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Safety-critical technical reference — read before use. Independent educational guidance for qualified AGL personnel. It is not an approved procedure or regulatory instruction and does not replace your aerodrome’s permit-to-work, isolation/LOTO and maintenance procedures or the manufacturer’s instructions. Series-circuit AGL equipment can carry lethal voltages. Read the full disclaimer ↓
Division 27 of 30

Preventive Troubleshooting

Proactive, before-the-fault reference for the AGL system's highest-frequency failure modes — how to keep water, heat, corrosion, misalignment, and process error from ever reaching the fault log in the first place. Each topic follows a preventive engineering record: failure mode addressed → equipment/system → contributing causes → tools/materials → safety → prevention procedure → inspection/monitoring points → effectiveness verification → response if failure occurs anyway → preventive programme integration.

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01 · Preventive Troubleshooting (20)

01 · Preventive Troubleshooting Topics

20 of 20 topics published
PRV-621 Preventing Transformer Water Ingress

Failure Mode Addressed — Water entering the base can and reaching the isolation transformer body, connectors, or leads before it ever causes an insulation failure — addressed here at the prevention stage rather than after the transformer has already failed.

Equipment / System

L-830 series-circuit isolation transformers and the base cans, connectors, and drainage provisions that house and protect them.

Contributing Causes
HighBase can without a functional drain path (weep hole, gravel sump) allowing water to pool around the transformer
HighDegraded or missing lid gasket allowing surface water to enter directly
MediumDuct entries into the can not sealed, letting water track in along the cable route
MediumConnector not properly greased/seated, giving water a path into the can interior over time
LowElevated local water table or poor site grading directing water toward the can regardless of can condition
LowCondensation inside a sealed can from thermal cycling, mistaken for ingress if not distinguished during inspection
Required Tools / Materials
Dielectric grease (correct specification)Base-can lid gasket, correct size/materialDuct entry seals/bootsDrainage rod or sump-clearing toolBase-can moisture inspection logSite drainage/grading reference
Safety Precautions
  • LOTO the circuit before opening any base can for inspection or preventive work.
  • Treat any base can with standing water as an electrocution hazard until isolation is confirmed.
  • Use appropriate PPE for pit/can entry per site procedure.
Prevention Procedure
  1. BaselineInclude base-can drainage function, not just visual seal condition, in the standard inspection checklist for every PM visit.
  2. PreventionConfirm the weep hole/gravel sump is clear and functioning at every can opened, clearing debris or silt as needed.
  3. PreventionVerify the lid gasket is present, correctly seated, and not perished; replace if any doubt exists rather than reusing a marginal gasket.
  4. PreventionSeal duct entries into the can with the correct boot/sealant so water cannot track in along the cable route.
  5. PreventionApply dielectric grease correctly at every connector reconnection, as a standard step rather than only when a fault is found.
  6. VerificationRe-inspect the can after the next significant rainfall event to confirm the preventive measures are holding before considering the item closed.
Inspection / Monitoring Points
Weep hole/sump function
Lid gasket condition
Duct entry seal condition
Connector grease coverage
Standing water presence after rainfall
Site grading relative to the can
Effectiveness Verification

Re-inspect the can dry and after the next significant rain event, confirming no standing water and no moisture at the connector or transformer body before closing the preventive work order.

If Failure Occurs Despite Prevention
  • If moisture is found despite prevention, isolate and megger the transformer before re-energising.
  • Replace the transformer if insulation resistance is below the acceptable threshold.
  • Re-open and correct the drainage/seal deficiency that allowed the ingress rather than only drying and closing the can.
Preventive Programme Integration
  • Add base-can drainage function as a mandatory PM checklist item, not an optional visual check.
  • Track chronically wet can locations in the CMMS and prioritise them for civil drainage improvement.
  • Standardise the gasket and duct-seal specification across the fleet.
  • Require dielectric grease application to be signed off on every connector work order.
Related References

SOP: SOP-PRV-01 (Preventive Maintenance Procedure), SOP-CIVIL-02 (Drainage and Base-Can Remediation Procedure)

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

Diagram: Base-Can Detail Drawing

Case Study: Division 23 — Root Cause Analysis (RCA-554 Repeated Water Ingress RCA)

Rev 0 — Initial issue
PRV-622 Preventing Transformer Overheating

Failure Mode Addressed — Isolation transformers or CCR output transformers running at an elevated operating temperature that shortens insulation life, addressed proactively before it progresses to a thermal insulation failure.

Equipment / System

L-830 isolation transformers and CCR internal transformers, including their wattage/tap rating relative to the connected load and their thermal environment.

Contributing Causes
HighWattage/tap mismatch — a transformer supplying a load above its rated capacity, running permanently hot
HighRestricted ventilation around the transformer (undersized base can, blocked CCR house vents) preventing normal heat dissipation
MediumElevated ambient temperature at the installation location beyond the transformer's design assumption
MediumSustained overvoltage or harmonic distortion from the CCR increasing core/winding losses
LowTransformer nearing end of insulation life, so normal heat now produces faster degradation than when new
LowIncorrect transformer type substituted during a past repair, rated for a different duty cycle
Required Tools / Materials
Thermal imaging cameraWattage/tap verification checklistCCR output voltage/THD loggerVentilation inspection checklist for CCR house/pitTransformer nameplate/rating referenceAmbient temperature logger
Safety Precautions
  • LOTO the circuit before physical inspection; use non-contact thermal imaging where possible on live equipment under proper procedure.
  • Allow adequate cool-down time before handling a transformer suspected of overheating.
Prevention Procedure
  1. BaselineVerify the wattage/tap rating of every transformer at installation and at every replacement against the connected fixture load, not assumed to match the previous unit.
  2. PreventionInclude thermal imaging of a representative sample of transformers/base cans in the periodic PM programme, especially in high-ambient locations.
  3. PreventionConfirm CCR house/pit ventilation paths are clear of debris, vegetation, or blockage at every PM visit.
  4. PreventionVerify CCR output voltage and monitor for harmonic distortion if the CCR is inverter-based, correcting any deviation from design spec.
  5. PreventionFlag transformers approaching design end-of-life for proactive replacement rather than waiting for a thermal failure.
  6. VerificationRe-check thermal imaging results at the next PM cycle to confirm temperatures remain within the normal range for that transformer class.
Inspection / Monitoring Points
Transformer wattage/tap vs. design load
Base-can/CCR house ventilation condition
CCR output voltage and THD
Thermal imaging reading vs. baseline
Ambient temperature at the location
Transformer age vs. design life
Effectiveness Verification

Confirm via thermal imaging at the next scheduled visit that the transformer operates within its normal temperature range under actual load, with no upward trend versus the previous reading.

If Failure Occurs Despite Prevention
  • Replace a transformer confirmed to be overheating with a correctly rated unit.
  • Clear or improve ventilation where restriction is confirmed as a contributing factor.
  • Correct CCR output voltage/harmonic issues at the source.
  • Reduce connected load or upgrade transformer rating if a genuine capacity mismatch is confirmed.
Preventive Programme Integration
  • Make wattage/tap verification a mandatory, signed-off step on every transformer changeout.
  • Include ventilation checks as a standard CCR house/pit PM item.
  • Trend thermal imaging results by location to catch developing hot spots early.
  • Track transformer age by installation cohort to plan proactive replacement before end of life.
Related References

SOP: SOP-PRV-01 (Preventive Maintenance Procedure), SOP-RCL-12 (Transformer Test and Replacement Procedure)

Standards: FAA AC 150/5345-26, IEEE C57.12.91

Diagram: Circuit Design Specification (wattage/tap schedule)

Case Study: Division 23 — Root Cause Analysis (RCA-546 Repeated Transformer Failure RCA)

Rev 0 — Initial issue
PRV-623 Preventing Connector Burning

Failure Mode Addressed — L-823 or similar plug/receptacle connectors overheating and showing carbon tracking, melted insulation, or burnt contacts due to progressively rising contact resistance, addressed before the connector reaches thermal failure.

Equipment / System

L-823 primary connectors and secondary lamp/transformer connectors across the series circuit.

Contributing Causes
HighLoose or improperly seated connector pins allowing contact resistance to rise under load current over time
HighCorrosion at the contact surface increasing resistance and generating localised heat under normal operating current
MediumIncorrect or absent dielectric grease allowing oxidation to progress faster than normal
MediumA connector carrying current beyond its rated capacity due to a circuit design or load mismatch
LowRepeated disconnect/reconnect cycles wearing the contact plating faster than its rated cycle life
LowA connector from a batch with a known plating or contact-spring defect
Required Tools / Materials
Contact resistance meterCorrect-torque connector assembly toolDielectric grease (correct specification)Thermal imaging cameraConnector inspection/teardown kitConnector torque specification sheet
Safety Precautions
  • LOTO the circuit before disconnecting, inspecting, or reassembling any connector.
  • Treat a connector with visible heat damage as potentially still hazardous; do not force a seized or fused connector apart without confirming isolation.
Prevention Procedure
  1. BaselineInclude contact resistance spot-checks on a representative sample of connectors in the periodic PM programme rather than relying on visual inspection alone.
  2. PreventionRe-seat and re-grease every connector opened for any reason, as a standard step, not only when a fault is suspected.
  3. PreventionVerify correct connector torque/seating technique is used at every reconnection, and confirm the crew is trained to the current procedure.
  4. PreventionUse thermal imaging on a sample of connectors during a live period to catch early-stage hot connections before visible damage occurs.
  5. PreventionConfirm the connector's current rating matches the actual circuit load at design/verification stage.
  6. VerificationRe-check contact resistance or thermal signature on any connector flagged as marginal at the next scheduled visit.
Inspection / Monitoring Points
Contact resistance vs. baseline/specification
Visual condition — discolouration, pitting, carbon tracking
Grease coverage and condition
Connector current rating vs. actual circuit load
Thermal imaging signature under live load
Connector age/cycle count where tracked
Effectiveness Verification

Confirm contact resistance is within the accepted range and thermal imaging shows no elevated signature at the next PM visit following any preventive re-termination.

