AGL-CS-049 — In-Pavement Light Repeated Failure
The AGL Knowledge Hub | Engineering Case Study Series. A reliability investigation where the same in-pavement centreline light location failed four times in eighteen months — from failure-history analysis through drainage inspection, pavement assessment, connector evaluation, and environmental correction.
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
An airport maintenance team reported that the same in-pavement runway centreline light location had failed four times within eighteen months.
Each failure was corrected by replacing the inset fixture, but the replacement fixture failed again after a relatively short operating period.
The Constant Current Regulator (CCR) remained healthy, adjacent fixtures operated normally, and no circuit alarms were present.
Because the failures repeatedly occurred at the same physical location, a detailed reliability investigation was conducted rather than another routine fixture replacement.
The investigation identified chronic water ingress caused by blocked base-can drainage, pavement settlement, and continuous moisture exposure, resulting in repeated connector corrosion, insulation deterioration, and thermal damage.
This case demonstrates that repeated in-pavement light failures usually indicate a location-specific reliability problem rather than repeated fixture defects.
2Learning Objectives
After completing this case study, the learner should be able to:
- Investigate repeated inset-fixture failures systematically.
- Distinguish component failure from location failure.
- Evaluate base-can drainage.
- Assess pavement and installation conditions.
- Investigate moisture and corrosion mechanisms.
- Analyze repeated thermal and electrical stress.
- Develop long-term corrective actions.
3System Background
An in-pavement light installation consists of:
- Inset fixture.
- Base can.
- Isolating transformer.
- Secondary cable.
- Connector assembly.
- Drainage system.
- Pavement interface.
- Sealing system.
Repeated failures may result from:
- Water ingress.
- Blocked drainage.
- Connector deterioration.
- Incorrect transformer loading.
- Thermal cycling.
- Mechanical loading.
- Pavement movement.
- Improper installation.
4Problem Statement
The reported condition was:
- Same fixture location repeatedly failing.
- Four fixture replacements in 18 months.
- Adjacent fixtures healthy.
- CCR healthy.
- No primary circuit abnormalities.
Why does the same in-pavement light location repeatedly fail despite fixture replacement?
5Initial Observations
| CCR status | Healthy |
| Adjacent fixtures | Operational |
| Failed location | Same position repeatedly |
| Replacement history | Four failures |
| Circuit alarms | None |
| Failure interval | Progressive |
The repeated location strongly suggested a site-specific reliability problem.
6Initial Engineering Hypotheses
The maintenance team considered:
Defective replacement fixtures.
Incorrect transformer VA selection.
Chronic water ingress.
Mechanical pavement stress.
Connector overheating.
7Repeated Failure Principle
When the same location repeatedly fails, the investigation should shift from component replacement to root-cause engineering.
8Test Equipment
The investigation used:
- True-RMS multimeter.
- Insulation resistance tester.
- Thermal imaging camera.
- Moisture inspection equipment.
- Drainage inspection tools.
- Pavement level measurement equipment.
- Low-resistance ohmmeter.
- Approved AGL circuit test equipment.
- Airport-approved PPE.
9Investigation
Step 1: Review Failure History
Maintenance records showed:
| Original | - |
| Replacement 1 | 7 months |
| Replacement 2 | 5 months |
| Replacement 3 | 4 months |
| Replacement 4 | 2 months |
The failure interval was decreasing.
Step 2: Verify CCR and Circuit
Results:
| CCR operation | Normal |
| Current regulation | Normal |
| Primary circuit | Healthy |
| Transformer primary | Healthy |
The primary system was healthy.
Step 3: Fixture Examination
All removed fixtures showed:
- Water contamination.
- Connector corrosion.
- Terminal oxidation.
- Insulation deterioration.
- Thermal discoloration.
The damage pattern was consistent across all failed fixtures.
Step 4: Base-Can Inspection
Inspection revealed:
- Standing water.
- Blocked drainage outlet.
- Sediment accumulation.
- Corrosion deposits.
- Moisture around the connector assembly.
The base can remained wet for prolonged periods.
Step 5: Pavement Assessment
Measurements showed:
- Pavement settlement.
- Localized depression.
- Water accumulation around the fixture.
- Poor surface drainage.
Surface water repeatedly entered the base can.
Step 6: Thermal Inspection
The connector assembly showed:
- Elevated operating temperature.
- High contact resistance.
- Thermal cycling.
- Progressive contact deterioration.
Moisture and heating were acting together.
Step 7: Insulation Testing
Results:
| Dry condition | Greater than 1000 MΩ |
| Wet condition | 12 MΩ |
Moisture significantly reduced insulation performance.
