AGL-CS-047 — Runway End Light Failure
The AGL Knowledge Hub | Engineering Case Study Series. A runway-end lighting investigation where one runway end 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 end light was found completely extinguished, interrupting the continuity of the red runway end lighting pattern.
The Constant Current Regulator (CCR) was operating normally, and the adjacent runway end lights remained operational.
Because the failure affected a single runway end fitting, the investigation focused on the associated isolating transformer, secondary circuit, connector assembly, and runway end fixture.
A systematic investigation identified failure of the transformer secondary connector caused by moisture ingress and contact corrosion, interrupting power to the individual runway end light.
This case demonstrates that runway end light failures are commonly localized secondary-side faults that can affect runway-end visual identification and operational safety.
2Learning Objectives
After completing this case study, the learner should be able to:
- Diagnose single runway end light failures.
- Understand runway end lighting system configuration.
- Differentiate runway end lighting from threshold lighting.
- Test transformer secondary circuits.
- Inspect connectors, secondary cables, and fixture terminals.
- Assess moisture-related connector deterioration.
- Restore runway end light operation safely.
3System Background
A runway end light is supplied through:
Runway end lights provide:
- Red light toward departing and landing aircraft.
- Runway-end identification.
- Runway-end boundary indication.
- Visual stop reference.
Common failure causes include:
- LED module failure.
- Transformer secondary failure.
- Secondary cable damage.
- Connector corrosion.
- Water ingress.
- Fixture terminal deterioration.
- Mechanical damage.
4Problem Statement
The reported condition was:
- One runway end light OFF.
- Adjacent runway end lights ON.
- CCR healthy.
- No circuit alarms.
- Threshold lights normal.
- Runway-end pattern incomplete.
Has the runway end 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 runway end lights | Operational |
| Failed runway end light | Completely OFF |
The healthy CCR and adjacent runway end lights indicated a localized field fault.
6Initial Engineering Hypotheses
The maintenance team considered:
LED module failure.
Transformer secondary failure.
Secondary cable open circuit.
Connector corrosion.
Fixture terminal failure.
7Runway End Light Diagnostic Principle
If adjacent runway end lights remain operational, the fault is usually localized to the individual secondary circuit.
8Test Equipment
The investigation used:
- True-RMS multimeter.
- Secondary voltage test equipment.
- Continuity tester.
- Low-resistance ohmmeter.
- Insulation resistance tester.
- 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 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.
- Intermittent contact during connector movement.
The fault was localized near the transformer connection.
Step 5: Connector Inspection
Inspection revealed:
- Moisture contamination.
- Corroded contact surfaces.
- Oxidized terminals.
- Damaged sealing.
- Reduced contact pressure.
The connector had failed electrically.
Step 6: Fixture Verification
The runway end fixture showed:
- Normal internal continuity.
- No optical damage.
- No LED module failure.
The fixture itself was healthy.
10Root Cause
The runway end light failed because corrosion and moisture ingress in the transformer secondary connector interrupted power delivery to the individual runway end fixture.
The primary circuit, transformer primary, and runway end fixture remained healthy.
The fault was localized to the secondary connector assembly.
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 runway end light operation.
- Conducted operational verification.
- Updated maintenance records.
12Post-Repair Verification
The runway end light returned to normal operation.
13Root-Cause Analysis
Runway end light OFF
Healthy
Healthy
No output
Open
Corrosion identified
Moisture-damaged secondary connector
Replace connector and restore sealing
14Why This Case Was Important
Runway end lights are operationally critical because they provide:
- Runway-end identification.
- Red runway-end reference.
- Departure guidance.
- Runway boundary indication.
A missing runway end light can reduce runway-end visual pattern integrity during night and low-visibility operations.
15Engineering Lessons
Single runway end light failures are usually localized secondary-circuit faults.
Single runway end light failures are usually localized secondary-circuit faults.
Runway-end lighting pattern integrity is operationally important.
Runway-end lighting pattern integrity is operationally important.
Connector corrosion is a common runway-end light failure mechanism.
Connector corrosion is a common runway-end light 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 runway-end pit reliability.
Moisture sealing is critical for runway-end pit reliability.
16Engineer's Decision Point
You observe: One runway end light OFF. Adjacent runway end lights ON. CCR healthy. No circuit alarms. What should you investigate first?
17Knowledge Check
18Interview Questions
Quick Reference: Runway End Light Colour & Intensity
Runway end light color is red, showing to an aircraft that is landing or taking off towards the end of the runway. Runway end light intensity is checked against the required photometric value at each brightness step, and a failed light here is an operational defect.
19Frequently Asked Questions
Quick answers about runway end light failure, based on this case study.
Q1What is AGL-CS-047?
AGL-CS-047 is an engineering training case study on a single runway end light that was OFF, breaking the red runway-end 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 runway end lights and the threshold lights were normal and there were no alarms, which indicated a localized field fault.
Q3What was the root cause?
Moisture ingress and contact corrosion in the transformer secondary connector interrupted power to the individual runway end fixture. The primary circuit, transformer primary and fixture remained healthy.
Q4What should you investigate first?
Verify transformer secondary voltage and inspect the secondary connector and cable. Replacing the CCR or all runway end 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 and thermal imaging camera.
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 and tested runway end light operation.
Q7How was the repair verified?
Transformer secondary voltage and the runway end light were restored, the runway-end pattern was complete and connector temperature was normal.
Q8What does the healthy CCR tell you in this case?
It shows the primary series circuit is intact, so the investigation can focus on the secondary connection of the one failed fixture.
Engineering & Expert Notes
Runway-End Pattern Integrity Matters
PriorityMissing end lights alter what the pilot sees. Restore promptly.
Confirm Secondary Voltage Before Replacing the Fixture
MethodQuick measurement avoids unnecessary part changes.
Replace Corroded Terminations Fully
RepairClean metal and new seals give the best chance of lasting repair.
Look at Neighbouring Connectors for the Same Problem
ScopeSimilar conditions may be affecting adjacent units.
20Case Study Conclusion
A single runway end light failure is usually a localized secondary-circuit fault involving the isolating transformer, secondary connector, cable, or fixture, while the CCR and primary circuit remain fully operational.
Systematic CCR verification, transformer secondary testing, connector inspection, secondary continuity testing, and moisture assessment can rapidly identify the failed component and restore runway-end lighting integrity.
In AGL engineering, a missing runway end light is often a secondary connector failure long before it becomes a fixture replacement issue.
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