Taxiway Intersection Light
A specialized taxiway guidance fixture installed at taxiway intersections to provide pilots with clear directional cues when navigating complex junction points. These lights use a combination of blue edge lights, green centreline lights, and sometimes yellow caution lights to define the intersection geometry and guide pilots through turns and crossing decisions.
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What Is It?
A Taxiway Intersection Light is a specialized taxiway guidance fixture installed at taxiway intersections to provide pilots with clear directional cues when navigating complex junction points. These lights use a combination of blue edge lights, green centreline lights, and sometimes yellow caution lights to define the intersection geometry and guide pilots through turns and crossing decisions. Intersection lights are critical for preventing wrong-turn errors, runway incursions, and ground collisions at busy airfields where multiple taxiways converge. They help pilots maintain situational awareness and make correct routing decisions during ground movement.
Purpose & Function
Taxiway intersections concentrate exactly the kind of decision-making risk simple edge and centreline lighting elsewhere on the taxiway doesn't have to handle: multiple possible paths converging in one place, where a wrong turn or a misjudged crossing can put an aircraft into conflict with another that has right of way. The intersection light's purpose is to make the geometry of that junction visually unambiguous, so a pilot can see at a glance which path leads where before committing to a turn.
Layering blue edge, green centreline, and yellow caution lighting together at these points gives pilots the same trusted colour vocabulary they use everywhere else on the airfield, but concentrated and combined precisely where the risk of a wrong-turn error or ground conflict is highest, which is what makes intersection-specific lighting a meaningful safety addition beyond standard taxiway guidance alone.
Where Is It Used?
Taxiway intersection lights are installed at all types of taxiway junctions and complex ground movement areas. They are used on:
- Complex taxiway intersections where multiple taxiways converge
- Apron entry/exit points where aircraft transition between apron and taxiway
- Runway holding position intersections where taxiways meet the runway
- Angled intersections requiring clear directional cues
- Low visibility operations where enhanced guidance is essential
- Military airfields with complex taxiway layouts
Installation & Location
Fixtures are set out at the specific geometry of the intersection they serve, with blue edge, green centreline, and yellow caution lights positioned according to the actual paths and turn radii available at that junction rather than a generic straight-taxiway spacing. Mounting is typically inset to match the surrounding standard taxiway lighting, with fixture positions tied to the same survey used to lay out the intersection's pavement markings so the lit geometry and the painted geometry agree. Because intersections often see lighting elements from more than one taxiway segment converging in a small area, cable runs and circuit assignments are planned so each segment's lighting remains on its own circuit through the intersection, preserving the ability to isolate one taxiway's lighting for maintenance without affecting an intersecting one. Sightlines from each approach direction into the intersection are checked during installation to confirm no fixture is shadowed by another light, a sign, or pavement furniture from the angle a pilot will actually be approaching from.
How Does It Work?
Taxiway intersection lights operate using a coordinated lighting strategy:
- Edge Lighting: Blue edge lights are installed along the edges of all taxiways entering the intersection, maintaining the standard taxiway edge definition.
- Centreline Guidance: Green centreline lights are installed through the intersection along the primary taxiway routes, providing continuous guidance.
- Caution Indication: Yellow or amber lights may be used at the intersection to alert pilots to the presence of a junction and the need for caution.
- Directional Cues: At complex intersections, lights may be configured to provide directional guidance, using either flashing or steady patterns to indicate the preferred route.
- Integration: The system is integrated with other taxiway guidance systems (edge lights, centreline lights, holding position lights) and the overall AGL control system.
System Architecture & Control Logic
An intersection is a meeting point of circuits, not a single controlled object — the blue edge lights, green centreline lights, and any yellow/amber caution or directional lights present are each part of their own series loop and their own CCR, and each is controlled and fault-reported independently even though they physically converge in the same few metres of pavement. The ALCMS coordinates the picture a pilot actually sees by managing these circuits together rather than by controlling the intersection as a unit: it can, for instance, keep edge and centreline lighting continuously energised while switching a directional or caution indication on and off for a specific routing. At complex or high-traffic intersections this coordination increasingly moves into A-SMGCS route-sequencing logic, which can command specific centreline segments through the junction to create a "follow-the-greens" path for a particular aircraft — a capability that depends on the centreline circuit through the intersection being individually switchable rather than one continuous loop. Because each colour's circuit is independent, a fault on the caution lighting at an intersection has no effect on the edge or centreline guidance running through the same point.
Three Colours Defining One Junction
Unlike the single-turn geometry of a runway exit, an intersection light has to define a junction where several paths meet: blue edge lights run continuously along every taxiway approaching the intersection, green centreline lights carry each through-route across the junction without a break, and a yellow caution marker sits at the point of convergence itself — giving the pilot both "which lane" and "junction ahead" information in the same glance.
