Always verify current + voltage + frequency + application + secondary requirement + standard.
2. Ignoring connector compatibility
The electrical rating and the physical connector arrangement must both be correct.
3. Mixing primary and secondary requirements
The primary series circuit and the secondary fitting circuit are different parts of the system.
4. Ignoring photometry
A fitting is not acceptable simply because it illuminates; its photometric performance must satisfy the application.
5. Ignoring installation conditions
The same component may need different mounting or protection depending on whether it is in pavement, beside pavement, on an elevated structure, in an underground pit or in an approach-lighting area.
QUICK REVISION SHEET
| Topic | Remember |
|---|---|
| Electrical chain | CCR → Primary Cable → Isolation Transformer → Secondary Cable → Fixture |
| Primary circuit | Carries the controlled series current from the CCR |
| Isolation transformer | Provides isolation and supplies the individual fitting |
| Secondary circuit | Connects the transformer to the fixture |
| Connectors | Reliable field electrical connections |
| Fixtures | Provide the required visual guidance |
| Signs | Information and mandatory guidance |
| PAPI | Vertical approach guidance |
| Control system | Controls and monitors the installation |
| Photometry | Confirms lighting performance |
One-page memory map
AGL SYSTEM ├── LIGHTING Runway · Taxiway · Approach · Stop bars · Guard lights · PAPI/APAPI ├── ELECTRICAL CCR · Primary cable · Isolation transformer · Secondary cable · Connectors ├── GUIDANCE Airfield signs · Marking interface · Visual guidance systems ├── CONTROL Control panel · Monitoring · Remote control · Fault indication ├── INSTALLATION Pits · Junction boxes · Mounting · Frangible supports · Earthing/bonding └── ASSURANCE Electrical testing · Photometric testing · Inspection · Maintenance · Compliance
EXAM / INTERVIEW QUESTIONS
What is the main purpose of an isolation transformer?
To electrically isolate an individual AGL fitting from the primary series circuit and transfer the required electrical energy to the fitting.
What is the function of a CCR?
A Constant Current Regulator maintains controlled current in the AGL series circuit and normally provides selectable intensity levels.
Why are isolation transformers used in a series-circuit AGL system?
They allow individual fittings to be connected to the series circuit while maintaining electrical isolation and circuit continuity.
What is the difference between primary and secondary cable?
The primary cable forms the high-voltage, current-controlled series circuit between the CCR and the isolation transformers. The secondary cable connects an isolation transformer to an individual fitting.
What should be checked before selecting an isolation transformer?
Wattage, primary current, secondary requirement, frequency, insulation requirements, the connected fitting and the applicable specification.
What is an L-823 connector used for?
Electrical connection arrangements in airfield lighting circuits, subject to the applicable specification and configuration.
Why is photometry important?
AGL performance depends not only on whether a light operates, but on whether its intensity, colour and light distribution meet the required photometric performance.
What are the main types of AGL fixtures?
Elevated and inset fixtures are the two broad installation categories.
What is the purpose of a stop bar?
A stop bar gives a visual holding indication at designated runway/taxiway holding positions.
What is the difference between L-828 and L-829 regulators?
L-828 is a constant current regulator without monitoring and L-829 is a regulator with monitoring. Class 1 is 6.6 A and Class 2 is 20 A; Style 1 has 3 brightness steps and Style 2 has 5.
What is the basic AGL electrical chain?
CCR → Primary Series Cable → Isolation Transformer → Secondary Cable → AGL Fixture.
FINAL STUDY TAKEAWAY
Understand an AGL system as a complete integrated system, not a collection of products. Connect: Lighting → Photometry → Electrical circuit → Transformer → Cable → Connector → Control → Installation → Testing → Maintenance.
Correct selection needs more than a catalogue check. Always verify Application + Electrical rating + Photometric requirement + Installation + Standard + Compatibility + Testing.
AGL component knowledge = Function + Electrical + Photometry + Installation + Testing + Compliance. A reliable system is one where every component works correctly as part of the whole.
ENGINEERING & EXPERT NOTES
Learn the Chain Before the Catalogue
Study MethodTrace one light from supply through CCR, cable, transformer and fixture. When you can follow that path, every component stops being an isolated item and becomes part of a fault-finding map.
Never Select by Appearance
SelectionConnectors, transformers and fixtures can look interchangeable yet differ in type, rating or approval. Verify the specification and the approved combination, not the physical fit.
Water Is the Common Enemy of Almost Every Component
ReliabilityBases, connectors, seals and cable joints all fail through moisture sooner or later. Inspect sealing and drainage as part of every component check.
Keep the Register as Good as the Hardware
RecordsA component list that matches the field makes fault finding, spares planning and audits far easier. Update it whenever anything is replaced.
REFERENCES & FURTHER READING
These notes are a study aid. Verify details against the primary sources below.
| # | Source | Use it for |
|---|---|---|
| 1 | FAA AC 150/5345-10H – Constant Current Regulators and Regulator Monitors | CCR classes, styles, designations (L-827/828/829). |
| 2 | FAA AC 150/5345-47C – Series to Series Isolation Transformers | L-830/L-831 isolation transformers. |
| 3 | FAA AC 150/5345-7F – L-824 Underground Electrical Cable | Primary and secondary cable. |
| 4 | FAA AC 150/5345-26E – L-823 Plug and Receptacle, Cable Connectors | Connectors. |
| 5 | FAA AC 150/5345-46F – Runway, Taxiway, Heliport and Vertiport Light Fixtures | Elevated and in-pavement fixtures. |
| 6 | FAA AC 150/5345-44L – Runway and Taxiway Signs | Signs. |
| 7 | FAA AC 150/5345-28H – PAPI Systems | PAPI. |
| 8 | FAA AC 150/5340-30J – Design and Installation Details for Airport Visual Aids | Installation and design. |
| 9 | FAA AC 150/5340-26C – Maintenance of Airport Visual Aid Facilities | Testing and maintenance. |
| 10 | ICAO Annex 14, Volume I (Chapter 5 visual aids, Chapter 8 electrical systems) and Doc 9157 Parts 4 and 5 | International requirements and design guidance; check the current edition. |
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