If Failure Occurs Despite Prevention
  • Replace any connector found with visible carbon tracking, melting, or pitting rather than attempting to clean and reuse it.
  • Re-terminate with correct grease and torque where the connector body itself is still serviceable.
  • Investigate circuit loading if a rating mismatch is suspected as a contributing factor.
Preventive Programme Integration
  • Make dielectric grease application and correct torque a mandatory, signed-off step on every connector work order.
  • Add thermal imaging of connectors to the periodic PM programme, prioritising high-load or high-cycle locations.
  • Track connector batch/date-code for early detection of a defective lot.
  • Refresh training on connector assembly technique at defined intervals.
Related References

SOP: SOP-PRV-01 (Preventive Maintenance Procedure), SOP-RCL-03 (Fixture Replacement Procedure)

Standards: FAA AC 150/5345-26, FAA AC 150/5345-46 (L-852)

Diagram: Connector Assembly Specification

Case Study: Division 23 — Root Cause Analysis (RCA-549 Repeated Connector Failure RCA)

Rev 0 — Initial issue
PRV-624 Preventing Cable Insulation Failure

Failure Mode Addressed — Primary or secondary series cable insulation degrading toward failure — from moisture, mechanical stress, thermal cycling, or age — addressed through proactive testing and protection before an actual insulation breakdown occurs.

Equipment / System

L-824 primary series cable and secondary cable, including duct banks, pull boxes, and field splices along the route.

Contributing Causes
HighChronic moisture at a duct/pull-box location progressively degrading insulation even without a visible fault yet
HighCable approaching end of design life across an installation-date cohort, with insulation resistance trending downward
MediumMechanical stress from ground movement, civil works, or vehicle loading at a specific route section
MediumSustained CCR output voltage or harmonics exceeding the cable insulation's comfortable operating margin
LowSubstandard splice/joint technique used during a past repair, creating a weak point before it fully fails
LowChemical exposure (de-icing fluid, fuel) attacking the cable jacket at a specific location
Required Tools / Materials
1000V/2500V insulation resistance testerInsulation resistance trend log by circuit/segmentAs-built route drawingCivil works/vehicle-loading history for the routeSplice kit specification sheetCCR output voltage/harmonic logger
Safety Precautions
  • LOTO the CCR before any insulation testing or cable work.
  • Obtain excavation clearance before any preventive work requiring pavement or verge opening.
  • Coordinate airside access through ATC/airfield operations.
Prevention Procedure
  1. BaselineInclude full-loop insulation resistance testing and trending, not spot checks alone, in the periodic PM programme for every circuit.
  2. PreventionPlot insulation resistance trends by circuit and by installation-date cohort to identify cable approaching end of life before it fails.
  3. PreventionFlag and prioritise chronically wet duct/pull-box locations for drainage remediation before insulation degrades further.
  4. PreventionVerify CCR output voltage and harmonic content remains within the cable's design margin.
  5. PreventionCoordinate with civil works teams on any excavation or resurfacing near known cable routes to avoid mechanical damage.
  6. VerificationConfirm insulation resistance trend has stabilised or improved at the next PM cycle following any preventive remediation.
Inspection / Monitoring Points
Insulation resistance trend by circuit/segment
Installation-date cohort vs. design life
Duct/pull-box moisture condition along the route
CCR output voltage/harmonic content
Civil works activity near the route
Splice/joint condition at known repair points
Effectiveness Verification

Re-test insulation resistance at the next two scheduled PM visits following any preventive action and confirm the trend has stabilised within the acceptable range before closing the item.

If Failure Occurs Despite Prevention
  • Repair or replace cable segments where insulation resistance has fallen below the acceptable threshold, before a full fault occurs.
  • Remediate duct/pull-box drainage at chronically wet locations.
  • Correct any confirmed CCR overvoltage/harmonic issue at the source.
Preventive Programme Integration
  • Trend insulation resistance by installation cohort to plan proactive replacement ahead of expected end of life.
  • Standardise splice kit specification and require photo documentation of every buried splice.
  • Maintain accurate as-built records of every joint, pull box, and repair splice for future reference.
  • Include cable route condition in the risk assessment for any nearby civil works project.
Related References

SOP: SOP-PRV-01 (Preventive Maintenance Procedure), SOP-RCL-02 (Series Circuit Fault Location Procedure)

Standards: IEC 60364, IEEE 43, ICAO Annex 14 Vol I

Diagram: As-Built Duct and Cable Route Drawing

Case Study: Division 23 — Root Cause Analysis (RCA-548 Repeated Cable Failure RCA, RCA-555 Repeated Insulation Failure RCA)

Rev 0 — Initial issue
PRV-625 Preventing Fixture Water Ingress

Failure Mode Addressed — Water entering an inset or elevated fixture housing before it reaches the lamp/LED module, optics, or wiring and causes an operational failure, addressed at the seal and drainage stage.

Equipment / System

Inset L-852 fixtures and elevated fixture housings, including their lens/optic seals, gaskets, cable entries, and base-can drainage.

Contributing Causes
HighDegraded or improperly seated lens/optic gasket allowing water directly into the fixture head
HighBase-can water accumulation reaching the fixture body through the base connection
MediumCable entry into the fixture not properly sealed, allowing water to track in along the secondary cable
MediumPhysical damage (impact, jet blast debris) compromising the housing seal without a full fixture failure yet
LowFixture design/model with a known marginal seal at that specific joint
LowCondensation from thermal cycling inside a sealed fixture, distinct from true ingress
Required Tools / Materials
Lens/optic gasket, correct type and sizeCable entry seal/glandBase-can drainage inspection kitFixture housing inspection checklistTorque specification for lens/housing fastenersMoisture indicator or visual inspection light
Safety Precautions
  • LOTO the circuit before opening any fixture housing.
  • Coordinate airside access through ATC/airfield operations.
  • Use FOD-safe tools and account for every item before leaving the movement area.
Prevention Procedure
  1. BaselineInclude lens/optic gasket and cable entry seal condition in the standard fixture PM inspection checklist, not only when a fault is reported.
  2. PreventionReplace gaskets showing any sign of perishing, compression set, or improper seating, rather than reusing marginal seals.
  3. PreventionVerify base-can drainage is functional at every fixture serviced, since a wet can will eventually compromise even a well-sealed fixture.
  4. PreventionConfirm lens/housing fasteners are torqued to specification at every reassembly.
  5. PreventionInspect fixtures in high-impact zones (jet blast, snow-plough routes) more frequently for seal-compromising physical damage.
  6. VerificationRe-inspect the fixture after the next significant rainfall event to confirm no moisture has entered before considering the item closed.
Inspection / Monitoring Points
Lens/optic gasket condition
Cable entry seal condition
Base-can drainage function
Housing fastener torque
Physical damage signature (impact, cracking)
Moisture presence after rainfall
Effectiveness Verification

Re-inspect the fixture dry and after the next significant rainfall event, confirming no moisture at the lens, optic, or wiring before closing the preventive work order.

If Failure Occurs Despite Prevention
  • Replace any gasket or seal found compromised rather than attempting a field repair with unsuitable material.
  • Remediate base-can drainage if a wet can is contributing to fixture ingress.
  • Replace the fixture if moisture has already reached the lamp/LED module or wiring with visible corrosion.
Preventive Programme Integration
  • Standardise gasket/seal specification and stock the correct part for the fixture models in use.
  • Add torque verification for lens/housing fasteners as a mandatory PM step.
  • Flag high-impact zones for more frequent fixture seal inspection.
  • Track fixture-level moisture findings in the CMMS to identify a design or batch pattern early.
Related References

SOP: SOP-PRV-01 (Preventive Maintenance Procedure), SOP-RCL-03 (Fixture Replacement Procedure)

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

Diagram: Fixture Housing and Seal Detail Drawing

Case Study: Division 23 — Root Cause Analysis (RCA-550 Repeated Fixture Failure RCA)

Rev 0 — Initial issue
PRV-626 Preventing LED Failure

Failure Mode Addressed — LED light-emitting modules degrading or failing before their rated life due to thermal stress, driver mismatch, or moisture, addressed proactively at the driver-matching and thermal-management stage.

Equipment / System

LED light-emitting modules and their drivers within AGL fixtures.

