AGL-CS-052 — Taxiway Centreline Light Failure
The AGL Knowledge Hub | Engineering Case Study Series. A taxiway centreline lighting investigation where one inset taxiway centreline light failed while the rest of the circuit remained operational — from CCR verification through transformer secondary testing, fixture inspection, water-ingress assessment, and drainage restoration.
Important: This is an engineering simulation created for training. It is not presented as an actual airport incident. All readings, values, dates and outcomes are illustrative, and no airport, organisation, person or manufacturer is identified or implied.
1Case Study Overview
During a routine night inspection before low-visibility operations, one taxiway centreline inset light was found completely extinguished, interrupting the green taxiway centreline guidance pattern.
The Constant Current Regulator (CCR) was operating normally, and the adjacent taxiway centreline lights remained operational.
Because the failure affected a single inset centreline fitting, the investigation focused on the associated isolating transformer, secondary circuit, connector assembly, and inset taxiway centreline fixture.
A systematic investigation identified water ingress into the fixture base-can assembly, causing corrosion of the secondary connector and failure of the transformer secondary connection.
This case demonstrates that taxiway centreline light failures are commonly localized inset-fixture or secondary-circuit faults, with water ingress and sealing deterioration being major reliability factors.
2Learning Objectives
After completing this case study, the learner should be able to:
- Diagnose taxiway centreline light failures.
- Understand taxiway centreline lighting system configuration.
- Investigate inset-fixture failures systematically.
- Test transformer secondary circuits.
- Inspect connectors, base cans, and sealing systems.
- Assess water-ingress-related failures.
- Restore taxiway centreline lighting safely.
3System Background
A taxiway centreline light is supplied through:
Taxiway centreline lights provide:
- Green taxi guidance.
- Taxi route definition.
- Runway exit guidance.
- A-SMGCS visual guidance.
- Low-visibility taxi guidance.
Common failure causes include:
- LED module failure.
- Water ingress.
- Connector corrosion.
- Transformer secondary failure.
- Secondary cable damage.
- Base-can drainage failure.
- Fixture sealing deterioration.
4Problem Statement
The reported condition was:
- One taxiway centreline light OFF.
- Adjacent centreline lights operational.
- CCR healthy.
- No circuit alarms.
- Low-visibility inspection in progress.
Has the inset taxiway centreline fixture failed, or has the secondary power supply to the fixture been interrupted?
5Initial Observations
| CCR status | Healthy |
| Selected current | 6.6 A |
| Actual current | 6.6 A |
| Output voltage | Normal |
| Adjacent centreline lights | Operational |
| Failed fixture | Completely OFF |
The healthy CCR and adjacent lights indicated a localized field fault.
6Initial Engineering Hypotheses
The maintenance team considered:
LED module failure.
Inset fixture water ingress.
Transformer secondary failure.
Connector corrosion.
Base-can drainage failure.
7Taxiway Centreline Diagnostic Principle
If adjacent centreline lights remain operational, the fault is usually localized to the transformer secondary circuit or the inset fixture itself.
8Test Equipment
The investigation used:
- True-RMS multimeter.
- Secondary voltage test equipment.
- Continuity tester.
- Low-resistance ohmmeter.
- Insulation resistance tester.
- Thermal imaging camera.
- Moisture inspection equipment.
- Approved AGL circuit test equipment.
- Airport-approved PPE.
9Investigation
Step 1: Verify CCR Operation
Results:
| Current regulation | Normal |
| Voltage regulation | Normal |
| CCR alarms | None |
The CCR was healthy.
Step 2: Verify Transformer Primary
The associated transformer showed:
- Primary current present.
- Normal primary continuity.
- Normal operating temperature.
Primary power was available.
Step 3: Measure Transformer Secondary Voltage
Results:
| Primary current | Present |
| Secondary voltage | Absent |
The secondary circuit was interrupted.
Step 4: Secondary Continuity Testing
Testing showed:
- Open continuity.
- Elevated connector resistance.
- Moisture-related resistance instability.
The fault was localized near the fixture connection.
Step 5: Fixture Removal and Inspection
The inset taxiway centreline fixture was removed.
Inspection revealed:
- Water accumulation.
- Corroded connector assembly.
- Oxidized terminals.
- Deteriorated sealing gasket.
- Contaminated electrical compartment.
The fixture had experienced progressive water-ingress deterioration.
Step 6: Base-Can Drainage Inspection
The base can showed:
- Blocked drainage holes.
- Standing water.
- Sediment accumulation.
- Poor water evacuation.
The drainage failure had increased long-term moisture exposure.
10Root Cause
The taxiway centreline light failed because water ingress entered the inset fixture and base-can assembly through a deteriorated sealing gasket and blocked drainage system, causing corrosion of the secondary connector and interruption of the transformer secondary connection.
The primary circuit and transformer remained healthy.
The fault was localized to the inset fixture secondary connection.
11Corrective Action
The maintenance team:
- Isolated the circuit.
