Diagnostic Decision Trees

Equipment / System

Constant Current Regulator (CCR) — SCR or IGBT-based — its control/logic board, main incoming supply, and start/enable circuitry.

Possible Causes

Required Tools

Safety Precautions

• LOTO the CCR before any internal access.
• Verify the incoming supply is de-energised before opening the cabinet.
• Treat the CCR as live until confirmed isolated.

Decision Tree / Diagnostic Procedure

1. ObservationCheck ALCMS for the CCR's reported status and any active alarm/fault code before touching the unit.
2. ObservationConfirm the local/remote selector position and that no E-stop or interlock is engaged at the panel.
3. MeasurementWith the cabinet open and supply confirmed present, verify incoming supply voltage at the main breaker and confirm the control power supply fuse/breaker is intact.
4. MeasurementAttempt a local start command and observe whether the control logic energises (indicator lamps, display) even if the output contactor does not close.
5. DecisionControl logic does not power up at all → incoming supply/control fuse fault. Control logic powers up but the output does not close → contactor/output stage or start-sequence fault.
6. Fault LocationIsolate to the incoming supply, control fuse, selector/interlock circuit, or output contactor/relay.
7. Root CauseConfirm the specific failed component before replacement.

Test Points

Root Cause Verification

After repair, start the CCR through a full run cycle at each intensity step and confirm ALCMS reports normal running status.

Corrective Action

• Reset or replace the tripped breaker after confirming no downstream fault.
• Replace the blown control fuse.
• Correct the selector switch or E-stop position.
• Repair the ALCMS-to-CCR comms link.
• Replace a faulty output contactor or control board.

Preventive Action

• Include a CCR start-sequence test in the periodic PM cycle.
• Verify the comms link integrity periodically.
• Check E-stop/interlock wiring for damage during PM.

Related References

SOP: SOP-CCR-01 (CCR Start-up and Verification Procedure), SOP-CCR-04 (CCR LOTO Procedure)

Standards: FAA AC 150/5345-10, ICAO Annex 14 Vol I

Diagram: CCR wiring/schematic diagram

Case Study: Division 01 — CCR Troubleshooting

Equipment / System

CCR overcurrent, short-circuit, and general protection trip circuitry, output stage, and the series circuit it feeds.

Possible Causes

Required Tools

Safety Precautions

• LOTO before investigating internal trip circuitry.
• Treat the series circuit as a possible short/ground fault until proven otherwise.
• Do not repeatedly reset the CCR without investigating the trip cause.

Decision Tree / Diagnostic Procedure

1. ObservationReview the CCR trip log/event history to identify which protection function (overcurrent, ground fault, overtemperature) initiated the trip and whether it is immediate or delayed.
2. ObservationNote whether the trip occurs on every start attempt or is intermittent.
3. MeasurementWith the circuit isolated, megger the full series loop to check for a hard short or ground fault before re-energising.
4. MeasurementIf insulation resistance is acceptable, re-energise briefly under supervision and clamp-meter the output current against the circuit's expected load.
5. DecisionMegger reveals a hard fault on the loop → route to the Series Circuit Failure or Cable Earth Fault trees. Megger is clean and output current is within range but the trip persists → CCR internal protection/output stage fault.
6. Fault LocationIsolate to the downstream circuit or to the CCR's own protection/output stage.
7. Root CauseConfirm the specific fault — external short vs. internal CCR fault — before returning the unit to service.

Test Points

Root Cause Verification

After repair, run the CCR through a full brightness-step cycle without a repeat trip and confirm the event log is clear.

Corrective Action

• Repair the identified circuit short or ground fault.
• Replace the faulty output component.
• Adjust the protection setpoint per manufacturer specification if confirmed a nuisance trip.
• Replace a failed cooling fan.

Preventive Action

• Trend CCR trip logs to catch developing faults before hard failure.
• Include protection setpoint verification in commissioning and PM.
• Keep the cooling system clean and unobstructed.

Related References

SOP: SOP-CCR-02 (CCR Trip Investigation Procedure), SOP-CCR-04

Standards: FAA AC 150/5345-10, ICAO Annex 14 Vol I

Diagram: CCR protection settings sheet

Case Study: Division 29 — Series Circuit Failure Decision Tree

Equipment / System

CCR earth-fault/ground-fault detection circuitry and the series circuit loop (cable, joints, isolation transformers) it protects.

