Taxiway Centreline / Guidance Lighting Troubleshooting

Equipment / System

Taxiway Centreline Lights (TCL) — inset, green L-852E in-pavement fixtures embedded along the taxiway centreline at standard spacing, fed via individual isolation transformers off a dedicated taxiway centreline series circuit, in-pavement base cans (L-867), primary series cable loop back to the CCR.

Possible Causes

Required Tools

Safety Precautions

• Coordinate all airside access through ATC/apron control before approaching a fixture on an active taxiway.
• Treat the series circuit as energised until confirmed isolated at the CCR and locked out.
• Use FOD-safe tools and account for every item before leaving the pavement.

Diagnostic Procedure

1. ObservationCheck the ALCMS/CCR panel to see whether this is a single light or part of a wider dark section, and confirm actual current output of the affected TCL series circuit.
2. ObservationConfirm with a taxiway inspection whether only the reported fixture is affected or a longer run beyond it is also out — a single dark light with the rest of the run lit points to that fixture; a dark run points to the loop upstream of it.
3. MeasurementWith the circuit isolated and LOTO applied, disconnect the fixture's L-823 plug and megger the isolation transformer primary and secondary windings.
4. MeasurementInspect the base can for water, debris, or a displaced/damaged connector, and check the lamp/LED module for visible failure.
5. DecisionTransformer or lamp confirmed faulty at this fixture only → isolated single-fixture fault, proceed under TCL-242. Fault traces onto the primary loop or affects multiple fixtures → route to TCL-254.
6. Fault LocationIsolate the fault to the fixture (transformer, lamp, connector) or to the series cable loop feeding it.
7. Root CauseConfirm the specific failed component before replacement rather than swapping parts speculatively.

Test Points

Root Cause Verification

After repair, re-energise the circuit, confirm the fixture lights at all intensity steps, and inspect the full run at night to confirm no adjacent lights were disturbed during access.

Corrective Action

• Replace the failed isolation transformer or lamp/LED module.
• Reseat or replace a corroded/damaged L-823 connector.
• Repair the identified series cable fault.
• Restore CCR output if the root cause was upstream rather than the fixture.

Preventive Action

• Include TCL fixture and connector inspection in the routine night flight-check and periodic maintenance cycle.
• Megger the series circuit periodically given continuous ground-traffic loading.
• Maintain an accurate base-can and circuit layout drawing to speed fault location.

Related References

SOP: SOP-TCL-01 (TCL Fault Isolation Procedure), SOP-CCR-04 (CCR LOTO Procedure)

Standards: ICAO Annex 14 Vol I, FAA AC 150/5340-30, FAA AC 150/5345-46 (L-852)

Diagram: TCL circuit layout drawing, base-can schedule

Case Study: Division 01 — CCR Troubleshooting (verify series circuit output); Division 24 — Complete Runway Lighting Failure

Equipment / System

TCL fixture, isolation transformer, and lens/optic assembly on the taxiway centreline series circuit.

Possible Causes

Required Tools

Safety Precautions

• LOTO the circuit before removing or cleaning a lens or accessing the fixture interior.
• Allow the fixture to cool before handling if recently energised at a high intensity step.

Diagnostic Procedure

1. ObservationCompare the reported fixture's apparent brightness against neighbouring fixtures at the same commanded step, ideally with a luminance meter.
2. MeasurementConfirm the series circuit current at the CCR matches the correct value for the commanded intensity step, to rule out a circuit-wide cause.
3. ObservationInspect the lens for fuel/oil residue, rubber deposit build-up, scratching, or degradation.
4. MeasurementWith the circuit isolated, check the isolation transformer secondary output and confirm its rated wattage/tap matches the design.
5. DecisionCircuit current correct and lens clean but output still low → transformer or lamp/LED degradation. Lens found contaminated → clean first and re-check before replacing parts.
6. Fault LocationIsolate to lens contamination, transformer output, or lamp/LED degradation.
7. Root CauseConfirm with a before/after luminance reading once the identified cause is addressed.