Contributing Causes
HighDriver supplying current outside the LED module's rated range, accelerating thermal degradation of the junction
HighInadequate heat sinking or restricted airflow at the fixture design/location shortening LED life
MediumVoltage transients or harmonic content from the CCR/driver stressing the LED junction over repeated cycles
MediumMoisture ingress at the optic seal degrading the module from behind the lens
LowA LED module batch with a known manufacturing defect
LowIncorrect LED module colour/type installed, drifting toward the edge of the chromaticity box faster than the correct type
Required Tools / Materials
Driver output current/voltage meterLED module datasheet and thermal derating curveThermal imaging cameraPhotometric test equipmentOptic seal inspection kitLED/driver compatibility reference table
Safety Precautions
  • LOTO the circuit before removing any LED module or driver.
  • Allow LED driver capacitors to discharge per manufacturer procedure before handling.
Prevention Procedure
  1. BaselineVerify driver-to-LED module compatibility at every installation and at every independent replacement of either component, not assumed to match automatically.
  2. PreventionInclude thermal imaging of a sample of LED fixtures in the periodic PM programme, particularly in warmer climates or high-ambient locations.
  3. PreventionConfirm optic seal integrity at every LED fixture serviced to prevent moisture reaching the module from behind.
  4. PreventionTrend photometric survey results by LED batch/installation cohort to catch early lumen depreciation ahead of a hard failure.
  5. PreventionVerify CCR/driver output quality and correct any confirmed overvoltage or harmonic issue.
  6. VerificationRe-check thermal imaging and photometric output at the next PM/survey cycle to confirm the module remains within normal operating parameters.
Inspection / Monitoring Points
Driver output current/voltage vs. LED module rating
Heat-sink/junction temperature (thermal imaging)
Photometric output trend by batch/cohort
Optic seal condition
LED module batch/date-code
CCR/driver output quality
Effectiveness Verification

Confirm at the next scheduled photometric survey and thermal check that the LED module's output and temperature remain within expected parameters for its hours in service.

If Failure Occurs Despite Prevention
  • Replace a mismatched driver with one correctly rated for the LED module.
  • Replace a LED module confirmed to be from a defective batch.
  • Improve thermal management at the fixture if elevated temperature is confirmed as a contributing factor.
Preventive Programme Integration
  • Capture LED/driver batch and installation date in the CMMS to enable hours-to-failure trending against rated life.
  • Make driver-to-module compatibility verification a mandatory step whenever either component is independently replaced.
  • Add thermal imaging of LED fixtures to the periodic PM programme in high-ambient locations.
  • Trend photometric results by batch, not only by division.
Related References

SOP: SOP-PRV-01 (Preventive Maintenance Procedure), SOP-PHM-01 (Photometric Survey Procedure)

Standards: FAA AC 150/5345-46 (L-852 LED), ICAO Annex 14 Vol I Appendix 2, IESNA LM-80/TM-21

Diagram: LED Fixture Thermal and Electrical Design Specification

Case Study: Division 23 — Root Cause Analysis (RCA-551 Repeated LED Failure RCA)

Rev 0 — Initial issue
PRV-627 Preventing Sign Board Failure

Failure Mode Addressed — Illuminated taxiway/runway guidance sign internal components (light source, driver, panel) degrading toward failure from heat, moisture, or vibration, addressed before an actual internal fault occurs.

Equipment / System

L-858 illuminated signs — housing, door seal, internal light source/driver, panel assembly, and cooling provision.

Contributing Causes
HighRestricted ventilation or a failing cooling fan allowing internal heat build-up over time
HighDegraded door seal or cable gland allowing gradual moisture ingress
MediumBallast/driver specification not correctly matched to the fitted light source, causing accelerated wear
MediumSign located in a zone with elevated vibration (adjacent to high-traffic taxiway) fatiguing internal connections
LowInternal wiring harness batch with a known defect
LowSign structure showing early signs of instability or impact exposure
Required Tools / Materials
Thermal imaging cameraDoor seal and cable gland inspection kitBallast/driver specification vs. fitted light source referenceCooling fan test procedureSign structural inspection checklistInternal wiring harness inspection kit
Safety Precautions
  • LOTO the circuit before opening the sign housing.
  • Confirm the sign structure is stable before working at height or near traffic.
  • Coordinate airside access through ATC/airfield operations.
Prevention Procedure
  1. BaselineInclude internal temperature, door seal, and cooling fan checks in the standard sign PM inspection checklist.
  2. PreventionVerify ballast/driver specification matches the fitted light source at every service, correcting any mismatch found.
  3. PreventionTest cooling fan operation, where fitted, at every PM visit rather than assuming continued function.
  4. PreventionReplace door seals and cable glands showing any sign of perishing before they fail completely.
  5. PreventionInspect signs in known high-vibration zones more frequently for connection fatigue.
  6. VerificationRe-check internal temperature and seal integrity at the next PM cycle to confirm preventive measures are holding.
Inspection / Monitoring Points
Internal housing temperature
Door seal and cable gland condition
Cooling fan function
Ballast/driver rating vs. fitted light source
Internal wiring harness condition
Sign structural stability and traffic proximity
Effectiveness Verification

Confirm at the next PM visit that internal temperature remains within normal range and no moisture staining or connection fatigue is present.

If Failure Occurs Despite Prevention
  • Replace a failing cooling fan or restore blocked ventilation before internal components are damaged by heat.
  • Restore door seal/gland integrity where early moisture signs are found.
  • Correct ballast/driver mismatch to the correct specification for the fitted light source.
Preventive Programme Integration
  • Add door seal and cooling-fan checks as standard, mandatory PM items for all illuminated signs.
  • Verify ballast/driver-to-light-source compatibility at every service, not only at initial installation.
  • Track sign ID-level condition trends in the CMMS to catch developing issues early.
  • Review sign siting relative to known vibration/traffic-proximity zones for future placements.
Related References

SOP: SOP-PRV-01 (Preventive Maintenance Procedure), SOP-SGN-01 (Illuminated Sign Maintenance Procedure)

Standards: FAA AC 150/5345-44 (L-858 signs), ICAO Annex 14 Vol I

Diagram: Sign Internal Wiring and Ventilation Detail Drawing

Case Study: Division 23 — Root Cause Analysis (RCA-552 Repeated Sign Failure RCA)

Rev 0 — Initial issue
PRV-628 Preventing CCR Overheating

Failure Mode Addressed — A Constant Current Regulator running at an elevated internal or house/pit temperature that stresses power electronics and shortens component life, addressed before it triggers a thermal trip or causes component degradation.

Equipment / System

CCR (transformer-type or TSCR/inverter-type) internal components and its house/pit ventilation and cooling provision.

Contributing Causes
HighRestricted CCR house/pit ventilation from blocked louvres, vegetation growth, or debris accumulation
HighA failing or undersized cooling fan/HVAC unit within the CCR house
MediumCCR operating consistently near its rated capacity for the connected load, generating more heat than a properly derated unit would
MediumElevated ambient temperature at the site beyond the CCR's design assumption, especially in peak summer conditions
LowInternal component degradation (capacitors, SCR/IGBT) increasing losses and heat generation as the unit ages
LowDust/dirt accumulation on heat sinks reducing their effective dissipation area
Required Tools / Materials
Thermal imaging cameraCCR house/pit temperature loggerVentilation/louvre inspection checklistCooling fan/HVAC test procedureHeat sink cleaning kitCCR load vs. rated capacity reference
Safety Precautions
  • LOTO the CCR before internal inspection or cleaning.
  • Allow discharge time for output capacitors per manufacturer procedure before handling internal components.
Prevention Procedure
  1. BaselineInclude CCR house/pit ventilation and internal temperature checks in the standard PM checklist for every visit.
  2. PreventionClear louvres, vents, and any vegetation or debris blocking airflow at every PM visit.
  3. PreventionTest cooling fan/HVAC operation and confirm correct thermostat setpoint where fitted.
  4. PreventionClean heat sinks and internal surfaces of dust/dirt accumulation on a defined interval.
  5. PreventionCompare actual CCR loading against rated capacity, flagging any unit consistently operating near its limit for capacity review.
  6. VerificationConfirm via thermal imaging at the next PM visit, ideally during peak-temperature season, that internal temperatures remain within the manufacturer's normal range.
Inspection / Monitoring Points
CCR house/pit internal temperature trend
Ventilation/louvre condition
Cooling fan/HVAC function
Heat sink cleanliness
CCR load vs. rated capacity
Ambient temperature at the site
Effectiveness Verification

Confirm via thermal imaging and temperature log review at the next PM cycle, particularly during the warmest season, that the CCR operates within its normal thermal range with no upward trend.

If Failure Occurs Despite Prevention
  • Clear ventilation blockages and repair or replace a failing cooling fan/HVAC unit promptly.
  • Clean heat sinks if dust accumulation is found to be significantly reducing dissipation.
  • Consider load redistribution or capacity upgrade if the CCR is confirmed to be consistently near its rated limit.
Preventive Programme Integration
  • Make ventilation and cooling-system checks a mandatory, signed-off PM item, not a discretionary one.
  • Trend CCR house/pit temperature over time to catch a developing issue before a thermal trip occurs.
  • Schedule heat sink cleaning on a defined interval appropriate to the site's dust/debris exposure.
  • Include CCR loading review in the periodic asset capacity assessment.
Related References

SOP: SOP-PRV-01 (Preventive Maintenance Procedure), SOP-CCR-04 (CCR LOTO Procedure)

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

Diagram: CCR House Ventilation and Layout Drawing

Case Study: Division 23 — Root Cause Analysis (RCA-547 Repeated CCR Trip RCA)

Rev 0 — Initial issue
PRV-629 Preventing CCR False Alarms

Failure Mode Addressed — A CCR generating nuisance alarms or trips (overcurrent, earth fault, communication) that do not correspond to a genuine fault, addressed at the settings, calibration, and signal-integrity level before they erode operator confidence in the alarm system.