- Removed the affected inset fixture.
- Replaced the damaged connector assembly.
- Installed a new approved sealing gasket.
- Cleaned and dried the base can.
- Restored drainage.
- Verified secondary continuity.
- Tested photometric performance.
- Reinstalled the fixture.
- Updated maintenance records.
12Post-Repair Verification
The taxiway centreline light returned to full operation.
13Root-Cause Analysis
Taxiway centreline light OFF
Healthy
Healthy
No output
Open
Water ingress found
Water-ingress-induced secondary connector failure
Replace connector and restore sealing and drainage
14Why This Case Was Important
Taxiway centreline lights are critical for:
- Low-visibility taxi operations.
- Surface movement guidance.
- Runway exit routing.
- A-SMGCS operations.
- Taxi route continuity.
Inset-fixture reliability directly affects taxiway operational guidance.
15Engineering Lessons
Taxiway centreline light failures are usually localized inset-fixture or secondary-circuit faults.
Taxiway centreline light failures are usually localized inset-fixture or secondary-circuit faults.
Water ingress is a major failure mechanism in taxiway centreline systems.
Water ingress is a major failure mechanism in taxiway centreline systems.
Base-can drainage is part of electrical reliability.
Base-can drainage is part of electrical reliability.
Secondary voltage testing is essential before fixture replacement.
Secondary voltage testing is essential before fixture replacement.
Connector corrosion often follows prolonged moisture exposure.
Connector corrosion often follows prolonged moisture exposure.
16Engineer's Decision Point
You observe: One taxiway centreline light OFF. Adjacent centreline lights ON. CCR healthy. No circuit alarms. What should you investigate first?
17Knowledge Check
18Interview Questions
Quick Reference: ICAO Taxiway Centerline Lights
ICAO taxiway centerline lights guide aircraft along the taxi route. They are normally green, and on runway exit sections Annex 14 sets a colour pattern to show the edge of the sensitive area. Check the colour coding for the exit taxiway you are working on against the current standard.
19Frequently Asked Questions
Quick answers about taxiway centreline light failure, based on this case study.
Q1What is AGL-CS-052?
AGL-CS-052 is an engineering training case study on a single taxiway centreline inset light that was OFF during a pre-low-visibility inspection, interrupting the green centreline pattern. It is an engineering simulation created for training, not a report of an actual airport incident.
Q2Was the fixture or the secondary supply at fault?
The case starts with that question. The CCR was healthy at 6.6 A, adjacent centreline lights worked and there were no alarms, which indicated a localized field fault.
Q3What was the root cause?
Water entered the inset fixture and base-can assembly through a deteriorated sealing gasket and blocked drainage, corroding the secondary connector and interrupting the transformer secondary connection. The primary circuit and transformer stayed healthy.
Q4What should you investigate first?
Verify transformer secondary voltage and inspect the inset fixture, connector assembly, sealing system and base-can drainage. Replacing the CCR or all taxiway centreline lights, or increasing the current setting, is not the right first step.
Q5Which test equipment was used?
The team used a true-RMS multimeter, secondary voltage test equipment, continuity tester, low-resistance ohmmeter, insulation resistance tester, thermal imaging camera and moisture inspection equipment.
Q6How was the light repaired?
The team isolated the circuit, removed the affected inset fixture and replaced the damaged connector assembly. They installed a new approved sealing gasket, cleaned and dried the base can, restored drainage, verified secondary continuity, tested photometric performance and reinstalled the fixture.
Q7How was the repair verified?
Transformer secondary and the taxiway centreline fixture were restored, the centreline pattern was continuous and drainage was restored.
Q8Why check drainage as well as the connector?
Blocked drainage and a deteriorated gasket together allowed the water in. Restoring drainage was part of the correction, not only replacing the corroded connector.
Engineering & Expert Notes
Clear the Base-Can Drain and Confirm It Flows
DrainageA blocked drain is part of the fault. Test that water leaves the can after cleaning.
Fit a New Gasket and Check the Seating Face
SealingSurface damage under the gasket can defeat a new seal. Inspect before reassembly.
Verify Secondary Voltage Before Replacing the Fixture
MethodThis identifies the connector as the cause and avoids needless part changes.
Note Pavement Condition Around the Fixture
CivilPonding or cracking nearby feeds water to the can. Report it to civil maintenance.
20Case Study Conclusion
A taxiway centreline light failure is usually a localized inset-fixture or secondary-circuit fault, with water ingress, connector corrosion, and base-can drainage failure being among the most significant reliability factors affecting taxiway centreline lighting systems.
Systematic CCR verification, transformer secondary testing, fixture inspection, connector assessment, sealing evaluation, drainage inspection, and photometric verification can rapidly identify the failed component and restore taxiway centreline lighting continuity.
In AGL engineering, a dark taxiway centreline light usually indicates a localized secondary-circuit reliability problem beneath the pavement, not a CCR problem in the substation.
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