Test Points

Root Cause Verification

Re-measure luminance output after corrective action and compare against neighbouring fixtures and the manufacturer's rated output for the commanded step.

Corrective Action

• Clean the lens using a fuel/rubber-deposit-rated method.
• Replace an isolation transformer with an incorrect or degraded rating.
• Replace a degraded lamp/LED module.
• Coordinate with apron/taxiway cleaning teams if fuel or oil spillage is the primary cause.

Preventive Action

• Include TCL lens cleaning in the taxiway/apron cleaning cycle given fuel-spill and rubber deposit exposure.
• Verify transformer rating matches the specified lamp/LED module at every replacement.
• Track luminance readings over time to catch gradual degradation before it becomes a reported fault.

Related References

SOP: SOP-TCL-02 (Lens Cleaning and Inspection Procedure)

Standards: ICAO Annex 14 Vol I (light intensity requirements), FAA AC 150/5340-30

Diagram: TCL Photometric Specification Sheet

Case Study: Division 26 — Photometric & Intensity Compliance

Equipment / System

TCL fixture, isolation transformer, connector, and the series circuit supplying it.

Possible Causes

Required Tools

Safety Precautions

• Treat intermittent faults as live until proven otherwise.
• LOTO the circuit before opening any base can even if the light appears steady at the time of access.

Diagnostic Procedure

1. ObservationConfirm whether the flicker is on a single fixture or several, and whether it correlates with a particular intensity step, ground-traffic movement, or weather condition.
2. MeasurementLog CCR output current over a period spanning the reported flicker to rule out a source-side instability.
3. MeasurementWith the circuit isolated, inspect and re-torque the L-823 connector, and megger the isolation transformer under light mechanical flexing to try to reproduce an intermittent fault.
4. MeasurementUse thermal imaging on the connector and transformer during a live period to spot a hot connection consistent with intermittent high resistance.
5. DecisionFlicker follows CCR current logging → CCR/source-side issue, route to Division 01. Flicker isolated to the fixture and reproducible by flexing the connector → connector or transformer fault.
6. Fault LocationIsolate to the connector, transformer, lamp/LED module, or cable.
7. Root CauseConfirm by replacing the suspect component and re-testing under conditions that previously produced the flicker.

Test Points

Root Cause Verification

Monitor the repaired fixture over several operating cycles, including varying intensity steps, before closing out.

Corrective Action

• Clean, re-grease, and properly seat the L-823 connector.
• Replace a transformer confirmed to have an intermittent internal fault.
• Replace a failing lamp/LED module.
• Repair the identified intermittent cable fault.

Preventive Action

• Torque-check connectors as a standard PM step given continuous ground-traffic vibration exposure.
• Include thermal imaging of connectors and transformers in the periodic PM cycle.
• Trend CCR output logs to distinguish source-side from fixture-side intermittent issues early.

Related References

SOP: SOP-TCL-01 (TCL Fault Isolation Procedure)

Standards: FAA AC 150/5345-46 (L-852 series), ICAO Annex 14 Vol I

Diagram: TCL circuit layout drawing

Case Study: Division 01 — CCR Troubleshooting (intensity step control)

Equipment / System

TCL fixture lens/filter assembly and lamp/LED colour source at a specific chainage along the centreline, lead-on, or lead-off zone.

Possible Causes

Required Tools

Safety Precautions

• LOTO the circuit before fixture access.
• Treat a confirmed wrong-colour fixture as a safety-critical discrepancy pending correction, since it can be misread as an incorrect guidance cue by flight crew or vehicle operators; notify airfield operations.

