AGL-CS-042 — Runway Edge Light Single Fixture Failure
The AGL Knowledge Hub | Engineering Case Study Series. A localized field investigation where one runway edge light failed while the rest of the circuit remained operational — from CCR verification through transformer secondary testing, connector inspection, and secondary-circuit 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, one runway edge light fixture was found completely extinguished, while all other runway edge lights in the circuit remained fully operational.
The Constant Current Regulator (CCR) was maintaining the selected 6.6 A current, output voltage was normal, and no CCR alarms were present.
Because the rest of the circuit was operating normally, the investigation focused on localized field components associated with the failed fixture.
A systematic investigation identified a failed isolating transformer secondary connection combined with moisture-contaminated connector contacts, which interrupted power delivery to the individual runway edge light.
This case demonstrates that single fixture failures are usually localized secondary-side faults and require structured field-level diagnosis rather than CCR or primary-circuit troubleshooting.
2Learning Objectives
After completing this case study, the learner should be able to:
- Diagnose single runway edge light failures.
- Differentiate primary and secondary circuit faults.
- Verify isolating transformer operation.
- Test secondary voltage and continuity.
- Inspect field connectors and secondary cables.
- Identify moisture-related connector failures.
- Restore individual fixture operation safely.
3System Background
A single runway edge light is supplied through:
Failure of any secondary component can extinguish the individual fixture while leaving the primary circuit and all other lights operational.
Common causes include:
- Lamp or LED module failure.
- Isolating transformer failure.
- Secondary cable open circuit.
- Connector corrosion.
- Moisture ingress.
- Mechanical cable damage.
- Fixture terminal failure.
4Problem Statement
The reported condition was:
- One runway edge light OFF.
- Adjacent lights ON.
- CCR healthy.
- Primary circuit operational.
- No circuit alarms.
- No recent excavation work.
Which localized field component has interrupted power to the failed runway edge light?
5Initial Observations
| CCR status | Healthy |
| Selected current | 6.6 A |
| Actual current | 6.6 A |
| Output voltage | Normal |
| Adjacent lights | Operational |
| Failed fixture | Completely OFF |
The healthy CCR and adjacent lights indicated that the primary series circuit was intact.
6Initial Engineering Hypotheses
The maintenance team considered:
LED module failure.
Isolating transformer failure.
Secondary cable open circuit.
Connector failure.
Fixture terminal corrosion.
7Single Fixture Failure Principle
If the primary circuit remains healthy, the fault is usually localized to the secondary circuit associated with the failed fixture.
8Test Equipment
The investigation used:
- True-RMS multimeter.
- Secondary voltage test equipment.
- Continuity tester.
- Low-resistance ohmmeter.
- Thermal imaging camera.
- Insulation resistance tester.
- 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 Primary Circuit
Primary measurements confirmed:
- Stable current.
- Transformer primary energized.
- No primary circuit abnormalities.
The transformer was receiving primary power.
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.
- Intermittent connection during connector movement.
- Elevated contact resistance.
The fault was downstream of the transformer.
Step 5: Connector Inspection
Inspection revealed:
- Moisture contamination.
- Corroded contacts.
- Oxidized terminals.
- Damaged sealing gasket.
- Reduced contact pressure.
The connector had deteriorated significantly.
Step 6: Transformer Verification
The transformer itself showed:
- Normal primary continuity.
- Normal secondary winding continuity.
- Acceptable insulation resistance.
The transformer was healthy.
10Root Cause
The runway edge light failed because corrosion and moisture contamination in the transformer secondary connector interrupted power delivery to the individual fixture.
The primary circuit remained intact, and the CCR continued regulating current normally.
The fault was localized to the connector and secondary connection.
11Corrective Action
The maintenance team:
- Isolated the circuit.
- Removed the damaged connector.
- Cleaned the transformer secondary terminals.
- Installed a new approved connector.
- Restored environmental sealing.
- Verified secondary continuity.
- Measured secondary voltage.
- Tested fixture operation.
- Performed thermal verification.
- Updated maintenance records.
12Post-Repair Verification
The individual runway edge light returned to normal operation.
13Root-Cause Analysis
Single fixture OFF
Healthy
Healthy
No output
Open
Corrosion identified
Moisture-damaged secondary connector
Replace connector and restore sealing
14Why This Case Was Important
Single fixture failures are the most common field maintenance events in runway edge lighting systems.
Efficient diagnosis avoids unnecessary replacement of:
- CCRs.
- Primary cables.
- Healthy transformers.