Possible Causes

Required Tools

Safety Precautions

• LOTO the CCR before any insulation testing or cable work.
• Treat a genuine earth-fault indication as a real hazard, not a nuisance, and do not simply reset without investigating.

Decision Tree / Diagnostic Procedure

1. ObservationReview the CCR's earth-fault trend log to see whether the fault is a hard trip or a gradually worsening marginal reading.
2. MeasurementWith the circuit isolated, megger the primary loop in segments from accessible pull boxes or base cans.
3. MeasurementCompare each segment's reading against its baseline/previous test value to identify the segment with the greatest drop.
4. DecisionDrop isolated to one segment, joint, or transformer → localised repair. Drop appears at the CCR terminals with the field loop disconnected → CCR internal detection fault.
5. Fault LocationIsolate to the specific cable segment, joint, or transformer winding.
6. Root CauseConfirm with a full-loop re-test that insulation resistance is restored to, or above, the acceptable threshold.

Test Points

Root Cause Verification

Re-megger the full loop after repair and monitor the CCR earth-fault trend over subsequent operating cycles.

Corrective Action

• Repair or replace the degraded cable segment or joint.
• Replace the transformer with the failing winding.
• Reseal an identified moisture entry point.
• Replace the CCR earth-fault detection module if confirmed internally faulty.

Preventive Action

• Schedule periodic full-loop insulation resistance testing and trend results.
• Prioritise ageing sections for proactive replacement.
• Seal known moisture entry points during PM.

Related References

SOP: SOP-CCR-03 (Earth Fault Investigation Procedure), SOP-CCR-04

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

Diagram: Circuit route drawing

Case Study: Division 29 — Low Insulation Resistance Decision Tree

Equipment / System

CCR cooling system (fans, vents, heat sinks), output stage, and enclosure/cabinet environment.

Possible Causes

Required Tools

Safety Precautions

• LOTO before internal inspection.
• Allow the unit to cool before opening if recently tripped on overtemperature.
• Use insulated tools when checking live connections.

Decision Tree / Diagnostic Procedure

1. ObservationReview the trip/alarm log to confirm overtemperature is the actual protection function and note the time-to-trip from start.
2. ObservationCheck the cabinet/enclosure environment for blocked vents, direct heat sources, or inadequate clearance.
3. MeasurementWith the unit isolated, inspect and test the cooling fan(s) and check the air filter for blockage.
4. MeasurementThermal-image the output stage and all high-current connections during a supervised run to locate a hot spot.
5. DecisionHot spot at a specific connection or component → localised fault, repair/replace. No localised hot spot but overall cabinet temperature is high → ventilation/ambient issue.
6. Fault LocationIsolate to the cooling system, a specific connection/component, or the installation environment.
7. Root CauseConfirm the temperature returns to normal operating range under full load after correction.

Test Points

Root Cause Verification

Run the CCR at full rated load for an extended period post-repair and confirm temperature stabilises within normal range without re-tripping.

Corrective Action

• Replace a failed fan or clean/replace the air filter.
• Re-torque or replace a loose high-current connection.
• Replace a degraded output component.
• Improve enclosure ventilation or shading.
• Recalibrate or replace the temperature sensor.

Preventive Action

• Clean and inspect the cooling system and filters on a defined PM interval.
• Include thermal imaging of connections in PM.
• Verify enclosure ventilation clearances at commissioning.

Related References

SOP: SOP-CCR-05 (Overtemperature Investigation Procedure)

Standards: FAA AC 150/5345-10

Diagram: CCR thermal design specification

Case Study: Division 29 — CCR Output Current Decision Tree

Equipment / System

CCR output regulation and current feedback circuitry, and the series circuit it supplies.

Possible Causes

Required Tools

Safety Precautions

• LOTO before any internal connection changes.
• Treat the output circuit as energised at the commanded current until confirmed isolated.

Decision Tree / Diagnostic Procedure

1. ObservationCompare the CCR's reported output current against the ALCMS-commanded intensity step and the circuit's expected rated current for that step.
2. MeasurementIndependently verify actual output current with a calibrated clamp meter at the CCR output terminals.
3. MeasurementIf the independent reading differs from the CCR's displayed value, suspect the feedback/sensing path; if they agree but are wrong for the step, suspect the regulation control loop or the circuit itself.
4. DecisionDisplayed and measured current agree but differ from the expected value for the circuit load → circuit-side issue, route to the Series Circuit Failure tree. Displayed and measured current disagree → CCR feedback/sensing fault.
5. Fault LocationIsolate to the current feedback/sensing component, the output regulation control loop, or the downstream circuit.
6. Root CauseConfirm the specific component or circuit condition responsible for the discrepancy.