Diagnostic Procedure

1. ObservationConfirm the reported colour against the as-built drawing for that exact chainage — straight TCL, lead-on, lead-off, or RET zone.
2. MeasurementInspect the fixture's lens/filter and lamp/LED part number against the maintenance specification for that location.
3. ObservationCheck lens integrity (cracking, missing lens) and confirm the lamp/LED source colour independent of the lens.
4. DecisionWrong lens/filter part installed → replace with correct part. Fixture installed at the wrong chainage relative to the zone boundary → relocate/reprogram per the zone drawing.
5. Fault LocationIsolate the discrepancy to the lens/filter, the lamp/LED source, or the fixture's physical position relative to the colour-sequence zone.
6. Root CauseVerify chromaticity meets the ICAO Annex 14 Vol I colour boundary for the specified colour after correction.

Test Points

Root Cause Verification

Re-check chromaticity after correction and confirm visually against neighbouring fixtures in the same colour-sequence zone at night.

Corrective Action

• Replace with the correct coloured lens/filter or fixture assembly for the specified zone.
• Relocate or reposition a fixture installed at the wrong chainage.
• Notify airfield operations/NOTAM if the discrepancy affected published guidance information.

Preventive Action

• Verify part numbers against the zone-specific specification sheet before any bulk lens/filter replacement.
• Include colour verification in the periodic night inspection.
• Maintain accurate lead-on/lead-off zone colour-sequence drawings.

Related References

SOP: SOP-TCL-04 (Colour Verification Procedure)

Standards: ICAO Annex 14 Vol I (colour specifications), FAA AC 150/5345-46

Diagram: Lead-On/Lead-Off Zone Colour Layout Drawing

Case Study: Division 26 — Photometric & Intensity Compliance

Equipment / System

TCL fixture and its feeding connector, transformer, base can, and cable segment.

Possible Causes

Required Tools

Safety Precautions

• LOTO the circuit before opening any base can, even if the fixture is currently dark and appears de-energised.
• Treat the circuit as energised until confirmed isolated at the CCR.

Diagnostic Procedure

1. ObservationLog the occurrence pattern — time of day, temperature, and any correlation with ground-traffic movement or weather.
2. MeasurementWith the circuit isolated, inspect and re-seat the L-823 connector and open the base can to check for moisture.
3. MeasurementMegger the isolation transformer and cable segment under light mechanical disturbance to attempt to reproduce the fault.
4. MeasurementCheck the CCR output terminal for the affected circuit is properly torqued.
5. DecisionFault reproduced by flexing the connector or transformer → component-level intermittent fault. Fault not reproduced but base can shows moisture → treat as a developing water-ingress fault (TCL-247).
6. Fault LocationIsolate to the connector, transformer, cable joint, or CCR terminal.
7. Root CauseConfirm by monitoring across several day/night and thermal cycles before closing out.

Test Points

Root Cause Verification

Monitor the fixture across several operating and thermal cycles after repair before closing out the fault as resolved.

Corrective Action

• Reseat or replace the connector.
• Replace the transformer with the confirmed intermittent fault.
• Repair the identified cable joint.
• Dry and reseal the base can; re-torque the CCR output terminal.

Preventive Action

• Standardise connector torque and seating checks in the PM cycle.
• Specify moisture-proof base can seals in higher-traffic sections.
• Include periodic CCR terminal torque checks.

Related References

SOP: SOP-TCL-01 (TCL Fault Isolation Procedure)

Standards: ICAO Annex 14 Vol I, FAA AC 150/5340-30

Diagram: TCL circuit layout drawing

Case Study: Division 01 — CCR Troubleshooting

Equipment / System

TCL in-pavement fixture and its base can mounting relative to the designed taxiway centreline geometry.

Possible Causes

Required Tools

Safety Precautions

• Coordinate airside access through ATC/apron control before working on an active taxiway.
• LOTO the circuit before fixture removal.
• Confirm no aircraft or vehicle movement is scheduled through the work area for the duration of the repair.