- Multiple field components.
15Engineering Lessons
A single fixture failure is usually a localized secondary-circuit problem.
A single fixture failure is usually a localized secondary-circuit problem.
Healthy adjacent lights strongly indicate a healthy primary circuit.
Healthy adjacent lights strongly indicate a healthy primary circuit.
Connector corrosion is a common secondary failure mechanism.
Connector corrosion is a common secondary failure mechanism.
Secondary voltage testing is the most important localization step.
Secondary voltage testing is the most important localization step.
Moisture sealing is critical for long-term connector reliability.
Moisture sealing is critical for long-term connector reliability.
16Engineer's Decision Point
You observe: One runway edge light OFF. Adjacent lights ON. CCR healthy. No circuit alarms. What should you investigate first?
17Knowledge Check
18Interview Questions
Quick Reference: Runway Edge Light Failure, Colour & Fixtures
This case is a runway lighting partial failure: one light is out while the rest of the circuit stays on. That pattern points to a fault at the fixture, its isolating transformer secondary or its connector, not to the CCR or the main cable.
What causes runway light failure? The usual causes are lamp or LED module failure, moisture in the fixture or connector, a failed isolating transformer, cable damage, and impact. If every light on a circuit is out, look at the CCR and the primary cable first.
FAA runway light fixtures such as the L-862 elevated runway edge light are covered by FAA fixture specifications, and the fixture type in use should match the project specification.
19Frequently Asked Questions
Quick answers about single runway edge light fixture failure, based on this case study.
Q1What is AGL-CS-042?
AGL-CS-042 is an engineering training case study on a single runway edge light fixture that was completely OFF while all other lights in the circuit worked. It is an engineering simulation created for training, not a report of an actual airport incident.
Q2How do you know the primary circuit is intact?
The CCR was maintaining 6.6 A with normal voltage and no alarms, and adjacent lights were operating. The healthy CCR and adjacent lights indicated the primary series circuit was intact.
Q3What was the root cause?
Corrosion and moisture contamination in the transformer secondary connector interrupted power delivery to the individual fixture. The primary circuit stayed intact and the CCR kept regulating normally.
Q4What should you investigate first for a single light OFF with a healthy CCR?
Verify transformer secondary voltage and inspect the secondary connector and cable. Replacing the CCR, increasing the current setting or replacing all runway edge lights 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, thermal imaging camera and insulation resistance tester, with approved AGL circuit test equipment.
Q6How was the light repaired?
The team isolated the circuit, removed the damaged connector and cleaned the transformer secondary terminals. They installed a new approved connector, restored environmental sealing, verified secondary continuity, measured secondary voltage, tested fixture operation and performed thermal verification.
Q7How was the repair verified?
Secondary voltage and fixture operation were restored, connector temperature was normal and the primary circuit remained normal. The individual runway edge light returned to normal operation.
Q8Why is the fault treated as localized?
Because only one fixture was affected, the investigation focused on the field components of that fixture rather than the whole circuit. Isolating the fault to the secondary connection avoided unnecessary equipment replacement.
Q9What color are runway edge lights?
Runway edge lights are white. On instrument runways the lights in the last part of the runway, normally the last 600 m or the last third of its length if that is less, are yellow, as a caution zone. Confirm the exact arrangement against the applicable standard.
Q10What causes runway light failure?
Runway lights fail from lamp or LED module failure, moisture in the fixture or connector, a failed isolating transformer, damaged cable, and impact. A single light out points to the fixture, transformer secondary or connector. A whole circuit out points to the CCR or the primary cable.
Engineering & Expert Notes
Test Secondary Voltage First
MethodMeasuring at the fixture separates secondary faults from fixture faults quickly.
Inspect the Secondary Connector Closely
TerminationsCorrosion often hides inside the connector. Open and examine it.
Healthy Neighbours Point to a Local Fault
PatternAdjacent lights working indicates the primary loop is intact.
Repair the Seal as Well as the Contact
SealingWithout a good seal the new contact will corrode again.
20Case Study Conclusion
A single runway edge light failure is usually a localized secondary-circuit fault involving the isolating transformer, secondary connector, cable, or fixture, while the CCR and primary series circuit remain fully operational.
Systematic CCR verification, primary-circuit confirmation, transformer secondary testing, connector inspection, secondary continuity testing, and moisture assessment can rapidly identify the failed component and restore individual fixture operation.
In AGL engineering, when only one runway edge light is dark, the fastest repair usually begins at the transformer secondary connector, not at the CCR.
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