Test Points

Root Cause Verification

Step the CCR through its full intensity range and confirm output current tracks the expected value at each step, matching an independent reference measurement.

Corrective Action

• Replace a faulty current sensing transformer or shunt.
• Repair or recalibrate the output regulation control loop.
• Correct the circuit load discrepancy.
• Recalibrate the CCR against a reference standard.

Preventive Action

• Include CCR output current calibration verification in the periodic PM/calibration cycle.
• Maintain an accurate as-built fixture count per circuit.

Related References

SOP: SOP-CCR-06 (CCR Calibration and Output Verification)

Standards: FAA AC 150/5345-10

Diagram: CCR calibration certificate

Case Study: Division 29 — Series Circuit Failure Decision Tree

Equipment / System

The complete series loop for a given circuit — CCR output, primary cable, isolation transformers, fixtures, and return path to the CCR.

Possible Causes

Required Tools

Safety Precautions

• Coordinate all airside access through ATC/apron control.
• Treat the circuit as energised until confirmed isolated and LOTO applied at the CCR.

Decision Tree / Diagnostic Procedure

1. ObservationCheck the CCR/ALCMS panel to confirm whether the CCR itself is producing normal output current for this circuit.
2. ObservationConfirm by field inspection whether the entire run is dark or only a section/group of fixtures.
3. MeasurementWith the circuit isolated, megger the full loop from the CCR output to identify whether an open circuit or a short/ground fault is present.
4. MeasurementIf an open circuit is indicated, use a TDR or sectional testing from accessible base cans/pull boxes to localise the break.
5. DecisionCCR output is abnormal → route to the CCR Output Current or CCR Trip trees. CCR output is normal but the loop shows an open or short → cable/circuit-level fault, proceed to isolate.
6. Fault LocationIsolate the open circuit or short/ground fault to a specific cable segment, joint, or transformer.
7. Root CauseConfirm the fault location by direct inspection or excavation before repair.

Test Points

Root Cause Verification

After repair, re-energise the circuit and confirm every fixture on the run illuminates correctly at all intensity steps during a night inspection.

Corrective Action

• Repair or replace the open cable section or failed joint.
• Restore CCR output if the root cause was upstream.
• Close any isolator/breaker inadvertently left open.
• Correct miswiring from recent work.

Preventive Action

• Maintain an accurate, current circuit and base-can layout drawing.
• Verify circuit continuity as a standard step after any excavation or joint work near the loop.

Related References

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

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

Diagram: Circuit route drawing

Case Study: Division 29 — Cable Open Circuit Decision Tree

Equipment / System

The individual fixture, its isolation transformer, L-823 connector, and base can.

Possible Causes

Required Tools

Safety Precautions

• Confirm the circuit is isolated and LOTO applied before opening the base can, even though the rest of the run remains lit.
• Use FOD-safe tools and account for every item before leaving the pavement.

Decision Tree / Diagnostic Procedure

1. ObservationConfirm via field inspection that only this single fixture is dark and the rest of the run is lit normally.
2. MeasurementWith the circuit isolated, disconnect the fixture's L-823 plug and megger the isolation transformer primary and secondary windings.
3. MeasurementInspect the base can for water or debris and check the lamp/LED module for visible failure.
4. DecisionTransformer or lamp confirmed faulty → replace at this fixture only. Transformer and lamp test good → suspect the connector or a short local cable run to the adjacent fixture.
5. Fault LocationIsolate to the transformer, lamp/LED module, connector, or the short cable segment feeding this fixture.
6. Root CauseConfirm the specific failed component before replacement rather than swapping parts speculatively.

Test Points

Root Cause Verification

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

Corrective Action

• Replace the failed isolation transformer or lamp/LED module.
• Reseat or replace a corroded/damaged connector.
• Drain and reseal the base can.

Preventive Action

• Include fixture, transformer, and connector inspection in the routine night flight-check and PM cycle.
• Maintain an accurate base-can schedule to speed fault location.

Related References

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

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

Diagram: Base-can schedule

Case Study: Division 29 — Multiple Light Failure Decision Tree

Equipment / System

The affected group of fixtures, the cable section(s) connecting them, and the upstream CCR/circuit.