Diagnostic Procedure

1. ObservationSurvey the fixture position against the design centreline chainage and offset.
2. ObservationWhere practical, visually confirm the beam direction is off the guidance line by observing from an approach angle representative of an approaching aircraft or vehicle.
3. MeasurementInspect the base can for rotation, tilt, or settlement relative to its as-installed position.
4. DecisionBase can position correct but beam rotated within the can → realign fixture in place. Base can itself displaced or settled → coordinate reset with civil works.
5. Fault LocationIsolate the misalignment to the fixture orientation within the base can, or to the base can position itself.
6. Root CauseConfirm the corrected position matches the design chainage/offset by re-survey.

Test Points

Root Cause Verification

Re-survey the fixture after correction and confirm visual alignment along the taxiway during a night inspection.

Corrective Action

• Re-set or realign the base can to the design position.
• Correct fixture orientation within an otherwise correctly positioned base can.
• Coordinate with civil works if pavement settlement is the underlying cause.

Preventive Action

• Verify fixture position and orientation as part of post-paving reinstatement checks.
• Include alignment spot-checks in the periodic inspection cycle.
• Track settlement-prone sections for ongoing monitoring.

Related References

SOP: SOP-TCL-05 (Fixture Alignment Verification Procedure)

Standards: ICAO Annex 14 Vol I, FAA AC 150/5340-30

Diagram: TCL Centreline Geometry Drawing

Case Study: Division 25 — Field Case Study Troubleshooting

Equipment / System

TCL base can, L-823 connector, and isolation transformer housing.

Possible Causes

Required Tools

Safety Precautions

• LOTO the circuit before opening the base can.
• Treat standing water in an electrical enclosure as energised until the circuit is confirmed isolated and verified de-energised.

Diagnostic Procedure

1. ObservationIsolate the circuit and open the base can to visually confirm water presence and level.
2. MeasurementMegger the transformer and fixture to assess whether moisture has compromised insulation.
3. ObservationInspect the gasket, connector boot, and can body to identify the ingress path.
4. DecisionInsulation resistance within acceptable limits after draining → dry, reseal, and monitor. Insulation resistance remains low after drying → component-level moisture damage, replace affected parts.
5. Fault LocationIsolate the ingress path to the gasket/seal, the can body, the connector boot, or local drainage.
6. Root CauseConfirm with a re-megger after drying and reseal, and monitor through the next rainfall event before closing out.

Test Points

Root Cause Verification

Re-megger after drying and reseal, and monitor through the next rainfall event before closing out.

Corrective Action

• Pump out and dry the base can.
• Replace the gasket or seal.
• Replace a damaged connector boot.
• Repair local drainage or grading if pooling is contributing.

Preventive Action

• Include base can seal condition in the periodic maintenance cycle.
• Prioritise low-point sections identified from drainage surveys for inspection.
• Use sealant rated for the local climate and freeze-thaw exposure.

Related References

SOP: SOP-TCL-06 (Base Can Moisture Inspection Procedure)

Standards: FAA AC 150/5345-46, ICAO Annex 14 Vol I

Diagram: TCL Base-Can Detail Drawing

Case Study: Division 25 — Field Case Study Troubleshooting

Equipment / System

TCL fixture lens, prism, and optical housing.

Possible Causes

Required Tools

Safety Precautions

• LOTO the circuit before lens or optic replacement.
• Treat broken lens fragments as a FOD hazard and account for every piece before leaving the pavement.

Diagnostic Procedure

1. ObservationVisually inspect the lens/prism for cracking, cloudiness, or displacement.
2. MeasurementCompare the observed beam pattern against the design spread using a field beam-check where available.
3. ObservationConfirm the installed lens/optic part number matches the specification for that fixture type.
4. DecisionLens/optic damaged or clouded → replace with the correct rated part. Correct part but housing itself deformed/cracked → replace the full fixture.
5. Fault LocationIsolate the defect to the lens, prism, or the optical housing.
6. Root CauseConfirm with a post-repair beam check that the corrected fixture matches the design spread and intensity.

Test Points

Root Cause Verification

Re-inspect and beam-check after lens/optic replacement, and confirm no fragments remain in the pavement area.

