AGL-CS-043 — Runway Edge Light Multiple Fixture Failure
The AGL Knowledge Hub | Engineering Case Study Series. A grouped-field investigation where six consecutive runway edge lights failed while the rest of the circuit remained operational — from failure-pattern analysis through primary-current verification, sectional testing, cable-joint excavation, and restoration of primary power.
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 night runway inspection, the maintenance team observed that six consecutive runway edge lights were not operating, 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 remained normal, and no CCR alarms were present.
The failure pattern suggested that the fault was localized to a common section of the field circuit rather than affecting the entire runway edge lighting circuit.
A systematic investigation identified failure of a primary cable joint feeding a group of isolating transformers, which interrupted primary power to the affected fixture section.
This case demonstrates that multiple consecutive fixture failures usually indicate a common upstream fault affecting several field units simultaneously.
2Learning Objectives
After completing this case study, the learner should be able to:
- Diagnose multiple runway edge light failures.
- Recognize failure patterns in AGL circuits.
- Differentiate localized group failures from complete circuit failures.
- Investigate common upstream field components.
- Perform sectional primary and secondary testing.
- Locate cable-joint and feeder faults.
- Restore grouped fixture operation efficiently.
3System Background
Each runway edge light is supplied through:
Multiple adjacent fixtures may share:
- Common primary cable sections.
- Common cable joints.
- Common field pits.
- Common installation zones.
Failure of a shared upstream component can disable several consecutive fixtures simultaneously.
4Problem Statement
The reported condition was:
- Six consecutive runway edge lights OFF.
- Adjacent sections operational.
- CCR healthy.
- Primary circuit apparently operational.
- No circuit alarms.
- Failure confined to one runway section.
Which common field component has interrupted power to multiple adjacent runway edge lights?
5Initial Observations
| CCR status | Healthy |
| Selected current | 6.6 A |
| Actual current | 6.6 A |
| Output voltage | Normal |
| Failed fixtures | Six consecutive lights |
| Adjacent fixtures | Operational |
The consecutive failure pattern suggested a shared upstream fault.
6Initial Engineering Hypotheses
The maintenance team considered:
Simultaneous LED failures.
Multiple transformer failures.
Primary cable interruption.
Common cable joint failure.
Field pit distribution failure.
7Failure Pattern Principle
Pattern recognition significantly reduces troubleshooting time.
8Test Equipment
The investigation used:
- True-RMS multimeter.
- Primary current measurement equipment.
- Secondary voltage test equipment.
- Continuity tester.
- Cable fault location equipment.
- Thermal imaging camera.
- 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 showed:
- Current present upstream.
- Current absent within the failed section.
- Current restored downstream through the remaining circuit.
A localized primary interruption was suspected.
Step 3: Transformer Primary Testing
Results:
| Upstream group | Present |
| Failed group | Absent |
| Downstream group | Present |
The affected transformers were not receiving primary power.
Step 4: Sectional Continuity Testing
The primary cable section feeding the failed group showed:
- Open continuity.
- Elevated resistance.
- Intermittent connection during testing.
The fault was localized to one field section.
Step 5: Cable Joint Inspection
Excavation revealed:
- Water ingress.
- Corroded conductor connection.
- Carbonized insulation.
- Partial conductor separation.
- High-resistance joint failure.
The joint had interrupted power to the transformer group.
Step 6: Secondary Verification
The transformers and fixtures themselves were healthy.
The fault was entirely upstream of the transformer group.
10Root Cause
The multiple runway edge light failure was caused by failure of a primary cable joint supplying a group of isolating transformers.
The joint deterioration interrupted primary power to six consecutive transformers, extinguishing the associated runway edge lights.
The CCR remained healthy because the overall series circuit continuity was maintained through the remaining circuit.
11Corrective Action
The maintenance team:
- Isolated the circuit.
- Excavated the failed cable joint.
- Removed the damaged conductor section.
- Installed a new approved primary cable joint.
- Restored conductor continuity.
- Performed insulation resistance testing.