Possible Causes

Required Tools

Safety Precautions

• Coordinate airside access through ATC/apron control.
• Treat the circuit as energised until confirmed isolated and LOTO applied.

Decision Tree / Diagnostic Procedure

1. ObservationMap exactly which fixtures are affected and confirm whether they are contiguous along the circuit or scattered.
2. ObservationCheck the CCR/ALCMS panel to confirm whether overall circuit output current is normal, reduced, or zero.
3. MeasurementWith the circuit isolated, megger the loop between the last known-good fixture and the first affected fixture to check for an open or short.
4. DecisionAffected fixtures are contiguous downstream of a single point → localise the fault to the cable/joint at that point. Affected fixtures are scattered with no common cable section → investigate CCR output or independent fixture-level faults for each.
5. Fault LocationIsolate to the specific cable segment or joint feeding the affected group, or to individual fixtures if scattered.
6. Root CauseConfirm the fault location by direct inspection before repair.

Test Points

Root Cause Verification

After repair, re-energise the circuit and confirm every fixture in the previously affected group illuminates correctly at all intensity steps during a night inspection.

Corrective Action

• Repair the identified cable section or joint.
• Restore CCR output if the root cause was upstream.
• Repair any individually faulted fixtures identified.

Preventive Action

• Maintain accurate circuit mapping to speed identification of contiguous vs. scattered failures.
• Monitor low-lying base can areas for seasonal water table effects.

Related References

SOP: SOP-TCL-11, SOP-CCR-04

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

Diagram: Circuit route drawing

Case Study: Division 29 — Series Circuit Failure Decision Tree

Equipment / System

Primary series circuit cable, joints, and terminations between the CCR and the affected fixtures.

Possible Causes

Required Tools

Safety Precautions

• LOTO the circuit before any cable testing or excavation.
• Call for utility/cable locates before any digging.
• Treat exposed conductors as live until confirmed isolated.

Decision Tree / Diagnostic Procedure

1. ObservationConfirm from the failure pattern (which fixtures are dark) which cable section is implicated.
2. MeasurementWith the circuit isolated, use a TDR to estimate the distance to the open from the nearest accessible termination.
3. MeasurementCross-check the TDR estimate against the as-built cable route drawing to identify the likely physical location (pull box, joint, or mid-run).
4. DecisionBreak located at an accessible joint/pull box → repair without excavation. Break located mid-run in buried cable → coordinate excavation and locates before repair.
5. Fault LocationConfirm the exact break location by direct inspection once access is achieved.
6. Root CauseDetermine whether the break resulted from mechanical damage, corrosion, or ground movement to inform the repair method and prevent recurrence.

Test Points

Root Cause Verification

After repair, megger and continuity-test the full loop, then re-energise and confirm all previously affected fixtures illuminate correctly.

Corrective Action

• Splice and properly seal the break using an approved airfield-rated splice kit.
• Replace the damaged cable section if the jacket is compromised over a length rather than at a single point.

Preventive Action

• Maintain accurate cable route drawings and provide them to any party performing ground works near the circuit.
• Include cable route condition in periodic PM where accessible.

Related References

SOP: SOP-TCL-11 (Circuit Fault Location Procedure)

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

Diagram: Cable route drawing

Case Study: Division 29 — Series Circuit Failure Decision Tree

Equipment / System

Primary series circuit cable, its jacket, joints, and route between the CCR and the fixtures it feeds.

Possible Causes

Required Tools

Safety Precautions

• LOTO before any insulation testing or cable work.
• Treat a marginal insulation reading as a developing hazard and investigate rather than resetting protection.

Decision Tree / Diagnostic Procedure

1. ObservationReview the CCR's earth-fault trend to establish whether this is a step-change (likely mechanical damage) or gradual (likely moisture/ageing).
2. MeasurementWith the circuit isolated, megger the cable in segments from accessible pull boxes to identify the affected segment.
3. MeasurementWithin the identified segment, narrow the location using a TDR referenced against the route drawing.
4. DecisionFault localises to a specific accessible point → repair without excavation. Fault requires excavation to access → coordinate locates and dig.
5. Fault LocationConfirm the exact fault point by direct inspection.
6. Root CauseDetermine whether mechanical damage, joint failure, or ageing caused the fault to guide the appropriate repair and prevention.

Test Points

Root Cause Verification

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

Corrective Action

• Repair or replace the damaged cable section or joint using an approved airfield-rated splice/repair kit.
• Reseal an identified moisture entry point.