Corrective Action

• Replace the cracked or degraded lens/prism.
• Correct a mismatched optic with the correctly rated part.
• Replace the full fixture if the optical housing itself is damaged.

Preventive Action

• Verify replacement lens/optic part numbers against the fixture specification before installation.
• Include lens condition in the periodic visual inspection.
• Review de-icing fluid application practice near in-pavement fixtures.

Related References

SOP: SOP-TCL-07 (Optical Assembly Inspection Procedure)

Standards: FAA AC 150/5345-46 (L-852), ICAO Annex 14 Vol I Appendix 2

Diagram: TCL Photometric Specification Sheet

Case Study: Division 26 — Photometric & Intensity Compliance

Equipment / System

Lead-on lights — green (or alternating green/yellow within a runway crossing zone) in-pavement lights extending from the runway exit onto the taxiway, fed off the taxiway centreline series circuit or a dedicated lead-on section, individual isolation transformers, in-pavement base cans.

Possible Causes

Required Tools

Safety Precautions

• Coordinate airside access via ATC given proximity to the active runway exit.
• LOTO the circuit/section before work.
• Treat the runway-adjacent end of the lead-on run as within the runway strip safety area, requiring runway protection procedures.

Diagnostic Procedure

1. ObservationConfirm from ALCMS/CCR and a runway inspection whether the fault is isolated to a single lead-on fixture or the whole lead-on run.
2. MeasurementCheck whether the lead-on section has its own isolator/tie point and confirm it is closed and passing current.
3. MeasurementWith the circuit isolated, megger the affected fixture's transformer and inspect its connector.
4. ObservationInspect for a colour-phase-specific fixture fault if an alternating green/yellow pattern is specified for that section.
5. DecisionFault isolated to one fixture → replace the failed component. Fault affects the whole lead-on run → check the section isolator/tie point first.
6. Fault LocationIsolate to the fixture (transformer, lamp, connector) or to the lead-on section isolator/tie point.
7. Root CauseConfirm the specific failed component before replacement.

Test Points

Root Cause Verification

Re-energise and confirm the full lead-on run illuminates correctly in the correct colour sequence, cross-checked against the zone drawing.

Corrective Action

• Replace the failed transformer, lamp, or connector.
• Close or repair a faulted section isolator.
• Correct a fixture installed with the wrong colour lens for its phase position.

Preventive Action

• Prioritise the lead-on run in periodic inspection given its role in runway exit guidance.
• Verify isolator/tie point integrity during PM.
• Maintain an accurate lead-on zone colour-sequence drawing.

Related References

SOP: SOP-TCL-08 (Lead-On/Lead-Off Light Fault Isolation Procedure)

Standards: ICAO Annex 14 Vol I, FAA AC 150/5340-30, FAA AC 150/5345-46

Diagram: Lead-On/Lead-Off Zone Colour Layout Drawing

Case Study: Division 24 — Complete Runway Lighting Failure

Equipment / System

Lead-off lights — alternating green/yellow in-pavement lights guiding an aircraft from the runway centreline onto the taxiway centreline at an exit, continuing the alternating pattern to a defined point before reverting to steady green taxiway centreline lighting.

Possible Causes

Required Tools

Safety Precautions

• Coordinate airside access via ATC — lead-off lights sit within the runway exit path with active aircraft movement.
• LOTO the circuit/section before work.
• Use runway protection procedures for any fixture within the runway strip.

Diagnostic Procedure

1. ObservationConfirm from ALCMS/CCR and inspection whether the fault is isolated to a single lead-off fixture or the alternating pattern is broken across the run.
2. MeasurementCheck the section isolator/tie point for the lead-off run.
3. MeasurementWith the circuit isolated, megger the affected fixture's transformer and inspect its connector.
4. ObservationConfirm the correct green/yellow colour sequence against the zone drawing.
5. DecisionFault isolated to one fixture → replace the failed component. Colour sequence reversed or incorrect → correct the lens/filter.
6. Fault LocationIsolate to the fixture, the section isolator/tie point, or a lens/colour-sequence error.
7. Root CauseConfirm the specific failed component or colour discrepancy before correction.