- Verified primary current distribution.
- Tested transformer operation.
- Restored runway edge lights.
- Updated maintenance records.
12Post-Repair Verification
All six runway edge lights returned to service.
13Root-Cause Analysis
Multiple consecutive fixtures OFF
Healthy
Localized group
No primary power
Primary interruption localized
Joint failure confirmed
Primary cable joint feeding transformer group
Replace joint and restore primary continuity
14Why This Case Was Important
Multiple fixture failures should immediately trigger pattern-based troubleshooting.
Replacing individual fixtures wastes time when the fault is a common upstream component.
Failure patterns often reveal the fault location before testing begins.
15Engineering Lessons
Consecutive fixture failures usually indicate a common upstream fault.
Consecutive fixture failures usually indicate a common upstream fault.
Pattern recognition is a powerful diagnostic tool.
Pattern recognition is a powerful diagnostic tool.
Transformer primary testing quickly distinguishes primary and secondary faults.
Transformer primary testing quickly distinguishes primary and secondary faults.
Cable joints can disable multiple fixtures simultaneously.
Cable joints can disable multiple fixtures simultaneously.
Sectional testing should follow the physical failure pattern.
Sectional testing should follow the physical failure pattern.
16Engineer's Decision Point
You observe: Six consecutive runway edge lights OFF. Adjacent lights ON. CCR healthy. No circuit alarms. What should you investigate first?
17Knowledge Check
18Interview Questions
19Frequently Asked Questions
Quick answers about multiple consecutive runway edge light failures, based on this case study.
Q1What is AGL-CS-043?
AGL-CS-043 is an engineering training case study on six consecutive runway edge lights that were OFF while the rest of the circuit worked. It is an engineering simulation created for training, not a report of an actual airport incident.
Q2What does a run of consecutive failures suggest?
The consecutive failure pattern suggested a shared upstream fault common to that group of lights, rather than six independent fixture failures.
Q3What was the root cause?
Failure of a primary cable joint supplying a group of isolating transformers. The joint deterioration interrupted primary power to six consecutive transformers and extinguished the associated lights.
Q4What should you investigate first?
Verify primary power to the affected transformer group and inspect the common cable joint feeding that section. Replacing all six fixtures, the CCR or all transformers is not the right first step.
Q5Which test equipment was used?
The team used a true-RMS multimeter, primary current measurement equipment, secondary voltage test equipment, continuity tester, cable fault location equipment and a thermal imaging camera.
Q6How was the circuit repaired?
The team isolated the circuit, excavated the failed joint and removed the damaged conductor section. They installed a new approved primary cable joint, restored conductor continuity, tested insulation resistance, verified primary current distribution and tested transformer operation.
Q7How was the repair verified?
Primary continuity and transformer primary current were restored, and all six affected fixtures and the adjacent fixtures were operational. Documentation was completed.
Q8What were the CCR readings during the fault?
The CCR stayed healthy at 6.6 A with normal output voltage and no alarms. Compare this with your own circuit design and drawings when using a case like this to reason about a real installation.
Engineering & Expert Notes
Test Transformer Primaries at the Boundary
Fault LocationChecking primary voltage at the edge of the dark group locates the break.
Recognise the Pattern of Consecutive Failures
PatternConsecutive dark lights point upstream, not to each fixture.
Inspect Joints in Wet Locations First
MoistureWater entry at the joint explains the failure and where to look for similar ones.
Check Each Transformer After Restoration
VerificationConfirm every light operates at all steps before leaving.
20Case Study Conclusion
Multiple consecutive runway edge light failures usually indicate a common upstream primary-circuit fault affecting a group of isolating transformers rather than simultaneous failure of individual fixtures.
Systematic CCR verification, failure-pattern analysis, transformer primary testing, sectional continuity testing, cable-joint inspection, and primary power verification can rapidly identify the common fault location and restore grouped fixture operation.
In AGL engineering, when several consecutive runway edge lights fail together, the pattern often identifies the fault before the meter does.
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