Preventive Action

• Schedule periodic insulation resistance testing and trend results over time.
• Prioritise ageing sections for proactive replacement.
• Provide accurate route drawings to any party performing ground works nearby.

Related References

SOP: SOP-TCL-11, SOP-CCR-03

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

Diagram: Cable route drawing

Case Study: Division 29 — Low Insulation Resistance Decision Tree

Equipment / System

The full series circuit loop under test — cable, joints, isolation transformers — and the test equipment itself.

Possible Causes

Required Tools

Safety Precautions

• LOTO before any insulation testing.
• Treat a marginal reading as a developing hazard rather than a nuisance.

Decision Tree / Diagnostic Procedure

1. ObservationConfirm the reading with a second, calibrated megger and a known-good test lead set to rule out a test equipment error before proceeding.
2. MeasurementMegger the loop in segments from accessible pull boxes/base cans, comparing each 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

Re-megger the full loop after repair and confirm the reading is restored to, or above, the acceptable threshold; trend over subsequent test 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.

Preventive Action

• Schedule periodic full-loop insulation resistance testing on a defined interval and trend results year over year.
• Prioritise ageing circuit sections for proactive cable replacement.

Related References

SOP: SOP-TCL-11, SOP-CCR-03

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

Diagram: Circuit route drawing

Case Study: Division 29 — Cable Earth Fault Decision Tree

Equipment / System

Individual series-circuit isolation transformer (primary/secondary), its base can, and connections.

Possible Causes

Required Tools

Safety Precautions

• LOTO before disconnecting or testing the transformer.
• Treat the base can as potentially energised until confirmed isolated.

Decision Tree / Diagnostic Procedure

1. ObservationConfirm which load (fixture, sign) is affected and note the transformer's rated ratio and VA against the connected load's specification.
2. MeasurementWith the circuit isolated, disconnect the transformer and megger the primary and secondary windings independently, and between windings and case.
3. MeasurementCheck primary and secondary winding continuity/resistance against manufacturer specification.
4. DecisionWinding open or insulation breakdown confirmed → replace transformer. Transformer tests within spec → look elsewhere in the circuit (connector, cable, load itself).
5. Fault LocationConfirm the transformer is the failed component rather than the connector or load it feeds.
6. Root CauseVerify the replacement transformer's rating matches the connected load's specification before re-energising.

Test Points

Root Cause Verification

After replacement, re-energise and confirm the connected load operates correctly at all intensity steps, and re-megger the loop.

Corrective Action

• Replace the failed transformer with one of the correct rating.
• Drain and reseal the base can if flooding contributed to failure.

Preventive Action

• Verify transformer rating against load specification at every replacement.
• Include transformer insulation testing in the periodic PM cycle.
• Address chronic base can flooding at its source.

Related References

SOP: SOP-TCL-01

Standards: FAA AC 150/5345-46

Diagram: Transformer specification sheet

Case Study: Division 29 — Single Light Failure Decision Tree

Equipment / System

L-823 primary/secondary connector set and its immediate base can environment.

Possible Causes

Required Tools

Safety Precautions

• LOTO before disconnecting or inspecting the connector.
• Treat the base can as potentially energised until confirmed isolated.

Decision Tree / Diagnostic Procedure

1. ObservationConfirm the connector is the suspected fault point based on the symptom pattern (intermittent, moisture-related, or immediately after recent work).
2. MeasurementWith the circuit isolated, disconnect and visually inspect the connector for corrosion, moisture, damaged pins, or an incomplete seal.
3. MeasurementTest contact resistance across the mated connector using a test adaptor if available.
4. DecisionVisible corrosion, damage, or moisture confirmed → clean, reseal, or replace. Connector appears sound and low-resistance → look elsewhere (transformer, cable) for the fault.
5. Fault LocationConfirm the connector is the failed component rather than the transformer or cable it joins.
6. Root CauseDetermine why the seal or connection failed (age, incorrect part, incomplete seating) to prevent recurrence.

Test Points

Root Cause Verification

After repair, re-energise and confirm the downstream load operates correctly, and re-check the connector at the next inspection cycle for continued integrity.

Corrective Action

• Clean, re-grease, and properly reseat the connector.
• Replace a corroded or damaged connector with the correct rated part.
• Reseal the base can.

Preventive Action

• Torque/seating-check connectors as a standard PM step.
• Use the correct dielectric grease at every mating.
• Include connector condition in the periodic night inspection.