Test Points

Root Cause Verification

Re-energise and walk/drive the full lead-off run to confirm the correct alternating colour sequence is restored, cross-checked at night.

Corrective Action

• Replace the failed transformer, lamp, or connector.
• Close or repair a faulted section isolator.
• Correct a reversed or mismatched colour lens.

Preventive Action

• Prioritise the lead-off run in periodic inspection given its runway-exit guidance role.
• Verify colour sequence during PM walk-throughs.
• Maintain accurate zone colour-sequence drawings.

Related References

SOP: SOP-TCL-08 (Lead-On/Lead-Off Light Fault Isolation Procedure)

Standards: ICAO Annex 14 Vol I, FAA AC 150/5340-30, FAA AC 150/5345-46

Diagram: Lead-On/Lead-Off Zone Colour Layout Drawing

Case Study: Division 24 — Complete Runway Lighting Failure

Equipment / System

TCL fixtures on a taxiway curve section, installed at reduced spacing per the curve radius to maintain continuous visual guidance through the turn.

Possible Causes

Required Tools

Safety Precautions

• Coordinate airside access; curve sections often coincide with higher ground-traffic density at taxiway junctions or runway exits.
• LOTO the circuit before work.

Diagnostic Procedure

1. ObservationConfirm from ALCMS/CCR and inspection how many and which curve fixtures are affected.
2. MeasurementAssess whether the resulting dark gap exceeds the guidance continuity tolerance for the curve radius.
3. MeasurementWith the circuit isolated, megger the affected fixture(s).
4. ObservationInspect base can condition for wear-related displacement.
5. DecisionGap within tolerance and isolated to one fixture → standard fixture-level repair. Gap exceeds tolerance or multiple adjacent fixtures affected → treat as priority repair given reduced guidance margin on the curve.
6. Fault LocationIsolate to the affected fixture(s) or to base can/spacing issues along the curve.
7. Root CauseConfirm restoration of continuous guidance by night inspection after repair.

Test Points

Root Cause Verification

Re-energise and confirm the curve section presents a continuous, evenly spaced light line at night, with no gap exceeding tolerance.

Corrective Action

• Replace the failed transformer, lamp, or connector.
• Reset a settled base can.
• Restore design spacing if a previous repaving altered fixture positions.

Preventive Action

• Prioritise curve sections in periodic inspection given the tighter guidance tolerance.
• Monitor base can condition on high-turning-load curves.
• Verify spacing is restored to design after any repaving.

Related References

SOP: SOP-TCL-09 (Curve/High-Density Section Inspection Procedure)

Standards: ICAO Annex 14 Vol I, FAA AC 150/5340-30

Diagram: TCL Curve Section Spacing Drawing

Case Study: Division 25 — Field Case Study Troubleshooting

Equipment / System

Rapid Exit Taxiway (RET) centreline and lead-off lighting — the curved, high-speed turnoff geometry lit with a lead-off light pattern designed for higher-speed exit from the runway, typically including the alternating colour sequence and closer curve spacing through the turnoff radius.

Possible Causes

Required Tools

Safety Precautions

• Coordinate airside access with heightened priority given RET use during active landing operations.
• LOTO the circuit before work.
• Use runway protection procedures for the runway-adjacent portion of the RET.

Diagnostic Procedure

1. ObservationConfirm from ALCMS/CCR and inspection the extent of the fault along the RET run.
2. MeasurementAssess against the RET's higher guidance-continuity requirement given exit speed.
3. MeasurementWith the circuit isolated, megger affected fixtures and the section isolator.
4. ObservationInspect base cans for wear-related faults from higher-speed loading.
5. DecisionFault isolated to one or two fixtures within tolerance → standard repair. Fault breaks guidance continuity through the curve or affects the isolator → treat as priority given reduced runway occupancy margin.
6. Fault LocationIsolate to the fixture(s), the section isolator/tie point, or drainage-related base can damage.
7. Root CauseConfirm restoration of continuous guidance by night inspection before returning the RET to service.