10Root Cause
The repeated in-pavement light failures were caused by chronic water ingress resulting from blocked base-can drainage and localized pavement settlement, which continuously exposed the connector and secondary circuit to moisture.
The repeated moisture exposure caused:
- Connector corrosion.
- Increased contact resistance.
- Thermal heating.
- Insulation deterioration.
- Progressive fixture damage.
Replacing the fixture alone did not remove the underlying environmental cause.
11Corrective Action
The maintenance team:
- Removed the affected fixture.
- Replaced the connector assembly.
- Restored base-can drainage.
- Removed sediment.
- Corrected pavement settlement.
- Improved surface drainage.
- Installed new sealing components.
- Verified insulation resistance.
- Performed thermal verification.
- Implemented periodic drainage inspection.
12Post-Repair Verification
No additional failures occurred after the environmental corrections.
13Root-Cause Analysis
Repeated fixture failures
Same location
Healthy
Water damage identified
Blocked drainage found
Settlement identified
Chronic water ingress from drainage and pavement defects
Restore drainage, pavement, sealing, and connector integrity
14Why This Case Was Important
Repeated fixture replacement without root-cause analysis:
- Increases maintenance cost.
- Increases runway closures.
- Reduces reliability.
- Repeats the same failure mechanism.
Reliability engineering focuses on eliminating the cause, not repeatedly replacing the symptom.
15Engineering Lessons
Repeated failure usually indicates a location problem.
Repeated failure usually indicates a location problem.
Base-can drainage is a critical reliability component.
Base-can drainage is a critical reliability component.
Pavement condition affects electrical reliability.
Pavement condition affects electrical reliability.
Moisture and thermal stress often act together.
Moisture and thermal stress often act together.
Failure-history analysis is a powerful diagnostic tool.
Failure-history analysis is a powerful diagnostic tool.
16Engineer's Decision Point
You observe: Same inset light location failed four times. Adjacent fixtures healthy. CCR healthy. Water present in the base can. What should you investigate first?
17Knowledge Check
18Interview Questions
19Frequently Asked Questions
Quick answers about repeated in-pavement light failure, based on this case study.
Q1What is AGL-CS-049?
AGL-CS-049 is an engineering training case study on an in-pavement runway centreline light location that failed four times in eighteen months. It is an engineering simulation created for training, not a report of an actual airport incident.
Q2Why did replacing the fixture not solve the problem?
The failures repeated at the same physical location while adjacent fixtures and the CCR were healthy. That pointed to a site-specific reliability problem, and replacing the fixture alone did not remove the underlying environmental cause.
Q3What was the root cause?
Chronic water ingress from blocked base-can drainage and localized pavement settlement continuously exposed the connector and secondary circuit to moisture.
Q4What damage did the repeated moisture cause?
Connector corrosion, increased contact resistance, thermal heating, insulation deterioration and progressive fixture damage.
Q5What should you investigate first when the same location keeps failing?
Investigate drainage, pavement condition, connector corrosion and environmental exposure at the failed location. Replacing the fixture again, replacing the CCR or increasing the current setting is not the right first step.
Q6How was the location corrected?
The team removed the fixture, replaced the connector assembly, restored base-can drainage and removed sediment. They corrected pavement settlement, improved surface drainage, installed new sealing components, verified insulation resistance, performed thermal verification and implemented periodic drainage inspection.
Q7How was the repair verified?
Base-can drainage was restored, standing water eliminated, connector temperature normal and insulation resistance greater than 1000 MΩ. No additional failures occurred after the environmental corrections.
Q8Which tools were used?
The team used a true-RMS multimeter, insulation resistance tester, thermal imaging camera, moisture inspection equipment, drainage inspection tools, pavement level measurement equipment and a low-resistance ohmmeter.
Engineering & Expert Notes
Look at the Pavement Around the Failure
CivilSettlement or cracking near the base can channel water to the fitting. Involve civil teams.
Clear and Verify the Drainage Path
DrainageTest that water can leave the base can after rain.
Map Repeat Failures
PatternCluster maps show where a civil or drainage fix is needed.
Fix the Location, Not Only the Light
StrategyReplacing the fixture again without addressing the location repeats the cost.
20Case Study Conclusion
Repeated in-pavement light failures are usually caused by location-specific environmental, drainage, installation, or mechanical problems rather than repeated fixture defects, and long-term reliability requires elimination of the underlying root cause.
Systematic failure-history analysis, drainage inspection, pavement assessment, connector evaluation, moisture investigation, thermal analysis, and environmental correction can permanently eliminate repeated inset-light failures and significantly improve AGL system reliability.
In AGL engineering, replacing the same fixture repeatedly repairs the symptom; repairing the drainage, pavement, and connector repairs the system.
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