Related References

SOP: SOP-TCL-01

Standards: FAA AC 150/5345-46

Diagram: Connector specification sheet

Case Study: Division 29 — Single Light Failure Decision Tree

Equipment / System

Individual runway/taxiway light fixture — lamp/LED module, lens, housing, and internal wiring.

Possible Causes

Required Tools

Safety Precautions

• LOTO before fixture access.
• Use FOD-safe tools and account for every item before leaving the pavement.
• Coordinate airside access through ATC/apron control.

Decision Tree / Diagnostic Procedure

1. ObservationConfirm the transformer, connector, and cable feeding this fixture have tested good, isolating the fault to the fixture itself.
2. MeasurementWith the circuit isolated, disconnect the fixture and inspect the lamp/LED module, internal wiring, lens, and housing for visible damage.
3. MeasurementBench-test the lamp/LED module independently if equipment is available.
4. DecisionLamp/LED module or internal wiring confirmed faulty → replace the module or repair internal wiring. Lens or housing damage found with a functional lamp/LED → repair/replace lens or housing only.
5. Fault LocationConfirm the specific failed fixture component before ordering replacement parts.
6. Root CauseDetermine whether the failure is normal end-of-life, physical damage, or a part number mismatch.

Test Points

Root Cause Verification

After repair, re-energise and confirm the fixture illuminates correctly at all intensity steps and matches the photometric output of neighbouring fixtures.

Corrective Action

• Replace the failed lamp/LED module.
• Repair internal wiring.
• Replace a cracked or missing lens.
• Replace or repair a damaged housing.

Preventive Action

• Include fixture-level inspection (lens, housing, module condition) in the routine night flight-check.
• Verify part numbers at every replacement.

Related References

SOP: SOP-TCL-02

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

Diagram: Fixture parts catalogue

Case Study: Division 29 — Single Light Failure Decision Tree

Equipment / System

Sign internal lighting module (lamp/LED panel), transformer, connector, and housing.

Possible Causes

Required Tools

Safety Precautions

• LOTO before sign access.
• Coordinate airside access through ATC/apron control.
• Treat the sign circuit as energised until confirmed isolated.

Decision Tree / Diagnostic Procedure

1. ObservationConfirm whether the entire sign is dark, only part of the legend is unlit, or the sign appears lit but with incorrect brightness/colour.
2. MeasurementWith the circuit isolated, megger the transformer feeding the sign and check connector condition, following the same approach as a fixture-level fault.
3. MeasurementIf the transformer and connector test good, open the sign housing and inspect the internal lamp/LED panel and wiring.
4. DecisionTransformer or connector confirmed faulty → replace, consistent with standard fixture-level procedure. Transformer/connector good but the sign is still faulty → internal panel or wiring fault.
5. Fault LocationIsolate to the transformer, connector, internal lamp/LED panel, or internal wiring.
6. Root CauseConfirm the specific failed component before replacement.

Test Points

Root Cause Verification

After repair, re-energise and confirm the full legend illuminates evenly and correctly at all intensity steps during a night inspection.

Corrective Action

• Replace the failed transformer, connector, or lamp/LED panel.
• Repair internal wiring.
• Reseal the housing.

Preventive Action

• Include sign legend and housing seal inspection in the routine night flight-check and PM cycle.

Related References

SOP: SOP-SGN-01 (Sign Fault Isolation Procedure)

Standards: FAA AC 150/5345-44, ICAO Annex 14 Vol I

Diagram: Sign parts catalogue

Case Study: Division 29 — Single Light Failure Decision Tree

Equipment / System

PAPI unit — lamp/LED source, colour filter/lens assembly, aiming mechanism, and its power supply/transformer.

Possible Causes

Required Tools

Safety Precautions

• LOTO before internal access.
• Coordinate airside access through ATC/apron control given PAPI proximity to the runway.
• Do not adjust aim without following the calibrated procedure and a subsequent flight check.

Decision Tree / Diagnostic Procedure

1. ObservationConfirm from the pilot/inspection report which specific bar or transition is affected and whether it is a colour, intensity, or complete outage issue.
2. MeasurementWith the circuit isolated, check the transformer and connector feeding the affected bar following standard fixture-level testing.
3. MeasurementIf the transformer/connector are good, inspect the lamp/LED source, lens/filter, and confirm unit aim against the calibrated elevation setting.
4. DecisionTransformer/connector or lamp/LED confirmed faulty → replace, consistent with standard fixture-level procedure. Aim found to have drifted → re-calibrate per the manufacturer procedure and confirm with a flight check.
5. Fault LocationIsolate to the power/connector path, the lamp/LED/lens assembly, or the aiming mechanism.
6. Root CauseConfirm the specific cause, especially for aim drift, to prevent recurrence.