Test Points

Root Cause Verification

Re-energise and confirm the full RET run — straight and curved portions — presents correct, continuous guidance lighting at night before returning the RET to service.

Corrective Action

• Replace the failed transformer, lamp, or connector.
• Close or repair a faulted section isolator.
• Address drainage or wear issues contributing to repeat faults.

Preventive Action

• Prioritise the RET in periodic inspection given its role in higher-speed runway exit and reduced runway occupancy time.
• Monitor base can condition given elevated mechanical loading.
• Verify drainage at low points along the RET.

Related References

SOP: SOP-TCL-10 (RET Lighting Inspection Procedure)

Standards: ICAO Annex 14 Vol I, FAA AC 150/5340-30 (RET design guidance)

Diagram: RET Geometry & Colour Sequence Drawing

Case Study: Division 24 — Complete Runway Lighting Failure

Equipment / System

High-speed taxiway centreline lighting — the longer connecting taxiway route beyond an RET or standard exit curve, lit to the same guidance continuity standard given the aircraft's elevated speed over a greater distance.

Possible Causes

Required Tools

Safety Precautions

• Coordinate airside access; account for the longer route length when planning inspection/repair time against available circuit-outage windows.
• LOTO the circuit before work.

Diagnostic Procedure

1. ObservationConfirm from ALCMS/CCR and a full-route inspection how many fixtures and what pattern of outage is present.
2. MeasurementDistinguish an isolated cluster from a circuit-wide (source-side) fault by checking CCR output.
3. MeasurementWith the circuit isolated, megger the affected section(s).
4. ObservationInspect for a fault pattern correlating with recent pavement maintenance activity.
5. DecisionIsolated cluster of fixture faults → standard multi-fixture repair. Fault correlates with CCR output or recent excavation → route to circuit-level investigation (TCL-254).
6. Fault LocationIsolate to the affected fixture cluster, cable segment, or the CCR source.
7. Root CauseConfirm restoration of continuous, evenly spaced guidance lighting along the full route after repair.

Test Points

Root Cause Verification

Re-energise and drive/inspect the full high-speed taxiway route at night to confirm continuous, evenly illuminated guidance before returning to service.

Corrective Action

• Replace failed transformer, lamp, or connector at each affected fixture.
• Repair a located cable/circuit fault.
• Coordinate with civil works if recent pavement activity caused the damage.

Preventive Action

• Include the full high-speed taxiway route in periodic inspection at a frequency reflecting its higher-speed operational role.
• Coordinate with pavement maintenance teams before works near known cable routes.
• Trend fixture failure history to identify weak sections.

Related References

SOP: SOP-TCL-01, SOP-TCL-09

Standards: ICAO Annex 14 Vol I, FAA AC 150/5340-30

Diagram: High-Speed Taxiway Route Layout Drawing

Case Study: Division 24 — Complete Runway Lighting Failure

Equipment / System

Taxiway guidance series circuit — the CCR-fed series loop supplying the taxiway centreline, lead-on/lead-off, and any RET/high-speed sections sharing a common circuit, including the primary cable route and all in-line isolation transformers.

Possible Causes

Required Tools

Safety Precautions

• LOTO the CCR before any circuit work.
• Obtain excavation clearance and utility locates before opening pavement if the fault requires digging.
• Coordinate extended taxiway closure with ATC/airfield operations given the circuit's shared scope.

