AGL-CS-038 — CCR Healthy but Field Lights Not Working
The AGL Knowledge Hub | Engineering Case Study Series. A field-light outage investigation where the CCR maintained perfect regulation but an entire runway section remained dark — from primary-circuit 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 routine night inspection, an airport maintenance team reported that an entire section of runway edge lights was not operating, even though the Constant Current Regulator (CCR) was functioning normally.
The CCR was maintaining the selected 6.6 A current, output voltage remained stable, and no CCR alarms were present.
Initial suspicion focused on a possible CCR output problem. However, systematic field investigation revealed that multiple isolating transformer secondary circuits had become disconnected due to a failed connector assembly inside a field pit.
This case demonstrates that normal CCR operation only confirms that the regulator and primary series circuit are functioning; it does not confirm that power is reaching the field lights through the secondary circuits.
2Learning Objectives
After completing this case study, the learner should be able to:
- Differentiate CCR health from field-light health.
- Diagnose field-light outages with a healthy CCR.
- Investigate secondary circuits systematically.
- Verify isolating transformer operation.
- Inspect connectors and secondary cables.
- Apply sectional fault localization.
- Develop an efficient field troubleshooting strategy.
3System Background
An AGL system consists of:
A healthy CCR confirms:
- Current regulation.
- Voltage regulation.
- Primary circuit operation.
Field-light failure may still occur due to:
- Transformer failure.
- Secondary cable failure.
- Connector failure.
- Fixture failure.
- Secondary open circuit.
- Water ingress.
- Mechanical damage.
4Problem Statement
The reported condition was:
- CCR operating normally.
- Selected current maintained.
- No CCR alarms.
- One runway section dark.
- Adjacent sections operational.
- No recent CCR maintenance.
How can field lights fail when the CCR is healthy?
5Initial Observations
| CCR status | Healthy |
| Selected current | 6.6 A |
| Actual current | 6.6 A |
| Output voltage | Normal |
| CCR alarms | None |
| Field lights | Section not operating |
The most important observation was that CCR electrical parameters were normal despite field-light failure.
6Initial Engineering Hypotheses
The maintenance team considered:
CCR output problem.
Primary cable failure.
Multiple transformer failures.
Secondary connector failure.
Field distribution interruption.
7Diagnostic Principle
A healthy CCR proves:
It does not prove:
- Secondary voltage available.
- Transformer output available.
- Connector continuity.
- Field fixture operation.
Therefore, troubleshooting must move from primary diagnostics to secondary diagnostics.
8Test Equipment
The investigation used:
- True-RMS multimeter.
- Clamp meter.
- Secondary voltage test equipment.
- Continuity tester.
- Low-resistance ohmmeter.
- Thermal imaging camera.
- Approved AGL circuit test equipment.
- Circuit drawings.
- Airport-approved PPE.
9Investigation
Step 1: Verify CCR Operation
Results:
| Current regulation | Normal |
| Voltage regulation | Normal |
| CCR alarms | None |
| Output stability | Normal |
The CCR was confirmed healthy.
Step 2: Verify Primary Circuit
Primary measurements confirmed:
- Circuit continuity.
- Stable current.
- Normal voltage distribution.
The primary series circuit was healthy.
Step 3: Transformer Primary Verification
The affected transformers showed:
| Primary current | Present |
| Primary continuity | Normal |
Primary power was reaching the transformers.
Step 4: Transformer Secondary Testing
Several transformers showed:
- No secondary voltage.
- Open secondary connection.
- Intermittent continuity.
The problem was localized to the secondary side.
Step 5: Connector Inspection
Inspection of the field pit revealed:
- Disconnected secondary connector.
- Corroded contacts.
- Moisture contamination.
- Damaged locking mechanism.
- Multiple secondary circuits affected.
The connector assembly had failed mechanically and electrically.
Step 6: Secondary Cable Verification
The secondary cables remained healthy.
The primary fault was the connector assembly, not the cable.
10Root Cause
The CCR was completely healthy.
The field lights were not operating because multiple transformer secondary circuits had become disconnected by a failed connector assembly inside a field pit.
The primary series circuit remained intact, allowing the CCR to regulate current normally.
The secondary power distribution was interrupted.
11Corrective Action
The maintenance team:
- Isolated the circuit.
- Removed the damaged connector assembly.
- Installed new approved connectors.
- Verified connector locking.