Test Points

Root Cause Verification

After repair or recalibration, confirm the correct bar pattern and colour transition visually and, for aim corrections, via a flight check per the applicable procedure.

Corrective Action

• Replace the failed lamp/LED, transformer, or connector.
• Replace a degraded lens/filter.
• Re-aim the unit to its calibrated elevation.

Preventive Action

• Include PAPI aim verification and lens condition in the periodic PM and flight-check cycle.
• Clear vegetation or obstructions from the unit's sight line regularly.

Related References

SOP: SOP-PAPI-01 (PAPI Calibration and Fault Procedure)

Standards: FAA AC 150/5345-28, ICAO Annex 14 Vol I

Diagram: PAPI calibration certificate

Case Study: Division 29 — Photometry Failure Decision Tree

Equipment / System

ALS fixture, its transformer/power supply (or flasher unit for sequenced lights), cable run along the approach light structure, and the CCR/flasher controller.

Possible Causes

Required Tools

Safety Precautions

• LOTO before any work.
• Use fall protection and structure-specific access procedures for elevated or over-water approach light structures.
• Coordinate access given proximity to the approach path.

Decision Tree / Diagnostic Procedure

1. ObservationConfirm whether the fault affects a single fixture, a flasher-sequenced group, or the full approach lighting system.
2. MeasurementFor a single fixture, apply standard fixture-level fault isolation (transformer, connector, lamp/LED).
3. MeasurementFor a sequenced flasher fault, check the flasher/sequencer unit output and timing against specification.
4. DecisionSingle fixture-level fault confirmed → proceed under standard fixture repair. Flasher/sequencer or wider circuit fault → isolate to the controller or the structure cable run.
5. Fault LocationIsolate to the specific fixture, the flasher/sequencer unit, or the structure cable run.
6. Root CauseConfirm the specific failed component, noting any access or environmental factors that may have contributed (weather exposure, structure movement).

Test Points

Root Cause Verification

After repair, confirm correct illumination or flash sequencing across the full ALS during a night inspection, including flash timing verification where applicable.

Corrective Action

• Replace the failed fixture component.
• Repair or replace the flasher/sequencer unit.
• Repair the structure cable run.
• Correct any mounting/alignment damage.

Preventive Action

• Include structure condition and cable run inspection in the periodic PM cycle, accounting for weather exposure.
• Verify flasher timing calibration periodically.

Related References

SOP: SOP-ALS-01 (Approach Lighting Fault Procedure)

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

Diagram: ALS as-built layout drawing

Case Study: Division 29 — Series Circuit Failure Decision Tree

Equipment / System

Stop bar fixture(s), transformer/connector, the dedicated stop bar circuit, and the ALCMS/CCR interface controlling its on/off state.

Possible Causes

Required Tools

Safety Precautions

• LOTO before any work.
• Treat a stop bar fault as safety-critical and notify ATC/airfield operations immediately, since it directly affects runway incursion protection.
• Do not leave a malfunctioning stop bar in an ambiguous state.

Decision Tree / Diagnostic Procedure

1. ObservationConfirm via ALCMS whether the commanded state matches the actual observed state of the stop bar, and whether the discrepancy is circuit-wide or fixture-specific.
2. ObservationNotify airfield operations/ATC of the discrepancy immediately given the safety-critical function.
3. MeasurementIf circuit-wide, check the CCR/relay logic for the stop bar interlock against the ALCMS command.
4. MeasurementIf fixture-specific, apply standard fixture-level fault isolation (transformer, connector, lamp/LED).
5. DecisionDiscrepancy traces to CCR/relay/interlock logic → circuit-level fault, isolate at the controller. Discrepancy isolated to one or more fixtures → fixture-level fault.
6. Fault LocationIsolate to the specific fixture, the circuit, or the ALCMS/CCR interlock logic.
7. Root CauseConfirm the specific cause before returning the stop bar to service, given its safety-critical function.

Test Points

Root Cause Verification

After repair, cycle the stop bar through on/off selection via ALCMS multiple times and confirm the physical state matches the command every time before returning to service.