Diagnostic Procedure

1. ObservationConfirm at the CCR/ALCMS whether the fault presents as a complete loss of output (source-side) or a partial dark section with the CCR still delivering rated current (downstream fault).
2. ObservationCross-reference the extent of the dark section against the circuit layout drawing to identify candidate cable segments and branches.
3. MeasurementWith the circuit isolated, megger the primary cable in segments from accessible pull boxes or transformer base cans.
4. MeasurementUse a TDR or fault locator to estimate fault distance if a direct segment test is inconclusive.
5. DecisionInsulation resistance fails on a specific segment → cable/joint fault in that segment. All segments megger clear but a specific transformer reads shorted → that transformer is loading down the loop.
6. Fault LocationPhysically locate and expose the faulted cable segment or confirm the single shorted transformer.
7. Root CauseConfirm the cause of the cable fault (mechanical damage, water tracking, age-related insulation breakdown) once exposed.

Test Points

Root Cause Verification

After repair, megger the full circuit end-to-end, re-energise, and confirm every fixture on the loop — centreline, lead-on/off, and any RET/high-speed sections — illuminates correctly at all intensity steps.

Corrective Action

• Repair or replace the faulted cable segment.
• Replace the shorted isolation transformer.
• Close or repair the open section isolator.
• Restore duct/cable protection where mechanical damage was the cause.

Preventive Action

• Schedule periodic full-loop insulation resistance testing and trend results over time.
• Maintain accurate as-built records of every joint, pull box, and repair splice.
• Coordinate with civil works teams before any excavation near known circuit routes.

Related References

SOP: SOP-TCL-11 (Guidance Circuit Fault Location Procedure), SOP-CCR-04 (CCR LOTO Procedure)

Standards: IEC 60364 (insulation testing), ICAO Annex 14 Vol I, FAA AC 150/5340-30

Diagram: Taxiway Guidance Circuit Route Drawing

Case Study: Division 01 — CCR Troubleshooting; Division 25 — Field Case Study Troubleshooting

Equipment / System

Taxiway centreline series circuit primary cable and its insulation system, including cable jacket, joints, and transformer windings across the loop.

Possible Causes

Required Tools

Safety Precautions

• LOTO the CCR before any insulation testing or cable work.
• Treat a marginal insulation reading as a developing hazard rather than a nuisance — do not simply reset the CCR's earth-fault protection without investigating.

Diagnostic Procedure

1. ObservationReview the CCR's earth-fault/ground-fault trip history and trend to establish whether the insulation resistance is degrading gradually or a step-change occurred.
2. MeasurementWith the circuit isolated, megger the primary cable in segments from accessible pull boxes or transformer base cans, comparing each segment against its baseline/previous test value.
3. MeasurementIdentify the segment or transformer contributing the greatest drop in insulation resistance.
4. DecisionDrop isolated to one segment/joint → localised repair. Drop distributed across many segments → treat as cumulative circuit ageing and plan proactive replacement.
5. Fault LocationIsolate to the specific cable segment, joint, or transformer winding contributing most to the reduced reading.
6. Root CauseConfirm with a full-loop re-test that the reading is restored to, or above, the acceptable threshold.

Test Points

Root Cause Verification

After repair, re-megger the full loop and confirm the reading is restored to (or above) the acceptable threshold, and monitor the CCR earth-fault trend over subsequent operating cycles.

Corrective Action

• Repair or replace the identified degraded cable segment or joint.
• Replace the transformer with the failing winding.
• Reseal an identified moisture entry point at a pull box or base can.

Preventive Action

• Schedule periodic full-loop insulation resistance testing on a defined interval and trend results year over year rather than waiting for a nuisance trip.
• Prioritise ageing circuit sections for proactive cable replacement.
• Seal known moisture entry points identified during PM.

Related References

SOP: SOP-TCL-11 (Guidance Circuit Fault Location Procedure), SOP-CCR-04 (CCR LOTO Procedure)

Standards: IEC 60364 (insulation testing), ICAO Annex 14 Vol I, FAA AC 150/5340-30

Diagram: Taxiway Guidance Circuit Route Drawing

Case Study: Division 25 — Field Case Study Troubleshooting