AGL-CS-057 — Taxiway lighting configuration error
The AGL Knowledge Hub | Engineering Case Study Series. A taxiway lighting investigation where operational route selection illuminated the wrong taxiway — from CCR verification through circuit assignment review, field identification inspection, switching-group verification, and commissioning record 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
Following commissioning of a newly modified taxiway lighting circuit, pilots reported incorrect taxiway guidance indications during night operations.
Several taxiway centreline lights illuminated when a different taxi route was selected, while part of the intended taxiway remained dark.
The Constant Current Regulator (CCR) was operating normally, all fixtures were functional, and no electrical faults were present.
Because the lighting operated electrically but did not match the intended taxiway routing configuration, a detailed configuration investigation was initiated covering circuit assignments, switching groups, fixture identification, control logic, and taxiway routing verification.
The investigation identified incorrect field-circuit configuration and fixture-group assignment during commissioning, which caused multiple taxiway lighting groups to operate in the wrong configuration.
This case demonstrates that taxiway lighting configuration errors can create operational guidance hazards even when the electrical installation is fully functional.
2Learning objectives
After completing this case study, the learner should be able to:
- Diagnose taxiway lighting configuration errors.
- Verify fixture-to-circuit assignments.
- Check switching group configuration.
- Validate taxiway routing logic.
- Inspect field identification and labeling.
- Perform commissioning verification.
- Restore correct taxiway operational guidance.
3System background
A taxiway lighting control system includes:
- CCR circuits.
- Switching groups.
- Field circuit assignments.
- Taxiway edge lights.
- Taxiway centreline lights.
- Lead-on and lead-off lights.
- Stop bars.
- Control logic.
- A-SMGCS interfaces.
Configuration errors may result from:
- Incorrect circuit assignment.
- Wrong fixture numbering.
- Incorrect cable termination.
- Switching-group programming errors.
- Control-system mapping errors.
- Documentation discrepancies.
- Commissioning mistakes.
4Problem statement
The reported condition was:
- Taxiway lighting functional.
- Wrong taxi route illuminated.
- Intended route partially dark.
- CCR healthy.
- No electrical alarms.
- Pilot guidance complaints.
Is the taxiway lighting electrically faulty, or has the lighting configuration been assigned incorrectly?
5Initial observations
| CCR status | Healthy |
| Circuit continuity | Normal |
| Fixture operation | Functional |
| Route selection | Incorrect response |
| Switching behavior | Incorrect |
| Pilot reports | Negative |
The lighting was operating, but the operational configuration was incorrect.
6Initial engineering hypotheses
The maintenance team considered:
Fixture failure.
CCR malfunction.
Incorrect circuit assignment.
Control logic programming error.
Field identification error.
7Configuration error principle
Correct configuration:
Incorrect configuration:
Configuration errors affect system behavior rather than electrical continuity.
8Test equipment
The investigation used:
- Taxiway circuit drawings.
- CCR circuit schedules.
- Control-system configuration data.
- Fixture identification records.
- Multimeter.
- Circuit tracer.
- Switching verification equipment.
- Approved AGL commissioning tools.
- Airport-approved PPE.
9Investigation
Step 1: Verify electrical operation
Results:
| CCR operation | Normal |
| Current regulation | Normal |
| Circuit continuity | Normal |
| Fixture functionality | Normal |
No electrical fault was identified.
Step 2: Operational route verification
ATC selected:
Taxi Route B
Observed:
- Taxiway C centreline illuminated.
- Part of Taxiway B remained dark.
- Incorrect lead-off section energized.
The operational response was incorrect.
Step 3: Circuit assignment verification
Comparison of field records and circuit drawings showed:
| Circuit | Intended | Actual |
| TCL-B1 | Taxiway B | Taxiway C |
| TCL-C1 | Taxiway C | Taxiway B |
Two centreline circuit groups had been interchanged.
Step 4: Field identification inspection
Inspection revealed:
- Incorrect field labels.
- Swapped cable identification.
- Transformer group numbering error.
- Inconsistent commissioning records.
The field identification process was defective.
Step 5: Switching-group verification
Control-system testing showed:
- Incorrect output mapping.
- Wrong switching-group assignment.
- Route-selection logic using incorrect field groups.
The control logic matched the incorrect field assignments.
Step 6: Commissioning record review
The review identified:
- Cable termination changes.
- Incomplete as-built documentation.
- Unverified field testing.
- Missing route-verification checklist.
The configuration error originated during commissioning.