Corrective Action

• Repair or replace the failed fixture component.
• Repair the CCR/relay interlock logic fault.
• Restore the comms link between ALCMS and the CCR.

Preventive Action

• Include stop bar state-verification (commanded vs. actual) in the routine inspection cycle.
• Test the interlock logic periodically, not only fixture condition.

Related References

SOP: SOP-SB-01 (Stop Bar Fault and Interlock Verification Procedure)

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

Diagram: Stop bar interlock logic diagram

Case Study: Division 29 — ALCMS Communication Failure Decision Tree

Equipment / System

The fixture(s) under test, their lamp/LED source, lens/filter, alignment, and the CCR output feeding them.

Possible Causes

Required Tools

Safety Precautions

• LOTO before physical fixture adjustment.
• Coordinate airside access through ATC/apron control.
• Treat the circuit as energised until confirmed isolated for any hands-on work.

Decision Tree / Diagnostic Procedure

1. ObservationConfirm the specific parameter that failed (intensity, beam spread, or chromaticity) and by how much it deviates from tolerance.
2. MeasurementInspect and, if needed, clean the lens, then re-measure to rule out contamination as the cause.
3. MeasurementIf still out of tolerance, check fixture aim/alignment against the specified pattern using an aiming tool.
4. DecisionCleaning alone resolves the deviation → contamination was the root cause, close out. Cleaning does not resolve it → check alignment, lamp/LED output, and CCR current at the tested step in turn.
5. Fault LocationIsolate to lens contamination, misalignment, lamp/LED degradation, filter condition, or CCR output current.
6. Root CauseConfirm the specific cause with a re-test after each corrective action rather than changing multiple variables at once.

Test Points

Root Cause Verification

Re-test photometrically after correction and confirm the fixture meets specification at the relevant intensity step(s).

Corrective Action

• Clean the lens.
• Re-aim the fixture to the specified pattern.
• Replace a degraded lamp/LED module or filter.
• Correct CCR output current if found to be the source of the deviation.

Preventive Action

• Include lens cleaning and aim verification in the periodic PM cycle given fuel-spill, rubber deposit, and vibration exposure.
• Trend photometric readings over time to catch gradual degradation before it becomes a compliance failure.

Related References

SOP: SOP-PHM-01 (Photometric Compliance Procedure)

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

Diagram: Photometric test report

Case Study: Division 29 — CCR Output Current Decision Tree

Equipment / System

ALCMS server/workstation, communication network (fibre, copper, or wireless links), and the CCR/field device communication interfaces.

Possible Causes

Required Tools

Safety Precautions

• Follow standard electrical safety practice when working in CCR cabinets even though this is a communications, not lighting-circuit, fault.
• Coordinate any network changes with airfield operations given the operational reliance on ALCMS status.

Decision Tree / Diagnostic Procedure

1. ObservationConfirm from ALCMS whether the affected CCR(s)/devices are actually failing to communicate, and cross-check the CCR's actual lighting status locally to confirm it is a comms issue and not a real lighting fault also being missed.
2. ObservationIdentify whether one device, several on a common network segment, or all devices are affected, which indicates how far upstream the fault lies.
3. MeasurementTest the physical communication link (cable continuity, fibre optical power) between ALCMS and the affected point.
4. MeasurementIf the physical link tests good, check the network switch/media converter and the device's communication configuration/address.
5. DecisionPhysical link fault confirmed → repair/replace the cable, fibre, or connector. Physical link good but the device fails to communicate → network component or configuration fault.
6. Fault LocationIsolate to the physical link, a network component, or a software/configuration issue.
7. Root CauseConfirm the specific cause and, for a single-device failure following recent configuration changes, review what was changed.

Test Points

Root Cause Verification

After repair, confirm the affected CCR(s)/devices report status to ALCMS consistently and match actual field lighting status over a sustained monitoring period.

Corrective Action

• Repair or replace the damaged cable/fibre/connector.
• Replace the failed network switch/media converter/communication card.
• Correct the device's communication configuration/address.

Preventive Action

• Include communication link testing (cable/fibre condition, network component health) in the periodic PM cycle, separate from lighting-circuit PM.
• Maintain an accurate, current network architecture drawing.
• Verify comms status as a standard step after any configuration or firmware change.

Related References

SOP: SOP-ALCMS-01 (Communication Fault Isolation Procedure)

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

Diagram: ALCMS/CCR network architecture drawing

Case Study: Division 29 — CCR Not Starting Decision Tree