- Restored secondary continuity.
- Performed voltage verification.
- Tested field-light operation.
- Conducted thermal inspection.
- Restored the circuit.
- Updated maintenance records.
12Post-Repair Verification
All affected runway edge lights returned to service.
13Root-Cause Analysis
Field lights not operating
Healthy
Healthy
Power available
No output
Disconnection identified
Failed secondary connector assembly
Replace connector and restore secondary continuity
14Why This Case Was Important
A common maintenance error is stopping the investigation after confirming that the CCR is healthy.
Field-light failures frequently occur in:
- Secondary connectors.
- Transformer secondary circuits.
- Secondary cables.
- Field fixtures.
Primary and secondary systems must be diagnosed separately.
15Engineering Lessons
A healthy CCR does not guarantee healthy field lights.
A healthy CCR does not guarantee healthy field lights.
Primary and secondary circuits require independent verification.
Primary and secondary circuits require independent verification.
Connector failures can disable multiple field lights simultaneously.
Connector failures can disable multiple field lights simultaneously.
Secondary voltage testing is essential during field investigations.
Secondary voltage testing is essential during field investigations.
Systematic fault localization prevents unnecessary CCR replacement.
Systematic fault localization prevents unnecessary CCR replacement.
16Engineer's Decision Point
You observe: CCR healthy. Selected current maintained. No CCR alarms. One runway section dark. What should you investigate first?
17Knowledge Check
18Interview Questions
Quick Reference: CCR Healthy but Lights Not Working
When people search for a CCR not working airport fault, the CCR is often fine. If the CCR output current and voltage are normal and there are no alarms, the problem is in the field. For a runway light not working or a taxiway light not working, check the fixture, transformer secondary and connector first. If a whole group is dark, check the circuit for an open or a failed section.
19Frequently Asked Questions
Quick answers about field lights failing while the CCR is healthy, based on this case study.
Q1What is AGL-CS-038?
AGL-CS-038 is an engineering training case study on a section of runway edge lights that did not work even though the CCR was healthy. It is an engineering simulation created for training, not a report of an actual airport incident.
Q2How can field lights fail when the CCR is healthy?
Normal CCR operation only confirms that the primary series circuit is intact. Here the CCR maintained 6.6 A with normal voltage and no alarms, but the secondary power distribution to the lights was interrupted.
Q3What was the root cause?
A failed connector assembly inside a field pit disconnected multiple isolating transformer secondary circuits. The primary series circuit remained intact, so the CCR regulated current normally.
Q4What should you investigate first?
Verify transformer secondary voltage and inspect secondary connectors and cables. Replacing the CCR, increasing the current setting or replacing all field fixtures is not the right first step.
Q5Which test equipment was used?
The team used a true-RMS multimeter, clamp meter, secondary voltage test equipment, continuity tester, low-resistance ohmmeter, thermal imaging camera and circuit drawings.
Q6How was the circuit repaired?
The team isolated the circuit, removed the damaged connector assembly and installed new approved connectors. They verified connector locking, restored secondary continuity, performed voltage verification, tested light operation, conducted thermal inspection and restored the circuit.
Q7How was the repair verified?
The primary circuit was normal, secondary voltage was restored, connector integrity was verified and all affected runway edge lights returned to service.
Q8What is the key lesson?
Do not stop at the CCR when the CCR is healthy. Separate the primary and secondary circuits and check secondary voltage and connectors to find why the lights are not working.
Engineering & Expert Notes
Test Primary and Secondary Separately
MethodA healthy CCR and intact primary loop do not guarantee secondary power. Check at the secondary.
Inspect Shared Connector Assemblies
Common CauseOne failed assembly feeding several secondaries explains multiple dead lights.
Measure Secondary Voltage at the Fixture
VerificationThis quickly confirms whether power reaches the light.
Understand How the Pit Is Wired
LayoutKnowing which items share a connector assembly shapes the search.
20Case Study Conclusion
A healthy CCR confirms proper primary current regulation but does not guarantee that power is reaching the field lights through the transformer secondary circuits, connectors, cables, and fixtures.
Systematic CCR verification, primary circuit confirmation, transformer secondary testing, connector inspection, secondary continuity testing, and field voltage verification can accurately identify secondary-side failures and restore reliable airfield lighting operation.
In AGL engineering, a healthy CCR tells you where the fault is not; the field circuit tells you where the fault is.
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