Equipment / System

CCR protection relays, alarm thresholds, ALCMS/SCADA interface, and associated sensors/wiring.

Contributing Causes
HighProtection relay thresholds set tighter than the circuit's genuine operating tolerance, triggering on normal variation
HighSensor or signal wiring picking up electromagnetic interference from nearby equipment, generating a false reading
MediumALCMS/SCADA software or firmware not updated to the current version, carrying a known alarm-logic bug
MediumLoose or corroded sensor wiring connection causing intermittent false signals
LowA commissioning-stage setting never re-validated after a circuit modification changed the genuine tolerance
LowOperator/maintenance staff resetting and dismissing alarms without logging the pattern, masking a developing genuine issue as "just another false alarm"
Required Tools / Materials
Protection relay settings printout vs. design calculationALCMS/SCADA alarm log with timestamp and typeEMI survey equipment, if warrantedSensor wiring continuity/insulation testerFirmware/software version logAlarm pattern trend chart
Safety Precautions
  • LOTO the CCR before any internal relay or wiring inspection.
  • Do not disable or widen alarm thresholds without an engineering review confirming the change is safe.
Prevention Procedure
  1. BaselineVerify protection relay thresholds against the design calculation at commissioning and after any circuit modification, not left at generic factory defaults.
  2. PreventionRoute and shield sensor/signal wiring away from known high-power or high-EMI equipment during installation and rework.
  3. PreventionKeep ALCMS/SCADA firmware and software on the current approved version to avoid known alarm-logic bugs.
  4. PreventionInspect and re-torque sensor wiring connections as part of the periodic PM programme.
  5. PreventionRequire every alarm event, including those dismissed as "false," to be logged with a brief cause note rather than silently reset.
  6. VerificationReview the alarm log at the next PM cycle to confirm the nuisance-alarm rate has genuinely reduced, not just been reset more quickly.
Inspection / Monitoring Points
Protection relay threshold vs. design calculation
Alarm log pattern by type and time
EMI presence near sensor wiring
Sensor wiring connection integrity
Firmware/software version vs. approved baseline
Alarm dismissal/logging discipline
Effectiveness Verification

Confirm via alarm log review at the next PM cycle that the nuisance-alarm frequency has dropped and that every alarm event, once genuinely resolved, is documented with its cause.

If Failure Occurs Despite Prevention
  • Re-calculate and adjust protection thresholds where confirmed tighter than the design tolerance.
  • Re-route or shield wiring where EMI is confirmed as the cause.
  • Update firmware/software where a known bug is implicated.
  • Re-terminate any loose or corroded sensor connection found.
Preventive Programme Integration
  • Require alarm threshold re-validation as a mandatory step after any circuit modification.
  • Maintain firmware/software on a defined update schedule aligned to manufacturer releases.
  • Build a non-punitive culture requiring every alarm to be logged with a cause, even if ultimately deemed non-genuine.
  • Periodically audit the alarm log for patterns suggesting an unaddressed nuisance source.
Related References

SOP: SOP-PRV-01 (Preventive Maintenance Procedure), SOP-CCR-07 (Protection Relay Verification), SOP-COMMS-01 (ALCMS/SCADA Network Maintenance Procedure)

Standards: ICAO Annex 14 Vol I, IEC 61439 (protection coordination)

Diagram: CCR Protection Coordination Study

Case Study: Division 23 — Root Cause Analysis (RCA-547 Repeated CCR Trip RCA, RCA-559 Repeated Communication Failure RCA)

Rev 0 — Initial issue
PRV-630 Preventing Earth Faults

Failure Mode Addressed — Earth bonding and earth-loop resistance degrading toward the point of triggering earth-fault protection, addressed through proactive bonding maintenance and resistance trending before a trip or a genuine insulation-to-earth fault occurs.

Equipment / System

AGL earthing/grounding system — CCR earth bar, transformer secondary earthing, fixture body earthing, earth electrodes, and ring conductors.

Contributing Causes
HighProgressive corrosion at bonding points, especially dissimilar-metal joints, gradually raising earth-loop resistance
HighLoose or under-torqued bonding connections that were never re-checked after initial installation
MediumRising soil resistivity at a location due to seasonal moisture change or soil composition, pushing resistance toward the threshold
MediumInsufficient earth electrode density or ring conductor sizing for a specific section relative to actual soil conditions
LowPhysical damage to buried earth conductors from unrelated civil works
LowProtection relay earth-fault threshold set tighter than the circuit's natural leakage tolerance
Required Tools / Materials
Earth resistance/loop testerBonding/connection inspection kit (torque wrench, wire brush, corrosion inhibitor)Soil resistivity meter, if availableAs-built earthing/grounding drawingEarth-loop resistance trend logCorrosion-resistant bonding hardware
Safety Precautions
  • LOTO the circuit before testing or working on earthing connections.
  • Treat any exposed conductive part as potentially live until earth continuity and isolation are confirmed.
  • Use appropriate PPE when excavating to expose buried earth electrodes.
Prevention Procedure
  1. BaselineInclude earth-loop resistance testing and trending, not a pass/fail spot check alone, in the periodic PM programme for every circuit.
  2. PreventionInspect and re-torque bonding connections on a defined interval, using corrosion-resistant hardware for dissimilar-metal joints.
  3. PreventionTrend earth-loop resistance by location and season to identify a rising pattern before it approaches the protection threshold.
  4. PreventionAdd supplementary earth electrodes proactively at locations with historically marginal or rising resistance.
  5. PreventionVerify earth-fault protection thresholds remain appropriately set relative to the circuit's actual leakage characteristics.
  6. VerificationRe-test earth-loop resistance after the next significant rainfall/seasonal change to confirm the trend has stabilised.
Inspection / Monitoring Points
Earth-loop resistance trend by location
Bonding connection torque and corrosion condition
Soil resistivity, seasonal comparison
Earth electrode density vs. design for the section
Protection relay earth-fault threshold vs. design tolerance
Trip history correlation with rainfall/season
Effectiveness Verification

Confirm via earth-loop resistance testing at the next two PM cycles, spanning at least one seasonal change, that the reading remains comfortably within the acceptable threshold.

If Failure Occurs Despite Prevention
  • Re-terminate corroded or loose bonding points with correctly rated, compatible-metal hardware.
  • Add supplementary earth electrodes where soil resistivity is confirmed as a contributing factor.
  • Re-calculate and adjust the earth-fault protection threshold if it is confirmed tighter than design tolerance.
Preventive Programme Integration
  • Make earth-loop resistance trending a standard, mandatory PM item across the full field, not only at flagged locations.
  • Standardise bonding hardware and corrosion-protection method for dissimilar-metal joints.
  • Flag locations with historically marginal earth resistance for closer seasonal monitoring.
  • Review earth-fault protection settings against actual circuit leakage characteristics after any circuit modification.
Related References

SOP: SOP-PRV-01 (Preventive Maintenance Procedure), SOP-EARTH-01 (Earthing System Test and Bonding Procedure)

Standards: IEC 60364-5-54, IEEE 142, ICAO Annex 14 Vol I

Diagram: As-Built Earthing and Grounding Ring Drawing

Case Study: Division 23 — Root Cause Analysis (RCA-553 Repeated Earth Fault RCA)

Rev 0 — Initial issue
PRV-631 Preventing Lightning Damage

Failure Mode Addressed — AGL equipment (CCR, transformers, fixtures, ALCMS/SCADA electronics) at risk of surge damage from a nearby or direct lightning strike, addressed through proactive surge protection and bonding rather than after equipment has already been damaged.

Equipment / System

Lightning/surge protection devices (SPDs) at CCR input/output, ALCMS/SCADA communication links, and the overall earthing/bonding system that provides the discharge path.

Contributing Causes
HighSurge protection devices (SPDs) that are aged, degraded, or already sacrificed from a prior event and not yet replaced
HighInadequate or missing SPD coverage at a critical interface point (e.g., communication links between buildings) leaving a surge path into sensitive electronics
MediumEarthing system resistance too high to effectively dissipate a surge, compounding SPD limitations
MediumSPDs of incorrect let-through voltage rating for the protected equipment's actual sensitivity
LowLack of a formal SPD inspection/replacement interval, so degraded units remain in service unnoticed
LowSurge protection scheme not extended to newer equipment added to the system after the original design
Required Tools / Materials
SPD condition indicator/testerEarth resistance testerSurge protection scheme drawingSPD manufacturer replacement-interval and let-through voltage referenceLightning strike/event log correlated with equipment fault historySPD inventory and spares
Safety Precautions
  • LOTO affected circuits before SPD inspection or replacement.
  • Treat any equipment following a known lightning event as potentially still hazardous until inspected.
  • Follow manufacturer procedure for SPD handling given potential residual energy after a strike.
Prevention Procedure
  1. BaselineInclude SPD condition indicator checks in the standard PM checklist at every CCR, ALCMS node, and other protected interface.
  2. PreventionReplace SPDs showing a degraded/end-of-life indicator immediately rather than waiting for a scheduled batch replacement.
  3. PreventionVerify earth-loop resistance at surge protection points meets the design requirement for effective discharge.
  4. PreventionExtend the surge protection scheme to any equipment added to the system since the original design, including new communication links.
  5. PreventionConfirm SPD let-through voltage ratings match the actual sensitivity of the protected equipment.
  6. VerificationRe-check SPD condition indicators at the next PM cycle and after any known regional lightning activity to confirm continued protection.
Inspection / Monitoring Points
SPD condition indicator status at each protected point
Earth-loop resistance at surge protection locations
SPD let-through voltage vs. equipment sensitivity
Surge protection coverage vs. current equipment inventory
Lightning event log vs. equipment fault correlation
SPD age vs. manufacturer replacement interval
Effectiveness Verification

Confirm all SPD condition indicators show a healthy state at the next PM cycle, and cross-check equipment fault logs following any known regional lightning activity for absence of surge-related damage.