Physical Construction
An intersection installation is a coordinated set of individually built fixtures rather than one combined unit: blue edge fixtures (LED or filtered 15W–45W halogen), green centreline fixtures (LED or filtered 45W–65W halogen), and where fitted, yellow/amber caution fixtures (LED or filtered 15W–45W halogen), each in its own die-cast aluminium body, gasket-sealed at the prism and rated IP67/IP68. Edge lights are typically elevated on frangible couplings seated in L-867 base cans around the intersection perimeter, while centreline and caution fixtures are flush-mounted in L-868 base cans through the pavement itself, load-rated for a 100,000 kg (220,000 lb) aircraft wheel. What makes the installation function as a single "intersection light" component is the coordinated wiring plan: each colour group runs back through its own isolating transformer (15W–65W depending on colour) to keep circuits separable for fault-finding, while the physical layout of edge, centreline, and caution fixtures is fixed by the intersection's geometry so the resulting light pattern reads unambiguously to an approaching pilot.
Technical Parameters
| Parameter | Typical Value |
|---|---|
| Light Source (Edge) | Blue LED array or 15W – 45W halogen with blue filter |
| Light Source (Centreline) | Green LED array or 45W – 65W halogen with green filter |
| Light Source (Caution) | Yellow/Amber LED array or 15W – 45W halogen with yellow filter |
| Edge Light Colour | Blue (standard taxiway edge) |
| Centreline Colour | Green (steady) |
| Caution Colour | Yellow/Amber (flashing or steady) |
| Luminous Intensity (Edge) | 100 – 1,000 candela |
| Luminous Intensity (Centreline) | 200 – 2,000 candela |
| Intensity Control | 3 to 5-step CCR controlled (2.8A – 6.6A) |
| Configuration | Edge lights along all taxiway edges + centreline lights through intersection |
| Mounting Type | Elevated (frangible) or Inset (flush) |
| Load Capacity (inset) | 100,000 kg (220,000 lbs) wheel load |
| Isolating Transformer | 15W – 65W (6.6A series circuit) |
| Protection Class | IP67 / IP68 (submersible) |
| Operating Temperature | -40°C to +55°C |
Electrical Requirements
| Requirement | Typical Value |
|---|---|
| Circuit Type | Series circuit, constant current (CCR fed) |
| Rated Series Current | 6.6A (5-step: 2.8A / 3.4A / 4.1A / 5.2A / 6.6A) |
| Isolation | Via dedicated isolating transformer (15W–65W, per light source) per unit |
| Multi-Source Wiring | Edge, centreline, and caution light sources within the fixture may be fed from separate series circuits so each function can be switched independently |
| Transformer Secondary | Matched to fixture wattage; sized to series circuit rating |
| Cable Type | L-824 single-conductor, direct-burial rated, 5kV or 600V per circuit design |
| Connector | L-823 primary connector, submersible-rated splice |
| Insulation Resistance | ≥ 50 MΩ (megger test, cable-to-ground) |
| Earthing/Grounding | Fixture body and base can bonded to airfield earth grid |
| Fault Protection | CCR-level ground fault and open-circuit detection |
| Power Source | CCR output, regulated per ICAO/FAA intensity step schedule |
Photometric Requirements
| Parameter | Typical Value |
|---|---|
| Edge Element Intensity | 100 – 1,000 cd (blue), where an edge light source is included |
| Centreline Element Intensity | 100 – 1,000 cd (green), where a centreline light source is included |
| Caution Element Intensity | 100 – 1,000 cd (yellow), where a caution light source is included |
| Independent Switching | Each colour element switched independently to mark the intersection geometry correctly for the active taxi route |
| Vertical Beam Spread | Main beam 2°–10° above horizontal (peak ~3°–4°) |
| Horizontal Beam Spread | Omnidirectional (360°) or directional per element, depending on intersection geometry |
| Isocandela Distribution | Per ICAO Annex 14 Attachment A / FAA AC 150/5345-46 intersection light figures |
| Chromaticity | Blue, green, and yellow elements within ICAO Annex 14 colour boundaries |
| Test Method | Mobile photometric van/goniophotometer per light source within the fixture |
Applicable Standards
ICAO Annex 14
Taxiway intersection lighting requirements and configuration standards
FAA AC 150/5345-46
Specification for Runway, Taxiway, Heliport, and Vertiport Light Fixtures — covers this fixture's general photometric and electrical requirements
IEC 61822
Constant current regulators and monitoring device for the series circuit(s) feeding this fixture
IEC 61821
Maintenance requirements for the AGL constant-current series circuits supplying this fixture
Installation Requirements
Base Can Excavation & Grade
CivilExcavate and set inset base cans to match the surrounding standard taxiway lighting, holding each flush with the pavement.