10Root cause
The taxiway lighting configuration error was caused by incorrect field-circuit assignment and switching-group configuration during commissioning, resulting in taxiway centreline lighting groups operating on the wrong taxiway routing commands.
The electrical installation was healthy, but the operational configuration was incorrect.
11Corrective action
The maintenance team:
- Verified field circuit identification.
- Corrected cable terminations.
- Restored proper fixture numbering.
- Corrected switching-group assignments.
- Updated control-system mapping.
- Verified taxiway routing logic.
- Conducted operational route testing.
- Updated as-built documentation.
- Performed ATC verification.
- Completed commissioning documentation.
12Post-repair verification
All taxiway routes illuminated correctly.
13Root-cause analysis
Incorrect taxiway guidance
Healthy
Incorrect response
Interchanged
Incorrect
Commissioning configuration error
Restore correct circuit and control assignments
14Why this case was important
Configuration errors can cause:
- Incorrect taxi guidance.
- Wrong route indication.
- Pilot confusion.
- ATC operational restrictions.
- A-SMGCS conflicts.
- Commissioning delays.
- ICAO compliance issues.
Operational verification is as important as electrical testing.
15Engineering lessons
A healthy circuit can still provide incorrect taxi guidance.
A healthy circuit can still provide incorrect taxi guidance.
Circuit assignment verification is essential during commissioning.
Circuit assignment verification is essential during commissioning.
Switching-group testing should include operational route verification.
Switching-group testing should include operational route verification.
Field identification errors can create major operational problems.
Field identification errors can create major operational problems.
As-built documentation must be verified before handover.
As-built documentation must be verified before handover.
16Engineer's decision point
You observe: Taxiway lights operational. Wrong taxi route illuminated. CCR healthy. No electrical faults. What should you investigate first?
17Knowledge check
18Interview questions
19Frequently Asked Questions
Quick answers about taxiway lighting configuration errors, based on this case study.
Q1What is AGL-CS-057?
AGL-CS-057 is an engineering training case study on a taxiway lighting configuration error found after commissioning a modified circuit. It is an engineering simulation created for training, not a report of an actual airport incident.
Q2What did pilots report?
Pilots reported incorrect guidance at night: taxiway centreline lights came on for a route other than the one selected, while part of the intended taxiway stayed dark. The CCR was normal, all fixtures worked and there were no electrical faults.
Q3Was the lighting electrically faulty?
No. The electrical installation was healthy, but the operational configuration was incorrect. The lighting operated but did not match the intended taxiway routing.
Q4What was the root cause?
Incorrect field-circuit assignment and switching-group configuration during commissioning, so centreline lighting groups operated on the wrong taxiway routing commands.
Q5What should you investigate first?
Verify circuit assignments, switching groups, control-system mapping and the operational route configuration. Replacing the CCR or taxiway fixtures, or increasing the current setting, is not the right first step.
Q6Which records and tools were used?
The team used taxiway circuit drawings, CCR circuit schedules, control-system configuration data, fixture identification records, a multimeter, a circuit tracer, switching verification equipment and approved AGL commissioning tools.
Q7How was the configuration corrected?
The team verified field circuit identification, corrected cable terminations, restored proper fixture numbering and corrected switching-group assignments. They updated control-system mapping, verified routing logic, conducted route testing, updated as-built documentation, performed ATC verification and completed commissioning documentation.
Q8How was the correction verified?
Circuit assignment, switching groups and route selection were correct, taxiway guidance was correct and documentation was updated. All taxiway routes illuminated correctly.
Engineering & Expert Notes
Test Switching Groups Against the Route Plan
CommissioningCommand each route from the control point and walk the airfield to confirm the right lights come on.
Verify Circuit and Field Labels Before Energising
IdentificationMislabelled circuits cause assignment errors. Check labels against drawings and physical routing.
Include Operations in the Acceptance Test
OperationsControllers see the airfield differently. Their check confirms the lighting matches the intended routing.
Update Configuration Records After Any Correction
RecordsKeep the control database and drawings aligned so errors are not reintroduced.
20Case study conclusion
Taxiway lighting configuration errors are operational-control problems caused by incorrect circuit assignments, switching-group mapping, and commissioning verification, and they can create significant taxi guidance hazards even when the electrical installation is fully functional.
Systematic circuit-assignment verification, switching-group testing, route-validation checks, field identification inspection, control-system mapping review, and operational commissioning verification can identify configuration errors before they affect aircraft ground operations.
In AGL engineering, a taxiway light that illuminates at the wrong time can be more dangerous than a taxiway light that does not illuminate at all.
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