If Failure Occurs Despite Prevention
  • Replace any SPD indicating degradation or sacrifice immediately.
  • Repair or replace equipment confirmed damaged by a surge event that bypassed protection.
  • Extend surge protection coverage to any gap identified during the review.
Preventive Programme Integration
  • Establish a defined SPD replacement interval based on manufacturer guidance rather than waiting for visible failure.
  • Maintain SPD spares inventory for rapid post-event replacement.
  • Review and update the surge protection scheme drawing whenever new equipment is added to the system.
  • Correlate regional lightning activity data with equipment fault trends to validate protection effectiveness.
Related References

SOP: SOP-PRV-01 (Preventive Maintenance Procedure), SOP-SURGE-01 (Lightning and Surge Protection Maintenance Procedure)

Standards: IEC 62305 (lightning protection), IEEE C62.41 (surge environments), ICAO Annex 14 Vol I

Diagram: Surge Protection Scheme Drawing

Case Study: Division 22 — Lightning and Surge Protection Troubleshooting

Rev 0 — Initial issue
PRV-632 Preventing Flood-Related Failures

Failure Mode Addressed — AGL equipment at risk of submersion or water damage during heavy rainfall, drainage overload, or seasonal flooding, addressed through proactive site drainage and equipment elevation review before an actual flood event causes widespread equipment loss.

Equipment / System

CCR houses/pits, base cans, pull boxes, and any low-lying equipment locations across the airfield relative to the site drainage system.

Contributing Causes
HighSite drainage system undersized or degraded (silted drains, blocked culverts) relative to actual peak rainfall intensity
HighEquipment sited at a low point in the local grading without adequate flood margin above known high-water levels
MediumSeasonal changes in drainage basin behaviour (upstream development, changed land use) not reflected in the original drainage design
MediumCCR house/pit flood barriers or seals absent or degraded
LowEmergency response plan for flood warning not clearly defined, delaying protective action
LowClimate-pattern shift increasing rainfall intensity beyond original design-basis assumptions
Required Tools / Materials
Site drainage survey/as-builtHistorical flood/high-water-level recordsCCR house/pit flood barrier inspection kitRainfall intensity/weather forecast monitoringEmergency response plan for flood eventsSump pump and emergency dewatering equipment
Safety Precautions
  • Never approach or work on electrical equipment in standing floodwater; treat it as energised and hazardous regardless of isolation status until confirmed safe by qualified personnel.
  • Follow site emergency procedures for flood warning and evacuation.
Prevention Procedure
  1. BaselineInclude site drainage capacity and condition as a standing item in the periodic infrastructure review, not only reactive after a flood event.
  2. PreventionMaintain drainage channels, culverts, and sumps clear of silt and debris on a defined schedule ahead of the wet season.
  3. PreventionReview equipment siting for any location below the known or design-basis high-water level, prioritising elevation or relocation where found.
  4. PreventionInstall or verify flood barriers/seals at CCR houses and pits in flood-risk zones.
  5. PreventionEstablish and rehearse a flood-warning emergency response plan, including pre-emptive equipment isolation if forecast conditions warrant.
  6. VerificationConfirm drainage clearance and barrier condition ahead of each wet season, and review equipment performance after any significant rainfall event.
Inspection / Monitoring Points
Drainage channel/culvert/sump condition
Equipment elevation vs. known high-water level
CCR house/pit flood barrier condition
Rainfall intensity trend vs. design basis
Emergency response plan currency
Post-event equipment inspection findings
Effectiveness Verification

Confirm ahead of the wet season that drainage is clear and barriers are intact, and confirm after any significant rainfall event that no equipment showed water intrusion.

If Failure Occurs Despite Prevention
  • Deploy emergency dewatering and isolate affected equipment immediately if flooding does occur.
  • Inspect and megger any equipment exposed to floodwater before re-energising, replacing as needed.
  • Escalate drainage capacity or equipment elevation deficiencies for capital improvement if a near-miss or actual event reveals a gap.
Preventive Programme Integration
  • Schedule drainage clearance ahead of the wet season as a standing annual task.
  • Maintain a register of equipment locations relative to known flood risk for prioritised improvement planning.
  • Integrate weather/rainfall forecast monitoring into the maintenance planning process.
  • Review and update the flood emergency response plan periodically, including a practice drill.
Related References

SOP: SOP-PRV-01 (Preventive Maintenance Procedure), SOP-CIVIL-02 (Drainage and Base-Can Remediation Procedure), SOP-EMRG-01 (Flood Emergency Response Procedure)

Standards: ICAO Annex 14 Vol I, local civil/drainage design codes

Diagram: Site Drainage and Flood Risk Map

Case Study: Division 24 — Complete Runway Lighting Failure

Rev 0 — Initial issue
PRV-633 Preventing Alignment Errors

Failure Mode Addressed — Fixture, PAPI/APAPI, or approach lighting element aim drifting out of tolerance over time due to foundation movement, mechanism wear, or procedural inconsistency, addressed proactively through survey trending and mounting hardware maintenance.

Equipment / System

Elevated and inset AGL fixtures with adjustable aim, PAPI/APAPI units, and their foundations and aiming mechanisms.

Contributing Causes
HighGround settlement or frost heave at a specific foundation gradually tilting the unit between survey cycles
HighAiming mechanism/mounting hardware that does not reliably hold torque after adjustment, allowing drift under normal vibration
MediumVibration from nearby high-traffic taxiway, road, or construction activity disturbing the mounting over time
MediumInconsistent aiming procedure or reference points used across different survey visits or technicians
LowSurvey equipment calibration drift producing an apparent alignment change that is partly a measurement artefact
LowPhysical disturbance from routine maintenance access (mowing, snow clearance) nudging the unit
Required Tools / Materials
Precision inclinometer/theodolite or PAPI aiming toolAlignment survey trend log by unitFoundation inspection checklistAiming mechanism torque specificationSurvey reference-point documentationVibration source mapping
Safety Precautions
  • LOTO the circuit before working on or near an energised elevated fixture.
  • Use fall-protection and stable access equipment when working on elevated units.
  • Coordinate airside access through ATC/airfield operations, particularly for PAPI/approach lighting units.
Prevention Procedure
  1. BaselineInclude alignment verification in the standard periodic survey programme with consistent reference points and equipment across all visits.
  2. PreventionInspect foundations for early signs of settlement or cracking at every alignment survey, not only when drift is already measured.
  3. PreventionVerify aiming mechanism hardware holds torque correctly at every adjustment, upgrading hardware where a unit repeatedly fails to hold.
  4. PreventionStandardise the aiming procedure and reference points across all technicians and survey visits.
  5. PreventionFlag units near known vibration sources for closer-interval survey.
  6. VerificationConfirm alignment remains within tolerance at the next scheduled survey following any preventive foundation or hardware work.
Inspection / Monitoring Points
Alignment drift trend, full survey history
Foundation condition (settlement, cracking)
Aiming mechanism torque-holding capability
Consistency of aiming procedure/reference points across visits
Proximity to known vibration sources
Survey equipment calibration status
Effectiveness Verification

Confirm at the next scheduled survey that alignment remains within tolerance, with a stable or improving trend versus the previous cycle.

If Failure Occurs Despite Prevention
  • Re-align any unit found outside tolerance using the standardised procedure and reference points.
  • Repair or reinforce a foundation showing confirmed settlement.
  • Replace aiming mechanism hardware confirmed unable to hold torque reliably.
Preventive Programme Integration
  • Standardise aiming mechanism hardware specification across the fleet to reduce hold-torque variability.
  • Include foundation visual inspection as a standard item during every alignment survey.
  • Flag units with any history of drift for closer-interval monitoring until the pattern is resolved.
  • Periodically cross-validate survey equipment and reference points across technicians.
Related References

SOP: SOP-PRV-01 (Preventive Maintenance Procedure), SOP-PAPI-01 (PAPI/APAPI Alignment Procedure)

Standards: ICAO Annex 14 Vol I (PAPI/APAPI alignment tolerance), FAA AC 150/5345-28

Diagram: PAPI/Fixture Foundation and Aiming Mechanism Detail Drawing

Case Study: Division 23 — Root Cause Analysis (RCA-557 Repeated Alignment Failure RCA)

Rev 0 — Initial issue
PRV-634 Preventing Incorrect Torque

Failure Mode Addressed — Electrical and mechanical connections (connectors, bonding points, mounting hardware, terminal lugs) being assembled to incorrect torque values, addressed proactively through standardised tooling, training, and verification before it produces a loose or overstressed joint.

Equipment / System

All torque-critical connections across the AGL system — connectors, earth bonding points, fixture mounting hardware, terminal lugs, and CCR internal connections.