Marking-Survey Set-out
CivilSet out blue edge, green centreline, and yellow caution light positions from the same survey used to lay out the intersection's pavement markings, following the actual paths and turn radii available rather than generic straight-taxiway spacing.
Multi-Approach Sightline Check
MechanicalCheck sightlines from each approach direction into the intersection, confirming no fixture is shadowed by another light, a sign, or pavement furniture from a pilot's actual approach angle.
Per-Segment Circuit Planning
ElectricalPlan cable runs and circuit assignments so each converging taxiway segment's lighting remains on its own circuit through the intersection, preserving the ability to isolate one segment for maintenance.
L-823 Connector Termination
ElectricalTerminate and seal the primary connector at each fixture per manufacturer procedure, keeping every splice submersible-rated before backfill.
Isolating Transformer Matching
ElectricalConfirm each isolating transformer's wattage matches its fixture and its segment circuit's rated current step before connection.
Load-Rated Housing Seating
MechanicalSeat each fixture housing fully home in its base can and confirm it sits flush and level.
Pre-Energisation Sign-off
DocumentationRecord base can positions, per-segment circuit assignment, and sightline check results as-built before backfill.
Testing & Commissioning
Insulation Resistance (Megger) Test
Pre-EnergisationMegger-test each colour group's isolating transformer and series loop before the circuit is energised, confirming insulation resistance clears the acceptable minimum ahead of backfill.
Loop Continuity & Resistance Test
Pre-EnergisationVerify series loop continuity for each colour group end to end and record total loop resistance, ruling out open circuits or high-resistance splices before first energisation.
Primary/Secondary Voltage Verification
EnergisationWith the CCR energised, confirm secondary voltage at each L-823 connector matches the transformer's rated ratio at the commissioned current step.
CCR Brightness Step Response
EnergisationCycle each colour group's CCR through every intensity step and confirm the corresponding fixtures respond correctly, ruling out marginal transformers or loose connections.
Colour-Coded Circuit Verification
Final AcceptanceConfirm blue edge, green centreline, and (where fitted) yellow caution fixtures each show the correct colour from their intended viewing direction, matching the intersection layout diagram.
Photometric Commissioning Test
Final AcceptanceMeasure beam intensity and colour for each fixture group with a calibrated photometer against ICAO/FAA commissioning tolerances prior to operational handover.
Frangibility / Base Can Verification
Pre-EnergisationConfirm the frangible coupling on elevated edge fixtures and base can depth on flush-mounted centreline/caution fixtures meet as-built tolerances before the site is finally backfilled.
Documentation & As-Built Sign-off
Final AcceptanceRecord insulation, continuity, voltage, and photometric readings for each colour group alongside as-built position in the commissioning dossier for handover.
Inspection & Maintenance
Configuration Documentation Audit
AnnualReview circuit and fixture-type documentation for the intersection to keep maintenance and troubleshooting accurate as configurations get complex.
Lens Cleaning
QuarterlyClean all fixture types at the intersection of rubber deposits, dust, and de-icing fluid residue to maintain light output and colour fidelity.
Colour Filter & Photometric Check
AnnualTest blue, green, and yellow filters for colour shift or reduced output and replace as needed.
Circuit & Connector Inspection
AnnualCheck wiring and connectors across the multiple circuits present at the intersection for corrosion or loose connections.
Housing & Seal Inspection
AnnualCheck fixture housings and seals for moisture ingress across all light types at the intersection.
Common Field Issues
Complex Configuration Management
Intersection lighting configurations can be complex, with multiple circuits and light types. Proper documentation and labelling are essential to ensure correct maintenance and troubleshooting. Mismatched configurations can lead to pilot confusion.
Lens Contamination
All intersection lights are exposed to rubber deposits, dust, and de-icing fluids. Regular cleaning with approved solvents and soft brushes is required to maintain light output and colour fidelity across all fixture types.
Colour Filter Degradation
Blue, green, and yellow filters are all susceptible to UV degradation and thermal stress. Over time, colour shift or reduced output can occur. Regular photometric testing and filter replacement is essential.
Troubleshooting Guide
Wrong Colour or Fixture Type Reported at an Intersection
Reduced Light Output or Colour Fidelity
Colour Filter Fade Across Blue, Green, or Yellow Fixtures
Isolated Fixture Dark Within a Complex Circuit
Failure Modes & Root Causes
Fixture Type / Configuration Mismatch
Lens Contamination Across Fixture Types
Colour Filter Degradation
Isolated Fixture Open Circuit
Safety & Operational Notes
Isolate All Circuits Feeding the Intersection
Electrical SafetyIntersection lights typically combine blue edge, green centreline, and sometimes yellow elements on separate circuits; de-energise and lock out every CCR involved and verify zero energy before opening any base can.