Contributing Causes
HighTorque specification not readily available to the technician at the point of work, leading to a "feel-based" assembly instead of a measured one
HighIncorrect or uncalibrated torque tool used for the task
MediumTime or access-window pressure leading to rushed assembly without verification
MediumInconsistent training across the maintenance team on correct torque technique for different connection types
LowA connection type where the specified torque value itself is ambiguous or missing from the documentation
LowOver-torquing in an attempt to "make sure it's tight," which can be as damaging as under-torquing
Required Tools / Materials
Calibrated torque wrench, correct range for the taskTorque specification reference card/tableTorque calibration verification recordWork order torque-value sign-off fieldTraining/competency record for torque-critical tasksConnection type-to-torque-value lookup table
Safety Precautions
  • LOTO the circuit before any torque-critical connection work.
  • Use the correct torque tool range for the fastener; an oversized wrench reduces accuracy on small fasteners.
Prevention Procedure
  1. BaselinePublish and distribute a single authoritative torque specification reference for every connection type in the AGL system, accessible to technicians in the field.
  2. PreventionRequire calibrated torque tools for all torque-critical work, with calibration status checked before each use period.
  3. PreventionAdd a torque-value sign-off field to the relevant work order types so the applied value is documented, not assumed.
  4. PreventionProvide standardised training on torque technique for each connection type, refreshed at a defined interval.
  5. PreventionAvoid scheduling torque-critical work under severe time pressure where verification would be skipped; build adequate time into the access window.
  6. VerificationSpot-check a sample of recently completed torque-critical work orders against the documented sign-off value during routine PM audits.
Inspection / Monitoring Points
Torque tool calibration status
Torque specification availability at point of work
Work order sign-off completion rate for torque-critical tasks
Sample re-check of applied torque on recent work
Technician training/competency record
Time pressure/access-window adequacy for the task
Effectiveness Verification

Confirm through periodic work-order audit that torque values are being documented and that sample re-checks of recent work fall within the specified range.

If Failure Occurs Despite Prevention
  • Re-torque any connection found outside specification during audit or inspection.
  • Provide targeted retraining where a technician-specific pattern of incorrect torque is identified.
  • Recalibrate or replace a torque tool found out of calibration.
Preventive Programme Integration
  • Make torque specification reference material a standard part of every relevant work package, not something the technician must look up separately.
  • Build torque tool calibration checks into the tool-issue/return process.
  • Include torque-value sign-off as a mandatory, non-skippable field on relevant work orders.
  • Periodically audit closed work orders for torque documentation completeness.
Related References

SOP: SOP-PRV-01 (Preventive Maintenance Procedure), SOP-QA-01 (Work Order Closure and Verification Procedure)

Standards: ISO 9001:2015 Cl. 8.5/8.7, manufacturer torque specifications for each connection type

Diagram: Torque Specification Reference Table

Case Study: Division 23 — Root Cause Analysis (RCA-562 Installation Error Root Cause)

Rev 0 — Initial issue
PRV-635 Preventing Improper Cable Jointing

Failure Mode Addressed — Field splices and cable joints assembled with incorrect technique, kit selection, or environmental protection, addressed proactively before the joint becomes a future insulation or connection failure point.

Equipment / System

Field splices and joints on primary series cable, secondary cable, and any buried or in-pull-box cable connections.

Contributing Causes
HighIncorrect splice kit selected for the cable voltage class or environmental exposure (buried vs. above-ground) at that location
HighSplice assembled without proper surface preparation (cleaning, stripping to correct dimension) before the kit is applied
MediumCuring/setting time for the splice kit not respected due to schedule pressure, compromising the seal before full cure
MediumInconsistent technique across different technicians due to a lack of standardised, hands-on training on the specific kit type in use
LowSplice performed in unsuitable field conditions (rain, excessive dust) without adequate protection during assembly
LowNo photographic or documented record of the completed splice before backfill, preventing later verification of technique
Required Tools / Materials
Correct splice kit for the cable voltage class and installation environmentCable preparation tools (stripper, cleaner)Splice kit manufacturer instruction sheetCamera for splice documentation before backfillWeather protection/tent for field splicing in adverse conditionsSplice quality checklist
Safety Precautions
  • LOTO the CCR before any cable splicing work.
  • Obtain excavation clearance and utility locates before opening pavement or verge for a new splice.
  • Coordinate airside access through ATC/airfield operations.
Prevention Procedure
  1. BaselineStandardise splice kit selection by cable voltage class and installation environment across the organisation, removing technician-level judgement calls.
  2. PreventionRequire a documented pre-splice checklist covering surface preparation, correct kit selection, and environmental protection before assembly begins.
  3. PreventionRespect manufacturer-specified curing/setting time before backfill or re-energisation, building this into the work schedule rather than treating it as optional.
  4. PreventionProvide standardised, hands-on training on the specific splice kit types in current use, refreshed periodically.
  5. PreventionRequire photographic documentation of every completed splice before backfill, retained in the CMMS/project record.
  6. VerificationMegger the completed splice section before backfill and again after curing to confirm the joint meets insulation resistance requirements before the excavation is closed.
Inspection / Monitoring Points
Splice kit type vs. cable voltage class/environment
Pre-splice surface preparation checklist completion
Curing/setting time respected vs. manufacturer spec
Photographic documentation on file
Insulation resistance test before and after backfill
Technician training/competency record for the kit type
Effectiveness Verification

Confirm insulation resistance meets requirements immediately after splicing and again at the next scheduled PM visit, with photographic documentation on file, before considering the splice fully verified.

If Failure Occurs Despite Prevention
  • Re-excavate and re-splice any joint failing insulation resistance testing before backfill is finalised.
  • Re-splice using the correct kit if an incorrect kit is identified during a later inspection.
  • Retrain technicians where a pattern of substandard splice technique is confirmed.
Preventive Programme Integration
  • Standardise splice kit selection and stock the correct kits by cable class/environment to remove ad hoc substitution.
  • Mandate photographic documentation and insulation testing as non-negotiable steps before backfill on every splice work order.
  • Build curing/setting time into project schedules from the outset, not as an afterthought.
  • Periodically audit recent splice records for checklist and documentation completeness.
Related References

SOP: SOP-PRV-01 (Preventive Maintenance Procedure), SOP-RCL-02 (Series Circuit Fault Location Procedure)

Standards: IEC 60364, manufacturer splice kit installation instructions, ICAO Annex 14 Vol I

Diagram: Splice Kit Selection and Installation Reference

Case Study: Division 23 — Root Cause Analysis (RCA-548 Repeated Cable Failure RCA)

Rev 0 — Initial issue
PRV-636 Preventing Maintenance-Induced Failures

Failure Mode Addressed — A fault or degradation introduced by a maintenance action itself — rather than by the equipment's normal operating environment — addressed proactively through process, verification, and training controls before it becomes a source of repeat failures.

Equipment / System

Applies across the maintenance process itself — work order procedures, PM checklists, technician practices, and closure verification — rather than to any single component.

Contributing Causes
HighA repair or PM task performed without a subsequent functional/closure verification step, so an incomplete or incorrect fix is recorded as successful
HighA checklist or SOP that does not include the actual root-cause verification step for a given fault type, so the symptom is treated but the cause remains
MediumParts or materials substituted under time pressure without proper specification verification
MediumInconsistent technique across technicians due to a training gap on a specific task
LowTime or access-window pressure leading to a rushed or incomplete repair
LowA documentation/communication gap between shifts or crews leaving relevant fault history unavailable to the technician performing follow-up work
Required Tools / Materials
Work order closure checklist with mandatory verification stepPM/SOP documents reviewed for completeness against known fault typesTechnician training/competency recordsSpares specification verification referenceRepeat-fault interval report from the CMMSShift handover/communication log
Safety Precautions
  • Apply standard LOTO and access procedures for any verification work performed as part of the preventive review.
  • Ensure process changes intended to prevent maintenance-induced failures do not themselves compromise established safety steps.
Prevention Procedure
  1. BaselineRequire a documented closure-verification step (functional test, insulation check, or equivalent) before any work order can be marked complete.
  2. PreventionPeriodically review PM checklists and SOPs against actual fault history to confirm they include the verification step needed to catch each fault type.
  3. PreventionVerify parts/materials against specification before use, rather than accepting a "close enough" substitute under time pressure.
  4. PreventionProvide targeted training on tasks with a known technician-competency gap, identified through repeat-fault tracking.
  5. PreventionBuild adequate time into access windows for the task at hand rather than scheduling repairs that structurally require rushing.
  6. VerificationIntroduce a repeat-fault flag in the CMMS that auto-escalates any fault recurring within a defined interval of a prior closure, for immediate review.
Inspection / Monitoring Points
Closure-verification step completion rate
PM checklist/SOP completeness vs. known fault types
Parts specification compliance on recent work orders
Repeat-fault interval report from the CMMS
Technician training/competency gaps by task type
Access-window adequacy for the task type
Effectiveness Verification

Confirm through CMMS repeat-fault tracking over the following review period that the recurrence rate for previously affected fault types has dropped to the expected baseline.

If Failure Occurs Despite Prevention
  • Re-open and properly verify any work order found closed without adequate verification.
  • Provide immediate retraining where a technician/crew-specific pattern is confirmed.
  • Correct spares stocking to ensure correctly specified parts are available when needed.
Preventive Programme Integration
  • Make closure verification a mandatory, non-skippable field on all relevant work order types.
  • Periodically audit closed work orders against SOP compliance, not only open/overdue ones.
  • Foster a non-punitive reporting culture so time/access pressures are surfaced rather than hidden in closure notes.
  • Review technician competency on high-repeat-rate fault types as part of ongoing training planning.
Related References

SOP: SOP-PRV-01 (Preventive Maintenance Procedure), SOP-QA-01 (Work Order Closure and Verification Procedure)

Standards: ISO 9001:2015 Cl. 10.2, ISO 55001

Diagram: Work Order Process Flow Diagram

Case Study: Division 23 — Root Cause Analysis (RCA-560 Repeated Maintenance Failure RCA)

Rev 0 — Initial issue
PRV-637 Preventing Repeated Circuit Trips

Failure Mode Addressed — A series or parallel circuit trending toward its performance margin — reduced current headroom, marginal insulation across many components, or an outdated design calculation — addressed proactively before it produces recurring trips or partial dark sections.

Equipment / System

The complete circuit — CCR, series/parallel loop, and all fixtures and transformers on it — evaluated at the circuit-design-margin level rather than component by component.

Contributing Causes
HighOriginal circuit design calculation not re-validated after fixtures were added or the loop extended during later projects
HighCumulative small deficiencies across many components (marginal insulation, slightly under-spec transformers) that individually pass inspection but collectively erode the circuit's design margin
MediumCCR output current-step calibration drifting over time without periodic re-verification
MediumA maintenance practice of "swap the obvious faulty part" without full-loop verification, leaving marginal components in place
LowA shared environmental factor (drainage basin, high water table) affecting multiple base cans on the same circuit simultaneously
LowCircuit protection thresholds not re-aligned to the current as-built configuration
Required Tools / Materials
Circuit design calculation and as-built topology drawingFull-loop insulation resistance test recordCCR output current/voltage calibration recordChange-control log for circuit modificationsCircuit-level fault frequency report from the CMMSSite drainage/water-table mapping for the circuit route
Safety Precautions
  • LOTO the CCR before any full-loop testing or circuit-wide work.
  • Coordinate any extended circuit outage with ATC given its runway/taxiway function.
Prevention Procedure
  1. BaselineRequire circuit design re-validation as a mandatory step whenever fixtures are added or the loop is extended, rather than an optional review.
  2. PreventionPerform full-loop insulation resistance testing periodically, not only in response to a fault, to track the circuit's overall margin over time.
  3. PreventionInclude CCR output current/voltage calibration verification in the periodic PM programme.
  4. PreventionRequire full-loop verification, not just point-fix testing, whenever a circuit records more than one fault within a defined period.
  5. PreventionReview circuit topology change history periodically against the current design calculation to catch any unreconciled additions.
  6. VerificationConfirm via full-loop testing and CCR calibration check that the circuit remains within its design margin at each periodic review.
Inspection / Monitoring Points
Circuit design calculation vs. current as-built fixture count/loop length
Full-loop insulation resistance trend
CCR output current/voltage calibration status
Circuit-level fault frequency trend
Topology change/modification log currency
Shared environmental factors along the route
Effectiveness Verification

Confirm via full-loop testing and CCR calibration verification at each periodic review that the circuit's operating margin remains within design tolerance, with fault frequency at or below the expected baseline.

If Failure Occurs Despite Prevention
  • Recalibrate or replace CCR components confirmed to be degraded.
  • Re-validate and, where necessary, re-design the circuit for its current actual fixture count and loop length.
  • Replace marginal components identified during full-loop testing before they cause the next fault.
Preventive Programme Integration
  • Establish a change-control process requiring circuit re-calculation whenever fixtures are added or the loop is extended.
  • Track circuit-level (not only fixture-level) fault frequency in the CMMS to catch a developing pattern earlier.
  • Include CCR output calibration checks in the periodic PM programme as standard.
  • Periodically review topology change history for reconciliation against the design calculation.
Related References

SOP: SOP-PRV-01 (Preventive Maintenance Procedure), SOP-CCR-04 (CCR LOTO Procedure), SOP-DESIGN-02 (Circuit Design Change Control)

Standards: ICAO Annex 14 Vol I, FAA AC 150/5340-30, FAA AC 150/5345-10

Diagram: Circuit Design Calculation and As-Built Topology Drawing

Case Study: Division 23 — Root Cause Analysis (RCA-558 Repeated Circuit Failure RCA)

Rev 0 — Initial issue
PRV-638 Preventing Photometry Non-Compliance

Failure Mode Addressed — Fixture intensity, chromaticity, or beam-spread output drifting toward the edge of the compliant tolerance band between survey cycles, addressed proactively through cleaning-interval management and lumen-depreciation tracking before a survey records an actual non-compliance.

Equipment / System

AGL fixture optics, lamp/LED modules, and the photometric survey history across the fixture population.

Contributing Causes
HighContamination (dust, rubber deposits, de-icing fluid film) accumulating faster than the standard cleaning interval accounts for at high-traffic or spray-exposed locations
HighProgressive lamp/LED lumen depreciation approaching end of rated life across a fixture generation
MediumOptic degradation (UV yellowing, micro-cracking) not visually obvious but measurably affecting output over time
MediumAlignment drift gradually shifting beam pattern away from the design aim point
LowPhotometric test equipment calibration drift producing measurement inconsistency across survey cycles
LowA fixture type installed that is marginal for its intensity category even when new and clean
Required Tools / Materials
Photometric survey trend log by fixture/locationCalibrated photometer/goniophotometer or mobile survey vehicleLamp/LED hours-in-service logOptic cleaning schedule and materialsFixture mounting torque specificationPhotometric equipment calibration record
Safety Precautions
  • LOTO the circuit before optic cleaning, lamp replacement, or alignment work.
  • Coordinate airside access and survey timing through ATC/airfield operations.
  • Use appropriate PPE when handling contaminated optics (de-icing fluid, fuel residue).
Prevention Procedure
  1. BaselineSegment the PM cleaning schedule by contamination-risk zone rather than applying a single field-wide interval, based on actual survey trend data.
  2. PreventionTrend photometric results by fixture installation cohort to anticipate lumen-depreciation-driven non-compliance ahead of the next survey.
  3. PreventionInspect optics under magnification/UV light periodically for early-stage degradation not visible in normal inspection.
  4. PreventionInclude mounting hardware torque-check as a standard step whenever a fixture is serviced, to prevent alignment-driven output loss.
  5. PreventionMaintain photometric test equipment calibration on a documented schedule and cross-validate periodically.
  6. VerificationConfirm via the next scheduled photometric survey that intensity, chromaticity, and beam spread remain comfortably within the compliant tolerance band, not just passing at the margin.
Inspection / Monitoring Points
Photometric survey trend (intensity, chromaticity, beam spread) by fixture cohort
Lamp/LED hours-in-service vs. rated life
Optic condition under magnification/UV inspection
Mounting torque/alignment stability
Photometric equipment calibration status
Cleaning interval vs. actual contamination rate at the location
Effectiveness Verification

Confirm via the next scheduled photometric survey that all monitored fixtures remain comfortably within tolerance, with any fixture trending toward the margin flagged for proactive action before the following cycle.

If Failure Occurs Despite Prevention
  • Shorten the cleaning interval for fixtures in a confirmed high-contamination zone.
  • Proactively replace lamp/LED modules approaching end of rated lumen-maintenance life ahead of the next survey.
  • Replace optics showing confirmed UV or mechanical degradation.
Preventive Programme Integration
  • Trend photometric results by fixture cohort to plan proactive maintenance ahead of the compliance threshold, not react after a failed survey.
  • Maintain a segmented, risk-based cleaning schedule rather than a uniform field-wide interval.
  • Include mounting torque-check as a standard PM step for all serviced fixtures.
  • Maintain photometric equipment calibration on a documented, auditable schedule.
Related References

SOP: SOP-PRV-01 (Preventive Maintenance Procedure), SOP-PHM-01 (Photometric Survey Procedure)

Standards: ICAO Annex 14 Vol I Appendix 2, FAA AC 150/5340-30, IESNA measurement practice

Diagram: Photometric Survey Trend Chart by Fixture Cohort

Case Study: Division 23 — Root Cause Analysis (RCA-556 Repeated Photometry Failure RCA); Division 26 — Photometric Compliance Troubleshooting

Rev 0 — Initial issue
PRV-639 Preventing Connector Installation Errors

Failure Mode Addressed — Connectors being installed with incorrect seating, missing grease, wrong torque, or an incompatible mating type, addressed proactively through standardised procedure, tooling, and verification before the installation itself becomes the root cause of a later fault.

Equipment / System

L-823 primary connectors, secondary lamp/transformer connectors, and their assembly procedure across new installation and maintenance replacement work.