Colour/Circuit Verification Before Restoration
ComplianceConfirm each lens colour is reconnected to its correct circuit and position before re-energising; a swapped blue/green/yellow element at a junction can mislead a pilot's routing decision and contribute to a runway incursion.
Airside Work Coordination
OperationalComplex junction points see converging traffic from multiple taxiways; coordinate with ATC/ground control, raise a NOTAM for any degraded guidance, and keep personnel clear of the through paths.
FOD Control at the Base Can
OperationalKeep tools, fasteners, and gaskets accounted for while any base can at the intersection is open, and secure or remove loose material before reinstating the fixtures.
Insulation Test Before Re-Energisation
Electrical SafetyMegger test each affected circuit after any cable, connector, or transformer work before restoring power, since a residual fault can take down the whole junction's guidance pattern.
PPE & Grounding
Personnel SafetyUse insulated tools and appropriate PPE on series-circuit connections, and confirm bonding/grounding of each base can before reconnecting.
Restore to Compliant State
ComplianceVerify full intersection geometry reads correctly to a pilot from all approach legs before closing out the work and cancelling the NOTAM.
Engineering & Expert Notes
Colour/Circuit Mapping Belongs in the As-Built, Not Memory
ComplianceComplex junctions combining blue edge, green centreline, and yellow elements are exactly where "the technician remembers how it goes together" fails during a callout at short notice; keep an accurate as-built wiring diagram at the junction, since guessing a colour-to-circuit mapping under time pressure is how incursion-risk swaps happen.
Geometry Reads Differently From Each Approach Leg
DesignA junction that looks correct when checked while standing on one taxiway can present a confusing or contradictory picture from a different approach leg; walk and view the intersection from every leg used in service, not just the one nearest the work area.
Trend Loop Readings, Don't Just Spot-Check
TroubleshootingMoisture ingress at an L-823 connector usually shows up first as a slow drift in loop insulation resistance, not a hard fault. Logging megger readings over successive maintenance cycles catches a failing splice months before it takes the loop down.
Balance Loops Sharing One CCR
DesignWhere multiple series loops run off a single CCR, unequal loop lengths or lamp counts between loops can produce visibly uneven brightness even though each individual fixture tests within photometric tolerance. Balance loop impedance at the design stage, not after commissioning complaints.
Size the Transformer to the Load, Not the Legacy Lamp
ElectricalReusing an isolating transformer sized for the old incandescent wattage on a much lower-draw LED fixture is a common source of premature transformer failure and nuisance loop trips; re-select VA rating against the actual LED load rather than assuming the existing transformer is "close enough."
De-Icing Fluid Ages Seals Faster Than UV Alone
DurabilityRepeated exposure to glycol-based de-icing fluid degrades gaskets and lens seals faster than sun and weather alone at a junction that sees concentrated de-icing traffic from multiple directions. Specify seal materials rated for glycol contact and inspect gasket condition at overhaul, not only at initial install.
Frequently Asked Questions
Short answers about taxiway intersection lights: colour combinations, switching, standards and maintenance.
Q1What is a taxiway intersection light?
It is a taxiway guidance fixture arrangement installed at junctions to give pilots clear directional cues where several taxiways converge. It combines blue edge, green centreline and yellow caution lighting.
Q2What colours are used at taxiway intersections?
Blue for the taxiway edges, green for centreline guidance through the intersection and yellow or amber for caution, flashing or steady, to alert pilots to the junction.
Q3Why are intersection lights configured differently from normal taxiway lights?
Intersections concentrate decision-making risk, with multiple possible paths in one place. Layering the familiar colour code exactly where the geometry gets complex reduces the chance of a wrong turn.
Q4Can each colour at an intersection be switched separately?
Yes. Each colour element can be switched independently so the intersection geometry is marked correctly for the active taxi route.
Q5Where are taxiway intersection lights installed?
At complex taxiway junctions, apron entry and exit points, runway holding position intersections and angled intersections, and in low-visibility operations.
Q6Which standards apply to taxiway intersection lights?
The main references are ICAO Annex 14 and FAA AC 150/5345-46, with IEC 61822 for the constant current regulators and IEC 61821 for maintenance of the series circuits. Always verify the current edition.
Q7How often should taxiway intersection lights be maintained?
Typical intervals are an annual configuration documentation audit, quarterly lens cleaning, and annual colour filter and photometric checks and circuit and connector inspection.
Q8What should I do if the wrong colour or fixture type appears at an intersection?
Compare the installed fixture against the current intersection lighting configuration drawing. It is often a repair with the wrong replacement unit, so replace it with the correct type and update the documentation and labelling.
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