Contributing Causes
HighNo standardised, readily accessible assembly procedure at the point of work, leading to inconsistent technique across technicians
HighDielectric grease omitted or an incompatible grease type used during assembly
MediumConnector not seated to the full engagement point, verified only by feel rather than a positive confirmation method
MediumIncompatible connector types mixed at the same joint due to inventory mix-up or lack of clear labelling
LowIncorrect torque applied due to tool or specification unavailability at the point of work
LowNo photographic or sign-off record of the completed connection, preventing later verification of technique
Required Tools / Materials
Standardised connector assembly procedure/reference cardCorrect dielectric grease, stocked and labelled by typeConnector torque specification and calibrated toolConnector inventory management/labelling systemCamera for installation documentationWork order sign-off field for connector assembly
Safety Precautions
  • LOTO the circuit before any connector installation or replacement work.
  • Use appropriate PPE when handling grease and connector components.
Prevention Procedure
  1. BaselinePublish and distribute a single standardised connector assembly procedure, accessible to every technician at the point of work.
  2. PreventionStock and clearly label the correct dielectric grease type to prevent an incompatible substitute being used.
  3. PreventionRequire a positive engagement confirmation (visual/audible click, or specified insertion depth check) rather than seating by feel alone.
  4. PreventionMaintain clear inventory labelling and segregation to prevent incompatible connector types being mixed at installation.
  5. PreventionRequire torque verification using a calibrated tool as a standard, documented step.
  6. VerificationSpot-check a sample of recently completed connector installations against the standardised procedure during routine PM audits.
Inspection / Monitoring Points
Assembly procedure availability and currency at point of work
Grease type used vs. specification
Connector engagement/seating verification method
Connector type compatibility at the joint
Torque tool calibration and applied value
Installation documentation/sign-off completion
Effectiveness Verification

Confirm through periodic work-order and field audit that connector installations are following the standardised procedure, with sample re-checks of recent work meeting specification.

If Failure Occurs Despite Prevention
  • Re-terminate any connector found improperly seated, greased, or torqued during audit or inspection.
  • Correct any confirmed connector-type mismatch by replacing with the correct compatible part.
  • Provide targeted retraining where a technician-specific pattern of installation error is identified.
Preventive Programme Integration
  • Make the standardised assembly procedure a mandatory part of every relevant work package.
  • Build grease-type and torque verification into the work order as non-skippable fields.
  • Maintain clear connector inventory labelling to prevent type mix-ups.
  • Periodically audit recent connector installations for procedure compliance.
Related References

SOP: SOP-PRV-01 (Preventive Maintenance Procedure), SOP-RCL-03 (Fixture Replacement Procedure)

Standards: FAA AC 150/5345-26, FAA AC 150/5345-46 (L-852)

Diagram: Connector Assembly Specification

Case Study: Division 23 — Root Cause Analysis (RCA-549 Repeated Connector Failure RCA, RCA-562 Installation Error Root Cause)

Rev 0 — Initial issue
PRV-640 Preventing Recurring AGL Failures

Failure Mode Addressed — A field-wide, system-level pattern of the same fault types resurfacing across multiple divisions and locations despite individual repairs, addressed at the programme level through FRACAS integration, trend review, and cross-division learning rather than one fault at a time.

Equipment / System

The AGL system as a whole — CCR, series circuits, fixtures, signs, earthing, communications — and the overarching maintenance/quality management programme that governs it.

Contributing Causes
HighNo formal, structured link between individual fault closures and a system-wide trend review, so recurring patterns across the field are not surfaced until they become severe
HighRCA findings from individual investigations not fed back into standard PM checklists, training, or design standards, so lessons are not institutionalised
MediumNo repeat-fault escalation trigger in the CMMS, allowing the same fault type to recur many times across the field before it draws management attention
MediumFragmented record-keeping across divisions/teams preventing a field-wide view of failure patterns
LowLessons learned from one division's RCA not communicated to other divisions facing structurally similar equipment or conditions
LowNo periodic review cadence to look across all Division 23 RCA findings collectively rather than division by division
Required Tools / Materials
CMMS/FRACAS system with field-wide trend and Pareto reportingPeriodic cross-division RCA review meeting cadencePM checklist and SOP update/change-control processRepeat-fault escalation trigger configurationTraining curriculum update trackingStandards/design review update tracking
Safety Precautions
  • This is a programme-level preventive topic; apply the safety precautions of the specific underlying fault type whenever field verification work is performed as part of the review.
Prevention Procedure
  1. BaselineEstablish a periodic (e.g. quarterly) cross-division review of all closed RCA findings to identify field-wide patterns rather than treating each RCA as a closed, isolated item.
  2. PreventionRequire every RCA corrective/preventive action to explicitly identify whether it should be applied field-wide, not only at the specific location investigated.
  3. PreventionFeed confirmed RCA findings into PM checklist, SOP, training curriculum, and design standard updates as a formal, tracked step, not an informal follow-up.
  4. PreventionConfigure the CMMS to auto-flag any fault type recurring above a defined field-wide frequency threshold for programme-level review.
  5. PreventionMaintain a consolidated, searchable record of all RCA findings (this division) so future investigations can quickly check for a previously identified pattern.
  6. VerificationReview field-wide fault-type trend data at each periodic cycle to confirm previously addressed patterns are trending down and not simply resurfacing under a different fault code.
Inspection / Monitoring Points
Field-wide fault-type frequency trend, Pareto by category
RCA-to-PM/SOP/training update completion rate
CMMS repeat-fault escalation trigger status
Cross-division review meeting cadence and attendance
Consolidated RCA record accessibility and currency
Design standard update tracking against confirmed design-level RCA findings
Effectiveness Verification

Confirm at each periodic cross-division review that field-wide fault-type trends for previously addressed patterns are declining, and that new RCA findings are being systematically fed into PM checklists, training, and standards.

If Failure Occurs Despite Prevention
  • Re-open programme-level review for any fault type showing a renewed upward trend despite a prior corrective action.
  • Accelerate feedback into PM/SOP/training where a confirmed pattern has not yet been institutionalised.
  • Escalate to design/standards review where a recurring pattern points to a systemic design gap rather than a maintenance-level fix.
Preventive Programme Integration
  • Formalise the cross-division RCA review as a standing item on the maintenance/quality management calendar.
  • Track RCA-to-action-closure (PM/SOP/training/design update) as a KPI in its own right, separate from individual fault closure.
  • Maintain the consolidated RCA and preventive-topic record as a living reference for both new investigations and new-technician onboarding.
  • Periodically benchmark field-wide fault frequency against industry/peer data where available to validate the programme's overall effectiveness.
Related References

SOP: SOP-RCA-01 (Root Cause Analysis and FRACAS Procedure), SOP-PRV-01 (Preventive Maintenance Procedure), SOP-QA-01 (Work Order Closure and Verification Procedure)

Standards: ISO 9001:2015 Cl. 10.2, ISO 55001 (asset management), ICAO Doc 9859 (SMS principles)

Diagram: Field-Wide Fault-Type Pareto and Trend Dashboard

Case Study: Division 23 — Root Cause Analysis (all topics); Division 21 — Preventive Maintenance Troubleshooting

Rev 0 — Initial issue
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Frequently Asked Questions

Quick answers about Division 27 — Preventive Troubleshooting in the AGL Troubleshooting Atlas.

Q1What does Division 27 of the AGL Troubleshooting Atlas cover?

Division 27 is the Preventive Troubleshooting reference. It publishes 20 diagnostic topics, PRV-621 to PRV-640, in a single subsection.

Q2What information does each topic include?

Every topic follows the same diagnostic record: the symptom, equipment/system, possible causes ranked by likelihood (high, medium or low), required tools, safety precautions, diagnostic procedure, test points, root cause verification, corrective action, preventive action and related references (SOPs, standards, diagrams and case studies).

Q3Which topics are in Division 27?

The 20 topics are PRV-621 to PRV-640: Preventing Transformer Water Ingress; Preventing Transformer Overheating; Preventing Connector Burning; Preventing Cable Insulation Failure; Preventing Fixture Water Ingress; Preventing LED Failure; Preventing Sign Board Failure; Preventing CCR Overheating; Preventing CCR False Alarms; Preventing Earth Faults; Preventing Lightning Damage; Preventing Flood-Related Failures; Preventing Alignment Errors; Preventing Incorrect Torque; Preventing Improper Cable Jointing; Preventing Maintenance-Induced Failures; Preventing Repeated Circuit Trips; Preventing Photometry Non-Compliance; Preventing Connector Installation Errors; Preventing Recurring AGL Failures.

Q4How does a diagnostic procedure begin in Division 27?

Each procedure starts with observation before any intervention. For example, PRV-621 (Preventing Transformer Water Ingress) begins: Include base-can drainage function, not just visual seal condition, in the standard inspection checklist for every PM visit.

Q5What safety precautions apply in Division 27?

Each topic lists its own precautions. For example, PRV-621 (Preventing Transformer Water Ingress) starts with: LOTO the circuit before opening any base can for inspection or preventive work.

Q6Which SOPs are referenced in Division 27?

Related references in the topics include SOP-PRV-01 (Preventive Maintenance Procedure), SOP-CIVIL-02 (Drainage and Base-Can Remediation Procedure), SOP-RCL-12 (Transformer Test and Replacement Procedure), SOP-RCL-03 (Fixture Replacement Procedure), SOP-RCL-02 (Series Circuit Fault Location Procedure), SOP-PHM-01 (Photometric Survey Procedure), SOP-SGN-01 (Illuminated Sign Maintenance Procedure) and SOP-CCR-04 (CCR LOTO Procedure), and 9 more.

Q7Which standards are referenced in Division 27?

Where a standard applies, it appears in the topic's Related References. Those cited in this division include ICAO Annex 14 Vol I, FAA AC 150/5340-30, FAA AC 150/5345-26, IEEE C57.12.91, FAA AC 150/5345-46, IEC 60364, IEEE 43, ICAO Annex 14 Vol I Appendix 2, FAA AC 150/5345-44 and FAA AC 150/5345-10, among others.

Q8How can I find a specific topic in Division 27 quickly?

Use the search box at the top of the page to filter the 20 published topics by code, fault name or keyword; matching topics open automatically. Each diagnostic record can also be downloaded as a Word (.doc) file.

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